00 Saip 75

BS ISO 20431:2023
BSI Standards Publication
Heat treatment — Control of quality

BS ISO 20431:2023 BRITISH STANDARD
National foreword
This British Standard is the UK implementation of ISO 20431:2023.
The UK participation in its preparation was entrusted to Technical
Committee RHE/13, Liquid fuel firing.
A list of organizations represented on this committee can be obtained on
request to its committee manager.
Contractual and legal considerations
This publication has been prepared in good faith, however no
representation, warranty, assurance or undertaking (express or
implied) is or will be made, and no responsibility or liability is or will be
accepted by BSI in relation to the adequacy, accuracy, completeness or
reasonableness of this publication. All and any such responsibility and
liability is expressly disclaimed to the full extent permitted by the law.
This publication is provided as is, and is to be used at the
recipient’s own risk.
The recipient is advised to consider seeking professional guidance with
respect to its use of this publication.
This publication is not intended to constitute a contract. Users are
responsible for its correct application.
© The British Standards Institution 2023
Published by BSI Standards Limited 2023
ISBN 978 0 539 21870 1
ICS 25.200
Compliance with a British Standard cannot confer immunity from
legal obligations.
This British Standard was published under the authority of the
Standards Policy and Strategy Committee on 31 July 2023.
Amendments/corrigenda issued since publication

Date Text affected
BS ISO 20431:2023
INTERNATIONAL ISO
STANDARD 20431
First edition
2023-07-14

Traitement thermique — Maîtrise de la qualité
Reference number
ISO 20431:2023(E)
© ISO 2023
BS ISO 20431:2023
ISO 20431:2023(E)

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© ISO 2023, Published in Switzerland
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ii © ISO 2023 – All rights reserved

BS ISO 20431:2023
ISO 20431:2023

Contents Page
Foreword...........................................................................................................................................................................................................................................v
Introduction................................................................................................................................................................................................................................. vi
1 Scope.................................................................................................................................................................................................................................. 1
2 Normative references....................................................................................................................................................................................... 1
3 Terms and definitions...................................................................................................................................................................................... 1
4 System for assessment and scoring of requirements and recommendations....................................... 3
4.1 General............................................................................................................................................................................................................ 3
4.2 General requirements........................................................................................................................................................................ 4
4.3 Scoring of requirements and recommendations........................................................................................................ 4
4.3.1 General...................................................................................................................................................................................... 4
4.3.2 Scoring of requirements............................................................................................................................................. 4
4.3.3 Scoring of recommendations................................................................................................................................. 4
4.4 Assessment of the heat treatment facility........................................................................................................................ 5
5 Requirements and recommendations............................................................................................................................................ 6
5.1 General organisation of a heat treatment facility...................................................................................................... 6
5.1.1 Documentation (references GO1 to GO3).................................................................................................... 6
5.1.2 Management responsibility (references GO4 and GO5)................................................................. 6
5.1.3 Human resources management (references GO6 to GO10)........................................................ 6
5.1.4 Infrastructure and equipment management (references GO11 to GO25)...................... 7
5.1.5 Internal audit (reference GO26 and GO27)................................................................................................ 8
5.1.6 Control of nonconforming product (references GO28 to GO36)............................................. 8
5.1.7 Continuous improvement (references GO37 and GO38)............................................................... 9
5.1.8 Failure mode, effect and criticality analysis (FMECA) (references
GO39 to GO41).................................................................................................................................................................... 9
5.1.9 Monitoring plan (references GO42 to GO44)........................................................................................... 9
5.1.10 Preproduction quality planning (reference GO45 and GO46)................................................... 9
5.1.11 Statistics: (references GO47 to GO49)............................................................................................................ 9
5.1.12 Controlling monitoring and recording (references GO50 to GO62).................................. 10
5.2 Contract review and heat-treatment conception.................................................................................................... 11
5.2.1 Contract review............................................................................................................................................................... 11
5.2.2 Heat-treatment conception.................................................................................................................................. 11
5.3 Carrying out heat treatments: preparation.................................................................................................................. 11
5.3.1 General................................................................................................................................................................................... 11
5.3.2 Load preparation........................................................................................................................................................... 12
5.4 Carrying out heat treatment: Control of the thermal cycle............................................................................ 13
5.4.1 Temperature drift and heat-treatment temperature error (references
T1 to T10)............................................................................................................................................................................ 13
5.4.2 Measuring equipment error SAT (system accuracy test) (references
T11 to T17)......................................................................................................................................................................... 15
5.4.3 Temperature uniformity survey (TUS) of furnace (references T18 to T31).............. 17
5.4.4 Drift of the soak times of the various heat-treatment phases (references
HTT1 to HTT2)................................................................................................................................................................ 20
5.5 Mastering of the heat-treatment medium..................................................................................................................... 21
5.5.1 General................................................................................................................................................................................... 21
5.5.2 Control of carbon-containing atmosphere.............................................................................................. 21
5.5.3 Control of nitriding, nitrocarburising and derived heat-treatment
atmospheres...................................................................................................................................................................... 22
5.5.4 Control of salt bath and drift of treatment medium........................................................................ 22
5.5.5 Control of operational conditions of surface hardening after induction
superficial heating........................................................................................................................................................ 22
5.5.6 Laser hardening (references L1 to L4)....................................................................................................... 23
5.5.7 Vacuum or low-pressure heat treatment (references V1 to V7).......................................... 24
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5.6 Control of cooling................................................................................................................................................................................ 24

5.6.1 Equipment control and heat-treatment reproducibility (references
CEQ1 to CEQ3)................................................................................................................................................................. 24
5.6.2 Control of cooling parameters (references CPM1 to CPM12)................................................. 24
5.7 Control of product.............................................................................................................................................................................. 25
5.7.1 Drift of testing means (references CP1 and CP2).............................................................................. 25
5.7.2 Non-conforming product (references CP3 to CP5).......................................................................... 25
5.8 Finishing process................................................................................................................................................................................ 25
Annex A (normative) Equipment calibration and frequency control..............................................................................27
Annex B (informative) Example of scoring table for requirements and recommendations....................29
Annex C (informative) Example of heat-treatment facility assessment.........................................................................35
Annex D (normative) Measuring chain testing methods (SAT - system accuracy test)..................................36
Bibliography.............................................................................................................................................................................................................................. 41
iv © ISO 2023 – All rights reserved

BS ISO 20431:2023
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Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.
org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 244, Industrial furnaces and associated
processing equipment.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2023 – All rights reserved v

BS ISO 20431:2023
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Introduction
This document draws a list of best practices in order to ensure quality control in the application of
heat treatment. This document is for use with equipment constructed in accordance with International
Standards for thermoprocessing equipment. These concepts are also suitable for application with other
heat-treatment processes.
This document is a reference for assessment and continuous improvement which is part of the quality
management system of a heat-treatment facility.
Figure 1 shows the typical flowchart for a heat-treatment process. The main steps are subject to
requirements and recommendations in this document.
Key
A general organisation of a heat-treatment facility (see 5.1) F control of the heat-treatment medium (see 5.5)
B contract review and heat-treatment conception (see 5.2) G control of cooling (see 5.6)
C carrying out the heat treatment H control of product testing (see 5.7)
D preparation (see 5.3) I finishing (see 5.8)
E control of the thermal cycle (see 5.4)
Figure 1 — Heat-treatment process
vi © ISO 2023 – All rights reserved

BS ISO 20431:2023
INTERNATIONAL STANDARD ISO 20431:2023
1 Scope
This document defines the quality requirements and recommendations applicable to heat treatment
on mechanical parts intended to be used in the industry (e.g. car manufacturing, aerospace, pipeline
systems, civil engineering equipment, earth moving machinery, agricultural equipment, naval industry,
energy equipment, tooling, fasteners).
This document provides a reference for quality audit and for the inspection of heat-treatment facilities,
whether these are integrated or belonging to subprime contractors. This document can also be used as
a basis for discussion and development of specifications.
A description of the equipment calibration and the frequency of the controls is given in Annex A.
An example of scoring table is given in Annex B. An example of audit report is given in Annex C. The
different measuring chain testing methods (SAT) are presented in Annex D.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 4885, Ferrous materials — Heat treatments — Vocabulary
ISO 6506 (all parts), Metallic materials — Brinell hardness test
ISO 6507 (all parts), Metallic materials — Vickers hardness test
ISO 6508 (all parts), Metallic materials — Rockwell hardness test
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 4885 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
heat-treatment facility
set of equipment implementing processes associated with each other used to modify, through a thermal
cycle, the physical, mechanical and/or chemical properties of a metallic material
3.2
recommendation
preferred advice and criterion (criteria) providing guidance, but not required to be in accordance with
this document
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3.3
requirement
criterion (criteria) to be complied with in order to achieve conformity with this document
Note 1 to entry: A requirement not fulfilled can have an impact on the special characteristic(s) (3.5) of the
final product.
3.4
contract review
systematic procedure carried out in order to identify the requirements (3.3) and expectations for the
process outputs as expressed in documents and that they may be carried out
Note 1 to entry: Requirements and expectations for the process can be internal (inhouse heat treatment) or
external (from customer).
3.5
special characteristic
feature or property of a final product which impacts, contributes, or affects safety or compliance with
regulations, fit, function, performance or subsequent processing of product
3.6
preproduction quality planning
process which defines the rules for planning of all the manufacturing steps of a product, from offer
review to delivery, in order to meet the customer’s requirements (3.3)
Note 1 to entry: Preproduction quality planning is well known as advanced production quality planning (APQP)
in the automotive industry.
Note 2 to entry: Requirements can be internal (inhouse heat treatment) or external (from customer).
3.7
verification
provision of objective evidence that a given item fulfils specified requirements (3.3)
[SOURCE: ISO/IEC Guide 99:2007, 2.44, modified — EXAMPLES and NOTES removed.]
3.8
calibration
set of operations that establishes, under specified conditions, the relationship between values of
quantities indicated by a measuring instrument or measuring system, or values represented by a
material measure or a reference material, and the corresponding values realised by standards
Note 1 to entry: Adapted from ISO/IEC Guide 99:2007, 2.39.
3.9
measuring chain
series of elements of a measuring system constituting a single path of the signal from a sensor to an
output element
EXAMPLE A display or recording system.
Note 1 to entry: Each element of the measuring chain is characterised by its metrological properties which are,
mainly, the measuring range, the freedom from bias, the reproducibility, the resolution, the drift depending
on influence quantities, the drift over time depending on the conditions of use and, as a consequence, the
measurement uncertainty.
[SOURCE: ISO/IEC Guide 99:2007, 3.10, modified — Note 1 to entry added and EXAMPLES 1 and 2
replaced by EXAMPLE.]
3.10
regulation system
device(s) composed of sensor(s) which measure(s) a physical characteristic to be monitored and
supplying control signals for action to the control system to respect the tolerance threshold
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3.11
monitoring chain
system composed of monitoring element(s) which transmits a signal (e.g. voltage, current) to a
recording system
3.12
major modification
modification of the process parameters referenced in the validation file (qualification parts) and which
has an impact on the special characteristic(s) (3.5) of the final product
3.13
soak time
hold time
time increment of the thermal cycle during which the temperature is held constant
Note 1 to entry: The soak time begins when the load TC reaches the minimum temperature of the tolerance. The
soak time finishes when the load TC leaves the minimum temperature of the tolerance.
3.14
responsibilities matrix
detailed description of designated personnel for key heat-treatment management and supervisory
functions including their back-up
3.15
heat-treatment conception
phase during which the organization analyses the customer’s requirements (3.3), assesses whether they
are technically feasible and identifies the conditions necessary for a smooth running of its process
Note 1 to entry: This phase includes in particular the results of the feasibility confirmation tests, the tests results
under industrial conditions, the development of a recipe, the verification (3.7) of capability and any limitations or
warnings to be brought to the attention to the customer.
3.16
heat-treatment plan
procedure or specification which describes at least the parameters and tolerances of the heat-treatment
process, the controls, the equipment verifications (3.7) and frequencies
3.17
electronic record
any combination of text, graphics, data, audio, pictorial, or other information representation in digital
form that is created, modified, maintained, archived, retrieved, or distributed by a computer system
4 System for assessment and scoring of requirements and recommendations
4.1 General
The assessment shall focus on the requirements and recommendations listed in Clause 5 and identified
according to their nature, in accordance with Table 1.
Table 1 — Identification of requirements and recommendations

Requirement or recom- Subclause in this docu-
Nature of the requirement or recommendation
mendation identifier ment
GO General Organisation 5.1
CR Contract Review 5.2.1
HTP Heat-Treatment Conception 5.2.2
PR Preparation 5.3
T Heat-treatment Temperature 5.4.1 to 5.4.3

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Requirement or recom- Subclause in this docu-

Nature of the requirement or recommendation
mendation identifier ment
HTT Heat-Treatment Time 5.4.4
C atmospheres containing Carbon 5.5.2
Nitriding and nitrocarburising atmospheres and derived 5.5.3
N
treatments
SB Salt Baths 5.5.4
SH Surface Hardening (quenching after surface heating) 5.5.5
L Laser hardening 5.5.6
V Vacuum or low-pressure heat treatment 5.5.7
CEQ Cooling EQuipment 5.6.1
CPM Cooling ParaMeters 5.6.2
CP Control of Product testing 5.7
F Finishing 5.8
4.2 General requirements

To declare the heat-treatment facility in accordance with this document, a quality-management system
shall exist which meets the requirements of its customers.
Any subcontracted process shall be assessed in accordance with this document.
NOTE 1 Customers can be internal and external.
NOTE 2 The basic repository used is often completed with other certifications and accreditations, where
necessary (e.g. ISO 9001).
4.3 Scoring of requirements and recommendations
4.3.1 General
Determination of acceptable scores are typically part of the contractor agreement.
4.3.2 Scoring of requirements
The requirements shall be scored in accordance with the following criteria:

— a satisfied requirement scores 100;
— a non-satisfied requirement scores 0.
A non-satisfied requirement shall give rise to a systematic action plan.
4.3.3 Scoring of recommendations
Recommendations shall be scored according to the criticalities listed in Table 2.
Table 2 — Scoring of recommendations according to their criticality

Recommendation criticality Score
Satisfied recommendation 100
Recommendation partially fulfilled without new corrective action proposed 80
Recommendation partially fulfilled with corrective action proposed 50
No conformity with corrective action proposed 20

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All the requirements and recommendations listed in Clause 5 shall be scored in accordance with criteria
in 4.3.2 and 4.3.3. If a requirement or recommendation is not relevant for the heat-treatment facility
under assessment, it shall be scored as “N/A” (not applicable).
If the audit is not completed, the customer and the supplier shall agree to use the final scores according
to this document. In this case the requirements and recommendations not seen during the audit shall
be scored as "N/A" and shall be documented in the audit report.
The scoring table given in Table B.1, should be used.
All corrective actions and non-satisfied requirements identified should be recorded in a report intended
to monitor the continuous improvement of the quality program of the heat treatment facility.
4.4 Assessment of the heat treatment facility

The final assessment of the heat treatment facility shall be carried out in accordance with the
following criteria.
— Final score: ratio between the weighted sum of the scores of the requirements and recommendations
and the number of the applicable scored requirements and recommendations (A).
— Final requirements only score: ratio between the weighted sum of the scores of the requirements
and the number of the applicable scored requirements.
— Score depending on the nature of the requirements and recommendations: for each nature of
requirements and recommendations, this is the ratio between the sum of the scores of requirements
and recommendations and the number of the applicable scored requirements and recommendations
(N0, N20, N50, N80 and N100). The calculation of scores by requirement is performed using Formula (1)
line by line.
S = (B + C + D +E)/ A (1)
where
S is the score;
B is the number N20 of non-conforming recommendations with corrective action proposed mul-
tiplied by 20;
C is the number N50 of recommendations partially fulfilled with corrective action proposed mul-
tiplied by 50;
D is the number N80 of recommendations partially fulfilled without new corrective action proposed
multiplied by 80;
E is the number N100 of satisfied recommendations multiplied by 100;
A is the number of the applicable scored requirements and recommendations.

NOTE 1 The scores are proportional to the level of quality.
The heat treatment facility shall be assessed using Table 3.
Table 3 — Heat treatment facility assessment

Requirements Recommendations
Reference Audit section A Score
N0 N100 N20 N50 N80 N100
General organisation of the
5.1
heat treatment facility

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Requirements Recommendations
Reference Audit section A Score
N0 N100 N20 N50 N80 N100
Contract review and heat treat-
5.2
ment preparation
5.3 Preparation
Control of ther-
5.4
mal cycle
Carrying out
the heat treat- Control of heat
5.5 ments: treatment
medium
Control of
5.6
cooling
5.7 Control of product testing
5.8 Finishing
Final result (for the entire audit)
Where a minimum score is to be obtained, and/or recommendations are to be fulfilled as requirements,

the customer shall inform the supplier with a delay agreed between the two parties or by default two
weeks before the audit.
NOTE 2 Annex C gives an example of assessment and score calculation.
5 Requirements and recommendations
5.1 General organisation of a heat treatment facility
5.1.1 Documentation (references GO1 to GO3)
Requirement GO1: For each heat treatment, preparation or testing process, a heat-treatment plan shall
be available for all personnel involved in the use of the heat-treatment equipment. All the steps of the
process and the main operating parameters, with their tolerances, shall be specified in this document.
Requirement GO2: The heat-treatment plan shall specify responses in case of incident and/or
emergency situation for the process (e.g. power failure which leads to start or restart an equipment after
shutdown, batch allocation and management of suspicious or non-compliant products, cyber-attacks).
Requirement GO3: Any major modification shall be documented and shall be validated by the customer
in the context of formal approval of a production (e.g. type of oil, heat-treatment devices, key process
parameters).
5.1.2 Management responsibility (references GO4 and GO5)
Requirement GO4: In order to provide proof of their commitment to develop and implement the quality-
management system, the managers shall carry out, at least once per year, a review of the performance
or managing indicators related to the heat treatment process. This review shall be documented.
Requirement GO5: The management review shall lead to the implementation of corrective and
preventive actions if the objectives have not been reached.
5.1.3 Human resources management (references GO6 to GO10)
Requirement GO6: A skill qualification matrix shall exist for the personnel allowed to carry out heat-
treatment process operations. This matrix shall be up-to-date or its revision shall be planned.

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Requirement GO7: A responsibilities matrix including authorization shall exist ensuring that the main
management and supervision tasks are carried out by competent personnel (usual personnel and back-
up). This matrix shall be current and available to the management at all times.
Requirement GO8: The management shall implement suitable training to obtain the necessary skills
according to the heat-treatment process. This document shall be available to management at all times
or posted on the heat-treatment facility.
Requirement GO9: The personnel of the heat-treatment facility who could have an impact on the
customer product shall have their skills verified periodically. The overall monitoring of assessments
and additional trainings needed shall be documented.
Recommendation GO10: The person as a referent for heat treatment should be a permanent employee
whose position and responsibilities should be reflected in the organization chart. This position should
be held by a competent person with significant experience whose training and qualifications (in
metallography, heat treatment process and equipment) are approved by the company.
NOTE For experience, five years is a typical minimum.
5.1.4 Infrastructure and equipment management (references GO11 to GO25)
Requirement GO11: The nature and conformity of the products which come into contact with the
parts and which are used for heat treatment shall be identified and validated upon receipt.
Recommendation GO12: The supplier of products in contact with the part should be qualified
and evaluated.
Requirement GO13: A documented preventive maintenance plan shall exist. This plan shall take into
account the maintenance actions (failures and incidents), the quality scraps, the results of the initial
samples and the operator information.
Recommendation GO14: Maintenance data should be collected and analysed as part of predictive
maintenance program.
Requirement GO15: The process / alarm data shall be reviewed and authorized by competent
personnel before sending the products (related to this process data) to the customer. The product shall
be released by quality department or its representative before sending the products to the customer.
Requirement GO16: A list of critical alarms for product quality shall be drawn through participation
of various functions or departments (production, maintenance, etc.).
Recommendation GO17: Except for digital equipment with controlling and monitoring system, a
schedule for checking the alarms critical for product quality should be defined and followed up. The
check frequency should be defined depending on the risk assessment.
Requirement GO18: Acknowledgment (reset) of critical alarms for product quality shall be checked at
regular intervals and traced.
Requirement GO19: The process data, including critical alarms, shall be continuously recorded
and preserved.
Recommendation GO20: The environment, the working conditions (including, e.g. temperature of the
air inside the facility, emission of fumes) and the cleanliness of the plant should allow better quality
control, improvement and working in safety conditions. Steps can be implemented to assess these
criteria (e.g. a cleanliness audit).
Requirement GO21: A back-up for plant and equipment taking into account all the means necessary to
ensure the production shall be implemented.
Recommendation GO22: The security plan should be tested and validated.

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Requirement GO23: The zones in which parts are retained throughout the heat treatment process
shall be identified and documented.
Recommendation GO24: The zones in which parts are retained throughout the heat-treatment
process (e.g. trap points) should be monitored at least during each maintenance operation or at a
defined frequency.
Recommendation GO25: Handling, storage and packaging should not affect the quality of the
final product.
5.1.5 Internal audit (reference GO26 and GO27)
Requirement GO26: A schedule of audits for each process of the heat treatment facility, taking into
account the risks, shall be defined and complied with. The audit frequency should be reviewed every
year. The audit frequency shall not exceed three years for each process.
Requirement GO27: The internal auditor for heat-treatment control of quality assessment shall be
qualified for this task and referenced in the skill qualification matrix.
5.1.6 Control of nonconforming product (references GO28 to GO36)
Requirement GO28: A procedure shall be implemented to identify and monitor each batch at each
stage in the process. This procedure shall include measures to prevent batch mixing, incorrect heat
treatments, risks of contamination of heat-treated batches by non-treated products and shipment of
batches on which all tests have not been carried out.
Requirement GO29: A procedure shall be implemented for the management of suspect or non-
conforming products. This procedure shall provide identification and quarantine of suspect or non-
conforming products. It shall define the incoming and outgoing flows of suspect or non-conforming
products to the non-conforming hold area or the continuation of production.
Requirement GO30: The quality manager or his/her authorized representative shall approve and
document the final release of quarantined parts.
Recommendation GO31: A procedure specifying the conditions of heat retreatment should be
implemented and documented. The conditions for heat retreatment should be validated by the customer.
This procedure should specify the documentation to be set and the personnel authorized to define and
apply the heat retreatment conditions.
Requirement GO32: The documentation to be set shall include at least the part number and name,
batch number, original furnace number, quantity, rework cause, retreatment process.
Requirement GO33: The customer shall be advised of the non-conformity of the product except if there
is an agreement or if it is specified in the heat-treatment plan.
Requirement GO34: In case of retreatment on quenching/tempering, operation shall be performed
under control.
Recommendation GO35: If the customer approved the retreatment at the preproduction quality
planning or production parts approval process stage, the organization should describe the retreatment
process of the parts in the FMECA or specification and in the control plan. In this case, the retreatment
may be carried out before notification to the customer. See 5.1.8.
Requirement GO36: The result of retreatment shall be validated, and the release of retreated parts
shall be approved by the authorized person appointed by the organization. When recommendation
GO35 has not been implemented the customer shall approve the outcome.

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5.1.7 Continuous improvement (references GO37 and GO38)
Requirement GO37: A continuous improvement plan for each process or a continuous improvement
plan representative of each process shall be implemented and shall define priority actions planned in
order to improve quality and performance. The efficiency of the programme shall be demonstrated.
Requirement GO38: The quality department shall review, process and document customer claims and
internal problems through a methodical problem-solving approach.
5.1.8 Failure mode, effect and criticality analysis (FMECA) (references GO39 to GO41)
Requirement GO39: There shall be a procedure which plans to perform the FMECA of each process of
the heat-treatment facility. It shall identify and take account of the special characteristics and require
the participation of several functions (production, maintenance, etc.).
Requirement GO40: When a product/process FMECA(s) is required by the customer, it shall be
performed in cooperation with the customer.
Recommendation GO41: Any modification of each process should lead to a review of the
relevant FMECA.
5.1.9 Monitoring plan (references GO42 to GO44)
Recommendation GO42: A procedure to define and implement monitoring plans should be

implemented. This procedure should identify and take into account the special characteristics
and include the consistency with the related documentation [work instructions, follow-up sheets,
FMECA(s), etc.].
Recommendation GO43: Monitoring plans should be defined and validated by the customer in
accordance with its requirements concerning the process, the parts or the part families.
Recommendation GO44 Any modification of each process should lead to review the relevant
monitoring plan.
5.1.10 Preproduction quality planning (reference GO45 and GO46)
Recommendation GO45: A preproduction quality planning procedure should be applied at the

customer’s request and with the customer’s participation. This request and the needed information are
forwarded by the customer.
Recommendation GO46: The organization should study the effectiveness of production and control
process capacities including the initial-stage equipment rearrangement/relocation, overhaul, mass
production and engineering change.
5.1.11 Statistics: (references GO47 to GO49)
Recommendation GO47: Statistical analysis should be performed using data on special characteristics
and/or the heat-treatment process parameters.
Recommendation GO48: Capability measurements should be carried out in accordance with the prime
contractor’s requirements or a procedure or ISO 22514‑6.
Recommendation GO49: If the results or other statistical characterisations of the process do not meet
the customer’s requirements, an action plan should be implemented.
NOTE The conventional capability measurement methods are usually not applicable to heat-treatment
processes. In these conditions, low capabilities can be measured with these methods; however, these values will
not be representative of a malfunction with the heat-treatment process. If the prime contractor requests these
measurements, they will be provided for information and will not lead to any specific action plan.

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5.1.12 Controlling monitoring and recording (references GO50 to GO62)
Requirement GO50: The controllers, monitoring and sensors of the critical process parameters shall be
connected to a recording system (chart recorder, electronic data recorder or data acquisition system).
Recommendation GO51: Digital recorders creating electronic records should be used.
Recommendation GO52: Measures (e.g. procedures, technical documentation of the system) should be
taken to ensure the integrity of the records.
Recommendation GO53: When a system software and playback utilities are used, measures (e.g.
procedures, technical documentation of the system) should be taken to provide means of examining
and/or compiling the record data.
Recommendation GO54: The recording system should provide the ability to generate accurate and
complete copies of the records in both human-readable and electronic form suitable for inspection,
review and copying.
Requirement GO55: When an electronic recording is used, the system shall be able to provide evidence
the record was reviewed – such as by recording an electronic review, or a method of printing the record
for a physical marking indicating review.
Requirement GO56: The system shall support protection, retention and retrieval of accurate records
throughout the record retention period or adequate procedure for recording file backup in digital or
paper format.
Recommendation GO57: When an electronic recording is used, the system should provide methods
(e.g. passwords) to limit system access to authorized personnel as stated in the documentation.
Recommendation GO58: The resolution for analogue chart recording instrument should comply
with Table 4.
Table 4 — Resolution for analogue chart recording instrument

Furnace class Max. degrees per centimetre of chart paper Max. chart recording increment
1 11 1
2 33 3
3 33 3
4 55 5
5 55 5
6 77 15
Requirement GO59: Digital recording instruments shall have a minimum readability of 0,1 °C.
Recommendation GO60: The timing function for all digital recording instruments and data acquisition
systems should be calibrated annually and shall be accurate to ±1 min/h.
NOTE A documented digital synchronization of timing systems to NIST (or international equivalent)
via satellite, internet, or telephonic systems periodically (at least monthly) to support a ±1 min/h accuracy
is acceptable.
Requirement GO61: With control, monitoring and recording digital instruments evidence shall be
provided, that software revisions are verified to ensure continued compliance with the material or
process specification requirements.
Requirement GO62: If offsets are used, a documented procedure describing maximum offsets and
when and how to perform manual and electronic offsets shall be implemented.

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5.2 Contract review and heat-treatment conception
5.2.1 Contract review
5.2.1.1 Modification not taken into account (references CR1 to CRC3)
Recommendation CR1: The general heat-treatment standards (ISO, ASTM, etc.) referenced by
the customer(s) should be made available, reviewed and updated within a timeframe of less than
three months since dates of availability of the regional published standards.
Requirement CR2: During the contract review or the offer review, the standards and specifications
supplied by the customer(s) shall be taken into account.
Recommendation CR3: In case of modification(s) or change(s) to a specification, the customer(s) should
be informed of the planned implementation or of the rejection of such modification(s) within two weeks.
5.2.1.2 Mistake in the identification of part batches (reference CR4 and CR5)
Requirement CR4: The facility shall ensure that the data entered in the receiving system matches the
information on the customer's shipping documents.
NOTE A detailed procedure can be implemented to solve any possible discrepancy between the information
contained in the shipment documents and the received products.
Requirement CR5: The product shall be clearly identified and staged throughout the heat-treatment
process and batch(es) traceability and integrity maintained throughout all processes.
5.2.2 Heat-treatment conception
5.2.2.1 Heat-treatment planning (references HTP1 and HTP2)
Requirement HTP1: All the heat-treatment process phases (preparations, intermediate heat
treatments and finishing) shall be defined and documented according to the special characteristics
expected for the product.
Requirement HTP2: The parameters of the heat-treatment operations (preparations, intermediate
heat treatments and finishing) and their tolerances shall be clearly documented and applied.
5.2.2.2 Defective or nonconforming equipment (reference HTP3 and HTP4)
Recommendation HTP3: The process and product testing equipment should be checked and calibrated
in accordance with the provisions specified in Table A.1.
Equipment items not listed in Table A.1 should be covered by a specific procedure which defines the
check and calibration procedures.
Requirement HTP4: The heat-treatment plan shall describe the verification procedures of the
measuring devices needed before restarting the equipment taking into account different cases and
different factors (e.g. time, reason).
5.3 Carrying out heat treatments: preparation
5.3.1 General
The main steps of heat treatment are the following:

— a preparation phase including surface-preparation phases, batch preparation, etc., depending on
the types of heat treatment and the customer’s requirements;

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— the heat treatment itself, characterised by the requested control of thermal cycle(s) followed by
cooling in defined conditions. Several heat treatments can be performed successively;
— possible finishing processes;
— testing during production and/or release checks.
5.3.2 Load preparation
5.3.2.1 Product non-conformity (references PR1 and PR2)
Requirement PR1: The furnace-loading parameters shall be specified, documented and followed up, at
least: belt speed, number of parts per load, distribution of the parts on the belt or in the jigs and weight
of the load.
Recommendation PR2: Alarm and/or Poka-yoke should be implemented to prevent any risk of
incorrect loading.
5.3.2.2 Mixing of parts (reference PR3)
Requirement PR3: Procedures or devices shall be used to prevent part mixing and contamination by
inappropriate materials (for instance, check of containers, flow management, blocked parts, etc.).
5.3.2.3 Degreasing of products (references PR4 to PR7)
Recommendation PR4: Parts before heat treatment should be cleaned to be free of grease or oil.
Recommendation PR5: All key process parameters impacting the degreasing should be defined in an
internal procedure and regularly checked accordingly.
Recommendation PR6: The washing-solution concentration and oil content tests should be carried out
once per week, or at a specified interval based on an available and documented experience. A specified
interval of washing bath and cleaning tank should be documented.
Recommendation PR7: The temperature of the washing solution should be monitored (only if the
specified temperature is above the room temperature) by means of a supervision system or, failing
that, it should be checked before each use or once per day of use.
Recommendation PR8: The chloride content in the washing solutions should be checked at least once
every three months or at a different frequency based on an available and documented experience.
5.3.2.4 Heat treatment
Recommendation PR9: A furnace class should be chosen following the heat-treatment type and the
temperature uniformity required. See Table 5.
Table 5 — Furnace classes uniformity tolerances

Furnace class Furnace uniformity (°C)
1 ±3
2 ±5
3 ±8
4 ±10
5 ±15
6 ±30

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5.4 Carrying out heat treatment: Control of the thermal cycle
5.4.1 Temperature drift and heat-treatment temperature error (references T1 to T10)
Requirement T1: The furnace(s) shall be equipped with temperature-measuring instruments. The
main types of thermocouples used in heat treatment of metals are described in Table 6.
NOTE 1 The temperature is measured by a sensor (usually a temperature sensor) connected to a measuring
device which can be a display, a recorder or a controller that allows the temperature to be maintained within a
defined range for heat treatment.
Table 6 — Designation, composition and maximum operating temperature of thermocouples

and resistance temperature detector (RTDs)
Elements and nominal alloy compositions by weight Maximum operat-
ing temperature
Letter (°C)
Classification
designation Positive conductor Negative conductor
(informative
value)
R Platinum – 13 % rhodium Platinum 1 600
Noble metal S Platinum – 10 % rhodium Platinum 1 600
B Platinum – 30 % rhodium Platinum - 6 % rhodium 1 700
J Iron Copper - nickel 750
T Copper Copper - nickel 350
Base metal E Nickel - chromium Copper - nickel 900
K Nickel - chromium Nickel - aluminium 1 200
N Nickel - chromium - silicon Nickel - silicon 1 200
C Tungsten – 5 % rhenium Tungsten – 26 % rhenium 2 315
Refractory
A Tungsten – 5 % rhenium Tungsten – 20 % rhenium 2 500
RTDs Pt 100 Platinum -200 / 850
Requirement T2: The calibration of the temperature sensor shall comply with the following:
— a primary temperature sensor shall be calibrated by comparing it against a reference standard
sensor. A secondary sensor may be created by a calibration against a primary temperature sensor;
— the temperature sensors installed on the furnace (control, temperature high limit, load) shall be
calibrated by comparing it against a primary or a secondary temperature sensor;
— the calibration can be implemented on the temperature sensor itself or on the coil of wire from
which it is made. In this event, calibration shall be performed at both ends of the coil;
— the temperature sensors should be calibrated before the first use and then replaced following the
limit of service. See Table 7;
— the non-expendable noble metal temperature sensors may be recalibrated after reaching the use
duration limit. The non-expendable base metal temperature sensors shall not be recalibrated after
reaching the use duration limit.

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Table 7 — Calibration or change and limit of service

Recalibration Maximum dura-
Maximum
Type of thermocouple Use or replacement tion of service
number of use
(months) (months)
Primary N/A 36 N/A N/A
Secondary N/A 24 N/A N/A
TUS SAT
Control
Non-expendable noble metal 24 N/A N/A
High limit temper-
ature
Non-expendable noble metal Load 6 N/A N/A
TUS SAT
Non-expendable base metal over Control
12 N/A N/A
760 °C
High limit temper-
ature
TUS SAT
Non-expendable base metal under Control
24 N/A N/A
760 °C
High limit temper-
ature
Non-expendable base metal over
Load N/A 1 N/A
1 260 °C
Non-expendable base metal be-
Load N/A 10 3
tween 1 204 °C and 1 260 °C
Non-expendable base metal be-
Load N/A 90 3
tween 980 °C and 1 204 °C
Non-expendable base metal under
Load N/A 180 6
980 °C
Expendable base metal over 760 °C Load N/A 1 N/A
Expendable base metal under 760 °C Load N/A 30 3
SAT : Systems Accuracy Tests
TUS : Temperature Uniformity Surveys
N/A : Not Applicable
NOTE 2 The minimum frequency can be subject of agreement between the customer and the subcontractor,
considering the field of the industry.
NOTE 3 The calibration period begins at first use if the storage period does not exceed the calibration period.
The calibration accuracy of the primary and secondary temperature sensor shall be ±0,6 °C or 0,1 % of
the range, the largest of both.
The calibration accuracy of the temperature sensors used for SAT, TUS or process control, monitoring
and recording shall be ±1,1 °C or 0,4 % of the range, the largest of both.
The tolerance on the recalibration and the duration of service is 15 days.
Requirement T3: The following headings shall be included in the calibration report of a
temperature sensor:
— calibration date;
— source of calibration data;
— identification of the sensor tested;

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— identification of the test sensor;

— identification of the test instrument;
— identification of the operator performing the test;
— company having performed the test (if not carried out in-house);
— signature of the calibration company representative (if not carried out in-house);
— nominal test temperature;
— actual test temperatures recorded;
— calibration technique;
— correction factor for each calibration temperature (traceable to national standards);
— indication of test acceptance or failure.
NOTE 3 The usage of the temperature sensor and the conditions under which it is used, determine the rules to
be applied for its recalibration and use:
— control and monitoring thermocouples (for display and recording of furnace parameters);
— thermocouples used for systems accuracy tests (SAT) or for temperature uniformity surveys (TUS);
— reference thermocouples, which serve to verify and calibrate the previously mentioned sensors.
Requirement T4: The company shall determine and supply the resources to ensure the measurements
conformity. The checking of the furnace and of the instruments shall be mentioned in the heat-
treatment plan.
Requirement T5: The checking frequencies shall be mentioned in the heat-treatment plan in accordance
with the furnace use.
Requirement T6: The critical process temperature(s) shall be monitored.
Requirement T7: The monitoring shall be continuously recorded.
Requirement T8: If there is no supervision system (set point alarm and recording), the check of heat-
treatment temperatures inside the work zone shall be carried out and documented by signature at least
once per heat treatment or a minimum once per two hours.
Recommendation T9: For quenched parts heat treated in a continuous belt furnace and when there
is no temperature control system in the furnace output zone, a device should be fitted to check
the temperature of the parts in the output zone with an alarm set to 25 °C below the working zone
temperature.
Recommendation T10: Digital controllers and data recording should be used. The digital data should
be readable at least for five years.
5.4.2 Measuring equipment error SAT (system accuracy test) (references T11 to T17)
Requirement T11: A heat-treatment plan shall be issued and applied. This heat-treatment plan shall
take the following into account:
— management of temperature measuring chain;

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— management of temperature detectors or sensors such as:

— thermocouples, platinum-resistance temperature sensors, thermal-profiling systems (on-board
system) and infrared pyrometers;
— management of the checking of the temperature controllers and recorders;
— management of thermocouple simulators and reference voltmeter;
— heat-treatment plan for furnace(s) and furnace instrumentation check and for furnace(s)
homogeneity check.
Requirement T12: The minimum frequency of checks shall comply with Table 8 in accordance with the
used methods described in Annex D.
Table 8 — Check recommendations for measuring chains (sensor, recorder controller)

Minimum frequency Grace period
Measuring chain Use for methods 1 and 3 for methods 1
(months) and 3(days)
Reference chain Calibration 12 10
Test measuring chain
Calibration 12 10
(SAT and TUS)
Class 1 furnace 1 3
Class 2 furnace 3 5
Class 3 furnace 3 5
Class 4 furnace 6 7
Control, recording, Class 5 furnace 6 7
display measuring Class 6 furnace 12 10
chain
Temperature control of quench media tank 12 10
Temperature control of degreasing equip-
36 15
ment
Sub-zero equipment 12 10
Infrared pyrometer 12 10
NOTE 1 The minimum frequency can be subject of agreement between the customer and the subcontractor,
considering the field of the industry.
If using the method 2, the frequency shall be 1 month with a grace period of 3 days.
Requirement T13: The calculated SAT difference shall be under ±5 °C for the methods 1 and 3 (see
Annex D) and ±1 °C for the method 2.
NOTE 2 Uncertainties calculation of the measurements allows to adapt the precision of the measurement
equipment following the application. Examples of uncertainty calculations are given in CETIM 9Q347[5].
Requirement T14: Thermocouples and standard devices used for SAT shall comply with 5.4.1.
Recommendation T15: Measuring chains should comply with the following:
— control measuring chains (sensor, recorder and controller) installed on the furnace should be
checked using one of the three SAT methods described in Annex D;
— reference or test equipment (sensor, recorder, controller and voltammeter) used for SAT and TUS
should be calibrated every year;
— reference, test and control measuring chains installed on the furnace should be checked in
accordance with the heat-treatment plan.

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Requirement T16: If the checking of the measuring chain is not correct according to the heat-treatment
plan, an action plan shall be achieved.
Requirement T17: Calibration and verification of measuring chains shall be recorded in a report
indicating as a minimum the data below:
— identification of the sensor tested;
— identification of the test sensor;
— identification of the test instrument;
— date and time of test;
— furnace set point during the test;
— value read on the furnace instrument;
— value read on the test instrument;
— correction factors applied to the test sensor and the test instrument;
— corrected value of the test instrument;
— calculated error of the measuring chain;
— indication of test acceptance or failure;
— identification of the operator performing the test;
— company that realised the SAT (if not carried out in-house);
— signature of the calibration company representative (if not carried out in-house);
— quality department validation.
5.4.3 Temperature uniformity survey (TUS) of furnace (references T18 to T31)
Requirement T18: The heat-treatment company shall define and apply a heat-treatment plan
performed by pyrometric check or by product dispersion and follow-up check.
Recommendation T19: If the checking of the furnace temperature uniformity (mapping) is performed
through pyrometric check, it is recommended to carry out the uniformity check, at least the following:
— every year or with the indication of the heat-treatment plan and,
— after the following operations:
— implementation;
— relocation of the facility;
— reduction of the furnace class;
— any maintenance operation likely to affect the homogeneity of the furnace.
Maintenance operations that affect the furnace temperature uniformity should be documented.
Requirement T20: Thermocouples and standard devices used for TUS shall comply with
indications of 5.4.1.
Requirement T21: When a pyrometric check is performed, the temperature uniformity at a given level
shall be verified by installing sensors within the work zone of the furnace and ensuring that none of
them exceeds the specified limits for the furnace class (see Table 5).

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An adjustment should be made to the measuring instrument (to correct the measurement deviation).
Calibrations before and after adjustment shall be recorded on the report in order to monitor any drift of
the measuring instruments over time. See Figure 2.
NOTE 1 When heating a load in a furnace, three distinct phases can be observed: the heating period, a
transition regime and a steady-state operating regime.
Key
a temperature k steady-state operating regime
b time l regulation range
c setpoint temperature m temperature offset
d upper temperature limit for the furnace class n overshoot
e maximum temperature deviation in steady-state o maximum total temperature deviation
operating regime
f furnace class tolerance p maximum temperature deviation in steady-state
operating regime
g coldest sensor q temperature uniformity
h lower temperature limit for the furnace class r median temperature
i transition regime s maximum temperature in steady-state
operating regime
j heating period t minimum temperature in steady-state
operating regime
Figure 2 — Heating phases and control
Requirement T22: The work zones of the equipment shall be defined in the heat-treatment plan.
Requirement T23: The temperature uniformity survey shall be conducted under steady-state
operating conditions. The minimum duration shall be indicated in the heat-treatment plan.
Requirement T24: During the transition regime, an overshoot can occur. The overshoot temperature
shall not exceed the upper limit set for the furnace class (see Figure 2).
Recommendation T25: The number of sensors used for heat-treatment equipment should comply with
the recommendations given in Tables 9 and 10.

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Table 9 — Minimum number of sensors for heat-treatment equipment, depending on the

useful volume
Useful volume Vu (m3) Minimum number of sensors Locations of sensors
Vu < 0,1 5
0,1 ≤ Vu < 8,5 9
9 + 1 sensor per m3, with a

8,5 ≤ Vu
maximum of 24
Table 10 — Minimum number of sensors for a continuous furnace, depending on dimensions

Furnace dimensions
Working section Minimum number of Locations of sensors
Height (H) Width (w)
(S) sensors
N/A 3
w < 2,4 m
H ≤ 0,3 m
N/A 3 + 1 sensor every 0,6 m
w ≥ 2,4 m
for a with beyond 2,4 m
N/A S < 0,75 m2 5
N/A 0,75 m2 ≤ S 7
<1,5 m2
H > 0,3 m
N/A 1,5 m2 ≤ S 8
Requirement T26: The temperatures chosen for the test shall, as a minimum, encompass the extreme
processes temperatures.
NOTE 2 Intermediate temperatures can be defined to ensure that the temperature uniformity is constant over
the whole operating temperature range. A furnace can have various uniformity ranges. For example, ±5 °C from
500 °C to 650 °C and ±10 °C from 650 °C to 900 °C.

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Recommendation T27: The uniformity check should be performed with a load and an atmosphere
representative of the usual condition of use of the furnace and indicated in the heat-treatment plan.
Requirement T28: A minimum testing time, generally 30 min, shall be defined from the start of the
steady-start operating regime. The testing time shall be indicated in the heat-treatment plan.
Recommendation T29: If the check of the furnace uniformity survey (mapping) is performed
through pyrometric check, the check report should be drafted in the form of a calibration certificate in
accordance with a documentation template or in the form indicated as a minimum the data following:
— furnace reference;
— set point temperature and furnace setting parameters;
— temperature recording;
— instrument reference;
— brand name and model of the calibrated instrument;
— standard used during calibration;
— calibration method (manufacturer's instructions, other);
— required accuracy;
— as found and as left data at calibration point;
— offset as found and as left;
— sensitivity (if verified);
— declaration of test acceptance or failure;
— any limitations or restrictions relating to calibration;
— date of the calibration;
— date of the next calibration;
— authority having performed calibration or verification;
— quality department approval.
Recommendation T30: If the check of the furnace temperature uniformity (mapping) is performed
through dispersion measurements and product follow-up, the heat-treatment plan specifying the
conditions of implementation and validation of the check should be defined and applied.
Requirement T31: If the checking of the TUS is not correct according to the heat-treatment plan, an
action plan shall be achieved.
5.4.4 Drift of the soak times of the various heat-treatment phases (references HTT1 to HTT2)
Requirement HTT1: Procedures shall indicate the method for measuring the soak time of the various
heat-treatment phases for each process and indicate the soak time parameters and tolerances.
Requirement HTT2: The soak times of the various heat-treatment phases shall be monitored by a set
point alarm, followed by a recording or be checked and documented by signature at least once per heat-
treatment procedure or twice per work shift.
NOTE Usually, a soak time at the heat-treatment temperature is indicated (maximum, minimum soak, or
soak time). For some furnaces or equipment, the heat-treatment soak time can be characterised in the form of a
particular parameter: feed speed, belt speed, etc.

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5.5 Mastering of the heat-treatment medium
5.5.1 General
The medium in which the heat treatment is carried out can be solid, liquid (salt bath treatment), gaseous
or low pressure (vacuum).
NOTE During thermochemical treatments, the medium allows the surface to be enriched with one or more
chemical elements. At the opposite, in some cases (quenching, annealing, tempering, etc.), it is better that the
treatment medium is neutral for the part to be treated.
Solid media are not frequently used and they are covered by particular agreements between the heat-
treatment facility and the customer.
5.5.2 Control of carbon-containing atmosphere
5.5.2.1 General
The heat treatments concerned are those treatments performed under atmosphere and in which carbon
is the main element, e.g. case hardening, carbonitriding and derived heat treatments.
Low-pressure case hardening heat treatments are not concerned.
5.5.2.2 Atmosphere drift (references C1 to C6)
Requirement C1: Atmosphere furnaces, atmosphere generators and measurement devices shall be
operated by competent operator(s). If the flow is the only checking means, it shall be equipped with a
calibrated device used to measure the flow for all fluids and shall be subject to scheduled maintenance.
Requirement C2: The different gas flow parameters with tolerances shall be indicated in the heat-
treatment plan.
Recommendation C3: A means for continuous recording of the carbon content in the heat-treatment
atmosphere should be provided. The heat-treatment plan should indicate the nominal value of the
carbon content in the atmosphere with the tolerance.
Recommendation C4: In a carburising atmosphere, a soot burning programme for the furnaces and
generators should be foreseen. Its set up conditions should be documented.
Requirement C5: If one (or several) atmosphere generator(s) is (are) used, the temperature and the
atmosphere shall be continuously monitored.
Requirement C6: The atmosphere in the furnaces shall be monitored by a set point alarm, followed
by a recording or checked and documented by signature at least once per heat-treatment procedure or
twice per work shift.
5.5.2.3 Drift of measuring equipment (references C7 and C8)
Recommendation C7: For annealing, quench hardening, normalising, stress relieving treatments,
case hardening or carbonitriding in atmosphere, the carbon content in the heat-treatment atmosphere
should be checked at least twice per week, using another checking method (alternative method e.g.
oxygen probes or online infrared (IR) gas analysis).
Recommendation C8: When the alternative method is no longer correlating with the main method
within the prescribed limits, actions should be implemented to restore correlation between the
two methods.

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5.5.2.4 Presence of unwanted gases (references C9 and C10)
For furnaces with ammonia supply also used to perform heat treatments without ammonia, the
following recommendations should apply.
Recommendation C9: A device intended to eliminate any risk of accidental introduction of ammonia
in the furnace should be mounted. A three-valve ammonia (fail safe valve system) is permitted with
one manual and two electrical magnetic valves in series.
Recommendation C10: The ammonia should be removed from the furnace prior to performing any
heat treatment without ammonia, in accordance with a defined procedure.
5.5.3 Control of nitriding, nitrocarburising and derived heat-treatment atmospheres
For nitriding, the atmosphere drift is taken into account with requirements and recommendations
(references N1 to N6).
Requirement N1: Atmosphere furnaces and atmosphere generators for which the flow is the only
checking means shall be equipped with flowmeters (or equivalent checking devices) for all gases and
be subjected to scheduled maintenance. A procedure shall indicate the different flow parameters with
tolerances according to the heat-treatment cycle.
Requirement N2: If one (or several) atmosphere generator(s) is (are) used, the temperature and the
atmosphere shall be continuously monitored.
Requirement N3: The atmosphere in the furnaces shall be monitored by a set point alarm according
to the tolerance defined in the procedure, followed by a recording or be checked and documented by
signature at least once per heat-treatment procedure or twice per work shift.
Recommendation N4: During gas nitriding, and if there are no continuous checks with alarm
(hydrogen sensor, gas or flow infrared analysis), dissociation of ammonia should be checked at least
once per heat-treatment procedure or twice per work shift, and this shall be documented by signature.
Recommendation N5: For ferritic nitrocarburizing, and if there are no continuous checks with alarm,
the gas mixture should be checked at least once per heat-treatment procedure or twice per work shift,
and it shall be documented by signature.
Recommendation N6: For gaseous nitriding treatment the nitrogen potential should be monitored,
recorded and alarmed.
5.5.4 Control of salt bath and drift of treatment medium
The control of the drift of the heat-treatment medium is taken into account with requirements
(references SB1 to SB2).
Requirement SB1: For austenitising salt baths, the composition of the bath or the decarburisation of
the parts shall be checked before each use of the heat-treatment equipment and at least once per week
(e.g. foil).
Requirement SB2: For nitriding and nitrocarburizing salt baths, the chemical composition of the bath
shall be checked once per week.
5.5.5 Control of operational conditions of surface hardening after induction superficial heating
5.5.5.1 Error on the quenching profile or on the heat treatment characteristics of the product
(references SH1 to SH2)
Recommendation SH1: The heat-treatment plan should define the different process parameters such
as frequency, power, feed speed, cooling spray delay, heating temperature, heating time, inductor speed
for continuous heating, as well as nominal values with tolerances and periodic checking.

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Recommendation SH2: The temperature of the quenching fluid should be monitored by an alarm.
5.5.5.2 Part treatment lead time (reference SH3)
Recommendation SH3: A system for managing the inductors and cooling systems should be provided
with the following means:
— templates and/or drawings enabling quick manufacturing of spare inductors;
— available spare inductors;
— modification of the inductors after approval from the customer within two weeks.
5.5.5.3 Heat-treatment reproducibility (references SH4 to SH10)
Recommendation SH4: The quenching system should be automated, unless otherwise specified and
approved by the customer.
Recommendation SH5: A heat-treatment plan should define the control of the inductor and the
specified interval of exchange.
Recommendation SH6: The influent parameters (voltage, current, power, etc.) should be monitored
using a supervision device (set point alarm and recording) or documented by signature at least once
per heat-treatment procedure or twice per work shift.
Requirement SH7: For each start-up, end of production run, pre and post tool change, equipment
repair, station alarm (shutdown, malfunction, etc.), metallurgical characteristics shall be checked on
one part (induction pattern dimensions, surface hardening depth or total hardening depth, surface
and core hardness, microstructural observation). The checking frequency during production shall be
defined in a heat-treatment plan.
Recommendation SH8: The flow rate of the sprays should be automatically controlled or, failing
that, the spraying system should be checked and/or cleaned once per work shift or at documented
intervals suited to the risk. An alarm system for quench pressure and flow rate for high and low limit is
recommended. In the absence of an alarm system, the quench pressure and the flow should be checked
at start-up and at specified intervals.
Recommendation SH9: Solids in suspension in the quenching fluid should be checked every three
months, or at a different interval based on an available and documented experience. A complete
replacement of the quench media and cleaning of the tank at the same intervals satisfies this
recommendation.
Recommendation SH10: The concentration and/or density of the quenching fluid (polymers, brine
and caustic solutions) should be checked daily, or at a specified interval based on available and
documented experience.
5.5.6 Laser hardening (references L1 to L4)
Recommendation L1: A procedure should define the nominal value and tolerance of key process
parameters to monitor, record and alarm (frequency, speed, cycle of the speed if needed, cycle time,
amplitude, temperature regulation, etc.).
Recommendation L2: A pre-study should define the type of laser to use, the shape of the beam and the
major process parameters to apply.
Recommendation L3: In case of water-cooling copper bars, the follow-up of water temperature, water
flow should be monitored. The gap between bars and the part should be checked regularly according
to experience.
Recommendation L4: Positioning of the parts thanks to fixturing should ensure the repeatability of
the results.

BS ISO 20431:2023
ISO 20431:2023

5.5.7 Vacuum or low-pressure heat treatment (references V1 to V7)
Recommendation V1: The vacuum furnaces for thermochemical heat treatments should be equipped
with flowmeters (or equivalent checking devices) for all treatment gases and be subjected to scheduled
maintenance. See Table A.1.
Recommendation V2: The temperature, the pressure or vacuum and the gas flows should be
continuously monitored.
Recommendation V3: The time needed to reach the limit vacuum before heating should be monitored
with a set point alarm.
Recommendation V4: A leakage rate should be done every month, except for aeronautical
parts every week.
Recommendation V5: The leak test should be lower than 4 Pa/h except for titanium alloys lower
than 2 Pa/h.
NOTE 1 Pa is equivalent to 0,01 mbar.
Recommendation V6: The dew point of the different gases should be monitored with a set point alarm.
Recommendation V7: The characteristics of the electrical power delivered by the bias power supply of
plasma furnaces (amperage, voltage, duty cycle) should be monitored with a set point alarm.
5.6 Control of cooling
5.6.1 Equipment control and heat-treatment reproducibility (references CEQ1 to CEQ3)
Requirement CEQ1: All quench tanks shall be equipped with temperature measuring instruments.
Recommendation CEQ2: The quenching systems should be equipped with monitoring means or
equipment (e.g. control of agitation, temperature, level).
Recommendation CEQ3: The level, temperature and agitation of the quench tank should be monitored
by means of a supervision device (set point alarm and recording) or documented by signature at least
once per heat-treatment procedure or twice per work shift.
5.6.2 Control of cooling parameters (references CPM1 to CPM12)
Requirement CPM1: The quenching time shall be documented.

Requirement CPM2: Soak times before tempering or before cold treatment shall be documented.
Requirement CPM3: For batch furnaces or pushing type load continuous furnaces, the transfer
overtime shall be alarmed.
Recommendation CPM4: For batch furnaces or pushing type load continuous furnaces, the transfer
time should be monitored by a supervision system.
Recommendation CPM5: The quenching media should be checked at a specified interval based on the
acquired documented experience according to a specification.
The requirements related to the checks of the quenching fluids depend on the nature of these fluids and
are defined in accordance with Table 11.

BS ISO 20431:2023
ISO 20431:2023

Table 11 — Types and frequencies of the checks of quenching fluid

Nature of the Frequency or periodicity Requirement or recommen-
Check to be performed
fluid of the check dation
Daily or at different fre-
quencies defined from an
Polymer concentration Requirement CPM6
Polymers available and documented
experience
Solids in suspension Every six months Requirement CPM7
Every year or at a different
Solids in suspensiona ,
frequency defined from an
Water pH level, chloride content, Requirement CPM8
available and documented
etc.
experience
Solids in suspension Every six months Recommendation CPM9
Brines Concentration and/or den-
Daily Recommendation CPM10
sity
To be defined on the basis
of an experience (water
Oils content, solids in suspension, Every six months Requirement CPM11
viscosity, cooling curve, acid
value and flash point)
Analysis of baths and check
Salts At least once a year Requirement CPM12
of contaminants
a Mud, paste, soot and rust or metallic particles can be present as solids in suspension.
5.7 Control of product
5.7.1 Drift of testing means (references CP1 and CP2)
Requirement CP1: Product testing equipment shall be checked in accordance with the standards in
force and, for equipment listed in Annex A, at the frequencies given in Table A.1.
Requirement CP2: Hardness testing equipment shall be checked and calibrated in accordance with
the ISO 6506, ISO 6507 and ISO 6508 series and at the frequency defined in Annex A.
5.7.2 Non-conforming product (references CP3 to CP5)
Requirement CP3: The product shall be tested in accordance with the standards in force or using other
defined methods.
Requirement CP4: The documents drafted in accordance with the customer’s specifications and
defining the parameters of the product to be tested and the frequencies of these tests shall be supplied
and applied.
Requirement CP5: The product data shall be recorded and follow-up.
5.8 Finishing process

Recommendation F1: The tolerances of use related to the testing of soluble oils used as
corrosion inhibitors should be defined according to expiration or life duration and environment
protection durability.
Recommendation F2: The soluble oil concentration test should be carried out once per week, or at a
different frequency based on an available and documented experience.
Recommendation F3: The washing solution concentration and oil content tests should be carried out
once per week, or at a specified interval based on an available and documented experience. A specified
interval of washing bath and cleaning tank should be documented.

BS ISO 20431:2023
ISO 20431:2023

Recommendation F4: The temperature of the washing solution should be monitored (only if the
specified temperature is above the room temperature) by means of a supervision system or, failing
that, it should be checked before each use or once per day of use.
Recommendation F5: The chloride content in the washing solutions should be checked at least once
every three months or at a different frequency based on an available and documented experience.

BS ISO 20431:2023
ISO 20431:2023

Annex A
(normative)
Equipment calibration and frequency control
When used during the heat-treatment process, the testing or measuring equipment shall be checked in
terms of drift control or calibrated according to the specified intervals described in Table A.1.
All requirements in Table A.1 shall be scored according to 4.3.2.
In case of a non-conform drift control or calibration or at least every three years the equipment shall be
sent to supplier for maintenance.
Table A.1 — Calibration and drift control or routine check minimum intervals of available
measuring equipment related to the process
Equipment Drift control or routine check Calibration Example of control
Dew-point measuring Not required Calibration once a year (by
device the supplier or third party
or exchanged)
Gas analyser for CO / Weekly in case of continuous Calibration once per year by Using standard gases
CO2 / CH4 furnace or before each use return to the supplier
Gas analyser for Weekly in case of continuous Calibration once per year by Using standard gases
hydrogen furnace or before each use return to the supplier
Spark emission spec- Not applicable Calibration after a main- Using certified refer-
trometer or GDOES tenance and according to ence material (CRM)
return of experience standard
Device for deter- Daily or before each use Calibration once per year Using certified
mination of carbon reference material
through combustion (CRM) standard with a
(chips) defined percentage of
carbon
Non-automatic re- Before each use or at least once Calibration after an accident Zero with distilled
fractometer per day water
Oxygen/lambda Test the gauges with an alter- Calibration once per calen- Using a standard gas
probe native method (e.g. combustion dar year with a time frame
gas analyser, chips). The routine not exceeding 18 months
check period should be indicated
in the heat-treatment plan.
Gas or liquid mass or Regular cleaning according to Calibration once a year by
Coriolis flow meter return of experience return to the supplier
Volume flow meter, Checking monthly the good Calibration once per year or
rotameter and elec- functioning and integrated in the according to the return of
trovalve maintenance plan experience
Pressure manometer Checking twice a year Calibration every three
(overpressure) years for vacuum furnace
and/or according to the fre-
quency of use and integrated
into the maintenance plan
Vacuum gauge (pri- Twice per year Calibration of new or re- For the drift control:
mary and secondary paired devices or if the drift verification with a
vacuum) control is not compliant calibrated gauge

BS ISO 20431:2023
ISO 20431:2023

Equipment Drift control or routine check Calibration Example of control

Water flowmeter for Checking quarterly the good Calibration once per year or
vacuum furnace functioning and integrated in the according to the return of
maintenance plan experience
Thermocouples for Not applicable According to 5.4.1 and 5.4.2
endothermic- and ex-
Recalibration or replace-
othermic-atmosphere
ment once per year
generator
Rotation direction of Yearly checking and after a major Not applicable Visual checking
turbines and stirrers maintenance
Voltmeter and am- Quarterly functioning checking Calibration of voltmeter and
meter for the furnace ammeter for plasma and
power supply low-pressure furnaces once
per year
Level indicator Quarterly functioning checking Not applicable By manual action on
the sensor
Belt speed or convey- Twice a year and/or after main- Not applicable
or speed tenance and/or exchange of
conveyor parts
Automatic feeder Quarterly or following heat-treat- Calibration once a year for Drift control by check-
(weight and vibration ment plan indications the weight ing the number of
given the quantity of parts after a controlled
parts/meter) time
Overall state of belt Continuously on the fly and im- Not applicable
or loading jigs or plementation of a visual control
conveyor according to the furnace and the
frequency of use with integration
of it into the maintenance plan
Weight measurement Not applicable Calibration by the supplier Calibration using a
or a third party once per standard weight
year or if the drift control is
not compliant

BS ISO 20431:2023
ISO 20431:2023

Annex B
(informative)
Example of scoring table for requirements and recommendations
Table B.1 may be used to score the heat-treatment facility according to Clause 4.
Table B.1 — Example of scoring table for requirements and recommendations of the heat-
treatment facility
Assessment
Reference Score
100 80 50 20 0 N.A.
Documentation
Requirement GO1
Requirement GO2
Requirement GO3
Management responsibility
Requirement GO4
Requirement GO5
Management of human resources
Requirement GO6
Requirement GO7
Requirement GO8
Requirement GO9
Recommendation GO10
Infrastructure and equipment management
Requirement GO11
Recommendation GO12
Requirement GO13
Recommendation GO14
Requirement GO15
Requirement GO16
Recommendation GO17
Requirement GO18
Requirement GO19
Recommendation GO20
Requirement GO21
Recommendation GO22
Requirement GO23
Recommendation GO24
Recommendation GO25
Internal audit
Requirement GO26
Requirement GO27

BS ISO 20431:2023
ISO 20431:2023

Assessment
Reference Score
100 80 50 20 0 N.A.
Control of non-conforming product
Requirement GO28
Requirement GO29
Requirement GO30
Recommendation GO31
Requirement GO32
Requirement GO33
Requirement GO34
Recommendation GO35
Requirement GO36
Continuous improvement
Requirement GO37
Requirement GO38
FMECA
Requirement GO39
Requirement GO40
Recommendation GO41
Monitoring plan
Recommendation GO42
Recommendation GO43
Recommendation GO44
Preproduction quality planning
Recommendation GO45
Recommendation GO46
Statistics
Recommendation GO47
Recommendation GO48
Recommendation GO49
Controlling, monitoring and recording
Requirement GO50
Recommendation GO51
Recommendation GO52
Recommendation GO53
Recommendation GO54
Requirement GO55
Requirement GO56
Recommendation GO57
Recommendation GO58
Requirement GO59
Recommendation GO60
Requirement GO61
Requirement GO62
Contract review

BS ISO 20431:2023
ISO 20431:2023

Assessment
Reference Score
100 80 50 20 0 N.A.
Recommendation CR1
Requirement CR2
Recommendation CR3
Requirement CR4
Requirement CR5
Heat-treatment conception
Requirement HTP1
Requirement HTP2
Recommendation HTP3
Requirement HTP4
Load preparation
Requirement PR1
Recommendation PR2
Requirement PR3
Recommendation PR4
Recommendation PR5
Recommendation PR6
Recommendation PR7
Recommendation PR8
Recommendation PR9
Heat-treatment temperature error
Requirement T1
Requirement T2
Requirement T3
Recommendation T4
Requirement T5
Requirement T6
Requirement T7
Requirement T8
Recommendation T9
Recommendation T10
Requirement T11
Measuring equipment error SAT
Requirement T12
Requirement T13
Requirement T14
Recommendation T15
Requirement T16
Requirement T17
Requirement T18
Survey of furnace Temperature Uniformity
Recommendation T19
Requirement T20

BS ISO 20431:2023
ISO 20431:2023

Assessment
Reference Score
100 80 50 20 0 N.A.
Requirement T21
Requirement T22
Requirement T23
Requirement T24
Recommendation T25
Requirement T26
Recommendation T27
Requirement T28
Recommendation T29
Recommendation T30
Requirement T31
Drift of the soak times of the various heat-treatment
phases
Requirement HTT1
Requirement HTT2
Atmosphere drift
Requirement C1
Requirement C2
Recommendation C3
Recommendation C4
Requirement C5
Requirement C6
Recommendation C7
Recommendation C8
Recommendation C9
Recommendation C10
Control of nitriding, nitrocarburising and derived
heat-treatment atmospheres
Requirement N1
Requirement N2
Requirement N3
Recommendation N4
Recommendation N5
Recommendation N6
Control of salt bath and drift of treatment medium
Requirement SB1
Requirement SB2
Control of operational conditions of surface harden-
ing after induction superficial heating
Recommendation SH1
Recommendation SH2
Recommendation SH3
Recommendation SH4
Recommendation SH5

BS ISO 20431:2023
ISO 20431:2023

Assessment
Reference Score
100 80 50 20 0 N.A.
Recommendation SH6
Requirement SH7
Recommendation SH8
Recommendation SH9
Recommendation SH10
Laser hardening
Recommendation L1
Recommendation L2
Recommendation L3
Recommendation L4
Vacuum or low-pressure heat treatment
Recommendation V1
Recommendation V2
Recommendation V3
Recommendation V4
Recommendation V5
Recommendation V6
Recommendation V7
Equipment control and heat-treatment reproducibil-
ity
Requirement CEQ1
Recommendation CEQ2
Recommendation CEQ3
Control of cooling parameters
Requirement CPM1
Requirement CPM2
Requirement CPM3
Recommendation CPM4
Recommendation CPM5
Requirement CPM6
Requirement CPM7
Requirement CPM8
Recommendation CPM9
Recommendation CPM10
Requirement CPM11
Requirement CPM12
Drift of testing means
Requirement CP1
Requirement CP2
Non-conforming product
Requirement CP3
Requirement CP4
Requirement CP5

BS ISO 20431:2023
ISO 20431:2023

Assessment
Reference Score
100 80 50 20 0 N.A.
Finishing process
Recommendation FM1
Recommendation FM2
Recommendation FM3
Recommendation FM4
Recommendation FM5

BS ISO 20431:2023
ISO 20431:2023

Annex C
(informative)
Example of heat-treatment facility assessment
The final assessment of the heat-treatment facility is based on the following criteria:
— final score: the final score is calculated using Formula (1) (see 4.4);
— score according to the requirements and recommendations:
Score per audit section is calculated using Formula (1), row by row. The results are given in Table C.1 in
the last column.
Table C.1 — Results of the audit, scoring matrix

Reference Audit section A N0 N20 N50 N80 N100 Score
General organisation of the
5.1 31 3 2 5 8 13 72
heat-treatment facility
Contract review and heat-treat-
5.2 7 0 0 1 5 1 79
ment preparation
5.3 Preparation 2 1 0 0 0 1 50
Control of the
5.4 15 1 2 2 3 7 72
Carrying out thermal cycle
heat treat- Control of the
5.5 ments: heat-treatment 13 2 2 0 4 5 66
medium
5.6 Cooling control 9 2 1 6 0 0 36
5.7 Control of product testing 4 1 0 0 0 3 75
5.8 Finishing 5 0 0 0 3 2 88
Final result
86 10a 7b 14 23 32 68
(for the whole audit)
a Number of non-satisfied requirements: corresponds to the sum of values of the column (N0): 10.
b Number of recommendations with a score of 20: corresponds to the sum of the values of column (N20): 7.

BS ISO 20431:2023
ISO 20431:2023

Annex D
(normative)
Measuring chain testing methods (SAT - system accuracy test)
D.1 General
This annex provides the different methods for measuring chain testing.
D.2 Method 1
Method 1 is described in Figure D.1.
Key
A1 regulation system and monitoring chain
A11 controller
A12 recorder
A13 control thermocouple
B1 test chain
B11 test recorder
B12 test or resident thermocouple
C1 furnace wall
D1 work zone
E1 Max. distance between the two thermocouples: 80 mm
Figure D.1 — Measuring chain using method 1
The test thermocouple is placed as close as possible to the thermocouple to be tested (maximum 80
mm). The difference between the indication of the test chain and the indication of the control chain to
be tested shall be measured.
The test thermocouple may be a resident thermocouple. The test recorder can be replaced by a
test controller.

BS ISO 20431:2023
ISO 20431:2023

The deviation (SAT value) shall be the difference between the control measuring chain (regulation
system and monitoring chain) and the test chain values corrected with the test thermocouple correction
factor and the test recorder or controller correction factors.
The measurement deviations of the measuring chain and, when known, the measurement deviations of
the control chain to be tested, should be corrected.
The practice will consist in measuring the deviation between the chains at defined intervals.
For example, when checking a chain at a set point temperature of 850 °C, the following readings at 10 s
intervals are obtained as in Table D.1.
Table D.1 — Example of readings taken during verification of a measuring chain using method 1
Average
Measurement
1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th tempera-
(°C)
ture
Test chain 850,0 849,8 850,3 850,2 850 849,9 850 850,1 850,2 849,9 850,0
Control chain
852,1 851.0 853,2 853,2 852,8 853 853,1 854 852,9 853 852,8
to be tested
The calculated deviation can be expressed following Formula (D.1):

A1 = (B1 + C1) – (D1 + E1) (D.1)
where
A1 is the deviation SAT value;
B1 is the measurement control chain;
C1 is the correction factor test thermocouple;
D1 is the measurement test chain;
E1 is the correction factor test recorder or controller.
If B1 is 852,8 °C, if C1 is −0,2 °C, if D1 is 850 °C and if E1 is 0,1 °C, then A1 is 2,5 °C.
D.3 Method 2
The method 2 is a comparison between the temperature high limit thermocouple already installed in
the work zone of the furnace and the control measuring chain (regulation system and monitoring chain)
with two different thermocouples material natures but with the same precision. Method 2 is described
in Figure D.2.

BS ISO 20431:2023
ISO 20431:2023

Key
A21 controller
A22 recorder
A23 control thermocouple
B2 temperature high limit chain
B21 temperature high limit recorder
B22 temperature high limit thermocouple
C2 furnace wall
D2 work zone
The difference between the temperature of the control chain (regulation system and monitoring,
control thermocouple, recorder and controller) and the temperature high limit recorder or controller
is measured.
The deviation (SAT value) is the difference between the two measurements corrected with the
thermocouple correction factors.
For example, when checking a chain at a set point temperature of 830 °C, the following readings at 10 s
intervals are obtained as in Table D.2.
Table D.2 — Example of readings taken during verification of a measuring chain using method 2
Average
Measurement
1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th tempera-
(°C)
ture
Test chain 829,7 829,8 829,9 829,7 830,1 829,7 829,5 829,8 830,0 829,9 829,8,0
Control chain
829,1 829,3 829,4 829,1 828,9 829,5 829,3 829,4 829,2 829,1 829,2
to be tested
The calculated deviation (SAT value) can be expressed using Formula (D.2):
A2 = (B2 + C2) – (D2 + E2) (D.2)

BS ISO 20431:2023
ISO 20431:2023

where
C2 is the correction factor test thermocouple;
D2 is the measurement temperature high limit thermocouple;
E2 is the correction factor high limit thermocouple.
If B2 is 829,2 °C, if C2 is −0,2 °C, if D2 is 829,8 °C and if E2 is 0,1 °C, then A2 is -0,9 °C.
D.4 Method 3
The method 3 is only used when the methods 1 and 2 cannot be applied. The method 3 consists in
replacing a thermocouple (new or recalibrated) and in controlling the controller, the recorder and the
cable of the furnace thanks to a temperature calibrator or a thermocouple simulator. The method 3 is
described in Figure D.3.
Key
A31 controller
A32 recorder
A33 thermocouple cable
B3 test equipment
B31 temperature calibrator or thermocouple simulator
B32 new control thermocouple or new thermocouple calibration
C3 furnace wall
D3 work zone
The controller and the recorder are calibrated using a temperature calibrator or a thermocouple
simulator which sends a voltage corresponding to the process temperatures. The difference between
the displayed temperature and the defined temperature is the deviation (SAT value) corrected with the
thermocouple correction factor.
The difference between the simulated value and the value indicated on the working instrument
(recorder or controller) constitutes the measurement deviation of the instrument in the tested chain
named deviation chain instrument. The calibrated thermocouple also has a calibration measurement
deviation named correction factor thermocouple.

BS ISO 20431:2023
ISO 20431:2023

For example, when checking a chain at a simulated temperature of 870 °C. The displayed value is
870,8 °C. The deviation of the chain instrument is 0,8 °C (see Table D.2).
The total measurement deviation of the chain is given using Formula (D.3):
A3 = B3 + C3 (D.3)
where
C3 is the correction factor test thermocouple.
If B3 is 0,8 °C and if C3 is +0,4 °C then A3 is 1,2 °C.

BS ISO 20431:2023
ISO 20431:2023

Bibliography
[1] ISO/IEC Guide 99:2007, International vocabulary of metrology — Basic and general concepts and
associated terms (VIM)
[2] ISO 10012, Measurement management systems — Requirements for measurement processes and
measuring equipment
[3] ISO 22514‑6, Statistical methods in process management — Capability and performance — Part 6:
Process capability statistics for characteristics following a multivariate normal distribution
[4] IEC 60584‑2, Thermocouples — Part 2: Tolerances
[5] CETIM 9Q347, Temperature control in heat treatments chambers

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BS ISO 20431:2023

BSI Standards Publication

Heat treatment — Control of quality

Amendments/corrigenda issued since publication

Heat treatment — Control of quality

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5.6 Control of cooling................................................................................................................................................................................ 24

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Figure 1 — Heat-treatment process

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Heat treatment — Control of quality

3 Terms and definitions

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4 System for assessment and scoring of requirements and recommendations

Table 1 — Identification of requirements and recommendations

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Requirement or recom- Subclause in this docu-

4.2 General requirements

4.3 Scoring of requirements and recommendations

Determination of acceptable scores are typically part of the contractor agreement.

4.3.2 Scoring of requirements

The requirements shall be scored in accordance with the following criteria:

4.3.3 Scoring of recommendations

Recommendations shall be scored according to the criticalities listed in Table 2.

Table 2 — Scoring of recommendations according to their criticality

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4.4 Assessment of the heat treatment facility

E is the number N100 of satisfied recommendations multiplied by 100;

A is the number of the applicable scored requirements and recommendations.

The heat treatment facility shall be assessed using Table 3.

Table 3 — Heat treatment facility assessment

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Final result (for the entire audit)

Where a minimum score is to be obtained, and/or recommendations are to be fulfilled as requirements,

5 Requirements and recommendations

5.1 General organisation of a heat treatment facility

5.1.1 Documentation (references GO1 to GO3)

5.1.2 Management responsibility (references GO4 and GO5)

5.1.3 Human resources management (references GO6 to GO10)

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5.1.4 Infrastructure and equipment management (references GO11 to GO25)

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5.1.5 Internal audit (reference GO26 and GO27)

5.1.6 Control of nonconforming product (references GO28 to GO36)

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5.1.7 Continuous improvement (references GO37 and GO38)

5.1.9 Monitoring plan (references GO42 to GO44)

Recommendation GO42: A procedure to define and implement monitoring plans should be

5.1.10 Preproduction quality planning (reference GO45 and GO46)

Recommendation GO45: A preproduction quality planning procedure should be applied at the

5.1.11 Statistics: (references GO47 to GO49)

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5.1.12 Controlling monitoring and recording (references GO50 to GO62)

Table 4 — Resolution for analogue chart recording instrument

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