TECHNICAL ISO/TS

SPECIFICATION 4949

Second edition
2016-##-##

Steel names based on letter symbols

Désignations des aciers fondées sur des lettres symboles

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PROOF/ÉPREUVE
Reference number
ISO/TS 4949:2016(E)

© ISO 2016
ISO/TS 4949:2016(E)


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COPYRIGHT PROTECTED DOCUMENT

© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
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copyright@iso.org
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ii © ISO 2016 – All rights reserved

 ISO/TS 4949:2016(E)


Contents Page

Foreword......................................................................................................................................................................................................................................... iv
1 Scope.................................................................................................................................................................................................................................. 1
2 Normative references....................................................................................................................................................................................... 1
3 Terms and definitions...................................................................................................................................................................................... 1
4 Principles...................................................................................................................................................................................................................... 1
4.1 A unique steel name............................................................................................................................................................................ 1
4.2 Formulation of steel names........................................................................................................................................................... 1
4.3 Allocation of steel names................................................................................................................................................................ 1
5 Reference to product standards............................................................................................................................................................ 1
6 Classification of steel names..................................................................................................................................................................... 2
7 Structure of steel names................................................................................................................................................................................ 2
7.1 Initial symbol for steel castings................................................................................................................................................. 2
7.2 Steels designated according to their application and mechanical or physical
properties (group 1)........................................................................................................................................................................... 2
7.3
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Steels designated according to chemical composition (group 2)................................................................ 4

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7.3.1 Non-alloy steels (except free-cutting steels) with an average manganese

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content < 1 % (sub-group 2.1).............................................................................................................................. 4

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7.3.2 Non-alloy steels with an average manganese content ≥ 1 %, non-alloy
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free-cutting steels and alloy steels (except high speed steels) where the
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average content, by mass, of every alloying element is < 5 % (sub-group 2.2).......... 4

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7.3.3 Alloy steels (except high speed steels) where the average content by mass
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of at least one alloying element is ≥ 5 % (sub-group 2.3)............................................................. 5

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7.3.4 High speed steel (sub-group 2.4)....................................................................................................................... 5

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8 Additional symbols............................................................................................................................................................................................. 5
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Annex A (normative) Additional symbols indicating special requirements................................................................ 6

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Annex B (normative) Additional symbols indicating type of coating.................................................................................. 7

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Annex C (normative) Additional symbols indicating treatment condition................................................................... 8

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Bibliography................................................................................................................................................................................................................................. 9
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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 documents 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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
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Any trade name used in this document is information given for the convenience of users and does not

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constitute an endorsement.

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For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,
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as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the
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Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.

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The committee responsible for this document is ISO/TC 17, Steel.

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This second edition cancels and replaces the first edition (ISO/TS  4949:2003), which has been
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technically revised.
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iv PROOF/ÉPREUVE © ISO 2016 – All rights reserved

TECHNICAL SPECIFICATION ISO/TS 4949:2016(E)

Steel names based on letter symbols

1 Scope
This document specifies rules for the designation of internationally standardized steel grades by means
of symbolic letters and numbers to express application and principal characteristics (e.g. mechanical,
physical, chemical) so as to provide an abbreviated identification of steel grades.
NOTE 1 In order to avoid ambiguity, the principal symbols established according to this document can be
supplemented by additional symbols identifying additional characteristics of the steel or steel product, e.g.
suitability for use at high or low temperatures, surface condition, treatment condition, deoxidation.

NOTE 2 These rules can also be applied to nationally or regionally standardized steels.

2 Normative references
There are no normative references in this document. ) EW

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3 Terms and definitions
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For the purposes of this document, the terms and definitions in ISO 4948-1, ISO 4948-2 and
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ISO 6929 apply.
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ISO and IEC maintain terminological databases for use in standardization at the following addresses:
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— IEC Electropedia: available at http://www.electropedia.org/

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— ISO Online browsing platform: available at http://www.iso.org/obp

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4 Principles
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4.1 A unique steel name

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There shall be one unique steel name for each steel.

4.2 Formulation of steel names

Unless otherwise specified in this document, the symbols used in the steel name shall be written
without spaces.

4.3 Allocation of steel names

For steels specified in International Standards, Technical Specifications or Technical Reports, steel
names shall be allocated by the relevant subcommittee of ISO/TC 17.

5 Reference to product standards

The complete designation of a steel product where quoted in orders or similar contractual documents
shall include, in addition to the steel name, an indication of the technical delivery requirement in which
the steel is specified. For steels specified in standards this shall be the reference number of the relevant
product standard.

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Details of the structure of the steel name for the steel or steel product shall be provided in the relevant
product or dimensional standard.

6 Classification of steel names

For the purpose of designation, steel names are classified into two main groups.
— Group 1: Steels designated according to their application and mechanical or physical properties.
See 7.2.
— Group 2: Steels designated according to their chemical composition and further divided into four
sub-groups. See 7.3.

7 Structure of steel names

7.1 Initial symbol for steel castings

Where a steel is specified in the form of a steel casting, its steel name as specified in 7.2 and 7.3 shall be
preceded by the letter G.
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7.2 Steels designated according to their application and mechanical or physical

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properties (group 1)
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The coding shall comprise the following principal symbols.

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a) S = structural steels.
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P = steels for pressure purposes.

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L = steels for linepipe.

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E = engineering steels.
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Each followed by a number being the specified minimum yield strength in MPa for the smallest
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thickness range.
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NOTE 1 The term “yield strength” as used in this document refers to upper or lower yield strength, ReH or
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ReL , proof strength, Rp, or proof strength total extension, Rt , depending on the requirement specified in the
relevant product standard.

NOTE 2 1 MPa = 1 N/mm2.

When the specified minimum tensile strength is used instead of the specified minimum yield
strength, the letter T shall be added after the principal symbol, e.g. PT.
In order to distinguish structural steels of different regions an additional letter “G” may be added,
e.g. steel grade SG345, see ISO 630-2.
b) B = steels for reinforcing concrete.
Followed by a number being the characteristic yield strength in MPa.
c) Y = steels for pre-stressing concrete.
Followed by a number being the specified nominal tensile strength in MPa.
d) R = steels for or in the form of rails.
Followed by a number being the specified minimum Brinell hardness (HBW).

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e) H = cold rolled flat products of high strength steels for cold forming.
Followed by a number being the specified minimum yield strength in MPa or, where only the
tensile strength is specified, the letter T followed by a number being the minimum specified tensile
strength in MPa.
f) D = flat products for cold forming [except those in 7.2 (e)].
Followed by one of the following letters:
1) C for cold rolled products;
2) D for hot rolled products for direct cold forming;
3) X for products the rolled condition of which is not specified; and by two symbols characterizing
the steel allocated by the responsible body. See 4.3.
g) T = tinmill products (steel products for packaging).
Followed by the following letters:
1) for batch annealed grades, the letter S followed by a number being the specified nominal yield
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2) for continuously annealed grades, the letter H followed by a number being the specified
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nominal yield strength in MPa.
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NOTE 3 In the current version of International Standards for tinmill products ISO 11949:2016,
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ISO 11950:2016 and ISO 11951:2016, the steel names are designated not only according to the nominal yield
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strength, but also according to Rockwell HR30T hardness values. Since the last available techniques should
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be reflected in International Standards on packaging steels, the possibility of using the tensile test as the
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reference test for determining the mechanical properties would be considered during the next revision of
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these International Standards.

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h) M = electrical steels.
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Followed successively by the following:

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1) a number being 100 × the specified maximum specific loss expressed in W/kg, corresponding
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to the nominal product thickness, for a magnetic polarization at 50 Hz of

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i) 1,5 Tesla for semi-finished, non-oriented and normal grain oriented steels,
ii) 1,7 Tesla for reduced loss or high permeability grain oriented steels;
2) a number being 100 × the nominal thickness of the product in millimetres;
3) a letter indicating the type of electrical steel, i.e.
i) A for non-oriented products,
ii) D for non-alloy semi-finished (not finally annealed) products,
iii) E for alloy semi-finished (not finally annealed) products,
iv) N for normal grain oriented products,
v) S for reduced loss grain oriented products,
vi) P for high permeability grain oriented products.
NOTE 4 A hyphen is used to separate symbols (1) and (2).

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NOTE 5 The symbols to be indicated after the letter M concern electrical steels for use at the industrial
frequency of 50  Hz. For other uses such as steel products for relays and high frequency applications, the
principal symbols are not yet established.

7.3 Steels designated according to chemical composition (group 2)

7.3.1 Non-alloy steels (except free-cutting steels) with an average manganese content < 1 %
(sub-group 2.1)

The coding shall comprise successively the following symbols.

a) The letter C.
b) A number being 100 × the specified average percentage carbon content. Where the carbon content
is not specified by a range, the subcommittee responsible for the relevant product standard shall
select a suitably representative value.
NOTE To distinguish between two similar steel grades, the number indicating carbon content can be
increased or decreased by one unit.

The coding should be supplemented as follows: ) EW

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— E = with specified max sulfur content.
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— R = with specified sulfur content range.
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— D = for wire drawing.

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— C = for cold forming, e.g. cold heading, cold extrusion.

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— S = for springs.
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— U = for tools.
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— W = for welding rod.

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— G = other characteristics followed where necessary, by 1 or 2 digits.

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7.3.2 Non-alloy steels with an average manganese content ≥ 1 %, non-alloy free-cutting steels
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and alloy steels (except high speed steels) where the average content, by mass, of every alloying
element is < 5 % (sub-group 2.2)

The coding shall comprise successively the following symbols.

a) A number being 100 × the specified average percentage carbon content. Where the carbon content
is not specified by a range the subcommittee responsible for the relevant product standard shall
select a suitably representative value.
NOTE To distinguish between two similar steel grades, the number indicating carbon content can be
increased or decreased by one unit.

b) Chemical symbols indicating the alloying elements that characterize the steel. The sequence of
symbols shall be in decreasing order of the value of their content; where the values of contents are the
same for two or more elements, the corresponding symbols shall be indicated in alphabetical order.
c) Numbers indicating the values of contents of alloy elements. Each number represents the average
percentage content of the element indicated multiplied by the factors given in Table 1 and rounded
to the nearest integer. The numbers referring to the different elements shall be separated by
hyphens.
However, in order to follow the principle of keeping names as short as practical, one or more of
these digits may be omitted as long as there is no danger of confusion with a similar grade.

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Table 1 — Factors for alloying elements for steels in sub-group 2.2

Element Factor
Co, Cr, Mn, Ni, Si, W 4
Al, Be, Cu, Mo, Nb, Pb, Ta, Ti, V, Zr 10
Ce, N, P, S 100
B 1 000

7.3.3 Alloy steels (except high speed steels) where the average content by mass of at least one
alloying element is ≥ 5 % (sub-group 2.3)

The coding shall comprise successively the following symbols.

a) The letter X.
b) A number being 100 × the specified average percentage carbon content. Where the carbon content
is not specified by a range the subcommittee responsible for the relevant product standard shall
select a suitably representative value.
NOTE To distinguish between two similar steel grades, the number indicating carbon content can be
increased or decreased by one unit.
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c) Chemical symbols indicating the alloying elements that characterize the steel. The sequence of
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symbols shall be in decreasing order of the value of their content; where the values of contents are the
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same for two or more elements, the corresponding symbols shall be indicated in alphabetical order.
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d) Numbers indicating the values of contents of alloying elements. Each number represents the
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average percentage content of the element indicated rounded to the nearest integer. The numbers
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referring to the different elements shall be separated by hyphens.

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7.3.4 High speed steel (sub-group 2.4)

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The coding shall comprise successively the following symbols.

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a) The letters HS.

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b) Numbers indicating the values of percentage contents of alloying elements indicated in the
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following order:
1) tungsten (W);
2) molybdenum (Mo);
3) vanadium (V);
4) cobalt (Co).
Each number shall represent the average percentage content of the respective element rounded to the
nearest integer; the numbers referring to the different elements shall be separated by hyphens.

8 Additional symbols
Additional symbols indicating special requirements, the type of coating and the treatment condition
shall be used as specified in Tables A.1, B.1 and C.1 respectively.

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