ESR of High Technological Steels
ESR of High Technological Steels
ESR of High Technological Steels
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Abstract
This work aims at the suitability of electroslag process on production of high technological steels
such as Maraging steel, modified high speed tool steel (niobium, high nitrogen, and free nitrogen)
has been investigated. The experimental results show that high recovery of alloying elements
during electroslag remelting of such steels especially high nitrogen tool steel. The previous results
are attributed to the slag used in electroslag protect the molten metal from atmospheric oxygen.
Also higher recovery of alloying elements during remelting high nitrogen high speed tool steel are
due to partial dissolution of nitrides during remelting of such steel which increase nitrogen con-
tent above the molten slag which decrease the partial pressure of oxygen leads to protection of
molten metal from further oxidation. Also, the results show that, produced ingots are free from
internal pipes, porosity and other surface defects. Microstructure obtained for remelted steels are
very fine and well distributed for all steel under investigation. In the case of electroslag remelted
Maraging steels lower non-metallic inclusions with very fine inclusions and redistribution re-
tained austenite with very fine structure leads to increasing all tensile properties of investigated
steels. In the case of high speed tool steels, also the structure is very fine, well distributed, densely
and short carbides with lower non-metallic inclusions contents. High cooling rate accompanying
with electroslag process has a great effect on type, morphology and content of carbides precipi-
tated in both nitrogen and niobium modified tool steels.
Keywords
Electroslag, Maraging, Cobalt Free, Tool-Steel, Nitrogen, Niobium
1. Introduction
Maraging steels were originally developed at the Inco R and D Center [1]. They were produced by American
How to cite this paper: Halfa, H. and Reda, A.M. (2015) Electroslag Remelting of High Technological Steels. Journal of Min-
erals and Materials Characterization and Engineering, 3, 444-457. http://dx.doi.org/10.4236/jmmce.2015.36047
H. Halfa, A. M. Reda
Steel Industry and finally by production on a worldwide basis. These alloys are iron nickel martensites that are
hardened by precipitation of Mo and Ti containing inter-metallic compounds. The absence of carbon in the al-
loys confers significantly better harden-ability, toughness and weld-ability compared to conventional high
strength steels. Notable developments in recent years have been cobalt free grades of Maraging steels, and
number of other specialized compositions [2].
A combination of Co and Mo was found to produce much greater hardening during Maraging than the sum of
the individual Co and Mo hardening contributions [3]. Work with the Co-Mo hardening system led to the de-
velopment of three new Maraging steels compositions, the so-called 18 Ni (200), 18 Ni (250) and 18 Ni (300)
alloys. The numbers in parenthesis refer to the nominal recovery strengths of the alloys in Ksi units after aging.
Titanium was also added to these alloys as a supplemental hardener [4]. The properties of these alloys were con-
siderably better than the earlier 25 Ni and 20 Ni steels.
High speed steels are high alloyed carbon steels with a complex pattern of carbide. They are employed in cut-
ting tools operating at high speeds. Further, nitrogen and niobium have been used in the recent years as alloying
elements in many steel grades [5] [6]. AISI M41 high speed tool steels may be considered as high speed AISI
M2 tool steel but with addition of cobalt (5% - 10%). The increased cobalt aids the crystallization of primary
carbonitride phase colonies. Size and quantity of such colonies increasing with the higher cobalt alloying be-
cause cobalt removes carbon and nitrogen from the solid solution resulting in increasing the carbonitrides quan-
tity [7].
It seems very attractive to examine the possibility of alloying the high speed steel with niobium and nitrogen
and study its effect on the refining and mechanical properties of one of the most important high speed steel
(AISI M41).
These quality steel grades require sophisticated production technology. The properties of Maraging steel and
high speed tool steels containing niobium and nitrogen depend to a large extent on the production and refining
technology which affect the recovery and homogeneity of alloying elements as well as the cleanness of the pro-
duced steel [8].
The contamination of these steels with non-metallic inclusion (NMI), the homogeneity of matrix composition
and zone segregation of alloying elements has great influence of their properties.
Among the different refining processes such as vacuum arc remelting, electron beam remelting, plasma arc
remelting and electroslag remelting, electroslag remelting (ESR) process is considered as the most distinguished
secondary refining process due to its reality, economical production cost, low needed investments, system with
non-complicated upgrading and the competitive and high efficiency in refining different and complicated steel
grades. ESR of Maraging, high speed tool steels containing niobium and nitrogen have many advantages that
could be concluded in the improvement of quality structure, chemistry, processing, application and properties
[8]-[10].
The improvement in the quality of steel ingots produced by ESR process arises from obtaining sound ingots
with complete absence of pipes and porosity, clean smooth surface and high product yield. The structure of ESR
ingots may be improved through the uniformity, elimination of banding and zone segregation, control over the
direction and rate of solidification, control of grain size and control of carbides size [9] [10].
ESR process produces much cleaner ingots with smaller and uniform non-metallic inclusions (NMI), un-
iformly chemical composition, higher recovery of alloying elements, controlled reduction of undesirable ele-
ments, ability to correct out the electrode chemistry by proper slag chemistry and protection of molten metal
from atmospheric oxidation. ESR process improves the processing of steel ingots as it improves the weld-ability
and the workability and needs fewer critical conditions in electrode castings [9]-[11].
Refining of steels by ESR process improves their properties through improvement of ductility, impact transi-
tion characteristics, transverse properties, elevated temperature properties and corrosion resistance [9]-[11].
This work aims at study the suitability of electroslag process on production different advanced material such
as Maraging steel, niobium containing, high nitrogen and free nitrogen high speed tool steels.
2. Experimental Work
2.1. Melting
With the objective of this study, cobalt free low nickel newly developed Maraging steel and a new grade of
modified super hard high speed tool steel (niobium containing, nitrogen free and nitrogen containing) AISI M41
445
H. Halfa, A. M. Reda
have been produced. The investigated steels were produced by double melting routine [8] [10] [11]. A medium
frequency induction furnace (IF) was used to produce the investigated steels (Maraging and modified high speed
tool steels). The molten metal was casted in form of rods with 75 mm diameter and 120 mm height, where these
rods were forged and used as consumable electrodes in ESR process. Such electrodes were electro-slag remelted
under pre-fused calcium fluoride (CaF2) based slag with different additions of alumina (Al2O3), calcium oxide
(CaO) and titanium oxide (TiO2). These slags have approximately the same density and different viscosity and
interfacial tension, Table 1.
2.2. Evaluation
2.2.1. Non Destructive Test and Chemical Analysis
The produced ingots were first examined by radiographic tests to make sure they are free from solidification de-
fects. Then the produced ingot was cut in the longitudinal and transverse directions to physically examine the
presence of any cavity or holes. To evaluate the efficiency of ESR process, effect of slag chemical and physical
properties and the behavior of alloying elements during the refining process, samples from consumable electrode
produced by air melting induction furnace, IF and ingots produced by electroslag remelting, ESR at the top and
the bottom of the ingots were taken both at the center, half radius and the edge then chemically analyzed by us-
ing spectrographic analysis (SPGA).
where IA is the average of the integrated intensity from the (111)A and (200)A planes and IM is the intergraded in-
tensity from the (110)M planes. The correction factor 1.4 was determined experimentally by many investigator
[13] [14].
The investigated Maraging steel was solution-treated at 820˚C for 1 h and then air-cooled to room tempera-
ture. The aging treatments were performed at optimum condition [15]. To investigate the mechanical properties,
the plane strain tension Maraging steels test specimens were made according to ASTM specification E-8. The
data reported in this investigation are average values of three tests for each investigated steels.
Table 1. Chemical composition and physical properties [12] of synthetic slags at 1600˚C.
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H. Halfa, A. M. Reda
Table 2. Chemical composition of the consumable electrodes and the produced ingots by ESR
processes of investigated steel.
Recovery, %
Steel No. Process
C Si Cr Mo Ni Al Ti
ESR1 155.44 118.87 101.21 102.03 88.51 33.10 17.28
M3 ESR2 146.89 108.49 90.95 99.07 87.40 10.85 15.95
ESR3 150.26 135.85 96.78 99.66 94.90 55.66 39.88
*
Recovery = Metal output/Metal input * 100.
447
H. Halfa, A. M. Reda
higher elements recovery comparing with that obtained by remelting under slag 2.
The small deviation in chemical composition in produced ingot than consumable electrode may be attributed
to transfer of oxygen from atmosphere into metal through slag enhancing oxidation process. Thus, most alloying
elements (expect carbon) are slightly lower in ingot than consumable electrode. On the contrary to the other al-
loying elements, carbon content in the ingot is slightly higher than consumable electrode. This behavior may be
attributed to the effect of carbon content in slag at the start of operation. This slag was pre-fused in an arc fur-
nace. Carbon is picked up by slags to some extent. The greatest degree of carbon pick up is with slag containing
free lime, the lime combining with the graphite to form carbide
CaO + 3C= CaC2 + CO (2)
XRD showed CaC2 in investigated slags after fusion. As it is usual for refining under such slags, the carbon,
C in the slag enters the metal being refined, and carbon (C) is expected to be increased during ESR operation
and this explains the slight higher carbon content in the ingot comparing with the consumable electrode. In the
process of remelting under slags containing metals of variable valency, metal such as Al, Fe, Mn, Ti anions of
these metals ( AlO −2 , FeO −2 , MnO −2 , TiO −2 ) diffuse through the slag to the metal. Their passage to the metal is
accelerated substantially by convective current in the metal. At the slag-metal interface, anions of trivalent met-
als are reduced to bivalent ones, as shown in Equation (3):
( )
2 MeO −2 + [ Fe
= ( ) (
] 2 Me2+ + Fe2+ + 4 O2− ) ( ) (3)
Since oxygen passes from the slag to the metal by the reaction:
( Fe ) + ( O ) =[ Fe] + [O]
2+ 2−
(4)
Equation (3) shows that high oxygen dissolved in the molten metal which lead to high loss of alloying ele-
ments that have high affinity to oxygen Ti, Al, Cr, Mo, Ni in the molten metal pool. Table 3 illustrates the vari-
ation of different alloying elements content in the produced steels remelted under the different investigated slag
compositions comparing with the initial alloying elements content in consumable electrode. It is clear from Ta-
ble 2 that the degree of oxidation of alloying elements is depending on the slag composition and residual deoxi-
dation elements. The variation in alloying elements content depends on the affinity of such elements towards
oxygen. Element which has a low affinity towards oxygen such as Ni and Cr, its content has a little change. On
the other hand, titanium with its higher affinity towards oxygen suffers from a high change in its content.
It is known that [18], there are two valances of chromium (Cr2+ and Cr3+) dissolved in their slag. The ratio
Cr2+/Cr3+ increases with increasing temperature, decreasing oxygen potential and decreasing slag basicity. Under
ESR condition, i.e. in the basic slags and at low oxygen potential (at slag-metal interface), the bivalent chro-
mium predominates in the slag. As the chromic oxide particles in the slag react with de-oxidant elements Ti, Al
in molten metal droplets and slag metal interfaces, resulting in some recovery back into the steel. The tempera-
ture and molten metal composition have a significant effect on the direction of the reaction. Chromium is recov-
ered from slag by reducing its oxide with Ti, Al, Si. Under this reducing condition (molten metal/slag interface
and molten metal droplet/slag interface) the reaction to be considered is as formulated below
2 ( CrO ) + [Si ]= 2 [ Cr ] + ( SiO 2 ) (5)
As it is seen from experimental data, the higher slag basicity (high CaO) and the higher de-oxidant elements
content of steel, the lower is the change of chromium, i.e. the greater the chromium recovery from the slag.
Due to the high affinity of titanium towards oxygen to form TiO2 and its affinity to nickel to form Ni-Ti in-
termetallic compound, it could be expected that for high titanium steels content, the losses of titanium and Ni
content either by forming titanium oxide or Ni-Ti intermetallic compound is associated with increment of chro-
mium in the produced ingot. The decreasing of Ni content in different steels may be explained by formation
Ni-Ti intermetallic compound with rather big volume which picked in slag layer during ESR process.
448
H. Halfa, A. M. Reda
Unfortunately, due to the lack of published data on the nature of alloying elements during ESR process, one
could expect the oxidation behavior of alloying elements during the electroslag process in the following:
• As the temperature of slag bath rises above the melting point of the metal, droplets melt off the tip of the
electrode fall through the slag.
• As the temperature of fallen droplet is fairly high, the oxidation of constituent elements is taken place de-
pending on its affinity towards oxygen.
• Increasing the wetting of fallen droplet with slag, i.e., decreasing the interfacial tension represents a protec-
tive layer against diffusion of oxygen towards metal droplet with the result of decreasing the oxidation rate and
hence increasing the recovery of alloying elements.
• Inhibition of the diffusion of oxygen towards metal droplet by increasing the slag viscosity results in increas-
ing the recovery of alloying elements. So one could expect that among the three used slags, the slag with the
highest viscosity and the lowest interfacial tension will lead to the highest recovery of alloying elements Ni, Cr
and Ti.
The recovery of alloying elements in ESR can be carried with the physical properties of slags, Table 2 and
Table 3. Table 2 and Table 3 show clearly the effect of slag viscosity and slag/metal interfacial tension on the
behavior of different alloying elements during ESR process. Among the three investigated slags, slag 1 has the
lowest viscosity and highest interfacial tension. As the temperature of slag bath rises above the melting point of
the metal, droplets melt off the tip of electrode fall through the slag. Inhibition of the diffusion of oxygen
through slag towards metal droplet by increasing the slag viscosity results in decreasing the oxidation of alloy-
ing elements and consequently increasing of the recovery of these elements, Table 3. Furthermore, increasing
the wetting of fallen droplet with slag, i.e. decreasing the interfacial tension, represents a protective layer against
diffusion of oxygen towards metal droplet with the result of decreasing the oxidation rate and hence increasing
the recovery of alloying elements, Table 3. This explains the higher recovery of alloying elements by remelting
under either slag 2 or 3 comparing with that obtained by remelting under slag 1.
The role of slag viscosity is clearly shown in steels with high titanium content. Increasing the slag viscosity
from 0.25 poise (slag 1) to 3 poise (slag 3) through 0.8 poise (slag 2) is accompanied by increasing the recovery
of Cr, Ni, Mo and Ti alloying elements.
Generally, we can conclude that, there is a trend to increase the recovery of alloying element, i.e. decreasing
the losses during ESR process by increasing the viscosity of used slag and decreasing the slag/metal interfacial
tension of used slag.
Furthermore, increasing the TiO2 content in the used slag increases the tendency to equilibrium situation
(Ti)/[Ti], which in turn decreases the oxidation of titanium element at metal droplet/slag interface. This pheno-
menon leads to decreasing the percentage of Ti losses. So, it is expected that the highest recovery of titanium
will be obtained by increasing TiO2 in slag 3% to 30%.
3.1.2. Metallography
Figure 1 shows the microstructure of different heats of Maraging steel under investigation produced by induc-
tion furnace (IF) and electroslag remelting (ESR) after optimum aging conditions. Microstructure of steel pro-
duced by both IF and ESR comprises martensite + retained austenite. By comparing between microstructure of
investigated steels we found that, the structure of ESR are very finer, well distributed and free from segregation
or band structure than IF steels.
Typical optical micrographs of the material produced by IF and aged under optimum condition are shown in
first column in Figure 1. The microstructure, in general appeared lamellar in morphology. The prior-austenite
grain boundaries could not be resolved easily. The bright patchy regions, shown by arrows in the micrograph,
correspond to regions having considerable volume fraction of reverted austenite. The presence of inter lath aus-
tenite, though not fully resolved, is also indicated in the microstructure.
The optical micrographs of the material produced by ESR in the peak-aged conditions are shown in Figure 1.
The microstructure in the peak-aged condition essentially consisted of packets of martensite, within prior-aus-
tenite grains. The austenite grains, which had transformed into packets of martensite, could still be recognized
due to the preferential etching along their boundaries and also due to the fact that the martensite packets within
an austenite grain did not extend beyond the respective prior-austenite grain boundary. The martensite substruc-
ture could not be observed because of the narrowness of the martensite laths. During aging of the steels under
investigation the well-known precipitation reactions occur which leading to hardening. It is generally believed
449
H. Halfa, A. M. Reda
Figure 1. Metallographical microscope observation of investigated steel before and after ESR.
that initial precipitation in cobalt free molybdenum containing Maraging steel at 480˚C occurs as Ni3Mo, which
on prolonged aging is replaced by either Fe2Mo or the σ phase [19]. Since the alloy additionally contains tita-
nium as a supplemental hardener, the precipitation of Ni3Ti has also been reported; alternatively, it has been
suggested that part of the titanium may be present in the molybdenum precipitate, i.e. as Ni3(Mo, Ti) [2]-[20].
450
H. Halfa, A. M. Reda
800
M (110)
a)
600
400
M (211)
M (220)
A (111)
M (200)
A (200)
200
Intinisty (a.u)
0
800
M (110)
b)
600
400
A (111)
M (211)
M (200)
M (220)
A (200)
200
0
0 20 40 60 80 100 120
2 theta
(a)
600
a)
M(110)
400
M(211)
M(200)
M(220)
A(111)
A(200)
200
600
0
M(110)
Arbutary unit
400 b)
A(111)
M(211)
M(200)
M(220)
A(200)
200
600
0
M(110)
c)
400
M(211)
M(200)
M(220)
A(111)
A(200)
200
0
0 20 40 60 80 100
2 theta
(b)
Figure 2. (a) X-Ray pattern of M3 Maraging steel before ESR. a) Solid solution annealing at 820˚C, b) Solid
solution annealing at 820˚C and Aging; (b) X-ray diffraction pattern for steel M3 after ESR. a) Under slag 1
(70/15/15), b) Under slag 2 (52.5/22.5/25), c) Under slag 3 (70/30).
Heat treatment
Mechanical properties measurements
condition Retained
Steel No. Process
Temp. Time, Austenite, % Y.S U.T.S Reduction
Elong., %
˚C hr (MPa) (MPa) of area, %
451
H. Halfa, A. M. Reda
as intermetallic compound could be in solution causing solid solution strengthening. Consequently, the streng-
thening effect of titanium solution treated Maraging steel is combined effects of solid solution, microstructure
refinement, non-metallic precipitation and intermetallic precipitation strengthening.
Table 5. Chemicalcomposition of the high nitrogen and free nitrogen steels (wt%).
Table 6. Chemical composition of the niobium containing high speed tool steels (wt%).
Recovery %
Steel No. process
C Si Cr Mo Co V W
ESR1 103.4 105.6 99.3 98.0 99.4 94.3 96.3
M41 ESR2 93.7 80.5 91.5 92.5 98.6 86.9 93.5
ESR3 100.3 98.2 97.4 98.0 99.6 97.3 99.0
ESRN1 102.9 98.4 96.6 96.1 104.4 96.7 99.0
M41N ESRN2 104.1 96.1 93.0 96.2 104.7 94.1 91.6
ESRN3 116.7 97.0 95.5 99.1 104.5 101.4 101.5
*
Recovery = Metal output/Metal input * 100.
452
H. Halfa, A. M. Reda
Table 8. Recovery* of different elements during ESR process niobium containing high speed tool steels.
Recovery, %
Steel No. process
C Si Cr Mo Co V W Nb
HSS-Nb 1 ESR1 87.7 71.46 92.78 92.70 98.81 90.15 99.18 95.35
HSS-Nb 2 ESR2 80.33 55.75 94.04 93.81 100 91.13 97.57 90.00
HSS-Nb 3 ESR3 91.80 100 95.27 94.70 102.18 93.60 98.53 96.48
*
Recovery = Metal output/Metal input * 100.
As it is clear from Table 7 and Table 8, high recovery values for all elements were obtained by electroslag
remelting under all investigated slags. However, remelting under either slag 1 or slag 3 produced steel ingots
with much higher elements recovery comparing with that obtained by remelting under slag 2.
It is noticeable that recoveries of alloying elements in ESR are high. This result could be attributed to the
physical properties of slags, Table 7 and Table 8. Among the three investigated slags, slag 2 has the lowest
viscosity and highest interfacial tension. As the temperature of slag bath rises above the melting point of the
metal, droplets melt off the tip of electrode fall through the slag. Inhibition of the diffusion of oxygen through
slag towards metal droplet by increasing the slag viscosity results in decreasing the oxidation of alloying ele-
ments and consequently increasing the recovery of these elements. Furthermore, increasing the wetting of fallen
droplet with slag, i.e. decreasing the interfacial tension, represents a protective layer against diffusion of oxygen
towards metal droplet with the result of decreasing the oxidation rate and hence increasing the recovery of al-
loying elements. This explains the higher recoveries of alloying elements by remelting under either slag 1 or 3
comparing with that obtained by remelting under slag 2.
It is also noticeable that recoveries of alloying elements are higher for steel M41N comparing with that of
steel M41. This could be explained by the behavior of nitrogen during remelting process. A part of nitrogen
transfers to slag and surrounding atmosphere from the consumable electrode. This is expected to reduce the par-
tial pressure of oxygen and retard oxidation process with the consequence of increasing the recovery of alloying
elements.
As it is clear from Table 8, high recovery values for niobium was obtained by electroslag remelting under
slag no. 1 and slag no. 3 with lower viscosity. This result can be also attributed to the same reasons of nitrogen
containing and nitrogen free high speed tool steel.
453
H. Halfa, A. M. Reda
Table 9. EDS analysis of NMI of investigated nitrogen free high tool speed steel, AISIM41.
C N V Cr Fe Co W Mo MxCy
Table 10. EDS analysis of NMI of investigated nitrogen high tool speed steel, AISIM41.
and directional solidification, which do not allow elements, above all carbon to segregate. Therefore, carbides
grow longer and thicker and make their distribution more uniform.
X-ray diffraction pattern confirms the presence of the phases recognized from the metallographic observations.
The presence of MC, M6C, M2C and M23C6 carbides is ascertained depends on the chemical compositions of
steels. The chemical composition of the carbides was determined using EDS microanalysis in the SEM.
Typical composition of carbides in wt%, as determined by EDS microanalysis are presented in Tables 9-11.
For all steel under investigation, the major chemical elements in M6C carbide are tungsten, molybdenum and
iron. For standard high speed tool steel, AISI M41 M2C carbide contains nearly four times as much-chromium
and three times as much-vanadium as M6C carbide. Molybdenum in M6C carbides is three times greater than
M2C carbides while tungsten in M2C is two times greater than M6C.
On the other hand, for niobium containing steel, molybdenum and in particular tungsten concentrations in
M2C are generally less than in M6C. The considerable amount of iron in the M2C carbide is presumably due to
the high cooling rate during solidification, as high cooling rates are prevailing in the ESR process. As well as
MC carbides are vanadium rich carbide in standard steel while in niobium containing steel, this carbide mainly
consists of niobium which dissolve considerable amount of vanadium, tungsten and molybdenum. EDS micro-
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H. Halfa, A. M. Reda
Table 11. EDS analysis of NMI of investigated Nb-containing high speed tool steels.
HSS-3Nb 21.77 0.67 8.6 1.07 6.65 53.3 4.22 3.77 NbC
chemical analysis of carbide precipitated during cooling/solidification of investigated steel show that the M6C
carbides in AISI M41 contain two times more tungsten than niobium containing steels, Table 11. From the re-
sults summarized in Table 11, the M2C and M4C3 type carbides may precipitate also in certain solidifica-
tion/cooling conditions. The fine (dispersive) carbides of the MC, M2C and M4C3 types precipitate during solidi-
fication in electroslag remelting process. The considerable amount of the M2C carbide is presumably due to the
high cooling rate during solidification/cooling, as high cooling rates are prevailing in the ESR process. From the
result of X-ray diffraction and micro-chemical analysis, carbides precipitate from standard steel specimens has
been identified mainly as MC, M2C, M6C and M23C6 on the other hand; decrease of M23C6 carbides for niobium
containing steels was presumably.
4. Conclusions
4.1. Recovery and Homogeneity of Alloying Elements
• Recovery of all alloying elements in ESR is very high.
• Higher recovery of alloying elements is obtained by ESR under slag of high viscosity and low interfacial ten-
sion (slags 1 and 3).
• The new production technique “air induction melting followed by ESR” is suitable technique for production
this kind of steels.
4.2. Microstructure
• In the case of Maraging steels, the structure of induction heats are lath martensite + austenite and NMI. On
the other hand microstructure of ESR ingots was very fine and well distributed and austenite grain are impeding
between lath martensite.
• For high speed tool steels, solidification parameters in electroslag remelting process not only change the
amount of carbides precipitated but also the morphology and the chemical composition of this carbides.
• Nb-alloying improves the shape, size and distribution of carbides precipitated in the produced ingot.
• For high speed tool steels, added niobium causes a strong stabilization of the MC carbide and the MC stabili-
ty strongly increases with increasing niobium content.
• Extracted carbides precipitated from investigated electroslag remelted steel specimens have been identified
mainly as MC, M2C, M6C and M23C6. But niobium carbides (NbC) precipitated from niobium containing steels
restricted the formation of M23C6. Quantity of M23C6 carbides precipitated from niobium containing steel is low
than that precipitated from standard steel.
• The main carbides in the free nitrogen and nitrogen contained high speed steels are M6C and M7C3.
• The nitrogen contained high speed steel has the highest precipitates content among the investigated steels.
455
H. Halfa, A. M. Reda
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