Materials and Design 30 (2009) 340–345

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Materials and Design

journal homepage: www.elsevier.com/locate/matdes

Phase diagram calculation of high chromium cast irons and influence

of its chemical composition
Da Li a, Ligang Liu a, Yunkun Zhang a, Chunlei Ye a, Xuejun Ren b, Yulin Yang a, Qingxiang Yang a,*
a
National Key Laboratory of Metastable Materials Science and Technology, College of Material Science and Engineering, Yanshan University, Qinhuangdao 066004, PR China
b
School of Engineering, Liverpool John Moores University, Liverpool L3 3AF, UK

a r t i c l e i n f o a b s t r a c t

Article history: The phase transformation and the carbide precipitation temperatures of the high chromium cast iron
Received 12 July 2007 with Cr content of 15% were measured by using differential scanning calorimetry (DSC). The matrix
Accepted 26 April 2008 and the type of carbides of the specimen after quenching were determined by using X-ray diffraction
Available online 3 May 2008
(XRD) in this work. Meanwhile, the shape and the number of carbides in the different specimens were
detected by using optical microscope, scanning electron microscope (SEM) & energy dispersive spectrom-
Keywords: eter (EDS). The equilibrium phase of this high chromium cast iron was calculated by using Thermo-Calc
High chromium cast iron
software based on above experiments. The calculation results obtained from Thermo-Calc software is
Phase diagram calculation
Thermo-Calc
agreed with the ones from experiments. The work provides a practical method for engineers and
researchers in related areas.
Ó 2008 Elsevier Ltd. All rights reserved.

1. Introduction In this work, the specimen was taken from the high chromium
cast iron with 15% Cr. The equilibrium phase for this high chro-
High chromium cast iron is an important abrasion-resistant mium cast iron was calculated by using Thermo-Calc software.
material [1]. Because of the excellent abrasion resistance and The types of equilibrium phase of the high chromium cast iron at
the presence of hard carbides in their microstructures, high different temperature were forecasted and evaluated. The influ-
chromium cast iron was widely applied in the domains of mech- ence of Cr and C contents on the phase diagram was discussed,
anism, metallurgy and mine [2–4]. Its outstanding service perfor- which provides the basis for investigating and developing high
mance is due to more M7C3-type carbides with high hardness chromium cast iron with excellent performance.
distributing on the matrix, which is composed of martensite
and small amount retained austenite after heat treatment [3– 2. Experimental material and method
7]. However, the application conditions of the high chromium
The chemical composition of the high chromium cast iron is listed in Table
cast iron have gradually become more complicated [8] and need
1.The specimens were machined into circular cylinder (Ø 4 mm  4 mm) by wire
to find ways to solve these problems. Therefore, it is important cutting machine, then alcohol was used to clean the surface. The specimen was
to investigate the effect of different factors on abrasion, improve heated up from room temperature to 1500 °C, and then cooled to the room temper-
abrasion resistance of metal and develop new abrasion-resistant ature with speed of 5 °C/min. The differential scanning calorimetry (DSC) curves of
alloys. heating and cooling processes were determined by analyzing exothermic and endo-
thermic peak position and shape, the temperature of phase transformation and the
According to the characteristics of high chromium cast iron, if
carbide precipitation temperature of the specimen.
its chemical composition can be controlled and proper heat treat- Three specimens were taken to heat up to 1200 °C and held for 10 min. After the
ment be adopted, the abrasion resistance and hardness of high specimens were cooled to 1100 °C, 900 °C, 700 °C in the furnace, respectively, they
chromium cast iron are better than most other carbon steels were quenched into water. The specimens were recorded as A, B, C, respectively,
after grinded, they were corroded with 4% nitric acid spirit of alcohol. The micro-
[1,9,10]. While the composition of the present high chromium cast
structure of the specimens was observed by using the optical microscope of type
iron has no uniform criterion and lack of correlation alloy phase XJG-05 and the hardness was determined by the Rockwell tester. The carbides types
diagram, so it is difficult to avoid the repeat and blindness in the of the quenched specimens were determined by X-ray diffraction (XRD) of type D/
research work of high chromium cast iron. max-2500/PC.
Based on above experiments, the equilibrium phase diagram of high chromium
cast iron with composition of C-2.0%, Cr-15%, Mo-0.20%, Ni-1.0% was calculated by
using Thermo-Calc software, and compared with the experimental results. Then,
the equilibrium phase type at various temperatures with different C and Cr contents
* Corresponding author. Tel.: +86 335 838 7471; fax: +86 335 807 4545. of high chromium cast iron were forecasted and evaluated by Thermo-Calc
E-mail addresses: qxyang@ysu.edu.cn, yqxsyfys@yahoo.com (Q. Yang). software.

0261-3069/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.matdes.2008.04.061
 D. Li et al. / Materials and Design 30 (2009) 340–345 341

Table 1 3.2. Microstructure observation and XRD curve of the high chromium
The chemical composition of the high chromium cast iron cast iron
Element
C Cr Ni Mo The specimens were heated up to 1200 °C and held for 10 min,
Content/wt% 2–2.7 12–18 1–1.5 0.1–0.4 after cooled to 1100 °C, 900 °C and 700 °C in furnace, then
quenched into water, whose microstructures and XRD diagram
are shown in Figs. 2–4.
It can be seen from the Fig. 2a and b that, the matrix in this
microstructure is composed with residual austenite and martens-
3. Results and discussion
ite when the specimen was quenched at the temperature
1100 °C, and the eutectic carbides M7C3 are precipitated from the
3.1. DSC curve of the high chromium cast iron
matrix, which are with lath shape and discontinuous net distribu-
tion. The hardness of the specimen is HRC 45.6, which is lower than
The DSC curve during cooling process of the high chromium cast
that in cast state. So it can be known that after quenching at
iron is shown in Fig. 1. It can be seen from Fig. 1, the temperature of
1100 °C, more amount of austenite can be formed.
the specimen is recorded from 1500 °C and an exothermic peak is
From Fig. 3a and b that, the microstructure of the specimen is
appeared when the temperature is cooled to 1315 °C. The reason is
composed with eutectic carbides, martensite and small amount
possibly caused by the primary austenite formed from the liquid
austenite, meanwhile the secondary carbides are also precipitated
phase. When the temperature is cooled to 1234 °C, the second peak
at the temperature 900 °C. The phase with net shape is carbide and
is appeared in the curve, which maybe the eutectic reaction and
that with black massive shape is martensite. The hardness of the
the eutectic austenite and the carbides are formed.
specimen is HRC 64.1, which is higher than that at 1100 °C.
From Fig. 4a and b that, the eutectoid transformation occurred
when the specimen was cooled to 700 °C, the microstructure is
composed with pearlyte and a few carbides.
As shown in the above experiment, the microstructure of the
high chromium cast iron at quenching condition mainly is
composed with martensite and residual austenite. The type of
0.02 the carbides mainly is M7C3 (Cr7C3, (Fe, Cr)7C3). Combined micro-
0.00 structures and the hardness value, it can be known that when
-0.02 the specimen was quenched at 900 °C, the number of the carbide
is increased and that of residual austenite is reduced obviously,
DSC/(mW * mg-1)

-0.04
and the hardness is highest.
-0.06
-0.08 4. Phase diagram calculation and the influence of its chemical
-0.10 composition
-0.12
1315 °C 4.1. Phase diagram calculation
-0.14
-0.16 The composition of the high chromium cast iron was chosen as
1234 °C
-0.18 C-2.0%, Cr-15%, Mo-0.20%, Ni-1.0%. Its equilibrium phase diagram
was calculated by using Thermo-Calc software, which is shown
0 200 400 600 800 1000 1200 1400 1600
in Fig. 5.
Temperature/°C
It can be seen from Fig. 5, the eutectic temperature nearby
Fig. 1. DSC curve of the high chromium cast iron. 3.6%C (the ratio of the chromium to carbon is about 4.17) in this
phase diagram. The primary austenite dendrite structure starts to

a b
300
A
B A- γ
250
B-α-Fe
C-(Fe,Cr)7C3
200 D-Cr7C3
Intensity

B
150 C
D
A
100 C
D
A B A
50 C B C A
D C A B
μ
50 μm B D D B
0
20 40 60 80 100 120
2-Theta (°)

Fig. 2. The microstructure and the XRD diagram of the high chromium cast iron quenched at 1100 °C. (a) Microstructure, (b) XRD diagram.
342 D. Li et al. / Materials and Design 30 (2009) 340–345

a b
400 B
C A-γ
D B-α-Fe
C-(Fe,Cr)7C3
300
D-Cr7C3

Intensity
200

100
B
C C
AC D
D
50 μm CD C A A B
0
20 40 60 80 100 120
2-Theta (°)

Fig. 3. The microstructure and the XRD diagram of the high chromium cast iron quenched at 900 °C. (a) Microstructure, (b) XRD diagram.

a b
400
B
350 C A-γ
D B-α-Fe
300
C-(Fe,Cr)7C3
250 D-Cr7C3
Intensity

200

150

100
A C
50 CC D A
D
DD C A B B
50 μm 0
20 40 60 80 100 120
2-Theta (°)

Fig. 4. The microstructure and the XRD diagram of the high chromium cast iron quenched at 700 °C.

be formed when the temperature is decreased to 1290 °C. The car- 1245 °C and is finished at 1210 °C. The eutectic temperature calcu-
bon content of the surplus liquid phase gradually approached to lated by Thermo-Calc software is quite close to the result deter-
the eutectic composition (approximately 3.6%C). The eutectic reac- mined by DSC.
tion L ? c + M7C3 occurs when the temperature is decreased to At the temperature range from 735 °C to 1210 °C, the two phase
area of austenite and M7C3 carbide exist in the phase diagram. The
1600 secondary carbide M7C3IIis precipitated continuously with the
1500 decreasing of the temperature, so the number of c is decreased
L
L+δ while that of M7C3 is increased gradually. The austenite composi-
1400
L+δ+γ tion is the eutectic one when the temperature is decreased to
δ+γ L+γ L+M7C3
1300 735 °C and eutectoid reaction c ? P (a + M7C3) occurs, the trans-
Temperature/°C

γ
formation is finished when the temperature is decreased to 700 °C.
1200
γ+M 7C3 L+γ +M7C3 The balance microstructure of the high chromium cast iron at
1100 room temperature is P(a + M7C3) + Le(P + M7C3 + M7C3II) + M7C3II
γ+M 23C6+M7C3
1000 and the equilibrium phase is a + M7C3. As shown in the above anal-
γ+M 23C6 ysis, the phase of each sector and the transformation temperature
900
α+γ+ M7C3 of the high chromium cast iron calculated by Thermo-Calc soft-
800 ware are agreed with the experimental results, so it can instruct
δ+M23C6 the phase diagram calculation and the composition design of the
700 α+ M23C6+M7C3
+M7C3 new type of high chromium cast iron.
600
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
4.2. Influence of Cr content on phase diagram
Content of C/wt%

Fig. 5. The equilibrium phase diagram of 15Cr–1Ni–0.2Mo high chromium cast The composition of high chromium cast iron is 2C–15Cr–1Ni–
iron. 0.2Mo. In the process of calculation, other element contents are
 D. Li et al. / Materials and Design 30 (2009) 340–345 343

a 1600 b 1600
L L
1500 1500
1400 1400
L+γ
L+γ
1300 1300 γ

Temperature/°C
Temperature/°C

γ
1200 γ+K 2 1200
1100 L+γ+K2 1100 L + γ +K 2
γ+K2
1000 γ+K1 1000
γ+K1
γ+K 1+K2 900 γ+K1+K2
900
α+K2
800 800

700 α+K1+K2 700 α+K1+K2

α+K 2
600 600
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Content of C/wt% Content of C/wt%

c 1600 d 1600
1500 1500 L
L
1400 1400
γ L+γ L+K2
1300 1300

Temperature/°C
Temperature/°C

1200
γ+ K2 1200
1100 L+γ
1100 γ+ K2
1000 γ+K 1
γ+K1+K2 1000 γ+K 1 γ+K1+K2
900
900
800
800
700
α+K1+K2 α+K2
600 700 α+K1+K2 α+K 2

500 600
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Content of C/wt% Content of C/wt%

Fig. 6. The equilibrium phase of high chromium cast iron calculated by Thermo-Calc software (a) Cr10%; (b) Cr15%; (c) Cr20%; (d) Cr25% L-liquid; c-austenite; a-ferrite;
K1-(Fe, Cr)23C6; K2-(Fe, Cr)7C3.

mium cast iron are listed in Table 3. It can be seen from Figs. 5
Table 2 and 3 that the eutectic, liquidus and solidus temperatures are re-
Eutectic transformation parameter in high chromium cast iron phase diagram with duced with the increasing of C content. The reason is that the car-
different content of Cr element
bon content dissolved in austenite is increased so that the stability
Content Eutectic transition Eutectic C Eutectic Eutectic of austenite in the transformed region is reduced. The tendency of
of Cr/% temperature/°C content/% transformation carbide eutectoid transforms is increased and each phase transformation
product type
temperatures are reduced. It can be also seen from Fig. 7, the crys-
10 1210 4.0 c + K2 K2 tal temperature range is reduced and the eutectic transition tem-
15 1250 3.75 c + K2 K2
perature range is expanded with the increasing of the C content.
20 1270 3.45 c + K2 K2
25 1280 3.2 c + K2 K2 When the C content is constant, the temperature range between li-
quid and solid phase is increased with the decreasing of Cr content,
i.e. it is reduced with the increasing of ratios of chromium to car-
bon content, and the value is minimum at the eutectic
temperature.
constant. The composition with (%) 10, 15, 20 and 25 Cr were
chosen to calculate the phase diagram by Thermo-Calc software, 5. Discussion
whose results are shown in Fig. 6 and listed in Table 2. It can
be seen from Fig. 6 and Table 2 that, with the increasing of Cr From the theory of casting technology, if the eutectic temper-
content, the eutectic transition temperature is increased, the sin- ature is low and is the constant temperature, the fluidity is good,
gle-phase zone scope of austenite is reduced and the content of the centralized shrink hole easy to be formed, the thermal crack
eutectic carbon is decreased. The eutectic transformation product and the segregation tendency is small. However the large the
is c + M7C3. temperature range between liquid and solid phase is, the worse
the fluidity and the more the dispersible shrink hole is. Therefore,
4.3. Influence of C content on phase diagram the composition of the casting alloy should be selected close to
eutectic one [11]. As shown in the above analysis, if the ratio of
The equilibrium phase diagrams of the high chromium cast iron the chromium to carbon is about 4.17 at eutectic temperature
with different carbon content are shown in Fig. 7. The influences of of this high chromium cast iron, it will be with the good casting
C content on phase transformation temperature of the high chro- property.
344 D. Li et al. / Materials and Design 30 (2009) 340–345

a 1400 b 1400
L
1300 L+γ 1300
L+γ

1200 1200

Temperature/°C
γ+ K2
Temperature/°C

1100 γ+ K2 1100

1000 1000

α+γ+K1 + K2
γ+ K1 γ+ K1
900 900
γ+K1+K2 γ+K 1+K 2
800 800

700 α+K2 α+K1+K2 α+K1 700 α+K 2 α+K 1+K 2 α+K11

600 600
0 5 10 15 20 25 30 35 40 0 5 10 15 20 25 30 35 40
Content of Cr/wt% Content of Cr/wt%

c 1400 L d 1400
L
1300 1300
L+γ
1200 1200 L+γ L+K 2

Temperature/°C
γ+ K2
Temperature/°C

1100 1100
γ+ K 2
1000 1000
γ+ K1
900 γ+K 1+K2 900
γ+K 1+K 2

800 800

700 α+K 2 α+K1+K2 700 α+K 2 α+K 1+K 2

600 600
0 5 10 15 20 25 30 35 40 0 5 10 15 20 25 30 35 40
Content of Cr/wt% Content of Cr/wt%

Fig. 7. The equilibrium phase of high chromium cast iron calculated by Thermo-Calc software (a) C2.0%; (b) C2.5%; (c) C3.0%; (d) C3.5% L-Liquid; c-austenite; a-ferrite;
K1-(Fe, Cr)23C6; K2-(Fe, Cr)7C3.

Table 3
The phase transformation temperature of the high chromium cast iron with different content of eutectic carbon is decreased and the range of sin-
content of C gle-phase of austenitic is reduced with the increasing of the
Cr content. After Cr content is taken as constant, the content
C Liquidus Eutectic Solidus Temperature range of
content% temperature/ temperature/ temperature liquid and solid phase/ of C should be lower than the eutectic carbon one; other-
°C °C /°C °C wise, the massive thick primary carbides can be appeared
2.0 1375 1280 1270 105
in the microstructure.
2.5 1340 1270 1265 75
3.0 1290 1270 1260 30
3.5 1270 1265 1255 15 Acknowledgement

The author would like to express their gratitude for projects

supported by key project of Science and Technology of Hebei prov-
6. Conclusion ince (04212201D).

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