Co-Precipitation Behavior in Ferrite Region During Isothermal Process in Ti-Mo-Cu Microalloyed Steel
TANG Shuai1(), LAN Huifang1, DUAN Lei1, JIN Jianfeng2, LI Jianping1, LIU Zhenyu1, WANG Guodong1
1.State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China 2.School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
Cite this article:
TANG Shuai, LAN Huifang, DUAN Lei, JIN Jianfeng, LI Jianping, LIU Zhenyu, WANG Guodong. Co-Precipitation Behavior in Ferrite Region During Isothermal Process in Ti-Mo-Cu Microalloyed Steel. Acta Metall Sin, 2022, 58(3): 355-364.
The coprecipitation of carbides and copper (Cu) particles is an effective technique for strengthening microalloyed steel. In this study, OM and TEM techniques were used to investigate the coprecipitation behavior of carbides and ε-Cu in Ti-Mo-Cu microalloyed steel at different isothermal temperatures. A solid solution precipitation model and the classical nucleation theory of precipitates were used to calculate the precipitation kinetics in the Ti-Mo-Cu microalloyed steel. The results show that (Ti, Mo)C and ε-Cu precipitated independently, and they showed the N-W and K-S orientations with the ferrite matrix, respectively. The dominant precipitates at 600oC are ε-Cu. (Ti, Mo)C and ε-Cu were coprecipitated at 620oC. At 640-660oC, (Ti, Mo)C was mainly precipitated in the form of interphase precipitation. Thermodynamic calculations showed that in the range of 600-660oC with an increase in temperature, the Ti/Mo atomic ratio in (Ti, Mo)C increases from 2.5 to 4.5, and the carbide changes from Ti0.71Mo0.29C to Ti0.79Mo0.21C. The precipitation-temperature-time (PTT) curves of (Ti, Mo)C and ε-Cu intersect at 616oC, indicating simultaneous precipitation of (Ti, Mo)C and ε-Cu. (Ti, Mo)C and ε-Cu preferentially precipitate below and above 616oC, respectively. The calculation and experimental results are consistent.
Fund: National Natural Science Foundation of China(51774083);Fundamental Research Funds for the Central Universities of China(N2107002);Project of Introducing Talents of Discipline to Universities(B20029);National Key Research and Development Program of China(2017YFB0304402)
About author: TANG Shuai, associate professor, Tel: 17640032562, E-mail: tangshuai@ral.neu.edu.cn
Fig.1 OM images of experiment steel with different holding temperatures (F—ferrite, B—bainite, M—martensite)
Fig.2 TEM bright field images and SAED pattern of the interphase precipitate in speciments isothermally treated at 600oC (IP—interphase precipitation)
Fig.3 TEM bright field images of the interphase precipitate in speciments isothermally treated at 620oC (a), 640oC (b), and 660oC (c), and dark filed image at 660oC and corresponding SAED pattern (inset) (d)
Symbol
Description
Magnitude
Unit
Ref.
aTiC
Lattice constant of TiC at room temperature
0.433
nm
[29]
aMoC
Lattice constant of MoC at room temperature
0.428
nm
[35]
aCu
Lattice constant of ε-Cu at room temperature
0.362
nm
[36]
aFe
Lattice constant of α-Fe at room temperature
0.287
nm
αTiC
Linear expansion coefficient of TiC
7.86 × 10-6
K-1
[37]
αMoC
Linear expansion coefficient of MoC
6.88 × 10-6
K-1
[38]
αCu
Linear expansion coefficient of Cu
16.5 × 10-6
K-1
[39]
QTi
Activation energy of Ti in α-Fe
248
kJ·mol-1
[40]
QMo
Activation energy of Mo in α-Fe
229
kJ·mol-1
[41]
QCu
Activation energy of Cu in α-Fe
284
kJ·mol-1
[41]
vFe
Poisson ratio of Fe
0.291
[41]
vCu
Poisson ratio of Cu
0.345
[41]
GFe
Shear modulus of Fe
89334 - 29.688T
GPa
[30]
GCu
Shear modulus of Cu
44689 - 15.936T
GPa
[30]
k
Boltzmann constant
1.38 × 10-23
J·K-1
Table 1 Parameters used in calculations[29,30,35-41]
Fig.4 Thermodynamics/kinetics calculation results of precipitation of (Ti, Mo)C and ε-Cu in ferrite at different temper-atures (PPT—precipitation-temperature-time, t0—the precipitation start time, t0.05—the time of pricipitates fraction of 5%)
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LIU Wenchang; CHEN Zonglin; XIAO Furen; YAO Mei; WANG Shaogang;LIU Runguang(College of Material Engineering; Yanshan University; Qinhuangdao 066004);(Shenyang Liming Engine Manufacturing Company; Shenyang 110043);(School of Materials Engineering; Harbin Institute of Technology; Harbin 150001)Correspondent:LIU Wenchang;associate professor; Tel: (0335)8057047. EFFECT OF COLD ROLLING ON THE KINETICS OF δ PHASE PRECIPITATION IN INCONEL 718[J]. 金属学报, 1998, 34(10): 1049-1054.
