Microstructure and Mechanical Properties of 14Cr-ODS Steel Fabricated by Ultra-High Pressure Sintering
WANG Tao1, LONG Dijun2, YU Liming1(), LIU Yongchang1, LI Huijun1, WANG Zumin1
1.State Key Laboratory of Hydraulic Engineering Simulation and Safety, School of Materials Science and Engineering, Tianjin University, Tianjin 300354, China 2.Nuclear Power Institute of China, Chengdu 610041, China
Cite this article:
WANG Tao, LONG Dijun, YU Liming, LIU Yongchang, LI Huijun, WANG Zumin. Microstructure and Mechanical Properties of 14Cr-ODS Steel Fabricated by Ultra-High Pressure Sintering. Acta Metall Sin, 2022, 58(2): 184-192.
Due to its superior mechanical, processing, and service properties, oxide dispersion-strengthened (ODS) alloy (particularly Fe base ODS steel) has emerged as the most promising future candidate for advanced reactor structural materials. However, there are some problems with hot isostatic pressing sintering ODS steels, such as higher sintering temperature, longer sintering time, and relatively coarse grains. In this work, 14Cr-ODS steels were prepared by ultra-high pressure sintering with a sintering pressure of 3, 4, and 5 GPa, respectively. The microstructure and mechanical properties of the ultra-high pressure sintered 14Cr-ODS steel samples were characterized by density test, SEM, TEM, hardness test, and tensile test. Based on the contrast analysis of microstructure and mechanical properties, the effect of sintering pressure on the microstructure and mechanical properties of ultra-high pressure sintered 14Cr-ODS steel was investigated, and the effect mechanism was thoroughly analyzed. Analysis results show that the main oxide precipitate of ultra-high pressure sintered 14Cr-ODS steel is Ti2O3, and the average grain size of 14Cr-ODS steel prepared by ultra-high pressure sintering is less than 300 nm, which is approximately 5% of the average grain size of 14Cr-ODS steel prepared by conventional hot isostatic pressing sintering. The average grain size of samples prepared by ultra-high pressure sintering decreased initially and then increased as sintering pressure increased. The Vickers hardness of ODS steel samples sintered at 4 GPa can reach 604 HV, and the tensile strength is approximately 1.5 GPa, which is 1.6 times than that of 14Cr-ODS steel samples with a similar composition prepared by conventional hot isostatic pressing sintering. Ultra-high pressure sintered 14Cr-ODS steel with good sintering formability and a density greater than 99% can be obtained at lower sintering temperatures and shorter sintering times. Its excellent performance can be mainly associated with the comprehensive influence of the plastic deformation effect produced by ultra-high pressure sintering on grain nucleation and atom diffusion in sintered samples.
Fig.1 SEM image (a) and particle size distribution (b) of mechanically alloyed powders (AVG—average grain size)
Fig.2 SEM images (a, c, e) and grain size distributions (b, d, f) of ultra-high pressure sintered 14Cr-ODS samples with sintering pressures of 3 GPa (a, b), 4 GPa (c, d), and 5 GPa (e, f)
Fig.3 Low (a, c, e) and high (b, d, f) magnified TEM images of microstructure in ultra-high pressure sintered 14Cr-ODS samples with sintering pressures of 3 GPa (a, b), 4 GPa (c, d), and 5 GPa (e, f)
Fig.4 High magnified TEM image and EDS result (inset) (a), and low magnified TEM image and SAED pattern (inset) (b) of the ultra-high pressure sintered 14Cr-ODS sample with 4 GPa sintering pressure
Fig.5 Tensile curves of ultra-high pressure sintered 14Cr-ODS samples with 3, 4, and 5 GPa sintering pressures
Fig.6 SEM images of tensile fracture of ultra-high pressure sintered 14Cr-ODS samples with sintering pressures of 3 GPa (a), 4 GPa (b), and 5 GPa (c)
Initial pair
1NN
2NN
configuration
Ref. [33]
Ref. [34]
Ref. [33]
Ref. [34]
Ysub + Ysub
0.20
0.21
0
0.02
Ysub + Tisub
0.28
0.32
0.15
0.15
Tisub + Tisub
0.29
0.32
0.15
0.16
Ysub + Osub
-0.33
-0.30
-0.30
-0.28
Tisub + Osub
0.82
0.88
1.69
1.73
Oint + Tisub
-0.27
-0.21
-0.55
-0.50
Oint + Ysub
0.28
0.33
-0.85
-0.80
Oint + Osub
-1.29
-1.21
0.19
0.26
Osub + Osub
2.03
2.10
-
-
Oint + Oint
0.40
0.46
-
-
Table 1 Formation energies of various possible pair configuration in bcc lattice Fe[33,34]
Element
800oC[35]
1150oC[32]
Y
2.8 × 10-20
2.9 × 10-17
Ti
2.5 × 10-15
3.7 × 10-13
O
5.7 × 10-13
1.5 × 10-10
Table 2 Diffusion coef?cients of constituent in the bcc lattice Fe at 800 and 1150oC[32,35]
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