Effect of Cryogenic Treatment Time on Microstructure and Mechanical Properties of a Low-carbon High-alloy Martensite Steel

doi:10.12382/bgxb.2024.0532

Abstract

Abstract:

To achieve the superior performance of aerospace bearing steel by controlling the retained austenite content,the optimization of cryogenic treatment parameters is an effective approach.The microstructure and mechanical properties of a low-carbon Co-Cr-Mo-Ni-W high-alloy martensite steel after quenching,cryogenic treatment at -75℃ for different times and tempering are investigated.The results show that the microstructure of the martensite steel after cryogenic tempering contains the complex phases with tempered martensite,retained austenite and nano-carbides.As the cryogenic time increases from 2 to 6h,the strength of the steel significantly improves and its ductility reduces due to the refinement of tempered martensite lath and the decrease in residual austenite volume fraction,the increase in dislocation density and the increase in the quantity of nano-carbides with more uniform distribution.When the cryogenic time exceeds 6h,the strength and ductility of the steel change slightly because the retained austenite volume fraction decreases,the dislocation density increases and the nano-carbide sizes coarsen with the decrease in quantity.An excellent balance of strength and ductility,with the mean yield strength of about 1690MPa,the ultimate strength of about 1940MPa and the mean elongation of about 14.3%,is achieved for the steel after quenching,cryogenic treatment for 6-10h and tempering.

Key words: low-carbon high-alloy steel, cryogenic treatment, retained austenite, nano-carbide, mechanical property

HE Jin, YANG Bin, WANG Yingchun, CHI Hongxiao, ZHOU Jian, CHENG Xingwang. Effect of Cryogenic Treatment Time on Microstructure and Mechanical Properties of a Low-carbon High-alloy Martensite Steel[J]. Acta Armamentarii, 2025, 46(6): 240532-.

Figures/Tables 8

Table 1 Composition of the steel (wt.%)

元素	C	Co	Cr	Mo	Ni	W	V	Nb	Fe
含量	0.12	14.05	11.49	3.63	3.67	1.15	0.81	0.03	余量

Fig.1 TEM images of the steel cryogenically treated for different times

Fig.2 DF-TEM images of the steel cryogenically treated for different times showing the morphology and distribution of retained austenite

Fig.3 XRD diffraction patterns of the steel cryogenically treated for different times

Fig.4 DF-TEM images of the steel cryogenically treated for different times showing the morphology and distribution of carbides

Fig.5 Characterization of carbides and EDS analysis

Fig.6 Engineering stress-engineering strain curves of the steel

Table 2 Mechanical properties of the steel cryogenically treated for different times

深冷时间/h	屈服强度/MPa	抗拉强度/MPa	延伸率/%
2	1489±8	1768±3	16.8±0.1
4	1619±1	1881±5	14.8±0.5
6	1685±3	1946±5	14.5±0.2
8	1701±23	1928±3	14.5±0.1
10	1691±8	1961±1	13.9±0.3

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