深冷时间对低碳高合金马氏体钢组织性能的影响

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 6 h,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 6 h,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 1 690 MPa,the ultimate strength of about 1 940 MPa and the mean elongation of about 14. 3%,is achieved for the steel after quenching,cryogenic treatment for 6-10 h and tempering.