关键词: 低碳高合金钢, 深冷处理, 纳米碳化物, 残余奥氏体, 力学性能

Abstract: Microstructure and mechanical properties of a low-carbon Co-Cr-Mo-Ni-W high-alloy martensite steel after quenching, cryogenic treatment for different time and tempering were investigated. The results show that the microstructure under different conditions contains the complex phases with tempered martensite, retained austenite and nano-carbides. With increasing cryogenic time from 2 to 6h, the strength significantly improves but ductility reduces due to the combination of the refinement of tempered martensite lath, the decrease of retained austenite volume fraction, the increase of dislocation density and the number increase of nano-carbides with more uniformly distribution. When cryogenic time over 6 h, both strength and ductility change slightly because retained austenite volume fraction decreases, dislocation density increases and nano-carbide sizes coarsen with number decreasing. An excellent combination of strength and ductility, having a yield strength of 1685 MPa, an ultimate strength of 1946 MPa, an elongation of 14.5%, is achieved for the steel after quenching, cryogenic treatment for 6h and tempering.

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