奥氏体化对3Cr-3Mo-Nb二次硬化钢的组织和力学性能的影响

研究了淬火奥氏体化温度和保温时间对3Cr-3Mo-Nb二次硬化钢的组织和力学性能的影响.结果发现,由于微合金化元素Nb的加入有效阻止了淬火保温时奥氏体晶粒的长大,当淬火温度高于1100℃时,奥氏体晶粒才显著长大.随淬火温度的升高,碳化物溶解更充分,强度和硬度增加,塑韧性在1100℃出现峰值.1050℃淬火保温时间少于30min时,碳化物未充分溶解,强度和塑性都较低.因此,为保证回火时有足够的M2C型二次硬化碳化物析出,最佳淬火温度为1050～1100℃,保温时间为30～60min.

Effect of austenitizing on microstructures and mechanical properties of 3Cr-3Mo-Nb secondary hardening steel

The quenched and tempered microstructures and the mechanical properties of a secondary hardening steel with nominal composition of 0.25C-3Cr-3Mo-Ni-Nb were investigated. It is found that the addition of Nb has hindering effects on the growth of prior austenite grains at high temperature. The austenite grains pronouncedly grow only at an austenitizing temperature of over 1100℃. With the increase of austenitizing temperature, resulting from the contradictory effects of the gradual dissolution of carbides and the austenite grain growth, the strength and hardness of the steel increase, and the, ductility and impact toughness peak at 1100℃. When the austenitizing holding time is shorter than 30min, the insufficient dissolution of carbides results in the strength, ductility and impact toughness of the steel to be low. Therefore, in order to ensure an effective precipitation of the M 2C type secondary hardening carbides during tempering, the optimum quenching temperature for the current steel is about 1050～1100℃, with holding time of 30～60min.