第二次回火工艺对机械用CrMo合金钢性能的影响

Effect of Second Tempering Process on Properties of CrMo Alloy Steel for Machinery

采用755℃×4 h退火后炉冷至300℃空冷＋850℃×20 min油淬＋500℃×5 h第一次回火和不同的第二次回火工艺对机械用Cr Mo合金钢进行了热处理,并对其进行了-40℃低温冲击试验和1000次25~500℃冷热循环试验。结果表明,随第二次回火温度从350℃增大至550℃或回火时间从1 h延长到6 h,Cr Mo合金钢的低温冲击吸收功先增大后减小,热疲劳裂纹级别数值表现为先减小后增大,钢的低温冲击性能和热疲劳性能先提高后降低。最佳第二次回火工艺为：475℃×5 h。

CrMo alloy steel for machines was heat-treated by using annealing of 755 ℃ ×4 h/furnace to 300 ℃/air cooling＋ oil quenching of 850℃×20 min＋the first tempering of 500 ℃×5 h＋the second different tempering process. And the impact test at low temperature of-40 ℃and 1000 times cool-thermal cycling test at 25-500 ℃ were carried out. The results show that with the second tempering temperature increasing from 350 ℃ to 550 ℃, or the second tempering time increasing from 1 h to 6 h, the low temperature impact absorbing energy of Cr Mo alloy steel increases firstly and then decreases, the thermal fatigue crack grade of the steel decreases firstly and then increases, and the impact property at low temperature and thermal fatigue property of the steel firstly improve and then decline. The optimized second tempering process is 475℃×5 h.