P20塑料模具钢的回火工艺

Tempering process of P20 plastic die steel

采用扫描电镜、洛氏硬度计对P20塑料模具钢进行淬火及回火后的显微组织观察及硬度测试,研究其在不同回火处理工艺下的硬度及显微组织变化规律,同时利用回火参数P研究了P20塑料模具钢的回火工艺。结果表明,在350~450℃,随回火温度的增加,硬度变化不大;在450~650℃回火,试样的硬度发生明显下降趋势;随回火保温时间的延长,在350~450℃,硬度降低趋势较小;在500~650℃回火,在最初的8 h内,硬度迅速降低,继续延长保温时间,硬度下降速率变慢;随回火温度和保温时间的延长,碳化物析出量越来越多,并逐渐球化聚集长大,马氏体板条边界逐渐模糊,有些板条被早期形成的碳化物钉扎,致使部分板条马氏体粗化,有些板条合并变宽,导致其硬度降低。结合本文试验数据及回火参数P,可确定试验P20钢的最佳回火工艺为600℃×1 h。

Microstructure observation and hardness test of P20 plastic die steel after quenching and tempering were analyzed by means of scanning electron microscopy and Rockwell hardmeter. The change law of hardness and microstructure of the tested steel after different tempering processes were investigated,and tempering parameter P was used to study the tempering process of P20 plastic die steel. The results show that with the increase of the tempering temperature,the hardness of the tested steel changes a little when it is tempered at 350-450 ℃,while the hardness of it shows an obvious declined trend when tempered at 450-650 ℃. With the tempering time prolonging,the decrease trend of the hardness is not significant at the tempering temperature of 350-450 ℃,and when the tempering temperature in 500-650 ℃,the hardness reduces rapidly in the first 8 h and then the decline rate becomes slowly. With the increase of tempering temperature and tempering time prolonging,the precipitation of carbides increases and the carbides spheroidize and grow up gradually. The martensite lath boundaries become blurring,and some laths are pinned by the early formed carbides and leading to the coarsening of some lath martensite and some merger and widen,which finally lead to the reduction of hardness. The optimum tempering process of the tested P20 steel is tempering at 600 ℃ for 1 h combined with the test data and the tempering parameter P.