热处理中高铬钢激光熔凝层的组织转变

Effect of heat treatment on microstructure of high chrome steel by laser surface melting

采用激光熔凝处理方法对高铬钢进行表面强化,然后在300～650℃区间回火处理,利用SEM、XRD和TEM等手段分析热处理对激光熔凝层组织的影响。结果表明,高铬钢激光熔凝处理后,得到的奥氏体组织中合金元素固溶度较高且晶粒细小,具有较高的回火稳定性。激光熔凝层450℃回火后硬度开始升高,560℃时达到最大值(672 HV0.2),回火温度高达650℃时硬度迅速降低。450℃回火后细小M23 C6碳化物优先从过饱和奥氏体中析出,同时少量马氏体的生成使熔凝层硬度略有增加。560℃回火后由于M7 C3和M23 C6碳化物的析出、大量高硬度马氏体的生成以及位错强化的共同作用使硬度达到峰值,同时,马氏体组织中有少量的M3C渗碳体析出。650℃回火后基体完全转变为铁素体,析出大量层片状M3C渗碳体,硬度显著降低。

Laser surface melting was carried on surface of high chrome steel,and then the samples were tempered in the range of 300-650 ℃.The effect of heat treatment on microstructure of the laser melted coating was investigated by means of SEM,XRD and TEM.The results show that the austenite in the laser melted coating possesses a high tempering stability due to the increase of alloying elements in solid solution and refined grains.The hardness of the laser melted coating is elevated after tempering at 450 ℃ and reaches a peak of 672 HV0.2 at 560 ℃ and then decreases quickly at 650 ℃.After tempering at 450 ℃ the precipitation of fine M23 C6 carbides and a small amount of martensite from the supersaturated austenite are contributed to the slight increase of hardness.At 560 ℃ the combined effect of the martensite phase transformation and the precipitation of carbides within the refined microstructure results in the maximum.At the same time,a small amount of M3 C carbides precipitates from the martensite.Moreover,the decrease of hardness at 650 ℃ is caused by the formation of ferrite matrix and large quality of lamellar M3 C cementite.