深冷处理对H13钢组织和热疲劳性能的影响

Effect of cryogenic treatment on microstructure and thermal fatigue properties of H13 steel

采用OM、SEM、TEM、XRD、显微硬度计以及热疲劳试验机等方法研究了深冷处理对H13型热作模具钢的组织和性能的影响,并与常规淬回火工艺进行了对比分析。结果表明,在常规的淬回火工艺的基础上增加深冷处理有利于细化试验钢的晶粒组织并促进残留奥氏体向马氏体转变。此外,在深冷处理的条件下马氏体晶格由于在极低温易发生收缩而促使碳原子在位错等缺陷处偏聚,回火过程中以碳化物的形式析出。这些析出的大量细小弥散分布的碳化物可钉扎位错,对热循环引起的应力集中起到一定的缓解作用,减缓降低热疲劳裂纹扩展速率。且深冷处理后细小弥散分布的碳化物析出降低了H13钢热疲劳过程中碳化物长大速率,减少了热疲劳裂纹的数量,从而提高热疲劳性能。

Effect of cryogenic treatment on microstructure and properties of the H13 hot-working die steel was studied by means of OM,SEM,TEM,XRD,microhardness tester and thermal fatigue testing machine,and compared with the conventional quenching and tempering process.The results show that,the addition of cryogenic treatment on the basis of conventional quenching and tempering process is beneficial to refine the grain microstructure of the tested steel and promote the transformation of retained austenite to martensite.In addition,under the condition of cryogenic treatment,the martensite lattice is easy to shrink at extremely low temperature,which promotes the carbon atom segregation at defects such as dislocations and the precipitation in form of carbides during the tempering process.These precipitated large number of fine and dispersed carbides can pin dislocations,play a certain role in alleviating the stress concentration caused by thermal cycling,and slow down the growth rate of thermal fatigue cracks.And the precipitation of fine and dispersed carbides after cryogenic treatment reduces the growth rate of carbides during thermal fatigue of the H13 steel,reduces the number of thermal fatigue cracks,and improves thermal fatigue properties.