深冷处理对35MnB合金钢残余应力的调控机理

Control mechanism of residual stress in 35MnB alloy steel by deep cryogenic treatment

以35MnB合金钢为研究对象,运用正交试验法,设计了以深冷温度、深冷时间和交变次数为自变量,残余应力为因变量的正交试验。通过X射线衍射仪测得试样表面的残余应力分布情况,运用极差法分析深冷工艺参数对试样残余应力的影响因素;通过扫描电镜观测试样在不同深冷处理工艺参数下的微观组织形貌,结合X射线衍射图谱定量分析了深冷处理后残留奥氏体体积分数的变化,从微观角度综合探索了残余应力的消减机理。结果表明:35MnB合金钢深冷工艺参数对试样残余应力的影响因素依次为:深冷温度>交变次数>深冷时间,最佳组合为:深冷温度-160℃,深冷时间12 h,交变次数1次。经深冷处理之后,残留奥氏体细化并转变为新生马氏体,分布在马氏体晶体边界处的残留奥氏体可以松弛马氏体界面上因位错堆积而造成的应力集中,从而减少了组织内部的残余应力。

With 35 MnB alloy steel as the object of study,an orthogonal test was designed with the cryogenic temperature,cryogenic time and alternating times as the independent variables and the residual stress as the dependent variable.By means of X-ray diffractometer,the distribution of residual stress on the specimen surface was measured,and the influence factors of the cryogenic process parameters on residual stress in the specimens were analyzed by range analysis method.Via scanning electron microscope,the microstructure and morphology of the specimens under different cryogenic treatment process parameters were observed,and the change of retained austenite volume fraction after cryogenic treatment was quantitatively analyzed by means of X-ray diffractometer.The mechanism of residual stress reduction was comprehensively explored from the microscopic point of view.The results show that the influencing factors of cryogenic process parameters on residual stress of the 35 MnB alloy steel are as follows:cryogenic temperature>alternating times>cryogenic time,and the optimal combination is the cryogenic temperature of -160℃,cryogenic time of 12 h,alternating number of 1 time.After cryogenic treatment,the retained austenite is refined and transformed into new martensite.The retained austenite distributed at the martensite boundary can relax the stress concentration caused by dislocation accumulation at martensite interface,thus reducing the residual stress inside the microstructure.