The Influence Of Heat Treatment On The Microstructure And Properties Of Low Alloy ZG20CrMnMoNi

At present,low alloy cast steel has serious problems such as high strength,low toughness and poor strength and toughness match,and its application is severely restricted.This paper is intended to improve the strength and toughness match and wear resistance of low-alloy steel,as well as expands the scope of application of low-alloy steel.The influence of quenching and tempering process on the microstructure and properties of low alloy ZG20 CrMnMoNi was studied systematically by designed the three-factor four-level of orthogonal experiment including the quenching temperature(860?,890?,920?),quenching time(60min,90 min,120min),tempering temperature(570 ?,600 ?,630 ?)tempering time(90min,120 min,150min).The optical microscopy(OM),scanning electron microscopy(SEM),electronic universal testing machine,Brinell hardness tester and other means were applied.Then,the gray relative analysis method mathematical model was used to analyze the influence of conditioning parameters on the comprehensive performance of low alloy steel,and the quenching and tempering parameters were optimized to improve the comprehensive performance of low alloy steel.The conclusions can be drawn as follows:The microstructure of the granite bainite can be obtained by the preheating normalizing treatment of the low alloy ZG20 CrMnMoNi at 850?,90 min austenitizing.It is found that the quenching process parameters have no obvious effect on the microstructure of the alloy.However,the tempering process parameters have significant influence on the microstructure.With the increase of the tempering temperature(570? ~630?),the recovery of the ferrite and large amount of carbides precipitates along with the growing,coarsening and nodulizing of the precipitates appear in the tempering stage.The influence of quenching and tempering process parameters on the mechanical properties of the quenched and tempered process parameters is not obvious,but with the tempering process parameters show a obvious regularity.With the increase of the tempering temperature(570 ? ~ 630 ?),the martensite began to dissolve and the solid solution strengthening effect gradually disappeared,leading to the decrease of the strength.Meanwhile,the precipitated alloy carbides were dispersed on the substrate,which promoted the plasticity and toughness of the material.The wear of low alloy steel is affected by thehardness and toughness of the material and the number of impact factors.When the hardness and toughness of the material match well,the wear amount is small,vice versa.At the same time,the amount of wear is small with the number of impacts decreased,and the increase is high with the number of impacts increased.Based on the grayness theory,(a):the influence levels of the quenching and tempering parameters are obtained: tempering temperature > tempering time > quenching time > quenching temperature.(b): based on the hierarchy analysis,the optimal quenching temperature,quenching time,tempering temperature and tempering time are 890 ?,90 min,600 ?,120 min,respectively.The optimal mechanical properties are obtained by applying the optimal heat treatment parameters.