4330M钢连续冷却过程中的组织转变特征

Microstructure transformation characteristic of 4330M steel during continuous cooling process

采用Gleeble-3500热模拟试验机对4330M钢进行连续冷却转变试验,研究了冷却速率在0.8~10℃/s范围内连续冷却过程中组织结构转变特征。采用热膨胀、硬度测试及彩色金相等试验测定4330M钢的连续冷却转变(CCT)曲线。结果表明,4330M钢在冷却过程中存在铁素体、贝氏体和马氏体相变区,没有珠光体相变区。随着冷却速率的增加,过冷奥氏体依次分解为铁素体+粒状贝氏体、粒状贝氏体+下贝氏体+马氏体和完全马氏体,马氏体的临界冷却速率约为3℃/s。下贝氏体中铁素体和渗碳体的取向关系为(110)_(α)//(102)_(Fe3C)和[111]_(α)//[201]_(Fe3C)。结合维氏硬度试验与彩色金相定量分析,建立了4330M钢硬度-体积分数模型HBW=-0.07-4.69f_(F)+4.02f_(GB)+4.63f_(LB)+4.82f_(M)。

Continuous cooling transformation test of 4330 M steel was carried out by Gleeble-3500 thermal simulation test machine,and the microstructure transformation characteristic during continuous cooling process between cooling rate of 0.8-10℃/s was studied.The CCT curves of the steel were determined by means of thermal dilatometry method,hardness test and color metallography.The results show that the CCT curves of the 4330M steel contain ferrite,bainite and martensite transformation region,but there is no pearlite transformation region.With the increase of cooling rate,supercooled austenite is decomposed into ferrite+granular bainite,granular bainite+lower bainite+martensite and full martensite in turn.The critical cooling rate of martensite transformation is ascertained to be about 3℃/s.The orientation relationship of ferrite and cementite in lower bainite is(110)_(α)∥(102)_(Fe3C) and[111]_(α)//[201]_(Fe3C).Combined the Vickers hardness test and quantitative analysis of color metallography,a hardness-volume fraction model is established to predict the hardness of 4330M steel as HBW=-0.07-4.69f_(F)+4.02f_(GB)+4.63f_(LB)+4.82f_(M).