345MPa级耐火钢CCT曲线分析

Analysis on CCT(Continuous Cooling Transformation)Curve of 345 MPa Grade Fire-resistant Steel

通过绘制345 MPa级耐火试验钢的连续冷却转变曲线(CCT曲线),分析了耐火试验钢的连续冷却转变特征,并观察在1~100℃/s间不同冷却速度下试验钢显微组织。结果显示,当冷速为1℃/s时,试验钢发生铁素体与珠光体转变;当冷速为8~20℃/s时,试验钢发生铁素体和贝氏体转变,珠光体完全消失,晶粒尺寸减小,贝氏体组织占比升高;当冷却速度在50~100℃/s之间时,试验钢的组织转变主要为贝氏体转变,铁素体转变占比很低,晶粒尺寸进一步减小;当冷速增加到100℃/s时,铁素体完全消失,组织全部变为贝氏体,且有明显的板条化倾向。通过对耐火试验钢的连续冷却转变曲线和显微组织分析,为345 MPa级耐火钢生产过程中冷却工艺的制定提供了理论依据。

The characteristics of continuous cooling transformation of fire-resistant test steel are analyzed as well as its microstructure at different cooling rates within 1~100℃/s are observed through drawing the continuous cooling transformation(CCT)curve of 345 MPa grade fire-resistant test steel.The results showed that there were ferritic and perlitic transformations of test steel when cooling rate was 1℃/s;there were ferritic and bainite transformations of test steel when cooling rate was 8~20℃/s,pearlite completely disappeared,grain size was reduced and proportion of bainite structure was increased;microstructure transformation of test steel was mainly bainite transformation,proportion of ferritic transformation was very low and grain size was further reduced when cooling rate was 50~100℃/s;ferrite disappeared completely,all the microstructure was changed to bainite and was with obvious tendency of lath when cooling rate was increased to 100℃/s.The analysis of CCT curve and microstructure for fire-resistant test steel provides theoretical basis for formulating cooling processes in the production process of 345 MPa grade fire-resistant test steel.