Influence of on-line tempering parameters on microstructure of medium-carbon steel  

作　　者：Hua Zhang Yan-xin Wu Jian-xun Fu Jie Xu Qi-jie Zhai 

机构地区：[1]State Key Laboratory of Advanced Special Steel,Shanghai University,Shanghai 200072,China

出　　处：《Journal of Iron and Steel Research International》2017年第1期59-66,共8页

基　　金：sponsored by Key Projects in the National Science&Technology Pillar Program of China(2013BAE07B00);State Natural Science Fund Projects of China(51474142,51671124);Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher Learning(2012);China Postdoctoral Science Foundation(2015M580316)

摘　　要：A new process involving ultra-fast cooling（UFC）and on-line tempering（OLT）was proposed to displace austempering process,which usually implements in a salt/lead bath and brings out serious pollution in the industrial application.The optimization of the new process,involving the evolution of the microstructure of medium-carbon steel during various cooling paths,was studied.The results show that the cooling path affected the final microstructure in terms of the fraction of pearlite,grain size and distribution of cementite in pearlite.Increasing the cooling rate or decreasing the OLT temperature contributes to restraining the transformation from austenite to ferrite,and simultaneously retains more austenite for the transformation of pearlite.It is also noted that bainite was observed in the microstructure at the cooling rate of 45℃/s and the OLT temperature of 500℃.Through either increasing the cooling rate or decreasing the OLT temperature,the distribution of cementite in pearlite is more dispersed and grain is refined.Taking the possibility of industrial applications into account,the optimal process of cooling at 45℃/s followed by OLT at 600℃ after hot rolling was determined,which achieves a microstructure containing nearly full pearlite with an average grain size of approximately 7μm and a homogeneously dispersed distribution of cementite in pearlite.A new process involving ultra-fast cooling（UFC）and on-line tempering（OLT）was proposed to displace austempering process,which usually implements in a salt/lead bath and brings out serious pollution in the industrial application.The optimization of the new process,involving the evolution of the microstructure of medium-carbon steel during various cooling paths,was studied.The results show that the cooling path affected the final microstructure in terms of the fraction of pearlite,grain size and distribution of cementite in pearlite.Increasing the cooling rate or decreasing the OLT temperature contributes to restraining the transformation from austenite to ferrite,and simultaneously retains more austenite for the transformation of pearlite.It is also noted that bainite was observed in the microstructure at the cooling rate of 45℃/s and the OLT temperature of 500℃.Through either increasing the cooling rate or decreasing the OLT temperature,the distribution of cementite in pearlite is more dispersed and grain is refined.Taking the possibility of industrial applications into account,the optimal process of cooling at 45℃/s followed by OLT at 600℃ after hot rolling was determined,which achieves a microstructure containing nearly full pearlite with an average grain size of approximately 7μm and a homogeneously dispersed distribution of cementite in pearlite.

关 键 词：Medium-carbon steel Ultra-fast cooling On-line tempering Phase transformation kinetics 

分 类 号：TG142.1[一般工业技术—材料科学与工程] TG161[金属学及工艺—金属材料]