含Cu低碳球扁钢球头与腹板的组织性能差异

Difference of microstructure and properties between bulb and flat of Cu-bearing low-carbon bulb flat steel

利用电子背散射衍射(EBSD)、场发射扫描电镜(FE-SEM)和能谱仪(EDS)分析含Cu低碳球扁钢在热轧-感应加热-固溶-时效后的组织演变规律,并根据强化机制,分析造成球头、腹板存在差异的原因。结果表明,在不同热处理阶段,含Cu低碳球扁钢腹板晶粒尺寸均小于球头,腹板处富Cu相析出进程落后于球头,680℃时效2 h后,腹板强度及硬度高于球头,伸长率稍弱于球头;热轧-感应加热-固溶-时效过程,球扁钢依次经历热变形、铁素体-奥氏体转变、马氏体相变及回复阶段;造成球头、腹板存在约50 MPa强度差异的原因,富Cu相尺寸差异为主要因素,晶粒尺寸差异为次要因素,位错密度差异为微弱因素。

Microstructure evolution of Cu-bearing low-carbon bulb flat steel during hot-rolling-induction heating-solid solution-tempering treatment was characterized using electron back-scattered diffraction(EBSD),field emission scanning electron microscopy(FE-SEM)and energy disperse spectroscopy(EDS).The difference between the bulb and flat was analyzed based on the strengthening mechanism.The results show that at different heat treatment stages,the grain size of flat is smaller than that of the bulb,while the precipitation of Cu-rich particles in the flat is improved.After aging at 680 C for 2 h,compared with the bulb,the flat exhibit a higher strength and hardness and a relatively lower elongation.During hot-rolling-induction heating-solid solution-tempering process,the bulb flat steel undergoes thermal deformation,ferrite austenite transformation,martensitic transformation,and recovery stages in sequence.The strength diference of about 50 MPa between the flat and the blub is attributed to the major factor of the size difference of Cu-rich particles,the secondary factor of the difference in grain size and the weak factor of the difference in dislocation density.