Element segregation and homogenization heat treatment of DIE VAR hot working die steel
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利用光学显微镜(OM)、扫描电镜能谱分析(SEM/EDS)、电子探针(EPMA)、Thermo-Calc热力学计算等方法,分析了 DIEVAR热作模具钢电渣锭的铸态组织、析出相及元素偏析特征,并研究了高温均匀化热处理(1260、1280、1300℃)对其微观组织、碳化物及元素分布的影响规律.结果表明,DIEVAR热作模具钢铸态枝晶组织发达,二次枝晶较显著,Cr、Mo、V元素在枝晶间富集,其偏析程度大小顺序依次为Mo＞V＞Cr,枝晶间析出相为M23C6、M6C和MC碳化物;随着均匀化温度的升高和保温时间的延长,枝晶组织逐渐变得模糊直至消失,碳化物回溶形成一定的元素扩散区并逐渐扩散,直至与基体充分融合,期间元素扩散快慢程度依次为Cr＞Mo＞V;根据均匀化热处理后枝晶形貌、碳化物回溶、元素扩散及Mo元素的残余偏析指数情况,综合实际工业生产成本考虑,确定DIEVAR钢的最佳均匀化热处理工艺为1280 ℃ ×8 h.
As-cast microstructure,precipitated phases and element segregation characteristics of DIE VAR hot working die steel electroslag ingot were analyzed by the means of optical microscope(OM),scanning electron microscope(SEM/EDS),electron probe(EPMA),Thermo-Calc thermodynamic calculation.Then the effect of homogenization heat treatment on the microstructure and carbide and element distribution was studied.The results show that the as-cast dendrite structure of the tested steel is well developed,and the secondary dendrites are obvious.The Cr and Mo and V elements are inter-dendritically enriched,and the segregation order is Mo＞V＞Cr.The interdendritic precipitated phases are M23C6,M6C and MC carbides.With the increase of homogenization temperature and the extension of holding time,the dendrite microstructure gradually becomes fuzzy and even disappears,and the carbide redissolution forms a certain element diffusion zone and gradually diffuses until it is fully redissolved into the matrix,the element diffusion rate is Cr＞Mo＞V during the homogenization heat treatment.According to dendrite morphology,carbide redissolution,element diffusion and residual segregation index of Mo element after homogenization heat treatment,and considering the actual industrial production cost,the optimal homogenization heat treatment process of the DIEVAR steel is 1280 ℃ ×8 h.
DIEVAR hot working die steelmicrostructuresegregationhomogenization
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