改型617合金的铸态组织特征及均匀化工艺

As-cast microstructure and homogenization process of modified alloy 617

利用扫描电镜分析、模拟热处理等方法,研究了700℃超超临界电站汽轮机转子用改型617合金双真空冶炼（VIM＋ESR）后的铸态组织特征和均匀化热处理后的微观组织变化。结果表明,铸态组织存在明显的偏析,主要偏析元素为Mo和Ti,偏聚于枝晶间;枝晶间和晶界上分布有块状和连续的碳化物;均匀化热处理后枝晶明显消除,块状碳化物部分溶解,晶界连续碳化物充分溶解;该合金成分均匀化主要受Mo原子扩散控制。提出改型617合金均匀化热处理工艺应为1180-1200℃保温24 h以上。

Nickel-based superalloy modified 617 ingots for 700 ℃ ultra-supercritical turbine rotor were prepared by vacuum-inductionmelting and electroslag-remelting,and the as-cast microstructure of the alloy after homogenization heat treatment was investigated by SEM analysis. The results show that the major microstructural features of the as-cast alloy are identified to be the presence of marked elements segregations,especially Mo and Ti segregating within dendrites,and inter-and intragranular carbides. After homogenization the elements segregation are almost eliminated and carbides both within dendrites and along grain boundary dissolve to some extent. The research also shows that the homogenization microstructure of the alloy 617 is mainly controlled by the diffusion of Mo, and the appropriate homogenization process for this alloy is heating at 1180-1200 ℃ for over 24 h.