改型IN617合金大锭型的铸态组织及均匀化工艺

As-cast microstructure and homogenization process of large-scale ingots of modified IN617 superalloy

利用光学显微镜、扫描电镜和能谱分析仪对700℃超超临界电站汽轮机转子用改型IN617合金三联工艺冶炼后的铸态组织和均匀化热处理后的微观组织变化进行研究。结果表明:采用三联工艺生产的7 t级自耗锭与两联工艺生产的5 t级电渣锭相比,偏析明显减弱,析出相主要为富Mo、Nb和Ti的一次MC型碳化物,碳化物呈不规则状或长条状,在枝晶间大量分布,且棱角比较尖锐;均匀化热处理后枝晶消除明显,块状及条状碳化物碎化,棱角钝化;1180~1200℃保温48 h以上,可以作为此大锭型改型IN617合金均匀化热处理的工艺;处理后试样经大变形量压缩后无裂纹出现,表明该均匀化制度下的合金表现出良好的塑性。

As-cast microstructure and microstructure change after homogenization treatment of modified IN617 alloy for the application of 700℃ultra-supercritical turbine rotor were studied by means of optical microscopy,scanning electron microscopy and energy dispersive X-ray spectroscopy.The modified IN617 ingots produced by ESR(electroslag remelting)and VAR(vacuum arc remelting)processes respectively were studied comparatively.The results show that the dendrites and element segregation of the 7 t VAR-produced ingot are obviously weaker than that of the 5 t ingot produced by the ESR process.The precipitates of the 7 t VAR ingot are mainly primary MC-type carbides rich in Mo,Nb and Ti,in shape of irregular or long strips with sharp edges,and distribute between the dendrites.After homogenization,the dendrites are almost eliminated,and the block and strip carbides are fragmented and with obtuse edges.It is found that after appropriate homogenization at 1180-1200℃for over 48 h,the 7 t VAR ingot exhibits excellent workability without cracking.