Abstract: Using optical microscope， scanning electron microscope and energy dispersive spectrometer， the casting microstructure of 12 tons of ingots of as-cast condition C650R nickel-based alloy used in the 650 ℃ultra-supercritical steam turbine rotor， smelted by the three-process method （VIM+PESR+VAR）， and the microstructure after different homogenization treatments were studied. The high-temperature thermoplasticity before and after homogenization treatment was also compared. The results show that in the self-consumption ingots of ϕ960 mm ingot size produced using the three-process smelting method， there is a significant segregation. The main segregation elements are Mo， Nb， and Ti， which are segregated between dendrites. Within the crystal， the main precipitated phase is a MC-type primary carbide rich in Mo， Nb， Ti， and Zr. The carbides have an irregular shape， with small granular M₂₃C₆ primarily at the grain boundaries， along with a small amount of irregular MC-type primary carbide rich in Mo， Nb，and Ti. Based on the results of dendrite elimination， carbides re-dissolution， and changes in the residual segregation coefficients of three elements （Mo， Nb， Ti） after different homogenization treatments， it was determined that the homogenization process for a 12-ton C650 nickel-based alloy ingot should be 1 200 ℃-1 220 ℃ with a holding time of over 96 hours. Compared to the cast state， the samples after homogenization treatment show a significant improvement in high-temperature plasticity， which lays a favorable foundation for the smooth casting of the ingot.

Key words: C650R Nickel-based Alloy, Large Ingot, Segregation, Homogenization

摘要： 借助光学显微镜、扫描电子显微镜、能谱分析仪，研究了650 ℃超超临界汽轮机转子用C650R镍基合金三联工艺（VIM+PESR+VAR）冶炼的12 t铸锭冒口端的铸态组织及不同均匀化处理后的显微组织，并对比了均匀化处理前后的高温热塑性。结果表明，采用三联工艺冶炼的ϕ960 mm锭型的自耗锭中存在明显的偏析，主要偏析元素为Mo、Nb、Ti，均偏析于枝晶间，晶内主要析出相为富含Mo、Nb、Ti的MC型一次碳化物，碳化物形状不规则，晶界上以小颗粒状的M₂₃C₆为主，并含少量不规则的富含Mo、Nb、Ti、Zr的MC型一次碳化物。依据不同均匀化处理后枝晶消除、碳化物回溶、3种元素（Mo、Nb、Ti）残余偏析系数变化，确定了12 t级C650镍基合金铸锭的均匀化工艺为1 200～1 220 ℃保温96 h以上。与铸态相比，经均匀化处理后的试样高温热塑性显著增强，为铸锭顺利开坯奠定了有利基础。

关键词: C650R镍基合金, 大型铸锭, 偏析, 均匀化