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

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960 mm ingot size produced using the three-process smelting method， there is a significant segregation. T

he 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 M

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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.