Bright white spot segregation on the surface of 42CrMo steel forgings used in wind turbine gearbox was observed and analyzed by OM,SEM,EDS and other technologies.The results show that the bright white spots segregating on the surface of the forging are tempered bainite.This is due to the existence of composition segregation of the 42CrMo steel ingot,which shows strip and spot bainite segregation after forging.After conventional post-forging heat treatment(normalizing+high temperature tempering),the chemical composition is not homogenized,and the bainite segregation evolves into aggregated granular Cr and Mo carbide segregation.After further quenching and tempering treatment,the microstructure is tempered bainite with varying sizes and uneven distribution in the tempered sorbite matrix.
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