Abstract: Microstructure of as-cast H13 steel and microstructure evolution and component segregation during diffusion annealing were studied by means of OM and SEM. The results show that the as-cast microstructure of the electroslag remelt H13 steel is thick martensite+bainite+liquid-dissected carbides. High melting point liquid-dissected carbides and large size secondary carbides are distributed between dendrites and grain boundaries, and there are serious dendritic segregation and component segregation. With the increase of diffusion annealing temperature, the carbide gradually dissolve into the matrix, and the dissolution rate of carbides and the diffusion rate of elements in the dendrites are obviously faster than those at the interdendritic region and grain boundaries, which will preferentially meet the requirements of composition uniformity. When the diffusion annealing is 1240 ℃, the large size secondary carbides between dendrites are almost all dissolved back into the matrix, and the amount of high melting point liquid-dissected carbides at the grain boundary is obviously reduced, and only a few small particles of liquid-dissected carbides are left. For considering the energy saving and the yield improving, it is suggested that diffusion annealing at 1240 ℃ for 10 h is better process for the H13 steel.

Key words: H13 steel, diffusion annealing, microstructure, component segregation, liquid-dissected carbides