A homogenization treatment(1250℃+12 h)was carried out to minimize the micro-segregation of bulk 718H martensitic mold steel,as verified by advanced experimental characterization and kinetic model of diffusion.However,new research found that there are still limitations in the use of the homogenization process.The result indicates that the chemical heterogeneity can be significantly reduced after homog-enization.The segregation ratio of Cr and Mo elements of sample decreased by 40.9％and 35.6％of the original level,respectively.Simultaneously,the test steel with higher strength and toughness is produced by controlling micro-segregation tempered from 540℃to 650℃.Importantly,it reveals that the impact energy is increased by up to 27.3％.The isotropy of impact energy in different directions can reach 0.89,resulting in an overall improvement in the isotropy.Toughness mainly depends on the orientation rela-tionship between the crack propagation direction and the band segregation region.The chain carbides formed due to the decomposition of the micro-segregated region during tempering are considered the main source of cracks.The more evenly distributed the subsequent tempered carbides after homogeniza-tion,resulting in an increase in toughness.However,an abnormal phenomenon is found in which the yield strength after homogenization is lower than that of the untreated sample tempered at 700℃.This result can be attributed to the combined influences of precipitation strengthening and fine grain strength-ening by analyzing various strengthening mechanisms.The mutually restrictive strengthening effect leads to the limitations of the homogenization process of bulk martensitic mold steel.

Hanghang Liu;Paixian Fu;Hongwei Liu;Chen Sun;Ningyu Du;Dianzhong Li

Shenyang National Laboratory for Materials Science,Shenyang 110016,China;Institute of Metal Research,Chinese Academy of Sciences,Shenyang 110016,China;School of Materials Science and Engineering,University of Science and Technology of China,Shenyang 110016,China

材料科学技术（英文版）

[1]Hanghang Liu;Paixian Fu;Hongwei Liu;Chen Sun;Ningyu Du;Dianzhong Li-.Limitations of the homogenization process of bulk martensitic mold steel-depending on the comprehensive manifestation of various strengthening)[J].材料科学技术（英文版）,2022(22):120-132

homog,enization,homogeniza

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