Limitations of the homogenization process of bulk martensitic mold steel-depending on the comprehensive manifestation of various strengthening  

作　　者：Hanghang Liu Paixian Fu Hongwei Liu Chen Sun Ningyu Du Dianzhong Li 

机构地区：[1]Shenyang National Laboratory for Materials Science,Shenyang 110016,China [2]School of Materials Science and Engineering,University of Science and Technology of China,Shenyang 110016,China [3]Institute of Metal Research,Chinese Academy of Sciences,Shenyang 110016,China

出　　处：《Journal of Materials Science & Technology》2022年第22期120-132,共13页材料科学技术（英文版）

基　　金：The work was financially supported by the China Postdoctoral Science Foundation(No.2019M661153);The authors also appreciate the financial support by Young Talent Project by Shenyang National Laboratory for Materials Science(No.2020000358);Doctoral Research Startup Fund Guidance Program Project of Liaoning Province(No.2020-BS-004);Project to Strengthen Industrial Development at the Grass-roots Level(No.TC190A4DA/35);Guangdong Basic and Applied Basic Research Foundation(No.2019A1515110886).

摘　　要：A homogenization treatment(1250 °C + 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 homogenization. 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 °C to 650 °C. 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 relationship 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 homogenization, 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 °C. This result can be attributed to the combined influences of precipitation strengthening and fine grain strengthening by analyzing various strengthening mechanisms. The mutually restrictive strengthening effect leads to the limitations of the homogenization process of bulk martensitic mold steel.

关 键 词：Martensitic mold steel Strength-toughness MICRO-SEGREGATION Synergistic strengthening 

分 类 号：TG142.1[一般工业技术—材料科学与工程]