1. School of Materials Science and Engineering, Southeast University, Nanjing 211189, Jiangsu, China 2. Jiangsu Engineering Research Center of Tool and Die Steel, Tiangong Group, Danyang 212312, Jiangsu,China 3. Institute for Special Steels, Central Iron and Steel Research Institute, Beijing 100081, China
Phase Transformation of a Cold Work Tool Steel during Tempering
1. School of Materials Science and Engineering, Southeast University, Nanjing 211189, Jiangsu, China 2. Jiangsu Engineering Research Center of Tool and Die Steel, Tiangong Group, Danyang 212312, Jiangsu,China 3. Institute for Special Steels, Central Iron and Steel Research Institute, Beijing 100081, China
ժҪ The hardness and microstructure evolution of a 8% Cr cold work tool steel during tempering for 40 h were investigated. Transmission electron microscope examinations showed that M3C carbides precipitated from supersaturated martensite after tempering at 350 ��. When the tempering temperature was higher than 520 ��, the M23C6 carbides precipitated to substitute for M3C carbides. After ageing at the temperature of 520 �� for 40 h, it was observed that very fine and dense secondary Mo2C precipitates were precipitated. Thus, it can be concluded that the early stage of Mo2C-carbide precipitation is like to be Gunier-Preston (G-P) zone formed by ��Mo-C�� segregation group which is responsible for the secondary hardening peak at 520 ��. Overageing at 700 �� resulted in recovery of martensitic microstructure and precipitation of M23C6 carbides. When ageing at 700 �� for more than 20 h, recrystallization occurred, which resulted in a change of the matrix morphology from martensitic plates to equiaxed ferrite. It was noticed that the size of recrystallized grain/subgrain was very fine, which was attributed to the pinning effect of M23C6 precipitates.
Abstract��The hardness and microstructure evolution of a 8% Cr cold work tool steel during tempering for 40 h were investigated. Transmission electron microscope examinations showed that M3C carbides precipitated from supersaturated martensite after tempering at 350 ��. When the tempering temperature was higher than 520 ��, the M23C6 carbides precipitated to substitute for M3C carbides. After ageing at the temperature of 520 �� for 40 h, it was observed that very fine and dense secondary Mo2C precipitates were precipitated. Thus, it can be concluded that the early stage of Mo2C-carbide precipitation is like to be Gunier-Preston (G-P) zone formed by ��Mo-C�� segregation group which is responsible for the secondary hardening peak at 520 ��. Overageing at 700 �� resulted in recovery of martensitic microstructure and precipitation of M23C6 carbides. When ageing at 700 �� for more than 20 h, recrystallization occurred, which resulted in a change of the matrix morphology from martensitic plates to equiaxed ferrite. It was noticed that the size of recrystallized grain/subgrain was very fine, which was attributed to the pinning effect of M23C6 precipitates.
��������:National Key Technologies Research and Development Program of China
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E-mail: chihongxiao@163.com
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Hong-xiao CHI,,,Dang-shen MA,Hui-xia XU,Wang-long ZHU,Jian-qing JIANG. Phase Transformation of a Cold Work Tool Steel during Tempering[J]. �й������ڿ���, 2016, 23(5): 484-488.
Hong-xiao CHI,,,Dang-shen MA,Hui-xia XU,Wang-long ZHU,Jian-qing JIANG. Phase Transformation of a Cold Work Tool Steel during Tempering. Chinese Journal of Iron and Steel, 2016, 23(5): 484-488.
2016, Vol. 23 
