High-temperature properties and microstructure of Mo microalloyed ultra-high-strength steel

Qi-hang Han1),Yong-lin Kang1,2),Xian-meng Zhao1),Lu-feng Gao1),and Xue-song Qiu1)1) School of Materials Science and Engineering,University of Science and Technology Beijing,Beijing 100083,China 2) State Key Laboratory for Advanced Metals and Materials,University of Science and Technology Beijing,Beijing 100083,China

摘 要：The high-temperature mechanical properties and microstructure of forging billets of C-Si-Mn-Cr and C-Si-Mn-Cr-Mo ultra-high-strength cold-rolled steels（tensile strength≥1000 MPa,elongation≥10%） were studied.Through the comparison of reduction in area and hot deformation resistance at 600-1300°C,the Mo-containing steel was found to possess a higher strength and a better plasticity than the Mo-free one.The equilibrium phase diagram and atom fraction of Mo in different phases at different temperatures were calculated by Thermo-Calc software（TCW）.The results analyzed by using transmission electron microscopy and TCW show that precipitates in the Mo-containing steel are primarily M23C6,which promote pearlite formation.The experimental data also show that a lower ductility point existing in the Mo-free steel at 850°C is eliminated in the Mo-containing one.This is mainly due to the segregation of Mo at grain boundaries investigated by electron probe microanalysis（EPMA）,which improves the strength of grain boundaries.

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