Influence of N/C ratio on microstructure and properties of new high-strength weathering steels
Jian Cheng1,2 Yue-hua Guo3 Ming Liu3 Hou-fa Shen2
1 The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, Hubei, China 2 Key Laboratory for Advanced Materials Processing Technology, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China 3 Pangang Group Research Institute Co., Ltd., State Key Laboratory of Vanadium and Titanium Comprehensive Utilization, Panzhihua 617000, Sichuan, China
Influence of N/C ratio on microstructure and properties of new high-strength weathering steels
Jian Cheng1,2 Yue-hua Guo3 Ming Liu3 Hou-fa Shen2
1 The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, Hubei, China 2 Key Laboratory for Advanced Materials Processing Technology, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China 3 Pangang Group Research Institute Co., Ltd., State Key Laboratory of Vanadium and Titanium Comprehensive Utilization, Panzhihua 617000, Sichuan, China
摘要 Influence of the N/C ratio on the microstructure and properties of new-generation high-strength weathering steels was investigated using calculation of phase diagram (CALPHAD) and experiments. The microstructures of weathering steels containing different N/C ratios were predicted by a CALPHAD approach, and only three phases were predicted in these steels within the rolling temperature range of 850–1050 C. The precipitation fraction of VN/V(C, N) increases with increasing N/C ratio. Microstructures of the four tested steels were all experimentally determined to contain bainite, ferrite, and VN precipitates after air cooling to room temperature. The bainite fraction increases with increasing N/C ratio, and it is 85% in the steel containing 0.038% N and 0.032% C. The results of the tensile tests and impact tests demonstrated that the yield strength and tensile strength of the steel containing 0.038% N and 0.032% C are greater than 550 and 650 MPa, respectively, and the elongation is greater than 24%, which satisfies the design objectives for mechanical properties. The impact toughness values of the four steels at 0, - 20, and - 40 C are all greater than 24 J. With increasing N/C ratio, the bainite fraction and the precipitation fraction of VN/V(C, N) increase, resulting in increasing yield strength and tensile strength.
Abstract：Influence of the N/C ratio on the microstructure and properties of new-generation high-strength weathering steels was investigated using calculation of phase diagram (CALPHAD) and experiments. The microstructures of weathering steels containing different N/C ratios were predicted by a CALPHAD approach, and only three phases were predicted in these steels within the rolling temperature range of 850–1050 C. The precipitation fraction of VN/V(C, N) increases with increasing N/C ratio. Microstructures of the four tested steels were all experimentally determined to contain bainite, ferrite, and VN precipitates after air cooling to room temperature. The bainite fraction increases with increasing N/C ratio, and it is 85% in the steel containing 0.038% N and 0.032% C. The results of the tensile tests and impact tests demonstrated that the yield strength and tensile strength of the steel containing 0.038% N and 0.032% C are greater than 550 and 650 MPa, respectively, and the elongation is greater than 24%, which satisfies the design objectives for mechanical properties. The impact toughness values of the four steels at 0, - 20, and - 40 C are all greater than 24 J. With increasing N/C ratio, the bainite fraction and the precipitation fraction of VN/V(C, N) increase, resulting in increasing yield strength and tensile strength.
Jian Cheng,Yue-hua Guo,Ming Liu, et al. Influence of N/C ratio on microstructure and properties of new high-strength weathering steels[J]. Journal of Iron and Steel Research International, 2019, 26(1): 84-90.
2019, Vol. 26 
