Effect of tempering temperature on microstructure and mechanical properties of 700 MPa grade beam steel
ZHOU Qiang1,2, CAO Yanguang2, YANG Gengwei1, LI Zhaodong2, WAN Guoxi3, WANG Wenjun4
1. The key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, Hubei, China; 2. Institute of Structural Steels, Central Iron and Steel Research Institute Co., Ltd., Beijing 100081, China; 3. Technology Center, Anyang Iron and Steel Group Co., Ltd., Anyang 455004, Henan, China; 4. CITIC Metal Co., Ltd., Beijing 100004, China
Abstract：It is common that microalloying elements are not precipitated completely in hot rolled steel. When there are oversaturated solid solution microalloying elements in steel,tempering can precipitate them in the matrix and affect the mechanical properties. The effect of tempering temperature on microstructure and properties of Nb-Ti microalloying hot rolled 700 MPa automobile beam steel was studied by means of SEM,EBSD,TEM and tensile test. The results show that when tempering at 450 ℃ to 600 ℃,the matrix structure of the experimental steel is almost identical to the hot-rolled experimental steel,and it is mainly quasi-polygonal ferrite with slightly larger size. When tempering at 700 ℃,the microstructure of the experimental steel transforms to polygonal ferrite,the grain size increases rapidly,the grain boundary density decreases,and partial recrystallization occurs. When tempering,the oversaturated solid solution Ti and Nb in the hot rolling stage will precipitate in the form of (Ti,Nb)C. The higher the tempering temperature,the shorter the precipitation incubation period of (Ti,Nb)C and the larger the precipitation content. The average particle size will first decrease and then increase. When the tempering temperature is 600 ℃,the average particle size of (Ti,Nb)C is the smallest,only 5.47 nm. The tensile strength,yield strength and elongation increase with the increase of temperature when the experimental steel is tempered in the range of 450 ℃ to 600 ℃. When the tempering temperature rises to 700 ℃,the yield strength and tensile strength of the experimental steel decrease significantly and the elongation increases. When the tempering temperature is 600 ℃,the mechanical properties of the experimental steel are optimal. The tensile strength,yield strength and elongation are 803 MPa,755 MPa and 24.6%,respectively. The strengthening mechanism analysis shows that the yield strength improvement of the experimental steel is mainly caused by the precipitation strengthening of microalloying elements Ti and Nb during the tempering process.
周强, 曹燕光, 杨庚蔚, 李昭东, 万国喜, 王文军. 回火温度对700 MPa级大梁钢组织和性能的影响[J]. 钢铁, 2023, 58(10): 102-110.
ZHOU Qiang, CAO Yanguang, YANG Gengwei, LI Zhaodong, WAN Guoxi, WANG Wenjun. Effect of tempering temperature on microstructure and mechanical properties of 700 MPa grade beam steel[J]. Iron and Steel, 2023, 58(10): 102-110.
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2023, Vol. 58 
