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| Effects of Processing Variables on Microstructure and Yield Ratio of High Strength Constructional Steels |
| Jian KANG1,Cheng-ning LI1,Xiao-lei LI1,2,Jin-hua ZHAO1,Guo YUAN1,Guo-dong WANG1 |
1. State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, Liaoning, China
2. Shougang Qian��an Iron and Steel Co., Ltd., Qian��an 064404, Hebei, China |
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Abstract The process of ��controlled rolling+relaxation+ultra fast cooling (UFC)�� for high strength constructional steel with low yield ratio was presented. Microstructure and corresponding relationship with low yield ratio were investigated. The results showed that the constructional steels with multiphase microstructure of bainitic ferrite, martensite-austenite (M-A) and lath bainite were obtained through the creative process. The grain size decreased with the decrease in finish rolling temperature, which enhanced the strength by the grain refinement strengthening. The proper relaxation treatment promoted the bainitic ferrite lath width and the formation of blocky M-A constituent. In addition, both the tensile and yield strength increased with the decrease in finish rolling temperature and UFC final temperature, but the yield strength increased more significantly than tensile strength, which caused the increase in yield ratio. By using the process of ��controlled rolling+relaxation+ultra fast cooling��, the excellent comprehensive mechanical properties of 780 MPa grade constructional steels of 12-40 mm in thickness were achieved.
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Received: 17 November 2015
Published: 09 August 2016
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| Fund:National Natural Science Foundation of China |
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2016, Vol. 23 
