Microstructural Characterization and Softening Mechanism of Ultra-Low Carbon Steel and the Control Strategy in Compact S
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Microstructural Characterization and Softening Mechanism of Ultra‑Low Carbon Steel and the Control Strategy in Compact Strip Production Process Bo Jiang1 · Xuewen Hu1,2 · Guoning He1 · Huan Peng2 · Haibo Wang1 · Yazheng Liu1 Received: 24 June 2019 / Accepted: 21 July 2019 © The Korean Institute of Metals and Materials 2019
Abstract In this paper, the microstructures and properties of hot rolled ultra-low carbon steel sheet produced by different compact strip production (CSP) processes were investigated. The softening mechanism was also discussed and the control strategy was proposed in order to obtain optimum properties. Result showed that the average ferrite grain sizes of austenite rolling sheet and multiphase rolling sheet were 31.0 μm and 74.6 μm, respectively. The sheet after austenite rolling had a slightly higher yield and tensile strength while had a 6.3% higher elongation than that of the sheet after multiphase rolling. The higher dislocation in the sheet after multiphase rolling increased the strength while decreased the elongation. The softening mechanism of the sheet after multiphase rolling was the coarsening of ferrite grain. The combined role of {001} and {111} orientation resulted in a slight increase of the r and r̄ value in the sheet after multiphase rolling. It was a wise choice to conduct rolling at the A c1 temperature in CSP process to increase the grain size and decrease the dislocation density. Then, the strength of the sheets could be further reduced and the elongation could also be improved. Keywords CSP · Ultra-low carbon steel · Softening mechanism · EBSD · Yield strength
1 Introduction CSP process has been widely built in the steel mill plant over years for plenty of advantages as been evidenced before [1–4]. A lot of high strength hot rolled steel sheets could be easily produced in CSP process due to grain boundary strengthening and precipitation strengthening. However, the current products of CSP process can not satisfy the requirements of higher formability and thinner steel sheet which has a wider market and better price. Consequently, it is urging to develop new CSP process or optimize the current process to produce the steel sheet with lower strength.
* Bo Jiang [email protected] * Yazheng Liu [email protected] 1
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
Technology Center, Maanshan Iron & Steel Co., Maanshan 243002, China
2
Many researchers have focused on the researches to get optimization of CSP process parameters, especially on the flow stress, recrystallization behavior, microstructures and properties after rolling in single ferrite region [5–9]. Jeong investigated the effect of hot-rolling temperature on cold rolled microstructure and texture of an IF steel and found that the texture of hot-rolled steel sheet has a substantial influence on the textural evolution of the cold-rolled and annealed steel sheets [9]. Liu reported the deformation microstructure of various warm rolled steels whi
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