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Open AccessArticle

Evolution of Phase Transition and Mechanical Properties of Ultra-High Strength Hot-Stamped Steel During Quenching Process

by Shuang Liu 1,2, Mujun Long 1,2,*, Songyuan Ai 1,2, Yan Zhao 3,*, Dengfu Chen 1,2, Yi Feng 3, Huamei Duan 1,2 and Mingtu Ma 3
1
State Key Laboratory of Coal Mine Disaster Dynamics & Control, College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China
2
Chongqing Key Laboratory of Vanadium-Titanium Metallurgy and New Materials, Chongqing University, Chongqing 400044, China
3
China Automotive Engineering Research Institute Co. Ltd., Chongqing 401122, China
*
Authors to whom correspondence should be addressed.
Metals 2020, 10(1), 138; https://doi.org/10.3390/met10010138
Received: 30 November 2019 / Revised: 29 December 2019 / Accepted: 14 January 2020 / Published: 16 January 2020
(This article belongs to the Special Issue Forming and Heat Treatment of Modern Metallic Materials)
Hot stamping process is widely used in the manufacture of the high strength automotive steel, mainly including the stamping and quenching process of the hot-formed steel. In the hot stamping process, the steel is heated above the critical austenitizing temperature, and then it is rapidly stamped in the mold and the quenching phase transition occurs at the same time. The quenching operation in the hot stamping process has a significant influence on the phase transition and mechanical properties of the hot-stamping steel. A proper quenching technique is quite important to control the microstructure and properties of an ultra-high strength hot-stamping steel. In this paper, considering the factors of the austenitizing temperature, the austenitizing time and the cooling rate, a coupled model on the thermal homogenization and phase transition from austenite to martensite in quenching process was established for production of ultra-high strength hot-stamping steel. The temperature variation, the austenite decomposition and martensite formation during quenching process was simulated. At the same time, the microstructure and the properties of the ultra-high strength hot-stamping steel after quenching at different austenitizing temperature were experimental studied. The results show that under the conditions of low cooling rate, the final quenching microstructure of the ultra-high strength hot-stamping steel includes martensite, residual austenite, bainite and ferrite. With the increase of the cooling rate, bainite and ferrite gradually disappear. While austenitizing at 930 °C, the tensile strength, yield strength, elongation and strength-ductility product of the hot-stamping steel are 1770.1 MPa, 1128.2 MPa, 6.72% and 11.9 GPa%, respectively. View Full-Text
Keywords: phase transition; mechanical properties; quenching; ultra-high strength steel phase transition; mechanical properties; quenching; ultra-high strength steel
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Liu, S.; Long, M.; Ai, S.; Zhao, Y.; Chen, D.; Feng, Y.; Duan, H.; Ma, M. Evolution of Phase Transition and Mechanical Properties of Ultra-High Strength Hot-Stamped Steel During Quenching Process. Metals 2020, 10, 138.

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