Effect of lower bainite/martensite/retained austenite triplex microstructure on the mechanical properties of a low-carbon steel with quenching and partitioning process |
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| Authors: | Wan-song Li Hong-ye Gao Zhong-yi Li Hideharu Nakashima Satoshi Hata Wen-huai Tian |
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| Affiliation: | 1. School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China;2. Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Fukuoka 8168580, Japan |
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| Abstract: | We present a study concerning Fe–0.176C–1.31Si–1.58Mn–0.26Al–0.3Cr (wt%) steel subjected to a quenching and partitioning (Q&;P) process. The results of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and tensile tests demonstrate that the microstructures primarily consist of lath martensite, retained austenite, lower bainite (LB), and a small amount of tempered martensite; moreover, few twin austenite grains were observed. In the microstructure, three types of retained austenite with different sizes and morphologies were observed: blocky retained austenite (~300 nm in width), film-like retained austenite (80–120 nm in width), and ultra- fine film-like retained austenite (30–40 nm in width). Because of the effect of the retained austenite/martensite/LB triplex microstructure, the specimens prepared using different quenching temperatures exhibit high ultimate tensile strength and yield strength. Furthermore, the strength effect of LB can partially counteract the decreasing strength effect of martensite. The formation of LB substantially reduces the amount of retained austenite. Analyses of the retained austenite and the amount of blocky retained austenite indicated that the carbon content is critical to the total elongation of Q&;P steel. |
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| Keywords: | low-carbon steel quenching partitioning retained austenite microstructure mechanical properties |
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