Effect of heat treatment on formability in 0.15C−1.5Si−1.5Mn multiphase cold-rolled steel sheet |
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Authors: | Chang Gil Lee Sung-Joon Kim Byung-Hwan Song Sunghak Lee |
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Affiliation: | (1) Materials Processing Department, Korea Institute of Machinery and Materials, 66 Sangnam-dong, 641-010 Changwon, Korea;(2) R & D Center, Taegu Tec Corporation, 304 Yonggye-ri, Gachang-myeon, Dalseong-gun, 711-860 Daegu, Korea;(3) Center for Advanced Aerospace Materials, Pohang University of Science and Technology, San 31 Hyoja-dong, Nam-gu, 790-784 Pohang, Korea |
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Abstract: | The effects of volume fraction and the stability of retained austenite on the formability of a 0.15C−1.5Si−1.5Mn (hereafter
all in wt.%) TRIP-aided multiphase cold-rolled steel sheet were investigated after various heat treatments. The steel sheets
were intercritically annealed at 800°C, and isothermally treated at 400°C and 430°C. Microstructural observation, tensile
tests and limiting dome height (LDH) tests were conducted on the heat-treated sheet specimens, and the changes in retained
austenite volume fraction as a function of tensile strain were measured using an X-ray diffractometer. The results showed
a plausible relationship between formability and retained austenite stability. Although the same amount of retained austenite
was obtained after isothermal holding at different temperatures, better formability was obtained in the specimens with the
higher stability of retained austenite. If the stability of the retained austenite is high, the strain-induced transformation
of retained austenite to martensite can be stably progressed, resulting in a delay of necking to the high strain region and
improvement in formability. |
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Keywords: | multi-phase cold-rolled steel sheet TRIP retained austenite stability formability |
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