Abstract
Conventional CMnSi transformation-induced plasticity (TRIP)-aided steels are a promising solution for producing lighter, crash-resistant car bodies, due to their high-strength and large uniform elongation. The CMnSi TRIP-aided steels, with more than 1 mass pct Si, have the drawback of poor galvanizability due to the presence of complex Si-Mn oxides on the surface. The full substitution of the Si by Al in cold-rolled and intercritically annealed TRIP-aided steels, therefore, was evaluated in detail. The phase-transformation kinetics during the intercritical annealing and the isothermal bainitic transformation were investigated by means of dilatometry. The allotropic phase-boundary was determined both by thermodynamic calculations and the experimental determination of the C content in the retained austenite. The results imply that short isothermal bainitic transformation times are sufficient to obtain the TRIP microstructure and that the processing of CMnAl TRIP-aided steels in a continuous annealing line not equipped for overaging is possible. The mechanical properties were evaluated for CMnAl TRIP-aided steels obtained using an industrial thermal cycle: the properties matched those of the conventional CMnSi TRIP-aided steels, where it was found that the high-Al CMnAl TRIP-aided steel had a high strain-hardening coefficient of 0.25, which was stable up to a true strain of 0.25.
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on leave from the Yawata R&D Laboratory, Nippon Steel Corporation, Tobihata-cho, Japan. S. CLAESSENS, Product Research Manager, is with OCAS NV, Research Centre of the Sidmar Group, ARBED Group Flat Rolled Products Division, B-9060 Zelzate, Belgium.
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Mahieu, J., De Cooman, B.C. & Maki, J. Phase transformation and mechanical properties of si-free CMnAl transformation-induced plasticity-aided steel. Metall Mater Trans A 33, 2573–2580 (2002). https://doi.org/10.1007/s11661-002-0378-9
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DOI: https://doi.org/10.1007/s11661-002-0378-9