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Vol.34, No.12, 1533 ~ 1543, 1996

Title

Research Paper - Transformations - : Effects of Mn and Hot Coiling Temperature on Microstructure Evolution and r - Value of Continuously Annealed Low Carbon Steels

곽재현Jai Hyun Kwak, 정진환Jin Hwan Chung, 장삼규Sam Kyu Chang, 조경목Kyung Mox Cho

Abstract

Systematic microstructure control of low carbon steels processed by the continuous annealing could improve formability. In the present study, microstructure evolution including grain size, carbides and MnS(or (Fe, Mn)S) precipitates in hot coiled and annealed low carbon Al killed steel sheets was investigated as the function of Mn content and hot coiling temperature. r￣-value and mechanical properties were measured to check the formability of the steels. Results showed that increased r￣-value revealed for the steel containing low Mn and coiled at high temperature due to the coarsened carbides in hot rolled steel sheets. It was found that the improvement of r￣-value is closely related to the development of high intensity of {222} texture and low intensity of {200} and {110} texture, which were obtained with coarsened carbides during the recrystallization stage. Lowering Mn content might improve the strength of low carbon Al-killed steel as a result of grain refinement by fine Mn-sulfides precipitation. However there exists the lower limit of Mn content of the steels to prevent hot rolled edge cracks and to maintain higher elongation. Optimum Mn content was found about 0.1wt.% for the 0.02wt.%C-0.008wt.%S steels used in this study.

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