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http://dx.doi.org/10.3365/KJMM.2010.48.07.615

Tensile and Charpy Impact Properties of High-Strength Bainitic Steels Fabricated by Controlled Rolling Process  

Sung, Hyo Kyung (Center for Advanced Aerospace Materials, Pohang University of Science and Technology)
Shin, Sang Yong (Center for Advanced Aerospace Materials, Pohang University of Science and Technology)
Hwang, Byoungchul (Ferrous Alloys Research Group, Korea Institute of Materials Science)
Lee, Chang Gil (Ferrous Alloys Research Group, Korea Institute of Materials Science)
Kim, Nack J. (Graduate Institute of Ferrous Technology, Pohang University of Science and Technology)
Lee, Sunghak (Center for Advanced Aerospace Materials, Pohang University of Science and Technology)
Publication Information
Korean Journal of Metals and Materials / v.48, no.7, 2010 , pp. 615-624 More about this Journal
Abstract
This study is concerned with tensile and Charpy impact properties of high-strength bainitic steels fabricated by controlled rolling process. Six kinds of steels were fabricated by varying finish rolling temperature, start cooling temperature, and cooling rate, and their microstructures and tensile and Charpy impact properties were investigated. Their effective grain sizes were also characterized by the electron backscatter diffraction analysis. The microstructures of the steels rolled in the single phase region were most similar to those of the steels rolled in the two phase region. The steels cooled from $700{^{\circ}C}$ were composed mainly of granular bainites, while those cooled from $600{^{\circ}C}$ contained a number of bainitic ferrites, which resulted in the decrease in ductility and upper shelf energy in spite of the increase in strength. In the steels cooling from $600^{\circ}C$, fine acicular ferrites were well formed when the cooling rate was slow, which led to the best combination of high ductility, high upper shelf energy, and low energy transition temperature according to the decrease in the overall effective grain size due to the presence of acicular ferrites having smaller effective grain size.
Keywords
bainitic steels; metals; rolling; strength; tensile test;
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