| 摘要 |
PROBLEM TO BE SOLVED: To improve blankability by providing a specific composition consisting of C, Si, Mn, P, total Al, and the balance essentially Fe, also providing a structure in which carbides of a specific average grain size and a specific spheroidizing rate are dispersed through a ferritic matrix of specific grain size, and further providing a specific notch tensile elongation. SOLUTION: The steel sheet has a composition consisting of, by weight, 0.70-1.20% C, <=0.40% Si, <=1.0% Mn, <=0.03% P, <=0.10% total Al, and the balance essentially Fe and also has a structure in which carbides of 0.3-1.2μm average grain size and >=80% spheroidizing rate are dispersed through a ferritic matrix of >=5μm ferrite grain size. Further, when tensile test is performed by using a test piece which is prepared by providing a V-notch of 45 deg. opening angle and 2 mm depth to width-directional both sides in the central position, in a longitudinal direction, of the parallel part of a JIS No.5 tensile test piece, the notch tensile elongation represented as an elongation percentage after breaking based on 10 mm gauge length in the central part in the longitudinal direction of the parallel part is regulated to >=10%.
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