| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-carbon cold-rolled steel sheet which has superior formability for an extension flange before being quenched, and acquires predetermined hardness and toughness after having been quenched, though causing little deformation due to quenching. SOLUTION: The high-carbon cold-rolled steel sheet having the superior formability for the extension flange has a composition including, by mass%, 0.20-0.60% C and 0.005% or less S; and includes crystal grains of ferrite with an average grain size of 5μm or larger, and with the standard deviation of the grain sizes of 0.50 or less. In addition, it is preferable for the steel sheet to contain inclusions of which the ratio of a major axis to a minor axis in the shape is controlled to 2.0 or less, and to contain 0.010-0.050% Ti and 0.0003-0.0050% B. COPYRIGHT: (C)2006,JPO&NCIPI
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