COLD ROLLED STEEL SHEET WITH EXCELLENT COATING/BAKING HARDENABILITY AND NATURAL AGING RESISTANCE, AND ITS MANUFACTURING METHOD

摘要

PROBLEM TO BE SOLVED: To provide a cold rolled steel sheet having excellent coating/baking hardenability and natural aging resistance, and also to provide its manufacturing method.;SOLUTION: The cold rolled steel sheet excellent in coating/baking hardenability and natural aging resistance has a composition which consists of 0.001 to 0.01% C, 0.01 to 2% Mn, 0.005 to 0.1% Si, 0.001 to 0.1% P, 0.001 to 0.03% S, 0.01 to 0.1% Al, 0.001 to 0.01% N, 0.001 to 0.1% Ti and the balance Fe with inevitable impurities and in which respective contents of C, Ti and N satisfy 0.002{C(%)-Ti(%)/4+6N(%)/7}0.005 (where C(%), Ti(%) and N(%) represent their respective contents (mass%)). The main structure of the steel sheet is composed of ferrite phase, and further, the distribution number density of precipitates having an interface coherent partly with the matrix phase of the steel sheet is 1×10¹⁶ to 1×10¹⁸ pieces/cm³ and the maximum length of the precipitates is 5 to 10 nm.;COPYRIGHT: (C)2005,JPO&NCIPI