| 摘要 |
<p>A cold rolled steel sheet or galvanized steel sheet, for deep drawing, improved in fatigue properties of a base metal and fatigue properties of a spot weld zone, is provided. The cold rolled steel sheet or galvanized steel sheet comprises by weight C: 0.0001 to 0.0026%, Si: not more than 1.2%, Mn: 0.03 to 3.0%, P: 0.015 to 0.15%, S: 0.0010 to 0.020%, Al: 0.005 to 0.1%, N: 0.0005 to 0.0080% and B: 0.0003 to 0.0030% with the balance consisting of Fe and unavoidable impurities. A process for producing the above steel sheet is also provided which comprises the steps of: performing hot roll finishing of a slab having the above chemical composition at the Ar3 transformation point or above; preferably, then cooling the hot rolled strip, within 1.5 sec after the completion of the hot rolling, to 750 DEG C at a rate of not less than 50 DEG C/sec; coiling the strip in the temperature range of from room temperature to 750 DEG C; cold rolling the coiled strip a reduction ratio of not less than 70%; subjecting the cold rolled strip to continuous annealing at 600 to 900 DEG C or to continuous galvanizing by the sendzimer method; and performing temper rolling with a reduction ratio of not less than 1.5 x (1 - 400 x C) % and not less than 2080 x (C - 0.0015) wherein C represents the carbon content in % by weight. <IMAGE></p> |
