Continously annealed cold-rolled steel sheet excellent in balance between deep drawability and resistance to secondary-work embrittlement and method for manufacturing same

摘要

A continuously annealed cold-rolled steel sheet excellent in balance between deep drawability and resistance to secondary-work embrittlement, which consists essentially of: under 0.0030 wt. % carbon, up to 0.05 wt. % silicon, from 0.05 to 0.20 wt. % manganese, up to 0.02 wt. % phosphorus, up to 0.15 wt. % sulfur, from 0.025 to 0.06 wt. % soluble aluminum, up to 0.0030 wt. % nitrogen, from 0.02 to 0.10 wt. % titanium, from 0.0003 to 0.0010 wt. % boron, and the balance being iron and incidental impurities, where a value of an index (X) representing a content rate of titanium to boron, as calculated by specific formulae, is of from 9.2 to 11.2. The above-mentioned continuously annealed cold- rolled steel sheet is manufactured by: carrying out a finishing-rolling in a hot-rolling of a steel slab having the above-mentioned chemical composition so that a reduction rate distribution function (Y) as expressed by another specific formula is satisfied; completing the finishing-rolling at a temperature of from 880° to 920° C.; then coiling the resultant hot- rolled steel strip; then cold-rolling the hot- rolled steel strip at an accumulative reduction rate of at least 70%; and then continuously annealing the resultant cold-rolled steel strip in a temperature region of from 750° C. to an Ac.sub.3 transformation point.