| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a high-strength cold-rolled steel sheet superior in deep-drawability and bake hardenability and having a tensile strength of 440 MPa or higher, an average r value of 1.20 or higher, and a bake hardening value of 40 MPa or higher. <P>SOLUTION: The high-strength cold-rolled steel sheet, having a structure including a ferrite phase of 70% or higher by an area ratio and a martensite phase of 3% or higher by an area ratio, is obtained by hot-rolling a steel raw material with a component composition containing 0.010-0.06 mass% of C, higher than 0.5 mass% and 1.5 mass% or less of Si, 1.0-3.0 mass% of Mn, 0.010-0.090 mass% of Nb and 0.015-0.15 mass% of Ti and satisfying a relation: (Nb/93)/(C/12)∠0.20 and a solid solution C amount of 0.005-0.025%, cold rolling the steel raw material, heating the steel raw material from 700-800°C to 800-900°C° at an average temperature increase rate of less than 3° C/s, soaking the steel raw material, and performing annealing by cooling from the soaking temperature to a cooling stop temperature of 500°C or lower at a cooling rate of 5°C/s or more. <P>COPYRIGHT: (C)2012,JPO&INPIT |
