| 摘要 |
<p>A process for producing a high-strength cold rolled steel sheet of low YP with less material quality fluctuation, comprising sequentially subjecting a steel containing, by mass, more than 0.01 to less than 0.08% C, 0.2% or less Si, 0.8 to less than 1.7% Mn, 0.03% or less P, 0.02% or less S, 0.3% or less sol. Al, 0.01% or less N and more than 0.4 to 2% Cr so that the relationships 1.9<([%Mn]+1.3x[%Cr])<3 and 0.34<=[%Cr]/[%Mn]are satisfied and containing the balance iron and unavoidable impurities to hot rolling and cold rolling, heating at an average heating rate of less than 3°C/sec between 680°and 740°C, annealing at an annealing temperature of higher than 740°to lower than 820°C and cooling at an average cooling rate of 2°to 30°C/sec between the annealing temperature and 650°C, at an average cooling rate of 10°C/sec or greater between 650°C and the following Tc and at an average cooling rate of 0.2°to 10°C/sec between the Tc and 200°C. Tc = 410-40x[%Mn]-30x[%Cr]([%Mn]and[%Cr]represent the contents of Mn and Cr, respectively.)</p> |
