| 摘要 |
<p>A method for the manufacturing of high strength cold rolled steel sheets includes continuously annealing a cold rolled steel sheet that has a composition containing C: 0.05 to 0.3% by mass, Si: 0.6 to 3.0% by mass, Mn: 1.0 to 3.0% by mass, P: not more than 0.1% by mass, S: not more than 0.02% by mass, Al: 0.01 to 1% by mass, N: not more than 0.01% by mass, and Fe and inevitable impurities: balance, in a manner such that the cold rolled steel sheet is heated in a furnace using an oxidizing burner to a steel sheet temperature of not less than 700°C, thereafter the steel sheet is soak-annealed in a reducing atmosphere furnace at 750 to 900°C, and the steel sheet is cooled in a manner such that the average cooling rate between 500°C and 100°C is not less than 50°C/s. According to the method, high-Si cold rolled steel sheets that have high strength and good phosphatability while containing Si at 0.6% or more can be obtained without controlling conditions so as to increase the dew point in the reducing atmosphere in the soaking furnace or to increase the vapor hydrogen partial pressure ratio.</p> |
