Patent ID: 11946112
Assignee: JFE STEEL CORPORATION
Field: Materials, metallurgy (Chemistry)
Classification: CPC C  B | IPC C

Claim 7:
8. The method for producing a high-strength steel sheet according to claim 6, wherein the annealing step is a step performed in a manner such that the cold-rolled steel sheet obtained in the cold rolling step is heated to a temperature range of 780 to 900° C.; thereafter, the steel sheet is soaked in the temperature range for 20 seconds or more; then, primary cooling is performed to cool the steel sheet from the soaking temperature to a rapid cooling start temperature of 580° C. or higher at an average primary cooling rate of 1 to 100° C./s; thereafter, secondary cooling is performed to cool the steel sheet from the rapid cooling start temperature to 300° C. or lower at an average secondary cooling rate of 80° C./sec or greater and less than 2000° C./sec, the average secondary cooling rate being an average cooling rate for a range from the rapid cooling start temperature to 300° C.; then, the steel sheet is held under conditions including a retention time for a temperature range of 450 to 130° C. of 10 to 1000 seconds; and then, tertiary cooling is performed to cool the steel sheet over a temperature range of 130 to 50° C. at an average tertiary cooling rate of 5° C./sec or greater.