| 摘要 |
Provided is a process for producing a high-strength hot-dip galvanized steel sheet which has a tensile strength TS of 540 MPa or higher and which is excellent in terms of material-quality stability, processability, and deposit appearance. A steel sheet that contains, in terms of mass%, 0.04-0.13% C, 0.7-2.3% Si, 0.8-2.0% Mn, up to 0.1% P, up to 0.01% S, up to 0.1% Al, and up to 0.008% N is subjected to a first heating step in which the steel sheet is heated to 400-750ºC in an atmosphere having an O2 concentration of 0.1-20 vol.% and an H2O concentration of 1-50 vol.% and then heated to 600-850ºC in an atmosphere having an O2 concentration of 0.01-0.1 vol.%, excluding 0.1 vol.%, and an H2O concentration of 1-20 vol.%. The steel sheet is subsequently subjected to a second heating step in which the steel sheet is held at 750-900ºC for 15-600 seconds in an atmosphere having an H2 concentration of 1-50 vol.% and a dew point of 0ºC or lower, cooled to a temperature in the range of 450-550ºC, and then held at this temperature for 10-200 seconds. Thereafter, the steel sheet is subjected to hot-dip galvanization. |
