| abstract |
(57) [SUMMARY] [PROBLEMS] 440-7 excellent in shape freezing property and impact resistance An 80 MPa class high-strength steel sheet, a high-strength hot-dip galvanized steel sheet, a high-strength alloyed hot-dip galvanized steel sheet, and methods for producing them are provided. SOLUTION: In mass%, C is 0.04 to 0.22%, Si is 1.0% or less, Mn is 3.0% or less, P is 0.0 5% or less, S is 0.01% or less, Al is 0.01-0. 1% and N in an amount of 0.001 to 0.005%, and if necessary, further contains at least one selected from Nb, Ti, and V in a total amount of 0.008% to 0.05%, and the balance Fe And a ferrite phase with a ferrite crystal grain size of 8 μm or less, an <110> X-ray random intensity ratio ≧ 4, and a martensite area ratio of the second phase. The steel sheet is 5% or more, and the steel sheet is galvanized or galvannealed on the surface. |