Method for producing ultra-high strength alloyed hot-dip galvanized steel sheet, and obtained alloyed hot-dip galvanized steel sheet

摘要

A method for producing a coated steel sheet having a tensile strength TS of at least 1450 MPa and a total elongation TE of at least 17%, in weight percent, 0.34% ≦ C ≦ 0.45%, 1.50% ≦ Mn ≦ 2.30%, 1.50 ≦ Si ≦ 2.40%, 0% Cr ≦ 0.7%, 0% ≦ Mo ≦ 0.3%, 0.10% ≦ Al ≦ 0.7% And optionally providing 0% ≦ Nb ≦ 0.05%, the step of providing a cold rolled steel sheet made of steel having a chemical composition that is Fe and inevitable impurities, and from the Ac3 transformation point of the steel The step of annealing the cold-rolled steel sheet at a high annealing temperature AT and quenching the annealed steel sheet by cooling to a quenching temperature QT included between 150 ° C. and 250 ° C. lower than the Ms transformation point of the steel. Step and hardened steel plate, Reheating to a distribution temperature PT between 50 ° C. and 450 ° C. and maintaining the steel plate at the distribution temperature PT for a distribution time Pt of at least 80 seconds and alloying comprised between 470 ° C. and 520 ° C. Coating the steel sheet by alloying hot dip galvanizing at a temperature GAT.