Provided are a high-yield-ratio high-strength galvanized steel sheet that includes a Mn-containing steel sheet serving as a base material, and a production method therefor.

The high-yield-ratio high-strength galvanized steel sheet includes a steel sheet having a specific composition and a metallographic structure including, by area percentage, 20% or less ferrite, 40% or more in total of bainite and tempered martensite, and 60% or less as-quenched martensite, the bainite having an average grain size of 6.0 m or less, and a coated layer arranged on the steel sheet, the coated layer having a coating weight per side of 20 to 120 g/m.sup.2 and having a Mn content of 0.05 g/m.sup.2 or less, in which the high-yield-ratio high-strength galvanized steel sheet has a yield ratio of 65% or more and a tensile strength of 950 MPa or more.

A method for manufacturing a product from a flexibly rolled strip material includes the steps of: providing a strip material made from sheet steel; flexibly rolling the strip material such that a variable thickness is produced along the length of the strip material; electrolytically coating the strip material with a metallic coating material containing at least 93% of zinc by mass after the flexible rolling; heat treating at temperature above 350 C. and below a solidus line of the coating material after the electrolytic coating; working a blank from the flexibly rolled strip material; and hot forming the blank.

A cold-rolled steel sheet has a predetermined chemical composition, in which a structure before and after a hot-stamping includes ferrite: 30 area % to 90 area %, martensite: 0 area % or more and less than 20 area %, pearlite: 0 area % to 10 area %, retained austenite: 5 volume % to 20 volume %, and rest structure: bainite, a hardness of the retained austenite measured with a nano indenter before and after the hot-stamping satisfies relations of H2/H1<1.1 and HM<20, and a relation of TSEl20000 MPa.Math.% is satisfied.

A method of manufacturing a high-strength steel sheet includes, on a mass percent basis, 0.03%-0.10% C, 0.01%-0.5% Si, 0.001%-0.100% P, 0.001%-0.020% S, 0.01%-0.10% Al, 0.005%-0.012% N, the balance being Fe and incidental impurities, and microstructures that do not contain a pearlite microstructure, wherein, when Mnf=Mn [% by mass]?1.71?S [% by mass], Mnf is 0.3 to 0.6, including: forming a slab by vertical-bending type continuous casting or bow type continuous casting, wherein surface temperature of a slab corner in a region where the slab undergoes bending deformation or unbending deformation is 800? C. or lower, or 900? C. or higher; forming a steel sheet by hot-rolling the slab followed by cold rolling; annealing the steel sheet after the cold rolling; and skinpass rolling at a draft of 3% or less after the annealing.

The invention relates to sheet steel, more particularly a coated sheet steel, which is skin-pass rolled with a deterministic surface structure, and to a method for producing this steel.