Disclosed is a method for manufacturing a stainless steel for a polymer electrolyte membrane fuel cell separator, and more particularly, a method for manufacturing a stainless steel for a polymer electrolyte membrane fuel cell separator capable of obtaining low contact resistance and high corrosion resistance by effectively removing a non-conductive coating and forming a new coating. According to an embodiment, the disclosed method for manufacturing a stainless steel for a polymer electrolyte membrane fuel cell separator includes performing alternating current electrolysis by immersing, in a sulfuric acid solution, a stainless steel having a passivation coating formed on a surface thereof by cold rolling and bright annealing, wherein the alternating current electrolysis is performed by applying a current density of 10 to 30 A/dm.sup.2.

A coated steel member includes: a steel sheet substrate containing, as a chemical composition, by mass %, C: 0.25% to 0.65%, Si: 0.10% to 1.00%, Mn: 0.30% 1.00%, P: 0.050% or less, S: 0.0100% or less, N: 0.010% or less, Ti: 0.010% to 0.100%, B: 0.0005% to 0.0100%, Nb: 0.02% to 0.10%, Mo: 0.10% to 1.00%, Cu: 0.15% to 1.00%, and Ni: 0.05% to 0.25%; and a coating formed on a surface of the steel sheet substrate and containing Al and Fe. The maximum Cu content in a range from the surface to a depth of 5.0 μm is 150% or more of the Cu content of the steel sheet substrate.

A press hardening method includes the following steps: A. the provision of a steel sheet for heat treatment, precoated with a zinc- or aluminum-based pre-coating for anti-corrosion purpose, B. the deposition of a hydrogen barrier pre-coating over a thickness from 10 to 550 nm, C. the batch annealing of the precoated steel sheet in an inert atmosphere to obtain a pre-alloyed steel sheet, D. the cutting of the pre-alloyed steel sheet to obtain blank, E. the thermal treatment of the blank to obtain a fully austenitic microstructure in the steel, F. the transfer of the blank into a press tool, G. the hot-forming of the blank to obtain a part, H. the cooling of the part obtained at step G).

The present invention relates to a steel material including, in mass %: 0.310≤C≤0.410; 0.001≤Si≤0.35; 0.45≤V≤0.70; Cr≤6.00; 6.25≤Mn+Cr; Mn/Cr≤0.155; Cu+Ni≤0.84; 0.002≤P≤0.030; 0.0003≤S≤0.0060; P+5S≤0.040; 2.03<Mo<2.40; 0.001≤Al≤0.050; and 0.003≤N≤0.050, with the balance being Fe and unavoidable impurities.

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% includes the successive steps of providing a cold rolled steel sheet made of a steel having a chemical composition comprising, in weight %: 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 0%≤Nb≤0.05%, the remainder being Fe and unavoidable impurities, annealing the cold-rolled steel sheet at an annealing temperature AT higher than the Ac3 transformation point of the steel, quenching the annealed steel sheet by cooling it down to a quenching temperature QT lower than the Ms transformation point of the steel and comprised between 150° C. and 250° C., and reheating the quenched steel sheet to a partitioning temperature PT between 350° C. and 450° C. and maintaining the steel sheet at the partitioning temperature PT for a partitioning time Pt of at least 80 s, and coating the steel sheet by galvannealing, with an alloying temperature GAT comprised between 470° C. and 520° C.

Embodiments of the present disclosure provides an aluminum alloy-plated steel sheet having high surface quality and weldability, a hot-formed member, and methods for manufacturing the aluminum alloy-plated steel sheet and the hot-formed member. The aluminum alloy-plated steel sheet includes: a base steel sheet; and an aluminum alloy plating layer formed on the base steel sheet, wherein the aluminum alloy plating layer includes, by weight %, Zn: 21% to 35%, Si: 1% to 6.9%, Fe: 2% to 12%, and the balance of Al and inevitable impurities.

Provided is a hot rolled steel sheet having excellent formability and fatigue properties comprising, in percentage by weight: 0.3-0.8% of C; 13-25% of Mn; 0.1-1.0% of V; 0.005-2.0% of Si; 0.01-2.5% of Al; 0.03% or less of P; 0.03% or less of S; 0.04% or less (excluding 0%) of N; and the balance being Fe and inevitable impurities, wherein, when viewed in a cross section in the thickness direction, the hot rolled steel sheet comprises, by area fraction, 20-70% of a non-recrystallized structure and 30-80% of a recrystallized structure.

The present disclosure relates to an ultra-high-strength plated steel sheet and a method for molding the same, and more particularly, to an ultra-high-strength plated steel sheet having high tensile strength without the occurrence of plating peeling and hydrogen delayed fracture phenomenon during roll forming molding, and a method for molding the same.

A method is for producing a high strength coated steel sheet having a yield stress YS>800 MPa, a tensile strength TS>1180 MPa, and improved formability and ductility. The steel contains: 15%≤C≤0.25%, 1.2%≤Si≤1.8%, 2%≤Mn≤2.4%, 0.1%≤Cr≤0.25%, Al≤0.5%, the remainder being Fe and unavoidable impurities. The sheet is annealed at a temperature higher than Ac3 and lower than 1000° C. for a time of more than 30 s, then quenched by cooling it to a quenching temperature QT between 250° C. and 350° C., to obtain a structure consisting of at least 60% of martensite and a sufficient austenite content such that the final structure contains 3% to 15% of residual austenite and 85% to 97% of martensite and bainite without ferrite, then heated to a partitioning temperature PT between 430° C. and 480° C. and maintained at this temperature for a partitioning time Pt between 10 s and 90 s, then hot dip coated and cooled to the room temperature.

A steel part includes a steel sheet substrate and a coating on at least one surface of the steel sheet substrate. The coating includes between 0.2 and 0.7% by weight of Al, with a remainder of the metal coating being Zn and inevitable impurities. The steel sheet substrate and the coating have at least one deformation. An outer surface of the coating has a waviness Wa.sub.0.8 of less than or equal to 0.43 μm.