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 ferritic stainless steel sheet includes a base metal and a nitrided layer that is formed on a surface of the base metal, a chemical composition of the base metal contains, in mass %, C: 0.001 to 0.020%, Si: 0.01 to 1.50%, Mn: 0.01 to 1.50%, P: 0.010 to 0.050%, S: 0.0001 to 0.010%, Cr: 16.0 to 25.0%, N: 0.001 to 0.030%, Ti: 0.01 to 0.30%, and optional elements, with the balance: Fe and unavoidable impurities, a steel microstructure of the base metal includes, in volume ratio, 95% or more of a ferritic phase, the nitrided layer is a layer that is present in a region from a surface of a rolled surface to a 0.05 μm depth position in a sheet thickness direction, and an average nitrogen concentration in the nitrided layer is, in mass %, 0.80% or more.

Example embodiments relate to alloys having high corrosion resistance and high wear resistance. In particular, example embodiments relate to an iron-based alloy including 20 wt % to 50 wt % Cr; 0 wt % to 15 wt % Mo; 0 wt % to 15 wt % W; 3 wt % to 6 wt % B; and a balance of iron and impurities. In example embodiments, the pitting resistance equivalent number (PREN) is greater than 30 at 1300 K under substantially equilibrium solidification conditions. In example embodiments, the mole fraction of a hard phase of the alloy is between 45% and 80% at 1300K under substantially equilibrium solidification conditions. The liquidus of the alloy may be less than 2000K under substantially equilibrium solidification conditions.

A steel sheet has a predetermined chemical composition, in which a microstructure in a ¼ width portion, a microstructure in a ½ width portion, and a microstructure in a ¾ width portion, include, by area %, ferrite: 80% or more, martensite: 2% or less, and residual austenite: 2% or less, in which a proportion of unrecrystallized ferrite in the ferrite is 5% to 60%, an average grain size of carbonitrides is 6.0 nm to 30.0 nm, and Expressions (2) to (5) are satisfied.

Δ.sub.SF/μ.sub.SF≤0.10  (2)

Δ.sub.dF/μ.sub.dF≤0.20  (3)

Δ.sub.SUF≤20  (4)

Δ.sub.dC/μ.sub.dC≤0.50  (5)

A method for manufacturing of steel tube from a long steel strip, including providing a length of steel strip material to the process, forming a tube of the steel strip material, welding the formed tube in longitudinal direction, giving the tube a heat treatment wherein the mentioned steps are performed in one continuous in-line manufacturing line and the heat treatment includes a heating regime such that in successive cross-sections of the tube a microstructure is achieved which holds at least 50 vol % austenite and a cooling trajectory to re-introduce ferrite, and/or bainite in desired volume fractions.

The invention relates to a method for producing a component from a medium manganese flat steel product having 4 to less than 10 wt. % Mn, 0.0005 to 0.9 wt. % C, 0.02 to 10 wt. % Al, the remainder iron, including unavoidable steel-accompanying elements, and having a TRIP effect at room temperature. In order to produce a component, which is distinguished by very high strengths and an increased residual strain and re-shaping capacity, the flat steel product, according to the invention, is re-shaped by at least one re-shaping step to form a component and, before and/or during and/or after the at least one re-shaping step, the flat steel product is cooled down to a temperature of the flat steel product of less than room temperature to −196° C. The invention further relates to a component produced by this method and to a use for said components.

A method of shaping an article from a zinc or zinc alloy coated steel blank, including the steps of: a) providing a blank of the zinc or zinc alloy coated steel; b) reheating of the blank obtained in step a) to a reheating temperature T.sub.RH in the range Ac3-200° C. of the steel; c) soaking the blank for a time up to 3 minutes at the reheating temperature T.sub.RH; d) shaping the article in a press; and e) cooling the article. The steel includes (in wt. %) C: 0.01-0.2; Mn: 3.1-9.0; Al: 0.5-3.0; and optionally further alloying elements selected from Si, Cr, V, Nb, Ti and Mo; inevitable impurities and the balance is Fe.

A high-strength steel having excellent low-yield-ratio characteristics, according to one embodiment of the present invention, comprises, by wt %, 0.06-0.12% of C, 0.2-0.5% of Si, 1.5-2.0% of Mn, 0.003-0.05% of Al, 0.01% or less of N, 0.02% or less of P, 0.003% or less of S, 0.05-0.5% of Cr, 0.05-0.5% of Mo, 0.01-0.05% of Nb, 0.0005-0.005% of Ca and the balance of Fe and other inevitable impurities, and comprises polygonal ferrite as a microstructure, wherein the area fraction of the polygonal ferrite is 10-30% and the average hardness of the polygonal ferrite can be 180 Hv or less.

A preferable aspect of the present invention provides a hot-rolled steel sheet with excellent low-temperature toughness, a steel pipe using the same, and a manufacturing method therefor, wherein the hot-rolled steel sheet contains, by weight, 0.35-0.65% C, 0.01-0.4% Si, 13-26% Mn, 0.01-0.3% Ti, 0.01% or less B, 4% or less Al, 1-6% Cr, 0.05% or less P, 0.02% or less S, 0.01% or less N, 0.01-2% Cu, 0.001-0.015% Nb, and the balance Fe and other unavoidable impurities, the alloy elements satisfying the following relational formulas—[Relational formula 1] 70<[10*(C/12)+(Mn/55)+(Al/27)]*100<95 and [Relational formula 2] 4<100*(Cr/52+100*(Nb/93))<9; wherein a microstructure comprises, by area fraction, 97% or more (including 100%) of austenite and 3% or less (including 0%) of a carbide, the crystal grain size of the austenite being 18-30 μm or less; and wherein the size of the carbide is 0.5 μm or less.

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.