A zinc-plated steel sheet for hot stamping includes a steel sheet having a predetermined chemical composition and a zinc plating film disposed on the steel sheet. In the zinc plating film, the plating adhesion amount is 15.0 g/m.sup.2 or more and less than 40.0 g/m.sup.2, the Fe concentration is 1.5 mass % or more and 8.0 mass % or less, the Al content is 100 mg/m.sup.2 or more and 400 mg/m.sup.2 or less, the Al concentration is 0.50 mass % or more and 3.00 mass % or less, and the remainder consists of Zn and impurities.

The invention relates to a method for manufacturing strips of stainless steel, comprising hot rolling in an initial process (A) and subsequently cold rolling in a cold rolling line (B). The hot rolling is stopped when the strip thickness has been reduced to a thickness between 2.0 mm and 6.5 mm. The subsequent cold rolling is passed at least one time through said cold rolling line, which comprises in the following order: At least one cold rolling mill (11-13) in the initial part of the line, at least one annealing section (17), a scale breaking step (21), a shot blasting step (23) and at least one pickling section (26, 27) utilizing a mixture of nitric acid HNO.sub.3, hydrofluoric acid HF and optionally sulphuric acid H.sub.2SO.sub.4.

A hot press member includes excellent indentation peel strength which has a tensile strength of 1780 MPa or more. A plating layer has at a surface thereof a 10-point average roughness Rzjis of 25 μm or less, and a steel sheet contains, in mass %, not less than 0.25% but less than 0.50% of C, 1.5% or less of Si, 1.1-2.4% of Mn, 0.05% or less of P, 0.005% or less of S, 0.01-0.50% of Al, 0.010% or less of N, 0.001-0.020% of Sb, 0.005-0.15% of Nb, and 0.005-0.15% of Ti, the balance being Fe and incidental impurities. The average crystal grain size of prior austenite is 7 μm or less and the volume proportion of martensite is 90% or more, within 50 μm in the thickness direction from the surface of the steel sheet excluding the plating layer.

A high strength steel sheet according to the present invention contains a predetermined chemical composition, a metallographic structure includes, by an area ratio, ferrite: 20% to 70%, residual austenite: 5% to 40%, fresh martensite: 0% to 30%, tempered martensite and bainite: 20% to 75% in total, and pearlite and cementite: 0% to 10% in total, in a range of a ⅛ thickness to a ⅜ thickness from a surface, a number proportion of residual austenite having an aspect ratio of 2.0 or more with respect to the number of all residual austenite is 50% or more, at a sheet thickness ¼ position of a cross section parallel to a rolling direction and perpendicular to the surface, a standard deviation of area ratios of ferrite measured at 10 points every 50 mm along a width direction is less than 10%, and a tensile strength is 780 MPa or more.

A steel product includes the following chemical composition in wt. %: C: 0.01 to <0.3, Mn: 4 to <10, Al: 0.003 to 2.9, Mo: 0.01 to 0.8, Si: 0.02 to 0.8, Ni: 0.005 to 3, P: <0.04, S: <0.02, N: <0.02, with the remainder being iron including unavoidable steel-associated elements, wherein an alloy composition satisfies the equation 6<1.5 Mn+Ni<8; or the equation 0.11<C+Al<3, or an alloy composition contains, in addition to Ni, at least one or more of the elements, in wt. %, B: 0.0005 to 0.014; V: 0.006 to 0.1; Nb: 0.003 to 0.1; Co: 0.003 to 3; W: 0.03 to 2 or Zr: 0.03 to 1. The steel product has a microstructure of 2 to 90 vol. % austenite, less than 40 vol. % ferrite and/or bainite, with the remainder being martensite.

A surface-treated steel sheet of the present invention includes a base steel sheet and a Ni—Co—Fe alloy-plated layer on at least one surface of the base steel sheet, in which, in the alloy-plated layer, a Ni coating weight is 7.1 to 18.5 g/m.sup.2, a Co coating weight is 0.65 to 3.6 g/m.sup.2, and a total of the Ni coating weight and the Co coating weight is in a range of 9.0 to 20.0 g/m.sup.2. In a surface layer of the alloy-plated layer, a Co concentration is in a range of 20 to 60 atom %, and a Fe concentration is in a range of 5 to 30 atom %. In the alloy-plated layer, a region having a thickness of 2 μm or more, in which a total of a Ni concentration and the Co concentration is 10 atom % or more and the Fe concentration is 5 atom % or more, is present. The base steel sheet has a predetermined chemical composition, and a ferrite grain size number is 10 or more.

Provided is an Al or Al alloy-coated stainless steel sheet having a coating substrate and a hot-dip Al or Al alloy coated layer provided on a surface of the coating substrate, the coating substrate having a predetermined chemical composition, the Mo content and W content of the chemical composition of the coating substrate, the thickness of the coating substrate, and the thickness of the hot-dip Al or Al alloy coated layer satisfying predetermined relations.

One aspect of the present invention relates to a plated steel sheet for hot press forming, having an excellent impact property.

The present invention is a method to treat an external layer on a steel or stainless steel substrate. More particularly the disclosure provides a method to increase the amount of manganochromite spinel (Cr.sub.2MnO.sub.4) in the outer most surface of a steel or a stainless steel. The present disclosure seeks to provide a process to prepare a treatment of an external surface on a steel or stainless steel substrate by subjecting the surface to an atmosphere of steam and air or synthetic air (a combination of oxygen and other inert gases such as nitrogen or argon) while subjecting the substrate to a static electrical charge from +7.0 to +14.0 kV. The present disclosure also seeks to provide the coated substrate.

A hot-dip coated steel substrate coated with a layer of Sn directly topped by a zinc or an aluminum based coating is provided, the steel substrate having the following chemical composition in weight percent: 0.10≤C≤0.4%, 1.2≤Mn≤6.0%, 0.3≤Si≤2.5%, Al<2.0%, and on a purely optional basis, one or more elements such as P<0.1%, Nb ≤0.5%, B≤ 0.005%, Cr≤1.0%, Mo≤0.50%, Ni≤1.0%, Ti≤0.5%,
the remainder of the composition making up of iron and inevitable impurities resulting from the elaboration, the steel substrate further having between 0.0001 and 0.01% by weight of Sn in the region extending from the steel substrate surface up to 10 μm.