A cold rolled and heat treated steel sheet having a composition including the following elements, expressed in % by weight: 0.1%≤carbon≤0.6% 4%≤manganese≤20% 5%≤aluminum≤15% 0≤silicon≤2% aluminium+silicon+nickel≥6.5% and can possibly contain one or more of the following optional elements: 0.01%≤niobium≤0.3%, 0.01%≤titanium≤0.2% 0.01%≤vanadium≤0.6% 0.01%≤copper≤2.0% 0.01%≤nickel≤2.0% cerium≤0.1% boron≤0.01% magnesium≤0.05% zirconium≤0.05% molybdenum≤2.0% tantalum≤2.0% tungsten≤2.0% the remainder being composed of iron and unavoidable impurities caused by elaboration, wherein the microstructure of said steel sheet includes in area fraction, 10 to 50% of austenite, the austenite phase optionally including intragranular kappa carbides, the remainder being regular ferrite and ordered ferrite of D03 structure (Fe,Mn,X).sub.3Al, optionally including up to 2% of intragranular kappa carbides (Fe,Mn).sub.3AlC.sub.x said steel sheet presenting a ultimate tensile strength higher than or equal to 900 MPa. It also deals with a manufacturing method and with use of such grade for making vehicle parts.

A method for the manufacture of a cold rolled, recovered TWIP steel sheet coated with a metallic coating is provided including the following steps: (A) the feeding of a slab having the following composition: 0.1<C<1.2%, 13.0≤Mn<25.0%, S≤0.030%, P≤0.080%, N≤0.1%, Si≤3.0%, and on a purely optional basis, one or more elements such as Nb≤0.5%, B≤0.005%, Cr≤1.0%, Mo≤0.40%, Ni≤1.0%, Cu≤5.0%, Ti≤0.5%, V≤2.5%, Al≤4.0%, 0.06≤Sn≤0.2%, the remainder of the composition making up of iron and inevitable impurities resulting from elaboration; (B) Reheating such slab and hot rolling it; (C) A coiling step; (D) A first cold-rolling; (E) A recrystallization annealing; (F) A second cold-rolling; and (G) A recovery heat treatment performed by hot-dip coating.

A stainless steel foil having a chemical composition comprising, by mass %, C: 0.015% or less, Si: 0.50% or less, Mn: 0.50% or less, P: 0.040% or less, S: 0.010% or less, Cr: 10.0% or more and less than 16.0%, Al: 2.5 to 4.5%, N: 0.015% or less, Ni: 0.05 to 0.50%, Cu: 0.01 to 0.10%, Mo: 0.01 to 0.15%, at least one selected from the group consisting of Ti: 0.01 to 0.30%, Zr: 0.01 to 0.20%, Hf: 0.01 to 0.20%, and REM: 0.01 to 0.20%, where Ti+Zr+Hf+2REM≥0.06 and 0.30≥Ti+Zr+Hf are satisfied.

A high-strength steel includes a steel structure with: in area fraction, 60.0% to less than 90.0% of ferrite, 0% to less than 5.0% of unrecrystallized ferrite, 2.0% to 25.0% of martensite, 0% to 5.0% of carbide, and 0% to 3.0% of bainite; in volume fraction, more than 7.0% of retained austenite; in a cross-sectional view of 100 μm×100 μm, a value obtained by dividing number of retained austenite that are not adjacent to retained austenite whose crystal orientations are different by a total number of retained austenite being less than 0.80, an average crystal grain size of the ferrite being 6.0 μm or less, an average crystal grain size of the retained austenite being 3.0 μm or less, and a value obtained by dividing, by mass %, an average content of Mn in the retained austenite by an average content of Mn in steel being 1.50 or more.

A high-strength steel sheet includes a steel structure with: ferrite being 35% to 80%, martensite being 5% to 35%, and tempered martensite being 0% to 5% in terms of area fraction; retained austenite being 8% or more in terms of volume fraction; an average grain size of: the ferrite being 6 μm or less; and the retained austenite being 3 μm or less; a value obtained by dividing an area fraction of blocky austenite by a sum of area fractions of lath-like austenite and the blocky austenite being 0.6 or more; a value obtained by dividing, by mass %, an average Mn content in the retained austenite by an average Mn content in the ferrite being 1.5 or more; and a value obtained by dividing, by mass %, an average C content in the retained austenite by an average C content in the ferrite being 3.0 or more.

A high strength hot dip galvanised steel strip consisting, in mass percent, of the following elements: 0.10-0.21% C, 1.45-2.20% Mn, max. 1.50% Si, 0.1-1.50% Al, 0.001-0.04% P, 0.0005-0.005% B, 0.005-0.30% V, max. 0.015% N, max. 0.05% S, and, optionally, one or more elements: max. 0.004% Ca, max. 0.10% Nb, max. 0.50% Cr, max. 0.20% Mo, max. 0.20%, Ni, max. 0.20% Cu, and max. 0.20% Ti the balance of the composition consisting of Fe and inevitable impurities. The steel has good surface finish and increased mechanical strength, in particular high overall strength, ductility and plasticity. It also relates to a process for the manufacture of a high strength hot dip galvanised steel strip and to the products thereof.

Provided herein is a plated steel sheet having a yield ratio, strength (tensile strength), elongation, hole expansibility, and CTS. A method for producing the plated steel sheet is also provided, among others. A steel sheet of a specific composition is provided that has a micro structure containing 70 to 90% of ferrite, 5 to 20% of martensite, 5% or less of retained austenite, 10% or less of bainite, and 5% or less of perlite by volume. The ferrite has an average crystal grain diameter of 20 m or less. The martensite has an average crystal grain diameter of 5 m or less. The retained austenite has an average crystal grain diameter of 5 m or less. The bainite has an average crystal grain diameter of 7 m or less. The steel sheet has a tensile strength of 590 MPa or more.

A hot dip galvanized steel sheet and hot dip galvannealed steel sheet improved in uniform ductility and local ductility, yield strength and tensile strength, and low temperature impact property, characterized by having a predetermined chemical composition, having a metal structure containing, by volume %, retained austenite: over 5.0% and tempered martensite: over 5.0%, having retained austenite containing C: 0.85 mass % or more, and having a ratio [C].sub.gb/[P].sub.gb of an amount of segregation of C (number of atoms/nm.sup.2): [C].sub.gb to an amount of segregation of P (number of atoms/nm.sup.2): [P].sub.gb at prior austenite grain boundaries of 4.0 or more.

A high-strength steel sheet includes a steel structure with: ferrite being 35% to 80% and tempered martensite being greater than 5% and 20% or less in terms of area fraction; retained austenite being 8% or more in terms of volume fraction; an average grain size of: the ferrite being 6 m or less; and the retained austenite being 3 m or less; a value obtained by dividing an area fraction of blocky austenite by a sum of area fractions of lath-like austenite and the blocky austenite being 0.6 or more; a value obtained by dividing, by mass %, an average Mn content in the retained austenite by an average Mn content in the ferrite being 1.5 or more; and a value obtained by dividing, by mass %, an average C content in the retained austenite by an average C content in the ferrite being 3.0 or more.

A cold rolled heat treated steel sheet having a composition with the following elements, expressed in percentage by weight 0.1%Carbon0.5%, 1%Manganese3.4%, 0.5%Silicon2.5%, 0.03%Aluminum1.5%, 0%Sulfur0.003%, 0.002%Phosphorus0.02%, 0%Nitrogen0.01% and can contain one or more of the following optional elements 0.05%Chromium1%, 0.001%Molybdenum0.5%, 0.001%Niobium0.1%, 0.001%Titanium0.1%, 0.01%Copper2%, 0.01%Nickel3%, 0.0001%Calcium0.005%, 0%Vanadium0.1%, 0%Boron0.003%, 0%Cerium0.1%, 0%Magnesium0.010%, 0%Zirconium0.010%, the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of the steel sheet having in area fraction, 10 to 30% Residual Austenite, 50 to 85% Bainite, 1 to 20% Quenched Martensite, and less than 30% Tempered Martensite.