A method for partial hardening of an austenitic steel by utilizing during cold deformation the TWIP (Twinning Induced Plasticity), TWIP/TRIP or TRIP (Transformation Induced Plasticity) hardening effect. Cold deformation is carried out by cold rolling at least one surface of the steel with forming degree () of 560% in order to achieve in the steel at least two consecutive areas with different mechanical values in thickness, yield strength (R.sub.p0.2), tensile strength (Rm) and elongation, having a ratio (r) between the ultimate load ratio (F) and the thickness ratio (t) of 1.0>r>2.0, and in which the areas are mechanically connected to each other by a transition area having a thickness that is variable from the thickness of the first area in the deformation direction to the thickness of the second area in the deformation direction.

A steel sheet having a specified chemical composition and a method for producing the steel sheet. The steel sheet has a microstructure including martensite and bainite. The total area fraction of the martensite and the bainite to the entirety of the microstructure is more than 90% and 100% or less. The microstructure includes inclusion clusters A and B, the content of the clusters A in the microstructure being 2 clusters/mm.sup.2 or less, and the content of the clusters B in the microstructure being 5 clusters/mm.sup.2 or less. The microstructure includes carbide particles including Fe as a main constituent which have an aspect ratio of 2.0 or less and a major axis of 0.30 m or more and 2 m or less. The content of the carbide particles in the microstructure is 4000 particles/mm.sup.2 or less. The microstructure includes prior grains having an average size of 6 to 15 m.

A method is disclosed for the operationally reliable production of a cold-rolled flat steel product of ?0.5 mm in thickness for deep-drawing and ironing applications. In the method, a steel melt which (in wt %) comprises up to 0.008% C, up to 0.005% Al, up to 0.043% Si, 0.15-0.5% Mn, up to 0.02% P, up to 0.03% S, up to 0.020% N and in each case optionally up to 0.03% Ti and up to 0.03% Nb and, as a remainder, iron and unavoidable impurities, is, with the omission of a Ca treatment, subjected to a secondary metallurgical treatment which, in addition to a vacuum treatment, comprises a ladle furnace treatment and during which the steel melt to be treated is kept under a slag, the Mn and Fe contents of which are, in sum total, <15 wt %. From the steel melt, a thin slab or a cast strip are produced, which are subsequently hot-rolled to form a hot strip with a thickness of <2.5 mm and wound to form a coil. Subsequently, the hot strips are cold-rolled to form a flat steel product of up to 0.5 mm in thickness.

A high strength steel sheet having excellent surface quality and formability with a tensile strength of 980 MPa or more and a TS-El balance of 30000 MPa % or more is provided. A high strength steel sheet comprises: a chemical composition containing C: 0.08% to 0.30%, Si: 2.0% or less, Mn: more than 3.0% and 10.0% or less, P: 0.05% or less, S: 0.01% or less, Al: 1.5% or less, Ti: 0.010% to 0.300%, and N: 0.0020% to 0.0100% in a range satisfying 1.1(Ti+Mn.sup.1/2/400)/(0.01+5N)6.0; and a microstructure including a retained austenite phase and a ferrite phase, wherein a ratio Mn/Mn of an average Mn concentration (Mn) of the retained austenite phase to an average Mn concentration (Mn) of the ferrite phase is 1.5 or more.

A strong and ductile automotive steel comprising 8-11 wt. % Mn, 0.1-0.35 wt. % C, 1-3 wt. % Al, 0.05-0.5 wt. % V, and a balance of Fe. By tuning the amount of austenite stabilizers, a dual phase microstructure of martensite and austenite with proper phase fraction can be achieved at room temperature. The martensite partitions C into the retained austenite grains. The martensite matrix can ensure the higher strength of automotive steel while the retained austenite grains with varied mechanical stability can improve the ductility of automotive steel, achieving the strength of 1500 MPa and the ductility of 20% simultaneously. The method for fabricating this automotive steel circumvents the high quenching temperature of conventional Q&P steels and therefore reduces the production price and is easy for mass production.

A method of manufacturing a low-density clad steel sheet, including: preparing a base material, a lightweight steel sheet including C: 0.3 to 1.0%, Mn: 4.0 to 16.0%, Al: 4.5 to 9.0%, and Fe; preparing cladding materials, each being martensitic carbon steel including C: 0.1 to 0.45%, Mn: 0.1 to 3.0%, and Fe; disposing the base material between the cladding materials to obtain a laminate; welding an edge of the laminate, and heating the welded laminate to 1050 to 1350? C.; finish-rolling the heated laminate to 750 to 1050? C. with a rolling reduction ratio of 30% or more in a first pass, to obtain a hot-rolled steel sheet; coiling the hot-rolled steel sheet at 400 to 700? C.; applying a cold-reduction ratio of 35 to 90% to obtain a cold-rolled steel sheet; and annealing the cold-rolled steel sheet at 550? C. or higher and A3+200? C. or lower of the cladding materials.

This disclosure describes methods for improving the performance and consistency of steels by closely controlling the initial homogenization of steel compositions prior to hot working. Experimental data is provided illustrating that the traditional austenitization techniques do not take into account diffusion of the various components within a steel composition and, as such, may not completely homogenize the steel composition. In the methods described in this disclosure, the initial step of austenitizing the steel ingot is altered to achieve a more homogenous distribution of the different components throughout the ingot. The improved method includes heating the steel composition to a temperature within the upper half of the pure austenitic phase temperature range and maintaining the steel composition at that temperature for a period of time determined based on the diffusivity in the austenitic phase of the steel composition of at least one constituent of the steel.

A deformation-hardened component is made of galvanized steel by cutting a plate from a steel strip or steel sheet coated with zinc or with a zinc-based alloy and subsequently heating the plate to a deformation temperature above Ac3 for deformation and hardening. The galvanized steel has an at least partially martensitic transformation structure and includes as a chemical composition in wt. % C: 0.10-0.50, Si: 0.01-0.50, Mn: 0.50-2.50, P<0.02, S<0.01, N<0.01, Al: 0.015-0.100, B<0.004, remainder iron, including unavoidable smelting-induced, steel-accompanying elements. The chemical composition further includes at least one element selected from the group consisting of Nb, V, Ti, with a sum of the contents Nb+V+Ti being in a range of 0.01 to 0.20 wt. %. The structure of the steel after deformation-hardening has an average grain size of the former austenite grains of <15 ?m.

A high-strength steel sheet that has a predetermined component composition, that has a steel microstructure in which an area percentage of ferrite ranges from 5% to 50% in a thickness cross-section in a rolling direction, a total area percentage of fresh martensite and retained ranges from 2% to 30%, each of the fresh martensite and the retained has an average grain size of 5 m or less, and a ratio of the fresh martensite and the retained adjacent only to ferrite with respect to the fresh martensite and the retained from a surface to 200 m in the thickness direction is 30% or less in total area percentage, and that has a yield strength of 550 MPa or more.

A cold-rolled and annealed ferritic steel sheet is provided. The steel has a composition comprising, expressed by weight: 0.001C0.15%; Mn1%; Si1.5%; 7.5%AI10%; 0.020%Ti0.5%; S0.050%; and P0.1%.
A balance of the composition includes iron and inevitable impurities resulting from the smelting. The structure includes kappa () precipitates and equiaxed ferrite, an average grain size d of the equiaxed ferrite is less than 50 microns, and a linear fraction f of intergranular precipitates is less than 30%. The linear fraction f is defined by $f=\frac{{}_{\left(A\right)}\mathrm{di}}{{}_{\left(A\right)}\mathrm{Li}}.$
.sub.(A)di denotes the total length of grain boundaries containing precipitates relative to an area (A) and .sub.(A)Li denotes the total length of the grain boundaries relative to the area (A). A content of carbon in solid solution is less than 0.005% by weight, and the cold-rolled and annealed ferritic steel sheet has a thickness between 0.6 mm and 1.5 mm. A skin part or structural part for the automotive field is also provided.