A tempered and coated steel sheet having a composition containing the following elements, expressed in percentage by weight: 0.17%?carbon?0.25%, 1.8%?manganese?2.3%, 0.5%?silicon?2.0%, 0.03%?aluminum?1.2%, sulphur?0.03%, phosphorus?0.03%,
the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel sheet containing in area fraction, 4 to 20% residual austenite, 0 to 15% of ferrite, 40 to 85% tempered bainite and a minimum of 5% of tempered martensite, wherein the cumulated amounts of tempered martensite and residual austenite is between 10 and 30%. The composition may also contain one or more of the following elements: chromium?0.4%, molybdenum?0.3%, niobium?0.04%, titanium?0.1%. Manufacturing methods and use of tempered and coated steel sheet for making vehicle parts are also described.

Provided is a grain-oriented electrical steel sheet including a base steel sheet, an intermediate layer which is disposed in contact with the base steel sheet and mainly includes silicon oxide, and an insulation coating which is disposed in contact with the intermediate layer and mainly includes phosphate and colloidal silica, in which the base steel sheet contains predetermined chemical composition, BN having an average particle size of 50 to 300 nm is present, when an emission intensity of B is measured using glow discharge emission analysis, predetermined conditions are satisfied, and a ratio of a major axis to a minor axis of BN is 1.5 or less.

A method for manufacturing a high strength galvanized steel sheet which has a zinc coating layer with an amount of deposition of coating of 20 to 120 g/m.sup.2 per one surface on the surface of a base steel sheet having a chemical composition comprising C: 0.03% to 0.35%, Si: 0.01% to 0.50%, Mn: 3.6% to 8.0%, Al: 0.001% to 1.000%, P0.10%, S0.010%, and the balance comprising Fe and incidental impurities, on a percent by mass basis, is provided. In annealing and galvanization treatment of the base steel sheet in a continuous galvanizing line, the maximum steel sheet temperature in an annealing furnace is 600 C. or higher and 750 C. or lower, the steel sheet transit time in a temperature region of the steel sheet temperature of 600 C. or higher and 750 C. or lower is specified to be 30 seconds or more and 10 minutes or less, and the dew point in an atmosphere is specified to be 10 C. or higher.

A TWIP steel sheet is provided having an austenitic matrix including by weight: 0.1C1.2%, 13.0Mn<25.0%, 0.1Si3.0%, 0.1Cu5.0%, S0.030%, P0.080%, N0.1%, 0.1Al4.0% and 0.1V2.50% in such way that:when the amount of Al<2.0%, the weight ratio Al/V is between 0.2 and 8 orwhen the amount of Al2.0%, the amount of V>0.25%, and on a purely optional basis, one or more of Nb0.5%, B0.005%, Cr1.0%, Mo0.40%, Ni1.0%, Ti0.5%, and/or 0.06Sn0.2%, the remainder of the composition being made of iron and inevitable impurities resulting from elaboration.

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%, 13.0Mn<25.0%, S0.030%, P0.080%, N0.1%, Si3.0%, and on a purely optional basis, one or more elements such as Nb0.5%, B0.005%, Cr1.0%, Mo0.40%, Ni1.0%, Cu5.0%, Ti0.5%, V2.5%, Al4.0%, 0.06Sn0.2%, 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.

Warming a metastable steel after coating and before or during cold rolling suppresses the transformation of austenite to martensite, resulting in lower mill loads and higher amounts of reduction at similar loads. As-warm rolled steel has enhanced mechanical properties when compared to steel reduced the same amount by cold rolling at room temperature.

A cold rolled and annealed steel sheet includes by weight: 0.6<C<1.3%, 15.0Mn<35%, 6.0Al<15%, Si2.40%, S0.015%, P0.1%, N0.1%, optionally one or more elements chosen among Ni, Cr and Cu in an individual amount of up to 3% and optionally one or more elements chosen among B, Ta, Zr, Nb, V, Ti, Mo, and W in a cumulated amount of up to 2.0%, the remainder of the composition making up of iron and inevitable impurities resulting from elaboration, a microstructure of said sheet comprising at least 0.1% of intragranular kappa carbides, wherein at least 80% of said kappa carbides have an average size below 30 nm, optionally up to 10% of granular ferrite, the remainder being made of austenite, an average grain size of the austenite being below 6 m, an average aspect ratio of the austenite being between 1.5 and 6, an average grain size of the ferrite, when present being below 5 m, and an average aspect ratio of the ferrite, when present, being below 3.0.

A hot-rolled steel sheet having a composition comprising, in mass %, C: 0.06 to 0.3%, Si: 0.4 to 2.5%, Mn: 0.6 to 3.5%, P: at most 0.1%, S: at most 0.05%, Ti: 0 to 0.08%, Nb: 0 to 0.04%, a total content of Ti and Nb: 0 to 0.10%, sol.Al: 0 to 2.0%, Cr: 0 to 1%, Mo: 0 to 0.3%, V: 0 to 0.3%, B: 0 to 0.005%, Ca: 0 to 0.003%, REM: 0 to 0.003%, the remainder Fe and impurities, is cold rolled, then heated at an average heating rate of at least 15 C./sec so that a proportion of an unrecrystallization of a region not transformed to austenite at a time of reaching (Ac.sub.1 point+10 C.) is at least 30 area %, and then held for 30 seconds at temperature of at least (0.9Ac.sub.1 point+0.1Ac.sub.3 point) and at most (Ac.sub.3 point+100 C.).

A grain-oriented electrical steel sheet is a grain-oriented electrical steel sheet which does not have an inorganic coating containing forsterite as a main component and which includes: a base steel sheet containing a prescribed chemical component; a silicon-containing oxide layer provided on the base steel sheet; an iron-based oxide layer provided on the silicon-containing oxide layer; and a tension-insulation coating provided on the iron-based oxide layer, having a thickness of 1 to 3 ?m, and containing phosphate and colloidal silica as main components. When the tension-insulation coating undergoes elemental analysis using a glow discharge optical emission spectrometry in a sheet thickness direction from a surface of the tension-insulation coating, a peak Si emission intensity satisfies a prescribed requirement.

A high-strength hot-dip galvanized steel sheet containing a main component, the steel sheet having at least 40 wt. % of ferrite as a main phase in terms of the volumetric ratio, and 8-60% inclusive of residual austenite, the remaining structure comprising one or more of bainite, martensite, or pearlite. Austenite particles within a range where the average residual stress (sigmaR) thereof satisfies the expression 400 MPa<=sigmaR<=200 MPa (formula (1)) are present in an amount of 50% or more in the hot-dip galvanized steel sheet. The surface of the steel sheet has a hot-dip galvanized layer containing less than 7 wt. % of Fe, the remainder comprising Zn, Al and inevitable impurities.