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

[00001]$f=\frac{{}_{\left(A\right)}.Math.\mathrm{di}}{{}_{\left(A\right)}.Math.\mathrm{Li}}.$

.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.

Provided is a steel sheet and a method for manufacturing same, the steel sheet, which can be used for automobile parts and the like, having superb bendability, and excellent balance of strength and ductility and of strength and hole expansion ratio. The steel sheet includes: by wt %, C: 0.25 to 0.75%, Si: 4.0% or less, Mn: 0.9 to 5.0%, Al: 5.0% or less, P: 0.15% or less, S: 0.03% or less, N: 0.03% or less, a balance of Fe, and unavoidable impurities; and as microstructures, ferrite which is a soft structure, and tempered martensite, bainite, and retained austenite which are hard structures.

The invention relates to a hot-rolled ferritic steel sheet, the composition of the steel of which comprises, the contents being expressed by weight: 0.001C0.15%, Mn1%, Si1.5%, 6%Al10%, 0.020%Ti0.5%, S0.050%, P0.1%, and, optionally, one or more elements chosen from: Cr1%, Mo1%, Ni1%, Nb0.1%, V0.2%, B0.010%, the balance of the composition consisting of iron and inevitable impurities resulting from the smelting, the average ferrite grain size d.sub.IV measured on a surface perpendicular to the transverse direction with respect to the rolling being less than 100 microns.

Billets and methods for manufacturing them are disclosed. The billets include a cladding member including an alloy selected from the group including stainless steel, nickel-chrome, nickel-copper, and copper-nickel alloys, and a steel body that is positioned so that it has an interface with the cladding member, the steel body having a formation in which the scavenging metal is located and elements being provided for separating the scavenging metal from the cladding member at the interface.

Provided are: a galvannealed steel sheet, improved in the adhesiveness of a plated layer with a base steel sheet, as a galvannealed steel sheet, prepared by using a high-strength steel sheet as a base material; and a method for producing the galvannealed steel sheet. A galvannealed layer is formed on the base steel sheet including a high-strength steel having a predetermined composition. The average amount of Fe in the galvannealed layer is 8.0 to 12.0%. The absolute value of a difference (Fe) between the amount of Fe in the vicinity of an interface with the base steel sheet and the amount of Fe in the vicinity of the external surface of the plated layer in the plated layer is 0.0 to 3.0%.

A hot rolled steel sheet with a yield stress greater than 690 MPa and less than or equal to 840 MPa, with strength between 780 MPa and 950 MPa, elongation at failure greater than 10% and a hole expansion ratio (Ac) greater than or equal to 50% is described. Methods for the fabrication of the sheet are also described.

Provided is a method of manufacturing a clad steel sheet. The method includes: preparing a base material including C: 0.3 to 1.0%, Mn: 4.0 to 16.0%, Al: 4.5 to 9.0%, and a remainder of Fe and inevitable impurities; preparing a cladding material including C: 0.1 to 0.45%, Mn: 0.1 to 3.0%, and a remainder of Fe and inevitable impurities; disposing the base material between two of the cladding material to obtain a laminate; welding an edge of the laminate; heating the welded laminate between 1050 and 1350 C.; finish-rolling the heated laminate between 750 and 1050 C. with a rolling reduction ratio of 30% or more in a first pass; coiling the hot-rolled steel sheet between 400 and 700 C.; pickling the coiled hot-rolled steel sheet, and applying a cold-reduction ratio of 35 to 90%; and annealing the cold-rolled steel sheet between 550 C. and A3+200 C. of the cladding material.