Provided is a steel sheet and a method for manufacturing same, the steel sheet, which is optimized a composition and microstructure, and which can be used for automobile parts and the like, having superb bendability, and superior balance of strength and ductility and of strength and hole expansion ratio.

Provided is a steel sheet which can be used for automobile parts and the like, and relates to a steel sheet having a superior balance of strength and ductility and strength and hole expansion ratio and superior bending formability, and a method for manufacturing same.

Disclosed are a low-cost ultra-high-strength multiphase steel plate/steel strip and its manufacturing method. Said steel plate/steel strip comprises the following components in percentage by weight: 0.03 to 0.07% of C, 0.1 to 0.5% of Si, 1.3 to 1.9% of Mn, less than or equal to 0.02% of P, less than or equal to 0.01% of S, 0.01 to 0.05% of Al, 0.2 to 0.5% of Cr, 0.07 to 0.14% of Ti, less than 0.03% of (Ni+Nb+Mo+V), and the balance being Fe and other inevitable impurities; and Mn+1.5Cr+5(Ti+Al+Cu)+10(Mo+Ni)+20(Nb+V)<3.0; Mn+2Cr+4Ti+4Nb+4V+4Mo—Si/3+2C≤3.0. The steel plate is mainly used for the manufacturing of automotive chassis and suspension system parts.

Provided is a steel sheet which can be used for automobile parts and the like, and relates to a steel sheet having a superior balance of strength and ductility and strength and a hole expansion ratio and superior bending formability, and a method for manufacturing same.

An austenitic stainless steel material that has a passivation film on a surface is provided. The austenitic stainless steel material has a chemical composition consisting of, in mass%, C: 0.10% or less, Si: 1.0% or less, Mn: 8.0-10.0%, P: 0.030% or less, S: 0.003% or less, Cr: 15.0-18.0%, Ni: 7.0-9.0%, N: 0.15-0.25%, Al: 0.005-0.20%, Ca: 0.0005-0.01%, Cu: less than 1.0%, Mo: less than 1.0%, B: 0-0.0050%, Nb: 0-0.50%, Ti: 0-0.50%, V: 0-0.50%, W: 0-0.50%, Zr: 0-0.50%, Co: 0-0.50%, Mg: 0-0.005%, Ga: 0-0.005%, Hf: 0-0.10%, REM: 0-0.10%, and the balance: Fe and impurities. An f value, namely, [Ni + 0.72Cr + 0.88Mo + 1.11Mn - 0.27Si + 0.53Cu + 12.93C + 7.55N], is more than 29.5 and less than 32.5.

A steel sheet includes a predetermined composition satisfying Expression (1), in which the microstructure at the ¼ thickness position from the surface in the sheet thickness direction includes, by vol %, ferrite: 95% or more and a remainder of the microstructure: 5% or less, has a proportion of unrecrystallized ferrite in the ferrite of 5% or less, and a half width w and an X-ray wavelength λ at a peak of (200) plane of the ferrite satisfy Expression (2).

0.80≤{(Ti/48−N/14)+Nb/93}/(C/12)≤5.00  (1)

w×λ≥0.20  (2)

Method for the manufacture of a galvannealed steel sheet includes the following steps: A) the provision of a pre-coated steel sheet coated with a first coating comprising iron and nickel, such steel sheet having the following chemical composition in weight percent 0.10<C<0.40%, 1.5<Mn<3.0%, 0.7<Si<2.0%, 0.05<Al<1.0%, 0.75<(Si+Al)<3.0% and on a purely optional basis, one or more elements such as Nb≤0.5%, B≤0.005%, Cr≤1.0%, Mo≤0.50%, Ni≤1.0%, Ti≤0.5%, the remainder of the composition making up of iron and inevitable impurities resulting from the elaboration, B) the thermal treatment of such pre-coated steel sheet at a temperature between 600 to 1000° C., C) the hot-dip coating of the steel sheet obtained in step B) with a second coating based on zinc and D) an alloying treatment to form a galvannealed steel sheet.

A production method for a high-strength steel sheet having a tensile strength TS of 780 MPa or more is provided. The production method comprises: heating a steel slab having a predetermined chemical composition; hotrolling the steel slab; coiling the hot-rolled sheet; subjecting the hot-rolled sheet to pickling treatment; holding the hot-rolled sheet in a pre-determined temperature range for predetermined time; cold rolling the hot-rolled sheet to obtain a cold-rolled sheet; subjecting the cold-rolled sheet to first annealing treatment; cooling the cold-rolled sheet at a pre-determined average cooling rate; cooling the cold-rolled sheet to room temperature; reheating the clod-rolled sheet to perform second annealing treatment; cooling the cold-rolled sheet at a first average cooling rate; cooling the cold-rolled sheet at a second average cooling rate; reheating the cold-rolled sheet to a predetermined reheating temperature range; and holding the cold-rolled sheet in the reheating temperature range.

A sheet or strip made of a hardenable aluminum alloy, a vehicle part made therefrom, a use, and a method for producing the sheet or strip are disclosed. In order to insure a powerful paint bake response (PBR), it is proposed for the aluminum alloy to have from 4.0 to 5.5 wt % magnesium (Mg) and from 2.5 to 5.5 wt % zinc (Zn) and for it to be in the T4-FH state, wherein the wt % of magnesium (Mg) is greater than the wt % of zinc (Zn).

A steel sheet has a composition comprising 0.060%≤C≤0.085%, 1.8%≤Mn≤2.0%, 0.4%≤Cr≤0.6%, 0.1%≤Si≤0.5%, 0.010%≤Nb≤0.025%, 3.42N≤Ti≤0.035%, 0≤Mo≤0.030%, 0.020%≤Al≤0.060%, 0.0012%≤B≤0.0030%, S≤0.005%, P≤0.050%, 0.002%≤N≤0.007% and optionally 0.0005%≤Ca≤0.005%, the remainder of the composition being iron and unavoidable impurities. The microstructure consists of 34% to 80% bainite, 10% to 16% martensite, and 10% to 50% of ferrite. The surface fraction of unrecrystallized ferrite, with respect to the whole structure, is of less than 30%. The martensite consists of self-tempered martensite and fresh martensite, the surface fraction of self-tempered martensite being comprised between 4% and 10%.