COLD-ROLLED AND HEAT TREATED SHEET STEEL, METHOD FOR MANUFACTURE THEREOF AND APPLICATION OF SUCH STEEL IN MANUFACTURE OF VEHICLE PARTS

摘要

FIELD: metallurgy.;SUBSTANCE: invention relates to the area of metallurgy, namely to cold-rolled and heat-treated sheet steel used in automotive industry. The steel has a composition containing the following elements, % wt.: 0.15 ≤ carbon ≤ 0.6, 4 ≤ manganese ≤ 20, 5 ≤ aluminum ≤ 15, 0 ≤ silicon≤ 2, aluminum + silicon ≥ 6.5, if necessary, at least one element from: 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 ≤ 0.01, boron ≤ 0.01, magnesium ≤ 0.05, zirconium ≤ 0.05, molybdenum ≤ 2.0, tantalum ≤ 2.0 and tungsten ≤ 2.0, the rest is iron and inevitable impurities. The microstructure of the steel sheet comprises from 10 to 50% austenite in surface area fractions, wherein said austenite phase optionally includes intragranular kappa carbides, wherein the residue constitutes regular ferrite and ordered ferrite with a D0₃ structure and optionally includes up to 2% intragranular kappa carbides.;EFFECT: steel exhibits the required density of no more than 7.4, ultimate tensile strength of no less than 900 MPa and uniform relative elongation of no less than 9%.;10 cl, 1 dwg, 4 tbl