COLD-ROLLED AND HEAT-TREATED SHEET STEEL AND METHOD FOR MANUFACTURE THEREOF Russian patent published in 2021 - IPC C22C38/58 C22C38/40 C22C38/38 C22C38/34 C22C38/18 C22C38/06 C21D8/02 

FIELD: metallurgy.

SUBSTANCE: invention relates to the field of metallurgy, namely to cold-rolled and heat-treated sheet steel used for manufacturing automobile parts. The steel has the following chemical composition, wt.%: 0.10 ≤ carbon ≤ 0.5, 1 ≤ manganese ≤ 3.4, 0.5 ≤ silicon ≤ 2.5, 0.03 ≤ aluminium ≤ 1.5, sulphur ≤ 0.003, 0.002 ≤ phosphorous ≤ 0.02, nitrogen ≤ 0.01, optionally no less than one element from: 0.05 ≤ chrome ≤ 1, 0.001 ≤ molybdenum ≤ 0.5, 0.001 ≤ niobium ≤ 0.1, 0.001 ≤ titanium ≤ 0.1, 0.01 ≤ copper ≤ 2, 0.01 ≤ nickel ≤ 3, 0.0001 ≤ calcium ≤ 0.005, vanadium ≤ 0.1, boron ≤ 0.003, cerium ≤ 0.1, magnesium ≤ 0.010 and zirconium ≤ 0.010, the rest iron and inevitable impurities. The microstructure of the sheet steel comprises, as expressed in terms of surface fraction concentration, 10 to 30% residual austenite, 5 to 50% annealed bainite, 10 to 40% bainite, 1 to 20% hardened martensite and less than 30% tempered martensite, wherein the combined amount of bainite and residual austenite accounts for 30% or more.

EFFECT: steel characterised simultaneously by a high tensile strength greater than or equal to 950 MPa and a high total elongation greater than or equal to 20%.

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