COLD-ROLLED ANNEALED STEEL SHEET WITH HIGH DEGREE OF HOLE EXPANSION AND METHOD OF ITS MANUFACTURING Russian patent published in 2022 - IPC C21D9/46 C21D8/02 C22C38/38 C22C38/32 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to cold-rolled annealed steel sheet used for fabrication of vehicle structural elements. Sheet has a chemical composition which includes the following in wt.%: 0.30 ≤ C ≤ 0.50; 1.00 ≤ Mn ≤ 2.50; 1.00 ≤ Si ≤ 2.00; Al ≤ 2.00; Cr ≤ 0.100; 0.100 ≤ Mo ≤ 0.500; 0.020 ≤ Nb ≤ 0.200; B ≤ 0.0005; P ≤ 0.02; S ≤ 0.005; N ≤ 0.01, Fe and unavoidable impurities are the rest. Content of carbon, manganese, chromium, molybdenum and boron satisfy the condition: 250 % C + 120 % Mn – 200 % Cr + 200 % Mo – 10,000 % B ≥ 320. Sheet microstructure contains, in surface fractions, from 35 % to 45 % of martensite and residual austenite (M-A) islands, total amount of residual austenite is 24 % or more, while the rest consists of bainitic ferrite.

EFFECT: steel sheet has tensile strength of more than 1,100 MPa, uniform elongation of more than 16 % and degree of expansion of the hole of more than 15 %.

12 cl, 4 tbl