FIELD: metallurgy.
SUBSTANCE: to provide mechanical strength of 1180–1320 MPa, coefficient of hole distribution Ac. % of more than 20 %, and bending angle greater than or equal to 40°, cold-rolled and annealed steel sheet with thickness of 0.7–2 mm is obtained, chemical composition of which contains the following, wt. %: 0.09 ≤ C ≤ 0.11, 2.6 ≤ Mn ≤ 2.8, 0.20 ≤ Si ≤ 0.55, 0 25 ≤ Cr < 0.5, 0.025 ≤ Ti ≤ 0.040, 0.0015 ≤ B ≤ 0.0025, 0.005 ≤ Al ≤ 0.18, 0.08 ≤ Mo ≤ 0.15, 0.020 ≤ Nb ≤ 0.040, 0.002 ≤ N ≤ 0.007, 0.0005 ≤ S ≤ 0.005, 0.001 ≤ P ≤ 0.020, Ca ≤ 0.003, iron and unavoidable impurities, the sheet having a microstructure including martensite and/or lower bainite, and said martensite includes fresh martensite and/or self-tempered martensite, sum of surface area of martensite and lower bainite makes 40–70 %, 15–45 % of surface of low-carbon bainite, from 5 % to less than 20 % - share of ferrite surface, fraction of non-recrystallised ferrite with respect to total fraction of ferrite is less than 15 % and less than 5 % surface area of residual austenite in the form of islets, fraction of former austenite grains with size less than at least one micrometer is 40–60 % of total amount of said former austenite grains.
EFFECT: providing mechanical strength of 1180–1320 MPa, an opening coefficient of Ac % of more than 20%, and a bending angle greater than or equal to 40°.
19 cl, 4 dwg, 5 tbl
