HIGH-STRENGTH THICK STEEL SHEET FOR PIPELINE, HAVING EXCELLENT LOW-TEMPERATURE IMPACT STRENGTH AND DUCTILITY, AS WELL AS LOW RATIO OF YIELD STRENGTH TO ULTIMATE STRENGTH, AND METHOD OF ITS PRODUCTION Russian patent published in 2022 - IPC C22C38/58 C21D8/02 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to high-strength thick steel sheet used as material for construction of pipelines. Sheet has a composition containing the following components, wt.%: 0.03–0.055 C; 0.1–0.35 Si; 1.7–2.2 Mn; 0.01–0.04 Al; 0.005–0.025 Ti; 0.008 or less of N; 0.08–0.12 Nb; 0.2–0.45 Cr; 0.2–0.35 Ni; 0.05–0.3 Cu; 0.2–0.4 Mo; 0.0067 or less of P; 0.002 or less of S; 0.0005–0.004 Ca; 0.01–0.04 V; 0.0005 or less of B, Fe and unavoidable impurities are the rest. Components of the steel composition satisfy the following ratios: 19≤(Mo/96)/(P/31)≤30, 1.42≤Cr+2Mo+Cu+Ni+1000B≤1.75, 4<{3C/12+Mn/55}×100≤4.9 and 600≤400C+6800Nb+600V+800Ti+300Al≤820, where content of components is expressed in wt.%. Microstructure of steel sheet contains, in % of area, 1–5 % of polygonal ferrite, 60–75 % of needle ferrite, 20–30 % of bainitic ferrite and 5 % or less of martensite-austenitic component.

EFFECT: sheet has a yield point in direction of 30° with respect to rolling direction 550 MPa or more, tensile strength of 660 MPa or more, ratio of yield strength to ultimate strength of 0,83 or less, separation length at -10 °C less than 5 mm, impact energy at -10 °C of 320 J or more, full elongation of 42 % or more, and a minimum temperature at which a plastic cracking percentage of 85 % or more is satisfied in a drop weight tear test (DWTT) of -30 °C or lower.

12 cl, 6 tbl