HIGH-STRENGTH STEEL HAVING EXCELLENT LOW-TEMPERATURE VISCOSITY AND EXCELLENT VISCOSITY IN THERMALLY AFFECTED ZONE OF WELDING JOINT (OPTIONS), METHOD FOR MANUFACTURING SUCH STEEL, METHOD FOR MANUFACTURING SHEET FROM INDICATED STEEL, HIGH-STRENGTH STEEL TUBE (OPTION), AND A METHOD FOR MANUFACTURING HIGH-STRENGTH STEEL TUBE

摘要

FIELD: steel making.;SUBSTANCE: invention relates to such type of steel that is employed in welded structures such as gas conduits, petroleum pipelines, as well as in high-pressure vessels. Steel according to invention contains, wt %: C 0.02-0.10, Si up to 0.6, Mn 1.5-2.5, P up to 0.015, S up to 0.003, Ni 0.01-2.0, Mo 0.2-0.6, Nb below 0.010, Ti up to 0.030, Al up to 0.070, N up to 0.0060, Fe and unavoidable impurities - the rest, provided that parameter P = 2.7C+0.4Si+Mn+0.8Cr+0.45(Ni+Cu)+2V+Mo-0.5 is within a range of 1.9 to 3.5. Microstructure of steel is mainly composed of martensite and bainite. Steel sheet is manufactured by heating casting to at least Ac₃, subjecting it to hot rolling, and cooling sheet at a rate 1C/sec to temperature not exceeding 550C. Sheet is further used to manufacture a tube. When laying multilayer welding joint, energy absorbed in the Charpy impact test at -40C is at least 200 J.;EFFECT: achieved elongation strength at least 800 MPa.;21 cl, 1 dwg, 9 tbl, 5 ex