PIPE WITH HIGH STRAIN CAPACITY OF STRENGTH CLASS K65 AND METHOD FOR ITS PRODUCTION Russian patent published in 2023 - IPC C21D8/10 C22C38/14 C22C38/16 C22C38/50 C22C38/58 B21C37/08 

FIELD: metallurgy.

SUBSTANCE: invention is related specifically to electric-welded longitudinal pipes of strength class K65 with an outer diameter of 508-1422 mm for the construction of gas pipelines designed for operating pressures up to 11.8 MPa inclusive, including those operated at the intersection of active tectonic faults, increased seismicity and permafrost soils, as well as in areas with weakly bearing, heaving and subsidence soils. The pipe is made of a steel sheet by moulding into a tubular billet when their longitudinal axes of symmetry are aligned, followed by welding of a technological seam in a shielding gas atmosphere and multi-arc submerged arc welding of the longitudinal edges of the tubular billet from the inner and outer surfaces and expansion. The steel sheet contains in % by weight: carbon 0.04-0.07, silicon 0.10-0.35, manganese 1.45-1.90, chromium not more than 0.10, nickel 0.15-0.30, copper not more than 0.15, the total content of titanium, vanadium and niobium is 0.05-0.15, molybdenum 0.15-0.25, nitrogen not more than 0.007, aluminium 0.02-0.06, sulphur not more than 0.003, phosphorus not more than 0.013, iron and impurities - the balance. In the longitudinal direction, the pipe has a yield strength at full strain of 0.5% equal to 525-665 MPa, a tensile strength of 620-760 MPa, a ratio of yield strength at full strain of 0.5% to a tensile strength of not more than 0.91, relative elongation of at least 19%. In the transverse direction, the pipe has a yield strength at full strain of 0.5% equal to 555-665 MPa, a tensile strength of 650-760 MPa, a ratio of yield strength at full strain of 0.5% to a tensile strength of not more than 0.90, relative elongation of at least 18 %, impact strength on samples with a V-shaped notch at a test temperature of minus 40°C not lower than 250 J/cm², the proportion of the viscous component in the fracture when tested by a falling load at a test temperature of minus 40°C not less than 85% and critical opening at the crack tip at a test temperature of minus 20°C not less than 0.20 mm. The welded joint has a tensile strength of 650-760 MPa, impact strength on transverse samples with a V-shaped notch in the centre of the weld and along the fusion line of at least 70 J/cm² at a test temperature of minus 40°C, and critical opening at the crack tip on transverse specimens with a notch along the fusion line of at least 0.15 mm at a test temperature of minus 20°C.

EFFECT: achievement of increased strain capacity, determined by the requirements for the shape of the stretching curve in the area of plastic deformation.

5 cl, 5 tbl