METHOD FOR PRODUCTION OF HOT-ROLLED SHEETS FROM LOW-ALLOY STEEL OF STRENGTH CLASS K65 FOR ELECTRIC-WELDED LONGITUDINAL PIPES WITH HIGH STRAIN CAPACITY Russian patent published in 2023 - IPC C21D8/02 C21D9/46 C22C38/58 C22C38/60 

FIELD: metallurgy.

SUBSTANCE: The invention is related in particular to the production of hot-rolled steel intended for the manufacture of electric-welded longitudinal pipes of strength class K65 used for the construction of pipelines in the areas of intersection of active tectonic faults, increased seismicity, permafrost soils. The method for the production of hot-rolled sheets from low-alloy steel of strength class K65 for electric-welded longitudinal pipes includes obtaining of continuously cast billets from low-alloy steel, their austenitisation, roughing-down with regulated reduction per pass, chilling of the rolls, finishing rolling to obtain sheets, their cooling in still air, followed by accelerated cooling in a controlled cooling unit and straightening. Continuously cast billets are made from steel with the following ratio of elements, wt. %: carbon is 0.04-0.07, silicon is 0.10-0.35, manganese is 1.45-1.90, chromium is no more than 0.10, nickel is 0.15-0.30, copper is not more than 0, 15, the total content of titanium, vanadium and niobium is 0.05-0.15, molybdenum is 0.15-0.25, nitrogen is not more than 0.007, aluminium is 0.02-0.06, sulphur is not more than 0.003, phosphorus is not more than 0.013, iron and impurities - the balance. Austenitisation of continuously cast billets is carried out up to a temperature of 1190-1240 °C, roughing-down is started at a temperature not lower than 980 °C and is carried out for a rolled thickness of at least 4 thicknesses of the finished sheet, finishing rolling is started and completed in the temperature range of 760-820 °C , after which the sheets are cooled in still air to an accelerated cooling start temperature of 710-750 ° C, and then subjected to accelerated cooling in a controlled cooling installation at a cooling rate of 10-35 °C/s to a temperature not exceeding 200 °C, then the sheets are subjected to straightening in a roller straightening machine.

EFFECT: high strain capacity of hot-rolled sheets is provided, determined by the requirements for the shape of the tensile curve in the area of plastic deformation, intended for the manufacture of electric-welded longitudinal pipes of strength class K65, used in laying pipelines for operating pressures up to 11.8 MPa.

2 cl, 4 tbl