FIELD: metallurgy.
SUBSTANCE: invention refers to metallurgy. To ensure the tensile strength limit YS equal to 450 MPa or more and resistance to softening during a long time in the intermediate temperature range, the steel pipe is manufactured by electric resistance welding of hot-rolled steel sheet. To produce the sheet, heating and holding are carried out at a temperature of more than 1200°C and 1280°C or less for 90 minutes or more of the steel material containing, in wt %: C 0.026 or more and 0.084 or less, Si 0.10 or more and 0.30 or less, Mn 0.70 or more and 1.90 or less, Al 0.01 or more and 0.10 or less, Nb 0,001 or more and 0.070 or less, V 0.001 or more and 0.065 or less, Ti 0.001 or more and 0.033 or less, Ca 0.0001 or more, and 0.0035% or less, under the condition under which the parameter Pcm is 0.20 or less, then hot rolling with a thickness reduction ratio in the absence of recrystallization of 20% or more, cooling the hot-rolled sheet based on the temperature of the central portion of the sheet thickness, an average cooling rate 7°C/sec or more and 299°C/sec or less in the temperature range from 780°C to 620°C; and subsequent thermal treatment in which the total holding time in the temperature range from 480°C to 350°C is 2 hours or more and 20 hours or less, forming a continuous hot-rolled steel sheet into a tube, resistance electric welding. The welded steel pipe is subjected to heat treatment at these operation parameters, in which the entire thickness of the sheet is heated to a temperature of 800°C or more and 1150°C or less, and then cooled, starting from temperatures of the central portion of the sheet thickness, an average cooling rate 7°C/sec or more and 299°C/sec or less in the temperature range from 780°C to 620°C, and then the steel sheet is subjected to further processing in which the total holding time in the temperature range from 500°C to 360°C is 2 seconds or longer and 200 seconds or less.
EFFECT: invention extends the range of steel pipes, due to the method of welding-electric resistance welding, which increases its strength.
7 cl, 8 tbl, 2 dwg
