HIGH STRENGTH STEEL PIPES with a low YIELD TO tensile strength welded pin, ELECTRIC WELDING, STEEL STRIP FOR tubes welded pin, ELECTRIC WELDING, AND METHODS FOR THEIR MANUFACTURE

摘要

1. A method for producing a steel pipe welded electric resistance welding, comprising the step of hot rolling in which the steel material is heated and formed into a hot rolled steel strip roughing rolling and finish rolling, and hot-rolled steel strip is wound, and tube manufacturing step in which the hot rolled steel strip winded continuously fed and formed in a substantially cylindrical open pipe rolls and round end portions of the open pipe are aligned relative to each other and subjected to electron an insulating resistance welding, the composition of the steel material contains 0,38-0,45% C, 0,1-0,3% Si, 1,0 -1,8% Mn, 0.03% or less P, 0.03 % or less S, 0,01-0,07% sol. Al and 0.01% or less N, by weight, the rest Fe and unavoidable impurities; finish rolling is rolling with finish rolling initial temperature of 950 ° C or lower and a final finish rolling temperature of 820-920 ° C; winding temperature at which the coiled hot rolled steel strip is 650-800 ° C; and pipe fabrication step is performed at room temperature.2. A method for producing a steel pipe welded electrical contact welding according to Claim. 1, wherein the composition of the steel material additionally comprises one or more components selected from 0,03-0,4% Cu, 0,03-0,3% Ni and 0.001 -0,005% Sn on masse.3. A method for producing a steel pipe welded electrical contact welding according to Claim. 1 or 2, wherein the composition of the steel material further comprises 0.001-0.003% by weight. Sa.4. High strength steel pipe with a low ratio of yield strength to tensile strength welded electric resistance welding, the composition comprising 0,38-0,45% C, 0,1-0,3% Si, 1,0-1,8% Mn, 0.03% or less P, 0.03% or less S, 0,01-0,07% sol. Al, and 0.01% or less N, by weight, the rest Fe and unavoidable impurities, they