A steel pipe welded in the longitudinal direction of 500 MPa class having a low yield ratio and a method for manufacturing the same

摘要

A 500 MPa grade longitudinally welded steel pipe with a low yield ratio and a manufacturing method therefor, the components thereof by weight percentages being as follows: C 0.11%-0.16%, Si 0.15%-0.35%, Mn 0.8%-1.5%, V 0.06%-0.15%, Al 0.002%-0.04%, Ti 0%-0.05%, Nb 0%-0.05%, the balance being Fe and inevitable impurities, and the carbon equivalent Ceq being not more than 0.4%. According to the above component design, molten steel is subjected to smelting in a converter or electric furnace, and is cast into a slab; the slab is heated at 1,200° C.-1,300° C. and rolled into a plate strip, with the finished rolling temperature of the plate strip being between 840° C.-940° C.; the rolled plate strip is subjected to laminar flow cooling with a water curtain, the laminar flow cooling adopting the manner of rear-section cooling, and is coiled into a plate roll when being cooled to the temperature interval of 500° C.-560° C.; and after welding formation, a heat treatment on the welding seams is carried out at a heating temperature of 950° C.±50° C. The steel pipe of the present invention has the characteristics of an excellent welding property, a high strength and toughness, a low yield ratio and the like, and the yield strength thereof is greater than 500 MPa and the yield ratio thereof is less than 0.85.