Patent ID: 9663840
Date: 2017-05-30
CPC Classifications: B21C,B23K,C21D,C22C,F16L

Claim:
1. A method of manufacturing a longitudinally welded steel pipe comprising a) 0.11 wt %-0.16 wt % carbon (C); b) 0.15 wt %-0.35 wt/o silicon (Si); c) 0.8 wt %-1.5 wt % manganese (Mn); d) 0.06 wt %-0.15 wt % vanadium (V); e) 0.002 wt %-0.04 wt % aluminum (Al); f) 0 wt %-0.05 wt % titanium (Ti); g) 0 wt %-0.05 wt % niobium (Nb); and h) a balance of iron (Fe) and inevitable impurities; wherein the steel pipe has a carbon equivalent (Ceq) of <0.4%, and the steel pipe exhibits a yield strength of greater than 500 MPa, a yield ratio of less than 0.85 and a 0° C. full-scale impact energy of greater than 100 J; the method comprising: a) smelting molten steel; b) casting the smelted steel into a slab; c) heating the slab to a temperature of 1200° C.-1300° C.; d) rolling the heated slab into a plate strip at a temperature of about 840° C.-940° C.; e) laminar flow cooling the rolled plate strip with a water curtain, the laminar flow cooling adopting the manner of rear-section cooling, with the number of closed cooling water valves in the front section accounting for 15%-40% of the total number of cooling water valves, and cooling the strip to the temperature interval of 500° C.-560° C. within 30 seconds; f) coiling the cooled strip into a plate roll; g) welding the plate roll into a pipe; and h) heat treating welding seams of the welded pipe at a heating temperature of 950° C.±50° C.