Kenyon & Kenyon
Production method of steel pipe excellent in corrosion resistance and weldability
 A steel pipe having excellent corrosion resistance in an environment containing wet carbon dioxide and a small amount of hydrogen sulfide and having also excellent weldability is produced at a low production cost and with high productivity. The production method comprises heating to a temperature of 1,050.degree. to 1,300.degree. C. a slab containing, in terms of wt %, 0.01 to less than 1.2% of Si, 0.02 to 3.0% of Mn, 7.5 to 14.0% of Cr and 0.005 to 0.5% of Al, reduced C, N, P and S contents, at least one of Cu, Ni, Co, Mo and W, a balance of Fe and unavoidable impurities, and having an MC value of at least 0, finishing hot rolling within an austenite monophase temperature range, coiling the steel sheet as a hot coil having a sheet thickness of 3.0 to 25.4 mm, cooling the coil at a cooling rate of at least 0.01.degree. C./sec to at least 500.degree. C. to convert the steel sheet to a steel substantially consisting of martensite, reheating the steel to a temperature of 550.degree. C. to not more than an A.sub.c1 transformation point, holding it for at least 15 minutes, cooling the steel web to a normal temperature, cutting it into a predetermined width, and welding both ends of the steel by electric resistance welding while the steel coil is continuously shaped into a cylindrical shape. 
Nippon Steel Corporation
C C C C
C22C C21D C21D C21D
inventional inventional additional additional
Akihiro Masaaki Yasushi
Miyasaka Obata Suzuki