| 摘要 |
PURPOSE:To maintain high-temp. strength and toughness and to assure resistance to high-temp. corrosion by subjecting a surface-treated steel pipe contg. Cr at a high rate to TIG build-up welding by using a specifically composed welding wire after welding. CONSTITUTION:At least the welded and joined part of a surface-treated steel pipe contg. Cr at a high rate for a boiler tube is subjected to build-up welding by using a welding wire consisting, by weight, of 25-40% Cr, >=10% Ni, <=1% Si, <=2% Mn, <=0.5% Al and the balance Fe and impurities. The reason for limiting the compsn. of the welding wire lies in that <25W% content of Cr is not enough to improve the resistance to high-temp. corrosion and that the embrittlement arising in generation of an alpha phase in weld metal is of probelm with >40W% even if the content of N is increased. Formaion of the alpha phase is not observed with Ni under ordinary mild service conditions and therefore >=10W% suffices. The unstable structure causes if Si, Mn and Al exceed the upper limit. |
