Boiler steel having excellent electrical weldability and electrically welded boiler structural steel tube of this steel

摘要

This invention provides a boiler steel pipe that exhibits a high creep rupture strength on a high-temperature high-pressure side and is excellent in electric weldability, and an electric welded boiler steel pipe having fewer defects at an electric welded portion. The boiler steel contains, in terms of wt %, C: 0.01 to 0.20%, Si: 0.01 to 1.0% and Mn: 0.10 to 2.0%, contains further Cr: 0.5 to 3.5%, and limits p=0.030%, S=0.010% and 0=0.20%, wherein a weight ratio of (Si %)/(Mn %) or (Si %)/(Mn %+Cr %) is from 0.005 to 1.5, the balance Fe and unavoidable impurities, and the melting point of the mixed oxide of SiO2 and MnO, or SiO2, MnO and Cr2O3, is not higher than 1,600° C. The oxide that would otherwise result in the defects of the electric welded portion is molten and squeezed out as slag components. Therefore, a boiler steel excellent in electric weldability and the electric welded boiler steel pipe having fewer welding defects, excellent in creep rupture strength and toughness, and using the former, can be obtained.