| 摘要 |
PROBLEM TO BE SOLVED: To produce steel for an electric resistance welded boiler exhibiting high creep rupture strength on the side of high temp.-long time, small in defects in the electric resistance weld zone and excellent in electric resistance weldability and to provide a steel tube using it. SOLUTION: This steel for an electric resistance welded boiler small in welding defects and excellent in electric resistance weldability is the one having a compsn. contg., by weight, 0.01 to 0.20% C, 0.01 to 1.0% Si and 0.10 to 2.0% Mn or/and furthermore contg. 0.5 to 3.5% Cr, in which the contents of P, S and O are limited to <=0.030%, <=0.010% and <=0.020% respectively, and the balance Fe with inevitable impurities, also the weight ratio of Si, Mn or/and Cr is controlled to 0.005 to 1.5 by the value of (Si%)/(Mn%+Cr%), and by controlling the m.p. of two-dimentional or three-dimentional mixed oxides composed of SiO2, MnO and Cr2O3 present in the steel to <=1,600 deg.C, oxides to form into defects in the electric resistance weld zone are melted at the time of electric resistance welding and are squeezed out as slag components. Moreover, the electric resistance welded boiler steel tube excellent in creep rupture strength and toughness is the one using it.
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