STEEL SHEET FOR RESISTANCE WELDED STEEL TUBE HAVING LOW FRACTION DEFECTIVE IN NONDESTRUCTIVE TESTING

摘要

PURPOSE:To obtain the steel sheet having low fraction defective in nondestructive testing at the time of manufacturing resistance welded steel tubes by regulating the contents of Ca and Al in a molten steel and regulating composite inclusions having specified compsn. as deoxidation products. CONSTITUTION:A steel sheet contg. 0.05 to 0.35% C, 0.02 to 0.5% Si and 0.5 to 2% Mn as well as 0.0005 to 0.008% Ca and 0.005 to 0.08% Al and the balance iron with impurities, in which composite inclusions (CaO)m(Al2O3)n are regulated as deoxidation products and whose molecular constitutional ratio is regulated to the range of 1m/n is prepd. If required, one or more kinds among 0.1 to 1% Mo, 0.01 to 0.1% Nb, 0.01 to 0.1% V, 0.001 to 0.05% Ti and 0.0005 to 0.004% B and/or one or more kinds among 0.1 to 0.5% Cu, 0.1 to 3% Ni and 0.1 to 3% Cr are furthermore added to the above components.