Low failure rate of non-destructive inspection high toughness ERW steel pipe for steel plate

摘要

PURPOSE:To obtain the steel sheet having low fraction defective in nondestructive testing at the time of manufacturing resistance welded steel tubes and free from the deterioration of low temp. toughness 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, furthermore contg. 0.0005 to 0.005% Ca and 0.005 to 0.08% Al and the balance Fe with impurities, in which composite inclusions (CaO)m(Al2O3)n are regulated as deoxidation products and whose molecular constitutional ratio (m):(n) is regulated to the range of 1:1 to 1:6 is prepd. If required, one ore 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.