MANUFACTURE OF REFINED THICK STEEL PRODUCTS WITH SUPERIOR CHARACTERISTIC STOPPING BRITTLE RUPTURE PROPAGATION

摘要

PURPOSE:To obtain steel products with superior characteristics stopping brittle rupture propagation by subjecting a steel slab contg. a specified percentage of C, Si, Mn, Al, Nb, etc. to rolling, heating, cooling and tempering under specified conditions. CONSTITUTION:A steel slab consisting of, by wt., 0.02-0.2% C, 0.05-0.50% Si, 0.5-2.0% Mn, 0.005-0.1% Al and 0.01-0.08% Nb as basic components, =0.006% S and the balance Fe or further contg. 0.003-0.04% Ti, =1 kinds among =1.0% Ni, =0.4% Mo, =0.5% Cu, =0.1% V, =0.5% Cr and =0.003% B, and 0.001% Ca and/or REM is rolled at above a temp. at which 0.01% Nb is converted into soluble Nb, and it is further rolled at =900 deg.C and =40% reduction ratio. The rolled slab is cooled to the Ar1 transformation point or below, heated to a temp. 50 deg.C above the Ac1 point to the Ac3 point in =20min, held at the temp. for 5min, cooled at the air cooling rate or above, and tempered at the Ac1 point or below.