STEEL PLATE WITH EXCELLENT HYDROGEN INDUCED CRACKING RESISTANCE, AND MANUFACTURING METHOD OF THE SAME

摘要

PURPOSE: A steel sheet and a manufacturing method thereof are provided to easily manufacture a steel sheet having an adequate hydrogen-induced crack resistance. CONSTITUTION: A steel sheet includes 0.02 to 0.20 mass% of C, 0.02 to 0.50 mass% of Si, 0.6 to 2.0 mass% of Mn, 0.030 mass% or less of P, 0.004 mass% or less of S, 0.010 to 0.08 mass% of Al, 0.001 to 0.01 mass% of N, 0.002 to 0.06 mass% of Nb, 0.0003 to 0.0060 mass% of Ca, 0.0040 mass% or less of O, 0.0002 to 0.05 mass% of REM, 0.0003 to 0.020 mass% of Zr, and the remaining amount of Fe and inevitable impurities. In the composition of inclusions with widths above 1μm in steel for the steel sheet, a mass ratio (RES/CaS) between an REM sulfide (RES) and a Ca sulfide (CaS) is above 0.05, the amount of Zr is 5 to 60 mass%, and the amount of Nb is 5 mass% or less. [Reference numerals] (AA) Inclusion; (BB,EE) Width; (CC,DD) Maximum projection length