PURPOSE:To manufacture a steel sheet having superior resistance to hydrogen induced cracking by specifying the relation between the hardness of the segregated part of a steel sheet contg. specified percentages of C, Si, Mn, P, S and Al and the total length of inclusions in the part whose hardness has been measured. CONSTITUTION:A steel sheet consisting of, by weight, 0.01-0.30% C, 0.02-0.60% Si, 0.50-2.50% Mn, =0.020% P, =0.010% S, 0.005-0.060% Al and the balance Fe with inevitable impurities is manufactured. When the Vickers hardness Hv of the segregated part of the steel sheet is =230, the relation among the hardness Hv, the total length A(mum) of A type inclusions of =10mum length in 10mm2 area of the part whose hardness has been measured and the total length B(mum) of B type inclusions is specified so as to satisfy a formula Hv=230-4/10X(A+B/2). Thus, a steel sheet causing no hydrogen induced cracking in an environment of about 3pH is obtd.
展开▼
