HIGH STRENGTH STEEL MEMBER EXCELLENT IN DELAYED BREAKDOWN RESISTANCE

摘要

PURPOSE: To produce a practical high strength steel member excellent in delayed breakdown resistance by regulating the content of Ni to a certain one or above and furthermore concentrating the concn. of Ni in the suface compared to that on the inside in a specified range. ;CONSTITUTION: This high strength steel member is the one contg., by weight, ≥0.25%, preferably 0.25 to 7.0% Ni, in which the concn. of Ni in the surface is regulated to double that on the inside or above and having excellent delayed breakdown resistance. This steel member preferably contains 0.2 to 0.6% C, 0.2 to 2.0% Si, 0.2 to 2.0% Mn, ≤0.020% P, ≤0.015% S and 0.25 to 7.0% Ni. This steel moreover contains one or more kinds among 0.2 to 2.0% Cr, 0.1 to 0.5% Mo, 0.05 to 1.0% Cu, 0.0003 to 0.0050% B, 0.01 to 0.04% Ti and 0.03 to 0.50% W according to necessary. Furthermore, the content of Ni is preferably regulated to 0.25 to 3.0% from the viewpoint of profitability.;COPYRIGHT: (C)1996,JPO