STRUCTURAL STEEL WITH EXCELLENT INTERCRYSTALLINE STRAIN CORROSION CRACK RESISTANCE

摘要

PURPOSE:To remarkably improve intercrystalline strain corrosion crack resistance by performing the fixation of P in intercrystalline interface in addition to immobilizled skin forming capacity. CONSTITUTION:Said structural steel comprises, in the % basis, 0.005-0.05 C, 0.1-2.0 Mn, 2-6 Cr, 0.01-0.2 Al, 0.01-0.35 Nb, 0.020 or less S, La added to the aformentioned main components in an amount so as to satisfy a formula in a content of P and Si and the remainder of Fe substantially. Because intercrystalline crack is generated due to segregation of P and Si to intercrystalline interface caused by heat history such as hot rolling, heat treatment or the like, from relation with a tempering temp., it is necessary to adjust a value of (Si + 0.05)XP% to 0.00375 or less. Herein, because reduction of P is extremely difficult and increases a cost, La is used and, because 1% thereof fixes 1/4.5% P, it is necessary to satisfy the formula. Because La is a strong sulfide and oxide forming element, it is necessary to preliminarily carry out sufficient deacidification.