The fitting material and its production manner null which are superior in waterproof element being induced crack Characteristic and resistance sulfide stress corrosion crack

摘要

PURPOSE: To provide a high tensile strength steel plate for fitting material, excellent in hydrogen induced cracking resistance and sulfide stress corrosion cracking resistance, by specifying a composition consisting of C, Si, Mn, P, S, Al, Nb, Ti, N, Ca, REM, and Fe and also specifying a structure after hardening. ;CONSTITUTION: This steel plate has a composition consisting of, by weight, 0.05-0.15% C, ≤0.5% Si, 0.6-1.5% Mn, ≤0.015% P, ≤0.005% S, 0.001-0.060% Al, 0.005-0.04% Nb, 0.005-0.03% Ti, ≤0.005% N, 0.0005-0.004% Ca or 0.0005-0.004% REM as inclusion-controlling element, and the balance iron with inevitable impurities, further containing, if necessary, one or more kinds among 0.05-0.50% Mo, 0.05-0.50% Cr, 0.05-0.50% Ni, 0.05-0.50% Cu, and 0.010-0.10% V as hardenability-regulating elements, and satisfying 0.30≤Ceq≤0.50. Moreover, the ratio of the structure of this steel plate is regulated so that it consists of ≤30% polygonal ferrite and the balance bainite by controlling the cooling rate at the time of hardening after hot forming to ≥5°C/sec.;COPYRIGHT: (C)1996,JPO