INTERCRITICAL HEAT TREATMENT PROCESS FOR TOUGHNESS IMPROVEMENT OF SA508 GR.3 STEEL

摘要

PURPOSE: A method for manufacturing a high toughness SA508 Gr. 3 steel is provided in which fracture toughness is improved by using the intercritical heat treatment. CONSTITUTION: In a method for manufacturing an SA508 Gr. 3 steel comprising quenching, tempering and heat treatment process after welding, the SA508 Gr. 3 steel comprises 0.25 wt.% or less of C, 1.2 to 1.5 wt.% of Mn, 0.15 to 0.4 wt.% of Si, 0.015 wt.% or less of P, 0.015 wt.% or less of S, 0.4 to 1.0 wt.% of Ni, 0.25 wt.% or less of Cr, 0.45 to 0.6 wt.% of Mo, 0.04 wt.% or less of Al, 0.06 wt.% or less of Cu, 0.03 wt.% or less of V and a balance of Fe, intercritical heat treatment process which is performed at a temperature of 680 to 750 deg.C for 1 to 8 hours is added between the quenching process and the tempering process, and the tempering process is carried out at a temperature less than 635 deg.C after the intercritical heat treatment process.