Method of manufacturing a high-strength steel plates for building structure having excellent ultra-high heat input welding heat affected zone toughness

摘要

PROBLEM TO BE SOLVED: To provide a method for producing a high strength thick steel plate for building structure having excellent toughness in a super-large heat input welding-affected zone.;SOLUTION: This production method employs a steel blank having a composition containing, by mass%: 0.05 to 0.15% C, 0.05 to 0.50% Si, 0.6 to 1.6% Mn, ≤0.005% S, and an appropriate amount of P, Al, Cu, and Ni. The steel blank further contains 0.005 to 0.030% Ti, 0.0003 to 0.0050% B, 0.0005 to 0.0050% Ca, 0.0030 to 0.0060% N, 0.0010 to 0.0030% O, and has 0.2 to 0.8 ACR defined by ACR={Ca-(0.18+130Ca)×O}/(1.25×S) and ≤0.47 Ceq. The steel blank is heated to a temperature in the range of 1,000 to 1,300°C, and subjected to hot-rolling having ≥900°C rolling finish temperature and then to accelerated cooling to ≤600°C at ≥1°C/s cooling speed. Further, this rolled steel plate is heated to a reheating temperature in two-phase range of (Ac1+10°C) to (Ac1+70°C) and desirably held for 5 to 60 min and thereafter rapidly cooled, subjected to reheating quenching and then tempering. Then, this steel blank may contain one or more kinds of Cr, V and Mo.;COPYRIGHT: (C)2005,JPO&NCIPI