Production manner null of the HT590 class structural extremely thick steel sheet which is superior in

摘要

PROBLEM TO BE SOLVED: To stably obtain an HT590 class extra thick steel plate for construction use, excellent in weldability, at a low cost by specifying a composition consisting of C, Si, Mn, Nb, Al, Cu, Ni, Cr, Mo, V and Fe and also providing a structure containing retained austenite by a specific quantity or more. ;SOLUTION: A composition, which consists of, by weight, 0.05-0.10% C, 0.03-0.30% Si, 0.80-1.60% Mn, 0.005-0.015% Nb, 0.005-0.100% Al, further one or more kinds among 0.10-0.80% Cu, 0.10-0.70% Ni, 0.10-0.50% Cr, 0.05-0.25% Mo, and 0.005-0.050% V, and the balance Fe with inevitable impurities and further contains, if necessary, prescribed amounts of S, Ti, N, Ca, and REM and in which the value of Pcm represented by equation is regulated to 0.19-0.21%, is provided. Further, retained austenite is contained in the steel by ≥1.0%. This ultra thick steel plate can be obtained by successively applying heating, rolling, hardening, heating treatment, cooling, and tempering to the steel with the above composition under respectively prescribed conditions.;COPYRIGHT: (C)1998,JPO