Abstract: The present invention relates to a high tensile welded steel plate consisting essentially of, by weight, C: 0.03 to 0.20%, Si: 0.6 to 2.0%, Mn: 0.6 to 2.0%, Al: 0.01 to 0.08%, B: not more than 0.0020%, and N: 0.002 to 0.008% and optionally at least one element selected from Cu, Mo, Ni, Cr, Nb, V, Ti, Ca, and REM with the balance consisting of Fe and unavoidable impurities, and a process for producing a high tensile welded steel plate, usually comprising the steps of: subjecting a slab comprising the above chemical compositions to hot rolling or alternatively hot rolling followed by controlled rolling. The present invention enables fatigue cracking of the as-welded steel, in its heat-affected zone, to be prevented and, at the same time, the propagation of the crack to be prevented or inhibited.

Abstract: A steel plate having a high toughness, low yield ratio and high fatigue strength is provided by preserving the fine metallographical microstructure of martensite or bainite while austenitizing extremely fine portions of the microstructure, and during cooling, dispersing the portions as martensite, retained austenite, cementite or mixture thereof in a tempered martensite or tempered bainite phase.