METHOD OF PRODUCING AS ROLLED HIGH TOUGHNESS STEEL

摘要

A method has been developed for making high strength and high toughness steel having superior toughness even at heat affected zones due to welding. The method consists of preparing a cast steel of strictly controlled chemical composition by an oxygen converter followed by continuous casting, heating the steel at a considerably lower temperature of 950.degree. - 1050.degree.C and subjecting the heated steel to controlled rolling so that the steel can be rolled at a temperature within an austenite single phase region. The controlled chemical composition of the steel is maintained to have 0.01 - 0.15% C, not more than 0.6% Si, 0.8 - 2.0% Mn, 0.01 - 0.08% Al, not more than 0.008% S, 0.008 - 0.025% Ti, 0.001 - 0.007% N all being by weight and the balance Fe and incidental impurities. By virtue of the lowered content of S and small amount of added Ti and N combined with rapid cooling rate obtained through the continuous casting method and through the controlled rolling the rolled steel plate has very fine grained micro structure together with minimum anisotropy in mechanical property even in the direction of the thickness of the plate. Due to these features, the steel obtained by this method is particularly suitable for weld construction members used at low temperature such as line pipes, ship building and so on. The steel may further contain one or more of other alloying elements such as Nb, V, Ni, Cu, Cr and Mo.