NIOBIUM-CONTAINING WELDABLE STRUCTURAL STEEL HAVING GOOD WELDABILITY

摘要

Disclosed herein is a niobium-containing weldable structural steel having good weldability which consists of 0.005 0.04% of C, 0.01 - 0.50% of Si, 1.20 - 2.50% of Mn, 0.01 - 0.07% of Nb, 0.005 - 0.030% of Ti, 0.005 - 0.06% of A? and the balance of iron and inevitable impurities whereby ¢C(%) + lON(%)! is not greater than 0.10% and Ti(%/¢C(%) + lON(%)! is from 0.05 to 0.60 in order to restrict the amount of martensite islands in the weld heat affected zone to not greater than 15% in terms of the area fraction. Steel according to the present invention is advantageous for ultra-cold applications. The steel does not cause embrittlement of the weld heat affected zone and exhibits good notch toughness even when having been welded with a large weld heat input.