HIGH-STRENGTH THICK STEEL PRODUCTS EXCELLENT IN TOUGHNESS AND WELDABILITY, HIGH-STRENGTH ULTRA-THICK H SHAPE STEEL AND PROCESSES FOR MANUFACTURING BOTH

摘要

This invention relates to reducing the C content and the N content , a proper amount of Si, Mn, Nb, Ti, B, and containing O, the content of C and Nb , satisfy C-Nb / 7.74 0.004 , and the density is from 30 to 300 of the Ti-containing oxide particle diameter of 0.05 to 10 / , and the particle diameter exceeds 10 the density of Ti -containing oxides of 10 / or less as the toughness and high-strength steel material having excellent weldability and , after adjusting to 0.005 to 0.015 % by mass of dissolved oxygen by the preliminary deoxidation treatment , the addition of Ti , and further vacuum degassing to conduct more than 30 minutes after heating the solvent to a billet obtained by continuous casting , and 1100 to 1350 , and hot rolling to a thickness of 40 to 150 mm is , it is cooled to manufacture .