Patent ID: 8303734

Claim:
A high strength thick steel material excellent in toughness and weldability characterized by containing, by mass %, C: 0.005% to 0.030%, Si: 0.05% to 0.50%, Mn: 0.4% to 2.0%, Nb: 0.02% to 0.25%, Ti: 0.005% to 0.025%, B: 0.0003% to 0.0030%, and O: 0.0005% to 0.0035%, limited to P: 0.030% or less, S: 0.020% or less, and N: 0.0045% or less, and having a balance of Fe and unavoidable impurities, having contents of C and Nb satisfying C—Nb/7.74≦0.02, having a density of Ti-containing oxides of a particle size of 0.05 to 10 μm of 30 to 300 /mm 2 , and having a density of Ti-containing oxides of a particle size over 10 μm of 10 /mm 2 or less.