Patent ID: 8882936

Claim:
High-tensile steel material with excellent weldability and toughness, and with a tensile strength in at least the 550 MPa class, the high-tensile steel material consisting of, by mass %: C: 0.005 to 0.10%, Si: 0.01 to 0.40%, Mn: 0.10 to 3.0%, Al: 0.010 to 0.10%, W: 0.10 to 3.0%, V: 0.010 to 0.50%, and Nb: 0.010 to 0.080%, and a balance of Fe and unavoidable impurities, wherein B: 0.0003 to 0.0035%, Ca: 0.0003 to 0.0045%, Mg: 0.0003 to 0.0045%, Y: 0.001 to 0.050%, Ce: 0.001 to 0.050%, and La: 0.001 to 0.050% are optionally present, and P, S, N, O, and Ti are present at most as impurities in amounts of: to P: 0.020% or less, S: 0.0040% or less, N: 0.006% or less, O: 0.0060% or less, Ti: less than 0.005%, and Cr: 0.020 to 0.60%; wherein EC* as given by the following equation is greater than 0.020: EC*= 2[ C ]−[ Nb ]/9−[ V ]/12−[ M ] where, [M]=[Cr]/23, and where [C], [Nb], [V], and [Cr] represent the mass % of C, Nb, and V; and wherein W precipitation is present in the steel material in an amount of 0.0050 mass % or less, based on an analytical value obtained by quantitative analysis of potential electrolysis extraction residue by fluorescent X-ray analysis, and 60 area % or more of the structural composition of the high-tensile steel material in a cross-section of the steel has a bainite structure.