Patent ID: 6966955

Claim:
A weldable structural steel product having TiN and ZrN precipitates, comprising, in terms of percent by weight, 0.03 to 0.17% C, 0.01 to 0.5% Si, 0.4 to 2.0% Mn, 0.005 to 0.2% Ti, 0.0005 to 0.1% Al, 0.001 to 0.03% Zr, 0.008 to 0.030% N, 0.0003 to 0.01% B, 0.001 to 0.2% W, at most 0.03% P, at most 0.03% S, at most 0.01% O, and balance Fe and incidental impurities while satisfying conditions of 1.2≦Ti/N≦2.5, 0.3≦Zr/N≦2.0, 10≦N/B≦40, 2.5≦Al/N≦7, and 6.8≦(Ti+Zr+2Al+4B)/N≦17, and having a microstructure essentially consisting of a complex structure of ferrite and pearlite having a grain size of 20 μm or less, wherein said ZrN precipitates and TiN precipitates having a grain size of 0.01 to 1 μm are dispersed at a density of 1.0×10 7 /mm 2 or more and a spacing of 0.5 μm or less.