Excellent steel weather resistance

Mainly used outdoors, such as bridges, to provide suitable weathering steel as a structural steel material, especially high temperature and in an environment in which period there is dried rainfall is small, such as dry season. Specific amounts of C, Si, Mn, P, S, Al, Cu, Nb, Sn, In addition, at least (1), with satisfying either of (2), and satisfying the expression (3), requires depending on, Ni, Cr, Mo, W, Co, Sb, Ti, V, Zr, B, REM, Ca, one or more of Mg, steel balance of iron and unavoidable impurities. (Cu-0.01) × (Sn -0.005) × (Nb-0.005) × 10 4 ≧ 0.08 (1), (Cu-0.01) × (Ni-0.01) × (Cr-0.01) × 50 ≧ 0.08 (2), (Cu + 10 × Sn) / (2 × Ni + 0.5 × Si) <10 (3), wherein each atomic symbol content (wt% ) shows, an element that does not contain is 0.