| 摘要 |
PROBLEM TO BE SOLVED: To provide steel capable of forming stable rust good in protecting properties in an environment high in the content of salt such as a coastal region and also excellent in earthquake resistance including weldability in the heat affected zone. SOLUTION: This steel has a compsn. contg., by mass, 0.001 to 0.030% C, <=0.60% Si, 0.50 to 3.00% Mn, <=0.005% S, <=0.10% Al and 0.0003 to 0.0050% B, moreover contg. one or >= two kinds selected from 0.005 to 0.15% P, 0.1 to 1.5% Cu, 0.1 to 6.0% Ni and 0.005 to 0.5% Mo and also satisfying (11P+4.0Cu+3.1Ni+2.6Mo)/(1-0.1(10000B)0.35)>=1+13X [(where P, Cu, Ni, Mo and B: the content (mass%) of each element, and X: the content of salt to be flown (mg/ dm2/day)], and in which the value of the total (dA+dB) of the content of A series inclusions and the content of B series inclusions is <=0.030%.
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