The steel null for the ship which C is superior corrosion-resistant and brittle crack

摘要

PROBLEM TO BE SOLVED: To provide marine steel which has excellent corrosion resistance to such an extent that it can be put to practical use even without coating or electrical protection and in which the propagation of initiated brittle cracks can be arrested and the cracks are hardly propagated.;SOLUTION: The marine steel has a composition composed of, (by mass, the same applies to the following), 0.01 to 0.2% C, 0.01 to 0.5% Si, 0.01 to 2% Mn, 0.05 to 0.5% Al, 0.010 to 1.5% Cu, 0.010 to 1% Cr, ≤0.02% (not including 0%) P, ≤0.01% (not including 0%) S and the balance Fe with inevitable impurities. When observing the metallic structure of the steel, the average grain size of ferrite grains in the region between the surface of the steel and a position at a depth of t/100 from the surface is ≤25μm, where the (t) means the thickness (mm) of the steel.;COPYRIGHT: (C)2007,JPO&INPIT