To provide a cold-rolled steel sheet and a plated steel sheet both with a high strength, which are superior in shielding property from the earth magnetism, in other words, have a high relative permeability in a magnetic filed of about 0.3 oersted by a direct current, and a method for manufacturing them.
This manufacturing method comprises, (1) employing a dead-soft steel with C of 0.0040% or less, which is strengthened not with precipitation but with solid solution, (2) deoxidizing it with Si so that Al may not substantially remain in the steel, or adding B to inhibit a precipitation of AlN when deoxidizing with Al, (3) finish rolling at a temperature of 750-980°C, (4) subjecting it to a cold rolling of 60-90%, and (5) annealing it at a temperature of 750°C or higher and Ac3 point or lower in a continuous annealing facility or a continuous hot-dip galvanizing facility in a line, to make a ferrite grain-size in the metal structure 10-30 μm.
TANAKA AKIRA
KUBOTA TAKESHI
