PURPOSE: To obtain a soft starting sheet for surface treatment having 1-3 degree of tempering by means of superrapid-heating and short-time continuous annealing equipment capable of high temp. annealing and being compact in size and reduced in equipment costs by specifying steel components and respective conditions for hot rolling, cold rolling, and continuous annealing, respectively.
CONSTITUTION: A slab of a steel which has a composition consisting of, by weight, 0.0005-0.0030% C, 0.05-0.60% Mn, 0.001-0.025% P, 0.001-0.025% S, 0.012-0.120% sol.Al, ≤0.0050 N, ≤0.0070% T.O, and the balance Fe and containing, if necessary, B so that the ratio of B to N becomes (0.4-2.5) by atomic weight is heated and hot-rolled under ordinary hot rolling conditions and coiled. The resulting hot rolled steel strip is cold-rolled at ≥85%. The cold rolled sheet is heated up to 650-850°C at a rate of (300 to 2000)°C/s through the temp. region of ≥at least 500°C and held for ≤3sec by means of continuous annealing and then cooled down to room temp. to undergo recrystallization annealing, followed by temper rolling at 0.5-5%.
ODA MASAHIKO
EZURE KAZUYA
HARADA TAKESHI
