PURPOSE: To improve drawability, longitudinal crack resistance and enamel adhesiveness by subjecting a continuously cast slab contg. Si, Mn, P, S, Cu, Ti, Nb, etc., at specified ratios to a heat treatment under prescribed conditions.

CONSTITUTION: The steel having the compsn. which contains, by weight % ≤0.005% C, ≤0.03% Si, 0.05W0.3% Mn, 0.005W0.025% P, 0.002W0.022% S, 0.025W0.045% Cu, 0.01W0.09% Ti, 0.01W0.05% Nb, ≤0.09% solAl, and 0.003W0.014% N, and is limited in the ratios between the above-mentioned Cu and P, P and S, and Nb and C, and further in the content ratio of N to Ti and the content ratio of the total sum of N and S is melted. Such molten steel is continuously cast by using CC powder contg. ≤1.5% C. After such cast slab is rolled, the rolled steel is subjected to continuous annealing at 900°C recrystallization temp., 1W100°C/sec cooling rate, and ≤450°C overaging treatment temp.