| 摘要 |
PROBLEM TO BE SOLVED: To obtain a uniform forsterite coating film free from defects over the whole width and whole length of a coil and excellent in adhesion by incorporating a specified amt. of Cr into a steel slab and producing spinel type Cr oxide into an oxidized film formed on the surface layer of a steel sheet at the time of decarburizing annealing. SOLUTION: By weight, 0.1 to 1.0% Cr is incorporated into a steel slab. It is preferable that 0.005 to 0.20% Bi is incorporated into the steel slab, and spinel type Cr oxide in an oxidized film (subscale) is composed of FeCr2O4 or (Fe, Mn) Cr2O4. Preferably, the decarburizing annealing is executed under the conditions in which the temp. rising rate from ordinary temp. to 700 deg.C is controlled to 10 to 50 deg.C/s, the temp. rising rate from the temp. region of 700-800 deg.C to 850 deg.C is controlled to 1 to 9 deg.C/s, moreover, the atmospheric oxidizing degree at the time of soaking is controlled to 0.30 to 0.50, and furthermore, (the atmospheric oxidizing degree in a soaking zone-the atmospheric oxidizing degree in a heating zone) is controlled to 0.05 to 0.20, and the coating weight of oxygen in the surface layer of the steel sheet after the decarburizing annealing satisfies 0.35 to 0.95g/m3. |
