| 摘要 |
PURPOSE:To form a forsterite insulating film having a superior characteristic, by holding a specific quantitative relation between the oxygen content in the sub-scale and the coating quantity of the annealing separating agent, in case that the annealing separating agent is coated to the directional silicon steel plate to anneal it after the sub-scale is formed on this plate. CONSTITUTION:The directional silicon steel plate which was processed to the final target thickness by cold rolling is heated at 700-900 deg.C in wet hydrogen and is decarburized and annealed. At this time, a sub-scale where oxygen content OC constituted by SiO2 and fayalite (Fe2SiO4) is 1.0-2.0g/m<2> is formed on the surface of the steel plate. Next, after the annealing separating agent which consists of MgO and Mg(OH)2 and has hydration rate alpha of 0.01-0.04 is applied, the steel plate is taken up into a coil and is heated and annealed in the H2 atmosphere at 1,100- 1,250 deg.C. In this case, the relation indicated by expression [I] is held among the coating quantity CA(g/m<2>) of the annealing separating agent, OC, and alpha, so that a uniform-thickness forsterite insulating film difficult to exfoliate can be formed. |
