| 摘要 |
PROBLEM TO BE SOLVED: To produce a grain oriented magnetic steel sheet having good properties by depositing silicon nitride.SOLUTION: Steel having a composition containing, by mass%, C:0.08% or less, Si:2.0 to 4.5% and Mn:0.5% or less, S, Se and O each limited to less than 50 ppm, sol.Al limited to less than 100 ppm, further N of 80 ppm or less and in a range satisfying sol.Al(ppm)-N(ppm)×(26.98/14.00)≤30 ppm and the balance Fe with inevitable impurities is subjected to a nitriding treatment with an increase in nitrogen amount of 50 ppm to 1000 ppm, during or after a primary recrystallization annealing. In this case, the maximum temperature of the primary recrystallization annealing is set to 780 to 1,000°C, a soaking time is set to 10 sec. to 200 sec., and further total retention time in the temperature range of 700°C or higher during heat treatment including the primary recrystallization annealing and the nitriding treatment is set to 600 sec. or less, so that the crystal grain size of a primarily recrystallized structure having a nitriding concentrated layer adjacent to a surface of the steel sheet is set at 8 μm to 30 μm. |
