Patent ID: 6331215
Filing Date: 2001-12-18
Classification: C21D,C22C,H01F

Abstract:
A process for production of a grain-oriented electromagnetic steel sheet having a low ratio of iron loss in a weaker magnetic field to that in a stronger magnetic field, which comprises:casting molten steel into a silicon steel slab, said molten steel comprising about,C: 0.005 to 0.070% by weight,Si: 1.5 to 7.0% by weight,Mn: 0.03 to 2.5% by weight,Al: 0.005 to 0.017% by weight andN: 0.0030 to 0.0100% by weight,said molten steel further including at least one member selected from the group consisting of,Ti: about 0.0005 to 0.0020% by weight,Nb: about 0.0010 to 0.010% by weight,B: about 0.0001 to 0.0020% by weight andSb: about 0.0010 to 0.080% by weight,subjecting said slab to hot rolling by heating at a temperature of lower than about 1,250.degree. C., or to direct hot rolling;the outlet temperature of finish hot rolling being in the range of about 800 to 970.degree. C., followed by quenching said steel sheet at a cooling speed of above about 10.degree. C./sec and by subsequent winding of said steel sheet in coiled form at a temperature of lower than about 670.degree. C.:annealing the resultant sheet while said resultant sheet is being maintained at a temperature of about 800 to 1,000.degree. C. for a period of shorter than about 100 seconds with a temperature rise of about 5 to 25.degree. C./sec;cold-rolling said annealed sheet at a reduction of about 80 to 95% with use of a tandem rolling mill:decarburization-annealing said cold-rolled sheet with a ratio of partial steam pressure to partial hydrogen pressure ((P(H2O)/P(H2)) below about 0.7 in the course of constant heating and with P(H2O)/P(H2) lower in the course of temperature rise than in said constant heating;coating an annealing separator on to said decarburization-annealed sheet, said separator containing a Ti compound in an amount of about 1 to 20% by weight and B in an amount of about 0.04 to 1.0% by weight; andsubsequently finish annealing said coated sheet while said coated sheet is being subjected to a temperature rise in a hydrogen-containing atmosphere at at least above about 850.degree. C.