Method of manufacturing a grain-oriented electromagnetic steel sheet
AssigneeKawasaki Steel Corporation
InventorsMichiro Komatsubara, Kazuaki Tamura, Mitsumasa Kurosawa
Life of this patent
Estimating the term…
Abstract
A method of making a grain-oriented electromagnetic steel sheet having a low iron loss and a high magnetic flux density, from a steel slab with 0.03 to 0.095 wt % carbon, about 1.5 to 7.0 wt % Si, about 0.03 to 2.50 wt % manganese, about 0.003 to 0.040 wt % sulfur and/or selenium, about 0.0010 to 0.0070 wt % borbon, about 30 to 120 wtppm nitrogen, about 0.015 wt % or less aluminum, and about 0.010 wt % or less vanadium by subjecting the steel slab to reheating, hot rolling, rapid cooling, cold rolling, primary recrystallization annealing, coating with an annealing separator, final annealing, secondary recrystallization, and coiling.
Claims23
In a method of making a grain oriented electromagnetic steel sheet having a high magnetic flux density and a very low iron loss, from a steel slab comprising about 0.030 to 0.095 wt % carbon, about 1.5 to 7.0 wt % silicon, about 0.03 to 2.50 wt % manganese, about 0.003 to 0.040 wt % sulfur and/or selenium, and about 0.0010 to 0.0070 wt % boron,
- said steel slab containing nitrogen in an amount of about 30 to 120 wtppm, a limited aluminum impurity of about 0.015 wt % or less, and a limited vanadium impurity of about 0.010 wt % or less, and
- said slab containing an element effective to accelerate fine precipitation of BN, comprising the steps of:
- reheating said steel slab at a temperature of over about 1,350° C.,
- hot-rolling the reheated steel slab to make a sheet, said hot rolling being performed for a period of about 50 to 220 seconds and at a hot rolling finishing temperature of at least about 850° C.;
- rapidly cooling said steel sheet after completion of said hot rolling at a cooling rate of at least about 30° C./sec,
- coil said sheet at a temperature of about 700° C. or less,
- subjecting said hot-rolling steel sheet to one or more stages of cold rolling under conditions including a final cold rolling reduction of from about 80 to 95% into a final thickness,
- conducting primary recrystallization annealing of said sheet,
- coating said sheet with an annealing separator,
- applying final annealing including applying secondary recrystallization annealing to said sheet, and
- accelerating said precipitation of BN to improve the texture of primary recrystallized gains of the steel immediately before subjecting the same to said secondary recrystallization annealing with said element present in said steel sheet.
In a method of making a grain oriented electromagnetic steel sheet having a high magnetic flux density and a very low iron loss, from a steel slab comprising about 0.030 to 0.095 wt % carbon, about 1.5 to 7.0 wt % silicon, about 0.03 to 2.50 wt % manganese, about 0.003 to 0.040 wt % sulfur and/or selenium, and about 0.0010 to 0.0070 wt % boron,
- said steel slab containing nitrogen in an amount of about 30 to 120 wtppm, a limited aluminum impurity of about 0.015 wt % or less, and a limited vanadium impurity of about 0.010 wt % or less and
- said slab containing an element effective to accelerate fine precipitation of BN as one or more selected from the group consisting of 0.0005 to 0.100 wt % bismuth and 0.005 to 0.500 wt % germanium, said method comprising the steps of:
- reheating said steel slab at a temperature of over about 1,350° C.,
- hot-rolling the reheated steel slab to make a sheet, said hot rolling being performed for a period of about 50 to 220 seconds and at a hot rolling finishing temperature of at least about 850° C.;
- rapidly cooling said steel sheet after completion of said hot rolling at a cooling rate of at least about 30° C./sec,
- coiling said sheet at a temperature of about 700° C. or less,
- subjecting said hot-rolled steel sheet to one or more stages of cold rolling under conditions including a final cold rolling reduction of from about 80 to 95% into a final thickness,
- conducting primary recrystallization annealing of said sheet,
- coating said sheet with an annealing separator,
- applying final annealing including applying secondary recrystallization annealing to said sheet, and
- accelerating said precipitation of BN to improve the texture of primary recrystallized grains of the steel sheet immediately before subjecting the same to said secondary recrystallization annealing with said element present in said steel sheet.
In a method of making a grain oriented electromagnetic steel sheet having a high magnetic flux density and a very low iron loss, from a steel slab comprising about 0.030 to 0.095 wt % carbon, about 1.5 to 7.0 wt % silicon, about 0.03 to 2.50 wt % manganese, about 0.003 to 0.040 wt % sulfur and/or selenium, and about 0.0010 to 0.0070 wt % boron,
- said steel slab containing nitrogen in an amount of about 30 to 120 wtppm, a limited aluminum impurity of about 0.015 wt % or less, and a limited vanadium impurity of about 0.010 wt % or less, and
- said slab containing an element effective to accelerate fine precipitation of BN as one or more selected from the group consisting of 0.0005 to 0.100 wt % bismuth and 0.005 to 0.500 wt % germanium, said method comprising the steps of:
- reheating said steel slab at a temperature of over about 1,350° C.,
- hot-rolling the reheated steel slab to make a sheet, said hot rolling being performed for a period of about 50 to 220 seconds and at a hot rolling finishing temperature of at least about 850° C.;
- rapidly cooling said steel sheet after completion of said hot rolling at a cooling rate of at least about 30° C./sec,
- coiling said sheet at a temperature of about 700° C. or less,
- subjecting said hot-rolled steel sheet to one or more stages of cold rolling under conditions including a final cold rolling reduction of from about 80 to 95% into a final thickness,
- conducting primary recrystallization annealing of said sheet,
- coating said sheet with an annealing separator,
- applying final annealing including applying secondary recrystallization annealing to said sheet, and
- accelerating said precipitation of BN to a fineness of about 10-500 nm in average diameter to improve the texture of primary recrystallized grains of the steel sheet immediately before subjecting the same to said secondary recrystallization annealing.
A method of making a grain oriented electromagnetic steel sheet from steel slab comprising about 0.030 to 0.095 wt % carbon, about 1.5 to 7.0 wt % silicon, about 0.03 to 2.50 wt % manganese, about 0.003 to 0.040 wt % sulfur and/or selenium, about 0.0010 to 0.0070 wt % boron, and about 30 to 120 wtppm nitrogen in which said sheet is subjected to secondary recrystallization annealing, comprising the steps of:
- incorporating into said sheet prior to said secondary recrystallization annealing reactive amounts of said silicon, said nitrogen, and an element selected from the group consisting of bismuth, germanium and mixtures thereof, and
- performing said secondary recrystallization annealing under conditions wherein said element is used in accelerating precipitation of fine BN in said steel, said conditions including:
- having a heating rate in a first annealing in a cold rolling process higher than about 5° C./sec in a temperature over 500° C.;
- having a temperature of the first annealing higher than at least about 950° C. if said element contains bismuth only and 1,000° C. if said element contains germanium;
- and
- having a final cold rolling within the range of about 80% to 95%.
A method of making a grain oriented electromagnetic steel sheet, said sheet comprising an inhibitive amount of boron, comprising the steps of:
- subjecting said steel sheet to primary recrystallization annealing followed by secondary recrystallization annealing;
- subsequent to said primary recrystallization annealing and prior to commencement of said secondary recrystallization, applying a nitriding treatment to said steel sheet by adding nitrogen in an amount of from about 150-250 wtppm;
- coprecipitating silicon and nitrogen as silicon nitride before conducting said secondary recrystallization annealing, and thereby introducing at least about 50 wtppm of supersturated nitrogen into said steel;
- and
- subjecting said steel, in the presence of said boron, said silicon and said nitrogen, to a first annealing with cold rolling, having an annealing temperature higher that at least about 950° C. if said element contains bismuth only and 1,000° C. if said element contains germanium, and having a heating rate in a first annealing higher than about 5° C./sec in a temperature over 500° C.;
- final cold rolling said steel sheet within the range of about 80% to 95%;
- subsequently heating said steel thereby converting at least some of said silicon nitride into finely divided boron nitride;
- and
- performing secondary recrystallization annealing wherein said boron nitride is precipitated in finely divided form into said steel using an element contained in said steel to accelerate said precipitation, and serves as a powerful inhibitor of growth of crystal grains of a particular orientation in said steel during said secondary recrystallization step.
Dependencies are inferred from the claim text.