Method for producing non-oriented electrical steel sheet, method for producing motor core, and motor core
There are provided a method for producing a non-oriented electrical steel sheet, a method for manufacturing a motor core from such a steel sheet, and a motor core. In the production of a non-oriented electrical steel sheet by subjecting a steel slab containing given amounts of C, Si, Mn, P, S, Al, N, Ti, Nb and V, provided that Si, Al and Mn satisfy Si-2Al—Mn≥0, to hot rolling, cold rolling, finish annealing and stress relief annealing, whereby a high-strength rotor core and a stator core having excellent magnetic properties after stress relief annealing can be obtained from the same steel material.
1. A method for producing a non-oriented electrical steel sheet, the method comprising subjecting a steel slab to hot rolling, cold rolling, finish annealing, and stress relief annealing, wherein:
the steel slab has a chemical composition comprising:
C: not more than 0.0050 mass %,
Si: 2.5 to 6.5 mass %,
Mn: 0.05 to 2.0 mass %,
P: not more than 0.2 mass %,
S: not more than 0.005 mass %,
Al: not more than 3 mass %,
N: not more than 0.005 mass %,
Ti: not more than 0.003 mass %,
Nb: not more than 0.005 mass %,
V: not more than 0.005 mass %, and
Fe and inevitable impurities,
provided that Si, Al and Mn satisfy the following equation (1):
Si-2Al—Mn≥0 (1),
the stress relief annealing is conducted such that a soaking temperature is 780 to 950° C. and a cooling rate from the soaking temperature to 650° C. is in the range of 1 to 10° C./min, and
conditions of the finish annealing and stress relief annealing are adjusted such that:
a yield stress after the finish annealing is not less than 400 MPa,
iron loss W 10/400 after the stress relief annealing, in units of W/kg, satisfies the following equation (2):
W 10/400 ≤10+25 t (2)
in relation to a sheet thickness t, in units of mm,
an average value λ o-p (bake) of magnetostriction in a rolling direction and magnetostriction in a direction perpendicular to the rolling direction at 400 Hz and 1.0 T after the stress relief annealing is not more than 5.0×10 −6 , and
a ratio (λ o-p (bake)/λ o-p (green)) of the above average value λ o-p (bake) of magnetostriction after the stress relief annealing to an average value λ o-p (green) of magnetostriction in the rolling direction and magnetostriction in the direction perpendicular to the rolling direction at 400 Hz and 1.0 T before the stress relief annealing is less than 0.8.
2. The method for producing a non-oriented electrical steel sheet according to claim 1 , wherein the chemical composition further comprises at least one group selected from the following groups A-D:
Group A: one or two selected from Mo and W in an amount of 0.0020 to 0.10 mass % in total,
Group B: one or two selected from Sn: 0.005-0.20 mass % and Sb: 0.005-0.20 mass %,
Group C: one or two selected from Ca and Mg in an amount of 0.001-0.010 mass % in total, and
Group D: one or more selected from Cu: 0.01-0.2 mass %, Ni: 0.05-1 mass % and Cr: 0.01-0.5 mass %.
3. A method for manufacturing a motor core, the method comprising:
producing the non-oriented electrical steel sheet according to claim 1 ; and
simultaneously taking out rotor core materials and stator core materials from a the non-oriented electrical steel sheet.
4. The method for manufacturing a motor core according to claim 3 , wherein the non-oriented electrical steel sheet contains at least one group selected from the following groups A-D in addition to the above chemical composition:
Group A: one or two selected from Mo and W in an amount of 0.0020 to 0.10 mass % in total,
Group B: one or two selected from Sn: 0.005 to 0.20 mass % and Sb: 0.005 to 0.20 mass %,
Group C: one or two selected from Ca and Mg in an amount of 0.001 to 0.010 mass % in total, and
Group D: one or more selected from Cu: 0.01 to 0.2 mass %, Ni: 0.05 to 1 mass % and Cr: 0.01 to 0.5 mass %.