Non-oriented electrical steel sheet and method for producing the same, and motor core and method of producing the same

1. A non-oriented electrical steel sheet having a chemical composition comprising C: not more than 0.005 mass %, Si: 1.0-5.0 mass %, Mn: 0.04-3.0 mass %, sol. Al: not more than 0.005 mass %, P: 0.03-0.2 mass %, S: not more than 0.005 mass %, N: not more than 0.005 mass %, B: not more than 0.001 mass %, Se: not more than 0.001 mass %, provided that sol. Al, C, B and Se satisfy the following equation:

sol. Al+C+5B+5Se≤0.005 mass %,

and the remainder being Fe and inevitable impurities, wherein S/2M is not less than 1.0 and S/5C is not less than 1.0 wherein X-ray intensity ratios of {001}<250>, {111}<112> and {001}<100> in a central layer in a thickness direction are defined as S, M and C, respectively.

2. The non-oriented electrical steel sheet according to claim 1 , wherein the chemical composition of the non-oriented electrical steel sheet further contains at least one of the following Group A and Group B:

Group A: one or two selected from Sn: 0.01-0.2 mass % and Sb: 0.01-0.2 mass %, and

Group B: one or more selected from REM: 0.0005-0.005 mass %, Mg: 0.0005-0.005 mass % and Ca: 0.0005-0.005 mass %.

3. The non-oriented electrical steel sheet according to claim 1 , wherein an average crystal grain size is less than 40 μm.

4. The non-oriented electrical steel sheet according to claim 2 , wherein an average crystal grain size is less than 40 μm.

5. A method of producing a non-oriented electrical steel sheet comprising a series of steps of hot rolling a steel slab having a chemical composition as claimed in claim 1 , conducting a hot band annealing at a soaking temperature of 800-1200° C. for a soaking time of not more than 5 minutes, performing one cold rolling or two or more cold rollings interposing an intermediate annealing therebetween to obtain a cold rolled sheet with a final thickness and subjecting the sheet to finish annealing, wherein a temperature of the sheet at an outlet side of a rolling machine in at least one pass of the final cold rolling is set to a range of 100-300° C., thereby resulting in the non-oriented electrical steel sheet having S/2M being not less than 1.0 and S/5C being not less than 1.0 wherein X-ray intensity ratios of {001}<250>, {111}<112> and {001}<100> in a central layer in a thickness direction are defined as S M and C, respectively.

6. A method of producing a non-oriented electrical steel sheet comprising a series of steps of hot rolling a steel slab having a chemical composition as claimed in claim 2 , conducting a hot band annealing at a soaking temperature of 800-1200° C. for a soaking time of not more than 5 minutes, performing one cold rolling or two or more cold rollings interposing an intermediate annealing therebetween to obtain a cold rolled sheet with a final thickness and subjecting the sheet to finish annealing, wherein a temperature of the sheet at an outlet side of a rolling machine in at least one pass of the final cold rolling is set to a range of 100-300° C., thereby resulting in the non-oriented electrical steel sheet having S/2M being not less than 1.0 and S/5C being not less than 1.0 wherein X-ray intensity ratios of {001}<250>, {111}<112> and {001}<100> in a central layer in a thickness direction are defined as S, M and C, respectively.

7. The method of producing a non-oriented electrical steel sheet according to claim 5 , wherein a rolling reduction of the final cold rolling is not less than 80%.

8. The method of producing a non-oriented electrical steel sheet according to claim 6 , wherein a rolling reduction of the final cold rolling is not less than 80%.

9. The method of producing a non-oriented electrical steel sheet according to claim 5 , wherein a soaking temperature in the finish annealing is greater than or equal to 600° C. and less than 900° C.

10. The method of producing a non-oriented electrical steel sheet according to claim 6 , wherein a soaking temperature in the finish annealing is greater than or equal to 600° C. and less than 900° C.

11. The method of producing a non-oriented electrical steel sheet according to claim 7 , wherein a soaking temperature in the finish annealing is greater than or equal to 600° C. and less than 900° C.

12. The method of producing a non-oriented electrical steel sheet according to claim 8 , wherein a soaking temperature in the finish annealing is greater than or equal to 600° C. and less than 900° C.

13. A motor core comprising a stator core and a rotor core formed by laminating non-oriented electrical steel sheet as claimed in claim 1 , wherein an average crystal grain size of the rotor core is less than 40 μm and an average crystal grain size of the stator core is not less than 40 μm.

14. A motor core comprising a stator core and a rotor core formed by laminating non-oriented electrical steel sheet as claimed in claim 2 , wherein an average crystal grain size of the rotor core is less than 40 μm and an average crystal grain size of the stator core is not less than 40 μm.

15. A method of producing a motor core comprising a stator core and a rotor core formed by laminating non-oriented electrical steel sheet according to claim 3 , wherein an average crystal grain size of the stator core is made to not less than 40 μm by subjecting to a stress relief annealing.

16. A method of producing a motor core comprising a stator core and a rotor core formed by laminating non-oriented electrical steel sheet according to claim 4 , wherein an average crystal grain size of the stator core is made to not less than 40 μm by subjecting to a stress relief annealing.