Method for refining magnetic domains of grain-oriented electrical steel sheet

1. A method for refining magnetic domains of a grain-oriented electrical steel sheet, comprising:

a step of preparing a grain-oriented electrical steel sheet; and

a step of forming a groove by irradiating a quasi-continuous laser beam of which a duty is from 98.0 to 99.9% on a surface of the grain-oriented electrical steel sheet,

wherein the duty is a ratio (T b /T a ) of [a time of irradiation with an output of 10% or more of a maximum output (Pmax)] Tb to [an output modulation cycle time] Ta in a time diagram for an output of a laser beam,

wherein the laser has a TEM 00 mode, and M 2 of a beam quality factor is 1.0 to 1.1, and

wherein a ratio P/W of an average output P of a laser beam for a quasi-continuous laser beam width W is from 30 W/μm to 300 W/μm.

2. The method for refining magnetic domains of the grain-oriented electrical steel sheet of claim 1 , wherein

a frequency of the quasi-continuous laser beam is from 100 Hz to 8 kHz.

3. The method for refining magnetic domains of the grain-oriented electrical steel sheet of claim 1 , wherein

a ratio W/L of a beam width W in a steel sheet rolling direction to a beam length L in a steel sheet width direction of the quasi-continuous laser beam is from 0.1 to 0.86.

4. The method for refining magnetic domains of the grain-oriented electrical steel sheet of claim 1 , wherein

3 to 8 grooves are intermittently formed in the width direction of the steel sheet.

5. The method for refining magnetic domains of the grain-oriented electrical steel sheet of claim 1 , wherein

the grooves are linear and are formed at an angle from 82° to 98° with respect to a rolling direction of the electrical steel sheet.

6. The method for refining magnetic domains of the grain-oriented electrical steel sheet of claim 1 , wherein

a depth D of the groove is formed from 3% to 8% of the thickness of the steel sheet.

7. The method for refining magnetic domains of the grain-oriented electrical steel sheet of claim 1 , further comprising,

after the step of forming the groove:

a step of forming an oxide layer on the surface of the steel sheet through decarburization annealing or nitride annealing; and

a step of coating an annealing separator on the surface of the steel sheet formed with the oxide layer and forming non-metal oxide layer on the surface of the steel sheet through high temperature annealing.

8. The method for refining magnetic domains of the grain-oriented electrical steel sheet of claim 7 , further comprising,

after the step of forming the non-metal oxide layer,

a step of forming an insulating coating layer on the non-metal oxide layer.