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KR-20260062158-A - NON-ORIENTED ELECTRICAL STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME

KR20260062158AKR 20260062158 AKR20260062158 AKR 20260062158AKR-20260062158-A

Abstract

The present invention provides a method for manufacturing a non-oriented electrical steel sheet comprising the steps of: providing a steel material comprising silicon (Si): 1.8 to 2.65 wt%, manganese (Mn): 0.1 to 0.5 wt%, aluminum (Al): 0.1 to 0.45 wt%, and the remainder being iron (Fe) and other unavoidable impurities; hot rolling the steel material; pre-annealing the hot-rolled steel material; cold rolling the pre-annealed steel material; and stress relief annealing the cold-rolled steel material in an unrecrystallized region; wherein the stress relief annealing step is performed at a temperature of 450 to 650°C.

Inventors

  • 이승태
  • 강춘구
  • 이강노
  • 곽민석

Assignees

  • 현대제철 주식회사

Dates

Publication Date
20260507
Application Date
20241025

Claims (13)

  1. A step of providing a steel material comprising silicon (Si): 1.8 to 2.65 wt%, manganese (Mn): 0.1 to 0.5 wt%, aluminum (Al): 0.1 to 0.45 wt%, and the remainder being iron (Fe) and other unavoidable impurities; A step of hot rolling the above steel material; A step of pre-annealing the above hot-rolled steel; The step of cold rolling the above-mentioned pre-annealed steel; and The method includes the step of performing stress relief annealing on the above cold-rolled steel in an unrecrystallized region; The stress relief annealing step is characterized by being performed at a temperature of 450 to 650℃. Method for manufacturing non-oriented electrical steel sheets.
  2. In Article 1, The above stress relief annealing step is, Performed in the recovery step of the above cold-rolled steel, Method for manufacturing non-oriented electrical steel sheets.
  3. In Article 1, The above stress relief annealing step is, A step comprising annealing at a temperature of 450°C or higher and less than 550°C for 70 to 120 seconds, or annealing at a temperature of 550°C or higher and less than 650°C for 30 to 70 seconds, Method for manufacturing non-oriented electrical steel sheets.
  4. In Article 1, The above preliminary annealing step includes an annealing heat treatment in which the temperature is increased by more than 10℃/s and maintained at a temperature of 900 to 1100℃ for 30 to 100 seconds, Method for manufacturing non-oriented electrical steel sheets.
  5. In Article 1, The above hot rolling step is performed under conditions where the reheat temperature (SRT) is 1100 to 1200℃ and the finishing rolling temperature (FDT) is 800 to 900℃, Method for manufacturing non-oriented electrical steel sheets.
  6. In Article 1, The thickness of the hot-rolled steel is 1.6 to 2.6 mm, and the thickness of the cold-rolled steel is 0.2 to 0.5 mm, Method for manufacturing non-oriented electrical steel sheets.
  7. In Article 1, After performing the stress relief annealing step described above, the final microstructure is characterized by a kernel average misorientation (KAM) of 1.3° or more and less than 1.7°, Method for manufacturing non-oriented electrical steel sheets.
  8. In Article 1, The above steel further comprises carbon (C): greater than 0 and less than or equal to 0.003 wt%, sulfur (S): greater than 0 and less than or equal to 0.003 wt%, nitrogen (N): greater than 0 and less than or equal to 0.003 wt%, and titanium (Ti): greater than 0 and less than or equal to 0.003 wt%. Method for manufacturing non-oriented electrical steel sheets.
  9. It is a non-oriented electrical steel sheet comprising silicon (Si): 1.8 to 2.65 wt%, manganese (Mn): 0.1 to 0.5 wt%, aluminum (Al): 0.1 to 0.45 wt%, and the remainder being iron (Fe) and other unavoidable impurities, and The final microstructure has a kernel average misorientation (KAM) of 1.3° or greater and less than 1.7°, and tensile strength of 800 MPa or higher, Non-oriented electrical steel sheet.
  10. In Article 9, Characterized by a yield ratio of 95% or more, Non-oriented electrical steel sheet.
  11. In Article 9, Characterized by having an iron loss of 50 to 70 W/kg (W 10/400 ), Non-oriented electrical steel sheet.
  12. In Article 9, Characterized by an iron loss (W 10/400 ) increase rate of 10% or less when tested for 7 days at 20,000 rpm, Non-oriented electrical steel sheet.
  13. In Article 9, Carbon (C): greater than 0 and less than or equal to 0.003 wt%, Sulfur (S): greater than 0 and less than or equal to 0.003 wt%, Nitrogen (N): greater than 0 and less than or equal to 0.003 wt%, Titanium (Ti): greater than 0 and less than or equal to 0.003 wt%, further comprising Non-oriented electrical steel sheet.

Description

Non-oriented electrical steel sheet and method for manufacturing the same The present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, and more specifically, to a non-oriented electrical steel sheet with excellent mechanical properties and a method for manufacturing the same. Electrical steel sheets can be classified into oriented and non-oriented electrical steel sheets based on their magnetic properties. Oriented electrical steel sheets are manufactured to facilitate magnetization along the rolling direction, resulting in particularly excellent magnetic properties in that direction; consequently, they are primarily used as cores for large, medium, and small transformers that require low iron loss and high permeability. In contrast, non-oriented electrical steel sheets possess uniform magnetic properties regardless of the sheet's orientation, making them widely used as core materials for small electric motors. In particular, as conventional internal combustion engine vehicles are rapidly being replaced by electric vehicles (EVs), interest in non-oriented electrical steel sheets used as drive motor core materials is increasing, and specification standards are also becoming more sophisticated. When electric vehicles (EVs) rotate at high speeds (400 Hz or higher), the motor rotor is subjected to stress fluctuations resulting from changes in rotational speed as well as centrifugal force; consequently, there is a risk that motor efficiency and noise/vibration (NVH) performance will deteriorate due to deformation and fatigue failure. As such, non-oriented electrical steel sheets used in high-speed rotating motors require high mechanical properties capable of withstanding centrifugal force and stress fluctuations. Conventionally, research has been conducted to strengthen tensile strength to the level of 500–700 MPa, but there is a need to develop electrical steel sheets that satisfy mechanical properties beyond this level. Methods to increase the mechanical strength of non-oriented electrical steel include adding alloying elements and reducing grain size. Among the alloying elements, C, N, and S form fine precipitates, which improve strength but have the disadvantage of rapidly degrading iron loss, potentially lowering motor efficiency. Techniques involving the addition of alloying elements such as Nb, V, and Cu also result in the problem of rapid deterioration of magnetism. Furthermore, the method of reducing grain size has the disadvantage of increasing material non-uniformity due to the incorporation of unrecrystallized regions, leading to greater quality variation in mass-produced products. FIG. 1 is a flowchart illustrating a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention. FIG. 2 is a diagram illustrating the strength characteristics of a steel sheet according to temperature during stress relief annealing in a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention. Figure 3 is a photograph showing the final structure of a non-oriented electrical steel sheet manufactured according to one embodiment of the present invention. A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention is described in detail. The terms described below are appropriately selected considering their functions in the present invention, and the definitions of these terms should be based on the content throughout this specification. Non-oriented electrical steel sheets A non-oriented electrical steel sheet implemented according to one embodiment of the present invention is a non-oriented electrical steel sheet comprising silicon (Si): 1.8 to 2.65 wt%, manganese (Mn): 0.1 to 0.5 wt%, aluminum (Al): 0.1 to 0.45 wt%, carbon (C): greater than 0 and less than 0.003 wt%, sulfur (S): greater than 0 and less than 0.003 wt%, nitrogen (N): greater than 0 and less than 0.003 wt%, titanium (Ti): greater than 0 and less than 0.003 wt%, and the remainder being iron (Fe) and other unavoidable impurities, characterized in that the KAM value in the final microstructure is 1.3° or more and less than 1.7°, and the tensile strength is 800 MPa or more. The above-mentioned non-oriented electrical steel sheet not only has a very high tensile strength of 800 MPa or higher, but also excellent yield strength, allowing for a yield ratio (yield strength (YS) / tensile strength (TS)) of 95% or higher. More specifically, the yield ratio can be secured at 95% or higher and less than 100%. The yield ratio is an indicator representing how much plastic deformation can be accommodated from the point at which initial plastic deformation occurs (yield point) up to maximum tension. Since a lower yield ratio results in more plastic deformation after the yield point, a smaller yield ratio is disadvantageous for deformation occurring during