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KR-20260065016-A - NON-ORIENTED ELECTRICAL STEEL SHEET AND METHOD OF MANUFACTURING THE SAME

KR20260065016AKR 20260065016 AKR20260065016 AKR 20260065016AKR-20260065016-A

Abstract

The present invention relates to a method for manufacturing a non-oriented electrical steel sheet, comprising: a hot rolling step of manufacturing a hot-rolled sheet by hot rolling a slab comprising, in wt%, silicon (Si): 3.0 wt% to 3.8 wt%, manganese (Mn): 0.2 wt% to 0.5 wt%, aluminum (Al): 0.8 wt% to 1.5 wt%, carbon (C): greater than 0 and less than or equal to 0.005 wt%, phosphorus (P): greater than 0 and less than or equal to 0.02 wt%, sulfur (S): greater than 0 and less than or equal to 0.005 wt%, nitrogen (N): greater than 0 and less than or equal to 0.005 wt%, titanium (Ti): greater than 0 and less than or equal to 0.005 wt%, and the remainder being iron (Fe) and unavoidable impurities; and a hot rolling annealing step of manufacturing a hot-rolled annealed sheet by hot rolling annealing the hot-rolled sheet. A method for manufacturing a non-oriented electrical steel sheet is provided, comprising: a cold rolling step of manufacturing a cold rolled sheet by cold rolling the hot-rolled annealed sheet; and a cold rolling annealing step of manufacturing a cold-rolled annealed sheet by annealing the cold rolled sheet, wherein the temperature is 580°C or higher and 710°C or lower.

Inventors

  • 곽민석
  • 박준영
  • 이강노
  • 강춘구

Assignees

  • 현대제철 주식회사

Dates

Publication Date
20260508
Application Date
20241031

Claims (12)

  1. As a method for manufacturing non-oriented electrical steel sheets, A hot rolling step for manufacturing a hot-rolled plate by hot rolling a slab comprising, in wt%, silicon (Si): 3.0 wt% to 3.8 wt%, manganese (Mn): 0.2 wt% to 0.5 wt%, aluminum (Al): 0.8 wt% to 1.5 wt%, carbon (C): greater than 0 and less than or equal to 0.005 wt%, phosphorus (P): greater than 0 and less than or equal to 0.02 wt%, sulfur (S): greater than 0 and less than or equal to 0.005 wt%, nitrogen (N): greater than 0 and less than or equal to 0.005 wt%, titanium (Ti): greater than 0 and less than or equal to 0.005 wt%, and the remainder being iron (Fe) and unavoidable impurities; A hot rolling annealing step for manufacturing a hot rolling annealed plate by hot rolling and annealing the above hot rolling plate; A cold rolling step for manufacturing a cold rolled plate by cold rolling the above hot-rolled annealed plate; and A method for manufacturing a non-oriented electrical steel sheet, comprising a cold rolling annealing step in which the above cold-rolled sheet is annealed to produce a cold-rolled annealed sheet, wherein the temperature is 580°C or higher and 710°C or lower.
  2. In paragraph 1, A method for manufacturing a non-oriented electrical steel sheet, wherein the unrecrystallized structure included in the above non-oriented electrical steel sheet refers to a structure in which the aspect ratio among the grains classified under the said condition is less than 0.31 when the classification of grain boundaries is set to a misorientation of 5° or more.
  3. In paragraph 2, A method for manufacturing a non-oriented electrical steel sheet, wherein the aspect ratio of the unrecrystallized structure included in the non-oriented electrical steel sheet is 0.082 or higher and 0.169 or lower.
  4. In paragraph 2, A method for manufacturing a non-oriented electrical steel sheet in which the fraction of the above unrecrystallized structure is 21% or more and 60% or less.
  5. In paragraph 2, A method for manufacturing a non-oriented electrical steel sheet, wherein the yield strength in the rolling direction (L direction) of the above non-oriented electrical steel sheet is 400 MPa or more.
  6. In paragraph 2, A method for manufacturing a non-oriented electrical steel sheet, wherein the yield strength in the rolling vertical direction (C direction) of the above non-oriented electrical steel sheet is 400 MPa or more.
  7. In paragraph 2, A method for manufacturing a non-oriented electrical steel sheet, wherein the ratio of the yield strength in the rolling direction (L direction) to the yield strength in the rolling vertical direction (C direction) of the above non-oriented electrical steel sheet is 0.9 or more and 1 or less.
  8. As a non-oriented electrical steel sheet, In wt%, silicon (Si): 3.0 wt% to 3.8 wt%, manganese (Mn): 0.2 wt% to 0.5 wt%, aluminum (Al): 0.8 wt% to 1.5 wt%, carbon (C): greater than 0 and less than or equal to 0.005 wt%, phosphorus (P): greater than 0 and less than or equal to 0.02 wt%, sulfur (S): greater than 0 and less than or equal to 0.005 wt%, nitrogen (N): greater than 0 and less than or equal to 0.005 wt%, titanium (Ti): greater than 0 and less than or equal to 0.005 wt%, and the remainder being iron (Fe) and unavoidable impurities, The unrecrystallized structure included in the above-mentioned non-oriented electrical steel sheet refers to a structure in which the aspect ratio among the grains classified under the said condition is less than 0.31 when the grain boundary classification is set to a misorientation of 5° or more. A non-oriented electrical steel sheet having an aspect ratio of an unrecrystallized structure containing the above non-oriented electrical steel sheet, wherein the aspect ratio is 0.082 or higher and 0.169 or lower.
  9. In paragraph 8, A non-oriented electrical steel sheet having a fraction of unrecrystallized structure of 21% or more and 60% or less.
  10. In paragraph 8, A non-oriented electrical steel sheet having a yield strength of 400 MPa or more in the rolling direction (L direction) of the above non-oriented electrical steel sheet.
  11. In paragraph 8, A non-oriented electrical steel sheet having a yield strength of 400 MPa or more in the rolling vertical direction (C direction) of the above non-oriented electrical steel sheet.
  12. In paragraph 8, A non-oriented electrical steel sheet having a ratio of the yield strength in the rolling direction (L direction) to the yield strength in the rolling vertical direction (C direction) of the above non-oriented electrical steel sheet being 0.9 or more and 1 or less.

Description

Non-oriented electrical steel sheet and method of manufacturing the same The present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Regarding non-oriented electrical steel sheets used in motors, the automotive industry is shifting toward reducing the production of internal combustion engine vehicles and increasing the production of electric vehicles. Consequently, along with the recent increase in demand for electric vehicles, there is a growing demand for high-efficiency and high-output electrical steel sheets, which are key components. As part of this effort, initiatives are underway to achieve faster rotational speeds than conventional motors by modulating the frequency, such as in BLDC (Brushless DC) motors. In particular, drive motors used in hybrid and electric vehicles require rotational speeds exceeding 16,000 rpm. In such cases, since the centrifugal force acting on the motor rotor is proportional to the square of the rotational speed, high-speed rotation exceeds the yield strength that conventional electrical steel sheets can withstand. This causes deformation of the motor, significantly impacting its lifespan and durability. Therefore, rotors for high-speed rotating equipment require high-strength materials. To manufacture high-strength electrical steel sheets, development has proceeded by performing final heat treatment at low or medium temperatures to maintain the cold-rolled structure, specifically the unrecrystallized structure. However, this material presents a problem in that there is a significant difference between the yield strength in the L-direction and C-direction—that is, between the yield strength when parallel to the rolling direction and when perpendicular to it. In other words, while maintaining the unrecrystallized structure helps improve yield strength, an excessive amount of this structure increases material anisotropy, which can lead to biased deformation in individual sheets during motor core fabrication. Additionally, since deformation and failure of the motor may occur in the direction of lower yield strength during high-speed rotation, uniform mechanical properties regardless of direction are required. FIG. 1 is a flowchart schematically illustrating a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention. Figures 2 to 4 are schematic photographs showing cross-sectional views of the microstructure within an electrical steel sheet according to the cold rolling annealing temperature. The present invention is capable of various modifications and may have various embodiments; specific embodiments are illustrated in the drawings and described in detail in the detailed description. The effects and features of the present invention, and the methods for achieving them, will become clear by referring to the embodiments described below in detail together with the drawings. However, the present invention is not limited to the embodiments disclosed below but can be implemented in various forms. In the following embodiments, terms such as first, second, etc. are used not in a limiting sense, but for the purpose of distinguishing one component from another component. In the following examples, singular expressions include plural expressions unless the context clearly indicates otherwise. In the following embodiments, terms such as "include" or "have" mean that the features or components described in the specification are present, and do not preclude the possibility that one or more other features or components may be added. In the drawings, the size of components may be exaggerated or reduced for convenience of explanation. For example, the size and thickness of each component shown in the drawings are depicted arbitrarily for convenience of explanation, so the present invention is not necessarily limited to what is illustrated. Where an embodiment can be implemented differently, a specific process sequence may be performed differently from the order described. For example, two processes described consecutively may be performed substantially simultaneously or proceed in the reverse order of the description. In this specification, "A and/or B" indicates the case where it is A, B, or both A and B. And, "at least one of A and B" indicates the case where it is A, B, or both A and B. Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. When describing with reference to the drawings, identical or corresponding components are given the same reference numerals, and redundant descriptions thereof will be omitted. FIG. 1 is a flowchart schematically illustrating a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention. FIG. 2 to 4 are photographs schematically showing cross-sectional views of the microstructure within an electrical steel sheet according to co