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US-12626844-B2 - Method of manufacturing grain-oriented electrical steel sheet

US12626844B2US 12626844 B2US12626844 B2US 12626844B2US-12626844-B2

Abstract

The method includes slab-heating a steel slab to a temperature of higher than a γ-phase precipitation temperature and 1380° C. or lower, subjecting the steel slab to rough rolling including at least two passes of rolling at a predetermined temperature with an introduced sheet thickness true strain ε t of 0.50 or more and to finish rolling with a rolling finish temperature of 900° C. or higher to obtain a hot-rolled sheet, cooling the hot-rolled sheet for 1 second or longer at a cooling rate of 70° C./s or higher within 2 seconds after finish rolling, coiling the sheet at a coiling temperature of 600° C. or lower, performing hot-rolled sheet annealing for soaking at a predetermined soaking temperature, and then performing cold rolling, primary recrystallization annealing, and secondary recrystallization annealing.

Inventors

  • Shigehiro Takajo
  • Hiroi Yamaguchi

Assignees

  • JFE STEEL CORPORATION

Dates

Publication Date
20260512
Application Date
20220302
Priority Date
20210304

Claims (20)

  1. 1 . A method of manufacturing a grain-oriented electrical steel sheet, comprising: preparing a steel slab having a chemical composition containing C: 0.005 mass % to 0.085 mass %, Si: 2.00 mass % to 4.50 mass %, Mn: 0.03 mass % to 1.00 mass %, sol.Al: 0.008 mass % or more and less than 0.030 mass %, and N: 0.004 mass % to 0.009 mass % or less, and further containing either or both of S: 0.0005 mass % to 0.02 mass % and Se: 0.0005 mass % to 0.02 mass %, with the balance being Fe and inevitable impurities, subjecting the steel slab to slab heating to a temperature of higher than a γ-phase precipitation temperature and 1380° C. or lower, the γ-phase precipitation temperature being determined by equilibrium calculation, next, subjecting the steel slab to rough rolling including at least two passes of rolling at a temperature of (temperature at which γ-phase fraction reaches its maximum −20° C.) or higher with an introduced sheet thickness true strain ε t of 0.50 or more for each pass to obtain a rough-rolled sheet, the temperature at which γ-phase fraction reaches its maximum being determined by equilibrium calculation, next, subjecting the rough-rolled sheet to finish rolling where a rolling finish temperature is 900° C. or higher to obtain a hot-rolled sheet, the hot-rolled sheet having a recrystallization ratio Y of 10% or higher and 60% or less, next, cooling the hot-rolled sheet for 1 second or longer at a cooling rate of 70° C./s or higher within 2 seconds after an end of the finish rolling, coiling the hot-rolled sheet obtained after cooling at a coiling temperature of 600° C. or lower, next, subjecting the hot-rolled sheet obtained after coiling to hot-rolled sheet annealing for soaking at a soaking temperature of 1000° C. or higher and (1150-2.5Y)° C. or lower for 60 seconds or longer to obtain a hot-rolled and annealed sheet, where Y (%) is a recrystallization ratio of a sheet thickness central layer of the hot-rolled sheet obtained after coiling, next, subjecting the hot-rolled and annealed sheet to cold rolling at a rolling ratio of 88% or more and 91% or less to obtain a cold-rolled sheet with a final sheet thickness, next, subjecting the cold-rolled sheet to primary recrystallization annealing to obtain a primary recrystallization annealed sheet, and next, subjecting the primary recrystallization annealed sheet to secondary recrystallization annealing to obtain a grain-oriented electrical steel sheet, wherein the sheet thickness true strain Et is calculated by the following equation (1) ε t =−ln(sheet thickness after rolling/sheet thickness before rolling) (1).
  2. 2 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the chemical composition further contains at least one selected from the group consisting of Sb: 0.005 mass % to 0.500 mass %, and Sn: 0.005 mass % to 0.500 mass %.
  3. 3 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the chemical composition further contains at least one selected from the group consisting of Ni: 0.01 mass % to 1.50 mass %, Cr: 0.005 mass % to 0.50 mass %, Cu: 0.03 mass % to 0.50 mass %, P: 0.005 mass % to 0.500 mass %, As: 0.0005 mass % to 0.050 mass %, Bi: 0.005 mass % to 0.500 mass %, Mo: 0.005 mass % to 0.100 mass %, B: 0.0002 mass % to 0.0025 mass %, Te: 0.0005 mass % to 0.0100 mass %, Zr: 0.001 mass % to 0.010 mass %, Nb: 0.001 mass % to 0.010 mass %, V: 0.001 mass % to 0.010 mass %, and Ta: 0.001 mass % to 0.010 mass %.
  4. 4 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the rough rolling includes at least one pass of rolling at a temperature of (the temperature at which γ-phase fraction reaches its maximum−20° C.) or higher and (the temperature at which γ-phase fraction reaches its maximum+50° C.) or lower.
  5. 5 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the rough rolling has four or more passes in total.
  6. 6 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the hot-rolled sheet obtained after the soaking is subjected to cooling where a first average cooling rate v 1 from the soaking temperature to 800° C. is lower than 40° C./s and a second average cooling rate v 2 from 800° C. to 650° C. is equal to or higher than v 1 .
  7. 7 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the recrystallization ratio Y is 18% or higher and 60% or less.
  8. 8 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein the recrystallization ratio Y is 20% or higher and 60% or less, and skin pass rolling with an elongation rate of 0.05% or more is performed after an end of the finish rolling and before hot-rolled sheet annealing.
  9. 9 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 1 , wherein a magnetic flux density B 8 in a rolling direction of the grain-oriented electrical steel sheet is 1.940 T or higher.
  10. 10 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 2 , wherein the chemical composition further contains at least one selected from the group consisting of Ni: 0.01 mass % to 1.50 mass %, Cr: 0.005 mass % to 0.50 mass %, Cu: 0.03 mass % to 0.50 mass %, P: 0.005 mass % to 0.500 mass %, As: 0.0005 mass % to 0.050 mass %, Bi: 0.005 mass % to 0.500 mass %, Mo: 0.005 mass % to 0.100 mass %, B: 0.0002 mass % to 0.0025 mass %, Te: 0.0005 mass % to 0.0100 mass %, Zr: 0.001 mass % to 0.010 mass %, Nb: 0.001 mass % to 0.010 mass %, V: 0.001 mass % to 0.010 mass %, and Ta: 0.001 mass % to 0.010 mass %.
  11. 11 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 2 , wherein the rough rolling includes at least one pass of rolling at a temperature of (the temperature at which γ-phase fraction reaches its maximum−20° C.) or higher and (the temperature at which γ-phase fraction reaches its maximum+50° C.) or lower.
  12. 12 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 2 , wherein the rough rolling has four or more passes in total.
  13. 13 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 2 , wherein the hot-rolled sheet obtained after the soaking is subjected to cooling where a first average cooling rate v 1 from the soaking temperature to 800° C. is lower than 40° C./s and a second average cooling rate v 2 from 800° C. to 650° C. is equal to or higher than v 1 .
  14. 14 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 2 , wherein the recrystallization ratio Y is 18% or higher and 60% or less.
  15. 15 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 2 , wherein the recrystallization ratio Y is 20% or higher and 60% or less, and skin pass rolling with an elongation rate of 0.05% or more is performed after an end of the finish rolling and before hot-rolled sheet annealing.
  16. 16 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 2 , wherein a magnetic flux density B 8 in a rolling direction of the grain-oriented electrical steel sheet is 1.940 T or higher.
  17. 17 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 3 , wherein the rough rolling includes at least one pass of rolling at a temperature of (the temperature at which γ-phase fraction reaches its maximum−20° C.) or higher and (the temperature at which γ-phase fraction reaches its maximum+50° C.) or lower.
  18. 18 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 3 , wherein the rough rolling has four or more passes in total.
  19. 19 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 3 , wherein the hot-rolled sheet obtained after the soaking is subjected to cooling where a first average cooling rate v 1 from the soaking temperature to 800° C. is lower than 40° C./s and a second average cooling rate v 2 from 800° C. to 650° C. is equal to or higher than v 1 .
  20. 20 . The method of manufacturing a grain-oriented electrical steel sheet according to claim 3 , wherein the recrystallization ratio Y is 18% or higher and 60% or less.

Description

TECHNICAL FIELD This disclosure relates to a method of manufacturing a grain-oriented electrical steel sheet. BACKGROUND Grain-oriented electrical steel sheets are mainly used as materials for iron cores inside transformers. It has been required to reduce iron loss in grain-oriented electrical steel sheets to improve the energy use efficiency of transformers. Examples of methods to reduce the iron loss of a grain-oriented electrical steel sheet include methods of increasing the specific resistance of the steel sheet, increasing the film tension, and reducing the thickness of the steel sheet, as well as a method of performing surface treatment on the steel sheet, and a method of sharpening the crystal orientation of crystal grain to {110}<001> orientation (hereinafter referred to as “Goss orientation”). The iron loss W17/50 per kg of the steel sheet when the steel sheet is magnetized to 1.7 T in an AC magnetic field with an excitation frequency of 50 Hz is mainly used as an index of magnetic properties, and, especially, the magnetic flux density B8 at a magnetic field strength of 800 A/m is mainly used as an index of sharpening of the crystal orientation of crystal grain to {110}<001> orientation (hereinafter referred to as “Goss orientation”). To increase the integration degree of the Goss orientation, it is important to create difference in grain boundary mobility so that only sharp Goss-oriented grains grow preferentially, that is, to make the texture of a primary recrystallized sheet into a specified structure, and it is important to utilize precipitates called inhibitors to suppress the growth of recrystallized grains other than Goss-oriented grains. For example, JP S40-15644 B (PTL 1) describes a method of using MN and MnS, and JP S51-13469 B (PTL 2) describes a method of using MnS and MnSe, as techniques that utilize inhibitors, and both methods have been put into practical use industrially. These inhibitors are preferably dispersed in steel uniformly and finely. Therefore, in a method that utilizes inhibitors, it is common to performing slab heating at high temperatures of 1300° C. or higher before hot rolling to solubilize inhibitor components and precipitate them finely in subsequent processes. For example, in JP 2001-60505 A (PTL 3), steel is added with Al, hot-rolled sheet annealing is performed at 750° C. to 1200° C. after hot rolling, and then rapid cooling is performed to precipitate fine MN to obtain an extremely high magnetic flux density. On the other hand, a method of manufacturing a grain-oriented electrical steel sheet that does not rely on inhibitors (inhibitor-less method) is also being studied. The method that does not rely on inhibitors is characterized by the use of steel with higher purity and the development of secondary recrystallization by controlling a crystal texture. This method does not require slab heating at high temperatures to solubilize inhibitor components, and therefore it is possible to manufacture a grain-oriented electrical steel sheet at low costs. For example, PTL 3 describes that the presence of many crystal grains in {554}<225> orientation and many crystal grains in {411}<148> orientation in a primary recrystallized texture increases the integration to the Goss orientation after secondary recrystallization and increases the magnetic flux density. CITATION LIST Patent Literature PTL 1: JP S40-15644 BPTL 2: JP S51-13469 BPTL 3: JP 2001-60505 A SUMMARY Technical Problem To increase the magnetic flux density of a grain-oriented electrical steel sheet, it is necessary to strictly control the texture of a primary recrystallized sheet as well as inhibitors. However, fine particle distribution of inhibitors in steel, which is for the purpose of active use of inhibitors, usually refine the texture before cold rolling, rendering it difficult to control the primary recrystallized texture. In conventional manufacturing processes of a grain-oriented electrical steel sheet, fine inhibitors are formed during hot-rolled sheet annealing, and these inhibitors significantly inhibit the grain growth of recrystallized grains in a subsequent intermediate annealing process. Further, as the crystal grain size before cold rolling increases, the frequently of the formation of Goss-oriented grains in a subsequent primary recrystallization process also increases. Therefore, fine crystal grains in intermediate annealing are extremely disadvantageous to the formation of Goss orientation. It could thus be helpful to provide a method of manufacturing a grain-oriented electrical steel sheet that exhibits excellent magnetic properties compared to conventional techniques, by strictly controlling the texture of a primary recrystallized sheet and actively utilizing inhibitors. Solution to Problem We made intensive studies to solve the above problem. As a result, we found that, in order to form a texture that is suitable for obtaining good magnetic properties in a primary recrystallized sheet, it i