JP6676952B2 - Hot rolled sheet for unidirectional magnetic steel sheet, method for producing the same, and method for producing the same - Google Patents

Description

  The present invention relates to a hot-rolled sheet for a unidirectional magnetic steel sheet in which precipitates used for manufacturing a unidirectional magnetic steel sheet used for an iron core material of a transformer are controlled, and a method for producing the hot-rolled sheet, and the unidirectionality thereof. The present invention relates to a method for manufacturing an electromagnetic steel sheet.

  The grain-oriented electrical steel sheet is used as a core material of a transformer. A grain-oriented electrical steel sheet is required to have a high magnetic flux density in the direction in which it is magnetized, and is manufactured by selectively growing a crystal orientation excellent in magnetic properties called Goss using secondary recrystallization. It is a functional material.

  In recent years, in order to improve the energy efficiency of transformers, it has been required to further reduce iron loss of a grain-oriented electrical steel sheet. Since the iron loss can be reduced by reducing the thickness of the unidirectional electrical steel sheet, a thin unidirectional electrical steel sheet has been demanded.

  In order to reduce the iron loss of the grain-oriented electrical steel sheet, by appropriately controlling the precipitates serving as inhibitors related to the mechanism of secondary recrystallization, a secondary recrystallized structure with a high Goss accumulation degree is obtained. The magnetic flux density must be improved. Generally, sulfide (MnS or the like) or nitride (AlN or the like) is known as a precipitate used as an inhibitor. Although research on inhibitor control has been conducted in the past, the hot rolling step in which MnS is completely dissolved and then MnS is finely precipitated as an inhibitor is performed by stabilizing the secondary recrystallized structure and reducing high magnetic flux density. This is an important process in realizing the production of grain-oriented electrical steel sheets. Further, MnS precipitated in the hot-rolled sheet obtained by the hot rolling step becomes a precipitation site of AlN in the subsequent hot-rolled sheet annealing, and together with AlN, further decarburizing annealing is performed on the steel sheet after the cold rolling. Determine the particle size of the resulting primary recrystallized grains. Therefore, MnS precipitated on the hot-rolled sheet directly or indirectly governs the behavior of the secondary recrystallization.

  In addition, secondary recrystallization starts from a decrease in inhibitor strength due to oxidation of AlN or the like near the surface of a steel sheet that is easily affected by the atmosphere during finish annealing. The ratio of the area in the thickness direction to be received increases. Therefore, as the sheet thickness becomes thinner, the inhibitor strength is rapidly reduced due to oxidation of the AlN inhibitor, and the preferential growth of Goss-oriented grains in the vicinity of the steel sheet surface is weakened. Are likely to occur, and secondary recrystallization becomes unstable. Another reason that the preferential growth of Goss-oriented grains in the vicinity of the steel sheet surface is weakened is also that primary crystal grains having random orientations other than Goss become larger than Goss-oriented grains.

  Therefore, in order to stabilize the secondary recrystallization structure and produce a high-magnetic-density unidirectional electrical steel sheet, the preferential growth of Goss-oriented grains near the steel sheet surface during the secondary recrystallization is further improved. In order to increase the crystallinity, it is necessary to control the primary recrystallization texture such as inhibitor control and crystal grain size control. In order to control such a primary recrystallization texture, the conditions of the hot rolling step may be controlled.

  As a technique for controlling the conditions of the hot rolling step, for example, techniques disclosed in Patent Documents 1 to 4 are known. In the technique disclosed in Patent Document 1, the conditions of temperature and time are specified in a hot rolling process of a slab for a grain-oriented electrical steel sheet after a complete solution of a precipitate, and the hot rolling is characterized by slow cooling. Through the process, MnS used as an inhibitor is uniformly deposited as fine particles at a high distribution density to improve magnetic properties. However, this technique cannot eliminate the non-uniformity of secondary recrystallization, which occurs particularly with thin materials.

  Further, in the technology disclosed in Patent Document 2, the slab is once cooled and then reheated, and the slab after the reheating is subjected to hot rolling. However, although this technique can improve the surface properties of the steel sheet, it controls the primary recrystallization texture such as inhibitor control and crystal grain size control in order to stabilize the secondary recrystallization texture. is not.

  In the technique disclosed in Patent Document 3, the slab is heated and hot-rolled, and then reheated. In the hot rolling step of hot-rolling the reheated steel sheet again, the rolling temperature and the inter-pass time are reduced. Stipulates. However, this technique is intended to prevent the occurrence of edge cracks in the hot rolling step when producing ultra-high silicon steel, and to produce a secondary recrystallized structure in steel having a silicon concentration of about 3% by mass. It does not control the primary recrystallization texture such as inhibitor control or crystal grain size control in order to stabilize.

  In the technology disclosed in Patent Document 4, the slab is heated and hot-rolled, then reheated, and the reheated steel sheet is hot-rolled again to control the crystal grain size. However, in this technique, at the time of reheating after the first hot rolling, the precipitation is soaked, so that the effect of stabilizing the secondary recrystallization structure cannot be obtained.

JP-A-48-69720 JP-A-5-179347 JP-A-6-150162 JP-A-48-53919

  The present invention has been made in view of the above problems, and can stabilize a secondary recrystallized structure in a thin unidirectional magnetic steel sheet used for an iron core material for improving the efficiency of a transformer. In addition, an object of the present invention is to provide a hot-rolled sheet for a grain-oriented electrical steel sheet and a method for producing the same, and a method for producing the grain-oriented electrical steel sheet, in which inhibitor control and grain size control are performed in a hot rolling step. .

  The present inventors have investigated the cause of non-uniform secondary recrystallization in a thin unidirectional magnetic steel sheet in order to solve the above problems. As a result, the preferential growth in secondary recrystallization increases with the orientation grains having a large grain size at the completion of primary recrystallization, so in order to stabilize the secondary recrystallization structure in a thin unidirectional electrical steel sheet, At the point of completion of the primary recrystallization, the average grain size of the crystal grains including the Goss orientation grains in the region near the surface is made coarser than that in the central region, and the intensity of the inhibitor near the steel sheet surface decreases rapidly during the secondary recrystallization. Even if it occurs, it has been found that it is effective to maintain the preferential growth of Goss-oriented grains near the steel sheet surface.

  At the time of completion of the primary recrystallization, the conditions of the hot-rolled sheet and hot-rolling were studied so that the average grain size of the crystal grains including the Goss-oriented grains in the region near the surface could be made coarser than in the central region. As a result, a hot-rolled sheet in which the average grain size of the crystal grains in the near-surface region is larger than that in the center region, and all or part of hot rolling under the condition that the temperature in the near-surface region of the steel sheet is higher than the temperature in the center region Has been found to be practically applicable.

  The present invention has been made based on these findings, and the gist of the present invention is that, in mass%, C: 0.1% or less, Si: 2.5 to 4.0%, Mn: 0.05 to 0. 1%, S: 0.01 to 0.04%, Al: 0.01 to 0.05%, and N: 0.001 to 0.030%, with the balance being Fe and unavoidable impurities. A hot-rolled sheet for a grain-oriented electrical steel sheet, wherein the average of crystal grains in a region near the surface of a 1/10 to 1/5 layer thickness with respect to the average grain size of the crystal grains in the central region of the 1/5 layer thickness to the center A hot-rolled sheet for a grain-oriented electrical steel sheet, wherein the ratio of the particle diameters is 1.10 or more.

  Another gist of the present invention is the above-described hot-rolled sheet for unidirectional magnetic steel sheets, wherein the sheet thickness is 1/5 layer to 1/10 to 1/5 layer with respect to the average grain size of MnS in the central region of the center. Wherein the ratio of the average particle size of MnS in the region near the surface is 1.10 or more.

  Another gist of the present invention is the above-described hot-rolled sheet for a grain-oriented electrical steel sheet, in which the distribution thickness of MnS in the region near the surface of 1/10 to 1/5 layer thickness is 1/5 layer thickness to center. Wherein the ratio of the distribution density of MnS in the central region is 1.10 or more.

  Another aspect is the above-described hot-rolled sheet for a grain-oriented electrical steel sheet, wherein 1% selected from the group consisting of Bi, Pb, As, and Te in mass% instead of a part of the Fe. Species or two or more: 0.0002% to 0.02% in total, and one or two or more selected from the group consisting of Sb, Sn, and P: 0.0004% to 0.5% in total A hot-rolled sheet for a grain-oriented electrical steel sheet, comprising:

  Further, the other point is that, in mass%, C: 0.1% or less, Si: 2.5 to 4.0%, Mn: 0.05 to 0.1%, S: 0.01 to 0.04. %, Al: 0.01 to 0.05%, and N: 0.001 to 0.030% in a hot rolling step of hot rolling a slab composed of Fe and unavoidable impurities. The true strain of rolling applied to a steel sheet in a state where the surface temperature Ts1100 to 1200 ° C and the sheet thickness center temperature Tc1000 to 1100 ° C satisfy the relationship of Ts-Tc> 50 ° C is 40% of the true strain of the entire hot rolling. % Of the hot-rolled sheet for a grain-oriented electrical steel sheet.

  Another aspect is a method for manufacturing a hot-rolled sheet for a unidirectional magnetic steel sheet, wherein the slab is cooled to 900 ° C. or less as a surface temperature in the hot rolling step. A hot-rolled sheet for a unidirectional magnetic steel sheet, wherein the hot-rolled sheet is charged into a heating furnace at 1200 ° C. or higher and the slab extracted from the heating furnace is subjected to the hot rolling within 1 hour after the charging. It is a manufacturing method.

  Another aspect is a method for manufacturing a hot-rolled steel sheet for a unidirectional magnetic steel sheet, wherein the hot-rolled steel sheet has a surface temperature Ts of 1100 ° C. or more and 600 to 750 ° C. After cooling at an average cooling rate of 2 ° C./s or more to a temperature of not more than 2 ° C./s and maintaining the temperature in a temperature range of 600 to 750 ° C. for 0 s to 300 s, the above-mentioned rolled steel sheet is brought to a surface temperature Ts of 1100 ° C. to 1150 ° C. A method for producing a hot-rolled sheet for a grain-oriented electrical steel sheet, which further comprises rolling after heating.

  Another aspect is a method for manufacturing a hot-rolled steel sheet for a unidirectional magnetic steel sheet, in which the slab is heated to 1250 to 1400 ° C. at a surface temperature in the hot rolling step. A method for producing a hot-rolled sheet for unidirectional magnetic steel sheets, wherein the hot slab is subjected to the hot rolling described above.

  Another aspect is a method for manufacturing a hot-rolled sheet for a grain-oriented electrical steel sheet, wherein the cast slab is made of Bi, Pb, As, and by mass% instead of a part of the Fe. One or more selected from the group consisting of Te: 0.0002% or more and 0.02% or less in total, and one or two or more selected from the group consisting of Sb, Sn, and P: 0 in total A method for producing a hot-rolled sheet for a grain-oriented electrical steel sheet, further comprising 0.0004% to 0.5%.

  Further, another gist is a hot-rolled sheet manufacturing process for manufacturing a hot-rolled sheet for a unidirectional magnetic steel sheet by performing the above-described method for manufacturing a hot-rolled sheet for a unidirectional magnetic steel sheet, A hot-rolled sheet annealing step of performing hot-rolled sheet annealing on a hot-rolled sheet, a cold-rolling step of performing cold rolling on the steel sheet after the hot-rolled sheet annealing, and performing a decarburizing annealing on the cold-rolled steel sheet A method for producing a unidirectional magnetic steel sheet, comprising: a decarburizing annealing step; and a finish annealing step of subjecting the steel sheet after the decarburizing annealing to finish annealing.

  Another aspect is a method for manufacturing the above-described grain-oriented electrical steel sheet, wherein the hot-rolled sheet for a grain-oriented electrical steel sheet is subjected to a temperature range of 900 to 1050 ° C. for 60 s or more in the hot-rolled sheet annealing step. This is a method for producing a grain-oriented electrical steel sheet, characterized by subjecting the retained hot-rolled sheet to annealing.

  Furthermore, another gist is the method for manufacturing the above-described grain-oriented electrical steel sheet, wherein in the decarburizing annealing step, the steel sheet after the cold rolling is heated from a temperature of 350 ° C or less to a temperature of 700 ° C or more and 850 ° C or less. A method for producing a grain-oriented electrical steel sheet, wherein the steel sheet after the cold rolling is subjected to the decarburizing annealing after heating at a heating rate of 100 ° C./s or more in a heating process of raising the temperature to the temperature. It is.

  According to the present invention, a heat treatment for a grain-oriented electrical steel sheet used for producing a thin ultra-low iron loss unidirectional electrical steel sheet having excellent magnetic properties by expressing uniform secondary recrystallization. The present invention can provide a rolled sheet, a method for manufacturing the same, and a method for manufacturing the grain-oriented electrical steel sheet.

  Hereinafter, the hot-rolled sheet for a grain-oriented electrical steel sheet of the present invention, a method for producing the same, and a method for producing the grain-oriented electrical steel sheet are described in detail.

A. Hot rolled sheet for unidirectional magnetic steel sheet The hot rolled sheet for unidirectional magnetic steel sheet of the present invention is a hot rolled sheet for unidirectional magnetic steel sheet having the following chemical components, and has a thickness of 1/5 layer to the center. The ratio of the average grain size of the crystal grains in the region near the surface of the 1/10 to 1/5 layer with respect to the average grain size of the crystal grains in the central region is 1.10. Hereinafter, the hot-rolled sheet for a grain-oriented electrical steel sheet of the present invention will be described in detail.

1. Chemical Components Hereinafter, the reasons for limiting the chemical components in the present invention will be described in detail. In the following, the content of each component is a value in mass%.

(1) C
The addition of C is a useful element because the nucleation and growth of MnS during hot rolling can be controlled by the austenite phase formed, but if added in excess of 0.1%, decarburization or purification becomes difficult. . When C remains on the product plate, an aging phenomenon in which the magnetic properties deteriorate is caused. Therefore, the upper limit of the content is set to 0.1%.

(2) Si
Si is added in an amount of 2.5 to 4.0% because it is a useful element for increasing the specific resistance and reducing iron loss. If added excessively, hot rolling or cold rolling becomes difficult, so the upper limit of the content is set to 4.0%.

(3) Mn
Mn is an element necessary for finely precipitating MnS during hot rolling, so Mn is added in an amount of 0.05 to 0.1%. If the content is less than this, a sufficient volume ratio of MnS cannot be obtained, and the structure cannot be controlled. Therefore, the lower limit of the content is set to 0.05%. Further, even if Mn is excessively added, the effect of controlling the structure cannot be improved, so the upper limit of the content is set to 0.1%.

(4) S
S, like Mn, is an essential element for precipitating MnS, so is added in an amount of 0.01 to 0.04%. If the content is less than this, a sufficient volume ratio of MnS cannot be obtained and the structure cannot be controlled, so the lower limit of the content is set to 0.01%. When excessively added, MnS is likely to be coarsened, and hot rolling is difficult due to red-hot embrittlement. Therefore, the upper limit of the content is set to 0.04%.

(5) Al
Al is an element necessary to precipitate fine AlN on the interface between fine MnS and ground iron by annealing a hot-rolled sheet after hot rolling that causes fine precipitation of MnS. Is added for the purpose of improving the magnetic flux density of 0.01 to 0.05%. If the content is less than this, an effective precipitation amount of AlN cannot be obtained, and it cannot contribute to the structure control during finish annealing, and the magnetic flux density of the grain-oriented electrical steel sheet does not improve. 01%. On the other hand, if the content is larger than this, the growth of AlN is accelerated, and AlN is easily precipitated by hot rolling alone, so that AlN is relatively coarsely precipitated and a pin effective in secondary recrystallization is effective. Since the stop force is not exerted and the preferential growth of the Goss-oriented grains is adversely affected and the magnetic flux density decreases, the upper limit of the content is set to 0.05%.

(6) N
N, like Al, is an element necessary for annealing a hot-rolled sheet to precipitate fine AlN, and is added in an amount of 0.001 to 0.030%. If the content is less than this, an effective precipitation amount of fine AlN cannot be obtained, and the grain boundary pinning force required for controlling the structure at the time of finish annealing cannot be exerted. %. On the other hand, if the content is larger than this, AlN is apt to precipitate alone by hot rolling, so that AlN precipitates relatively coarsely, does not exhibit an effective pinning force in secondary recrystallization, and has a Goss orientation. Since the magnetic flux density is lowered by adversely affecting the preferential growth of grains, the upper limit of the content is set to 0.030%.

(7) Others One or more selected from the group consisting of Bi, Pb, As, and Te are added in a total amount of 0.02% or less, and one selected from the group consisting of Sb, Sn, and P It is preferable to add at least 0.5% of a kind or two or more kinds. In the hot rolling step described in “B. Method for Manufacturing Hot Rolled Sheet for Unidirectional Electrical Steel Sheet 1. Hot Rolling Step” described later, the sheet thickness center temperature of the slab after the heating is higher than the surface temperature. By lowering, the grain boundary mobility becomes smaller in the central region of the slab after the heating than in the region near the surface. Further, since the movement speed of the grain boundary is slowed by the segregation of the above-mentioned elements, the crystal grain size is significantly smaller in the central region of the slab after the heating than in the region near the surface. As a result, in the hot-rolled sheet for unidirectional electromagnetic steel sheets, the average grain size of the crystal grains in the region near the surface of the sheet thickness of 1/10 to 1/5 layer is larger than that in the central region of the sheet thickness of 1/5 layer to the center. Since it can be remarkably coarsened, even if the inhibitor strength decreases rapidly near the steel sheet surface during the secondary recrystallization, the preferential growth of Goss orientation grains near the steel sheet surface is remarkably maintained. This is because the secondary recrystallized structure in the thin unidirectional magnetic steel sheet can be remarkably stabilized.
Note that Sn, Bi, Tepb, Sb and Se, and Sb, Sn and P are added instead of part of Fe.

(8) Remainder The remainder is Fe and inevitable impurities. Of the unavoidable impurities, Ti, V, Nb, and Zr, which adversely affect the grain growth, are desirably reduced as much as possible, and each is desirably 0.008% or less.

2. Average grain size of crystal grains In the hot-rolled sheet for a grain-oriented electrical steel sheet of the present invention, the thickness of 1/10 layer to 1/5 layer relative to the average grain size of crystal grains in the central region of the center is 1/5 layer. The ratio of the average grain size of the crystal grains in the region near the surface is 1.10 or more. Thereby, at the time of completion of the primary recrystallization, the average grain size of the crystal grains including the Goss orientation grains in the region near the surface can be made larger than that in the central region. Even if the strength rapidly decreases, the preferential growth of Goss-oriented grains near the steel sheet surface can be maintained, and the secondary recrystallized structure in the thin unidirectional magnetic steel sheet can be stabilized.
Here, in the present invention, the “average grain size of crystal grains” means a value obtained by averaging the diameters of circles having the same area with respect to the projected area for a plurality of observed crystal grains.

  The ratio of the average grain size of the crystal grains in the region near the surface of the 1/10 to 1/5 layer thickness to the average grain size of the crystal grains in the central region from the 1/5 layer thickness to the center is 1.10 or more. It is preferable that it is 1.20 or more. This is because the preferential growth of Goss-oriented grains in the vicinity of the steel sheet surface can be remarkably maintained.

3. Precipitates Hereinafter, the precipitates of MnS will be described in detail.

(1) Average Particle Size In the hot-rolled sheet for a grain-oriented electrical steel sheet of the present invention, the surface of the sheet thickness of 1/10 to 1/5 layer with respect to the average particle size of MnS in the central region of the thickness of 1/5 layer. The ratio of the average particle size of MnS in the vicinity region is preferably 1.10 or more. Since the MnS becomes finer and denser in the central region than in the region near the surface layer, the primary recrystallized structure in the region near the surface is made to be a structure that is significantly advantageous for preferential growth of Goss-oriented grains. Since the growth of crystal grains can be significantly suppressed, the preferential growth of Goss orientation grains near the steel sheet surface is remarkably maintained, and the secondary recrystallization structure in thin unidirectional magnetic steel sheets is significantly stabilized. This is because it can be done.

  Here, in the present invention, the “average particle size of MnS” means a value obtained by calculating the diameters of circles having the same area with respect to the projected area for a plurality of observed MnS. In the hot-rolled sheet for unidirectional magnetic steel sheets, when the total amount of MnS precipitated is the same, MnS precipitates at a higher distribution density as the average particle size of MnS is smaller.

  The ratio of the average particle size of MnS in the region near the surface of the 1/10 to 1/5 layer thickness to the average particle size of MnS in the central region from the 1/5 layer thickness to the center should be 1.20 or more, among others. Is preferable, and it is particularly preferable that it is 1.30 or more. Homogeneous and fine MnS suppresses crystal grain growth in the central region, and suppresses crystal grain growth in the central region at a high temperature, and secondary recrystallization starts by Ostwald-grown MnS in the region near the surface layer. This is because secondary recrystallization, which progresses after eating the food, is more likely to occur.

  The average particle size of MnS in the region near the surface of the 1/10 to 1/5 layer is preferably 80 nm to 300 nm, more preferably 80 nm to 200 nm, and particularly preferably 80 nm to 160 nm. This is because when MnS has this average particle size, a sharp secondary recrystallization structure can be obtained. Further, the average particle size of MnS in the central region from the 厚 layer thickness to the center is preferably 50 nm to 200 nm, more preferably 50 nm to 180 nm, particularly preferably 50 nm to 120 nm. This is because, by dispersing fine MnS in the central region, crystal grain growth in the central region during finish annealing is suppressed, and secondary recrystallization is significantly stabilized.

(2) Distribution Density In the hot-rolled sheet for a grain-oriented electrical steel sheet of the present invention, the central region from the 1/5 layer thickness to the center with respect to the distribution density of MnS in the region near the surface of 1/10 to 1/5 layer thickness. Is preferably 1.10 or more. Since the MnS becomes finer and denser in the central region than in the near-surface region, the primary recrystallized structure in the near-surface region becomes a structure that is significantly advantageous for preferential growth of Goss-oriented grains. Since the growth of crystal grains can be significantly suppressed, the preferential growth of Goss orientation grains near the steel sheet surface is remarkably maintained, and the secondary recrystallization structure in thin unidirectional magnetic steel sheets is significantly stabilized. This is because it can be done.

  Here, in the present invention, “MnS distribution density” means a value obtained by dividing the number of MnS counted by observing a mirror-polished cross section by the area of the observation visual field.

4. Plate thickness The hot-rolled sheet for unidirectional magnetic steel sheets of the present invention is premised on being obtained by performing inhibitor control such that uniform secondary recrystallization is exhibited when manufacturing thin unidirectional magnetic steel sheets. . Therefore, the thickness of the hot-rolled sheet is 2.3 mm or less, preferably 2.1 mm or less, more preferably 2.0 mm or less. In the subsequent cold rolling step, cold rolling is performed at a rolling reduction of 85% or more and 92% or less. To obtain a final plate thickness. On the other hand, the thickness of the hot-rolled sheet is preferably set to 1.5 mm or more because the sheet thickness after cold rolling becomes extremely thin and the improvement according to the present invention is not seen.

5. Manufacturing method The hot-rolled sheet for unidirectional electromagnetic steel sheets of the present invention is manufactured by the method for manufacturing a hot-rolled sheet for unidirectional electromagnetic steel sheets described in “B. It is preferred to manufacture.

B. Method for Manufacturing Hot-Rolled Sheet for Unidirectional Electrical Steel Sheet The method for manufacturing a hot-rolled sheet for unidirectional electrical steel sheet according to the present invention includes a hot rolling step of performing hot rolling on a slab having the above-mentioned chemical composition. Hereinafter, a method for producing a hot-rolled sheet for a grain-oriented electrical steel sheet according to the present invention will be described.

1. Hot Rolling Step In the hot rolling step, a slab having the above-mentioned chemical components is subjected to hot rolling. In the hot rolling step, the true strain of rolling applied to the steel sheet in a state where the surface temperature Ts1100 to 1200 ° C and the thickness center temperature Tc1000 to 1100 ° C satisfies the relationship of Ts-Tc> 50 ° C, 40% or more of the true strain of the entire hot rolling. Thereby, in the hot-rolled sheet for unidirectional electromagnetic steel sheets, the average grain size of the crystal grains in the region near the surface of the 1/10 to 1/5 layer thickness is larger than that in the central region of the 1/5 layer thickness to the center. It can be coarsened. As a result, at the time of completion of the primary recrystallization, the average grain size of the crystal grains including the Goss-oriented grains in the region near the surface can be made larger than that in the central region. Even if the strength rapidly decreases, the preferential growth of Goss-oriented grains near the steel sheet surface can be maintained, and the secondary recrystallized structure in the thin unidirectional magnetic steel sheet can be stabilized. Here, the true strain of the entire hot rolling is preferably 50% or more. Thereby, the precipitation of MnS is promoted, and the above-mentioned effect is significantly enhanced.

  Here, in the present invention, the “surface temperature Ts of the steel sheet” means a temperature measured by a contact-type thermometer or a radiation thermometer. Further, in the present invention, the “thickness center temperature Tc of the steel sheet” means a temperature obtained by a heat conduction analysis by a generally known difference method.

  A slab having the above-mentioned chemical components is obtained, for example, by melting steel in a converter or an electric furnace, subjecting the steel to vacuum degassing if necessary, and then performing continuous casting or ingot casting followed by ingot rolling. Can be

  In the hot rolling step, the slab is subjected to rough rolling and finish rolling to finish a hot-rolled sheet having a desired thickness. At this time, the hot rolling may be performed after the slab is heated under the conditions described below. Further, the steel sheet which has been subjected to one or two or more rolling passes in the rough rolling may be cooled and held under the conditions described below, and then subjected to the finish rolling by further heating.

  In the hot rolling step, the true strain of rolling applied to the steel sheet in a state where the surface temperature Ts1100 to 1200 ° C and the thickness center temperature Tc1000 to 1100 ° C satisfies the relationship of Ts-Tc> 50 ° C is determined by the hot rolling. To be 40% or more of the entire true distortion means that one or two or more rolling passes arbitrarily selected from all the rolling passes of the rough rolling and the finish rolling are performed on the steel sheet in a state satisfying the above relationship, and the above relationship is satisfied. This means that the true strain of the one or more rolling passes performed on the steel sheet in the state is 40% or more of the true strain of all the rolling passes of the rough rolling and the finish rolling.

  Further, in the hot rolling step, the true strain of the rolling applied to the steel sheet in a state where the surface temperature Ts1100 to 1200 ° C and the thickness center temperature Tc1000 to 1100 ° C satisfies the relationship of Ts-Tc> 50 ° C, As conditions for the operation management to make the true strain of the entire cold rolling 40% or more, there are mainly the following two preferable conditions.

  In the first condition, the slab cooled to 900 ° C. or less as the surface temperature was charged into a heating furnace having an ambient temperature of 1200 ° C. or more, and the slab was extracted from the heating furnace within 1 hour after the charging. The slab is subjected to the above hot rolling. As a result, a difference between the surface temperature of the slab and the center temperature of the plate thickness is ensured, and in the subsequent hot rolling step, one or more rolling passes are performed with the surface temperature Ts1100 to 1200 ° C and the plate thickness center temperature Tc1000.に 1100 ° C. is performed on the steel sheet in a state where Ts−Tc> 50 ° C. is satisfied. Then, the true strain of the one or more rolling passes performed on the steel sheet while satisfying the above relationship is set to 40% or more of the true strain of the entire hot rolling.

  In the second condition, the rolled steel sheet is cooled at a mean cooling rate of 2 ° C./s or more from 1100 ° C. or more to 600 to 750 ° C. or less at a surface temperature Ts, and 0s to 300s in a temperature range of 600 to 750 ° C. After the holding, the rolled steel sheet is heated to a temperature of 1100 ° C. or more and 1150 ° C. or less with the surface temperature Ts, and then further rolled. Specifically, for example, the steel sheet after one or more rolling passes performed in the rough rolling or the finish rolling is subjected to an average temperature of 2 ° C./s or more from 1100 ° C. or more to 600 to 750 ° C. or less as a surface temperature Ts. After cooling at a cooling rate and maintaining 0 to 300 s in a temperature range of 600 to 750 ° C., after heating the steel sheet after the above one or more rolling passes to a surface temperature Ts and heating it to a temperature of 1100 ° C. to 1150 ° C. Further, one or more rolling passes are performed in the finish rolling.

  Thereby, a difference between the surface temperature of the steel sheet and the sheet thickness center temperature after one or more rolling passes performed in the rough rolling or the finish rolling is secured, and one or more rolling passes performed in the subsequent finish rolling are performed. Is performed on the steel sheet in a state where the surface temperature Ts1100 to 1200 ° C and the thickness center temperature Tc1000 to 1100 ° C satisfy the relationship of Ts-Tc> 50 ° C. Then, the true strain of the one or more rolling passes performed on the steel sheet while satisfying the above relationship is set to 40% or more of the true strain of the entire hot rolling.

  In the above-mentioned hot rolled sheet manufacturing process, the surface temperature Ts1100 to 1200 ° C and the sheet thickness center temperature Tc1000 to 1100 ° C satisfy the relationship of Ts−Tc> 50 ° C. The true strain of the rolling applied to the steel sheet at the temperature Ts1100 to 1150 ° C is preferably 40% or more, more preferably 50% or more of the true strain of the entire hot rolling. In the hot-rolled sheet for unidirectional magnetic steel sheets, the average grain size of the crystal grains in the region near the surface of 1/10 to 1/5 layer thickness is significantly larger than that in the central region of 1/5 layer thickness to center. It can be kept. As a result, at the time of completion of the primary recrystallization, the average grain size of the crystal grains including the Goss orientation grains in the region near the surface can be remarkably coarsened as compared with the central region. The secondary recrystallized structure can be remarkably stabilized.

  In the hot rolling step, the slab is preferably heated to a surface temperature of 1250 to 1400 ° C., and then the hot slab is subjected to the hot rolling. Since the MnS already precipitated before the hot rolling can be completely solution-solutioned, the MnS is reduced in the central region from the 1/5 layer thickness to the center by performing the hot rolling. It is possible to deposit finer and more densely than the 1/10 to 1/5 layer near the surface. As a result, the growth of the crystal grains in the central region is remarkably suppressed, so that the primary recrystallized structure becomes a structure remarkably advantageous to the preferential growth of the Goss-oriented grains, and the growth of the primary recrystallized grains during the final annealing is remarkably suppressed. This is because the preferential growth of Goss-oriented grains in the vicinity of the steel sheet surface can be remarkably maintained, and the secondary recrystallized structure in the thin unidirectional magnetic steel sheet can be remarkably stabilized.

  Further, in the hot rolling step, the slab is one or more selected from the group consisting of Bi, Pb, As, and Te in mass% instead of a part of the Fe: , And one or more selected from the group consisting of Sb, Sn, and P: preferably 0.5% or less in total. In the hot rolling step, the sheet thickness center temperature of the cast slab after the heating is lower than the surface temperature, so that the grain boundary mobility is greater than the surface near region in the center region of the cast slab after the heating. Become smaller. Further, since the movement speed of the grain boundary is slowed by the segregation of the above-mentioned elements, the crystal grain size is significantly smaller in the central region of the slab after the heating than in the region near the surface. As a result, in the hot-rolled sheet for unidirectional electromagnetic steel sheets, the average grain size of the crystal grains in the region near the surface of the sheet thickness of 1/10 to 1/5 layer is larger than that in the central region of the sheet thickness of 1/5 layer to the center. Since it can be remarkably coarsened, even if the inhibitor strength decreases rapidly near the steel sheet surface during the secondary recrystallization, the preferential growth of Goss orientation grains near the steel sheet surface is remarkably maintained. This is because the secondary recrystallized structure in the thin unidirectional magnetic steel sheet can be remarkably stabilized.

2. Hot rolled sheet for unidirectional magnetic steel sheet The hot rolled sheet for unidirectional magnetic steel sheet manufactured by the method for manufacturing a hot rolled sheet for unidirectional magnetic steel sheet of the present invention is not particularly limited. The hot rolled sheet for unidirectional magnetic steel sheets described in “A. Hot rolled sheet for unidirectional magnetic steel sheets” is preferred. This is because it can be used to produce a thin unidirectional magnetic steel sheet having more excellent magnetic properties by expressing more uniform secondary recrystallization.

C. Method for Producing Unidirectional Electrical Steel Sheet The method for producing a unidirectional electrical steel sheet according to the present invention is described in the above "B. Method for producing hot rolled sheet for unidirectional electrical steel sheet". A hot-rolled sheet manufacturing step of performing a sheet manufacturing method to manufacture a hot-rolled sheet for a unidirectional electromagnetic steel sheet, and a hot-rolled sheet annealing step of performing a hot-rolled sheet annealing on the hot-rolled sheet for a unidirectional electromagnetic steel sheet, A cold rolling step of performing cold rolling on the steel sheet after the hot-rolled sheet annealing, a decarburizing annealing step of performing decarburizing annealing on the steel sheet after the cold rolling, and a finish annealing on the steel sheet after the decarburizing annealing. And a finishing annealing step to be performed.
Hereinafter, each step in the method for producing a grain-oriented electrical steel sheet of the present invention will be described.

1. Hot Rolled Sheet Manufacturing Step In the hot rolled sheet manufacturing step, the manufacturing method of the hot rolled sheet for unidirectional magnetic steel sheet described in the above “B. Method for manufacturing hot rolled sheet for unidirectional magnetic steel sheet” is performed. Manufactures hot rolled sheets for unidirectional electrical steel sheets.

  The conditions for manufacturing the hot-rolled sheet are as described in the item “B. Method for manufacturing hot-rolled sheet for unidirectional magnetic steel sheet 1. Hot rolling step”. The configuration of the hot-rolled sheet for unidirectional magnetic steel sheets is as described in the above item “A. Hot-rolled sheet for unidirectional magnetic steel sheets”.

2. Hot Rolled Sheet Annealing Step In the hot rolled sheet annealing step, the hot rolled sheet for the unidirectional magnetic steel sheet is subjected to hot rolled sheet annealing.

The hot-rolled sheet annealing conditions are not particularly limited, but in the hot-rolled sheet annealing step, the hot-rolled sheet for unidirectional magnetic steel sheets is maintained in a temperature range of 900 to 1050 ° C for 60 s or more. preferable. This is because by performing hot-rolled sheet annealing under such conditions, AlN precipitates and acts as an inhibitor, and as a result, the degree of integration in the secondary recrystallization structure in the Goss orientation is significantly improved.
In the hot-rolled sheet annealing step, the steel sheet after the finish hot-rolling may be wound into a coil, and may be held in the above-mentioned temperature range by self-held heat, or may be subjected to annealing on the hot-rolled sheet after cooling. May be maintained in the above temperature range.

3. Cold Rolling Step In the cold rolling step, the steel sheet after the hot-rolled sheet annealing is subjected to cold rolling.

4. Decarburizing annealing step In the decarburizing annealing step, the steel sheet after the cold rolling is subjected to decarburizing annealing.

  The decarburizing annealing conditions are not particularly limited, but in the decarburizing annealing step, the cold-rolled steel sheet is heated from a temperature of 350 ° C or less to a temperature of 700 ° C or more and 850 ° C or less. It is preferable that the steel sheet after the cold rolling is subjected to the decarburizing annealing after heating at a heating rate of 100 ° C./s or more in the temperature process. This is because, by the action of rapid heating at an elevated temperature during primary recrystallization, when primary recrystallization is completed, Goss-oriented grains can be made larger in the entire sheet thickness direction than primary crystal grains having random orientations other than Goss. . This produces a synergistic effect with the action of the structure of the hot-rolled sheet in the present invention, so that at the time of completion of the primary recrystallization, the average grain size of the Goss-oriented grains in the region near the surface is significantly increased, and the secondary recrystallization Even if the inhibitor strength near the steel sheet surface sometimes decreases rapidly, it can be expected that the preferential growth of Goss-oriented grains near the steel sheet surface is remarkably maintained. As a result, the secondary recrystallized structure in the thin unidirectional magnetic steel sheet can be remarkably stabilized.

5. Finish Annealing Step In the above-described finish annealing step, the steel sheet after the decarburizing annealing is subjected to finish annealing. As a result, secondary recrystallization occurs in the steel sheet after the decarburizing annealing to obtain a unidirectional magnetic steel sheet.

6. Others The method for producing a grain-oriented electrical steel sheet of the present invention may further include a step generally performed in the method for producing a grain-oriented electrical steel sheet. Typical steps other than those described above include melting, casting, hot rolling, pickling, nitriding annealing, application of an annealing separator, purification annealing, and application of an insulating film. These steps may be performed in a single pass through a single manufacturing apparatus. These steps may be performed by repeating a certain step a plurality of times or by changing the order.

  In the method for producing a grain-oriented electrical steel sheet according to the present invention, when single AlN is precipitated by hot rolling and hot-rolled sheet annealing and the precipitation density of AlN is insufficient, nitriding is performed after the decarburizing annealing step and before the finish annealing step. A nitriding annealing process for performing annealing may be included. Thereby, it is possible to prevent the precipitation density of AlN from becoming insufficient.

  In the nitriding annealing step, it is preferable to perform nitriding annealing by holding the steel sheet after the decarburizing annealing in a temperature range of 700 ° C to 800 ° C for 30 s to 300 s.

  The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and has the same effect. Within the technical scope of

  Hereinafter, the present invention will be specifically described by way of examples and comparative examples.

(Example 1)
The slabs of steel Nos. 1 to 16 and steel Nos. 20 to 36 having the chemical components shown in Table 1 below were charged into a heating furnace having an ambient temperature of 1320 ° C. and maintained for 30 minutes to obtain a surface temperature. After heating to the slab heating temperature Ts0 shown in 2-1, the slab extracted from the heating furnace was subjected to rough rolling and finish rolling under the conditions shown in Table 2-1 below. Moreover, after cooling the slabs of steel Nos. 17 to 19 having the chemical components shown in Table 1 to 850 ° C. as the surface temperature, the slabs were charged into a heating furnace having an ambient temperature of 1320 ° C. and held for 30 minutes. After the surface temperature was increased to the slab heating temperature Ts0 shown in Table 2-1 below, the slab extracted from the heating furnace was subjected to rough rolling and finish rolling under the conditions shown in Table 2-1 below.

In the above rough rolling, the surface temperature Ts1 [° C.], the thickness center temperature Tc1 [° C.], and the thickness t1 [mm] of the steel sheet on the entry side of the slabs of steel numbers 1 to 36 are shown in Table 2-1 below. The first rolling pass was performed as shown in FIG. Further, in the rough rolling and the finish rolling, in a plurality of rolling passes continuously performed on the steel sheet in a state where the surface temperature Ts1100 to 1200 ° C and the sheet thickness center temperature Tc1000 to 1100 ° C satisfy the relationship of Ts-Tc> 50 ° C. The steel sheet surface temperature Tss [° C.], the sheet thickness center temperature Tcs [° C.], Tss-Tcs [° C.], and the sheet thickness ts [mm] at the entry side of the first rolling pass, and the steel sheet satisfying the above relations Surface temperature Tsf [° C.], sheet thickness center temperature Tcf [° C.], Tsf-Tcf [° C.], and sheet thickness tf [ mm] as shown in Table 2-1 below, a plurality of rolling passes continuously performed on the steel sheet in a state satisfying the above relationship.
In hot rolling with steel numbers where Tss, Tcs, and ts are Ts1, Tc1, and t1, the first rolling pass in the rough rolling is the same as that in the rough rolling and finish rolling. This corresponds to the first rolling pass in a plurality of rolling passes continuously performed on the steel sheet in a state where is satisfied.

  As described above, a hot-rolled sheet having a finished sheet thickness tff of 2.3 mm was obtained by performing the rough rolling and the finish rolling. Further, the true strain ep [-] of the rolling performed in a plurality of rolling passes continuously performed on the steel sheet while satisfying the above relationship, and the true strain et [of the entire hot rolling including the rough rolling and the finish rolling described above. -] Are as shown in Table 2-1 below. In addition, the ratio Ce (ep / et × 100) [%] of the true strain ep to the true strain et was as shown in Table 2-1 below.

Furthermore, the average grain size Ds [μm] of the crystal grains, the average grain size ds [nm] of MnS, and the distribution density of MnS in the region near the surface of the obtained hot-rolled sheet having a thickness of 1/10 to 1/5 layer ρs [μm ⁻² ], average grain size Di [μm] of crystal grains in the central region from the １ ／ layer thickness to the center of the obtained hot-rolled sheet, MnS average grain size di [nm], and MnS Was investigated for the distribution density ρi [μm ⁻² ]. The ratio Ds / Di [-] of the average grain diameter Ds of the crystal grains in the vicinity of the surface to the average grain diameter Di of the crystal grains in the center area, and the average of MnS in the vicinity of the surface with respect to the average grain diameter di of MnS in the center area. The ratio ds / di [−] of the particle diameter ds and the ratio ρi / ρs [−] of the distribution density ρi of MnS in the central region to the distribution density ρs of MnS in the region near the surface were calculated. The average grain size of the crystal grains is a value obtained by calculating and averaging the diameters of circles having the same area with respect to the projected area for a plurality of observed crystal grains, and the average grain size of MnS is the same as the projected area for a plurality of observed MnS. The diameter of each area circle was determined and averaged, and the distribution density of MnS was a value obtained by dividing the number of MnS counted by observing a mirror-polished cross section by the area of the observation visual field. The results obtained are shown in Table 2-2 below.

  Since the true strain ratio Ce of the hot-rolled sheet of steel No. 20 was lower than the range of the present invention, the average grain size ratio Ds / Di of the crystal grains was lower than the range of the present invention. In addition, since the hot rolled sheet of steel No. 21 has a low Ts0, the entire hot rolling is performed in a state where Ts1100 to 1200 ° C and Tc1000 to 1100 ° C do not satisfy the relationship of Ts−Tc> 50 ° C. Therefore, the ratio Ds / Di of the average grain size of the crystal grains was below the range of the present invention. Further, in the hot-rolled sheet of steel No. 22, the thickness center temperature Tcs increased during the rough rolling, so that Ts1100 to 1200 ° C and Tc1000 to 1100 ° C continuously satisfies the relationship of Ts-Tc> 50 ° C. The true strain ep applied in a plurality of rolling passes performed at the same time was reduced, and the ratio Ds / Di of the average grain size of the crystal grains was below the range of the present invention.

  Further, in the hot-rolled sheet of steel No. 24, since the slab heating temperature Ts0 was lower than 1250 to 1400 ° C. which is a preferable range of the present invention, the dispersion of MnS was insufficient, and the ratio of the average particle size of MnS ds / di. The ratio ρi / ρs of the distribution density was lower than the preferred range of the present invention, and the ratio Ds / Di of the average grain size of the crystal grains was lower than the range of the present invention.

  Further, in the hot-rolled sheet of steel No. 25, the slab heating temperature Ts0 exceeded the preferred range of the present invention, 1250 to 1400 ° C., so the ratio of the average particle diameter of MnS ds / di and the ratio of the distribution density ρi / ρs Was below the preferred range of the present invention, and the ratio Ds / Di of the average grain size of the crystal grains was below the range of the present invention.

  Further, in the hot-rolled sheet of steel No. 26, not only the C content exceeded the range of the present invention but also the true strain ratio Ce was lower than the range of the present invention. Di was below the scope of the present invention. Further, in the hot-rolled sheets of steel Nos. 27 and 28, not only the Si content was out of the range of the present invention but also the true strain ratio Ce was lower than the range of the present invention. / Di was below the range of the present invention.

  Moreover, since the Mn content of the hot-rolled sheets of steel Nos. 29 and 30 was outside the range of the present invention, the ratio Ds / Di of the average grain size of the crystal grains was lower than the range of the present invention. Further, in the hot-rolled sheets of steel Nos. 31 and 32, since the S content was outside the range of the present invention, the ratio Ds / Di of the average grain size of the crystal grains was lower than the range of the present invention.

  The hot rolled sheets of steel Nos. 33 and 34 had an Al content outside the range of the present invention. In Example 3 described below, secondary recrystallization did not occur due to finish annealing held at 1200 ° C. A grain-oriented electrical steel sheet having an extremely poor density was obtained. Further, in the hot-rolled sheets of steel Nos. 35 and 36, the N content was out of the range of the present invention, and in Example 3 described below, secondary recrystallization did not occur due to finish annealing held at 1200 ° C. A grain-oriented electrical steel sheet having an extremely poor density was obtained.

  On the other hand, the hot-rolled sheets of steel Nos. 1 to 19 which were hot-rolled under the conditions satisfying the requirements in the method for producing a hot-rolled sheet for unidirectional magnetic steel sheets of the present invention have an average grain size of crystal grains. Is within the range of the present invention, and the ratio ds / di of the average particle size of MnS and the ratio ρi / ρs of the distribution density are within the preferable range of the present invention.

(Example 2)
The slabs of steel Nos. 37 to 57 having the chemical compositions shown in Table 3 below were charged into a heating furnace having an atmosphere temperature of 1320 ° C. and held for 30 minutes to obtain a surface temperature, and the casting shown in Table 4-1 below was performed. After heating to the slab heating temperature Ts0, the cast slab extracted from the heating furnace was subjected to rough rolling and finish rolling under the conditions shown in Table 4-1 below.

  In the rough rolling, the first rolling pass was performed with the thickness t1 [mm] of the steel sheet on the entry side as shown in Table 4-1 below. Further, a plurality of rolling passes continuously performed on the steel sheet in a state where the surface temperature Ts1100 to 1200 ° C and the sheet thickness center temperature Tc1000 to 1100 ° C satisfy the relationship of Ts−Tc> 50 ° C are first performed in the plurality of rolling passes. Surface temperature Tss [° C.], sheet thickness center temperature Tcs [° C.], Tss-Tcs [° C.], and sheet thickness ts [mm] of the steel sheet on the entry side of the rolling pass, and final values in the plurality of rolling passes. The surface temperature Tsf [° C.], the thickness center temperature Tcf [° C.], Tsf-Tcf [° C.], and the thickness tf [mm] of the steel sheet at the exit side of the rolling pass are set as shown in Table 4-1 below. went. In the rough rolling, the true strain epr [-] of the rolling performed in a plurality of rolling passes continuously performed on the steel sheet in a state satisfying the above relationship is as shown in Table 4-1 below. By performing the rough rolling, a rough-rolled sheet having a thickness tff1 of 6.0 mm or 8.0 mm after the rough rolling was obtained.

  Then, as shown in the conditions shown in Table 4-1 below, the rough-rolled sheet obtained by the above-mentioned rough rolling is cooled to a surface temperature from a cooling start speed of 1100 ° C. [° C.] to a cooling reaching speed of 550 to 800 ° C. [ ° C] at an average cooling rate of 1.5 to 2.5 ° C / sec [° C / sec], and then maintained isothermally at the above cooling attainment rate for a holding time of 180 to 600 sec [sec] to obtain a surface temperature. After heating to the temperature [° C.] at which the temperature was raised again, the above finish rolling was performed under the conditions shown in Table 4-1 below.

  In the finish rolling, the plurality of rolling passes continuously performed on the steel sheet in a state where the surface temperature Ts1100 to 1200 ° C and the sheet thickness center temperature Tc1000 to 1100 ° C satisfy the relationship of Ts-Tc> 50 ° C, Surface temperature Tss [° C.], sheet thickness center temperature Tcs [° C.], Tss-Tcs [° C.], and sheet thickness ts [mm] of the steel sheet on the entry side of the first rolling pass in Table 4-1 shows the surface temperature Tsf [° C.], the thickness center temperature Tcf [° C.], Tsf-Tcf [° C.], and the thickness tf [mm] of the steel sheet at the exit side of the final rolling pass in the rolling pass. Was performed as shown in FIG. In the finish rolling, the true strain epf [-] of rolling performed in a plurality of rolling passes continuously performed on the steel sheet in a state satisfying the above relationship is as shown in Table 4-1 below. By performing the finish rolling, a hot-rolled plate having a finished plate thickness tff2 of 2.3 mm was obtained.

  In addition, the true strain et [-] of the entire hot rolling including the rough rolling and the finish rolling was as shown in Table 4-1 below. Further, the total true strain ep of the true strain epr applied to the steel sheet in a state where the above relationship is satisfied in the rough rolling and the true strain epf applied to the steel sheet in a state where the above relationship is satisfied in the finish rolling is shown in Table 4 below. -1. Further, the ratio Ce (ep / et × 100) [%] of the true strain ep to the true strain et was as shown in Table 4-1 below.

Furthermore, the average grain size Ds [μm] of the crystal grains, the average grain size ds [nm] of MnS, and the distribution density of MnS in the region near the surface of the obtained hot-rolled sheet having a thickness of 1/10 to 1/5 layer ρs [μm ⁻² ], average grain size Di [μm] of crystal grains in the central region from the １ ／ layer thickness to the center of the obtained hot-rolled sheet, MnS average grain size di [nm], and MnS Was investigated for the distribution density ρi [μm ⁻² ]. The ratio Ds / Di [-] of the average grain diameter Ds of the crystal grains in the vicinity of the surface to the average grain diameter Di of the crystal grains in the center area, and the average of MnS in the vicinity of the surface with respect to the average grain diameter di of MnS in the center area. The ratio ds / di [−] of the particle diameter ds and the ratio ρi / ρs [−] of the distribution density ρi of MnS in the central region to the distribution density ρs of MnS in the region near the surface were calculated. The average grain size of the crystal grains is a value obtained by calculating and averaging the diameters of circles having the same area with respect to the projected area for a plurality of observed crystal grains, and the average grain size of MnS is the same as the projected area for a plurality of observed MnS. The diameter of each area circle was determined and averaged, and the distribution density of MnS was a value obtained by dividing the number of MnS counted by observing a mirror-polished cross section by the area of the observation visual field. The results obtained are shown in Table 4-2 below.

  Since the true strain ratio Ce was lower than the range of the present invention, the ratio Ds / Di of the average grain size of the hot rolled sheets of steel numbers 56 and 57 was lower than the range of the present invention.

  On the other hand, the hot-rolled sheets of steel Nos. 37 to 50 which were hot-rolled under the conditions satisfying the requirements in the method for producing a hot-rolled sheet for unidirectional electromagnetic steel sheets of the present invention have an average grain size of crystal grains. The ratio Ds / Di was within the range of the present invention, and the ratio ds / di of the average particle size of MnS and the ratio ρi / ρs of the distribution density were within the preferable ranges of the present invention.

  Above all, for the hot rolled sheets of steel Nos. 37 to 46 satisfying the preferable cooling rate after rough rolling, the cooling reaching temperature, and the holding time of the present invention, the ratio Ds / Di of the average grain size of the crystal grains is more preferable. It became. Among them, the hot-rolled sheets of steel Nos. 37, 40, and 42 having the true strain ratio Ce of 40 to 42% have the same chemical components and the true strain ratio Ce of 40 to 42%. The ratio Ds / Di of the average grain size of the crystal grains was more preferable range than steel number 1. Similarly, the hot-rolled sheets of steel Nos. 38, 41 and 44 having the true strain ratio Ce of 50 to 52% have the same chemical composition and the true strain ratio Ce of 50 to 52%. The ratio Ds / Di of the average grain size of the crystal grains was in a more preferable range than that of steel No. 3.

(Example 3)
A part of the hot-rolled sheets manufactured in Examples 1 and 2 was wound around a coil at a winding temperature CT [° C.] shown in Table 5 below, and then hot-rolled under the conditions shown in Table 5 below. Plate annealing was performed. Specifically, for hot rolled sheets of steel numbers 1, 3, 6, 17, 19, 37, 38, 40, 45, 20, 26, 28, 33, 34, 35, 36, and 56, 550 ° C. The coil wound at the winding temperature CT was heated to 1150 ° C., and then subjected to hot rolled sheet annealing at 900 ° C. for 80 seconds. In addition, as for the hot rolled sheets of steel numbers 43, 44, and 46, the coil wound at the winding temperature CT of 950 ° C. was subjected to hot rolled sheet annealing in which the coil was maintained at the winding temperature CT for 80 seconds. After annealing these hot-rolled sheets, as shown in Table 5 below, each hot-rolled annealed sheet was subjected to cold rolling to obtain a cold-rolled sheet having a thickness tffff of 0.23 mm. . After the cold rolling, the cold rolled sheet was subjected to decarburizing annealing under the conditions shown in Table 5 below. Specifically, for hot rolled sheets other than steel No. 40, decarburization annealing is performed at 835 ° C. for 120 seconds, and when the temperature is raised to 835 ° C. for decarburization annealing, the temperature is raised from 300 ° C. to 750 ° C. During the heating process, the heating rate was set to 10 ° C./sec. In addition, the hot rolled sheet of steel No. 40 is subjected to decarburizing annealing at 835 ° C. for 120 seconds, and when the temperature is raised to 835 ° C. for decarburizing annealing, the temperature is raised from 300 ° C. to 750 ° C. , The temperature was raised at a rate of 200 ° C./sec. After performing decarburization annealing, the temperature was raised to 1200 ° C., and finish annealing was performed at 1200 ° C. Thereby, a grain-oriented electrical steel sheet was manufactured.

  A magnetic measurement test piece of 60 mm x 300 mm was sheared from the grain-oriented electrical steel sheet manufactured in this manner, subjected to strain relief annealing at 700 ° C, and then the magnetic flux density B8 [T] was measured. The results are shown in Table 5 below. In Table 5 below, the secondary recrystallization stability is indicated by a circle assuming that the secondary recrystallization is stabilized in the samples with B8 of 1.90 T or more, and the secondary recrystallization stability is shown in the samples with B8 of 1.95 T or more. The secondary recrystallization stability is indicated by ◎ as the crystal is further stabilized, and the secondary recrystallization stability is indicated as で は in the sample in which B8 is less than 1.90 T as the secondary recrystallization is not stabilized. In addition, those for which secondary recrystallization was not obtained were indicated by x marks for secondary recrystallization stability.

  As shown in Table 2-1 above, the true strain ratio Ce was lower than the range of the present invention in the hot-rolled sheets of steel Nos. 20 and 26, and therefore, the ratio Ds / Di of the average grain size of the crystal grains was lower than that of the present invention. As a result, in the grain-oriented electrical steel sheets of steel Nos. 20 and 26, B8 was less than 1.90T and was inferior.

  On the other hand, in the hot-rolled sheet of Steel No. 1 having the same chemical composition as Steel No. 20, since the true strain ratio Ce was within the range of the present invention, the ratio Ds / Di of the average grain size of the crystal grains was low. As a result of being within the scope of the present invention, in the grain-oriented electrical steel sheet of steel No. 1, B8 was higher than 1.90T. Further, the hot-rolled sheet of Steel No. 3 has the same chemical composition as Steel No. 1, but unlike Steel No. 1, the true strain ratio Ce is 50% or more of the preferred range of the present invention, and As a result of the average particle diameter ratio Ds / Di being 1.20 or more, which is the preferred range of the present invention, B8 was 1.946T, which was higher than steel number 1. The hot-rolled sheet of steel No. 6 has a true strain ratio Ce similar to that of steel No. 1, but differs from steel No. 1 in that it contains Bi, a segregating element, and has an average grain size of crystal grains. As a result of the ratio Ds / Di being larger than steel number 1, B8 was 1.951T, which was higher than steel number 1. Further, the hot-rolled sheet of steel No. 17 has the same chemical composition as steel No. 1, and the true strain ratio Ce is almost the same as steel No. 1, but unlike steel No. 1, the slab is heated to the surface temperature. After cooling to 850 ° C., the sample was placed in a heating furnace having an ambient temperature of 1320 ° C., and maintained for 30 minutes, so that the surface temperature was increased to the slab heating temperature Ts0 shown in Table 2-1 above. It was subjected to the above rough rolling and finish rolling, and as a result of the ratio Ds / Di of the average grain size of the crystal grains being larger than steel number 1, B8 was 1.944T, which was higher than steel number 1.

  The hot rolled sheet of steel No. 19 is different from steel No. 1 in that it contains the segregating elements Bi and Sn, and the slab is cooled to 850 ° C. at the surface temperature, followed by heating at an ambient temperature of 1320 ° C. After being charged into a furnace and held for 30 minutes, the surface temperature was increased to the slab heating temperature Ts0 shown in Table 2-1 above, and then the above rough rolling and finish rolling were performed. The ratio Ce is at least 50% of the preferred range of the present invention. In the unidirectional electrical steel sheet of steel No. 19, B8 was 1.960T, which was significantly higher than steel No. 1.

  Further, in the hot-rolled sheet of steel No. 26, not only the C content exceeded the range of the present invention, but also the true strain ratio Ce was lower than the range of the present invention, and the ratio Ds of the average grain size of the crystal grains was Ds. As a result of / Di falling below the range of the present invention, in the case of the grain-oriented electrical steel sheet No. 26, B8 was extremely inferior to 1.844T.

  Further, in the hot-rolled sheet of steel No. 27, not only the Si content exceeded the range of the present invention, but the true strain ratio Ce was lower than the range of the present invention, and the ratio Ds of the average grain size of crystal grains was Ds. As a result of the fact that / Di was less than the range of the present invention, remarkable cracking occurred in the above cold rolling, and it was not possible to produce a grain-oriented electrical steel sheet.

  In the hot-rolled sheets of steel Nos. 33 and 34, the true strain ratio Ce falls within the range of the present invention, and the ratio Ds / Di of the average grain size of the crystal grains falls within the range of the present invention. Since the amount was out of the range of the present invention, the distribution density of AlN was not sufficient and secondary recrystallization did not occur. Similarly, in the hot-rolled sheets of steel Nos. 35 and 36, the true strain ratio Ce is within the range of the present invention, and the ratio Ds / Di of the average grain size of the crystal grains is within the range of the present invention. The content was out of the range of the present invention, and the distribution density of AlN was not sufficient, and secondary recrystallization did not occur.

  Further, in the hot-rolled sheet of steel No. 56, the ratio Ce of the true strain in the rough rolling and the finish rolling is lower than the range of the present invention, and the ratio Ds / Di of the average grain size of the crystal grains is in the range of the present invention. As a result, B8 was inferior to 1.868T.

  On the other hand, the hot-rolled sheets of steel numbers 37, 38, 40, 43, 44, 45, and 46 have a true strain ratio Ce in the rough rolling and the finish rolling within the range of the present invention, and As a result of the ratio Ds / Di of the average particle diameter of the particles being within the range of the present invention, B8 exceeded 1.950T, and good magnetic properties were obtained. Among these hot-rolled sheets, the hot-rolled sheet of steel No. 38 has a true strain ratio Ce in the rough rolling and the finish rolling of 50% or more within a preferable range of the present invention, and has an average grain size of crystal grains. As a result of the diameter ratio Ds / Di being larger than steel No. 37, B8 was 1.958T, which was higher than steel No. 37. Further, the hot-rolled sheet of steel No. 40 has a true strain ratio Ce in the rough rolling and the finish rolling similar to that of steel No. 37, and a ratio Ds / Di of the average grain size of the crystal grains is equal to that of steel No. 37. However, unlike steel No. 37, when the temperature was raised to 835 ° C. for decarburizing annealing, the temperature was raised from 300 ° C. to 750 ° C., and the heating rate was 200 ° C./sec. As a result, B8 was 1.960T, which was higher than steel number 37. Further, the hot-rolled sheet of steel No. 43 has a true strain ratio Ce in the rough rolling and the finish rolling that is substantially the same as steel No. 37, but differs from steel No. 37 at a winding temperature CT of 950 ° C. The rolled coil was subjected to hot-rolled sheet annealing at a winding temperature CT of 80 seconds, and as a result, B8 became 1.956T, which was higher than steel number 37. Further, the hot-rolled sheet of steel No. 45 has a true strain ratio Ce in the rough rolling and the finish rolling similar to that of steel No. 37, and a ratio Ds / Di of the average grain size of crystal grains is equal to that of steel No. 37. Although it was about the same, unlike steel No. 37, as a result of containing the segregating element Bi, B8 was 1.963T, which was higher than steel No. 37.

  Further, the hot-rolled sheets of steel Nos. 44 and 46 have a true strain ratio Ce in the rough rolling and the finish rolling of 50% or more within a preferable range of the present invention, and a ratio Ds / Di of the average grain size of the crystal grains. Became larger than steel No. 37, and, unlike steel No. 37, the coil wound at a winding temperature CT of 950 ° C. was subjected to hot-rolled sheet annealing at a winding temperature CT of 80 sec. Was 1.970 or more, and extremely good magnetic properties were obtained.

Claims (10)

In mass%, C: 0.1% or less, Si: 2.5 to 4.0%, Mn: 0.05 to 0.1%, S: 0.01 to 0.04%, Al: 0.01 -0.05%, and N: 0.001 to 0.030%, the balance being a hot-rolled sheet for a grain-oriented electrical steel sheet comprising Fe and unavoidable impurities,
Ri der ratio 1.10 of the average grain size of the crystal grains near the surface regions of the plate thickness 1 / 10-1 / 5-layer to the average particle diameter of the crystal grains in the central region of thickness 1/5 layer to the center ,
A ratio of the average particle size of MnS in the region near the surface of the 1/10 to 1/5 layer with respect to the average particle size of MnS in the central region of the thickness of 1/5 layer to the center is 1.10 or more;
The ratio of the distribution density of MnS in the central region from the 1 / 5th layer thickness to the center with respect to the distribution density of MnS in the region near the surface of the 1/10 to 1/5 layer thickness is 1.10 or more. Hot rolled sheet for unidirectional magnetic steel sheets. One or more selected from the group consisting of Bi, Pb, As, and Te in mass% instead of a part of the Fe: 0.0002% to 0.02% in total, and Sb; The heat for a grain-oriented electrical steel sheet according to claim 1, wherein one or more selected from the group consisting of Sn and P: a total of 0.0004% or more and 0.5% or less. Rolled board. A method for producing a hot-rolled sheet for a grain-oriented electrical steel sheet according to claim 1,
In mass%, C: 0.1% or less, Si: 2.5 to 4.0%, Mn: 0.05 to 0.1%, S: 0.01 to 0.04%, Al: 0.01 Surface temperature Ts1100 to 1200 ° C. in a hot rolling step of performing hot rolling on a slab containing 0.05% and N: 0.001 to 0.030%, with the balance being Fe and unavoidable impurities. In addition, the true strain of the rolling applied to the steel sheet in a state where the thickness center temperature Tc1000 to 1100 ° C satisfies the relationship of Ts−Tc> 50 ° C is set to be 40% or more of the true strain of the entire hot rolling. A method for producing a hot-rolled sheet for a grain-oriented electrical steel sheet. In the hot rolling step, the slab cooled to 900 ° C. or less as a surface temperature was charged into a heating furnace having an atmospheric temperature of 1200 ° C. or more, and extracted from the heating furnace within 1 hour after charging. The method for producing a hot-rolled sheet for a grain-oriented electrical steel sheet according to claim 3 , wherein the hot rolling is performed on the slab. In the hot rolling step, the rolled steel sheet is cooled at a mean cooling rate of 2 ° C./s or more from 1100 ° C. or more to 600 to 750 ° C. or less at a surface temperature Ts, and 0s to 600 ° C. to 750 ° C. after 300s retained, unidirectional according to claim 3 or 4, characterized in further applying the rolled after heating until said temperature steel plate with a surface temperature Ts of 1100 ° C. or higher 1150 ° C. or less after the rolling Manufacturing method of hot rolled sheet for electrical steel sheet. In the hot rolling step, after heating the slab to 1,250 to 1,400 ° C. in the surface temperature, the claims 3 to 5, characterized in that performing the hot rolling to the slab after said heating The method for producing a hot-rolled sheet for a grain-oriented electrical steel sheet according to any one of the above. The slab is one or more selected from the group consisting of Bi, Pb, As, and Te in mass% instead of a part of the Fe: 0.0002% or more and 0.02% in total. hereinafter, as well as Sb, Sn, and one or more selected from the group consisting of P: claim claim 3, characterized in that it contains further 0.5% 0.0004% or more in total 6 The method for producing a hot-rolled sheet for a grain-oriented electrical steel sheet according to any one of the above. A hot rolled sheet manufacturing process for manufacturing a hot rolled sheet for a unidirectional magnetic steel sheet by performing the method for manufacturing a hot rolled sheet for a unidirectional magnetic steel sheet according to any one of claims 3 to 7 ,
Hot-rolled sheet annealing step of performing hot-rolled sheet annealing on the hot-rolled sheet for unidirectional magnetic steel sheet,
A cold rolling step of performing cold rolling on the steel sheet after the hot-rolled sheet annealing,
A decarburizing annealing step of performing decarburizing annealing on the steel sheet after the cold rolling,
A finishing annealing step of subjecting the steel sheet after the decarburizing annealing to finish annealing. In the hot rolled sheet annealing process, according to claim 8, characterized by applying hot rolled sheet sintered pure holding 60s than the grain-oriented electrical steel sheet for hot-rolled sheet in the temperature range of 900 to 1050 ° C. one Manufacturing method of grain-oriented electrical steel sheet. In the decarburizing annealing step, the steel sheet after the cold rolling was heated at a heating rate of 100 ° C./s or more in a heating process of increasing the temperature from 350 ° C. or less to a temperature of 700 ° C. or more and 850 ° C. or less. The method for producing a grain-oriented electrical steel sheet according to claim 8 or 9 , wherein the steel sheet after the cold rolling is subjected to the decarburizing annealing.