JP4599843B2 - Method for producing non-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a method for producing a non-oriented electrical steel sheet. In particular, the present invention relates to a method for producing a non-oriented electrical steel sheet suitable as an iron core material for electric vehicles, air conditioners, generators and the like.

  Because of the need to reduce global warming gas, it is important to develop new products that consume less energy in the fields of automobiles and home appliances. For example, in the automobile field, there are low fuel consumption vehicles such as a hybrid drive vehicle (HEV) combining a gasoline engine and a motor, and a motor drive electric vehicle. In the field of home appliances, there are high-efficiency air conditioners, refrigerators, etc. with low annual electricity consumption. These common technologies are motors, and high efficiency of the motors is an important technology. As one of the technologies supporting the high efficiency of the motor, it is known to reduce the iron loss of the non-oriented electrical steel sheet as the iron core.

  Various methods have been proposed for reducing iron loss of non-oriented electrical steel sheets. The method is roughly divided into the first to third methods. The first method is a method of increasing eddy current loss by increasing the specific resistance of the steel sheet by increasing components such as Si and Al. The second method is a method of reducing the hysteresis loss component by reducing the impurity components such as C, N, S, and Ti in the steel as much as possible and increasing the crystal grain size of the steel. The third method is a method of controlling a texture that is advantageous for magnetic properties by subjecting steel to hot-rolled sheet annealing to increase the crystal grain size before cold rolling.

  However, the hot-rolled steel sheet with increased purity by increasing the amount of Si and Al as in the first method and reducing the impurity components as much as in the second method is as in the third method. Since the crystal grain size is increased by annealing the hot-rolled sheet, the toughness of the hot-rolled steel sheet is significantly reduced. For this reason, there is a problem that the yield of the steel sheet is remarkably lowered due to breakage during cold rolling. Moreover, as a technique for avoiding this, there is a warm rolling technique at 300 ° C. to 600 ° C. However, there is a problem that special equipment is required and the manufacturing cost increases.

  Patent Document 1 discloses a technique for increasing the equiaxed crystal ratio of a continuously cast slab when manufacturing a non-oriented electrical steel sheet. In the invention described in Patent Document 1, since the hot-rolled sheet annealing step is omitted, breakage during cold rolling is suppressed. However, the magnetic properties are not sufficiently improved.

Japanese Patent Publication No. 7-33544

  This invention is made | formed in view of the said problem, and it aims at providing the manufacturing method of the non-oriented electrical steel sheet which was excellent in cold-rollability and excellent in the magnetic characteristic.

In order to solve the above problems, the present invention provides, in mass%, C: 0.004% or less, Si: 1.5% to 4%, Mn: 0.1% to 2%, P: 0.2% Hereinafter, S: 0.002% or less, Al: 0.1% to 3%, N: 0.003% or less, O: 0.003% or less, B: 0.0050% or less, Ti: 0.003% Hereinafter, steel containing Ca: 0.005% or less, Sn, Sb, Si and Al in the steel satisfy the following formulas (1) and (2), and the balance is substantially composed of Fe and impurities. The step of hot-rolling the ingot or steel slab, the step of subjecting the hot-rolled steel sheet obtained by hot rolling to hot-rolled sheet annealing, and the hot-rolled steel sheet subjected to the hot-rolled sheet annealing once or intermediate annealing A non-directional method comprising a step of performing cold rolling twice or more sandwiched between and a step of annealing the cold-rolled steel sheet obtained by the cold rolling. A method for producing an electrical steel sheet, wherein the equiaxed crystal ratio of the steel ingot or steel slab is 30% or more, the thickness of the hot-rolled steel sheet is 2.5 mm or less, and the annealing temperature of the hot-rolled sheet annealing is further set. Provided is a method for producing a non-oriented electrical steel sheet, characterized by being 750 ° C. or higher and 1100 ° C. or lower.
Sn + Sb ≦ 0.1% (1)
Si + Al ≧ 2% (2)
(In the formula (1) and the formula (2), Sn, Sb, Si and Al are numerical values representing the content of each element in mass%.)

  In the method for producing a non-oriented electrical steel sheet according to the present invention, by increasing the equiaxed crystal ratio of the slab and reducing the thickness of the hot-rolled steel sheet, it has excellent magnetic properties without breaking during cold rolling. A non-oriented electrical steel sheet can be manufactured.

  According to the present invention, a non-oriented electrical steel sheet having excellent magnetic properties can be produced without breaking during cold rolling.

  Hereinafter, the manufacturing method of the non-oriented electrical steel sheet of this invention is demonstrated in detail.

“%” Indicating the content of each element in the steel means “% by mass” unless otherwise specified . Et al is sometimes a steel ingot or slab of the slab. Moreover, the steel plate which gave the hot-rolled sheet annealing to the hot-rolled steel sheet manufactured from the slab is called a hot-rolled annealed sheet.

The manufacturing method of the non-oriented electrical steel sheet according to the present invention is, in mass%, C: 0.004% or less, Si: 1.5% to 4%, Mn: 0.1% to 2%, P: 0.2. %: S: 0.002% or less, Al: 0.1% to 3%, N: 0.003% or less, O: 0.003% or less, B: 0.0050% or less, Ti: 0.003 %, Ca: 0.005% or less, Sn, Sb, Si and Al in the steel satisfy the following formulas (1) and (2), and the balance is substantially composed of Fe and impurities. A step of hot-rolling a steel ingot or steel slab, a step of subjecting the hot-rolled steel sheet obtained by hot rolling to hot-rolled sheet annealing, and a hot-rolled steel sheet subjected to the hot-rolled sheet annealing once or in the middle A method comprising two or more cold rolling steps with annealing and a step of annealing the cold-rolled steel sheet obtained by the cold rolling. A method for producing a heat-resistant electrical steel sheet, wherein the steel ingot or steel piece has an equiaxed crystal ratio of 30% or more, the thickness of the hot-rolled steel sheet is 2.5 mm or less, and the annealing temperature of the hot-rolled sheet annealing Is 750 ° C. or higher and 1100 ° C. or lower.
Sn + Sb ≦ 0.1% (1)
Si + Al ≧ 2% (2)
In the above formulas (1) and (2), Sn, Sb, Si and Al are numerical values representing the content of each element in mass%.

  The present inventors have a viewpoint that there is a method for suppressing breakage that occurs when cold-rolling a hot-rolled steel sheet for a non-oriented electrical steel sheet having a high specific resistance with good magnetic properties and a small amount of impurity components. Since then, we have accumulated extensive research. As a result, by reducing specific impurity components, increasing the equiaxed crystal ratio of the steel ingot or billet, and reducing the thickness of the hot-rolled steel sheet, the cold rolling property is excellent and the magnetic properties are excellent. It has been found that a grain-oriented electrical steel sheet can be obtained. Hereinafter, the knowledge that has led to the present invention and the experimental results leading to this will be described.

  In the converter-RH-continuous casting process, the main components are C: 0.002%, Si: 3.0%, Mn: 0.2%, P: 0.01%, S: 0.0006%, Al: 0.7%, N: 0.002%, O: 0.002%, B: <0.0003%, Ti: 0.002%, Ca: <0.0003%, Sn: 0.001% , Sb: <0.001%, slab having a thickness of 250 mm with an equiaxed crystal ratio of 0% to 60%, heated to 1150 ° C., and then subjected to a finishing condition of 850 ° C. to a thickness of 2.0 mm, 2.4 mm, Hot rolling was performed up to 2.6 mm. These steel sheets were pickled, annealed at 800 ° C. for 10 hours, and cold-rolled. FIG. 1 shows these results.

  FIG. 1 is a graph showing the relationship between the equiaxed crystal ratio of a slab, the thickness of a hot-rolled steel sheet, and the presence or absence of cold rolling fracture. The horizontal axis in FIG. 1 indicates the equiaxed crystal ratio of the slab, and the vertical axis in FIG. 1 indicates the thickness of the hot-rolled steel sheet. In addition, “◯” in FIG. 1 indicates that no fracture occurred during cold rolling, and “X” represents that fracture occurred during cold rolling. As shown in FIG. 1, it has been found that a hot-rolled annealed plate manufactured from a slab having an equiaxed crystal ratio of less than 30% breaks during cold rolling. Further, it has been found that a hot-rolled sheet annealed plate obtained by annealing a hot-rolled steel sheet having a thickness exceeding 2.5 mm also breaks during cold rolling. On the other hand, it has been found that a hot-rolled sheet annealed plate produced by hot rolling a slab having an equiaxed crystal ratio of 30% or more until the thickness becomes 2.5 mm or less does not break during cold rolling. The equiaxed crystal ratio of the slab was obtained from the area ratio of the equiaxed crystal portion observed in the slab cross section perpendicular to the casting direction and in the center portion of the slab width.

  Although it is not necessarily clear about the rupture reduction effect of cold rolling by increasing the equiaxed crystal ratio of the slab, the present inventors infer as follows. The crystal structure of steel with a high amount of Si and Al is a body-centered cubic structure from solidification to room temperature, and there is no phase transformation at intermediate temperatures. Therefore, the slab manufactured by continuous casting has a very coarse columnar crystal solidification structure. Further, since this columnar crystal has a (100) plane orientation that is difficult to recrystallize during hot rolling, a coarse structure remains even after hot rolling.

  When the hot-rolled steel sheet as described above is annealed, it becomes a non-uniform structure and coarse crystal grains are scattered. This tendency becomes more prominent in a steel sheet in which impurity components such as S and Ti are reduced to reduce iron loss. Since the toughness of a hot-rolled steel sheet deteriorates as the crystal grain size increases, it is considered that in cold rolling, the steel sheet having coarse crystal grains is likely to break. In the present invention, since the equiaxed crystal ratio of the slab is increased, it is presumed that recrystallization during hot rolling is likely to occur, the structure of the hot-rolled steel sheet is uniform, and cold-rolling fracture is unlikely to occur. Further, when the thickness of the hot-rolled steel sheet is increased, plastic deformation is strongly restrained and the crack progress energy of the brittle cracks is reduced, so that it is considered that the hot-rolled steel sheet is easily cracked during cold rolling.

  In the present invention, the breaking of cold rolling is reduced by increasing the equiaxed crystal ratio of the steel ingot or steel slab, but the effect is effectively drawn out and other characteristics necessary for the electromagnetic steel sheet are satisfied. To achieve this, it is necessary to limit the equiaxed crystal ratio, hot-rolled steel sheet thickness, and hot-rolled sheet annealing temperature of the steel component, steel ingot or steel slab, as will be described later. Hereinafter, the steel component, the equiaxed crystal ratio of the steel ingot or steel slab, the hot-rolled steel sheet thickness, and the hot-rolled sheet annealing temperature in the method for producing the non-oriented electrical steel sheet of the present invention will be described.

1. Steel composition ・ C
It is important to reduce C in the steel as much as possible because carbides (cementite, ε carbide) are formed in the steel by low temperature aging at about 200 ° C. and cause deterioration of the magnetic properties of the steel. When the C content in the steel exceeds 0.004%, the magnetic properties of the steel deteriorate due to aging. Therefore, the C content in the steel is limited to 0.004% or less.

・ Si
Si in steel is effective in reducing iron loss of steel because it increases the specific resistance of steel. However, if the Si content in the steel is less than 1.5%, the iron loss of the steel cannot be sufficiently reduced. On the other hand, if the Si content in the steel exceeds 4%, the steel sheet is easily broken during cold rolling, and the production cost is remarkably increased. Therefore, the Si content in steel is 1.5% or more and 4% or less. In order to further reduce the iron loss of the steel, the Si content in the steel is preferably 2% or more.

・ Mn
Mn in steel is effective in reducing iron loss of steel because it increases the specific resistance of steel. However, the effect is smaller than that of Si. When the Mn content in the steel is less than 0.1%, MnS is finely dispersed in the steel and the iron loss of the steel is deteriorated. On the other hand, if the Mn content in the steel exceeds 2%, the raw material cost increases. Therefore, the Mn content in the steel is limited to 0.1% or more and 2% or less.

・ P
P is an impurity in the steel and lowers the toughness of the hot-rolled steel sheet. Therefore, it is preferable to reduce the P content in the steel as much as possible. When the P content in the steel exceeds 0.2%, the toughness of the steel is remarkably deteriorated, and the steel plate is broken during cold rolling. Therefore, the P content in steel is limited to 0.2% or less. On the other hand, P has the effect of improving the magnetic flux density of the steel. Therefore, in order to minimize the toughness deterioration of the hot-rolled steel sheet and improve the magnetic flux density of the steel in a high magnetic field, the P content is reduced to 0. It is preferable to set it to 0.03% or more and 0.12% or less.

・ S
S is an impurity in steel and does not need to be added. If the S content in the steel exceeds 0.002%, fine MnS is formed in the steel and the iron loss of the steel deteriorates. Therefore, the S content in the steel is limited to 0.002% or less. In order to further reduce the iron loss of the steel, the S content in the steel is preferably 0.001% or less.

・ Al
Al in steel increases the specific resistance of steel in the same manner as Si, and is therefore effective in reducing iron loss of steel. Further, Al is effective for deoxidation of steel and is important for increasing the cleanliness of the steel and increasing the toughness of the hot-rolled steel sheet. However, when the Al content in the steel exceeds 3%, the saturation magnetic flux density of the steel is remarkably lowered and the iron core performance of the steel is deteriorated. On the other hand, if the Al content in the steel is less than 0.1%, AlN is finely dispersed in the steel and the iron loss of the steel is reduced. Therefore, the Al content in the steel is limited to 0.1% or more and 3% or less. In order to further improve the toughness of the hot-rolled steel sheet, the Al content in the steel is preferably set to 1% or more and 2.5% or less. Furthermore, the total of the Si content in steel and the Al content in steel is limited to 2% or more. This is because if the total of the Si content in steel and the Al content in steel is less than 2%, the specific resistance of the steel sheet is not sufficiently increased and eddy current loss increases.

・ N
N is an impurity in steel and does not need to be added. If the N content in the steel exceeds 0.003%, a large number of AlN and TiN precipitate in the steel and the magnetic properties of the steel deteriorate. Therefore, the N content in the steel is limited to 0.003% or less.

・ O
O is an impurity element in steel, and it is essential to reduce it as much as possible in the present invention. When the O content in the steel exceeds 0.003%, the toughness of the hot-rolled steel sheet is deteriorated, and it is easy to break during cold rolling. Therefore, the O content in the steel is limited to 0.003% or less. In addition, O content in steel in this invention is taken as the quantity analyzed using the steel plate which removed the insulation coating in the surface of a non-oriented electrical steel plate completely by grinding | polishing.

・ B
B is not an essential element in the present invention. However, by setting the B content in the steel to 0.0003% or more, the toughness of the hot-rolled steel sheet is improved, and it is difficult to break during cold rolling. On the other hand, if the B content in the steel exceeds 0.0050%, a coarse B compound is produced in the steel, and on the other hand, there is a possibility of breaking during cold rolling. Therefore, the B content in the steel is limited to 0.0050% or less. From the viewpoint of steel sheet manufacturability, the B content in the steel is preferably 0.0003% or more and 0.0030% or less.

・ Ti
Ti forms carbides, nitrides, and sulfides in the steel, which deteriorates the magnetic properties of the steel and lowers the toughness of the hot-rolled steel sheet, so it needs to be reduced as much as possible. If the Ti content in the steel exceeds 0.003%, Ti-based precipitates are dispersed in the steel and the toughness of the hot-rolled steel sheet deteriorates. Therefore, the Ti content in the steel is limited to 0.003% or less.

・ Ca
Ca is not an essential element in the present invention. However, when the Ca content in the steel is 0.001% or more, sulfides, oxides, etc. in the steel are coarsened, so this is an effective element for reducing the iron loss of the steel. On the other hand, when the Ca content in the steel exceeds 0.005%, the toughness of the hot-rolled steel sheet deteriorates. Therefore, the Ca content in the steel is limited to 0.005% or less. In order to further reduce the iron loss of the steel, the Ca content in the steel is preferably 0.001% or more and 0.003% or less.

・ Sn, Sb
Sn and Sb are effective elements for improving the magnetic properties of the non-oriented electrical steel sheet by adding a small amount. However, if the total content of Sn and Sb in the steel exceeds 0.1%, the toughness of the hot-rolled steel sheet is significantly reduced. Therefore, the total content of Sn and Sb in the steel is limited to 0.1% or less. In order to minimize the toughness deterioration of the hot-rolled steel sheet and improve the magnetic properties, it is more preferable that the total content of Sn and Sb in the steel is 0.01% or more and 0.03% or less. .

2. Equiaxial crystal ratio In the present invention, it is important to increase the equiaxed crystal ratio of a steel ingot or steel slab in order to improve cold rollability. In order to obtain the effect sufficiently, an equiaxed crystal ratio of 30% or more is necessary. Specific methods for increasing the equiaxed crystal ratio include generally known electromagnetic stirring of molten steel, reduction of molten steel overheating temperature (= casting temperature−solidification temperature) during casting, and the like. The equiaxed crystal ratio of the steel ingot or steel slab is calculated from the area ratio of the equiaxed crystal portion observed in the slab cross section perpendicular to the casting direction and at the center portion of the slab width.

3. Hot rolling method Although a normal method can be used as hot rolling in the present invention, in order to suppress crack fracture in cold rolling, strong rolling at a rolling reduction of 25% or more is performed at the stage of rough rolling. It is preferable to perform one or more passes.

4). Thickness of hot-rolled steel sheet A hot-rolled steel sheet having a high Si content and a low impurity content is easily cracked in cold rolling. Cracks in cold rolling have a strong correlation with the thickness of the hot-rolled steel sheet. For example, when the thickness of the hot-rolled steel sheet exceeds 2.5 mm, the breaking rate in cold rolling becomes extremely high. Therefore, the thickness of the hot-rolled steel sheet is limited to 2.5 mm or less. More preferably, it is 2.3 mm or less. In order to further improve the magnetic properties of the steel, the thickness of the hot rolled steel sheet is preferably 2.0 mm or less. Further, the lower limit of the thickness of the hot-rolled steel sheet is not particularly necessary for preventing cracking during cold rolling. However, when the plate thickness is reduced, the magnetic properties tend to be improved, but on the other hand, the surface area of the hot-rolled steel plate increases and the pickling efficiency decreases. If importance is attached to the pickling efficiency, the lower limit of the thickness of the hot-rolled steel sheet is preferably 0.8 mm.

5. Hot-rolled sheet annealing temperature In the present invention, hot-rolled sheet annealing is an essential process for improving the magnetic properties of the steel sheet. When the hot-rolled sheet annealing temperature is lower than 750 ° C., the crystal grain size of the hot-rolled annealed sheet becomes small, so that a texture that is advantageous for magnetic properties does not develop. Therefore, the magnetic properties of the final product are reduced. On the other hand, if the hot-rolled sheet annealing temperature exceeds 1100 ° C., the crystal grain size of the hot-rolled annealed sheet becomes too large, so that it is easy to break in cold rolling. Therefore, the hot-rolled sheet annealing temperature is limited to 750 ° C. or higher and 1100 ° C. or lower.

  In addition, this invention is not limited to embodiment mentioned above. The above-described embodiment is an exemplification, and it is the present invention that has substantially the same configuration as the technical idea described in the claims of the present specification and has the same effect. It is included in the technical scope of the invention.

(Example)
230 ton of molten steel decarburized and desulfurized in a converter was put into a ladle, and the ladle was moved to an RH type vacuum degassing apparatus. Thereafter, decarburization of the molten steel is performed with an RH vacuum degassing apparatus, and after the C concentration in the molten steel is set to 0.005% or less, components of Si, Mn, P, S, Al, B, Ca, Sn, and Sb are included. The slab was adjusted with a continuous casting machine. Table 1 shows component analysis values of each slab (steel A to steel P). The unit of component analysis values in Table 1 is mass%. As shown in Table 1, any of the steel components of steel A to steel G is within the limited range of the present invention, and any of the steel components in steel H to steel P is out of the limited range of the present invention. Yes. Note that the steel P is out of the limited range of the present invention because the sum of the Si content and the Al content is less than 0.2%.

  Next, Steel A to Steel P were heated to 1150 ° C. in a heating furnace, and hot-rolled at a finishing temperature of 850 ° C. to 880 ° C. and a winding temperature of 500 ° C. to obtain a steel plate having a thickness of 1.4 mm to 3.0 mm. . Next, the steel plate is not pickled and descaled, annealed at 720 ° C for 10 hours, annealed at 800 ° C for 10 hours, and annealed at 1120 ° C for 30 seconds before pickling. Each process was given separately. Next, each steel plate was cold-rolled to a thickness of 0.35 mm and finish-annealed at 1030 ° C. After finish annealing, an insulating film was applied to the surface of each steel plate. 28 cm Epstein specimens were collected from these steel plates, and the iron loss was measured by the method defined in JIS-C-2550.

Table 2 shows the production conditions, presence / absence of cold-rolling fracture, and magnetic properties of the steel sheet. As shown in Table 2, in the actual施例4 Example 8, the steel composition, etc. JikuAkiraritsu, thickness and hot rolled sheet annealing temperature of hot-rolled steel sheet is within the limited range of the present invention. On the other hand, in Comparative Examples 1 to 19, any of the steel components, the equiaxed crystal ratio, the thickness of the hot-rolled steel sheet, and the hot-rolled sheet annealing temperature is out of the limited range of the present invention.

(Evaluation)
In actual施例4 Example 8, both without breakage during cold rolling, and iron loss W15 / 50 of the steel sheet was a satisfactory value of less than 2.3 W / kg. On the other hand, the steel plates of Comparative Examples 1 and 2 whose equiaxed crystal ratio is less than the limited range of the present invention, the steel plates of Comparative Examples 3 and 4 whose hot-rolled steel plate thickness exceeds the limited range of the present invention, and the hot-rolled sheet annealing temperature The steel plate of Comparative Example 6 exceeding the limited range of the present invention broke during cold rolling. In addition, the steel sheet of Comparative Example 5 having a hot-rolled sheet annealing temperature less than the limited range of the present invention was significantly deteriorated in magnetic properties. Further, the steel sheets of Comparative Examples 7 to 9 in which the hot-rolled sheet annealing was omitted had deteriorated magnetic properties as compared with the same-component steel sheets subjected to the hot-rolled sheet annealing treatment. Moreover, the steel plates of Comparative Examples 11, 12, 15, and 17 in which the content of any one of Ti, O, B, Ca, and Sn, which are steel components, exceeds the limited range of the present invention, fractured during cold rolling. . Furthermore, the steel sheets of Comparative Examples 10, 13, 14, 16, 18, and 19 in which the content of any of the steel components N, Mn, Al, S, and (Si + Al) is outside the limited range of the present invention are magnetic properties. Deteriorated.

  From the above, by limiting the steel component, equiaxed crystal ratio, hot-rolled steel sheet thickness and hot-rolled sheet annealing temperature within the scope of the present invention, there is no breakage during cold rolling and low iron It was confirmed that a steel plate with a loss could be produced.

It is a graph which shows the relationship between the equiaxed crystal ratio of a slab, the thickness of a hot-rolled steel plate, and the presence or absence of cold rolling fracture.

Claims (1)

In mass%, C: 0.004% or less, Si: 1.5% to 4%, Mn: 0.1% to 2%, P: 0.03% to 0.2 %, S: 0.002% Hereinafter, Al: 1 % to 3%, N: 0.003% or less, O: 0.003% or less, B: 0.0050% or less, Ti: 0.003% or less, Ca: 0.005% or less A step of hot rolling steel ingots or steel slabs containing Sn, Sb, Si and Al satisfying the following formulas (1) and (2), the balance being Fe and inevitable impurities: And a step of subjecting the hot-rolled steel sheet obtained by the hot rolling to hot-rolled sheet annealing, and a hot-rolled steel sheet subjected to the hot-rolled sheet annealing at least once, or two or more cold rolling sandwiched between intermediate annealing. A method for producing a non-oriented electrical steel sheet, comprising: a step of applying, and a step of annealing the cold-rolled steel sheet obtained by the cold rolling, The equiaxed crystal ratio of the steel ingot or steel slab is 30% or more, the thickness of the hot-rolled steel sheet is 2.0 mm or less, and the annealing temperature of the hot-rolled sheet annealing is 750 ° C. or more and 1100 ° C. or less. The manufacturing method of the non-oriented electrical steel sheet characterized by these.
Sn + Sb ≦ 0.1% (1)
Si + Al ≧ 2% (2)
(In the formula (1) and the formula (2), Sn, Sb, Si and Al are numerical values representing the content of each element in mass%.)

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