JP4329550B2 - 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 a material for an iron core such as a motor, a generator, or a transformer.

  From the viewpoint of preventing global warming and promoting energy saving, various types of electrical equipment are being made more efficient and smaller. In order to increase the efficiency and miniaturization of electrical equipment, it is effective to improve the magnetic properties of electrical steel sheets that are the core material of electrical equipment. Conventionally, it is generally known that when a strain is applied to a steel sheet in the manufacturing process of the electromagnetic steel sheet, the magnetic properties of the steel sheet deteriorate due to the accumulation of internal stress. This is because the domain wall movement in the magnetization process of the steel sheet is suppressed by the internal stress.

  However, since iron-based soft magnetic materials (such as Si steel plates) have a positive magnetostriction, when a recrystallization treatment is performed by applying an appropriate tension to the soft magnetic material during the final annealing of the soft magnetic material, The magnetic properties of the soft magnetic material in the longitudinal direction (same as the direction in which tension is applied) are improved. For example, in Patent Document 1, the production of a non-oriented electrical steel sheet excellent in iron loss characteristics and magnetic flux density in a low magnetic field characterized by controlling the maximum heating temperature and unit tension according to the Si content of the steel sheet A method has been proposed. However, this method focuses only on the amount of Si in the steel sheet, and the influence of other components (for example, P) has not been studied. Further, this method is said to be effective in improving the magnetic flux density of the steel plate in a low magnetic field, but there is a problem that the magnetic flux density of the steel plate in a high magnetic field cannot be improved.

Japanese Patent Publication No. 7-5985

  The present invention has been made in view of the above problems, and provides a method for producing a non-oriented electrical steel sheet in which not only iron loss but also both magnetic flux density in a low magnetic field and magnetic flux density in a high magnetic field are improved. The task is to do.

In order to solve the above-mentioned problems, the present invention provides, in mass%, C: 0.005% or less, Si: 1.2% to 3.5%, Mn: 0.1% to 2%, P: 0.00. 03% to 0.15%, S: 0.004% or less, Al: 0.2% to 3%, Ti: 0.003% or less, N: 0.005% or less, Ca: 0.01% or less Contained in the cold rolled steel sheet, the balance of which is substantially made of Fe and impurities, maximum temperature: 900 ° C. to 1150 ° C., tension applied in the rolling direction of the cold rolled steel sheet: 1 MPa to 4 MPa, and the steel plate temperature is Provided is a method for producing a non-oriented electrical steel sheet, characterized in that finish annealing is performed under a condition in which time of 900 ° C. or higher: t (s) and the tension P (MPa) satisfy the following formula (1). .
20 ≦ t ≦ 150-30P (1)

  In the method for producing a non-oriented electrical steel sheet according to the present invention, only the iron loss is obtained by appropriately controlling the maximum temperature of the steel sheet in the finish annealing treatment, the tension applied in the rolling direction of the steel sheet, and the holding time of the steel sheet temperature. Instead, a non-oriented electrical steel sheet in which both the magnetic flux density in a low magnetic field and the magnetic flux density in a high magnetic field are improved can be manufactured.

  ADVANTAGE OF THE INVENTION According to this invention, not only an iron loss but the non-oriented electrical steel sheet in which both the magnetic flux density in a low magnetic field and the magnetic flux density in a high magnetic field were improved can be manufactured. If an iron core manufactured with this non-oriented electrical steel sheet is incorporated into an electrical device, the efficiency of the electrical device will be good over a long period of time. Such energy saving effects can contribute to the creation of a future with less burden on the global environment.

  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 .

The manufacturing method of the non-oriented electrical steel sheet of this invention is the mass%, C: 0.005% or less, Si: 1.2% -3.5%, Mn: 0.1% -2%, P: 0 0.03% to 0.15%, S: 0.004% or less, Al: 0.2% to 3%, Ti: 0.003% or less, N: 0.005% or less, Ca: 0.01% or less A cold-rolled steel sheet, the balance of which is substantially composed of Fe and impurities, the highest temperature: 900 ° C. to 1150 ° C., the tension applied in the rolling direction of the cold-rolled steel sheet: 1 MPa to 4 MPa, and the steel plate temperature The time when the temperature becomes 900 ° C. or higher: finish annealing is performed under the condition that t (s) and the tension P (MPa) satisfy the following formula (1).
20 ≦ t ≦ 150-30P (1)

  The present inventors performed various tension-added annealings on electrical steel sheets with varying P content, and investigated the magnetic properties of these electrical steel sheets. As a result, the present inventors not only improve the iron loss of the electrical steel sheet, but appropriately control the annealing time and the tension condition applied to the steel sheet rather than controlling the maximum temperature during annealing, The inventors have found that the magnetic flux density of the electrical steel sheet in a low magnetic field and a high magnetic field can be effectively improved, and completed the present invention. Hereinafter, the knowledge that has led to the present invention and the experimental results leading to it will be described.

  In the vacuum melting furnace, the main components are C: 0.002%, Si: 2.7%, Mn: 0.2%, S: 0.001%, Al: 0.3%, N: 0.002%, Ti: 0.001%, Ca: <0.0003%, and slabs were prepared by changing the P content from 0.001% to 0.25%, and the slabs were heated to 1100 ° C. A hot-rolled steel sheet having a thickness of 2.6 mm was prepared under finishing conditions at 850 ° C. These hot-rolled steel sheets were ground to a thickness of 2.1 mm, annealed at 800 ° C. for 4 hours, and further cold-rolled to a thickness of 0.35 mm. These cold-rolled steel sheets are subjected to finish annealing for 10 seconds to 200 seconds while applying various tensions in the rolling direction in the temperature range of 900 ° C. to 1050 ° C., and are punched into a shape with a width of 30 mm and a length of 100 mm. The magnetic properties were measured with a single plate magnetometer. FIG. 1, FIG. 2 and FIG. 3 show these results.

  FIG. 1 shows the effect of the time for annealing the steel sheet and the tension applied to the steel sheet during annealing on the magnetic flux density B1 of the 0.07% P-containing steel sheet at a low magnetic field (100 A / m) of 50 Hz. It is a graph which shows. The vertical axis in FIG. 1 shows the tension applied to the steel plate during annealing, and the horizontal axis in FIG. 1 shows the time for annealing the steel plate. In addition, “◯” in FIG. 1 indicates a case where the magnetic flux density B1 of the steel sheet exceeds 1.0 T, and “X” in FIG. 1 indicates that the magnetic flux density B1 of the steel sheet is less than 0.8 T. Indicates.

In FIG. 1, since “◯” marks are concentrated within a certain range, in order to improve the magnetic flux density B1 of the steel sheet, the time for annealing the steel sheet and the tension applied to the steel sheet during annealing are determined. It can be seen that it is effective to control within a certain range. From FIG. 1, the proper conditions are that the tension P (MPa) applied to the steel sheet is 1 MPa to 4 MPa, and the annealing time t (s) and the tension P satisfy the relationship of the following formula (1). I understand that.
20 ≦ t ≦ 150-30P (1)

  FIG. 2 is a graph showing the relationship between the P content in the steel sheet and the magnetic flux density B50 of the steel sheet at a high magnetic field (5000 A / m) of 50 Hz (tensile applied to the steel sheet: 2 MPa, annealing conditions: 900 ° C. to 1000 ° C. Hold for 30 seconds in the temperature range of ° C) The vertical axis in FIG. 2 indicates the magnetic flux density B50 of the steel plate, and the horizontal axis in FIG. 2 indicates the P content in the steel plate. As is apparent from FIG. 2, it is understood that the magnetic flux density B50 of the steel sheet is improved when the P content in the steel sheet is 0.03% or more and 0.15% or less.

  FIG. 3 shows a steel sheet annealed under the above-mentioned proper conditions (the time t (s) when the steel sheet temperature during finish annealing is 900 ° C. or higher = 40 s, the maximum temperature reached during finish annealing = 1020 ° C., and the tension P (MPa) = 3 MPa) and outside the proper conditions (time t (s) = 40 s when the steel plate temperature during finish annealing is 900 ° C. or higher, maximum reached temperature during finish annealing = 1020 ° C., tension P (MPa) = 5 MPa) It is a graph which shows the relationship between iron loss W15 / 50 of steel and P content in a steel plate. The vertical axis in FIG. 3 shows the magnetic flux density B50 of the steel plate, and the horizontal axis in FIG. 3 shows the P content in the steel plate. As apparent from FIG. 3, the iron loss of the steel sheet is improved by producing the steel sheet by appropriately controlling the annealing conditions of the steel sheet and the P content in the steel sheet.

  About the reason of the improvement effect of the low magnetic field magnetic flux density by tension addition annealing, the present inventors estimate as follows. It is speculated that when magnetic steel sheets are subjected to tension annealing at a high temperature of 900 ° C. or higher, a minute stress remains inside the magnetic steel sheets, so that the magnetic domain structure is stabilized so that the magnetization vector is oriented in the vicinity of the tension direction (same as the rolling direction). Is done. Since the domain wall motion is the main mechanism in the magnetization process in a low magnetic field, the low magnetic flux density in the rolling direction is remarkably improved by such a domain structure change. On the other hand, the magnetic flux density in the perpendicular direction deteriorates conversely. However, since the improvement effect in the rolling direction is great, the magnetic flux density averaged in both directions is improved. However, if the annealing time becomes longer, a large amount of strain accumulates inside the magnetic steel sheet, so that the domain wall movement is remarkably suppressed and the magnetic flux density is lowered.

  Moreover, the present inventors consider the reason for improving the high magnetic flux density of the steel sheet by adding P as follows. Since the P-containing steel sheet has a high crystal orientation grain density having a (001) plane advantageous for magnetization, it is considered that the texture of the steel sheet is improved by the addition of P.

  Further, the reason why the iron loss W15 / 50 of the steel sheet is improved by the combination of the tension addition annealing and the P addition is presumed as follows. In order to magnetize the non-oriented electrical steel sheet up to 1.5T, domain wall movement and magnetization rotation are the main mechanisms. In order to improve the iron loss, it is important that there are few obstacles in the magnetization process. As described above, the tension-added annealing of the steel sheet is effective for the domain wall movement, and the texture control of the steel sheet by adding P is effective for the magnetization rotation. Therefore, it is presumed that the iron loss of the steel sheet was improved as a result of appropriately controlling the magnetic domain structure and texture of the steel sheet by combining the tension addition annealing and the P addition.

  In the present invention, by properly controlling the annealing time in finish annealing and the tension applied to the steel plate during finish annealing, the magnetic properties of the steel are improved. In order to satisfy other necessary characteristics, it is necessary to limit the steel components, the conditions of finish annealing, and the hot-rolled sheet annealing temperature as described later. Hereinafter, the steel component in the non-oriented electrical steel sheet of the present invention, conditions during finish annealing, and hot-rolled sheet annealing temperature will be described.

1. Steel composition ・ C
Since C is an inevitable impurity in steel, it is not necessary to add C in particular. However, C in the steel forms carbides (cementite, ε carbide, etc.) in the steel due to aging and causes deterioration of the magnetic properties of the steel, so it is important to reduce it as much as possible. When the C content in the steel exceeds 0.005%, the iron loss of the steel due to aging becomes remarkable. Therefore, the C content in the steel is limited to 0.005% or less.

・ Si
Si in steel is effective in reducing iron loss of steel because it increases the specific resistance of steel. What is necessary is just to determine Si content in steel according to a required iron loss characteristic. However, if the Si content in the steel exceeds 3.5%, the steel sheet tends to break during cold rolling, and the manufacturing cost increases significantly. On the other hand, if the Si content in the steel is less than 1.2%, the high-temperature strength of the steel sheet becomes low, and strain accumulates during annealing, thereby degrading the magnetic properties of the steel sheet. Therefore, the Si content in the steel is limited to 1.2% to 3.5%. Furthermore, in order to improve the iron loss of the steel sheet, it is desirable that the Si content in the steel is 1.5% 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 of Mn on reducing the iron loss of steel is smaller than that of Si. Moreover, if the Mn content in the steel exceeds 2%, the raw material cost increases. On the other hand, when the Mn content in the steel is less than 0.1%, MnS is finely dispersed in the steel, so that the magnetic properties of the steel deteriorate. Therefore, the Mn content in the steel is limited to a range of 0.1% to 2%.

・ P
P is an essential element in the present invention and is effective in improving the magnetic flux density of steel in a high magnetic field by texture control. However, if the P content in the steel is less than 0.03%, the texture of the steel is not improved and the magnetic flux density of the steel is not improved. On the other hand, even if the P content in the steel exceeds 0.15%, the effect of improving the magnetic flux density of the steel is saturated, and there is a possibility that cold rolling breakage may occur due to a reduction in the toughness of the steel plate. Therefore, the P content in steel is limited to 0.03% or more and 0.15% or less. Furthermore, in order to improve the magnetic flux density of steel in a high magnetic field, the P content in the steel is preferably 0.05% or more.

・ S
Since S is an unavoidable impurity in steel, it is not necessary to add S. However, if the S content in the steel exceeds 0.004%, a large amount of MnS is formed in the steel, so that the magnetic properties of the steel deteriorate. Therefore, the S content in the steel is limited to 0.004% or less. In particular, in order to improve the iron loss characteristics of steel, it is desirable that the S content in the steel be less than 0.002%.

・ Al
Al is an element effective for deoxidation of steel and, like Si, increases the specific resistance of steel and is effective in reducing iron loss of steel. However, when the Al content in the steel is less than 0.2%, AlN precipitates finely in the steel, so that the magnetic properties of the steel deteriorate. On the other hand, 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. Therefore, the Al content in the steel is limited to 0.2% or more and 3% or less. In order to improve the magnetic flux density of steel in a high magnetic field, the Al content in the steel is desirably 2% or less.

・ Ti
Ti is an unavoidable impurity in steel, so it is not necessary to add Ti. However, even if the Ti content in the steel exceeds only 0.003%, precipitates such as TiN, TiS, and TiC are finely dispersed in the steel and deteriorate the magnetic properties of the steel. Therefore, the Ti content in the steel is limited to 0.003% or less.

・ N
Since N is an inevitable impurity in steel, it is not necessary to add N. However, if the N content in the steel exceeds 0.005%, a large amount of AlN is dispersed in the steel and the magnetic properties of the steel deteriorate. Therefore, the N content in the steel is limited to 0.005% or less.

・ Ca
Ca does not need to be added to the steel. However, if Ca is contained in the steel in an amount of 0.0005% or more, oxides, sulfides, and the like in the steel are coarsened, so that the magnetic properties of the steel are improved. On the other hand, a cast slab containing Ca exceeding 0.01% has deteriorated toughness, so that there is a risk of cracking in the slab during cooling or heating. Therefore, the Ca content in the steel is limited to 0.01% or less. Preferably it is 0.005% or less. In order to improve the magnetic properties, the Ca content in the steel is preferably limited to 0.0005% or more.

-Other inevitable impurities Cu, Ni, Cr, etc. exist as components that may be mixed in the steel making process by 0.01% or more of impurities mixed in the steel. If any of Cu, Ni, and Cr is reduced to 0.1% or less in steel, the effect of the present invention is not impaired. Moreover, the impurity components other than the above components do not affect the effects of the present invention as long as the content in steel is reduced to 0.01% or less.

2. Tension during finish annealing Controlling the tension applied to the steel sheet during finish annealing is extremely important in the present invention. The effect of this control is as described above, but when the tension applied in the rolling direction of the cold rolled steel sheet is less than 1 MPa, the magnetic flux density of the steel sheet in a low magnetic field is hardly improved. Moreover, the flatness of the cold rolled steel sheet is deteriorated. On the other hand, when the tension exceeds 4 MPa, strain is introduced into the steel sheet, so that both the iron loss and magnetic flux density of the steel sheet deteriorate. Therefore, the tension is limited to 1 MPa or more and 4 MPa or less.

3. Other conditions for finish annealing Finish annealing is a very important process for improving the magnetic properties of steel sheets by releasing the strain accumulated in the steel sheets by cold rolling and growing crystal grains in the steel sheets. is there. When the maximum temperature reached during finish annealing is less than 900 ° C., the crystal grain size of the steel sheet becomes small, so the magnetic properties of the steel sheet deteriorate. On the other hand, when the maximum temperature reaches 1150 ° C., the flatness of the steel sheet is significantly deteriorated, so that the space factor of the iron core is lowered. In addition, for example, when a steel sheet having deteriorated flatness is wound in a coil shape, a part thereof is plastically deformed, and the magnetic characteristics are also deteriorated. Therefore, the maximum temperature reached during finish annealing is limited to 900 ° C. or higher and 1150 ° C. or lower.

Furthermore, the time t (s) when the steel plate temperature during finish annealing is 900 ° C. or more and the tension P (MPa) need to satisfy the following formula (1).
20 ≦ t ≦ 150-30P (1)

  If the time during which the steel sheet temperature during finish annealing is maintained at 900 ° C. or more is less than 20 seconds, the crystal grain size of the steel sheet may be reduced, and the magnetic domain structure control by tension may be insufficient. For this reason, the magnetic flux density, iron loss, etc. of the steel sheet in a low magnetic field deteriorate. On the other hand, if the time during which the steel plate temperature during finish annealing is maintained at 900 ° C. or more exceeds (150-30 P) seconds, a large amount of strain accumulates in the steel plate, so that the magnetic properties of the steel plate deteriorate.

4). Hot-rolled sheet annealing temperature Hot-rolled sheet annealing is not an essential process of the present invention, but is effective in enhancing the magnetic properties of the steel sheet. In order to sufficiently obtain the effect of hot-rolled sheet annealing, the operating temperature of hot-rolled sheet annealing needs to be 750 ° C. or higher. On the other hand, if the operating temperature exceeds 1100 ° C., the crystal grain size of the hot rolled sheet becomes too large, so that the steel sheet tends to break during cold rolling. Therefore, the operating temperature when carrying out hot-rolled sheet annealing is limited to 750 ° C. or higher and 1100 ° C. or lower.

(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. After depressurizing the molten steel with an RH vacuum degassing device to reduce the C content in the steel to 0.005% or less, the contents of Si, Mn, P, S, Al, and Ca in the molten steel are adjusted. The slab was made by a continuous casting machine.

  The slab was heated to 1150 ° C. in a heating furnace and hot-rolled at a finishing temperature of 850 ° C. and a coiling temperature of 500 ° C. to obtain a steel plate having a thickness of 2.0 mm. Next, the steel sheet was pickled and descaled and subjected to hot rolled sheet annealing at 800 ° C. for 10 h, then cold rolled to a thickness of 0.35 mm, finish annealed, and an insulating film was applied to the surface. A 28 cm Epstein specimen was taken from this steel plate, and the iron loss and magnetic flux density were measured by the method defined in JIS-C-2550. Moreover, these steel plates were put on a surface plate, and the flatness was measured by the method defined in JIS-C-2550. Table 1 shows the component analysis values of each steel plate (Steel A to Steel J), and Table 2 shows the annealing conditions, the measurement results of the magnetic properties, and the measurement results of the flatness of each steel plate. The flatness shown in Table 2 is represented by a “◯” mark if the side wave height of the steel sheet is 1 mm or less, and is represented by a “x” mark if the side wave height of the steel sheet is 2 mm or more.

(Evaluation)
As shown in Table 1, the content of all the components in steel of Steel A to Steel E is within the limited range of the present invention. On the other hand, steel F to steel J have any steel component content outside the limit of the present invention. Further, as shown in Table 2, Example A-1, A-2, Example B-1, B-2, Example C-1, Example D-1 Contact and Example E-1, E- In 2, the annealing conditions are within the limited range of the present invention. On the other hand, in the comparative examples A-1 to A-6, the comparative example B-1, the comparative example C-1, the comparative example D-1, and the comparative example E-1, any annealing condition is outside the limited range of the present invention. It is.

As is apparent from Table 2, the steel plates of Examples A-1 and A-2 manufactured from Steel A were compared with the steel plates of Comparative Examples A-1 to A-6 manufactured from Steel A, and the magnetic flux density in a low magnetic field. The magnetic flux density and iron loss characteristics in high magnetic field are improved. Similarly, the steel plates of Examples B-1 and B-2, the steel plates of Example C- 1, the steel plates of Example D- 1 and the steel plates of Examples E-1 and E-2 are respectively Comparative Example B-1. Compared with the steel plate of Comparative Example C-1, the steel plate of Comparative Example D-1 and the steel plate of Comparative Example E-1, the magnetic flux density in the low magnetic field, the magnetic flux density in the high magnetic field, and the iron loss characteristics are improved. Therefore, if the steel components are within the limited range of the present invention and the finish annealing conditions are within the limited range of the present invention, the magnetic flux density in the low magnetic field, the magnetic flux density in the high magnetic field, and the iron loss characteristics are improved. I understand that. In addition, the steel plate with a small tension at the time of annealing as in Comparative Example A-3 and Comparative Example D-1 and the steel plate with a high maximum temperature at the time of annealing as in Comparative Example A-6 are flat as well as magnetic properties. Degree has deteriorated.

  Steels E to G have the same Si, Mn, and Al contents, but the steel sheets of Comparative Examples F-1 and G-1 have a magnetic flux density in a low magnetic field, a magnetic flux density in a high magnetic field, and iron loss characteristics. Has not improved. Therefore, even if the finish annealing condition is within the limited range of the present invention, the magnetic flux density in the low magnetic field, the magnetic flux density in the high magnetic field, and the iron loss characteristics are not improved unless the components in the steel are within the limited range of the present invention. I understand. In addition, the steel plates of Comparative Examples H-1, I-1, and J-1 manufactured from Steel H to Steel J containing components outside the limited range of the present invention all have low magnetic flux density in a low magnetic field, and iron loss. The characteristics are also inferior.

  From the above, the steel sheet produced from the steel containing the components within the limited range of the present invention under the annealing conditions within the limited range of the present invention has a magnetic flux density in a low magnetic field, a magnetic flux density in a high magnetic field, and iron loss characteristics. It was confirmed that it was improving.

It is a graph which shows the influence which the time which performs annealing, and the applied tension during annealing exert with respect to magnetic flux density B1 of a 0.07% P content steel plate in a 50Hz low magnetic field. It is a graph which shows the relationship between magnetic flux density B50 of the steel plate in a high magnetic field of 50 Hz, and P content in a steel plate. It is a graph which shows the relationship between the iron loss W15 / 50 of the steel plate annealed on appropriate conditions, and the steel plate annealed on the outside of appropriate conditions, and P content in a steel plate.

Claims (1)

In mass%, C: 0.005% or less, Si: 1.2% to 3.5%, Mn: 0.1% to 2%, P: 0.03% to 0.15%, S: 0.00. 004% or less, Al: 0.2% to 3%, Ti: 0.003% or less, N: 0.005% or less, Ca: 0.01% or less, with the balance being Fe and inevitable impurities Maximum temperature reached to cold rolled steel plate: 1000 ° C. to 1150 ° C., tension applied in the rolling direction of the cold rolled steel plate: 2.5 MPa to 4 MPa, and time for the steel plate temperature to be 900 ° C. or higher: t (s) And a method of manufacturing a non-oriented electrical steel sheet, wherein finish annealing is performed under a condition that the tension P (MPa) satisfies the following formula (1).
20 ≦ t ≦ 150-30P (1)

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