JP6024867B2 - Steel sheet for motor cores with excellent iron loss characteristics after punching - Google Patents

Description

  The present invention relates to a steel sheet for a motor core, in which deterioration of iron loss characteristics due to punching is small.

  In general, a motor core is made by punching a magnetic steel sheet as a material into a shape of the motor core, and then laminating and fastening by a caulking method or a welding method, and then applying a winding and press-fitting into a motor case (housing) or Manufactured by fixing by shrink fitting. Therefore, the electromagnetic steel sheet used for the motor core is subject to various distortions, and the iron loss characteristic after assembly to the motor core is greatly deteriorated (increased) compared to the iron loss characteristic of the material measured by the Epstein method or the like. Are known.

  Among the strains received by the motor core, the width of the test piece used for the Epstein test is 30 mm, but the width of the tooth portion of the motor core is about 5 mm even for a relatively large motor. Since the thickness is about 2 mm, the influence of the strain caused by the punching process is large, and the iron loss of the motor core is increased by about 30 to 50% compared to the iron loss of the material measured by the Epstein test or the like. Therefore, there is a demand for an electromagnetic steel sheet that has a small deterioration in iron loss characteristics due to punching.

  As a technique for solving such a problem, for example, in Patent Document 1, coarse MnS is precipitated with an S content of 0.015 to 0.035 mass%, and shear resistance during punching is reduced. Discloses a technique for reducing punching distortion and reducing deterioration of iron loss characteristics.

Japanese Patent Application Laid-Open No. 08-246052

  However, the technique disclosed in Patent Document 1 has a problem in that the iron loss characteristics of the raw steel plate itself before punching are greatly deteriorated because the amount of MnS precipitates increases.

  The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide a steel sheet for a motor core in which deterioration of iron loss characteristics due to punching is small.

  The inventors have intensively studied to solve the above problems. As a result, in order to reduce the deterioration of iron loss characteristics due to punching, the Si content of the steel sheet surface layer portion is increased from the steel sheet inner layer portion, and the ratio (multilayer ratio) of the steel sheet surface layer portion to the total plate thickness is within an appropriate range. It is effective to control, and in order to prevent cracking due to punching due to the high Si, it is effective to control the Si amount in the steel sheet inner layer part and the elongation of the steel sheet surface layer part within an appropriate range. As a result, the present invention was completed.

The present invention based on the above knowledge has a composition in which the surface layer portion of the steel sheet is composed of Si: 4 to 7 mass%, Al: 3 mass% or less, the balance is composed of Fe and inevitable impurities, and the inner layer portion of the steel sheet is Si: 3. 7-5 mass% , Al: 3 mass% or less, the balance has a component composition consisting of Fe and inevitable impurities, the average Si amount of the surface layer portion is 0.5 mass% or more higher than the average Si amount of the inner layer portion, The motor core steel sheet has a multilayer ratio, which is a ratio of the thickness of the surface layer portion to the total plate thickness, of 0.1 to 0.7 and an elongation of the surface layer portion of 5% or more.

  The surface layer part and the inner layer part in the steel sheet for motor core of the present invention are characterized in that Nb: 0.0010 mass% or less and / or Mo: 0.01 mass% or less.

  According to the present invention, it is possible to provide a steel sheet for a motor core that has a small deterioration in iron loss characteristics due to punching distortion. Therefore, a compressor motor for an air conditioner, a drive motor for a hybrid vehicle or an EV vehicle, a motor for an information device, etc. This greatly contributes to reducing iron loss in motors with narrow teeth.

It is a graph which shows the influence which the amount of Si of a steel plate surface layer part has on iron loss. It is a graph which shows the influence which the multilayer ratio of a steel plate surface layer part and an inner layer part has on iron loss. It is a graph which shows the influence which the difference of Si amount of a steel plate surface layer part and an inner layer part has on iron loss.

First, basic experiments that have triggered the development of the present invention will be described.
In order to investigate the deterioration of magnetic properties due to punching, Si: 4.0 mass%, the balance of Fe and unavoidable impurities are melted in the laboratory, cast into a steel ingot, Hot rolled, annealed at 900 ° C. × 30 s, and cold rolled to a thickness of 0.20 mm.
Thereafter, the cold-rolled sheet is subjected to finish annealing at 1000 ° C. × 30 s to form a cold-rolled annealed sheet, and then, from each of the rolling direction and the perpendicular direction of rolling of the cold-rolled annealed sheet, a width of 30 mm × a length of 180 mm, Two types of Epstein test pieces of 5 mm × 180 mm in length were collected by punching.
On the other hand, the cold-rolled sheet was subjected to a siliconizing process for 8 minutes at a temperature of 1200 ° C., and the average amount of Si from both surfaces to the 30% portion of the sheet thickness was set to 6.3 mass%. A steel plate having an average Si amount of 4.5% from the center of the layer (up and down from the center of the layer) of 4.5% is also produced. Similarly, from each of the rolling direction and the direction perpendicular to the rolling direction, the width is 30 mm × length is 180 mm and the width is 5 mm × An Epstein specimen having a length of 180 mm was collected by punching.

Table 1 shows the iron loss measurement results for these test pieces. From this result, it is understood that the iron loss of the test piece having a width of 5 mm is increased by about 30% as compared with the test piece having a width of 30 mm in a material having a uniform Si amount in the plate thickness direction. This is presumably because the end surface of the steel sheet is subjected to plastic deformation by punching, and compressive stress remains by processing.
On the other hand, in the test piece with the Si amount concentration gradient in the sheet thickness direction, the iron loss value of the 30 mm wide test piece is the same level as that of the material having uniform Si, but the iron loss deterioration rate of 5 mm width is 5 It can be seen that the deterioration of the iron loss is significantly suppressed as compared with the material having uniform Si.
As described above, the reason why the deterioration of the iron loss due to the punching process is suppressed in the steel plate with the Si layer increased is not clear yet, but the magnetostriction of the steel plate surface layer portion is low due to the high Si content. This is considered to be because the tensile residual stress was generated in the surface layer portion of the steel sheet due to becoming high Si, and the compressive stress at the time of punching was offset, making it less susceptible to the residual stress.

Next, in order to investigate the influence of the Si content in the surface layer portion, a steel having a component composition containing Si: 3.0 mass%, Al: 0.20 mass%, and the balance consisting of Fe and inevitable impurities in a laboratory. After melting and casting to form a steel ingot, it is hot-rolled, annealed at 900 ° C. for 30 seconds, pickled, cold-rolled to a thickness of 0.20 mm, and then 1200 ° C. Silicone treatment for 1 to 20 minutes was performed at a temperature to variously change the amount of Si in the steel sheet surface layer. In addition, the thickness of the high Si portion of the surface layer portion was controlled to be 25% of the plate thickness (12.5% on one side). From each of the rolling direction and the perpendicular direction of rolling of these materials, Epstein test pieces having a width of 5 mm and a length of 180 mm were sampled by punching, and the iron loss W _{10 / 2k} was measured.

  Here, for the section of the steel sheet surface layer portion and the inner layer portion and the Si amount, in the plate thickness direction, the portion where the Si amount is higher than the average value of the Si amount of the total thickness of the steel plate is the surface layer portion, and the lower portion is the inner layer portion, The average Si amount in the surface layer portion was defined as the Si amount in the surface layer portion, and the average Si amount in the inner layer portion was defined as the Si amount in the inner layer portion.

In FIG. 1, the relationship between the amount of Si of a steel plate surface layer part and the iron loss _{W10 / 2k} of a width 5mm test piece is shown. From this figure, it can be seen that when the Si amount in the surface layer portion is 4 mass% or more, the iron loss is greatly reduced (iron loss characteristics are improved). Therefore, in the present invention, the Si amount in the steel sheet surface layer portion is 4 mass% or more, preferably 4.5 mass% or more. On the other hand, if the Si amount exceeds 7 mass%, the punching processability is lowered, so the upper limit is set to 7 mass%.

  Next, in order to examine the amount of Si in the inner layer portion, a steel containing Si: 1 to 4 mass%, Al: 0.20 mass%, the balance being Fe and inevitable impurities is melted in a laboratory, and cast. And then ingot, then hot-rolled, annealed at 900 ° C for 30s, pickled, cold-rolled to form a cold-rolled sheet with a thickness of 0.20mm, and then at 1200 ° C. A steel plate was produced by performing a siliconizing treatment at a temperature of 1 to 20 minutes to change the Si amount of the steel sheet surface layer portion to 6 mass% and variously changing the Si amount of the inner layer portion. When punching was performed on these steel sheets, if the Si amount in the inner layer exceeded 5 mass%, the steel sheet was cracked during punching, and it was sometimes impossible to produce an Epstein specimen. Therefore, in the present invention, the Si amount in the inner layer portion is limited to 5 mass% or less.

Next, in order to examine the appropriate range of the multilayer ratio, that is, the ratio of the thickness of the surface layer portion to the total plate thickness (surface layer thickness / total plate thickness), various amounts of Si in the material steel plate and the silicidation time were varied. The surface layer portion is made Si: 6 mass%, Al: 0.20 mass%, the inner layer portion is made Si: 3 mass%, Al: 0.20 mass%, and the multilayer ratio is 0.05-0. Steel plates with a thickness of 0.20 mm varied in the range of 9 were prepared, and Epstein test pieces having a width of 5 mm and a length of 180 mm were taken from each of the rolling direction and the perpendicular direction of the rolling by punching. The iron loss W _{10 / 2k} was measured.

FIG. 2 shows the relationship between the multilayer ratio and the iron loss W _{10 / 2k} . From this figure, it can be seen that the iron loss rapidly decreases when the multilayer ratio is 0.1 or more. This is presumably because when the high Si portion of the surface layer is less than 0.1, the amount of the magnetostriction-reduced portion and the tensile stress applying portion is small, and the effect of suppressing iron loss deterioration during punching is small. On the other hand, if the multilayer ratio exceeds 0.7, cracking occurs during the punching process. Therefore, in this invention, a multilayer ratio shall be the range of 0.1-0.7.

Next, in order to examine the influence of the difference between the Si amount in the surface layer portion and the Si amount in the inner layer portion, Si: 4.5 mass%, Al: tr. The remainder of the steel consisting of Fe and unavoidable impurities is melted in the laboratory, cast into a steel ingot, hot rolled, annealed at 900 ° C. for 30 s, pickled, cold Rolling was performed to obtain a sheet thickness of 0.20 mm, and thereafter, a silicon immersion treatment was performed at a temperature of 1200 ° C. for 1 to 20 minutes to variously change the Si amount of the steel sheet surface layer. At this time, the multilayer ratio was 0.3, that is, the total of the front and back surface portions was 30% of the total thickness. From each of the rolling direction and the perpendicular direction of rolling of these materials, Epstein test pieces having a width of 5 mm and a length of 180 mm were sampled by punching, and the iron loss W _{10 / 2k} was measured.

FIG. 3 shows the relationship between the Si amount in the surface layer portion and the Si amount in the inner layer portion and the iron loss W _{10 / 2k} . From this, it can be seen that the iron loss greatly decreases when the difference in Si amount between the surface layer portion and the inner layer portion is 0.5 mass% or more. This is presumably because when the difference in Si amount increases, the tensile stress generated in the surface layer also increases, so that iron loss deterioration due to punching strain is suppressed.

  By the way, when a multilayer steel sheet having a high Si content in such a steel sheet surface layer is punched, even if the surface Si content is 7 mass% or less, cracks may occur in the surface layer portion near the shear surface in the punching process. It was recognized that there was. With wide materials with a width of about 30 mm, the increase in iron loss is small even if cracks exist in the vicinity of the shear plane, but with narrow materials with a width of about 5 mm, the ratio of crack occurrence width to the plate width increases. The iron loss characteristics are easily affected by cracks.

  Therefore, in order to investigate the cause of cracking, a steel plate of 0.2 mm thick material was chemically polished from one surface side, leaving only the high Si portion (0.04 mm from the surface) of the other surface layer. A test piece was prepared and a tensile test in the rolling direction was performed. As a result, it is clear that the elongation of the above-mentioned test pieces is less than 5% in the material in which the occurrence of cracks is observed, whereas the elongation is 5% or more in the material in which the occurrence of cracks is not observed. It became. From this result, it is considered that the material in which the crack was generated by the punching process had cracks generated by the punching process because the elongation of the surface layer portion was small.

  Furthermore, when the crack part was observed in detail about the material in which the crack generate | occur | produced by SEM, many cracks along a grain boundary were recognized. This is thought to be because impurities such as oxygen generated from oxides existing on the surface of the steel plate before the siliconization treatment diffused into the grain boundaries during the siliconization treatment and lowered the grain boundary strength. Therefore, the surface of the steel sheet was rubbed with a brush to remove dirt, alkali degreased, and then subjected to a siliconization treatment. With these materials, cracks in the surface layer due to punching were not observed, and the elongation of the steel sheet surface layer was not observed. It was found that 5% or more could be secured. Therefore, in the present invention, the elongation of the steel sheet surface layer portion is defined as 5% or more.

Next, component composition other than Si of the steel sheet for motor cores of this invention is demonstrated.
Al: 3 mass% or less Al is an element effective in increasing the specific resistance of steel and reducing iron loss. However, if it exceeds 3 mass%, the steel sheet becomes hard and it becomes difficult to punch. Therefore, Al is 3 mass% or less in both the surface layer portion and the inner layer portion.

  About components other than Si and Al mentioned above, if it is a component normally contained in the material for motor cores, it can contain without a restriction | limiting in particular. For example, Mn, P, Sn, Sb, Ni, Cu, Ca, Mg are Mn: 0.05-5 mass%, P: 0.005-0.2 mass%, Sn: 0.005-0.1 mass%, Sb: 0.005 to 0.1 mass%, Cu: 0.05 to 2 mass%, Ni: 0.05 to 5 mass%, Ca: 0.001 to 0.006 mass%, Mg: 0.001 to 0.005 mass% If it is within the range, it may be contained.

However, Nb and Mo are preferably limited to the following ranges.
Nb: 0.0010 mass% or less Nb is a harmful element that forms carbonitrides and increases iron loss. Particularly, when Nb exceeds 0.0010 mass%, the influence becomes large. Therefore, in the present invention, it is preferable to limit the upper limit of Nb to 0.0010 mass%.

Mo: 0.01 mass% or less Mo, like Nb, is a harmful element that forms carbonitrides and increases iron loss. When the content exceeds 0.01 mass%, the effect becomes large. Therefore, in the present invention, it is preferable to limit the upper limit of Mo to 0.01 mass%.

Next, the manufacturing method of the steel sheet for motor cores of this invention is demonstrated.
In the motor core steel sheet of the present invention, it is important to change the amount of Si in the surface layer portion and the inner layer portion, and as a method therefor, for example, the steel having the above-described component composition is melted by a known refining process, Steel material (slab) by continuous casting, etc., hot rolled, pickled, predetermined by one or more cold rolling or warm rolling, or two or more cold rolling or warm rolling with intermediate annealing And a method of increasing the Si content of the surface layer portion by subsequently performing a siliconization treatment. In this case, the finishing temperature, the coiling temperature, etc. during hot rolling are not particularly limited, and hot-rolled sheet annealing after hot rolling may be performed, but is not essential.

  However, in order to stabilize the elongation of the surface layer portion of the steel sheet to 5% or more, it is preferable to remove the dirt on the surface of the steel sheet by performing brushing and alkali degreasing prior to the above-described siliconization treatment. In this case, the brush used for brushing is preferably made of a resin such as nylon, and the cleaning liquid used for alkaline degreasing is preferably sodium orthosilicate.

  In addition, as another method of changing the Si amount of the surface layer portion and the inner layer portion, after bonding ingots having different Si amounts, hot rolling, cold rolling, and finish annealing are performed so that the surface layer has high Si content. You may use the method of using this steel plate.

  In addition, although it does not prescribe | regulate especially about the board thickness of the steel plate for motor cores of this invention, it is preferable to set it as 0.35 mm or less from a viewpoint of reducing an iron loss, More preferably, it is 0.2 mm or less. The lower limit plate thickness is preferably 0.05 mm or more from the viewpoint of productivity.

  A steel having a composition other than Si shown in Table 2 is melted by a conventional refining process, continuously cast into a steel slab, the steel slab is heated at 1140 ° C. × lhr, and finish rolling finish temperature The steel sheet was hot rolled to a temperature of 800 ° C. to obtain a hot rolled sheet having a thickness of 2.0 mm, wound around a coil at a coiling temperature of 610 ° C., and then annealed at 900 ° C. × 30 s. Next, the hot-rolled sheet is pickled, cold-rolled to obtain a cold-rolled sheet having a thickness of 0.20 mm, and further subjected to a siliconization treatment under various conditions shown in Table 2, and Si shown in Table 2 is also obtained. It was set as the multilayer steel plate which has quantity and multilayer ratio. In addition, some steel plates were excluded and the steel plate surface was brushed and alkali degreased before the siliconization treatment. The diffusion treatment after the siliconization treatment was performed at 1200 ° C. for 10 minutes.

Two types of Epstein test pieces having a width of 30 mm × a length of 180 mm and a width of 5 mm × a length of 180 mm were cut out from the steel sheet thus obtained from the rolling direction and the direction perpendicular to the rolling direction, and the iron loss W _{10 / 2k} was measured. The results are also shown in Table 2. From this result, it is understood that by setting the Si amount and the multilayer ratio of the surface layer portion and the inner layer portion within the scope of the present invention, it is possible to obtain a steel sheet for a motor core that has a low iron loss and does not crack during punching. .

  The steel sheet of the present invention has a small deterioration in iron loss characteristics due to punching, and can be suitably used for, for example, a core material of a small generator in addition to a motor for a hybrid vehicle and a compressor motor for an air conditioner.

Claims (2)

The surface layer portion of the steel plate has a component composition consisting of Si: 4 to 7 mass%, Al: 3 mass% or less, and the balance is composed of Fe and inevitable impurities, and the inner layer portion of the steel plate is Si: 3.7 to 5 mass% , Al: 3 mass. % Or less, and the balance is composed of Fe and inevitable impurities,
The average Si amount of the surface layer portion is 0.5 mass% or more higher than the average Si amount of the inner layer portion,
The multilayer ratio, which is the ratio of the thickness of the surface layer portion to the total plate thickness, is 0.1 to 0.7,
A steel sheet for a motor core, wherein the surface layer has an elongation of 5% or more. The steel sheet for motor core according to claim 1, wherein the surface layer portion and the inner layer portion are Nb: 0.0010 mass% or less and / or Mo: 0.01 mass% or less.

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