JP6772911B2 - Non-oriented electrical steel sheet - Google Patents

Description

The present invention relates to a non-oriented electrical steel sheet having excellent magnetic properties, which is used as an iron core material for electrical equipment.

In recent years, in the fields of electrical equipment, especially rotating machines, small and medium-sized transformers, and electrical components in which non-oriented electrical steel sheets are used as the core material, they are representative of global power and energy savings, CO ₂ reduction, etc. With the movement to protect the global environment, the demand for higher efficiency and smaller size is increasing. Under such a social environment, it is an urgent issue to improve the performance of non-oriented electrical steel sheets as a matter of course.

Punching accuracy is one of the characteristics required for non-oriented electrical steel sheets for improving the characteristics of motors. In many cases, the motor characteristics can be improved by narrowing the gap between the stator (stator) and the rotor (rotor). However, if the stator and the rotor come into contact with each other during operation, the motor will be damaged. Therefore, it is necessary to improve the accuracy of the dimensions and shape of the stator and the rotor, and a non-oriented electrical steel sheet having good punching accuracy is required.

One of the means for improving the punching accuracy is a means for increasing the hardness of the non-oriented electrical steel sheet. The method of adding 0.1% or more of P to a steel sheet as described in Patent Document 1 has a problem that productivity is deteriorated in a material having a large amount of Si. Further, the hardness can be increased by oxidizing the surface layer of the non-oriented electrical steel sheet, but as described in Patent Documents 2 to 4, if the internal oxide layer exceeds 0.5 μm, the iron loss is adversely affected. It is known to give. That is, it has not been possible to obtain a non-oriented electrical steel sheet that achieves both improvement in punching accuracy and reduction in iron loss of the non-oriented electrical steel sheet.

Japanese Patent No. 4329538 Japanese Patent No. 3307897 Japanese Patent No. 4116748 Japanese Patent No. 41167479

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-oriented electrical steel sheet having both improved punching accuracy and low iron loss.

The present inventors have conducted extensive research on a method for reducing iron loss even in the presence of an internal oxide layer in non-oriented electrical steel sheets. As a result, it was clarified that the internal oxide layer can be partially formed by controlling the timing of generating the internal oxide layer and its thickness, the punching accuracy can be remarkably improved, and a material having low iron loss can be realized. That is, by annealing the steel sheet after hot rolling with the surface scale attached, an internal oxide layer is formed on the entire surface of the steel sheet by utilizing the oxygen contained in the surface scale, and then pickling and cold rolling. By doing so, it was found that the internal oxide layer is divided to partially expose the base iron to improve punching accuracy, and further, finish annealing is performed after cold rolling to obtain a steel sheet with low iron loss. .. It was also found that by controlling the atmosphere of finish annealing after cold rolling, it is possible to prevent deterioration of magnetic properties due to an increase in the internal oxide layer during finish annealing.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] In terms of mass%, C: 0.0030% or less, Si: 2.0% or more and 4.0% or less, Al: 0.1% or more and 3.0% or less, Mn: 0.10% or more 2. It contains 00% or less, P: 0.09% or less, S: 0.0050% or less, N: 0.0050% or less, consists of the balance Fe and impurity elements, and the total surface area covered by the internal oxide layer on the surface is the total surface area. A non-directional electromagnetic steel sheet having an average internal oxide layer thickness of 0.5 μm to 10 μm in a region having an internal oxide layer, which is 10 to 70% of the above.
[2] In addition to the above steel components, in terms of mass%, Sn: 0.02% or more and 0.40% or less, Cu: 0.10% or more and 1.00% or less, Sb: 0.02% or more and 0.40 Non-oriented electrical steel sheet containing 1 type or 2 or more types of% or less.
[3] In addition to the above steel components, in mass%, REM: 0.0005% or more and 0.0400% or less, Ca: 0.0005% or more and 0.0400% or less, Mg: 0.0005% or more and 0.0400. Non-oriented electrical steel sheet containing% or less.

As described above, according to the non-oriented electrical steel sheet of the present invention, it is possible to provide a non-oriented electrical steel sheet that achieves both improved punching accuracy and low iron loss. The present invention can provide non-oriented electrical steel sheets having excellent punching accuracy and low iron loss, which are desirable as iron core materials for electrical equipment, particularly iron core materials for rotating machines, small and medium-sized transformers, electrical components, and the like. It is possible to sufficiently meet the urgent demand for high efficiency and miniaturization in the field of these electric devices in which grain-oriented electrical steel sheets are used as the core material, and its industrial value is extremely high.

The schematic diagram explaining the manufacturing method of the non-oriented electrical steel sheet of this embodiment. Test number No. An optical micrograph of a cross section in the rolling direction showing an internal oxide layer of the non-oriented electrical steel sheet of 1.

Hereinafter, the present invention will be described in detail.
The non-directional electromagnetic steel plate of the present embodiment has C: 0.0030% or less, Si: 2.0% or more and 4.0% or less, Al: 0.1% or more and 3.0% or less, Mn in mass%. : 0.10% or more and 2.00% or less, P: 0.09% or less, S: 0.0050% or less, N: 0.0050% or less, consisting of the balance Fe and impurity elements, inside the surface It is a non-directional electromagnetic steel plate in which the surface area covered by the oxide layer is 10 to 70% of the total surface area, and the average internal oxide layer thickness in a region having an internal oxide layer is 0.5 μm to 10 μm.

First, the reason for limiting the steel component of the present invention will be described.
C is a harmful component that increases iron loss and causes magnetic aging, so it should be 0.0030% or less.

As described above, Si is a component having an effect of reducing iron loss by increasing electrical resistance and reducing eddy current loss, and punching into an iron core by increasing the yield ratio. It also has the effect of improving sex. In order to exert these effects, it is necessary to contain 2.0% or more. On the other hand, when the content is increased, the magnetic flux density is lowered, and the workability such as cold rolling is lowered and the cost is high even in the manufacturing process of the non-oriented electrical steel sheet, so the content is 4.0% or less. To do.

As described above, Al is also a component having an effect of reducing iron loss by increasing electric resistance and reducing eddy current loss like Si, but the increase in hardness is smaller than that of Si. In addition, the ratio of the magnetic flux density B50 to the saturated magnetic flux density Bs: B50 / Bs is increased, and the magnetic flux density is also improved. For this purpose, it is necessary to contain 0.1% or more. On the other hand, when the content increases, the saturation magnetic flux density itself decreases, which causes a decrease in the magnetic flux density, and further causes a decrease in the yield ratio, which also deteriorates the punching accuracy. Therefore, the punching accuracy is set to 3.0% or less. ..

Mn has the effect of increasing the electrical resistance to reduce the eddy current loss and improving the primary recrystallization texture to develop the {110} <001> crystal orientation which is desirable for improving the magnetic characteristics in the rolling direction. Furthermore, it suppresses the precipitation of fine sulfides such as MnS, which are harmful to crystal grain growth. For these purposes, it should be contained in an amount of 0.10% or more. However, when the content increases, the crystal grain growth property itself at the time of annealing decreases and the iron loss increases, so the content is set to 2.00% or less.

P has the effect of improving the punching accuracy and may be added, but as the content of P increases, the steel sheet containing Si ≧ 2% becomes very brittle, so the content is set to 0.09% or less.

S is 0.0050% or less because it inhibits recrystallization and grain growth during finish annealing and the like due to fine precipitation of sulfides such as MnS.

N is 0.0050% or less because it inhibits recrystallization and grain growth during finish annealing and the like due to fine precipitation of sulfides such as AlN.

Sn, Cu, and Sb develop into a {110} <001> texture that is desirable for improving the primary recrystallization texture of the steel sheet and improving the magnetic properties in the rolling direction, and {111} <112 that is not desirable for the magnetic properties. > It has the effect of suppressing the texture and the like. Further, it has the effect of controlling the surface oxidation of the steel sheet and sizing the crystal grain growth. It also has the effect of reducing the thickness of the internal oxide layer, and may be added as needed. For these purposes, Sn and Sb should be contained in an amount of 0.02% or more, and Cu should be contained in an amount of 0.10% or more. On the other hand, even if the content is increased, the action is saturated, and rather, the crystal grain growth itself at the time of finish annealing is suppressed, so Sn and Sb are 0.40% or less, and Cu is 1.00% or less. To do.

REM, Ca, and Mg fix S as a sulfide or acid sulfide, avoid fine precipitation of MnS and the like, and promote recrystallization and grain growth during finish annealing and the like. For this purpose, it is necessary to contain 0.0005% or more. On the other hand, when the content is increased, the sulfide or acid sulfide itself becomes excessive, which inhibits recrystallization and grain growth during finish annealing and the like, so the content is 0.0400% or less.

Other than the above-mentioned components, Fe and impurity elements.

Next, the non-oriented electrical steel sheet of the present embodiment has an internal oxide layer on the surface, and the surface area covered by the internal oxide layer on the surface of the steel sheet may be 10 to 70% of the total surface area. desirable. The internal oxide layer has a higher hardness than the base iron, and the punching accuracy is improved. In order to obtain this effect, it is necessary to cover 10% or more of the total surface area with an internal oxide layer. However, if the surface area covered by the internal oxide layer is large, the iron loss is exacerbated. Therefore, the surface area covered by the internal oxide layer needs to be 70% or less of the total surface area.

Further, in the place where the internal oxide layer exists, if the internal oxide layer is thin, the effect of improving the punching accuracy cannot be obtained. Therefore, it is necessary to make the internal oxide layer thickness 0.5 μm or more on average. On the other hand, if the thickness of the internal oxide layer is too thick, iron loss deteriorates, so the thickness must be 10 μm or less.

The internal oxide layer according to the present invention refers to a layer containing a region in which Si, Al, Mn and the like form particulate oxide and are dispersed inside iron, and this layer is, for example, FIG. 1 ( As shown in E), it is formed in an island shape on the surface of the steel plate. Such an internal oxide layer is formed, for example, by the procedure described below. That is, as shown in FIG. 1 (A), the hot-rolled steel sheet having an oxide layer (surface scale (external oxide layer)) formed on the surface thereof is hot-rolled as shown in FIG. 1 (B). By annealing, oxygen is diffused into the ground iron from the surface oxide layer to form a layered internal oxide layer. Then, as shown in FIG. 1 (C), the external oxide layer is removed by pickling, and further, as shown in FIGS. 1 (D) and 1 (E), a cold rolling step is performed to perform internal oxidation. Divide the layer into islands. As shown in FIG. 1A, the layered oxide layer covering the surface of the steel sheet after hot spreading is called an external oxide layer, and is distinguished from the internal oxide layer according to the present invention. The internal oxide layer of the present embodiment is not formed on the entire surface of the ground iron, but is formed in an island shape on the ground iron. Therefore, in the region where the internal oxide layer is formed, as shown in FIG. 1 (E), a two-layer structure of the internal oxide layer and the ground iron is formed from the outermost layer side, but the internal oxide layer is formed. In the area where it is not, it will be formed only by the ground iron.

The lower layer of the internal oxide layer is ground iron. Since the internal oxide layer has large irregularities on the interface with the ground iron, it obstructs the flow of magnetic flux and significantly deteriorates the high frequency iron loss, so special care must be taken.

The internal oxide layer can be observed by measuring the polished surface of the steel plate cross section at a magnification of 1000 times or more by SEM-EDX, but the SEM image is not a normal secondary electron but a backscattered electron image. The thickness of the internal oxide layer can be clearly seen. The thickness of the internal oxide layer is the center line of the unevenness at the upper and lower interfaces (when a straight line parallel to the average line of the unevenness curve is drawn, the area surrounded by this straight line and the unevenness curve is equal on both sides of this straight line. It is defined as the difference between (the center line). Further, as a simple means for observing the internal oxide layer, observation of a mirror-polished steel sheet cross section with an optical microscope at a magnification of about 1000 times can be mentioned.

The abundance ratio of the internal oxide layer may be measured as follows. Observe the surface area of 100 μm or more with the secondary electron image of SEM. Then, the distance that the internal oxide layer is on the surface layer is obtained, and the value is divided by the observed distance and expressed as a percentage. This value is taken as the abundance ratio of the internal oxide layer.

Further, the method for measuring the thickness of the internal oxide layer and the method for determining the average thickness may be measured and determined as follows. Observe the surface area of 100 μm or more with the secondary electron image of SEM. Then, 10 or more vertical lines are drawn in the region where the internal oxide layer is present, and the thickness of the internal oxide layer on the vertical lines is obtained. The average value of the internal oxide layer thickness is defined as the average thickness of the internal oxide layer.

Next, in order to produce the non-oriented electrical steel sheet of the present embodiment, it is necessary to continuously cast, hot-roll, pickle, and cold-roll the molten steel composed of the above-mentioned components, and then perform finish annealing.

In order to suppress the development of {111} directional grains having poor magnetic properties during finish annealing, the crystal grain size before cold rolling may be coarsened. Specific methods include performing hot-rolled sheet annealing between hot rolling and pickling, performing high-temperature finishing by hot rolling, and covering with a heat-retaining cover after winding. ..

The greatest feature of the present invention is that the abundance of the internal oxide layer is reduced to 10 to 70% after finish annealing. The internal oxide layer has a higher hardness than the base iron, and the punching accuracy is improved. In order to obtain this effect, it is necessary to cover 10% or more of the total surface area with an internal oxide layer. However, if the surface area covered by the internal oxide layer is large, there is a demerit that iron loss is deteriorated. Therefore, the surface area covered by the internal oxide layer needs to be 70% or less of the total surface area.

Further, in the place where the internal oxide layer exists, if the thickness of the internal oxide layer is thin, the effect of improving the punching accuracy cannot be obtained. Therefore, it is necessary to make the thickness of the internal oxide layer 0.5 μm or more on average. On the other hand, if the thickness of the internal oxide layer is too thick, iron loss deteriorates, so the thickness must be 10 μm or less.

One of the means for producing a steel sheet satisfying the above conditions is a method in which an internal oxide layer is left on the steel sheet before cold rolling with a thickness of about 10 μm or less. A steel sheet having the characteristics of the present invention can be obtained by leaving an internal oxide layer before cold rolling, cold rolling at 50% or more, and then annealing in a dry atmosphere.

FIG. 1 shows the reason why the area covered by the internal oxide layer on the surface is 10 to 70% of the total area by the above method.

As shown in FIG. 1 (A), the hot-rolled plate is usually composed of an external oxide layer and ground iron. When annealed at 750 ° C. or higher with an external oxide layer present, a part of oxygen in the external oxide layer moves to the ground iron side to form an internal oxide layer as shown in FIG. 1 (B). Then, the amount of pickling is adjusted so that only the external oxide layer is removed while leaving the internal oxide layer (FIG. 1 (C)). When the pickled steel sheet is cold-rolled, the base iron is stretched, but unlike the base iron, the internal oxide layer is hard and brittle, so it is divided into islands as shown in FIG. 1 (D), and further, FIG. As shown in (E), it is pressed into the ground iron. During cold rolling, the steps shown in FIGS. 1 (D) and 1 (E) occur at the same time.

Conventionally, when hot-rolled plate is annealed, in order to prevent deterioration of magnetic properties due to the internal oxide layer, it is annealed after pickling (after removing the external oxide layer), or a pickling accelerator (thiosulfate) is added to the pickling solution after annealing. Sodium, etc.) was added to completely remove the internal oxide layer. However, the present invention exhibits a condition in which both magnetism and punching property can be achieved by annealing while leaving the external oxide layer to intentionally form an internal oxide layer, and further leaving only an appropriate amount of the internal oxide layer in pickling. Is.

As a method for adjusting the amount of pickling, it is effective to shorten the pickling time, lower the temperature of the pickling solution, or add a commercially available pickling inhibitor (polyamine + formic acid or the like). In the present invention, the method of adjusting the pickling amount is not limited as long as the internal oxide layer can be left with a thickness of 0.5 to 10 μm.

The effect of the pickling inhibitor will be described. The main component of the pickling inhibitor is polyamine, and this polymer has the property of easily adhering to iron atoms. The adhesion of the polymer to the surface of the base iron reduces the area in contact with the acid and suppresses the pickling rate. Formic acid and the like are known as additives that enhance this effect.

The effect of the pickling accelerator will be described. The pickling accelerator has a property of easily absorbing an iron atom chelating agent, that is, an iron ion. The pickling solution has the property of dissolving iron, but when the iron ion concentration in the pickling solution increases, the rate of dissolving iron slows down. In particular, the liquid in contact with the steel sheet locally reduces the dissolution rate of iron. When the pickling accelerator is added, the pickling proceeds because the concentration of iron ions dissolved in the pickling solution is lowered. As the pickling accelerator, for example, sodium thiosulfate and the like are known.

Further, when the annealing temperature is 800 ° C. or higher, the internal oxide layer thickness may exceed 10 μm when pickling by the above means. Therefore, the annealing temperature is preferably less than 800 ° C.
On the other hand, it is known that coarsening the particle size of the hot-rolled plate improves the crystal orientation of the final product and improves the magnetic flux density. When the annealing temperature is set to 800 ° C. or higher for this purpose, the development of the internal oxide layer may be suppressed by adding Sn, Cu, and Sb. At this time, it is necessary to contain Sn and Sb in an amount of 0.02% or more and Cu in an amount of 0.1% or more. On the other hand, even if the content is increased, the action is saturated, and rather, the crystal grain growth itself at the time of finish annealing is suppressed, so Sn and Sb are 0.40% or less, and Cu is 1.0% or less. To do.
Of course, when the internal oxide layer becomes too thick without adding Sn, Cu, and Sb, it is possible to control the pickling amount in the subsequent pickling to adjust the thickness to an appropriate level.

The mechanism by which the addition of Sn, Cu, and Sb suppresses the development of the internal oxide layer is not yet well understood, but it is believed that these elements gathered between the scale and the ground iron and inhibited the exchange of oxygen.

When annealed at a temperature of hot-rolled plate annealing below 700 ° C., the required amount of internal oxide layer may not be formed. Therefore, in the present invention, it is recommended that the hot-rolled plate annealing temperature be 700 ° C. or higher. More preferably, it is 750 ° C. or higher.
Further, the annealing time may be appropriately adjusted so that the thickness of the internal oxide layer is in the range of 0.5 to 10 μm.

The finish annealing atmosphere after cold rolling is also important in the present invention. It is better to lower the dew point of the atmosphere at the time of finish annealing, and it is desirable to keep it below -25 ° C. The reason is that the internal oxide layer is not formed by finish annealing. Since the internal oxide layer formed during finish annealing oxidizes the entire steel sheet surface, the magnetism is significantly deteriorated. In order to achieve both magnetism and punching property, it is preferable to suppress the formation of an internal oxide layer during finish annealing.

Next, an example of the present invention will be shown.

(Example 1)
Steel is cast with the components shown in Table 1 in mass% and hot-rolled to prepare a hot-rolled plate having a plate thickness of 2.0 mm. Then, heat treatment (atmosphere: 100% nitrogen) is performed for 1 minute at the hot-rolled plate annealing temperature shown in Table 1 to form an internal oxide layer on the surface. Then, it is pickled by immersing it in hydrochloric acid (7.5 wt%) at 85 ° C. to which the additive (0.07 wt%) shown in Table 1 is added for 30 seconds. After that, it was cold-rolled to a thickness of 0.5 mm at a rolling reduction of 75%, and finish-annealed at 1050 ° C. for 30 seconds in the atmosphere of the dew point shown in Table 1, and the punching accuracy and magnetic characteristics (iron loss) described below were performed. To measure. The measurement results are also shown in Table 1.

-Punching accuracy A ring-shaped sample with an inner diameter of 100 mm and an outer diameter of 120 mm is punched. The clearance at this time is 8% of the plate thickness. Next, the inner diameter is measured at angles of 0 °, 45 °, 90 °, and 135 ° with respect to the rolling direction. If the difference between the maximum value and the minimum value of the inner diameter of each angle is 2 μm or less, the punching accuracy is considered to be good.

-Iron loss A 55 mm square sample is taken, and W15 / 50 (iron loss when the steel sheet is magnetized to a magnetic flux density of 1.5 T at 50 Hz) is measured by Single Sheet Tester (SST). I think that 2.9 W / kg or less is good.

No. Since No. 3 has a large content of P, it becomes brittle and breaks. No. In No. 8, since Na thiosulfate was used as an additive during pickling, the internal oxide layer did not remain and the punching property was deteriorated. In Nos. 9 and 10, since the dew point at the time of finish annealing is high, an internal oxide layer is formed at the time of finish annealing, the abundance of the surface becomes high, and the iron loss worsens. No. In No. 11, the hot-rolled plate annealing temperature is high, the internal oxide layer becomes thick, and the iron loss worsens. However, No. No. 11 states that the effect of the present invention can be obtained by appropriately adding Sn, Cu, and Sb even at the same hot-rolled plate annealing temperature. It is shown by 12 to 23. No. If the amount added is small as in 12, 16 and 20, the effect of suppressing the internal oxide layer cannot be sufficiently obtained. On the other hand, No. When the amount of addition is large as in 15, 19 and 23, the iron loss tends to be a little worse, and in particular, No. In No. 23, the internal oxide layer is also reduced too much, so that the punching accuracy deteriorates.

No. The internal oxide layer observation photograph of No. 1 is shown in FIG. The white part at the bottom is the ground iron, the black part at the top is air, and the gray part in the middle is the internal oxide layer. FIG. 2 is obtained by observing the surface layer of the mirror-polished sample with an optical microscope.

(Example 2)
Steel is cast with the components shown in Table 2 in mass%, and after casting, it is hot-rolled to produce a hot-rolled plate having a plate thickness of 2.0 mm. Then, heat treatment (atmosphere: 100% nitrogen) is performed at 750 ° C. for 1 minute to form an internal oxide layer on the surface. Then, it is soaked in hydrochloric acid (7.5 wt%) at 85 ° C. to which the additive (0.07 wt%) shown in Table 2 is added for 30 seconds and pickled. After that, it was cold-rolled to a thickness of 0.5 mm at a rolling reduction of 75%, and finish-annealed at 1050 ° C. for 30 seconds in the atmosphere of the dew point shown in Table 2, and the punching accuracy and magnetic characteristics (iron loss) described below were performed. To measure. The measurement results are also shown in Table 2.

The method of iron loss value and punching accuracy is as described in Example 1. However, since iron loss and punching accuracy fluctuate even if Si and Al are changed, the reference values are the invention examples of the same Si and Al amounts.

Even if Si and Al are changed within the specified range, both iron loss and punching accuracy are achieved as compared with the conventional example. Since No. 32, 35, 38, and 41 used a pickling accelerator (sodium thiosulfate), the internal oxide layer disappeared and the punching accuracy deteriorated. No. Since the dew points of 33, 36, 39, and 42 are high during finish annealing, an internal oxide layer is formed during finish annealing, the abundance of the surface is high, and iron loss is exacerbated.

Claims (3)

By mass%
C: 0.0030% or less,
Si: 2.0% or more and 4.0% or less,
Al: 0.1% or more and 3.0% or less,
Mn: 0.10% or more and 2.00% or less,
P: 0.09% or less,
S: 0.0050% or less,
N: Contains 0.0050% or less, and consists of the balance Fe and impurity elements.
A non-oriented electrical steel sheet characterized in that the surface area covered by the internal oxide layer on the surface is 10 to 70% of the total surface area, and the average internal oxide layer thickness in a region having an internal oxide layer is 0.5 μm to 10 μm. In addition by mass%
Sn: 0.02% or more and 0.40% or less,
Cu: 0.10% or more and 1.00% or less,
Sb: The non-oriented electrical steel sheet according to claim 1, which contains one or more of 0.02% or more and 0.40% or less. In addition by mass%
REM: 0.0005% or more and 0.0400% or less,
Ca: 0.0005% or more and 0.0400% or less,
Mg: The non-oriented electrical steel sheet according to claim 1 or 2, which contains one or more of 0.0005% or more and 0.0400% or less.