JP2021123764A - Non-oriented electromagnetic steel sheet and method for manufacturing the same - Google Patents

Abstract

To provide a non-oriented electromagnetic steel sheet capable of resolving the variation "skid mark" of magnetic properties in the longitudinal direction to improve the entire magnetic properties, and a method for manufacturing the same.SOLUTION: A non-oriented electromagnetic steel sheet includes, by mass%, C:0.005% or less, Si:2.0-3.5%, Al:0.3-1.0%, Mn:0.20% or less, S:0.0020% or less, N:0.0030% or less and the remainder consisting of Fe and inevitable impurities. When setting a plate thickness to t and setting a smaller circle equivalent average particle size to GS1 and a larger one to GS2 in a circle equivalent average particle size on a rolling direction cross section in a region at a 1/4t position in the plate thickness direction from one surface and a circle equivalent average particle size on a rolling direction cross section in a region at a 3/4t position in the plate thickness direction from the one surface, a circle equivalent average particle size ratio R=GS2/GS1 is 1.5 or less.SELECTED DRAWING: Figure 6

Description

The present invention relates to a non-oriented electrical steel sheet having no change in magnetic characteristics in a coil due to hot rolling and a method for manufacturing the same.

Non-oriented electrical steel sheets are widely used mainly as iron core materials for rotating equipment. In particular, in response to the recent demand for energy saving, stable and good magnetic characteristics and productivity, as well as cost reduction are required. In addition, the demand for non-oriented electrical steel sheets is rapidly increasing due to the increase in consumption in the transportation equipment field and the rapid progress of electrification in developing countries.

Since electrical steel sheets are used in electrical equipment, their magnetic properties are important. In particular, in order to ensure good iron loss characteristics (small iron loss value) for non-oriented electrical steel sheets, high-grade non-oriented electrical steel sheets with good iron loss characteristics have traditionally been made of Al and Si. It contains the next largest amount.

Further, in recent years, in high-grade non-oriented electrical steel sheets, "more addition" of Al has not only detoxified C, N, S, etc., but also improved specific resistance and cost and characteristics like Si. The effect of improvement costs (cost performance) has also come to be taken into consideration.

The magnetic properties of non-oriented electrical steel sheets are built in by final annealing in addition to hot rolling, hot rolling sheet annealing, and cold rolling, starting with component adjustment in steelmaking. The final annealing is basically carried out by continuously changing the annealing temperature and time in a dry atmosphere with a mixed gas of nitrogen and hydrogen. At this time, the magnetic characteristics may fluctuate significantly in the longitudinal direction of the coil, especially in the high-grade grade.

It is known that this phenomenon is caused by the difference in temperature history during slab heating and soaking in hot rolling. In the heating furnace in hot rolling, a "skid" exists to hold the slab, and uniform heating of the slab is being attempted. Since this skid is cooled with water and is in contact with the slab, it is inevitable that the temperature is low. The temperature deviation in this slab heating stage may affect the characteristics of the product due to the precipitation phenomenon in the subsequent process. The fluctuation of characteristics due to this temperature deviation is called "skid mark".

As shown in Table 1, in non-oriented electrical steel sheets, iron loss is generally excellent in a portion near a skid pipe where the temperature is relatively low, and where the temperature between the skid pipes is high is inferior. This is called a skid mark.

Patent Document 1 states that non-oriented electrical steel sheets can be stably produced without simply containing a large amount of alloying elements such as Si and Al, and inevitably by purifying the steel. A technique is disclosed in which the skid mark that becomes apparent due to the influence of mixed Ti can be eliminated by making it possible to raise the level of the slab heating temperature.

Japanese Unexamined Patent Publication No. 5-140649

However, the reverse phenomenon may occur in non-oriented electrical steel sheets. That is, the magnetic characteristics of the portion corresponding to the skid portion may be inferior, and the magnetic characteristics of the corresponding portion between the skids may be good. This is called the "reverse skid mark".

There was a need to eliminate these opposite phenomena. However, since it is the opposite phenomenon, there is no appropriate countermeasure within a wide range of manufacturing conditions, and the improvement of magnetic characteristics is not sufficient.

Therefore, the present invention makes the crystal grain size of the non-oriented electrical steel sheet in the coil plate thickness direction uniform, realizes this state over the entire length of the coil, and eliminates the fluctuation "skid mark" of the magnetic characteristics in the longitudinal direction. It is an object of the present invention to obtain a non-oriented electrical steel sheet, an electromagnetic steel sheet, and a method for manufacturing the same, in which the overall magnetic characteristics are improved.

As a result of diligent studies by the present inventors, the "reverse skid mark" is dramatically achieved by hot rolling in a region outside the hot rolling conditions of conventional non-oriented electrical steel sheets and by optimizing the composition of the steel sheet. We found that it could be improved. The present invention has been further studied based on the above findings, and the gist thereof is as follows.

(1) In mass%, C: 0.005% or less, Si: 2.0 to 3.5%, Al: 0.3 to 1.0%, Mn: 0.20% or less, S: 0.0020 % Or less, N: 0.0030% or less, and in a non-oriented electrical steel sheet composed of the balance Fe and unavoidable impurities, when the plate thickness is t, it is located at 1/4 t position in the plate thickness direction from one surface. Of the circle-equivalent average particle diameter in the rolling direction cross section of the region and the circle-equivalent average particle diameter in the rolling direction cross section of the region 3/4 t in the plate thickness direction from the surface, the smaller one is GS1 and the larger one is GS2. A non-oriented electrical steel sheet having an average particle size ratio R = GS2 / GS1 equivalent to a circle of 1.5 or less.

(2) The method for producing the non-directional electromagnetic steel plate according to the above (1), which is a slab heating step of heating a steel slab having a chemical component of the above (1) and hot rolling of the heated steel slab. A hot rolling step of winding and obtaining a hot-rolled hot steel strip, a hot-rolled steel strip annealing step of quenching the hot-rolled hot-rolled strip to obtain a tempered hot-rolled strip, and the tempered hot-rolled strip. A cold-rolling step of cold-rolling to obtain a cold-rolled steel strip, and a finish annealing step of finishing-anning the cold-rolled steel strip to obtain a non-directional electromagnetic steel plate. In the manufacturing method, in the slab heating step, the average cross-sectional temperature of the slab on the skid is 1150 ° C. or higher, and in the hot rolling step, the skid is extracted from the heating furnace and then up to the finish rolling start temperature. A method for producing a non-directional electromagnetic steel plate, characterized in that the average cooling rate of the coldest part of the slab located above is 1.0 ° C./sec or less, and the finish rolling start temperature is 950 ° C. or higher. ..

(3) In the hot-rolled steel strip annealing step, the non-oriented electrical steel sheet according to (2) is characterized in that the hot-rolled steel strip is continuously annealed at a temperature of 950 ° C. or higher and 1000 ° C. or lower for 30 seconds or longer. Production method.

When this technology is applied, the characteristics of non-oriented electrical steel sheets are highly stable, fluctuations in the magnetic characteristics of rotating equipment are minimized, and energy loss is drastically reduced.

It is a figure which shows the way of thinking in the case of the conventional purity. It is a figure which shows the way of thinking in the case of high-purity steel in this invention. It is a figure which shows the temperature history of a coil, and the precipitation curve. It is a figure which shows the iron loss of the total length of a coil measured by the continuous iron loss measuring instrument at the time of the final annealing. It is a figure which shows the example of the cross-sectional structure of the final product corresponding to the skid by the conventional hot rolling technique and the skid by this invention, (a) is by the conventional hot rolling technique, (b) is by this invention. .. It is a figure which shows the relationship between the average particle diameter ratio R equivalent to a circle, and the relative value of iron loss.

As a result of diligent studies, the present inventors have found that the "reverse skid mark" is dramatically improved by optimizing the regions and components that deviate from the conventional hot rolling conditions. The present invention proposes a method for reducing this phenomenon.

The generation of skid marks in the heating furnace during hot rolling is considered as follows.

The melted and continuously cast slab contains unavoidable impurities C, N, S, Ti and the like. These impurities form a compound with Mn, Al and the like. The solid solution / precipitation of these compounds, AlN, MnS, Ti- (N, C), BN, Nb- (C, N), and Zr- (C, N) is a function of temperature. That is, it dissolves solidly above a certain temperature.

These impurities have two effects on the properties of non-oriented electrical steel sheets. One is grain growth, and the other is history loss among iron losses. This phenomenon depends mainly on the content of impurities, the time and temperature of slab heating. In this way, impurities not only hinder the movement of grain boundaries, but also cause an increase in historical loss among iron losses. Therefore, it has been sought to reduce impurities as much as possible. The present inventors have reached a solution after diligent studies.

The details will be described below.

First, since the non-directional electromagnetic steel plate is mainly used for rotating equipment, the crystal orientation is such that <100> orientations are randomly arranged in the rolled surface, and the primary recrystallization consists of crystal grains that are uniform throughout the coil and do not exceed 200 μm. It is required to have a crystal structure.

When the scale is small, such as in the research stage, the characteristic evaluation of non-oriented electrical steel sheets does not cause a big problem in the variation in the material part such as the coil, and the uniformity is maintained. However, due to the recent increase in mass production and production scale that contribute to productivity improvement, the manufacturing unit is increasing. Specifically, the slab coil has a large unit weight, and along with this, the non-uniformity in the coil inevitably becomes remarkable. A typical example of this is the occurrence of skid marks.

Conventionally, as described above, the non-uniformity in the coil is considered to be the non-uniformity of grain growth due to the non-uniform heat history in the coil length direction. However, recently, it has been found that this non-uniformity in the length direction is also caused by the non-uniformity in the thickness direction. That is, the non-uniformity of the two-dimensional magnetic characteristics of the thin steel sheet.

The main part of the present invention is that the precipitation behavior of MnS and the like is synchronized with the cooling during hot rolling. Therefore, it is important to reduce the amount of MnS precipitated to reduce the cooling dependence of precipitation. Although the temperature history of the coil is not much different from the conventional one, the voids of the precipitation curve are sewn and rolled.

The precipitation phenomenon of precipitates that affects grain growth during final annealing of non-oriented electrical steel sheets is mainly divided into two. These are the initial state during (X) slab heating and soaking, and the dynamic behavior during (Y) hot rolling.

(X) In the initial state at the time of slab heating and soaking, the temperature on the skid is low and the temperature between the skids is high. Depending on this temperature and the amount of precipitate-forming elements, the precipitation state is as follows.

The temperature range of the skid part and the solidification / precipitation of the precipitate are thermodynamically related, and the solid dissolution curve generally draws a quadratic function if both compounds are linear mutual terms, and the solid dissolution corresponding to the content. Above the temperature, there is no amount of precipitation, so the solid solution curve becomes horizontal. This limit point changes depending on the content. If there is a large amount of precipitate elements as in the past, it will already precipitate in the heating furnace under equilibrium conditions. That is, the low temperature portion is precipitated, and the high temperature portion is finely precipitated from the solid solution state during hot rolling.

On the other hand, in the case of high-purity steel as in the present invention, the precipitation state in the heating furnace is almost the same on the skid and between the skids, and during hot rolling, in the high temperature part (between the skids). The precipitation is delayed, and the low temperature part is close to the precipitation nose, so that the precipitation is made finer and the grain growth property at the time of final annealing is hindered. In such a case, a reverse skid type state occurs.

The present invention not only reduces the amount of impurity elements, but also controls the hot rolling conditions of (Y) to realize an intermediate state between a reverse skid type and a forward skid type.

As shown in FIG. 1, in the forward skid type, the high temperature portion is solid-solved, and since the temperature is high during hot rolling, precipitates such as MnS are finely precipitated.

Further, in the case of high-purity steel, the amount of solid solution in the initial state does not differ in the precipitation state (solid solution state) in the temperature range of the skid portion, but the temperature is high during hot rolling unless the hot rolling conditions are controlled. In the part, the precipitate is deposited late, resulting in a non-uniform precipitation state.

Although the temperatures on and between the skids are the same, comparing FIGS. 1 and 2, the higher the purity of the steel sheet component (FIG. 2), the thermodynamically lower the temperature at point A (solid solution limit).

Comparing FIGS. 1 and 2, the range on the right side (high temperature range) from point A expands due to high purity, and uniform precipitation is performed by utilizing this expansion. However, if it is left as it is, uniform fine separation will occur, so positive precipitation will be carried out by hot-rolled sheet annealing to make it harmless as a whole.

FIG. 3 shows the temperature history of the coil and the precipitation curve. The solid line in FIG. 3 represents the prior art, and the broken line represents the present invention. The arrow simulates the total length of the coil.

As shown in FIG. 3, in the reverse skid type, in the dynamic behavior during (Y) hot rolling, in the case of high-purity steel, the precipitation state at the time of heating is almost the same in both the high temperature portion and the low temperature portion. When the slab in this state is hot-rolled, the precipitation start time is delayed, the precipitation rate is slowed, and the width of the precipitation curve is widened as compared with the case where a large amount of impurity components described later are contained in the whole. By performing hot rolling between the voids, the precipitation behavior becomes uniform. The solid line is steel containing a large amount of impurity components. In addition, the broken line extends to the low temperature side, the long time side, and the interval.

In the present invention, since the amounts of Mn and S are small, the start of precipitation of MnS is delayed, the equal precipitation curve interval is widened, and the entire length of the coil is inserted between them to realize uniform precipitation. In the conventional state, since the contents of Mn and S are large, the precipitation of MnS starts earlier, and since the interval is wide, non-uniform precipitation occurs.

<Average particle size ratio R equivalent to a circle>
FIG. 4 shows a chart in which the iron loss of the entire coil length was measured by a continuous iron loss measuring instrument at the time of final annealing.

An example of the non-uniformity of the crystal grains in the thickness direction in the cross section at the position (1) in FIG. 4 is shown in FIG. 5 (a). The upper side of the paper surface corresponds to the upper surface of the slab during heating in the hot rolling heating furnace, and the rolling direction is from left to right on the paper surface. The plate thickness is 0.5 mm. In this way, it was found that the particle size changed almost continuously in the plate thickness direction from the lower surface to the upper surface during slab heating. In order to quantify this, the smaller of the circle-equivalent average particle diameter in the rolling direction cross section at the 1 / 4t position and the 3/4t position (1 / 4t position from the other surface) of the total plate thickness from one surface of the steel sheet. Was GS1 and the larger one was GS2, and the circle-equivalent average particle size ratio RGS2 / GS1 was defined. When GS1 = GS2, R = 1. By the way, since non-oriented electrical steel sheets are wound, forked, and unwound in many steps after hot rolling (coiling, uncoiling), the upper surface and the lower surface during slab heating are replaced. Therefore, in the present invention, "one surface" and "the other surface" are relativized.

As a result of the study by the present inventors, it was found that the reverse skid mark does not occur when the circle-equivalent average particle size ratio R ≦ 1.5. Originally, it is estimated that this R is still a small value (more uniform), but in reality, 1.5 is the boundary. Think of this as follows.

The grain size of the high-grade non-oriented electrical steel sheet at the final product stage exceeds 100 μm and is relatively large. Therefore, the grain shape changes from a polyhedron to a small polyhedron. In the case of a small polyhedron (large grain), the deviation from the sphere is large. Therefore, in the case of large grains, it is overestimated as a representative value indicating the grain size. That is, the circle-equivalent average particle size ratio R ≦ 1.5 is estimated to be smaller than 1.5 in the ideal three-dimensional particle size evaluation. FIG. 5B shows an example of the cross-sectional structure corresponding to the skid of the final product obtained by the present invention.

FIG. 6 shows the relationship between the circle-equivalent average particle size ratio R and the iron loss relative value (W15 / 50 ratio). The relative iron loss value (W15 / 50 ratio) is obtained by dividing the maximum iron loss value by the minimum iron loss value in the length direction of the steel sheet.

In FIG. 6, Si = 2.6%, Mn = 0.20%, Al = 0.45%, C = 0.0015%, S = 0.00018%, N = 0.0015%, Ti = 0. A non-oriented electrical steel sheet slab containing 0019% of unavoidable impurities in the balance was heated and leveled at 105 to 1180 ° C. for 350 to 400 minutes by a conventional method to obtain 50A290 in JIS C 2552. This is the result of the circle-equivalent average particle size ratio R and the relative value of iron loss in the case of non-oriented electrical steel sheets.

The portion where the circle-equivalent average particle size ratio R is small has good characteristics, but when the circle-equivalent average particle size ratio R exceeds 1.5, the iron loss is significantly deteriorated and W15 / 50 does not satisfy 2.9 W / kg. This is a result obtained from various parts of the coil where the reverse skid mark is generated. Thus, the best point is 2.4 W / kg, but the worst point is 3.2 W / kg, which is more than 30% iron. Deterioration of loss fluctuation is observed and deviates from the 50A290 standard.

<Ingredient composition>
The composition of the components will be described below. Hereinafter,% means mass%.

Si: 2.00 to 3.50%
Si: 2.00 to 3.50%. Si is an element that increases the intrinsic resistance and contributes to the improvement of iron loss characteristics. If it is less than 2.00%, γ-α transformation occurs during hot rolling and reverse skid marks do not occur. Forward skid marks may occur. If it is more than 3.50%, breakage occurs frequently in the manufacturing process, especially in rolling, and commercial production is practically impossible.

Al: 0.30 to 1.00%
Al is also added to secure the inherent resistance. When Al exceeds 1.00%, roll wear of various rolling mills is remarkably generated and production is hindered. Further, when it is 0.30% or less, the effect of improving iron loss is small.

Mn: 0.20% or less Mn is present as MnS by combining with S and deteriorates the magnetic characteristics, so a smaller amount is preferred, but a cost increase occurs in order to realize low Mn. Regarding the morphological control of MnS, which is the main purpose, the smaller the amount, the longer the precipitation of MnS is delayed, and the fluctuation in the precipitation state of MnS in the hot-rolled steel strip is reduced.

S: 0.0020% or less Reducing the S content is the skeleton of this technology, and it is essential that it is 0.0020% or less. If there are more than this, skid marks will occur (in order) instead of the opposite. Similar to Mn, the smaller the amount of MnS in the morphological control, the longer the precipitation of MnS is delayed, and the fluctuation in the precipitation state of MnS in the hot-rolled steel strip is reduced.

C: 0.0050% or less C, N, Ti and the like are well-known elements as unavoidable impurities and are elements that form precipitates. It is better that the number of elements forming these precipitates is small, but it is necessary to consider the cost.

If C is not 0.0050% or less, magnetic aging will occur and it will be fatal in terms of quality, and it will be 0.0050% or less. Of course, this value is not a regulation value at the steelmaking stage, but a regulation value for the final product, non-oriented electrical steel sheet. More preferably, it is 0.0030% or less.

N: 0.0030% or less N not only hinders grain boundary movement but also causes an increase in history loss among iron losses, so the content needs to be reduced. Since the non-oriented electrical steel sheet of the present invention contains a large amount of Al, N may form and precipitate AlN, and the content of N may be 0.0030% or less. Further, the precipitation of AlN during hot rolling is slower than that of MnS, and the influence in the present invention is extremely weak.

Other elements that are unavoidably contained in the steel sheet body in the end include P, Sn, Sb, B and the like, although Se, Nb, Cu and the like are artificially added. The amount of elements unavoidably mixed is required to be small, and is preferably 0.005% or less. As the elements to be added, Sn, Sb, and P are added up to about 0.05%. Further, B is a special element, and it is not preferable to add it to the high-grade non-oriented electrical steel sheet of the present invention, and it is preferably 0.0010% or less.

<Manufacturing method>
This is the core process of this technology, and compared to the conventional technology, it is characterized by heating high-purity non-oriented electrical steel sheet slabs at a low temperature and hot rolling at a high temperature.

The idea of the present invention is to realize a uniform state of impurities that have a great influence on the grain growth of the non-directional electromagnetic steel plate, and particularly in the case of the present technology, the thickness is 1.6 to 2.8 mm, the width is 1000 mm to 1300 mm. A coil having a length of about 2000 m is suitable, and a uniform state of unavoidable impurities of the Mn—S (−Cu) compound is realized over the entire length of the coil. For this purpose, the precipitation curve in hot rolling and the cooling conditions of the coil must be aligned.

For this purpose, first, the content of S is reduced as described above. Then, the hot rolling heating temperature is lowered to promote the precipitation of MnS as much as possible, and the decrease in the hot rolling temperature is slowed down as much as possible.

<Slab heating>
(Average cross-sectional temperature of slab on skid ≧ 1150 ℃
When the average cross-sectional temperature of the slab on the skid is less than 1150 ° C., even a high-purity steel as in the present invention approaches the nose of the precipitation curve shown in FIG. 3 during hot rolling, and non-uniform precipitation occurs across the skid. Therefore, the average cross-sectional temperature of the slab on the skid is set to 1150 ° C. or higher. The cross-sectional temperature of the slab on the skid can be obtained by the measured value of the portion that can be measured by the radiation thermometer and the heat transfer calculation.

<Hot rolling>
(Average cooling rate of the coldest part of the slab ≤ 1.0 ° C / sec)
When the average cooling rate of the coldest part of the slab exceeds 1.0 ° C./sec, the nose of the precipitation curve shown in FIG. 3 during hot rolling even for high-purity steel as in the present invention, as in the case of slab heating. Cross-crossing non-uniform precipitation occurs. Therefore, the average cooling rate of the coldest part of the slab is set to 1.0 ° C./sec or less. Here, the "slab coldest part" corresponds to the part of the slab located on the skid in the heating furnace.

(Finish rolling start temperature TF0 ≧ 950 ° C)
When the finish rolling start temperature TF0 is less than 950 ° C., the precipitation curve shown in FIG. Cross-crossing non-uniform precipitation occurs as it approaches the nose. Therefore, the finish rolling start temperature TF0 is set to 950 ° C. or higher.

The idea of realizing this high-temperature hot rolling is the opposite of the conventional hot rolling conditions for non-oriented electrical steel sheets.

<Hot rolled plate annealing>
In the present technology, it is preferable to perform hot-rolled plate annealing during the final cold rolling after hot rolling. This heat treatment is also effective in controlling precipitates. This is to cause recrystallization of the pre-cold rolling structure and more perfect precipitation of MnS. The former recrystallization is for improving and ensuring magnetic properties, and the latter is for obtaining a completely precipitated state of MnS remaining precipitated. The temperature is preferably 950 ° C to 1000 ° C. If it is lower than this, recrystallization in the pre-cold rolling structure is not sufficient and the magnetic properties are inferior. If the value is high, recrystallization is sufficient, but MnS is resolidified and reverse skid marks are generated. If the time is 30 seconds or more, the above effect can be obtained. It is possible to exceed 60 seconds, but the productivity is inferior.

<Product thickness>
The product thickness is up to the lower limit of 0.18 mm in actual production. Although it is possible to produce a product thinner than 0.18 mm, if the roll diameter is large, the thickness accuracy (plate thickness fluctuation of 5% or less) is satisfied and rolling cannot be performed satisfactorily. The thicker one has a larger absolute value iron loss of the grain-oriented electrical steel sheet, so the upper limit of the Japanese Industrial Standards is 0.50 mm.

The present invention is a technique for preventing non-uniformity of magnetic characteristics in the coil length direction of non-oriented electrical steel sheets. Since the absolute value of the magnetic characteristics depends on the components and the like, in this example, the evaluation was made not by the absolute value iron loss but by the fluctuation value (average particle size ratio R equivalent to a circle).

A non-directional electromagnetic steel sheet slab having the components shown in Table 2 was hot-rolled under the conditions shown in Table 3 to obtain a hot-rolled plate having a thickness of 2.0 mm, and the hot-rolled plate was annealed under the conditions shown in Table 3. After pickling, it was made into a cold-rolled steel sheet of 0.5 mm. Then, final annealing was performed at 975 to 1050 ° C. for about 60 seconds. Then, the circle-equivalent average particle diameter at the 1 / 4t position and the 3/4t position of the steel sheet in the plate thickness direction was determined, and the circle-equivalent average particle diameter ratio R was determined. Further, the maximum value and the minimum value of the iron loss in the length direction of the steel sheet were obtained, and the relative iron loss value of 1.03 or less was regarded as acceptable.

When the present invention is applied in this way, fluctuations in the crystal grain size of the entire coil length are drastically reduced, and a uniform product can be obtained.

The present invention realizes uniform characteristics of non-oriented electrical steel sheets. Generally, non-oriented electrical steel sheets are produced in a coil shape, and the larger the size, the better the productivity. For example, thickness (0.35 mm, 0.50 mm, etc.) x width (about 1200 mm) x length (more than 5000 m). In the conventional technique, the magnetic characteristics fluctuate due to the temperature deviation due to the skid of the hot rolling heating furnace in the length of more than 5000 m. And since the rating (certification of the representative value of the characteristic) performed for each coil is performed using the worst value in the coil, if there is a fluctuation in the coil, the worst value is applied and the actual over-specification or aim is made. Product characteristics cannot be built in, resulting in a decrease in productivity. The application of this technology can greatly contribute to the production of non-oriented electrical steel sheets that eliminate such a phenomenon.

Claims (3)

By mass%
C: 0.005% or less,
Si: 2.0-3.5%,
Al: 0.3-1.0%,
Mn: 0.20% or less,
S: 0.0020% or less,
N: In non-oriented electrical steel sheets containing 0.0030% or less and consisting of the balance Fe and unavoidable impurities.
When the plate thickness is t, the average particle size equivalent to a circle in the rolling direction cross section of the region 1 / 4t in the plate thickness direction from one surface and the rolling direction of the region 3/4t in the plate thickness direction from the surface. Of the circle-equivalent average particle diameters in the cross section, when the smaller one is GS1 and the larger one is GS2, the non-directional electromagnetic wave is characterized in that the circle-equivalent average particle diameter ratio R = GS2 / GS1 is 1.5 or less. Steel plate. The method for manufacturing a non-oriented electrical steel sheet according to claim 1.
A slab heating step for heating a steel slab having the chemical composition according to claim 1,
A hot rolling process in which a heated steel slab is hot-rolled and wound to obtain a hot-rolled hot steel strip.
The hot-rolled steel strip annealing step of annealing the hot-rolled hot steel strip to obtain an annealed hot-rolled steel strip,
A cold rolling step of cold-rolling the annealed hot-rolled steel strip to obtain a cold-rolled steel strip,
A finish annealing step of finishing and annealing the cold-rolled steel strip to obtain a non-oriented electrical steel sheet,
In the manufacturing method of non-oriented electrical steel sheet consisting of
In the slab heating step, the average cross-sectional temperature of the slab on the skid is 1150 ° C. or higher.
In the hot rolling step, the average cooling rate of the coldest part of the slab located on the skid after extracting the slab from the heating furnace is 1.0 ° C./sec or less and up to the finish rolling start temperature. The finish rolling start temperature is 950 ° C. or higher.
A method for manufacturing non-oriented electrical steel sheets, which is characterized by this. The method for producing a non-oriented electrical steel sheet according to claim 2, wherein in the hot-rolled steel strip annealing step, the hot-rolled steel strip is continuously annealed at a temperature of 950 ° C. or higher and 1000 ° C. or lower for 30 seconds or longer. ..

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