JPH03120316A - Production of nonoriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To produce a silicon steel sheet having low iron loss and high magnetic flux density by carrying out reversing rolling at least in one stage among rolling stages at the time of rolling a slab of a steel containing specific amounts of Si, Al, and Mn into a metal sheet by means of hot rolling and cold rolling in manufacturing a nonoriented silicon steel sheet. CONSTITUTION:A slab of a steel having a composition which contains, by weight, >=1.8%, in total, of Si and Al and 0.5-2.0% Mn and in which relationships represented by Si(%)+Al(%)-0.5XMn(%)=1.8-3.0% exist among respective contents of Si, Al, and Mn mentioned above is hot-rolled, and the resulting hot rolled plate is subjected to recrystallization annealing and then to surface descaling treatment, or, the above hot rolled plate is descaled, recrystallization-annealed, cold-rolled once or cold-rolled or warm-rolled twice or more while process-annealed between the cold rolling stages to the final sheet thickness, and further finish-annealed so as to be formed into a silicon steel sheet. By carrying out reversing rolling at least in one stage among the above rolling stages, the nonoriented silicon steel sheet having high magnetic flux density and low iron loss can be stably produced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing a so-called high-grade non-oriented electrical steel sheet containing a total of 1.8 weight percent or more of Si and octane.
In particular, the present invention relates to a method for producing non-oriented electrical steel sheets with excellent magnetic flux density and low iron loss.

(Prior technology) Non-oriented electrical steel sheet is a magnetic material mainly used as the iron core of motors and transformers. After that, recrystallization annealing is performed before or after descaling, and the final thickness is achieved by cold rolling or warm rolling once or twice with intermediate annealing, and then finish annealing is performed. ing. The hot rolling, cold rolling or warm rolling is usually carried out in a continuous tandem mill with excellent productivity.

By the way, since non-oriented electrical steel sheets are used for the above-mentioned purposes, they are required to have low iron ti and high magnetic flux density as their characteristics. Iron loss is the heat generated when magnetizing an iron core, and the iron loss value is the heat loss expressed per unit weight of the iron core. The smaller this value is, the less power loss there is, and high-grade electrical steel sheets with low core loss are generally used in large equipment that is difficult to cool and equipment where circuit stability due to heat generation is a problem. Magnetic flux density indicates the degree of concentration of magnetic energy in the iron core, and the larger this value, the smaller the size of the iron core, which is advantageous in reducing the size of equipment.

It is known that the former type of steel is controlled by two factors: eddy current loss and hysteresis. is II loss due to eddy currents induced by magnetization, and depends on the electrical resistance and thickness of the steel. In other words, the larger the electrical resistance or the thinner the plate thickness, the smaller the eddy current loss. Therefore, in order to reduce iron loss, it is effective to increase the plate thickness to h4 or to increase the electrical resistance of the steel. .

Regarding the plate thickness, if it is made too thin, there are problems such as the work of laminating the iron core takes time, so the JIS standard is 0.3.
5-1, 0.50-1, and 0.65 mm are specified for the effi resistance, which contains Si, A, and
l.

It is increased by adding various alloying elements such as Me. Among them, a large amount of Si is added, which has a large effect and is inexpensive. This is why electrical steel sheets are also called silicon steel sheets, and the higher the 81 content, the higher the quality of electrical steel sheets with lower iron IQ.

During the process of magnetization, the hysteresis is smaller as the grain boundaries and precipitates such as fine carbides, nitrides, sulfides, and oxides that obstruct the movement of the stone wall are small. For example, Ti, Nb with low content of C and N are used, and steel with few impurities is used, and manufacturing conditions are adopted to facilitate the growth of crystal grains.
, ■ The formation of carbides and nitrides is suppressed by using steel that does not contain carbonitride-forming elements. Low-grade IT&IIWJ sheets usually do not have Al added to them, whereas high-grade electrical steel sheets have a large amount of ^2 added for the purpose of reducing eddy current loss. to avoid negative effects. For Pi oxides and oxides,
This problem is dealt with by minimizing the amount of S and oxygen in the steel. Furthermore, by adjusting the annealing conditions, the crystal grains are grown sufficiently and controlled to have an appropriate grain size.

However, all of the methods described above tend to lower the magnetic flux density. When a large amount of an alloying element such as Si is added for the purpose of reducing eddy currents, the iron content decreases by that amount, resulting in a lower magnetic flux density. If we use steel with few impurities and grow crystal grains to reduce hysteresis,
Texture (crystal orientation) that is usually unfavorable for magnetic properties
develops and the magnetic flux density decreases.

For this reason, various methods of achieving both high magnetic flux density and low iron loss have been studied, and it is generally said that a method of controlling H of the texture is effective.

Grain-oriented electrical steel sheets make the most of this method; they do not easily magnetize, and by aligning the 100> axis in the rolling direction, both iron loss and magnetic flux density in that direction are excellent. be. However, in the case of non-oriented electrical steel sheets,
Unlike grain-oriented electrical steel sheets, it is necessary that many <100> axes exist not only in the rolling direction but also in all directions within the sheet surface, and there are more crystal grains parallel to the sheet surface (1001 planes). However, when the crystal grains are enlarged by final annealing as described above (1001
The number of crystal grains on the surface decreases, and the magnetic flux density decreases.

On the other hand, various methods have been proposed for improving the texture of non-oriented 1i magnetic steel sheets. (Japanese Patent Application Laid-open No. 60-152628),
Warm rolling is performed instead of cold rolling (Japanese Unexamined Patent Publication No. 58-18
1822), etc. Although these methods can improve the texture to some extent, the effects are not as great as expected, and all of these methods are difficult to implement industrially.

As described above, in the conventional method, it is difficult to achieve both low iron member and high magnetic flux density, and it is especially difficult for high-grade electrical steel sheets containing a large amount of Si and ^E. For this reason, even if the iron loss is low, the magnetic flux density is low, making it impossible to reduce the size of the iron core, leading to an increase in NHK's manufacturing costs, which negates the advantages of using high-grade materials. If a device with a low magnetic flux density is used with an unreasonably high magnetic flux density, the iron loss will increase due to an increase in the excitation current, and the loss of the entire device may actually increase.

(Problems to be Solved by the Invention) An object of the present invention is to provide an industrially practicable method that can reduce iron loss and improve magnetic flux density at the same time. That is, the object of the present invention is (1) to provide a method that can easily produce a non-oriented electrical steel sheet with high double density and low core loss.

(Means for solving the problem) Conventionally, in the production of non-oriented IIT magnetic steel sheets, both the hot rolling process and the cold rolling process are carried out in a highly productive continuous tandem mill. The inventors performed one or both of these steps by reverse rolling,
The magnetic flux density of the product is significantly improved, and the material contains S.
It has been found that the properties can be further improved by using steel with low impurities whose contents of i, AP and Hn are specified.

The present invention was completed based on the above knowledge, and its gist is ``A process of hot rolling a steel slab containing a total of 1.8% or more of Si and Al as a starting material. ,
By going through the steps of recrystallization annealing before or after descaling, a step of cold rolling or warm rolling one time or two or more times with intermediate annealing to achieve the final plate thickness, and a step of applying finish refining. A method for producing a non-oriented electrical steel sheet, characterized in that at least one of the hot rolling step, cold rolling step, or warm rolling step is performed by reverse rolling. "It is in.

In the present invention, a total of 1 Si and A2 is added to the above starting material.
．． If a steel slab is used that contains 8 weight percent or more, 0.5 to 2.0 weight percent of -1, and the content of SN, Al, and Mn satisfies the following formula 0, it will have the same characteristics as - stage. Excellent non-oriented electrical steel sheets can be manufactured.

Si (%) + Al (%) 0.5%Mn (%) -1,
8-3.0C%)・・■ However, "%" of the element in the formula is "1%".

(Function) In the present invention, Si and Al are used as starting materials! A steel slab containing 1.8% by weight or more of , in total is used.

Even so-called low-grade materials with a total content of Si and A2 of less than 1.8% are not incapable of obtaining the effects of reverse rolling, which will be described later, but because they have α/T transformation, they cannot be hot-rolled. It is difficult to be affected by the rolling direction in the rolling process, and the upper limit of finish annealing is regulated by the transformation point, so even if reverse rolling is performed, the effect is small because it is difficult for the crystal grains to become black.

In addition, low-grade non-directional IT materials generally have high magnetic flux density and have few problems, and are also materials with strong demands for economic efficiency, so we purposely adopted the present invention to improve iron loss and magnetic flux density. Because of this, Si
A steel slab containing a total of 1.8% or more of aluminum and aluminum was used as the starting material.

As starting materials, at least Si and ^i with a total of 1.8
Using steel slabs with less impurities and containing more than % by weight,
If manufactured using the method described below, it will be non-directional with high magnetic flux density and low iron loss! Magnetic steel sheets can be obtained. Furthermore, it contains 0.5 to 2.0111% of Mn as a material, and SI,
By using a steel slab whose AN and Mn content satisfies the above formula 0, it is possible to produce a non-oriented electrical steel sheet with low core loss and excellent magnetic flux density.

Mn has not been used much in the past because its electrical resistance increase rate per unit area is about half that of Si and Al, and the effect of reducing eddy current loss is small. However, according to the results of the studies conducted by the present inventors, Mn It has been found that it has less adverse effect on magnetic flux density than Al and Al, and when added in an appropriate range depending on the contents of Sl and A2, it is possible to achieve both high magnetic flux density and low core loss. The reason for this is currently unknown, but it is thought to be due to the effect of improving the texture, or due to differences in atomic radius or electronic structure depending on the type of alloying element. However, if the Mn content is less than 0.5% by weight, the above-mentioned effects cannot be obtained, and if the content exceeds 2.0% by weight, not only will the steel become brittle, but the growth of crystal grains will also be impaired.

Furthermore, even if Hn is included in the range of 0.5 to 2.0% by weight, the value expressed as [Si% + A1% - 〇, 5 × Mn%] is 1
．． If it is less than 8%, a transformation point appears and it becomes difficult to control the grain size of the crystal grains, making it difficult to ensure low iron loss. On the other hand, if the value shown by [0.5 x Mn% to Si% + 8P%] exceeds 3.0%! It will be difficult to secure one batch of tickets to the east.

The steel slab used in the present invention contains at least 1.8% by weight or more of Si and ^2 in total, but even if the total content is 1.8% or more, one or the other may be present in an excessive amount. If the amount is too low, sufficient characteristics cannot be obtained, and when the amount is too high, harmful effects may occur. Desirable individual contents are as follows.

As mentioned above, Si has the effect of increasing the electrical resistance of steel and reducing eddy current loss, but if it is too low, it will be difficult to secure the level of iron 1 member required for high-grade non-oriented electrical steel sheets, and if it is too high, Since cold rolling property is significantly impaired, 1.5~
It is preferable to have a content of about 3.5% by weight.^2 Also, high-grade non-directional 1 is used in magnetic steel sheets to increase electrical resistance and l! N
It is added for the purpose of coarsening, but if it is too little, the effect will be small, and if it is added too much, no greater effect will be obtained and only the cost will increase, so 0.1 to 1. The content is preferably about 0% by weight.

In addition to the above-mentioned components, the high-grade non-oriented electrical steel sheet targeted by the present invention contains C, P, and S.

Contains components such as N.

Since C is a component that forms carbides and deteriorates all magnetic properties, it is better to keep the content as low as possible.In particular, to prevent magnetic aging, it should be less than 0.005 C, preferably 0.003 C. % or less.

P may be included for the purpose of adjusting strength and increasing electrical resistance, but since adding too much impairs cold rollability, the iA content is preferably 0.1% by weight or less.

Since S is a component that forms sulfide-based precipitates and deteriorates magnetic properties, the content is preferably 0.005% by weight or less, preferably 0.002% by weight or less.

Since N is also a component that forms nitrides and deteriorates magnetic properties, the content should be less than 0.00% by weight, preferably 0.0000% by weight.
The content is preferably 0.03% by weight or less.

In the method of the present invention, a steel slab containing the above-mentioned components is used as a starting material, a step of hot rolling it, a step of recrystallization annealing before or after descaling, and a step of performing one or two intermediate annealing steps.
The process of achieving the final plate thickness by cold rolling or warm rolling more than once,
A non-oriented electrical steel sheet is manufactured through a process of final annealing and final annealing.What is important is that at least one of the hot rolling, cold rolling, or warm rolling processes is performed by reverse rolling. It is.

If at least one of the hot rolling process, cold rolling process, or warm rolling process is performed by reverse rolling, the degree of rotation will be significantly improved.The detailed mechanism is currently unknown, but In continuous rolling by a tandem mill, the rolling direction is unidirectional, whereas in a lever-type mill, the rolling direction is sequentially reversed, which is presumed to change the fine structure of the rolling & [I weave.0 For example, It is thought that the crystal structure and orientation near the grain boundaries are subtly affected, and as a result, the texture after final annealing is improved, thereby improving the magnetic flux density.

When producing non-oriented 1 magnetic steel sheets through a hot rolling process and a cold rolling process, or when manufacturing a magnetic steel sheet through a hot rolling process and a warm rolling process, in either case, rolling in both processes is reverse rolling. It is most preferable to perform reverse rolling, but only the hot rolling process, the cold rolling process, or the warm rolling process can be performed by reverse rolling. Even just the - process can improve the magnetic flux density. . When the hot rolling process is performed by reverse rolling, both rolling and finish rolling may be performed by reverse rolling, but if finishing rolling is performed by reverse rolling, a special insulating furnace is required to ensure the finishing temperature. Therefore, in the case of a hot rolling process, it is more realistic to perform rough rolling by reverse rolling. If the rough rolling mill of the hot rolling mill is not a lever type, it is also effective to reverse roll the steel slab to intermediate JV in a thick plate mill.

The effect of reverse rolling is greater in the cold rolling process or the warm rolling process than in the hot rolling process.

This is thought to be because the closer the process is to the final set & [l weave, the more direct the influence can be exerted.

Desirable conditions for each step will be explained below.

(+)! If the heating temperature of the iii slab is too low, it will be difficult to secure the hot rolling finishing temperature and surface defects will increase. On the other hand, if heated at high temperatures, thick scale will form and the yield will decrease, so 110
A temperature of 0 to 1250°C is suitable.

(2) Hot rolling When hot rolling is performed by reverse rolling, it is desirable to perform three or more passes.Also, it is generally desirable to have a higher finishing temperature, so rough rolling is performed at 950″C or higher, and finishing is performed at 8°C.
It is preferable to carry out the process at a temperature of 00°C or higher.

The winding temperature is 55% due to the balance with pickling and descaling properties.
A range of 0 to 650″C is preferable.

(3) Recrystallization annealing The annealing temperature should be 750°C or higher, preferably 850°C or higher. However, if the temperature is too high, the crystal grains will become coarser than necessary and cracks will easily occur during cold working. Therefore, the upper limit is preferably about 1000'C.

(4) Cold Rolling When reverse rolling is performed by cold rolling, it is also preferable to perform three or more passes.

Cold rolling may be performed once or twice or more, but if magnetic flux density is important, it is better to perform cold rolling once at a reduction rate of 75 to 85%.If iron loss is important, intermediate annealing is recommended. sandwich 2
It is preferable to carry out the rolling process using a double cold rolling method.

A suitable temperature for intermediate annealing is 800 to +000°C.

(5) If the warm-rolled steel slab is a material with poor cold-rollability that contains a large amount of alloys such as Si, instead of the above-mentioned cold rolling,
The final plate thickness may be obtained by warm rolling in a temperature range of 3 or more baths when warm rolling is performed by reverse rolling.

(6) Finish annealing Finish annealing is preferably carried out by continuous annealing at a temperature of 850 to 1050'C for up to 3 minutes.

The present invention will be further explained below with reference to Examples.

(Example) A 230 mm thick steel slab with the chemical composition shown in Table 1 was used, hot rolled under various conditions shown in Table 2, recrystallized annealed before or after pickling, and then cooled. After the final plate thickness was achieved by intermediate rolling or warm rolling, final annealing was performed.

In the examples of the present invention, either hot rolling, cold rolling, or warm rolling was performed using a liver mill. In the comparative examples, hot rolling, cold rolling, or warm rolling was performed using a continuous tandem mill.

The results of examining the iron content and magnetic flux density of the non-oriented electrical steel sheet thus obtained are shown in Table 2 together with the manufacturing conditions.

In addition, in Table 2, "R" shown in the In rolling method column and cold rolling surface means reverse rolling, and "TJ" means continuous rolling.

(The following is a blank space) From Table 2, all of the examples of the present invention are better in iron 1 member and magnetic flux density than those of the comparative examples. especially,?
Contains 0.5% or more of In, Sl, Al! and 8117, Code 9, in which at least one step of hot rolling, cold rolling, or warm rolling was performed by reverse rolling, using steel type D-F whose Mn content was adjusted to meet the above conditions as a starting material (1).
Mail has even better iron tl and magnetic flux density.

(Effects of the Invention) As explained above, according to the method of the present invention, a low-iron one-member non-oriented electrical steel sheet with a high magnetic flux density can be stably produced.

Claims (2)

[Claims] (1) Using a steel slab containing 1.8% by weight or more of Si and Al in total as a starting material, hot rolling it, recrystallization annealing before or after descaling, single or intermediate annealing In a method of manufacturing a non-oriented electrical steel sheet by passing through two or more cold rolling or warm rolling steps to achieve the final thickness, and a step of final annealing, the hot rolling step, the cold rolling step, and a final annealing step are performed. A method for manufacturing a non-oriented electrical steel sheet, characterized in that at least one rolling step of the rolling step or the warm rolling step is performed by reverse rolling. (2) The starting material contains 1.8% by weight or more of Si and Al in total and 0.5 to 2.0% by weight of Mn, and Si, Al
The method for producing a non-oriented electrical steel sheet according to claim 1, wherein the steel slab has a content of Mn and Mn that satisfies the following formula. Si (%) + Al (%) - 0.5 x Mn (%) = 1.8
~3.0 (%) However, "%" of the element in the formula is "% by weight".