JPH02104619A - Production of non-oriented magnetic steel sheet having excellent iron loss characteristic - Google Patents

Abstract

PURPOSE:To produce the title non-oriented magnetic steel sheet having a composition similar to that of a conventional cold-rolled steel sheet and having high magnetic flux density and low iron loss by rolling a steel having a specified composition under specified process conditions. CONSTITUTION:A steel wherein the mean diameter of the ferrite grains prior to rolling at <=Ar3 transformation point is controlled to >=200mum and contg., by weight, <=0.05% C, <=0.010% N, <=1% Si, <=1.5% Mn, <=0.15% P, <=0.010% S, <=0.3% Al, the balance iron, and inevitable impurities is prepared. the steel is rolled at least 30% draft at a temp. ranging from 500 deg.C to the Ar3 transformation temp., finished at >=500 deg.C, cold-rolled as such or after the annealing of the hot-rolled sheet, and then cold rolled and annealed after acid washing. B is added, as required, to the steel in about >=1.5 of B/N. By this method, the amts. of the alloying elements to obtain the equivalent electromagnetic characteristic can be reduced, and the steel sheet having a composition similar to that of the conventional cold-rolled steel sheet and having high magnetic flux density and low iron loss can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a non-oriented electrical steel sheet with low core loss and high magnetic flux density.

(Prior art) Conventional electrical steel sheets are generally made of St or M as a means of reducing iron loss from the viewpoint of reducing eddy current loss due to increased specific resistance.
Methods have been used to increase the content of In addition, as a method to obtain excellent electromagnetic properties without adding these alloy components, there is a method in which cold-rolled/annealed sheets are subjected to several percent skin pass rolling, punched by the user, and then subjected to strain relief annealing ( JP-A No. 60-17014, etc.).

In these conventional methods, the finish hot rolling is generally 800°C or higher, and if the winding temperature is low and recrystallization has not progressed sufficiently,
After performing high-temperature hot-rolled sheet annealing, the product was cold-rolled by 75% or more and subjected to high-temperature short-time annealing. However, in the latter semi-process, as described above, several percent of skin pass rolling is performed thereon.

(Problems to be Solved by the Invention) Problems to be solved by the present invention are to reduce the amount of expensive alloying elements added to reduce iron loss and to omit the rolling process.

(Means for Solving the Problems) In order to solve the problems, the present invention provides a method in which the average grain size of ferrite grains before rolling below the ^r3 transformation point is 200 μm.
C: 0.05% or less, N: 0.01 in weight% of m or more
0% or less, Si: l1% or less, Mn: 1.5% or less, P: 0.15% or less, S: 0.010% or less, M: 0.3% or less, and if necessary, replace B with B. /N for 1.
5 or less, and the balance is Fe and unavoidable impurities.
At least 3 in the temperature range below r3 transformation point and above 500℃
After 0% rolling and finishing at a temperature of 500℃ or higher, it is either as-is or hot-rolled and annealed, followed by pickling and normal cold rolling and annealing.It has low iron loss and magnetic flux density. The present invention provides a method for manufacturing a non-oriented electrical steel sheet with high viscosity.

The reasons for limiting the constituent elements of the present invention will be explained below.

In addition, % in the following description is weight %.

First, in the chemical composition of the steel of the present invention, a small amount of C is preferable in order to improve iron loss, and a preferable content is 0.005% or less in order to prevent magnetic deterioration due to aging. However, in the process of the present invention, the effect of improving iron loss was confirmed up to 0.05% of C, so the upper limit of the amount of C was set to 0.05%. Si is added for the purpose of improving iron loss, but as the amount of Si increases, the magnetic flux density decreases, and the difference in the iron loss obtained by the manufacturing method of the present invention over the iron loss obtained by the conventional method becomes smaller. Not only this, but also the S
The upper limit of the amount of i added is 1%. In order to improve iron loss, it is better to have a small amount of N, and in the steel of the present invention, the condition was 0.010%. In particular, when suppressing AjN precipitation and lowering iron loss, it is desirable to add B to precipitate BN, but if B/N exceeds 1.5, excess B deteriorates magnetism, so the upper limit of the B amount is The B/N was set at 1.5. When the amount of Si is small in the steel of the present invention, P is added for the purpose of increasing strength to prevent the steel plate from becoming too soft and making punching work difficult. Addition of P also improves the strength of iron, but if it exceeds 0.15%, hot workability deteriorates and there is a risk of hot rolling cracking, etc., so the upper limit was set at 0.15%. Like Si, M may be added for the purpose of improving iron loss, but the upper limit was set to 0.31% in order to suppress the cost increase due to alloy addition. Also, like P, Mn is added to increase strength, but 1
．． If it exceeds 5%, the transformation point decreases, ferrite-austenite transformation tends to occur during annealing, and deterioration of magnetism is observed. Therefore, the upper limit of the addition amount was set at 165%. Furthermore, since S forms nonmetallic inclusions such as MnS that are harmful to improving magnetism, a stable effect of improving magnetism cannot be obtained unless the content is 0.010% or less.

Next, we will discuss limitations on processing conditions.

Ar3 transformation point (Ars('C)=916 509C-6
The reason why the average grain size of the ferrite grains before rolling (4Mn+33Si+50AZ+250P) or less is set to 200 μm or more is because if the ferrite structure becomes finer than this condition, the magnetism of the final product will deteriorate.

The present inventors investigated the relationship between the grain size before rolling and the recrystallized texture after rolling in the Ar temperature range below the transformation point. If there,
It was found that the (100) orientation, which is favorable for magnetism, is strongly developed.

Conventionally, it has been reported that the orientation of recrystallized grains generated when coarse grains are rolled is mainly the (110) orientation, but the present inventors investigated the rolling temperature and recrystallization of materials with such coarse grain structures. We investigated the relationship between the crystal textures in detail and found that when rolled in a certain temperature range, the main orientation of the recrystallized texture becomes close to (100). It was also found that this orientation remains relatively strong even after cold rolling and annealing, improving the magnetism of the final product.

In other words, the ferrite grain size before rolling below the Ar3 transformation point has a great influence on the subsequent texture formation, and 2
It is believed that rolling a ferrite structure with an average grain size of 00 μm or more improves the magnetism of the final product. Ar3
The means for making the average grain size of ferrite grains 200 μm or more before rolling below the transformation point may be obtained by cooling a cast slab, or by reheating a slab that has been supercooled by - good.

8. The reason why at least 30% of rolling must be carried out below the transformation point is that rolling below the Ar3 transformation point freezes the (111) strength of the final product sheet, and other strengths, especially (100
) This is because the strength is increased and the electromagnetic properties are improved, and the rolling reduction ratio at which the effects are fully manifested is 30% or more. In addition,
This effect becomes more noticeable by reducing the shear deformation of the surface layer of the plate and making the texture uniform in the thickness direction. In order to reduce shear deformation of the plate thickness surface layer, it is preferable that the average coefficient of friction between the hot rolling roll and the steel plate is 0.2 or less. The lower limit of this rolling temperature was set at 500°C because dynamic strain aging occurs at temperatures below this.
This is because the 110) orientation increases, which not only hinders the development of the (100) orientation of the final product sheet, but also increases the deformation resistance, causing defects in the shape of the steel sheet, which poses manufacturing difficulties.

In the method of the present invention, even if the as-hot-rolled material is directly sent to the cold-rolling process after hot-rolling, the iron loss characteristics will be significantly improved compared to when a material with the same composition is manufactured using the conventional process. When hot-rolled sheet annealing is performed, the improvement in iron loss characteristics becomes even more remarkable, and the magnetic flux density also improves.

Materials obtained by cold-rolling and annealing hot-rolled sheets rolled under the above manufacturing conditions exhibit lower iron loss than conventional cold-rolled and annealed materials, and can achieve low iron loss that is close to that of semi-processed materials subjected to strain relief annealing. .

In addition, if the steel of the present invention is subjected to 2 to 10% skin bath rolling and used as a semi-processed material, and then subjected to strain relief annealing, a higher magnetic flux density and lower iron loss can be obtained than conventional materials, so it can be used as a semi-processed material. This is not contrary to the gist of the present invention.

(Example) Table 1 shows the components, process conditions, and magnetic properties of the product sheets of the steel of the present invention and comparative steel. These materials are manufactured by sending continuously cast slabs directly to the hot rolling process without reheating them, or by heating them at 1350°C.
After reheating at a temperature of 750° C., continuous hot rolling was performed to obtain a hot rolled sheet with a thickness of 3.0 mm, and then cold rolling was performed to obtain a final sheet thickness of 0.5 mm. The recrystallization treatment after cold rolling was carried out by continuous annealing at 800 to 900" C x 2 minutes. The material with hot-rolled plate annealing was subjected to 800 to 100 cm. The particle size is the average particle size determined by the linear intercept method.Electromagnetic characteristics: Iron loss in both directions: -1,7.

and magnetic flux density B,. showed that. Further, the average friction coefficient of rolling at Ar=~500'C when lubricated rolling was performed during hot rolling was 0.2 or less, and about 0.28 in the non-lubricated state. This friction coefficient is a value calculated from the actually measured advance rate.

Examples No. 1 to No. 14 in Table 1 are ultra-low carbon steels with a low Si content of 0.02% or less. The iron loss value obtained by the method of the present invention for this steel type is around 6 W/kg, which is about 6 W/kg for comparison steel N.
The value obtained by the conventional method found in α7 is 8.6W
This is a marked improvement compared to around /kg. It is recognized that hot-rolled sheet annealing and lubricated rolling contribute to improving iron loss.

Example Nα6.8.10 was rolled in the austenite region and the ferrite grain size before rolling below the Ar3 transformation point was changed, but when the grain size is less than 200-, the iron loss increases and the magnetic flux density decreases. The anisotropy also increases.

Examples k11.12 are examples of thin slab materials, and the slab thicknesses are 6 nm+ and 4IllIl, respectively.゛Also, Example N+lL5 is a material hot-rolled in the CC-DR process. On the other hand, kl~4, 9.13 to 15 were rolled after being reheated at 870'C for 4 hours.

In Examples k13 and 14, B was added so that the B/N was approximately 1, but compared to the comparative steel (Nα14) produced by the conventional method in which hot rolling is carried out at a temperature exceeding the Ar3 transformation point. , it can be seen that the steel of the present invention (Nα13) exhibits excellent electromagnetic properties. In addition, in Example Nα15°16, St is 0.8
%, the iron loss of invention steel No. 15 is superior to that of ultra-low carbon steel, but the effect of improving iron loss by the method of the invention is not as remarkable in the case of ultra-low carbon steel.

Examples 17 and 18 are examples of CIo, 04% low carbon steel;
Although the iron loss increases as the amount of C increases, it can be confirmed that the iron loss is improved by passing through the process of the present invention.

Example 19.20 is a sample with Mn added, Nα21°2
2 is an example of a sample to which P was added, and it can be seen that in both cases the iron content is improved by the rolling process according to the method of the present invention.

(Effects of the Invention) According to the method of the present invention, not only can alloying elements (particularly Si:ii) be significantly reduced to obtain equivalent electromagnetic properties, but also the amount of alloying elements (particularly Si: ii) can be significantly reduced. It is possible to obtain excellent electromagnetic properties that could only be obtained by rolling and final strain relief annealing by the user, and according to the present invention, the composition system is comparable to that of Tsukyo's cold rolled steel sheets. Since non-oriented electrical steel sheets with high magnetic flux density and low core loss can be manufactured economically, there are great industrial benefits.

Claims (3)

[Claims] (1) C: 0.05 in weight% of ferrite grains with an average grain size of 200 μm or more before rolling below the Ar_3 transformation point
% or less, N: 0.010% or less, Si: 1% or less, Mn
: 1.5% or less, P: 0.15% or less, S: 0.010
% or less, Al: 0.3% or less, the balance consisting of Fe and unavoidable impurities, after rolling at least 30% in a temperature range of 500°C or higher below the Ar_3 transformation point and finishing at a temperature of 500°C or higher. A method for producing a non-oriented electrical steel sheet having excellent core loss properties, which comprises: directly or hot-rolled sheet annealing, followed by pickling followed by ordinary cold rolling and annealing. (2) The steel according to claim 1, which contains B in B/N of 1.5 or less, is rolled by at least 30% in a temperature range of below Ar_3 transformation point and 500°C or above, and finished at a temperature of 500°C or above. A method for producing a non-oriented electrical steel sheet having excellent iron loss characteristics, which is characterized in that the sheet is then subjected to annealing as it is or hot-rolled, and after pickling, ordinary cold rolling and annealing are performed. (3) 3 in the temperature range below Ar_3 transformation point and above 500℃
3. The method for producing a non-oriented electrical steel sheet having excellent iron loss characteristics according to claim 1 or 2, wherein the rolling is performed by 0% or more with lubrication and with an average friction coefficient between the roll and the steel sheet of 0.2 or less.