JPS5831367B2 - Method for manufacturing non-oriented electrical steel strip with excellent magnetic properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a non-oriented electrical steel strip with excellent magnetic properties, and in particular, the present invention relates to a method for manufacturing a non-oriented electrical steel strip with excellent magnetic properties, and particularly relates to a full process or semi-process non-oriented electrical steel strip with extremely high magnetic flux density and low iron loss. The present invention relates to a method for manufacturing electromagnetic steel strip.

There are various grades of non-oriented electrical steel strips depending on their magnetic properties, and depending on their magnetic properties, they are used as core materials for large- and medium-sized rotating machines, general-purpose motors, home appliance motors, transformers, ballasts, etc. It will be done.

In recent years, it has become increasingly necessary to improve the magnetic properties of electromagnetic steel strips used to improve the efficiency or downsize various electrical devices in order to save energy.

In particular, for iron core materials for home appliances such as small motor ballasts, there is a strong demand for the development of electromagnetic steel strips that have high magnetic flux density and low iron loss in order to reduce copper loss.

Incidentally, it has long been considered advantageous to increase the crystal grain size of the material before cold rolling in order to lower the core loss of electrical steel sheets.

For this purpose, a method of box annealing a hot rolled steel strip has conventionally been used.

For example, according to U.S. Pat. A method is disclosed in which a product with low core loss is obtained by coarsening the steel, followed by conventional cold rolling and annealing.

Also, according to Japanese Patent Publication No. 40-4139, containing added silicon, C 0.15% or less, Mn 0.75% or less, PO, 07
5% to 0.50% or less, SO. 025% or less, NO.
A method for producing an electrical steel sheet with low iron loss is disclosed, which comprises hot rolling a steel consisting of 0.004% or less, the balance being iron, and annealing the hot rolled sheet at a temperature of 732°C or higher.

Also, according to Special Publication No. 42-11139, Po. 15 or less, SiO. C0.05% to o. i oblique, Mn 0. 15φ to 1%, hot-rolled at a temperature not higher than 620°C to form finely dispersed carbides therein, and pickled. A ferromagnetic material with low iron loss is produced by decarburizing annealing at a high temperature to decarburize the carbon in it to 0.005% or less, producing columnar particles by changing the phase, and then cold rolling to a rate of 40 to 80%. A method of manufacturing has been proposed.

The above-mentioned U.S. Pat. No. 2,358,788 discloses a method characterized by subjecting hot-rolled silicon steel to cold working to introduce critical strain to coarsen grains in subsequent annealing. Also, the above-mentioned Japanese Patent Publication No. 40-4139 discloses a method characterized by annealing a hot-rolled steel sheet containing no added silicon,
In addition, Japanese Patent Publication No. 11139/1986 discloses steel containing up to 0.1% silicon, hot-rolled steel containing as much as 0.05 to 0.1% of silicon, and then decarburized and annealed to reduce C to 0.005%. This method is characterized by the following.

All of these three methods are related to methods for enlarging the crystal grains of the material before cold rolling, but the annealing for coarsening the crystal grains requires long-term annealing using box annealing. I couldn't reach my goal.

Moreover, when carrying out such box annealing, it usually takes several days, which has the disadvantage of not only poor production efficiency but also high cost.

The present inventors have conducted various studies on hot rolling conditions for hot rolled steel strips and subsequent manufacturing process methods in order to improve the magnetization properties of electrical steel strips.

and Japanese Patent Application No. 54-111640 (Japanese Unexamined Patent Publication No. 56-38
No. 420), a full-process non-oriented electrical steel strip or 2
In the method for manufacturing semi-processed non-oriented electrical steel strips using the recurrent cold rolling method, the hot rolling end temperature is the Ar3 transformation temperature calculated from the chemical composition weight of the steel material, that is, (891-9
00 (C width) + 50 (Si bun) ss (Mn%) + 190
(P%)+380(Az%))℃ and Arl transformation temperature, i.e. (ss2-5750(C%)+58800(C width)2+
50 (Si related) - 82 (Mn%) + 170 (P%) + 3
A non-oriented electromagnetic steel with excellent magnetic properties, which is within the temperature range between the median value of 80 (Al1)) °C and 750 °C, and the winding temperature after hot rolling is at least 680 °C. A method of manufacturing a belt is disclosed.

However, in the production of non-oriented electrical steel strips, this method means that the magnetic properties of the product will deteriorate if the hot rolling end temperature exceeds the Ar3 transformation temperature, so this production method is not used very often. It cannot be said that it is advantageous.

The present invention provides a copper strip that has a higher magnetic flux density and lower core loss than the copper strip produced by the so-called full-process or semi-process non-oriented electrical steel strip manufacturing method, which is conventionally used mainly as a material for household electrical equipment. The purpose is to provide a method for manufacturing process or semi-process non-oriented electrical steel strip at a relatively low cost.
The above object can be achieved by the method described in the claims.

Next, the present invention will be explained in detail.

The present inventors previously invented and applied for a patent in the patent application filed in 1984-1.
As a result of further research on No. 11640, it was found that at temperatures above the Ar3 transformation temperature, that is, the steel structure
When hot rolling is completed in a phase state, and then the hot rolled steel strip is annealed at a temperature below the A3 transformation point, the annealing is not a long annealing like box annealing, but a short continuous annealing of 15 minutes or less. They discovered that it is possible to make the crystal grains of a hot rolled steel strip abnormally coarse at low cost, and furthermore, the copper strip with such coarse grains is subjected to cold rolling and annealing using a normal method to complete the full process or process. The present invention was completed based on the finding that an electromagnetic steel strip with extremely excellent magnetic properties can be obtained when made into a semi-processed electromagnetic steel strip.

Next, the present invention will be explained based on experimental results.

Figures 1, 2 and 3 are C0,010, SiO
, 34%, Mn 0.14%, Po, 073%, acid soluble AJ! Three slabs made from 0.0004% molten steel were heated to 1250°C, and the hot rolling end temperatures were controlled to 915°C, 875°C, and 815°C, respectively, and the thickness was 2.3M. It is a micrograph showing the crystal structure of rolled steel strip samples A, B, and C.

By the way, as the inventors showed in the above-mentioned Japanese Patent Application No. 54-111640, the Ar3 transformation temperature is determined by (
891-900 (C width) + 50 (Si'%) -88 (
Mn%) + 190 (P%) + 380 (A7)) ℃ The Arl transformation temperature is (882-5750
(Cda) +58800 (C%) 2 + 50 (Si) -8
2 (Mn%) + 170 (P%) + 3 s o (Az%
)) °C, so in the above slab, the Ar3 transformation temperature is 901 °C, and the Arl transformation temperature is 84 °C.
Therefore, the hot rolling end temperatures of Samples A, B, and C were set to 915°C, 875°C, and 815°C, respectively, because the steel structures at the end of hot rolling were r phase, α+r phase, and
It is in the α phase.

These hot rolled steel strip samples A, B, and C were annealed at 840°C below the A3 transformation temperature for 5 minutes. Micrographs are shown in FIGS. 4, 5, and 6.

In addition, hot-rolled steel strip samples A, B, and C were annealed for 5 minutes at 930°C above the A3 transformation temperature (hereinafter represented by G, H, and ■, respectively). Microscopic photographs of the crystal structure of the sample are shown in FIGS. 7, 8, and 9.

As can be seen from these figures, the hot rolling end temperature is 915°C.
In other words, sample A that had been hot rolled with an r-phase structure was then annealed for a short time of 5 minutes at 840°C below the A3 transformation temperature to form crystal grains as shown in Figure 4. It is clear that the area has become abnormally coarse.

It was found that the C content after this annealing was o, o1o%, indicating that there was no decarburization at all.

Furthermore, even if the hot rolling is completed in the r phase, the crystal grains near the surface of the copper strip are only somewhat coarsened as shown in Figure 7 in the case of those annealed above the A3 transformation point of 930°C. The inside of the plate in the thickness direction remained fine crystal grains.

Next, for samples B and C, which finished hot rolling at 875°C and 815°C, that is, α+r phase and α phase, respectively, hot rolled steel strips were annealed at 840°C, which is below the A3 transformation temperature. Samples E and F (see Figs. 5 and 6) obtained by hot-rolled steel strip annealing at 930°C above the A3 transformation temperature, and samples H and I (Figs. 8 and 9) obtained by annealing the hot rolled steel strip at 930°C above the A3 transformation temperature reference)
In both cases, only a few coarse grains can be seen near the surface of the copper strip, and the interior in the thickness direction remains fine grains.

That is, when hot rolling an electromagnetic steel material, the present inventor sets the hot rolling end temperature to the temperature of the r-phase structure, and then anneales the hot rolled steel strip for a short time of 15 minutes or less at a temperature below the A3 transformation temperature. We have newly found that it is possible to make the crystal grains of a hot-rolled copper strip abnormally coarse through simple processing without decarburization.

Next, steel strips E and F having crystal structures as shown in FIGS. 4 to 6 were pickled in the usual manner, and
! Table 1 shows the magnetic properties after cold rolling to a thickness and bright annealing at 800° C. for 2 minutes.

As shown in Table 1, the sample has an r-phase structure at the end of hot rolling and has been annealed at 840°C below the A3 transformation temperature for 5 minutes, resulting in abnormally coarse grains. , the magnetic flux density B50 is extremely high at 1.80T, and the iron loss value is also 5.
As low as 61 W/Ky, the structure at the end of hot rolling is α+
It is clear that this is superior to Samples E and F, which have r-phase and α-phase.

As mentioned above, the end temperature of hot rolling is determined by the r
When the hot-rolled steel strip is annealed at a temperature that is equal to the phase structure, and then the hot-rolled steel strip is annealed at a temperature below the A3 transformation point, the annealing time is as short as 15 minutes or less, and unlike the conventional technology, it is substantially The crystal grains can be easily coarsened without decarburization, and the crystal grains can be coarsened by inexpensive continuous annealing instead of expensive box annealing as in the conventional technology. This is a feature of the present invention.

Although it is not clear why crystal grains can easily grow abnormally in a short period of 15 minutes or less even in Si-containing steel,
In terms of phenomena, the crystal structure of the product hot-rolled in the r phase is extremely fine and uniform, as shown in FIG.

When the matrix crystal structure is fine in this way, when the next hot-rolled sheet is annealed at a temperature below the A3 transformation point,
This is thought to be because if slightly coarse crystal grains are generated somewhere, they can easily eat up fine matrix crystals and grow.

Next, the reason why the chemical components of the material are limited in the present invention will be explained.

According to the present invention, hot rolling is completed at the temperature of the r-phase structure, and then the hot rolled steel strip is annealed at a temperature below the A3 transformation temperature to coarsen the grains, but the C content of the material is 0.02%. When it is as high as above, it becomes difficult to coarsen the grains during annealing of the hot rolled steel strip.

In addition, in the case of non-oriented electrical steel strips, C is 0.00 in the final product from the viewpoint of the magnetic properties of the product and deterioration due to magnetic aging.
It needs to be as low as 4 or less.

Therefore, if the starting material has a high C content, it is necessary to decarburize it to a desired value by continuous annealing.

This is not a desirable method because it creates a harmful oxide layer on the surface of the steel strip.

For these reasons, in the present invention, the amount of C in the material must be 0.02% or less.

In the present invention, an r-phase must exist at the end hot rolling temperature, but Si or (Si+AA) is 1.
If it exceeds 5%, the temperature at which the r-phase exists becomes high, making it necessary to increase the hot rolling end temperature, which causes difficulties in hot rolling.

Therefore, it is necessary to reduce the amount of Si or (Si+At) to 15% or less.

Mn is added as a deoxidizing agent and to suppress hot embrittlement caused by S, but if it exceeds 1.0%, it becomes magnetically harmful, so it must be kept at 1% or less.

P is sometimes added to increase the hardness of non-oriented electrical steel strips and improve punchability, but if it exceeds 0.2%, the plate becomes brittle and cold rolling becomes difficult. So 0
．． It needs to be 2% or less.

Next, the present invention will be explained with reference to examples.

Example 1 Molten steel produced in a converter and subjected to RH depressurization treatment was continuously cast to 22
I made a 0M thick slab.

Its chemical composition is C0,003%, Si0.28%, Mn
o, 3o%, PO, 021g, acid soluble AA 0.000
It was 5%.

The Ar3 transformation temperature determined from the chemical composition of this material using the calculation formula described in the claims is 880°C.

These slabs were heated to 1250'C, and as a comparison material, the hot rolling finish temperature was set at 860°C, which is considered to be the optimum temperature using the conventional method.
According to the present invention, the hot rolling end temperature was set to 920° C., which is higher than the Ar3 transformation temperature, and hot rolling was carried out to a thickness of 2.3 w/l.

The winding temperature after hot rolling was 650±20°C.

Next, the comparison material of hot-rolled steel strip is a full process product made by the normal one-time cold rolling method, and the hot-rolled steel strip is pickled and then processed at 0.50 w/l.
It was cold rolled and bright annealed in a continuous furnace at 800°C for 2 minutes to obtain a finished product.

Hot-rolled steel strips with a hot-rolling end temperature equal to or higher than the Ar3 transformation point are then subjected to continuous annealing at 850°C for 5 minutes using the present invention method, and a reference method in which hot-rolled steel strips are not annealed. Divided into steps.

All of these were then subjected to the same treatment as the above-mentioned comparative material after pickling, and were made into full-processed products by one-time cold rolling.

750, which assumes re-annealing of these products and customers.
Table 2 shows the magnetic properties after annealing for 2 hours at °C.

As is clear from Table 2, the iron loss W1.
5150 value and magnetic flux density B50 value, the present invention material has a low iron loss value and a particularly high magnetic flux density, which is an excellent value, and the magnetism of the present invention material is even more excellent after reannealing. I understand.

Further, even if the hot rolling finishing temperature is within the claimed range of the present invention, the reference material which was not subjected to hot rolled steel strip annealing has poor magnetism.

In other words, just setting the hot-rolling finishing temperature within the claimed range of the present invention results in poor magnetism, but by combining the hot-rolled steel strip annealing specified in the present invention, extremely excellent non-directional electromagnetic properties can be obtained. It is clear that a steel strip is obtained.

Example 2 C0,004%, Si0.40 by the same method as Example 1
%, Mn 0.27%, Po, 068%, acid soluble Az
A slab containing 3% o, ooo was produced.

The Ar3 transformation temperature determined from these chemical components using the calculation formula in the claims is 897°C.

The slab was heated to 1250° C., and the hot-rolled finishing temperature was set to 860° C., which is appropriate for the conventional method as a comparison material, and 930° C. for the present invention material, and a hot-rolled steel strip having a thickness of 2.371 gl1 was obtained.

The winding temperature after hot rolling was 650±20°C in all cases.

The comparative hot-rolled steel strip was then made into a finished product using the usual two-step rolling method for manufacturing semi-processed materials.

That is, the hot rolled steel strip was pickled, subjected to a first cold rolling, then continuous annealing at 750° C. for 2 minutes as intermediate annealing, and then a second inter-rolling at a rolling reduction of 8 parts.

After hot rolling, the inventive steel strip was annealed at 860°C for 5 minutes in a continuous annealing furnace.
First inter-examination rolling, intermediate annealing, and second inter-examination rolling were performed.

Test samples of these comparative materials and the products of the present invention were heated in N2 at 75%
Strain relief annealing was performed at 0°C for 2 hours, and the magnetism was measured.

The results of these implementations are shown in Table 3. In view of the results in Table 3, the hot rolling end temperature is set to be higher than the A r 3 transformation source degree determined from the calculation formula described in the claims of the present invention, and then the hot rolled steel strip is annealed at a temperature lower than the A3 transformation point. When the treatment of the present invention is carried out, compared to the conventional comparative material, the iron loss Wl
It is clear that a semi-processed non-oriented electrical steel strip having extremely excellent B50 value and magnetic flux density B50 value can be obtained.

Example 3 C01008% in a similar manner to Example 1.2.

A slab containing 1.04% Si, 27% Mno, 056% Po, and 7% acid-soluble klO was fabricated.

The Ar3 transformation temperature determined from these chemical components using the formula described in the claims is 923°C.

The slab was heated to 1250°C, and the hot rolling finishing temperature was set to 870°C for the conventional method and 950°C for the material of the present invention to produce a hot rolled steel strip having a thickness of 2.31/g/l.

The winding temperature after hot rolling was 650±20°C in all cases.

The hot-rolled steel strip manufactured by the conventional method was made into a thickness of 0.50M by the usual one-step cold rolling process for full-process product manufacturing, that is, pickling and cold rolling, and bright annealed at 850°C for 2 minutes in a continuous annealing furnace. I did it.

The hot-rolled steel strip produced by the method of the present invention is then subjected to a continuous annealing furnace at 870°C.
The hot-rolled steel strip was annealed for 5 minutes at ℃, and then subjected to the same one-time cold rolling process as conventionally rolled steel to produce a fully processed product.

Table 4 shows the magnetic properties of the products of this example.

From Table 4, it is clear that the material of the present invention is extremely superior to the conventional material in terms of iron loss Wl 5150 value and magnetic flux density B50 value.

[Brief explanation of the drawing]

Figures 1, 2, and 3 show the hot rolling finishing temperatures of 915°C (r phase), 875°C (α+r phase), and 875°C (α+r phase), respectively.
Micrographs (50x magnification) of the crystal structures of hot-rolled steel strip samples A, B, and C when heated to 15°C (α phase), Figures 4, 5, and 6 are hot-rolled steel strip samples, respectively. Micrographs (50x magnification) of the crystal structures of A, B, and C after annealing for 5 minutes at 840°C below the A3 transformation temperature, and Figures 7, 8, and 9 are hot-rolled specimens, respectively. Steel strip sample A
, B, and C, micrographs of crystal structures after annealing for 5 minutes at 930°C above the A3 transformation temperature (magnification: 5
0 times).

Claims (1)

[Claims] 1. A low carbon steel ingot or fallen slab is heated and subsequently hot rolled into a hot rolled steel strip, and this copper strip is annealed,
In the manufacturing method of non-oriented electrical steel strip, which is then pickled, followed by one cold rolling and then annealing, or two cold rolling with intermediate annealing and then further annealing. C0,02 or less, total fall of Si or Si and Af, 5% or less, Mnt, o% or less, PO
When heating either a steel ingot or a slab with a diameter of 020φ or less, the balance being Fe and unavoidable impurities, and then hot rolling it into a hot rolled steel strip, the hot rolling end temperature is set according to the chemical composition of the steel. The temperature is expressed by the following formula, (891-90
0 (C) + 50 (Si%) - 88 (Mn%) + 190
(P%) +380(At%)'C or above, and then annealing the hot rolled steel strip at a temperature below the A3 transformation temperature of the steel for a period of 30 seconds to 15 minutes. Method for manufacturing grain-oriented electrical steel strip.