JPS58204126A - Production of nondirectional electrical steel strip having excellent magnetic characteristic - Google Patents

Abstract

PURPOSE:To produce a titled steel strip, by using a slab contg. a limited compsn. of components, subjecting the same to hot rolling that ends in a specific temp. range, coiling the strip at a specific temp. or above and annealing the coiled strip for a short time at a specific temp. CONSTITUTION:Low carbon steel consisting, by weight %, <=0.02 C, <=1.5 Si or (Si+Al), <=1.5 Mn, <=0.2 P and the balance Fe and unavoidable impurities is hot- rolled and the hot rolling is completed at 600-700 deg.C, whereby a hot-rolled steel strip is produced. The strip is coiled at >=500 deg.C and the coiled strip is annealed for 30sec-15min at the A3 transformation point or below. The annealed strip is thereafter subjected to pickling, cold rolling and annealing by an ordinary method.

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 to a method for manufacturing a non-oriented electrical steel strip with extremely high magnetic flux density and low iron loss. Regarding the manufacturing method.

Non-oriented electrical steel strips are used as core materials for generators, electric motors, small transformers, ballasts, etc.

However, in recent years, there has been a strong demand for energy conservation, and in order to improve the efficiency or downsize electrical equipment, the demand for iron core materials with high magnetic flux density and low core loss is increasing.

As a conventional technique for manufacturing non-oriented electrical steel strip, it is known that increasing the grain size of the material before cold rolling is effective in improving magnetic properties.

The present inventors previously disclosed in Japanese Patent Application No. 55-110314 a method for coarsening grains before cold rolling. In this method, when hot-rolling a steel ingot or strip having a chemical composition within the limit hole range into a hot-rolled steel strip, the hot rolling end temperature is determined according to the following formula (1) according to the chemical composition of the steel. Ar3 expressed as
Above the transformation point temperature, (891-900 (Cm) + 5
0(Si4) -88(Mn%)+190(P%)+3
80(Ars))℃・・・(1) Then, this hot-rolled steel strip is heated to 30℃ below the A3 transformation point temperature of the steel.
The main feature of this method is that it is annealed for a time of at least 1 second and at most 15 minutes, and this method has made it possible to manufacture a non-oriented electromagnetic copper strip with excellent magnetic properties. In the above method ri disclosed by the present inventors, the annealing of the hot rolled steel strip to coarsen the grain size of the hot rolled steel strip does not involve long annealing as in conventional box annealing, and also requires decarburization. This method successfully coarsened the grains of a hot rolled steel strip easily and relatively inexpensively in a short period of 15 minutes or less.

The purpose of the present invention is to obtain
It is an object of the present invention to provide a novel method for manufacturing a fully processed or semi-processed non-oriented electrical steel sheet which has an extremely high magnetic flux density and a low core loss, which is a further improvement on the invention of No. 110314.

The gist of the present invention is as follows.

a step of hot rolling the low carbon steel into a hot rolled steel strip; a step of annealing the hot rolled copper strip and then pickling;
a step of forming a cold-rolled steel strip by two times of cold rolling or two times of intermediate annealing; and a step of subjecting the cold-rolled steel strip to full-process or semi-process annealing. In the method for manufacturing a non-oriented electrical steel sheet, the low carbon steel has a weight ratio of C: 0.02 or less, Si or (
Either Si+A/) is 1.5 or less, Mn: 1.0
% or less, P: 0, 204 or less, the remainder consisting of Fe and unavoidable impurities, the rolling end temperature in the hot rolling step is 600 to 700°C, the winding temperature is in the temperature range of 500°C or more, and then This is a patented method for manufacturing a non-oriented electromagnetic copper strip, characterized in that the rolled steel strip is annealed at a temperature below the A3 transformation point for a period of 30 seconds to 15 minutes.

In the method disclosed in the above-mentioned Japanese Patent Application No. 55-110314, the present inventors considered the reason why the crystal grains become coarser due to secondary recrystallization due to hot rolled steel strip annealing as follows. That is, since the crystal structure of the hot-rolled steel strip after hot rolling is fine, when this copper strip is annealed at a temperature below the A3 transformation temperature, slightly coarse crystal grains are generated locally.
It was thought that it would easily grow by eating fine matrix crystals.

In order to obtain a hot-rolled steel strip with such an initially fine crystal structure, it is necessary to set the hot rolling finish temperature to the r-phase region. We thought that this would be impossible under extended conditions.

However, since then, non-inventors have
As a result of research on the combination of the hot rolling end temperature in the extremely low temperature range of 580°C, which is much lower than the hot rolling temperature of 0°C or higher, and the winding temperature after hot rolling, it was found that the hot rolling end temperature is We discovered that a hot rolled steel strip having a fine crystal structure can be obtained by controlling the hot rolling temperature curve and the winding temperature within a certain appropriate range even if it is not in the r-phase region. It was completed.

Non-oriented electromagnetic copper strips are manufactured by conventional processes.

That is, the raw material is usually a low carbon steel slab with a C ratio of 0.02 or less, which is hot-rolled by a known method to give a roughness of 1.5 to 3. 0
It is finished into a hot rolled steel strip with a thickness of mm.

This hot rolled steel strip is pickled to remove scale.

This pickled steel strip is made into a cold-rolled steel strip by cold rolling once or twice with intermediate annealing, depending on the steel type. The cold-rolled steel strip is subjected to different annealing processes according to the so-called 7-process or semi-process. , the non-oriented electrical steel sheet is 70%
Annealing below 0°C results in high hardness, and annealing above 850'C results in too soft hardness, resulting in poor punchability, so annealing is performed at a temperature in the range of 700 to 850°C. This is semi-process annealing, and after punching, the customer performs box annealing at the same temperature of 700 to 850° C. for 0.5 to 3 hours in order to recover the magnetic properties. However, for products that do not require an annealing process after punching, so-called full process annealing at 800 to 950°C is performed. These annealing temperatures may be appropriately determined depending on the annealing time, and the annealing method may be either continuous annealing or box annealing.

In the above-mentioned conventional method for manufacturing a non-oriented electrical steel sheet, the present invention has found that excellent magnetic properties can be obtained by regulating the hot rolling conditions and hot rolled steel strip annealing conditions in addition to the steel components. The reason for the above limitation in the present invention will be explained below.

First, the reason for limiting the composition of the steel material will be explained.

C: C is a harmful element in terms of magnetic properties, and the less it is, the better.
It should be at least 0.02% or less.

That is, if it exceeds 0.02%, it becomes difficult to coarsen the grains by annealing the hot rolled steel strip according to the present invention, and magnetic aging due to precipitation of C becomes significant in the final product stage, resulting in deterioration of magnetic properties. It was limited to 0.021 or less.

Separate structure (Si + AI): If the fall of Sl or Fi (separate + 1) exceeds 165 circles, it will not be possible to obtain a hot rolled steel strip with a fine crystal structure in the hot rolling operation according to the present invention. It was limited to 1.54 or less.

Mn: Mn is necessary as a deoxidizing agent and to prevent red heat embrittlement caused by S, but if it exceeds 1.01, the magnetic properties deteriorate, so it was limited to 1.0 or less.

P: P is an element that is effective in adjusting the hardness of the product and improving punching properties, but if it exceeds 0.20%, it becomes brittle and cold rolling becomes difficult, so it was limited to 0.20 q6 or less.

Next, the reasons for limiting the hot rolling conditions according to the present invention, particularly the hot rolling end temperature, winding temperature, and annealing conditions for the hot rolled steel strip will be explained based on the experimental results of the present inventors.

Three slabs A, B, and C were manufactured from molten steel having the composition shown in Table 1 and were used as test materials.

Table 1 The above three test materials A, B, and C were all heated to 1250° C. and then hot rolled under different hot rolling conditions as shown in Table 2.

Table 2 The crystal structures of these hot-rolled steel strips A, B, and C are shown in FIG. 1 (5), (B), and (C). These hot-rolled steel strips A, B, and C were heated to 850°C, which is below the A3 transformation point temperature.
The hot rolled steel strip was annealed for 5 minutes.

The crystal structures after annealing are shown in Figure 2 (8), (B), and (
As shown in C).

Figure 1 (5), (B), (C) and Figure 2 (5)
), (B), and (C), the test specimens were annealed at 850°C, below the A3 transformation point temperature, for 5 minutes after the rolling end temperature was 650°C and the winding temperature was 550°C. Material B has coarse grains due to abnormal grain growth due to secondary recrystallization, and is obtained by first rolling a copper strip hot-rolled at a rolling end temperature in the range of 600 to 700°C at a temperature of 500°C or higher. By subjecting this rolled steel strip to hot-rolled copper strip annealing for 5 minutes at 850°C below the A3 transformation point, the hot-rolled copper strip, which has a fine crystalline structure when hot-rolled, has abnormal grains due to secondary recrystallization. It grows and becomes coarse grains. However, coarse crystal flowers did not occur in specimens A and C, which were hot-rolled outside of the hot-rolling conditions, and even under the same hot-rolling conditions as specimen B, the hot-rolled steel strip was annealed to the A3 transformation point. It has been found that even if the temperature is higher than that, transformation does not occur and coarse grains do not form.

Based on the findings from the above experimental results, the inventors conducted numerous experiments and found that the hot rolling end temperature was 700°C.
If it exceeds , the grain size after hot rolling becomes large.

Even if the hot rolled steel strip is annealed under the same conditions as above, secondary recrystallization grain growth does not occur, so the upper limit of the hot rolling end temperature is set at 700°C.
It turned out that this should be done. Also, the hot rolling end temperature is 6
When the temperature is lower than 00°C, the load on the rolling mill increases, making rolling difficult, and the winding temperature is also inevitably low, so that recrystallization due to self-annealing after winding does not occur. In addition, the hot-rolling end temperature is set to less than 600°C, and as a result, the winding temperature is also low, and even if recrystallization does not occur due to self-annealing of the hot-rolled steel strip, the hot-rolled steel strip can be annealed separately to form fine particles. If the hot-rolled copper band is annealed at a temperature below the A3 transformation temperature after forming a recrystallized structure, it is possible to coarsen the mother band grains, but this method is disadvantageous in terms of production cost. Therefore, the hot rolling finish temperature is 60
It should be limited to a temperature range of 0-700°C. In addition, if the winding temperature after hot rolling is less than 500°C, as in the case of sample C, the hot rolled steel strip will not have enough thermal energy to recrystallize the hot rolled steel strip. The lower limit of the winding temperature should be 500°C.

If the hot-rolled steel strip satisfies the above-mentioned requirements for the hot rolling end temperature and winding temperature, the second step is to set the hot-rolled steel strip annealing temperature in the next step below the A3 transformation point temperature. It was found that coarse grains were formed due to abnormal grain growth due to secondary recrystallization as shown in (B). The holding time for annealing the hot rolled steel strip varies depending on the annealing method and the steel type, but a short time of 30 seconds to 15 minutes is sufficient.

As described above, as long as the above-mentioned hot rolling requirements and winding requirements are satisfied, coarsening of crystals can easily occur due to secondary recrystallization-like abnormal growth by short-time annealing for 15 minutes or less at a temperature below the A3 transformation point temperature. is a completely new discovery (11). The reason for this is not clear, but since the crystal structure of the hot rolled steel strip before annealing is an extremely fine recrystallized structure as shown in Figure 1 (B), slightly larger crystal grains among the fine grains become nuclei. This is thought to be due to abnormal grain growth occurring due to secondary recrystallization by eating other fine matrix grains.

From the above experimental results, when producing a non-oriented electromagnetic copper strip, the rolling end temperature should be determined when hot rolling a slab with the above limited composition.
600 to 700°C, and the winding temperature is 500°C or higher, and the hot rolled copper strip is annealed in a temperature range below the A3 transformation point for 30 seconds to 15 minutes, as shown in Figure 2. However, since it was found that coarse grains as shown in () could be formed, this requirement was made a limiting condition of the present invention. In addition, the C content after annealing of the hot rolled steel strip in the above experiment was 0.005q6, which was hardly decarburized. No treatment was found to be necessary. First, in order to confirm the magnetic properties of non-oriented electrical steel sheets according to the requirements of the present invention, test materials A, B, and C having the crystal structure after hot-rolled (12) copper band annealing as shown in FIG. The hot rolled steel strips were pickled under the same conditions, then cold rolled to a thickness of 0.50m+n, bright annealed at 750°C for 2 minutes, and their magnetic properties were measured. The results are shown in Table 3. As shown below.

Table 3 As is clear from Table 3, the crystal structure of the hot rolled steel strip satisfies the hot rolling requirements and hot rolled steel strip annealing requirements according to the present invention.
Sample B, which has extremely fine grains as shown in Figure (B), becomes coarse grained as shown in Figure 2 (B) by hot-rolled steel strip annealing.
The magnetic flux density Boo value is extremely high at 1.81T, and the iron loss W1
It was found that the duck Fis was very low in oaW and had much better magnetic properties than the test materials A and C, which did not satisfy the limiting requirements according to the present invention.

Example I C: 0,007q6, Si: 0.29%, Mn: 0.2
Molten steel having a limited composition according to the present invention of 0, p:o, o1s, acid soluble 1:o, 0007 is heated in a converter and R,
It was melted in an H vacuum processing furnace and made into a slab with a thickness of 220°C by continuous casting. When this slab was heated to 1250°C and hot rolled, the hot rolling end temperature of the material of the present invention was 630°C, and the winding temperature t'' was 540°C.

The comparative material had a hot rolling finish temperature of 810°C and a winding temperature of 57°C.
Both were bound to 2.3 onn thick hot-rolled steel strips at 0°C. Next, the material of the present invention is heated to a temperature of 8 below the A3 transformation point in a continuous annealing furnace.
The hot-rolled steel strip was annealed at 50°C for 5 minutes, then conventionally pickled and cold rolled to a thickness of 0.50 m, and then bright annealed at 800°C for 2 minutes in a continuous annealing furnace to produce a finished product. This is a full-process product using a so-called one-time cold rolling bed. A hot-rolled steel strip subjected to comparative annealing was subjected to ordinary pickling, then cold-rolled and bright annealed under the same conditions as the material of the present invention to obtain a finished product.

As a reference, a hot-rolled steel strip having the limited composition of the present invention and satisfying the hot-rolling and winding requirements of the present invention was not subjected to hot-rolled steel strip annealing. This was used as reference material.

The magnetic properties of the above-mentioned inventive material, comparative material, and reference material products, as well as the magnetic properties after annealing at 750° C. for 2 hours, assuming re-annealing at the customer, are as shown in Table 4.

Table 4 As is clear from Table 4, the comparative material whose hot rolling finish temperature is higher than the limiting requirements of the present invention and which is not annealed hot rolled steel strip has magnetic properties both as a finished product and after reannealing as in accordance with the present invention. Even if the hot-rolling end temperature and the winding temperature after hot rolling were the same as the inventive material, the reference material, which was not annealed, had far superior magnetic properties than the inventive material. Inferior. Book (15) shows that extremely excellent magnetic properties can only be obtained by satisfying all the requirements according to the invention.

Example 2 C: 0.0 OJt%, Sl: 0 using the same method as Example 1
．． 3211. Mn: 0.23%, P: 0.07
A molten steel satisfying the limited composition according to the present invention of 6%, acid solubility 1:0, 0004% was melted and made into a 220 mm thick slab by continuous casting. When this slab was heated to 1250°C and hot rolled, the material of the present invention had a hot rolling finish temperature fi of -680°C and a winding temperature after hot rolling of 560°C.
A hot rolled steel strip with a thickness of 2.3 mm was used. The material of the present invention was then annealed at 850°C for 5 minutes, followed by full pickling, and then rolled at 750°C.
A so-called two-coat semi-processed product was produced by performing continuous annealing for 2 minutes and performing second-coat rolling at a rolling reduction of 8 inches. The comparative material was hot rolled at a temperature of 8 using the conventional method.
Similarly, the hot-rolled steel strip had a thickness of 2.3 nm with a winding temperature of 20°C and a winding temperature of 580°C. The comparative material was then immediately pickled without annealing the hot-rolled steel strip (16), and after the first coat rolling, a semi-processed product was obtained using the second coat rolling method in the same steps as the present invention material.

Both the present invention material and the comparative material were annealed at 750° C. for 2 hours, and then their magnetic properties were measured, and the results are shown in Table 5.

Table 5 It is clear from Table 5 that in any case, the comparatively soft material which is not subjected to hot rolling at the high temperature end temperature of rolling by the conventional method and annealing after hot rolling copper strip is superior to the material of the present invention. This shows that a semi-processed product with far inferior magnetic properties and excellent magnetic flux density and iron loss can be obtained if all the requirements of the present invention are satisfied.

Example 3 Using the same method as Example 1, C: 0.005 chi, Sl: 1.
13%, Mn: 0.361, P: 0.0191°A/:
Molten steel satisfying the limiting composition according to the present invention of 0.25% was melted and continuously cast into a slab with a thickness of 220 mm. When this slab was heated to 1250°C and hot rolled, the material of the present invention was made into a hot rolled steel strip with a thickness of 2 to 3 mm with a hot rolling end temperature of 650°C and a winding temperature after hot rolling of 550°C. was manufactured. This hot-rolled steel strip was annealed at 870°C for 5 minutes, lifted by 0.50 plate by end-to-end rolling after normal pickling, and then bright annealed at 850°C for 2 minutes in a continuous annealing furnace. The product was made into a finished product.

On the other hand, the comparative material was hot rolled at a temperature of 835°C using the conventional method.
A hot-rolled steel strip with a thickness of 2 to 3 mm was obtained at a winding temperature of 600°C, and then the hot-rolled copper strip was pickled as it was without annealing, and then treated in the same manner as the material of the present invention. and 0.5
A 0 mm thick product was obtained. The results of measuring the magnetic properties of the thus obtained materials of the present invention and comparative materials are shown in Table 6.

Table 6 As is clear from Table 6, the present invention material has a higher magnetic flux density B10 value and iron loss value W15,1' than the comparative material. It turns out that both are far superior.

As is clear from the above examples, the present invention uses a slab with a limited composition, and during hot rolling, the rolling end temperature is 600 to 700°C, and the winding temperature after hot rolling is 50°C.
The temperature is regulated to 0°C or higher, and a step of annealing the hot rolled steel strip for a short time of 30 seconds or more and 15 minutes or less at a temperature below the A3 transformation point of the steel is added, followed by pickling, cold rolling, and annealing steps. The product obtained by the conventional method also had the effect of being able to obtain an excellent non-oriented electrical steel strip having an extremely high magnetic flux density and a low iron loss value.

This is because the crystal structure of the hot-rolled steel strip obtained by the method of the present invention is extremely fine, and by annealing the hot-rolled steel strip at a temperature below the tAs transformation point, coarse grains are formed due to abnormal grain growth due to secondary recrystallization. This is due to the fact that it was possible to obtain this, which is a major feature of the present invention. Furthermore, according to the present invention, the hot rolling end temperature is 600 to 700°C, which is significantly lower than that of conventional methods (19), and the hot rolled steel strip can be annealed for 15 minutes or less at a temperature below the A3 transformation point. Since it only takes a short time, it also has the secondary effect of saving energy and reducing manufacturing costs.

[Brief explanation of drawings]

Figure 1 (5), @, ρ) is a 30x micrograph showing the crystal structure of each hot-rolled steel strip of test materials A, B, and C shown in Table 2 in the basic experiment of the present invention. , Figure 2 (5),
(B) and (C) are the hot rolled steel strips of test materials A, B, and C.
It is a 30x micrograph showing each crystal structure after hot-rolled steel strip annealing at ℃ for 5 minutes. Agent Takeo Nakaji (20)

Claims (1)

[Claims] (1) A process of hot rolling low carbon steel into a hot rolled steel strip;
a step of annealing and then pickling the hot rolled steel strip; a step of forming the pickled steel strip into a cold rolled steel strip by one cold rolling or two cold rollings sandwiching intermediate annealing; a step of annealing the cold-rolled steel strip by a full process or a semi-process;
In the method for producing a non-oriented electrical steel sheet, the low carbon steel has a weight ratio of C: 0.02% or less, and either Si or (Si + A/ ) (7) 1.51 or less, Mn: 1.0 or less, p: o, 2o or less, the remainder consisting of Fe and unavoidable impurities, the rolling end temperature in the hot rolling process is 600 to 700°C, and the winding temperature is 500'C or more. First, the rolled steel strip is annealed at a temperature below the A3 initial point for a period of 30 seconds or more and 15 minutes or less.