JPH021893B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a non-oriented electrical steel strip that exhibits excellent magnetic properties and is suitable for rotating equipment such as generators and electric motors, and in particular, a non-oriented electrical steel strip that has a uniformly high magnetic flux density in each direction of the plate surface. The present invention provides a method for manufacturing a belt at low cost. In general, the applications of non-oriented electrical steel strips are roughly divided into iron core materials for so-called stationary equipment such as small transformers and ballasts, and iron core materials for so-called rotating equipment such as motors and generators. Due to the recent demand for energy conservation, there is an increasing need for electrical equipment to be smaller or more efficient, and for this reason, electrical steel strips are required to have high magnetic flux density and low iron loss. ing. By the way, even among non-oriented magnetic steel strips, the direction of magnetization is limited when used as a core material for stationary equipment, so it is advantageous to impart directionality to the magnetism in order to improve the characteristics of the equipment, but for rotating equipment Since the iron core material is magnetized in each direction of the plate surface, a so-called in-plane non-directional material is required, which has no directionality in magnetism. As is well known, the magnetic properties of non-oriented electrical steel strip are
As specified in JIS-C-2550, evaluation was made using the measured values of 25 cm Epstein samples taken in equal amounts from the rolling direction (hereinafter referred to as L) and the direction perpendicular to the rolling direction (hereinafter referred to as C). ing. In this way, the magnetic properties of non-oriented electrical steel strips evaluated using the L+C 25 cm Epstein sample are reflected in the properties of stationary equipment where the magnetization direction is limited, but the magnetic properties of electrical steel strips for rotating equipment are , L+C 25
It is required that the magnetic properties of the ring sample, which is close to the excitation state of the rotating equipment, be better than the magnetic properties measured with the cm Epstein sample. As a manufacturing technology for non-oriented electrical steel strip, it is already known that increasing the size of the mother strip grains before cold rolling improves the magnetic properties of the final product. Based on this knowledge, the present inventors have published JP-A No. 57-35628,
Japanese Patent Application No. 57-18909 and Japanese Patent Application No. 57-86281 disclose a method for producing a non-oriented electrical steel strip with excellent magnetic properties. The invention of JP-A No. 57-35628 is
Ar _3, which determines the hot rolling end temperature depending on the chemical composition
It is characterized by forming the γ phase region immediately above the transformation point and then annealing for a short time. Also, the patent application No. 18909/1983 is
The hot rolling end temperature is in the γ phase region like the invention of JP-A No. 57-35628 mentioned above, and the coiling temperature is high. The rolling end temperature is lower than normal,
It is characterized in that it is then annealed for a short time, and in both of these methods, the core grains before cold rolling are coarsened to improve magnetic properties. In addition, as shown in JP-A No. 54-76422, a method has been proposed in which the coiling temperature during hot rolling is increased to improve magnetism through the growth of matrix grains through self-annealing. However, according to these manufacturing methods, although the magnetism of L+C is improved, the magnetism in the direction of about 55° from the rolling direction is on the contrary worse than that of ordinary magnetic steel strips, so the magnetism in the ring sample is comparable to that of ordinary magnetic steel strips. The characteristics are almost the same, and even if such a material is used for the iron core of rotating equipment, the characteristics cannot be improved. On the other hand, as a manufacturing method for so-called {100} in-plane non-oriented material suitable for rotating equipment,
No. 1, a method was proposed in which a hot-rolled material of 2.0 to 5.0 mm is subjected to one round of strong cold rolling of 85% or more, finished to a thickness of 0.35 mm or less, and then subjected to annealing that also serves as decarburization. ing. However, the thickness of the JIS standard S-30 and below is 0.50mm and 0.65mm, and 0.50mm is often used as a material for ordinary rotating equipment. The proposed method is not suitable for practical use. Also, special public service in 1977-
No. 19767 discloses that a hot-rolled sheet made of appropriate ingredients is cold-rolled twice with an intermediate annealing in between, and then annealed at high temperature for a long period of time, and secondary recrystallization is used to form {100} on the sheet surface.
A method for manufacturing a material with a surface has also been proposed, but this method requires a complicated process and is expensive to manufacture.
Moreover, it has drawbacks such as not being suitable for mass production. This invention was made in view of the above circumstances, and is intended to mass produce a non-oriented electromagnetic steel strip that has a high magnetic flux density in a ring sample, is suitable for rotating equipment, and has a thickness suitable for practical use. The purpose of this invention is to provide a method that can be manufactured easily and at low cost on a large scale. In order to produce the so-called {100} in-plane non-oriented electrical steel strip suitable for rotating equipment by the economically advantageous one-step cold rolling method, cold rolling rolling as described in the above-mentioned Japanese Patent Publication No. 51-942 is required. It is generally accepted that the higher the rate, the better. That is, if the cold rolling reduction ratio is 85% or more, the {111} planes, which are harmful to magnetism, will decrease and the {100} planes will increase, improving the magnetism. However, according to this method, for example, if the cold rolling reduction rate is 90, where {100} planes are likely to occur,
% or more, if the final plate thickness is 0.50mm,
The thickness of the hot-rolled steel strip must be 5 mm or more, which makes handling and cold rolling of the hot-rolled steel strip difficult.
In fact, it is unsuitable for industrial scale production. Therefore, the present inventors determined not only the cold rolling reduction rate but also
As a result of considering the hot rolling conditions and conducting various experiments and research, we were able to control the hot rolling end temperature and coiling temperature during hot rolling within a certain appropriate temperature range, and to achieve an appropriate cold rolling reduction rate. They discovered that the above-mentioned object could be achieved by combining the materials and ingredients, leading to the completion of this invention. That is, the manufacturing method of the present invention involves manufacturing a non-oriented electrical steel strip by hot rolling low carbon steel into a hot rolled steel strip, then cold rolling once to obtain the final thickness, and subsequently annealing. In the method, the low carbon steel has a total content of Si and Al of 1.5% by weight or less,
Using steel with the remainder substantially consisting of Fe, and setting the rolling end temperature in the hot rolling to within a temperature range of 600 to 700°C, and setting the coiling temperature after hot rolling to a temperature of 500°C or less, and further once. The rolling reduction ratio in cold rolling is within the range of 75 to 85%. The method of the present invention will be explained in more detail below. First, to explain the components of the low carbon steel material used in the method of this invention, Si and
Al is effective in lowering the iron loss of the product by increasing the resistivity and reducing eddy current loss, but if the total amount exceeds 1.5%, the hot rolling conditions and cold rolling reduction ratio of this invention are applied. Not only is the effect not as expected, but shape defects after cold rolling, or so-called ridging, occur due to columnar crystals in the slab found in non-transformed steel.
The total content of (Si+Al) should be
It is necessary to regulate it to 1.5% or less. Other C, S,
Impurity components such as N and O form inclusions and precipitates such as MnS and AlN, inhibit the growth of crystal grains during annealing performed after cold rolling, and increase iron loss. It is desirable to reduce it as much as possible. Low-carbon steel materials with the above-mentioned components can be used in electric furnaces,
It is melted by a known method such as an open hearth or a converter, and is made into a slab by a known ingot-blowing method or continuous casting method. The slab is then hot rolled, pickled, and cold rolled once. In these steps, the present invention particularly focuses on the hot rolling end temperature.
The temperature should be in the range of 600 to 700°C, the coiling temperature of the steel strip immediately after hot rolling should be 500°C or less, and the reduction rate in cold rolling should be in the range of 75 to 85%. Hot rolling conditions in this invention as described above,
In particular, the reasons for limiting the hot rolling end temperature, the hot rolled steel strip winding temperature, and the cold rolling reduction will be explained below based on the experimental results of the present inventors. Three slabs A, B, and C were created from molten steel containing 0.11% Si and 0.003% Al, and these were used as test materials. These slabs A, B, and C were heated to 1250° C. and then hot-rolled under the hot-rolling conditions shown in Table 1.

[Table] As shown in Table 1, slab A was hot-rolled at a higher hot-rolling finish temperature and coiling temperature than the present invention, and slab B had a hot-rolling finish temperature within the range of the present invention. Hot rolling was carried out under conditions where the coiling temperature was higher than that of the present invention, and slab C was hot rolled under hot rolling conditions where both the hot rolling end temperature and coiling temperature were within the range of the present invention. Hot rolled steel strips A, B, obtained under these hot rolling conditions,
The crystal structure of C is shown corresponding to FIG. 1 A, B, and C, respectively. A and B in Fig. 1, which are the crystal structures of hot-rolled steel strips A and B that were hot-rolled under hot-rolling conditions different from those of the present invention, have different crystal grain sizes; It has a recrystallized structure. On the other hand, FIG. 1C, which shows the crystal structure of hot-rolled steel strip C whose hot-rolling conditions are within the range of the present invention, shows a rolled texture with crystal grains extending in the rolling direction over almost the entire thickness of the sheet. In other words, it has a so-called unrecrystallized structure. Obtaining a hot rolled steel strip having such an unrecrystallized structure is a necessary condition for achieving the intended purpose of the present invention, as will be described later. The present inventors conducted various experiments to find hot rolling conditions to obtain this unrecrystallized structure, and found that if the hot rolling end temperature during hot rolling exceeds 700°C, dynamic recrystallization during hot rolling and water cooling rolling will occur. Recrystallization may occur during the time it is taken, and
If the hot-rolling end temperature is less than 600℃, the load on the rolling mill becomes unnecessarily large, making rolling difficult. Furthermore, if the coiling temperature exceeds 500℃, recrystallization will occur due to self-annealing due to the heat retained in the hot-rolled steel strip. Turns out it happens. Therefore, the hot rolling end temperature of hot rolling is
Within the range of 600℃~700℃, and the winding temperature is 500℃
Limited to the following. Next, hot rolled steel strip A hot rolled under each of the above conditions,
After pickling B and C, when performing cold rolling, the rolling reduction ratio is 70%, 75%, 80%, 85%, 90%.
After bright annealing at 750° C. for 2 minutes, these were punched into rings with an inner diameter of 65 mm and an outer diameter of 85 mm, and the magnetic flux density B ₅₀ value of each ring sample was measured. The results are shown in FIG. From FIG. 2, the _B50 value of the rings of all hot-rolled steel strips increases as the cold rolling reduction increases, but the _B50 value of the rings of hot-rolled steel strip C that satisfies the hot-rolling conditions of the present invention increases.
It is clear that the B ₅₀ values of the rings of hot rolled steel strips A and B, which do not satisfy the hot rolling limiting conditions of the present invention, are particularly high. Here, the lower limit of the cold rolling reduction ratio is set to 75% because
When the cold rolling reduction is lower than 75%, not only does the _B50 value decrease, but the thickness of the hot rolled steel strip required to finish the product to the 0.50 mm thickness often used for rotating equipment is 1.7 mm. This is because the thickness becomes as thin as 1 mm, resulting in a decrease in efficiency in each process such as pickling efficiency after the hot rolling process. In addition, the upper limit of the cold rolling reduction rate was set at 85% because the _B50 value of the ring tends to be slightly higher when the rolling reduction rate is 85% or more, but the final product thickness is 0.50 mm.
This is because it is necessary to increase the thickness of the hot-rolled steel strip to 3.3 mm in order to finish it, which poses difficulties in handling and cold-rolling the hot-rolled steel strip. As described above, in the method of the present invention, during hot rolling, the hot rolling end temperature is set at 600°C to 700°C, the coiling temperature is set at 500°C or less, and the By combining the cold rolling reduction rate of 75% to 85% with respect to the hot rolled steel strip, it is possible to produce a non-oriented electrical steel strip of an appropriate thickness with a high ring _B50 value without reducing productivity. It has now become possible to manufacture on a mass production scale without the need for any damage. Further, (200) pole figures of the hot rolled steel strips A, B and C after hot rolling under the respective hot rolling conditions in the above experiment are shown corresponding to FIGS. 3A, B and C, respectively.
As is clear from Fig. 3, the hot rolling end temperature is 630°C and the coiling temperature is 450°C, which are within the range of the hot rolling conditions of this invention.
Compared to hot rolled steel strips A and B obtained under conditions outside the scope of the present invention, the hot rolled steel strip C obtained under the conditions shown in FIG. It has a so-called rolling texture with very strong rotation. In addition, these hot rolled steel strips A, B, and C were pickled, rolled to a thickness of 0.50 mm at a cold rolling rate of 78%, and then
(200) pole figures after bright annealing at 750° C. for 2 minutes are shown in FIGS. 4A, B, and C, respectively. From FIG. 4, the texture of the final product of the hot-rolled steel strip C of the present invention is {100} suitable for use in rotating equipment.
It can be seen that there is so-called in-plane non-direction of <o, v, w>. The reason why a random in-plane non-directional texture is obtained in the rolling plane is that the cold rolling reduction is 80% or more, preferably 90% or more.
According to the common theory that (100) planes are likely to develop if the rolling reduction rate is higher than By applying cold rolling of 75% to 85%, the condition is essentially the same as that of hard rolling of 85% or more, and this results in a (100) plane component that is advantageous for improving the _B50 value of the ring. This is considered to have increased. In addition, annealing after cold rolling is done in accordance with the usual method.
It may be carried out at a temperature of about ℃ to 950℃. Examples of this invention are described below. Example 1 Molten steel containing 0.006% C, 1.08% Si, and 0.28% Al was melted in a converter and RH vacuum treatment, and then continuously cast into a 220 mm thick slab. this slab
When heated to 1260℃ and hot rolled, the material of the present invention has a hot rolling finish temperature of 680℃ and a coiling temperature of 490℃.
℃, and the comparative material was hot-rolled using the conventional method with a finishing temperature of 850℃ and a coiling temperature of 580℃, both of which were 2.3
It was made into a hot-rolled steel strip with a thickness of mm. Next, both the hot-rolled steel strip of the present invention and the comparative hot-rolled steel strip were pickled, followed by cold rolling to a thickness of 0.50 mm at a cold rolling reduction of 78%, and then annealing at 830°C for 2 minutes in a continuous annealing furnace. The product was produced by bright annealing. These products have an outer diameter of 85mm and an inner diameter of
A 65mm ring was punched out and its magnetic properties were measured. The results are shown in Table 2.

[Table] As is clear from Table 2, the material of the present invention whose hot rolling conditions and cold rolling reduction satisfy the limiting conditions of the present invention has a higher ring _B50 value than the comparative material, making it suitable for materials for rotating equipment. I know that there is. Example 2 C0.005%, Si0.32%,
Molten steel containing 0.0008% Al is made and continuously cast to 220
A slab of mm thickness was obtained. This slab was heated to 1250°C and hot rolled. The material of the present invention had a hot rolling end temperature of 620°C and a coiling temperature of 480°C, while the comparative material had a hot rolling end temperature of 780°C using the conventional method. ℃, the coiling temperature was 540℃, and both were hot-rolled steel strips with a thickness of 2.5 mm. Next, the hot-rolled steel strips of the present invention material and comparative material were pickled and then cold-rolled at a reduction rate of 80%.
After making it 0.50mm thick, it was heated to 800℃ in a continuous annealing furnace for 2 hours.
The product was made into a product by bright annealing for 1 minute. These products were punched into rings with an outer diameter of 85 mm and an inner diameter of 65 mm, and the magnetic properties of the rings were measured. Table 3 shows the results.

[Table] From Table 3, it is clear that the B ₅₀ value of the ring made of the present invention material is superior to that of the comparative material. As is clear from the above examples, according to the method of the present invention, the total content of Si and Al can be reduced to 1.5
When hot rolling a slab regulated to weight% or less, the hot rolling end temperature is regulated to 600 to 700℃, the coiling temperature is regulated to 500℃ or less, and the cold rolling reduction rate of the obtained hot rolled steel strip is 75. By performing normal annealing after cold rolling to 85% to 85%, it is possible to obtain a non-oriented electrical steel strip with a high magnetic flux density _B50 value in the ring, which is suitable for so-called rotating equipment. can. Furthermore, according to the method of the present invention, a non-oriented electrical steel strip having a thickness suitable for practical use can be obtained without particularly hindering productivity, and moreover, it is possible to obtain a non-oriented electrical steel strip with a thickness suitable for practical use, and also at a low cost, such as not requiring particularly complicated processes. A remarkable effect is obtained in which a non-oriented electrical steel strip with excellent properties can be manufactured on a mass production scale.

[Brief explanation of drawings]

Figures A, B, and C are 30x microscopic photographs showing the crystal structures of hot-rolled steel strips in the basic experiments of this invention, in which A is the hot-rolled steel strip of sample A in Table 1, B
indicates the structure of the hot rolled steel strip of sample material B, C indicates the structure of the hot rolled steel strip of sample material C, and Figure 2 shows the structure of the hot rolled steel strip of sample material A,
Graph showing the relationship between the cold rolling reduction ratio of B and C and the magnetic flux density _B50 value of the product ring sample, Figure 3 A, B,
C is the (200) pole figure of hot-rolled steel strips of test materials A, B, and C; A is of test material A, B is of test material B, and C.
Figure 4 shows the pole figures of each hot-rolled steel strip of sample material C, and Figure 4 A, B, and C are the (200) pole figures of the products of sample materials A, B, and C; Pole figures are shown for the products of material A, B for sample material B, and C for sample material C, respectively.

Claims (1)

[Claims] 1. A method for producing a non-oriented electrical steel strip, which comprises hot rolling low carbon steel to obtain a hot rolled steel strip, then cold rolling once to obtain the final thickness, and subsequently annealing. In, as the low carbon steel, a steel is used in which the total content of Si and Al is 1.5% by weight or less, and the balance is substantially Fe, and the rolling end temperature in the hot rolling is 600 to 700 ° C., and the coiling temperature is A method for producing a non-oriented electrical steel strip, characterized in that the temperature is 500°C or less, and the rolling reduction in the one cold rolling is 75 to 85%.