JPS631371B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention produces a unidirectional silicon steel sheet with excellent magnetism in which the body-centered cubic lattice crystal grains constituting the steel sheet have an orientation represented by {110}<001> in Miller index. The present invention relates to a method of manufacturing a hot-rolled sheet (steel strip) made from a single hot-rolling process.

Unidirectional silicon steel sheets are used as soft magnetic materials for the cores of transformers and generators, and must have good magnetic properties such as magnetization properties and iron loss properties. The quality of magnetization characteristics is determined by the magnitude of the magnetic flux density (represented by _B8 ) induced within the iron core by a constant applied magnetic field. Materials with high magnetic flux density are desirable because electrical equipment can be made smaller. Iron loss (represented by W _17/50 ) is the power loss consumed as thermal energy when a specified alternating magnetic field is applied to the iron core. The quality of iron loss is determined by magnetic flux density, plate thickness, amount of impurities,
The effects of resistivity and crystal grain size are known. Recently, the demand for unidirectional silicon steel sheets with low iron loss has increased, reflecting trends in energy conservation.

By the way, unidirectional silicon steel sheets are produced by finishing high-temperature annealing of the steel sheets that have reached their final thickness through hot rolling and cold rolling, resulting in so-called secondary recrystallization, in which primary recrystallized grains with {110}<001> orientation grow selectively. Obtained by recrystallization. In order to cause secondary recrystallization, the presence of fine precipitates such as MnS and AlN in the steel sheet before final high-temperature annealing (inhibitor effect)
It is necessary to suppress the growth of primary recrystallized grains other than the {110}<001> orientation during final high-temperature annealing. By controlling such secondary recrystallization, accurate {110}<
001> Magnetic flux density can be increased by increasing the proportion of oriented grains. Since products with high magnetic flux density make it possible to reduce the size of electrical equipment and improve core loss, it is important to establish manufacturing conditions for high magnetic flux density unidirectional silicon steel sheets. Representative techniques include methods described in Japanese Patent Publication No. 40-15644 by Satoru Taguchi et al. and Japanese Patent Publication No. 13469-1983 by Takuichi Imanaka et al.
In recent years, the industrialization of the continuous casting method has been actively promoted, and even for unidirectional silicon steel sheets, it is possible to reduce manufacturing costs by saving labor and improving yield, and to make the magnetic properties uniform in the longitudinal direction of the finished product by making the chemical composition uniform. In anticipation of this, continuous casting processes are being applied. However, after heating the continuous casting slab to over 1280℃,
Products obtained using hot-rolled steel sheets as starting materials often have linear secondary recrystallization imperfections, resulting in poor magnetic properties. As a countermeasure to these problems, MFLittman proposed a technique in Japanese Patent Application Laid-Open No. 48-53919, in which hot-rolled sheets are produced from continuously cast slabs through two hot-rolling processes. Furthermore, Akira Sakakura et al., in Japanese Patent Publication No. 50-37009, proposed a technique for producing hot-rolled plates from continuously cast slabs through two hot-rolling processes in the production of high magnetic flux density unidirectional silicon steel plates. However, all of these prior art techniques produce hot-rolled sheets through two hot-rolling steps, and cannot be said to be techniques that fully utilize the advantages of continuous casting. Later, as a manufacturing method using continuous casting slabs, Morio Shiozaki et al.
The techniques disclosed in Japanese Patent Application Laid-open No. 19913 and Japanese Patent Application Laid-open No. 120214/1983 by Fumio Matsumoto et al. were proposed. However, all of these technologies require new measures to be taken for equipment. Further, even if these measures are taken, the occurrence of linear secondary recrystallization defects cannot be completely solved. That is, recently there has been an increasing demand for low core loss unidirectional silicon steel sheets for the purpose of energy saving, and in order to meet this demand, it is important to increase the magnetic flux density and increase the Si content. In particular, the technology disclosed in Japanese Patent Publication No. 40-15644 is a one-time rolling method, so the manufacturing cost is low, and a unidirectional silicon steel sheet with high magnetic flux density can be obtained, so it has high Si
If this becomes possible, the iron loss will be greatly improved. However, when the Si content is increased, the occurrence of secondary recrystallization defects rapidly increases, and especially in the case of such a high Si content, the linear secondary recrystallization defects that occur when continuously cast slabs are used further increase. Therefore, the Si content is
If it exceeds 3.0%, stable industrial production becomes extremely difficult. This was published in 1973 by Akira Sakakura and others.
As stated in Publication No. 51852, increasing the Si content makes it difficult to secure adequate AlN for secondary recrystallization, and especially when continuous casting slabs are used, this inappropriate AlN This is thought to be because defects in secondary recrystallization become more noticeable. As described above, the biggest problem in producing high magnetic flux density unidirectional silicon steel sheets by the single rolling method is that secondary recrystallization becomes unstable as the Si content increases. The basic metallurgical idea of this method is that α → γ during annealing.
Since the purpose is to create an appropriate AlN state using transformation, it is thought that increasing the Si will naturally change the α→γ transformation behavior, making it difficult to control the appropriate AlN state, and the higher the Si, the more difficult it will be to control the appropriate AlN state. This corresponds to an increase in secondary recrystallization defects.

The present inventors have completely prevented secondary recrystallization defects that occur when using continuous casting slabs, and in particular
We have developed a method that can stably produce high magnetic flux density unidirectional silicon steel sheets using a single rolling method that reduces secondary recrystallization defects that increase as the content increases. What is even more revolutionary is that according to this method, the slab is heated to a high temperature of over 1280℃ prior to hot rolling, which has traditionally been considered essential in the production of unidirectional silicon steel sheets. It has been found that this is not necessarily necessary, and that even better iron loss can be obtained by heating the slab at a lower temperature. In the manufacturing method of high magnetic flux density unidirectional silicon steel sheet based on Japanese Patent Publication No. 40-15644, it is necessary to bring MnS and AlN, which are precipitated dispersed phases necessary for secondary recrystallization, into an appropriate dispersed state. , the heating temperature of the slab during hot rolling was increased. In particular, Japanese Patent Application Laid-Open No. 1973-1564 by Akira Sakakura et al. concerning improvements to the method described in Japanese Patent Publication No. 15644-1973
As in the method described in Publication No. 51852, when the Si content increases, AlN precipitation during hot rolling starts in a high temperature range, so it is necessary to heat the slab to a high temperature.
For example, 1250℃ or higher for 2.8%Si, 1350℃ for 3.05%Si
It is ℃. Increasing the amount of Si in order to improve iron loss requires increasing the slab heating temperature, which increases the energy used when heating the slab, lowers yield due to the generation of slag during heating, and increases repair costs, resulting in manufacturing costs. There was a problem with height.

According to the present invention, even when the Si content is as high as 3.0% or more, secondary recrystallization can be performed in a sufficiently stable manner at a low slab heating temperature that does not exceed 1280°C. In fact, the iron loss obtained is better than that of high-temperature slab heating materials, and the value is higher than the current highest grade Japanese Industrial Standard (JIS) G6H (W _17/50 with a thickness of 0.30 mm).
1.05w/Kg or less) or more.

As described above, according to the present invention, high Si
The highest grade high magnetic flux density unidirectional silicon steel sheet can be stably manufactured using continuous cast slabs containing the same, regardless of the high or low slab heating temperature during hot rolling. That is, the present invention has C: 0.025-0.075%, Si: 3.0-4.5%, acid-soluble
Al: 0.010~0.060%, N: 0.0030~0.0130%,
S: 0.007% or less, Mn: 0.08-0.45%, P: 0.015
~0.045%, Cr: 0.07~0.25%, balance Fe and unavoidable impurities, a continuously cast slab for unidirectional silicon steel sheet is heated without preliminary hot rolling, then hot rolled to form a hot rolled sheet, and then the slab is heated without preliminary hot rolling. hot rolled plate
After short-term continuous annealing in the range of 850 to 1200℃, reduction rate
The final plate thickness is obtained by cold rolling with a strong reduction of 80% or more, and the obtained cold rolled plate is continuously decarburized and annealed in a wet hydrogen atmosphere, and then an annealing separator is applied and a final high temperature annealing is performed. The main purpose of this paper is to provide a method for manufacturing unidirectional silicon steel sheets with excellent iron loss.

The present invention will be explained in detail below.

First, the reasons for limiting the steel components of the present invention will be described. The molten steel used in the present invention may be produced by any method such as a converter furnace, an electric furnace, or an open hearth furnace, but the component content must fall within the following range.

If C is less than 0.025%, secondary recrystallization becomes unstable, and even if secondary recrystallization occurs, the magnetic flux density is poor (only 1.80T or less can be obtained with B ₁₀ ).
Must be 0.025% or more. On the other hand, if the amount of C is too large, the decarburization annealing time becomes long, which is not economical, so it is set at 0.075% or less.

If Si exceeds 4.5%, cracking during cold rolling becomes significant, so it was set to 4.5% or less. In addition, if it is less than 3.0%, it is impossible to obtain the highest grade iron loss with W _17/50 of 1.05w/Kg or less at a product thickness of 0.30mm, so it is set to 3.0% or more. It is preferably 3.2% or more.

In the present invention, as a precipitate necessary for secondary recrystallization,
Use AlN. Therefore, in order to ensure the minimum amount of AlN required, 0.010% or more of acid-soluble Al,
N is required to be 0.0030% or more. acid soluble Al
If it exceeds 0.060%, AlN in the hot rolled sheet becomes inappropriate and secondary recrystallization becomes unstable, so it was set to 0.060% or less. Regarding N, if it exceeds 0.0130%, ``blistering'' on the surface of the steel plate will occur, so it was set to 0.0130% or less.

One of the features of the present invention is to reduce the S content to 0.007% or less. When producing a high magnetic flux density unidirectional silicon steel sheet by a single rolling method using AlN as an inhibitor, S is an essential element for obtaining magnetism, as disclosed in Japanese Patent Publication No. 15644/1983. Furthermore, as shown in Japanese Patent Publication No. 47-25250, S is necessary to form MnS, which is a precipitate effective in causing secondary recrystallization.
In these known techniques, S is defined as being effective for secondary recrystallization. However, it was not known that the inclusion of S was harmful to secondary recrystallization. The present inventors reduced the S content to 0.007% when manufacturing high magnetic flux density unidirectional silicon steel sheets by a single rolling method using AlN as an inhibitor.
By reducing the following, linear secondary recrystallization defects that occur when continuously cast slabs are used as raw materials and secondary recrystallization defects that occur when high Si-containing slabs are used as raw materials (this is It has been found that when the heating temperature is lowered, the phenomenon (which occurs particularly markedly) disappears.

Figure 1 shows C: 0.058%, Si: 3.35%, Mn: 0.23
%, P: 0.036%, acid-soluble Al: 0.033%, N:
Contains 0.0085%, Cr: 0.13%, and S is 0.002~
After heating the continuous casting slab which is 0.033% to 1410℃,
A hot-rolled sheet of 2.3 mm was made by hot rolling, and after continuous annealing at 1150°C for 2 min, it was cold rolled to a thickness of 0.30 mm in wet hydrogen.
This figure shows the incidence of linear secondary recrystallization defects in products obtained by performing decarburization annealing at 850°C for 2 minutes, applying MgO as an annealing separator, and increasing the final high temperature annealing at 1200°C for 20 hours. It can be seen that as the S content decreases, the occurrence of linear secondary recrystallization defects decreases, and at 0.007% or less, no linear secondary recrystallization defects occur.

Figure 2 shows C: 0.050%, Si: 3.45%, Mn: 0.25
%, P: 0.040%, acid-soluble Al: 0.027%, N:
Contains 0.0080%, Cr: 0.18%, and S is 0.002~
A small specimen with a thickness of 40 mm containing 0.035% was heated to 1200℃, and after slab extraction, it was cooled to 1000℃ in the atmosphere.
It was held in a furnace at 1000℃ for 30 seconds, then hot-rolled in 3 passes to 2.3mm, continuously annealed at 1120℃ for 2 minutes, further cold-rolled to 0.30mm, and then rolled at 850℃ in a wet hydrogen atmosphere.
This figure shows the incidence of secondary recrystallization defects for products that were decarburized for 2 minutes, coated with MgO as an annealing separator, and then subjected to final high-temperature annealing at 1200°C for 20 hours. As can be seen from FIG. 2, no secondary recrystallization failure occurs when the S content is 0.007% or less. In the range where S is 0.007% or less, the smaller the amount of S, the more stable the secondary recrystallization becomes. Further, it is desirable to lower the S content at the molten steel stage because this facilitates the S removal treatment during final high-temperature annealing. With the current melting technology, the S content can be easily lowered to 0.001% or more without increasing costs.

The second feature of the present invention lies in Mn and P. Since the present invention is characterized by reducing the S content in the material, the presence of MnS is eliminated and the magnetic flux density of the finished product is deteriorated. However, the present inventors have found that even in the case of such a low S material, the magnetic flux density can be improved by adjusting the Mn and P contents in the material to appropriate amounts.

Figure 3 shows C: 0.060%, Si: 3.33%, S: 0.004
%, acid soluble Al: 0.032%, N: 0.0090%, Cr:
After heating the continuous casting slab containing 0.15% to 1350℃,
A hot-rolled plate with a thickness of 2.3 mm is made by hot rolling at 1150℃
After continuous annealing for 2 min, it was cold rolled to 0.30 mm, decarburized at 850°C for 2 min in a wet hydrogen atmosphere, coated with MgO as an annealing separator, and heated to 1200°C.
The influence of the Mn and P contents in the slab on the magnetic flux density (B ₁₀ ) of a product obtained by finishing high-temperature annealing for 20 hours is shown. When the amount of Mn decreases, secondary recrystallization becomes unstable, and when it increases, B ₁₀ increases, but even if it is added above a certain level, there is no difference in the improvement effect and the number of added alloy layers increases, which is uneconomical. As for P, if the content is low, the B ₁₀ will be bad, while if the content is high, the frequency of cracking during cold rolling will increase, and the incidence of secondary recrystallization failure will increase. From the above, Mn: 0.08-0.45%, P: 0.015-0.045 is a range with high _B10 , stable secondary recrystallization, and few cracking problems.
% was defined as the scope of the present invention. (In Figure 3, × means
B ₁₀ <1.80, △ is 1.80B ₁₀ <1.89, 〇 is 1.89B ₁₀
<1.92, ● is 1.92B ₁₀ 1.93, ○ is 1.93<B ₁₀ . Unit Tesla) Figure 4 shows C: 0.045%, Si: 3.35%, S: 0.002
%, acid soluble Al: 0.028%, N: 0.0075%, Cr:
A small specimen with a thickness of 40 mm containing 0.18% was heated to 1150℃,
After extracting the slab, it was hot-rolled in 3 passes to form a hot-rolled sheet with a thickness of 2.3 mm (the hot-rolling completion temperature at this time was approximately 820°C), continuously annealed at 1120°C for 2 minutes, and then cold-rolled to 0.30 mm. , shows the influence of Mn and P on the magnetic flux density (B ₁₀ ) of a product that was decarburized annealed in a wet hydrogen atmosphere, coated with MgO as an annealing separator, and then subjected to a final high temperature annealing at 1200°C for 20 hours. 1410℃ shown in Figure 3
Overall _B10 is 0.01~0.03T compared to slab heating material
However, the influence trends of Mn and P are the same as in the case of Fig. 3. (In Figure 4, × means
B ₁₀ <1.80, △ is 1.80B ₁₀ <1.89, 〇 is 1.89B ₁₀
1.91, ● is 1.91<B ₁₀ . (Unit: Tesla) The third feature of the present invention is that magnetism is stabilized by containing an appropriate amount of Cr. Although the technology disclosed in Japanese Patent Publication No. 15644/1973 can obtain high magnetic flux density, acid-soluble Al in steel
It is necessary to control the amount within a narrow range, which poses a problem for stable industrial production. Since the production method based on the present invention also uses AlN as an inhibitor, acid-soluble
It is necessary to strictly control Al. As a result of further research, the present inventors have found that by incorporating an appropriate amount of Cr into steel, the range of acid-soluble Al content that can provide high magnetic flux density can be expanded. Furthermore, we found that products manufactured from Cr-containing materials have superior iron loss under the same magnetic flux density.

Figure 5 shows C: 0.06%, Si: 3.33%, Mn: 0.30
%, P: 0.035%, acid-soluble Al: 0.029%, N:
After heating the continuous casting slab containing 0.0090% to 1350℃, it was hot-rolled into a hot-rolled plate with a thickness of 2.3mm.
Continuously annealed at ℃×2min, further cold rolled to 0.30mm,
Decarburized and annealed in a wet hydrogen atmosphere and used as an annealing separator.
The effect of Cr on the relationship between magnetic flux density (B ₁₀ ) and iron loss (W _17/50 ) of a product obtained by applying MgO and finishing annealing at 1200°C for 20 hours is shown. It can be seen that as the amount of Cr increases, the iron loss improves under the same magnetic flux density.

Even if the Cr content is further increased, the effect will not particularly increase, but rather the problem will arise that the decarburization rate during decarburization annealing will be delayed, so if the Cr content exceeds 0.25%
Addition is inappropriate.

Molten steel containing the above-mentioned components is continuously cast into a slab, and hot rolled into a hot-rolled plate. Continuously cast slabs are of limited scope since one of the objects of the present invention is to apply the advantages of using continuously cast slabs. However, if continuous casting equipment is not available, there is no particular problem in using a slab produced by the blooming method.

Next, we will discuss the slab heating temperature. In the case of the component range limited in the present invention, the higher the slab heating temperature, the higher the magnetic flux density. However, as shown in FIG. 6, it has been found that according to the present invention, in order to obtain a high magnetic flux density, high-temperature heating exceeding 1300° C., which was conventionally considered essential, is no longer necessary. Furthermore, in a groundbreaking comparison under the same magnetic flux density, we found that the lower the slab heating temperature, the better the iron loss. When the slab heating temperature is high, the magnetic flux density is high and the highest grade G6H or higher can be obtained, and if the finished product is subjected to magnetic domain control treatment (for example, laser irradiation), the iron loss can be further improved. When the slab heating temperature is low, the iron loss under the same magnetic flux density is good and the highest grade G6H or higher can be obtained, so there is no slag generation when heating the slab with the aim of reducing manufacturing costs.
A temperature of 1280°C or lower can be employed in the present invention.

Figure 6 shows C: 0.050%, Si: 3.45%, Mn: 0.25
%, S: 0.002%, P: 0.040%, acid soluble Al:
After heating a continuously cast slab containing 0.027%, N: 0.0080%, and Cr: 0.18%, it was hot-rolled into a 2.5 mm hot-rolled plate, and after continuous annealing at 1120°C for 2 min, it was cold-rolled to a plate thickness of 0.30 mm. 850℃× in a wet hydrogen atmosphere
Perform decarburization annealing for 2 min and use as an annealing separator.
The effect of slab heating temperature on the magnetic flux density of a product obtained by coating MgO and final annealing at 1200°C for 20 hours is shown. This figure shows that the higher the slab heating temperature, the higher the magnetic flux density, and it becomes especially high at 1300°C or higher. However, it can be seen that the temperature exceeding 1300°C, which was conventionally considered essential, is not necessarily required to obtain a high magnetic flux density, and heating at a lower temperature may be sufficient. On the other hand, if the slab heating temperature is too high, the heating furnace cannot withstand the equipment, and 1430°C is the upper limit for industrial production. There is no particular need to determine the lower limit of the slab heating temperature, but if it falls below 1050°C, the power required during hot rolling will increase and the shape of the steel sheet will deteriorate, so 1050°C or higher is desirable for stable industrial production.

Figure 7 shows the magnetic properties of a product obtained by applying a tension coating mainly composed of colloidal silica to a product obtained by changing only the slab heating temperature to 1150°C under the same conditions as shown in Figure 3. show. When the slab heating temperature is low, the magnetism is better than when it is high, and the core loss is better under the same magnetic flux density. The reason for this is not necessarily clear, but it is thought to be related to the fact that the grain boundaries of the product produced by low-temperature slab heating are irregular and that microcrystal grains with a diameter of about 2 mm are mixed.

As described above, in the present invention, which enables the highest grade of iron loss by heating the slab at low temperature, a hot rolling method having the following advantages can be easily used.

Due to recent advances in continuous casting technology, the productivity of continuous casting has become so great that it rivals the capacity of continuous hot rolling mills. No more waiting time for materials. Therefore, we have developed a method of directly hot-rolling the slab using sensible heat without cooling the slab after continuous casting, or charging the slab into a recuperation furnace if the slab temperature, especially the surface temperature, has dropped slightly. This is a method of heating the steel for a short time in a simple heating furnace for ordinary steel, and then hot rolling it. Such hot rolling methods are increasingly being used in the production of ordinary steel for the purpose of energy saving. However, since unidirectional electrical steel sheets require slab heating at high temperatures and for long periods of time, it is necessary to install a high-temperature slab heating furnace exclusively for unidirectional electrical steel sheets, and a direct connection process of continuous casting and continuous hot rolling is required. It was not possible to hire. If low-temperature slab heating can be used as in the present invention, a direct connection process can be easily adopted, and hot rolling can be carried out as efficiently as ordinary steel. Furthermore, in a direct connection process that does not require cooling after casting, silicon steel has the following advantages. In other words, because slabs containing Si have poor thermal conductivity, the temperature difference between the surface layer and the center increases during cooling of the slab, generating thermal stress, causing internal cracks in the slab, and reducing yield. If the slab is not cooled as in the process, this problem of internal cracking of the slab will be resolved.

The hot-rolled sheet obtained as described above is subjected to continuous annealing for a short period of time in the range of 850 to 1200°C. The annealing temperature is
If it is less than 850°C, high magnetic flux density cannot be obtained, and if it exceeds 1200°C, secondary recrystallization will be incomplete. If the annealing time exceeds 30 minutes, production efficiency will be extremely poor.
If the time is less than 30 seconds, the effect of heat treatment is almost lost.

After continuous annealing of the hot-rolled sheet, the final thickness is obtained by cold rolling. Since the present invention aims to obtain a high magnetic flux density unidirectional silicon steel sheet, the cold rolling reduction ratio is 80
% or more of pressure is required. Next, decarburization annealing is performed in a wet hydrogen atmosphere. Decarburization annealing has the role of decarburizing and primary recrystallization and at the same time generating an oxide layer necessary for forming an insulating film on the surface of the product. An annealing separator is applied to the surface of the steel sheet after decarburization annealing to prevent seizure during final high-temperature annealing and to form an insulating film on the surface of the product. The main component of the annealing separator is MgO, and TiO ₂ , depending on the purpose.
It is possible to use a material to which Al ₂ O ₃ , CaO, a B compound, an S compound, and an N compound are added. Subsequently, final high temperature annealing is performed. The purpose of this annealing is secondary recrystallization, purification, and the formation of an insulating film mainly composed of forsterite, a mixture of MgO and SiO ₂ , on the surface of the product, and is usually performed at temperatures of 1100°C or higher.
The test is carried out in hydrogen or a mixed atmosphere containing hydrogen for 5 hours or more. As the finishing high-temperature annealing conditions employed in the present invention, gradual heating within the temperature range in which secondary recrystallization is performed is particularly effective for stably obtaining a high magnetic flux density. The metallurgical idea behind this gradual heating operation in the secondary recrystallization temperature range is that secondary recrystallized grains with a smaller inclination from the {110} <001> orientation will occur at a lower temperature, as is conventionally known. In fact, by performing slow heating, the volume ratio of secondary recrystallized grains close to the {110} <001> orientation generated at low temperatures in the product is increased, and the magnetic flux density is increased. In the case of the present invention where the S content is low, that is, when the suppressing function against crystal grain growth by fine MnS is small, grain growth is relatively large in a low temperature range, so slow heating can reduce {110}<001> It is particularly effective to increase the volume ratio of secondary recrystallized grains generated at a low temperature close to the orientation of the product to increase the magnetic flux density.

Figure 8 shows C: 0.060%, Si: 3.42%, Mn: 0.25
%, S: 0.002%, P: 0.040%, acid soluble Al:
After heating a continuously cast slab containing 0.032%, N: 0.009%, and Cr: 0.15% to 1410℃, the plate thickness is reduced by hot rolling.
A hot-rolled sheet of 2.3 mm was made, and after continuous annealing at 1150°C for 2 min, it was cold-rolled to 0.30 mm and heated to 850 mm in a wet hydrogen atmosphere.
Magnetic flux density (B ₁₀ ) of the product obtained by performing decarburization annealing at ℃×2 min, applying MgO as an annealing separator, and performing final high temperature annealing at 1200℃×20 hr, and 700 ~ at the time of final high temperature annealing. FIG. 3 is a diagram showing the relationship between heating rates in a temperature range of 1100°C. This figure shows that the slower the heating rate, the higher the magnetic flux density, especially at 15℃/
It can be seen that it becomes significantly higher below hr. When the heating rate is within a range of 15° C./hr or less, the magnetic flux density does not change significantly, but the variation in the magnetic flux density decreases as the heating rate decreases. However, considering economic efficiency, the lower limit is about 7°C/hr. This 700～
After secondary recrystallization is completed by slow heating in the 1100°C range, purification annealing is generally performed in pure H ₂ at a high temperature of around 1200°C to reduce N and S in the steel as much as possible. be.

As described above in detail, the present invention uses continuous casting slabs as a starting material, which can be manufactured at low cost and can be industrially stably produced with uniform magnetic properties due to uniform composition in the longitudinal direction of the finished product, by heating the slab during hot rolling. This prevents the occurrence of linear secondary recrystallization defects at high temperatures (this is especially noticeable in high-Si materials), making it possible to produce products with high magnetic flux density and high iron loss. Furthermore, when the slab heating temperature during hot rolling is low, secondary recrystallization defects do not occur even in high-Si materials, and high iron loss is possible due to the characteristics of the product crystal grains unique to the low temperature slab heating temperature. This also solves the extremely difficult restrictions on controlling Al in steel in the conventional single-rolling process, making stable industrial production possible.

Example 1 C: 0.060%, Si: 3.38%, Mn 0.20%, P:
0.040%, S: 0.005%, acid-soluble Al: 0.033%,
Molten steel containing 0.0085% N, 0.16% Cr, and the balance consisting of Fe and unavoidable impurities was made into a slab by continuous casting, heated at a temperature of 1400°C, and then hot rolled to make a 2.3 mm hot rolled plate. . Hot-rolled plate at 1120℃
After annealing for 2 minutes, it was cold rolled to a final thickness of 0.30 mm, and decarburized annealed at 850°C for 2 minutes in a wet hydrogen atmosphere. After coating with MgO, final high-temperature annealing was performed at 1200°C for 20 hours. This finish high temperature annealing is 700 ~
The heating rate in the range of 1100°C was 10°C/hr.
Furthermore, a film containing chromic anhydride as the main component was baked onto the surface of the steel plate. The magnetic property of the finished product in the rolling direction is B ₁₀ =
1.93Tesla, W _17/50 = 0.99w/Kg. As a result of dotted laser irradiation in the C direction on the surface of this product, extremely excellent magnetism was obtained with B ₁₀ =1.93 Tesla and W _17/50 =0.88 w/Kg.

Example 2 C: 0.053%, Si: 3.35%, Mn: 0.25%, P:
0.035%, S: 0.003%, acid-soluble Al: 0.029%,
Continuously cast slab containing N: 0.0080%, Cr: 0.15%, balance Fe and unavoidable impurities.
After heating to a temperature of °C, it was hot rolled to make a 2.3 mm hot rolled sheet. After annealing hot rolled plate at 1080℃×2min, 0.30
Cold rolled to a final thickness of 850 mm in a wet hydrogen atmosphere.
Decarburization annealing was performed at ℃×2 min. After coating with MgO, final high-temperature annealing was performed at 1200°C for 20 hours. The heating rate of this final high temperature annealing in the range of 700 to 1100°C was 20°C/hr. Furthermore, a film containing chromic anhydride as the main component was baked onto the surface of the steel plate. The magnetic properties of this product in the rolling direction are B ₁₀ = 1.91Tesla,
W _17/50 = 0.97w/Kg. It can be seen that when the slab heating temperature during hot rolling is low, the iron loss is excellent compared to the magnetic flux density.

Example 3 C: 0.053%, Si: 3.45%, Mn: 0.23%, P:
0.037%, S: 0.003%, acid-soluble Al: 0.027%,
Molten steel containing 0.0090% N, 0.20% Cr, and the remainder Fe and unavoidable impurities was cast by continuous casting in a 250 mm thick mold. After the molten steel solidifies, it is immediately charged into a trolley-type heat retention furnace without cooling, and when the average slab temperature reaches approximately 1130℃, it is hot rolled.
A 2.3mm hot-rolled plate was made. This hot-rolled plate is heated to 1080℃×
After annealing for 2 minutes, it was cold rolled to a final thickness of 0.30 mm, and decarburized annealed at 850°C for 2 minutes in a wet hydrogen atmosphere. After coating with MgO, final high-temperature annealing was performed at 1200°C for 20 hours. This finishing high temperature annealing is 700−
The heating rate in the range of 1100°C was 10°C/hr.
Furthermore, a film containing chromic anhydride as the main component was baked onto the surface of the steel plate. The magnetic property of this product in the rolling direction is B ₁₀
= 1.90 Tesla, W _17/50 = 1.01w/Kg. There was no occurrence of secondary recrystallization defects.

Example 4 C: 0.053%, Si: 3.45%, Mn: 0.23%, P:
0.037%, S: 0.003%, acid-soluble Al: 0.027%,
250% of molten steel containing N: 0.0090% and Cr: 0.20%
It was cast by continuous casting in a mm thick mold. As a consideration to minimize cooling after solidification of molten steel,
We carried out heat insulation inside the continuous casting machine and short-term gas heating of the end face of the slab, which tends to get cold. The slab was quickly moved to the entrance of the hot rolling mill, and hot rolling was started when the center of the cross section of the slab was approximately 1200°C and the surface layer was approximately 1050°C, resulting in a hot rolled sheet with a thickness of 2.3 mm. This hot-rolled plate is heated to 1080℃×
After annealing for 2 minutes, it was cold rolled to a final thickness of 0.30 mm, and decarburized annealed at 850°C for 2 minutes in a wet hydrogen atmosphere. After coating with MgO, final high-temperature annealing was performed at 1200°C for 20 hours. The magnetic properties of this product in the rolling direction were B ₁₀ = 1.90 Tesla and W _17/50 = 1.03 w/Kg.

[Brief explanation of the drawing]

Figure 1 shows C: 0.058%, Si: 3.35%, Mn: 0.23
%, P: 0.036%, acid-soluble Al: 0.033%, N:
Contains 0.0085%, Cr: 0.13%, and S is 0.002~
After heating the continuous casting slab which is 0.033% to 1410℃,
A hot-rolled sheet of 2.3 mm was made by hot rolling, and after continuous annealing at 1150°C for 2 min, it was cold rolled to a thickness of 0.30 mm in wet hydrogen.
Diagram showing the incidence of linear secondary recrystallization defects in products obtained by performing decarburization annealing at 850°C for 2 minutes, applying MgO as an annealing separator, and performing final high-temperature annealing at 1200°C for 20 hours. , Figure 2 shows C: 0.050%, Si:
3.45%, Mn: 0.25%, P: 0.040%, acid soluble
Contains Al: 0.027%, N: 0.0080%, Cr: 0.18%,
Furthermore, a small specimen with a thickness of 40 mm containing 0.002 to 0.035% S was heated to 1200 °C, and after slab extraction, it was cooled to 1000 °C in the air, and kept in a furnace at 1000 °C for 30 seconds.
Then hot rolled in 3 passes to 2.3mm, 1120℃×2min
Secondary product that is continuously annealed, further cold rolled to 0.30 mm, decarburized in a wet hydrogen atmosphere at 850℃ for 2 minutes, coated with MgO as an annealing separator, and then subjected to final high-temperature annealing at 1200℃ for 20 hours. A diagram showing the recrystallization defect incidence rate, Figure 3 shows C: 0.060%, Si: 3.33%, S:
0.004%, acid-soluble Al: 0.032%, N: 0.0090%,
After heating the continuous casting slab containing 0.15% Cr to 1350℃, it was hot-rolled into a hot-rolled plate with a thickness of 2.3mm.
After continuous annealing at ℃×2min, it is cold rolled to 0.30mm.
Decarburization annealing was performed at 850°C for 2 min in a wet hydrogen atmosphere, MgO was applied as an annealing separator, and annealing was performed at 1200°C for 2 min.
A diagram showing the effect of Mn and P contents in the slab on the magnetic flux density (B ₁₀ ) of the finished product obtained by finishing high temperature annealing for 20 hours. Figure 4 shows C: 0.045%, Si: 3.35%,
S: 0.002%, acid-soluble Al: 0.028%, N: 0.0075
%, Cr: A small specimen with a thickness of 40 mm containing 0.18% was heated to 1150°C, and after slab extraction, it was hot-rolled in 3 passes to form a hot-rolled plate with a thickness of 2.3 mm, and then continuously annealed at 1120°C for 2 min, and then further heated to 0.30 mm. cold rolled, decarburized annealed in a wet hydrogen atmosphere, coated with MgO as an annealing separator, and then heated at 1200℃
A diagram showing the influence of Mn and P on the magnetic flux density (B ₁₀ ) of a product that has been subjected to high temperature finishing annealing for 20 hours. Figure 5 shows C: 0.06%, Si: 3.33%, Mn: 0.30%, P:
A continuously cast slab containing 0.035%, acid-soluble Al: 0.029%, and N: 0.0090% was heated to 1350°C, then hot-rolled into a hot-rolled plate with a thickness of 2.3mm, continuously annealed at 1120°C for 2 minutes, and then Cold rolled to 0.30mm, decarburized annealed in a wet hydrogen atmosphere, coated with MgO as an annealing separator,
A diagram showing the influence of Cr on the relationship between magnetic flux density (B ₁₀ ) and iron loss (W _17/50 ) of a product obtained by final annealing at 1200°C x 20 hours. Figure 6 shows C: 0.050%. ,
Si: 3.45%, Mn: 0.25%, S: 0.002%, P:
0.040%, acid-soluble Al: 0.027%, N: 0.0080%,
After heating a continuous casting slab containing Cr: 0.18%,
A hot-rolled sheet of 2.5 mm was made by hot rolling, and after continuous annealing at 1120°C for 2 min, the plate thickness was reduced to 0.30 mm by cold rolling, and decarburization annealed at 850°C for 2 min in a wet hydrogen atmosphere, and MgO was added as an annealing separator. Figure 7 shows the effect of slab heating temperature on the magnetic flux density of a product obtained by coating and final annealing at 1200℃ x 20 hours. of
A diagram showing the magnetism after applying a tension coating mainly composed of colloidal silica to a product obtained by changing the temperature to 1150°C. Figure 8 shows C: 0.060%.
Si: 3.42%, Mn: 0.25%, S: 0.002%, P:
0.040%, acid-soluble Al: 0.032%, N: 0.0090%,
A continuous cast slab containing 0.15% Cr was heated to 1410℃ and then hot-rolled into a hot-rolled plate with a thickness of 2.3mm.
After continuous annealing at ℃×2min, it was cold rolled to 0.30mm.
Decarburization annealing was performed at 850°C for 2 min in a wet hydrogen atmosphere, MgO was applied as an annealing separator, and annealing was performed at 1200°C for 2 min.
Magnetic flux density (B ₁₀ ) of the product obtained by finishing high-temperature annealing for 20 hours and 700 to 1100℃ during finishing high-temperature annealing
It is a figure showing the relationship of heating rate in the temperature range of.

Claims (1)

[Claims] 1 C: 0.025-0.075%, Si: 3.0-4.5%, acid-soluble Al: 0.010-0.060%, N: 0.0030-0.0130%,
S: 0.007% or less, Mn: 0.08-0.45%, P: 0.015
A continuously cast slab for unidirectional silicon steel sheet consisting of ~0.045%, Cr: 0.07~0.25%, balance Fe and unavoidable impurities is heated and hot rolled into a hot rolled sheet, and then the hot rolled sheet is heated at 850~1200°C. After continuous annealing for a short time in the range of A method for producing a unidirectional silicon steel sheet with excellent iron loss, which is characterized by coating and finishing high-temperature annealing. 2 700 to 1100 during heating during final high temperature annealing
2. The method according to claim 1, wherein the temperature is increased within a temperature range of 15° C./hr or less at a heating rate of 15° C./hr or less. 3 Continuous casting slab for unidirectional silicon steel plate at 1280℃
The method according to claim 1, wherein the hot-rolled sheet is obtained by hot rolling after heating to a temperature not exceeding . 4 Continuously cast slab for unidirectional silicon steel plate at 1280℃
The method according to claim 1, wherein after heating to the above temperature, a hot rolled sheet is obtained by hot rolling. 5. The method according to claim 1, wherein hot rolling is carried out directly after continuous casting using slab sensible heat without cooling the continuous casting slab.