KR100276341B1 - The manufacturing method of highmagnetic flux density oriented electric steel sheet of slab low temperature heating - Google Patents

Abstract

PURPOSE: A method for manufacturing oriented electrical steel sheets having high magnetic induction is provided to improve productivity of slab manufacturing by controlling temperature condition. CONSTITUTION: The oriented electrical steel sheet is manufactured by heating silicon steel slab comprising C 0.025-0.08wt.%, Si 2.5-4.5wt.%, Sol-Al 0.020-0.040wt.%, N 0.0150wt.%, Mn 0.01-0.25wt.%, S 0.013-0.022, B 0.0005-0.010wt.%, a balance of Fe, and inevitable impurities in the temperature range of 1100 to 1320deg.C; hot rolling; preliminary annealing the hot rolled slab; cold rolling the slab to target thickness; decarburizing annealing; nitriding it under ammonia atmosphere in the temperature range of 600 to 800deg.C; and then high temperature annealing and coating. In the method, the amount of nitrogen solidified into the slab is 200-800ppm, and Mn/S ranges 4 to 12.

Description

Manufacturing method of high magnetic flux density oriented electrical steel sheet by slab low silver heating

The present invention relates to a method for manufacturing a high magnetic flux density oriented electrical steel sheet used as iron core materials for transformers, stop machines, rotary machines, and the like, and more specifically, to slab low temperature heating, which improves productivity decrease due to high temperature slab heating. It relates to a method of manufacturing a high magnetic flux density oriented electrical steel sheet.

About 3% silicon is added to the grain-oriented electrical steel sheet, and hot rolled, cold rolled, and heat-treated are recrystallized with the {110} plane on the rolled surface and the <001> axis on the rolling direction for magnetization of iron in the rolling direction. It is a soft magnetic material with an aggregate structure (also called a goth structure). It is mainly used as an iron core of a transformer or a generator by using excellent magnetic properties.

The properties required for such oriented electrical steel sheets are high magnetic flux density and low iron loss. The magnetic flux density is determined according to the extent that the <001> axes are arranged in the rolling direction. If the magnetic flux density is high, the same performance can be achieved even if fewer iron core materials are used, so that the electric apparatus can be miniaturized.

In addition, the iron loss is the energy loss of the electrical equipment by the iron core material, in general, the higher the magnetic flux density, the lower the iron loss, and depends on the thickness of the product, the content of impurities in the material, the specific resistance, the grain size, etc. The energy efficiency of the electric equipment becomes high.

Therefore, there is a growing need for oriented electrical steel sheets having high magnetic flux density and low iron loss in miniaturization of electrical equipment and energy saving resources.

On the other hand, oriented electrical steel sheet is divided into high magnetic flux density oriented electrical steel sheet and general oriented electrical steel sheet according to the manufacturing method and properties, each price and use is different.

The grain-oriented electrical steel sheet is subjected to hot rolling and cold rolling to a final thickness, followed by primary recrystallization annealing, followed by high temperature annealing to selectively grow {110} <001> primary recrystallization rup, ie, secondary By recrystallization, a grain-oriented electrical steel sheet can be produced. At this time, the precipitates such as MnS and AlN are finely and uniformly dispersed in the steel before the high temperature annealing to suppress the coarse growth of the primary recrystallized grains before the start of the second recrystallization, and to selectively grow only {110} <001>. very important.

As such, the most important technique in the production of grain-oriented electrical steel sheet is to suppress the growth of primary recrystallized grains before the secondary recrystallization is initiated. In this case, as the inhibitor, compounds such as MnS and AlN are mainly used, and segregation elements such as Sb and Sn are used as auxiliary.

N.P. in 1933 Various compounds have been tried since Goss developed a means of using MnS as an inhibitor, but the current worldwide use is MnS alone or MnS + AlN system. The essential property of the inhibitor should be to suppress the growth of the primary recrystallization grains until the temperature at which the secondary recrystallization begins, to create an environment where the secondary recrystallization grains can grow greatly, and to grow coarsely after the secondary recrystallization is initiated. It should not be deterred or terminated by employment and interfere with the secondary re-decision. To this end, the inhibitor must be finely and uniformly dispersed, and conventionally, a method of heating the slab at a high temperature around 1400 ° C. in the hot rolling process to completely dissolve MnS or AlN and then finely depositing it in the hot rolling process.

In addition, Japanese Patent Publication No. 51-13469, which is a conventional representative method using segregation elements, has high manufacturing costs using expensive and toxic elements such as Sb and Se, and has problems of safety and pollution during production.

In addition, the so-called Hi-B method, represented by Japanese Patent Publication No. 40-15644, obtains this effect by finely depositing AlN and MnS during hot rolling. However, this method has a very narrow range of manufacturing conditions for obtaining good magnetism and a very difficult manufacturing method, making it difficult to secure stable magnetism.

In particular, the above two methods have a problem in that the slab from steelmaking and playing to heat the slab from the steelmaking and playing in order to completely solidify the precipitate to be heated for 4 hours or more. High temperature slab heating consumes a lot of energy, and when slab is heated to high temperature, silicon oxide with low melting point flows out of the surface, causing a lot of material loss, and the silicon oxide erodes the refractory of the heating furnace. It is expensive because the refractory needs to be replaced.

Due to this problem, a lot of researches have recently been conducted to heat the slab at a low temperature, and examples thereof include Japanese Patent Application Laid-Open No. 59-56522, Japanese Patent Application Laid-Open No. 62-40315, and the like. The method uses only AlN in place of AlN and MnS, which are used as conventional inhibitors. It is characterized by uniformly dispersing fine AlN before high temperature annealing to cause secondary recrystallization. Therefore, MnS or AlN is not controlled during hot rolling, and thus high temperature heating of the slab is not necessary.

This method is an innovative method capable of reheating the lower temperature of 1280 ℃ or less compared to the conventional technology for heating the slab to a high temperature. However, this technique uses AlN alone as the primary recrystallization growth inhibitor, which has the advantage of saving manufacturing cost compared to the conventional method, but only AlN should be used as a means of countering the primary recrystallization before the second recrystallization starts. It is not satisfactory because the magnetism is less than or equal to that of the prior art, which causes the stability of the recrystallization.

More specifically, since the conventional method uses only AlN instead of AlN and MnS, which are used as conventional inhibitors, the inhibitory power for inhibiting growth of primary recrystallized grains until the second recrystallization is weak, thus the direction of the secondary recrystallized grains, that is, rolling There is a problem in that the orientation of the <001> axis in the direction is not precise and there are many deviations, which deteriorates the magnetic properties and deteriorates the magnetic characteristics.

In this case, the reason why MnS is not used as a primary recrystallization growth inhibitor is that high heating temperature around 1400 ° C. is required to completely solidify MnS.

Therefore, in the conventional slab low temperature heating technology, the S content is managed to 0.007% or less by weight ratio.

In addition, in the slab low temperature heating process, fine precipitation of MnS or AlN is rather harmful to magnetism in the hot rolling process, so that the precipitate is coarsened by heating the slab to 1200 ° C or less. Therefore, the hot rolling temperature is lower than that of ordinary carbon steel compared to the general one, so that the load of the hot rolling mill is large, and it is difficult to manage the production schedule during the mixed production with the carbon steel, resulting in a decrease in productivity.

Therefore, the present invention was made to solve the above-mentioned conventional problem, by using MnS and AlN precipitate as a growth inhibitor of the primary recrystallization to obtain excellent magnetic stability, low temperature below 1250 ℃ instead of ordinary high temperature slab heating The purpose of the present invention is to provide a method for manufacturing high magnetic flux density oriented electrical steel sheet, which has been improved in slab heating productivity.

The present invention for achieving the above object is a method of manufacturing a high magnetic flux density oriented electrical steel sheet, C: 0.025-0.08%, Si: 2.5-4.5%, Sol-Al: 0.020-0.040%, N: 0.0150% Hereinafter, silicon steel composed of Mn: 0.01 to 0.25%, S: 0.013 to 0.022%, B: 0.0005 to 0.010%, Mn / S ratio 4 to 12, and remainder Fe and other unavoidable impurities. After heating the slab at a temperature of 1100-1320 ° C. and hot rolling, the hot rolled plate is pre-annealed and cold rolled once to the thickness of the final product, and then the cold rolled plate is subjected to decarbonization annealing as primary recrystallization. Then, the present invention relates to a method for producing a high magnetic flux density oriented electrical steel sheet by low temperature heating of slab formed by nitriding for a short time in an atmosphere containing ammonia at a temperature of 600 to 800 ° C., followed by high temperature annealing and insulation coating.

Hereinafter, the present invention will be described in detail.

The present invention is to reduce the content of Mn, S in the silicon steel components to enable low-temperature reheating, and also to distribute the AlN in the steel by low-silver slab heating and low-heat hot rolling, and then to distribute the AlN by nitriding treatment after the hot rolling process To stabilize the secondary recrystallization.

To this end, the content of C is not good enough for phase transformation in hot rolling when the content is less than 0.025%, and the columnar normal tissue of the slab is not destroyed by hot rolling, which is not good for the development of aggregates, and its content is 0.08% If it is above, since decarburization does not occur properly and magnetic aging occurs and it is harmful to a magnetic, it is preferable to add in 0.025-0.08%.

When the content of Si is 2.5% or less, the resistivity is low, so that the iron loss is high. If the content of Si is 4.5% or more, the cold rolling property is bad, it is preferably added in the range of 2.5-4.5%.

When the content of Sol-A1 is 0.020% or less, the inhibitory power by AlN is weak, and when it is 0.040% or more, AlN is easily coarse before the second recrystallization, so it is preferably added in the range of 0.020-0.040%.

When the content is more than 0.015%, the brittleness during cold rolling becomes strong and fragile, so it is preferable to limit it to 0.015% or less.

When the content of Mn is 0.01% or less, brittleness is easily caused by glass S not bonded to MnS, and when the content is 0.25% or more, MnS tends to be coarse, so it is preferable to add Mn in the range of 0.01-0.25%. .

When the content of S is 0.013% or less, the primary recrystallization growth inhibition by MnS is small, and when the content is 0.022% or more, it is difficult to prepare by slab low temperature heating, so it is preferably added in the range of 0.013-0.022%.

Since B is an effective element that forms BN precipitates to supplement primary recrystallization growth inhibition, it is added. If the content is less than 0.0005%, there is no effect of adding B, and if B is more than 0.010%, the magnetic properties are poor and brittle. Since rolling is difficult, it is preferable to add in 0.0005 to 0.010% of range.

Since the Mn / S ratio is a different concept from using MnS in normal high temperature slab heating, the ratio is important. Because the amount of S is added less than the high temperature slab heating, if the amount of Mn is large, the precipitate of MnS is coarsened and the growth inhibitory power of the primary recrystallized grain by MnS is weakened. When the amount of Mn is small, S, which is a low melting point material that cannot be bonded with MnS, is segregated at grain boundaries to promote the occurrence of cracks. Preferred ratio of Mn / S is 4-12.

The low temperature reheating of the silicon steel slab prepared as described above is preferable in the temperature range of 1100-1320 ° C. The reason is that when the slab heating temperature is 1100 ° C or lower, the hot rolling end temperature cannot be set to 900 ° C or higher. It is because productivity will worsen by high temperature slab heating if a slab heating temperature is 1320 degreeC or more.

As described above, the slabs are reheated and hot-rolled. The hot-rolling is composed of rough rolling and filamentous rolling. In consideration of the fine precipitation of MnS, the hot rolling end temperature is preferably 900 ° C. or higher.

After hot rolling as described above, the hot rolled plate is preliminarily annealed to a final product thickness by cold rolling once, and decarburized to 30 ppm or less of carbon having no self aging.

The decarburized plate is subjected to nitriding in an atmosphere containing ammonia, and the more preferable nitrogen content after the nitriding treatment is 200-800 ppm. If it is 200 ppm or less, AlN formation by nitriding is somewhat insufficient, and if it is 800 ppm or more, AlN tends to coarsen before starting secondary recrystallization.

After completion of the nitriding treatment, MgO co-toning is carried out and subjected to high temperature annealing to cause secondary recrystallization in a mixed atmosphere of hydrogen and nitrogen, followed by insulation coating to produce a final product.

The nitriding treatment is preferably performed at 600-800 ° C., because the temperature is too low at 600 ° C. or lower, so that nitriding is difficult, and the nitriding is excessive at 800 ° C. or higher, so that the nitrogen content in the steel sheet is too high. Because there is.

On the other hand, the high temperature annealing is preferably carried out at 750-950 ℃, because the decarburization reaction does not occur actively at 750 ℃ or less, the amount of carbon remaining in the steel sheet is too high, there is a fear of self aging phenomenon, 950 ℃ This is because a thick oxide film containing FeO as a main component may be formed on the surface of the steel sheet, resulting in peeling of the insulating coating.

Hereinafter, the present invention will be described in detail through examples.

Example 1

Based on C: 0.045%, Si: 3.01%, Sol-Al: 0.028%, N: 0.009%, and B: 0.0030%, the slabs of which Mn and S were changed as shown in Table 1 were changed at 4 at 1290 ° C. After the heating time was hot rolled to make a hot rolled sheet of 2.3mm thickness. After pre-annealing the hot rolled sheet to 0.30mm by cold rolling once, decarbonized annealing for 3 minutes in a wet atmosphere mixed with hydrogen and nitrogen at 830 ℃ and then mixed with hydrogen and nitrogen ammonia at 700 ℃ for 3 minutes Nitriding was performed in the atmosphere. After the nitriding treatment, the Mg0 coating was followed by high temperature annealing in a mixed atmosphere of hydrogen and nitrogen, followed by insulation coating. Then, the magnetic properties were measured, and the results are shown in Table 1 below.

At this time, when the intensity of the measurement of the magnetic properties is 1000Amp / m, the magnetic flux density values BD (Tesla) and B10 is 1.7 test, the iron loss when the frequency is 50Hz W17 / 50 (W / kg). The higher the magnetic flux density value, the better the efficiency of the electric equipment, and the smaller the iron loss, the smaller the energy loss by the iron core.

TABLE 1

As can be seen from Table 1, Mn: 0.01-0.25%, S: 0.013-0.022%, Mn / S was found to have excellent magnetic properties in the condition of the condition of 4-12.

Example 2

Slabs varying in Boron amount based on C: 0.040%, Si: 3.25%, Sol-Al: 0.026%, N: 0.008%, S: 0.014%, Mn: 0.12%, and are shown in Table 2. After 4 hours of heating, hot rolling was carried out to form a hot rolled sheet having a thickness of 2.3 mm. After pre-annealing the hot rolled sheet to 0.30mm by cold rolling, and then decarbonized for 3 minutes in a wet atmosphere mixed with hydrogen and nitrogen at 830 ℃, and then mixed with hydrogen and nitrogen for 3 minutes at 700 ℃. Nitrided at After nitriding, Mg0 was coated, followed by high temperature annealing in a mixed atmosphere of hydrogen and nitrogen, followed by insulation coating.

TABLE 2

As can be seen in Table 2, the Boron amount was excellent in the magnetic properties of the invention steel in the range of 5-10ppm.

Example 3

Slab of C: 0.046%, Si: 3.15%, Sol-Al: 0.027%, N: 0.009%, B: 0.0040, Mn: O.12, S: 0.013% for 4 hours at various heating temperature conditions I was. After the slab heating was finished, hot rolling was made into a hot rolled sheet having a thickness of 2.3 mm. After pre-annealing the hot rolled sheet to make 0.30mm by cold rolling, and then decarbonized for 3 minutes in a wet atmosphere mixed with hydrogen and nitrogen at 830 ℃, and then mixed with hydrogen and nitrogen for 3 minutes at 700 ℃. Nitrided at After nitriding, Mg0 was coated, followed by high temperature annealing in a mixed atmosphere of hydrogen and nitrogen, followed by quench coating.

TABLE 3

As can be seen in Table 3, the invention steel in the slab heating temperature range of 1150-1300 ℃ was excellent in magnetism, it was easy to manufacture.

As described above, the present invention is improved by the slab low temperature heating technology using AlN and MnS precipitate at the same time, compared to the conventional method of manufacturing high magnetic flux density oriented electrical steel sheet by high temperature slab heating, thereby improving the realization rate and productivity. In addition, the present invention enables a method of manufacturing a high magnetic flux density oriented electrical steel sheet having excellent magnetic properties and productivity compared to a method of manufacturing a high magnetic flux density oriented electrical steel sheet by conventional slab low temperature heating. The high magnetic flux density oriented electrical steel sheet produced by the present invention has a useful effect that can be applied to the field of electrical equipment manufacturing such as transformer.

Claims (2)

In the method for producing a high magnetic flux density oriented electrical steel sheet, C: 0.025 to 0.08%, Si: 2.5 to 4.5%, Sol-Al: 0.020 to 0.040%, N: 0.0150% or less, Mn: 0.01 to 0.25%, S: 0.013 to 0.022%, B: 0.0005 to 0.010%, Mn / S ratio of 4 to 12, the silicon steel slab consisting of the remaining Fe and other unavoidable impurities are heated at a temperature of 1100 ~ 1320 ℃ and hot rolled Thereafter, the hot rolled sheet is pre-annealed and cold rolled once to the thickness of the final product, and the cold rolled sheet is subjected to decarbonization annealing as primary recrystallization, and then ammonia is contained at a temperature of 600 to 800 ° C. A method of manufacturing a high magnetic flux density oriented electrical steel sheet by slab low temperature heating, which is made by nitriding in an atmosphere for a short time and then performing high temperature annealing and insulation coating. The method according to claim 1, wherein the nitriding is performed so that the amount of nitrogen is 200-800 ppm.