KR20010048860A - A method for manufacturing low temperature reheated grain-oriented electrical steel sheet having no glass film - Google Patents

Abstract

PURPOSE: A method for manufacturing a low temperature reheating oriented electrical steel sheet without a glass film is provided to obtain an oriented electrical steel sheet in which punching property is improved without glass film by using a composition in which alumina powder is added to an alumina sol a main constituent of as a fusion preventing agent. CONSTITUTION: In a method for manufacturing an oriented electrical steel sheet comprising the processes of hot rolling after low temperature reheating to a temperature of 1250 to 1340 deg.C a steel slab comprising 2.9 to 3.3 wt.% of Si, 0.025 to 0.045 wt.% of C, 0.015 wt.% or less of P, 0.08 to 0.020 wt.% of sol-Al, 0.0080 to 0.012 wt.% of N, 0.007 wt.% or less of S, 0.12 to 0.42 wt.% of Mn, 0.6 wt.% or less of Cu and a balance of Fe and other inevitable impurities; annealing the hot rolled steel slab at a temperature of 1000 deg.C or less; cold rolling the annealed steel slab, thereby adjusting to a final thickness by performing two times of cold rollings including decarburization annealing under the humid environment in the middle of the cold rollings; coiling to a large scale coil by coating the recovery annealed steel slab with a fusion preventing agent after recovery annealing the cold rolled steel slab under the dry environment of 600 deg.C or less; performing finishing high temperature annealing passing through the heat cycle steps of comprising maintaining a temperature increasing ratio of 15 deg.C/hr in the range of 700 to 1200 deg.C, uniformly heating the steel slab at the temperature of 1200±10 deg.C for more than 20 hours and cooling the steel slab; and coating a tension coating agent on the resulting steel slab, wherein the fusion preventing agent comprises solid contents of 10 to 25 wt.% of alumina sol and 5 to 20 wt.% of alumina powder, and coated in an amount of 3 to 7 g/m2.

Description

A method for manufacturing low-temperature reoriented electrical steel without glass coating {A METHOD FOR MANUFACTURING LOW TEMPERATURE REHEATED GRAIN-ORIENTED ELECTRICAL STEEL SHEET HAVING NO GLASS FILM}

The present invention relates to a grain-oriented electrical steel sheet produced by applying the low-temperature slab heating method during hot rolling operation, and more particularly, by using a composition mainly composed of alumina sol as a fusion preventive agent, The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet without a low-temperature reheated glass coating having improved magnetic properties and improved magnetic properties.

A grain-oriented electrical steel sheet is an electrical steel sheet having an aggregate structure in which the orientation of grains is aligned in the direction of (110) [001]. It has extremely excellent magnetic properties in the rolling direction, so that iron core materials such as transformers, electric motors, generators and other electronic devices are used. Used as

In general, a grain-oriented electrical steel sheet is a steel slab made of 2 to 4 silicon and mostly MnS or AlN as a grain growth inhibitor, (reheating and hot rolling)-(preliminary annealing)-(one cold annealed with intermediate annealing). It is manufactured through a complex process such as rolling)-(decarbonization annealing)-(application of anti-fusion agent)-(final finishing high temperature annealing). The most difficult process among these complex manufacturing processes is the slab reheating process that performs high temperature heat treatment. In this step, the steel slab is maintained at a high temperature of about 1400 ° C. for about 5 hours to completely disperse the precipitates such as MnS and AlN, which are used as grain growth inhibitors, and then deposit finely. At this time, an oxide called Pyrite (Fe ₂ SiO ₄ ) is formed on the surface of the hot slab. Since the melting point is about 1340 ° C. and it melts from the surface, some of them are designed to flow outward, but most of them are refractory parts of the furnace. Accumulation causes problems that complete internal repair is inevitable at the end of the work.

In order to solve the above problems, efforts have been made to lower the slab reheating temperature. As a result, Korean Patent Application No. 93-23751 sets up a component system for performing hot rolling by heating a conventional grain-oriented electrical steel sheet in the vicinity of 1250 ~ 1340 ° C, and in a manufacturing method that can work without additional equipment supplementation or establishment in the existing manufacturing process. The invention has been disclosed. Further elementary technologies have been disclosed in 94-21388, 94-21389, 94-21390, and 94-21391. These inventions have a low temperature reheating method, there is an advantage to produce a product having a high error rate and excellent magnetic properties during production, but because the glass film is present in the oriented electrical steel sheet manufactured as described above, such as iron core core for transformer There is a problem that punchability is not good in manufacturing.

That is, when manufacturing the iron core core for transformers using the directional electrical steel sheet manufactured as described above, the real yoga perform the slitting work, punching work, heat treatment and assembly work, among which the punching work is to improve productivity and cost In terms of savings, it is the most important manufacturing process.

When punching the directional product at demand, the punchability is divided into three materials: the hardness of the material itself, the glass film (the primary component is a Forsterite (2MgO · SiO ₂ )) layer, and the tension coating layer (the second insulating film). Mostly determined by. The glass coating layer is formed on the surface of the material by reaction of MgO used as a fusion inhibitor during secondary annealing and SiO ₂ based oxide on the surface of the material. In order to improve the punchability in the aromatic product, the insulating film layer It is preferable that it is a single coating layer only for the tension coating layer without this glass coating layer. Accordingly, much attention and research and development have been made regarding the manufacture of grain-oriented electrical steel sheets without a glass film.

Such efforts are being promoted in two directions. First, as in the conventional method, MgO is the main component of the fusion inhibitor, and chlorides such as Ca, Li, K, Na, and Ba are added thereto so that these chlorides react with the surface of the material to form a FeCl ₂ film during high temperature annealing. After the evaporation is removed from the surface, the invention itself to block the formation of the glass film layer, US Patent 4875947 is representative. However, according to the present invention, the coating workability is excellent, but it is difficult to strictly control and control the oxide layer to completely remove the glass coating, and the improvement effect of iron loss that may be caused by the absence of the glass coating layer due to the overetching action by the chloride addition is reduced. Can be.

As another method, there is a method of applying Al ₂ O ₃ powder which has no reactivity with the oxide layer on the surface of the material, but the Al ₂ O ₃ powder is usually about 2 to 10 μm commercially even when mechanically crushed into ultra fine particles There is a problem that it can only be miniaturized and it is difficult to keep this powder in a dispersed state with water. To solve this problem, the Japanese Patent Unexamined Patent 6-136555 discloses the Al ₂ O ₃ powder to the fully dispersed state by mixing Al ₂ O ₃ powder, but discloses a method of coating a material surface or the like organic solvent in an organic solvent It is impossible to make it exist stably, and there exists a problem which pollutes the environment by volatilization of the organic solvent, etc. at the time of slurry drying. Accordingly, Japanese Patent Laid-Open No. 6-41642 discloses an electrostatic coating method, but commercial production is difficult due to equipment restrictions.

In order to solve the above problems of the prior arts, the present inventors conducted research and experiments, and proposed the present invention based on the results, and the present invention provides a fusion inhibitor in the method for producing a grain-oriented electrical steel sheet. It is an object of the present invention to provide a method for manufacturing a low-temperature reheating oriented electrical steel sheet, which can obtain a grain-oriented electrical steel sheet having improved punching characteristics without using a glass coating by using a composition containing alumina sol as the main component thereof.

In the present invention, Si: 2.9 to 3.3, C: 0.025 to 0.045, P: 0.015 or less, dissolved Al: 0.08 to 0.020, N: 0.0080 to 0.012, S: 0.007 or less, Mn: 0.12 to 0.42, Cu: 0.6 The steel slab composed of the remaining Fe and other unavoidable impurities is then hot-rolled after low-temperature reheating at 1250 to 1340 ° C, and then hot-rolled at an temperature of 1000 ° C or lower, followed by decarbonization in a wet atmosphere. After performing cold rolling twice to adjust the final thickness, and then recovering and annealing in a dry atmosphere of 600 ℃ or less, and then coated with a fusion inhibitor and wound with a large coil, the temperature increase rate of 700 ~ 1200 ℃ section is 15 ℃ In the method of producing a grain-oriented electrical steel sheet by maintaining a temperature of at least / hr, and after finishing for 20 hours at a temperature of 1200 ± 10 ° C, after finishing a high temperature annealing through cooling cycle, applying a tension coating agent,

The coating of the fusion inhibitor is a low-temperature reheat oriented electrical steel sheet without a glass coating, characterized in that the coating is made by applying a fusion inhibitor composed of alumina sol having a solid content of 10 to 25 and alumina powder of 5 to 20 to a thickness of 3 ~ 7g / ㎡ It relates to a manufacturing method of.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The inventors of the present invention examined alumina particles having excellent dispersibility in a water-soluble state, and since alumina sol is present as a colloidal dispersion of ultrafine particles, not only has excellent liquid dispersibility, but also has an appropriate viscosity, thereby producing a cotarol in a production plant. It was confirmed that the coating workability by the excellent, and came to complete the present invention.

That is, the present inventors, in order to provide a method of manufacturing a grain-oriented electrical steel sheet without a glass coating as a punching improvement method that can achieve cost reduction and productivity improvement during processing and assembling of iron core core for transformer at demand. Alumina sol is used as the main component of the coating agent.

Usually, the glass coating layer is an insulating coating layer formed by a forsterite formation reaction (2MgO.SiO ₂ ) with MgO applied as an fusion inhibitor and SiO ₂ and Fe ₂ SiO ₄ which are material surface oxide layers. Therefore, in the present invention, Al ₂ O ₃ having no reactivity with the decarbonate layer on the material surface was used as the main component of the fusion inhibitor.

The Al ₂ O ₃ is preferable because the colloidal alumina sol having a size of 10 to 100 mμ is semipermanent in solution dispersibility and has a liquid viscosity of at least 50 cps or more so that it can be applied by cotarol. Such liquid stability is possible because the Al ₂ O ₃ surface in the colloidal state is positively charged by a very small amount of chlorine ions or acetate ions used as a liquid stabilizer. It exists in an amorphous state in manufacturing, but similarly to the crystalline phase, there is no chemical reaction with the material oxide layer, and its viscosity is large to ensure sufficient adhesion on the material surface, so that the coating amount management is relatively easy.

Hereinafter, the reason for range limitation of the present invention steel will be described.

The C is an element that plays a role of fine solid dispersion of AlN precipitate, rolling structure formation, imparting processing energy during cold rolling, etc., but it is advantageous to upwardly manage as much as possible, but to 0.025 ~ 0.045 considering the difficulty of decarburization process. It is desirable to set.

The Si is an element that serves to lower the iron core loss by increasing the resistivity value, the iron loss characteristics are worse when the content is less than 2.9, the steel is vulnerable when the excessive amount is added, so the cold rolling property is extremely bad, it is preferably set to 3.3 or less Do.

The Mn is an element that lowers the solid solution temperature of the precipitate upon reheating and prevents cracks formed at both ends of the material during hot rolling. It is advantageous to add more, but worsens iron loss by Mn oxide when more than 0.42 is added. The upper limit is 0.42.

The dissolved Al forms a precipitate of AlN together with N to secure the grain growth inhibitory power. If the content is less than 0.008, it does not have sufficient inhibitory power required for secondary recrystallization, and small grain size and incomplete fine particles appear. If added above 0.020, the inhibitory power is too strong, making the secondary recrystallization itself difficult and rapidly deteriorating magnetic properties. In this invention, it is preferable to limit to 0.008-0.020.

The N is an essential component for forming the secondary precipitates by forming reaction precipitates with dissolved Al. If the content is less than 0.008, the precipitates are insufficient, and if it is 0.012 or higher, a blister on the surface of the steel sheet causes defects. Since surface characteristics deteriorate, in the present invention, it is set to 0.008 to 0.012.

Cu combines with S, which is an impure component, to form a Cu ₂ S precipitate, and it is better to add as much as possible because it is solid-solution at the lowest temperature among the precipitates. However, if it is more than 0.6, it is preferable to set the upper limit to 0.6 because the oxide formed during decarbonization annealing adversely affects the insulation film formation.

Next, the manufacturing process will be described.

The steel slabs having the above-mentioned composition are preferably reheated to a low temperature in the range of 1,250 ° C. to 1340 ° C., which is a temperature just before slab melting, to ensure magnetic properties. Thereafter, hot-rolled sheet annealing is performed at a temperature of 1000 ° C. or lower, and primary cold rolling is performed while adjusting the intermediate thickness so that the final cold rolling rate is 46 to 69.

Then, an intermediate decarbonization annealing is performed, which is preferably performed in a humid atmosphere in the range of 890 to 960 ° C. The reason for this is that decarburization is poor at 890 ° C. or lower, and excessive holes due to high temperature occur at 960 ° C. or higher.

Subsequently, secondary cold rolling is carried out to adjust the final thickness, followed by recovery annealing at a temperature of 600 ° C. or lower, and an fusion inhibitor containing alumina sol as a main component and alumina powder added thereto.

When the alumina sol is pure alumina sol, a small portion between materials during high temperature annealing of 7 to 10 tons of heavy coil is fused, which may cause a big problem in later workability. Do. If the solids contained in the alumina sol is less than 10, the viscosity is low, so it is difficult to maintain the surface adhesion amount of the material suitable for coating amount management, that is, 3 to 7 g / m 2, and the coating workability by the cotalol is insufficient, and thus excluded from the present invention. . On the other hand, when the solid content exceeds 25, the thickness management is difficult and there is a problem in the liquid stability, in the present invention, the solid content is limited to 10 to 25.

In addition, the reason for including the alumina powder in the fusion inhibitor as described above is as follows. That is, the alumina sol alone can produce a product without a glass coating, but considering the workability problem caused by sticking between the edges of the plate during high temperature annealing by proper coating amount management, it is preferable to add an aluminum powder. . In particular, when the alumina sol contains a solid content of less than 10, if the surface coating amount of the material is managed as thin as 3g / ㎡, the problem occurs that the plate adhesion phenomenon occurs on the coil edge side during high temperature annealing, such defects, In particular, the edge plate of the coil of the heavy end can be completely prevented by adding about 5 to 20 μm of alumina powder having a size of 2 to 10 μm that can be easily purchased on the market. The size of the alumina powder is advantageous in terms of dispersibility, such as 10㎛ or less, but is not particularly limited under the conditions of the present invention. The addition amount is preferably set to 5 to 20, but if it is less than 5, the effect of coating amount management is less effective, and there is a possibility that workability problems may occur due to plate defects at high temperature annealing. This is because the thickness is difficult to manage.

In coating the fusion inhibitor of the present invention, the coating amount is preferably 3 to 7 g / m 2. The reason for this is that plate defects may appear at 3 g / m 2 or less, and the effect of improving characteristics is less at 7 g / m 2 or more.

Then, it is wound up and made into a large coil, followed by final finishing annealing. For example, the final finishing annealing is performed at a temperature of 1200 ± 10 ° C. at a temperature of 700 ° C. to 1200 ° C. at a temperature of 1200 ° C./hr in 100 hydrogen atmospheres. This can be carried out by undergoing a thermal cycle of cooling after cracking for 20 hours or longer at.

After completion of the secondary recrystallization and pickling treatment to adjust the surface, and finally apply a tension coating agent, the composition of the tension coating agent is not particularly limited in the present invention, for example, consisting of colloidal silica, aluminum phosphate and chromic anhydride Tension coating agents can be applied. Then, it is dried at 900 ℃ to produce an electrical steel sheet product.

Hereinafter, it demonstrates through an Example.

Example 1

A 220 mm thick slab was made using components of the composition consisting of 3.18i, 0.037, 0.013P, 0.012 dissolved Al, 0.0088, 0.007, 0.21Mn, 0.38u and the balance Fe by weight. This was reheated at a temperature of 1320 ° C. for 4 hours, followed by hot rolling to make a hot rolled sheet having a thickness of 2.0 mm. Subsequently, hot-rolled sheet annealing was performed at 950 ° C, followed by primary cold rolling to a thickness of 0.65 mm after pickling, followed by intermediate decarbonization annealing. Decarbonization annealing was performed for 4 minutes in a 910 degreeC temperature and wet atmosphere. Subsequently, secondary cold rolling was performed to adjust the final thickness to 0.35 mm, recovery annealing was performed at 600 ° C. in a dry atmosphere, and then a fusion inhibitor was applied.

At this time, the anti-fusion agent was coated with cotarol as the composition of the present invention, in which the basic composition of Ti0 ₂ powder was added 1.5 to MgO, which is a conventional composition, and the alumina powder was added to the alumina sol of solid content 11, and the coating amount was 4.2 g / It was set to m <2>. This is dried in a direct-drying furnace at 600 ° C. for 15 seconds, then wound up to form a large coil, followed by the final finishing annealing process. At this time, the final finishing annealing is carried out by a thermal cycle of cooling after cracking at a temperature of 1200 ° C. for 25 hours while maintaining a temperature increase rate of 100 ° C. at a temperature of 700 ° C. to 1200 ° C. at 15 ° C./hr. Recrystallization annealing was completed. After pickling to remove the unreacted fusion inhibitor on the surface and finally applied a tension coating agent consisting of aluminum phosphate, colloidal silica and chromic anhydride based on 3.5g / ㎡ to produce a grain-oriented electrical steel sheet. The glass film formation state, magnetic properties and punchability of these were measured and shown in Table 1. The magnetic properties were measured by iron plate (W _17/50 ) and magnetic flux density (B ₁₀ ) with a single plate measuring instrument, and the _{punching property} was able to work with the same mold of 10mmΦ until the burr height was 0.05mm. It was measured by the number of punches.

Psalter Fusion inhibitor Glass coating Magnetic properties Tamarisu (Manta) Magnetic flux density (T) Iron loss (W / kg) Conventional MgO + TiO ₂ Formed 1.88 1.19 1.1 Invention Alumina Sol + Alumina Powder none 1.88 1.15 3.9

As shown in Table 1 above, the glass coating was formed in the conventional material, and the punching number was only 100,000 shots. However, since the glass coating was not formed in the present invention, the iron loss was about 3, showing excellent magnetic properties. In addition, it can be seen that the punching water is about 3.5 times better than the conventional material.

Example 2

In the secondary recovery annealing plate of Example 1, the fusion inhibitor was applied as a composition in which the addition amount of the alumina sol and the alumina powder having a particle size of 3 to 5 μm was changed, and coated with cotarol and dried at a temperature of 550 ° C., followed by winding up. Thereafter, in the same manner as in Example 1, a grain-oriented electrical steel sheet was manufactured. At this time, the coating amount of the fusion inhibitor composition was kept constant at 5 g / m 2, the ease of coating amount management and the rate of occurrence of sheeting defects during tension coating after the final high temperature annealing were examined, and the results are shown in Table 2.

Psalm Number Addition amount of alumina powder () Ease of coating management Plate Defect Rate () Comparative Material 1 0 Somewhat good 4.2 Invention 1 5 Good 0 Invention 2 12 Good 0 Invention 3 20 Good 0 Comparative Material 2 30 Rather thick 0

As can be seen in Table 2, the comparative material (1) in the pure alumina sol state was difficult to manage the proper coating amount due to the small coating amount, and also appeared to be plate defects in the coil edge portion during tension coating after hot annealing. On the other hand, the comparative material (2) in which the alumina powder was over-added to 30, the coating amount was too large, it appeared difficult to manage the appropriate coating amount.

As described above, according to the present invention, when the fusion inhibitor is a composition in which the main component is alumina sol and alumina powder is added thereto, there is no glass coating on the surface of the hot slab, and thus a grain-oriented electrical steel sheet having excellent punching characteristics and magnetic properties can be obtained. It has an effect.

Claims (1)

By weight, Si: 2.9 to 3.3, C: 0.025 to 0.045, P: 0.015 or less, dissolved Al: 0.08 to 0.020, N: 0.0080 to 0.012, S: 0.007 or less, Mn: 0.12 to 0.42, Cu: 0.6 or less, and the balance Steel slab composed of Fe and other unavoidable impurities is hot-rolled after low-temperature reheating at 1250 ~ 1340 ° C, followed by hot rolled annealing at a temperature below 1000 ° C, and decarbonized annealing in a wet atmosphere. After cold rolling, adjust to final thickness, and then recover and anneal in a dry atmosphere of 600 ℃ or less, apply fusion inhibitor, wind up with large coil, and raise the temperature in 700 ~ 1200 ℃ section to 15 ℃ / hr or more. In the method of manufacturing a grain-oriented electrical steel sheet by holding a high temperature annealing, and then applying a tension coating agent after the crack is maintained for 20 hours or more at a temperature of 1200 ± 10 ° C., followed by cooling. The coating of the fusion inhibitor is a low-temperature reheat oriented electrical steel sheet without a glass coating, characterized in that the coating is made by applying an fusion inhibitor composed of alumina sol having a solid content of 10 to 25 and alumina powder of 5 to 20 in an amount of 3 to 7 g / m 2. Manufacturing Method