KR970007032B1 - Method for manufacturing oriented electrical steel sheet having excellent plating properties - Google Patents

Abstract

In the fabrication of the oriented electric steel sheet, the fabricating method includes reheating to hot-roll a steel slab composed of 0.035-0.050 wt.% of C, 2.9-3.3 wt.% of Si, less than 0.016 wt.% of P, 0.011-0.017 wt.% of dissolved Al, 0.008-0.012 wt.% of N, less than 0.007 wt.% of S, 0.06-0.18 wt.% of only Ni or Cr or their combination, less than 0.32 wt.% of Mn, less than 0.6 wt.% of Cu, and the balance being Fe and evitable impurities at a temperature of 1250-1320 degrees centigrade; controlling the thickness of the steel slab at 0.6-0.75 mm through primarily cold rolling without annealing the hot-rolled sheet; decarbonization-annealing the steel sheet at the wet hydrogen atmosphere at 820-870 degrees centigrade, and secondly cold rolling the steel sheet; intermediate annealing at 600-750 degrees centigrade and PH20/PH2 of 0.62-0.88 under the wet atmosphere for 45 seconds-2 minutes; coating the sheet with an annealing separator composed of principally MgO; finally annealing the sheet at 1150-1200 degrees centigrade for at least 10 hours.

Description

Manufacturing method of oriented electrical steel sheet with excellent glass coating properties

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet used in iron core materials such as transformers, electric motors, generators and other electronic devices, and more particularly, a process before final finishing annealing in a low temperature slab heating method. The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet having excellent glass coating properties by improving a secondary recovery annealing process. The present invention is an improvement of Korean Patent Application No. 93-23751.

A grain-oriented electrical steel sheet has an aggregate structure in which the orientation of grains is aligned to (110) [001], and this product has extremely excellent magnetic properties in the rolling direction. Therefore, it uses transformers, motors, oscillators, and other electronic devices. Used as an iron core material. This (110) [001] texture is obtained by using a secondary recrystallization phenomenon, which is a nucleus having a specific orientation of nuclei, ie, the orientation of (110) [001], among the fine grains produced by ordinary recrystallization. The growth of the entire specimen is abnormal. For the smooth growth of the secondary recrystallized grains in this particular orientation, it is necessary to suppress the growth of the primary recrystallized grains. For this purpose, precipitates such as MnS, AIN, and BN are mainly used.

The grain-oriented electrical steel sheet products can be divided into two categories based on their magnetic characteristic values. That is, the development from the early 60's, in use the magnetic flux density B ₁₀ based on the 1.80 to 1.86 tesla (Tesla) a conventional grain-oriented electrical steel sheet and the magnetic flux density B ₁₀ value developed after the 1.89 level with the characteristics of the tesla or more efficient than in It can be divided into high magnetic flux density oriented electrical steel sheet having the characteristics of, and they have some differences in components, manufacturing method, and error rate based on initial grain growth inhibitor.

The manufacturing process of conventional grain-oriented electrical steel sheet is generally 2-4% of silicon and grain growth inhibitor, and mostly contains MnS or MnSe, and then melts to make slab (slab heating and hot rolling) → (hot rolled sheet annealing) → (Cold Cold Rolling) → (Intermediate Annealing) → (Second Cold Rolling) → (Decarbon Annealing) → (Annealing Separator Doping) → (Final High Temperature Annealing) → (Tension Coating) Finished with the product.

Among the complicated manufacturing processes of oriented electrical steel sheets, the most difficult manufacturing process is the slab reheating process which performs heat treatment at high temperature. This slab reheating process is subjected to annealing for about 5 hours at a high temperature of about 1400 ° C. At this time, molten slag melts from the slab surface and accumulates in the furnace, which hinders continuous operation of the slab. There are tremendous economic burdens such as reduced productivity and rising costs.

On the other hand, in the production of aromatic products, secondary recrystallization is necessary to obtain magnetic properties of the product, and after the second recrystallization, it is necessary to remove the impurities such as S and N, which have adverse effects on the properties, at a high temperature of 1200 ° C. For a long time or longer purifying process is required, since the fusion phenomenon of the winding coil during the long time annealing at such a high temperature appears to prevent the fusion during the annealing is applied an annealing separator containing MgO as a main component. At this time, an external oxide layer formed in a wet atmosphere during decarbonization annealing, that is, an oxide of FeO system, pyrite (Fe ₂ SiO ₄ ), and silica (SiO ₂ ) inside, reacts with MgO coated with a fusion inhibitor. A composite oxide layered stone mainly composed of forsterite (Mg ₂ SiO ₄ ), which is called a glass film or a glassy insulating film, is formed on the material surface. At this time, the characteristics of the formed glass coating layer have some influence on the magnetism of the final product, but it mainly affects the quality of the product such as surface quality characteristics, such as insulation, adhesion, surface roughness, appearance, and especially the demand of the film peeling and powder during processing It plays an important role in greatly affecting workability and productivity.

The present inventors reheated the conventional oriented electrical steel sheet in the vicinity of 1200-1320 ° C., which is the same as the reheating condition of general steel in the steelworks but begins to melt with slag, in order to solve the problem of the reheating process performed at a high temperature for a long time. We designed a new component system to perform hot rolling, and established a manufacturing process capable of forming a stable secondary recrystallization of the orientation (110) [001] for magnetization without supplementing or establishing a facility in an existing manufacturing process. This manufacturing process is characterized by eliminating the hot-rolled sheet annealing process, performing decarburization annealing at the intermediate thickness, and then performing final rolling. After rolling to the final thickness, the intermediate recovery annealing is performed in a completely dry atmosphere. As for carrying out the process, this manufacturing process is presented in Korean Patent Application No. 93-23751.

However, this manufacturing method does not perform decarbonization annealing at a final thickness of 0.27mm or 0.30mm, which is a common method, but lacks a total amount of oxide formation by decarbonization annealing at a thickness of 0.60-0.75mm in an intermediate rolling state. As the rolling to the final thickness is performed again after the oxide is formed, crack formation of the oxide layer and partial cracking of the oxide layer appear due to the crack. These oxide-free parts have very good adhesion due to the impossibility of glass film formation reaction with MgO powder coated with fusion inhibitor during finishing annealing and the characteristics of the process itself, but relatively insufficient insulation due to the thin thickness of the formed glass film. In addition, there is a problem in that there are partial cracks and defective parts of the glass coating.

The present inventors conducted research and experiments to solve the above problems, and based on the results, the present invention proposes the present invention, and the present invention enables the formation of oxides in the atmosphere of the intermediate recovery annealing process in the existing completely dry atmosphere. It is managed with a wet atmosphere, and the annealing temperature is increased to favor the formation of oxides.Glass film formation example gives an optimum optimum annealing condition to produce a grain-oriented electrical steel sheet having excellent magnetic properties and excellent glass coating properties. , Its purpose is.

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

The present invention is in weight%, C: 0.035-0.050%, Si: 2.9-3.3%, P: 0.016% or less, dissolved Al: 0.011-0.017%, N: 0.0080-0.012%, S: 0.007% or less, Ni and Steel slab composed of Cr alone or composite 0.06-0.18%, Mn: 0.32% or less, Cu: 0.6% or less, balance Fe and other unavoidable impurities is reheated at a temperature range of 1250-1320 ° C, and hot rolled. It is 0.60-0.75mm thick by primary cold rolling without plate annealing, then decarbonized annealing in a wet hydrogen atmosphere at 820-870 ° C., and then secondary cold rolling to the final thickness, and then the intermediate recovery annealing is performed. In the method for producing a grain-oriented electrical steel sheet by applying an annealing separator containing MgO as a main component, and then performing final finishing annealing at 1150-1200 ° C. for at least 10 hours, the intermediate recovery annealing is performed at a temperature section of 600-750 ° C. Grass characterized in that it is conducted for 45-2 minutes in a humid atmosphere with P _H20 / P _H2 of 0.62-0.88 The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent coating properties.

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

Since the present invention has a special metallurgical background that only needs to be decarbonized in an intermediate thickness state, it is essential to maintain optimal conditions in terms of decarburization in which the carbon content of the material should be reduced. On-site management is also an important goal in terms of the quality and quantity of external oxides in the material formed during annealing. However, due to the difficulty in managing their stable film properties, there are tremendous production benefits of low-temperature reheating, but they have to be difficult to apply to mass production. It is becoming.

The inventors closely followed the factors related to the surface characteristics in the working process and found that the oxide layer formed during the decarbonization annealing at the intermediate thickness partially cracked during cold rolling to the final thickness, and the external oxide of some FeO centers. The layer was partially peeled off, and since these parts were formed of unstable forsterite coating, the color of the entire coating was uneven and the inferior portion was found in partial insulation or surface roughness. In addition, since the internal oxides centered on SiO ₂ or Fe ₂ SiO _4, etc., remain inside the cracks and the peeled portions, FeO formation with the conviction that FeO, which is a reaction catalyst in the formation of fosderite film, is required. It was confirmed that it is necessary to secure the operating conditions to maintain the recovery tissue that is not detrimental to the optimum magnetic formation while giving favorable conditions to the magnetic formation.

Investigating each of the factors to ensure optimum operating conditions, the improvement of intermediate recovery annealing temperature can give the most favorable condition for FeO formation. However, the annealing conditions in which the primary recrystallized grains may be formed in the intermediate recovery annealing process should be imparted, and the increase of the intermediate recovery annealing temperature may be followed by the formation of the first and second recrystallized crystals, which should be generated during the final finishing annealing. Can cause fatal defects. Therefore, it is essential to properly manage the annealing time in addition to raising the annealing temperature. When the annealing temperature and annealing time are determined, the oxidation reaction on the surface of the material is determined by the P _H20 / P _H2 of the atmosphere gas, and the present invention requires an oxide centered on FeO. Therefore, the ratio of P _H20 / P _H2 should be controlled rather high. In particular, since the partial pressure of the H 2 gas by the atmospheric gas P _H20 / P _H is central to the oxidizing ability, it is preferable from the aspect of management to adjust the H2 partial pressure to 20-25% or less in terms of stable management. When the partial pressure of H2 is determined, it is necessary to manage the appropriate P _H20 / P _{H2 at} the dew point, and the oxide required for recovery annealing is the formation of FeO-based oxide at the crack or peeling part during the secondary annealing, so that P _H20 / P _H2 Should be kept as high as possible to prevent the formation of pyrerite or silica compounds on the surface and should be kept somewhat high in consideration of site management aspects.

In addition, the annealing time at this time is not more than a recovery annealing, and should be considered in terms of securing the magnetic stability in consideration of the temperature at the same time, it is advantageous to manage the temperature as high as possible and the time is short.

The production of conventional oriented electrical steel sheet based on the application of low-temperature reheating technology has enormous expected benefits and the manufacturing technology that can secure stable magnetic properties has been established. Since the characteristics of the glass film that could be caused are secured, the platelet of the low temperature reheating manufacturing technology becomes possible.

EMBODIMENT OF THE INVENTION Hereinafter, the component range of this invention, the reason for limitation of a manufacturing process, etc. are demonstrated.

Since C is required to form an appropriate hot-rolled structure and imparts high processing energy during cold rolling, at least 0.020% or more is required. However, when C is 0.050% or more, decarburization annealing becomes difficult, resulting in poor workability and residual carbon. When the amount is high, the deterioration of the magnetic is severe, it is preferable to limit the content of C to 0.020-0.050%.

The Si is a basic component of the electrical steel sheet to increase the resistivity of the material to reduce the core loss, or iron loss of the magnetic properties, when the content is less than 2.9%, the iron loss characteristics worsen, if the content is more than 3.3% Since the steel is vulnerable, the cold rolling property is extremely bad and the secondary recrystallization is unstable, which causes a bond called streak, which is a secondary recrystallization incomplete formation in the longitudinal direction, so the content of Si is 2.9-3.3%. It is desirable to limit.

The Mn lowers the solid solution temperature of the precipitate during slab heating, prevents cracks formed at both ends of the material during hot rolling, and forms a precipitate with a small amount of S, the content of which is added in excess of 0.32%. In this case, the adhesion of the forsterite insulating film formed during high temperature annealing by the Mn oxide formed during decarbonization annealing is deteriorated, so the Mn content is preferably limited to 0.32% or less.

S plays an auxiliary role of AIN because it forms a precipitate in the form of Cu or Mn and an emulsion to act as a grain growth inhibitor. Usually, S is basically contained in the manufacturing process and needs to be managed as low as possible. At this time, if it contains more than 0.007%, S segregation becomes severe at the center of the slab as the slab is manufactured and solidified in the performance, and it is difficult to solidify and diffuse the center segregation part by performing low temperature slab heating in hot rolling, resulting in characteristic deviation in the final product. Because it may appear, it is preferable to limit the content to less than 0.007% by strongly suppressing by employing a de-S process.

The Al component forms a precipitate of AIN together with N to secure grain growth inhibition, and the amount of Al in the dissolved state is important, rather than the total amount of Al management. If the content is less than 0.007%, sufficient amount for secondary recrystallization is required. Since it does not have the grain growth force, it is not preferable because the final grain size is small and incomplete fine grains are generated, and when it exceeds 0.012%, the secondary recrystallization of the (110) [001] orientation with excellent magnetic strength is too strong because the grain growth inhibition force is too strong. Since the magnetic properties deteriorate rapidly due to difficulty in the development of, the content of Al is preferably limited to 0.007-0.012% by the amount of dissolved Al.

N is an essential component in the formation of secondary recrystallization because it forms a reaction precipitate with dissolved A1 and acts as a grain growth inhibitor of primary recrystallization. When the content is less than 0.008%, the precipitate formed is insufficient and exceeds 0.012%. When added to the surface of the steel sheet defects (Blister) is caused to deteriorate the surface properties of the product, so the content of N is preferably limited to 0.008-0.012%.

The P has a property of weakening steel, so the smaller the amount of the mixture, the better. However, the lower limit of the control range of the plant is 0.016%. The content is preferably limited to 0.015% or less.

Cu combines with S to form a precipitate of Cu ₂ , and is a component which is easily dissolved at the lowest temperature of the precipitate and precipitates at low temperature during hot rolling to supplement the grain growth inhibition of AIN, thereby easily causing secondary recrystallization. If the added amount exceeds 0.6%, the oxide formed during the decarbonization annealing will adversely affect the formation of the insulating film, and the secondary recrystallization grain becomes too large, so that the magnetic flux density is good, but the iron loss may deteriorate, so the total amount of Cu is 0.6%. It is preferable to limit to the following.

The Ni and Cr not only refine the primary recrystallized grain but also because the precipitate dispersion effect can widen the proper slab heating temperature range because of its size, so that the slab heating temperature can be basically used at 1250-1320 ° C. Since the addition of at least 0.06% or more is required, and when the addition of 0.18% or more is combined with the C component in the material, the decarburizing property is deteriorated. Therefore, the Ni and Cr are preferably limited to 0.06-0.18% alone or in combination.

The above component system is an essential condition to lower slab heating temperature, which is the biggest problem in producing oriented electrical steel sheet. When using this component system, it is possible to secure excellent magnetic properties even when the slab heating temperature is operated at 1250 ℃, the slab heating temperature of ordinary steel. It is possible that the economic effect is great.

At temperatures below 1250 ° C, precipitates such as AIN have a coarse and uneven distribution, which is a form of low grain growth inhibition, and thus secondary recrystallization becomes unstable, and above 1320 ° C, electrical steel slab starts to melt and the real rate Since the slab heating temperature in the present invention is lowered, it is preferable to limit the slab heating temperature to 1250-1320 ° C., which is the most economical and easy slab heating temperature in steel mills.

The steel slab formed as described above is heated to the above-mentioned heating temperature, and then subjected to two cold rolling, intermediate annealing and final finishing high temperature annealing treatment including hot rolling and decarbonization annealing in a conventional manner, thereby having excellent magnetic properties. A grain-oriented electrical steel sheet is produced.

That is, the steel slab formed as described above is heated to the above-described heating temperature, and then hot-rolled and then hot-rolled sheet annealing is performed, preferably by primary cold rolling, to make the thickness of 0.60-0.75 mm, preferably Decarbonized annealing in a wet hydrogen atmosphere at 820-870 ° C., followed by secondary cold rolling to a final thickness, followed by 45 seconds under a temperature range of 600-750 ° C. and a wet atmosphere with a P _H20 / P _H2 of 0.62-0.88. After performing an intermediate recovery annealing for -2 minutes, an annealing separator based on MgO is applied, and a final finish high temperature annealing is performed at 1150-1200 ° C. for at least 10 hours, thereby producing a grain-oriented electrical steel sheet having excellent glass coating properties. .

In the above-described intermediate recovery annealing process, when the annealing temperature is 600 ° C. or less, the oxide formation rate is too economical because it is too slow. When the annealing process is more than 750 ° C., primary recrystallization is formed in this annealing process, which may be a fatal defect in magnetic properties. For this reason, in the present invention, the intermediate recovery annealing temperature is limited to 600-750 ° C.

On the other hand, as the atmosphere gas during the intermediate recovery annealing, a complex gas of N ₂ and H ₂ is used, the amount of these gases is not particularly limited and the P _H20 / P _H2 ratio should be limited to 0.62-0.88.

That is, the reason for limiting the P _H20 / P _H2 ratio in the atmosphere gas to 0.62-0.88 is that the oxide formation rate is too slow when the ratio is 0.62 or less, and the glass film formed is black, uneven and rough when the ratio is 0.88 or more, resulting in a drop of the final product. This is because the rate can be lowered.

In addition, when the annealing time during the intermediate recovery annealing is 45 seconds or less, if the oxide formation itself is nonuniform, and when the annealing time is 2.0 minutes or more, the first recrystallization may occur in this process, so the intermediate recovery annealing time should be limited to 45 seconds to 2.0 minutes. desirable.

When treated under the above-described intermediate recovery annealing conditions, it is possible to form a homogeneous glass film as compared with the conventional material, thereby ensuring excellent surface quality characteristics.

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example 1)

By weight, C: 0.042%, Si: 3.117%, Mn: 0.205%, S: 0.006%, N: 0.0098%, P: 0.014%, Cu: 0.496%, Cu: 0.496%, Cr: 0.04%, Ni A slab of 200 m thickness having a steelmaking composition of 0.06% and dissolved Al: 0.014% was prepared. This was reheated at 1300 ° C. for 3 hours, followed by hot rolling to make a hot rolled sheet having a thickness of 2.3 mm. Thereafter, without performing hot-rolled sheet annealing, the first cold rolling was performed to adjust the thickness to 0.65 mm, and the residual carbon content of the material was reduced by decarbonization annealing in a wet atmosphere at 860 ° C., followed by final cold rolling to a thickness of 0.30 mm. .

Following recovery from the secondary annealing in a 10% hydrogen-containing nitrogen atmosphere into the annealing furnace atmosphere temperature of 550-800 ℃ water content (P _H20 / P _H2) of the conventional dry (dry) up to 0.96 atmosphere, the annealing time 0.5-2.5 bun Changed until. After that, a conventional grain-oriented electrical steel sheet was manufactured through a process such as MgO coating and final high temperature annealing at 1200 ° C. for 20 hours.

For the steel sheet manufactured as described above, the glass coating properties (appearance and insulation) and the magnetic properties (magnetic flux density and iron loss) according to the recovery annealing conditions were measured, and the results are shown in Table 1 below.

The appearance shape of the glass film in the following Table 1 was observed with the naked eye, and the insulation property is represented by Amp by measuring the storage current through the film when 0.5Volt, 1.0Amp is applied by Frank insulation measuring instrument according to ASTMA 717-15. In the state of good insulation, the smaller the storage current value, the better the product.

On the other hand, the magnetic properties are measured by a single-plate magnetometer, the magnetic flux density B ₁₀ value is shown in Tesla, the iron loss, the core loss value is shown in W _17/50 compared to W / kg.

TABLE 1

As shown in Table 1, in the case of the comparative material (a) having an intermediate recovery annealing temperature of 550 ° C., the magnetic properties were good, but the glass film was thin and passed, thus showing an inferior insulation property, whereas the range of the present invention was 650 ° C. In the case of Inventive Example (a), the thickness is rather thin, but the target insulation value is in a satisfactory state, and further, the bh of the temperature up to 750 ° C is excellent in not only magnetic properties but also glass coating properties. It can be seen.

However, it can be seen that in the case of the comparative material (b) having an intermediate recovery annealing temperature of 800 ° C., the film is rough, and in particular, the magnetic deterioration rapidly occurs.

On the other hand, in the case of a conventional dry atmosphere having a low moisture content in the furnace or a comparative material (C) having a ratio of P _H20 / P _H2 having a low moisture content in the furnace of 0.45, the magnetic properties are good in the case of intermediate recovery annealing in the furnace atmosphere. In the invention example (ah) in the case of intermediate recovery annealing in the range 0.62-0.88 of the present invention, while the glass film is thin, rough and lacking in insulation, the film is uniform, the color is filthy and the insulation is good, It can be seen that the comparative material (d) is rather black and rough and the insulation is deteriorated.

In addition, in the case of the comparative example (e) of the intermediate recovery annealing time of 30 seconds, the time is too short to help the formation of the film, whereas in the case of the invention example (ah) at the time of 0.8-2.0 minutes of the present invention, Although optimum coating properties can be obtained, it can be seen that the deterioration of magnetic properties, which is a fundamental requirement, appears in Comparative Example (f) in the case of annealing for a longer time.

In addition, in the case of the conventional material (b) manufactured under the conventional intermediate recovery annealing conditions, it was found that the magnetic properties were good, but the glass film was somewhat rough and inferior to insulation properties.

Claims (1)

By weight%, C: 0.035-0.050%, Si: 2.9-3.3%, P: 0.016% or less, dissolved Al: 0.011-0.017%, N: 0.0080-0.012%, S: 0.007% or less, Ni and Cr alone Or composite: 0.06-0.18%, Mn: 0.32% or less, Cu: 0.6% or less, steel slab composed of residual Fe and other unavoidable impurities, reheated at a temperature range of 1250-1320 ° C and hot rolled, followed by annealing It is 0.60-0.75mm thick by primary cold rolling, and then decarbonized annealing is carried out in a humidified hydrogen atmosphere of 820-870 ° C, followed by secondary cold rolling to the final thickness, followed by intermediate recovery annealing, In the method for producing a grain-oriented electrical steel sheet by applying an annealing separator containing MgO as a main component, and then performing final finishing annealing at 1150-1200 ° C. for at least 10 hours, the intermediate recovery annealing is performed at a temperature range of 600-750 ° C. and P. Glass coating, characterized in that it is carried out for 45 seconds -2 minutes in a humid atmosphere where _H20 / P _H2 is 0.62-0.88 Method for producing a grain-oriented electrical steel sheet having excellent characteristics.