KR20000001998A - Preventing method against edge adhesion in high temperature annealing of low temperature reheating directional electric steel plate - Google Patents

Abstract

PURPOSE: The method is to prevent steel plate edges from sticking together in a large roll of coil form in the final process of high temperature annealing when producing the directional electric steel plate. CONSTITUTION: The method reheats at the temperature of 1,250-1,340°C a silicon steel slab to hot roll and anneal at 1000 or less°C for softening the plate, and then cold-rolls twice including decarbon-annealing under a humid environment to the final thickness. The method further performs recover-annealing at a dry environment to coat a melt-fusion preventive agent and roll into a coil.

Description

How to prevent edge plate sticking during high temperature annealing of low temperature reheat oriented electrical steel sheet

The present invention relates to a method of preventing the edge plate sticking phenomenon of a large coil generated in the finishing high temperature annealing process in the production of grain-oriented electrical steel sheet by slab low temperature reheating.

In detail, by adjusting the composition and the mixing ratio of the MgO center fusion inhibitor applied to the steel sheet to improve the adhesion to ensure excellent MgO coating properties, to prevent the sliding phenomenon to the center of the coil during the drying of the MgO slurry in the finish high temperature annealing It is to prevent the edge plate sticking. Accordingly, it is to provide an edge plate pasting prevention technology of low-temperature oriented electrical steel sheet which can greatly improve workability and error rate and ensure product quality stability.

A grain-oriented electrical steel has an aggregate structure in which the orientation of grains is aligned in the direction of (110) [001], and this product has extremely excellent magnetic properties in the rolling direction. It is used as iron core material for electric equipment. The manufacturing process of general oriented electrical steel sheet is about 2-4% of silicon and grain growth inhibitor, and melts the component system containing mostly MnS or MnSe to make slab, and then re-heats and hot rolls → pre-annealed → intermediate annealing. The final product is completed through a complex process such as two times cold rolling, decarburization annealing, application of anti-deposition agent, and final high temperature annealing.

Among the complicated manufacturing processes, the most difficult in manufacturing is the slab reheating process, which is heat-treated at a high temperature. This slab reheating process needs to be maintained at high temperature of about 1400 ℃ for 5 hours in order to completely disperse the precipitates such as MnS and AlN used as grain growth inhibitors. At this time, on the surface of the hot slab, an oxide called pyrite (Fe ₂ SiO ₄ ), in which Si and Fe components are combined, is formed by oxidation with air, and the dioxide melts and flows down from the surface upon reheating due to its low melting point. At this time, the molten oxide is designed to flow out of the furnace partly, but most of it is accumulated in the refractory of the upper part of the furnace, so that the entire internal repair for removing the oxide is inevitable at the end of the work.

Efforts to lower the slab reheating temperature are proceeding with full attention from leading manufacturers, and various methods are being proposed. That is, the basic component system is adjusted on the basis of heating the reheating temperature at about 1350 ° C. or less at which the pyrite oxide does not dissolve, and in addition to the component design, a precipitate management method during the manufacturing process and the like have been proposed.

Therefore, the present inventors have designed a component system to heat-treat conventional directional electrical steel in the vicinity of 125-1340 ° C. to perform hot rolling, and establish a new manufacturing method that can work without additional equipment supplement or new installation in the existing manufacturing process. Accordingly, Korean Patent Application No. 93-23751 proposes additional element technologies such as 94-21388, 21389, 21390, and 21391.

By using the low temperature reheating method proposed above, it was possible to produce a product with high real rate and excellent magnetic properties in actual production. Characteristic of this manufacturing method is decarbonization annealing at the intermediate thickness of 0.60 ~ 0.70mm after the first cold rolling, and then adjusted to the final thickness by secondary cold rolling, followed by recovery-annealing at 600 ℃ or less. It is applied in a slurry state and dried to make a large coil, followed by final finishing high temperature annealing for secondary recrystallization.

However, when the finishing high temperature annealing is annealed at a high temperature around 1200 ° C. for the highest cracking temperature, the coating property of the fusion inhibitor is poor at the edge of the coil, or the edges of the plates adhere to each other due to edge flare. Appears. Since the coil is attached to the plate between subsequent removal of unreacted MgO and subsequent application of the final tension coating agent, the plate breakage occurs because the coil is not released and the plate is torn, thus paralyzing the entire continuous work process. It is greatly reduced and the economic loss is inevitably large.

Therefore, in order to prevent the edge part sticking at the time of high temperature annealing, the present inventors have reviewed all the process conditions related to this problem and found that the coating characteristics of the coil edge part are unstable or bad compared to the middle part when applying the fusion inhibitor. It was confirmed and suggested a way to improve it.

An object of the present invention is to provide a method capable of preventing the edge portion sticking of the grain-oriented electrical steel sheet.

The present invention for achieving the above object, Si: 2.9 ~ 3.3%, C: 0.025 ~ 0.045%, P: 0.015% or less, dissolved Al: 0.008 ~ 0.020%, N: 0.0080 ~ 0.012%, S: Silicon steel slab consisting of 0.007% or less, Mn: 0.12 to 0.42% or less, Cu: 0.6% or less, and Fe and other inevitable impurities is reheated to 1250-1340 ° C. at low temperature, and hot rolled to 1000 ° C. or less. After hot-rolled annealing at the temperature, adjusted to the final thickness by two cold rollings including decarbonization annealing in a wet atmosphere, followed by recovery annealing in a dry atmosphere below 600 ° C., MgO: 12-13% by weight, TiO ₂ : 1-2% by weight compared to MgO, magnesium sulfate or aluminum sulfate selected by applying a fusion inhibitor composed of 0.5-2% compared to MgO, dried and wound to make a coil, wound coil 100% 20 hours or more at 1200 ± 10 ℃ while maintaining the temperature increase rate of 700-1200 ℃ in the hydrogen atmosphere over 15 ℃ / hr It is configured to include a high-temperature finish annealing step of cooling after.

Hereinafter, the present invention will be described.

The inventors of the present invention have found the following facts as a result of finding out the problem that the poor adhesion of the fusion inhibitor coating property of the coil edge portion during the high temperature annealing of low-temperature reheating oriented electrical steel sheet.

In other words, the process specificity of low-temperature reheat oriented electrical steel sheet, that is, the oxide layer formed during the primary intermediate annealing and decarburization is separated and removed from the plate edge part due to the rolling characteristics in the secondary cold rolling process. It was confirmed that the action. However, the most important factor is that the MgO slurry coated with the fusion inhibitor is poor in the surface coating property of the MgO slurry, so that the MgO slurry is extremely thin or hardly applied at the edge of about 1 mm or less at the edge portion.

Therefore, as a result of in-depth study of ways to improve the coating properties of the edge portion, a method of improving the adhesiveness of the fusion inhibitor has been devised.

In general, the anti-fusion agent composition, since the surface appearance phenomenon during the high temperature annealing finish with MgO coating properties are required to have a characteristic that does not adversely affect the formation of the glass insulation film. It was confirmed that the compound capable of performing these two roles is a solute element, and as an additive of the anti-fusion agent, sulphate of magnesium and aluminum, which is advantageous for film formation, was selected.

First, magnesium sulfate is decomposed into MgO and sulfuric acid gas before high temperature annealing, and MgO reacts with the main components of the fusion inhibitor, and sulfuric acid gas prevents the external diffusion of secondary recrystallization growth inhibitors in the material. It can play a useful role in helping to improve magnetic properties. In addition, in case of aluminum sulfate, it is decomposed at high temperature annealing and decomposed into Al ₂ O ₃ and sulfuric acid gas.Al ₂ O ₃ acts as a useful material for forming a glass insulating film, which is useful for improving the characteristics of the material. Can be.

In order to examine the coating properties when the magnesium sulfate and aluminum sulfate are added, 1.5% of TiO ₂ is basically added to water containing 12% of MgO, which is a conventional anti-fusion agent composition, and magnesium sulfate and aluminum sulfate are added thereto. The characteristics were compared.

The MgO mixture was mixed with water, stirred for 5 minutes, and examined for adhesion of the slurry solution, and expressed as cps. In addition, in order to compare the MgO coating properties, the total amount of MgO slurry attached to the specimens by stirring time when the decarburized plate of 7 × 7 cm was deposited on the mixed slurry liquid was investigated and shown in Table 1 below.

number sulfate Coating amount by stirring time (g) Kinds Amount 5 minutes 10 minutes 15 minutes 20 minutes 25 minutes A No addition 0 1.28 1.33 1.35 1.34 1.33 B Magnesium sulfate One 1.49 1.56 1.63 1.68 1.72 C Magnesium sulfate 2 1.54 1.66 1.73 1.86 1.97 D Aluminum sulfate One 1.53 1.59 1.70 1.83 1.88 E Aluminum sulfate 2 1.60 1.75 1.87 1.92 2.03

In Table 1, in the sludge of the mixture to which only MgO and TiO ₂ are added, the viscosity of the coating liquid is low, so that the coating amount for each stirring time is also small at 1.28-1.33 g. However, it can be seen that when magnesium sulfate is added to this mixture, the viscosity of the coating liquid is increased to significantly improve the coating properties. In addition, even when aluminum sulfate was added, it was confirmed that coating properties were greatly improved similarly to the case of addition of magnesium sulfate.

The present invention is to complete the fusion preventive agent that can be applied to the low-temperature reheating oriented electrical steel sheet through the above research and experiment. Specifically, the anti-fusion agent of the present invention is MgO: 12 to 13% by weight, TiO ₂ : 1-2% by weight compared to MgO, magnesium sulfate or aluminum sulfate is selected from 0.5-2% by weight compared to MgO.

If the MgO is less than 12%, the overall thickness becomes thin, and if it exceeds 13%, thickness management becomes unstable due to excessive coating amount, which is a major factor in deterioration of surface properties. In addition, when TiO ₂ powder is used as an adjuvant, it is effective.If the content is less than 1%, the formed film becomes thin and the edge plate is partially present. If the content exceeds 2%, the surface color of the final product is slightly changed to black. Can be lowered. In addition, the solute element of magnesium sulfate or aluminum sulfate is added to improve the adhesion of the fusion inhibitor. At this time, when the addition amount is less than 0.5%, the effect of improving the adhesion is small due to the small amount of adhesion improvement. If it exceeds, the adhesiveness is too high, so that it is difficult to manage the coating thickness and cause defects such as oxidation discoloration of the formed film.

The fusion preventive agent of the present invention can be applied to the manufacturing process of the grain-oriented electrical steel sheet subjected to the cold rolling process and the final high temperature annealing process including low temperature reheating and intermediate annealing.

In particular, the fusion preventive agent of the present invention in weight%, Si: 2.9 ~ 3.3%, C: 0.025 ~ 0.045%, P: 0.015% or less, dissolved Al: 0.008 ~ 0.020%, N: 0.0080 ~ 0.012%, S: 0.007 It is very suitable for grain-oriented electrical steel sheets composed of% or less, Mn: 0.12 to 0.42% or less, Cu: 0.6% or less, and Fe and other inevitable impurities.

Hereinafter, the reason for numerical limitation of a typical grain-oriented electrical steel sheet component to be applied to the present invention and a manufacturing method thereof will be described.

C is advantageous to finely disperse AlN precipitates, form an appropriate rolled structure, and give processing energy during cold rolling, so it is advantageous to manage it upwards as much as possible, but it is 0.025-0.045 considering the difficulty of decarburization process. It is preferable to add in the range of%.

Si plays a role of lowering iron loss by increasing the resistivity of the material, but the content of iron is poor at the addition content of less than 2.9%, and the steel is vulnerable and the cold rolling property is extremely bad at the addition content of more than 3.3%. It is preferable to limit to 2.9-3.3%.

Mn lowers the solubility temperature of the precipitate during reheating and prevents crack formation at both ends of the material during hot rolling.It is disadvantageous for the formation of precipitates when less than 0.12%. Since the adhesion of the forsterite film to be deteriorated, it is preferable to add 0.12-0.42%.

S needs to be managed as low as possible, and if it contains more than 0.007%, it is difficult to employ and diffuse the central segregation part during low temperature reheating in hot rolled steel.

Al forms the precipitate of AlN together with N to secure grain growth inhibition. At less than 0.008%, Al has a small grain size and incomplete grains. It is a representative component that needs to be focused, since its suppressive force is so strong that it makes it difficult to form secondary recrystallization. Therefore, Al is preferably limited to 0.008-0.020%.

N forms a reaction precipitate with dissolved Al, which is an essential component in the formation of secondary recrystallization, and below 0.008%, the formation of precipitates is insufficient. When 0.012% or more is added, a blister defect occurs on the surface of the steel sheet, resulting in a surface characteristic of the product. Since it deteriorates, excess content is suppressed.

Cu combines with S, which is an impure component, to form a precipitate of Cu ₂ S, and it is advantageous to add as much as possible because it is solid-solution at the lowest temperature among the precipitates. However, if more than 0.6%, the oxide formed during decarbonization annealing adversely affects the formation of the insulating film, so it is limited to 0.6%.

The slab formed as described above is a low-temperature reheating, the heating temperature of the slab is suitable 1340 ℃ immediately before the slab melting at 1250 ℃ that can secure the magnetic properties. Thus, after reheating the low temperature, the slab is hot rolled, hot-rolled sheet annealing is performed at a temperature of 1000 ° C. or lower, and the intermediate thickness is adjusted so that the final secondary cold rolling rate is 46 to 69% during the primary cold rolling. At this time, the intermediate decarbonization annealing is performed in a wet atmosphere at a temperature of 890 ° C to 960 ° C, because decarburization is poor at temperatures below 890 ° C and excessive pore generation due to high temperatures above 960 ° C. After performing the second cold rolling as described above, after adjusting to the final thickness, recovery annealing is carried out at a temperature of 600 ° C. or lower, MgO: 12 to 13% by weight, TiO ₂ : 1-2% by weight of MgO, selected from magnesium sulfate or aluminum sulfate. 1 type is 0.5-2% of MgO, and the fusion inhibitor of the present invention is applied.

The cold rolled steel sheet coated with the above-mentioned fusion inhibitor is dried, and then wound into a large coil, and the wound coil is finished by high temperature annealing. The final finish annealing is 100% hydrogen atmosphere in all sections, the temperature increase rate of 700 ~ 1200 ℃ is maintained at 15 ℃ / hr or more, and it undergoes heat cycle to cool after cracking for 20 hours or more at 1200 ± 10 ℃. Complete the secondary recrystallization.

Subsequently, pickling treatment removes the unreacted MgO from the surface. In this case, the pickling condition may be performed at 60-90 ° C. with H ₂ SO ₄ solution. Thus, after the pickling treatment, it is possible to produce a grain-oriented electrical steel sheet by including a tension coating agent.

Except for the composition of the fusion preventive agent in the configuration of the present invention described above is a method commonly used in the field of low-temperature reheat oriented electrical steel sheet manufacturing, these conventional manufacturing conditions can be variously changed, so the present invention is limited thereto. no.

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

Example 1

Si: 3.13%, C: 0.035%, P: 0.015%, Dissolved Al: 0.014%, N: 0.0092%, S: 0.005%, Mn: 0.24%, Cu: 0.48% by weight, 220mm thick Made a slab. This was reheated for 4 hours at a temperature of 1300 ° C. without surface melting, followed by hot rolling to make a hot rolled sheet having a thickness of 2 mm. Subsequently, hot-rolled sheet annealing was performed at 900 ° C, and after cold pickling, primary cold rolling was performed to 0.7 mm thickness, followed by intermediate decarbonization annealing. Decarbonization annealing was performed for 3 minutes in a humid atmosphere at the temperature of 900 degreeC. Subsequently, secondary cold rolling was carried out to adjust the final thickness to 0.30 mm, recovery annealing was carried out in a dry atmosphere at 550 ° C., and a fusion inhibitor containing MgO as a main component was applied.

In this case, the composition of the anti-fusion agent is 12% of MgO in water as usual, and 1.5% of TiO ₂ powder is added to MgO as the basic composition, and magnesium sulfate or aluminum sulfate is further added thereto. The addition amount was changed to 3% compared to MgO. This mixed composition was mixed with water and vigorously stirred for 5 minutes to form MgO slurry and then applied to the surface. This is dried in a direct-drying furnace at 700 ° C for 13 seconds, then wound up to make a large coil, followed by a final finishing annealing process. At this time, the final finishing annealing is 100% hydrogen atmosphere in all sections, and secondary recrystallization annealing through thermal cycle cooling after cracking at 120 ℃ for 25 hours while maintaining the temperature raising rate of 700 ~ 1200 ℃ at 18 ℃ / hr. Completed. After pickling to remove the fusion inhibitor of the unreacted MgO main component of the surface and finally applied to the tension coating agent to produce a grain-oriented electrical steel sheet products. The number of edge plates attached to the coil during the coating operation of the tension coating agent, the number of errors in this step, and the surface appearance were investigated, and the results are summarized in Table 2 below.

division Addition amount (%) Operating characteristics Magnesium sulfate Aluminum sulfate Plate number Process yield Surface appearance Conventional Materials 1 - - 50 or more 78 Good Comparative Material 1 0.2 - 12 93 Good Invention 1 One - 0 98 Good Invention 2 1.5 - 0 98 Good Comparative Material 2 3 - 0 98 Oxidation discoloration Comparative Material 3 - 0.3 8 86 Good Invention 3 - 1.2 0 98 Good Comparative Material 4 - 2.5 0 98 Oxidation discoloration

As shown in Table 2, in the conventional material (1) to which magnesium sulfate or aluminum sulfate is not added, the plate adhesion due to the edge portion is severe and the process yield is lowered. On the other hand, the invention material (1-3) to which aluminum sulfate or magnesium sulfate was added up to 0.5-2% had no edge plate adhesion and no surface appearance color defects, and the process yield was excellent at 98%.

However, in the case of the comparative materials (1, 3), there is a partial fine plate sticking to reduce the process error rate. In addition, as in the case of the comparative materials (2, 4), the application amount is excessively increased when an excessive amount of additive is added, so there is no edge plate defect, but defects of oxidation discoloration due to the exposure of the substrate appear on the surface of the material, which causes problems in normal product. According to the conditions of the present invention.

Example 2

The magnesium sulfate of the present invention in the composition to change the mixing ratio of MgO in water to 12-14% and TiO ₂ 0.5-2.5% compared to MgO in the secondary recovery annealing plate of Example 1 On the basis of the addition, we tried to compare the operation and surface quality characteristics after the high temperature annealing according to the change of the MgO mixing ratio and the TiO ₂ addition ratio (the conventional materials are not magnesium sulfate added). The sludge of this changed composition was applied and dried upon drying after drying in a direct heating at 720 ° C. After finishing high temperature annealing, pickling was performed to remove fusion inhibitor of unreacted MgO main component on the surface. Finally, tension coating was applied to make oriented electrical steel sheet. At this time, the number of the edge plate of the coil adhered when coating the coating agent, the real rate in this process, and the surface appearance state were investigated and the results are summarized in Table 3.

division Addition amount (%) Operating characteristics MgO Mixing Ratio TiO ₂ addition ratio Plate number Process yield Surface appearance Conventional material 2 12 1.5 4 89 Good Invention 4 13 1.5 0 98 Good Comparative Material 5 14 1.5 0 98 discoloration Comparative Material 6 13 0.5 2 96 Good Invention 5 13 1.5 0 98 Good Comparative Material7 13 2.5 0 98 Oxidation discoloration

As shown in Table 3, some plate adhesion phenomenon was observed under the conditions of the conventional material (2), and the discoloration of the surface color appeared in the comparative material (5) in which the MgO mixing ratio was excessive. In addition, in the TiO ₂ additive change test, 0.5% additive and 2.5% additive were excluded from the scope of the present invention because they were not commercialized due to partial plate adhesion and surface color change.

As described above, the present invention significantly improves the process yield, and also ensures the quality stability of the overall product, and in particular, has the effect of preventing the edge portion sticking of the grain-oriented electrical steel sheet.

Claims (1)

By weight% Si: 2.9 ~ 3.3%, C: 0.025 ~ 0.045%, P: 0.015% or less, dissolved Al: 0.008 ~ 0.020%, N: 0.0080 ~ 0.012%, S: 0.007% or less, Mn: 0.12 ~ 0.42% Below, silicon steel slab consisting of Cu: 0.6% or less and Fe and other unavoidable impurities is reheated to 1250-1340 ° C. at low temperature, hot rolled and then hot rolled at 1000 ° C. or lower in a wet atmosphere. Adjust the final thickness by two cold rolling including decarbonization annealing, then recover and anneal in a dry atmosphere below 600 ℃, apply MgO-based fusion inhibitor, dry it and wind it up to make a coil, and wound coil 100% In the method of manufacturing a low-temperature reheat oriented electrical steel sheet by performing a high temperature annealing that is cooled after cracking for more than 20 hours at a temperature of 1200 ± 10 ° C. while maintaining a temperature rising rate of 700-1200 ° C. over 15 ° C./hr in a hydrogen atmosphere. , The fusion inhibitor is a grain-oriented electrical steel sheet characterized in that it comprises MgO: 12 ~ 13% by weight, TiO ₂ : 1-2% by weight compared to MgO, magnesium sulfate or aluminum sulfate 0.5-2% by weight compared to MgO To prevent edge sticking