KR20060013177A - Method for making forsterite film of grain-oriented electrical steel sheets - Google Patents

Abstract

The present invention relates to a method for forming a glass film of a grain-oriented electrical steel sheet, by weight% Si: 3.0 to 3.3%, C: 0.040 to 0.062%, dissolved Al: 0.023 to 0.030%, N: 0.006 to 0.009%, S: 0.010 % Or less, Mn: 0.008 ~ 0.016%, Cr: 0.04-0.12%, Slabs composed of balance Fe and other unavoidable impurities are hot rolled after low temperature reheating at 1380 ℃ or lower and hot rolled plate of 2.0 ~ 2.3mm. Hot-rolled sheet annealing at a temperature of 1100 ℃ or less, adjusted to a final thickness of 0.27 ~ 0.30mm by pickling and cold rolling, and then decarburized near 840 ~ 890 ℃ under a humid atmosphere of hydrogen and nitrogen Next, a mixture of MgO and a small amount of TiO ₂ and Na ₂ B _{4 4} O ₇ is applied as a slurry, dried, and then wound up to form a large coil, and heated to a temperature of 700 to 1200 ° C. in a nitrogen atmosphere of 25% or less. The temperature is raised while maintaining the rate at 15 ° C / hr or more, and 20 hours at the maximum temperature of 1200 ° C. In the method for producing a grain-oriented electrical steel sheet subjected to the final finishing high temperature annealing through a heat cycle to cool after cracking over abnormal time; The tension applied to the coil during the final finishing high temperature annealing is maintained at 2.5 to 4.5Kg / mm ² , and the heating is performed at a temperature rising rate of 30 ° C./hr or less until the central temperature of the plate width direction reaches 550 ° C. and at the same time in the width direction. Hydration moisture of MgO is maintained at 0.12 ~ 0.45% to suppress defects in tissue exposure of large coils and improve the error rate.

Description

Glass film formation method of grain-oriented electrical steel sheet {METHOD FOR MAKING FORSTERITE FILM OF GRAIN-ORIENTED ELECTRICAL STEEL SHEETS}

The present invention relates to a method for forming a glass film of a grain-oriented electrical steel sheet, and more particularly, by exposing optimally to the glass film forming process, the exposure of a tissue film which is an absolute shortage problem of the amount of glass film formed in the outermost part of a large coil during final finishing high temperature annealing. The present invention relates to a method for forming a glass film of a grain-oriented electrical steel sheet to suppress the occurrence of defects to improve the real error rate.

In general, oriented electrical steel sheet contains 3.1% of Si, has grain structure aligned in the direction of (110) [001], and has very good magnetic properties in the rolling direction. And steel sheets used as iron core materials such as electronic devices.

A grain-oriented electrical steel sheet is made of 2-4% Si and grain growth inhibitor using AlN and MnS-containing steel, hot-rolled, pre-annealed, one-time or two-times cold rolled, decarbonized, and annealed with MgO. It is manufactured through processes such as separating agent application, high temperature finishing annealing, and tension coating, where the high temperature annealing process is made of MgO coated with annealing separator and iron olivine (Fayalite: Fe ₂ SiO ₄ ) and silicon dioxide (SiO ₂ ) formed on the material surface. Reacts with ordinarily to form a conventional glass film (Forsterite: Mg ₂ SiO ₄ ) to not only provide electrical insulation and adhesion, but also to complete the secondary recrystallization that has the most important magnetic properties, the product's magnetic It is the process of giving a characteristic.

The excellent glass coating properties should basically have a uniform color without defects on the surface of the material, but the technique mainly used to improve electrical insulation and enhance film adhesion by incorporating various techniques to provide functionality.

However, with the recent commercialization of high magnetic flux oriented electrical steel sheets, it has been confirmed that the formation and amount of high-strength coating applied to the final insulating film greatly contributes to the improvement of the magnetic properties of the final product. The importance of the film is mainly extended not only to the appearance surface quality but also to the improvement of the magnetic properties.

Until now, the control method of various process factors has been applied to improve the characteristics of the glass film.

For example, the technique of forming an oxide layer having an optimum composition by appropriate control such as oxidation ability (PH ₂ O / PH ₂ ) in the atmosphere gas during decarbonization annealing disclosed in Korean Patent Application Nos. 94-21390 and 97-49226 is disclosed. This is to improve the characteristics of the glass film by appropriately controlling the composition of the decarburized oxide disclosed in Japanese Patent Laid-Open No. Hei 6-184638.

Furthermore, Japanese Patent Laid-Open No. 59-200670 refers to the overall characteristics of the glass coating by controlling the characteristics of MgO, but it has not been very helpful for improving the glass coating characteristics of the outermost winding of a large coil.

This is because the glass coating of the outermost portion of the glass coating is determined by the special condition of the rapid heating portion at the time of high temperature annealing, and thus, the inferior factors must be discovered and the management of the special operating conditions for this is necessary.

The present invention has been made in view of the above-described problems of the prior art, and has been created to solve this problem, and the amount of CaO content used while using a low activity star with a slightly late chemical reactivity (activation ability) when MgO is applied as an annealing separator after decarbonization annealing. In order to control the amount of hydration water contained in the outermost material by giving sufficient time to the initial temperature increase rate up to 550 ℃ for the average temperature in order to manage extremely low and smoothly discharge the hydrated water during the final high temperature annealing. It is an object of the present invention to provide a method for stably forming a glass film having no exposure defects.

The present invention, in order to achieve the above technical problem, Si: 3.0 to 3.3%, C: 0.04 to 0.062%, dissolved Al: 0.023 to 0.030%, N: 0.006 to 0.009%, S: 0.010% or less, Based on Mn: 0.008 to 0.016% and Cr: 0.04-0.12%, the slab of the composition containing the balance Fe and other unavoidable components is hot rolled after reheating at a temperature of 1380 ° C. or lower and hot rolled to 2.0 to 2.3 mm. Plates are made, hot-rolled sheet annealing is carried out at a temperature of 1100 ℃ or below, and the final thickness is adjusted to 0.27 ~ 0.30 mm by pickling and cold rolling, and then decarburization is performed near 840 ~ 890 ℃ under the wet atmosphere of mixed hydrogen and nitrogen gas. After performing the annealing separator, MgO and a small amount of TiO ₂ and Na ₂ B ₄ O ₇ are dispersed in a slurry, applied, dried, and wound up. The final finishing high temperature annealing is a hydrogen atmosphere containing nitrogen at 25% or less and 700 to 1200. While maintaining the temperature increase rate of 15 ℃ / hr or more, the temperature is raised to the maximum temperature of 1200 ℃. In the manufacturing process of oriented electrical steel sheet which finishes high temperature annealing after cracking for 20 hours or more and cools, it is necessary to improve texture exposure defects caused by the lack of glass film formation mainly generated in the outermost part of a large coil. In particular, when the coil is wound under a tension of 2.5 to 4.5 Kg / mm ² , the temperature rise rate up to 550 ° C. is heated to 30 ° C./Hr or less at the time of high temperature annealing. It is characterized by providing a manufacturing method for stably forming a glass film of the outer peripheral part of the high-temperature annealing process of the grain-oriented electrical steel sheet by managing 0.12 to 0.45%.

Hereinafter, the present invention will be described in detail.

According to the present invention, the deterioration of magnetic uniformity and surface quality characteristics due to the weight increase of the coil is caused by the lack of the amount of formation of the glass film formed on the outer coil of the coil during high temperature annealing. Control of chemical properties and finishing of hydration moisture In the situation where incorporation into the high temperature annealing furnace is inevitable, the reaction rate is fast during the annealing process and the control to suppress the formation of FeO oxides, which is extremely unfavorable for forming glass films, is achieved. By increasing the amount of glass film formed on the winding part to obtain a stable glass film to improve the magnetic uniformity and surface quality characteristics of the large coil.                     

That is, in the case of controlling the chemical properties of MgO, which is a central component of the annealing separator, since some MgO is produced by precipitating MgO from Mg ions in seawater, it is inevitable that some impurities are mixed in the seawater. It is necessary to control the minimum amount of CaO, which is a key fatal component, as well as a method of appropriately suppressing the increase of hydration moisture by controlling the activation property (also called CAA, citric acid activation degree), which is a chemical characteristic of MgO itself. The CAA 40% is intended to have a low activity of 75 to 95 seconds.

In addition, in controlling the formation of FeO-based oxides, which are extremely disadvantageous in forming the glass film, the temperature in the furnace is controlled by appropriately controlling the temperature increase rate in the furnace so as to contain only hydrated moisture capable of forming an oxide which is advantageous to the coil's material sheet temperature of 550 ° C. It is to increase the amount of formation.

That is, the main component that is inevitably incorporated in the control of the characteristics of MgO, which is a central component of the annealing separator, is CaO, which absorbs and reacts with water or carbon dioxide gas in the air to react with Ca (OH) ₂ or CaCO ₃ . And become part of the hydration moisture during the high temperature annealing process, which adversely affects the formation of the glass film. Therefore, its characteristic control becomes an essential requirement of the present invention.

In addition, the present invention is to adjust the activation of the chemical properties of the MgO itself to appropriately delay the hydration of water production reaction to have a low activity star chemical properties of 75 ~ 95 seconds of the activation value (CAA 40%) of the MgO powder It is possible to reduce the increase of hydration water during the MgO mixing and drying process, and the reaction can be started at a slightly higher temperature than the high MgO during high temperature annealing, so that the surface oxide layer can be adjusted during hot annealing. Will be more advantageous.

Particularly, since hydration water contained in MgO is inevitably mixed in the finishing high temperature annealing furnace, hydration until the plate reaction rate is reached at 550 ° C., which is relatively slow, in order to suppress the formation of FeO oxide, which is extremely disadvantageous in forming the base coating during high temperature annealing. It is desirable to control the amount of water so that it can have only hydrated water that can form an advantageous oxide.

At this time, the hydration of the titration is 0.12% or more at a temperature of 550 ℃, it was confirmed through the experiment 0.45% or less.

Hydrated moisture reduction control technology in the present invention, in addition to the use of low activity star MgO, it is necessary to easily remove the contained hydration moisture by ensuring low-temperature section air permeability during finishing high temperature annealing.

Therefore, in order to secure breathability, the coiling tension of the coil should be reduced to a certain amount or less, and the optimum condition considering the breathability and poor shape is 2.5 to 3.5 kg / mm ² .

Another method is to secure the discharge time of hydration moisture removal by low temperature rising as much as possible, and at this time, it was preferable that the minimum temperature increase rate considering economical efficiency is 30 degreeC / Hr.

Hereinafter, the reason for limitation on the composition ratio of the slab for the present invention will be described.

[C: 0.040-0.062%]                     

C plays a role of imparting fine solid dispersion of AlN precipitates and rolling structure to impart processing energy during cold rolling. Therefore, it is reasonable to limit C to 0.062% or more considering the difficulty of decarburization process.

[Si: 3.0 ~ 3.3%]

Since Si plays a role of lowering iron loss or iron loss by increasing the resistivity, the iron loss property becomes worse at 3.0% or less, and the steel becomes vulnerable when the excess content is excessive, so cold rolling is extremely bad and should be managed at 3.3% or less.

[Mn: 0.008-0.016%]

Mn lowers the solid solution temperature of the precipitate during reheating and prevents cracks formed at both ends of the material during hot rolling, so at least 0.08% or more is required, and Mn oxide deteriorates iron loss by more than 0.16%. Should be suppressed.

[Al: 0.023-0.030%]

Al is the central element that forms the precipitate of AlN together with N to secure grain growth inhibitory power.In the case of 0.023% or less, Al has little grain size and incomplete fine grains, and in 0.030% or more, it suppresses the grain growth. This strength is so strong that it is difficult to form secondary recrystallization, so that the magnetic property is rapidly deteriorated, so the central management is required, and the above-mentioned composition range is most appropriate.

[N: 0.006-0.009%]

N is an essential component in forming secondary reacted crystals with dissolved Al, and the amount of formed precipitates is insufficient at 0.006% or less, and is preferably limited to the above range in consideration of additional sedimentation at 0.009% or more.

Next, the manufacturing process of the present invention will be described.

The steel slab having the composition is reheated in the range of 1150 ° C. to 1380 ° C. in consideration of hot rolling and securing magnetic properties, and then hot rolled to form a hot rolled plate having a thickness of 2.0 to 2.3 mm.

Subsequently, hot-rolled sheet annealing is performed at a temperature of 1100 ° C. or lower, and adjusted to a final thickness of 0.23 to 0.35 mm by pickling and cold rolling.

Thereafter, decarburization is performed at about 840 to 890 ° C under a humid atmosphere of hydrogen and nitrogen mixture. This manufacturing process is not particularly limited because it uses an existing treatment method.

Then, when the annealing separator is applied, TiO ₂ powder and Na ₂ B ₄ O ₇ are added in an amount of 3 to 5% and Na ₂ B ₄ O ₇ is added as an auxiliary additive to MgO, which is a main component, and the additive is not particularly limited.

At this time, MgO is required to manage the amount of CaO component having the greatest influence on the hydration moisture in order to exhibit the characteristics of the present invention, the less is advantageous to the glass film formation, but in the present invention up to 0.16% for proper management in the manufacturing process Set log management goals.

Meanwhile, activation degree (CAA), which is a measure of chemical reactivity of MgO, needs low activation compared to conventional materials.

At this time, the proper management value is difficult to manage the hydration moisture at 75 seconds or less, and the reactivity at the time of high temperature annealing is slightly slower at 95 seconds or more, so that the film is sometimes formed thinly, so the time therebetween is limited to the management value.                     

The annealing separator composition of the composition is applied in a slurry state and coated with cotarol, dried at a temperature of 700 ° C. or less, and then wound to make a large coil.

At this time, winding tension is a very important influence factor, edge flare defects occur at 2.5kg / mm ² or less, HCL workability is poor, and breathability of hydration moisture is poor at 3.5kg / mm ² or more. Since proper control is difficult, the value between them is especially preferable.

The final high temperature annealing is a hydrogen atmosphere containing nitrogen below 25%, and the temperature is raised while maintaining the temperature rising rate of 700 to 1200 ° C over 15 ° C / hr, and undergoes a heat cycle of cooling after cracking for 20 hours or more at the maximum temperature of 1200 ° C. To do that.

At this time, it is necessary to manage the temperature increase rate to 30 ℃ / hr or less at a temperature up to 550 ℃ which is important for oxide formation in the initial temperature increase process for stabilizing the glass film of the present invention, the proper hydration moisture management is impossible at higher temperature increase rate Do.

At the same time, the average amount of hydration in the width MgO is required to be 0.12 ~ 0.45%, and when it is contained more than 0.45%, tissue exposure defects are easily generated by over-oxidation of the outer outer region. It is necessary to pay attention because the excessive formation of the surface oxide during the temperature increase process results in poor formation of the glass film, resulting in defects in tissue exposure.

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

Example 1

Si: 3.1%, C: 0.048%, Dissolved Al: 0.028%, N: 0.009%, S: 0.007% or less, Mn: 0.011%, Cr: 0.10% by weight, and other inevitable ingredients The slab composed of the remainder including Fe was hot-rolled after reheating at 1200 ° C. to make 2.2 mm hot rolled plate.

Subsequently, hot-rolled sheet annealing was performed at a temperature of 1100 ° C., and the final thickness was adjusted to 0.30 mm by pickling and cold rolling, followed by decarburization at 855 ° C. under a humid atmosphere of hydrogen and nitrogen mixed gas to give [O] content of the decarburized plate. Was administered at 720 ~ 780ppm.

Then, annealing separator composition was mixed with 5 parts by weight of TiO ₂ and 0.3 parts by weight of Na ₂ B ₄ O ₇ to 100 parts by weight of low activity MgO of 85 seconds based on CAA as an annealing separator. / m ² was applied, dried at a temperature of 650 ℃ and unit tension was wound to 3.5Kg / mm ² to make a 9 ton weight large coil.

Afterwards, the final finishing high temperature annealing is 25% of nitrogen-containing hydrogen atmosphere from the start of temperature rise to 1200 ° C, more than 20 hours of cracking at 1200 ° C, and 10% or less of nitrogen-containing hydrogen atmosphere in the cooling atmosphere thereafter. Secondary recrystallization annealing was carried out through a thermal cycle maintained at a temperature increase rate of 15 ° C./hr or more to complete the glass coating and the magnetic properties.

At this time, in the final finishing high temperature annealing, the temperature increase rate up to 550 ° C based on the center of the plate width direction was adjusted to 10 ~ 300 ° C / Hr, and the conditions for changing the water content of hydration to 0.05 ~ 2.32% by adjusting MgO coating conditions, etc. To compare the incidence of tissue exposure defects in the outer skin of the coil, the glass film formation of the central surface of the 1 ton point in the outermost region was investigated by fluorescence X-ray analysis.

Here, the case where the glass film formation amount is usually 1.5 g / m ² is referred to as a tissue exposure defect, and the smaller the formation amount, the more severe the defect.

 division  Temperature increase rate (℃ / hr)  Hydration Moisture (%) Glass film formation amount (g / m ² )  Organizational Exposure Defect Normal Goods 1 200 2.05 1.11 Somewhat stronger Normal Goods 2 300 2.42 0.75 Strong defect Comparative Material 1 10 0.05 1.56 Weak defect Comparative Material 2 50 0.75 1.48 Weak defect Comparative Material 3 120 1.73 1.32 Weak defect Invention 1 15 0.18 2.83 Good Invention 2 20 0.27 3.45 Good Invention 3 27 0.41 3.36 Good

As shown in Table 1, the temperature increase rate is too slow, as in Comparative Material 1, and therefore, when the hydration water content is lower than the range of the present invention, it was confirmed that the film formation defects were rather weak due to the lack of the amount of film formation.

However, in the case of the invention materials 1, 2, and 3, in which the temperature increase rate is 30 ° C / hr within the range of the present invention, and the amount of hydration water is 0.12 to 0.45%, which is the range of the invention, the amount of film formation is large and at the same time, the glass film is good. It was confirmed that the appearance color was shown.

On the other hand, in the case of the temperature increase rate and the hydration water amount exceeding the scope of the present invention, the comparative material 2, 3 and the normal material 1, 2 also lacks the amount of film formation, so that the texture (Grain) of the entire material is visible to the naked eye Exposure was indicated.

Example 2

The amount and structure of the glass film formed after the final high temperature annealing was applied by using MgO 7 in the amount and activation degree of CaO in the annealing separator MgO using the decarbonized annealing plate of Example 1 The exposure defects were observed and shown in Table 2.

At this time, the temperature increase rate in the finish high temperature annealing was carried out under the reference conditions 27 ℃ / hr.

 division  CaO content (℃ / hr)  Activation (CAA) (sec) Glass film formation amount (g / m ² )  Organizational Exposure Defect Trade goods 0.24 65 1.12 Somewhat stronger Comparative Material 1 0.13 65 1.83 Weak defect Comparative Material 2 0.24 77 1.75 Weak defect Comparative Material 3 0.10 103 2.32 Very weak Comparative Material 4 0.24 103 1.81 Weak defect Invention 1 0.12 77 3.03 Good Invention 2 0.10 85 3.28 Good Invention 3 0.09 93 3.31 Good

As shown in Table 2, in the case of the conventional material or the comparative material 1 and 2, when the amount of CaO component and the activation degree in the MgO is higher or lower than the range of the present invention, the amount of glass film formation is small, indicating that the defects in the texture of the material are observed. Could know.

However, in the case of invention materials 1, 2, and 3 which are included in the scope of the present invention, it can be seen that a good film having no defects is formed even if a large amount of glass film is formed.

In addition, it was confirmed that even when the activation degree or CaO content is out of the scope of the invention as in Comparative Materials 3 and 4, tissue exposure defects were also observed.

As described in detail above, according to the present invention, it is possible to stably form the glass coating of the grain-oriented electrical steel sheet by suppressing the generation of tissue exposure defects due to the glass coating not forming in the outer coil portion of the large coil.

Claims (2)

Si: 3.0 to 3.3%, C: 0.040 to 0.062%, dissolved Al: 0.023 to 0.030%, N: 0.006 to 0.009%, S: 0.010% or less, Mn: 0.008 to 0.016%, Cr: 0.04-0.12 Based on%, the slab composed of the balance Fe and other unavoidable impurities is hot-rolled after low temperature reheating at below 1380 ℃ to make hot rolled sheet of 2.0 ~ 2.3mm, and hot-rolled annealing at below 1100 ℃. After pickling and cold rolling, the final thickness was adjusted to 0.27 ~ 0.30mm, and then decarburized near 840 ~ 890 ℃ under hydrogen and nitrogen wet atmosphere, and then MgO and a small amount of TiO ₂ and Na ₂ B _{4 were used as} annealing separator. The mixture of 4O ₇ is applied in a slurry state, dried, and then wound up to make a large coil. The temperature is elevated at a temperature of 700 to 1200 ° C. in a hydrogen atmosphere containing 25% or less and maintained at a temperature of 700 ° C. to 1200 ° C. or higher, at a maximum temperature of 1200 ° C. Finishing hot station with thermal cycle to cool after cracking over 20 hours in In the method for producing a grain-oriented electrical steel sheet to dull; The tension applied to the coil during the final finishing high temperature annealing is maintained at 2.5 ~ 4.5Kg / mm ² , The glass film of the grain-oriented electrical steel sheet characterized by heating at a heating rate of 30 ° C./hr or lower until the central temperature in the sheet width direction reaches 550 ° C. and maintaining the hydration moisture in the width direction MgO at 0.12 to 0.45%. Formation method. The method according to claim 1, The CaO component of the MgO is 0.16% or less, and activation degree (CAA) value of 75 ~ 95 low activity star MgO, characterized in that the annealing separator using a glass film of a grain-oriented electrical steel sheet, characterized in that.