KR20050066237A - Method for manufacturing grain-oriented electrical steel sheet with excellent glass film properties - Google Patents

Abstract

The present invention is based on Si: 2.9 to 3.3%, C: 0.040 to 0.059%, dissolved Al: 0.021 to 0.030%, N: 0.006 to 0.010%, Mn: 0.008 to 0.012%, Cr: 0.04 to 0.12% After reheating the slab composed of Fe with other components inevitably mixed under 1250 ℃ and hot rolling to make a hot rolled plate of 2.0 ~ 2.3mm, and then hot-rolled sheet annealing at a temperature of 1100 ℃ After pickling and cold rolling, the final thickness was adjusted to 0.27-0.30 mm, and then the oxide of the decarburized plate was sintered in the vicinity of 840-890 ° C. under a humid atmosphere mainly composed of hydrogen under [380] of 380-540 ppm. According to the analysis value of O] amount X (ppm), the amount of hydrated water (LOI) Y (%) and the amount of coating Z (g / m 2) of the annealing separator of the MgO main component are then calculated by Equation 1 Z = (634-X). ) / 5.6 Y ± 0.2 ------ (Equation 1) Controlled decarburization, followed by a mixture of MgO and a small amount of TiO2 and Na2B4O7 as an annealing separator. After applying, drying, and winding to make it into a large coil, it is heated up while maintaining the temperature increase rate of 700 ~ 1200 ℃ over 15 ℃ / hr, and cracked for more than 20 hours at the maximum temperature of 1200 ℃. The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent glass coating characteristics, characterized by performing a high temperature finish annealing.

Description

Method for manufacturing grain-oriented electrical steel sheet with excellent glass film properties

The present invention relates to a production method capable of forming a glass film having excellent tension imparting ability without producing a characteristic of the glass film, that is, the surface appearance defect of the glass film in the production of grain-oriented electrical steel sheet. In particular, according to the amount of [O] of the SiO 2 compound state in the oxide formed during the decarbonization annealing, the high temperature annealing is managed by controlling the amount of hydration (LOI, loss on ignition) and coating amount of the MgO core powder, which is the main component of the annealing separator, afterwards. The present invention relates to a method for producing a grain-oriented electrical steel sheet having a glass coating having high tensile coating properties.

Ordinary oriented electrical steel sheets contain 3.0% Si and have a grain structure where grain orientations are aligned in the (110) [001] direction. This product has very good magnetic properties in the rolling direction. It is used as a core material for transformers, electric motors, generators and other electronic devices.

A grain-oriented electrical steel sheet is generally made of 2-4% Si and steel containing AlN and MnS as a grain growth inhibitor. (Hot rolled)-(Pre-annealed)-(1 or 2 cold rolled by annealing) It is manufactured through the process of-(Decarbon annealing)-(MgO main component annealing separator)-(High temperature finishing annealing)-(Tension coating).

Here, the high temperature annealing process reacts with MgO coated with annealing separator and Fayalite (Fayalite, Fe2SiO4) and SiO2 formed on the surface of the material to form a conventional glass film (Forsterite, Mg2SiO4) to provide electrical insulation and adhesion, In the final product, unnecessary S or N components are removed from the material, and the most important purpose is to complete the secondary recrystallization which has magnetic properties to give the magnetic properties of the product.

The excellent glass film should basically have a uniform color without defects in appearance, but it was mainly used to improve electrical insulation and enhance the adhesion of the film by incorporating various technologies to provide functionality. However, with the recent commercialization of high-strength oriented electrical steel sheets, tension coating is applied to the surface of the material as the final insulating film, and the glass coating tension imparting ability of the lower layer also contributes to the improvement of the magnetic properties of the final product. Improving the high tensioning function of the glass film is being developed with a new technology.

Until now, various process factors control techniques have been applied to improve the characteristics of glass coatings, and the oxidation performance in atmospheric gas during decarbonization such as Korean Patent Application Nos. 94-21390 and 97-49226 has been applied (PH2O / PH2). A technique for forming an oxide layer having an optimum composition by proper control of the core) is the core. Japanese Patent Laid-Open No. Hei 6-184638 provides a technique for properly controlling the composition of decarburized oxide to provide characteristics of a glass film. It was intended to improve. However, the final quality performance of the glass film is determined by the amount of hydrated water (LOI) and coating amount in the MgO used as the decarburization layer and the annealing separator. It is determined by the sum of the quality and amount of oxides formed at the time. Moreover, the final quality of the glass film is inevitably determined by the adjustment of various complex factors according to the high-temperature annealing facilities and operating conditions of each manufacturer, so that the product is produced in a state in which it is insufficient to secure various required functional characteristics. It's happening.

The present invention has been prepared to solve the problems in the prior art, a comprehensive review of all relevant factors related to the formation of glass film management core factors were selected, and their management techniques were completed, and the high temperature unique to each manufacturer by the same technique. A method for producing an optimum glass film having high tensile strength by comprehensive management of SiO2 content during the high temperature annealing process, which is additionally formed by managing the total amount of SiO2 oxide and annealing separator hydration during decarbonization in an annealing facility. It is provided for that purpose.

The present invention enables the improvement of characteristics by a combination of three process factors, which are largely controlled by two management techniques.

First of all, in order to form an optimal glass film, an essential management item for the amount of [O] constituting SiO 2 oxide in decarburized oxide among various characteristic factors, and the amount of [O] at this time is 380 to 540 ppm.

Second, according to the analysis result of [O] amount of SiO2 oxide in the decarburized oxide, the hydration water content and coating amount of the annealing separator are subsequently adjusted according to a specific formula to obtain an optimum glass film. The relationship between the amount of hydrated water Y (%) in MgO and the amount of coating Z (g / m 2) at this time is as follows.

[Equation 1]

Z = (634-X) / 5.6 Y ± 0.2

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention is based on Si: 2.9 to 3.3%, C: 0.040 to 0.059%, dissolved Al: 0.021 to 0.030%, N: 0.006 to 0.010%, Mn: 0.080 to 0.120%, Cr: 0.04 to 0.12% After reheating the slab of the composition consisting of Fe and other components inevitably mixed at 1250 ° C. or lower and hot rolling to form a hot rolled sheet of 2.0 to 2.5 mm, followed by hot rolling annealing at a temperature of 1100 ° C. or below, After pickling and cold rolling, the final thickness is adjusted to 0.27 to 0.30 mm, and then decarburization is performed near 840 to 890 ° C, which is mainly hydrogen. Subsequently, as an annealing separator, a composition mainly composed of MgO is applied as a slurry in a slurry state, dried at a temperature of 700 ° C. or lower, and wound up to form a large coil. The final finishing high temperature annealing is 50% or less of hydrogen-containing hydrogen atmosphere up to 1100 ℃, then a temperature of 20 hours or more at 1200 ℃, and a 100% hydrogen atmosphere in the cooling atmosphere afterwards. Secondary recrystallization annealing is performed through a thermal cycle maintained at 15 ° C / hr or more. Subsequently, the unreacted composition is removed, and finally, a grain-oriented electrical steel sheet is produced by applying an insulating coating agent consisting of a small amount of chromic anhydride to a mixed phosphate and colloidal silica component of magnesium, aluminum, and calcium.

In the decarburization annealing, the oxide of the decarburized plate has an amount of [O] in the SiO2 state of 380 to 540 ppm, and according to the analysis value X (ppm) of the amount of [O] at this time, the hydration moisture of the annealing separator of the main MgO component ( The directional electrical steel sheet having excellent glass coating properties, characterized by forming a high-strength glass film after finishing annealing by controlling and managing the relationship between the LOI amount Y (%) and the coating amount Z (g / m2) in accordance with Equation 1 above. It relates to a manufacturing method.

Hereinafter, the present invention will be described in detail.

Although the manufacturing process of oriented electrical steel sheet varies somewhat from manufacturer to manufacturer, it is common to adjust the thickness in steelmaking, manufacture slabs, reheat and hot roll, hot-rolled sheet annealing and cold rolling to adjust thickness, decarbon annealing, and secondary recrystallization. It is usually manufactured by hot annealing and final insulation coating process. The establishment of such a manufacturing process is a process based on a mass production system, and an important key factor of the mass production system is the establishment of a finishing high temperature annealing process. In recent years, directional electrical steel sheet production of high magnetic flux density has become the center of electrical steel sheet production. Moreover, as the center of production cost is shifted due to the production of thin products, it is important to secure better magnetic properties. The new functional role of iron loss reduction method by the high tension of

It is reported that the tension imparting ability of the conventional glass coating is 0.25 to 0.35 kg / mm2, and the magnetization of the final product has an improvement effect of about 2 to 3% even by applying such tension. Therefore, the increase in high tensile ability of the glass film may contribute to the magnetic improvement rate. Magnetic improvement due to high tension of the coating layer affects the iron core loss, or iron loss, in the magnetic layer. As the magnetic domain becomes finer by the tension applied to the material, the vortex loss is reduced, and the magnetism is improved.

Therefore, the present inventors studied the relationship with the tension imparting ability centering on the amount of glass film formation, and confirmed that even when the amount of glass film formation was too large, the tension imparting capacity was reduced, and even when the amount of film formation was insufficient, the tension imparting capacity was reduced. It was. In particular, when the amount of glass film formation is excessive, film defects such as annealing oxidation, discoloration, and discharge hole appear simultaneously on the surface, and the composition of the film is a Fe2SiO4 based FeO center, which is not a component of Mg2SiO4 which is excellent in tensioning. It was confirmed that the components were incorporated into the coating, which adversely affected the coating defect and the tension imparting ability.

The glass coating having the best tension imparting ability and excellent appearance characteristics is a coating layer composed of pure Mg 2 SiO 4 components, and the optimum coating amount is 3.2 g / m 2. The 3.2 g / m2 glass film amount is 1.37 g / m2 formed in terms of SiO2 amount, which is 634 ppm when calculated on both sides. That is, the fact that the amount of [O] in the oxide SiO 2 for imparting the highest tension was 634 ppm, constituted the present invention.

On the other hand, the glass film formed during finishing hot annealing is a chemical bond between SiO 2 in the material surface oxide and MgO applied with an annealing separator, and SiO 2 in the material surface is formed during the high temperature annealing with SiO 2 in the oxide formed during the initial decarbonization annealing. Final determination is made by the sum with SiO 2.

Oxides formed during high temperature annealing are partially released to the outside of the total water content, which is the sum of the water content of MgO, which is the main component of the annealing separator, and the amount of their application during the high temperature annealing, but many moisture are formed by further oxidizing the material surface. to be.

When there is excess water in the large coil, the FeO-based oxide is mainly formed at about 900 ° C, which is the start temperature of the glass film formation reaction, whereas Fe 2 SiO 4 and SiO 2 -based oxides are formed when the moisture content is small.

At this time, the total amount of water represented by the product of the amount of water hydrated in MgO and the amount of coating was confirmed by converting the amount of SiO2 effective for forming a glass film among the oxides additionally formed under normal operating conditions of high temperature annealing. In the presence of 0.01 grams of water in the sugar it was confirmed that additional generation of 5.6ppm [O]. Therefore, the total amount of water converted (% of hydrated water in MgO x coating amount g / m 2) is divided by a factor of 5.6 to calculate the amount of [O] composed of SiO 2. On the other hand, taking into account the convenience of on-site work in terms of coating amount management at this time, managing the management deviation to the upper and lower 0.2g / m2 is an appropriate amount for the optimum film formation.

Therefore, the management method of hydration water content and coating amount during MgO coating process is to analyze the [O] amount of SiO2 state in the oxides formed during decarbonization annealing, and then to control and control the hydration water content and coating amount of annealing separator applied later. It can form a film.

Putting this together, the formula shows that the amount of [O] in the SiO 2 state of the decarburized plate is X (ppm), the amount of hydrated water of the powder of the MgO main component of the annealing separator is Y (%), and the coating amount at this time is Z (g / m 2). ), The correlation of these three individuals can be represented by the above formula (1).

Thus, transplantation can be used and site key factors can be managed.

Hereinafter, the reason for limitation of the range of this invention steel is demonstrated.

C plays a role in dispersing fine solid solution of AlN precipitates, forming a rolled structure, giving processing energy during cold rolling, and limiting it to 0.059% at least 0.040% in consideration of the decarburization process.

   Si increases the resistivity and lowers iron core loss. Below 2.9%, the iron loss characteristics deteriorate, and when excessively contained, the steel becomes vulnerable and cold rolling is extremely bad.

   Mn lowers the solubility temperature of precipitates during reheating and prevents cracks formed at both ends of the material during hot rolling. Therefore, Mn needs to be added at least 0.08% and suppresses 0.12% due to deterioration of iron by Mn oxide.

    The Al component forms a precipitate of AlN together with N to secure grain growth inhibition. At 0.021% or less, it does not have sufficient inhibitory power for secondary recrystallization, resulting in small grain size and incomplete fine particles. It is a component that needs to be managed because the restraining force is so strong that it makes the second recrystallization difficult and the magnetic properties deteriorate rapidly.

 Next, the manufacturing process of this product is demonstrated.

Steel slabs having the above composition are hot rolled after being reheated at a temperature of 1250 ° C. or less in consideration of hot rolling and securing a magnetic property to make a hot rolled plate having a thickness of 2.0 to 2.3 mm. Subsequently, hot-rolled sheet annealing is carried out at a temperature of 1100 ° C. or lower, and adjusted to a thickness of 0.27-0.30 mm, which is the final thickness by pickling and cold rolling. Thereafter, decarburization is performed at about 840 ° C to 890 ° C under a humid atmosphere mainly composed of hydrogen. This manufacturing process is not particularly limited because it uses an existing treatment method.

However, managing the [O] amount of SiO 2 in the oxide during decarburization to 380 to 540 ppm is an essential condition for forming an optimum glass film thereafter. At this time, the film becomes thinner or oxidative defects occur in the glass film even after controlling the conditions below 380ppm. On the other hand, at 560 ppm or more, the glass film of high tension due to the generation of oxidative defects could not be produced even by the management of the process conditions, which were excluded from the scope of the present invention.

Then, the annealing separator is added to the active component MgO as an additive, TiO2 and Na2B4O7 as an additive to make a slurry as water, and then applied to the surface of the material by roll coating, dried and wound into a large coil.

At this time, the amount of hydrated water and the amount of the coating of the composition of the annealing separator should follow Equation 1 of the present invention.

 The final finishing high temperature annealing is a nitrogen atmosphere of 50% or less up to an elevated temperature of 1200 ° C., followed by a crack of 20 hours or more at 1200 ° C. and a 100% hydrogen atmosphere in a cooling atmosphere thereafter. At this time, secondary recrystallization annealing is performed through a thermal cycle that maintains the temperature increase rate of 700 to 1200 ° C. over 15 ° C./hr. Finally, an insulating coating agent composed of a small amount of chromic anhydride is applied to a mixed phosphate and colloidal silica component of magnesium, aluminum, and calcium to prepare a final grain-oriented electrical steel sheet product. Here, the final finishing hot annealing conditions and the application of the insulating coating agent are described in other patents and are not particularly limited.

  Hereinafter, the present invention will be described in more detail.

Example 1

Composition based on Fe: 3.1%, C: 0.048%, dissolved Al: 0.028%, N: 0.008%, Mn: 0.12%, Cr: 0.11% The slab of is reheated at 1250 ° C. or lower and hot rolled to make a hot rolled plate of 2.2 mm. Then, the hot rolled sheet is annealed at a temperature of 1100 ° C., adjusted to a final thickness of 0.30 mm by pickling and cold rolling, and then hydrogen is The decarburization treatment was performed at 855 ° C. under a humid atmosphere having a predominant dew point temperature. The amount of [O] in the SiO 2 state in the oxide of the decarburized plate was changed to 350 to 610 ppm.

Subsequently, a composition obtained by mixing 5 parts by weight of TiO2 and 0.3 parts by weight of Na2B4O7 to 100 parts of active MgO as an annealing separator was applied as a slurry and dried at a temperature of 700 ° C. or below to control the coating amount to 9.5 to 13.5 g / m2. It is then wound up to make a large coil. The final finishing high temperature annealing is a hydrogen atmosphere containing 25% nitrogen up to 1200 ° C, followed by 20 hours or more of cracking at elevated temperature and 1200 ° C, and a 100% hydrogen atmosphere in the cooling atmosphere afterwards. Secondary recrystallization annealing was performed through a thermal cycle maintained at hr to complete the glass coating and magnetic properties.

At this time, the characteristics of the glass film according to the amount of [O] in the SiO 2 state of the decarburized oxide, the amount of hydration water (LOI) of the annealing separator, and the coating amount were compared. The characteristics of the glass coating were calculated by g / m2 by detecting the amount formed by the chemical wet method, and the tension imparting capacity was expressed by kg / mm2 by measuring the degree of cross-section bending. The overall appearance characteristics were observed by visual observation.

division [O] content of SiO2 state (ppm) Hydration Moisture of Annealed Separator (%) Coating amount (g / m2) Glass film formation amount (g / m2) Tensioning ability (kg / mm2) Appearance Characteristics Comparative Material 1 350 4.5 12.2 3.56 0.31 Oxidation discoloration Comparative Material 2 395 3.3 13.5 3.48 0.35 Annealing Oxidation Comparative Material 3 " 2.8 10.5 3.06 0.37 Good Invention 1 " 3.8 11.2 3.23 0.41 Good Comparative Material 4 450 3.8 10.1 3.46 0.36 Outlet Invention 2 " 2.2 14.8 3.18 0.39 Good Invention 3 " 2.8 11.8 3.21 0.40 Good Comparative Material 5 " 3.2 9.5 2.98 0.34 tenuity Comparative Material 6 510 3.3 10.5 3.53 0.33 Oxidation discoloration Invention 4 " 2.1 10.5 3.20 0.41 Good Comparative Material7 " 1.8 11.1 3.05 0.34 Outlet Comparative Material 8 610 2.5 11.5 3.33 0.31 Annealing Oxidation

As shown in Table 1, when the amount of [O] in the SiO 2 state, such as Comparative Materials 1 and 8, is out of the scope of the present invention, appearance defects are generated and therefore high tensile strength is impossible.

On the other hand, when the amount of [O] in the SiO2 state is 395 ppm, even when the product of the hydration water content and the coating amount is out of the present invention (Comparative Materials 2 and 3), the appearance property and the film formation amount are inadequate, and thus the tension imparting capacity is somewhat lower than the required level. .

Even when the amount of [O] in the SiO 2 state was 450 ppm, even when the product of the amount of hydrated water and the amount of coating was outside the present invention (Comparative Materials 4 and 5), the appearance property and the amount of film formation were inadequate, so that the tension imparting ability was also insufficient compared to the control level. Do.

When the amount of [O] in the SiO 2 state was 510 ppm, even when the product of the amount of hydrated water and the amount of coating was outside the present invention (Comparative Materials 6 and 7), the appearance property and the amount of film formation were inadequate, so that the tension imparting ability was lower than the required level.

However, in the case of Inventive Materials 1 to 4 in which the amount of [O] in the SiO 2 state is in the range of 380 to 540 ppm of the present invention, and the product of the amount of hydrated water and the amount of coating satisfies the present formula, the appearance property is good and the glass film is appropriately tensioned. It has excellent glass coating properties exceeding the required level of 0.39kg / mm2.

 As described above, in the present invention, the amount of [O] in the decarbonized annealing SiO 2 state satisfies the basic requirement of 380 to 540 ppm, and at the same time, the amount of [O] in the decarburized plate, the powder of hydrated powder of the MgO main component of the annealing separator, and The glass film formed after finishing annealing by controlling and managing in relation to the coating amount at the time has an effect of producing a glass film having not only excellent appearance characteristics but also excellent high tensile strength imparting ability.

Claims (1)

Si: 2.9 to 3.3% by weight, C: 0.040 to 0.059%, dissolved Al: 0.021 to 0.030%, N: 0.006 to 0.010%, Mn: 0.008 to 0.012%, Cr: 0.04 to 0.12% After reheating the slab of composition composed of Fe and the hot rolled sheet after making it reheat at 1250 ℃ or less to make 2.0 ~ 2.3mm hot rolled plate, and then hot-rolled sheet annealing at the temperature below 1100 ℃ And cold rolling to adjust the final thickness to 0.27 ~ 0.30mm thickness, and then the amount of [O] in the decarburized plate in the vicinity of 840 ~ 890 ℃ under the wet atmosphere, which is mainly hydrogen, under the amount of [O] in 380 ~ 540ppm. According to the analysis value of X (ppm), the amount of hydrated water (LOI) Y (%) and coating amount Z (g / m2) of the annealing separator of the main MgO component are then calculated by Equation 1.                 Z = (634-X) / 5.6 Y ± 0.2 ------ (Equation 1) After controlling and controlling the decarburization, the mixture of MgO and a small amount of TiO2 and Na2B4O7 as a slurry is applied as a slurry, dried and wound up to make a large coil, and then the temperature rising rate of 700 to 1200 ° C is increased to 15 ° C /. A method of manufacturing a grain-oriented electrical steel sheet having excellent glass coating characteristics, characterized in that the film is heated at a temperature of more than hr and cracked at a maximum temperature of 1200 ° C. for at least 20 hours, followed by a high temperature finish followed by cooling.