JPH02274882A - Production of grain-oriented silicon steel sheet having good forsterite insulating film in coil state - Google Patents

Abstract

PURPOSE:To produce the grain-oriented silicon steel sheet having a uniform and good forsterite insulating film by subjecting a cold rolled silicon steel strip to a decarburization annealing and adequately applying a specific annealing and separating agent thereon, then subjecting the steel sheet as a coil to a finishing high-temp. annealing. CONSTITUTION:The silicon steel strip cold rolled to a desired final sheet thickness is decarburization annealed at about 850 deg.C in wet hydrogen to form the sub-scale of an oxide film contg. SiO2 on the surface thereof. This steel strip is coated with the annealing and separating agent essentially consisting of MgO2 and is then taken up as a strip coil. This coil is subjected to the finish high temp. annealing at about 1200 deg.C to form the forsterite. The annealing and separating agent in the abovementioned process for producing the grain oriented silicon steel sheet is formed of the agent prepd. by adding a Ca compd. contg. O and a compd. contg. S thereto in combination at the equiv. of the S of 0.4 to 1.4 times the equiv. of the Ca. Further, this annealing and separating agent is applied on the strip surface at such a ratio at which the component of the CaO attains 0.04 to 0.35g/m<2>. The good forsterite insulating film in the coil state is formed by controlling the generated [O] in this way.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a manufacturing method capable of forming a good forsterite insulating film in the manufacturing process of a unidirectional silicon steel sheet in which final high-temperature annealing is performed in the form of a strip coil. (One conventional technique) The MgOSing-based insulating film mainly composed of forsterite on the surface of the unidirectional silicon steel sheet not only improves the appearance of the product, but also provides the necessary glabellar resistance between the steel sheets. It also plays an important role in terms of magnetic properties, reducing product iron loss due to the tensile stress that acts between them. This forsterite film is usually produced by the following method. First, a material for unidirectional silicon steel containing about 3 to 4% by weight of silicon is cold-rolled once or twice or more with intermediate annealing to the final thickness, and then rolled in wet hydrogen to a 700 to 90%
Decarburization annealing is performed in the range of 00°C, and at the same time an oxide film containing SiO2 is formed on the surface of the steel sheet. Next, a slurry-like annealing separator containing MgO as a main component is applied to the surface of the steel sheet, then wound into a coil and subjected to final annealing. The MgO-5iO1-based solid phase reaction that occurs during this process is used to convert forsterite ( MgzSi04) is formed. However, the properties of the forsterite film produced at this time depend on the properties of the decarboxylated film, the type of magnesia, the amount and properties of trace additives to the magnesia powder, or the atmosphere during final annealing, and are affected by mechanical and Much research has been conducted on methods for forming forsterite films with excellent magnetic properties. For example, according to Japanese Patent Publication No. 51-12451, adhesion and
It has been reported that a forsterite film with excellent uniformity can be obtained. Furthermore, JP-A No. 54-66935 discloses that in order to obtain a forsterite film with good adhesion because it is composed of forsterite particles with a small average particle size, the amount of CaO and water in magnesia powder is appropriately controlled. ing. Further, JP-A-55-58331 discloses a method for obtaining a good forsterite film by limiting the activity of magnesia used. What these methods have in common is that they all propose improvements to annealing separators whose main component is magnesia.
Although many of these methods are recognized to be effective, from an industrial standpoint, they often lead to high costs and are difficult to control the process. Furthermore, a more fundamental problem is that MgO-5 on the surface of the steel sheet
i (When forming a forsterite film by h-based solid-phase reaction, even if only the annealing separator, that is, MgO side is unilaterally specified in this way, there is a limit to the improvement in the properties of the resulting forsterite film. For example, the steel plate tension of the forsterite film obtained by such a method is about 400 g/- at most, and in the actual process, as disclosed in Japanese Patent Publication No. 53-28375, forsterite film is It is necessary to further improve the steel sheet tension by applying a secondary coating mainly composed of colloidal silica etc. on top of the film.On the other hand, as a method for regulating the atmosphere during finish high-temperature annealing, Japanese Patent Application Laid-Open No. 116998/1983 discloses , 55-1107
Examples include the inert neutral gas passage method for iron and iron oxides shown in Japanese Patent No. 26, and the dew point control method shown in Japanese Patent Application Laid-Open No. 53-5800. These methods were mainly proposed to solve the problems of the forsterite film forming method in the method for manufacturing unidirectional silicon steel sheets with high magnetic flux density, as disclosed in Japanese Patent Application Laid-open No. 49-61019. That is, JP-A-49-
The method disclosed in Publication No. 61019 requires heating at a constant temperature of 800 to 920"C for 10 to 100 hours during final finish annealing, but during this time, the iron oxide in the oxide scale is It was found that significant defects in the forsterite film occurred when an atmosphere of
Publication No. 0726). In addition, after maintaining the constant temperature between 800 and 920 degrees Celsius, when the temperature is raised to 1,150 to 1,250 degrees Celsius, the atmosphere is hydrogen gas, the dew point at that time is in the range of -20 to +20 degrees Celsius, and the average dew point thereafter is +10 degrees Celsius. JP-A-53-5800 discloses a method of reducing the average grain size of forsterite to 0.7 nm or less by lowering the temperature to 0.7 nm or less. The former proposal is to ensure an appropriate amount of Si0g on the steel plate side during the MMgO-5in reaction, and the latter proposal is to control the generation of forsterite grains at the start of the reaction and the subsequent grain growth by controlling the oxygen partial pressure of the atmosphere. That is. All of these methods were proposed on the premise of final annealing, which is characterized by constant temperature maintenance at a constant temperature between 800 and 920'C, as shown in Japanese Patent Application Laid-open No. 49-61019. It is a method of forming
It cannot be said that this is necessarily general to other finish annealing cycles. Furthermore, even if the average crystal grain size of the obtained forsterite film is 0.7μ or less, the bending adhesion of the film is about 10-1 at the minimum peel radius, and it cannot be said that sufficient adhesion is necessarily ensured. Moreover, in this method, the tension that the coating imparts to the steel sheet is insufficient, and a secondary coating containing colloidal silica as a main component is often required, leading to an increase in manufacturing costs. All of the above techniques for regulating the external atmosphere during final high-temperature annealing describe the effect of controlling the oxygen potential to be slightly higher than the supply atmosphere, but the conditions differ slightly. This is probably because (when steel plates are annealed in a coiled state, it is extremely difficult to control the atmosphere in the gap between the steel plates by introducing an external annealing atmosphere; This is thought to be because the appearance of the appropriate annealing atmosphere differs due to differences in the application density of the separating agent, etc. (Problems to be Solved by the Invention) The purpose of the present invention is to create an external annealing atmosphere with a narrow gap between the steel sheets. To provide a method for producing a unidirectional silicon steel sheet that makes it possible to control the oxygen potential to be suitable for forming a forsterite film even during finishing high-temperature annealing in a coiled state in which it is difficult for oxygen to penetrate to the surface of the steel sheet. According to the present invention, a forsterite film with a defect-free appearance, good adhesion, and high film tension can be uniformly obtained over the entire length and width of the coil. (Means for Solving the Problem) This invention The feature of the invention is that a Ca compound containing an oxygen element is added to an annealing separator containing MgO as a main component per a certain surface area of the steel sheet.
0.04 to 0.35 g/rd as O content, further adding a compound containing S in an amount such that the S equivalent in the S compound is 0.4 to 1.4 times the Ca equivalent, CaO+
[0] generated by the reaction of S-+CaS + (0)
], it is possible to accurately control the oxygen potential in the steel plate gap. The effects of combined addition of a Ca compound and an S compound will be described below using embodiments of the present invention as examples. Cj 0.047%, Si: 3.25%, Mn in weight%
=0.13%, S: 0.007%, acid soluble Aj: 0.
After heating the slab containing 0.030%, T, N: 0.0078%, balance Fe and unavoidable impurities to 1200°C, 2. Hot-rolled plate with Ovn thickness, 1100℃ x 2s
In, cold rolled to 0.20mm thickness, 850°C
Decarburization annealing was carried out in wet hydrogen for 90 seconds at
Coat og/%, wind up into a coil after drying, N275
%+H2 25% atmosphere to 1200°C, 1
Finish annealing was performed at 1200°C for 20 hours at Itloo%. The presence or absence of film defects in this product (dot-shaped missing parts in the forsterite part), the film tension determined from the bending of the plate when the forsterite insulating film on one side of the product was removed with acid, and the About 6CIX30
Cut out many C11 veneers Bs=1.93Tes l
Figure 1 shows the iron loss measured for item a. As shown in Figure 1, if the amount of CaO added is too small, defects in the film will occur, and if it is too large, the film tension will be large;
If the film becomes too thick, iron loss will worsen. It is also found that if the S content is too low, defects will occur in the missing parts of the film, and if it is too high, the film tension will be weak and the iron loss will be poor. The present inventors believe that the reason for the formation of a forsterite film with no film defects and a high film tension due to the combination of appropriate addition amounts of CaO and S is CaO+S→cas(0).
This was thought to be due to the appropriate supply of oxygen potential through the reaction. According to thermal analysis, this reaction

[0] Release is approximately 9
It turns out that it starts at 20°C. On the other hand, forsterite film formation (2MgO+5iOz→2 MgO・5
Since t(h) is carried out at approximately 950 to 1120°C, it corresponds to the above (0) after the start of release, and promotes the formation of forsterite film, which is conventionally said, such as forming and supplying Stow, and adding MgO and 5t(h). Figure 2 shows that the same material as in Figure 1 was treated in the same process, and MgO + 3% Tl (h + 5% ferromanganese nitride) was added as an annealing separator. % of CaO and various S amounts were applied at 10 g/rrf (total on both sides), the film tension, presence or absence of film missing parts, and B a = 1
．． The results of FIG. 1 are also shown for the iron loss in the 93 Te5la region. From FIG. 2, the S/Ca equivalent is 0, 4 to 1.
It can be seen that the iron loss is good within the range of 4 times, and there is no occurrence of film defects. Next, implementation of the present invention Jl! Explain the situation. The molten steel used in the present invention can be obtained using a converter, an electric furnace, etc., and any method of molten steel may be used. As a component, Si constituting SiO□ is necessary for forming a forsterite film. The amount is not particularly specified, but if it exceeds 4.5%, cracking during cold rolling becomes significant, so it is recommended that it be 4.5% or less, or 1.5% or less.
If it is less than 1.5%, the crystal orientation will be destroyed due to α→T transformation during final high-temperature annealing, so 1.5% or more is desirable. In the present invention, MnS and A are used as inhibitors necessary for secondary recrystallization.
Although it is possible to use AjN, (Aj, 5t)N, etc., it is possible to use AjN, (Aj, 5t), which can produce high magnetic flux density materials.
N is desirable. Regarding MnS, when increasing the S content in steel,
It is difficult to use with high Si materials and thin products because linear secondary recrystallization defects occur. In particular, in the present invention, since CaO added to the annealing separator reacts with S in the steel, an effect different from the intention of the present invention appears. For these reasons, it is preferable for the material of the present invention to have a small amount of S in the steel, and 0.012% or less satisfies the above conditions. The above-mentioned molten steel is made into a hot-rolled plate by hot rolling after passing through a casting slab, or into a cast plate by directly casting into a thin layer. These steel plates are finished to their final thickness through one or two cold rolling processes with intermediate annealing in between. The sheet cold-rolled in this manner is then decarburized annealed in warm hydrogen, and during the annealing, an oxide film containing Si islands is formed on the surface of the steel sheet. After decarburization annealing, an annealing separator containing MgO as a main component is applied to the surface of the steel sheet to prevent seizure during final high-temperature annealing and to form a forsterite-based insulating film, and the steel sheet is dried and wound into a coil. The feature of the present invention is that the oxygen potential control in the gap between the steel sheets in the coiled state is performed using CaQ+S.
→Released by CaS+(0) reaction

It lies in what we do with [0]. Ca compounds include CaO, Ca(OH
)z, CaCO5, sulfate group Ca compound, nitrate group Ca
There are organic compounds, Ca compounds, CaO, Ca(O
H)z, The latter three other than CaCO5 decompose during finishing high temperature annealing and generate large amounts of C, N, and S, which have a negative effect on secondary recrystallization and film formation, so it is difficult to use them. However, these Ca compounds Also, carbon is released by thermal decomposition during the drying process after application.
, N, and S can be removed. Note that the remaining forms at this time are substantially CaO and Ca(OH)t. Considering this addition process and the unit price of Ca compounds, the only Ca sources that can be used are CaO, C
a(OH)z, CaCO3. CaO is optimal because its reaction with S is approximately within the forsterite formation temperature range. Since Ca (OH) t has a decomposition temperature of 580°C, it decomposes when the temperature is raised during final high-temperature annealing, and becomes CaO above that temperature, so it has the same effect as CaO.
Since the decomposition temperature of CaC0z is 898 °C, such high temperature treatment is impossible in the drying process of the annealing separator.
The CaC01 is brought to the final high temperature annealing process. After decomposition, it is thought that the effect of CaO and the influence of CO8 appear, but the film properties are slightly worse than in the case of CaO alone. Regarding S compounds, a powder of simple S is optimal because it is cheap and does not introduce other constituent elements, but sulfurized metals such as FeS and sulfated metals such as FeSO4 are also effective. . The appropriate amount of Ca compound added is the optimum amount for film formation.

In order to supply [0], the surface area of the steel sheet should be 0.04 to 0.35 g/rrf in terms of CaO. If it is less than 0.04g/rr1, there is no addition effect, and 0.35
If you cross g/bo

[0] becomes excessive, the forsterite film becomes too thick, and the iron quality deteriorates. This coating amount is hardly affected by the thickness of the steel sheet, but if the winding force of the steel sheet is large, less is better. The minimum amount of annealing separator necessary to prevent seizure of a steel plate is about 4 g/rd, and even if it is applied in excess of 12 g/%, MgO remains unreacted and is wasteful. Therefore 4-1
Any CaO addition method that achieves the above CaO amount G within a coating amount range of 2 g/ml may be used. The optimal method is to carry out the annealing in an external annealing atmosphere during final high-temperature annealing that is almost in equilibrium with the oxygen partial pressure determined by the applied amount, in a so-called ``charcoal-burning'' state.The amount of S added is affected by the amount of S in the steel. If the S content in the steel is large, it is better to keep the amount of S added within a small range.Subsequently, finish high-temperature annealing is performed.The purpose of this process is secondary recrystallization, forsterite film formation, and purification.
It is usually carried out at 1100"C or more for 5 hours in hydrogen or a mixed atmosphere containing hydrogen. In addition to the above-mentioned embodiments, the present invention can easily exhibit the effects of the present invention in a range where the S content in the steel is low. As an inhibitor for secondary recrystallization, it is better to secure (A#, 5i) N by nitriding treatment at any stage from decarburization annealing to before the start of secondary recrystallization in final high-temperature annealing. (Example) The present invention will be explained based on Examples. (Example 1) C: 0.048%, Si: 3.27%, Mn in weight%
: 0.10%, S: O, OO7%, acid soluble Aj
: 0.029%, T, N: 0.0080%, balance containing Fe and unavoidable impurities.
After heating to "C", it is made into a 2.0 m thick hot-rolled plate and heated at 1100°.
CX2m1n was annealed, cold-rolled to a plate thickness of 0.20 mm, decarburized in wet hydrogen at 850° CX for 90 seconds, and (8) (MgO + 3% TiO, +
5% ferromanganese nitride + 1, 2% CaO + 0.7% S
) and (B) (MgO + 3% Ti01 + 5% ferromanganese nitride + 3% CaO + 0.7% S) were applied at 8 g and 13 g per sheet surface area (total on both sides), and after drying, wound into a coil. Heat up to 1200°C in an atmosphere of N275% + H225%, and reduce the temperature to 1200°C at nztoo%.
Finishing high temperature annealing was performed at 00°C for 20 hours. The film properties and magnetic properties of this product are shown in Table 1. The S equivalent/Ca equivalent in case (A) corresponds to 1.0, and that in case (B) corresponds to 0.4. As can be seen from Table 1, when the amount of CaO in the range of the present invention is included, both the film properties and magnetic properties are good, but 0.39
When the amount of OCaO is 0 g/n1, the film properties are the best, but the magnetic properties are poor. This is because when the amount of CaO increases, the film becomes too thick. (Example 2) C: 0.048%, Si: 3.27%, Mn in weight%
20.10%, S: 0. OO7%, acid soluble IV
: 0.029%, T, N: 0.0080%, balance containing Fe and unavoidable impurities.
After heating to ℃, plate thickness 2.3 yra, 2.0 mg+, 1
．． 8mm thick hot rolled sheet, 2.3mm thick hot rolled sheet is 0
．． 30m5+ thickness, 2.0m thick hot rolled plate is 0.23f
A 1.8 m thick hot rolled plate is cold rolled to 0.20 m thick, and a 0.30 mm thick cold rolled plate is rolled at 850°C for 120 s.
EC, 0.23mm thick cold rolled plate for 100sec, 0
．． A cold-rolled sheet with a thickness of 20 mm was decarburized and annealed in wet hydrogen for 90 seconds, and (MgO + 3% Ti0t + 5
% ferromanganese nitride + 1.2% CaO + 0.7% S)
Coated at 10 g/% (total on both sides), wound up into a coil after drying, and heated at 1200 g/% in an atmosphere of NZ75% + H225%.
Heat up to °C, 1200°C x 20h at 100% Hz
Finishing high temperature annealing of r was performed. The film properties and magnetic properties of this product are shown in Table 2. As can be seen from Table 2, each plate thickness was good with no film missing parts, and the magnetic properties were excellent commensurate with the plate thickness. It should be noted that the tension decreases as the plate thickness increases, but this decrease was calculated because the thickness of the base metal increases while the coating thickness remains approximately constant. (Example 3) For the same cold rolled sheet as in Example 1, 850°C x 90se
Decarburization annealing was performed in wet hydrogen at step c, and (Mg
O + 3% rtoz + 5% ferromanganese nitride + 0.5%
10g (total of both sides) of CaO, Ca(OH)t, and CaCO5 added in the prescribed amounts shown in Table 3 is applied to S), dried, wound into a coil, and coated with N875%.
Heat up to 1200℃ in +H225% atmosphere, Hz1
Final high temperature annealing was performed at 1200° C. for 20 hours at 0.00%. The film properties and magnetic properties of this product are shown in Table 3. Note that the amount of CaO in any of these annealing separators corresponds to 0.2 g/rrf. As can be seen from Table 3, Ca(OH)x, CaCO5
As with CaO, both film properties and magnetic properties are good. (Example 4) For the same cold-rolled sheet as in Example 1, 850°C x 90se
Decarburization annealing was performed in wet hydrogen at step c, and (Mg
O + 3% Ti01 + 5% ferromanganese nitride) and CaO
The predetermined amounts of S, FeS, and S shown in Table 4 were added to the tog/po (total of both sides), dried, wound into a coil, and heated for 12 hours in an atmosphere of 15% Nt and 25% Ht.
Heat up to 00°C, 1200″CX2 at HzlOO%
Finishing high temperature annealing was performed for 0 hr. The film properties and magnetic properties of this product are shown in Table 4. Note that 1.4% FeS corresponds to 0.5% S. As can be seen from Table 4, the annealing separator B, which contains less CaO and S and less SCaO, has missing film parts.
Tension is low and iron loss is also not good. (Effects of the Invention) As described in detail above, the present invention provides oxygen suitable for the formation of a forsterite film even in finish annealing in a coiled state where the gap between the steel plates is narrow and the external annealing atmosphere is difficult to penetrate to the surface of the steel plate. The purpose is to provide a method for manufacturing unidirectional silicon steel sheets that enables control over the potential, whereby CaO and S in the annealing separator react with each other.

[0]
It is possible to optimally control the oxygen potential in the steel plate gap. According to the present invention, a unidirectional silicon steel plate having good coating properties over the entire length and width of the coil can be obtained.

[Brief explanation of drawings]

Figure 1 shows C: 0.047%, Si: 3.25 in weight%.
%, Mn: o, 13%, S: 0.007%,
Acid soluble M: 0.030%, T, N j 0.007
After heating the slab containing 8% Fe and unavoidable impurities to 1200°C, it was made into a 2.0 mm thick hot-rolled plate, annealed to 1100"C x 2m1n, and 0.20 m
It was cold-rolled to a thickness of a, decarburized in wet hydrogen at 850° (:
A mixture of 0z+5% ferromanganese nitride with appropriate amounts of CaO and S added is applied by Log/rrf, and after drying, it is wound into a coil shape and N! 75% 12 in an atmosphere of H225%
Heat up to 00"C, 1200"CX2 at HzlOO%
When finishing high-temperature annealing was performed for 0 hr, the presence or absence of film defects (dot-shaped missing parts of forsterite parts), film tension, and iron loss in the B s-1,93Te5la part were calculated using CaO
It is shown in terms of the relationship between the addition ratio of and S. Figure 2 shows 10g of the same material as in Figure 1 treated in the same process, with MgO + 3% TiOz + added as an annealing separator, 2% CaO added to 5% ferromanganese nitride, and the amount of S varied. /rrf (total of both sides) Film tension when applied, presence or absence of film defects (point-like missing parts of forsterite part), and B, -1,93Tes 1 a
The iron loss of the portion is shown in relation to S equivalent/Ca equivalent. 2nd vR 5 equivalent procedure amendment (voluntary) May 29, 1 year

Claims (1)

[Claims] A silicon steel strip that has been cold-rolled to a desired final thickness is decarburized and annealed to generate subscales containing SiO_2 on its surface, then an annealing separator containing MgO as a main component is applied, and then it is wound up into strips. In a method for manufacturing a grain-oriented silicon steel sheet in which a coil is formed and final high-temperature annealing is performed to form forsterite, the annealing separator is a Ca compound containing an oxygen element and a compound containing S.
4 to 1.4 times the amount is added, and the CaO content is 0.04 to 0.35 g/m^2 on the strip surface.
A method for producing a unidirectional silicon steel sheet which forms a good forsterite insulating film in a coil state, the method comprising controlling the oxygen potential in the gap between the steel sheets in a strip coil by applying the coating in such a manner that the coating is applied as follows.