JPH0744097B2 - Method for forming insulating film for electromagnetic steel sheet without seizing of steel sheet during stress relief annealing - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an insulating film treating agent for grain-oriented electrical steel sheets, and in particular, a steel sheet formed by fusion of a surface film during stress relief annealing after forming during the manufacture of a wound core. The present invention relates to a method for manufacturing an electrical steel sheet having an insulating film that is free from seizure and has good film adhesion.

<Prior art> Grain-oriented electrical steel sheets, which are generally used as iron core materials for electric motors, transformers, etc., are slit into a desired width and then cut → wound → pressed by a winding type iron core forming machine such as a progressive type or a trunco machine type. Then 800-8
Annealing at 50 ℃ in a continuous furnace or box-type furnace to eliminate work strain and improve magnetic properties.

If seizing of the steel sheets occurs due to the strain relief annealing at this time, conduction between the steel sheets occurs, deterioration of insulation properties of the insulating coating due to seizure, reduction of coating tension, etc., and deterioration of transformer iron loss. In the case of seizure, a great deal of labor is required to separate the steel sheets during a winding operation called lacing after strain relief annealing, which causes a serious problem in terms of workability.

Therefore, it has been conventionally desired to develop a coating treatment agent that does not cause seizure as a seizure prevention measure in stress relief annealing.

As the insulating coating used for the grain-oriented electrical steel sheet, a coating mainly composed of a compound having a small thermal expansion is generally used in order to improve core loss, magnetostriction characteristics and insulating properties.

For example, JP-B-53-28375 discloses a colloidal silica-aluminum phosphate system for improving iron loss and magnetostriction.
In 79442, a colloidal silica-magnesium phosphate coating is disclosed as a method for improving magnetostriction.

However, when a steel sheet coated with these phosphate-based coating agents and baked is used in the manufacture of wound cores, high pressure of several tens of kg / cm ² to 100 kg / cm ² or more is applied during press forming after winding. Therefore, there is a problem that when the strain relief annealing is performed at a high temperature of 800 to 850 ° C., the above-mentioned problems such as magnetic defects and workability defects are easily caused by baking.

Further, there has been a demand for improvement of the problem of working environment due to generation of film dust during the racing work due to the deterioration of film adhesion due to the erosion of the glass film by the insulating film treating agent during stress relief annealing.

<Problems to be Solved by the Invention> An object of the present invention is to provide effective improvement in seizure property and film adhesion of a grain-oriented electrical steel sheet during stress relief annealing.

<Means for Solving the Problem> The inventors of the present invention have studied the conditions of the components constituting the phosphate in the phosphate-colloidal silica-chromium compound-based insulating film treatment agent, and in particular the phosphate. It was found that the oxide / hydroxide / H ₃ PO ₄ ratio in the production of Al has a very important effect on the seizure phenomenon of the film and the decrease in adhesion during stress relief annealing.

That is, as a phosphoric acid that is generally manufactured and marketed, what is called a diphosphate in calculation,
For example, in the case of aluminum phosphate, the theoretical formula is Al ₂ O ₃ + 6H ₃
PO ₄ → 2Al (H ₂ PO ₄ ) ₃ + 3H ₂ O having an aluminum diphosphate composition and an Al ₂ O ₃ / H ₃ PO ₄ molar ratio of 0.16 composition. In the case of Mg phosphate, In theory, MgO + 2H ₃ PO ₄ → Mg (H ₂ P
O ₄ ) ₂ + H ₂ O with a heavy phosphoric acid composition, MgO / H ₃ PO ₄
Has a molar ratio of 0.50 composition. However, these phosphates are composed of not only theoretical compounds but also phosphate compounds having other structures, free H ₃ PO _{4, and the} like. In addition, since the stability of the constituent compounds in the solution of these phosphates varies depending on the concentration, the stability is generally 50% as a solution of aluminum phosphate Al ₂ O ₃ / H ₃
PO ₄ molar ratio 0.16 to 0.17, magnesium phosphate 50%
A solution MgO / H ₃ PO _{4 having} a molar ratio of about 0.4 to 0.5 is commercially available.

The present inventors have made extensive studies on the above-mentioned molar ratios constituting these phosphates, and as a result, in the case of aluminum phosphate, the molar ratio of the phosphate in the coating treatment agent is Al ₂ O ₃ / H ₃ PO.
Molar ratio of ₄ is 0.17 or more, in case of divalent metal phosphate M ⁺⁺ O / H ₃
By setting the molar ratio of PO ₄ to 0.5 or more, the seizure phenomenon during strain relief annealing was remarkably improved, and the adhesion of the coating was not deteriorated.

<Structure / Operation of Invention> In the colloidal silica-phosphate-chromium compound-based insulating film treating agent of the present invention, the molar ratio of the phosphate is M ⁺⁺⁺ ₂ O ₃ / H ₃ PO ₄
By using 0.17, M ⁺⁺ O / H ₃ PO ₄ 0.5, compared to the case of using a phosphate that is conventionally generally manufactured, when molding and annealing the wound core, there is no seizure, An insulating film treatment agent with excellent film adhesion and excellent magnetic and insulating properties.

Next, an explanation will be given based on experimental data.

C: 0.072, Si: 3.28, Mn: 0.075, S: 0.026, acid-soluble Al in weight%:
A silicon steel slab containing 0.029, N: 0.0080 is hot-rolled → annealed → cold-rolled by a known method to a final sheet thickness of 0.30 mm, and then decarburized and annealed, and then an annealing separator containing MgO as a main component is applied. , 1200 ℃
Final finishing annealing was performed for 20 hours.

By this finish annealing, a glass film (forsterite film) was formed on the surface of the steel sheet by the reaction between the annealing separator and the oxide layer mainly composed of SiO ₂ formed by decarburization annealing.
After that, the excess annealing separator on the surface of the steel sheet was removed by washing with water and light pickling to obtain a test material. 20% colloidal silica on this steel plate
As a 50% aluminum phosphate solution for 100 parts by volume:
Al ₂ O ₃ / H ₃ PO ₄ (molar ratio) = 0.16 ,: molar ratio = 0.20 each by volume of 60 parts by volume and chromic anhydride by 6 parts by weight, a solution after baking is 6 g / m ² And apply it to 800
Heat flattening treatment and baking treatment were performed in a continuous annealing line at 30 ° C for 30 ″.

Samples were cut out from these coils, laminated as shown in FIG. 1 (A), tightened with tightening bolts with a compressive force of 100 kg / cm ² , and then annealed at 850 ° C. × 4 ^H.

As shown in Fig. 1 (B), the seizure state of the steel sheet after annealing was measured by the spring measurement of the peeling load of each steel sheet, and the bending test result and the magnetic measurement of the steel sheet 200 mmφ after annealing were performed. The results are shown in Table 1.

The peeling load after annealing was 80 g / cm ^{2 on} average when the Al ₂ O ₃ / H ₃ PO ₄ molar ratio was 0.16, while the Al ₂ O ₃ / H ₃ PO ₄ molar ratio was 0.20. In this case, there was almost no seizure at 5 g / cm ^2, and there was a tendency for a marked improvement. Also, in the bending peeling test with 20 mmφ, when the Al ₂ O ₃ / H ₃ PO ₄ molar ratio was 0.16, some peeling occurred, whereas when the Al ₂ O ₃ / H ₃ PO ₄ molar ratio was 0.20, there was no peeling. There was no

Regarding the magnetic properties, the Al ₂ O ₃ / H ₃ PO ₄ molar ratio of 0.20 did not change at all during annealing, whereas the molar ratio of 0.16 showed a deterioration of iron loss of about 3%.

The reason why the improvement effect is caused by increasing the molar ratio is that the relative decrease of H ₃ PO ₄ reduces the free phosphate content in the phosphate and the ratio of unstable phosphate. It is speculated that this is due to the decrease in seizure due to ▲ PO ^--- ₄ ▼, etc. separated from the film components during stress relief annealing at high temperature. As a result, it is considered that the iron loss is not deteriorated due to the deterioration of the coating. Similarly, those with an increased molar ratio do not cause an erosion reaction of the glass film during annealing due to free phosphoric acid, etc.
Adhesion will also be improved.

Next, the composition of the treatment agent applied to the grain-oriented electrical steel sheet after finish annealing in the present invention to form an insulating film will be described.

Al relative to 100 parts by weight of colloidal silica as SiO ₂ in the present invention, one phosphate such as Mg or the like or two or more of 100 and 300
Is a coating treatment agent comprising 10 to 50 parts by weight of CrO ₃ as a chromium compound, and the composition of the phosphate used in this case is a molar ratio of ▲ M ⁺³ ₂ ▼ O ₃ / H ₃ PO ₄ ≧ 0.17, M ⁺² O / H ₃ PO ₄ ≧ 0.
The composition of the phosphate and the compounding ratio used are limited so as to be 50.

The reasons for these limitations will be described.

In calculation, the molar ratio of the phosphate used as the heavy phosphate is 0.17 or more in the case of aluminum phosphate as described above,
In the case of Mg divalent metal salt, 0.50 or more is preferable. This is because the seizure phenomenon and the like during strain relief annealing are remarkably improved when the above molar ratios are exceeded. Preferably, it is 0.18 or more in the case of aluminum phosphate and 0.55 or more in the case of magnesium phosphate. On the other hand, the smaller the molar ratio, the more markedly the seizure becomes and the larger the film peeling after annealing.

Colloidal silica reduces the coefficient of thermal expansion of the film, imparts tension to the steel sheet during film baking treatment, improves iron loss, and forms a film that is smooth and has excellent insulation due to the dense film forming ability. It is effective for If the compounding ratio is out of the above range, the effect of tension of the coating becomes extremely weak and the improvement of iron loss becomes small.

Chromic anhydride or a chromic acid compound forms a stable compound such as CrPO ₄ by the reaction with the phosphoric acid content in the film, and has the effect of preventing the hygroscopicity of the film. Compounding ratio is heavy phosphate
10 to 50 parts by weight as CrO ₃ has this effect against 100 to 300 parts by weight, but if it is less than this, the effect of preventing stickiness is weak,
Above this level, the phenomenon of stickiness due to Cr ^+6, which is rather bad, is observed.

The insulating film treating agent is applied to the steel sheet after finish annealing, and the baking temperature is 350 ° C or higher. Below this temperature Cr ⁺⁶
Is limited because the progress of the reduction reaction from Cr to Cr ⁺³ is incomplete and hygroscopic.

Next, examples will be described.

<Example 1> Samples were cut adjacent to each other from the same coil after the final finishing annealing of grain-oriented electrical steel sheet (thickness 0.3 mm), and the annealing separator on the surface was removed by washing with water and light pickling to obtain a test material. This glass film is also used as a phosphate on a steel sheet, and a treatment liquid prepared by changing the molar ratio of aluminum phosphate and magnesium phosphate at the compounding ratio shown in Table 2 is used at 5 g / side of the steel sheet. After coating at m ^2, it was dried and baked in a continuous furnace at 800 ° C for 30 ″. A sample was cut from this steel plate and weighed 60 kg.
After tightening with a tightening pressure of / cm ² , bolt and tighten at 850 ° C for 4 hours.
Was annealed.

Table 2 shows the peeling load of each steel sheet after annealing and the evaluation results of film adhesion by 20 mmφ bending. When both aluminum phosphate and magnesium phosphate had a high molar ratio, there was almost no seizure due to annealing and no deterioration in film adhesion was observed. There was a tendency that the coating adhesion after annealing was significantly reduced.

<Effects of the Invention> Since the present invention is configured and operated as described above, seizure does not occur during strain relief annealing performed after molding at the time of manufacturing a wound core from a grain-oriented electrical steel sheet, and It is possible to obtain a grain-oriented electrical steel sheet having excellent film adhesion, which has a great industrial effect.

[Brief description of drawings]

FIG. 1 (A) is a diagram showing a laminated state of the sample at the time of stress relief annealing of the sample in the example of the method for forming a film for electromagnetic steel sheets of the present invention, and FIG. It is a figure which shows the aspect at the time of investigating the baking state between layers.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-53-110931 (JP, A) JP-A-52-25296 (JP, A) JP-A-48-39338 (JP, A)

Claims (1)

[Claims] 1. A with respect to 100 parts by weight of colloidal silica as SiO _2, Al, 1 type of phosphate selected from among Mg or 2
In an insulating film treating agent comprising 100 to 300 parts by weight of one or more kinds and 10 to 50 parts by weight of one or two or more chromium compounds as CrO ₃ , the molar ratio of the phosphate (the number of moles of oxide / H ₃ P
O ₄ mole number) is 0.17 or more for Al and 0.5 or more for Mg. A coating treatment agent is applied on the annealed electrical steel sheet and baked at 350 ° C or more. A method for forming an insulating film on a grain-oriented electrical steel sheet without sticking.