JPS58144429A - Manufacture of unidirectional silicon steel sheet free from deterioration of iron loss - Google Patents

Abstract

PURPOSE:To manufacture the unidirectional silicon steel sheet whose iron loss is not deteriorated by strain relief annealing, by reducing the total value of S and Se contents in a steel sheet including a forsterite film by acid-pickling before coating it with a phosphate film. CONSTITUTION:An S or Se-contg. silicon steel sheet blank is hot-rolled and then cold-rolled in accompaniment with intermediate annealing into a cold-rolled steel sheet having final thickness. Thereafter, the cold-rolled steel sheet is decarburization-annealed, MgO is applied to the surface of the steel sheet, and then the steel sheet is finally finish annealed. in succession, the total value of analyzed S and Se contents in the steel sheet including a forsterite film formed on its surface is controlled below 0.01% by the step of acid-pickling, and a phosphate film is formed on the forsterite film by coating. The coated steel sheet is then worked and strain-relief annealed, to manufacture the unidirectional silicon steel sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a unidirectional silicon steel sheet without deterioration in iron loss, and particularly relates to a method of manufacturing a unidirectional silicon steel sheet without deterioration in iron loss due to strain relief annealing.

Unidirectional silicon steel sheets are mainly used as iron cores for transformers and other electrical equipment, and are required to have good magnetic properties such as magnetic flux density, iron loss properties, and magnetostriction properties.

A conventional method for manufacturing a unidirectional silicon steel sheet will be explained.

In addition to S or Se added as an inhibitor, a siliceous steel ingot containing 40% or less of Si is hot-rolled, annealed and cold-rolled repeatedly to obtain a cold-rolled steel sheet with a final thickness of ji1', and the cold-rolled steel sheet is removed. Charcoal annealing, then magnesia (M
gO) is applied to prevent the steel plate from being burnt during final annealing. This MgO-coated steel sheet is subjected to the most important final annealing process, also called box annealing, which consists of a secondary recrystallization stage and a final purification stage where the temperature is raised to around 1200°C. It will be implemented for the following three purposes.

The purpose of Ml is for secondary recrystallization, and the precipitated phases MnS and MnSe finely dispersed in the steel after decarburization annealing act as an inhibitor to suppress normal grain growth, which is usually referred to as Goss orientation (110 )[:001] becomes a crystal structure, resulting in a material that exhibits excellent magnetic properties in the rolling direction.

The second purpose is to purify the material. MnS and MnSe, which act as inhibitors as described above, will deteriorate the magnetic properties, especially the iron loss properties, if they remain in the steel even after the final product is made. In the finishing stage, the temperature was raised to around 1200°C and purification annealing was carried out in hydrogen, and the precipitated phase MnS,
A part of MnSe decomposes and escapes into the gas phase in the form of S and Se, or it concentrates in the forsterite coating or at the interface between the forsterite coating and the steel base in the form of MnS and lMnSe. removed from the steel.

The third purpose is to form a forsterite (2Mg0.Sin, ) film, which is usually called a glass film.

This coating is formed by a solid phase reaction between the S10° subscale formed on the surface of the steel sheet during decarburization annealing and the magnesia applied to prevent seizure in the final annealing process. be.

After final annealing, unreacted magnesia on the surface of the steel sheet is usually washed with water. However, if unreacted magnesia is severely burned, light pickling with phosphoric acid or sulfuric acid is performed to remove it.

After removing magnesia from the surface of the steel plate, a phosphate-based coating treatment solution is applied and baked to form an overcoat insulation coating in order to further increase the insulation resistance between the layers. Phosphate-based coatings include, in addition to the conventionally known magnesium phosphate-based coatings, which have been developed in recent years and are applied to high magnetic flux density grain-oriented silicon steel sheets with a particularly well-aligned crystal texture in the rolling direction. Japanese Patent Publication No. 50-794
42, or JP-A-52-25296. Japanese Unexamined Patent Publication No. 1973-
No. 28,043 discloses a low thermal expansion, tensioned phosphate-based coating consisting of colloidal silica, magnesium or aluminum phosphate, and chromic anhydride.

The unidirectional silicon steel plate coated by the above process is usually sheared into a predetermined size and used as a stacked core or wound core for a power transformer core. In the process of assembling the core of a transformer, mechanical strain is inevitably introduced into the steel plate, which deteriorates the magnetic properties, especially the iron loss properties. In order to remove this mechanical strain, strain relief annealing is usually performed at around 800°C. The material for the stacked core is a single plate, and the material for the wound core is annealed in a coiled state after bending.

However, even if mechanical strain is removed by strain relief annealing, it often happens that iron loss does not recover to the properties of the material before annealing. In particular, it has been recognized that there is significant deterioration in the case of wound cores that are coiled and annealed for long periods of time, and this deterioration is a major reason why the material properties as a transformer cannot be maximized. Loss characteristics are becoming increasingly important from the viewpoint of energy conservation due to the recent rise in energy costs, and deterioration of iron loss due to strain relief annealing has become a very serious problem.

An object of the present invention is to solve the problems of the prior art described above and to provide a method for manufacturing a unidirectional silicon steel sheet without deterioration of core loss due to strain relief annealing.

The gist of the present invention is as follows.

That is, a step of cold rolling a silicon steel sheet material containing S or Se, including hot rolling and intermediate annealing, a step of decarburizing the cold rolled steel sheet and final finish annealing, and a step of decarburizing the cold rolled steel sheet and final finish annealing, and forming a silicon steel sheet material on the surface of the final finished steel sheet. a coating treatment step of forming a phosphate film on the forsterite film;
In the method for producing a unidirectional silicon steel sheet, which comprises the step of processing the coated steel sheet and then subjecting it to strain relief annealing, a forsterite film is applied before forming a phosphate film in the coating treatment step. This is a method for producing a unidirectional silicon steel sheet without iron loss deterioration, characterized by having a pickling step in which the total analysis value of 8 and Se contained in the steel sheet is 0.01% or less.

The present inventors conducted intensive studies to investigate the cause of iron loss deterioration due to strain relief annealing, and found that S and Se, which were removed from the steel during the purification stage during final finish annealing, returned to the steel during strain relief annealing. In addition, the increase in iron loss due to stress relief annealing is limited to cases where a phosphate coating is applied, and is not observed when only an orsterite coating is formed after the final annealing. I found out that there is no.

This figure shows the analysis results of S and Se before and after the final annealing of the plate, and especially the analysis values of the base steel containing a forsterite film (hereinafter simply referred to as "with film").

From Table 1, it can be seen that although the final annealing purifies the S and Se in the steel to a very low level, the film analysis value shows that about 80'% of the S and Se before annealing remain.

Figure 1 shows Si: 2.98%, Mn: 0.06%, S
: 0,005%, Se: 0.018%, sb: o,
o 15% steel ingot is hot rolled and 0.3
A study was conducted on a unidirectional silicon steel plate with a forsterite coating that was cold rolled to a thickness of 0 mm, then subjected to decarburization annealing and final finish annealing.S, Se during strain relief annealing with and without phosphate coating This shows the difference in penetration into steel. In the figure, ○ marks are those that have undergone final finish annealing, Δ marks are those that have been subjected to strain relief annealing in nitrogen at 800°C x 3 hours after final finish annealing, X marks are phosphate-based coatings after final finish annealing, It was strain relief annealed in nitrogen at 800°C for 3 hours. The horizontal axis is the chemical polishing depth (μ) from the surface of the base steel directly under the 7-orsterite coating after the phosphate coating and forsterite coating were removed in 100% NaOH molten salt. The vertical axis is the total analysis value of S and Se measured by fluorescent X-ray for each polished surface.

From Figure 1, it is clear that S and Se penetrate into the steel in the case of the phosphate-based coated material marked with x, and even in the material marked with ○ after final finish annealing, in which 8 and Se do not penetrate into the steel. Near the iron light surface, S and Se are considerably concentrated;
It is shown that this exists at the interface between the base steel and the 7-orsterite film or at the surface layer of the base steel. It is said that 51Se normally exists in the form of MnS and MnSe at or near the interface between the forsterite film and the steel base, so when it invades into steel, it is considerably absorbed in the surface layer of the steel, as shown in Figure 1. S and Se will increase. Furthermore, S
, iron loss deterioration occurs only when Se penetrates into the steel, and B
Materials marked with an x in Figure 1 (I & final annealing phosphate-based coating - iron loss deterioration in the case of strain relief annealing Wl)
. The displayed value was 0.05 W/kg. Figure 1 shows the total analysis value of S + Se, but the individual analysis value with film after annealing 'M, final' is S-0,003'', >o, 5e
-0,017%, and the S and Se of the internal steel were both 0.001% or less.

As shown in Figure 1, the detailed reason why phosphate-based coach (S, 5eO only when there is /) occurs and iron loss increases is unknown, but it is probably due to forsterite. It is assumed that the MnS and Se that exist directly under the coating decompose for some reason when the phosphate coating is present, causing S and Se to infiltrate into the steel.

Next, as mentioned in 8 above, as a result of considering the prevention of SeD penetration into steel, after final annealing and before applying phosphate coating, the analysis value of S or Ss with a film was reduced to 0.01 by pickling.
% or less, it is possible to effectively prevent iron loss deterioration due to strain relief annealing.

Next, the reason why the analytical value of S10Se in pickling was limited to 0.01% or less will be explained. Si:2.8~36
2%, Mn: 0.05-0.07%, S: 0.00
4-0.025%, Se: <0.001-0.0
20%, sb: <α001~0.020% (1
) Ingredients
After cold rolling to the final plate thickness, decarburization annealing and final finish annealing were performed, and then pickling was performed under various pickling conditions to achieve S + Se
We manufactured test materials with different analysis values with a film of
A coating treatment solution consisting of colloidal silica, magnesium phosphate, and chromic acid anhydride disclosed in Japanese Patent No. 79442 was applied and baked. Next, the above sample material was heated to 800°C for 3 hours.
r, iron loss W1 before and after complete failure annealing after fatal annealing in nitrogen
? The change in angle of 15° was investigated, and the relationship with the analysis value of the film after pickling is shown in Figure 2. As is clear from Fig. 2, by reducing the film deposition analysis value to 0.01% or less, it is possible to effectively prevent an increase in iron loss caused by strain relief annealing. The SiSe film deposition analysis value was limited to α old (11)% or less.

The pickling process of the present invention is not limited to the type of acid, concentration, or nutrient content of the pickling bath, but if the pickling conditions are too severe, the forsterite coating itself will be eroded and the adhesion of the coating after coating will be reduced. It is necessary to carry out pickling to the extent that the adhesion of the film does not deteriorate. To achieve the purpose of the present invention, 1 to 20% of phosphoric acid, sulfuric acid,
It is desirable to immerse the steel plate in an acid bath of nitric acid for 3 to 120 seconds. However, the thickness and structure of the forsterite film,
Since the removability of S and Se differs depending on the S and Se content, pickling conditions are not limited to the above pickling conditions, but pickling conditions that can reduce the film-attached analysis values of S and Se to 0.01% or less are selected. Should. While the conventional pickling after final finish annealing is aimed at removing magnesia on the surface of the steel, the pickling of the present invention removes S and Se with film analysis values of 0.0.
1% (managed to prevent iron loss deterioration after strain filling annealing).

Example r12) Two types of Quartzite steel ingots having the chemical compositions shown in Table @2 were hot rolled, then cold rolled to a plate thickness of 0.30 mm, and subjected to decarburization annealing.

Table 2 An annealing separator mainly consisting of MgO was applied to the surface of this steel sheet, final annealing was performed to form a forsterite film on the surface of the steel sheet, and then pickling was performed under the conditions shown in Table 3. Some of the comparative examples omitted pickling, but these steel plates were prepared using colloidal silica disclosed in JP-A No. 62-25296.
Magnesium phosphate and anhydrous chromium were coated with a coating treatment solution to form a 2μ film on one side and heated at 800℃XIM.
Baked in nitrogen system. These coated plates were processed by shearing them into 30mm + x 280mm.
Strain relief annealing was performed at 00° C. for 3 hours in nitrogen. The analysis values of these steel plates after pickling are 8.8, Se and the magnetic flux density is 13t after pickling, processing, and strain relief annealing.

and iron loss W17/6° are also shown in Table 3.

From the results in Table 3, it is clear that in the examples of the present invention in which the film-based analysis values of S and St were reduced to 0.01% or less by pickling, the magnetic properties were not deteriorated by strain relief annealing. On the other hand, the analysis value of Ss with film is 0.01%
In Comparative Examples exceeding 10%, the magnetic properties deteriorate due to strain relief annealing with or without pickling.

As is clear from the above examples, the present invention provides silicon steel sheets with S and Ss film deposition analysis values of 0.0 after final annealing.
By pickling to a concentration of 1% or less, it is possible to produce unidirectional silicon steel sheets that do not suffer from iron loss deterioration due to stress relief annealing, which prevents heat generation inside the core and achieves a major energy-saving effect. It was.

[Brief explanation of the drawing]

Figure 1 is a correlation diagram showing the relationship between the surface depth of a silicon steel plate base metal and the analytical value of S+8e, and Figure 2 shows the change in iron loss of a silicon steel plate due to strain relief annealing (14) and S and Ss after pickling. FIG. 3 is a correlation diagram showing the relationship between the total analysis value with a film and the total analysis value with a film. Agent Takeo Nakaji

Claims (1)

[Claims] (1) A silicon steel sheet material containing S or Se is heated through a hot process, a coating treatment step to form a phosphate film on the forsterite film formed on the surface of the final finished steel sheet, and a coating treatment step to form a phosphate film on the forsterite film formed on the surface of the final finished steel sheet. A method for manufacturing a unidirectional silicon steel sheet comprising the steps of processing a steel sheet and then subjecting it to strain relief annealing, wherein a method of manufacturing a steel sheet containing a 7-orsterite coating before forming a phosphate-based coating in the coating treatment step. A method for producing a unidirectional silicon steel sheet without iron loss deterioration, which includes a pickling process in which the total analysis value of S and Se is 0°01% or less.