JP2647341B2 - Manufacturing method for ultra-low iron loss grain-oriented electrical steel sheets - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a grain-oriented electrical steel sheet having extremely low iron loss. In particular, complete the secondary recrystallization step (finish annealing step) without forming a forsterite (hereinafter, referred to as glass) film on the surface, and then perform magnetic domain refinement, tension coating, etc., and iron loss properties The goal is to improve.

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet is used as a magnetic iron core in many electric appliances. Unidirectional silicon steel sheet
Contains 0.8 to 4.8% of Si and has crystal grains of $ 11
It is a steel sheet highly integrated in the 0 ° <001> direction. Its magnetic properties require high magnetic flux density and low iron loss. In particular, recently, there has been an increasing demand for reduction of iron loss from the viewpoint of energy saving. In order to meet this demand, a technique for subdividing magnetic domains has been developed as a means for reducing iron loss of a grain-oriented silicon steel sheet.

[0003] In the case of a stacked iron core, a method of irradiating a steel beam after finish annealing with a laser beam to apply local minute strain to subdivide magnetic domains to reduce iron loss is disclosed in, for example, JP-A-58-26405. It is disclosed in the gazette. Further, in the case of a wound iron core, a method in which the magnetic domain subdividing effect is not lost even if the core is processed and then subjected to stress release annealing (stress release annealing) is disclosed in
It is disclosed in JP-A-2-8617. Iron loss has been greatly reduced by subdividing magnetic domains by these technical means.

However, observation of the movement of these magnetic domains reveals that some magnetic domains do not move. Therefore, in order to further reduce the iron loss value of the grain-oriented electrical steel sheet, it is necessary to eliminate the pinning effect of the glass coating on the steel sheet surface and the inclusions immediately below the surface, which inhibit the movement of the magnetic domain in conjunction with the magnetic domain refinement. It turned out to be important.

[0005] To this end, it is effective not to form a glass coating on the surface of the steel sheet that hinders the movement of the magnetic domains. As a means for preventing the formation of a glass film by using coarse high-purity alumina as an annealing separator, for example, U.S. Pat. S. Patent 3785882. However, this method cannot eliminate inclusions just below the surface, and the improvement in iron loss is at most 2% in _{W15 / 60.}
It's just

As a method of controlling the inclusions immediately below the surface and achieving a mirror surface of the surface, there is a method of performing chemical polishing or mechanical polishing after finish annealing. However,
Although these methods can process small samples of materials at the laboratory level, it is difficult to control chemical concentration and wastewater treatment in chemical polishing, and wide in mechanical polishing to perform on an industrial scale. It is difficult to smooth a surface having an area on the same basis.

[0007]

SUMMARY OF THE INVENTION The present invention provides an industrial means for producing a low iron loss grain-oriented electrical steel sheet by realizing a mirror surface material having good surface smoothness uniformly on a surface having a large area. With the goal. The present invention provides a method for removing a oxidized film formed during decarburization annealing in finish annealing of a silicon steel sheet, achieving a surface mirror finish at the end of finish annealing, and realizing a grain-oriented electrical steel sheet with low iron loss. It is.

[0008]

DISCLOSURE OF THE INVENTION The present inventors investigated the process of adding various chlorine-containing compounds to an annealing separator to remove an oxide film on the surface of a steel sheet during finish annealing. As a result, it was found that when the compound containing Bi and the metal chloride were added to the annealing separator, the steel sheet surface after the finish annealing became mirror-finished. The iron loss characteristics of these grain-oriented electrical steel sheets are those obtained by removing the glass film by pickling, JP-A-64-62417.
The present invention was found to be lower than that obtained by removing an oxide film using a chloride disclosed in JP-A-2-228481 and JP-A-2-228481, and completed the invention.

The gist of the present invention is that Si: 0.
A silicon steel slab containing 8 to 4.8% is hot rolled, annealed if necessary, and subjected to one cold rolling or intermediate annealing 2
Cold rolling more than once, decarburizing annealing, bismuth chloride or a bismuth compound and a chlorine compound of metal as an annealing separating agent, in the method of manufacturing a grain-oriented electrical steel sheet to apply and dry and finish annealing By setting the reaction start temperature of the product and hydrogen to be 600 ° C. or higher, a steel sheet having good surface smoothness can be realized uniformly over a wide area. Here, the reaction start temperature of chloride and hydrogen is controlled by the atmosphere gas during the finish annealing and the hydration moisture in the annealing separator. Hereinafter, the details will be described.

[0010] The present inventors have added various metal chlorides to the annealing separator and investigated the steel sheet surface during the finish annealing in detail. As a result, when the substance to be added is (1) bismuth chloride, or (2) group A: bismuth alone or a bismuth compound, and group B: metal chloride, when both groups A and B are included. Only after finishing annealing, the mirror finish of the steel plate was realized. Here, specific substances of the groups A and B are as described in claims 2 and 3. Although this phenomenon has not been elucidated in detail, we think as follows.

At the time of finish annealing, after BiCl ₃ is formed by the reaction between the bismuth compound and the metal chloride, BiOCl (bismuth oxychloride) is formed in the presence of H ₂ O. Due to chlorine or hydrochloric acid released when the BiOCl is decomposed at a high temperature, the ground iron adjacent to the surface oxide layer becomes a vapor of FeCl ₂ (ferrous chloride), and the oxide layer and the ground iron are separated. It is presumed that at a high temperature of 1000 ° C. or more, a surface state becomes a mirror state due to diffusion of surface Fe atoms.

In this way, it was confirmed that the surface was mirror-finished with a small number of samples at the laboratory level. Immediately, an experiment for realizing mirror-mirror with a coil having a width of about 1 m was carried out. This resulted in variations in iron loss characteristics. So we think that the cause is BiOC
1 was determined to be due to the difference in the decomposition temperature in the coil width direction. That is, the decomposition reaction in the presence of hydrogen BiOCl, a _{2BiOCl + 3H 2 = 2Bi + 2HCl} + 2H 2 O, since the equilibrium is changed by the amount of moisture in the annealing separator (H ₂ O), the temperature for generating a constant amount of HCl in Is changed.

Therefore, in order to solve this problem, it is necessary to find production conditions which are not affected by the amount of water in the annealing separator. The inventors considered that by increasing the decomposition reaction temperature of BiOCl, the hydration water in the annealing separator was removed as much as possible before the decomposition reaction, and the influence of hydration water on the BiOCl decomposition reaction was considered. . FIG. 1 shows the BiOCl reaction temperature with respect to the oxygen potential of the atmosphere. The oxygen potential was controlled by changing the partial pressure of nitrogen or argon in the atmosphere. From this, it can be seen that when the oxygen potential in the annealing atmosphere is increased, the reaction start temperature increases.

In practice, the oxygen potential is adjusted by (1) controlling the partial pressure of nitrogen or argon and (2) controlling the dew point between plates. However, although the control of the partial pressure of nitrogen or argon in (1) is relatively simple, it is very difficult to accurately control the dew point between the plates (2). Therefore, the control of the inter-plate dew point is performed instead of changing the amount of hydrated water in the annealing separator. Note that the hydrated water amount described here is an amount that decomposes at a temperature of 100 ° C. or more by heating with a hydroxide or the like to release water.

FIG. 2 shows the degree of specularity when the amount of hydrated water in the annealing separator and the partial pressure of nitrogen or argon in the atmosphere are changed. 5% BiOCl in the annealing separator
Has been added. Investigating the degree of specularity, width 80 mm x length 32
When packing a sample of 5 mm with foil at the time of finish annealing, it was divided into a single layer and a triple layer. Here, the reason why the single-pack and triple-pack are separated is to evaluate the difference in the specularity in the width direction of the coil having a width of 1 m with a relatively small sample at the laboratory level. That is, the single pack was evaluated as representing the outer portion in the width direction of the 1 m wide coil, and the triple pack was evaluated as representing the inner portion in the width direction. Both single and triple packs have a mirror surface when the mirror surface is ○ (that is, there is no variation in the specularity in the coil width direction); Indicated by the mark.

From these results, it can be seen that there is an optimum range of hydration water content for each partial pressure of nitrogen or argon. When the partial pressure of nitrogen or argon is high (when the reaction start temperature of BiOCl and hydrogen is high), the range of the optimum hydrated water content is found to be wide. The frame shown in FIG. 2 is the range of the present invention, and the reaction starting temperature of BiOCl and hydrogen at the lower limit of the partial pressure of nitrogen or argon (50%) in this range is about 600 as shown in FIG. ° C.

[0017]

EXAMPLES By weight, C: 0.05%, Si: 3.3%,
Mn: 0.14%, S: 0.008%, Al: 0.02
A slab containing 9% and N: 0.007% was heated at 1150 ° C and hot rolled to obtain a 1.8 mm thick Hot Coil. After annealing at 1120 ° C., it was cold rolled to 0.18 mm,
Decarburization annealing was performed at ℃. And, by weight composition,
₂ O ₃ : 82%, Mg (OH) ₂ : 13%, BiOC
1: An annealing separator (4.0% in terms of hydrated water content) of 5% was applied, and finish annealing was performed at 1200 ° C. for 20 hours. The atmosphere of the finish annealing is as follows: H ₂ 10% -N ₂ 90
%, And the H ₂ 75% -N ₂ 25% by coil B.

Although both the coils A and B were entirely mirror-finished in the width direction, the coil B seemed to have a slightly different mirror surface state. After finish annealing, one coil in the width direction of coils A and B
Cut out into 5 veneer sheets (width 60 mm x length 300 mm)
After subjecting to magnetic domain refinement, strain relief annealing was performed. Table 1 shows the results of the respective magnetic measurements. Iron loss is tension 1.5
It is a value measured by applying kgf / mm ² . It can be seen that the variation in iron loss in the coil width direction is improved by employing the conditions according to the present invention.

[0019]

[Table 1]

[0020]

According to the present invention, a grain-oriented electrical steel sheet having a very low low iron loss can be manufactured by controlling the atmosphere of the annealing separator and the finish annealing.

[Brief description of the drawings]

FIG. 1 is a table showing the reaction temperature of BiOCl and hydrogen with respect to the degree of oxidation of atmosphere gas (P H ₂ O / P H ₂ ).

FIG. 2 is a table for examining the mirror state of the surface when the amount of hydrated water in the atmosphere gas and the annealing separating agent is changed.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kizu Ishibashi 1-1-1, Hibata-cho, Tobata-ku, Kitakyushu City Inside Nippon Steel Corporation Yawata Works

Claims (3)

(57) [Claims] 1. A silicon steel slab containing Si: 0.8-4.8% by weight is hot-rolled, and if necessary, annealed.
The method for producing a grain-oriented electrical steel sheet in which one cold rolling or two or more cold rollings sandwiching intermediate annealing is performed, and after decarburizing annealing, an annealing separator is applied and dried to perform finish annealing, (1) bismuth Using an annealing separator containing chloride, or (2) bismuth alone or a bismuth compound and a metal chlorine compound, the atmosphere during the temperature raising process during the finish annealing is set to 50% or more and 98% or less of nitrogen or argon and the balance of hydrogen. A method for producing an ultra-low iron loss grain-oriented electrical steel sheet, wherein the amount of hydrated water in the annealing separator is 0.5 to 7.0%. 2. A compound of bismuth, one or a mixture of bismuth oxide, bismuth hydroxide, bismuth sulfide, bismuth sulfate, bismuth phosphate, bismuth carbonate, bismuth nitrate, organic acid bismuth and bismuth halide. The method for producing an ultra-low iron loss grain-oriented electrical steel sheet according to claim 1, wherein the steel sheet is used. 3. The ultra-low iron loss grain-oriented electrical steel sheet according to claim 1, wherein one or a mixture of two or more of iron chloride, cobalt chloride and nickel chloride is used as the metal chlorine compound. Manufacturing method.