JPS61190021A - Method for manufacturing unidirectional electrical steel sheet with good magnetism - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a unidirectional electrical steel sheet with excellent magnetism, which is mainly used in electrical equipment such as transformer cores.

(Conventional technology) Due to the recent rise in energy costs, there is a strong demand worldwide for unidirectional electrical steel sheets to have low core loss.In order to achieve such low core loss, a new technology has been specially developed for the manufacturing conditions. Publication No. 56-130454, Japanese Patent Publication No. 57-41
As disclosed in Publication No. 326, etc., steel companies are competing to improve quality by further increasing St, refining magnetic domains, and thinning steel.

(Problems to be solved by the invention) However, the trend toward thinning not only leads to a decrease in work efficiency and higher costs in terms of manufacturing conditions, but also in conventional unidirectional electrical steel sheets, a layer called glass is formed on the surface of the steel sheet. Since the stellite coating is formed at the thickness of the laying line, the thinner the plate thickness is, the greater the influence it has on magnetic deterioration.

In addition, in order to perform secondary recrystallization more effectively than conventionally, S.

Inhibitors such as Mn, ht#Ss, Sb*Sn+Cu, etc. have been used, but the optimal secondary crystal grains depending on the inhibitor used cannot be obtained by conventional decarburization annealing methods. In other words, in the conventional method, the temperature at which decarburization is possible is limited to around 850°C, resulting in a mixed grain structure of fine grains, and as the thickness of the product plate is reduced, the stable secondary crystal structure is affected by this. There was a problem that was difficult to solve.

(Means for Solving the Problems) In order to solve the above problems, the present inventors have investigated various decarburization annealing methods that are advantageous in terms of optimum generation of primary crystal grains, efficiency, and cost. If an aqueous alkali metal salt solution is applied to a cold-rolled sheet before decarburization annealing, and after drying, decarburization annealing is performed, decarburization is possible even if the decarburization temperature is raised to 850 to 1000℃, 6D, and the time is less than that of conventional decarburization. It was discovered that it is possible to decarburize up to a predetermined amount of C in a short period of time.

The present invention will be described in detail below. The present inventors applied K Co , KCl t Na2CO3a to a thick cold-rolled sheet of unidirectional electrical steel products before decarburization annealing.
Apply an aqueous solution of an alkali metal salt such as NaC1 so that the alkali metal salt has an adhesion resistance of 092 to 397 m'', and the plate temperature is 1.
After heating to 00℃ and drying, it is heated to 850 to 1000 in a decarburization annealing furnace.
℃ to change the temperature to PH, which is a conventional high humidity hydrogen atmosphere.
10/PH20, 3-0.5 to low partial pressure ratio PH10/
Results of decarburization annealing with pH changed to 20.2 or less 1.
If the temperature is increased to 925-950℃, the decarburization time will be less than that of conventional decarburization, and if PH2o/PHffi is less than 0.2, decarburization to less than 20 ppm of carbon can be achieved without forming an oxide layer on the surface. I found out what I can do. In addition, in the conventional method of decarburization at 850°C, the primary crystal grain size after annealing is non-uniform;
By annealing at high temperatures of 25 to 950°C, the primary crystal grain size grows uniformly, and the secondary recrystallization has been unstable until now.
．． Stable secondary recrystallization was obtained even with 18m thick material9. Furthermore, since the water vapor partial pressure ratio in the decarburizing atmosphere was set to 0.2 or less, a surface quality without the formation of a surface oxidation layer was obtained.

In conventional decarburization annealing, when the temperature is raised to 850℃ or higher, an oxidized layer such as KSiO□ forms on the surface of the steel sheet, which inhibits decarburization and necessitates long-term annealing in a high partial pressure atmosphere. According to the present invention, an aqueous alkali metal salt solution is applied, and by preventing oxidation in a low partial pressure atmosphere, high-temperature decarburization that increases the diffusion rate of C, and furthermore, secondary decarburization due to uniform growth of primary recrystallized grains. The two problems of stabilizing recrystallized grains can now be solved at once.

The material components used in the present invention may be those of ordinary unidirectional electrical steel sheets, and may be those of ordinary means such as hot rolling, pickling, hot rolling plate annealing, and cold rolling. Conventionally used converters, continuous casting, hot rolling, cold rolling,
Any equipment for annealing will suffice.

In the present invention, the lower limit of the decarburization annealing temperature is set to 850°C. The reason why the lower limit of the decarburization annealing temperature is 850°C is that at a temperature lower than that, the decarburization rate decreases due to a decrease in the diffusion rate of C in the steel, and the decarburization time becomes longer. This is because they cannot make full use of it. Regarding the upper limit temperature of 1000°C, decarburization is theoretically possible even at higher temperatures, but from the point of view of on-site workability, it is limited because it causes serious damage to the hearth rolls of the annealing furnace and reduces workability.

Also, the amount of alkali metal salt adhering to the steel plate surface is 0.2.
If it is less than 1/m2, it will be difficult to adhere uniformly to the surface of the steel plate, and even if it exceeds 317 m'', no further effect will be seen, so it was limited to a range of 0.2 to 3 V-.

Examples will be described below.

(Example) C: 0.04811;; , 81: 3.
24111; , Mn: 0.06%, S
2. A unidirectional electrical steel sheet containing 0.026% gold was hot rolled to a thickness of 2.2m by normal means, hot rolled sheet annealed at 980°C, and then pickled to a thickness of 0.65mm and 0.02mm thick. , 50cm thick, and further intermediately annealed at 980°C, 0.65+w to 0.225vm (9m1t) 0.50m to 0.
Each sheet was cold-rolled to a thickness of 18 m (7 m1t) to obtain a product plate thickness. After that, a 2% concentration 2C03 aqueous solution was applied thinly, dried, and the steel plate surface was coated with Co to a resistance of 0.517 m, and then decarburized and annealed for 20 p as shown in Table 1.
Decarburization was performed until C was below pm. Table 1 also shows conventional methods. The primary recrystallization microscopic structure of the same material is shown in FIG. 1 in comparison with the conventional method.

From the results in Table 1, the conventional method decarburizes at 850°C for 150 seconds, but the 2CO3 coated material was sufficiently decarburized at 920°C for 60 seconds and 950°C for 30 seconds for both 7ml and 9ml thick materials. It can be seen that decarburization is possible at a temperature of 70 to 80 tons or more and in a time less than the conventional annealing temperature of A, compared to the annealing temperature of conventional materials.

Further, as shown in FIG. 1, the primary crystal grain size of the material of the present invention is uniform and regular, compared to the conventional decarburized material at a temperature of 850°C. MgO was applied as an annealing separator to the sample after decarburization annealing, and pure H
Perform secondary recrystallization annealing in 2 atmospheres, then 850℃
We performed strain relief annealing and measured the magnetism. In the secondary recrystallization annealing, the conventional dew point adjustment annealing was omitted. Display the results -
Shown in 2.

From the results in Table 2, for the conventional method applied to 0.180m thick material, 1200℃X15Hr and 20Hr
Linear fine grains were generated in both the finish annealed materials, and linear fine grains were generated in the 0.225 m thick material as well as in the conventional decarburized material heated at 1200°C x 15 hours, resulting in poor magnetic properties.

In contrast, 0, 180sIs, 0.2 according to the method of the present invention
For both the 25m materials, a stable secondary recrystallized structure was obtained, and excellent magnetism was obtained.

(Effects of the Invention) According to the present invention, high-speed decarburization is possible by decarburization annealing using an alkali metal salt coating on a cold-rolled sheet, and the decarburization temperature can be freely selected according to the optimal primary recrystallization structure. This method stabilizes recrystallization and can also be applied to the production of thin grain-oriented electrical steel sheets that are unstable in secondary recrystallization.

In addition, according to the present invention, in conventional secondary recrystallization annealing, the amount of water contained in the annealing separating agent for the purpose of forming a uniform and fine glass coating on the surface can be small, and the water content can be reduced even in a relatively low temperature range. There is no need for dew point adjustment time, and the effect of reducing costs and improving capacity, which was not possible in the conventional production of unidirectional electrical steel sheets, is extremely large.

Furthermore, in terms of quality, the elements added to the annealing separator applied after secondary recrystallization annealing for the purpose of improving magnetism permeate into the base material easily because there is no glass coating. easy.

In addition, by preventing the surface oxidation layer on product sheets, we have achieved a mirror finish effect that could not be achieved with conventional unidirectional electrical steel sheets.
It is expected that magnetic properties will be improved by increasing the space height.

Furthermore, it is now possible to manufacture thick materials with a product thickness of 0.50 m, which was previously considered difficult, by greatly improving decarburization annealing, and it is also possible to manufacture unidirectional electrical steel sheets at lower cost.

[Brief explanation of drawings]

FIG. 1 is a metallurgical micrograph showing the primary recrystallization microstructure of the present invention material and the conventional material after decarburization annealing.

Claims (1)

[Claims] Normal unidirectional electrical steel sheet components are hot-rolled and then pickled as is or hot-rolled plate annealed and then pickled, followed by one cold rolling or two or more cold rollings including intermediate annealing to produce a product. In the manufacturing process, which involves adjusting the plate thickness, decarburizing annealing, secondary recrystallization annealing, and coating, an aqueous alkali metal salt solution is applied to the steel sheet before decarburizing annealing, drying, and decarburizing annealing at a temperature of 850 to 1000 ° C. A method for producing a unidirectional electrical steel sheet with good magnetic properties.