JPS5848630A - Heat treatment of directional electrical steel plate in treatment of insulating coat - Google Patents

Abstract

PURPOSE:To enhance the shape setting performance of a steel plate without deteriorating the magnetism by increasing the temp. raising rate during drying in the treatment of an insulating film. CONSTITUTION:A phosphate-base treating liq. for an insulating coat is applied to a directional electrical steel plate after annealing at a high temp. and dried at 50-80 deg.C average temp. raising rate. It is backed at a prescribed temp., made flat, annealed, and cooled. By the rapid heating during the drying of the insulating film, the temp. of edges of the steel plate in the lateral direction rises. By utilizing the temp. difference in the lateral direction, contraction force is allowed to act on the edges, and by the uniform heating in the following baking stage, the elongated side strain and the shape of earing are set.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat treatment method for treating a grain-oriented electrical steel sheet with an insulation coating, and its purpose is to improve the shape straightening ability of the steel sheet.

As is well known, in directional electromagnetic MS, flattening annealing is performed to flatten the shape of a steel sheet that has been plastically deformed due to curling after hot plate annealing at high temperature. Generally, this is carried out simultaneously with the insulation coating treatment of grain-oriented electrical steel sheets using a water bath solution or the like. In this process, a low furnace tension of o, o8%c is applied as a total elongation rate, drying is carried out at 760 to 830°C, and baking is carried out at a temperature of 830 to 870°C.

By the way, after annealing a grain-oriented electrical steel sheet in a patch-type high-temperature annealing furnace, the coil shape is as shown in Figure 1, where the lower part of the coil is the pacer due to the difference in thermal expansion and contraction rates between the lower part of the coil 1 and the pace grade 2. The phenomenon of being pulled by the grate and the buckling phenomenon due to insufficient cleavage strength in the width direction of the coil under high temperature combine to cause deformation of the lower part of the coil called lateral strain 3.

As measures to prevent side distortion, it has been proposed to apply refractory powder on the pace grate or to adopt a split pace grate, and although these measures have been quite effective, it is impossible to completely eliminate side distortion. has not yet been reached.

In addition, there are ear waves 4 at the ends of the steel sheet in the center direction that are generated in processes before patch type high temperature annealing and remain after annealing, or ears generated due to thermal stress due to temperature differences in the width direction of the coil during cooling during batch type high temperature annealing. Wave 4 is directional electric current ll#I during flattening annealing.
Annealing at low furnace tension, which does not deteriorate the magnetic properties of the plate, may not eliminate the problem, and the defective shape has to be cut out before use, resulting in a reduction in yield.

Therefore, the present inventor discovered that the rate of temperature increase during drying of the insulation coating treatment liquid during the insulation coating flattening treatment of grain-oriented electrical steel sheets has a close relationship with the above-mentioned ability to correct the shape of side distortion and ear waves. did. That is, by drying a steel plate coated with an insulating coating treatment liquid by raising the temperature more rapidly than the conventional rate, the temperature at the ends in the width direction of the steel plate becomes higher than that at the center. Therefore, the ends of the steel plate try to expand, but because the temperature in the center, which accounts for most of the temperature in the width direction of the steel plate, is low, the expansion of the end of the coil is inhibited, and compressive stress is eventually applied to the ends in the width direction of the steel plate. .

In other words, the feature of the present invention is that by increasing the temperature rise rate during drying during insulation coating treatment, the temperature difference that occurs in the direction of the steel sheet is used to apply a shrinkage force to the ends of the steel sheet in the direction of the center, thereby reducing the The purpose is to correct the elongated lateral distortion and the shape of the ear waves at the ends in the width direction of the steel plate by uniform heating without causing magnetic deterioration.

By the way, a method of correcting the shape of a steel plate by heating the ends in the width direction of the steel plate has already been proposed in Japanese Patent Publication No. 47-21806. According to this method, the temperature at the ends of the steel plate in the width direction, which inhibits the flattening of the steel plate, is raised by 20°C or more from the center, thereby first softening the ends of the steel plate in the width direction, and applying tension in the furnace to the center of the steel plate in the middle direction. The magnetic properties of the electromagnetic steel sheet tend to deteriorate due to excessive tensile strength.

In contrast, the method of the present invention utilizes the compressive stress generated at the ends of the steel plate by raising the temperature of the ends of the steel plate in the width direction by rapid heating during drying. They are used to correct a stretched shape, and the two are completely different.

The inventor investigated the rate of temperature increase during drying due to the generation of compressive stress at the ends in the width direction of the steel plate, and found that the rate of temperature increase was 5.
It turns out that 0-b. Note that, conventionally, the temperature is about 0° C./second or less.

It has been found that if the drying rate is less than 50° C./sec, no compressive stress is generated at the ends of the steel sheet in the direction of the center, and if it exceeds 80° C., the magnetic properties, particularly the magnetostriction, are adversely affected. In addition, a radiant tube is usually used as a heating source in a flattening annealing furnace, but the temperature increase rate during drying can be efficiently increased to 50~SOC.
It is preferable to use a direct flame burner for K in /sec, because this increases the steel plate temperature in the first half of the flattening annealing furnace and reduces the heat loss in the second half of the flattening annealing furnace. , total energy saving operation is possible.

Hereinafter, an example of a heat treatment method for treating a grain-oriented electrical steel sheet with an insulation coating according to the present invention will be described in detail with reference to FIG. 2.

In FIG. 2, a steel plate 6 is coated with a phosphate-based aqueous solution using a coating roll 7, and then enters a drying oven 8.

50% by using direct flame burner 5 on the steel plate in this drying oven.
~b The edge coating is dried and deposited, and then enters a heating furnace 9 using a radiant tube, where the insulating coating is baked onto the steel plate and the steel plate is flattened, and the annealing is completed after passing through a jet cooling type cooling chamber 10. That is, the present invention specifies a heat treatment method in the drying oven 8, and is intended to correct the shape of the mid-direction ridge of a K steel plate. In this case, it is an effective method to add edge heating in addition to rapid temperature rise.

Example The thickness of the grain-oriented electrical steel sheet used was 0.27 m.

0.30 wm, 0.35-, board width is 980-1
020■, and the threading speed is 80W on the line shown in Figure 2.
'mln and processed 8000 tons.

) After cleaning the grain-oriented electrical steel sheet after high-temperature annealing using the 4-7-chi method in the flattening annealing line shown in Figure 2, a phosphate-based aqueous solution was applied using a coating roll, and the temperature was increased at 70°C/sec. 800 in speed
It was heated to 850°C, dried, and then baked at 850°C to perform flattening annealing.

In addition, the tension in the furnace is 0.42 rm when the plate thickness is 0.2□7-
'.

0.45 kg/sag' for 30 mm, o
, for 35 wm, 0.50ψ-2 and 5 thickness 0.35■
For this, edge heating was added.

Table 1 shows the results of the conventional method with a self-coalescence and a heating rate of 36 C/sec. The numerical values shown in Table 1 are expressed as a percentage of the Al1 ratio occupied by side strain or ear waves per grain-oriented electromagnetic steel sheet coil. Table 1 shows that the method of the present invention is particularly effective in correcting lateral distortion and ear waves.
・Table 1

[Brief explanation of the drawing]

FIG. 1 shows the shape of the coil after annealing. FIG. 2 is a process diagram for flattening the insulation film. Rod 1st 2nd

Claims (1)

[Scope of Claims] When drying, baking, and cooling are performed after applying an insulation coating treatment liquid to a grain-oriented electrical steel sheet, the temperature increase rate in the drying process after applying the treatment liquid to the steel sheet is set to an average of 50 to 50 b. Heat treatment method for insulation coating treatment of magnetic electrical steel sheets.