JPS6344804B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing an ultra-low iron loss unidirectional electrical steel sheet whose magnetic properties do not deteriorate even when strain relief annealing is performed using a unidirectional electrical steel sheet whose magnetic domains are artificially controlled. It is. [Prior Art] In recent years, it has been desired to reduce iron loss in grain-oriented electrical steel sheets from the viewpoint of energy conservation.
As a method for reducing iron loss, a method of subdividing magnetic domains by laser irradiation has already been disclosed in Japanese Patent Publication No. 58-26405. The reduction in core loss by this method is due to the strain introduced by the laser.
Therefore, it can be used for laminated core transformers that do not require strain relief annealing, but cannot be used for wound core transformers that require strain relief annealing.
Furthermore, in Japanese Patent Application Laid-Open No. 59-100222, a secondary recrystallization annealed steel plate was subjected to local heat treatment at 800°C.
A method of introducing artificial grain boundaries by performing annealing at a temperature above is disclosed. In this method, a reduction in core loss is achieved by refining magnetic domains using artificial grain boundaries introduced into the steel sheet. Since the annealing is performed at a temperature of 800° C. or higher, the effect of strain relief annealing is not lost, but from the perspective of the examples, it is difficult to obtain an iron loss equivalent to the iron loss value reduction method using laser irradiation described above. In addition, Special Publication No. 14827 (1982) and Special Application No. 14827 (1982)
As shown in No. 236974, a method has been proposed in which fine primary recrystallized grains are generated in the surface layer of secondary recrystallized grains in a grain-oriented electrical steel sheet to subdivide the magnetic domain and reduce iron loss. There is. [Problems to be solved by the present invention] In particular, the present invention solves the following problems when forming a recessed portion by pressing.
For example, the aim is to improve the quality of steel sheets by preventing twins and film deterioration that occur when forming grooves using the pressing method described in the above-mentioned Japanese Patent Application No. 59-236974. It is something to do. [Means for Solving the Problems] The present invention applies an average load of 70 to
When forming recesses in the form of lines, dots, broken lines, etc. at 220Kg/ ^mm2 , the temperature of the steel plate is set to 50℃ to 500℃, and then heat treatment is performed at a temperature of 750℃ or higher to form inside the grains. The aim is to create fine recrystallized grains to refine the magnetic domains, thereby providing a unidirectional electrical steel sheet that exhibits an iron loss value comparable to that of laser irradiation even after strain relief annealing. It is something. The present invention will be explained in detail below. A slab containing 4% Si or less is heated and hot-rolled to an intermediate thickness. If necessary, heat treatment is performed at this stage and cold-rolled once or twice with intermediate annealing in between to achieve the final thickness. The obtained cold-rolled sheet is decarburized and annealed, coated with an annealing separator, and then subjected to high-temperature, long-term finish annealing to develop secondary recrystallized grains with (110) <001> orientation, or to create a steel sheet under tension. A coating liquid for forming an insulating film such as a coating is applied and baked, and the average load of the stress-applied area (the value obtained by dividing the applied stress by the stress-applied area on the plate surface viewed from the normal direction of the plate surface) is 70~ Add processing that is 220Kg/mm ² . As is well known, unidirectional electrical steel sheets have large grain sizes, usually 3 to 10 mm, and have an insulating film formed on their surfaces. Therefore, when this steel sheet is subjected to local processing, not only strain is introduced, but also twinning occurs at room temperature, resulting in deterioration of the coating, and the rate of improvement in magnetic properties after strain relief annealing is also low.
In order to solve this problem, the inventors conducted various studies and found that the most effective method is to process the steel plate at a higher temperature. Figure 1 shows a steel plate (on top of the coating) observed with an optical microscope after being processed with a gear roll and then subjected to strain relief annealing at 800°C for 4 hours. Figure 1a shows a steel plate processed by heating it to 300°C using the method of the present invention, and Figure 1b shows a steel plate processed at room temperature. As can be seen from these figures, there is little damage to the coating in figure a, but in figure b, twins have occurred and cracks have occurred in the coating. These twins are generated due to deformation, but since the amount of strain in the twins is small, they almost disappear after annealing. However, if the amount of twins increases, such as when the steel sheet temperature during processing is low or the Si content is high, recrystallization occurs from the twin portions, which is unfavorable for improving magnetic properties. Figure 2 shows the relationship between the steel plate temperature during processing and the magnetic properties after strain relief annealing. It can be seen that raising the temperature of the steel sheet during pressing at 130Kg/mm ² to a temperature higher than room temperature has an effect on iron loss characteristics, but it is not preferable to exceed 500℃. Figure 3 shows fine recrystallized grains formed on the surface layer of the steel sheet after stress relief annealing. In figure a, the steel plate temperature during processing is about 300°C, and in figure b, it is room temperature.
The average load applied to the steel plates was 130Kg/mm ² in both cases. It can be seen that the recrystallized grains of the specimen processed at 300°C are smaller than at room temperature. This is thought to be because the amount of strain during processing is smaller than when processed at room temperature, but it is important to not make the fine recrystallized grains coarser than necessary in order to reduce iron loss. Next, Figure 4 shows the relationship between the average load applied to the steel plate and iron loss. The steel plate temperatures during processing are 50℃, 300℃, and 500℃. From now on, the average load that will improve iron loss will be 70 to 220.
It can be said that it is in the range of Kg/mm ² . That is, the average weight is 70
When it is smaller than Kg/mm ² , the amount of introduced strain is small, so fine grains are not generated, or even if they are generated, they do not affect the magnetic domains. On the other hand, if it exceeds 220Kg/ ^mm2 , relatively low temperature processing (50
~100°C), the amount of strain increases and the recrystallized grains become coarser. Further, when the steel plate temperature is 450°C to 500°C, the steel plate becomes soft, the recesses become deep, the magnetic flux density decreases, and no improvement in characteristics is observed. The optimum shape of the stress applying portion, that is, the recess, when applying such an average load to the steel plate is as follows.
First, the distance between the recesses in the rolling direction is 1
~20mm is preferred. Next, the width of the recess is 10 to 300 μm, preferably 50 to 200 μm. The minimum value of the recess width for processing is 10 μm, and if it exceeds 300 μm, the recrystallized grains will become too large, which is not desirable in terms of characteristics. The shape of the recess is not particularly important. The depth of the recess is preferably greater than 5 μm in the steel plate base portion. This depth becomes deeper as the load during processing increases or as the temperature of the steel plate becomes higher. If the recesses are too deep, the magnetic flux density will decrease, which is undesirable. The preferred range is 5-20 μm.
The direction of the recess is preferably 45° to 90° with respect to the rolling direction. Further, the shape of the recessed portion in plan view may be linear, dotted, or broken. In the present invention, heat treatment is performed at 750° C. or higher after introducing strain, and FIG. 5 shows changes in iron loss value (W17/50w/Kg) when various heat treatments are performed after introducing strain. As can be seen from this figure, the iron loss value before the introduction of strain deteriorates once after the introduction of strain, but after a short heat treatment, the iron loss value becomes extremely low. From this, after final annealing, it is possible to recrystallize the strain-introduced portion by utilizing the heat treatment during baking of the insulating coating treatment, which is performed after strain introduction, to reduce the iron loss value compared to before strain-relief annealing. In this case, it can also be used as a transformer material for stacked iron cores without strain relief annealing. In the present invention, strain is introduced at a temperature of 50°C to 500°C.
℃ range, so it is necessary to reheat the steel plate, but it is more energy efficient if it is carried out during the cooling process after baking annealing for insulation coating treatment. In addition, although the example of this invention showed the example which formed a recessed part with a gear type|mold roll, it is not limited to this example and any method which can apply the load referred to in this invention locally may be used. In order to manufacture the product most economically, we have explained the steel sheet with a finish annealing coating or a phosphoric acid tension imparting coating, but the present invention applies to secondary recrystallized steel sheets with no coating at all. Even if this method is applied, the effect of reducing iron loss can be expected. Example 1 A high magnetic flux density unidirectional electrical steel sheet product (with tension coating) with a plate thickness of 0.23 mm containing 3.2% Si, a gear pitch of 5 mm, a tooth width at the tip of the gear of 50 μm, a flat blade shape,
Strain was introduced by forming a linear recess under a load of 150 kg/mm ² using a gear-shaped roll whose blades are inclined at 15 degrees with respect to the gear axis direction. The steel plate temperature at the time of strain introduction is room temperature, 100℃, 200℃
It was warm at ℃. After introducing strain, strain relief annealing was performed at 850°C for 4 hours. Table 1 shows its magnetic properties.

[Table] Increasing the temperature of the steel plate when strain is introduced improves iron loss characteristics. Example 2 A high magnetic flux density unidirectional electrical steel sheet with a thickness of 0.20 mm containing 3.2% Si, a gear pitch of 8 mm, and a gear tip curvature radius.
Strain was introduced at a load of 150 Kg/mm ² using a gear-shaped roll with a diameter of 100 μm and a blade inclination of 15 degrees with respect to the gear axis direction. The steel plate temperature at the time of strain introduction is room temperature, 200℃, 400℃
It was warm at ℃. After introducing strain, it was coated with a phosphoric acid-based tension coating solution, and baked and annealed at 850°C for 30 seconds.
Thereafter, annealing was performed at 800°C for 4 hours. The magnetic properties are shown in Table 2.

[Table] Example 3 A high magnetic flux density unidirectional electrical steel sheet with a plate thickness of 0.20 mm after finish annealing, a gear pitch of 5 mm, and a tooth width at the tip of the gear.
50μm, flat cutting edge shape, gear-shaped roll with a blade inclination of 15 degrees to the gear axis direction allows a load of 130
Strain was introduced at Kg/ ^mm2 . The steel plate temperature at the time of strain introduction was room temperature, 200°C. Thereafter, it was coated with a phosphoric acid-based tension coating solution and heat-treated at 850°C for 60 seconds. The magnetic properties at that time are shown in Table 3.

〔Effect of the invention〕

The present invention is capable of improving magnetic properties even more than conventional techniques in magnetic domain control technology by pressing, so its industrial effects are enormous.

[Brief explanation of drawings]

Figure 1 is an optical metallurgical micrograph of a steel plate that has been subjected to stress relief annealing after being pressed by the present invention a and conventional method b. Figure 2 is the relationship between the steel plate temperature during processing and the magnetic properties after strain relief annealing. FIG. 3 is an optical metallurgical micrograph of the surface layer of a steel plate in the present invention a and conventional method b. FIG. 4 is a diagram showing the relationship between processing temperature and average load and iron loss. FIG. 5 is a diagram showing the relationship between strain relief annealing conditions and iron loss in the method of the present invention.

Claims (1)

[Claims] 1. A unidirectional electrical steel sheet that has been finish annealed or that has been treated with an insulating coating after finish annealing is subjected to a load of 70 to 220 Kg/mm ² within a range of 45° from a right angle to the rolling direction. After forming a recess (groove) with a depth of more than 5 μm in the base metal part, 750
A method for producing a unidirectional electrical steel sheet in which heat treatment is performed in a temperature range of ℃ or higher, the method comprising: heating the substrate at a depth of 5 μm to the base metal portion;
A method for producing a low iron loss unidirectional electrical steel sheet, characterized in that ultra-high concave portions (grooves) are formed in a temperature range of 50 to 500°C. 2 The spacing is 1 to 20 mm in the rolling direction, and the width is 10 to 300 μm.
Claim 1 forming a recess (groove) that is
The method described in section. 3. The method according to claim 1, wherein the recess (groove) has a dotted or broken line shape.