JPH0240724B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to magnetic properties, particularly to a method of manufacturing a grain-oriented electrical steel sheet with low core loss. A grain-oriented electrical steel sheet is a steel sheet that has a (110) <001> crystal texture called the Goss orientation, and the axis of easy magnetization <001> is aligned in the rolling direction.
It has excellent magnetic properties in that direction. Taking advantage of this feature, steel plates are used as cores for transformers, turbo generators, etc. A particularly important magnetic property of steel sheets is that they have low energy loss, ie, iron loss, when used as iron cores. Due to the current energy situation, steel plates with particularly low iron loss are required. The iron loss of grain-oriented silicon steel plate consists of two parts. One is called hysteresis loss, and this loss decreases as the crystal orientation becomes more aligned and the amount of Si increases. Recent metallurgical techniques have improved the alignment of crystal orientation to the point where it is almost like a single crystal, and the amount of Si has been increased to near the limit that can be cold rolled. This method of reducing hysteresis loss is almost reaching its limit.
Another component of iron loss is eddy current loss. The interior of a ferromagnetic material such as an electrical steel sheet is made up of a collection of magnets called magnetic domains, and the boundaries between magnetic domains are called domain walls. When a steel plate is magnetized, it is magnetized by the movement of this domain wall, but when the domain wall moves, eddy currents flow around it, causing so-called Joule loss. This loss is called eddy current loss. As a method of reducing eddy current loss, first of all, methods to reduce the plate thickness or to increase the specific resistance can be considered. However, the plate thickness is determined by standards, and increasing the amount of Si in order to increase the resistivity approaches the limit of what can be cold rolled as described above, so these methods are not suitable. Therefore, it is practically impossible to reduce eddy current loss. Another possible method for reducing eddy current loss is to narrow the interval between 180° domain walls, which account for the majority of the domain walls of grain-oriented electrical steel sheets, to reduce the moving speed of the domain walls, thereby reducing eddy current loss. One method is to apply tensile stress in the rolling direction of the steel plate, but although it is somewhat effective, it is difficult to make a steel plate with a magnetic flux density of 1.7T and an iron loss of W17/50 at a frequency of 50Hz, which is less than 1.00W/Kg. It was impossible. An object of the present invention is to provide a method for producing grain-oriented electrical steel sheets having an iron loss lower than that of conventional grain-oriented electrical steel sheets. A method for manufacturing grain-oriented electrical steel sheets with low core loss by detecting the grain size of secondary recrystallized grains in annealed grain-oriented electrical steel sheets and introducing pseudograin boundaries into steel sheets whose average grain size is 3 mm or more. The above objective can be achieved by providing the following. Next, the present invention will be explained in detail. The present inventors first investigated what determines the spacing between the 180° domain walls, and found that it is mostly the size of the secondary recrystallized grains, that is, the secondary recrystallized grain size (hereinafter simply referred to as grain size). ) has been newly discovered. However, when the grain size is metallurgically reduced, the alignment of crystal orientation often deteriorates, and no significant reduction in iron loss has been observed. As a result of further investigation, it was found that by introducing pseudograin boundaries into steel sheets after final annealing with an average grain size (average diameter when crystal grains are approximated as circles) of 3 mm or more, the alignment of crystal orientations could be worsened. We have newly discovered that iron loss can be significantly reduced without any problems, and have come up with the present invention. The term "pseudograin boundary" as used herein refers to a small magnetically hard region artificially created within a secondary recrystallized grain, which functions magnetically in the same way as a grain boundary. FIG. 1 shows the effect of pseudograin boundaries introduced by the method shown in Examples described later. One of the major features of the present invention is that the effect of these pseudograin boundaries is not seen at all in steel sheets with an average grain size of less than 3 mm, and rather deteriorates iron loss, whereas in steel sheets with an average grain size of 3 mm or more, the This is due to new knowledge that losses are significantly improved. Pseudo-crystal grain boundaries are introduced by producing distorted regions of the crystal lattice in the form of lines, chain lines, dots, or curves within secondary recrystallized grains by electron beam processing. The width of this line and the diameter of the dots are not particularly limited, but are preferably in the range of about 0.1 μm to 2 mm. It is preferable that the grain boundaries be introduced at a place where the secondary recrystallized grains are equally divided in the rolling direction, but they may be introduced at equal intervals of 1 to 50 mm. When introducing pseudo-grain boundaries, the above-mentioned processing is performed, and it has been found that the effect of pseudo-grain boundaries is influenced by the processing energy during this processing. In other words, as a result of various studies on machining energy, we found that the effect of pseudograin boundaries does not depend on the machining energy density (energy per unit area), but rather on the machining power density (unit time, energy per unit area). ) and has a power density of 1.0
It has become clear that processing at less than ×10 ⁵ W/cm ² not only does not produce the effect of pseudograin boundaries, but also sometimes deteriorates the iron loss of the steel sheet. An example is shown in FIG. This method introduces pseudocrystalline boundaries by irradiating the steel plate with electron beams of various power densities after finish annealing, but if the power density is less than 1.0 × 10 ⁵ W/cm ² , it is not effective or deteriorates. power density 1.0×
A clear improvement in iron loss is observed in steel sheets with an average grain size of 3 mm or more at 10 ⁵ W/cm ² or more. The effect of the pseudograin boundaries described above was observed regardless of the presence or absence of an insulating coating and the surface shape of the steel sheet as long as the steel sheet had an average grain size of 3 mm or more after final annealing, that is, after completion of secondary recrystallization. As a method of introducing pseudo-crystal grain boundaries, an electron beam processing method is used, and its power density is 1.0×10 ⁵ watt/cm ²
If it is above, pseudo-crystal grain boundaries can be introduced, and the average grain size is 3
A significant reduction in iron loss was observed for steel plates with a diameter of mm or larger. Next, the present invention will be explained with reference to examples. Example 1 Pseudo-crystal grain boundaries were introduced into five types of finish-annealed grain-oriented electrical steel sheets having different average grain sizes using an electron beam with a power density of 5.6×10 ⁶ W/cm ² . The direction of the pseudograin boundaries was perpendicular to the rolling direction, and they were introduced uniformly at 5 mm intervals. The width of the pseudograin boundary was approximately 0.2 mm.
Table 1 shows the magnetic flux density B ₁₀ in a magnetic field of 1000 A/m before and after the introduction of pseudograin boundaries, and the iron loss W17/50 at a magnetic flux density of 1.7 T and a frequency of 50 Hz. In steel sheets with an average secondary grain size of less than 3 mm, iron loss and magnetic flux density both deteriorate, whereas in steel sheets with a secondary grain size of 3 mm or more, magnetic flux density did not deteriorate and iron loss was significantly improved.

[Table] Example 2 A power density of 4.8×10 ⁴ W/cm ² and 2.3× was applied to grain-oriented electrical steel sheets after finish annealing with two types of average grain sizes
Pseudo-crystal grain boundaries were introduced by irradiation with an electron beam of 10 ⁷ W/cm ² . The introduction location is the same as in Example 1. Table 2 shows the magnetic properties before and after introduction.

[Table] Average particle size 3mm or more, power density 1.0×10 ⁵ W/cm ²
In the above cases, a significant decrease in iron loss was observed. As described above, according to the present invention, by introducing pseudo-grain boundaries into a grain-oriented electrical steel sheet that has been finish annealed, the iron loss of the steel sheet can be significantly reduced without impairing the alignment of the crystals. Can be done.

[Brief explanation of drawings]

Figure 1 shows the average secondary grain size of a grain-oriented electrical steel sheet after final annealing and the results before and after introducing pseudo-crystal grain boundaries into the steel sheet by irradiating it with an electron beam with a power density of 1.0×10 ⁵ watt/cm ² or more. FIG. 2 is a diagram showing the relationship between the machining power density for introducing pseudo grain boundaries and the iron loss difference before and after the introduction.

Claims (1)

[Claims] 1. During a series of processes for producing grain-oriented electrical steel sheets using conventional methods, 1.0×
A method for producing a grain-oriented electrical steel sheet with low iron loss, characterized in that pseudo-grain boundaries are introduced into the steel sheet by irradiating the steel sheet with an electron beam having a power density of 10 ⁵ watt/cm ^{2 or} more.