CN101528951B - Unidirectional magnetic steel sheet excellent in iron loss characteristic - Google Patents

Abstract

A unidirectional magnetic steel sheet excellent in iron loss to conventional is produced by dividing the iron loss of a unidirectional magnetic steel sheet into which strain is introduced by laser beam application into the hysteresis loss and the eddy current loss and quantitatively and adequately controlling the distributions including the direction of the sheet thickness of the strain and the residual stress in view of the eddy current loss. By applying a laser beam or the like, linear strain generally perpendicular to the rolling direction is introduced into a unidirectional magnetic steel sheet uniformly in the direction of the sheet thickness and periodically in the rolling direction to control the magnetic domains. The strain is so introduced that the integral of the compression residual stress in the rolling direction computed in the region of the cross-section where the compression residual stress is present lies in a predetermined range, in the two-dimensional distribution of the residual stress in the rolling direction caused near one strain-introduced portion in the cross-section perpendicular to the direction of the sheet width.

Description

Grain-oriented electrical steel sheet with excellent iron loss properties

technical field

The present invention relates to a grain-oriented electrical steel sheet excellent in iron loss characteristics in which magnetic domains are controlled by introducing residual stress by laser irradiation or the like.

Background technique

A grain-oriented electrical steel sheet having an easy-magnetization axis in the rolling direction of the steel sheet is mainly used for iron cores of transformers, etc. In recent years, reduction of iron loss in iron cores has been strongly demanded from the viewpoint of energy conservation.

The iron loss (iron loss; iron loss) of the electromagnetic steel sheet roughly includes hysteresis loss and eddy current loss. It is known that hysteresis loss is affected by crystal orientation, defects, grain boundaries, etc., and that eddy current loss is affected by plate thickness, electrical resistance, magnetic domain width, and the like. There is a limit to the method of controlling and improving the crystal orientation in order to reduce the hysteresis loss. Therefore, in order to reduce the eddy current loss which accounts for a large amount of iron loss in recent years, many magnetic domain width subdivisions, that is, magnetic domain control technology, have been proposed.

As a method thereof, in Japanese Patent Publication No. 6-19112, as a method of manufacturing grain-oriented electrical steel sheets, it has been proposed to periodically introduce linear lines substantially perpendicular to the rolling direction in the rolling direction by irradiating YAG laser light. Strain, to reduce the method of iron loss. The principle of this method, called laser domain control, is that the 180° magnetic domain width is subdivided due to the surface strain caused by scanning laser beam irradiation, and iron loss can be reduced.

In addition, JP-A-2005-248291 proposes a new idea focusing on the maximum value of the residual stress in the rolling direction formed on the surface of the steel sheet.

Contents of the invention

Regarding laser magnetic domain control, in which iron loss is reduced by subdividing the 180° magnetic domain width by introducing local strain on the steel sheet surface, most of the previous proposals including Patent Document 1, which is a prior art, have been carried out. As a result of the experiment, many irradiation parameters such as the type of laser, the shape of the laser beam spot, the laser energy density, and the laser irradiation interval were further limited. The content of the proposal was very one-sided and lacked unity. The reason is that there is no quantitative discussion on strain or residual stress, which are the main factors that cause magnetic domain subdivision and reduce iron loss. Speaking of which, in terms of improving iron loss by laser irradiation, even under the same irradiation conditions, depending on the absorption rate of the steel plate (determined by the laser wavelength, surface texture, shape, and film composition) and the thickness of the film, the energy from the laser energy to the thermal energy is different. The conversion (temperature distribution, temperature history) is also different, so even if the laser irradiation conditions are the same, the introduced strain will be different due to the different properties of the steel sheet. Furthermore, even with the same heat energy (temperature distribution, temperature history), the residual stress is also different due to the difference in the composition of the steel sheet (such as Si content) and the difference in physical property values (such as Young's modulus, yield stress value). Therefore, even if the optimum laser irradiation conditions for a certain steel plate can be obtained, as long as the state of the film changes slightly, the way in which the strain caused by the laser enters is also different, and the iron loss value will change. Therefore, the laser conditions and the iron loss The reduction does not correspond one-to-one. Therefore, for iron loss, it is required to find a more essential influencing factor. Although Patent Document 2 quantitatively discusses unique strain and residual stress, there is a limit to the reduction of iron loss if only the strain and tensile residual stress on the steel plate surface are controlled.

The object of the present invention is to divide the iron loss of grain-oriented electrical steel sheet into hysteresis loss and eddy current loss, and especially from the viewpoint of eddy current loss, quantitatively and appropriately include not only the surface but also the internal thickness direction. Conditions control the distribution of strain and residual stress, thereby providing a grain-oriented electrical steel sheet that is superior in iron loss compared to conventional ones.

The inventors of the present invention conducted experiments on magnetic domain control, introduced strain and residual stress into the grain-oriented electrical steel sheet by laser irradiation, etc., studied hard on the obtained low iron loss grain-oriented electrical steel sheet, and investigated the distribution of the introduced residual stress . As a result, it was found that if the correlation between residual stress and eddy current loss is found, and the compressive stress value and strain interval are controlled, a grain-oriented electrical steel sheet with excellent iron loss characteristics can be realized. The gist of the present invention is as follows.

(1) A grain-oriented electrical steel sheet, which is a grain-oriented electrical steel sheet having a linear strain approximately perpendicular to the rolling direction by irradiating a continuous wave laser beam, the linear strain being in the direction perpendicular to the rolling direction, namely The plate is uniform in the transverse direction and is periodic in the rolling direction. The grain-oriented electrical steel sheet is characterized in that the compressive residual stress in the rolling direction generated near a strain introduction portion is in a cross-section perpendicular to the plate transverse direction. In the two-dimensional distribution above, the value obtained by integrating the compressive residual stress in the rolling direction in the region where the compressive residual stress exists in the cross section is 0.20N to 0.80N.

(2) The grain-oriented electrical steel sheet according to (1) above, wherein the periodic intervals of the uniform strain in the transverse direction of the sheet caused by laser beam irradiation in the rolling direction are 2 mm to 8 mm .

Description of drawings

Fig. 1 is a schematic diagram of an apparatus used in the method for producing a grain-oriented electrical steel sheet of the present invention.

Fig. 2 is a two-dimensional distribution of residual stress in the rolling direction in the vicinity of the laser irradiation position on a section in the rolling direction/thickness direction.

Fig. 3 is a graph showing the relationship between the maximum value of the tensile residual stress in the rolling direction and the iron loss W _17/50 .

Figure 4 is a graph showing the relationship between the integral compressive stress value σS and the eddy current loss We (the irradiation interval is fixed at 4mm).

Figure 5 is a graph showing the relationship between the integral compressive stress value σS and the iron loss W _17/50 (the irradiation interval is fixed at 4mm).

Fig. 6 is a graph showing the relationship between the irradiation interval PL and the iron loss W _17/50 (the irradiation diameter DL in the rolling direction is fixed at 0.1 mm, and the irradiation diameter DC in the scanning direction is fixed at 0.5 mm).

Fig. 7 is a graph showing the relationship between the maximum value of the compressive residual stress in the rolling direction and the iron loss W _17/50 .

Detailed ways

The inventors of the present invention irradiated the surface of the grain-oriented electrical steel sheet with laser light, and introduced linear strains approximately perpendicular to the rolling direction at constant intervals in the rolling direction to improve iron loss. For various laser irradiation conditions, Focusing on the two-dimensional distribution of residual stress in the rolling direction on a cross section perpendicular to the lateral direction of the sheet and the laser irradiation interval (pitch) in the rolling direction, the conditions for obtaining a grain-oriented electrical steel sheet excellent in iron loss characteristics were found. Here, the plate transverse direction is a direction perpendicular to the rolling direction. As a method of introducing the above-mentioned linear strain into the surface of the grain-oriented electrical steel sheet, in addition to the laser irradiation method, ion implantation method, electric discharge machining method, partial plating method, ultrasonic vibration method, etc. can be mentioned, and this condition is for A grain-oriented electrical steel sheet to which strain has been introduced by any method is applicable. The grain-oriented electrical steel sheet obtained by laser irradiation according to the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram of a laser beam irradiation method according to the present invention. In the present embodiment, the continuous oscillation (CW) laser beam LB output from the laser device 3 is scanned and irradiated onto the grain-oriented electrical steel sheet 1 using the polygon mirror 4 and the fθ lens 5 . By changing the distance between the fθ lens 5 and the grain-oriented electrical steel sheet 1, the focusing diameter d1 of the laser beam in the rolling direction is changed. 6 is a cylindrical lens or a plurality of cylindrical lens groups. Regarding the focusing point of the laser beam, the focusing diameter (length of the scanning direction) dc of the scanning direction of the beam (the transverse direction of the plate perpendicular to the rolling direction) changes according to requirements, from a circle Shaped to an ellipse to control the spotlight shape. Average irradiation energy density Ua [mJ/mm ² ], laser power P [W], plate transverse scanning (scan) speed Vc [m/s] of the laser beam in the transverse direction of the plate, laser irradiation interval PL in the rolling direction PL [mm ], defined as: Ua(mJ/mm ² )=P/(Vc×PL). The laser scanning speed is determined by the rotation speed of the polygon mirror. Therefore, the average irradiation energy density can be adjusted by changing the laser power, the rotation speed of the polygon mirror, and the laser irradiation interval. Fig. 1 is an example using a set of laser and laser beam scanning devices, but it is also possible to arrange a plurality of the same devices in the transverse direction of the steel plate according to the width of the steel plate.

The present inventors used a continuous oscillation fiber laser device with a fiber core diameter of 10 μm, and changed the irradiation conditions by various combinations of the spot shape and the average irradiation energy density Ua. A laser beam is scanned linearly in an approximately vertical direction, and an experiment of laser irradiation is carried out. The two-dimensional distribution of residual stress in the rolling direction, iron loss, and hysteresis loss on a section perpendicular to the transverse direction of the plate were measured, and the iron loss was separated into hysteresis loss and eddy current loss for investigation. The measurement of the two-dimensional distribution of residual stress in the rolling direction on a cross section perpendicular to the transverse direction of the sheet is to measure the lattice spacing by X-ray diffraction method, and convert the physical property values such as elastic modulus into stress. The iron loss was measured by SST (Single Sheet Tester; Single Sheet Tester) measuring instrument W _17/50 . W _17/50 is the iron loss at a frequency of 50Hz and a maximum magnetic flux density of 1.7T. For the grain-oriented electrical steel sheet sample used in this example, W _17/50 before laser irradiation was 0.86 W/kg when the plate thickness was 0.23 mm. The hysteresis loss was calculated from the hysteresis loop, and the eddy current loss was a value obtained by subtracting the hysteresis loss from the aforementioned iron loss.

FIG. 2 shows a representative example of the two-dimensional distribution of compressive residual stress in the rolling direction generated in the vicinity of the laser irradiation position on a cross section perpendicular to the transverse direction of the sheet. Regarding the steel sheet where improvement in iron loss is seen, although the absolute value of residual stress varies depending on the laser irradiation conditions, there is a large tensile stress near the surface of the steel sheet, and a compressive stress is seen below it in the thickness direction. exist. In addition, the width in the rolling direction in which residual stress and plastic strain exist is approximately proportional to the rolling direction diameter d1 of the laser focus point.

The inventors of the present invention investigated the relationship between the maximum value of tensile residual stress and compressive residual stress on the surface of the steel plate and the iron loss of the steel plate irradiated with laser light using a continuous oscillation laser. The relationship between the maximum value of tensile residual stress and iron loss is shown in FIG. 3 , and the relationship between the maximum value of compressive residual stress and iron loss is shown in FIG. 7 . With regard to the maximum value of the tensile residual stress, no iron loss correlation and/or optimum value can be seen. On the other hand, when the maximum value of the compressive residual stress is 100 MPa or more indicated by the chain line, the core loss is good, but the upper limit is not clear. As a result, iron loss in magnetic domain control by laser irradiation cannot be explained by the maximum value of tensile residual stress, nor can it be explained by the maximum value of compressive residual stress at all. The possibility that another feature quantity exists is conceivable.

Therefore, the present inventors studied the data carefully, and as a first point of view, focused on: the maximum value of the tensile residual stress is larger than the compressive residual stress and the tensile residual stress is concentrated in a narrow region; Stress is the area of plastic strain; on the other hand, there are many relationships between the maximum value of compressive residual stress and iron loss. As a second point of view, focus on: even if the maximum value of compressive residual stress is the same, the distribution of compressive residual stress in the depth There are differences in the direction of expansion. That is to say, the main factor to achieve the reduction of iron loss and the subdivision of magnetic domains, from the first point of view, it is not the tensile stress that is important, but the compressive stress, and from the second point of view, it is not the residual The maximum value of the stress, but the expansion of the distribution.

The inventors of the present invention define the distribution of compressive stress for reducing iron loss as the characteristic quantity "integrated compressive stress value σS" as in the following equation (1).

σS＝ _∫S σds...(1)

That is, in the two-dimensional distribution of the compressive residual stress in the rolling direction generated near the laser irradiation part, that is, near the strain introduction part, on a cross section perpendicular to the transverse direction of the sheet, the integrated compressive stress value σS[N] is given by The compressive residual stress in the rolling direction is set to σ[MPa], the region where the compressive residual stress exists in the section is set to S[mm ² ], the area unit is set to ds, and σS is defined as the corresponding stress σ in the area S The value obtained by performing the integration. That is, the integrated compressive stress value is the sum of compressive residual stresses introduced by laser irradiation.

Set the laser irradiation interval PL in the rolling direction to 4mm (constant), and set the shape of the laser spot to: 20×2500μm, 100×500μm, 100×2000μm, 300×200μm, for each case, step by step For the grain-oriented electrical steel sheet irradiated with varying laser power, the integral compressive stress value was obtained by the above-mentioned method. On the other hand, the eddy current loss was obtained by subtracting the hysteresis loss from the iron loss measured for each case. FIG. 4 is a diagram showing the relationship between the integral compressive stress value σS and the eddy current loss We plotted on the abscissa for each electrical steel sheet. From this result, the integrated compressive stress value and the eddy current loss are inversely proportional to each other regardless of the shape of the spot. This means that the reduction of eddy current loss, that is, the magnetic domain subdivision effect is proportional to the sum of the introduced compressive residual stresses. This phenomenon is examined from a physical principle as follows. Magnetoelastic performance E:

E＝-C×σ×M×cos ² θ

Among them, C is a constant, σ is the residual stress, M is the magnetic moment, and θ is the angle formed by σ and M. At this time, in the case of compressive residual stress in the rolling direction, E is the smallest when θ is 90°, so note that σ is a negative value, and the direction of the magnetic moment is perpendicular to the rolling direction. Therefore, due to the compressive stress, the easy axis of magnetization is generated not only in the rolling direction but also in its perpendicular direction. Generally, it is called a circulating magnetic domain. If circulating magnetic domains exist, the magnetostatic energy increases and becomes unstable. Therefore, it is conceivable to subdivide the magnetic domains and reduce the magnetostatic energy for stabilization. Therefore, it can be considered that the more circulating magnetic domains there are, that is, the stronger and wider the compressive residual stress occurs, the higher the magnetic domain subdivision effect is, and the lower the eddy current loss is.

FIG. 5 is a graph showing the relationship between the integrated compressive stress value σS on the abscissa and the attained iron loss W _17/50 on the ordinate using the data and measured iron loss used in FIG. 4 . From this result, in the range of 0.20N ≤ σS ≤ 0.80N shown by the dotted line, compared with the iron loss W _17/50 = 0.86W/kg before magnetic domain control, it is possible to realize the The iron loss improvement rate is 13% or more (W _17/50 ≤ 0.75W/kg), which is a good iron loss. Furthermore, iron loss improvement rate η is defined as: η(%)={(iron loss of material-arrival iron loss)/iron loss of material}×100. Since the eddy current loss is high when the integrated compressive stress value σS is less than 0.20N, the iron loss cannot be reduced. It can be considered that when the integrated compressive stress value σS exceeds 0.80N, although the eddy current loss decreases, the hysteresis loss increases due to the plastic strain caused by the tensile residual stress near the surface, and the iron loss cannot be reduced. As mentioned above, it can be seen that if the integral compressive stress value σS is adjusted to the range of 0.20N≤σS≤0.80N, good iron loss improvement can be obtained. It can be seen that if it is more preferably adjusted to the range of 0.40N≦σS≦0.70N, the effect of further improving the iron loss can be obtained.

In the foregoing, the laser irradiation interval PL in the rolling direction was fixed at 4 mm, but the influence was investigated by further changing the laser irradiation interval PL in the rolling direction. At this time, the focus shape of the laser beam has a diameter of 0.1 mm in the rolling direction and a diameter of 0.5 mm in the scanning direction (transverse direction of the plate), and Ua is adjusted so that the integrated compressive stress value σS is in the range of 0.20N≤σS≤0.80N. Fig. 6 is a graph showing the relationship between the laser irradiation interval PL in the rolling direction plotted on the abscissa and the iron loss W _17/50 plotted on the ordinate. From this result, when PL is in the range of 2 mm to 8 mm, it is possible to realize a good iron loss with an improvement rate of iron loss of 13%. When the PL is in the range of less than 2 mm, the hysteresis loss increases, so that the core loss cannot be reduced. When PL is in a range larger than 8 mm, eddy current loss cannot be reduced, and thus iron loss cannot be reduced. It can be seen that if the laser irradiation interval PL in the rolling direction is adjusted to the range of 2 mm≤PL≤8 mm as described above, good improvement in iron loss can be obtained.

Example 1

Using a grain-oriented electrical steel sheet with a thickness of 0.23 mm, the surface of the steel sheet is irradiated with a continuous wave laser under the irradiation conditions shown in Table 1. After measuring the residual stress, the integral compressive stress value is calculated, and the respective iron losses are measured. (W _17/50 ). The results are summarized in Table 1. In Example 1, the laser power was fixed at 200 W, and the laser irradiation interval in the rolling direction was fixed at 4 mm. The integral compressive stress value is calculated by measuring the residual stress (strain) in the rolling direction using the X-ray diffractometry, and the compressive stress is obtained by formula (2).

It is clear from Table 1 that the integrated compressive stress values σS in the rolling direction of the electrical steel sheets shown in Test No.1 to No.8 (example of the present invention) are all within the range specified by the present invention: 0.20N≤σS≤0.80 N, therefore, can be reduced to a low iron loss value (W _17/50 ) of 0.75 W/kg or less, which is an iron loss improvement rate of 13%. On the other hand, the electrical steel sheets shown in Test No.9 to No.12 (comparative example) out of the condition range of 0.20N≤σS≤0.80N cannot achieve a low iron loss value (W _17/50 ) of 0.75W/kg or less . As described above, according to the present invention, a grain-oriented electrical steel sheet excellent in iron loss characteristics can be obtained.

Example 2

The surface of a grain-oriented electrical steel sheet with a plate thickness of 0.23 mm was irradiated with a continuous wave laser under the irradiation conditions shown in Table 2. After measuring the residual stress of the irradiated part, the integral compressive stress value was calculated, and the iron loss (W _17/50 ), these values are summarized in Table 2. In this second example, the laser power was fixed at 200W as in the previous example.

It is clear from Table 2 that the integrated compressive stress value σS in the rolling direction and the laser irradiation interval (strain interval) PL in the rolling direction of the electrical steel sheets shown in Test No.1 to No.6 (example of the present invention) , are all in the scope of the present invention 0.20N≤σS≤0.80N, 2mm≤PL≤8mm, so it can be reduced to a low iron loss value (W _17/50 ) of 0.75W/kg or less, which is an iron loss improvement rate of 13%. . On the other hand, although the integrated compressive stress value σS satisfies the condition, the electrical steel sheets shown in Test No. 7 and No. 8, in which the irradiation interval PL deviates from the condition, cannot achieve a low iron loss value (W _17/50 ) of 0.75W/ Below kg. As described above, according to the present invention, a grain-oriented electrical steel sheet excellent in iron loss characteristics can be obtained.

Industrial Utilization Possibility

According to the present invention, by quantitatively and appropriately controlling the residual stress introduced into the grain-oriented electrical steel sheet, especially the compressive residual stress, it is possible to stably obtain a grain-oriented electrical steel sheet excellent in iron loss characteristics compared with conventional ones. By using the grain-oriented electrical steel sheet of the present invention as an iron core, a high-efficiency and compact transformer can be manufactured, so the industrial utility value of the present invention is very high.

In the present invention, "above" and "below" indicating a numerical range both include the original number.

Claims (1)

1. the manufacture method of a low iron loss one-way electromagnetic steel plate, it is characterized in that, with the direction of rolling direction approximate vertical on, and the periodic compartment of terrain irradiation continuous-wave laser beam of 2mm～8mm is set on rolling direction, give linear strain with the rolling direction approximate vertical, make and near the place strain introduction part of described low iron loss one-way electromagnetic steel plate, produce, in the bivariate distribution perpendicular to the compressive residual stress of the rolling direction on the horizontal cross section of plate, the value that in the zone of the compressive residual stress that has rolling direction the compressive residual stress integration of this rolling direction is obtained is 0.20N～0.80N.

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