Method for surface treatment of metal materials, method for surface treatment of metal sheets, and method for manufacturing grain-oriented electrical steel sheets

Abstract

Provided is a means for suppressing a decrease in thermal strain when production line speed is increased and achieving both an increase in production efficiency and stabilization of iron loss improvement effects during operation. Said means is a method for processing the surface of a metal material or a metal sheet by irradiating an energy beam at the surface of the metal material or the metal sheet, wherein the energy beam is irradiated using at least two focus settings.

Description

Technical Field

[0001] The present invention relates to a surface processing method for a metal material, a surface processing method for a metal plate, and a manufacturing method for a grain-oriented electrical steel sheet, which are performed by irradiating an energy beam.

Background Art

[0002] Surface processing of metal materials and metal plates by irradiating an energy beam is used in various applications such as quenching, printing, lithography, and introduction of thermal strain. In particular, in the technical field of grain-oriented electrical steel sheets, a technique is used in non-heat-resistant magnetic domain refinement, in which a high energy beam such as a laser, an electron beam, or a plasma flame is irradiated onto the grain-oriented electrical steel sheet after secondary recrystallization to introduce thermal strain, thereby significantly improving the iron loss of the electrical steel sheet.

[0003] Here, the iron loss of a grain-oriented electrical steel sheet mainly consists of hysteresis loss and eddy current loss. Among these, magnetic domain refinement is used as a technique for improving eddy current loss. In magnetic domain refinement, magnetic flux non-uniformity is introduced into the steel sheet, such as after finish annealing or after baking an insulating film, by a physical technique such as introducing grooves or local strain, thereby subdividing the width of the 180° magnetic domain (main magnetic domain) formed along the rolling direction and reducing the iron loss, particularly the eddy current loss, of the grain-oriented electrical steel sheet.

[0004] For example, Patent Document 1 proposes a technique for improving the iron loss, which was 0.80 W / kg or more, to 0.70 W / kg or less by introducing linear grooves with a width of 300 μm or less and a depth of 100 μm or less on the surface of the steel sheet. Further, Patent Document 2 discloses that by irradiating a plasma flame in the sheet width direction on the surface of the steel sheet after secondary recrystallization to locally introduce thermal strain, when the magnetic flux density (B8) of the steel sheet when excited with a magnetizing force of 800 A / m is 1.935 T, the iron loss (W 17 / 50 ) is improved to 0.680 W / kg or less when excited with a maximum magnetic flux density of 1.7 T and a frequency of 50 Hz.

[0005] Furthermore, the method of introducing linear grooves as disclosed in Patent Document 1 is called heat-resistant magnetic domain refinement because the magnetic domain refinement effect does not disappear even if strain-relieving annealing is performed after core forming. On the other hand, the method of introducing thermal strain as disclosed in Patent Document 2 is called non-heat-resistant magnetic domain refinement because the effect of introducing thermal strain is lost due to strain-relieving annealing.

[0006] Grain-grain electrical steel sheets are used as core materials for transformers, and it is known that the energy efficiency of a transformer is greatly affected by the iron loss of the grain-grain electrical steel sheet that forms the core. In recent years, from the perspective of energy conservation and environmental regulations, there has been a continuing trend of strengthening efficiency regulations for transformers worldwide, and there is a strong demand for reducing energy loss in transformers. As a result, the demand for low-iron-loss grain-grain electrical steel sheets has been steadily increasing recently. Therefore, the development of technologies to improve the iron loss of grain-grain electrical steel sheets through non-heat-resistant magnetic domain subdivision is extremely important. For example, in the manufacturing lines for grain-grain electrical steel sheets, there is a need to develop technologies to improve the efficiency of this non-heat-resistant magnetic domain subdivision process. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Special Publication No. 6-22179 [Patent Document 2] Japanese Patent Application Publication No. 7-192891 [Overview of the project] [Problems that the invention aims to solve]

[0008] One way to improve the processing capacity of non-heat-resistant magnetic domain subdivision in grain-oriented electrical steel sheets is to increase the speed of the manufacturing line. However, as the speed of the manufacturing line increases, the amount of thermal strain introduced into the steel sheet gradually decreases, which is a problem because the low iron loss effect due to magnetic domain subdivision gradually diminishes. If the output of the energy beam is increased in an attempt to resolve this problem, new problems arise, such as an increased risk of equipment failure due to increased thermal effects on the optical system in the case of lasers, or an increase in manufacturing costs due to increased power consumption in the case of electron beams. Therefore, the development of methods other than simply increasing the amount of heat input is required.

[0009] This invention has been made in view of the above circumstances, and aims to suppress the decrease in the amount of thermal strain introduced when the manufacturing line speed is increased, thereby achieving both improved manufacturing efficiency and stabilization of the iron loss improvement effect during operation. [Means for solving the problem]

[0010] The inventors diligently considered how to solve the above problem.

[0011] First, we investigated the reason why the amount of thermal strain introduced decreases when the manufacturing line speed is increased (hereinafter also referred to as high-speed operation). As a result, we found that the appropriate focusing conditions for the energy beam change significantly during high-speed operation compared to offline operation and low-speed operation. Here, offline operation refers to operation in which the beam focus is adjusted with the manufacturing line stopped, and test processing is performed using the focus setting obtained therein. Low-speed operation refers to operation at a manufacturing line speed in which no characteristic degradation occurs even when operating with the focus setting obtained in offline adjustment.

[0012] The detailed reasons for the significant change in the above focus conditions are not yet clear, but the inventors have the following hypothesis.

[0013] For example, in the process of applying non-heat-resistant magnetic domain subdivision to grain-oriented electrical steel sheets (hereinafter also simply referred to as steel sheets), thermal strain is introduced linearly in the direction in which the energy beam is scanned across the steel sheet as it passes through the production line, in a direction intersecting the direction of sheet passage (the rolling direction of the steel sheet). After this energy beam scan, the energy beam is stopped outside the production line and put into a standby state. Then, once the steel sheet has been transported a predetermined distance, the standby beam is scanned again in the same direction to introduce thermal strain. By repeating the above operations, a large number of thermal strain areas are introduced at equal intervals in the direction of sheet passage, thereby subdividing the magnetic domains.

[0014] In the magnetic domain subdivision process described above, when irradiating the steel plate with an energy beam, the energy beam repeatedly undergoes irradiation and waiting (stationing). However, increasing the production line speed reduces the stationary time after beam irradiation. In this case, if an electron beam is used as the energy beam, the electron beam is scanned by a magnetic field, so the next irradiation occurs before the residual magnetic field generated inside the coil that controls beam deflection has had time to relax. As a result, a composite magnetic field is generated in which the residual magnetic field is superimposed on the magnetic field applied for beam scanning, and we believe that this causes fluctuations in the focus of the electron gun.

[0015] On the other hand, when a laser is used as the energy beam, a polyhedral mirror is used to scan the laser. As the manufacturing line speed increases, the time during which the laser does not strike each face of the polyhedral mirror decreases. In other words, the time during which the laser strikes each face of the mirror increases, and it is presumed that the heating caused by the laser at this time slightly deforms the mirror surface, resulting in a change in focus.

[0016] Based on the above findings, further investigation revealed that it is particularly effective to irradiate the energy beam using a focus setting value suitable for high-speed operation. Specifically, instead of fixing the energy beam irradiation focus setting value to a single initial value set offline, as in the past, we found that by using one or more focus setting values ​​set according to the manufacturing line speed, and using a total of at least two focus setting values, it is possible to suppress the decrease in the amount of thermal strain introduced as the manufacturing line speed increases.

[0017] Here, focus setting refers to measuring the energy beam profile using techniques such as slits, knife edges, or pinholes, and adjusting the beam focusing system so that the resulting energy profile (energy intensity and spot diameter) takes on the desired shape. In this specification, the conditions for the focus setting determined in this way are referred to as the "focus setting value."

[0018] This invention is based on the above findings. In other words, the gist of this invention is as follows.

[0019] 1. A method for processing the surface of a metal material by irradiating the surface of the metal material with an energy beam, wherein the energy beam is irradiated using at least two focus settings.

[0020] 2. The surface processing method for a metallic material according to claim 1, wherein at least one of the focus setting values ​​is changed in accordance with a change in the processing interval time τ1 = 1 / fp - Ls / Ve, which is determined from the scan speed Ve of the energy beam, the scan range Ls, and the number of irradiations per unit time fp.

[0021] 3. The surface treatment method for a metal material according to 1 or 2, wherein the metal material is a grain-oriented electrical steel sheet.

[0022] 4. Using the surface processing method of the metal material described in 3 above, irradiate the surface of the oriented electrical steel sheet with the energy beam a plurality of times in a direction intersecting the rolling direction to introduce either or both of a plurality of heat affected zones and heat distortion zones. A method for manufacturing an oriented electrical steel sheet.

[0023] 5. A step of scanning an energy beam periodically in a direction intersecting the sheet passing direction on the surface of a metal sheet passing through a production line to introduce either or both of a plurality of heat affected zones and heat distortion zones that are parallel to each other with an interval Lp in the sheet passing direction. A method for surface processing of a metal sheet, wherein the energy beam is irradiated using at least two focus setting values.

[0024] 6. Change at least one of the focus setting values according to the change in the processing interval time τ2 = Lp / Vl - Ls / Ve determined from the production line speed Vl, the interval Lp, and the scan speed Ve and scan range Ls of the energy beam. The method for surface processing of the metal sheet according to 5 above.

[0025] 7. The method for surface processing of the metal sheet according to 5 or 6 above, wherein the metal sheet is an oriented electrical steel sheet.

[0026] 8. Irradiate the energy beam repeatedly at the processing interval time τ2 under operating conditions, and adjust the convergence system of the energy beam to a condition where the focus setting value of the energy beam becomes optimal when a steady state is reached. The method for surface processing of the metal sheet according to 6 or 7 above.

Advantages of the Invention

[0027] According to the present invention, it is possible to suppress a decrease in the amount of introduced heat distortion when increasing the production line speed, and to achieve both an improvement in production efficiency and a stabilization of the effect of improving iron loss during operation.

Brief Description of the Drawings

[0028] [Figure 1] It is a diagram showing the concept of the sheet passing speed. [Figure 2]This graph shows the relationship between the processing interval time τ2 and iron loss. [Figure 3] This graph shows the relationship between the processing interval time τ2 and noise. [Figure 4] This diagram explains how to set the focus during offline adjustments. [Figure 5] This diagram illustrates how to set the focus in a pattern that repeatedly scans and waits. [Figure 6] This diagram illustrates the procedure for evaluating the degree of resist peeling. [Figure 7] This diagram illustrates the procedure for evaluating the degree of resist peeling. [Modes for carrying out the invention]

[0029] The experimental results that led to the completion of this invention are described below.

[0030] (Experiment 1) Using steel slabs with the components shown in Table 1, a 300 mm wide (= electron beam scan range Ls) cold-rolled steel strip, manufactured using a general manufacturing process for grain-oriented electrical steel sheets, was subjected to magnetic domain refinement treatment by irradiating its surface with an electron beam. A conceptual diagram of the sheet-feeding speed in this experiment is shown in Figure 1. In Figure 1, "..." indicates repeated acceleration and stagnation. As shown in Figure 1, the manufacturing line speed Vl was increased in six stages from 10 m / min to 140 m / min by repeatedly accelerating at regular intervals. The electron beam used had an output of 1 kW, with a beam irradiation interval Lp of 9 mm in the steel sheet-feeding direction and a beam scan speed Ve of 80 m / s. In the above surface treatment by beam irradiation, the processing interval time τ2, which is the waiting time between beam irradiations, is given by the following equation τ² = Lp / Vl - Ls / Ve This can be determined by the following. As described above, the manufacturing line speed Vl was increased in six steps from 10 m / min to 140 m / min, and the processing interval time τ2 decreased in inverse proportion to this speed increase over the six steps.

[0031] [Table 1]

[0032] The above surface treatment was performed using an electron beam under the following four conditions. (1) The focus conditions (initial focus settings) set offline were continuously used throughout the entire section, regardless of the manufacturing line speed. (2) In addition to the focus conditions (initial focus setting) described in (1) above, the beam output was varied (corrected) according to the processing interval time τ2 in each of the six stages of the manufacturing line speed and irradiation was performed. The amount of output correction at this time was set to the beam output that resulted in the same intensity as the offline state when the beam profile obtained by the method described later was obtained. (3) In addition to the initial focus setting value, the appropriate focus setting value for each of the six stages of production line speed was investigated in advance for each processing interval time τ2, and the electron beam was irradiated using the weighted average value obtained by weighting these focus setting values ​​by the operating time of each production line speed as the focus setting value. (4) In addition to the initial focus setting, feedback control was performed according to the actual processing interval time during operation, and the focus setting was optimized and irradiated according to the change in processing interval time τ2. Here, the actual processing interval time during operation refers to the instantaneous value of τ2 calculated from Lp, Vl, Ls, and Ve during operation.

[0033] From the steel strips obtained by irradiation treatment according to the above conditions, beveled sections were cut out for each irradiation area to fabricate a three-phase stacked core model transformer (core weight 50 kg). The iron loss characteristics of this model transformer were measured when the magnetic flux density at the core legs was 1.7 T at a frequency of 50 Hz. The iron loss characteristics at 1.7 T and 50 Hz were measured as no-load loss using a wattmeter. Simultaneously, this model transformer was excited in a soundproof room under the conditions of maximum magnetic flux density Bm = 1.7 T and frequency of 50 Hz, and the noise level (dBA) was measured using a sound level meter.

[0034] The iron loss measurement results are shown in Figure 2, and the noise measurement results are shown in Figure 3. In method (1), the iron loss increases and the noise decreases as the processing interval time τ2 decreases. This is thought to be because the electron beam is defocused as the processing interval time τ2 decreases, reducing the amount of strain introduced. In method (2), the deterioration of iron loss with decreasing processing interval time τ2 is suppressed compared to method (1), but the noise increases. This is thought to be because the defocusing of the electron beam due to the decrease in processing interval time τ2 is corrected by increasing the beam heat input, so although the depth-direction strain distribution effective for magnetic domain subdivision is restored, the total amount of introduced thermal strain increases, resulting in noise deterioration.

[0035] On the other hand, the methods that correct the focus fluctuation itself under conditions (3) and (4) above achieve both low iron loss and low noise even when the processing interval time τ2 decreases. In particular, the effect was found to be high under condition (4), in which sequential correction was performed for changes in the manufacturing line speed.

[0036] Based on the above experimental results, the inventors diligently investigated the factors that enabled the simultaneous achievement of low iron loss and low noise using the methods described in conditions (3) and (4) above. As a result, they found that when the manufacturing line speed is increased, it is effective to use at least one additional focus setting value corresponding to the processing interval time τ2, for a total of at least two focus settings, rather than fixing the beam focus setting value to one as before (i.e., continuously using the initial focus setting value). This led to the completion of the present invention described above.

[0037] Preferred embodiments of the present invention will be described in detail below. However, the present invention is not limited to the configuration disclosed in these embodiments, and various modifications are possible without departing from the spirit of the invention.

[0038] <Surface processing methods for metal materials> The present invention relates to a method for processing the surface of a metal material by irradiating the surface of the metal material with an energy beam, wherein the irradiation of the energy beam is performed using at least two focus settings according to the manufacturing line speed of the metal material.

[0039] For example, in the quenching process, a metal component placed on a production line operating at a speed set offline is subjected to surface treatment by irradiating it multiple times with an energy beam under focus conditions (initial focus setting value) also set offline. In this surface treatment, when the production line speed is increased, it is crucial to irradiate the energy beam with one or more focus setting values ​​different from the initial focus setting value. These one or more focus setting values ​​different from the initial focus setting value can be set appropriately according to the increased production line speed, and may also be set according to the processing interval time τ1 described later.

[0040] Furthermore, it is preferable to change at least one of the two focus setting values ​​in accordance with the change in the processing interval time τ1 = 1 / fp - Ls / Ve, which is determined from the scan speed Ve, scan range Ls, and number of irradiations per unit time fp of the energy beam. In other words, it is preferable to change the focus setting in accordance with the interval time between beam irradiations (processing interval time τ1), rather than the beam scan time or scan pattern.

[0041] <Manufacturing method for grain-oriented electrical steel sheets> Furthermore, by using the above surface treatment method for metal materials, the metal material can be treated as a grain-oriented electrical steel sheet, and the energy beam can be irradiated onto the surface of the grain-oriented electrical steel sheet in a direction intersecting the rolling direction. This process can be repeated multiple times at intervals in the steel sheet rolling direction to introduce either or both of multiple heat-affected zones and thermal strain zones.

[0042] In this specification, the "heat-affected zone" introduced to the surface of a metal material or metal plate (including steel plates) refers to the region where physical changes such as melting and solidification due to thermal energy are observed. On the other hand, the "thermal strain zone" introduced to a metal material or metal plate (including steel plates) refers to the region where physical changes such as melting and solidification are not observed, but the magnetic properties are altered due to the introduction of energy.

[0043] <Methods for surface treatment of metal sheets> When surface processing is performed on metal plates passing through a manufacturing line using energy beam irradiation, the energy beam is irradiated using at least two focus settings, as described above. As the at least two focus settings, as described above, an initial focus setting set offline and one or more focus settings set appropriately according to the manufacturing line speed can be used in combination. If the manufacturing line speed is increased in multiple stages, for example, a focus setting optimized for the highest line speed may be used. Alternatively, the appropriate focus settings for each section of the multiple stages of manufacturing line speed, as described later, can be investigated in advance, and a weighted average value obtained by weighting these focus settings by the operating time of each manufacturing line speed can be used.

[0044] In a surface processing method for metal sheets passing through a manufacturing line, it is particularly advantageous to set the energy beam focus as follows: When periodically scanning the energy beam in a direction intersecting the direction of passage of the metal sheet, and introducing one or both of a plurality of heat-affected zones and thermal strain zones parallel to each other with a spacing Lp in the direction of passage, it is preferable to change at least one of the two focus settings stepwise or continuously in response to changes in the processing interval time τ2 = Lp / Vl - Ls / Ve, which is determined by the manufacturing line speed Vl, spacing Lp, energy beam scanning speed Ve, and scanning range Ls. Alternatively, all of the at least two focus settings may be changed in response to changes in the processing interval time. Furthermore, an initial focus setting value set offline may be used at the start of processing, and the focus setting value may be changed in response to changes in the processing interval time after processing has started.

[0045] In other words, it is preferable to optimize the focus settings by changing them according to the interval time between beam irradiations (the "processing interval time," which is the time from when the beam scan stops until the scan resumes), rather than the beam scan time, scan speed, or processing interval.

[0046] Next, we will specifically explain the focus adjustment method when changing the focus setting value according to the processing interval time τ1 or τ2 described above.

[0047] [Focus adjustment method] In this invention, the focus adjustment of the energy beam is performed by adjusting the beam focusing conditions so that the shape of the energy beam intensity distribution (energy profile) becomes a desired shape. By adjusting the beam focusing conditions, the spot diameter and energy intensity can be adjusted to obtain an energy profile of a desired shape. The energy profile may be a one-dimensional energy profile obtained by the slit method or the edge knife method, or a two-dimensional energy profile obtained by taking scan directions from multiple axes in either of the above methods. The criterion for changing the focus is preferably the processing interval time τ1 or τ2 as described above, but it may also be a single parameter that defines the processing interval time (at least one selected from the group consisting of the number of irradiations per unit time fp or the manufacturing line speed Vl, the energy beam scan speed Ve, the energy beam scan range Ls, and the irradiation interval Lp).

[0048] The desired energy profile shape during focus adjustment can be appropriately determined according to the purpose and know-how of the surface treatment. For example, if the surface treatment is magnetic domain subdivision by introducing thermal distortion, it is preferable to make the energy profile a Gaussian shape with a small beam halo. If the surface treatment is welding, it may be preferable to make the energy profile a ring shape or a shape with a wide halo from the viewpoint of preventing spatter generation. It is also possible to make the energy profile a semi-linear, elliptical, or dotted shape using optical elements.

[0049] In typical focus adjustment, the beam focusing conditions are adjusted so that the shape of the energy profile obtained by scanning the energy beam once over the slit or knife edge as shown in Figure 4 is the desired shape. The beam irradiation is then continued while maintaining these focusing conditions. Examples of beam focusing conditions to be adjusted include, but are not limited to, the current values ​​of various control coils for electron beams, and the angle of the focusing mirror and WD (working distance) for lasers. In this specification, this method of focus adjustment is referred to as offline adjustment.

[0050] On the other hand, a preferred embodiment of focus adjustment in the present invention is to repeatedly irradiate the energy beam at the processing interval time τ1 or τ2 under the operating conditions and adjust the convergence conditions of the energy beam so that the shape of the energy profile when a steady state is reached (when the focus change reaches saturation) is a desired shape.

[0051] In other words, instead of the offline adjustment pattern described above, irradiation is repeated N times at a processing interval time τ1 or τ2 determined by the operating conditions, as shown in Figure 5. This irradiation pattern is referred to as the N-shot pattern in this specification. At the Nth irradiation of this scan-wait pattern, an energy profile is acquired and focus adjustment is performed. At this time, the number of times N is performed for intermittent operation is not specifically defined, but since the focus changes continuously in the region where N is small, it is preferable to set it so that the focus change occurs after saturation. The convergence conditions of the energy beam are adjusted so that the shape of the energy profile acquired at the Nth irradiation is optimal. The number of N at which the focus change reaches saturation can vary depending on the equipment configuration and operating conditions of the energy beam irradiation, so an appropriate value of N is selected considering these factors. This selection can be appropriately carried out by a person skilled in the art based on common technical knowledge. In this way, focus setting values ​​corresponding to various processing interval times are determined in advance and used according to τ1 or τ2 during operation.

[0052] Alternatively, the system may be configured to switch between a focus setting value obtained through offline adjustment (Condition A) and a focus setting value obtained in a pattern that takes into account the processing interval time (scan waiting time) (Condition B) (for example, the method described in conditions (3) or (4) above). In this configuration, when acquiring an energy profile using Condition A with an N-shot pattern, it is preferable to use the waiting time or operating parameter at which the energy intensity when N=N falls below a certain level compared to the intensity when N=1 as the threshold for changing the irradiation conditions. The threshold for changing the irradiation conditions varies considerably depending on the accuracy of focus required for processing, so it is necessary to set an appropriate threshold for each processing content. As this threshold, for example, the τ1 or τ2 described above, which changes the focus setting value, can be used.

[0053] In the above embodiment, for example, when performing continuous machining using the focus setting value (condition A) adjusted offline, if the machining conditions result in the energy intensity at saturation being 80% or less for the first irradiation, a focus setting value (condition B) that takes machining time into account is used. Alternatively, the machining interval time τ1 or τ2 may be used as a threshold for changing irradiation conditions, and the initial focus setting value (condition A) adjusted offline may be used when τ1 or τ2 is sufficiently long, and the focus setting value (condition B) set taking τ1 or τ2 into account may be used when τ1 or τ2 is below a certain time. This is because the difference between the initial state and the saturation state is small when τ1 or τ2 is sufficiently long, but the difference between the initial state and the saturation state becomes larger as the machining interval time τ1 or τ2 becomes shorter.

[0054] [Metal material (metal plate)] The metal material (metal sheet) used in this invention is not particularly limited as long as it is a metal material having a component composition, shape, size, etc. that is applicable to the type of energy beam used for processing. For example, when processing with a laser, any metal material with an absorption rate of 20% or more for the wavelength of the laser used for processing is sufficient. In the case of electron beam processing, any metal material in which the mean free path of accelerated electrons does not exceed the sample thickness is sufficient. A typical example of such a metal material (metal sheet) is grain-oriented electrical steel sheet.

[0055] [Grain-oriented electrical steel sheet] The grain-oriented electrical steel sheet, which is the metallic material for which the effects of the present invention are most expected, will be described in detail below.

[0056] First, the composition of the slab for grain-oriented electrical steel sheets should be such that secondary recrystallization occurs. Furthermore, when using inhibitors, for example, if using an AlN-based inhibitor, appropriate amounts of Al and N should be included; if using a MnS·MnSe-based inhibitor, appropriate amounts of Mn, Se, and / or S should be included. Of course, both inhibitors may be used in combination. In this case, the preferred content of Al, N, S, and Se is as follows: Al: 0.010~0.065% by mass, N:0.0050~0.0120% by mass, S: 0.005~0.030 mass% and Se:0.005~0.030% by mass That is the case.

[0057] Furthermore, the present invention can also be applied to grain-oriented electrical steel sheets that do not use inhibitors and have limited Al, N, S, and Se content. In this case, the Al, N, S, and Se content is as follows: Al: Less than 0.010% by mass, N: Less than 0.0050 mass%, S: Less than 0.0050 mass% and Se: Less than 0.0050% by mass It is preferable to suppress it.

[0058] The following describes in detail the typical basic components and optional additives that can be applied to the steel material (slab) for grain-oriented electrical steel sheets of the present invention.

[0059] C: 0.08% by mass or less Carbon (C) is added to improve the structure of hot-rolled sheets. However, if the C content exceeds 0.08% by mass, it becomes difficult to decarburize to 50 ppm by mass or less during the manufacturing process, where magnetic aging does not occur. Therefore, it is preferable to keep the C content at 0.08% by mass or less. Furthermore, since secondary recrystallization occurs even in steel materials that do not contain C, no particular lower limit is set for the C content.

[0060] Si:2.0~8.0% by mass Si is an effective element for increasing the electrical resistance of steel and improving iron loss. If the Si content is less than 2.0 mass%, the improvement effect is not fully realized, while if it exceeds 8.0 mass%, workability and sheet pulsability deteriorate significantly, and the magnetic flux density also decreases. Therefore, it is preferable to keep the Si content in the range of 2.0 to 8.0 mass%.

[0061] Mn:0.005~1.0% by mass Mn is an essential element for improving hot workability, but its effect is difficult to obtain sufficiently if the content is less than 0.005 mass%. On the other hand, if it exceeds 1.0 mass%, the magnetic flux density deteriorates. Therefore, it is preferable to keep the Mn content in the range of 0.005 to 1.0 mass%.

[0062] In addition to the basic components mentioned above, the following optional additives, known to be effective in improving magnetic properties, may be included as appropriate. Ni: 0.03~1.50% by mass, Sn: 0.01~1.50% by mass, Sb: 0.005~1.50% by mass, Cu:0.03~3.0% by mass, P:0.03~0.50% by mass, Mo: 0.005~0.10 mass% and Cr:0.03~1.50% by mass One or more selected from among them

[0063] Ni is an effective element for improving the structure of hot-rolled sheets and enhancing their magnetic properties. However, if the content is less than 0.03 mass%, its contribution to the magnetic properties is small, while if it exceeds 1.50 mass%, secondary recrystallization becomes unstable and the magnetic properties deteriorate. Therefore, it is preferable to keep the Ni content in the range of 0.03 to 1.50 mass%.

[0064] Furthermore, while Sn, Sb, Cu, P, Mo, and Cr are also elements that improve magnetic properties, their effect is insufficient if their content is below the lower limit mentioned above, and if it exceeds the upper limit, the growth of secondary recrystallized grains is suppressed, resulting in a deterioration of magnetic properties. Therefore, it is preferable to keep the content of each element within the ranges mentioned above.

[0065] Furthermore, the components other than those mentioned above consist of Fe and unavoidable impurities.

[0066] After hot rolling the steel material (slab) of the grain-oriented electrical steel sheet consisting of the above-mentioned component system, hot-rolled sheet annealing is optionally performed. Next, cold rolling is performed once or twice or more with an intermediate annealing in between to finish it into a steel strip of the final thickness. After that, the steel strip is subjected to decarburization annealing, an annealing separating agent mainly composed of MgO is applied, and then it is wound into a coil and subjected to final annealing for the purpose of secondary recrystallization and forsterite coating formation. After the final annealing, the steel strip is subjected to planarization annealing, and then a magnesium phosphate-based tension coating is formed to form a steel strip for the product sheet.

[0067] In the present invention, the process after planarization annealing includes a magnetic domain refinement step in which thermal strain is introduced to the surface of the grain-oriented electrical steel sheet (steel strip) by energy beam irradiation. In non-heat-resistant magnetic domain refinement that introduces thermal strain, it is preferable to perform energy beam irradiation after the formation of a tension film. If it is performed before the formation of the tension film, the introduced thermal strain will be released by the baking during the formation of the tension film, and the magnetic domain refinement effect will not be obtained.

[0068] Furthermore, when performing heat-resistant magnetic domain refinement by groove machining as a metal surface treatment, it is preferable to irradiate with an energy beam before the formation of the tension film. This is because irradiating after the formation of the tension film will destroy the formed tension film.

[0069] Examples of metal surface processing methods in this invention include hardening, cleaning, resist stripping, localized thermal distortion introduction, and laser peening. This invention can be applied to any processing method that involves scanning a metal plate surface multiple times with an energy beam.

[0070] Of the above processing steps, the introduction of local thermal strain for magnetic domain subdivision requires the most precise focus control, and therefore the application of the present invention is most effective. The magnetic domain subdivision process will be described below.

[0071] [Beam irradiation conditions] To subdivide non-heat-resistant magnetic domains, it is effective to use lasers with wavelengths of 400 nm to 1200 nm, which have a high absorption rate in metals, as well as electron beams with high penetrating power.

[0072] The following describes in more detail the preferred irradiation conditions for the electron beam when implementing the present invention.

[0073] • Acceleration voltage: 60kV to 300kV A higher acceleration voltage is preferable because it increases the linearity of electrons and reduces the thermal impact on the area outside the beam irradiation zone. For this reason, the acceleration voltage is preferably 60kV or higher, more preferably 90kV or higher, and even more preferably 120kV or higher.

[0074] On the other hand, if the acceleration voltage is too high, it becomes difficult to shield the X-rays generated by the electron beam irradiation. Therefore, from a practical standpoint, it is preferable to keep it below 300kV, and more preferably below 200kV.

[0075] • Beam current: 0.5~40mA From the viewpoint of beam diameter, a smaller beam current is preferable. This is because increasing the beam current tends to broaden the beam diameter due to Coulomb repulsion. Therefore, in this invention, it is preferable to set the beam diameter to 40 mA or less. On the other hand, if the beam current is too small, there will be insufficient energy to form strain, so it is preferable to set it to 0.5 mA or more.

[0076] • Vacuum pressure within the beam irradiation area: 1 × 10⁻⁶ -5 Pa or more and 3Pa or less Electron beams are scattered by gas molecules, causing increases in beam diameter and halo diameter, as well as a decrease in energy. Therefore, a high vacuum level in the beam irradiation area is desirable, preferably below 3 Pa. There is no particular lower limit, but lowering it excessively will increase the cost of the vacuum system, such as vacuum pumps. For practical purposes, 1 × 10⁻¹⁶ Pa is preferable. -5 It is preferable to use a pressure of Pa or higher.

[0077] The following describes in more detail the preferred laser irradiation conditions for implementing the present invention.

[0078] • Laser output: 50W to 5000W If the laser output is low, the laser scanning speed needs to be reduced to provide sufficient energy to impart thermal strain. However, excessively slowing the speed can lead to a deterioration in manufacturing efficiency. On the other hand, while increasing the output makes it easier to impart thermal strain, it also increases damage to the laser transport system, leading to increased maintenance frequency and a decrease in manufacturing efficiency. From these perspectives, it is preferable to set the laser output between 50W and 5000W.

[0079] Furthermore, the following irradiation conditions are preferred for both electron beams and lasers.

[0080] • Spot diameter: 300 μm or less A smaller spot diameter is preferable because it allows for localized distortion. Therefore, in this invention, the beam diameter of the energy beam is preferably 300 μm or less, more preferably 280 μm or less, and even more preferably 260 μm or less. In this invention, the spot diameter refers to the full width at half maximum of the beam profile obtained by the slitting method using a slit with a width of 30 μm.

[0081] ·Deflection speed: 5~400m / s A slower beam deflection speed is preferable because it increases the amount of heat incident per unit length of steel sheet. However, excessively low speeds reduce the processing area per unit time, thus decreasing manufacturing efficiency. Therefore, a speed of 5 m / s or higher is preferable. On the other hand, excessively high speeds require a larger power supply to provide the heat input necessary for melting the steel sheet, leading to larger equipment. Therefore, a speed of 400 m / s or lower is preferable.

[0082] • Angle between the direction of thermal strain introduction and the direction perpendicular to the rolling direction: within ±30° The greater the inclination of the thermal strain introduction direction from the plate width direction, the fewer magnetic poles are generated at the interface between the circulating magnetic domain and the main magnetic domain, thus degrading the domain subdivision effect. Therefore, it is preferable that the angle between the thermal strain introduction direction and the plate width direction be within ±30°.

[0083] Next, the present invention will be specifically described based on examples. The following examples illustrate preferred examples of the present invention and do not limit the invention in any way. It is also possible to implement the invention with modifications to the extent that they are in line with the spirit of the invention, and such modifications are also included within the technical scope of the present invention. [Examples]

[0084] Using a steel slab with the alloy composition shown in Table 2, with the remainder being Fe and unavoidable impurities, a 2 μm thick resist coating was applied to the entire surface of one side of a 300 mm wide cold-rolled steel strip for grain-oriented electrical steel sheets, manufactured using a general manufacturing process. The resist was then removed by laser irradiation. The concept of the sheet feeding speed in this example is shown in Figure 1. As shown in Figure 1, the manufacturing line speed Vl was increased from 10 m / min to 140 m / min by repeatedly accelerating at regular intervals. At this time, the laser focus setting was performed under the five conditions listed in Table 3. In addition, the processing interval time τ2 was varied by combining the beam irradiation interval Lp in the steel sheet feeding direction and the beam scan speed Ve. The laser beam profile was measured using the 30 μm wide slit method, and the current value of each focusing coil was adjusted so that the shape of the beam profile was Gaussian.

[0085] [Table 2]

[0086] [Table 3]

[0087] The resulting steel strip was then observed using a laser microscope to assess the degree of resist peeling. The area ratio Rs of the peeled area per unit area of ​​the laser-irradiated area, the width WR of the peeled area, and the rectangularness Rr of the peeled area were specifically evaluated as follows, according to the procedures shown in Figures 6 and 7.

[0088] The area ratio Rs of the delamination zone was defined and evaluated as follows, as shown in Figure 6: Rs = A / (Φ*Ls) (where * represents the multiplication symbol), using the laser spot diameter Φ, scan range Ls, and the area A of the delamination zone calculated by the laser microscope. The closer the Rs value is to 1.0, the more the heat-affected zone and the delamination zone coincide, meaning that the laser-induced resist delamination is superior.

[0089] As shown in Figure 6, the peeled area width WR was calculated by measuring the length of the exposed base metal in the direction perpendicular to the scan direction (rolling direction) within the peeled area of ​​the scan range at 10 points in the plate width direction, and taking the average value. The closer the WR value is to the spot diameter Φ, the better the laser-based resist peeling performance.

[0090] As shown in Figure 7, the rectangularness Rr was evaluated by calculating the slope of the peeled area (Rr = d / l) from the resist thickness d and the irradiation area length l in the surface profile of the steel sheet. A larger Rr value indicates a steeper peeled edge of the resist, resulting in superior resistance in subsequent processes.

[0091] The evaluation results are shown in Table 4. It can be seen that by performing the machining under conditions (c), (d), and (e) that satisfy the requirements of the present invention, precise machining can be performed regardless of the machining interval time.

[0092] [Table 4] [Examples]

[0093] Using slabs with the component systems shown in Table 2, a 300 mm wide grain-oriented electrical steel strip was manufactured using a general manufacturing process, and after finish annealing, an insulating coating was formed. This strip was then irradiated with an electron beam to perform magnetic domain refinement. The concept of the sheet passing speed in this example is shown in Figure 1. As shown in Figure 1, the manufacturing line speed Vl was repeatedly accelerated at regular intervals, increasing from 10 m / min to 140 m / min.

[0094] At this time, the electron beam focus setting conditions were performed using the five conditions listed in Table 3. In addition, the processing interval time τ2 was varied by combining various combinations of beam irradiation interval in the steel sheet feeding direction and beam scan speed. The electron beam profile was measured using the slit method, and the current values ​​of the focusing lens and stigmeter were adjusted so that the shape of the beam profile was Gaussian.

[0095] From the resulting steel strip, angled steel was cut out to create a three-phase stacked core model transformer (core weight 50 kg). The iron loss characteristics were measured when the magnetic flux density at the core legs was 1.7 T at a frequency of 50 Hz. The iron loss characteristics at 1.7 T and 50 Hz were measured using a wattmeter to determine the no-load loss. Simultaneously, this model transformer was excited in a soundproof room under the conditions of maximum magnetic flux density Bm = 1.7 T and frequency 50 Hz, and the noise level (dBA) was measured using a sound level meter.

[0096] The evaluation results are shown in Table 5. A smaller value for iron loss (W / kg) indicates lower iron loss and superior iron loss characteristics. A smaller value for noise level (dBA) indicates lower noise and superior noise characteristics. It can be seen that by performing processing under conditions (c), (d), and (e) that satisfy the requirements of the present invention, precise processing is achieved regardless of the processing interval time, resulting in low iron loss and low noise.

[0097] [Table 5] [Industrial applicability]

[0098] The present invention can be used to modify the surface of a metallic material by irradiating it with an energy beam. In particular, it can be used to suppress the deterioration of processing accuracy that occurs when forming a heat-affected zone on a metal sheet at high speed, and to suppress the deterioration of iron loss characteristics and noise characteristics that occur when introducing thermal strain into grain-oriented electrical steel sheets at high speed.

Claims

1. A method for processing the surface of a grain-oriented electrical steel sheet by irradiating the surface of the grain-oriented electrical steel sheet with an energy beam, wherein the energy beam is irradiated using at least two focus setting values, including one or more focus setting values ​​set according to the manufacturing line speed, and at least one of the at least two focus setting values ​​is changed in accordance with a change in the processing interval time τ1 = 1 / fp - Ls / Ve, which is determined from the scan speed Ve of the energy beam, the scan range Ls, and the number of irradiations per unit time fp.

2. A method for manufacturing a grain-oriented electrical steel sheet, comprising using the surface processing method for grain-oriented electrical steel sheets described in claim 1, wherein the energy beam is irradiated multiple times on the surface of the grain-oriented electrical steel sheet in a direction intersecting the rolling direction to introduce one or both of a plurality of heat-affected zones and thermal strain zones.

3. The process includes periodically scanning the surface of a grain-oriented electrical steel sheet passing through a manufacturing line with an energy beam in a direction intersecting the direction of passage, thereby introducing one or both of a plurality of heat-affected zones and thermal strain zones that are spaced apart Lp in the direction of passage and parallel to each other, A surface processing method for grain-oriented electrical steel sheets, comprising irradiating an energy beam with at least two focus setting values, including one or more focus setting values ​​set according to the manufacturing line speed, and changing at least one of the at least two focus setting values ​​in accordance with a change in the processing interval time τ2 = Lp / Vl - Ls / Ve, which is determined from the manufacturing line speed Vl, the interval Lp, and the scan speed Ve and scan range Ls of the energy beam.

4. The surface processing method for grain-oriented electrical steel sheets according to claim 3, comprising repeatedly irradiating the sheet with an energy beam at the processing interval time τ2 under operating conditions, and adjusting the energy beam focusing system to the conditions under which the focus setting value of the energy beam is optimal when a steady state is reached.

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