Method for processing surface of metal material, method for processing surface of metal plate, and method for manufacturing grain-oriented electrical steel sheet

Abstract

Provided is a means for suppressing a reduction in the thermal strain amount when increasing the production line speed, and achieving both an improvement in production efficiency and a stabilization of the iron loss improvement effect during work. In a method for processing a surface of a metal material or a metal plate by irradiating the surface of the metal material or the metal plate with an energy beam, 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 by irradiating an energy beam, a surface processing method for a metal plate, and a method for producing a grain-oriented electromagnetic steel sheet. Background Art

[0002] Surface processing of metal materials or metal plates by irradiation with energy beams is used in various applications such as quenching, printing, photolithography, and the introduction of thermal strain. In particular, in the field of grain-oriented electrical steel sheets, this technology significantly improves the iron loss of grain-oriented electrical steel sheets by irradiating them with high-energy beams such as lasers, electron beams, or plasma flames after secondary recrystallization, introducing thermal strain. This technology is used for non-heat-resistant magnetic domain refinement.

[0003] Here, the iron loss of grain-oriented electrical steel sheets is primarily composed of hysteresis loss and eddy current loss. Magnetic domain refinement is used as a method to improve eddy current loss. In magnetic domain refinement, after final annealing or sintering of the insulating coating, magnetic flux inhomogeneity is introduced through physical methods such as grooves or local strain in the steel sheet. This refines the width of the 180° magnetic domains (main magnetic domains) formed along the rolling direction, thereby reducing the iron loss of the grain-oriented electrical steel sheet, particularly the eddy current loss.

[0004] For example, Patent Document 1 proposes a technique for improving the iron loss of 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 into the surface of a steel plate. Furthermore, Patent Document 2 proposes a technique for introducing local thermal strain by irradiating a plasma flame in the width direction of the steel plate surface after secondary recrystallization, thereby reducing the iron loss (W) when excited at a maximum magnetic flux density of 1.7 T and a frequency of 50 Hz to 1.935 T when the magnetic flux density (B8) of the steel plate is 800 A / m. 17 / 50 ) was improved to 0.680 W / kg.

[0005] The linear groove introduction method disclosed in Patent Document 1 maintains its magnetic domain refinement effect even after strain relief annealing is performed after core forming, and is therefore referred to as heat-resistant magnetic domain refinement. On the other hand, the thermal strain introduction method disclosed in Patent Document 2 loses the effect of thermal strain introduction due to strain relief annealing, and is therefore referred to as non-heat-resistant magnetic domain refinement.

[0006] It is known that grain-oriented electromagnetic steel sheets are used as core materials for transformers, and the energy efficiency of transformers is significantly affected by the iron loss of the grain-oriented electromagnetic steel sheets serving as the core. In recent years, from the perspective of energy conservation and environmental regulations, the world has continued to strengthen energy efficiency standards for transformers, and the need to reduce transformer energy loss has become increasingly urgent. As a result, the demand for grain-oriented electromagnetic steel sheets with low iron loss has continued to grow in recent years. Therefore, it is crucial to develop technologies that utilize non-heat-resistant magnetic domain refinement to improve the iron loss of grain-oriented electromagnetic steel sheets. For example, in the production line of grain-oriented electromagnetic steel sheets, it is urgent to develop technologies that improve the efficiency of the non-heat-resistant magnetic domain refinement treatment.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Publication No. 6-22179

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 7-192891 Summary of the Invention

[0011] One approach to improving the processing capability of non-heat-resistant magnetic domain refinement in grain-oriented electrical steel sheets is to increase the speed of the production line. However, increasing the production line speed gradually reduces the amount of thermal strain introduced into the steel sheet, diminishing the iron loss reduction effect of magnetic domain refinement. Increasing the energy beam output to address this issue creates new challenges: with lasers, the increased risk of device failure due to the increased thermal impact on the optical system; with electron beams, the increased power consumption leads to increased manufacturing costs. Therefore, the development of methods other than simply increasing the heat input is required.

[0012] The present invention has been made in view of the above circumstances, and an object thereof is to suppress a decrease in the amount of thermal strain introduced when the line speed is increased, thereby achieving both improvement in manufacturing efficiency and stabilization of the iron loss improvement effect during operation.

[0013] The inventors have conducted intensive studies to solve the above-mentioned problems.

[0014] First, we investigated the reason why the amount of thermal strain introduced decreases when increasing the production line speed (hereinafter referred to as high-speed operation). We found that the optimal focusing conditions for the energy beam significantly change during high-speed operation compared to offline or low-speed operation. Offline operation refers to operations in which the production line is stopped, the beam focus is adjusted, and test processing is performed using the focus setting obtained. Low-speed operation refers to operations at a production line speed that does not cause performance degradation even when operating at the focus setting obtained through offline adjustment.

[0015] Although the detailed reasons for the significant change in the focusing conditions are not yet clear, the inventors speculate as follows.

[0016] For example, a non-heat-resistant magnetic domain refinement treatment for grain-oriented electrical steel sheets (hereinafter referred to as steel sheets) involves scanning an energy beam in a direction intersecting the sheet feed direction (the sheet rolling direction) while the sheet is being fed through the production line. This introduces thermal strain linearly in that direction. After scanning the energy beam, the beam is placed in a standby state, stopping outside the production line. Subsequently, after the sheet is transported a specified distance, the beam in the standby state is scanned again in the aforementioned direction, introducing thermal strain. By repeating this process, multiple thermal strain regions are introduced at equal intervals in the sheet feed direction, achieving magnetic domain refinement.

[0017] In the aforementioned magnetic domain refinement process, when an energy beam is applied to a steel sheet, the beam repeatedly irradiates and then waits (dwells). However, increasing the production line speed reduces the dwell time after beam irradiation. When an electron beam is used as the energy beam, since the beam is scanned using a magnetic field, the next irradiation occurs before the residual magnetic field generated within the coil controlling beam deflection has dissipated. This creates a composite magnetic field, where the residual magnetic field overlaps with the magnetic field applied for beam scanning, causing fluctuations in the electron gun's focus.

[0018] On the other hand, when using a laser as the energy beam, since a polygonal mirror is used to scan the laser, the time during which the laser does not irradiate each surface of the polygonal mirror decreases as the production line speed increases. In other words, the laser irradiation time on each surface of the mirror increases, and the laser heats the mirror surface during this time, causing slight deformation of the mirror surface and resulting in a change in focus.

[0019] Based on this understanding, further research has revealed that using an appropriate focus setting for energy beam irradiation is particularly effective during high-speed operations. Specifically, rather than fixing the focus setting for the irradiation energy beam to a single initial value set offline, as is conventional practice, the team discovered that using a combination of at least two focus settings, set in accordance with the production line speed, can reduce the amount of thermal strain introduced as production lines speed up.

[0020] Here, focus setting refers to measuring the energy beam distribution using methods such as the slit method, knife-edge method, or pinhole method, and adjusting the beam focusing system so that the resulting energy distribution (energy intensity and spot diameter) has the desired shape. The focus setting conditions determined in this manner are referred to as "focus setting values" in this specification.

[0021] The present invention has been completed based on the above findings. Specifically, the gist of the present invention is as follows.

[0022] 1. A surface processing method for a metal material, comprising irradiating an energy beam onto the surface of the metal material to process the surface of the metal material, wherein the energy beam is irradiated using at least two focus setting values.

[0023] 2. A surface processing method for metal materials according to item 1 above, wherein at least one of the focus setting values ​​is changed according to a processing interval time τ1 = 1 / fp - Ls / Ve determined by the scanning speed Ve, scanning range Ls and number of irradiations per unit time fp of the energy beam.

[0024] 3. The surface processing method of a metal material according to 1 or 2 above, wherein the metal material is a grain-oriented electrical steel sheet.

[0025] 4. A method for manufacturing a grain-oriented electrical steel sheet, comprising: using the surface processing method for a metal material described in 3 above, irradiating the surface of the grain-oriented electrical steel sheet with the energy beam multiple times in a direction intersecting a rolling direction to introduce multiple heat-affected zones and thermally strained zones.

[0026] 5. A surface processing method for a metal plate, comprising periodically scanning an energy beam on the surface of a metal plate running on a production line in a direction intersecting the running direction of the plate, introducing one or two of a plurality of heat-affected parts and thermally strained parts that are parallel to each other at a distance Lp in the running direction, and irradiating the energy beam using at least two focus setting values.

[0027] 6. According to the surface processing method of the metal plate described in the above 5, at least one of the above-mentioned focus setting values ​​changes according to the change of the processing interval time τ2 = Lp / Vl-Ls / Ve determined by the production line speed Vl, the above-mentioned interval Lp and the scanning speed Ve and scanning range Ls of the above-mentioned energy beam.

[0028] 7. The surface processing method of a metal plate according to 5 or 6 above, wherein the metal plate is a grain-oriented electromagnetic steel plate.

[0029] 8. A surface processing method for a metal plate according to 6 or 7 above, wherein the focusing system of the energy beam is adjusted to the following conditions: the focusing setting value of the energy beam becomes the optimal condition when the energy beam is repeatedly irradiated with the above-mentioned processing interval time τ2 under the operating conditions to become a stable state.

[0030] According to the present invention, it is possible to suppress a decrease in the amount of thermal strain introduced when the line speed is increased, thereby achieving both improvement in manufacturing efficiency and stabilization of the iron loss improvement effect during operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This diagram shows the concept of board running speed.

[0032] Figure 2 This is a graph showing the relationship between the machining interval time τ2 and the iron loss.

[0033] Figure 3 This is a graph showing the relationship between the machining interval time τ2 and noise.

[0034] Figure 4 This is a diagram explaining a method of focus setting by offline adjustment.

[0035] Figure 5 This is a diagram explaining a method of setting focus in the repeated scanning and standby modes.

[0036] Figure 6 This is a diagram explaining the method of evaluating the peeling condition of the resist.

[0037] Figure 7 This is a diagram explaining the method of evaluating the peeling condition of the resist. DETAILED DESCRIPTION

[0038] Hereinafter, the experimental results that led to the completion of the present invention will be described.

[0039] (Experiment 1)

[0040] Using steel slabs having the components shown in Table 1, the surface of a cold-rolled steel strip having a width of 300 mm (= scanning range Ls of the electron beam) produced by a general production process of grain-oriented electrical steel sheets was irradiated with an electron beam to perform magnetic domain refinement. The concept of the plate feed speed in this experiment is shown in the figure. Figure 1 It should be explained that Figure 1 The “…” in the code indicates repeated acceleration and stopping. Figure 1 As shown in Figure 1, the line speed Vl is repeatedly accelerated in a certain interval, increasing the line speed Vl from 10m / min to 140m / min in 6 stages. The output of the electron beam used is 1kW, the interval Lp of the beam irradiation in the direction of the steel plate is set to 9mm, and the beam scanning speed Ve is set to 80m / s. In the surface processing using the above-mentioned beam irradiation, the processing interval time τ2, which is the waiting time after the beam irradiation until the next beam irradiation, can be calculated by the following formula:

[0041] τ2=Lp / Vl-Ls / Ve.

[0042] As described above, since the line speed V1 is increased from 10 m / min to 140 m / min in six stages, the processing interval time τ2 is reduced in six stages in inverse proportion to the speed increase.

[0043] Table 1

[0044]

[0045] In the above-mentioned surface processing, electron beam irradiation is performed according to the four conditions described below.

[0046] (1) The focus conditions (initial focus setting values) set in the offline state are continuously used in the entire section without taking the line speed into consideration.

[0047] (2) Based on the focus conditions (initial focus setting values) of (1) above, irradiation is performed by varying (correcting) the beam output according to the processing interval τ2 in each of the six stages of line speed. The output correction amount at this time is the beam output that achieves the same intensity of the beam distribution obtained by the method described later as that obtained during the offline process.

[0048] (3) Based on the initial focus setting value, for each interval of the production line speed in the six stages, the appropriate focus setting values ​​under the processing interval time τ2 are pre-investigated, these focus setting values ​​are weighted by the operation time of each production line speed, and the obtained weighted average value is used as the focus setting value for irradiating the electron beam.

[0049] (4) Based on the initial focus setting value, feedback control is performed based on the actual measured value of the processing interval during operation, and irradiation is performed by optimizing the focus setting value according to the change in the processing interval τ2. Here, the actual measured value of the processing interval during operation refers to the instantaneous value of τ2 calculated based on Lp, Vl, Ls, and Ve during operation.

[0050] From the steel strips irradiated under the above conditions, beveled test pieces were cut from each irradiated area in each section to create a three-phase laminated core model transformer (core weight 50 kg). The core loss characteristics of this model transformer were measured at a frequency of 50 Hz and a magnetic flux density of 1.7 T in the core leg portion. The core loss characteristics at 1.7 T and 50 Hz were measured using a power meter to measure no-load loss. Simultaneously, the model transformer was excited in a soundproof room at a maximum magnetic flux density of 1.7 T and a frequency of 50 Hz, and the noise level (dBA) was measured using a sound meter.

[0051] The iron loss measurement results are shown in Figure 2 , and the noise measurement results are shown in Figure 3. In the method of condition (1), iron loss increases and noise decreases as the processing interval time τ2 decreases. This is considered to be because the electron beam defocuses due to the decrease in the processing interval time τ2, and the amount of strain introduced decreases. In addition, in the method of condition (2), the deterioration of iron loss associated with the decrease in the processing interval time τ2 tends to be suppressed compared to the method of condition (1), but the noise increases. This is considered to be because the defocusing of the electron beam caused by the decrease in the processing interval time τ2 is corrected by increasing the beam heat input, so that the strain distribution in the depth direction effective for magnetic domain refinement is restored, but the total amount of introduced thermal strain increases, resulting in noise degradation.

[0052] On the other hand, in the method of correcting the focus variation itself in the above-mentioned conditions (3) and (4), even if the processing interval τ2 is reduced, low iron loss and low noise can be achieved simultaneously. In particular, it was found that this effect is higher in condition (4), which sequentially corrects the variation in line speed.

[0053] Based on the experimental results described above, the inventors conducted in-depth research on the key factors that enable both low iron loss and low noise to be achieved by the methods described in conditions (3) and (4). As a result, they discovered that, when increasing the production line speed, rather than fixing the beam focus setting value to a single value (i.e., continuing to use the initial focus setting value), it is very effective to use at least one additional focus setting value based on the processing interval τ2, for example, and to use at least two focus setting values ​​in total. This led to the completion of the present invention.

[0054] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the configuration disclosed in the present embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0055] <Surface processing methods of metal materials>

[0056] The present invention is a method for processing the surface of a metal material by irradiating the surface of the metal material with an energy beam. It is important that the irradiation of the energy beam is performed using at least two focus setting values ​​according to the production line speed of the metal material.

[0057] For example, in a quenching process, a metal component placed on a production line operating at a speed set offline is subjected to surface processing by repeatedly irradiating it with an energy beam using the focus conditions set offline (initial focus setting) to achieve heat absorption. In this surface processing, when the production line speed is increased, it is important to irradiate the energy beam using one or more focus settings different from the initial focus setting. These one or more focus settings different from the initial focus setting can be appropriately set based on the increased production line speed or based on the processing interval τ1 described below.

[0058] Furthermore, it is preferred that at least one of the at least two focus setting values ​​be varied in accordance with a processing interval τ1 = 1 / fp - Ls / Ve, which is determined by the energy beam scanning speed Ve, the scanning range Ls, and the number of irradiations per unit time fp. In other words, it is preferred that the focus setting be varied in accordance with the interval between beam irradiations (processing interval τ1), rather than the beam scanning time or scanning pattern.

[0059] <Method for Manufacturing Grain-Oriented Electrical Steel Sheet>

[0060] In addition, if the above-mentioned surface processing method of a metal material is used, the above-mentioned metal material is used as a oriented electromagnetic steel sheet, and the surface of the oriented electromagnetic steel sheet is irradiated with the above-mentioned energy beam in a direction intersecting with the rolling direction, and the irradiation is repeated multiple times at intervals in the rolling direction of the steel sheet, one or both of multiple heat-affected zones and thermally strained zones can be introduced.

[0061] In this specification, a "heat-affected zone" introduced on the surface of a metal material or metal plate (including a steel plate) refers to a region where physical changes such as melting and solidification due to thermal energy are observed. On the other hand, a "thermally strained zone" introduced on a metal material or metal plate (including a steel plate) refers to a region where physical changes such as melting and solidification are not observed, but where magnetic properties have changed due to the introduction of energy.

[0062] <Surface processing methods for metal sheets>

[0063] When surface processing is performed on a metal plate running on a production line using energy beam irradiation, the energy beam is also irradiated using at least two focus setting values ​​as described above. As the at least two focus setting values, as described above, a combination of an initial focus setting value set in an offline state and one or more focus setting values ​​appropriately set according to the production line speed can be used. When the production line speed is increased in multiple stages, for example, a focus setting value optimized for the highest production line speed can be used. Alternatively, a weighted average value can be obtained by weighting these focus setting values ​​by the operating time of each production line speed after pre-investigating the appropriate focus setting values ​​for each interval of the production line speed in multiple stages and the processing interval time τ2 described later.

[0064] In a method for surface processing a metal plate that travels on a production line, it is particularly advantageous to perform the following energy beam focus setting. The energy beam is periodically scanned in a direction intersecting the direction in which the metal plate travels. When the energy beam is introduced into one or two of a plurality of heat-affected zones and thermally strained zones that are parallel to each other at intervals Lp in the direction in which the plate travels, it is preferred that one or more of at least two focus setting values ​​be changed in stages or continuously according to changes in the processing interval time τ2 = Lp / Vl - Ls / Ve, which is determined by the production line speed Vl, the interval Lp, the energy beam scanning speed Ve, and the scanning range Ls. It should be noted that all of the at least two focus setting values ​​may also be changed according to changes in the processing interval time. Furthermore, an initial focus setting value set offline may be used at the start of processing, and after processing begins, the focus setting value may be changed according to changes in the processing interval time.

[0065] That is, it is preferable to optimize by changing the focus setting based on the interval time between beam irradiation (the "processing interval time" which is the time from when beam scanning stops to when scanning resumes) rather than based on the beam scanning time, scanning speed, and processing interval.

[0066] Next, a focus adjustment method when changing the focus setting value according to the above-mentioned processing interval time τ1 or τ2 will be specifically described.

[0067] [Focus adjustment method]

[0068] The focus adjustment of the energy beam of the present invention is performed by adjusting the convergence conditions of the beam so that the shape of the intensity distribution (energy distribution) of the energy beam becomes a desired shape. By adjusting the convergence conditions of the beam, the spot diameter and energy intensity are adjusted, and an energy distribution of a desired shape can be obtained. The energy distribution can be a one-dimensional energy distribution that can be obtained by a slit method or a knife-edge method, or it can be a two-dimensional energy distribution that can be obtained by obtaining scanning directions from multiple axes in any of the above methods. It should be noted that the above-mentioned processing interval time τ1 or τ2 is preferably used as a reference for focus change, or it can be a parameter monomer that determines the processing interval time (selected from at least one of the number of irradiations fp per unit time or the production line speed Vl, the scanning speed Ve of the energy beam, the scanning range Ls of the energy beam, and the irradiation interval Lp).

[0069] The shape of the desired energy distribution during focus adjustment can be appropriately determined based on the purpose of the surface processing and experience. For example, in the case where the surface processing is magnetic domain refinement performed by introducing thermal strain, it is preferred to make the energy distribution a Gaussian shape with a small beam halo. In the case where the surface processing is welding, from the viewpoint of preventing sputtering, it is also preferred to make the energy distribution an annular shape with a wide halo. In addition, optical elements can also be used to make the energy distribution a semi-linear shape, an elliptical shape, or a point array shape.

[0070] In the usual focus adjustment, on the above-mentioned slit or knife edge, such as Figure 4 As shown, the beam convergence conditions are adjusted so that the energy distribution obtained by scanning the energy beam once becomes the desired shape. This convergence condition is maintained while beam irradiation continues. Examples of adjusted beam convergence conditions include, but are not limited to, the current values ​​of various control coils for electron beams and the angle of the focusing mirror and the working distance (WD) for laser beams. In this manual, this method of focusing adjustment is referred to as offline adjustment.

[0071] On the other hand, as a preferred method of focusing adjustment in the present invention, it is preferred to repeatedly irradiate the energy beam within the above-mentioned processing interval time τ1 or τ2 under the operating conditions so as to adjust the convergence conditions of the energy beam so that the shape of the energy distribution when it becomes a stable state (a state where the focusing change reaches saturation) is the desired shape.

[0072] That is, Figure 5 As shown, instead of the above-mentioned offline adjustment mode, N repeated irradiations are performed in the processing interval time τ1 or τ2 determined by the operating conditions. This irradiation mode is referred to as the N irradiation mode in this specification. In the Nth irradiation of the repeated scan-standby mode, the energy distribution is obtained and the focus adjustment is performed. At this time, the number of intermittent operations N is not specifically specified. Since the focus changes continuously in the area with N smaller values, it is preferably set in a manner after the focus change is saturated. The convergence conditions of the energy beam are adjusted so that the shape of the energy distribution obtained in the Nth irradiation becomes optimal. The number N of times the focus change reaches saturation can be variously changed according to the device structure and operating conditions of the energy beam irradiation, so a suitable value of N is selected in consideration of these. This selection can be appropriately implemented by those skilled in the art based on technical common sense. In this way, the focus setting values ​​corresponding to various processing intervals are predetermined and used according to τ1 or τ2 in the operation.

[0073] Alternatively, a method may be employed in which the focus setting value (condition A) under offline adjustment is switched to the focus setting value (condition B) in a mode that takes into account the processing interval time (scanning standby time) (for example, the method of the above-mentioned condition (3) or (4)). In this method, when the above-mentioned condition A is used and the energy distribution is obtained in the N irradiation mode, it is preferable to set the standby time or operating parameter at which the energy intensity when N=N is reduced to a certain level relative to the intensity when N=1 as the threshold for changing the irradiation condition. The threshold for changing the irradiation condition varies depending on the focusing accuracy required for the processing, so it is necessary to set an appropriate threshold for each processing content. As this threshold, for example, the above-mentioned τ1 or τ2 that changes the focus setting value can be used.

[0074] In the above-described method, for example, when continuous machining is performed using the focus setting value adjusted offline (Condition A), the focus setting value in a mode that takes machining time into account (Condition B) is used under machining conditions where the energy intensity in the saturated state is 80% or less for the first irradiation. Alternatively, using the machining interval τ1 or τ2 as a threshold for changing irradiation conditions, the initial focus setting value adjusted offline (Condition A) is used when τ1 or τ2 is sufficiently long. When τ1 or τ2 is below a certain level, the focus setting value is switched to a focus setting that takes τ1 or τ2 into account (Condition B). This is because the deviation between the initial state and the saturated state is small when τ1 or τ2 is sufficiently long, while the deviation between the initial state and the saturated state increases as the machining interval τ1 or τ2 decreases.

[0075] [Metal material (metal plate)]

[0076] The metal material (metal plate) used in the present invention can be used without particular limitation, as long as it has a composition, shape, and dimensions suitable for the type of energy beam used in the process. For example, when processing with a laser, a metal material with an absorptivity of 20% or greater relative to the wavelength of the laser used in the process can be used. In the case of electron beam processing, a metal material in which the mean free path of the accelerated electrons does not exceed the thickness of the sample can be used. A typical example of such a metal material (metal plate) is a grain-oriented electromagnetic steel sheet.

[0077] [Grain-oriented electrical steel sheet]

[0078] Hereinafter, a grain-oriented electrical steel sheet as a metal material for which the application effect of the present invention can be most expected will be described in detail.

[0079] First, the composition of the steel slab for grain-oriented electrical steel sheet can be any composition that causes secondary recrystallization. Furthermore, when using inhibitors, for example, AlN-based inhibitors can contain appropriate amounts of Al and N. Furthermore, when using MnS / MnSe-based inhibitors, Mn, Se, and / or S can be contained in appropriate amounts. Of course, two inhibitors can also be used in combination. In this case, the preferred contents of Al, N, S, and Se are, respectively, 0.010-0.065 mass% for Al, 0.0050-0.0120 mass% for N, 0.005-0.030 mass% for S, and 0.005-0.030 mass% for Se.

[0080] Furthermore, the present invention can also be applied to grain-oriented electrical steel sheets that do not use inhibitors that limit the contents of Al, N, S, and Se. In this case, the contents of Al, N, S, and Se are preferably suppressed to less than 0.010 mass% for Al, less than 0.0050 mass% for N, less than 0.0050 mass% for S, and less than 0.0050 mass% for Se, respectively.

[0081] Representative basic components and optional added components of a steel billet (slab) for a grain-oriented electrical steel sheet applicable to the present invention will be specifically described.

[0082] C: 0.08 mass % or less

[0083] C is added to improve the hot-rolled sheet structure. However, if the C content exceeds 0.08 mass%, decarburization to 50 mass ppm or less, which does not cause magnetic aging, becomes difficult during the manufacturing process. Therefore, the C content is preferably 0.08 mass% or less. Furthermore, even steel billets containing no C undergo secondary recrystallization, so there is no particular lower limit on the C content.

[0084] Si: 2.0-8.0 mass%

[0085] Si is an element that effectively increases the electrical resistance of steel, thereby improving iron loss. If the Si content is less than 2.0 mass%, this improvement effect is not fully realized. On the other hand, if it exceeds 8.0 mass%, workability and sheet-forming properties are significantly degraded, and the magnetic flux density is also reduced. Therefore, the Si content is preferably within the range of 2.0 to 8.0 mass%.

[0086] Mn: 0.005-1.0 mass%

[0087] Mn is an element necessary for improving hot workability, but if the content is less than 0.005 mass%, this effect is not fully achieved. On the other hand, if it exceeds 1.0 mass%, the magnetic flux density deteriorates. Therefore, the Mn content is preferably in the range of 0.005-1.0 mass%.

[0088] In addition to the above-mentioned basic components, the following optional additives known to be effective in improving magnetic properties may be appropriately contained, selected from one or more of Ni: 0.03 to 1.50 mass%, Sn: 0.01 to 1.50 mass%, Sb: 0.005 to 1.50 mass%, Cu: 0.03 to 3.0 mass%, P: 0.03 to 0.50 mass%, Mo: 0.005 to 0.10 mass%, and Cr: 0.03 to 1.50 mass%.

[0089] Nickel is an effective element for improving the microstructure of hot-rolled sheets and enhancing magnetic properties. However, if the content is less than 0.03% by mass, its contribution to magnetic properties is minimal. On the other hand, if it exceeds 1.50% by mass, secondary recrystallization becomes unstable and magnetic properties deteriorate. Therefore, the Ni content is preferably within the range of 0.03 to 1.50% by mass.

[0090] Sn, Sb, Cu, P, Mo, and Cr are also elements that improve magnetic properties. However, if their contents are below the lower limits mentioned above, the effects are insufficient. If their contents exceed the upper limits, the growth of secondary recrystallized grains is inhibited, deteriorating the magnetic properties. Therefore, it is preferable that their contents be within the above-mentioned ranges.

[0091] Furthermore, components other than the above components are composed of Fe and inevitable impurities.

[0092] The grain-oriented electrical steel sheet (steel slab) composed of the aforementioned composition is hot-rolled and optionally annealed. It is then cold-rolled once or twice or more times with intermediate annealing to form a steel strip of the final thickness. The strip is then decarburized and annealed, coated with an annealing separator primarily composed of MgO, and wound into a coil for final annealing aimed at secondary recrystallization and the formation of a forsterite coating. After the final annealing, the strip is flattened and a magnesium phosphate tension coating is formed to produce the finished steel strip.

[0093] The present invention includes a magnetic domain refinement step in which thermal strain is introduced by irradiating the surface of the grain-oriented electrical steel sheet (strip) with an energy beam, as part of the post-flattening annealing process. In non-heat-resistant magnetic domain refinement, which introduces thermal strain, energy beam irradiation is preferably performed after the tension film is formed. This is because if the irradiation is performed before the tension film is formed, the introduced thermal strain is released by sintering during the tension film formation, preventing the magnetic domain refinement effect.

[0094] When heat-resistant magnetic domain refinement is performed using groove processing as metal surface processing, it is preferable to perform energy beam irradiation before forming the tension film. This is because if energy beam irradiation is performed after the tension film is formed, the formed tension film will be destroyed.

[0095] Examples of metal surface processing in the present invention include quenching, cleaning, resist stripping, local thermal strain introduction, laser shock, etc. The present invention is applicable to any processing method that scans an energy beam multiple times on a metal plate surface.

[0096] Among the above processes, the introduction of localized thermal strain for magnetic domain refinement requires the most precise focus control, and therefore the application effect of the present invention is the highest.

[0097] [Beam irradiation conditions]

[0098] For non-heat-resistant magnetic domain refinement, it is effective to use an electron beam having a high penetrating power in addition to a laser having a wavelength of 400 nm to 1200 nm which has a high absorption rate for metal.

[0099] Hereinafter, preferred electron beam irradiation conditions for carrying out the present invention will be described in further detail.

[0100] Accelerating voltage: 60kV~300kV

[0101] A high acceleration voltage is preferred because it increases the electron's linearity and reduces the thermal effects on the outside of the beam irradiation area. For these reasons, the acceleration voltage is preferably 60 kV or higher, more preferably 90 kV or higher, and even more preferably 120 kV or higher.

[0102] On the other hand, if the accelerating voltage is too high, it becomes difficult to shield the X-rays generated by electron beam irradiation. Therefore, from a practical point of view, it is preferably 300 kV or less, and more preferably 200 kV or less.

[0103] Beam current: 0.5~40mA

[0104] From the perspective of beam diameter, a low beam current is preferred. This is because increasing the beam current tends to widen the beam diameter due to Coulomb repulsion. Therefore, in the present invention, the beam diameter is preferably set to 40 mA or less. On the other hand, if the beam current is too low, the energy required to generate strain is insufficient, so it is preferably set to 0.5 mA or above.

[0105] Vacuum degree within the beam irradiation area: 1×10 －5 Pa~3Pa

[0106] The electron beam is scattered by gas molecules, resulting in an increase in beam diameter and halo diameter, and a decrease in energy. Therefore, it is better to have a higher vacuum degree in the beam irradiation area, and the pressure is preferably below 3 Pa. There is no particular restriction on the lower limit, but if it is too low, the cost of the vacuum system such as the vacuum pump will increase. Therefore, it is preferably 1×10 －5 Pressure above Pa.

[0107] Hereinafter, preferred laser irradiation conditions for carrying out the present invention will be described in further detail.

[0108] Laser output: 50W~5000W

[0109] If the laser output is low, the laser scanning speed needs to be slowed down to provide sufficient energy for the application of thermal strain. In this case, if the speed is too low, it will lead to a deterioration in manufacturing efficiency. On the other hand, if the output is high, although the application of thermal strain becomes easier, it will also increase damage to the laser delivery system, increase the frequency of maintenance, and reduce manufacturing efficiency. From the above perspectives, the laser output is preferably 50W to 5000W.

[0110] In addition, for both electron beams and lasers, the following irradiation conditions are preferable.

[0111] Spot diameter: 300μm or less

[0112] A smaller spot diameter is preferred because it allows for more localized strain to be introduced. Therefore, in the present invention, the beam diameter of the energy beam is preferably set to 300 μm or less, more preferably 280 μm or less, and even more preferably 260 μm or less. In the present invention, the spot diameter refers to the full width at half maximum of the beam profile obtained using a 30 μm slit using the slit method.

[0113] Deflection speed: 5~400m / s

[0114] The slower the beam deflection speed, the greater the amount of heat incident on the steel sheet per unit length, so a slower speed is preferred. However, excessively low speeds reduce the processing area per unit time, reducing manufacturing efficiency. Therefore, a speed of 5 m / s or higher is preferred. Furthermore, excessively high speeds increase the power capacity required to provide the heat input required to melt the steel sheet, leading to increased equipment size. Therefore, a speed of 400 m / s or lower is preferred.

[0115] Angle between thermal strain introduction direction and rolling right angle direction: within ±30°

[0116] The further the thermal strain introduction portion's extension direction tilts from the plate width, the fewer magnetic poles are generated at the interface between the circulating magnetic domains and the main magnetic domains, thus degrading the magnetic domain refinement effect. Therefore, the angle between the thermal strain introduction portion's extension direction and the plate width is preferably within ±30°.

[0117] Next, the present invention will be specifically described according to the embodiments. The following embodiments are preferred examples of the present invention and are not subject to any limitation of the present embodiments. The present invention may also be modified and implemented within the scope of the present invention, and such a mode is also included in the technical scope of the present invention.

[0118] Example 1

[0119] A steel billet having the alloy composition shown in Table 2 and the balance consisting of Fe and inevitable impurities was used. A 2 μm thick resist film was applied to the entire surface of a 300 mm wide cold-rolled steel strip for grain-oriented electrical steel sheet manufactured by a conventional manufacturing process. The resist was then removed by laser irradiation. The concept of the plate feed speed in the examples is as follows: Figure 1 As shown. Figure 1 As shown, the line speed Vl was repeatedly accelerated in a certain interval, from 10 m / min to 140 m / min. At this time, the laser focus setting value was set under the five conditions listed in Table 3. Furthermore, the processing interval τ2 was varied by varying the beam irradiation interval Lp in the steel plate feeding direction and the beam scanning speed Ve. The laser beam profile was measured using a 30 μm wide slit method, and the current values ​​of the focusing coils were adjusted to achieve a Gaussian beam profile.

[0120] Table 2

[0121]

[0122] Table 3

[0123]

[0124] The peeling state of the resist was observed on the steel strip obtained in this way using a laser microscope. Figure 6 and Figure 7 The method shown specifically evaluates the area ratio Rs of the peeling portion per unit area of ​​the laser irradiation portion, the width WR of the peeling portion, and the rectangularity Rr of the peeling portion as shown below.

[0125] like Figure 6 As shown, the area ratio Rs of the peeled portion is defined and evaluated based on the laser spot diameter Φ, the scanning range Ls, and the area A of the peeled portion calculated using a laser microscope, using the formula Rs = A / (Φ * Ls) (where * indicates a multiplication sign). A value of Rs closer to 1.0 indicates a closer alignment between the heat-affected zone and the peeled portion, indicating excellent resist releasability using a laser.

[0126] like Figure 6 As shown, the peeling width WR is the average length of the exposed portion of the steel base in the direction perpendicular to the scanning direction (rolling direction) of the peeling portion measured within a 10-point scanning range in the sheet width direction. The closer the WR value is to the spot diameter Φ, the better the resist stripping properties using the laser.

[0127] like Figure 7As shown, the rectangularity Rr is evaluated by calculating the slope of the peeling portion (Rr = d / l) based on the resist thickness d distributed on the surface of the steel plate and the irradiation portion length l. A larger Rr value means a steeper peeling edge of the resist, which improves the corrosion resistance in subsequent steps.

[0128] The above evaluation results are shown in Table 4. It is understood that by performing processing under the conditions satisfying the requirements (c), (d), and (e) of the present invention, precise processing can be performed regardless of the processing interval.

[0129] Table 4

[0130]

[0131] Example 2

[0132] Using steel slabs having the composition shown in Table 2, a 300 mm wide grain-oriented electrical steel strip was produced by a general manufacturing process and formed with an insulating film after final annealing, and subjected to an electron beam treatment for magnetic domain refinement. Figure 1 As shown. Figure 1 As shown, the production line speed Vl is repeatedly accelerated in a certain interval, increasing from 10m / min to 140m / min.

[0133] At this time, the electron beam focusing conditions were set using the five conditions listed in Table 3. Furthermore, the processing interval τ2 was varied by combining various combinations of the beam irradiation interval and beam scanning speed in the steel plate feeding direction. The electron beam distribution was measured using the slit method, and the current values ​​of the converging lens and the divergence corrector were adjusted to achieve a Gaussian beam distribution.

[0134] From the steel strip thus obtained, bevel-cut materials were cut into a three-phase laminated iron core model transformer (core weight 50 kg). The core loss characteristics were measured at a frequency of 50 Hz and a magnetic flux density of 1.7 T in the core leg portion. The core loss characteristics at 1.7 T and 50 Hz were determined by measuring the no-load loss using a wattmeter. Simultaneously, the model transformer was excited in a soundproof room at a maximum magnetic flux density of 1.7 T and a frequency of 50 Hz, and the noise level (dBA) was measured using a sound meter.

[0135] The above evaluation results are shown in Table 5. The smaller the value of the iron loss (W / kg), the lower the iron loss, that is, the better the iron loss characteristics. The smaller the value of the noise level (dBA), the lower the noise, that is, the better the noise characteristics. It can be seen that by performing processing under the conditions (c), (d), and (e) of the requirements of the present invention, precise processing can be performed regardless of the processing interval, achieving low iron loss and low noise.

[0136] Table 5

[0137]

[0138] Industrial applicability

[0139] The present invention can be used to modify the surface of metal materials by irradiating them with energy beams. In particular, it can be used to suppress the degradation of machining accuracy caused by forming heat-affected zones on metal sheets at high speed, and to suppress the degradation of iron loss and noise characteristics caused by introducing thermal strain into grain-oriented electrical steel sheets at high speed.

Claims

1. A method for processing a surface of a metal material by irradiating an energy beam onto the surface of the metal material to process the surface of the metal material, wherein: The energy beam is irradiated using at least two focus settings.

2. The surface processing method of a metal material according to claim 1, wherein: At least one of the focus setting values ​​is changed according to a change in a processing interval τ1 determined by a scanning speed Ve, a scanning range Ls, and a number of irradiations per unit time fp of the energy beam, τ1=1 / fp-Ls / Ve.

3. The surface processing method of a metal material according to claim 1 or 2, wherein: The metal material is a grain-oriented electromagnetic steel sheet.

4. A method for manufacturing a grain-oriented electromagnetic steel sheet, comprising: using the surface processing method for a metal material according to claim 3, irradiating the surface of the grain-oriented electromagnetic steel sheet with the energy beam multiple times in a direction intersecting a rolling direction to introduce multiple heat-affected zones and thermally strained zones.

5. A surface processing method for a metal plate, comprising: The process of periodically scanning the surface of a metal plate running on a production line with an energy beam in a direction intersecting the running direction, and introducing one or both of a plurality of heat-affected zones and thermally strained zones parallel to each other at intervals Lp in the running direction, Furthermore, the energy beam is irradiated using at least two focus settings.

6. The surface processing method of a metal plate according to claim 5, wherein: At least one of the focus setting values ​​is changed according to a change in a processing interval time τ2 determined by the line speed Vl, the interval Lp, the scanning speed Ve of the energy beam, and the scanning range Ls, τ2=Lp / Vl-Ls / Ve.

7. The surface processing method of a metal plate according to claim 5 or 6, wherein: The metal plate is a grain-oriented electromagnetic steel plate.

8. The surface processing method of a metal plate according to claim 6 or 7, wherein: The focusing system of the energy beam is adjusted to the following conditions: the energy beam is repeatedly irradiated at the processing interval time τ2 under the working conditions, so that the focus setting value of the energy beam when the stable state is achieved becomes optimal.

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