Surface processing method for metal material, surface processing method for metal sheet, and production method for grain-oriented electromagnetic steel sheet

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

METHOD FOR SURFACE PROCESSING OF METAL MATERIAL, METHOD FOR SURFACE PROCESSING OF METAL PLATE, AND METHOD FOR PRODUCING GRAIN-ORIENTED ELECTRICAL STEEL PLATE

[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, all of which are carried out by irradiating an energy beam.

[0002] Surface processing of metal materials and metal sheets by irradiation with energy beams is used in various applications such as hardening, printing, lithography, and thermal distortion introduction. In particular, in the technical field of grain-oriented electrical steel sheets, it is used for non-heat-resistant magnetic domain refinement, a technology that significantly improves the iron loss of grain-oriented electrical steel sheets by irradiating them with high-energy beams such as lasers, electron beams, and plasma flames to introduce thermal distortion after secondary recrystallization.

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

[0004] For example, Patent Document 1 proposes a technique for improving iron loss from 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 sheet. Also, Patent Document 2 proposes a technique for improving iron loss from 0.80 W / kg or more to 0.70 W / kg or less by irradiating a plasma flame in the width direction of the surface of a steel sheet after secondary recrystallization to locally introduce thermal strain, thereby reducing the magnetic flux density (B ８ ) is 1.935T, the iron loss (W 17 / 50 A method has been proposed to improve this to 0.680 W / kg.

[0005] 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 is not lost even when stress relief 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 stress relief annealing.

[0006] Grain-oriented electrical steel sheets are used as the core material of transformers, and it is known that the energy efficiency of transformers is significantly affected by the iron loss of the grain-oriented electrical steel sheets that make up the core. In recent years, from the perspectives of energy conservation and environmental regulations, transformer efficiency regulations have been tightening worldwide, and there is a strong demand for reducing energy loss in transformers. As a result, demand for low-core-loss grain-oriented electrical steel sheets has been steadily increasing. Therefore, the development of technology to improve the iron loss of grain-oriented electrical steel sheets by non-heat-resistant magnetic domain refinement is extremely important. For example, in the production line of grain-oriented electrical steel sheets, there is a need to develop technology to improve the efficiency of this non-heat-resistant magnetic domain refinement process.

[0007] Japanese Patent Publication No. 6-22179 Publication No. 7-192891

[0008] One way to improve the processing capacity of non-heat-resistant magnetic domain refinement for grain-oriented electrical steel sheets is to increase the speed of the production line. However, as the production line speed increases, the amount of thermal strain introduced into the steel sheet gradually decreases, and the low iron loss effect of magnetic domain refinement gradually diminishes. If the output of the energy beam is increased in an attempt to solve 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, and increased manufacturing costs due to increased power consumption in the case of electron beams. Therefore, there is a need to develop methods other than simply increasing the heat input.

[0009] The present 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 production line speed is increased, thereby achieving both improved production efficiency and stabilization of the iron loss improvement effect during operation.

[0010] The inventors have conducted extensive research to solve the above problems.

[0011] First, we investigated the reason why the amount of thermal strain introduced decreases when the production line speed increases (hereinafter referred to as high-speed operation). As a result, we found that the appropriate focus 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 while the production line is stopped, and test processing is performed using the focus setting value obtained there. Furthermore, low-speed operation refers to operation at a production line speed at which characteristic degradation does not occur even when operating with the focus setting value obtained through offline adjustment.

[0012] Although the detailed reason why the focus condition changes so greatly is not clear, the inventors speculate that it is due to the following.

[0013] For example, in a process for applying non-heat-resistant magnetic domain refinement to grain-oriented electrical steel sheet (hereinafter also referred to simply as steel sheet), an energy beam is scanned on the steel sheet on a production line in a direction intersecting the sheet passing direction (steel sheet rolling direction) as the steel sheet passes through the line, thereby introducing linear thermal strain in that direction. After this energy beam scan, the energy beam is stopped outside the production line and placed in a standby state. Then, once the steel sheet has been transported a predetermined distance, the standby beam is again scanned in the above direction to introduce thermal strain. By repeating the above operation, a large number of thermally strained portions are introduced at equal intervals in the sheet passing direction, thereby achieving magnetic domain refinement.

[0014] In the magnetic domain refinement process described above, when an energy beam is irradiated onto a steel sheet, the energy beam repeatedly irradiates and waits (stays). However, increasing the production line speed reduces the dwell time after beam irradiation. If an electron beam is used as the energy beam, the electron beam is scanned by a magnetic field, meaning that the next irradiation occurs before the residual magnetic field generated inside the coil that controls the beam deflection is relaxed. This results in a composite magnetic field in which the residual magnetic field is superimposed on the magnetic field applied for beam scanning, which is thought to result in fluctuations in the focus of the electron gun.

[0015] On the other hand, when a laser is used as the energy beam, the laser is scanned using a polygonal mirror, and as the production line speed increases, the time during which the laser does not hit each surface of the polygonal mirror decreases. In other words, the time during which the laser hits each surface of the mirror becomes longer, and it is estimated that the heating by the laser at this time causes a slight deformation of the mirror surface, resulting in a change in focus.

[0016] Based on the above findings, further studies were conducted and it was found that it is particularly effective to irradiate the energy beam using a focus setting value suitable for high-speed operation. That is, instead of fixing the focus setting value of the energy beam irradiation to a single initial value set offline as in the past, the present inventors have discovered that by using at least two focus settings in total, one or more focus settings set according to the production line speed, it is possible to suppress the reduction in the amount of thermal strain introduced due to the increase in production line speed.

[0017] Here, focus setting refers to measuring the profile of the energy beam using a technique such as a slit, knife edge, or pinhole, and adjusting the beam convergence system so that the obtained energy profile (energy intensity and spot diameter) has a desired shape. The focus setting conditions determined in this manner are referred to as "focus setting values" in this specification.

[0018] The present invention has been made based on the above findings. That is, the gist and configuration of the present invention are 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, the method comprising irradiating the surface of the metal material with the energy beam using at least two focus settings.

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

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

[0022] 4. A method for producing a grain-oriented electrical steel sheet, using the method for surface processing of a metal material described in 3 above, to irradiate the surface of the grain-oriented electrical steel sheet with the energy beam a plurality of times in a direction intersecting the rolling direction, thereby introducing a plurality of heat-affected zones and / or thermally strained zones.

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

[0024] 6. The metal plate surface processing method according to 5, wherein at least one of the focus setting values ​​is changed in response to changes in the production line speed Vl, the interval Lp, and the processing interval time τ2 = Lp / Vl - Ls / Ve determined from the scanning speed Ve and scanning range Ls of the energy beam.

[0025] 7. The method for surface processing a metal plate according to 5 or 6 above, wherein the metal plate is a grain-oriented electrical steel plate.

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

[0027] According to the present invention, it is possible to suppress the decrease in the amount of thermal strain introduced when the production line speed is increased, thereby achieving both improved production efficiency and stabilization of the iron loss improvement effect during operation.

[0028] FIG. 1 is a diagram illustrating the concept of strip passing speed. FIG. 2 is a graph illustrating the relationship between processing interval time τ2 and iron loss. FIG. 3 is a graph illustrating the relationship between processing interval time τ2 and noise. FIG. 4 is a diagram illustrating a method for setting focus in offline adjustment. FIG. 5 is a diagram illustrating a method for setting focus in a pattern in which scan-standby is repeated. FIG. 6 is a diagram illustrating a method for evaluating the peeling state of the resist. FIG. 7 is a diagram illustrating a method for evaluating the peeling state of the resist.

[0029] The experimental results that led to the completion of the present invention will be described below.

[0030] (Experiment 1) A steel slab with the chemical composition shown in Table 1 was used. A 300 mm-wide (=electron beam scanning range Ls) cold-rolled steel strip surface manufactured using a typical manufacturing process for grain-oriented electrical steel sheets was subjected to magnetic domain refinement by irradiating it with an electron beam. Figure 1 shows a conceptual diagram of the strip running speed used in this experiment. The "..." in Figure 1 indicates repeated acceleration and dwell. As shown in Figure 1, the production line speed Vl was repeatedly accelerated at regular intervals, increasing in six stages from 10 m / min to 140 m / min. The electron beam used had an output of 1 kW, the beam irradiation interval Lp in the steel sheet running direction was 9 mm, and the beam scanning speed Ve was 80 m / s. In the surface processing using beam irradiation, the processing interval time τ2, which is the waiting time between beam irradiations, can be calculated using the following equation: τ2 = Lp / Vl - Ls / Ve. As described above, the production line speed Vl was increased in six stages from 10 m / min to 140 m / min, and therefore the processing interval time τ2 was decreased in six stages in inverse proportion to this increase in speed.

[0031]

[0032] For the above surface processing, the electron beam was irradiated under the following four conditions. (1) The focus condition (initial focus setting value) set offline was used continuously throughout the entire section, regardless of the production line speed. (2) In addition to the focus condition (initial focus setting value) set in (1) above, the beam power was changed (corrected) according to the processing interval time τ2 for each section of the six production line speeds. The output correction amount was set to the beam power such that the intensity of the beam profile obtained using the method described below was equivalent to that obtained offline. (3) In addition to the initial focus setting value, each focus setting value appropriate for the processing interval time τ2 for each section of the six production line speeds was investigated in advance, and the weighted average of these focus setting values, weighted by the operating time of each production line speed, was used as the focus setting value for electron beam irradiation. (4) In addition to the initial focus setting value, feedback control was performed according to the actual processing interval time during operation, and the focus setting value was optimized according to changes in the processing interval time τ2 for irradiation. Here, the actual value of the processing interval time during operation means the instantaneous value of τ2 calculated from Lp, Vl, Ls, and Ve during operation.

[0033] From the steel strip obtained by the irradiation treatment under each of the above conditions, oblique beams were cut out for each irradiation region of each section, and a three-phase stacked core model transformer (core weight 50 kg) was produced. The iron loss characteristics of this model transformer were measured when the magnetic flux density in the core leg portion was 1.7 T at a frequency of 50 Hz. The iron loss characteristics at 1.7 T and 50 Hz were measured by measuring the no-load loss using a wattmeter. At the same time, this model transformer was excited in a soundproof room under conditions of a maximum magnetic flux density Bm = 1.7 T and a 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. With the method under condition (1), iron loss increased and noise decreased as the processing interval time τ2 decreased. This is thought to be because the electron beam was defocused by the reduction in processing interval time τ2, reducing the amount of introduced strain. Furthermore, with the method under condition (2), the deterioration of iron loss with the reduction in processing interval time τ2 tends to be suppressed compared to the method under condition (1), but noise increased. This is thought to be because the defocusing of the electron beam due to the reduction in processing interval time τ2 is compensated for by increasing the beam heat input, and although the depth direction strain distribution, which is effective for magnetic domain refinement, is restored, the total amount of introduced thermal strain increased, resulting in a deterioration in noise.

[0035] On the other hand, the methods of correcting the focus fluctuation itself under the above conditions (3) and (4) achieve both low iron loss and low noise even when the processing interval time τ2 is reduced. In particular, it was found that the effect was particularly high under condition (4), in which sequential correction was made in response to changes in the production line speed.

[0036] Based on the above experimental results, the inventors have thoroughly investigated the factors that enable both low iron loss and low noise to be achieved by the techniques of the above conditions (3) and (4). As a result, they have found that when the production line speed is increased, it is effective to use at least one other focus setting value corresponding to the processing interval time τ2, for example, a total of at least two focus setting values, rather than fixing the beam focus setting value to one as in the past (i.e., continuing to use the initial focus setting value), and have thus completed the present invention.

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

[0038] <Method for processing the surface of a metal material> 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, and it is essential that the irradiation of the energy beam is carried out using at least two focus setting values ​​according to the production line speed of the metal material.

[0039] For example, in a hardening process, a metal workpiece placed on a production line operating at a speed set offline is subjected to heat absorption surface processing by irradiating the workpiece with an energy beam multiple times under focus conditions (initial focus settings) also set offline. In this surface processing, when the production line speed is increased, it is essential to irradiate the workpiece with the energy beam at one or more focus settings different from the initial focus settings. The one or more focus settings different from the initial focus settings may be appropriately set according to the increased production line speed, or may be set according to the processing interval time τ1 described below.

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

[0041] <Method for manufacturing grain-oriented electrical steel sheet> Furthermore, by using the above-described method for surface processing of a metal material, the metal material can be made into 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, and this can be repeated multiple times at intervals in the rolling direction of the steel sheet, thereby introducing multiple heat-affected zones and / or thermally strained zones.

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

[0043] <Method for Surface Processing of Metal Sheet> When surface processing is performed on a metal sheet passing through a production line by irradiating it with an energy beam, the energy beam is irradiated using at least two focus settings as described above. As the at least two focus settings, as described above, a combination of an initial focus setting set offline and one or more focus settings 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 optimized for the maximum line speed can be used. Alternatively, each focus setting value that is appropriate for the processing interval time τ2 described below for each section of multiple production line speeds can be investigated in advance, and a weighted average of these focus settings weighted by the operating time of each production line speed can be used.

[0044] In a method for surface processing a metal sheet passing through a production line, it is particularly advantageous to set the focus of the energy beam as follows. When periodically scanning the energy beam in a direction intersecting the sheet passing direction to introduce multiple parallel heat-affected zones and / or thermally distorted zones at an interval Lp in the sheet passing direction, it is preferable to change one or more of at least two focus setting values ​​stepwise or continuously in response to changes in the processing interval 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 is also possible to change all of the at least two focus setting values ​​in response to changes in the processing interval. Alternatively, 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 after processing has begun.

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

[0046] Next, a focus adjustment method when changing the focus setting value in accordance with the above-mentioned processing interval time τ1 or τ2 will be specifically described.

[0047] [Focus Adjustment Method] In the present invention, the focus adjustment of the energy beam is performed by adjusting the beam convergence conditions so that the shape of the energy beam intensity distribution (energy profile) is the desired shape. By adjusting the beam convergence conditions, the spot diameter and energy intensity can be adjusted to obtain an energy profile with the desired shape. The energy profile may be a one-dimensional energy profile that can be obtained by the slit method or the edge knife method, or a two-dimensional energy profile that can be obtained by taking the scanning direction from multiple axes in either of the above methods. The focus change is preferably based on the above-mentioned processing interval time τ1 or τ2, but may also be based on a single parameter that determines the processing interval time (at least one selected from the group consisting of the number of irradiations per unit time fp or the production line speed Vl, the energy beam scanning speed Ve, the energy beam scanning range Ls, and the irradiation interval Lp).

[0048] The shape of the energy profile desired during focus adjustment may be determined appropriately depending on the purpose and know-how of the surface processing. For example, if the surface processing is magnetic domain refinement by introducing thermal strain, it is preferable to make the energy profile Gaussian with little beam halo. If the surface processing is welding, it may be preferable to make the energy profile ring-shaped or with a wide halo to prevent spatter. It is also possible to use optical elements to make the energy profile semi-linear, elliptical, or dot-sequence.

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

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

[0051] That is, instead of the offline adjustment pattern described above, as shown in FIG. 5, irradiation is repeated N times with a processing interval time τ1 or τ2 determined by the operating conditions. This irradiation pattern is referred to herein as an N-shot pattern. During the Nth irradiation of this scan-wait pattern, an energy profile is acquired and focus adjustment is performed. The number of intermittent operations N is not particularly specified, but since the focus changes continuously in areas where N is small, it is preferable to set it so that the focus change occurs after saturation. The energy beam convergence conditions are adjusted so that the shape of the energy profile acquired during the Nth irradiation is optimized. The number N at which the focus change reaches saturation can vary depending on the energy beam irradiation device configuration and operating conditions, so an appropriate value of N is selected taking these factors into consideration. This selection can be made appropriately by those 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, an embodiment may be employed in which a focus setting value obtained by offline adjustment (condition A) is switched to a focus setting value (condition B) for a pattern that takes into account the processing interval time (scan wait time) (e.g., the method of the above condition (3) or (4)). In this embodiment, when an energy profile is obtained using the above condition A for an N-shot pattern, it is preferable to set the threshold for changing the irradiation conditions to the wait time or operating parameter when the energy intensity at N = N drops below a certain level compared to the intensity at N = 1. The threshold for changing the irradiation conditions varies depending on the focus accuracy required for processing, so an appropriate threshold must be set for each processing content. For example, the above-mentioned τ1 or τ2, which changes the focus setting value, can be used as this threshold.

[0053] In the above-described embodiment, for example, when continuous processing is performed using a focus setting value (condition A) adjusted offline, under processing conditions where the energy intensity in the saturated state for the first irradiation is 80% or less, a focus setting value (condition B) in a pattern that takes processing time into consideration is used. Alternatively, a processing interval time τ1 or τ2 is used as a threshold for changing the irradiation conditions, and when τ1 or τ2 is sufficiently long, an initial focus setting value (condition A) adjusted offline is used, and under processing conditions where τ1 or τ2 is a certain time or less, the focus setting value (condition B) set taking τ1 or τ2 into consideration may be used. This is because if τ1 or τ2 is sufficiently long, the difference between the initial state and the saturated state is small, but the shorter the processing interval time τ1 or τ2, the greater the difference between the initial state and the saturated state.

[0054] [Metallic Material (Metal Plate)] The metallic material (metal plate) of the present invention can be any metallic material with a component composition, shape, size, etc. that is compatible with the type of energy beam used for processing, without any particular limitations. For example, when processing with a laser, the metallic material should have an absorptivity of 20% or more for the wavelength of the laser used for processing. In the case of electron beam processing, the metallic material should have a mean free path of accelerated electrons that does not exceed the sample thickness. A typical example of such a metallic material (metal plate) is grain-oriented electrical steel sheet.

[0055] [Grain-oriented electrical steel sheet] Grain-oriented electrical steel sheet, which is a metal material that is most likely to be affected by the application of the present invention, will be described in detail below.

[0056] First, the chemical composition of a slab for grain-oriented electrical steel sheet may be any chemical composition that allows secondary recrystallization to occur. Furthermore, when an inhibitor is used, for example, an AlN-based inhibitor may contain appropriate amounts of Al and N, or an MnS / MnSe-based inhibitor may contain appropriate amounts of Mn and Se and / or S. Naturally, both inhibitors may be used in combination. In this case, the preferred contents of Al, N, S, and Se are Al: 0.010 to 0.065 mass%, N: 0.0050 to 0.0120 mass%, S: 0.005 to 0.030 mass%, and Se: 0.005 to 0.030 mass%, respectively.

[0057] Furthermore, the present invention can also be applied to grain-oriented electrical steel sheets that do not use inhibitors and have limited contents of Al, N, S, and Se. In this case, the contents of Al, N, S, and Se are preferably restricted to the following amounts: Al: less than 0.010 mass%, N: less than 0.0050 mass%, S: less than 0.0050 mass%, and Se: less than 0.0050 mass%, respectively.

[0058] Representative basic components and optional additional components that can be applied to the steel material (slab) for the grain-oriented electrical steel sheet of the present invention will be specifically described below.

[0059] C: 0.08% by mass or less C is added to improve the hot-rolled sheet structure, but if the C content exceeds 0.08% by mass, it becomes difficult to decarburize to 50 ppm by mass or less, at which point magnetic aging does not occur during the manufacturing process, so the C content is preferably 0.08% by mass or less. Furthermore, since secondary recrystallization occurs even in steel materials that do not contain C, no lower limit for the C content is particularly set.

[0060] Si: 2.0 to 8.0 mass% Si is an element effective in 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 exerted, while if it exceeds 8.0 mass%, workability and threadability deteriorate significantly, and magnetic flux density also decreases. Therefore, the Si content is preferably in the range of 2.0 to 8.0 mass%.

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

[0062] In addition to the above basic components, the following optional additive components known to be effective in improving magnetic properties may be appropriately contained: one or more selected from 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%.

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

[0064] Sn, Sb, Cu, P, Mo, and Cr are also elements that improve magnetic properties, but if the content of any of them is less than the lower limit, the effect is insufficient, and if the content exceeds the upper limit, the growth of secondary recrystallized grains is suppressed, resulting in deterioration of magnetic properties. Therefore, it is preferable to keep the content of each element within the above range.

[0065] In addition to the above components, the alloy contains Fe and unavoidable impurities.

[0066] A slab of grain-oriented electrical steel sheet having the above-described chemical composition is hot-rolled and then optionally hot-rolled sheet annealed. Next, the steel sheet is cold-rolled once or twice or more times with intermediate annealing in between to produce a steel strip of the final thickness. The steel strip is then decarburized and annealed, coated with an annealing separator mainly composed of MgO, wound into a coil, and subjected to final annealing for the purposes of secondary recrystallization and the formation of a forsterite coating. After the final annealing, the steel strip is subjected to flattening annealing, and then a magnesium phosphate-based tension coating is formed to produce a steel strip product.

[0067] In the present invention, the process after planarization annealing includes a magnetic domain refining step in which thermal strain is introduced into the surface of the grain-oriented electrical steel sheet (steel strip) by irradiating it with an energy beam. In non-heat-resistant magnetic domain refining that introduces thermal strain, it is preferable to irradiate the energy beam after forming a tension coating. This is because if irradiated before forming the tension coating, the introduced thermal strain will be released by baking when the tension coating is formed, and the magnetic domain refining effect will not be obtained.

[0068] When heat-resistant magnetic domain refinement is performed by groove machining as a metal surface treatment, it is preferable to perform the energy beam irradiation before forming the tension coating, because if it is performed after forming the tension coating, the formed tension coating will be destroyed.

[0069] Examples of metal surface processing in the present invention include hardening, cleaning, resist stripping, localized thermal strain introduction, laser peening, etc. The present invention can be applied to any processing method that involves scanning an energy beam multiple times on the surface of a metal plate.

[0070] Of the above processes, the introduction of local thermal strain for magnetic domain refining requires the most precise focus control, and therefore is the most effective when applied to the present invention. The magnetic domain refining process will now be described.

[0071] [Beam Irradiation Conditions] To perform non-heat-resistant magnetic domain refinement, it is effective to use a laser having a wavelength of 400 nm to 1200 nm, which is highly absorbed by metals, as well as an electron beam with high penetrating power.

[0072] In the following, suitable irradiation conditions for the electron beam when carrying out the present invention will be explained in more detail.

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

[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, so from a practical standpoint, it is preferably 300 kV or less, and more preferably 200 kV or less.

[0075] Beam current: 0.5 to 40 mA A small beam current is preferable from the perspective of beam diameter. This is because increasing the beam current tends to widen the beam diameter due to Coulomb repulsion. Therefore, in the present 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 distortion, so it is preferable to set the beam current to 0.5 mA or more.

[0076] Vacuum degree in the beam irradiation area: 1 x 10 －５ Pa or more and 3 Pa or less The electron beam is scattered by gas molecules, which causes an increase in the beam diameter and halo diameter, a decrease in energy, etc. Therefore, the higher the vacuum level in the beam irradiation area, the better, and it is preferable to set the pressure to 3 Pa or less. There is no particular limit on the lower limit, but if it is lowered too much, the cost of the vacuum system, such as the vacuum pump, will increase. Therefore, in practice, it is recommended to set the vacuum level to 1×10 －５ It is preferable to set the pressure at 100 Pa or more.

[0077] The preferred laser irradiation conditions for carrying out the present invention will be explained in more detail below.

[0078] Laser output: 50 W or more and 5000 W or less When the laser output is low, it is necessary to slow down the laser scanning speed in order to provide sufficient energy for inflicting thermal distortion. In this case, excessive slowing down the speed leads to a deterioration in manufacturing efficiency. On the other hand, while increasing the output makes it easier to inflict thermal distortion, it also increases damage to the laser transport system, increasing the frequency of maintenance and reducing manufacturing efficiency. From the above perspectives, it is preferable that the laser output be 50 W or more and 5000 W or less.

[0079] For both the electron beam and the laser, the following irradiation conditions are suitable.

[0080] Spot diameter: 300 μm or less. A smaller spot diameter is preferable because it allows for more localized strain to be introduced. Therefore, in the present 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 the present invention, the spot diameter refers to the full width at half maximum of the beam profile obtained by the slit method using a 30 μm-wide slit.

[0081] Deflection speed: 5 to 400 m / s The slower the beam deflection speed, the more heat can be incident per unit length of the steel plate, so a slower speed is preferable. However, if the speed is too slow, the processing area per unit time decreases, resulting in a decrease in production efficiency. Therefore, a speed of 5 m / s or more is preferable. Furthermore, if the speed is too high, a power supply capacity is required to provide the heat input necessary to melt the steel plate, which leads to an increase in the size of the equipment. Therefore, a speed of 400 m / s or less is preferable.

[0082] Angle between the thermal strain introduction direction and the direction perpendicular to the rolling direction: within ±30°. The more the extension direction of the thermal strain introduction part is inclined from the sheet width direction, the fewer magnetic poles are generated at the interface between the closure domains and the main magnetic domains, and the magnetic domain refining effect deteriorates. Therefore, it is preferable that the angle between the extension direction of the thermal strain introduction part and the sheet width direction be within ±30°.

[0083] The present invention will now be described in detail with reference to examples. The following examples are intended to illustrate preferred examples of the present invention, and are not intended to limit the scope of the present invention. The present invention may be modified within the scope of the spirit of the present invention, and such modifications are also within the technical scope of the present invention.

[0084] A 300 mm-wide cold-rolled steel strip for grain-oriented electrical steel sheet, manufactured using a steel slab having the alloy composition shown in Table 2 with the remainder consisting of Fe and unavoidable impurities, was coated with a 2 μm-thick resist film on one entire side and then irradiated with a laser to remove the resist. The concept of the sheet running speed in the examples is as shown in Figure 1. As shown in Figure 1, the production line speed Vl was repeatedly accelerated at regular intervals from 10 m / min to 140 m / min. The laser focus setting was performed under the five conditions listed in Table 3. Various combinations of the beam irradiation interval Lp in the steel sheet running direction and the beam scanning speed Ve were used to change the processing interval time τ2. The laser beam profile was measured using a 30 μm-wide slit method, and the current value of each focusing coil was adjusted so that the beam profile shape was Gaussian.

[0085]

[0086]

[0087] The state of resist peeling of the steel strip thus obtained was observed using a laser microscope, and the area ratio Rs of the peeled portion per area of ​​the laser irradiated portion, the width WR of the peeled portion, and the rectangularity Rr of the peeled portion were specifically evaluated as follows, according to the procedures shown in Figures 6 and 7.

[0088] The area ratio Rs of the peeled portion was defined and evaluated as Rs = A / (Φ*Ls) (where * denotes a multiplication symbol) using the laser spot diameter Φ, the scanning range Ls, and the area A of the peeled portion calculated using a laser microscope, as shown in Figure 6. The closer the Rs value is to 1.0, the more the heat-affected zone and the peeled portion coincide, which means that the laser resist peelability is excellent.

[0089] The peeled portion width WR was determined by measuring the length of the exposed portion of the steel substrate in the direction perpendicular to the scanning direction (rolling direction) at 10 points in the sheet width direction in the peeled portion within the scanned area, as shown in Figure 6. The closer the WR value is to the spot diameter Φ, the better the peelability of the resist by the laser.

[0090] The rectangularity Rr was evaluated by calculating the slope of the peeled portion (Rr = d / l) from the resist thickness d and the length l of the irradiated portion in the surface profile of the steel sheet, as shown in Figure 7. A larger Rr value means that the peeled edge of the resist is steeper, and the resist properties in the subsequent processes are better.

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

[0092]

[0093] A 300 mm wide grain-oriented electrical steel strip was produced using a slab with the chemical composition shown in Table 2, and was subjected to a general manufacturing process. After finish annealing, an insulating coating was formed. The resulting steel strip was irradiated with an electron beam and subjected to magnetic domain refinement. The concept of the strip threading speed in the examples is as shown in Figure 1. As shown in Figure 1, the production line speed Vl was repeatedly accelerated at regular intervals, increasing from 10 m / min to 140 m / min.

[0094] At this time, the focus setting conditions of the electron beam were set under the five conditions shown in Table 3. In addition, the beam irradiation interval in the steel sheet running direction and the beam scanning speed were variously combined to change the processing interval time τ2. The electron beam profile was measured by the slit method, and the current values ​​of the focusing lens and stigmator were adjusted so that the beam profile shape would be a Gaussian shape.

[0095] The steel strip thus obtained was cut into diagonal strips to produce a three-phase stacked core model transformer (core weight 50 kg). The core loss characteristics were measured at a frequency of 50 Hz when the magnetic flux density in the core legs was 1.7 T. The no-load loss at 1.7 T and 50 Hz was measured using a wattmeter. At the same time, the model transformer was excited in a soundproof room under conditions of a maximum magnetic flux density Bm = 1.7 T and a frequency of 50 Hz, and the noise level (dBA) was measured using a sound level meter.

[0096] The above evaluation results are shown in Table 5. The smaller the iron loss (W / kg) value, the lower the iron loss and the better the iron loss characteristics. The smaller the noise level (dBA) value, the lower the noise and the better the 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 performed regardless of the processing interval time, and low iron loss and low noise are achieved.

[0097]

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

Claims

1. A method for processing a surface of a metal material by irradiating the surface of the metal material with an energy beam, the method comprising irradiating the surface of the metal material with the energy beam using at least two focus settings.

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

3. 3. The method for surface processing of a metallic material according to claim 1, wherein the metallic material is a grain-oriented electrical steel sheet.

4. A method for producing a grain-oriented electrical steel sheet, comprising: irradiating the surface of the grain-oriented electrical steel sheet with the energy beam a plurality of times in a direction intersecting the rolling direction, using the method for surface processing of a metal material according to claim 3, thereby introducing a plurality of heat-affected zones and / or thermally distorted zones.

5. The method includes a step of periodically scanning an energy beam on a surface of a metal sheet passing through a production line in a direction intersecting the sheet passing direction to introduce a plurality of heat-affected zones and / or thermally distorted zones that are parallel to each other and spaced apart by an interval Lp in the sheet passing direction, A method for surface processing of a metal plate, comprising irradiating the energy beam using at least two focus settings.

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

7. The method for surface processing a metal sheet according to claim 5 or 6, wherein the metal sheet is a grain-oriented electrical steel sheet.

8. 7. The surface processing method of claim 6, further comprising the steps of: repeatedly irradiating an energy beam at the processing interval time τ2 under operating conditions; and adjusting a focusing system of the energy beam to a condition in which a focus setting value of the energy beam when a steady state is reached is optimized.

9. A surface processing method for a metal plate as described in claim 7, comprising repeatedly irradiating an energy beam at the processing interval time τ2 under operating conditions, and adjusting the focusing system of the energy beam to conditions such that the focus setting value of the energy beam is optimal when a steady state is reached.