WO2020149332A1 - 方向性電磁鋼板の製造方法 - Google Patents
方向性電磁鋼板の製造方法 Download PDFInfo
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- WO2020149332A1 WO2020149332A1 PCT/JP2020/001166 JP2020001166W WO2020149332A1 WO 2020149332 A1 WO2020149332 A1 WO 2020149332A1 JP 2020001166 W JP2020001166 W JP 2020001166W WO 2020149332 A1 WO2020149332 A1 WO 2020149332A1
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Definitions
- the present invention relates to a method for manufacturing a grain-oriented electrical steel sheet that does not substantially have a forsterite coating.
- the present application claims priority based on Japanese Patent Application No. 2019-005399 filed in Japan on January 16, 2019, the contents of which are incorporated herein by reference.
- Grain-oriented electrical steel sheets are frequently used as magnetic iron core materials, and materials with low iron loss are particularly required to reduce energy loss. It is known that applying a tension to the surface of a steel sheet is effective as a means for reducing iron loss. In order to apply tension to the steel sheet, it is effective to form a coating film made of a material having a smaller coefficient of thermal expansion than the steel sheet at a high temperature.
- the finish annealing coating (forsterite coating) formed by the reaction between the oxide on the surface of the steel sheet and the annealing separator in the finish annealing step can give tension to the steel sheet and has excellent coating adhesion.
- Patent Document 1 discloses that the atmospheric oxidation degree P H2O /P H2 during heating is set to 0.01 to 0.15 in order to suppress the generation of iron-based oxides. Further, Patent Document 2 describes that decarburization can be efficiently performed by setting the heating rate from 770 to 860° C. to 9° C./s or more. However, in these patent documents, the plate thickness at the time of decarburization annealing is performed at 0.14 mm and 0.23 mm, and the application technology to thick materials (0.23 mm or more) is not described.
- the present invention is a method for producing a grain-oriented electrical steel sheet substantially free of a forsterite coating, and in a wide sheet thickness range, by promoting both decarburization promotion and oxidation inhibition of the steel sheet, it has excellent magnetic properties.
- An object is to provide a method for manufacturing a grain-oriented electrical steel sheet.
- a method for manufacturing a grain-oriented electrical steel sheet according to an aspect of the present invention includes an intermediate layer containing silicon oxide as a main component on a surface of a mother steel sheet substantially free of forsterite coating, and the surface of the intermediate layer.
- Decarburization annealing step to obtain, a finish annealing step of heating the decarburization annealed steel sheet in a state of applying an annealing separator on the surface of the decarburization annealed steel sheet to secondarily recrystallize the steel sheet, and the finish annealing step Removing step to obtain a finish annealed steel sheet by removing the annealing separation material on the steel sheet, an intermediate layer forming step of performing thermal oxidation annealing on the finish annealed steel sheet to form the intermediate layer, and forming the intermediate layer An insulating film forming step of forming the insulating film on the finished annealed steel sheet.
- a method for manufacturing a grain-oriented electrical steel sheet according to another aspect of the present invention has an intermediate layer containing silicon oxide as a main component on the surface of a mother steel sheet substantially free of forsterite coating, A method for producing a grain-oriented electrical steel sheet having an insulating coating on its surface, wherein decarburization annealing is performed on a cold-rolled steel sheet containing Si to obtain an oxygen content of 320 ppm or less and a carbon content of 25 ppm or less.
- Decarburization annealing step for obtaining a steel sheet
- finish annealing step for heating the decarburization annealed steel sheet in a state of applying an annealing separator on the surface of the decarburization annealed steel sheet to secondarily recrystallize the steel sheet
- finish annealing step A removal step of obtaining a finish annealed steel sheet by removing the annealing separation material on the subsequent steel sheet; an intermediate layer-insulating coating forming step of forming the intermediate layer and the insulating coating on the finish annealed steel sheet in one step; With.
- an atmospheric gas is applied to the soaking zone for decarburizing and annealing the cold rolled steel sheet. It may be introduced from two locations, the former stage and the latter stage of the soaking zone.
- the dew point DP1 of the atmospheric gas introduced from the previous stage of the soaking in the decarburization annealing step is 40 to 70° C.
- the dew point DP2 of the atmospheric gas introduced from the latter stage may be DP2 ⁇ DP1 and 60 ⁇ DP1 ⁇ DP2 ⁇ 100 ⁇ DP1.
- the cold-rolled steel sheet has a chemical composition of mass% of Si: 0.80 to 7.00. %, C: 0.085% or less, acid-soluble Al: 0.010 to 0.065%, N: 0.012% or less, Mn: 1.00% or less, total of S and Se: 0.003 to 0 0.015%, and the balance may be Fe and impurities.
- the above aspect of the present invention it is possible to provide a method for producing a grain-oriented electrical steel sheet that does not substantially have a forsterite coating.
- a method for producing a grain-oriented electrical steel sheet according to the above aspect by coexisting decarburization and steel sheet oxidation suppression in a wide sheet thickness range, a core loss is low, and a magnetic flux density after magnetic aging is high. can do.
- FIG. 4A or FIG. 4B It is a block diagram in the case of introducing an atmospheric gas from two places of the former stage and the latter stage of the soaking zone in the decarburization annealing furnace. It is explanatory drawing which shows the outline of the dew point distribution of the atmospheric gas in a furnace when the decarburization annealing furnace of FIG. 4A or FIG. 4B is used. It is a figure which shows the relationship between a magnetic characteristic and a dew point (previous stage dew point DP1, rear stage dew point DP2).
- the inventors of the present invention have studied a method for producing a grain-oriented electrical steel sheet that does not substantially have a forsterite coating.
- a grain-oriented electrical steel sheet that does not substantially have a forsterite coating an intermediate layer containing silicon oxide as a main component is formed on the surface of the mother steel sheet in order to secure the adhesiveness of the insulating coating, and the insulating layer is formed on the surface of the intermediate layer. It is premised on a manufacturing method for forming a film.
- a grain-oriented electrical steel sheet having an intermediate layer containing silicon oxide as a main component on the surface of a mother steel sheet substantially free of forsterite coating, and having an insulating coating on the surface of the intermediate layer is provided.
- the decarburization annealing step by treating under a specific condition, by adjusting the oxygen content and carbon content of the decarburized steel sheet to a specific range, decarburization and steel sheet oxidation in a wide thickness range It has been found that a grain-oriented electrical steel sheet having both excellent magnetic properties and excellent magnetic properties can be provided.
- the directionality manufactured by the method for manufacturing a grain-oriented electrical steel sheet according to one embodiment of the present invention (the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment) and the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment
- the electromagnetic steel sheet will be described in detail.
- a grain-oriented electrical steel sheet manufactured by the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment includes a mother steel sheet and silicon oxide. It is a grain-oriented electrical steel sheet having a three-layer structure having an intermediate layer as a main component and an insulating coating in this order.
- the basic structure of the three layers of the grain-oriented electrical steel sheet of this embodiment will be described.
- 1-1. Mother Steel Plate The magnetic steel sheet manufactured by the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment (the grain-oriented electrical steel sheet according to the present embodiment) has an insulating coating in contact with an intermediate layer mainly composed of silicon oxide.
- the constitution such as the chemical composition and structure of the mother steel sheet in the grain-oriented electrical steel sheet is not directly related to the layer constitution of such an insulating coating except that Si is contained as an essential component. Therefore, the mother steel plate in the grain-oriented electrical steel sheet of the present embodiment is not particularly limited as long as the action and effect obtained in the present embodiment can be obtained, and for example, the mother steel sheet in a general grain-oriented electrical steel sheet. Can be used.
- the mother steel plate in the grain-oriented electrical steel plate of the present embodiment will be described.
- the chemical composition of the mother steel sheet for example, the chemical composition of the mother steel sheet in a general grain-oriented electrical steel sheet can be used except that Si is contained as an essential component. Since the function of Si is the same as that of a general grain-oriented electrical steel sheet, the content may be determined within a general range from the characteristics required for the intended grain-oriented electrical steel sheet. In the following, the content of each component in the chemical composition of the mother steel sheet is the value in mass %. Further, the grain-oriented electrical steel sheet of the present embodiment has a stable chemical composition at a depth of 50 to 60 ⁇ m.
- a typical example of the chemical composition of the mother steel sheet is mass% and contains Si: 0.80% to 7.00% and Mn: 0.05% to 1.00%, the balance being Fe and impurities. It will be. Further, in addition to the above chemical composition, S and Se may be contained in a total amount of 0.003% or more and 0.015% or less. Hereinafter, the reason for limiting a typical example of the chemical composition will be described.
- Si 0.80% or more and 7.00% or less Si is an essential component and increases electric resistance to reduce iron loss. Further, by containing Si at a high concentration, a strong chemical affinity is developed between the intermediate layer mainly composed of silicon oxide and the intermediate layer and the mother steel sheet are more firmly adhered to each other. However, if the Si content exceeds 7.00%, cold rolling becomes extremely difficult, and cracks are likely to occur during cold rolling. Therefore, the Si content is preferably 7.00% or less. It is more preferably 4.50% or less, and further preferably 4.00% or less. On the other hand, if the Si content is less than 0.80%, ⁇ -transformation occurs during finish annealing, and the preferred crystal orientation of the grain-oriented electrical steel sheet is impaired. Therefore, the Si content is preferably 0.80% or more. It is more preferably 2.00% or more, still more preferably 2.50% or more.
- Mn 0.05% or more and 1.00% or less
- S and Se 0.003% or more and 0.015% or less in total Mn produces MnS and MnSe together with S and Se, and the composite compound is Functions as an inhibitor.
- the secondary recrystallization is stable when the Mn content is in the range of 0.05% to 1.00%. Therefore, the Mn content is preferably 0.05% to 1.00%.
- the Mn content is more preferably 0.08% or more, still more preferably 0.09% or more. Further, the Mn content is more preferably 0.50% or less, and further preferably 0.20% or less.
- the rest The balance consists of Fe and impurities.
- the “impurity” means an element that is inevitably mixed from the components included in the raw material or components that are mixed during the manufacturing process when the mother steel sheet is industrially manufactured.
- the intermediate layer is formed on the surface of the mother steel sheet and contains silicon oxide as a main component. Since the grain-oriented electrical steel sheet of this embodiment does not substantially have a forsterite coating, the intermediate layer is formed in direct contact with the surface of the mother steel sheet. The intermediate layer has a function of bringing the mother steel plate and the insulating coating into close contact with each other in the three-layer structure of the present embodiment.
- the intermediate layer means a layer existing between a mother steel sheet described later and an insulating coating (compound layer described later) described later.
- Silica (SiO 2 ) can be formed by sufficiently performing a heat treatment for forming silicon oxide on the surface of the steel sheet.
- Mainly composed of silicon oxide means that, as will be described later, the composition of the intermediate layer has an Fe content of less than 30 atomic %, a P content of less than 5 atomic %, a Si content of 20 atomic% or more, and an O content of 50 atomic. % Or more and the Mg content is 10 atomic% or less.
- the thickness of the intermediate layer is preferably 2 nm or more, more preferably 5 nm or more.
- the thickness of the intermediate layer is preferably 400 nm or less, more preferably 300 nm or less.
- the formation time can be shortened and it can contribute to high productivity, and at the same time, it is possible to prevent the space factor from decreasing when used as an iron core.
- the thickness is preferably 100 nm or less, more preferably 50 nm or less.
- the method for measuring the thickness and position of the intermediate layer is not particularly limited, but for example, the cross section of the intermediate layer can be formed by using an SEM (scanning electron microscope) or a TEM (transmission electron microscope) having an electron beam diameter of 10 nm as follows. It can be determined by observing and measuring. Specifically, a test piece is cut out by FIB (Focused Ion Beam) processing so that the cut surface is parallel to the sheet thickness direction and perpendicular to the rolling direction, and the cross-sectional structure of this cut surface is shown in each layer in the observation visual field. Observation (bright-field image) by STEM (Scanning-TEM) at a magnification that fits in. When each layer does not enter the observation visual field, the cross-sectional structure is observed in a plurality of continuous visual fields.
- SEM scanning electron microscope
- TEM transmission electron microscope
- Each layer is specified and the thickness of each layer is measured from the bright field image observation with the above-mentioned TEM, the quantitative analysis of TEM-EDS, and the electron beam diffraction result. Subsequent identification and thickness measurement of each layer are performed on the same scanning line of the same sample.
- ⁇ Determine the area where the Fe content is 80 atomic% or more to be the mother steel sheet. Insulating the region where the Fe content is less than 80 atomic%, the P content is 5 atomic% or more, the Si content is less than 20 atomic%, the O content is 50 atomic% or more, and the Mg content is 10 atomic% or less. It is determined that A region in which the Fe content is less than 30 atomic %, the P content is less than 5 atomic %, the Si content is 20 atomic% or more, the O content is 50 atomic% or more, and the Mg content is 10 atomic% or less. Is determined to be the middle layer.
- each layer is specified so as to have a three-layer structure of a mother steel sheet, an intermediate layer, and an insulating coating (including a composition variation layer).
- the judgment criteria are as follows. First, the blank area between the mother steel sheet and the intermediate layer is considered to be the mother steel sheet on the mother steel sheet side and the intermediate layer on the intermediate layer side with the center in the thickness direction of the blank area as a boundary.
- the blank region between the insulating coating and the intermediate layer is considered to be the insulating coating on the insulating coating side and the intermediate layer on the insulating layer side with the center in the thickness direction of the blank region as a boundary.
- Insulating coating An insulating coating is formed on the surface of the intermediate layer to apply tension to the steel sheets to reduce the iron loss as a single steel sheet. It has the function of ensuring electrical insulation.
- the composition of the insulating coating is not particularly limited and may be appropriately selected from known ones depending on the application etc. and may be either an organic coating or an inorganic coating.
- the organic coating include polyamine resin, acrylic resin, acrylic styrene resin, alkyd resin, polyester resin, silicone resin, fluororesin, polyolefin resin, styrene resin, vinyl acetate resin, epoxy resin, phenol resin, urethane resin, and melamine. Resin etc. are mentioned.
- examples of inorganic coatings include phosphate coatings, aluminum phosphate coatings, and organic-inorganic composite coatings containing the above resins. More specifically, a matrix in which particles of colloidal silica are dispersed may be baked.
- the "matrix” is a substrate of the insulating coating, and is composed of, for example, amorphous phosphate.
- the non-crystalline phosphate forming the matrix include aluminum phosphate, magnesium phosphate and the like.
- the insulating coating after baking is composed of a plurality of compounds containing at least one of P, O and S.
- the thickness of the insulating coating is preferably 0.1 ⁇ m or more, more preferably 0.5 ⁇ m or more.
- the thickness of the insulating coating exceeds 10.0 ⁇ m, cracks may occur in the insulating coating during the step of forming the insulating coating, so the thickness of the insulating coating is preferably 10.0 ⁇ m or less, and 5.0 ⁇ m or less. The following is more preferable.
- the insulating coating may be subjected to a magnetic domain refining treatment for forming a local minute strained region or groove by laser, plasma, mechanical method, etching, or other method.
- the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment is an intermediate product containing silicon oxide as a main component on the surface of the mother steel sheet substantially free of the forsterite coating described in the item “A.
- a method for producing a grain-oriented electrical steel sheet having a layer and having an insulating coating on the surface of the intermediate layer is a method of manufacturing a grain-oriented electrical steel sheet having a mother steel sheet, an intermediate layer formed on the surface of the mother steel sheet, and an insulating coating formed on the surface of the intermediate layer. Since the mother steel plate has no forsterite coating, the intermediate layer is formed in direct contact with the mother steel plate.
- the intermediate layer and the insulating coating are formed in separate steps. That is, the method for manufacturing a grain-oriented electrical steel sheet according to the first embodiment has the following steps.
- the intermediate layer and the insulating coating are simultaneously formed in one step. That is, the method for manufacturing a grain-oriented electrical steel sheet according to the second embodiment has the following steps.
- the effect of reducing the iron loss due to the insulating coating is prevented from being disturbed by the interface irregularities between the finish annealing coating and the mother steel sheet, and the insulating coating and the mother steel sheet are provided by the intermediate layer. It is possible to secure close contact with.
- the cold-rolled steel sheet may have the chemical composition of the mother steel sheet in a general grain-oriented electrical steel sheet except that it contains Si as an essential component. Since the function of Si in a magnetic steel sheet is similar to that of a general grain-oriented magnetic steel sheet, the content may be determined within a general range from the characteristics required for the intended magnetic steel sheet.
- the chemical composition of the cold-rolled steel sheet is, in mass %, Si: 0.80 to 7.00%, C: 0.085% or less, acid-soluble Al: 0.010 to 0.065%, N:0.
- An example is a chemical composition containing 0.012% or less, Mn: 1.00% or less, the sum of S and Se: 0.003 to 0.015%, and the balance Fe and impurities.
- a cold rolled steel sheet for example, after heating the slab, a hot rolling step of performing hot rolling to obtain a hot rolled steel sheet, and annealed steel sheet by subjecting the hot rolled steel sheet to hot rolling sheet annealing. It can be manufactured by a manufacturing method including a hot-rolled sheet annealing step to be obtained and a cold rolling step in which the annealed steel sheet is subjected to cold rolling once or twice or more with intermediate annealing interposed therebetween to obtain a cold rolled steel sheet.
- the slab is based on a known technique according to the chemical composition of the cold-rolled steel sheet to be obtained.
- a typical example of the chemical composition is mass%: Si: 0.80% to 7.00%, C: 0.085% or less, acid-soluble Al: 0.010% to 0.065%, N:0. 0.004% to 0.012%, Mn: 0.05% to 1.00%, and S and Se: 0.003% to 0.015% in total, with the balance being Fe and impurities Is.
- Si 0.80% to 7.00%
- Si is an essential component and increases electric resistance to reduce iron loss. Further, by containing Si at a high concentration, a strong chemical affinity is developed between the intermediate layer mainly composed of silicon oxide and the intermediate layer and the mother steel sheet are more firmly adhered to each other.
- the Si content is preferably 7.00% or less. It is more preferably 4.50% or less, and further preferably 4.00% or less.
- the Si content is preferably 0.80% or more. It is more preferably 2.00% or more, still more preferably 2.50% or more.
- C 0.085% or less C is an element effective in controlling the primary recrystallization structure, but adversely affects the magnetic properties. Therefore, decarburization annealing is performed before finish annealing. If the C content is more than 0.085%, the decarburization annealing time becomes long and the productivity in industrial production is impaired. For these reasons, the C content is preferably 0.085% or less.
- the lower limit of the C content is not particularly limited, but the C content is preferably 0.020% or more, more preferably 0.050% or more.
- Acid-soluble Al 0.010%-0.065%
- the acid-soluble Al combines with N and precipitates as (Al,Si)N, and functions as an inhibitor.
- the secondary recrystallization is stable when the content of the acid-soluble Al is in the range of 0.010% to 0.065%. Therefore, the content of acid-soluble Al is preferably 0.010% to 0.065%. Further, as will be described later, by concentrating Al on the steel sheet surface in finish annealing, this is one of Al and Mg present on the steel sheet surface at the time of forming the intermediate layer in the method for producing a grain-oriented electrical steel sheet of the present invention described later.
- the content of acid-soluble Al is preferably 0.015% or more, and more preferably 0.020% or more, from the viewpoint of utilization as Al. From the viewpoint of the stability of secondary recrystallization, the acid-soluble Al content is more preferably 0.050% or less, further preferably 0.035% or less.
- N 0.004% to 0.012% N combines with Al and functions as an inhibitor. If the N content is less than 0.004%, a sufficient amount of inhibitor cannot be obtained. Therefore, the N content is preferably 0.004% or more. It is more preferably 0.005% or more, still more preferably 0.006% or more. On the other hand, if the N content exceeds 0.012%, defects called blister are likely to occur in the steel sheet. Therefore, the N content is preferably 0.012% or less. It is more preferably 0.011% or less, still more preferably 0.010% or less.
- Mn 0.05% to 1.00%
- S and Se 0.003% to 0.015% in total Mn produces MnS and/or MnSe together with S and/or Se, and the complex compound functions as an inhibitor.
- the secondary recrystallization is stable when the Mn content is in the range of 0.05% to 1.00%. Therefore, the Mn content is preferably 0.05% to 1.00%.
- the Mn content is more preferably 0.08% or more, still more preferably 0.09% or more. Further, the Mn content is more preferably 0.50% or less, further preferably 0.20% or less.
- the total content of S and Se is within the range of 0.003% to 0.015%. Therefore, the total content of S and Se is preferably 0.003% to 0.015%.
- the total content of S and Se is 0.003% to 0.015%
- the mother steel sheet contains only one of S and Se, and one of S and Se.
- the mother steel sheet contains both S and Se, and the total content of S and Se is 0.003% to 0.015%. Means both.
- the balance consists of Fe and impurities.
- the “impurity” means an element that is mixed from a component contained in a raw material or a component mixed in a manufacturing process when the mother steel sheet is industrially manufactured.
- the slab is obtained, for example, by melting steel having the above-described chemical composition in a converter or an electric furnace, subjecting it to vacuum degassing treatment if necessary, and then performing continuous casting or ingot-making and slabbing. ..
- the thickness of the slab is not particularly limited, but is, for example, 150 mm to 350 mm, preferably 220 mm to 280 mm. Further, it may be a slab having a thickness of about 10 mm to 70 mm (so-called “thin slab”). When a thin slab is used, rough rolling before finish rolling can be omitted in the hot rolling process.
- the slab containing Si as described above is heated in a temperature range of, for example, 800° C. to 1300° C., and then hot rolled to obtain a hot rolled steel sheet.
- the heating temperature of the slab is 1200° C. or less, for example, various problems (requiring a dedicated heating furnace and a large amount of molten scale) when heating at a temperature higher than 1200° C. are avoided. It is preferable because it can If the heating temperature is too low, hot rolling may become difficult and productivity may be reduced. Therefore, the lower limit of the heating temperature of the slab is preferably 950°C. It is also possible to omit the slab heating step itself and start hot rolling after casting until the temperature of the slab falls.
- the slab after heating is subjected to rough rolling and finish rolling to obtain a hot rolled steel sheet having a predetermined thickness.
- the hot-rolled steel sheet is wound at a predetermined temperature.
- the plate thickness of the hot rolled steel plate is not particularly limited, but is 3.5 mm or less, for example.
- the hot rolled steel sheet is subjected to hot rolled sheet annealing to obtain an annealed steel sheet.
- the hot rolled sheet annealing conditions may be general conditions, but for example, the temperature is kept within a range of 750 to 1200° C. for 30 seconds to 10 minutes.
- the annealed steel sheet is subjected to cold rolling once or twice or more with intermediate annealing interposed therebetween to obtain a cold rolled steel sheet.
- the cold rolling rate (final cold rolling rate) in the final cold rolling is not particularly limited, but from the viewpoint of controlling the crystal orientation, it is preferably 80% or more, and more preferably 90% or more.
- the plate thickness of the cold-rolled steel plate is not particularly limited, but is preferably 0.35 mm or less and more preferably 0.30 mm or less in order to further reduce iron loss.
- the cold rolled steel sheet is subjected to decarburizing and annealing to obtain a decarburizing and annealing steel sheet.
- decarburization annealing primary recrystallization is caused in the cold rolled steel sheet, C contained in the cold rolled steel sheet is removed, and the carbon content of the steel sheet after decarburization annealing is 25 ppm or less.
- Decarburization annealing is preferably performed in a wet atmosphere to remove C.
- the amount of oxygen after decarburization annealing is controlled to 320 ppm or less by suppressing the oxidation.
- the decarburization annealing method included in the method for manufacturing a grain-oriented electrical steel sheet according to this embodiment will be described in detail.
- carbon is added in an amount of about 500 to 600 ppm in order to obtain a texture for improving magnetism.
- carbon (C) becomes unnecessary after the cold rolling process described above, it is necessary to remove the carbon amount after annealing in the decarburization annealing process to a level at which magnetic aging does not occur in the final product such as a transformer. There is.
- cold-rolled steel sheet is usually made to have a dew point of 60 to 70°C and a soaking temperature of 800 to 900°C. And anneal.
- a grain-oriented electrical steel sheet that does not substantially have a forsterite coating like the grain-oriented electrical steel sheet of the present embodiment, if it is annealed under the high dew point condition as described above, the oxide will be oxidized during high temperature annealing. (Mullite) is formed, and the smoothness of the surface is deteriorated by the oxidation of the steel sheet, and the magnetic properties are deteriorated. Further, when the dew point is reduced in order to avoid this, according to the study by the present inventors, it was found that the decarburization rate decreases, the residual carbon amount increases, and magnetic aging occurs. That is, since promotion of decarburization and suppression of oxidation of a steel sheet are contradictory phenomena in establishing atmospheric conditions, it is difficult to realize the dew point during decarburization annealing under constant conditions.
- the present inventors As a decarburization annealing treatment, the present inventors first preferentially perform decarburization at a high dew point, and then lower the dew point to minimize oxidation after completing decarburization. I thought that it would be possible to achieve both decarburization and suppression of oxidation. Based on this idea, the present inventor conducted the following experiment to investigate the influence of the dew point control in the first half of the decarburization annealing treatment and the dew point control in the latter half of the decarburization annealing treatment.
- This experiment was performed using a decarburization annealing furnace including a box-shaped heating furnace 1 and a soaking furnace 2 having the configurations shown in FIGS. 4A and 4B.
- the inside of the heating furnace 1 is a heating zone
- the inside of the soaking furnace 2 is a soaking zone. From the heating zone to the soaking zone, the rightward direction indicated by the arrows shown in FIGS. 4A and 4B.
- This is a decarburization annealing furnace that can horizontally convey steel sheets and can perform decarburization annealing treatment on the steel sheets during conveyance.
- the decarburization annealing furnace shown in FIG. 4B can supply atmospheric gas into the inside of the soaking furnace 2 from the side wall portion (after the soaking zone) near the outlet of the soaking furnace 2 in the direction opposite to the passing direction of the steel sheet and at the same time. It is a decarburization annealing furnace capable of supplying an atmospheric gas from the bottom portion near the inlet of the heating furnace 2 (before the soaking zone (after the heating zone)) toward the heating furnace 1 in the direction opposite to the conveying direction of the steel sheet.
- the former soaking zone means the heating zone side (upstream side) from the center of the soaking zone
- the latter soaking zone means a position downstream from the center of the soaking zone, for example, at the position shown in FIG. 4B. is there.
- the position where the atmospheric gas is introduced is preferably near the soaking zone inlet (the soaking temperature reaching position) in the former stage, and near the soaking zone outlet in the latter stage.
- the amount of carbon in the obtained steel sheet was analyzed by an infrared absorption method by burning in an oxygen stream to form CO gas.
- a sample was burned in a graphite crucible in an inert gas such as He to obtain CO gas, which was analyzed by an infrared absorption method.
- magnesia water slurry may be applied as in the conventional case, but in this case, unevenness of the surface oxide layer occurs due to reaction with silica in the final annealing step.
- FIG. 1 shows the relationship between the obtained steel sheet oxygen content and magnetic properties. From FIG. 1, it was found that the iron loss of all the samples deteriorated when the oxygen content of the steel sheet exceeded 320 ppm. This is because if the amount of oxidation in decarburization annealing exceeds 320 ppm, oxides (mullite) are formed during high temperature annealing and the smoothness of the steel sheet is lost, resulting in a decrease in iron loss.
- FIG. 2 shows the relationship between the aging time, the carbon content of the steel sheet, and the magnetic flux density obtained after holding at 150° C. for maximum 10 days while annealing. From FIG. 2, it was found that the holding power rapidly deteriorates in the sample having the steel plate carbon content of more than 25 ppm. It is considered that this is because carbides and nitrides precipitate due to aging, and these impede the movement of the domain wall.
- the controlling factors of decarburization and oxidation reaction were clarified, and a technique for achieving both decarburization and oxidation during low dew point decarburization annealing was examined.
- the decarburization reaction rate in the steel sheet is the diffusion-controlling rate of carbon in the steel sheet, and that the decarburization reaction starts at about 700° C. or higher. Therefore, at 700° C. or higher, it is considered important to improve the decarburization temperature, the decarburization time, and the gas oxidation degree of the atmosphere gas in order to improve the decarburization property.
- Non-Patent Document 1 describes the effect of the gas oxidation degree (P H2O /P H2 ) on the oxidation of a 3% Si steel sheet at 850° C. (see FIG. 3).
- the gas oxidation degree (P H2O /P H2 ) is 0.02 (in a 75% hydrogen atmosphere, the dew point is 18° C.) or less, the oxide formed on the steel sheet surface is The main component is SiO 2 . Since this SiO 2 is amorphous, it is known that the gas permeation effect is extremely small.
- SiO 2 is preferentially formed when annealed at a low dew point in a low temperature portion, in order to improve decarburization, annealing is performed at a relatively high dew point in the initial stage of oxidation to suppress the formation of SiO 2. It turns out that it is important to do.
- FIG. 4C shows the atmospheric gas dew point distribution (dotted line) in the furnace when the atmospheric gas is introduced from the latter stage of the soaking in the decarburization annealing furnace as shown in FIG. 4A, and the heating zone and the soaking zone as shown in FIG. 4B.
- the schematic diagram of the atmospheric gas dew point distribution (solid line) in a furnace when an atmospheric gas is introduced from a location is shown.
- FIG. 4A when the atmospheric gas is collectively introduced from the latter stage of the soaking zone 2, the water vapor in the atmospheric gas is consumed while flowing from the soaking zone 2 toward the heating zone side 1. It can be seen that the dew point of the atmospheric gas introduced in the latter part of the tropical zone 2 decreases toward the heating zone 1 as shown by the dotted line in FIG.
- the present inventors use the decarburization annealing furnace 10 shown in FIG. 4B to promote decarburization in the heating zone 1 and adjust oxidation in the soaking zone 2 under the processing conditions described in Table 2 below.
- the soaking temperature during decarburization annealing is determined as a condition where both decarburization and oxidation amount of the decarburized annealed steel sheet are compatible with each other, and may be performed at 800 to 870°C, preferably 805 to 850°C, and more preferably Is 820 to 835°C.
- the obtained decarburized annealed steel sheet was subjected to nitriding annealing as shown in Table 2, water slurry was applied using an annealing separating agent containing alumina as a main component, and finish annealing was performed.
- Magnetic properties were measured for a plurality of grain-oriented electrical steel sheets obtained by subdividing magnetic domains. For magnetic measurement, the iron loss W17/50 at 1.7 T and 50 Hz and the magnetic flux density B8 at a magnetizing force of 800 A/m were evaluated based on the Epstein method described in JIS C2550-1:2011. The test results are shown in FIG. In FIG. 5, ⁇ is an example in which the magnetic target was satisfied, and X is an example in which the magnetic target was not satisfied.
- DP2 decarburization is hindered because the progress of decarburization in the heating zone is delayed and the oxidation proceeds in the soaking zone where the plate temperature rises with respect to the heating zone. Therefore, it is preferable that DP2 ⁇ DP1. Further, when DP2 is less than (60-DP1), decarburization after decarburization annealing is insufficient, and when DP2 is more than (100-DP1), the thin material is excessively oxidized. Therefore, it is preferable to set DP2 in the range of 60-DP1 ⁇ DP2 ⁇ 100-DP1.
- Finish Annealing Step Removal Step
- the steel sheet is finish annealed. This causes secondary recrystallization in the steel sheet.
- a finish annealing film containing forsterite (Mg 2 SiO 4 ) as a main component is formed, generally, the surface of the decarburization annealed steel sheet has a high magnesia concentration (for example, MgO ⁇ 90).
- Mass %) An annealing separation material is applied and a final annealing step is performed.
- an annealing separation material for example, MgO: 10
- MgO for example, MgO: 10
- Al 2 O 3 including 90 to 50% by mass
- finish annealing is performed (secondary recrystallization), and then excess annealing separator is removed.
- the intermediate layer is formed so as not to form the final annealing film made of forsterite (Mg 2 SiO 4 ).
- the annealing separator is applied in order to prevent seizure between steel sheets after finish annealing and to form a finish annealing coating film made of forsterite (Mg 2 SiO 4 ).
- the annealing separator having a low magnesia concentration is used. To use.
- the heating conditions for the finish annealing may be general conditions, for example, heating rate: 5° C./s to 100° C./s, 1000° C. to 1300° C. for 10 hours to 50 hours.
- the gas can be cooled, for example, from 1100° C. to 500° C. in an atmosphere having an oxidation degree (P H2O 2 /P H2 ) of 0.0001 to 100,000. More specifically, in the cooling process after reaching the maximum temperature of the finish annealing step, T1 is set to 1100°C when the maximum temperature is 1100°C or higher, and T1 is set to the maximum temperature when the maximum temperature is less than 1100°C. , T1 to 500° C.
- a final annealed steel sheet can be obtained by removing the annealing separator after cooling.
- the method for removing the annealing separation material is not particularly limited, but it can be removed by rubbing with a brush of the mother steel plate surface.
- Intermediate layer forming step for example, after the finish annealed steel sheet is heated to an upper limit temperature range of more than 600°C, the steel sheet is heated to a temperature range of more than 600°C and not more than the upper limit temperature, and the degree of oxidation of gas is (P H2O 2 /P H2 ):
- P H2O 2 /P H2 degree of oxidation of gas
- the heating condition of the finish annealed steel sheet in the intermediate layer forming step is not particularly limited as long as it is heated to a temperature range of more than 600° C., for example, in a temperature range of 700° C. to 1150° C. for 10 seconds to 60 seconds. It is preferable to carry out under the condition of holding. From the viewpoint of reaction rate, the temperature needs to exceed 600°C, but if it becomes higher than 1150°C, it becomes difficult to keep the formation reaction of the intermediate layer uniform, and the unevenness of the interface between the intermediate layer and the mother steel plate becomes severe. Iron loss may be deteriorated, the strength of the steel sheet may be reduced, and the treatment in the continuous annealing furnace may be difficult, which may reduce the productivity.
- the holding time is preferably 10 seconds or more from the viewpoint of forming the intermediate layer, and is preferably 60 seconds or less from the viewpoint of productivity and avoiding a decrease in space factor due to an increase in the thickness of the intermediate layer. From the viewpoint of forming the intermediate layer with a thickness of 2 to 400 nm, it is preferable to hold the temperature in the temperature range of 650 to 1000° C. for 15 to 60 seconds, and to hold it in the temperature range of 700 to 900° C. for 25 to 60 seconds. More preferable.
- Insulating Film Forming Step After coating and baking the coating solution on the surface of the intermediate layer, for example, heating in a temperature range of 700° C. to 1150° C. for 5 to 60 seconds in an atmosphere of 100% nitrogen gas.
- the insulating coating is preferably formed to the thickness described in the item of “A. Grain-oriented electrical steel sheet 1-3. Insulating coating” described above.
- the coating solution is also not particularly limited, but a coating solution having colloidal silica and a coating solution having no colloidal silica can be used depending on the application. Examples of the coating solution containing no colloidal silica include a coating solution containing alumina and boric acid.
- the coating solution having colloidal silica examples include a coating solution containing phosphoric acid or phosphate, colloidal silica, and chromic anhydride or chromate.
- the chromate examples include chromates such as Na, K, Ca and Sr.
- the colloidal silica is not particularly limited, and its particle size can be appropriately used. Furthermore, various elements and compounds may be further added to the coating solution in order to improve various properties unless the effect required in the present embodiment is not lost.
- heating and annealing may be performed to 650 to 950° C. in an atmosphere having a gas oxidation degree (P H2O 2 /P H2 ) of 0.01 to 0.30.
- a gas oxidation degree P H2O 2 /P H2
- any gas that is generally used may be used, but for example, a gas consisting of hydrogen: 25% by volume and the balance: nitrogen and impurities can be used.
- the gas oxidation degree (P H2O /P H2 ) is less than 0.01, the insulating film may be decomposed, and if it exceeds 0.30, the mother steel sheet is significantly oxidized, Iron loss may deteriorate.
- the degree of oxidation (P H2O 2 /P H2 ) of the gas is more preferably 0.02 to 0.08, further preferably 0.03 to 0.05.
- the method for producing a grain-oriented electrical steel sheet according to the present embodiment may further include the steps generally performed in the method for producing a grain-oriented electrical steel sheet, and the secondary re-annealing from the start of decarburization annealing to finish annealing. It is preferable to further include a nitriding treatment step of performing a nitriding treatment for increasing the N content of the decarburized annealed steel sheet before the appearance of crystals. This is because the magnetic flux density can be stably improved even if the temperature gradient applied to the steel sheet at the boundary between the primary recrystallization region and the secondary recrystallization region is low.
- the nitriding treatment may be a general treatment, for example, a treatment of annealing in an atmosphere containing a gas having a nitriding ability such as ammonia, or an annealing separator containing a powder having a nitriding ability such as MnN.
- a general treatment for example, a treatment of annealing in an atmosphere containing a gas having a nitriding ability such as ammonia, or an annealing separator containing a powder having a nitriding ability such as MnN.
- the treatment include finish annealing of the decarburized annealed steel sheet.
- the step for the purpose of forming only the intermediate layer and the step for the purpose of forming the insulating coating are separately performed, but in the second embodiment, It differs from the first embodiment in that an insulating coating is formed at the same time. That is, unlike the first embodiment, the following intermediate layer-insulating coating forming step is performed instead of the intermediate layer forming step and the insulating coating forming step described above. Therefore, only the intermediate layer-insulating film forming step will be described below.
- the coating solution is applied to the surface of the finish-annealed steel plate, and, for example, in the temperature range of more than 650°C to 950°C or less, the degree of oxidation of gas (P H2O /P H2 ): 0.01 to
- P H2O /P H2 degree of oxidation of gas
- an intermediate layer containing silicon oxide as a main component and an insulating coating are simultaneously formed on the surface of the finish-annealed steel sheet.
- the coating solution is applied to the surface of the finish-annealed steel sheet and heat-treated, the intermediate layer and the metallic Fe phase are formed on the surface of the steel sheet by reducing Fe in the Fe-based oxide, and the coating solution is baked at the same time.
- An insulating coating is formed on the surface of the intermediate layer.
- the degree of gas oxidation (P H2O /P H2 ): 0.05 to 0.25 may be set. More preferably, the gas oxidation degree (P H2O /P H2 ): 0.10 to 0.20 is more preferable.
- the present invention is not limited to the above embodiment.
- the above-described embodiment is an exemplification, and it has substantially the same configuration as the technical idea described in the scope of claims of the present invention, and any one having the same operational effect is the present invention. It is included in the technical scope of the invention.
- the present invention will be specifically described with reference to examples.
- the conditions in the examples are one condition example adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to this one condition example.
- the present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
- Example 1 "When the plate thickness is 0.18 mm" Si: 3.45%, C: 0.060%, acid soluble Al: 0.030%, N: 0.008%, and Mn: 0.10%, and S and Se: 0.007% in total. A slab having a chemical composition containing Fe and impurities contained in the balance is soaked at 1150° C. for 60 minutes, and then the heated slab is hot-rolled to obtain a hot-rolled steel sheet having a thickness of 2.8 mm. It was Next, the hot-rolled steel sheet was held at 900° C. for 120 seconds and then subjected to hot-rolled sheet annealing for rapid cooling to obtain an annealed steel sheet. Next, after pickling the annealed steel sheet, the steel sheet after pickling was cold-rolled once or plural times to obtain a cold-rolled steel sheet having a final thickness of 0.18 mm.
- the soaking temperature was set to 820 to 835° C., and the atmospheric gas was introduced from two locations, the former stage and the latter stage of the soaking zone. Then, decarburization annealing was performed. At that time, the dew point DP1 of the atmospheric gas introduced from the former stage was changed to 30 to 80° C., and the dew point DP2 of the atmospheric gas introduced from the latter stage was changed to ⁇ 5 to 55° C.
- the target carbon amount [C] was 25 ppm or less, and the oxygen amount [O] was 320 ppm or less.
- the amount of carbon after decarburization annealing was analyzed by using an infrared absorption method by burning in an oxygen stream to form CO gas.
- an infrared absorption method by burning in an oxygen stream to form CO gas.
- a sample was burned in a graphite crucible in an inert gas such as He to obtain CO gas, which was analyzed by an infrared absorption method.
- an annealing separator containing alumina, which is difficult to react with silica, as a main component was applied with a water slurry, and then finish annealing was performed.
- the finish annealing was performed at a temperature rising rate of 15° C./Hr in an atmosphere gas of N 2 :25%+H 2 :75% up to 1200° C., and the annealing was switched to H 2 :100% at 1200° C. for 20 hours.
- the gas was cooled from 1100° C. to 500° C. in an atmosphere having a gas oxidation degree (PH 2 O 3 /PH 2 ) of 0.0001 to 100000.
- the cooling time for cooling under the above conditions was 5 to 30 hours.
- the annealing separation material of the steel sheet after the finish annealing is removed with a brush, and some of the steel sheets are 870° C. and the degree of oxidation of the atmospheric gas (P H2 O /P H2 ) is 0.01 for 60 seconds.
- P H2 O /P H2 the degree of oxidation of the atmospheric gas
- the thin material has better decarburizing property as compared with the thick material, but on the other hand, it is easy to oxidize. Therefore, good magnetic properties could not be obtained when the preceding dew point DP1 was 30°C and 80°C.
- a decarburized and annealed steel sheet having an oxygen content of 320 ppm or less and a carbon content of 25 ppm or less could be obtained in the decarburized and annealed steel sheet.
- the dew point DP1 of the atmospheric gas introduced from the former stage of the soaking zone is 40 to 70° C.
- a decarburized annealed steel sheet having an oxygen content of 320 ppm or less and a carbon content of 25 ppm or less could be obtained.
- the grain-oriented electrical steel sheet obtained by forming the intermediate layer and the insulating layer using these decarburized annealed steel sheets was an excellent electrical steel sheet with low iron loss. Further, the film adhesion was sufficient in all the examples.
- Example 2 "When the plate thickness is 0.23 mm" Si: 3.45%, C: 0.060%, acid soluble Al: 0.030%, N: 0.008%, and Mn: 0.10%, and S and Se: 0.007% in total. A slab having a chemical composition containing Fe and impurities contained in the balance is soaked at 1150° C. for 60 minutes, and then the heated slab is hot-rolled to obtain a hot-rolled steel sheet having a thickness of 2.8 mm. It was Next, the hot-rolled steel sheet was held at 900° C. for 120 seconds and then subjected to hot-rolled sheet annealing for rapid cooling to obtain an annealed steel sheet. Next, after pickling the annealed steel sheet, the steel sheet after pickling was cold-rolled once or plural times to obtain a cold-rolled steel sheet having a final thickness of 0.23 mm.
- an annealing separator containing alumina, which is difficult to react with silica, as a main component was applied with a water slurry, and then finish annealing was performed.
- the finish annealing was performed at a temperature rising rate of 15° C./Hr in an atmosphere gas of N 2 :25%+H 2 :75% up to 1200° C., and the annealing was switched to H 2 :100% at 1200° C. for 20 hours.
- the gas was cooled from 1100° C. to 500° C. in an atmosphere having an oxidation degree (PH 2 O 3 /PH 2 ) of 0.0001 to 100000.
- the cooling time for cooling under the above conditions was set to 5 to 30 hours.
- P H2O /P H2 the oxidation degree of the atmospheric gas
- Example 3 "When the plate thickness is 0.35 mm" Si: 3.25%, C: 0.050%, acid soluble Al: 0.030%, N: 0.008%, and Mn: 0.10%, and S and Se: 0.006% in total. A slab having a chemical composition containing Fe and impurities contained in the balance is soaked at 1150° C. for 60 minutes, and then the heated slab is hot-rolled to obtain a hot-rolled steel sheet having a thickness of 2.8 mm. It was Next, the hot-rolled steel sheet was held at 900° C. for 120 seconds and then subjected to hot-rolled sheet annealing for rapid cooling to obtain an annealed steel sheet. Next, after pickling the annealed steel sheet, the steel sheet after pickling was cold-rolled once or plural times to obtain a cold-rolled steel sheet having a final thickness of 0.35 mm.
- the soaking temperature is changed to 820 to 840°C
- the dew point DP1 of the former stage is changed to 30 to 80°C
- the dew point DP2 of the latter stage is changed to -15 to 55°C.
- Charcoal annealing was performed.
- an annealing separator containing alumina as a main component, which is difficult to react with silica was applied with a water slurry, and then finish annealing was performed.
- the finish annealing was performed at a temperature rising rate of 15° C./Hr in an atmosphere gas of N 2 :25%+H 2 :75% up to 1200° C., and the annealing was switched to H 2 :100% at 1200° C. for 20 hours.
- the gas was cooled from 1100° C. to 500° C. in an atmosphere having an oxidation degree (PH 2 O 3 /PH 2 ) of 0.0001 to 100000.
- the cooling time for cooling under the above conditions was 5 to 30 hours.
- the annealing separators of these samples were dedusted with a brush, and some of the steel sheets were annealed for 60 seconds in an atmosphere of 870° C. and an atmosphere gas oxidation degree (PH 2 O 2 /PH 2 ) of 0.01.
- An intermediate layer having a thickness of 20 nm was formed.
- An insulating coating having a thickness of m 2 and a thickness of 2 ⁇ m was formed.
- a decarburized and annealed steel sheet having an oxygen content of 320 ppm or less and a carbon content of 25 ppm or less could be obtained in the steel sheet after decarburization annealing.
- the grain-oriented electrical steel sheet obtained by forming the intermediate layer and the insulating layer using these decarburized annealed steel sheets was an excellent electrical steel sheet with low iron loss. Since decarburization becomes a bottleneck in the thick material and causes deterioration of the magnetic aging of the final product, good magnetic properties were not obtained in both cases when the pre-stage dew point DP1 was 30°C and 80°C.
- the oxygen amount is 320 ppm or less and the carbon amount is 25 ppm or less, and the iron loss is excellent. It was found that a grain-oriented electrical steel sheet having a thickness of more than 0.23 mm and a thickness of 0.35 mm can be obtained.
- the present invention it is possible to provide a method for manufacturing a grain-oriented electrical steel sheet that does not substantially have a forsterite coating.
- a method for producing a grain-oriented electrical steel sheet according to the above aspect by coexisting decarburization and steel sheet oxidation suppression in a wide sheet thickness range, a core loss is low, and a magnetic flux density after magnetic aging is high. can do.
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Abstract
Description
本願は、2019年01月16日に、日本に出願された特願2019-005399号に基づき優先権を主張し、その内容をここに援用する。
鋼板に張力を付与するためには、鋼板より熱膨張係数の小さい材質からなる被膜を高温で形成することが有効である。仕上げ焼鈍工程で鋼板表面の酸化物と焼鈍分離材とが反応して生成する仕上げ焼鈍被膜(フォルステライト被膜)は鋼板に張力を与えることができ、被膜密着性も優れている。
しかしながら、これらの特許文献では脱炭焼鈍時の板厚が0.14mm、0.23mmにて実施されており、厚手材(0.23mm以上)への適用技術については述べられていない。
本発明者らの検討の結果、フォルステライト被膜が実質的に存在しない母鋼板表面に酸化珪素を主成分とする中間層を有し、前記中間層の表面に絶縁被膜を有する方向性電磁鋼板を製造する方法において、脱炭焼鈍工程で、特定の条件で処理し、脱炭後の鋼板の酸素量及び炭素量を特定の範囲に調整することで、広い板厚範囲において脱炭と鋼板酸化とを両立でき、優れた磁気特性を有する方向性電磁鋼板を提供できることを知見した。
下記説明において数値範囲を「下限値~上限値」で示す場合には、特に断らない限り「下限値以上、上限値以下」であることを意味する。
本実施形態に係る方向性電磁鋼板の製造方法によって製造される方向性電磁鋼板(以下、本実施形態の方向性電磁鋼板と言う場合がある)は、母鋼板と、酸化珪素を主成分とする中間層、及び、絶縁被膜を、この順に有する三層構造の方向性電磁鋼板である。
以下、本実施形態の方向性電磁鋼板の三層の基本構造について説明する。
1-1.母鋼板
本実施形態に係る方向性電磁鋼板の製造方法によって製造される電磁鋼板(本実施形態の方向性電磁鋼板)は、酸化珪素を主体とする中間層に接する絶縁被膜を有するが、本実施形態の方向性電磁鋼板における母鋼板の化学組成や組織等の構成は、Siを必須成分として含有することを除いてこのような絶縁被膜の層構成とは直接関連しない。このため、本実施形態の方向性電磁鋼板における母鋼板は、本実施形態で求める作用効果が得られるものであれば特に限定されるものではなく、例えば、一般的な方向性電磁鋼板における母鋼板を用いることができる。以下、本実施形態の方向性電磁鋼板における母鋼板について説明する。
母鋼板の化学組成は、例えばSiを必須成分として含有することを除いて一般的な方向性電磁鋼板における母鋼板の化学組成を用いることができる。Siの機能は、一般的な方向性電磁鋼板における機能と同様であるため、含有量は目的とする方向性電磁鋼板に求められる特性から、一般的な範囲で定めればよい。
以下において、母鋼板の化学組成における各成分の含有量は質量%での値である。また、本実施形態の方向性電磁鋼板の化学組成が安定している深さ50~60μmにおける化学組成である。
Siは必須成分であり、電気抵抗を高めて鉄損を低下させる。また、Siを高濃度で含有することで、酸化珪素を主体とする中間層との間に強い化学親和力が発現し、中間層と母鋼板とがより強固に密着する。しかしながら、Siの含有量が7.00%を超えると、冷間圧延が極めて困難となり、冷間圧延時に割れが生じやすくなる。このため、Siの含有量は7.00%以下とすることが好ましい。より好ましくは4.50%以下であり、さらに好ましくは4.00%以下である。
一方、Siの含有量が0.80%未満であると、仕上げ焼鈍時にγ変態が生じ、方向性電磁鋼板の好ましい結晶方位が損なわれてしまう。このため、Siの含有量は0.80%以上とすることが好ましい。より好ましくは2.00%以上であり、さらに好ましくは2.50%以上である。
「SおよびSe」:合計で0.003%以上0.015%以下
Mnは、SおよびSeと共に、MnSおよびMnSeを生成し、複合化合物がインヒビターとして機能する。Mn含有量が0.05%~1.00%の範囲内にある場合に、二次再結晶が安定する。このため、Mnの含有量は、0.05%~1.00%とすることが好ましい。Mnの含有量は、0.08%以上であることがより好ましく、0.09%以上であることがさらに好ましい。また、Mnの含有量は、0.50%以下であることがより好ましく、0.20%以下であることがさらに好ましい。
残部はFeおよび不純物からなる。「不純物」とは、母鋼板を工業的に製造する際に、原材料に含まれる成分、または製造の過程で混入する成分から不可避的に混入する元素を意味する。
中間層は、母鋼板表面に形成され、酸化珪素を主成分とする。本実施形態の方向性電磁鋼板では、フォルステライト被膜を実質的に有しないので、中間層は母鋼板表面に直接接して形成される。中間層は、本実施形態の三層構造において母鋼板と絶縁被膜とを密着させる機能を有する。
中間層の主成分である酸化珪素は、SiOx(x=1.0~2.0)が好ましく、SiOx(x=1.5~2.0)がより好ましい。酸化珪素がより安定するからである。鋼板表面に酸化珪素を形成する熱処理を十分に施せば、シリカ(SiO2)を形成することができる。
酸化珪素を主体とするとは、後述するように中間層の組成としてFe含有量が30原子%未満、P含有量が5原子%未満、Si含有量が20原子%以上、O含有量が50原子%以上、Mg含有量が10原子%以下を満足することである。
具体的には、切断面が板厚方向と平行かつ圧延方向と垂直となるようにFIB(Focused Ion Beam)加工にて試験片を切り出し、この切断面の断面構造を、観察視野中に各層が入る倍率にてSTEM(Scanning-TEM)で観察(明視野像)する。観察視野中に各層が入らない場合には、連続した複数視野にて断面構造を観察する。
定量分析する元素は、Fe、P、Si、O、Mgの5元素とする。また、化合物層の特定には、EDSと合わせて、電子線回折による結晶相の同定を行う。
まず母鋼板と中間層との間のブランク領域は、ブランク領域の厚さ方向の中心を境界として、母鋼板側は母鋼板、中間層側は中間層とみなす。次に絶縁被膜と中間層との間のブランク領域は、ブランク領域の厚さ方向の中心を境界として、絶縁被膜側は絶縁被膜、中間層側は中間層とみなす。この手順により、母鋼板、絶縁被膜および中間層を分離できる。
絶縁被膜は、中間層表面に形成され、鋼板に張力を付与して鋼板単板としての鉄損を低下させる他、方向性電磁鋼板を積層して使用する際に方向性電磁鋼板間の電気的絶縁性を確保する機能を有する。
有機系被膜としては、例えばポリアミン系樹脂、アクリル樹脂、アクリルスチレン樹脂、アルキッド樹脂、ポリエステル樹脂、シリコーン樹脂、フッ素樹脂、ポリオレフィン樹脂、スチレン樹脂、酢酸ビニル樹脂、エポキシ樹脂、フェノール樹脂、ウレタン樹脂、メラミン樹脂等が挙げられる。また、無機系被膜としては、例えば、リン酸塩系被膜、リン酸アルミニウム系被膜や、更に前記の樹脂を含む有機-無機複合系被膜等が挙げられる。より具体的には、マトリックス中に、コロイド状シリカの粒子が分散されたものを焼き付けたものであっても良い。ここで、「マトリックス」とは、絶縁被膜の基質のことであり、例えば、非結晶性燐酸塩から構成されたものである。マトリックスを構成する非結晶性燐酸塩としては、例えば、燐酸アルミ、燐酸マグネシウム等が挙げられる。焼付け後の絶縁被膜は、P、O、Sのうち1種以上を含む複数の化合物からなる。
絶縁被膜には、必要に応じ、レーザー、プラズマ、機械的方法、エッチング、その他の手法で、局所的な微小歪領域または溝を形成する磁区細分化処理を施してもよい。
次に、本実施形態に係る方向性電磁鋼板の製造方法について説明する。
第一実施形態に係る方向性電磁鋼板の製造方法は、中間層と絶縁被膜とを別工程で形成する。すなわち、第一実施形態に係る方向性電磁鋼板の製造方法は、以下の工程を有する。
(I)Siを含む冷間圧延鋼板に脱炭焼鈍を施して、酸素量が320ppm以下、かつ炭素量が25ppm以下である脱炭焼鈍鋼板を得る脱炭焼鈍工程
(II)前記脱炭焼鈍鋼板の表面に焼鈍分離材を塗布した状態で前記脱炭焼鈍鋼板を加熱して鋼板(脱炭焼鈍鋼板)を二次再結晶させる仕上げ焼鈍工程
(III)前記仕上げ焼鈍工程後の前記鋼板(脱炭焼鈍鋼板)上の焼鈍分離材を除去することにより仕上げ焼鈍鋼板を得る除去工程
(IV)前記仕上げ焼鈍鋼板に熱酸化焼鈍を施して中間層を形成する中間層形成工程
(V)前記中間層を形成した仕上げ焼鈍鋼板に絶縁被膜を形成する絶縁被膜形成工程
第一実施形態に係る方向性電磁鋼板の製造方法は、中間層と絶縁被膜とを1工程で同時に形成する。すなわち、第二実施形態に係る方向性電磁鋼板の製造方法は、以下の工程を有する。
(I)Siを含む冷間圧延鋼板に脱炭焼鈍を施して、酸素量が320ppm以下、かつ炭素量が25ppm以下である脱炭焼鈍鋼板を得る脱炭焼鈍工程
(II)前記脱炭焼鈍鋼板の表面に焼鈍分離材を塗布した状態で前記脱炭焼鈍鋼板を加熱して鋼板(脱炭焼鈍鋼板)を二次再結晶させる仕上げ焼鈍工程
(III)前記仕上げ焼鈍工程後の前記鋼板(脱炭焼鈍鋼板)上の焼鈍分離材を除去することにより仕上げ焼鈍鋼板を得る除去工程
(IV’)前記仕上げ焼鈍鋼板に中間層と絶縁被膜とを一工程で形成する中間層-絶縁被膜形成工程
以下では、上述した特に特徴となる工程以外の条件は、一般的な条件を例として示したものであるから、充足しなかったとしても本実施形態の効果を得ることは可能である。
1.脱炭焼鈍工程に供する冷間圧延鋼板
最初に、後述する脱炭焼鈍に用いる冷間圧延鋼板について説明する。
冷間圧延鋼板は、Siを必須成分として含有することを除いて一般的な方向性電磁鋼板における母鋼板の化学組成を有することができる。Siの電磁鋼板における機能は、一般的な方向性電磁鋼板と同様であるため、含有量は目的とする電磁鋼板に求められる特性から、一般的な範囲で定めればよい。
例えば、冷間圧延鋼板の化学組成は、質量%で、Si:0.80~7.00%、C:0.085%以下、酸可溶性Al:0.010~0.065%、N:0.012%以下、Mn:1.00%以下、SおよびSeの合計:0.003~0.015%を含有し、残部がFe及び不純物からなる化学組成を例示することができる。
このような冷間圧延鋼板は、例えばスラブを加熱した後、熱間圧延を施して熱間圧延鋼板を得る熱間圧延工程と、当該熱間圧延鋼板に熱延板焼鈍を施して焼鈍鋼板を得る熱延板焼鈍工程と、当該焼鈍鋼板に一回または中間焼鈍を挟む二回以上の冷間圧延を施して冷間圧延鋼板を得る冷間圧延工程を備える製造方法によって製造することができる。
以下、スラブ及びそれによって得られる冷間圧延鋼板の化学組成の代表的な一例の限定理由について説明する。
Siは必須成分であり、電気抵抗を高めて鉄損を低下させる。また、Siを高濃度で含有することで、酸化珪素を主体とする中間層との間に強い化学親和力が発現し、中間層と母鋼板とはより強固に密着する。しかしながら、Siの含有量が7.00%を超えると、冷間圧延が極めて困難となり、冷間圧延時に割れが生じやすくなる。このため、Siの含有量は7.00%以下とすることが好ましい。より好ましくは4.50%以下であり、さらに好ましくは4.00%以下である。
一方、Siの含有量が0.80%未満であると、仕上げ焼鈍時にγ変態が生じ、方向性電磁鋼板の結晶方位が損なわれる。このため、Siの含有量は0.80%以上とすることが好ましい。より好ましくは2.00%以上であり、さらに好ましくは2.50%以上である。
Cは、一次再結晶組織の制御に有効な元素であるが、磁気特性に悪影響を及ぼす。このため、仕上げ焼鈍前に脱炭焼鈍を施す。C含有量が0.085%より多いと、脱炭焼鈍時間が長くなり、工業生産における生産性が損なわれてしまう。これらのことから、Cの含有量は0.085%以下であることが好ましい。C含有量の下限値としては、特に限定されないが、C含有量は0.020%以上であることが好ましく、0.050%以上であることがより好ましい。
酸可溶性Alは、Nと結合して(Al,Si)Nとして析出し、インヒビターとして機能する。酸可溶性Alの含有量が0.010%~0.065%の範囲内にある場合に二次再結晶が安定する。このため、酸可溶性Alの含有量は0.010%~0.065%とすることが好ましい。また、後述するように、仕上げ焼鈍において鋼板表面にAlを濃化させて、これを後述する本発明の方向性電磁鋼板の製造方法において中間層形成時の鋼板表面に存在するAlおよびMgのうちのAlとして活用する等の観点から、酸可溶性Alの含有量は0.015%以上であることが好ましく、0.020%以上であることがより好ましい。また、二次再結晶の安定性の観点から、酸可溶性Al含有量は0.050%以下であることがより好ましく、0.035%以下であることがさらに好ましい。
Nは、Alと結合してインヒビターとして機能する。N含有量が0.004%未満であると、十分な量のインヒビターを得ることができない。このため、N含有量は0.004%以上とすることが好ましい。より好ましくは0.005%以上であり、さらに好ましくは0.006%以上である。
一方、Nの含有量が0.012%を超えていると、鋼板中にブリスターとよばれる欠陥を生じ易くなる。このため、N含有量は0.012%以下とすることが好ましい。より好ましくは0.011%以下であり、さらに好ましくは0.010%以下である。
f.SおよびSe:合計で0.003%~0.015%
Mnは、Sおよび/またはSeと共に、MnSおよび/またはMnSeを生成し、複合化合物がインヒビターとして機能する。Mnの含有量が0.05%~1.00%の範囲内にある場合に、二次再結晶が安定する。このため、Mnの含有量は、0.05%~1.00%とすることが好ましい。Mnの含有量は、0.08%以上であることがより好ましく、0.09%以上であることがさらに好ましい。また、Mnの含有量は0.50%以下であることがより好ましく、0.20%以下であることがさらに好ましい。
化合物形成によるインヒビター機能の強化や磁気特性への影響を考慮して、残部のFeの一部に代えて様々な種類の元素を公知文献に従って含有させることができる。Feの一部に代えて含有させる元素の種類と含有量の目途としては、例えば、「Bi:0.010%以下」、「B:0.080%以下」、「Ti:0.015%以下」、「Nb:0.20%以下」、「V:0.15%以下」、「Sn:0.10%以下」、「Sb:0.10%以下」、「Cr:0.30%以下」、「Cu:0.40%以下」、「P:0.50%以下」、「Ni:1.00%以下」、「Mo:0.10%以下」等が挙げられる。
残部はFeおよび不純物からなる。「不純物」とは、母鋼板を工業的に製造する際に、原材料に含まれる成分、または製造の過程で混入する成分から混入する元素を意味する。
熱間圧延工程においては、上述したようなSiを含有するスラブを、例えば800℃~1300℃の温度域で加熱した後、熱間圧延を施して熱間圧延鋼板を得る。
スラブの加熱温度を1200℃以下とすることで、例えば、1200℃よりも高い温度で加熱した場合の諸問題(専用の加熱炉が必要なこと、および溶融スケール量の多さ等)を回避することができるため好ましい。
加熱温度が低すぎる場合、熱間圧延が困難になって、生産性が低下することがある。そのため、スラブの加熱温度の下限値は950℃とすることが好ましい。また、スラブ加熱工程そのものを省略して、鋳造後、スラブの温度が下がるまでに熱間圧延を開始することも可能である。
また、熱間圧延鋼板の板厚は、特に限定されないが、例えば、3.5mm以下とする。
熱延板焼鈍工程においては、熱間圧延鋼板に熱延板焼鈍を施して焼鈍鋼板を得る。熱延板焼鈍条件は、一般的な条件であればよいが、例えば、750~1200℃の範囲内の温度で30秒~10分間保持する。
冷間圧延工程においては、焼鈍鋼板に一回または中間焼鈍を挟む二回以上の冷間圧延を施して冷間圧延鋼板を得る。
最終の冷間圧延での冷間圧延率(最終冷延率)は、特に限定されないが、結晶方位制御の観点から、80%以上とすることが好ましく、90%以上とすることがより好ましい。
また、冷間圧延鋼板の板厚は、特に限定されないが、鉄損をより低下させるためには、0.35mm以下とすることが好ましく、0.30mm以下とすることがより好ましい。
脱炭焼鈍工程においては、冷間圧延鋼板に脱炭焼鈍を施して脱炭焼鈍鋼板を得る。
具体的には、脱炭焼鈍を施すことで、冷間圧延鋼板に一次再結晶を生じさせ、冷間圧延鋼板中に含まれるCを除去し、脱炭焼鈍後の鋼板の炭素量を25ppm以下にする。脱炭焼鈍は、Cを除去するために湿潤雰囲気中で施すことが好ましい。また、脱炭焼鈍工程では、酸化を抑制することで脱炭焼鈍後の酸素量を320ppm以下に制御する。
方向性電磁鋼板においては、磁性を良好とするための集合組織を得るために、炭素は500~600ppm程度添加されている。しかしながら、前述の冷間圧延工程後において、炭素(C)は不要となるため、脱炭焼鈍工程においては焼鈍後の炭素量は変圧器等の最終製品における磁気時効を発生しないレベルまで除去する必要がある。フォルステライト被膜を有する方向性電磁鋼板においては、鋼板表層にファイヤライトを有する酸化層を形成する必要があるため、通常、冷間圧延鋼板を露点60~70℃、均熱温度800~900℃にて焼鈍する。
図4A、図4Bに示すように加熱炉1の内部は加熱帯であり、均熱炉2の内部は均熱帯であり、加熱帯から均熱帯にかけて図4A、図4Bに示す矢印が示す右方向へ鋼板を水平搬送することができ、搬送途中で鋼板に対する脱炭焼鈍処理を実施できる脱炭焼鈍炉である。
図4Aに示す脱炭焼鈍炉は、均熱炉2の出口近くの側壁部(均熱帯後段)から均熱炉2の内部に鋼板の通過方向と反対方向向きに雰囲気ガスを供給出来る炉である。
図4Bに示す脱炭焼鈍炉は、均熱炉2の出口近くの側壁部(均熱帯後段)から均熱炉2の内部に鋼板の通過方向と反対方向向きに雰囲気ガスを供給出来るとともに、均熱炉2の入口近くの底部(均熱帯前段(加熱帯後段))から加熱炉1側に向かって鋼板の搬送方向と反対側向きに雰囲気ガスを供給出来る脱炭焼鈍炉である。
本実施形態において、均熱帯前段とは、均熱帯の中央より加熱帯側(上流側)、均熱帯後段とは、均熱帯の中央より下流側の位置を意味し、例えば図4Bに示す位置である。雰囲気ガスを導入する位置は、前段であれば均熱帯の入口付近(均熱温度到達位置)、後段であれば均熱帯の出口付近が好ましい。
本実施形態では図4Bに示す脱炭焼鈍炉を用いて、以下の表1に記載の処理条件において、均熱帯前段から露点(DP1)を30~70℃とした雰囲気ガスを導入し、かつ均熱帯後段から導入する雰囲気ガスの露点(DP2)を-20~50℃へ変更する試験を行った。続いて得られた脱炭焼鈍鋼板を表1に記載の窒化処理条件にて窒化処理を行い、脱炭焼鈍後の鋼板の炭素量と酸素量とを調査した。得られた鋼板中の炭素量については、酸素気流中にて燃焼させることでCOガスとし、赤外線吸収法を用いて分析を行った。酸素量については、Heなどの不活性ガス中にて黒鉛坩堝中にて試料を燃焼させることでCOガスとし、これを赤外線吸収法にて分析を行った。
得られた脱炭焼鈍鋼板については、従来のようにマグネシア水スラリーを塗布することもあるが、この例の場合、仕上げ焼鈍工程にてシリカと反応するために表層酸化層の凸凹が発生することから、本実験では、アルミナを主成分とする(例えば、MgO:10~50%程度、Al2O3:90~50%を含む)焼鈍分離剤を用いた水スラリー塗布を実施した。
次に、仕上げ焼鈍を実施し、さらに張力コーティング塗布を行い、その後にレーザー照射による磁区細分化を行って複数の方向性電磁鋼板を得た。これらの方向性電磁鋼板についてJISC2550-1:2011に記載のエプスタインン法に基づき、磁気特性(1.7T、50Hzにおける鉄損W17/50及び磁化力800A/mにおける磁束密度B8)の測定を行った。
図1より、鋼板酸素量が320ppm超になるといずれの試料も鉄損が悪化することが判明した。これは脱炭焼鈍における酸化量が320ppmを超えてしまうと、高温焼鈍時に酸化物(ムライト)が形成され、鋼板の平滑性が失われることで鉄損が低下するためである。
また、図2に、150℃にて焼鈍しながら最大10日間保持した後に得られた、時効時間と鋼板炭素量と磁束密度との関係を示す。図2より、鋼板炭素量が25ppm超の試料において保持力が急激に悪化することが判明した。これは、時効により炭化物や窒化物が析出し、これらが磁壁の移動を妨げるためであると考えられる。
鋼板中の脱炭反応速度については鋼板中の炭素の拡散律速であることが知られており、また、脱炭反応は約700℃以上から開始することが知られている。よって700℃以上において、脱炭温度、脱炭時間、及び雰囲気ガスのガス酸化度を向上させることが脱炭性を改善する上で重要となると考えられる。
非特許文献1には、3%Si鋼板を850℃にて焼鈍した際にガス酸化度(PH2O/PH2)が鋼板の酸化に与える影響について説明されている(図3参照)。図3に示されるように、ガス酸化度(PH2O/PH2)が0.02(75%水素雰囲気の場合、露点は18℃に相当)以下の場合、鋼板表面に形成される酸化物はSiO2が主体となる。このSiO2は非晶質であるため、ガス浸透効果が極めて小さいことが知られている。また、低温部において低露点で焼鈍した場合に、SiO2が優先的に形成されることから、脱炭改善のためには、酸化初期において比較的高露点で焼鈍し、SiO2の形成を抑制することが重要であることがわかる。
図4Aに示すように均熱帯2の後段から一括して雰囲気ガスを導入する場合、雰囲気ガス中の水蒸気は均熱帯2から加熱帯側1向かって流れていく間に消費されることから、均熱帯2の後段にて導入された雰囲気ガスの露点は、図4Cで点線で示されるように加熱帯1の方向に向かうに従い低下してゆくことがわかる。この露点低下は、非晶質SiO2の生成を促進することとなり、脱炭と酸化の両立を一層困難なものとする。また、脱炭は均熱温度到達時に完了することから、脱炭を促進するためには、高露点の雰囲気ガスを均熱温度到達前に供給することが有効である。
一方、図4Bに示すように加熱帯と均熱帯の2箇所から雰囲気ガスを導入する場合、前段にて高露点ガスを導入することで、前記非晶質SiO2の生成を抑制し、脱炭反応を促進することができる。一方、後段にて低露点ガスを導入することで脱炭後のSiの過剰酸化を抑制することができる。
以上の考察から、本実施形態では、図4Bの実線に示すように均熱帯2の前段(均熱温度到達点)において脱炭を促進するために、高露点(DP1)の雰囲気ガスを導入し、更に、均熱帯2の後段から過剰酸化を抑制するために低露点(DP2)の雰囲気ガスを導入する2段階のガス導入により、脱炭と酸化抑制との両立が可能になると考えた。
本発明者らは、図4Bに示す脱炭焼鈍炉10を用いて以下の表2に記載の処理条件において、加熱帯1にて脱炭を促進し、均熱帯2にて酸化を調整するために、脱炭焼鈍中の露点条件を焼鈍中に変更する実験を行った。脱炭焼鈍時の均熱温度については、脱炭焼鈍鋼板の脱炭と酸化量が両立する条件として決定され、800~870℃にて行えばよく、好ましくは805~850℃であり、より好ましくは820~835℃である。
図5にその試験結果を示す。図5において、〇は、磁性目標を満足した例であり、×は満足しなかった例である。図5に示す試験結果から、DP1が40~70℃、DP2≦DP1、かつ60-DP1≦DP2≦100-DP1の条件において、良好な磁気特性が得られることが判明した。
すなわち、脱炭焼鈍後の酸素量を320ppm以下、かつ炭素量を25ppm以下として、良好な磁気特性を得る場合、DP1が40~70℃、DP2≦DP1、かつ60-DP1≦DP2≦100-DP1となる条件で脱炭焼鈍を行うことが好ましい。
DP1が40℃未満の場合に厚手材の脱炭が困難になり、DP1が70℃超の場合は、薄手材の酸化が過剰となる。厚手材では、さらに好ましくは50~70℃であり、薄手材では、さらに好ましくは40~60℃である。
また、DP2が(60-DP1)未満の場合には脱炭焼鈍後の脱炭が不十分となり、DP2が(100-DP1)超の場合には薄手材の過剰酸化となる。そのため、DP2を60-DP1≦DP2≦100-DP1の範囲とすることが好ましい。
仕上げ焼鈍工程においては、鋼板に仕上げ焼鈍を施す。これにより、鋼板において二次再結晶を生じさせる。
通常の方向性電磁鋼板では、フォルステライト(Mg2SiO4)を主成分とする仕上げ焼鈍被膜を形成させるため、一般的に前記脱炭焼鈍鋼板の表面にマグネシア濃度の高い(例えば、MgO≧90質量%)焼鈍分離材を塗布して仕上げ焼鈍工程を行う。
これに対し、本実施形態に係る方向性電磁鋼板の製造方法の仕上げ焼純工程においては、前記脱炭焼鈍鋼板の表面にマグネシア濃度が低く酸化アルミニウムを含有する焼鈍分離材(例えば、MgO:10~50質量%程度、Al2O3:90~50質量%程度を含む)を塗布した状態で加熱して仕上げ焼鈍を施し(二次再結晶させ)、その後、余分な焼鈍分離材を除去することにより仕上げ焼鈍鋼板を得る。これらによって、フォルステライト(Mg2SiO4)からなる仕上げ焼鈍被膜が形成しないように中間層を形成する。
ここで、焼鈍分離剤とは、仕上げ焼鈍後の鋼板同士の焼きつきを防止するほか、フォルステライト(Mg2SiO4)からなる仕上げ焼鈍被膜を形成するために塗布するものである。本実施形態に係る方向性電磁鋼板の製造方法では、フォルステライト(Mg2SiO4)からなる仕上げ焼鈍被膜を形成しないように中間層を形成する必要があるため、マグネシア濃度の低い焼鈍分離剤を用いる。
当該加熱後の冷却時に、ガスの酸化度(PH2O/PH2):0.0001~100000の雰囲気下で、例えば1100℃から500℃まで冷却することができる。
より詳細には、前記仕上げ焼鈍工程の最高温度に到達した後の冷却過程において、最高温度が1100℃以上の場合はT1を1100℃とし、最高温度が1100℃未満の場合はT1を最高温度として、T1~500℃の温度域を、ガスの酸化度(PH2O/PH2):0.0001~100000の雰囲気下で冷却することができるが、これらの条件に制約されるものではない。好ましくは、ガス酸化度は0.3~100000である。
上記条件で冷却する冷却時間に、特に制限はないが、5~30時間とすることが好ましい。
冷却後、焼鈍分離材を除去することにより仕上げ焼鈍鋼板を得ることができる。焼鈍分離材の除去方法について、特に制限はないが、母鋼板表面ブラシでこする程度で除去することができる。
中間層形成工程においては、例えば、前記仕上げ焼鈍鋼板を、600℃を超える上限温度域まで加熱後、当該鋼板を600℃超、前記上限温度以下の温度領域で、ガスの酸化度(PH2O/PH2):0.001~0.04の雰囲気に保持しつつ焼鈍することにより、仕上げ焼鈍鋼板表面に酸化珪素を主成分とする中間層を形成することができる。
中間層は、上述した「A.方向性電磁鋼板 2.中間層」の項目に記載された厚さに形成することが好ましい。
保持時間は、中間層形成の観点からは10秒以上とし、生産性および中間層の厚さが厚くなることによる占積率の低下を回避するための観点から60秒以下とすることが好ましい。
中間層を2~400nmの厚さに成膜する観点から、650~1000℃の温度域で15~60秒保持することが好ましく、700~900℃の温度域で25~60秒保持することがより好ましい。
絶縁被膜形成工程においては、中間層表面にコーティング溶液を塗布して焼き付けた後、例えば窒素ガス100%の雰囲気下、700℃~1150℃の温度域で5~60秒間加熱することにより中間層表面に絶縁被膜を形成する。
絶縁被膜は、上述した「A.方向性電磁鋼板 1-3.絶縁被膜」の項目に記載された厚さに成膜することが好ましい。
コーティング溶液にも特に制限はないが、用途に応じて、コロイド状シリカを有するコーティング溶液とコロイド状シリカを有しないコーティング溶液を使い分けることができる。
コロイド状シリカを有しないコーティング溶液としては、例えばアルミナ及びホウ酸を含むコ-ティング溶液があげられる。
また、コロイド状シリカを有するコーティング溶液としては、例えば、燐酸または燐酸塩、コロイド状シリカ、および無水クロム酸またはクロム酸塩を含むコーティング溶液があげられる。クロム酸塩としては、例えば、Na、K、Ca、Sr等のクロム酸塩が挙げられる。コロイド状シリカは特に限定はなく、その粒子サイズも適宜使用することができる。
さらに、コーティング溶液には、本実施形態で求める効果が失われなければ、各種の特性を改善するために様々な元素や化合物をさらに添加してもよい。
本実施形態に係る方向性電磁鋼板の製造方法は、一般的に方向性電磁鋼板の製造方法において行われる工程をさらに有するものでもよく、脱炭焼鈍の開始から仕上げ焼鈍における二次再結晶の発現までの間に、脱炭焼鈍鋼板のN含有量を増加させる窒化処理を施す窒化処理工程をさらに有するものが好ましい。一次再結晶領域と二次再結晶領域との境界部位の鋼板に与える温度勾配が低くとも磁束密度を安定して向上させることができるからである。窒化処理としては、一般的な処理であればよいが、例えば、アンモニア等の窒化能のあるガスを含有する雰囲気中で焼鈍する処理、MnN等の窒化能のある粉末を含む焼鈍分離剤を塗布した脱炭焼鈍鋼板を仕上げ焼鈍する処理等が挙げられる。
第一実施形態では、個別に有する中間層の形成だけを目的とした工程と絶縁被膜の形成だけを目的とした工程を分けて行ったが、第二実施形態では、中間層と絶縁被膜を同時に形成する点が、第一実施形態と異なる。すなわち、上述した中間層形成工程と絶縁被膜形成工程との代わりに、以下の中間層-絶縁被膜形成工程を行う点が第一実施形態と異なる。
そのため、以下、中間層-絶縁被膜形成工程についてのみ説明する。
前記仕上げ焼鈍鋼板表面にコーティング溶液を塗布して、例えば、650℃超~950℃以下の温度領域で、ガスの酸化度(PH2O/PH2):0.01~0.30の雰囲気で5~300秒焼鈍することにより、仕上げ焼鈍鋼板表面に酸化珪素を主成分とする中間層と絶縁被膜とを同時に形成する。
仕上げ焼鈍鋼板表面にコーティング溶液を塗布して熱処理すると、Fe系酸化物中のFeを還元することによって該鋼板表面に中間層および金属Fe相が形成されるのと同時に、コーティング溶液が焼き付けられることによって中間層の表面に絶縁被膜が形成される。
熱酸化による中間層の形成とコーティング溶液の焼き付けによる絶縁被膜の形成とを同時に進行させるために、ガスの酸化度(PH2O/PH2):0.05~0.25の条件とすることがより好ましく、ガスの酸化度(PH2O/PH2):0.10~0.20の条件とすることがさらに好ましい。
「板厚0.18mmの場合」
Si:3.45%、C:0.060%、酸可溶性Al:0.030%、N:0.008%、およびMn:0.10%、ならびにSおよびSe:合計で0.007%を含有し、残部がFeおよび不純物からなる化学組成のスラブを1150℃で60分均熱した後、加熱後のスラブに熱間圧延を施して、板厚が2.8mmの熱間圧延鋼板を得た。次に、熱間圧延鋼板を、900℃で120秒保持した後、急冷する熱延板焼鈍を施して、焼鈍鋼板を得た。次に、焼鈍鋼板を酸洗後、酸洗後の鋼板に1回または複数回の冷間圧延を施し、最終板厚が0.18mmの冷間圧延鋼板を得た。
脱炭焼鈍後の炭素量については、酸素気流中にて燃焼させることでCOガスとし、赤外線吸収法を用いて分析を行った。酸素量については、Heなどの不活性ガス中にて黒鉛坩堝中にて試料を燃焼させることでCOガスとし、これを赤外線吸収法にて分析を行った。
これらの仕上げ焼鈍後の鋼板の焼鈍分離材をブラシにて除粉し、一部の鋼板については、870℃、雰囲気ガスの酸化度(PH2O/PH2)が0.01の雰囲気で60秒焼鈍することによって、厚みが20nmの中間層を形成した。鋼板を冷却後、コーティング溶液を塗布した後、840℃、雰囲気ガスの酸化度(PH2O/PH2)が0.03の雰囲気で60秒焼鈍することによって焼付け後の付着量が4.5g/m2、厚みが2μmである絶縁被膜を形成した。
また、その他の鋼板については、コーティング溶液を塗布したのちに450℃にて乾燥、続けて840℃、雰囲気ガスの酸化度(PH2O/PH2)が0.10の雰囲気で60秒焼鈍することによって、厚みが20nmの中間層と、焼付け後の付着量が4.5g/m2、厚みが2μmである絶縁被膜を形成した。
最後に、圧延方向に交差する方向に延びる線状の溝を所定間隔となるようレーザーにて磁区細分化処理を施した。
その後、得られた方向性電磁鋼板に対し、磁気測定を行った。磁気測定については、JISC2550-1:2011に記載のエプスタインン法に基づき、1.7T、50Hzにおける鉄損W17/50及び磁化力800A/mにおける磁束密度B8の評価を行った。磁気特性の評価については、鉄損W17/50が0.60W/kg未満であり、かつ磁束密度が1.60T超である場合に良好と判断した。
試験結果を以下の表3に示す。
また、表3に示すように、本発明例では、脱炭焼鈍後の鋼板において、酸素量320ppm以下、炭素量25ppm以下の脱炭焼鈍鋼板を得ることができた。特に、均熱帯の前段から導入する雰囲気ガスの露点DP1を40~70℃かつ、均熱帯の後段から導入する雰囲気ガスの露点DP2をDP2≦DP1かつ60-DP1≦DP2≦100-DP1とした場合に、酸素量320ppm以下、炭素量25ppm以下の脱炭焼鈍鋼板を得ることができた。そして、これらの脱炭焼鈍鋼板を用いて中間層と絶縁層とを形成して得られた方向性電磁鋼板は、鉄損の低い優れた電磁鋼板であった。また、いずれの例も被膜密着性は十分であった。
「板厚0.23mmの場合」
Si:3.45%、C:0.060%、酸可溶性Al:0.030%、N:0.008%、およびMn:0.10%、ならびにSおよびSe:合計で0.007%を含有し、残部がFeおよび不純物からなる化学組成のスラブを1150℃で60分均熱した後、加熱後のスラブに熱間圧延を施して、板厚が2.8mmの熱間圧延鋼板を得た。
次に、熱間圧延鋼板を、900℃で120秒保持した後、急冷する熱延板焼鈍を施して、焼鈍鋼板を得た。次に、焼鈍鋼板を酸洗後、酸洗後の鋼板に1回または複数回の冷間圧延を施し、最終板厚が0.23mmの冷間圧延鋼板を得た。
これらの仕上げ焼鈍後の鋼板の焼鈍分離材をブラシにて除粉し、一部の鋼板については、870℃、雰囲気ガスの酸化度(PH2O/PH2)が0.010の雰囲気で60秒焼鈍することによって、厚みが20nmの中間層を形成した。鋼板を冷却後、コーティング溶液を塗布した後、840℃、雰囲気ガスの酸化度(PH2O/PH2)が0.01の雰囲気で60秒焼鈍することによって焼付け後の付着量が4.5g/m2、厚みが2μmである絶縁被膜を形成した。また、その他の鋼板については、870℃、雰囲気ガスの酸化度(PH2O/PH2)が0.10の雰囲気で60秒焼鈍することによって、厚みが20nmの中間層と、焼付け後の付着量が4.5g/m2、厚みが2μmである絶縁被膜を形成した。
最後に圧延方向に交差する方向に延びる線状の溝を所定間隔となるようレーザーにて磁区細分化処理を施した。
その後、得られた方向性電磁鋼板に対し、磁気測定を行った。磁気測定については、JISC2550-1:2011に記載のエプスタインン法に基づき、1.7T、50Hzにおける鉄損W17/50及び磁化力800A/mにおける磁束密度B8の評価を行った。
磁気特性の評価については、鉄損W17/50が0.70W/kg未満であり、かつ磁束密度が1.60T超の場合に良好と判断した。結果を表4に示す。
表4に示すように、本発明例では、脱炭焼鈍後の鋼板において、酸素量320ppm以下、炭素量25ppm以下の脱炭焼鈍鋼板を得ることができた。そして、これらの脱炭焼鈍鋼板を用いて中間層と絶縁層を形成して得られた方向性電磁鋼板は、鉄損の低い優れた電磁鋼板であった。
また、DP2≦DP1かつ60-DP1≦DP2≦100-DP1の関係を満足することで、酸素量が320ppm以下、かつ炭素量が25ppm以下であり、鉄損が低い優れた方向性電磁鋼板を0.18mmより厚い0.23mm厚の鋼板においても得られることがわかった。
「板厚0.35mmの場合」
Si:3.25%、C:0.050%、酸可溶性Al:0.030%、N:0.008%、およびMn:0.10%、ならびにSおよびSe:合計で0.006%を含有し、残部がFeおよび不純物からなる化学組成のスラブを1150℃で60分均熱した後、加熱後のスラブに熱間圧延を施して、板厚が2.8mmの熱間圧延鋼板を得た。
次に、熱間圧延鋼板を、900℃で120秒保持した後、急冷する熱延板焼鈍を施して、焼鈍鋼板を得た。次に、焼鈍鋼板を酸洗後、酸洗後の鋼板に1回または複数回の冷間圧延を施し、最終板厚が0.35mmの冷間圧延鋼板を得た。
当該加熱後の冷却時においては、ガスの酸化度(PH2O/PH2):0.0001~100000の雰囲気下で、1100℃から500℃まで冷却した。また上記条件で冷却する冷却時間は、5~30時間とした。
これらの試料の焼鈍分離材をブラシにて除粉し、一部の鋼板については、870℃、雰囲気ガスの酸化度(PH2O/PH2)が0.01の雰囲気で60秒焼鈍することによって、厚みが20nmの中間層を形成した。鋼板を冷却後、コーティング溶液を塗布した後、840℃、雰囲気ガスの酸化度(PH2O/PH2)が0.01の雰囲気で60秒焼鈍することによって焼付け後の付着量が4.5g/m2、厚みが2μmである絶縁被膜を形成した。また、その他の鋼板については、絶縁被膜を塗布したのち450℃にて乾燥、続けて雰囲気ガスの酸化度(PH2O/PH2)を0.10として840℃で60秒間の焼鈍を行って、厚みが20nmの中間層と焼付け後の付着量が4.5g/m2、厚みが2μmである絶縁被膜を同時に形成した。
最後に圧延方向に交差する方向に延びる線状の溝を所定間隔となるようレーザーにて磁区細分化処理を施した。
その後、得られた方向性電磁鋼板に対し、磁気測定を行った。磁気特性の評価については、鉄損W17/50が0.77W/kg未満であり、かつ磁束密度が1.60T超である場合に良好と判断した。
結果を以下の表5に示す。
厚手材は脱炭がネックとなり、最終製品の磁気時効悪化の原因となるため、前段露点DP1が30℃、80℃の場合には、いずれも良好な磁気特性が得られなかった。
また、DP1=40~70℃、DP2≦DP1かつ60-DP1≦DP2≦100-DP1の関係を満足することで、酸素量が320ppm以下、かつ炭素量が25ppm以下であり、鉄損が低い優れた方向性電磁鋼板を0.23mmより厚い、厚さ0.35mmの厚手の鋼板においても得られることがわかった。
2…均熱炉
Claims (5)
- フォルステライト被膜が実質的に存在しない母鋼板表面に酸化珪素を主成分とする中間層を有し、前記中間層の表面に絶縁被膜を有する方向性電磁鋼板を製造する方法であって、
Siを含む冷間圧延鋼板に脱炭焼鈍を施して、酸素量が320ppm以下、かつ炭素量が25ppm以下である脱炭焼鈍鋼板を得る脱炭焼鈍工程と、
前記脱炭焼鈍鋼板の表面に焼鈍分離材を塗布した状態で前記脱炭焼鈍鋼板を加熱して鋼板を二次再結晶させる仕上げ焼鈍工程と、
前記仕上げ焼鈍工程後の前記鋼板上の焼鈍分離材を除去することにより仕上げ焼鈍鋼板を得る除去工程と、
前記仕上げ焼鈍鋼板に熱酸化焼鈍を施して前記中間層を形成する中間層形成工程と、
前記中間層を形成した仕上げ焼鈍鋼板に前記絶縁被膜を形成する絶縁被膜形成工程と、
を有することを特徴とする方向性電磁鋼板の製造方法。 - フォルステライト被膜が実質的に存在しない母鋼板表面に酸化珪素を主成分とする中間層を有し、前記中間層の表面に絶縁被膜を有する方向性電磁鋼板を製造する方法であって、
Siを含む冷間圧延鋼板に脱炭焼鈍を施して、酸素量が320ppm以下、かつ炭素量が25ppm以下である脱炭焼鈍鋼板を得る脱炭焼鈍工程と、
前記脱炭焼鈍鋼板の表面に焼鈍分離材を塗布した状態で前記脱炭焼鈍鋼板を加熱して鋼板を二次再結晶させる仕上げ焼鈍工程と、
前記仕上げ焼鈍工程後の前記鋼板上の焼鈍分離材を除去することにより仕上げ焼鈍鋼板を得る除去工程と、
前記仕上げ焼鈍鋼板に前記中間層と前記絶縁被膜とを一工程で形成する中間層-絶縁被膜形成工程と、
を有することを特徴とする方向性電磁鋼板の製造方法。 - 前記脱炭焼鈍工程において、前記冷間圧延鋼板を脱炭焼鈍するための均熱帯に対し、雰囲気ガスを前記均熱帯の前段および後段の2箇所から導入する
ことを特徴とする請求項1または請求項2に記載の方向性電磁鋼板の製造方法。 - 前記脱炭焼鈍工程において前記均熱帯の前記前段から導入する前記雰囲気ガスの露点DP1を40~70℃とし、前記均熱帯の後段から導入する前記雰囲気ガスの露点DP2をDP2≦DP1かつ60-DP1≦DP2≦100-DP1とする
ことを特徴とする請求項3に記載の方向性電磁鋼板の製造方法。 - 前記冷間圧延鋼板は、化学成分として、質量%で、
Si:0.80~7.00%、
C:0.085%以下、
酸可溶性Al:0.010~0.065%、
N:0.012%以下、
Mn:1.00%以下、
SおよびSeの合計:0.003~0.015%、
を含有し、残部がFe及び不純物からなる
ことを特徴とする請求項1~請求項4のいずれか一項に記載の方向性電磁鋼板の製造方法。
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- 2020-01-16 EP EP20741464.0A patent/EP3913085A4/en active Pending
- 2020-01-16 JP JP2020566452A patent/JP7260799B2/ja active Active
- 2020-01-16 KR KR1020217024635A patent/KR102583630B1/ko active IP Right Grant
- 2020-01-16 BR BR112021013687-8A patent/BR112021013687A2/pt active IP Right Grant
- 2020-01-16 US US17/421,766 patent/US20220090226A1/en active Pending
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US20220090226A1 (en) | 2022-03-24 |
BR112021013687A2 (pt) | 2021-09-21 |
CN113286908A (zh) | 2021-08-20 |
KR20210111812A (ko) | 2021-09-13 |
EP3913085A1 (en) | 2021-11-24 |
CN113286908B (zh) | 2023-03-14 |
JPWO2020149332A1 (ja) | 2021-12-02 |
EP3913085A4 (en) | 2022-09-21 |
JP7260799B2 (ja) | 2023-04-19 |
KR102583630B1 (ko) | 2023-10-04 |
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