JP6003321B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

The present invention relates to a manufacturing method and a grain-oriented electromagnetic steel sheet of a grain-oriented electrical steel sheet, specifically, in how to produce a grain-oriented electrical steel sheet of a low iron loss by irradiation with an electron beam subjected to magnetic domain refining treatment It is related.

  The grain-oriented electrical steel sheet is mainly used as an iron core material for transformers, electrical devices, etc., and therefore has excellent magnetic properties, and particularly excellent iron loss properties (low iron loss) from the viewpoint of energy saving. There is a strong demand for that. In order to reduce the iron loss of grain-oriented electrical steel sheets, the secondary recrystallized grains are highly aligned in the {110} <001> orientation (so-called “Goth orientation”), and the amount of impurities in the product steel sheet is reduced. It is important to reduce as much as possible.

  However, the crystal orientation control technology and the impurity reduction technology have reached a considerably high level so far, and further improvements are limited in view of the manufacturing cost. Therefore, a magnetic domain refinement technology that reduces iron loss by introducing non-uniformity (strain) into the surface of a steel sheet by some physical method and subdividing the width of the magnetic domain has been developed and put into practical use. Yes.

  For example, in Patent Document 1, a final product plate of a grain-oriented electrical steel sheet is irradiated with a laser beam, a linear high dislocation density region (thermal strain region) is introduced into the steel sheet surface layer, and the magnetic domain width is narrowed. Techniques for reducing iron loss have been proposed. Thereafter, the magnetic domain fragmentation technique using laser irradiation has been further improved to obtain grain-oriented electrical steel sheets with better iron loss characteristics (see Patent Documents 2 to 4).

  In addition, as a method for introducing a thermal strain region by means other than laser irradiation, for example, in Patent Document 5, a method of introducing a linear high dislocation density region by radiating a plasma flame on a steel sheet surface, Patent Document 6 proposes a method of introducing a linear high dislocation density region by irradiating a steel plate surface with an electron beam.

  However, irradiation with a beam having a high energy such as an electron beam or a laser beam melts or destroys the insulating coating formed on the surface of the steel sheet. Iron) is exposed. As a result, magnetic domains are subdivided by irradiation with a high-energy beam, and iron loss is reduced. However, the insulation and rust prevention (corrosion resistance) of the product steel plate deteriorate due to melting and destruction of the insulating coating. Will occur.

  In order to solve such a problem, a technique for repairing a damaged portion of the insulating coating has been proposed. For example, Patent Document 7 discloses a technique of recoating an insulating film on a film destroyed by magnetic domain fragmentation, and Patent Document 8 discloses a steel sheet in which a solid is added to the film to be recoated. A technique for improving the slipperiness of the image is disclosed.

Japanese Patent Publication No.57-002252 JP 2006-117964 A JP-A-10-204533 Japanese Patent Laid-Open No. 11-279645 JP 62-096617 A Japanese Patent Laid-Open No. 01-281708 JP-A-56-105421 Japanese Patent Laid-Open No. 04-165022

  However, the method of recoating the insulating film as in the techniques of Patent Document 7 and Patent Document 8 described above should be avoided as much as possible in order to increase the manufacturing cost. Therefore, although it is not optimal for improving the magnetic characteristics, the actual situation is that irradiation with a high energy beam is performed under the condition that the coating film does not break. However, when emphasizing magnetic characteristics, there are cases where it is necessary to irradiate a high energy beam under conditions that cause film destruction.

The present invention has been made in view of the above-mentioned problems of the prior art, and its purpose is to suppress film destruction even when irradiated with a high-energy beam under conditions where the effect of improving magnetic properties can be fully enjoyed. it can be, moreover, in a Turkey proposes a manufacturing method of the grain-oriented electrical steel sheet not having to re-applying an insulating coating.

  In order to solve the above-mentioned problems, the inventors made extensive studies by paying attention to a method for introducing thermal strain by electron beam irradiation in a high energy beam. As a result, after finishing annealing, the grain-oriented electrical steel sheet on which the tensile insulating film is formed is heated to a predetermined temperature, and then the surface is irradiated with an electron beam to introduce a thermal strain region. The present inventors have found that it is extremely effective for suppression and have completed the present invention.

That is, the present invention is directed to the direction crossing the rolling direction with respect to the surface of the grain-oriented electrical steel sheet formed by forming a tension insulating film having a film tension at room temperature of 5 MPa or more on the steel sheet surface after secondary recrystallization annealing. In the method for manufacturing a grain-oriented electrical steel sheet that irradiates an electron beam, introduces a point-like or linear thermal strain region, and performs magnetic domain subdivision treatment, the electron beam irradiation is performed at a temperature of 50 to 500 ° C. on the steel sheet surface. It is the manufacturing method of the grain-oriented electrical steel sheet characterized by performing by heating.
It is.

  The grain-oriented electrical steel sheet manufacturing method of the present invention is characterized in that the electron beam irradiation is performed on a steel sheet surface to which a compressive stress is applied.

  Moreover, the manufacturing method of the grain-oriented electrical steel sheet according to the present invention is characterized in that an insulating coating is not re-applied on the steel sheet surface irradiated with the electron beam.

  According to the present invention, since the destruction of the insulating coating can be suppressed even by irradiation with a high energy beam that can sufficiently enjoy the iron loss reduction effect due to the magnetic domain fragmentation of the grain-oriented electrical steel sheet, the insulating coating can be reused. It becomes possible to provide a grain-oriented electrical steel sheet with low iron loss that does not need to be applied.

It is a figure explaining the method of twisting and forming a curved part in a steel plate.

  First, in the present invention, a tension insulating coating is formed on the surface of a grain-oriented electrical steel sheet obtained by performing finish annealing that combines secondary recrystallization annealing and purification annealing, and then an electron beam is applied to the steel sheet surface. This is a method for producing a grain-oriented electrical steel sheet that is irradiated to introduce a point-like or linear heat-strain region to perform a magnetic domain refinement process.

  Here, the first important thing in the present invention is that the electron beam irradiation needs to be performed after finish annealing and deposition of a tensile insulating coating. This is because both the finish annealing process that causes secondary recrystallization to the raw steel sheet of grain-oriented electrical steel sheet and preferentially grows goth-oriented grains, and the film baking process that expresses the effect of imparting tension to the insulating film, both at high temperatures. This is because it is a heat treatment step, and even if thermal strain is applied by electron beam irradiation, the thermal strain is reduced or eliminated by the heat treatment, and the effect of subdividing the magnetic domain is lost.

  In addition, the second important thing in the present invention is that the tensile insulating film has a tensile stress of 5 MPa or more in total of a glassy film mainly composed of underlying forsterite and an insulating film formed after finish annealing. Is to give. This is because if it is less than 5 MPa, the effect of reducing iron loss cannot be obtained sufficiently.

The third important feature of the present invention is to prevent destruction of the insulating coating by performing the irradiation of the electron beam in a state where the steel plate is heated to a temperature of 50 to 500 ° C. The reason why the destruction of the coating is suppressed by heating the steel sheet and irradiating the electron beam has not been clarified yet at present, but the inventors consider as follows.
The portion irradiated with the electron beam is rapidly heated. At this time, an excessive tensile stress is applied to the coating due to a difference in thermal expansion between the ground iron and the insulating coating, and the coating is broken. Therefore, by heating the steel plate, the ductility of the coating is improved, and stress due to the difference in thermal expansion coefficient between the base iron and the coating is also relieved, so that coating failure is suppressed. As a result, when the present invention is applied, the insulation and corrosion resistance of the insulating film are preserved even after the magnetic domain fragmentation treatment is performed by irradiating the electron beam, so that it is not necessary to re-apply the insulating film. .

Next, the component composition of the grain-oriented electrical steel sheet according to the present invention will be described.
The grain-oriented electrical steel sheet to which the magnetic domain subdivision treatment of the present invention is applied may have any conventionally known component composition, and for example, preferably has the following component composition.
Si: 2.0 to 8.0 mass%
Si is an element effective for increasing the electrical resistance of steel and reducing iron loss. However, if the content is less than 2.0 mass%, a sufficient effect of reducing iron loss cannot be obtained. On the other hand, if it exceeds 8.0 mass%, not only the workability is remarkably lowered but also the magnetic flux density is lowered. Therefore, Si is preferably in the range of 2.0 to 8.0 mass%. More preferably, it is the range of 2.5-6.0 mass%.

C: 0.0050 mass% or less C contained in the product plate is an element that causes magnetic aging and deteriorates magnetic properties, and is preferably 0.0050 mass% or less.
In addition, since C contained in the slab used as the material of the grain-oriented electrical steel sheet of the present invention can be recrystallized even if it is 0.0050 mass% or less, there is no need to provide a lower limit, but the hot rolled sheet structure is improved. Therefore, it may be contained in excess of 0.0050 mass%. On the other hand, if the content exceeds 0.15 mass%, it becomes difficult to reduce C to 0.0050 mass% or less where magnetic aging does not occur in the production process. Therefore, the upper limit is preferably 0.15 mass% or less. More preferably, it is the range of 0.0050-0.10 mass%.

Mn: 0.005 to 1.0 mass%
Mn is an element necessary for improving the hot workability of steel. However, if it is less than 0.005 mass%, the effect of addition is poor, whereas if it exceeds 1.0 mass%, the magnetic flux density is lowered. Become. Therefore, Mn is preferably in the range of 0.005 to 1.0 mass%. More preferably, it is the range of 0.01-0.3 mass%.

In the grain-oriented electrical steel sheet of the present invention, components other than Si, C, and Mn are divided into cases where an inhibitor is used and cases where an inhibitor is not used in order to cause secondary recrystallization.
First, when an inhibitor is used to cause secondary recrystallization, for example, when an AlN-based inhibitor is used, Al and N are changed to Al: 0.01 to 0.065 mass%, N: 0.005. It is preferable to make it contain in 0.012 mass%. When using an MnS / MnSe-based inhibitor, the above-mentioned amounts of Mn and Se and / or S are in the range of S: 0.005 to 0.03 mass% and Se: 0.005 to 0.03 mass%, respectively. It is preferable to contain. AlN and MnS / MnSe inhibitors may be used in combination.

  On the other hand, when an inhibitor is not used to cause secondary recrystallization, the content of Al, N, S and Se, which are the above-described inhibitor forming components, is reduced as much as possible, Al: 0.01 mass% or less, N : 0.0050 mass% or less, S: 0.0050 mass% or less, and Se: 0.0050 mass% or less are preferable.

  The balance other than the above components in the grain-oriented electrical steel sheet of the present invention is Fe and inevitable impurities. However, for the purpose of improving magnetic properties, Ni: 0.03-1.50 mass%, Sn: 0.01-1.50 mass%, Sb: 0.005-1.50 mass%, Cu: 0.03-3 0.0 mass%, P: 0.03 to 0.50 mass%, Mo: 0.005 to 0.10 mass% and Cr: 0.03 to 1.50 mass% May be.

  Ni is an element useful for improving the magnetic properties by improving the structure of the hot-rolled sheet. However, if it is less than 0.03 mass%, the effect of improving the magnetic properties is small, while 1.5 mass% is reduced. If it exceeds, secondary recrystallization will become unstable and the magnetic properties will deteriorate, so it is preferable to be in the range of 0.03 to 1.5 mass%.

  Sn, Sb, Cu, P, Mo, and Cr are all effective elements for improving the magnetic properties. However, if the addition amount is less than the lower limit, the effect of improving the magnetic properties is small. Addition exceeding the above upper limit inhibits the development of secondary recrystallized grains. Therefore, each of the above elements is preferably contained in the above range.

Next, the manufacturing method of the grain-oriented electrical steel sheet of this invention is demonstrated concretely.
The method for producing a grain-oriented electrical steel sheet according to the present invention involves melting steel adjusted to the above-described component composition to obtain a steel material (slab), then hot rolling to obtain a hot rolled sheet, and hot rolling as necessary. It is subjected to sheet annealing, cold rolled to a cold-rolled sheet with the final thickness, primary recrystallization annealing that also serves as primary recrystallization annealing or decarburization, an annealing separator is applied to the steel sheet surface, and then secondary recrystallization is performed. It consists of a series of steps to perform magnetic domain refinement treatment on grain-oriented electrical steel sheets manufactured by a conventionally known method of applying a tension insulating coating on the steel sheet surface after finishing annealing that combines crystal annealing and purification annealing. .

  In the above production method, the method for melting steel may be carried out according to a conventional method, and there is no particular limitation. Moreover, the method of manufacturing a steel raw material (slab) may use any method of a continuous casting method and an ingot-making-slabbing method, and may use a thin slab casting method.

  Next, the steel material is hot-rolled by a conventional method to obtain a hot-rolled sheet. The slab heating temperature before hot rolling is preferably 1300 ° C. or higher in order to dissolve these components when they contain inhibitor forming components. On the other hand, if it does not contain an inhibitor-forming component, it may be lower than the above temperature as long as it can be hot-rolled, and it is immediately subjected to hot rolling after continuous casting without reheating in a heating furnace. May be. Furthermore, when the steel material is a thin slab, it may be hot-rolled or omitted.

  The hot-rolled sheet after hot rolling is subjected to hot-rolled sheet annealing as necessary. The temperature of this hot-rolled sheet annealing is preferably in the range of 800 to 1200 ° C. If the annealing temperature is less than 800 ° C., the band structure formed by hot rolling remains, it is difficult to adjust the primary recrystallized structure, the growth of the secondary recrystallized grains is hindered, and the goth of the product plate The organization cannot be highly developed. On the other hand, if the annealing temperature exceeds 1200 ° C., the crystal grains are excessively coarsened, and on the contrary, it is difficult to adjust the primary recrystallized structure.

  Next, the hot-rolled sheet is made into a cold-rolled sheet having a final thickness by one or more cold rollings with intermediate annealing, and then subjected to primary recrystallization annealing also serving as primary recrystallization annealing or decarburization annealing. After the application, for example, an annealing separator mainly composed of MgO is applied to the steel sheet surface, dried, and then subjected to secondary recrystallization and finish annealing for the purpose of forming and purifying the forsterite film. Note that the steel sheet may be subjected to nitriding treatment for the purpose of strengthening the inhibitor during the primary recrystallization annealing or after the primary recrystallization annealing until the start of the secondary recrystallization.

  The steel sheet that has been subjected to finish annealing is then coated with an insulating coating treatment liquid on the surface of the steel sheet and baked by flattening annealing that also serves as shape correction to form a tension insulating coating. Note that the tension film may be baked before or after the flattening annealing.

  Here, the tension insulating coating refers to an insulating coating capable of applying a tensile tension of 5 MPa or more to the steel sheet together with the underlying forsterite coating. As the kind of the coating, a conventionally known silica and phosphate as a main component, a coating using borate and alumina sol, or a composite hydroxide may be used, but aluminum phosphate or phosphoric acid may be used. It is preferable to use a vitreous tension insulating coating mainly composed of a phosphate such as magnesium and silica.

  The grain-oriented electrical steel sheet on which the tension insulating coating is formed is then subjected to a magnetic domain refinement process by irradiating the steel sheet surface with an electron beam to introduce a dotted or linear thermal strain region. Here, what is important in the present invention is that the electron beam irradiation needs to be performed in a state where the steel sheet is heated to a temperature of 50 to 500 ° C. The method for heating the steel plate is not particularly limited, and for example, methods such as induction heating, infrared heating, heating in an atmospheric furnace or roll heating (heating by heat conduction from a heated roll) can be used.

  The introduction of the thermal strain region by the electron beam irradiation is desirably performed in a direction intersecting with the rolling direction, preferably in a direction orthogonal to the rolling direction. The thermal strain region may be linear or dot-shaped, and the strain introduction depth is preferably about 5 to 30 μm. Moreover, it is preferable to set the space | interval (scanning space | interval) of the thermal-strain area | region to introduce | transduce the space | interval of 2-20 mm in a rolling direction from a viewpoint of expressing the iron loss reduction effect by magnetic domain subdivision effectively.

Further, in addition to heating the steel plate described above, the electron beam irradiation can be performed in a state in which a compressive stress is applied to the steel plate surface, thereby obtaining a further effect. The reason why such an effect is obtained is not yet clear at present, but the inventors consider as follows.
When an electron beam is irradiated onto the steel plate surface on which the tensile insulating coating is formed, the insulating coating on the irradiated portion is melted or subjected to rapid heating or rapid cooling. Here, when the insulating coating is melted, the coating is broken by the tensile stress applied by the insulating coating, and the ground iron is easily exposed. In addition, when the insulating coating is subjected to rapid heating or rapid cooling, an excessive tensile stress remains in the insulating coating due to the difference in thermal expansion between the ground iron and the coating, and the coating is liable to be broken. Therefore, it is considered that by applying a compressive stress to the insulating coating in advance, the tensile stress is relaxed and the destruction of the coating is suppressed. Accordingly, the effect of suppressing the coating film destruction by applying the compressive stress is larger as the film tension is larger.

  The method for applying compressive stress to the plate surface is not particularly limited. For example, as shown in FIG. 1, the steel plate is bent by being twisted and deformed into a shape in which the steel plate is wound around a cylinder or the like. A method of generating a compressive stress on the inner surface of the curved portion is preferable. This method has the merit that the steel plate can be easily bent only by bending the plate passage (pass line) of the steel plate, and the length required for bending the steel plate can be shortened.

  Here, when applying a compressive stress by curving a steel plate, the curvature radius of the curved portion is preferably 10,000 times or less of the plate thickness. When the radius of curvature exceeds 10,000 times the plate thickness, the compressive stress generated on the inner surface of the curved portion becomes small, and it is difficult to obtain the damage reducing effect of the present invention. On the other hand, if the radius of curvature is made too small and the compressive stress generated on the inner surface of the curved portion exceeds 90% of the yield stress of the steel plate, the steel plate is likely to be plastically deformed, resulting in deterioration of magnetic properties. Therefore, it is preferable to set the lower limit value so that the radius of curvature when bending the steel sheet is 10,000 times or less of the plate thickness and the compressive stress applied to the steel sheet is 90% or less of the yield stress.

Here, the compressive stress given to the curved steel sheet surface can be obtained by the following equation (1).
Σ = E · ε = E · (t / 2R) (1)
Here, E: Young's modulus E (= 1.4 × 10 ⁵ MPa) in the <100> direction (rolling direction) of the steel plate
ε: amount of strain on the steel sheet surface (ε = 0 at the center of the plate thickness)
R: radius of curvature (mm)
t: Plate thickness (mm)

  Further, when the steel plate is bent, there is no particular limitation, but if the angle formed by the rolling direction (traveling direction) of the steel plate and the generatrix of the curved surface is less than 5 °, the length necessary for bending the steel plate is long. Therefore, it is preferable to set the angle to 5 ° or more in order to lengthen the equipment.

By the way, it is known that the effect of the magnetic domain refinement treatment increases as the degree of integration in the Goth orientation of the secondary recrystallization of the grain-oriented electrical steel sheet increases. As a guide for the degree of orientation integration in a grain-oriented electrical steel sheet, a magnetic flux density B ₈ (magnetic flux density when magnetized at 800 A / m) is generally used, but as a grain-oriented electrical steel sheet to which the present invention is applied, B ₈ Is preferably 1.88T or more, and more preferably 1.92T or more. Moreover, it is known that the iron loss reduction effect by magnetic domain fragmentation is so large that the surface roughness of the base iron directly under a film is small, and it is preferable that arithmetic mean roughness Ra shall be 0.5 micrometer or less.

A cold-rolled sheet cold-rolled to a final sheet thickness of 0.23 mm containing 3.3 mass% of Si is subjected to annealing that combines decarburization and primary recrystallization annealing, and then an annealing separator mainly composed of MgO. After coating and drying, winding it on a coil, applying final finish annealing including secondary recrystallization process and purification process, and then applying an insulating coating solution consisting of 50mass% colloidal silica and magnesium phosphate, also for shape correction The steel plate was baked by flattening annealing at 800 ° C., and a tensile tension of about 14 MPa was applied to the steel plate surface in total for the forsterite coating and the insulating coating. The yield stress of this grain-oriented electrical steel sheet was 348 MPa. Next, two types of test pieces of 500 mmL × 300 mmC and 500 mmL × 150 mmC whose longitudinal direction is the rolling direction are cut out from the steel plate after the annealing, and the former test piece has an angle formed by the rolling direction and the generatrix of the curved portion of 10 mm. The latter test piece is bent at a curvature radius of less than 100 mm with an angle formed by the rolling direction and the generatrix of the bending portion being set at 10 to 30 °, and compressive stress or After the tensile stress was applied and the temperature was raised to various temperatures with infrared rays, an electron beam was irradiated under the conditions shown in Table 1 to perform magnetic domain fragmentation. Some test pieces were not curved or heated.
Here, the electron beam irradiation is performed under the conditions of an acceleration voltage of 150 kV, a beam diameter of 0.1 mmφ, and a scanning speed of 10 m / sec. The output of the electron beam at this time is an amount of heat per 1 cm ² of the steel plate surface. Converted. The scanning direction of the electron beam was perpendicular to the rolling direction (90 °), and the irradiation interval (scanning interval) with respect to the rolling direction was 5 mm.

The test piece after electron beam irradiation obtained as described above was subjected to the following evaluation test.
<Measurement of iron loss W _17/50 >
300 mmL × 100 mmC magnetic measurement test specimens were collected from the length direction and width direction central parts of each test piece subjected to the magnetic domain subdivision treatment, and the iron under the excitation conditions of 1.7 T and 50 Hz was obtained with the single plate magnetic measurement apparatus SST. The loss W _17/50 was measured. Incidentally, when the magnetic properties of the steel sheet before electron beam irradiation were measured, the iron loss W _17/50 was 0.89 W / kg, and the magnetic flux density B _{8 at a} magnetizing force of 800 A / m was 1.93 T.
<Measurement of interlayer resistance>
A sample of 400 mmL × 150 mmC was taken from the center of the length and width of each test piece subjected to the magnetic domain fragmentation treatment, and the interlayer resistance was measured according to the A method described in JIS C2550.
<Rust resistance>
A sample of 100 mmL × 50 mmC is taken from the center of the length and width of each test piece subjected to magnetic domain subdivision treatment, and kept in the atmosphere at a temperature of 50 ° C. and a dew point of 50 ° C. for 50 hours, and then on the sample surface. The rate of occurrence of generated rust was measured visually.

  The results of the above measurements are also shown in Table 1. From this result, the steel plate that has been subjected to the magnetic domain refinement treatment by heating under the conditions suitable for the present invention is more insulative and rust-resistant than the steel plate that has been subjected to the magnetic domain refinement treatment in a flat state as in the past. It turns out that it is excellent in. Furthermore, it can be seen that when the steel plate is bent and irradiated with an electron beam on the inner side, that is, in a state where compressive stress is applied to the steel plate, the above effect is further enhanced.

  The technology of the present invention can be applied not only to grain-oriented electrical steel sheets, but also to cold-rolled steel sheets, surface-treated steel sheets, stainless steel sheets, copper plates, aluminum plates and the like with electron beams and laser beams.

Claims (3)

Irradiate an electron beam in a direction intersecting with the rolling direction on the surface of the grain-oriented electrical steel sheet formed with a tension insulating film having a film tension of 5 MPa or more at room temperature on the steel sheet surface after secondary recrystallization annealing, In the method of manufacturing a grain-oriented electrical steel sheet in which a dotted or linear thermal strain region is introduced and subjected to magnetic domain subdivision processing,
A method for producing a grain-oriented electrical steel sheet, wherein the irradiation with the electron beam is performed by heating the steel sheet surface to a temperature of 50 to 500 ° C. The method of manufacturing a grain-oriented electrical steel sheet according to claim 1, wherein the electron beam irradiation is performed on a steel sheet surface to which a compressive stress is applied. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, wherein an insulating coating is not reapplied to the surface of the steel sheet irradiated with the electron beam.

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