RU2496905C1 - Electrical steel plate with oriented grains - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: plate is made from steel containing the following components, wt %: C 0.005 ore less, Si 10 to 8.0, Mn 0.005 to 1.0; one or more elements chosen from Nb, Ta, V and Zr; with that, their total content is 10 to 50 ppm, and Fe and inevitable impurities are the rest. At least 10% of Nb, Ta, V and Zr content is in the form of particles of the separated phase, the particles of which have average diameter, - diameter of equivalent circle - 0.02 to 3 mcm, and grains of a steel plate, which are recrystallised for the second time, have average size of 5 mm or higher.

EFFECT: reduction of deterioration of magnetic characteristics in case a plate is subject to shear as a result of the cutting process, even without performance of an annealing operation for release of stresses.

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Description

FIELD OF THE INVENTION

The present invention relates to oriented grain-oriented electrical steel sheets, which are suitably used, for example, as an iron core material for transformers and, in particular, are intended to reduce the deterioration of magnetic characteristics when the sheet is sheared.

State of the art

Sheets of electrical steel are a material that is widely used for the iron cores of various transformers, motors and the like. Among them, in particular, there are known sheets of electrical steel, which are called sheets of electrical steel with oriented grains, and have grains of crystallites with a high degree of orientation in the {110} <001> planes, which are called Goss orientation.

In the production of such oriented grain-oriented electrical steel sheets, a technique is usually used to perform secondary crystallization of grains of crystallites with Goss orientation during the final annealing, the precipitated phase being called an inhibitor.

For example, the publication of an examination of patent application JP 40-15644 discloses a method for including Al and S, which serve as inhibitor constituent elements and are present in predetermined amounts, that is, a method for using AlN and MnS as inhibitors. The publication of the appraised patent application JP 51-13469 describes a method for including at least one element of S and Se present in predetermined quantities, that is, a method for using MnS or MnSe as an inhibitor. These methods are used in industry. In addition, as proposed in the unexamined patent application JP 2000-129356, a technique for the development of grains with Goss orientation under the influence of secondary crystallization has recently been presented even in steel sheets containing no inhibitor-forming elements.

In the methodology described in JP 2000-129356, by minimizing impurities such as inhibitor-forming elements, the dependence of the grain boundary misorientation on the grain boundary energy upon the occurrence of primary recrystallization is established so that grains with the Goss orientation develop by secondary crystallization without inhibitors .

Due to the fact that in this method the elements forming the inhibitor are not required, the need for a purification step is eliminated in order to remove the elements forming the inhibitor. In addition, there is no need for a purification annealing at high temperature; there is no need for a stage of fine dispersion of the elements forming the inhibitor in steel, and therefore there is also no need for reheating the sheet blank at high temperature, which was necessary for fine dispersion. Thus, this method is very attractive given the number of stages, costs, equipment maintenance, etc.

Among the various characteristics of grain oriented electrical steel sheets, the most important is the characteristic of core losses, which are directly related to the energy loss in the device. To improve the characteristics of core losses, it is believed that it is necessary to reduce the indicator designated as W _17/50 (energy loss upon excitation of magnetic induction equal to 1.7 T and an excitation frequency of 50 Hz).

In transformers that use grain oriented electrical steel sheets, core loss performance is also considered an important feature. Even after the production of transformers, during their operation it is necessary to periodically measure the characteristics of losses in the core of transformers in order to control the rate of loss in the core.

SUMMARY OF THE INVENTION

The problem solved by the invention

Typically, electrical steel sheet products are in the form of sheets that are cut so as to obtain a predetermined size for the manufacture of transformers. Typically, the specified cutting is carried out by shear (also called cutting processing), in which two cutting inserts move vertically towards each other (finally cutting inserts slide along their surfaces) like scissors.

In steel sheets cut in such a way, on the obtained surfaces, places of scuffing are formed under the action of shear, and a large number of deformations appear in the steel sheets. Accordingly, there is a tendency to deterioration of magnetic characteristics in the cut sheets of electrical steel due to introduced deformations, which is a problem.

As a way to reduce the deterioration in magnetic performance due to cutting, annealing can be performed to relieve stresses at 700 ° C-900 ° C for several hours after cutting. However, annealing for stress relieving is carried out only for small transformers having a size (length) of 500 mm or less, and cannot be carried out, for example, for iron cores of large transformers having a size of several meters.

Accordingly, a method is demanded by which the deterioration of magnetic characteristics due to cutting sheets of electrical steel for large transformers having a size of several meters can be reduced.

Solution

The inventors performed a thorough study to achieve this goal and found that a small addition of an element such as niobium (Nb) can significantly reduce the above increase in core loss due to cutting.

In the future, experiments will be described by which the present invention has been carried out.

Experiment 1

Oriented grain electrical steel sheets containing in wt.%: From 3.30% to 3.34% Si, from 0.06% to 0.07% Mn, from 0.025% to 0.028% Sb, and from 0.03 % to 0.04% Cr; the addition of various amounts of Nb at a concentration of 4 ppm (at the level of inevitable impurities), 22 ppm, 48 ppm, 65 ppm, 90 ppm and 210 ppm; the rest of Fe and unavoidable impurities are obtained using a standard production method, including recrystallization annealing (primary recrystallization annealing) and final annealing (purification annealing). During the final annealing (cleaning annealing), the steel sheets are heated to a maximum temperature of 1200 ° C for the sheet to dissolve the precipitated element (Nb) forming precipitates, and then the sheet is cooled at an average cooling rate of 20 ° C / h from 900 ° C to 500 ° C and cooled to room temperature.

Thus obtained sheets of electrical steel with oriented grains are cut in the form of so-called Epstein samples having a size of 30 mm × 280 mm. At the same time, two types of samples are prepared using the process of slow cutting of steel sheets using wire shears, in which deformations do not appear in steel and using the usual process of cutting electrical steel sheets with oriented grains, in which steel sheets are cut using mechanical shears having a top a cutting insert and a lower cutting insert as described above. For the samples obtained, core losses were determined according to the method described in Japanese standard JIS C 2550.

Figure 1 shows the results of a study of the dependence of ΔW (ordinate: W / kg) on the Nb content in steel (abscissa: ppm by weight), and ΔW (hereinafter, in the present invention, the same determination is made) determined by subtracting the amount of core loss from the sample obtained by cutting with wire shears from the amount of core loss from the sample obtained by cutting with mechanical shears.

In the case of cutting with mechanical scissors, as described above, the indicators of residual deformation in steel sheets and core losses from steel sheets are deteriorated. On the contrary, it takes longer to cut with wire scissors, but steel sheets are cut with virtually no permanent deformation in the sheets.

Accordingly, it is believed that the ΔW value in the figure essentially represents the energy loss in the core, equivalent to the deterioration caused by permanent deformation. Thus, the figure shows that the presence of Nb reduces the deterioration of energy loss in the core due to cutting.

The reasons for reducing the deterioration in core loss of Nb-containing samples, as described above, are not entirely clear. The authors offer the following explanation.

An analysis of the microstructure of the Nb-containing material used in the experiment showed that Nb forms particles of the precipitated phase and disperses in steel. Small particles of the precipitated phase have a diameter of approximately 0.02 μm, and large particles of the precipitated phase have a diameter of approximately 3 μm. Since such particles of the precipitated phase are practically absent in ordinary sheets of oriented steel with oriented grains, the inventors believe that the presence of particles of the precipitated phase is likely to contribute to reducing the deterioration of core losses due to cutting.

The deterioration of core loss due to cutting is caused by the accumulation of deformations in the areas that were cut. Here, the accumulation of deformations is a phenomenon in which iron atoms regularly located in grains of iron crystallites are subjected to external stress or the like, while the arrangement of iron atoms is deformed or becomes irregular.

Consider the case where the above particles of the precipitated phase are present along with such regularly arranged iron atoms. When stress due to cutting or the like acts on the region containing particles of the precipitated phase to cut off the plate, the stress is concentrated around the periphery of the precipitated phase, and cracks are likely to form before deformation of the arrangement of the iron atoms. Given this mechanism of weakening the accumulation of deformations, we can explain the phenomenon described above.

Although the Nb contained in the steel sheet is in two states, forming a solid solution and a precipitated phase, as described above, it is apparently important that Nb is in the precipitated phase. For example, a sample containing 22 ppm Nb is measured in units of the percentage of Nb release (the percentage of Nb in the precipitated phase relative to the total Nb content).

In order to determine the percentage of Nb release (i.e., Nb in the particles of the precipitated niobium phase), it is first necessary to determine the total Nb content (mass% in the steel sheet). Total Nb can be determined by inductively coupled plasma optical emission spectrometry (ICP optical emission spectrometry), which is described in JIS G 1237. It should be noted that Ta, V, and Zr can be determined using the appropriate methods described in JIS standards G 1236, JIS G 1221 and JIS G 1232.

The Nb content in the particles of the precipitated phase (content in the steel sheet: wt.%) Can be determined by dissolving the steel sheet by electrolysis, capturing only the particles of the precipitated phase (by filtration), measuring the mass of Nb in the precipitated phase, and calculating the decrease in the mass of the steel sheet under the action of electrolysis, taking into account the mass of Nb in the precipitated phase.

Specifically, the quantitative content of Nb in the particles of the precipitated phase is determined as follows.

First, the resulting sheet is cut into 50 mm × 20 mm wafers and immersed for 2 minutes in a 10% HCl aqueous solution heated to 85 ° C to remove the coating and oxide films formed. After that, determine the mass of the obtained plate. The resulting plate was electrolyzed in a commercially available electrolyte solution (10% AA solution: 10% acetylacetone and 1% tetramethylammonium chloride in methanol) so that about 1 g of the obtained plate was electrolyzed. To remove particles of the precipitated phase adhering to the surface of the plate obtained after electrolysis, the resulting plate is immersed in an ethanol solution and subjected to ultrasonic treatment.

The specified ethanol solution and the electrolyte solution used in the electrolysis, which contains particles of the precipitated phase, is filtered through filter paper with holes of 0.1 μm (ensures the capture of particles of the precipitated phase, with a minimum size of the order of nanometers), to retain particles of the precipitated phase. After filtration, the particles of the precipitated phase collected by filtration are placed together with filter paper in a platinum crucible, heated at 700 ° C for one hour, mixed with Na ₂ B ₄ O ₇ and NaCO ₃ , and heated at 900 ° C for 15 minutes . The resulting material was cooled and then heated at 1000 ° C for 15 minutes.

After cooling, the substance in the crucible coagulates. The crucible containing the substance is placed in a 25% aqueous HCl solution, and the solution together with the crucible is heated at 90 ° C. for 30 minutes to completely dissolve the substance. The resulting solution was analyzed by ICP optical emission spectrometry, which is described in JIS G 1237, to determine the mass of Nb in the particles of the precipitated phase.

In order to determine the Nb content (wt.%) In the particles of the precipitated phase, the Nb mass is divided by reducing the mass of the obtained plate (steel sheet) under the action of electrolysis.

The Nb content (mass%) thus found in the particles of the precipitated phase is divided by the total Nb content (mass%) in order to determine the percentage of precipitated Nb.

The proportion of precipitated Nb in the sample is 65%. In addition, the inventors conducted studies and found that to ensure the advantages of the present invention, precipitation of at least 10% of the total Nb content is necessary.

Given the mechanism described above, the larger the amount of phase-forming element, such as Nb, remaining in the steel, apparently, the better the ΔW characteristic becomes. However, particles of the precipitated phase also worsen the loss characteristic in the core of the material being processed. Accordingly, the amount of particles of the precipitated phase is preferably small, in the range in which the deterioration in core loss due to cutting is small. In experiment 1, in materials having an Nb content of 65 ppm. or more, core losses from the materials themselves deteriorate, and therefore it is necessary that the niobium content be up to 50 ppm. or less.

Then, the effect of crystallite size of secondary recrystallized grains on ΔW was investigated. This is due to the assumption of the inventors that, in the presence of a large number of grain boundaries, deformation accumulation due to cutting is also likely to be weakened; accordingly, when the crystallite size is small and a large number of grain boundaries are present, situations are possible in which the deterioration of core losses due to cutting, as expected, will be small, and the above-described mechanism for weakening the accumulation of deformations due to particles of the precipitated phase, will not provide benefits.

Experiment 2

Steel sheet blanks containing in wt.%: 0.035% C, 3.31% Si, 0.13% Mn, 0.039% Sb, 0.05% Cr, and 0.012% P; 42 ppm nitrogen and 31 ppm sulfur; the rest of Fe and unavoidable impurities are produced by continuous casting, the sheet blank is reheated at 1250 ° C, then hot rolled to obtain hot rolled sheets having a thickness of 2.7 mm. Subsequently, these hot rolled sheets are annealed at 1000 ° C. for 15 seconds and then cold rolled to obtain sheets having a thickness of 0.30 mm.

The sheets are subjected to recrystallization annealing in a humid atmosphere of 50% N ₂ -50% H ₂ (decarburizing atmosphere) at a temperature range of 800 ° C to 880 ° C for 60 seconds. The sheets are then coated with an annealing separator, mainly containing MgO, and then subjected to a cleaning annealing by holding in the temperature range from 1050 ° C to 1230 ° C for 10 hours.

The temperature at the stages of recrystallization annealing and cleaning annealing is varied in order to change the size of crystallites obtained by secondary crystallization under the influence of cleaning annealing.

Then, leveling annealing is carried out at 900 ° C for 15 seconds, which also provides the formation of a tensile coating, mainly consisting of magnesium phosphate and boric acid. The resulting sheets were cut so that the strips had the size of Epstein samples (30 mm × 280 mm). At this time, as in the first experiment, cutting is carried out using wire scissors and cutting with mechanical scissors. For the obtained samples, measurements of core losses are carried out according to the procedure described in JIS C 2550.

After that, the steel substrates are subjected to etching, and the crystallite size of the secondary recrystallized grains is determined. For each set of conditions, crystallite size is determined by measuring grain size in four Epstein samples, and the measured grain sizes are averaged. When analyzing the components of steel substrates, it was found: 0.0018% C, 3.30% Si, 0.13% Mn, 0.039% Sb, 0.05% Cr and 0.011% phosphorus, the content of other elements was less than the sensitivity limit of the analysis. The dependence of the parameter ΔW (ordinate: W / kg), found by the above method, on the crystallite size (abscissa: mm) is shown in Fig.2.

Since no phase-forming elements, such as Nb, were absent in the second experiment, the advantages achieved in the 1st experiment did not appear. Accordingly, when the average crystallite size is large, ΔW is also large; when the average crystallite size is small, ΔW is small. In other words, the effect of reducing AW by adding a precipitating phase-forming element, such as Nb, occurs when the average size of the secondary recrystallized grains is 5 mm or more.

Based on the experiments described above, the inventors found that in the final plate made of oriented grain steel electrical steel sheet having a large secondary recrystallized grain size containing from 10 to 50 ppm, such an element as Nb, ensuring that at least 10% of the content of this element was in the form of particles of a precipitated phase, the deterioration of core losses due to cutting can be suppressed.

The present invention is based on such findings. Specific features of the present invention are as follows.

1. A sheet of electrical steel with oriented grains, characterized in that it contains in wt.%: 0.005% or less C, from 1.0% to 8.0% Si, and from 0.005% to 1.0% Mn; one or more elements selected from Nb, Ta, V and Zr, so that their total content is from 10 to 50 ppm; and the rest Fe and unavoidable impurities, in which at least 10% of the content of Nb, Ta, V and Zr is in the form of particles of the precipitated phase; particles of the precipitated phase have an average diameter (diameter of an equivalent circle) of 0.02 to 3 microns; and secondary recrystallized grains in the steel sheet have an average size of 5 mm or more.

2. A sheet of electrical steel with oriented grains according to paragraph 1, characterized in that it additionally contains in wt.% At least one element selected from: from 0.010% to 1.50% Ni, from 0.01% to 0 , 50% Cr, from 0.01% to 0.50% Cu, from 0.005% to 0.50% P, from 0.005% to 0.50% Sn, from 0.005% to 0.50% Sb, from 0.005% up to 0.50% Bi and from 0.005% to 0.100% Mo.

3. A sheet of electrical steel with oriented grains according to claim 1 or 2, characterized in that a groove is formed on the surface of the steel sheet, which has the form of a solid line or a broken line, with a width of 50 to 1000 μm and a depth of 10 to 50 μm, and extending at an angle of 15 ° or less relative to the direction perpendicular to the rolling direction of the steel sheet.

4. A method of producing an iron core, characterized by a sharp sheet of electrical steel with oriented grains according to any one of the above paragraphs 1-3 with the formation of plates and then stacking the plates, not subjected to annealing to relieve stresses.

The beneficial effect of the invention

According to the present invention, it is possible to effectively suppress the deterioration of the magnetic characteristics of oriented grain grains of electrical steel sheets due to cutting, and it is possible to obtain iron cores for transformers with low energy losses.

Brief Description of the Drawings

Figure 1 shows the dependence of the quantitative deterioration of core losses due to cutting (ΔW) (ordinate: W / kg) on the Nb content in steel (abscissa: ppm).

Figure 2 shows the dependence of the quantitative deterioration of core losses due to cutting (ΔW) (ordinate: W / kg) on the crystallite size of secondary recrystallized grains (abscissa: mm).

The implementation of the invention

The present invention will now be described more specifically.

First, the reasons why in the present invention the content of the components in the steel sheet is limited in the above ranges will be described. It is noted that "%" "ppm" for the components of the steel sheet respectively mean wt.% and ppm by weight, unless otherwise indicated. C: 0.005% or less

Carbon (C) is an element that is inevitably present in steel. Since carbon causes a deterioration in magnetic performance due to magnetic aging, it is desirable to minimize the C content. However, the complete removal of carbon is difficult, with a content of 0.005% or less being acceptable considering production costs, preferably a content of 0.002% or less. There is no reason for a specific definition of the lower limit of carbon content. From the point of view of industrial work, the C content is greater than zero. Si: 1.0% to 8.0%

Silicon (Si) is a necessary element to increase the resistivity of steel and achieve improvements in core losses from the final wafers. When the Si content is less than 1.0%, these beneficial properties are insufficiently manifested. When the Si content is more than 8.0%, the saturation of the magnetic induction of the steel sheet is significantly reduced. Therefore, the Si content is limited in the range from 1.0% to 8.0%. Preferably, the lower limit of the Si content is 3.0%. Preferably, the upper limit of the Si content is 3.5%.

Mn: 0.005% to 1.0%

Manganese (Mn) is a necessary element for improving the formability during hot rolling. When the Mn content is less than 0.005%, the effect of improving machinability is not sufficiently manifested. When the Mn content is greater than 1.0%, the secondary crystallization becomes unstable, and the magnetic characteristics deteriorate. Therefore, the Mn content is limited in the range from 0.005% to 1.0%. Preferably, the lower limit of the Mn content is 0.02%. Preferably, the upper limit of the Mn content is 0.20%.

In the present invention, it is necessary that one or more metals selected from Nb, Ta, V, and Zr (hereinafter referred to as “Nb or the like”) be in the form of a precipitated phase-forming element, in such an amount that the total content of said metal ranged from 10 to 50 ppm This is due to the fact that with a total Nb content or the like less than 10 ppm, particles of the precipitated phase to improve the characteristics of core losses, which is the main distinguishing feature of the present invention, are not allocated sufficiently. When the total content of Nb or the like exceeds 50 ppm, the core loss characteristic for the material itself deteriorates, as described above. Thus, the upper limit of the total Nb content or the like. defined as 50 ppm Preferably, the total content is in the range of 10 to 30 ppm.

It is necessary that the particles of the precipitated phase Nb or the like are present in a concentration of 10% or more, and the particles of the precipitated phase have an average diameter (diameter of an equivalent circle) of 0.02 to 3 μm. When the average diameter is less than 0.02 μm, the particles of the precipitated phase are too small, while the probability of stress concentration is reduced. When the average diameter exceeds 3 μm, the concentration (number) of particles of the precipitated phase present becomes small, and the number of areas where the stress is concentrated becomes small. Preferably, the particles of the precipitated phase have an average diameter of from 0.05 to 3 μm. More preferably, the lower diameter limit is 0.12 microns, even more preferably 0.33 microns. More preferably, the upper diameter limit is 1.2 microns, even more preferably 0.78 microns.

Preferably, the fraction of precipitation of particles of the precipitated phase Nb or the like is 20% or more, more preferably 31% or more, even more preferably 48% or more. There is no need to determine the upper limit, since the proportion of the deposition of 100% does not cause problems.

Preferably, the average particle diameter of the precipitated phase Nb or the like. determined as follows; the cross section of the obtained sample is examined by scanning electron microscopy; micrographs of approximately 10 viewing areas are viewed with an increase of about 10,000; micrographs of the image are analyzed and the average diameter of the equivalent circle is determined. Preferably, the fraction of particles of the precipitated phase (percentage of precipitation) is measured in accordance with the procedure described in experiment 1. When the steel sheet contains two or more elements, such as niobium or the like, the total content (mass%) of Nb or the like. P. in the particles of the precipitated phase, it should be divided into the total content (wt.%) of Nb or the like in the steel sheet.

Preferably, one or more of Nb, V, and Zr is selected as the element forming the precipitated phase, since it is unlikely that they would create defects in the steel sheets during hot rolling. Nb is particularly preferred since it helps to reduce defects during hot rolling. In such cases, the content is also in the range of 10 to 50 ppm, and a range of 10 to 30 ppm is preferred; moreover, the preferred particle diameter of the precipitated phase and the preferred percentage of precipitation have the same values as indicated above.

To control the particle diameter and the percentage of particles of the precipitated Nb phase or the like, it is effective to control the maximum temperature of the steel sheet during cleaning annealing, and the maximum temperature and cooling rate during subsequent cooling from 900 ° C to 500 ° C. This is due to the fact that for such particles of the precipitated phase, it is possible to control the diameter and the percentage of precipitation by conducting a cleaning annealing at high temperature in order to dissolve the particles of the precipitated phase and conduct cooling to cause re-deposition.

In general, for a phenomenon such as precipitation, a high cooling rate leads to a small number of particles of the precipitated phase (part remains in the form of a solid solution) and a small particle diameter of the precipitated phase; conversely, a low cooling rate usually leads to the opposite result.

As described above, for the manifestation of the effect of reducing ΔW due to the addition of the element forming the precipitated phase, it is necessary that the average size of the secondary recrystallized grains of the material is 5 mm or more. Although the indicated grain size is the usual size in electrical steel sheet for large transformers having a size of several meters, as described in the section "Problem Solved by the Invention", irrespective of this sheet size, by controlling the rate of temperature rise and secondary crystallization atmosphere, it is possible control an average grain size of 5 mm or more. Preferably, the average size of the secondary recrystallized grains is determined according to the procedure described in experiment 2.

It should be noted that the method of reducing ΔW by producing grains with an average secondary recrystallized grain size of less than 5 mm is not preferable, since the absolute value of the core loss and magnetic induction becomes small.

The main composition is described above.

If necessary, the elements described below can be appropriately added to the composition of the present invention.

Nickel (Ni): 0.010% to 1.50%

Ni may be added to enhance magnetic properties. In this case, when the amount of added Ni is less than 0.010%, the magnetic properties are not sufficiently enhanced. When the amount of Ni added exceeds 1.50%, the secondary crystallization becomes unstable, and the magnetic properties may deteriorate. Therefore, the preferred Ni content is in the range of 0.010% to 1.50%.

Chromium (Cr): 0.01% to 0.50%; Cu: from 0.01% to 0.50%; P: from 0.005% to 0.50%

At least one element of Cr, Cu and P can be added to reduce core loss. However, when the number of added elements is less than the lower limit, the core loss reduction effect is insufficient. When the number of added elements is greater than the upper limit, the growth of secondary recrystallized grains is suppressed, which leads to an unexpected increase in core losses. Therefore, it is preferable that the content of the corresponding elements is in the above ranges.

Sn: 0.005% to 0.50%; Sb: from 0.005% to 0.50%; Bi: from 0.005% to 0.50%; Mo: from 0.005% to 0.100%

In order to increase magnetic induction, at least one of the metals Sn, Sb, Bi, and Mo can be added. However, when the number of added elements is less than the lower limits, the effect of enhancing the magnetic properties is insufficiently manifested. When the number of added elements is greater than the upper limits, the growth of secondary recrystallized grains is suppressed, which leads to a deterioration in magnetic properties. Therefore, it is preferable that the content of the elements is in the corresponding ranges described above.

As a result, the sheet of electrical steel according to the present invention may further comprise at least one element selected from: Ni from 0.010% to 1.50%, Cr from 0.01% to 0.50%, Cu from 0.01% up to 0.50%, P from 0.005% to 0.50%, Sn from 0.005% to 0.50%, Sb from 0.005% to 0.50%, Bi from 0.005% to 0.50% and Mo from 0.005% up to 0.100%. In addition, with regard to a subgroup consisting of elements that are independently selected from the group of these elements, at least one is selected from the group consisting of elements (groups) constituting the subgroup, and they can be added to the composition.

In addition, if necessary, at least one combination of the elements forming the inhibitor (for example, the elements forming aluminum nitride - Al and N, the elements forming manganese sulfide - Mn and S, the elements forming manganese selenide - Mn and Se, and elements forming titanium nitride - Ti and N) can be added to the composition in the required amount known to specialists.

The rest of the composition is iron and ordinary inevitable impurities. Examples of unavoidable impurities include: P, S, O, Al, N, Ti, Ca and B (when Al and the like are not added as inhibitor constituents, they are impurities).

In the present invention, it is preferable that grooves are formed on the surface of the steel sheet, which have the form of a solid line or a dashed line, with a width of 50 to 1000 μm and a depth of 10 to 50 μm, and extending in a direction crossing a direction perpendicular to the rolling direction, at an angle of 15 ° or less. The formation of such grooves provides a cleansing effect of magnetic domains, which leads to an additional reduction in core losses. The distance between the grooves (pitch) is preferably from about 2 to 7 mm. When the grooves extend at an angle of 0 ° with respect to the direction perpendicular to the rolling direction, literally the grooves do not intersect the direction perpendicular to the rolling direction; however, such a case is also regarded as an intersection. As a result, it is necessary that the grooves are formed at an angle of 15 ° or less, relative to the direction perpendicular to the rolling direction.

As a result of the formation of these grooves, core losses from electrical steel sheets of the present invention are reduced by approximately 0.17 W / kg. It has been found that such an advantage can be achieved regardless of the nature of the element selected from Nb, Ta, V and Zr.

Hereinafter, a preferred method for producing a grain oriented electrical steel sheet according to the present invention will be described. In the specified production method, the technological stages of obtaining a standard sheet of oriented steel with oriented grains can be used as the main stages. Specifically, a number of steps can be used in which a sheet blank obtained from molten steel having a predetermined composition of components is subjected to hot rolling; the obtained hot-rolled sheets are optionally annealed after hot rolling and then processed at one stage of cold rolling or at two or more stages of cold rolling, between which intermediate annealing is performed so as to obtain the final thickness of the sheet; subsequently, the steel sheets are subjected to recrystallization annealing, then purification annealing, and optionally equalizing annealing; and then coated on the steel sheets.

In the case of controlling the composition of the components of the molten steel, when the amount of carbon introduced exceeds 0.10%, it is difficult to reduce the C content to 50 ppm in subsequent stages (0.005%) or less in which magnetic aging does not occur. Therefore, it is preferable that the amount of carbon added to the molten steel is 0.10% or less.

The silicon content can be adjusted in the range from 1.0% to 8.0%, which corresponds to the finally required content in the composition of the components of the molten steel. When using the method of increasing the Si content by siliconization or the like in the post-production step, the amount of Si added to the molten steel may be less than the finally required content.

The addition or removal of Nb, Ta, V, and Zr, which are essential components of the present invention, during the steps carried out after obtaining the molten state of the steel, is difficult. Therefore, it is most desirable that the required amount of these components be added when controlling the composition of the components of the molten steel.

A slab of molten steel containing the components described above can be made using a standard ingot process, or a standard continuous casting process, or else a thin cast slab having a thickness of 100 mm or less can be made by continuous casting. Although the slabs are heated and hot rolled in the traditional manner, instead, the slabs after casting can be directly hot rolled without heating. In the case of thin cast slabs, they can be hot rolled or transferred directly to the next stages without hot rolling.

The heating of the slabs to be hot rolled in a system of components containing an inhibitor forming element usually occurs at a high temperature of about 1400 ° C. On the contrary, heating in a system of components without inhibitor-forming elements usually occurs at a low temperature, 1250 ° C or less, which is advantageous since costs are reduced.

If necessary, then the hot-rolled sheet is annealed. To achieve good magnetic characteristics, the annealing temperature of the hot rolled sheet is preferably 800 ° C or more and 1150 ° C or less. This is due to the fact that when the annealing temperature of the hot rolled sheet is less than 800 ° C, a strip texture remains due to hot rolling, and it becomes difficult to obtain a primary recrystallization texture having uniform grain sizes; therefore, annealing of the hot-rolled sheet leads to a relatively limited effect, supporting the growth of secondary recrystallized grains. When the annealing temperature of the hot-rolled sheet exceeds 1150 ° C, the crystallite grains after annealing of the hot-rolled sheet become coarse. Therefore, in this case, it also becomes difficult to achieve a primary recrystallization texture having grains of uniform size.

After annealing the hot-rolled sheet, one or more cold rolling steps are carried out, between which an intermediate annealing step is optionally carried out, and then recrystallization annealing is carried out. To further enhance magnetic properties, it is effective when cold rolling is carried out at a temperature in the range from 100 ° C to 300 ° C and / or one or more aging steps in the range from 100 ° C to 300 ° C are carried out during the cold rolling process. In the case of recrystallization annealing, if decarburization is necessary, a humid atmosphere is used during recrystallization annealing; however, when decarburization is not necessary, recrystallization annealing can be carried out in a dry atmosphere. After recrystallization annealing, an operation can additionally be carried out to increase the silicon content by siliconization.

When core loss is considered an important factor and subsequently a forsterite coating forms, the sheets are coated with an annealing separator mainly containing MgO, and then subjected to final annealing (cleaning annealing) to develop a secondary crystallization texture and form a forsterite coating.

When the blanking characteristic is considered an important factor and the forsterite coating is not specially formed, the annealing separator is not used; or even if an annealing separator is used, it is necessary to use silica, alumina or the like, instead of MgO forming a forsterite coating.

For example, when the indicated annealing separator is used, an electrostatic coating is effectively carried out without introducing water. Sheets of heat-resistant inorganic materials (silica, alumina, or mica) may be used.

Final annealing is effectively carried out at a temperature that provides secondary crystallization, preferably at 800 ° C or higher. Annealing conditions are desirable under which secondary crystallization is completed, and it is usually advisable that the sheets are maintained at a temperature of 800 ° C or higher for 20 hours or more. When the blanking characteristic is considered an important factor and the forsterite coating does not form, since only secondary crystallization is required to complete, it is advisable that the holding temperature is from about 850 ° C to 950 ° C, and the final annealing can be completed during the specified aging operation. When core loss is considered important or noise reduction of the transformer is required and a forsterite coating is formed, it is advisable to increase the holding temperature to approximately 1200 ° C.

In the cooling step of said high temperature annealing, cooling is carried out at a rate of from 5 ° C / h to 100 ° C / h, at least in the temperature range from 900 ° C to 500 ° C. When cooling is carried out from a holding temperature below 900 ° C, cooling is carried out at a speed of 5 ° C / h to 100 ° C / h in the range from the holding temperature to 500 ° C. This is due to the fact that when the cooling rate exceeds 100 ° C / h in the indicated temperature range, there may be situations when the particles of the precipitated phase become too small, or the solid solution does not precipitate. When the cooling rate is less than 5 ° C / h, there may be situations where the particle diameter of the precipitated phase becomes too large, or the cooling time becomes excessively long, which leads, for example, to poor performance. More preferably, the lower limit of the cooling rate is 7.8 ° C / h. More preferably, the upper limit of the cooling rate is 30 ° C / hg. In view of the achievement of stable results, an upper limit of the cooling rate of 14 ° C / h is even more preferred.

After the final annealing, in order to remove the adhering annealing separator, it is advisable to carry out cleaning with water, brushing and / or etching. After this, it is advisable to subject the sheets to leveling annealing to correct their shape in order to reduce core losses.

When steel sheets are used in the form of plates, it is advisable to form an insulating coating on the surface of the steel sheets before or after leveling annealing to improve core loss performance. To reduce core loss, coatings that can transmit tensile forces to steel sheets are desirable. When using the method of coating the surface of a steel sheet with an inorganic substance using the stretch coating method with a binder, methods of physical vapor deposition, chemical vapor deposition or the like are used, moreover, the coating films exhibit excellent adhesion and core losses are significantly reduced, which is highly desirable.

To reduce losses in the core, it is advisable to carry out a cleaning treatment of magnetic domains. An example of this processing, which is usually carried out, is the method of grooving in the finished plates or the linear introduction of thermal deformation or impact deformation using a laser or plasma into the final plates, or the method of grooving in the intermediate products having the final sheet thickness, such as cold rolled sheets.

As a preferred method for producing an iron core using steel sheets according to the present invention, for example, a method has been developed that includes cutting steel sheets according to the present invention and laminating sheets without annealing them to relieve stresses. At this time, in the steel sheet according to the present invention, the loss in core loss of the steel sheets due to cutting can be reduced to 0.1 W / kg or less (preferably 0.041 W / kg or less). This method is particularly advantageous for producing large iron cores, for example, in situations where the steel sheet is cut into plates, the longest side of which is more than 500 mm. Parameters including the number of packed steel sheets, the size and shape of the steel sheets obtained by cutting, the presence or absence of grooves, the size of the grooves, the presence or absence of a coating, and the type of coating can be determined accordingly based on ordinary knowledge.

Example 1

Sheet blanks from steel containing 0.065% C, 3.25% Si, 0.13% Mn, 240 ppm Al, 70 ppm N, 36 ppm. S, and 25 ppm. Nb (only for steel No. 7, the content of niobium is 20 ppm), the rest of Fe and inevitable impurities are obtained by continuous casting. The steel sheet preforms are reheated at 1400 ° C and then hot rolled so that the sheets have a thickness of 2.4 mm. Then, the hot-rolled sheets are annealed at 1000 ° C for 40 seconds, followed by cold rolling so as to obtain a sheet thickness of 1.6 mm, intermediate annealing at 900 ° C, and then cold rolling so that the sheets have a thickness of 0, 23 mm.

Then, the obtained sheets are subjected to recrystallization annealing in a humid atmosphere of 60% N ₂ -40% H ₂ , under exposure conditions at 850 ° C for 90 seconds; after that, the sheets are covered with an annealing separator, mainly containing MgO, and subjected to a purification annealing at 1220 ° C for 6 hours.

During cleaning annealing, the cooling rate in the range from 900 ° C to 500 ° C is controlled as indicated in Table 1 in order to vary the particle diameter of the precipitated niobium phase and the percentage of Nb deposition. After that, the sheets are subjected to leveling annealing at 850 ° C for 20 seconds.

The resulting samples are cut so that they have a size of 30 mm × 280 mm. At the same time, cutting is carried out in two modes: cutting with wire scissors and cutting with mechanical scissors. The magnetic properties of the obtained samples are determined according to the method described in JIS C 2550, and the magnetic properties of the samples obtained by cutting using wire shears are shown in table 1.

Regarding core losses based on the conditions of the two cutting processes, ΔW values determined by subtracting core losses from a sample obtained by cutting using wire shears from core losses from a sample obtained by cutting by mechanical shears are also shown in Table 1.

Samples for which magnetic properties were measured are then etched to remove the coating and the crystallite size in the secondary recrystallized grains is determined. The results are also shown in table 1, together with the results of measurements of the diameter and percent precipitation of particles of the precipitated phase Nb. After etching, the component composition of the steel sheets in the samples with the removed coating is determined. As a result, the component composition was established: 0.0016% C, 3.24% Si, 0.13% Mn, and 18 ppm. Nb (only for steel No. 7, 15 ppm Nb), which meets the requirements of the present invention.

As can be seen from the data in Table 1, samples of all examples of the invention in which the crystallite size, diameter and percentage of precipitation of particles of the precipitated phase Nb satisfy the required ranges according to the present invention, have excellent magnetic properties and small ΔW values, which demonstrate that the loss of core loss cutting is negligible.

Example 2

Product plates were obtained (plate thickness: 0.23 mm) from oriented grain-oriented electrical steel sheets that contained the components shown in Table 2, and they were produced using a standard production method in which recrystallization annealing was carried out, followed by cleaning annealing at 1150 ° C and cooling at a rate of 25 ° C / hour in the range from 900 ° C to 500 ° C.

Grain oriented electrical steel sheets are cut so as to obtain a size of 30 mm × 280 mm. At the same time, cutting is carried out in two modes: cutting with wire scissors and cutting with mechanical scissors.

The magnetic properties of the samples obtained are determined by the method described in JIS C 2550, and the magnetic properties of the samples obtained by cutting using wire shears are shown in table 2. In addition, table 2 also shows the ΔW values found as in example 1.

Samples to be examined for magnetic properties are etched to remove the coating, the crystallite size in the secondary recrystallized grains is measured. The results are also shown in Table 2, together with the results of measurements of the diameter and percentage of precipitation of particles of the precipitated Nb phase or the like, it is noted that the component composition steel sheets in table 2 represents the result obtained when determining the component composition of samples with a removed coating after etching.

In addition, particles of the precipitated phase were investigated. As a result, it was found that the particles of the precipitated phase have an average diameter of 0.05 to 3.34 μm and a deposition percentage of 0% to 79%.

As can be seen from the data of table 2, samples of all examples of the invention, in which the crystallite size, diameter and percentage of precipitation of particles of the precipitated phase Nb satisfy the required ranges according to the present invention, have excellent magnetic properties and small ΔW values, which demonstrate that the loss in the core due to cutting is negligible.

Example 3

Sheet blanks from steel containing 0.065% C, 3.25% Si, 0.13% Mn, 0.05% Cr, 240 ppm Al, 70 ppm N, 36 ppm. S, 0.013% P, 0.075% Sn, 0.036% Sb, 0.011% Mo and 25 ppm. Nb, the rest of Fe and unavoidable impurities, are obtained by continuous casting. The steel sheet preforms are reheated at 1400 ° C and then hot rolled so that the sheets have a thickness of 2.4 mm. Then, the hot-rolled sheets are annealed at 1000 ° C for 40 seconds, followed by cold rolling so as to obtain a sheet thickness of 1.6 mm, intermediate annealing in the temperature range from 700 ° C to 1020 ° C, and then cold rolling in this way to obtain steel sheets having a thickness of 0.23 mm

Then, linear grooves having a width of 100 μm and a depth of 25 μm are formed on the surface of the steel sheets by local electrolytic etching of the surface. The grooves are formed in such a way that they extend at an angle of 10 ° with respect to the direction perpendicular to the rolling direction, in increments of 8 mm. Then the sheets are subjected to recrystallization annealing in a humid atmosphere of 60% N ₂ -40% H ₂ under conditions of exposure from 800 ° C to 900 ° C for 90 seconds. After that, the sheets are covered with an annealing separator, mainly containing MgO, and then subjected to a cleaning annealing at 1220 ° C for 6 hours. After that, the sheets are cooled in the range from 900 ° C to 500 ° C with a cooling rate of 10 ° C / hour.

Then the sheets are subjected to leveling annealing at 850 ° C for 20 seconds. The temperature of the intermediate annealing and the temperature of the recrystallization annealing are varied so as to change the grain size after secondary crystallization. The resulting sheets are cut in the form of Epstein samples having dimensions of 30 mm × 280 mm. At this time, cutting is carried out in two modes: using wire shears and cutting with shears.

The magnetic properties of the obtained samples are determined by the method described in JIS C 2550, and the magnetic properties of the samples obtained by cutting with scissors for wire are shown in table 3. In addition, table 3 also shows the ΔW values found as in example 1.

Samples to be examined for magnetic properties are etched to remove the coating, and the size of crystallites in secondary recrystallized grains is measured. The results are also shown in table 3, together with the results of measurements of the diameter and percent precipitation of particles of the precipitated phase Nb. After etching, the component composition of the steel sheets in the samples with the removed coating is determined. As a result, the component composition was established: 0.0016% C, 3.24% Si, 0.13% Mn, 0.05% Cr, 0.011% P, 0.074% Sn, 0.036% Sb, 0.011% Mo and 18 m. d. Nb, which meets the requirements of the present invention.

Table 3 No. Crystallite Size (mm) The diameter of the particles of the precipitated phase (μm) The percentage of deposition (%) B ₈ (T) W _17/50
(W / kg) ΔW (W / kg) Notes 24 3.8 0.56 71 1.855 0.867 0.015 Comparative example 25 7.5 0.78 65 1,908 0.695 0.024 An example of the invention 26 12.6 0.47 52 1,915 0.690 0,026 An example of the invention 27 15.0 0.33 48 1,910 0.681 0,033 An example of the invention 28 21.9 0.41 60 1,922 0.689 0,034 An example of the invention 29th 25,2 0.59 72 1,918 0.677 0,030 An example of the invention

As can be seen from the data of table 3, samples of all examples of the invention, in which the crystallite size, diameter and percentage of precipitation of particles of the precipitated phase Nb satisfy the required ranges according to the present invention, have excellent magnetic properties and small ΔW values that demonstrate that the loss in the core due to cutting is negligible.

The data of examples 1-3 demonstrate that according to the present invention can be obtained sheets of electrical steel with oriented grains, having for the most part a value of ΔW of 0.1 W / kg or less and undergoing a slight deterioration in magnetic characteristics due to cutting. Therefore, obtaining a plate iron core by cutting a steel sheet according to the present invention without annealing to relieve stresses is effective for improving the magnetic properties of the iron core, especially for improving the core loss characteristic.

In particular, in steel containing particles of the precipitated phase Nb, in examples 1-3, the diameter (average diameter) of the particles of the precipitated phase is 0.12 μm or more and 1.2 μm or less (preferably 0.78 μm or less; percent precipitation preferably 48% or more) ΔW is 0.038 W / kg or less. In this way, better performance can be achieved. The data of examples 1-3, etc. show that in order to achieve the indicated diameter and number of particles of the precipitated phase, preferably, the cooling rate of the steel after final annealing is in the range from 7.8 ° C / h to 30 ° C / h, more preferably from 7.8 ° C / h up to 14 ° C / h.

Industrial applicability

According to the present invention, the deterioration of the magnetic characteristics of the grain oriented electrical steel sheets due to cutting can be reduced. As a result, iron cores with low energy losses can be obtained, and thus, for example, it is possible to produce large transformers that are highly energy efficient.

Claims (4)

1. The sheet of electrical steel with oriented grains, containing, wt.%: 0.005 or less C, from 1.0 to 8.0 Si and from 0.005 to 1.0 Mn; one or more elements selected from Nb, Ta, V and Zr, so that their total content is from 10 to 50 ppm, and the rest is Fe and unavoidable impurities, in which at least 10% of the content of Nb, Ta, V and Zr are in the form of particles of the precipitated phase, and the particles of the precipitated phase have an average diameter — the diameter of the equivalent circle — from 0.02 to 3 μm, and the secondary crystallized grains in the steel sheet have an average size of 5 mm or more. 2. A sheet of electrical steel with oriented grains according to claim 1, which additionally contains, wt.%, At least one element selected from: from 0.010 to 1.50 Ni, from 0.01 to 0.50 Cr, from 0.01 to 0.50 Cu, from 0.005 to 0.50 P, from 0.005 to 0.50 Sn, from 0.005 to 0.50 Sb, from 0.005 to 0.50 Bi and from 0.005 to 0.100 Mo. 3. A sheet of electrical steel with oriented grains according to claim 1 or 2, on the surface of which a groove is formed, having the form of a solid line or a dashed line, with a width of 50 to 1000 microns, a depth of 10 to 50 microns and extending at an angle of 15 ° or less relative to the direction perpendicular to the rolling direction of the steel sheet. 4. A method of obtaining a steel core, comprising cutting a sheet of electrical steel with oriented grains according to any one of claims 1 to 3 with the formation of plates and their subsequent packaging without annealing to relieve stresses.

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