JP6891707B2 - Non-oriented electrical steel sheet and its manufacturing method - Google Patents

Description

The present invention relates to non-oriented electrical steel sheets and a method for producing the same.

In fields such as hybrid electric vehicles (HEVs), there is an increasing need for increasing the strength of non-oriented electrical steel sheets used for rotor materials as motors rotate at higher speeds.
Since non-oriented electrical steel sheets usually contain Si from the viewpoint of low iron loss, they enjoy solid solution strengthening by Si, but further increase in strength is required, and selection of additive elements is required. And the miniaturization of crystal grains are being studied.

In Patent Document 1, the Si content is 2.0 to 3.5%, the Ni or Ni and Mn contents are increased, ordinary cold rolling is performed, and the annealing conditions are controlled to achieve high tension and no directionality. A method for manufacturing electrical steel sheets has been proposed.
Further, in Patent Document 2, fine carbonitrides are formed by adding 0.05% or less of C and Nb, Ti, V, and Zr, and the tension of steel is increased by precipitation hardening and granulation hardening. Is disclosed.

Patent Documents 3 and 4 disclose that grain boundary segregation elements such as Te are effective elements for suppressing nitriding in the manufacturing process of non-oriented electrical steel sheets and avoiding microstructure miniaturization. There is.
Further, Patent Document 5 discloses a high-strength non-oriented electrical steel sheet utilizing the recrystallization suppressing effect of a grain boundary segregation element such as Te.

Japanese Unexamined Patent Publication No. 62-256917 Japanese Unexamined Patent Publication No. 06-330255 Japanese Unexamined Patent Publication No. 07-054044 Japanese Unexamined Patent Publication No. 11-071650 Japanese Unexamined Patent Publication No. 2011-084761

Generally, as the means for increasing the strength, solid solution strengthening, precipitation strengthening, and crystal grain refinement strengthening have been used. However, in the solid solution strengthening described in Patent Document 1, since it is necessary to add a relatively large amount of strengthening elements, problems such as a decrease in saturation magnetic flux density and deterioration in manufacturability occur.
Further, the present inventors have found that the crystal grain refinement utilizing the precipitate described in Patent Document 2 causes a problem that the crystal grain size varies widely in the steel sheet. This is basically due to the fact that in industrial products manufactured in large quantities in a very large size, fluctuations in conditions in the manufacturing process from casting to final heat treatment cannot be avoided. That is, segregation in the slab, fluctuation of the thermal history at the tip, center, rear end of the coil length, the edge of the coil width, etc., and the accuracy of manufacturing opportunity and manufacturing condition control by the manufacturing line are the causes. Although these fluctuations occur in various electrical steel sheets, especially in a situation where the morphology of the precipitate reacts sensitively and the crystal grain growth is not sufficiently performed by lowering the final annealing temperature, etc., the crystal grains It is considered that the variation in diameter becomes large. In the "non-transformation component system" that does not undergo α-γ transformation in the process of steel sheet manufacturing, that is, in steel materials with increased Si content, the variation in crystal grain size in the final product with finer crystal grain size is even more remarkable. It becomes.
It is considered that this is because in the non-transformation component type steel material, coarse grains are generated in the hot rolling step of being exposed to a high temperature of 1000 ° C. or higher from solidification in casting. That is, the coarse grain is a non-uniform structure in which the region near the grain boundary and the region inside the grain are distributed at large intervals. This is because in a situation where the growth is not sufficient, a large difference in crystal grain size depending on the location is likely to occur.
However, since Si is an element that is indispensable for ensuring the magnetic properties of non-oriented electrical steel sheets, it is not possible to control the variation in crystal grain size while maintaining the magnetic properties by reducing Si. Have difficulty.
Further, it is conceivable to add the Te element whose recrystallization suppressing effect has been confirmed in Patent Documents 3 to 5 to the steel material having an increased Si content to make the crystal grains finer, but the Te element is simplified. It was difficult to make the recrystallized particle size uniform just by adding it to. It is considered that this is because Te acts as a grain boundary segregation element and forms a precipitate of Te itself or a composite precipitate with a precipitate of another element, resulting in a complicated action.
The present invention has been made in view of the above circumstances, and the amount of the reinforcing element added is suppressed to a low level, the manufacturability is good, the material stability is excellent, and the iron loss having a uniform and fine crystal structure varies. An object of the present invention is to provide a small and high-strength non-oriented electrical steel sheet and a method for producing the same.

The present inventors have focused on the content of Te and the influence of trace additive elements that may be compound-precipitated with Te. As a result, the steel sheet containing Te, Al and N in an appropriate range is uniform and uniform. It was found that it is preferable to consider the contents of Mn and S because a fine crystal structure is obtained and the morphology of sulfide represented by MnS affects this effect.
Then, in consideration of industrial characteristics, the present invention shown below has been completed.

That is, in the non-directional electromagnetic steel plate having an average crystal grain size of less than 15 μm according to the present invention, Si is 2.0% by mass or more and 4.0% by mass or less, and Te is more than 0.007% by mass and 0.02% by mass. less, Al of 0.02 wt% or more than 0.3 mass%, and contains a N 0.002 mass% 0.01 0% by mass, C is at most 0.005 wt%, Mn is and 0.20 mass% or less, S is equal to or less than 0.0030 wt%, the remainder Ri is Do Fe and impurities, the standard deviation / average grain size of the crystal grain size is 0.30 or less, that It is a feature.

The non-directional electromagnetic steel plate of the present invention further contains 0.0005% by mass or more and 0.0015% by mass or less of Mg and Ca and / or 0.0030 % by mass or more and 0.010% by mass or less of REM in total. It is preferable to contain it.
In the method for producing a non-directional electromagnetic steel sheet of the present invention, Si is 2.0% by mass or more and 4.0% by mass or less, Te is more than 0.007% by mass and less than 0.02% by mass, and Al is 0.02% by mass. 0.3 wt% or less or more, and contains a N 0.002 mass% 0.01 0% by mass, C is at most 0.005 wt%, Mn is not more than 0.20 wt%, A step of hot-rolling a slab having S of 0.0030% by mass or less and the balance consisting of Fe and impurities to obtain a hot-rolled plate, a step of annealing the hot-rolled plate, and a step of annealing the annealed hot-rolled plate. It has a step of cold rolling to obtain a cold-rolled steel sheet and a step of finishing-annealing the cold-rolled steel sheet, and the annealing temperature in the finish annealing is set to 950 ° C. or higher at a temperature at which 50% of the structure is recrystallized. It is characterized by.
In the method for producing a non-directional electromagnetic steel sheet of the present invention, Si is 2.0% by mass or more and 4.0% by mass or less, Te is more than 0.007% by mass and less than 0.02% by mass, and Al is 0.02% by mass. 0.3 wt% or less, and 0.002 wt% 0.01 0 wt% or less of N, and C contained 0.05 wt% to 0.10% mass%, Mn 0.20 mass % Or less, S is 0.0030% by mass or less, the balance is composed of Fe and impurities, and a slab having a composition having an α-γ transformation point is hot-rolled to obtain a hot-rolled plate. A step of annealing the hot-rolled plate, a step of cold-rolling the annealed hot-rolled plate to obtain a cold-rolled steel plate, a step of decarburizing and annealing the cold-rolled steel plate, and a finish annealing of the decarburized and annealed steel plate. The heating temperature in the hot rolling is equal to or higher than the α-γ transformation point, and the content ratio of C in the steel sheet is reduced to 0.005% by mass or less by the decarburization annealing. It is characterized in that the annealing temperature is not more than the temperature at which 50% of the structure is recrystallized and not more than 950 ° C.
In the above production method, the slab further contains 0.0005% by mass or more and 0.0015% by mass or less of Mg and Ca and / or 0.0030% by mass or more and 0.010% by mass or less of REM. It is preferable to contain it.

According to the present invention, it is possible to provide a high-strength non-oriented electrical steel sheet having a fine crystal structure with reduced variation in iron loss, and a method for producing the same.

Hereinafter, the non-oriented electrical steel sheet according to the present invention and its manufacturing method will be described in order.
In the present invention, "%" means "mass%" unless otherwise specified.

A. Non-directional electromagnetic steel plate The non-directional electromagnetic steel plate having an average crystal grain size of less than 15 μm according to the present invention contains Si in an amount of 2.0% by mass or more and 4.0% by mass or less and Te in an amount of more than 0.007% by mass. It contains less than 02% by mass, Al is 0.02% by mass or more and 0.3% by mass or less, N is 0.002% by mass or more and 0.01% by mass or less, and C is 0.005% by mass or less. The balance is characterized by being composed of Fe and impurities.

The non-oriented electrical steel sheet of the present invention has high strength, and for example, it is possible to achieve a yield point (YP) of 450 MPa in a tensile test.

In the non-oriented electrical steel sheet of the present invention, the mechanism for obtaining the effect of reducing the variation in iron loss is estimated as follows, although there are some unclear points. In the description of the invention in the present specification, there is a description based on the following mechanism, but this mechanism is only a hypothesis. In the future, it may be found that the effects of the present invention are manifested by an action different from the mechanism described here, but such new findings do not deny the present invention.

It is generally known that the crystal structure, especially the crystal grain size, has a great influence on the iron loss, but in the non-oriented electrical steel sheet having a fine crystal structure, the relationship between the crystal structure and the iron loss becomes stronger. It is considered that if the crystal grain size becomes non-uniform, the iron loss will vary greatly.
The non-oriented electrical steel sheet of the present invention has a composition in which the concentrations of Te, Al, and N are specified in an extremely narrow range, so that a uniform and fine crystal structure can be obtained. Furthermore, by controlling the contents of Mn and S and / or containing sulfide-forming elements such as Mg, Ca, and REM, homogenization of the crystal structure is remarkably exhibited.
As described above, Te has been utilized as a grain boundary segregation element in non-oriented electrical steel sheets, but in the present invention, Te is mainly in a solid solution state or a solid solution state, not in a grain boundary segregation state. It is believed that it functions as TeFe, which is a precipitate of Te.
In the solid solution state, Te affects the behavior of Al or N in the α phase to precipitate AlN very finely.
Further, in the case of TeFe, TeFe is deposited very finely in the invention steel, which acts strongly as a precipitation nucleus of AlN, and as a result, AlN is precipitated very finely.
Since AlN has a grain boundary pinning effect, the crystal structure in the steel sheet becomes finer. Further, as described above, when AlN is fine, the pinning effect of the grain boundaries is unlikely to disappear even under high temperature or long-term heating conditions, so that the crystal structure is kept fine by appropriately performing heat treatment at high temperature for a long time. It is possible to make it uniform up to.
It should be noted that MnS formed in the steel acts as a precipitation nucleus of AlN and inhibits the realization of the above-mentioned preferable AlN form. Since MnS does not precipitate sufficiently finely as required by the present invention, AlN formed with MnS as a nucleus has a strong pinning effect that can realize the uniform and fine crystal grain size required by the present invention. Does not reach. Therefore, in the present invention, it is preferable to control the content of Mn and / or S in a low range so as to suppress the formation of MnS. Alternatively, it is preferable to add Mg, Ca, REM or the like so as not to form MnS to coarsen the sulfide to make it harmless.

[Composition of non-oriented electrical steel sheet]
The non-oriented electrical steel sheet of the present invention contains at least Si (silicon), Te (tellu), Al (aluminum) and N (nitrogen), and C is a specific amount or less, and the effect of the present invention is not impaired. It has a composition in which the balance is Fe (iron), which may contain impurities in the range. Further, Mn and S may be in a specific amount or less and may contain one or more elements selected from Mg, Ca and REM.

(2.0% ≤ Si ≤ 4.0%)
In the present invention, the non-oriented electrical steel sheet contains 2.0 to 4.0% of Si. Steel having a Si content of less than 2.0% undergoes α-γ transformation in the heat treatment process of the steel sheet manufacturing process, so that the problem of non-uniform crystal grain size as described above is unlikely to occur.
However, the inclusion of Si increases the electrical resistance of the steel and can reduce the eddy current loss that forms part of the iron loss. Therefore, if the Si content is less than 2.0, the magnetic properties will be improved. It gets worse. Therefore, the Si content cannot be less than 2.0% in order to make the crystal grain size uniform.
In the present invention, by setting the content of Te and the like, which will be described later, to a specific range, it is possible to uniformly refine the crystal grains while keeping Si in a high range of 2.0 to 4.0%. became. From the viewpoint of reducing eddy current loss, the Si content is preferably 2.5% or more, more preferably 3.0% or more. On the other hand, the Si content is preferably 3.5% or less from the viewpoint of improving the magnetic flux density of the grain-oriented electrical steel sheet and the workability during rolling.

(0.007% <Te <0.02%)
In the present invention, the non-oriented electrical steel sheet contains Te in an amount of more than 0.007% and less than 0.02%. By setting the Te content within the above-mentioned specific range, the refinement of AlN is promoted, and an extremely excellent effect on the uniform refinement of crystal grains, which is a feature of the present invention, can be obtained. If it is 0.007% or less, the effect of refining AlN is hardly obtained. In order to obtain the invention effect sufficiently, 0.011% or more is preferable. On the other hand, when it is 0.020% or more, not only the effect is saturated, but also a part of it acts as a grain boundary segregation element, so that it becomes difficult to maintain the uniformity of the crystal grains. Therefore, 0.017% or less is preferable.

(0.02% ≤ Al ≤ 0.3%)
In the present invention, the non-oriented electrical steel sheet contains 0.02 to 0.3% of Al. Al combines with N, which will be described later, to form fine AlN, which effectively acts as pinning particles for uniform refinement of crystal grains. In the present invention, Al is preferably 0.03% or more from the viewpoint of obtaining a sufficient effect as AlN as pinning particles. Al, which does not form AlN and is in a solid solution state, can be expected to have the effect of increasing the electrical resistance of steel as in Si, but since it is difficult to finely control AlN, the upper limit is set to 0.30%. Generally, considering the amount of N contained in steel, 0.15% or less is sufficient. Further, it is preferable to keep the Al content low in order to avoid a decrease in the saturation magnetic flux density due to the Al content.

(0.002% ≤ N ≤ 0.01%)
In the present invention, the non-oriented electrical steel sheet contains 0.002 to 0.01% of N. N combines with the acid-soluble Al to form fine AlN, and effectively acts as pinning particles for uniform fineness of crystal grains. N is preferably 0.003% or more from the viewpoint of obtaining a sufficient effect as AlN as pinning particles. On the other hand, even if a large amount of AlN is contained to form a large amount of AlN, not only the effect is saturated, but also the AlN hinders the movement of the domain wall when a magnetic field is applied, which worsens the iron loss. Further, if AlN is not formed and remains as a solid solution N, the magnetic characteristics deteriorate due to magnetic aging. Therefore, it is preferably 0.008% or less, and more preferably 0.006% or less.

(C ≤ 0.005)
In the present invention, the non-oriented electrical steel sheet has a C content of 0.005% or less. By setting the content to 0.005% or less, magnetic aging can be suppressed and an excellent non-oriented electrical steel sheet can be obtained. As will be described later, C can be used as an element for controlling transformation on the premise of decarburization in the manufacturing process, but there is no merit to include it in the obtained non-oriented electrical steel sheet. Therefore, the content of the non-oriented electrical steel sheet of the present invention is preferably zero.

(Mn ≤ 0.20)
In the present invention, the non-oriented electrical steel sheet preferably has a Mn content of 0.20% or less. When Mn is contained and S is further contained, Mn combines with S described later to form MnS. MnS acts as a precipitation nucleus of AlN, which is the point of the present invention, but it is difficult to precipitate MnS finely enough to expect the effect of the present invention, and AlN generated with MnS as a nucleus has the effect of the present invention. Makes little contribution. Therefore, even if an appropriate amount of Te, Al and N is contained, it becomes difficult to form sufficiently fine AlN necessary for obtaining the effect of the present invention. From this viewpoint, the lower the Mn content, the more preferable, 0.10% or less, and further preferably zero. Further, it is preferable to keep the Mn content low in order to avoid a decrease in the saturation magnetic flux density due to the Mn content.

(S ≦ 0.0030)
In the present invention, the non-oriented electrical steel sheet preferably has an S content of 0.0030% or less. When S is contained and further Mn is contained, S combines with Mn to form MnS. As described above, MnS inhibits the effect of the present invention. From this viewpoint, the lower the S content, the more preferable, 0.0010% or less, and further preferably zero.

(Mg, Ca, REM)
In order to detoxify the above-mentioned MnS, the non-oriented electrical steel sheet of the present invention preferably contains one or more of Mg, Ca, and REM, which are known as sulfide-forming elements stronger than Mn. In order to coarsen the sulfide to avoid the formation of insufficiently fine MnS and to detoxify the formation of sufficiently fine AlN, which is a key point in the present invention, one or more types of Mg and Ca should be added in total. It preferably contains 0.0005% or more and / or 0.0030% or more of REM. The upper limit is not particularly limited, but considering the upper limit of the amount of S, it is sufficient to contain 0.0030% in total for one or more types of Mg and Ca, and 0.030% for REM. Preferably, the total amount is 0.0008 to 0.0015% for one or more of Mg and Ca, and 0.0050 to 0.010% for REM.

The chemical composition is the composition of the steel constituting the steel sheet. If the steel sheet used as the measurement sample has an insulating film or the like on the surface, the measurement is performed after removing the insulating film or the like.
Examples of the method for removing the insulating film of the non-oriented electrical steel sheet include the following methods.
First, the non-oriented electrical steel sheet having an insulating film, etc., aqueous sodium hydroxide (NaOH: 10 _{wt% +} H 2 O: 90 wt%) in 15 minutes at 80 ° C., immersion. Then, it is immersed in an aqueous sulfuric acid solution (H ₂ SO ₄ : 10% by mass + H ₂ O: 90% by mass) at 80 ° C. for 3 minutes. Thereafter, an aqueous solution of nitric acid _(HNO 3: 10 _{wt% +} H 2 O: 90 wt%) by normal temperature for 1 minute just under (25 ° C.), washed immersed in. Finally, dry with a warm air blower for a little less than 1 minute. As a result, a steel sheet from which the insulating film described later has been removed can be obtained.

The content ratio of each element in the non-oriented electrical steel sheet can be measured by the following method according to the type of element under known measurement conditions.
Si, Te, Al, Mn, Mg, Ca, and REM can be measured by inductively coupled plasma mass spectrometry (ICP-MS method).
C and S can be measured by the combustion infrared absorption method.
Further, N can be measured by the heat melting-heat conduction method.

Specifically, first, a non-oriented electrical steel sheet to be measured is prepared. A part of the non-oriented electrical steel sheet is cut into pieces and weighed, and this is used as a measurement sample. In the combustion infrared absorption method and the heat melting-heat conduction method, the faceted measurement sample can be used as it is. Further, the measurement sample is dissolved in an acid to prepare an acid solution, the residue is collected from a filter paper and separately melted in an alkali or the like, and the melt is extracted with an acid to form a solution. By mixing the solution and the acid solution and diluting it if necessary, an ICP-MS measurement solution can be obtained.

The non-oriented electrical steel sheet of the present invention has an average crystal grain size of 15 μm or less. When the average crystal grain size is 15 μm or less, a high-strength non-oriented electrical steel sheet can be obtained. It is preferably 12 μm or less, more preferably 9 μm or less.

Further, in the non-directional electromagnetic steel sheet of the present invention, the standard deviation / average crystal grain size of the crystal grain size is preferably 0.30 or less, and more preferably 0.20 or less. The smaller the standard deviation / average crystal grain size of the crystal grain size, the smaller the variation in the material, which is preferable from the viewpoint of reducing the variation in iron loss.

The steel sheet of the present invention is basically a so-called completely recrystallized structure, but the remaining processed structure can be tolerated. The present invention is characterized in that the variation in iron loss is reduced by uniform refinement of crystal grains, and when the crystal structure is adjusted by cold rolling and finish annealing as described later, the crystal grains are uniformly refined. In terms of points, it is advantageous to lower or shorten the annealing temperature. Therefore, if the conditions are controlled near the limit, even if it is macroscopically judged to be completely recrystallized, it generally occurs that a few percent of the unrecrystallized structure remains in a microscopic viewpoint or a peculiar region. obtain. Further, in order to give priority to ensuring the strength, it is possible to intentionally shorten the annealing condition at a low temperature for a short time to leave an unrecrystallized structure.
The steel of the present invention enjoys the effect of the present invention that the crystal grain size is made finer and more uniform in the recrystallized region even in such an incomplete recrystallized structure, and the variation in iron loss is small. be able to. Further, in the steel sheet of the present invention, as will be described later, the hot-rolled structure also contributes to the miniaturization and homogenization of the crystal grain size, so that the unrecrystallized structure, which is a processed structure of the hot-rolled structure, is also made uniform. It is possible that there is.
However, in the steel sheet of the present invention, the crystal grain size is a basic feature for achieving high strength, and the recrystallization rate should be 50% or more so that the recrystallized structure region becomes the main component. It is also preferable from the viewpoint of achieving high strength. Further, considering the influence on the magnetic properties, the unrecrystallized structure has a particularly large adverse effect on iron loss, so the recrystallization rate is preferably 70% or more, more preferably 85% or more.

In the present invention, the average crystal grain size and the standard deviation of the crystal grain size in the steel plate are obtained from the measurement data of the crystal orientation by Electron Backscatter Diffraction (EBSD) after polishing the cross section of the steel plate.
As described above, the crystal structure of the steel sheet of the present invention may include an unrecrystallized region (processed structure), and the measurement of the crystal grain size in the present invention shall exclude such a region. ..
Specifically, in the EBSD data, the observation region is first divided into crystal grain regions having a crystal grain boundary of 15 ° or more. At the same time, for each measurement data, the KAM value is obtained by the Kernel Average Measurement method (KAM method), and the average value of the KAM values is obtained in each crystal grain region classified as described above. Then, the crystal grain region having an average KAM value of less than 1 ° is defined as a recrystallized grain, and the crystal grain region having an average KAM value of 1 ° or more is defined as an unrecrystallized grain.
For the average crystal grain size and the standard deviation of the crystal grain size of the steel plate of the present invention, the average grain size and the standard deviation of the recrystallized grains are obtained. Further, the recrystallization rate can be obtained by the percentage of the value obtained by dividing the total area of the recrystallized region by the total area of the recrystallized region and the unrecrystallized region.

The thickness of the non-oriented electrical steel sheet of the present invention may be appropriately adjusted according to the intended use and is not particularly limited, but is usually 0.10 mm or more and 0.50 mm or less from the viewpoint of manufacturing. More preferably, it is 0.15 mm or more and 0.50 mm or less. From the viewpoint of the balance between magnetic characteristics and productivity, 0.15 mm or more and 0.35 mm or less is preferable.

(Application of non-oriented electrical steel sheet)
The non-directional electromagnetic steel plate of the present invention is used in various applications such as servo motors used in electric devices, stepping motors, compressors of electric devices, motors used in industrial applications, electric vehicles, hybrid cars, and train drive motors. It can be suitably applied to any conventionally known application in which a non-directional electromagnetic steel plate is used, such as a generator, an iron core, a choke coil, a reactor, a current sensor, etc., and particularly an application requiring high strength (for example, an electric vehicle). It can be more preferably used by the motor of the above.

B. Method for manufacturing grain-oriented electrical steel sheet The following describes an example of a preferred embodiment of the method for manufacturing grain-oriented electrical steel sheet of the present invention. This description is merely an example of a preferable manufacturing method, and the steel sheet of the present invention is not limited to the manufacturing method described here.

In the first aspect of the method for producing a non-directional electromagnetic steel sheet according to the present invention, Si is 2.0% by mass or more and 4.0% by mass or less, Te is more than 0.007% by mass and less than 0.02% by mass, and Al. 0.02% by mass or more and 0.3% by mass or less, N is 0.002% by mass or more and 0.01% by mass or less, C is 0.005% by mass or less, and the balance is from Fe and impurities. A step of hot-rolling the slab to make a hot-rolled plate, a step of annealing the hot-rolled plate, a step of cold-rolling the annealed hot-rolled plate to make a cold-rolled steel plate, and a cold-rolled steel plate. It is characterized by having a step of finish annealing and setting the annealing temperature in the finish annealing to be equal to or higher than the temperature at which 50% of the structure is recrystallized and 950 ° C. or lower.

According to the method for manufacturing non-oriented electrical steel sheets of the present invention, high-strength non-oriented electrical steel sheets with small variation in iron loss can be produced.

In the first aspect of the method for producing a non-directional electromagnetic steel plate according to the present invention, first, Si is 2.0% by mass or more and 4.0% by mass or less, and Te is more than 0.007% by mass and less than 0.05% by mass. , Al is 0.02% by mass or more and 0.3% by mass or less, and N is 0.002% by mass or more and 0.01% by mass or less, C is 0.005% by mass or less, and the balance is Fe and Prepare a slab consisting of impurities.
A molten steel for manufacturing non-oriented electrical steel sheets, which is appropriately prepared to the above composition, is cast to obtain a slab (steel ingot) having the above composition. The casting method is not particularly limited, and a conventionally known method can be appropriately selected and used.

By using a slab having the above composition, in each step of the production method of the present invention described later, A.I. The "miniaturization and homogenization of the crystal structure by optimizing the contents of Te, Al and N" described in the non-oriented electrical steel sheet is achieved.

Next, the obtained slab is hot-rolled.
In the process of hot rolling and hot rolling plate annealing, which will be described later, the steel material undergoes processing and heat treatment, so that the structure is deformed and recrystallized. In this process, the refinement and homogenization of the crystal structure is achieved by optimizing the Te, Al and N contents.

In the present invention, the conditions for hot rolling are not particularly limited and may be adjusted as appropriate. For example, the surface temperature of the slab is preferably heated in the range of 1000 ° C. or higher and 1400 ° C. or lower.
By heating to 1000 ° C. or higher, efficient hot rolling can be carried out without impairing productivity. On the other hand, from the viewpoint of magnetic characteristics, a surface temperature of 1400 ° C. or lower is sufficient, and by setting the surface temperature to 1200 ° C. or lower, careless coarsening of the hot-rolled structure can be suppressed.
Further, in the present invention, the holding time of the surface temperature of the slab may be appropriately adjusted. It is preferably 5 minutes or more from the viewpoint that a non-oriented electrical steel sheet having excellent magnetic characteristics and suppressed variation can be obtained. On the other hand, 90 minutes or less is sufficient from the viewpoint of magnetic characteristics, and 90 minutes or less is preferable from the viewpoint of improving productivity and suppressing manufacturing costs.
The finishing temperature and winding temperature of hot rolling may be appropriately adjusted within a known range. As a general temperature, a finishing temperature of 700 to 950 ° C. and a winding temperature of 500 to 750 ° C. can be mentioned.
The thickness of the steel sheet after hot rolling is not particularly limited, but can be, for example, 1.8 to 3.5 mm. Other conditions relating to hot rolling are not particularly limited and may be adjusted as appropriate.

After hot rolling, hot-rolled sheet is annealed for the purpose of improving magnetic properties. The hot-rolled plate annealing is not particularly limited, and a known method may be appropriately selected. For example, hot-rolled sheet annealing can be carried out in a temperature range of 750 to 1200 ° C. for 30 seconds to 10 minutes. The steel sheet after hot rolling and annealing may be pickled, if necessary.

In the process of hot-rolling to hot-rolled sheet annealing, the steel material is processed and heat-treated, so that the structure is deformed and recrystallized. In this process as well, the same phenomenon as the above-mentioned "miniaturization and homogenization of crystal structure by optimizing the contents of Te, Al and N", which is a characteristic phenomenon of the electrical steel sheet of the present invention, may occur. Conceivable. This phenomenon acts on the hot-rolled steel sheet before cold-rolling, and as a contribution, the structure of the hot-rolled sheet becomes uniform and fine, which is the present invention in the subsequent recrystallization structure formation in cold-rolling and finish annealing. It works advantageously to obtain a fine and uniform structure, which is a characteristic of steel sheets.

Next, the steel sheet after hot rolling and annealing is cold-rolled. The intermediate annealing conditions in the cold rolling are not particularly limited, and for example, appropriate conditions may be selected such as carrying out in a temperature range of 750 to 1200 ° C. for 30 seconds to 10 minutes. The plate thickness after cold rolling is not particularly limited, but can be, for example, about 0.1 to 0.5 mm.

Subsequently, finish annealing is performed. The crystal structure is recrystallized by finish annealing. As described above, the recrystallization rate is preferably 70 to 100%.
The present invention is characterized in that the annealing temperature in the finish annealing is not more than the temperature at which 50% of the structure is recrystallized and not more than 950 ° C. According to the production method of the present invention, the effect of AlN as a pinning particle that suppresses grain growth in finish annealing lasts up to a high temperature, so that it is higher than that of a general steel sheet that imparts steel sheet strength by refining the crystal structure. Annealing at temperature is possible.
Since such a high annealing temperature makes the crystal structure uniform, it is possible to manufacture a high-strength non-oriented electrical steel sheet with small variation in iron loss.
Further, as for the time as well as the temperature, it can be annealed for a long time as compared with a steel sheet that imparts steel sheet strength by miniaturizing a general crystal structure, and the likelihood of the time range is wide. Since the annealing temperature for such a long time makes the crystal structure uniform, it is possible to manufacture a high-strength non-oriented electrical steel sheet with small variation in iron loss.

By carrying out the above-mentioned production, the growth of crystal grains is suppressed, so that a non-directional electromagnetic steel plate having crystal grains having an average crystal grain size of 15 μm or less, high strength and small material variation can be obtained. Can be done.

In the second aspect of the method for producing a non-directional electromagnetic steel sheet according to the present invention, Si is 2.0% by mass or more and 4.0% by mass or less, Te is more than 0.007% by mass and less than 0.02% by mass, and Al. 0.02% by mass or more and 0.3% by mass or less, N is 0.002% by mass or more and 0.01% by mass or less, and C is 0.05% by mass or more and 0.10% by mass or less, and the balance A step of hot-rolling a slab composed of Fe and impurities to make a hot-rolled plate, a step of annealing the hot-rolled plate, and a step of cold-rolling the annealed hot-rolled plate to make a cold-rolled steel plate. The cold-rolled steel sheet is finished and annealed, and the annealing temperature is set to 950 ° C. or higher, which is a temperature at which 50% of the structure is recrystallized in the finishing annealing.
In the second aspect, A. The steel material has an α-γ transformation point by increasing the content ratio of C in the slab to 0.05 to 0.10% with respect to the non-oriented electrical steel sheet after production described in 1.
Here, the "α-γ transformation point" means a temperature at which the formation of the γ phase starts during heating in a steel material which is an α single phase at room temperature. This temperature can be determined by measuring the behavior of thermal expansion with heating, commonly referred to as the Formaster test.

By increasing the content ratio of C in the slab to 0.05 to 0.10%, the steel material is assumed to have an α-γ transformation, and the hot rolling is performed under the condition that the α-γ transformation occurs during the hot rolling. Can be carried out at. The transformation causes the coarse crystal structure derived from the casting and slab heating structure to become finer, and rolling the fine structure makes it possible to uniformly disperse the recrystallized nucleation sites in the processed structure. The structure of the hot-rolled sheet can be further refined and made uniform.
In a general manufacturing method, a slab having a low C content is used as a material in order to avoid magnetic aging due to C. Therefore, in the production of a steel sheet containing 2.0% or more of Si, which is the subject of the present invention, α-γ transformation during hot rolling is rarely considered. On the other hand, in the production method of the present invention, the C content is lowered by decarburization annealing after hot rolling to avoid deterioration of magnetic aging, so that hot rolling is carried out in a slab having a high C content and is heated. It is possible to further miniaturize and homogenize the structure by utilizing the α-γ transformation during interrolling. Hereinafter, the parts different from the first aspect and the second aspect will be described in detail.

When the C content in the slab is increased to 0.05 to 0.10% and the transformation during hot rolling is utilized to suppress the coarsening of the hot-rolled structure, the hot rolling conditions are heating. As long as the temperature is equal to or higher than the α-γ transformation point, the temperature is not particularly limited and may be adjusted as appropriate. For example, the surface temperature of the slab is preferably in the range of 1000 ° C. or higher and 1400 ° C. or lower so as to form a structure containing the γ phase. The α-γ transformation point of the slab having a composition containing 2.0% or more and 4.0% or less of Si containing 0.05 to 0.10% C is 1000 ° C. or less.

When the content ratio of C in the slab is increased to 0.05 to 0.10%, the obtained cold-rolled steel sheet is then subjected to decarburization annealing. The content ratio of C in the steel sheet is reduced to 0.005% or less by decarburization annealing. By reducing C to 0.005% or less, an excellent non-oriented electrical steel sheet without magnetic aging can be obtained. The decarburization annealing conditions are not particularly limited as long as the crystal grains can be enlarged and decarburized without making them non-uniform. For example, the process is carried out in a temperature range of 700 to 900 ° C. for 30 seconds to 3 minutes. The conditions may be selected as appropriate.

[Other processes]
In the above-mentioned production method, a coating step may be carried out after the finish annealing step. The coating generally imparts insulating properties when the electromagnetic steel sheets are laminated and used, and the type thereof is not particularly limited. The coating may be an organic component, an inorganic component, and may further contain an organic component and an inorganic component. The inorganic component is, for example, dichromate-boric acid type, phosphoric acid type, silica type and the like. The organic component is, for example, a general acrylic-based, acrylic styrene-based, acrylic silicon-based, silicon-based, polyester-based, epoxy-based, or fluorine-based resin. Considering the coatability, the preferable resin is an emulsion type resin. A coating that exhibits adhesiveness by heating and / or pressurizing may be applied. Adhesive coatings are, for example, acrylic, phenolic, epoxy, and melamine resins. The thickness of the coating is not particularly limited, but is generally 0.05 μm to 2 μm as the film thickness per one side.

The present invention is not limited to the above embodiment. The above-described embodiment is an example, and any object having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect and effect is the present invention. Is included in the technical scope of.

Hereinafter, the present invention will be specifically described with reference to examples. It should be noted that these descriptions do not limit the present invention.

[Manufacturing of non-oriented electrical steel sheets]
Using a slab having the composition shown in Table 1 as a material, an electromagnetic steel sheet "Sample A" was produced under the conditions of hot rolling, hot rolling plate annealing, cold rolling, decarburization annealing, and finish annealing described in Table 2. Further, under the conditions shown in Table 2, "Sample B" was produced in which the hot rolling finish temperature was set 20 ° C lower, the hot rolling winding temperature was set 20 ° C lower, and the finishing annealing temperature was set 10 ° C lower. The difference in the temperature conditions for producing the sample A and the sample B is inevitably generated in the production of the industrial electromagnetic steel sheet, and reproduces the production timing and the temperature fluctuation in the coil, which are the main causes of the variation in the obtained steel sheet characteristics. It is set as a model condition. In the present invention, using "Sample A" and "Sample B" produced under such different temperature conditions, the difference in crystal grain size and the resulting difference in iron loss are evaluated as variations in characteristics.
The manufacturing conditions adopted in Sample A are as shown in Table 2. Sample A and Sample B were manufactured under the same conditions, including the composition, except for the three conditions of hot rolling finish temperature, hot rolling winding temperature, and finish annealing temperature.

[Crystal structure evaluation]
A sample for crystal structure evaluation was taken from the manufactured steel sheet. After polishing the L-direction cross section of each sample, crystal orientation data was obtained by Electron Backscatter Diffraction (EBSD) for the field of view of plate thickness length × total plate thickness. Then, for Sample A and Sample B, the average crystal grain size, the standard deviation of the crystal grain size, and the recrystallization rate were obtained by the above-mentioned method. The evaluation was performed using the average crystal grain size of Sample A and Sample B, the standard deviation of the crystal grain size, and the average value of the recrystallization rate.
Since the value of the standard deviation of the particle size tends to increase as the average particle size increases, in this example, the variation in the particle size is evaluated by the standard deviation of the particle size / the average crystal particle size.

[Strength characteristic evaluation]
A JIS No. 5 tensile test piece in the L direction was collected from the manufactured steel sheet and subjected to a tensile test. Since the test material had a low content of C and N and no yield point was observed, 0.2% proof stress was used as the yield stress, and the average of the evaluation values of Sample A and Sample B was used as the strength characteristic of each material.

[Evaluation of variation in iron loss]
A 55 mm × 55 mm angular magnetic measurement test piece was sampled from the manufactured steel sheet, and the iron loss (W15 / 50) under the conditions of a maximum magnetic flux density of 1.5 T and a frequency of 50 Hz was measured in the rolling direction (0 °) and the rolling perpendicular direction (0 °). 90 °) was measured, and the average value in the rolling direction and the rolling perpendicular direction was obtained. The absolute value of the difference between the iron loss of sample A and the iron loss of sample B was defined as Δiron loss.

The evaluation results are shown in Table 3. The evaluation results will be described below.
The magnetic flux density and iron loss, which are the basic characteristic values of electrical steel sheets, vary greatly depending on the basic composition and plate thickness. Therefore, in this embodiment, the effects of various invention provisions are confirmed within a group of "series" in which the basic composition and the plate thickness are substantially constant. In addition, although there are some exceptions, the hot rolling conditions and heat treatment conditions are fixed within the series.
By doing so, the absolute values of the magnetic flux density and the iron loss became values within a reasonable range in each series, that is, characteristic values generally considered to be appropriate depending on the composition and the plate thickness. Therefore, in the following description, the evaluation of these absolute values will not be mentioned, and the description will focus on the effects of the invention.

Steel No. 1 to 6 are series in which the influence of Te content was confirmed. Steel No. 1 whose Te content is within the scope of the invention. In Nos. 2 to 5, the crystal grain size is made finer and the strength is increased, and the variation in particle size is reduced, and as a result, the variation in iron loss (Δ iron loss) is also reduced.

Steel No. 7 to 14 are series in which the influence of Al and N contents was confirmed. Steel No. having Al and N contents within the scope of the invention. In Nos. 8 to 11, the crystal grain size is made finer and the strength is increased, and the variation in particle size is reduced, and as a result, the variation in iron loss (Δ iron loss) is also reduced. In this series, the amount of C in the slab is increased and decarburization annealing is performed during manufacturing, and the finish annealing temperature is set higher than in other series. Especially small.
Steel No. with too low Al and N contents. In Nos. 7 and 13, since AlN, which is the point of the invention, is not sufficiently formed, the effect of the invention is hardly obtained, the crystal grains are coarsened, and the high strength is insufficient. Further, the steel No. having an too high Al or N content. In 12 and 14, the morphology of AlN is not optimal, but a large amount is precipitated, and although the coarsening of crystal grains is suppressed to some extent, the influence of the morphological change of the abundantly precipitated AlN is also large, and the particle size and the particle size and It is not possible to suppress variations in iron loss.

Steel No. Reference numerals 15 to 21 are series in which the influence of Mn and S contents was confirmed. The effects of Mn and S are as follows: Steel No. The influence of the Al and N contents confirmed in 7 to 14 is not so large, and it can be said that all of the present examples have practically good characteristic levels, but when viewed in detail, Mn and S are within the preferable range. Steel No. Nos. 18, 20 and 21 are slightly inferior in characteristics in terms of finer grain size and variation in grain size and iron loss. Steel No. Since 18, 20 and 21 have a high Mn or S content, a relatively large amount of MnS is formed, which seems to have inhibited the preferred form of AlN for the invention.

Steel No. Nos. 22 to 32 are series in which the influence of the presence or absence of metamorphosis depending on the amount of Si is confirmed. Steel No. Nos. 22, 23, 27, and 28 are steel types having a transformation-type composition and undergo transformation during the manufacturing process, so that the texture uniformity is not so bad. However, since the amount of Si is low, the strength level is low. Although not shown in the table, it is a steel type whose iron loss cannot be reduced due to its low electrical resistance, and is outside the scope of the present invention. In addition, steel No. By comparing 22 and 23, or 27 and 28, the effect of Te addition on the transformed steel can be confirmed, but a remarkable characteristic difference does not appear. Steel No. Although 29 and 31 are non-transformed steels, the composition such as the amount of Te and the amount of Al is not appropriate, and the fineness of the crystal grain size and the variation in the grain size and the iron loss, which are the focus of the present invention, are very low. Stay on the level.

Steel No. Nos. 33 to 41 confirm the change in the amount of C and the effect of the invention due to decarburization annealing in the manufacturing process. The amount of C was increased with a slab, and after undergoing transformation in the hot rolling process, the amount of C was reduced by decarburization annealing. The steel Nos. 34, 36, 39, and 41 were set to extremely low C from the time of the slab, respectively. Compared with 33, 35, 38, and 40, it can be seen that they are superior in grain refinement and variation reduction. In addition, steel No. 37 is the steel No. No. 36 was manufactured under the same conditions except for the slab heating temperature, but the effect of the invention was that of Steel No. 36. Compared with 36, it is a little insufficient. It is considered that this is because the slab heating temperature was low and the amount of γ phase formed by the transformation in the hot rolling process was small.

Steel No. Nos. 42 to 44 are examples in which the recrystallization rate is changed by changing the finish annealing temperature, assuming that the composition and basic production conditions are suitable. Since the finishing temperature is low, it is natural that the crystal grain size becomes finer, but even in a situation where the unrecrystallized structure remains, sufficient invention effects can be confirmed with respect to the variation in particle size and the variation in iron loss.

Claims (6)

A non-oriented electrical steel sheet having an average crystal grain size of less than 15 μm.
Si is 2.0% by mass or more and 4.0% by mass or less, Te is more than 0.007% by mass and less than 0.02% by mass, Al is 0.02% by mass or more and 0.3% by mass or less, and N is 0. contained .002 wt% 0.01 0% by mass, C is at most 0.005 wt%, Mn is not more than 0.20 mass%, S is not more than 0.0030 mass%, the balance being Ri Do Fe and impurities, the standard deviation / average grain size of the crystal grain size is 0.30 or less, the non-oriented electrical steel sheet. The non-oriented electrical steel sheet further contains 0.0005 % by mass or more and 0.0015% by mass or less of Mg and Ca and / or 0.0030 % by mass or more and 0.010% by mass or less of REM in total. , The non-oriented electrical steel sheet according to claim 1. The method for manufacturing a non-oriented electrical steel sheet according to claim 1.
Si is 2.0% by mass or more and 4.0% by mass or less, Te is more than 0.007% by mass and less than 0.02% by mass, Al is 0.02% by mass or more and 0.3% by mass or less, and N is 0. contained .002 wt% 0.01 0% by mass, C is at most 0.005 wt%, Mn is not more than 0.20 mass%, S is not more than 0.0030 mass%, the balance being A step of hot-rolling a slab composed of Fe and impurities to make a hot-rolled plate, a step of annealing the hot-rolled plate, and a step of cold-rolling the annealed hot-rolled plate to make a cold-rolled steel plate. It has a process of finishing and annealing the cold-rolled steel sheet.
A method for producing a non-oriented electrical steel sheet, which comprises setting the annealing temperature to a temperature at which 50% of the structure is recrystallized or more and 950 ° C. or less in the finish annealing. The method for manufacturing a non-oriented electrical steel sheet according to claim 1.
Si is 2.0% by mass or more and 4.0% by mass or less, Te is more than 0.007% by mass and less than 0.02% by mass, Al is 0.02% by mass or more and 0.3% by mass or less, and N is 0. .002 wt% 0.01 0% by mass or less, containing C of 0.10% or less by mass% 0.05 mass%, Mn of not more than 0.20 mass%, S is 0.0030 wt% or less , and the balance being Fe and impurities, and a step of slabs and hot-rolled to hot-rolled sheet having a composition with alpha-gamma transformation point, a step of annealing the hot-rolled sheet and the annealing It has a step of cold-rolling a hot-rolled sheet to obtain a cold-rolled steel sheet, a step of decarburizing and annealing the cold-rolled steel sheet, and a step of finishing and annealing the decarburized and annealed steel sheet.
The heating temperature in the hot rolling is equal to or higher than the α-γ transformation point.
By the decarburization annealing, the content ratio of C in the steel sheet was reduced to 0.005% by mass or less.
A method for producing a non-oriented electrical steel sheet, which comprises setting the annealing temperature to a temperature at which 50% of the structure is recrystallized or more and 950 ° C. or less in the finish annealing. The method for manufacturing a non-oriented electrical steel sheet according to claim 2.
Si is 2.0% by mass or more and 4.0% by mass or less, Te is more than 0.007% by mass and less than 0.02% by mass, Al is 0.02% by mass or more and 0.3% by mass or less, and N is 0. It contains .002% by mass or more and 0.010% by mass or less, C is 0.005% by mass or less, Mn is 0.20% by mass or less, S is 0.0030% by mass or less, and Mg. , Ca is contained in a total of 0.0005% by mass or more and 0.0015% by mass or less and / or REM is contained in 0.0030% by mass or more and 0.010% by mass or less, and the balance is heat of slab composed of Fe and impurities. A step of hot-rolling to make a hot-rolled plate, a step of annealing the hot-rolled plate, a step of cold-rolling the annealed hot-rolled plate to make a cold-rolled steel plate, and a process of finishing-anbling the cold-rolled steel plate Has a process and
A method for producing a non-oriented electrical steel sheet, which comprises setting the annealing temperature to a temperature at which 50% of the structure is recrystallized or more and 950 ° C. or less in the finish annealing. The method for manufacturing a non-oriented electrical steel sheet according to claim 2.
Si is 2.0% by mass or more and 4.0% by mass or less, Te is more than 0.007% by mass and less than 0.02% by mass, Al is 0.02% by mass or more and 0.3% by mass or less, and N is 0. .002% by mass or more and 0.010% by mass or less, C is 0.05% by mass or more and 0.10% by mass or less, Mn is 0.20% by mass or less, and S is 0.0030% by mass or less. In addition, a total of one or more types of Mg and Ca is contained in an amount of 0.0005% by mass or more and 0.0015% by mass or less and / or REM is contained in an amount of 0.0030% by mass or more and 0.010% by mass or less, and the balance is Fe and impurities. A step of hot-rolling a slab having a composition having an α-γ transformation point to obtain a hot-rolled sheet, a step of annealing the hot-rolled sheet, and a cold-rolling of the annealed hot-rolled sheet. It has a step of making a cold-rolled steel sheet, a step of decarburizing and annealing the cold-rolled steel sheet, and a step of finishing and annealing the decarburized and annealed steel sheet.
The heating temperature in the hot rolling is equal to or higher than the α-γ transformation point.
By the decarburization annealing, the content ratio of C in the steel sheet was reduced to 0.005% by mass or less.
A method for producing a non-oriented electrical steel sheet, which comprises setting the annealing temperature to a temperature at which 50% of the structure is recrystallized or more and 950 ° C. or less in the finish annealing .