JP2017057455A - Electromagnetic steel sheet and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic steel sheet having improved strength without deteriorating electromagnetic property and thermal conductivity and a manufacturing method therefor.SOLUTION: There is provided an electromagnetic steel sheet containing, by mass%, Si:2 to 4%, Al:1 to 3%, Ni:1.5 to 4% and the balance Fe with inevitable impurities and having 30000/μmor more of intermetallic compounds of Al-Ni with an average of equivalent circle diameters calculated in terms of area of 1 to 10 nm and a standard deviation of 1 or less deposited. The electromagnetic steel sheet is manufactured by hot rolling, cold rolling and annealing a steel slab with the above described component, then adding a plastic deformation to make dislocation density 1×10/mor more and further conducting an aging treatment at 400 to 600°C.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a magnetic steel sheet having improved strength and a method for producing the same, and more particularly to a high-strength non-oriented electrical steel sheet and a method for producing the same.

  In recent years, drive motors used in hybrid electric vehicles (HEV) and electric vehicles (EV) have been revolving at a high speed, and non-oriented electrical steel sheets used for iron cores of those drive motors have low iron loss. In addition to electromagnetic characteristics, there is an increasing demand for higher strength. For strengthening steel sheets, solid solution strengthening, precipitation strengthening, grain refinement strengthening, dislocation strengthening, transformation strengthening, etc. are applied. Absent. In addition, solid solution strengthening has a great effect on increasing the strength while avoiding deterioration of magnetic properties, but at the same time, there are problems of increased rolling load and brittle fracture, so that the addition amount has an upper limit from the viewpoint of productivity.

Conventionally, regarding the increase in strength of such a non-oriented electrical steel sheet, as shown in Patent Document 1, in mass%, C: 0.0400% or less, Si: 0.2-4.0%, Mn: 0.05-5.0%, P: It contains 0.30% or less, S: 0.020% or less, Al: 8.0% or less, N: 0.0400% or less, and is composed of the balance Fe and unavoidable impurities, and the structure is a volume fraction of ferrite phase: 50% or more, martensite phase: Disclosure of technology to improve strength of electrical steel sheet mainly composed of ferrite phase within the range satisfying 50% or less by containing an intermetallic compound with a diameter of 0.050 μm or less at a density of 20 / μm ³ or more inside the steel material. ing.

JP 2005-264315 A

  However, there is a problem that the electrical conductivity of the electrical steel sheet in which the intermetallic compound is precipitated in the steel material to increase the strength tends to deteriorate. As described above, since heat generation increases with the recent high-speed rotation, the motor core is required to have excellent thermal conductivity. To drive the drive motor at high speed, the thermal conductivity is not deteriorated. The appearance of electrical steel sheets with increased strength is desired.

  An object of the present invention is to provide an electrical steel sheet having improved strength without deteriorating electromagnetic characteristics and thermal conductivity, and a method for producing the electrical steel sheet.

  The present inventors have conducted various experiments and studies in order to obtain an electromagnetic steel sheet having improved strength without deteriorating electromagnetic characteristics and thermal conductivity. In order to solve the above-mentioned problems, the present inventors precipitate fine intermetallic compounds mainly composed of Al and Ni in steel, and appropriately control the average value and standard deviation of the equivalent circle diameter and the precipitation density. Thus, it has been found that the strength can be improved without deteriorating the electromagnetic characteristics and the thermal conductivity. The main point of the technology of the present invention is to cause dislocations in the steel sheet after annealing, and to disperse and precipitate a uniform intermetallic compound of Al-Ni as much as possible in the steel sheet using the dislocations as precipitation sites. It is to improve the strength without deteriorating the electromagnetic properties and thermal conductivity of the electrical steel sheet. According to the present invention, the following electrical steel sheet and its manufacturing method are provided.

(1)
In mass%, Si: 2 to 4%, Al: 1 to 3%, Ni: 1.5 to 4%, comprising the balance Fe and inevitable impurities,
An electrical steel sheet having an average value of equivalent circle diameters determined on an area basis of 1 to 10 nm and an Al—Ni intermetallic compound having a standard deviation of 1 or less is deposited at 30000 / μm ³ or more.
(2)
The electrical steel sheet according to (1), further containing 1 or 2% by mass of Cr: 0.01 to 4%, Cu: 0.01 to 4%, Sn: 0.01 to 0.2%. .
(3)
A steel slab containing Si: 2 to 4%, Al: 1 to 3%, Ni: 1.5 to 4% and consisting of the balance Fe and inevitable impurities in hot mass, cold rolling and A method for producing an electrical steel sheet, wherein after annealing, plastic deformation is performed so that the dislocation density is 1 × 10 ¹⁴ / m ² or more, and an aging treatment is further performed at 400 to 600 ° C.
(4)
The steel slab further contains 1% or more of Cr: 0.01 to 4%, Cu: 0.01 to 4%, Sn: 0.01 to 0.2% by mass%, (3) The manufacturing method of the electrical steel sheet as described in 2.

  According to the present invention, it is possible to obtain a non-oriented electrical steel sheet that is excellent in magnetic properties and thermal conductivity and improved in strength, fatigue strength, and wear resistance. As a result, it is possible to obtain a high-speed rotating motor that satisfies the characteristics required for recent hybrid electric vehicles (HEV), electric vehicles (EV), and the like, and a motor in which a magnet is incorporated in a rotor. Further, according to the present invention, other than the motor, for example, high efficiency, downsizing, and long life of the electromagnetic switch material can be achieved.

It is a TEM observation photograph of the intragranular precipitate of an Example.

  Embodiments of the present invention will be described below.

  First, the component composition in the electrical steel sheet of the present invention will be described. The electrical steel sheet according to the present invention is based on mass%, Si: 2 to 4%, Al: 1 to 3% or less, Ni: 1.5 to 4%, and the balance Fe and inevitable impurities. To do.

Si: 2-4%
Si increases the specific resistance of steel, reduces eddy currents, lowers iron loss, and increases tensile strength, but the effect is small when the amount added is less than 2.0%. Moreover, since work hardening ability increases by addition, it also has the effect of increasing effectively the dislocation density by the process implemented before an aging heat processing. On the other hand, if Si exceeds 4%, the steel is embrittled and further the magnetic flux density of the product is lowered, so the content is made 4% or less.

Al: 1-3%
In the present invention, Al is an important element that is positively added as a constituent element of the intermetallic compound, but if it exceeds 3%, embrittlement becomes a problem, so the upper limit is made 3%. Al is usually added as a deoxidizing agent, but it is also possible to suppress the addition of Al and deoxidize with Si. On the other hand, in order to obtain the effect of precipitation strengthening of intermetallic compounds, at least 1% is contained. In addition, solute Al is known to have an effect of increasing electric resistance and improving iron loss. For this purpose, it is effective to contain more Al than that which forms Al—Ni precipitates.

Ni: 1.5-4%
Conventionally, Ni has been generally used as a solid solution strengthening element or a precipitation strengthening element such as carbide, nitride or the like. In the present invention, Ni is contained in order to form an intermetallic compound with Al and develop precipitation strengthening due to the intermetallic compound of Al-Ni. In order to develop precipitation strengthening by the intermetallic compound of Al—Ni, 1.5% or more of Ni is necessary. On the other hand, excessive addition deteriorates the ductility of the steel sheet and lowers the sheet-passability. In addition, the magnetic flux density is lowered and it is sometimes difficult to suppress preferable formation of intermetallic compounds in the production process. Considering the addition cost, the upper limit is made 4%.

  Moreover, the electrical steel sheet of the present invention may further include, as an optional component, 1% by mass of Cr: 0.01-4%, Cu: 0.01-4%, Sn: 0.01-0.2%. You may contain 2 or more. These elements are known as elements forming an intermetallic compound in the electrical steel sheet targeted by the present invention, and can contain one or two or more as necessary. However, excessive content deteriorates the ductility of the steel sheet and lowers the sheet passability, and may make it difficult to suppress preferable formation of intermetallic compounds in the production process. Further, considering the addition cost, 0.01 to 4% for Cr, 0.01 to 4% for Cu, and 0.01 to 0.2% for Sn.

  The electrical steel sheet of the present invention is based on the above component composition, and consists of the remaining Fe and inevitable impurities.

  C may degrade the magnetic properties, so 0.0400% or less is preferable. On the other hand, there is also an effect of increasing the work hardening ability and effectively increasing the dislocation density by the processing performed before the aging heat treatment. From the viewpoint of manufacturing cost, it is advantageous to reduce the amount of C by degassing equipment at the molten steel stage, and if it is 0.0030% or less, the effect of suppressing magnetic aging is remarkable, and carbide etc. as the main means of increasing strength In the steel of the present invention that does not use this non-metallic precipitate, it is more preferably 0.0020% or less, and further preferably 0.0015% or less. It may be 0%.

  Mn is effective as an element for increasing the strength by solid solution and increasing the electric resistance and improving the iron loss, and the steel of the present invention can also be used in accordance with known techniques. In addition, there is an effect of increasing the work hardening ability and effectively increasing the dislocation density by the processing performed before the aging heat treatment. From the viewpoint of increasing the strength, this is not particularly necessary in the present invention using a fine intermetallic compound. Although it may be 0%, in the industrial production method using iron ore as a raw material, about 0.01% is inevitably contained.

  N, like C, degrades the magnetic properties, so 0.0400% or less is preferable. The inclusion has the effect of increasing the work hardening ability and effectively increasing the dislocation density by the processing performed before the aging heat treatment. In particular, in the present invention, N is preferably low in order to avoid the formation of strong nitrides with Al, and if it is 0.0027% or less, the effect of suppressing property deterioration due to magnetic aging and fine nitride formation is remarkable, and more preferable. May be 0.0022%, more preferably 0.0015% or less, and 0%.

  Cu significantly reduces the saturation magnetic flux density Bs of iron, and B50 (magnetic flux density [T] when the magnetizing force is 5000 [A / m]). Since lowering of Bs and B50 leads to lowering of motor torque, in the present invention, non-oriented electrical steel sheets having high strength and low iron loss without requiring the inclusion of Cu, and without lowering of Bs and B50, and The manufacturing method can be realized. On the other hand, increasing strength by Cu precipitation is also known, and the steel according to the present invention can also be used according to known techniques.

  For Nb, precipitates such as NbC are effective for increasing the strength, but these precipitates inhibit the domain wall movement and greatly deteriorate the iron loss. Therefore, it is not necessary to add Nb for this purpose. On the other hand, solid solution Nb is effective not only for solid solution strengthening but also for increasing strength and improving high-frequency characteristics by refining crystal grains, and can be used in the steel of the present invention in accordance with known techniques.

  P is an element having a remarkable effect of increasing the tensile strength by strengthening the solid solution, but it is not necessary to add it for this purpose. It may be 0%. On the other hand, the work hardening ability is enhanced by the addition, and there is also an effect of effectively increasing the dislocation density by the processing performed before the aging heat treatment. If it exceeds 0.3%, brittleness is severe, and it is difficult to perform hot rolling and cold rolling on an industrial scale, so the upper limit is preferably set to 0.30%, more preferably 0.10%. It is as follows.

  Since S forms sulfides and may deteriorate magnetic properties, particularly iron loss, the S content is preferably as low as possible and may be 0%. In this invention, 0.020% or less is preferable, More preferably, it is 0.0040% or less, More preferably, it is 0.0020% or less, More preferably, it is 0.0010% or less.

Next, the manufacturing method of the electrical steel sheet of this invention is demonstrated. First, the steel containing the above components is melted in a converter in the same manner as a normal electromagnetic steel sheet, and steel slab is formed by continuous casting, followed by hot rolling, cold rolling and annealing, and then the dislocation density is 1 × 10. A plastic deformation of ¹⁴ / m ² or more is added, and an aging treatment is further performed at 400 to 600 ° C. In addition to these steps, the formation of an insulating film and a decarburization step do not impair the effects of the present invention.

The plastic deformation which makes the steel plate after annealing a dislocation density of 1 × 10 ¹⁴ / m ² or more can be performed by, for example, skin pass rolling or leveler correction. Further, the dislocation density can be set to 1 × 10 ¹⁴ / m ² or more by processing when punching into a motor core shape. And after making a steel plate the dislocation density of 1 * 10 < ¹⁴ > / m < ² > or more by these skin pass rolling, leveler correction, a punching process, etc., aging treatment is further performed at 400-600 degreeC. By performing such plastic deformation and aging treatment, the average value of equivalent circle diameters determined on an area basis is 1 to 10 nm, and the Al—Ni intermetallic compound having a standard deviation of 1 or less is 30000 / μm. It is possible to obtain a non-oriented electrical steel sheet having both excellent electromagnetic properties such as low iron loss and high magnetic flux density and high strength, which is deposited ^three or more times, and having no deteriorated thermal conductivity.

  Conventionally, most of the elements used to increase the strength of electrical steel sheets are not only problematic in terms of the cost of addition, but also have an adverse effect on the magnetic properties, but the effect of increasing the strength is small and there is a problem in cost performance. was there. In the present invention, Si, Al, and Ni are contained for the purpose of increasing the strength, but their technical effects and technical purposes are completely different from those of the prior art. In other words, the conventional additive elements were mainly used as solid solution strengthening elements or precipitation strengthening elements such as carbides and nitrides, whereas in the present invention, an intermetallic compound of Al-Ni is formed and the precipitation strengthening effect thereby is achieved. It is contained for expression.

  In addition, solid solution strengthening by Ni or refinement of crystal grains causes a considerable deterioration of iron loss. In addition, in order to ensure the strength that the customer satisfies only by solid solution strengthening without refining the crystal grains, the content of Si, Al, Ni must be increased, the alloy cost increases, Furthermore, there are problems such as an increase in rolling load and a decrease in productivity due to embrittlement.

The reason why the dislocation density of the steel sheet after plastic working is 1 × 10 ¹⁴ / m ² or more is that enough dislocations are generated in the steel sheet by plastic working, and the dislocation is used as a precipitation site to make the size as uniform as possible in the steel sheet. This is because an intermetallic compound of Al—Ni is dispersed and precipitated. If the dislocation density is less than 1 × 10 ¹⁴ / m ² , the precipitation site of the intermetallic compound is insufficient, and an Al—Ni intermetallic compound having a number density of 30000 / μm ³ or more cannot be obtained after aging. End up. In addition, when the number density of Al—Ni intermetallic compounds is small, the average value of the equivalent circle diameter of the intermetallic compounds is larger than 10 nm, and the variation in the size of each intermetallic compound is also increased. Will exceed 1. In addition, when the dislocation density of the steel sheet after annealing exceeds 3 × 10 ¹⁶ / m ² , the electromagnetic characteristics deteriorate, and the size, standard deviation, and number density of the Al—Ni intermetallic compound after aging are further reduced. There is a risk of deviating from the scope of the invention. Therefore, it is desirable that the dislocation density of the steel plate after annealing is 3 × 10 ¹⁶ / m ² or less.

  The aging treatment is performed at 400 to 600 ° C. When the temperature is lower than 400 ° C., sufficient intermetallic compounds cannot be obtained. On the other hand, when the temperature exceeds 600 ° C., the formed intermetallic compounds become coarse. In this case, the holding time is preferably 1 to 120 minutes. If it is too short, a sufficient intermetallic compound cannot be obtained. On the other hand, if it is too long, the formed intermetallic compound becomes coarse. In addition, the heating rate, the cooling rate, and the like may affect the state of precipitates that is a feature of the present invention. These heat treatment conditions are determined in consideration of components, productivity and the like according to the target characteristics. A person skilled in the art can easily determine appropriate conditions by several trials in accordance with the technical idea of the present invention.

By passing through the manufacturing process as described above, the average value of the equivalent circle diameter determined on an area basis is 1 to 10 nm, and the Al—Ni intermetallic compound having a standard deviation of 1 or less is 30,000 / μm ³ or more. A high strength electrical steel sheet can be obtained without depositing and substantially impairing the magnetic properties and thermal conductivity. The tensile strength of the electrical steel sheet of the present invention is increased by 100 MPa or more, or the hardness is increased by 1.1 times or more by aging heat treatment for hardening. Moreover, the thing whose final intensity | strength after an aging treatment will be 600 Mpa or more is made into the object of this invention.

If a large amount of coarse compounds having an average equivalent circle diameter of an intermetallic compound exceeding 10 nm is formed, the efficiency of increasing the strength is lowered and the magnetic properties may be deteriorated. In the present invention, the strength of the electrical steel sheet is improved while maintaining excellent magnetic properties and thermal conductivity by generating fine intermetallic compounds with high density. On the other hand, if the average value of the equivalent circle diameter of the intermetallic compound is less than 1 nm, the strengthening ability is small. Furthermore, in order to reliably achieve high strength, it is necessary that the sizes of the individual intermetallic compounds are uniform so that the standard deviation of the equivalent circle diameter is 1 or less. If this standard deviation exceeds 1, the size of the intermetallic compound becomes non-uniform, and it becomes difficult to improve the strength of the electrical steel sheet while maintaining the magnetic properties and the thermal conductivity. As the intermetallic compounds of Al-Ni to form in the steel material, NiAl, such as _Ni 3 Al it is commonly known. In addition, it is known that the element ratio of these compounds varies considerably, and those containing some impurity elements also correspond to the present invention.

From the viewpoint of increasing the strength, the number density of intermetallic compounds needs to be deposited at 30000 / μm ³ or more. Control of the intermetallic compound size and number density is very important from the viewpoint of achieving both high strength and magnetic properties and preventing deterioration of thermal conductivity. This is because they not only affect the strength, magnetic properties, and thermal conductivity, but also the behavior in which the strength, magnetic properties, and thermal conductivity change when they are changed. That is, it is necessary to control to a region where the effect of increasing the strength is high and the magnetic property deterioration and the thermal conductivity deterioration are small. For this purpose, it is effective to appropriately control the components and heat treatment conditions, as well as the dislocation density before the aging treatment as described above, so that the size and number density of the intermetallic compound are within a desired range.

  In the present invention, since the refinement of the crystal structure is not used as a main means for increasing the strength, the crystal grain size can be adjusted to an optimum range from the viewpoint of magnetic properties. Since the size and density of the intermetallic compounds that contribute to high strength can be controlled not only by the components but also by the final heat treatment, the crystal grain size can be controlled before the heat treatment. The control can be performed independently of the control of the intermetallic compound by the holding time in the region. The crystal grain size is usually 300 μm or less, preferably 30 to 250 μm. More preferably, it is 60-200 micrometers. In general, when the frequency of exciting current when using a steel plate is high, it is preferable to keep the crystal grains fine. Further, the effect of the present invention is not impaired at all even if the crystal grain size is increased to several centimeters using secondary recrystallization or the like as in the case of grain-oriented electrical steel sheets.

  The effect of the present invention can be applied to a non-oriented or directional electrical steel sheet because it does not depend on the manufacturing process, regardless of the presence and type of the surface coating usually formed on the surface of the electrical steel sheet. Further, the use is not particularly limited, and it is applied to all uses where strength and magnetic properties are required, in addition to the use of a rotor of a motor used in home appliances or automobiles.

  The hot-rolled steel sheet melted in vacuum shown in Table 1 was pickled, cold-rolled to a thickness of 0.20 mm, and annealed. Thereafter, plastic deformation with the dislocation density shown in Table 1 was added, an aging treatment was performed at 350 to 750 ° C. for 2 hours, and magnetic properties and mechanical properties were evaluated. The results are shown in Table 1. In Table 1, numerical values outside the range of the present invention are underlined.

The material whose component is within the range of the present invention was obtained by performing an aging treatment at 550 ° C. × 2 hours after normal finish annealing, thereby increasing YP: 140 to 160 MPa, TS: 160 to 180 MPa without deterioration of iron loss ( Reaching YP: 570 to 910 MPa, TS: 710 to 1130 MPa). As shown in FIG. 1, by using dark field TEM observation in consideration of the difference in crystal structure between α-Fe and β′-NiAl using a high-resolution TEM, fine precipitates of about 5 nm are formed in the crystal grains. A large amount was observed at a density of 3,000 / μm ² , and it was found that this was the cause of the strength increase. In FIG. 1, precipitates that appear white are Al—Ni intermetallic compounds having a diameter of about 5 nm, and the number density is about 3,000 / μm ² . This is the mechanism of strength increase that was first found by using this observation technique. The thickness of the observation region of the dark field TEM observation is about 0.1 [mu] m, 3,000 pieces / [mu] m ² is equivalent to 30,000 / [mu] m ^3.

When the dislocation density after plastic deformation is about 5 × 10 ¹³ / m ² , the average equivalent circle diameter of the precipitate was as small as about 3 nm, but the standard deviation was larger than 1, and the number density was about 5000 / μm. ^It became very few with ³ . In this case, the strength increase after the aging treatment was not obtained, and YP = 480 MPa. Even when the dislocation density after plastic deformation is about 1 × 10 ¹⁴ / m ² , when the aging treatment temperature is 350 ° C., almost no Al—Ni precipitates are observed, and an increase in strength after aging treatment is obtained. There wasn't. On the other hand, when the dislocation density after plastic deformation is about 1 × 10 ¹⁴ / m ² and the aging treatment temperature is 750 ° C., precipitates having an equivalent circle average diameter of 10 nm or more increase, and the number density is about 20000 / μm. ^It was few with ³ . In this case, not only the increase in strength after the aging treatment was not obtained, but also the iron loss W10 / 800 was greatly deteriorated to 32.0 W / kg.

  Ten disc samples each having a diameter of 10 mm were cut from each material, and the thermal conductivity was measured by the laser flash method. As a result, the variation in the measured thermal conductivity was larger in the comparative example than in the material of the present invention. . This is presumed to be due to the large size distribution of the precipitates. In particular, when the standard deviation exceeds 1, the variation in the measured values of thermal conductivity is as large as about ± 10% on average.

  Further, YP was improved by adding 0.01% or more by mass of Cu, and in the examples of the present invention, YP830 MPa or more was obtained by addition of 1% or 2%. Addition of Cr was effective in reducing iron loss W10 / 800, and addition of Sn improved the magnetic flux density B50. The effect was acquired by adding 0.01% or more by mass%, respectively.

Claims (4)

In mass%, Si: 2 to 4%, Al: 1 to 3%, Ni: 1.5 to 4%, comprising the balance Fe and inevitable impurities,
An electrical steel sheet having an average value of equivalent circle diameters determined on an area basis of 1 to 10 nm and an Al—Ni intermetallic compound having a standard deviation of 1 or less is deposited at 30000 / μm ³ or more.   The electrical steel sheet according to claim 1, further comprising one or more of Cr: 0.01 to 4%, Cu: 0.01 to 4%, Sn: 0.01 to 0.2% in mass%. . A steel slab containing Si: 2 to 4%, Al: 1 to 3%, Ni: 1.5 to 4% and consisting of the balance Fe and inevitable impurities in hot mass, cold rolling and A method for producing an electrical steel sheet, wherein after annealing, plastic deformation is performed so that the dislocation density is 1 × 10 ¹⁴ / m ² or more, and an aging treatment is further performed at 400 to 600 ° C.   The steel slab further contains, by mass%, one or more of Cr: 0.01 to 4%, Cu: 0.01 to 4%, and Sn: 0.01 to 0.2%. The manufacturing method of the electrical steel sheet as described in 2.