JP4855225B2 - Non-oriented electrical steel sheet with small anisotropy - Google Patents

Description

  The present invention relates to a non-oriented electrical steel sheet with small anisotropy used as a core (iron core) material of a motor or a transformer.

  In recent years, interest in electric vehicles has increased from the viewpoints of environmental protection and energy saving, and drive motors have become a fundamental frequency around 800 Hz along with high-speed rotation and miniaturization.

  For this reason, in the non-oriented electrical steel sheet that is the core material of the motor, in order to reduce eddy current loss, the sheet thickness is reduced, the specific resistance is increased, and further the steel sheet strength (increasing the rotor rigidity) is improved. Therefore, it is necessary to increase the Si content and the Al content.

  Furthermore, non-oriented electrical steel sheets are also required to have a high magnetic flux density in order to improve the initial torque of the motor.

  A motor core is manufactured by punching a non-oriented electrical steel sheet. Usually, since a single core is punched from a non-oriented electrical steel sheet, the magnetic properties are determined by the rolling direction of the steel sheet (coil longitudinal direction, hereinafter referred to as “L direction”). In the magnetic characteristics in the L direction and 90 ° (coil width direction, hereinafter referred to as “C direction”), and in the L direction and 45 ° direction (anisotropy). Is desired to be small (for example, see Patent Documents 1 to 4).

  However, in Patent Documents 1 to 4 shown as examples, although anisotropy of magnetic flux density is studied and investigated, the anisotropy of high-frequency iron loss necessary for current electric vehicles, particularly, the highest high-frequency iron loss is deteriorated. There is insufficient research and investigation on high-frequency iron loss in a direction that forms an angle of 55 ° with the L direction (hereinafter, referred to as “X direction”).

  Also, a method of adjusting the iron loss at the commercial frequency in the L direction and the C direction of the steel sheet by controlling the tension in the furnace during recrystallization annealing is known, but this method also has the highest frequency iron loss. It does not control the high-frequency iron loss in the X direction (see, for example, Patent Documents 5 to 9).

JP 2006-45613 A JP 2006-45641 A JP 2006-144036 A JP 2006-199999 A Japanese Patent Publication No. 47-505 JP 58-120733 A JP-A-3-223422 JP-A-3-271323 JP-A-7-179947

  The present inventor has improved the high-frequency iron loss in the direction in which the high-frequency iron loss is most deteriorated in order to improve the magnetic characteristics as a punched core, particularly the high-frequency iron loss, in the non-oriented electrical steel sheet, Research and development were conducted to bring the iron loss closer to the L direction iron loss.

  As a result, in order to improve the anisotropy of the high-frequency iron loss in which the high-frequency iron loss varies depending on the direction, it is effective to perform cold rolling under strong pressure (hereinafter sometimes referred to as “strong rolling cold rolling”). On the other hand, it has been found that the magnetic flux density at the overall angle deteriorates.

  Furthermore, it has been found that adding a predetermined amount of Sn is effective in preventing the deterioration of the magnetic flux density.

  However, when the plate thickness of the steel sheet is reduced and the amount of Si and / or Al is increased, there is a phenomenon in which the high-frequency iron loss is abnormally deteriorated in the direction in which the high-frequency iron loss is most deteriorated (X direction). It occurred frequently. That is, the high-frequency iron loss in a specific direction is abnormally reduced, and eventually, the non-oriented electrical steel sheet is not suitable for an integral core.

  Therefore, an object of the present invention is to provide a non-oriented electrical steel sheet with small anisotropy having optimum magnetic characteristics as a motor core.

  The present inventor is a non-oriented electrical steel sheet by cold rolling under strong pressure of 0.1 to 0.3 mm thickness containing Si: 2 to 4% and Al: 0.3 to 2% by mass%. The basic idea is to add a predetermined amount of Sn to increase {100} goth-oriented grains and improve the magnetic properties (high-frequency iron loss) at the overall angle on the steel sheet surface, making it ideal for use as an integral core We have eagerly studied the means to ensure the proper magnetic properties. As a result, the following knowledge was obtained.

(X) The difference (anisotropy) in magnetic properties (particularly high-frequency iron loss) in the L, direction, C direction, and X direction is the product sheet thickness, the reduction ratio (cold rolling ratio) in cold rolling, Although related to the three factors of the steel sheet width shrinkage ratio during crystal annealing, finally, if these are appropriately controlled, a high-frequency iron loss W _10/800 with small anisotropy can be secured.

  (Y) The magnetic characteristics in the X direction (the direction of 55 degrees with respect to the L direction) connecting the magnetic characteristics in the L direction and the C direction have the largest high-frequency iron loss, and as a result, dominate the magnetic characteristics as a core. Thus, as an important indicator, the magnetic characteristics are closely related to the degree of shrinkage (shrinkage rate) of the steel sheet width particularly during recrystallization annealing.

  This invention was made | formed based on the said knowledge, and the summary is as follows.

(1) By mass%, C: 0.005% or less, Si: 2-4%, Mn: 1% or less, Al: 0.3-2%, Sn: 0.003-0.2% The hot-rolled sheet comprising the balance Fe and inevitable impurities is subjected to hot-rolled sheet annealing, and then subjected to cold rolling with a rolling reduction of 84.4 to 95% once, followed by recrystallization annealing. It is a non-oriented electrical steel sheet having a thickness of 0.1 to 0.3 mm manufactured by controlling the steel sheet width shrinkage rate to 0.5% or less,
The iron loss _{W 10/800} in the rolling direction (L direction) (L), the iron loss _{W 10/800} in the rolling direction and 55 ° direction (X direction) (X) is, magnetic properties satisfying the following formulas (1) A non-oriented electrical steel sheet having small anisotropy, characterized by comprising:
W _10/800 (X) / W _10/800 (L) ≦ 1.20 (1)

(2) The non-oriented electrical steel sheet with small anisotropy according to (1), wherein the iron loss W _10/800 is 40 W / kg or less in the magnetic characteristics.

( 3 ) The non-oriented electrical steel sheet having a small anisotropy according to (1) or (2) , wherein the hot-rolled sheet annealing is performed at a temperature exceeding 900 ° C.

  ADVANTAGE OF THE INVENTION According to this invention, the non-oriented electrical steel sheet which has an optimal magnetic characteristic as an object for motor cores, especially an integral stamping core can be provided.

The present invention contains, in mass%, C: 0.005% or less, Si: 2-4%, Mn: 1% or less, Al: 0.3-2%, Sn: 0.003-0.2% Then, after hot-rolled sheet annealing was performed on the hot-rolled sheet consisting of Fe and inevitable impurities, the cold rolling with a rolling reduction of 84.4 to 95% was performed once, and then recrystallization annealing was performed. A manufactured non-oriented electrical steel sheet having a thickness of 0.1 to 0.3 mm,
(I) _performing recrystallization annealing while controlling the steel sheet width shrinkage during recrystallization annealing to 0.5% or less; and (ii) iron loss W _10/800 (L) in the L direction and the X direction. The iron loss W _10/800 (X) in the direction of 55 ° (L direction and 55 °) has a magnetic characteristic that satisfies the following formula (1).
W _10/800 (X) / W _10/800 (L) ≦ 1.20 (1)

Here, W _10/800 is an iron loss at a magnetic flux density of 1.0 T and a frequency of 800 Hz.

  First, the reason for limiting the component composition of the hot-rolled sheet will be described. Hereinafter, “%” means mass%.

  C is an element that reinforces the steel sheet. However, C is an element harmful in terms of magnetic properties and is preferably reduced as much as possible. Therefore, C is limited to 0.005% or less. Preferably, it is 0.003% or less.

Since Si is an element that increases the electrical resistance of the steel sheet and reduces iron loss, it contains 2% or more. If the content exceeds 4%, the steel plate becomes brittle, and the required iron loss W _10/800 cannot be obtained. Therefore, the upper limit of Si was set to 4%.

  Mn is an element that fixes S as MnS at the time of hot rolling and prevents steel plate ear cracks during hot rolling. Solid solution Mn increases the electrical resistance of the steel sheet and reduces iron loss. However, if Mn is too much, crystal grain growth is inhibited, so the upper limit of Mn is set to 1%.

  Al, like Si, is an element that increases the electrical resistance of the steel sheet and reduces the iron loss, so it is contained in an amount of 0.3% or more. On the other hand, if the content exceeds 2%, there is a concern about the problem of addition cost and a decrease in saturation magnetic flux density, so the upper limit was made 2%.

  Sn increases the number of {100} face orientation grains during recrystallization annealing after cold rolling under strong pressure in a non-oriented electrical steel sheet containing Si: 2-4% and Al: 0.3-2%. In particular, in order to improve the magnetic properties (magnetic flux density) in the L direction and the C direction, it is necessary to contain 0.003% or more. On the other hand, even if the content exceeds 0.2%, the above improvement effect is saturated and wrinkles increase due to hot brittleness, so the upper limit was made 0.2%.

  In addition to the above elements, the present invention contains S, P, N, Cu, Ni, Cr, Ca, REM, etc. as inevitable impurities within a range not impairing the mechanical and magnetic properties of the present invention. Also good. However, as in the past, it is preferable that S, P, and N as impurities are small. All of these components are preferably 0.003% or less. The composition ranges confirmed not to inhibit the target anisotropy are Cu <0.2%, Ni <0.1%, Cr <0.1%, Ca <0.01%, Nb <0. 002%, Ti <0.003%, REM <0.01%.

In the present invention, a hot-rolled sheet having the above component composition is subjected to hot-rolled sheet annealing, then cold-rolled once, and then subjected to recrystallization annealing, a 0.1 to 0.3 mm-thick steel sheet is It has the magnetic characteristic which satisfy | fills Formula (1), It is characterized by the above-mentioned.
W _10/800 (X) / W _10/800 (L) ≦ 1.20 (1)

  In general, it is considered that the performance of a motor core in which a stator core is integrally punched is regulated by the most deteriorated iron loss in each direction. In other words, even if the iron loss characteristic in the L direction is excellent, if the iron loss characteristic in the other direction is greatly inferior, the performance of the motor core is dragged by the inferior iron loss characteristic, and the excellent core characteristic Can't get.

When the magnetic properties of a high Si, high Al non-oriented electrical steel sheet having a thickness of 0.1 to 0.3 mm, in which Si and Al are within the scope of the present invention, are examined at every angle of 5 °, high-frequency iron loss W ₁₀ The worst value of _{/ 800} was found to be the direction rotated by 55 ° from the L direction (X direction).

This X direction is a slightly different direction from the 45 ° direction (the direction rotated 45 ° from the L direction), which has been conventionally known as the worst value of the low frequency characteristics. The _details of why the direction of the worst value of the high-frequency iron loss W _10/800 is the direction rotated by 55 ° from the L direction (X direction) must wait for further investigation. It is estimated that the skin effect of the magnetic flux in the high frequency range is the result of organic entanglement with the gradient in the thickness direction of the texture of the steel sheet. In any case, W _10/800 (X) / W _10/800 (L) is a very important index for judging the accuracy of the non-oriented electrical steel sheet.

In the present invention, W _10/800 (X) / W _10/800 (L) is regulated to 1.20 or less. If it exceeds 1.20, the anisotropy between the directions of the high-frequency iron loss increases, and the iron loss characteristics as a motor core are unsatisfactory.

  Since the present invention requires that hot-rolled sheet is subjected to hot-rolled sheet annealing, then cold-rolled once, and then recrystallized annealing, the preferable manufacturing requirements are described next. To do.

  About hot-rolled sheet annealing, high temperature annealing is preferable. When the crystal grain size of the hot-rolled sheet is increased by this annealing, the {111} -oriented grains tend to decrease after cold rolling and recrystallization. Therefore, the annealing temperature is preferably 900 ° C. or higher.

The rolling reduction in cold rolling is important because it sensitively affects the index: W _10/800 (X) / W _10/800 (L). If the _rolling reduction is large, W _10/800 (X) / W _10/800 (L) is improved, but if it exceeds 95%, the magnetic flux density B ₅₀ is _greatly deteriorated. On the other hand, when the rolling reduction is less than 80%, it is necessary to roll the hot-rolled sheet to a thickness in a thin region that is difficult industrially, and industrial productivity is poor. In the present invention, the lower limit of the rolling reduction is 84.4% as confirmed in the examples.

The product thickness of the non-oriented electrical steel sheet is 0.1 to 0.3 mm. If the product plate thickness is reduced, the high-frequency iron loss is improved, but if it is less than 0.1 mm, the productivity is industrially poor. On the other hand, if the product plate thickness exceeds 0.3 mm, the high-frequency iron loss W _10/800 of the present invention is unsatisfactory.

  In recrystallization annealing, the amount of creep deformation of the steel sheet during annealing, particularly the shrinkage in the width direction of the steel sheet, is important because it strongly affects the high-frequency iron loss in the X direction.

  The steel sheet of the present invention is thin and requires high-temperature annealing (the present invention is thin with high specific resistance, so there is little eddy current loss, so the crystal grain size is relatively coarse. Therefore, it is necessary to control the reduction of the steel plate width with particular care because the steel plate width is easily reduced and the steel plate width is reduced during recrystallization annealing.

  The amount of steel plate deformation during recrystallization annealing must be managed by the shrinkage ratio of the steel plate width. The shrinkage ratio of the steel plate width is obtained by dividing the reduction amount of the steel plate width before and after the recrystallization annealing by the steel plate width before the recrystallization annealing and multiplying by 100.

Although it is difficult to grasp the degree of deterioration of the high-frequency iron loss characteristics in the X direction with the conventional steel sheet elongation rate, the present inventor has found that the steel sheet width shrinkage rate and the X direction iron loss W _10/800 (X). I found that the correlation was better. That is, as the deformation mode, it is estimated that capturing in the C direction (width direction) is closer to the X direction and more appropriate.

  Moreover, the management of the steel plate width is simple because it can be easily measured with a portable tape measure (elongation in the longitudinal direction is troublesome because a marking line or the like is previously placed on the steel plate surface and obtained from the elongation).

W _10/800 (X) / W _10/800 (L) deteriorates when the shrinkage ratio of the steel plate width increases. The limit is 0.5%. When the shrinkage ratio of the steel plate width exceeds 0.5%, the anisotropy of the iron loss is increased, which is unsatisfactory.

  The shrinkage ratio of the steel sheet width depends on the steel sheet tension in the furnace, the steel sheet temperature, the degree of matching of the circulating speed between the hearth rolls, the deformation amount of the steel sheet at the hot leveler for shape correction, and so on. .

The iron loss W _10/800 is preferably 40 W / kg or less. This is because it is applied to a high-speed rotation specification for making a compact motor core.

  Next, examples of the present invention will be described. The conditions of the examples are one example of conditions adopted for confirming the feasibility and effects of the present invention, and the present invention is limited to this one example of conditions. Is not to be done. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

Example 1
The component composition was adjusted while melting steel in a vacuum melting furnace, and an ingot having the component composition shown in Table 1 was cast. This was heated to 1000 ° C. and subjected to hot rolling to obtain a hot rolled sheet. Next, annealing was performed by soaking at 900 ° C. for 200 seconds in an N ₂ atmosphere. After pickling, it was cold rolled to a thickness of 0.23 mm (cold rolling rate of 80% and 92%).

Next, recrystallization annealing was performed by soaking at 1050 ° C. for 15 seconds in an H ₂ atmosphere. The average crystal grain size was 180 μm. The shrinkage ratio of the steel plate width by recrystallization annealing was 0.15%. The magnetic characteristics were measured for each angle with a 55 mm square SST. The obtained results are shown in Table 1.

The magnetic flux density B ₅₀ is a magnetic flux density (unit T) at a magnetizing force of 5000 A / m, and is an average of measured values in the L direction and the C direction. W _10/800 is an iron loss at a magnetic flux density of 1.0 T and a frequency of 800 Hz, and is an average of measured values in the L direction and the C direction.

  The average crystal grain size was obtained by counting and averaging the number of crystal grain boundaries intersecting the line segment in the L direction in the structure obtained by observing the cross section of the steel sheet with an optical microscope.

The A value is defined by the following equation.
A value = W _10/800 (X) / W _10/800 (L)

  Example 2 and subsequent examples are also based on these symbols.

  If the amount of added Sn increases, the A value decreases, the anisotropy is improved, and the magnetic flux density tends to be improved. In particular, it can be seen that the effect of Sn addition is remarkable in cold rolling under strong pressure.

(Example 2)
In mass%, C: 0.003%, Si: 3%, Mn: 0.15%, Al: 0.4%, S: 0.0001%, N: 0.0010%, Sn: 0.05% The ingot containing was heated to 1200 ° C. to obtain hot-rolled sheets having various plate thicknesses shown in Table 2. After soaking at 1150 ° C. for 60 seconds in a N ₂ atmosphere and performing hot-rolled sheet annealing, it was cold-rolled to a thickness of 0.28 mm.

Next, recrystallization annealing was performed by soaking at 900 ° C. for 10 seconds in a 20% H ₂ + 80% N ₂ atmosphere. The average grain size was 50 μm. The shrinkage ratio of the steel plate width was 0.3%. The obtained results are shown in Table 2.

  It can be seen that as the cold rolling rate increases, the A value indicating anisotropy is improved. Moreover, it turns out that the outstanding magnetic flux density is obtained in the cold rolling rate of this invention range.

(Example 3)
In mass%, C: 0.002%, Si: 2.9%, Mn: 0.22%, Al: 1.1%, S: 0.001%, N: 0.0012%, Sn: 0.00. The slab containing 12% was heated to 1150 ° C. to obtain a 1.8 mm thick hot rolled coil.

  When other components (as inevitable impurities) were analyzed, P: 0.02%, Cu: 0.09%, Ni: 0.04%, Cr: 0.05%, Ca: 0.0013%, V: 0.001%, Ti: 0.002%, Nb: 0.001%, Mo: 0.002%, Sb: 0.0001%.

This hot-rolled coil was soaked at 910 ° C. for 100 seconds in an N ₂ atmosphere and subjected to hot-rolled sheet annealing, and then cold-rolled to 0.11 mm (cold rolling rate of 93.9%). The steel plate width was 1000 mm. Next, soaking at 1000 ° C. for 15 seconds was performed in a so-called floating furnace in which a 50% H ₂ + 50% N ₂ atmosphere was blown from below the steel plate.

The steel sheet tension in the furnace is 0.1 to 0.3 kgf / mm ^2, and the amount of shrinkage of the steel sheet width is adjusted by adjusting the amount of pressing of the central roll in the three hot levelers at 700 ° C. in the cooling zone. changed. The average grain size was 100 μm. The results are shown in Table 3.

B value = W _10/800 (C) / W _10/800 (L).

From Table 3, it can be seen that when the width shrinkage ratio (shrinkage ratio of the steel sheet width) increases and exceeds the range of the present invention, the high-frequency iron loss in the X direction is greatly deteriorated. Also, according to the B value, the high frequency iron loss in the C direction seems to be less problematic until the width shrinkage rate is 0.71%. In addition, when measured with the index W _15/50 (C) / W _15/50 (L), the experiment No. They were 1.09, 1.10, 1.10, 1.11 and 1.35 in the order of 1 → 5, respectively.

  From these facts, it can be seen that in order to obtain a core excellent in high-frequency iron loss, the shrinkage ratio in the width direction of the steel sheet must be strictly controlled within the scope of the present invention.

  As described above, according to the present invention, it is possible to provide a non-oriented electrical steel sheet having optimum magnetic properties for a motor or transformer core. Therefore, the present invention has great applicability in the electrical equipment manufacturing industry using non-oriented electrical steel sheets as raw materials.

Claims (3)

In mass%, C: 0.005% or less, Si: 2-4%, Mn: 1% or less, Al: 0.3-2%, Sn: 0.003-0.2%, the balance being After hot-rolled sheet annealing is performed on a hot-rolled sheet made of Fe and inevitable impurities , cold rolling with a rolling reduction of 84.4 to 95% is performed once, and then recrystallization annealing is performed on the steel sheet during the annealing. A non-oriented electrical steel sheet having a thickness of 0.1 to 0.3 mm produced by controlling the width shrinkage rate to 0.5% or less,
The iron loss _{W 10/800} in the rolling direction (L direction) (L), the iron loss _{W 10/800} in the rolling direction and 55 ° direction (X direction) (X) is, magnetic properties satisfying the following formulas (1) A non-oriented electrical steel sheet having small anisotropy, characterized by comprising:
W _10/800 (X) / W _10/800 (L) ≦ 1.20 (1) The non-oriented electrical steel sheet with small anisotropy according to claim 1, wherein the iron loss W _10/800 is 40 W / kg or less in the magnetic characteristics. The non-oriented electrical steel sheet with small anisotropy according to claim 1 or 2 , wherein the hot-rolled sheet annealing is performed at a temperature exceeding 900 ° C.