JP2011084778A - Nonoriented electrical steel sheet for high frequency excitation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonoriented electrical steel sheet which has reduced deterioration in core loss even if compressive stress is acted thereon, by which deterioration in core loss caused by assembling of an iron core can be suppressed, and finally, which can contribute to the improvement in the efficiency of a high performance motor or the like. <P>SOLUTION: The nonoriented silicon steel sheet for high frequency has a composition comprising, ≤0.002% C, 0.1 to 4.0% Si, 0.1 to 4.0% Al, and the balance iron with inevitable impurity elements, and in which a core loss deterioration rate A defined by A=[W<SB>1</SB>-W<SB>0</SB>]/W<SB>0</SB>(W<SB>1</SB>denotes a core loss value in a high frequency region upon stress application of 30 to 50 MPa; and W<SB>0</SB>denotes a core loss value in a high frequency region upon no application of stress) is ≤50%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a non-oriented electrical steel sheet that contributes to improving the efficiency of an iron core used by high-frequency excitation, such as a hybrid vehicle and an air conditioner compressor.

  In recent years, due to the trend of carbon dioxide reduction and the problem of exhaustion of petroleum resources, to improve the efficiency of high-performance motors used in hybrid vehicles that use gasoline engines and electric motors in order to reduce exhaust gas and improve fuel efficiency. Orientation is increasing. Since electric motors are more responsive than those of engines and enable precise torque control, they are being developed for sports vehicles that require excellent driving performance as well as support for the global environment. The drive motor of these electric vehicles is the heart of a drive mechanism that replaces the engine of a conventional vehicle, and the electromagnetic steel sheet greatly contributes to the improvement of EV drive performance and fuel consumption as a core material. For this reason, the request | requirement of the iron loss improvement in the high frequency region of the non-oriented electrical steel sheet used as an iron core of a high performance motor is increasing more than before.

  Until now, many measures have been taken to reduce iron loss of non-oriented electrical steel sheets. For example, from the viewpoint of reducing eddy current loss, a method of increasing the specific resistance by increasing the content of Si or Al is common. In addition, a method is generally used in which impurities such as C, N, and S are reduced as much as possible to obtain high-purity steel to reduce hysteresis loss. In addition, as in the REM addition technique described in Patent Document 1, a method has been developed that achieves both improvement in productivity and reduction in iron loss by cleaning steel and improving crystal grain growth.

  In improving the iron loss of the non-oriented electrical steel sheet as described above, the iron loss is usually evaluated by a method defined in JIS. That is, the average value of the iron loss in the two directions in the rolling direction of the steel sheet and the direction perpendicular to the steel plate is only measured in the state where no external force is applied. However, in an actual iron core, the steel sheet is punched into a predetermined shape and then laminated and fixed by a method such as bolting or caulking. Further, in a compressor motor or the like, it is fixed to the outer frame by shrink fitting. For these bolted, caulked, and shrink-fitted iron cores, it is known that a compressive stress acts on the iron core in the circumferential direction in the steel sheet surface, and the iron loss increases due to this stress.

  In view of this, Patent Document 2 and Patent Document 3 propose non-oriented electrical steel sheets with small performance deterioration against in-plane compressive stress.

  Moreover, in patent document 4, the iron loss deterioration by a compressive stress is made by making X-ray random intensity ratio of {111} surface parallel to the plate surface in the plate | board thickness center layer of a steel plate into 2.5 or more and 10.0 or less. A small non-oriented electrical steel sheet has been proposed.

WO2004 / 099457 pamphlet JP 2003-253404 A JP 2005-307258 A JP 2008-189976 A

  An object of the present invention is to provide a non-oriented electrical steel sheet in which deterioration of iron loss is small even when compressive stress acts. As a result, iron loss deterioration due to the assembly of the iron core can be suppressed to a small extent, which ultimately contributes to improving the efficiency of high performance motors and the like.

  As a result of repeated studies on the influence of the material factor of the steel sheet on the stress dependence of the iron loss, the present inventors have found that the crystal grain size of the steel sheet has a large influence on the iron loss under the stress, and the compression stress Has led to the development of non-oriented electrical steel sheets with low iron loss degradation. The gist of the present invention is a non-oriented electrical steel sheet having a small crystal grain size and a low iron loss deterioration rate under stress.

The specific gist of the present invention is as follows.
(1) In mass%,
C: 0.002% or less,
Si: 0.1% or more and 4.0% or less,
Al: 0.1% to 4.0%,
A non-oriented electrical steel sheet for high-frequency excitation, comprising a balance iron and unavoidable impurity elements and having an iron loss deterioration rate A defined by the formula (I) of 50% or less.

A = [W ₁ −W ₀ ] / W ₀ (I)
Here, _{W 1} is the iron loss value in the high frequency region of stress at 30MPa~50MPa addition, _{W 0} denotes the iron loss value in the high frequency range in the absence of stressing.
(2) In mass%,
The non-oriented electrical steel sheet for high frequency excitation according to claim 1, further comprising Cr: 3.0% or less and / or Mn: 1.0% or less.
(3) W ₁ and W ₀ are both average values of iron loss values measured by exciting in the rolling direction (L direction) and the direction perpendicular to rolling (C direction) of the steel sheet. The non-oriented electrical steel sheet for high frequency excitation according to (1) or (2).
(4) W ₁ is an iron loss value by 1700 Hz excitation when a stress of 30 MPa is applied, and W ₀ is an iron loss value by 1700 Hz excitation when no stress is applied. A non-oriented electrical steel sheet for high frequency excitation according to any one of the above.
(5) The non-oriented electrical steel sheet for high frequency excitation according to any one of (1) to (4), wherein the non-oriented electrical steel sheet has an average grain size of 100 μm or less.
(6) The non-oriented electrical steel sheet for high frequency excitation according to any one of (1) to (5), wherein the non-oriented electrical steel sheet has an average crystal grain size of 40 μm or less.
(7) The non-oriented electrical steel sheet for high-frequency excitation according to any one of (1) to (6), which is used for a motor core.
(8) By mass%
C: 0.002% or less,
Si: 0.1% or more and 4.0% or less,
Al: 0.1% to 4.0%,
The slab composed of the remaining iron and unavoidable impurity elements is subjected to hot rolling as a hot-rolled sheet by hot rolling, the surface scale is removed by pickling, and then cold-rolled to obtain a final sheet thickness of 850 to 850. A method for producing a non-oriented electrical steel sheet for high-frequency excitation with a low iron loss deterioration rate due to compressive stress, wherein finish annealing is performed at 1000 ° C. for 10 seconds to 1 minute.
(9) The method for producing a non-oriented electrical steel sheet for high-frequency excitation according to (8), wherein the slab further includes, by mass%, Cr: 3.0% or less and / or Mn 1.0% or less.

  When the non-oriented electrical steel sheet of the present invention is used as a core material for a motor, even if a compressive stress acts on the iron core, the iron core has little deterioration in iron loss, and can ultimately contribute to improving the efficiency of the motor.

The micrograph of the cross-sectional metal structure of the steel plate in different finish annealing temperature is shown. The crystal grain size dependence of iron loss due to the addition of stress 0 to 50 MPa at 50 Hz is shown. It shows the crystal grain size dependence of iron loss due to the addition of stress 0 to 50 MPa at 800 Hz. It shows the crystal grain size dependence of iron loss due to the addition of stress 0 to 50 MPa at 1700 Hz. The crystal grain size dependence of the iron loss due to the addition of stress 0 to 50 MPa at 3000 Hz is shown. The crystal grain size dependence of the iron loss deterioration rate (%) due to the addition of stress 0 to 50 MPa at 50 Hz is shown. The crystal grain size dependence of the iron loss deterioration rate (%) due to the addition of stress 0 to 50 MPa at 800 Hz is shown. It shows the crystal grain size dependence of the iron loss deterioration rate (%) due to the addition of stress 0 to 50 MPa at 1700 Hz. The crystal grain size dependence of the iron loss deterioration rate (%) due to the addition of stress 0 to 50 MPa at 3000 Hz is shown.

The present invention is described in detail below.

In the present invention, in order to reduce the iron loss deterioration due to the in-plane compressive stress, the iron loss deterioration rate defined by the ratio of the deterioration amount of the iron loss value under the 30 MPa pressure to the iron loss value in the absence of stress is 50 % Or less. That is, A = [W ₁ −W ₀ ] / W ₀ (W ₁ is the iron loss value in the high frequency range when stress 30 MPa to 50 MPa is applied, and W ₀ is the iron loss value in the high frequency range when no stress is applied. The iron loss deterioration rate at 30 MPa defined by (1) is 50% or less.

  The present inventors have found that the crystal grain size must be 100 μm or less in order to make the iron loss deterioration rate defined above 50% or less. Specifically, steel containing 0.01% C, 2.0% Si, 2.0% Al, and 2% Cr is hot-rolled and then subjected to hot-rolled sheet annealing, cold rolling, and finish annealing. A non-oriented electrical steel sheet was produced. At that time, various conditions of finish annealing were changed to change the average crystal grain size of the steel sheet. The final plate thickness is 0.25 mm. FIG. 1 shows a photomicrograph of the finish annealing temperature and the cross-sectional metal structure of the obtained steel sheet. Table 1 shows the finish annealing temperature and the average crystal grain size of the obtained steel sheet. In addition, the average particle diameter was calculated | required by the equivalent circle diameter from the area which counted the grain concerning a surface and an edge part as 1/2, and divided the total area by the number of crystal grains.

  Next, a 55 mm × 55 mm plate was cut out from the obtained steel plate and used as a sample for magnetic measurement. For the magnetic measurement, a double-yoke type H coil method single plate testing machine capable of performing magnetic measurement while applying compressive stress to the cross section of the steel plate was used. The compressive stress is 30 to 50 MPa, and the stress direction and the excitation direction are parallel.

  FIGS. 2 to 5 show irons when excited at 50 Hz, 800 Hz, 1700 Hz, and 3000 Hz in the rolling direction (L direction) and the direction perpendicular to the rolling direction (C direction), respectively, when stress is 0, and 30 MPa and 50 MPa are applied. The crystal grain size dependence of the loss value (average value in the L direction and C direction) is shown.

  As shown in FIG. 2, at low frequency (50 Hz), the iron loss value tends to increase as the crystal grain size decreases with and without stress applied, whereas at high frequency (800 to 3000 Hz). Shows that when stress is applied, the iron loss value decreases in a region where the crystal grain size is less than 100 μm and the average crystal grain size exceeds 100 μm, and the iron loss increases as the crystal grain size increases. Has been. This is in contrast to the fact that the iron loss value does not change with the crystal grain size when no stress is applied at high frequencies. That is, at high frequencies, it has been found that the dependence of the iron loss value on the crystal grain size varies greatly between when stress is applied and when no stress is applied. The present invention intends to control the iron loss value at high frequency based on the knowledge.

  FIGS. 6 to 9 show, based on FIGS. 2 to 5, the crystal grains of the ratio (%) of the iron loss deterioration amount due to the addition of stress 30 MPa and 50 MPa to the iron loss value by stress 0 at 50 Hz, 800 Hz, 1700 Hz, and 3000 Hz, respectively Diameter dependence is shown. As can be seen in FIGS. 5 to 8, it can be seen that the iron loss deterioration rate decreases as the crystal grain size decreases. In particular, at high frequencies, it can be seen that the average crystal grain is effective to be 100 μm or less, more preferably 40 μm or less, in order to make the iron loss deterioration rate 60% or less.

  Next, the reasons for limiting the steel components of the present invention will be described.

  C is a harmful element that increases iron loss and causes magnetic aging, so it is 0.002% or less.

  Si is an element that increases specific resistance and decreases eddy current loss. In order to enjoy the effect, it is necessary to contain 0.1% or more. However, if the content is excessively increased, in addition to a decrease in magnetic flux density, a decrease in cold-rollability is caused and the cost is further increased.

  Al, like Si, is an element that increases the specific resistance and needs to be contained in an amount of 0.1% or more. On the other hand, if it increases too much, in addition to the decrease in magnetic flux density, it causes a decrease in cold-rollability and further increases the cost, so 4.0% or less.

  Cr can be added in an amount of 3.0% or less in order to increase the specific resistance and decrease the eddy current loss. However, if it exceeds 3.0%, the magnetic flux density decreases, so the upper limit is set to 3.0%. It was.

  Mn is an element effective for increasing the electrical resistance, similar to Si, but if added over 1%, crystal grain growth during annealing is inhibited, so it is made 1% or less. Since Mn renders S in steel harmless (MnS), it is preferable to add 0.1% or more.

  Other elements are not particularly specified, but elements such as Sn, Sb, and Cu can be added in an appropriate amount for the purpose of preventing nitridation from the surface layer, and S, N, Ti, etc. It is desirable to reduce as much as possible the elements that generate inclusions and adversely affect magnetic properties and grain growth. It is also possible to add REM to fix S and Ti to clean the steel.

  Next, the manufacturing method for obtaining the steel plate of this invention is demonstrated.

  One of the manufacturing methods is to use a slab to which a predetermined element is added in a steelmaking process as a hot-rolled sheet by hot rolling, and after removing the surface scale by pickling without performing hot-rolled sheet annealing, once After the cold rolling is performed to obtain a final plate thickness, finish annealing for recrystallization is performed in a range of 850 to 1000 ° C. for 10 seconds to 1 minute.

  In another method, a slab to which a predetermined element is added in the steel making process is hot rolled into a hot-rolled sheet, subjected to hot-rolled sheet annealing, the surface scale is removed by pickling, and then cold-rolled to the final sheet. The thickness is a method in which finish annealing is performed for recrystallization in the range of 850 to 1000 ° C. for 10 seconds to 1 minute.

  If the finish annealing temperature exceeds 1000 ° C. or the finish annealing time exceeds 1 minute, the average crystal grain size tends to exceed 100 μm and become coarse. Further, if the final annealing temperature is less than 1000 ° C. or the final annealing time is less than 10 seconds, recrystallization is insufficient.

The Example of this invention is shown.
Example 1
C: 0.0020%, Si: 2.0%, Al: 0.3%, Mn 0.2%, balance Fe and steel made of inevitable impurities are hot-rolled to 2.3 mm, and hot-rolled sheet annealing is performed. Without application, after pickling, it was cold-rolled to a thickness of 0.5 mm (rolling rate: 78.3%). Thereafter, finish annealing was performed at 900 ° C. for 15 seconds to cut out a 55 mm SST sample. The average crystal grain size was 38 μm. Next, excitation was performed at a frequency of 1700 Hz to a magnetic flux density of 1.0 T, and the iron loss in a stressed state of 30 MPa and the iron loss without stress were measured, and the iron loss deterioration rate was calculated. The results are shown in Table 2.
(Comparative Example 1)
As Comparative Example 1, steel having the same composition as Example 1 was hot-rolled to 2.3 mm, pickled, and cold-rolled to a thickness of 0.5 mm. Thereafter, finish annealing was performed at 1000 ° C. for 2 minutes, and a 55 mm SST sample was cut out. The average crystal grain size was 105 μm. Next, excitation was performed up to 1.0 T at a frequency of 1700 Hz, and the iron loss in a stressed state of 30 MPa and the iron loss without application of stress were measured, and the iron loss deterioration rate was calculated. The results are shown in Table 2.
(Example 2)
C: 0.0020%, Si: 3.1%, Al: 1.1%, Mn: 0.35% Steel made of the remaining Fe and inevitable impurities and hot rolled to 1.8 mm, The hot-rolled sheet was annealed for a minute, pickled, and cold-rolled to a thickness of 0.35 mm (rolling rate: 80.5%). Thereafter, finish annealing was performed at 900 ° C. for 30 seconds, a 55 mm SST sample was cut out, and the average crystal grain size was 50 μm. Next, excitation was performed up to 1.0 T at a frequency of 800 Hz, and the iron loss in the stressed state of 30 MPa and the iron loss without stress were measured, and the iron loss deterioration rate was calculated. The results are shown in Table 2.
(Comparative Example 2)
As Comparative Example 2, a steel having the same composition as Example 2 was hot-rolled to 1.8 mm, annealed at 1000 ° C. for 2 minutes, pickled and cold-rolled, and 0.35 mm thick (rolling rate) Was 80.5%), and then finish annealing was performed at 1050 ° C. for 1 minute, and a 55 mm SST sample was cut out. The average crystal grain size was 110 μm. Next, excitation was performed up to 1.0 T at a frequency of 1700 Hz, and the iron loss in a stressed state of 30 MPa and the iron loss without application of stress were measured, and the iron loss deterioration rate was calculated. The results are shown in Table 2.
(Example 3)
C: 0.0010, Si: 2.0%, Al: 2.3%, Cr: 2.0%, Mn: 0.4% Hot-rolled steel made of Fe and unavoidable impurities to 2.5 mm Then, hot rolling annealing was performed at 800 ° C. for 2 minutes, pickling and cold rolling to obtain a thickness of 0.25 mm (rolling rate: 90%). Thereafter, finish annealing was performed at 900 ° C. for 30 seconds, and a 55 mm SST sample was cut out and subjected to magnetic measurement.
(Comparative Example 3)
As Comparative Example 3, steel having the same composition as Example 3 was hot-rolled to 2.5 mm, hot-rolled sheet annealed at 1000 ° C. for 2 minutes, pickled and cold-rolled, and 0.25 mm thick (rolling rate) Was 90%), and then a final annealing was performed at 1200 ° C. for 15 seconds to cut out a 55 mm SST sample. Next, excitation was performed up to 1.0 at a frequency of 3000 Hz, and the iron loss in a stressed state of 30 MPa and the iron loss without stress were measured, and the iron loss deterioration rate was calculated. The results are shown in Table 2.

  Referring to Table 2, in Examples 1 to 3, the average crystal grain size is 100 μm or less and the iron loss deterioration rate is 50% or less, while in Comparative Examples 1 to 3 having the same composition, the average It can be seen that the crystal grains exceed 100 μm and the iron loss deterioration rate also exceeds 50%.

  When the non-oriented electrical steel sheet of the present invention is used as a core material for a motor, even if a compressive stress acts on the iron core, the iron core has little deterioration in iron loss, and can ultimately contribute to improving the efficiency of the motor. High availability on.

Claims (9)

% By mass
C: 0.002% or less,
Si: 0.1% or more and 4.0% or less,
Al: 0.1% to 4.0%,
A non-oriented electrical steel sheet for high-frequency excitation waves, comprising a balance iron and unavoidable impurity elements and having an iron loss deterioration rate A defined by the formula (I) of 50% or less.
A = [W ₁ −W ₀ ] / W ₀ (I)
Here, W ₁ is the iron loss value in the high frequency region of stress at 30MPa~50MPa addition, W ₀ denotes the iron loss value in the high frequency range in the absence of stressing. % By mass
The non-oriented electrical steel sheet for high frequency excitation according to claim 1, further comprising Cr: 3.0% or less and / or Mn: 1.0% or less. W ₁ and W ₀ are both average values of iron loss values measured by exciting in the rolling direction (L direction) and the direction perpendicular to rolling (C direction) of the steel sheet. 2. A non-oriented electrical steel sheet for high frequency excitation according to 2. 4. W ₁ is an iron loss value by 1700 Hz excitation when stress 30 MPa is applied, and W ₀ is an iron loss value by 1700 Hz excitation when no stress is applied. Non-oriented electrical steel sheet for high frequency excitation.   5. The non-oriented electrical steel sheet for high-frequency excitation according to claim 1, wherein the non-oriented electrical steel sheet has an average crystal grain size of 100 μm or less.   The non-oriented electrical steel sheet for high frequency excitation according to any one of claims 1 to 5, wherein the non-oriented electrical steel sheet has an average crystal grain size of 40 µm or less.   The non-oriented electrical steel sheet for high frequency excitation according to any one of claims 1 to 6, which is used for an iron core of a motor. % By mass
C: 0.002% or less,
Si: 0.1% or more and 4.0% or less,
Al: 0.1% to 4.0%,
The slab composed of the remaining iron and unavoidable impurity elements is subjected to hot rolling as a hot-rolled sheet by hot rolling, the surface scale is removed by pickling, and then cold-rolled to obtain a final sheet thickness of 850 to 850. A method for producing a non-oriented electrical steel sheet for high-frequency excitation with a low iron loss deterioration rate due to compressive stress, wherein finish annealing is performed at 1000 ° C. for 10 seconds to 1 minute.   The said slab is a manufacturing method of the non-oriented electrical steel sheet for high frequency excitation of Claim 8 which is further mass% and contains Cr: 3.0% or less and / or Mn: 1.0% or less.