JP2013044012A - Non-oriented electromagnetic steel sheet, and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-oriented electromagnetic steel sheet having low high-frequency iron loss and a high flux density, and suitable for use in an iron core of a high efficiency motor primarily used in a high-speed rotation range.SOLUTION: The non-oriented electromagnetic steel sheet is characterized by including a chemical composition comprising, by mass, Si: at least 1.8% and not more than 3.0%, sol. Al: at least 0.1% and not more than 3.0%, Mn: at least 0.05% and not more than 3.0%, P: at least 0.03% and not more than 0.10%, S: at least 0.0010% and not more than 0.0050%, C: not more than 0.0050%, As: not more than 0.0050%, Nb: not more than 0.0030%, Ti: not more than 0.0030%, V: not more than 0.0030%, Zr: not more than 0.0030%, and N: not more than 0.0050% with the balance being Fe and impurities while satisfying the relation: S+As+Nb+Ti+V+Zr+N≤0.018, by having a steel structure in which the average crystal grain size is at least 60 μm and not larger than 180 μm, by having a magnetic characteristic being an iron loss Wof not greater than 50 W/kg, and by having a sheet thickness of at least 0.10 mm and not greater than 0.33 mm.

Description

  The present invention relates to a non-oriented electrical steel sheet and a method for producing the same. More specifically, the present invention can be used for iron cores of high-efficiency motors frequently used in a high-speed rotation range, such as compressor motors such as air conditioners and refrigerators, drive motors and generators such as electric vehicles and hybrid vehicles. The present invention relates to a suitable non-oriented electrical steel sheet and a method for producing the same.

  In order to reduce global warming gas, products with low energy consumption are rapidly spreading in the fields of automobiles and home appliances. For example, in the automobile field, there are low fuel consumption vehicles such as hybrid vehicles having a drive system in which a gasoline engine and a motor are combined, and motor-driven electric vehicles. In the field of home appliances, there are high-efficiency air conditioners, refrigerators and the like that consume less electricity annually. The technology common to these is the motor, and it is important to improve the motor efficiency. To increase the efficiency of the motor, iron loss reduction and magnetic flux density improvement of the non-oriented electrical steel sheet, which is the core material, are performed. Is required. Since motor drive motors and home appliance compressor motors such as those described above are frequently used in high-speed rotation regions, non-oriented electrical steel sheets with low iron loss under high-frequency conditions are suitable as the iron core material. .

  As a means for reducing the high-frequency iron loss, a means for reducing the plate thickness and a means for increasing the content of an alloy element having an effect of increasing the specific resistance such as Si and Al are generally used. However, since the manufacture becomes difficult as the plate thickness is reduced, there is a limit to reducing the iron loss by reducing the plate thickness. Further, since the magnetic flux density is reduced due to the increase in the amount of alloy elements and the motor torque is reduced, there is a problem that the motor needs to be enlarged.

  Moreover, as means for improving the magnetic flux density, means for positively adding P has been proposed (see Patent Document 1). The invention disclosed in Patent Document 1 enables high-frequency iron loss reduction by further increasing the amount of alloying elements by improving the magnetic flux density. It is a very excellent invention that contributes to efficiency.

JP 2005-200756 A

Due to the recent demand for higher motor efficiency, a means for improving the magnetic flux density that can further reduce the high-frequency iron loss is required.
The present invention has been made in view of the above circumstances, and its problem is high efficiency mainly used in a high-speed rotation range such as compressor motors such as air conditioners and refrigerators, drive motors and generators such as electric vehicles and hybrid vehicles. An object of the present invention is to provide a non-oriented electrical steel sheet having a low high-frequency iron loss and a high magnetic flux density that is suitable for use in a motor core.

  In order to solve the above problems, the present inventors have paid attention not only to the influence of P on the magnetic flux density but also to the influence of the interaction between P and other elements on the magnetic flux density. The idea of further improving the magnetic flux density by using it was newly conceived, and further intensive studies were carried out in order to establish manufacturing conditions for realizing this. As a result, after containing a small amount of S, the upper limit of the total content of S, As, Nb, Ti, V, Zr and N is regulated, and further, appropriate hot rolling conditions and cold rolling It has been newly found that the effect of improving the magnetic flux density by adding P can be effectively enhanced by combining the conditions. The present invention is based on these new findings, and the gist thereof is as follows.

That is, the present invention relates to mass%, Si: 1.8% to 3.0%, sol. Al: 0.1% to 3.0%, Mn: 0.05% to 3.0%, P: 0.03% to 0.10%, S: 0.0010% to 0.0050% Hereinafter, C: 0.0050% or less, As: 0.0050% or less, Nb: 0.0030% or less, Ti: 0.0030% or less, V: 0.0030% or less, Zr: 0.0030% or less, and N: 0.0050% or less, with the balance being Fe and impurities, having a chemical composition satisfying the following formula (1), and having an average crystal grain size of 60 μm or more and 180 μm or less The magnetic loss W _10/800 when magnetized at a frequency of 800 Hz and a magnetic flux density of 1.0 _T has a magnetic property of 50 W / kg or less, and the plate thickness is 0.10 mm or more and 0.33 mm or less. A non-oriented electrical steel sheet is provided.
S + As + Nb + Ti + V + Zr + N ≦ 0.018 (1)
(Here, each element symbol in the formula indicates the content (unit: mass%) of each element in the steel.)

Moreover, this invention provides the manufacturing method of the non-oriented electrical steel sheet characterized by having the following process (A)-(D).
(A) A hot rolling step in which hot rolling at a finishing temperature of 700 ° C. or higher and a winding temperature of 300 ° C. or higher is performed on a slab having the above chemical composition to form a hot rolled steel sheet;
(B) A pickling / hot-rolled sheet annealing step in which a hot-rolled steel sheet obtained by the hot-rolled rolling process is subjected to pickling and hot-rolled sheet annealing to obtain a hot-rolled annealed sheet;
(C) Cold rolling a cold rolled steel sheet having a sheet thickness of 0.10 mm to 0.33 mm by subjecting the hot rolled annealed sheet obtained by the pickling / hot rolled sheet annealing step to cold rolling with a reduction ratio of 85% or more. And (D) a finish annealing step for subjecting the cold-rolled steel sheet obtained by the cold rolling step to finish annealing.

  The non-oriented electrical steel sheet according to the present invention can be expected to improve motor efficiency. Moreover, since the manufacturing method of the non-oriented electrical steel sheet which concerns on this invention does not require special equipment, it is excellent also in terms of manufacturing cost.

  Hereinafter, the non-oriented electrical steel sheet and the manufacturing method thereof according to the present invention will be described in detail.

A. Non-oriented electrical steel sheet First, each structure in the non-oriented electrical steel sheet of the present invention will be described.
1. Chemical composition First, the reasons for limiting the chemical composition of the steel sheet will be described. “%” Indicating the content of each element means “mass%” unless otherwise specified.

  Si is an element effective for increasing the specific resistance of a steel sheet and reducing iron loss. Therefore, the Si content is 1.8% or more. Preferably, it is 2.0% or more. On the other hand, if it is contained excessively, the steel sheet is hardened and the breaking rate in cold rolling increases. For this reason, Si content shall be 3.0% or less.

  sol. Al is an element effective for increasing the specific resistance of the steel sheet and reducing iron loss. Therefore, sol. Al is 0.1% or more. Preferably, it is 0.6% or more. On the other hand, when it is excessively contained, the magnetic flux density is remarkably lowered. For this reason, sol. Al is 3.0% or less.

  Mn is an element effective for increasing the specific resistance of the steel sheet and reducing iron loss. Therefore, the Mn content is 0.05% or more. Preferably, it is 0.4% or more. On the other hand, since Mn has a higher alloy cost than Si and Al, an increase in Mn content is economically disadvantageous. For this reason, Mn content shall be 3.0% or less.

  P has the effect of improving the texture by improving the texture. Therefore, the P content is 0.03% or more. Preferably, it is 0.04% or more. On the other hand, when the P content is excessive, the grain boundary segregation of P becomes remarkable and the breaking rate in cold rolling increases. Therefore, the P content is 0.10% or less. Preferably, it is 0.08% or less.

  S is an element that is generally contained in steel as an impurity, and combines with Mn in steel to form fine MnS, which inhibits the growth of crystal grains during annealing and deteriorates magnetic properties. Conventionally, this element has been required to reduce its content. However, as a result of the above-described investigation by the present inventors, after adding a small amount of S, by regulating the upper limit of the total content of S, As, Nb, Ti, V, Zr and N, by adding P It has been clarified for the first time that the effect of improving the magnetic flux density can be effectively enhanced. Therefore, the S content is 0.0010% or more. On the other hand, when the S content is excessive, the deterioration of magnetic properties becomes significant due to the inhibition of crystal grain growth during annealing. Therefore, the S content is 0.0050% or less. Preferably, it is 0.0035% or less.

  C is an element that is contained as an impurity and deteriorates magnetic properties. For this reason, C content shall be 0.0050% or less. Preferably, it is 0.0035% or less.

  As, Nb, Ti, V, and Zr are elements that are contained as impurities and deteriorate magnetic properties. Therefore, As content is 0.0050% or less, Nb content is 0.0030% or less, Ti content is 0.0030% or less, V content is 0.0030% or less, Zr content is 0.0030%. The following. Preferably, the As content is 0.0035% or less, the Nb content is 0.0020% or less, the Ti content is 0.0020% or less, the V content is 0.0020% or less, and the Zr content is 0.0020. % Or less.

  N is contained as an impurity and combines with Al to form fine inclusions, which inhibits the growth of crystal grains during annealing and deteriorates magnetic properties. For this reason, N content shall be 0.0050% or less. Preferably, it is 0.0035% or less.

It has been conventionally known that iron loss is reduced by reducing the contents of impurity elements S, As, Nb, Ti, V, Zr and N. However, as a result of the above-described investigation by the present inventors, after adding a small amount of S, by regulating the upper limit of the total content of S, As, Nb, Ti, V, Zr and N, by adding P It has been clarified for the first time that the effect of improving the magnetic flux density can be effectively enhanced. Accordingly, the total content of S, As, Nb, Ti, V, Zr and N shall satisfy the following formula (1). Especially, it is preferable that the following formula (2) is satisfied, and it is more preferable that the following formula (3) is satisfied.
S + As + Nb + Ti + V + Zr + N ≦ 0.018 (1)
S + As + Nb + Ti + V + Zr + N ≦ 0.016 (2)
S + As + Nb + Ti + V + Zr + N ≦ 0.014 (3)
Here, each element symbol in the formula indicates the content (unit: mass%) of each element in the steel.

2. Average crystal grain size If the crystal grain size is too large or too small, the iron loss deteriorates. Therefore, the average crystal grain size is 60 μm or more and 180 μm or less.
The average crystal grain size may be the average value of the crystal grain sizes measured by the cutting method in the plate thickness direction and the rolling direction in the longitudinal sectional structure photograph. An optical micrograph can be used as the longitudinal cross-sectional structure photograph. For example, a photograph taken at a magnification of 50 times may be used.

3. Iron loss As the iron core material of a motor that is frequently used in a high-speed rotation region, a non-oriented electrical steel sheet having a low high-frequency iron loss is suitable. Therefore, the iron loss W _10/800 when magnetized at a frequency of 800 Hz and a magnetic flux density of 1.0 _T is _set to 50 W / kg or less. Preferably, it is 46 W / kg or less.

4). Thickness Compressor motors such as air conditioners and refrigerators, and drive motors and generators such as electric vehicles and hybrid vehicles are used in a wide range of rotational speeds by inverter control. Therefore, it is desirable that the non-oriented electrical steel sheet, which is a core material, has a low iron loss in a high frequency range. Since the iron loss is reduced as the plate thickness is reduced, the plate thickness is set to 0.33 mm or less. Preferably it is 0.30 mm or less. On the other hand, excessive thinning significantly reduces the productivity of steel plates and motors. Therefore, the plate thickness is 0.10 mm or more. Preferably it is 0.15 mm or more.

B. Next, a method for producing a non-oriented electrical steel sheet according to the present invention will be described.
The manufacturing method of the non-oriented electrical steel sheet of this invention has the following process (A)-(D), It is characterized by the above-mentioned.
(A) A hot rolling step in which hot rolling at a finishing temperature of 700 ° C. or higher and a winding temperature of 300 ° C. or higher is performed on a slab having the above chemical composition to form a hot rolled steel sheet;
(B) A pickling / hot-rolled sheet annealing step in which a hot-rolled steel sheet obtained by the hot-rolled rolling process is subjected to pickling and hot-rolled sheet annealing to obtain a hot-rolled annealed sheet;
(C) Cold rolling a cold rolled steel sheet having a sheet thickness of 0.10 mm to 0.33 mm by subjecting the hot rolled annealed sheet obtained by the pickling / hot rolled sheet annealing step to cold rolling with a reduction ratio of 85% or more. And (D) Finish annealing step for subjecting the cold-rolled steel sheet obtained by the cold rolling step to finish annealing Hereinafter, each step in the method for producing a non-oriented electrical steel sheet according to the present invention will be described.

1. Hot rolling step The finishing temperature in the hot rolling step is 700 ° C or higher, and the winding temperature is 300 ° C or higher. If the finishing temperature is less than 700 ° C. or the coiling temperature is less than 300 ° C., it may not be possible to obtain the effect of improving B ₅₀ by the desired addition of P. The upper limit of the finishing temperature and the winding temperature need not be specified from the viewpoint of magnetic properties, but the finishing temperature is preferably set to 1000 ° C. or less from the viewpoint of suppressing the yield reduction due to scale loss. Is preferably 800 ° C. or lower.
Other conditions in the hot rolling process are not particularly defined.

2. Pickling / Hot Rolled Sheet Annealing Process Various conditions in the pickling / hot rolled sheet annealing process are not specified, but the annealing temperature is 730 ° C. from the viewpoint of promoting recrystallization and ensuring excellent magnetic properties. Preferably, the annealing time is 1 hour or longer. More preferably, the annealing time is 3 hours or more. On the other hand, the annealing temperature is preferably 850 ° C. or less, and the annealing time is preferably 50 hours or less, from the viewpoint of load on equipment and manufacturing cost. The annealing temperature is more preferably 810 ° C. or less, and particularly preferably 790 ° C. or less. More preferably, the annealing time is 40 hours or less.
Pickling and hot-rolled sheet annealing are in no particular order, and hot-rolled sheet annealing may be performed after pickling, or pickling may be performed after hot-rolled sheet annealing.

3. Cold rolling step The rolling reduction in the cold rolling step is 85% or more. If the rolling reduction is less than 85%, it may not be possible to obtain the effect of improving B ₅₀ by adding desired P.
Other conditions in the cold rolling process are not particularly defined.

4). Finish annealing process The conditions in the finish annealing process are not particularly specified, but from the viewpoint of securing sufficient magnetic properties by promoting sufficient grain growth, the annealing temperature is preferably 900 ° C. or higher, and the annealing time. Is preferably 1 second or longer. On the other hand, the annealing temperature is preferably 1180 ° C. or less, and the annealing time is preferably 300 seconds or less, from the viewpoint of load on equipment and manufacturing cost.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

  Hereinafter, the present invention will be described specifically by way of examples and comparative examples.

[Example 1]
A slab having the chemical composition shown in Table 1 below was hot-rolled at a finishing temperature of 800 ° C. and a coiling temperature of 500 ° C. to obtain a hot-rolled steel plate having a thickness of 2.0 mm, and pickled. These pickled steel sheets were subjected to hot-rolled sheet annealing that was held at 790 ° C. for 10 to 20 hours, so that the average crystal grain size was adjusted to 100 μm. These hot-rolled annealed sheets were cold-rolled with a rolling reduction of 87.5% to obtain cold-rolled steel sheets with a finished sheet thickness of 0.25 mm. At this time, a part was broken by cold rolling. The cold-rolled steel sheet that did not break was subjected to finish annealing that was held at 1100 ° C. for 10 seconds to obtain a non-oriented electrical steel sheet having an average crystal grain size of 97 to 134 μm.

For these non-oriented electrical steel sheets, the iron loss W _10/800 when magnetized at a frequency of 800 Hz and a magnetic flux density of 1.0 _T and the magnetic flux density B ₅₀ when magnetized at a magnetizing force of 5000 A / m were measured. Here, the steel plate No. 1 is a reference material P are hardly added, B ₅₀ of the reference material and the steel sheet No. The difference ΔB ₅₀ between 2 and 12 B ₅₀ was calculated, and the magnitude of the B ₅₀ improvement effect due to the addition of P was evaluated. This means that the greater the ΔB ₅₀ , the greater the effect of improving B ₅₀ by adding P. Further, since ΔB ₅₀ increases as the P content increases, X is calculated from the following formula (4) in consideration of this point, and the target characteristic is that X is 0 or more.
X = ΔB ₅₀ −0.4 × (P−0.01) (4)
(Here, P in the formula represents the P content (unit: mass%) in the steel.)
The average crystal grain size and magnetic measurement results are shown together in Table 1.

Steel plate No. 3, 4, 10 and 11 contain S in a very small amount, and by making the total content of S, As, Nb, Ti, V, Zr and N within a predetermined range, Even if the crystal grain size was the same, the effect of improving B ₅₀ by adding P could be enhanced.
Steel plate No. No. 2 had a low S content, so No. 5 has a high total content of S, As, Nb, Ti, V, Zr and N. No. 6 had a high Ti and N content. No. 7 had high Nb and V contents. No. 8 had a high Zr and N content. Since No. 9 had high As and Ti contents, X <0, and the desired effect of improving B ₅₀ by adding P was not obtained. Steel plate No. Since No. 12 had a large P content, it was broken by cold rolling.

[Example 2]
A slab having the chemical composition shown in Table 2 below is subjected to hot rolling at a finishing temperature of 750 to 900 ° C. and a winding temperature of 500 to 600 ° C. to form a hot rolled steel sheet having a thickness of 1.6 to 2.5 mm, and an acid. Washed. These pickled steel sheets were subjected to hot rolled sheet annealing at 750 to 790 ° C. for 5 to 15 hours. These annealed sheets were cold-rolled to form cold-rolled steel sheets having a finished sheet thickness of 0.20 to 0.30 mm. These cold-rolled steel sheets were subjected to finish annealing at 950 to 1130 ° C. for 20 to 90 seconds to obtain non-oriented electrical steel sheets having an average crystal grain size of 75 to 156 μm.

These non-oriented electrical steel sheets were measured iron loss W _10/800 and the magnetic flux density B _50. Here, the steel plate No. No. 13 'is a steel plate No. No. 13 was produced under the same production conditions as in No. 13, and P was hardly added. It differs from 13 only in the P content and corresponds to a reference material for measuring the magnitude of the effect of improving B ₅₀ by adding P. Similarly, steel plate No. 14 ', 15', 16 ', and 17' are steel plate Nos. It corresponds to the reference materials of 14, 15, 16, and 17. B _{50 of} each reference material and steel plate No. A difference ΔB ₅₀ between 13 and 17 and B ₅₀ was calculated. Further, X is calculated from the above formula (4), and the target characteristic is that X is 0 or more.
Table 3 shows the manufacturing conditions, average crystal grain size, and magnetic measurement results.

Si, sol. If the content of Al and Mn, the content of impurity elements such as S, the plate thickness, and the production conditions are within the predetermined ranges, the desired effect of improving B ₅₀ by adding W _10/800 and P could be obtained. .

[Example 3]
The slab having the chemical composition shown in Table 4 below was hot-rolled steel sheet having a thickness of 1.8 to 2.4 mm by hot rolling at a finishing temperature of 650 to 900 ° C and a winding temperature of 250 to 600 ° C. These hot-rolled steel sheets were pickled and then cold-rolled at a rolling reduction of 84.2 to 86.4% to obtain cold-rolled steel sheets having a finished sheet thickness of 0.25 to 0.35 mm. These cold-rolled steel sheets were subjected to finish annealing that was held at 1100 ° C. for 5 seconds to obtain non-oriented electrical steel sheets having an average crystal grain size of 99 to 121 μm.

These non-oriented electrical steel sheets were measured iron loss W _10/800 and the magnetic flux density B _50. Here, the composition A contains almost no P, differs from the composition B only in the P content, and corresponds to a reference material for measuring the magnitude of the improvement effect of B ₅₀ by the addition of P. Using the composition A, the steel plate No. 18 to 23 were produced under the same production conditions, and used as reference materials. B _{50 of} each reference material and steel plate No. The difference ΔB ₅₀ between 18 and 23 and B ₅₀ was calculated. Further, X is calculated from the above formula (4), and the target characteristic is that X is 0 or more.
Table 5 shows the manufacturing conditions, average crystal grain size, and magnetic measurement results.

Steel plate No. No. 18 had a low finishing temperature in hot rolling. No. 19 was a steel plate No. 19 because the coiling temperature in hot rolling was low. Since No. 20 had a low rolling reduction in cold rolling, the effect of improving B ₅₀ by the desired addition of P could not be obtained. Steel plate No. No. 21 could not obtain the desired iron loss because the plate thickness was thick.

Claims (2)

In terms of mass%, Si: 1.8% to 3.0%, sol. Al: 0.1% to 3.0%, Mn: 0.05% to 3.0%, P: 0.03% to 0.10%, S: 0.0010% to 0.0050% Hereinafter, C: 0.0050% or less, As: 0.0050% or less, Nb: 0.0030% or less, Ti: 0.0030% or less, V: 0.0030% or less, Zr: 0.0030% or less, and N: 0.0050% or less, with the balance being Fe and impurities, having a chemical composition satisfying the following formula (1), and having an average crystal grain size of 60 μm or more and 180 μm or less The magnetic loss W _10/800 when magnetized at a frequency of 800 Hz and a magnetic flux density of 1.0 _T has a magnetic property of 50 W / kg or less, and the plate thickness is 0.10 mm or more and 0.33 mm or less. Non-oriented electrical steel sheet.
S + As + Nb + Ti + V + Zr + N ≦ 0.018 (1)
(Here, each element symbol in the formula indicates the content (unit: mass%) of each element in the steel.) A method for producing a non-oriented electrical steel sheet comprising the following steps (A) to (D):
(A) A hot rolling step in which hot rolling at a finishing temperature of 700 ° C. or higher and a winding temperature of 300 ° C. or higher is performed on the slab having the chemical composition according to claim 1 to obtain a hot rolled steel sheet;
(B) A pickling / hot-rolled sheet annealing step in which a hot-rolled steel sheet obtained by the hot-rolled rolling process is subjected to pickling and hot-rolled sheet annealing to obtain a hot-rolled annealed sheet;
(C) Cold rolling a cold-rolled steel sheet having a sheet thickness of 0.10 mm to 0.33 mm by subjecting the hot-rolled annealed sheet obtained by the pickling / hot-rolled sheet annealing step to cold rolling with a reduction rate of 85% or more. And (D) a finish annealing step for subjecting the cold-rolled steel sheet obtained by the cold rolling step to finish annealing.