JP2006328458A - Soft magnetic steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soft magnetic steel having high magnetic properties and deformability, and also having reduced deformation resistance. <P>SOLUTION: The soft magnetic steel has a composition containing, by mass, ≤0.015% C, 0.005 to 0.10% Si, 0.1 to 0.5% Mn, ≤0.02% P, ≤0.02% S, >0.010 to 1.3% Al, 0.02 to 0.20% Ti, ≤0.010% N and ≤0.020% O (oxygen), and the balance Fe with impurities, and satisfies inequality (1) and inequality (2): 0.85≤0.8-0.57C+0.82Si+0.07Mn+0.78P-3.56S+0.82Al-1.0N≤2.0 (1), and 0.015≤Ti-3.4N (2); wherein, each symbol in the inequality (1) and the inequality (2) is the content (mass%) of each element. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a soft magnetic steel material, and more particularly to a soft magnetic steel material used in an alternating magnetic field.

  Soft magnetic steel materials represented by soft iron, pure iron, silicon steel, and the like are used as core materials for electrical components such as motors and generators.

  Soft magnetic steel is used in a DC magnetic field or an AC magnetic field, but the magnetic properties required for the soft magnetic steel are different between the DC magnetic field and the AC magnetic field. When used in an AC magnetic field, soft magnetic steel materials are required to improve AC magnetic properties. Specifically, reduction of iron loss is required.

  By the way, the core material for an alternating magnetic field is usually formed by laminating a plurality of electromagnetic steel sheets and processing the laminated electromagnetic steel sheets by punching or the like. However, the core material formed by laminating a plurality of electromagnetic steel sheets has low strength and rigidity. Moreover, since the process of laminating | stacking a steel plate is included, manufacturing cost is high. Therefore, in recent years, core materials made of steel bars such as steel bars and wire rods have appeared. If the strip is made of a material, the core material can be formed by cold forging, and the material laminating process is not necessary, so that the manufacturing cost can be reduced. Furthermore, since it is not necessary to laminate | stack like an electromagnetic steel plate, the intensity | strength and rigidity of a core material can be improved.

  As described above, when a core material made of a steel bar is formed by cold forging, the steel bar which is a raw material is required to have high deformability and reduction in deformation resistance. This is because if the deformability is high, it becomes easier to mold a core material that has been downsized and complicated in recent years. Further, if the deformation resistance is low, the forging load can be reduced and the life of the mold used in cold forging can be improved.

  Therefore, soft magnetic steel materials for AC magnetic fields are required not only to improve AC magnetic characteristics but also to improve deformability and deformation resistance.

  A plurality of soft magnetic steels aimed at improving magnetic properties and deformability are disclosed. Patent Document 1 (Japanese Patent Laid-Open No. 2003-55745), Patent Document 2 (Japanese Patent Laid-Open No. 2003-226945), and Patent Document 3 (Japanese Patent Laid-Open No. 2003-226946) improve magnetic properties and cold forgeability. An intended soft magnetic steel is disclosed. However, the soft magnetic steels disclosed in these Patent Documents 1 to 3 are intended to improve the magnetic permeability and magnetic flux density, and are not sufficient to realize improvement of AC magnetic characteristics such as reduction of iron loss.

  Patent Document 4 (Japanese Patent Application Laid-Open No. 2000-73149) discloses a soft magnetic steel material having a large magnetic flux density, a small coercive force, and a large electric resistance. However, since the soft magnetic steel material of Patent Document 4 contains a large amount of ferrite strengthening elements Si, Al, and Cr, it is considered that the deformability is low and the deformation resistance is large.

Patent document 5 (Unexamined-Japanese-Patent No. 2001-115241) discloses the steel material for electromagnetic steel wires aiming at the improvement of an alternating current magnetic characteristic and wire drawing workability. Moreover, patent document 6 (Unexamined-Japanese-Patent No. 2001-131718) discloses the electromagnetic steel wire aiming at the improvement of a high frequency magnetic characteristic and workability. However, since the steel materials of Patent Document 5 and Patent Document 6 have a high Si content, it is considered that the deformability is low and the deformation resistance is large. Furthermore, since the total content of C, N, O (oxygen) and S is lowered, the manufacturing cost for refining and the like may increase.
JP 2003-55745 A JP 2003-226945 A JP 2003-226946 A JP 2000-73149 A JP 2001-115241 A JP 2001-131718 A

  An object of the present invention is to provide a soft magnetic steel material having excellent AC magnetic characteristics, high deformability, and low deformation resistance.

Means for Solving the Problems and Effects of the Invention

In order to secure a good balance of excellent AC magnetic properties, high deformability, and small deformation resistance in a substantially single-phase low-carbon steel, the present inventors have reached the present invention with the following technical idea. .
(A) First, the present inventors examined a method for reducing iron loss in order to improve AC magnetic characteristics. Iron loss is the sum of hysteresis loss and eddy current loss, but eddy current loss accounts for the majority of iron loss in AC magnetic fields. Therefore, in order to reduce the iron loss, it is necessary to particularly reduce the eddy current loss. In order to reduce eddy current loss, it is effective to increase the electrical resistance of steel. Further, although the ratio of iron loss is small, it is preferable to reduce hysteresis loss. If the ferrite grains are prevented from becoming finer, hysteresis loss can be reduced.
(B) The eddy current loss can be reduced by increasing the solid solution amount of Si, Mn, and Al, which has the effect of increasing the electrical resistance of the steel. Furthermore, S that forms sulfides with Mn and N that forms nitrides with Al have the effect of reducing the solid solution amount of Mn and Al and lowering the electrical resistance. Therefore, it is necessary to limit S and N.
(C) In order to reduce the hysteresis loss, it is necessary to suppress the formation of precipitates and inclusions that inhibit the growth of ferrite grains. Therefore, it is effective to reduce the contents of C, N, and S. It is also effective to suppress P, which increases the hysteresis loss due to grain boundary segregation.
(D) Next, the present inventors examined a method for improving the deformability. In order to improve the deformability, it is necessary to lower the content of the solid solution strengthening element and lower the content of the element contributing to age hardening.
(E) Therefore, Si, Mn, and Al that are effective in improving AC magnetic characteristics should not be contained excessively from the viewpoint of improving the deformability. Moreover, C and N which are age-hardening elements should be restricted from the viewpoint of improving deformability. Further, S that forms MnS and P that segregates at the grain boundaries also need to be lowered because they reduce the deformability.
(F) From the above viewpoint, the present inventors considered that all of Si, Mn, Al, C, N, S, and P strongly influence the AC magnetic characteristics and deformability. Therefore, the degree of influence of each element on AC magnetic properties and the degree of influence on deformability were examined. As a result, the present inventors have found that both the alternating magnetic properties and the deformability can be improved if the content of these elements satisfies the formula (1).
0.85 ≦ 0.8−0.57C + 0.82Si + 0.07Mn + 0.78P−3.56S + 0.82Al−1.0N ≦ 2.0 (1)

Here, the symbol in Formula (1) is content (mass%) of each element.
(G) The present inventors have found that if Ti is further contained, AC magnetic characteristics and deformability can be further improved, and deformation resistance can be improved.
(H) Ti is an element having a stronger affinity for S than Mn. Therefore, by forming sulfides with S in the steel, the amount of MnS produced is lowered and the MnS coarsening is suppressed. As a result, the deformability is improved. In addition, since the formation of MnS that inhibits the growth of ferrite grains is suppressed, the ferrite grains grow appropriately and the AC magnetic characteristics are improved. Therefore, in addition to satisfying the above formula (1), AC magnetic characteristics and deformability can be further improved by containing Ti.
(I) Furthermore, Ti is an element that has a stronger affinity for N than Al and a stronger affinity for C than Fe. Therefore, Ti fixes C and N in steel that causes age hardening by forming carbides, nitrides, and carbonitrides. As a result, age hardening is suppressed, the deformation resistance is reduced, and the deformability is increased.
(J) As described above, Ti combines with N, C, and S to improve AC magnetic characteristics and deformability and improve deformation resistance.
(K) Of N, C, and S, Ti preferentially bonds to N, but in order to obtain the above-described effect of Ti, Ti not only bonds to N but also needs to bond to C and S There is. Therefore, as a result of experiments and studies, the present inventors have found that if the expression (2) is satisfied, Ti not only binds to N but also C and S, and the above-described effects can be obtained effectively.
Ti-3.4N ≧ 0.015 (2)

  Here, the symbol in Formula (2) is content (mass%) of each element.

  As a result of the above examination, the present inventors have completed the following invention.

The soft magnetic steel material according to the present invention is, in mass%, C: 0.015% or less, Si: 0.005 to 0.10%, Mn: 0.1 to 0.5%, P: 0.02% or less, S: 0.02% or less, Al: more than 0.010 to 1.3%, Ti: 0.02 to 0.20%, N: 0.010% or less, O (oxygen): 0.020% or less And the balance consists of Fe and impurities, satisfying the formulas (1) and (2).
0.85 ≦ 0.8−0.57C + 0.82Si + 0.07Mn + 0.78P−3.56S + 0.82Al−1.0N ≦ 2.0 (1)
Ti-3.4N ≧ 0.015 (2)

  Here, the symbol in Formula (1) and (2) is content (mass%) of each element.

Preferably, the structure of the soft magnetic steel material is substantially composed of ferrite, and the ferrite particle diameter D (μm) satisfies the formula (3).
80 ≦ D <200 (3)

  Here, the ferrite particle diameter D is calculated as follows, for example. Observe 10 fields of view of the cross section of the soft magnetic steel material with a 100 to 400 times optical microscope, calculate the ferrite grain number in each field by a cutting method based on JISG0551, and average the 10 ferrite grain numbers calculated (Average ferrite grain size number) is obtained. The average area of each crystal grain is calculated based on the average ferrite grain size number. The equivalent circle diameter is calculated from the average area, and the obtained equivalent circle diameter is defined as the ferrite particle diameter D.

  Preferably, the soft magnetic steel material further contains B: 0.0005 to 0.005%.

  Preferably, the soft magnetic steel material further contains one or more of Te: 0.0005 to 0.01% and Ca: 0.0005 to 0.005%.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

1. Chemical Composition The soft magnetic steel material according to the embodiment of the present invention has the following chemical composition. Hereinafter, “%” related to elements means “% by mass”.

C: 0.015% or less C is an element that improves the strength of steel. However, in the present invention, C is an undesirable element that increases deformation resistance and deteriorates deformability by age hardening. However, industrially, the C content cannot be reduced to 0%, and the content of about 0.001% as an impurity cannot be avoided. When C is too high, the formation of Fe and cementite inhibits the growth of ferrite grains, and the precipitated magnetic cementite deteriorates AC magnetic properties. Therefore, the C content is 0.015% or less. A preferable C content is 0.008% or less.

Si: 0.005-0.10%
Si is an element that improves AC magnetic properties. Specifically, it is an element necessary to increase the electrical resistance of steel and reduce eddy current loss. Furthermore, it contributes to ferritization of steel. However, if the Si content is excessive, the deformability is lowered and the deformation resistance is increased. Therefore, the Si content is 0.005 to 0.10%. Considering the improvement of the deformability, the preferable Si content is 0.005 to 0.05%.

Mn: 0.1 to 0.5%
Mn, like Si, increases the electrical resistance of steel and reduces eddy current loss. Further, Mn is combined with S in steel to form MnS, thereby suppressing embrittlement due to S and improving deformability. Therefore, Mn needs to be contained in an amount of 0.1% or more. However, if the Mn content is excessive, the deformability decreases and the deformation resistance increases. Therefore, the Mn content is 0.1 to 0.5%.

P: 0.02% or less P is an undesirable element. Segregates at the grain boundaries of the steel, reducing the deformability. P also increases the deformation resistance of the steel by solid solution strengthening. Further, P segregates and deteriorates the AC magnetic characteristics. Therefore, the lower the P content, the better. It is necessary to make it 0.02% or less. A preferable P content is 0.016% or less.

S: 0.02% or less S combines with Mn in steel to form MnS. Although MnS has an effect of improving machinability, in the present invention, S is an undesirable element that reduces the solid solution amount of Mn having an effect of increasing electric resistance and increases eddy current loss. Further, since MnS is a non-metallic inclusion and inhibits the growth of ferrite grains, it also adversely affects hysteresis loss. Further, when the amount of MnS in the steel is large, the deformability is also lowered. Therefore, the S content is 0.02% or less. A preferable S content is 0.015% or less, more preferably 0.010% or less.

Al: more than 0.010 to 1.3%
Al improves AC magnetic properties. Specifically, it is an element that increases the electrical resistance of steel and reduces eddy current loss. Further, Al contributes to ferritization of steel like Si. When the Al content is low, the AC magnetic properties can be improved by increasing the Si and Mn contents, but the deformability decreases when the Si and Mn contents are high. On the other hand, if the Al content is excessive, the deformability is lowered and the deformation resistance is increased. Therefore, the Al content is more than 0.010 to 1.3%. In other words, the Al content is set higher than 0.010% and 1.3% or less. A preferable Al content is 0.05 to 1.0%.

Ti: 0.02 to 0.20%
Ti is an important element in the present invention. Ti forms carbides, nitrides, and carbonitrides to fix C and N that cause age hardening, reduce deformation resistance, and increase deformability. Moreover, by combining with S to form a sulfide, the amount of MnS produced is suppressed, and the deformability of the steel is improved. Furthermore, since Ti suppresses the formation of MnS that inhibits the growth of ferrite grains, the ferrite grains grow appropriately and improve the magnetic properties. In short, Ti does not deteriorate the AC magnetic characteristics, but rather improves the AC magnetic characteristics. Therefore, Ti improves AC magnetic properties, deformability and deformation resistance.

  However, if the Ti content is excessive, Ti carbide, Ti nitride, Ti carbonitride, and Ti sulfide are coarsened and the deformability is lowered. Therefore, the Ti content is 0.02 to 0.20%. A preferable Ti content is 0.02 to 0.10%.

N: 0.010% or less N is an undesirable element. N combines with Al to form AlN, thereby reducing the amount of Al solid solution and deteriorating AC magnetic characteristics. N further age-hardens the steel, increasing the deformation resistance and lowering the deformability. Therefore, the N content is 0.010% or less. A preferable N content is 0.005% or less.

O (oxygen): 0.020% or less O is an undesirable element. O forms an oxide and deteriorates magnetic properties. The formed oxide also reduces the deformability. Therefore, the O content is 0.020% or less. A preferable O content is 0.010% or less.

  The remainder is made of Fe, but may contain impurities other than those described above.

  The soft magnetic steel material according to the present embodiment further contains B as necessary.

B: 0.0005 to 0.005%
B is a selective element. B forms Nitride to fix N and suppress N from binding to Al. As a result, AC magnetic characteristics are improved by suppressing a decrease in the amount of Al solid solution. Even if B is contained excessively, the effect is saturated. Therefore, the B content is set to 0.0005 to 0.005%. A preferable B content is 0.0008% to 0.002%.

  The soft magnetic steel material according to the present embodiment further contains at least one of Te and Ca as necessary. Both Te and Ca improve the deformability.

Te: 0.0005 to 0.01%
Te is a selective element. In the present invention, the smaller the MnS, the better. Te spheroidizes MnS in this steel and improves the deformability. Furthermore, machinability is improved by making MnS spherical. Even if Te is contained excessively, the effect is saturated. Therefore, the Te content is set to 0.0005 to 0.01%. A preferable Te content is 0.0006 to 0.008%.

Ca: 0.0005 to 0.005%
Ca is a selective element. Ca spheroidizes MnS in steel and improves deformability. Even if Ca is contained excessively, the effect is saturated. Therefore, the Ca content is set to 0.0005 to 0.005%. A preferable Ca content is 0.0008 to 0.002%.

The soft magnetic steel material in the present embodiment satisfies the following formula (1) in addition to the above chemical composition.
0.85 ≦ fn1 ≦ 2.0 (1)

Here, fn1 is represented by the following formula (A).
fn1 = 0.8−0.57C + 0.82Si + 0.07Mn + 0.78P−3.56S + 0.82Al−1.0N (A)

  The symbol in fn1 is the mass% of each element.

  C, Si, Mn, P, S, Al, and N are elements that particularly affect AC magnetic properties and deformability. If the content of these elements is within the range of the chemical composition described above and satisfies the formula (1), both the AC magnetic characteristics and the deformability are improved.

  FIG. 1 is a diagram showing the relationship between fn1 and AC magnetic characteristics and deformability. FIG. 1 was obtained as follows. A plurality of soft magnetic steel materials having a chemical composition in the above-described range were prepared. The same test methods (AC magnetic property evaluation test and deformability evaluation test) as those of the examples described later were performed on each prepared soft magnetic steel material, and the total iron loss and the limit compression ratio were obtained. The total iron loss is an index of AC magnetic characteristics, and the critical compressibility is an index of deformability.

  With reference to the curve of the total iron loss in FIG. 1B, the total iron loss decreases as fn1 increases. In other words, the AC magnetic characteristics improve as fn1 increases. On the other hand, referring to the curve of the limit compression rate in FIG. 1A, the limit compression rate also decreases as fn1 increases. In other words, the deformability decreases as fn1 increases.

  If fn1 satisfies the formula (1), high AC magnetic characteristics and deformability can be obtained. Specifically, the total iron loss is 140 w / kg or less, and the critical compression ratio is 70% or more.

The soft magnetic steel material according to the present embodiment further satisfies the following formula (2).
fn2 ≧ 0.015 (2)

Here, fn2 is represented by the following formula (B).
fn2 = Ti-3.4N (B)

  The element symbol in fn2 is mass% of each element.

  As described above, Ti fixes N and C that cause age hardening, reduces deformation resistance, and improves deformability. Ti further combines with S to form sulfides, thereby suppressing the amount of MnS produced and improving deformability and AC magnetic properties. Therefore, Ti needs to bond not only to N but also to C and S. Among N, C, and S, N has the highest bonding strength with Ti. Therefore, if the Ti content is small with respect to the N, C, and S contents, most Ti will bond with N, and the effect of Ti on the C and S cannot be obtained. If there is a Ti content satisfying the formula (2), Ti can bond not only to N but also to C and S. As a result, the deformation resistance can be effectively reduced, and the deformability and AC magnetic characteristics can be effectively improved.

2. Structure The structure of the soft magnetic steel material according to the present embodiment is substantially made of ferrite. Specifically, ferrite accounts for 95% or more of the structure, and cementite is less than 5%. Cementite, like non-metallic inclusions such as MnS, deteriorates AC magnetic properties. By making the structure substantially a ferrite single phase, the AC magnetic characteristics can be improved.

In the soft magnetic steel material according to the present embodiment, preferably, the ferrite particle diameter D (μm) satisfies the following formula (3).
80 ≦ D <200 (3)

  Here, the ferrite grain size is calculated as follows. Observe 10 fields of view of the cross section of the soft magnetic steel material with an optical microscope of 100 to 400 times, calculate the ferrite grain number in each field by a cutting method in accordance with JISG0551, and further calculate the 10 ferrite grain numbers The average (average ferrite particle size number) is calculated. The average area of each crystal grain is calculated based on the average ferrite grain size number. Further, the equivalent circle diameter is calculated from the average area, and the obtained equivalent circle diameter is defined as the ferrite particle diameter.

  If the ferrite particle diameter D is 80 μm or more, the coercive force is lowered and the magnetic flux density is increased, so that the AC magnetic characteristics are further improved. Further, the strength is lowered and the deformation resistance is also lowered. On the other hand, if the ferrite particle diameter D is less than 200 μm, the deformability is further improved. Therefore, if the ferrite particle diameter D satisfies the formula (3), a soft magnetic steel material having more excellent AC magnetic properties, deformation resistance and deformability can be obtained. Even if the ferrite grain size D does not satisfy the formula (3), better AC magnetic characteristics and deformability than before can be obtained.

3. Manufacturing Method The soft magnetic steel material according to the present embodiment is a steel bar having soft magnetism, and more specifically, a steel bar or wire having soft magnetism. Hereinafter, the manufacturing method of the soft magnetic steel material of this Embodiment is demonstrated.

  The steel having the above chemical composition is melted and refined by a well-known method. Subsequently, the molten steel is made into a continuous cast material by a continuous casting method. The continuous cast material is, for example, bloom or billet. Alternatively, the molten steel is made into an ingot by the ingot-making method.

  A continuous cast material or a steel ingot is hot-worked into a soft magnetic steel material such as a bar steel and a wire. For example, a continuous cast material or the like is made into a billet by hot rolling, and the billet is hot worked to form a steel bar or wire having soft magnetism. You may make it the steel bar or wire which has soft magnetism by other processing methods.

  Annealing is performed on the soft magnetic steel material after hot working. The annealing temperature is preferably 700 to 900 ° C. By this annealing treatment, the steel structure becomes substantially a ferrite single phase, and the ferrite particle diameter D becomes a size satisfying the formula (3). When the annealing temperature is outside the range of 700 to 900 ° C., the ferrite particle diameter D does not satisfy the formula (3), but the structure is substantially made of ferrite.

Steels having chemical components shown in Table 1 were melted in a vacuum melting furnace to make 150 kg ingots.

  The “fn1” and “fn2” columns in Table 1 indicate the fn1 and fn2 of the steel of each steel type number calculated based on the formulas (A) and (B). Referring to Table 1, the chemical compositions of steel types A to J were within the scope of the present invention. In addition, fn1 and fn2 of steel type numbers A to J satisfied formulas (1) and (2), respectively.

  On the other hand, the chemical composition and / or fn1 and fn2 were out of the scope of the present invention. Specifically, the Al content of steel type number a was less than the lower limit of the present invention, and fn1 was also less than the lower limit. The Si content of steel type number b exceeded the upper limit of the present invention, and the Al content was less than the lower limit of the present invention. The Al content of steel type number c exceeded the upper limit of the present invention. The Si content of steel type numbers d and e exceeded the upper limit of the present invention. The Mn content of steel type number f was less than the lower limit of the present invention.

  Although the chemical composition of steel type number g was within the range of the present invention, fn1 was less than the lower limit of the present invention. Moreover, although the chemical composition of the steel type number h was within the scope of the present invention, fn2 was less than the lower limit of the present invention.

  The Ti content of steel type number i was less than the lower limit of the present invention, and the Ti content of steel type number j exceeded the upper limit of the present invention. The Al content, Ti content, fn1, and fn2 of steel type number k were outside the scope of the present invention.

Each ingot having a chemical composition shown in Table 1 was heated at 1000 to 1300 ° C., and the heated ingot was hot forged into a steel bar having a diameter of 40 mm. Then, the annealing treatment for 2 hours was implemented with respect to the created steel bar at the annealing temperature (degreeC) shown in Table 2.

  After the annealing treatment, the microstructure of the steel bars having the test numbers shown in Table 2 was investigated, and further, a deformability evaluation test, a deformation resistance evaluation test, and an AC magnetic property evaluation test were performed.

[Microstructure]
The microstructure of the cross section of the steel bar of each test number was observed. 1/4 of the test piece cut in the transverse direction of the steel bar (fan shape with a radius of 20 mm, thickness 10 mm) was filled with resin, and the cross section was polished. After polishing, the cross section was corroded with a nightite etchant. After the corrosion, the microstructure of the cross section was observed with an optical microscope of 100 to 400 times.

  The area ratio of the ferrite phase in the observed microstructure was measured. Specifically, an optical micrograph (magnification 100 times) of arbitrary 10 visual fields in the cross section was subjected to image processing, and the area ratio of the ferrite phase in the entire visual field area was calculated. As a result of the measurement, ferrite accounted for 95% or more in the microstructures of the steel bars of all test numbers. In other words, the steel structures of all the test numbers were substantially ferrite.

  Furthermore, the ferrite particle size was calculated with each test number. Arbitrary 10 fields of view were observed with a 100 to 400 times optical microscope in the cross section of the above-mentioned test piece, and the ferrite particle size number in each field was calculated by a cutting method based on JISG0551. The average of 10 calculated ferrite particle size numbers (average ferrite particle size number) was calculated. Subsequently, the average area of each crystal grain was calculated based on the average ferrite grain size number. Further, the equivalent circle diameter was calculated from the average area, and the obtained equivalent circle diameter was defined as the ferrite particle diameter. Table 2 shows the calculated ferrite particle size (μm).

[Deformability evaluation test]
A plurality of test pieces shown in FIG. 2 were produced from the steel bars of the respective test numbers by machining. The test piece was a cylinder having a diameter of 14 mm and a height of 21 mm, and a notch (slit part) was formed in the axial direction of the cylinder surface.

  The cold compression test was implemented with respect to the produced several test piece. A 500 ton crank press was used for the cold compression test. In the cold compression test, the amount of compression processing was changed, a plurality of test pieces were compressed at each compression processing amount, and it was investigated whether or not a crack occurred in the slit portion of the test piece. Of the test pieces after the test at each compression processing amount, the minimum compression processing amount at which the number of test pieces with cracks reached 50% or more was defined as the critical compression ratio. In this example, if the limit compression rate is 75% or more, it is determined that the deformability is very high (indicated by “◎” in Table 2), and if the limit compression rate is 70% or more and less than 75%, deformation occurs. It was determined that the performance was high (indicated by “◯” in Table 2), and the deformability was determined to be low if the critical compression rate was less than 70% (indicated by “×” in Table 2).

[Deformation resistance evaluation test]
The test piece shown in FIG. 3 was produced from the steel bar of each test number by machining. The test piece was a smooth cylindrical test piece having a diameter of 14 mm and a height of 21 mm. The cold compression test was implemented using the produced test piece. A 500 ton crank press was used for the cold compression test. In the cold compression test, the load when the compression rate (%) shown in the following formula (4) was 80% was measured.
Compression rate = (H0−H) / H0 × 100 (4)

  Here, H0 is the height (21 mm) of the test piece before the test, and H is the height (mm) of the test piece after compression.

Subsequently, the deformation resistance (MPa) was calculated by Equation (5) using the measured load.
Deformation resistance = 80% compression load L (N) / maximum cross-sectional area s (mm ² ) of the test piece perpendicular to the load direction (5)

  If the calculated deformation resistance is 630 MPa or less, it is determined that the deformation resistance is very small (indicated by “◎” in Table 2), and if the deformation resistance exceeds 630 MPa and 650 MPa or less, the deformation resistance is It was determined to be small (indicated by “◯” in Table 2). If the calculated deformation resistance was larger than 650 MPa, it was determined that the deformation resistance was large (indicated by “x” in Table 2).

[AC magnetic property evaluation test]
A ring-shaped test piece was produced from the steel bar of each test number by machining. The ring-shaped test piece had an outer diameter of 30 mm, an inner diameter of 20 mm, and a thickness of 5 mm.

A coil for applying a magnetic field and a coil for detecting magnetic flux were wound around a ring-shaped test piece, and the total iron loss Wt was measured in accordance with JISC2504. Specifically, the hysteresis loss Wh was measured with a DC magnetic field with a frequency of 50 Hz and a magnetic flux density of 1.5 T, and the eddy current loss We was measured with an AC magnetic field with a frequency of 50 Hz and a magnetic flux density of 1.5 T. The total iron loss Wt was determined by the following formula (6).
Wt = Wh + We (6)

  If the calculated total iron loss Wt is 130 W / kg or less, it is determined that the magnetic characteristics are very good (indicated by “◎” in Table 2), the total iron loss Wt exceeds 130 W / kg, and , 140 W / kg or less, the magnetic properties were determined to be good (indicated by “◯” in Table 2). When the calculated total iron loss Wt exceeded 140 W / kg, it was determined that the magnetic characteristics were poor (indicated by “x” in Table 2).

[Test results]
The test results of each evaluation test are shown in Table 2. Referring to Table 2, in Test Nos. 1 to 16, the chemical components and fn1 and fn2 were within the scope of the present invention. Further, the structure was substantially composed of ferrite, and the cementite in the structure was less than 5%. Therefore, AC magnetic characteristics, deformability, and deformation resistance were all good. Specifically, the total iron loss was 140 W / kg or less, the critical compression ratio was 70% or more, and the deformation resistance was 650 MPa or less.

  Furthermore, in all of the structures of test numbers 1, 2, 4, 6 to 11, 13, and 14, the ferrite particle diameter D satisfied the formula (3). Therefore, the limit compression ratios of test numbers 1, 2, 4, 6 to 11, 13, and 14 were all 75% or more, indicating very good deformability. Moreover, the deformation resistance of test numbers 1, 2, 4, 6 to 11, 13, and 14 was very small, and all were 630 MPa or less. Furthermore, all the iron losses of test numbers 1, 2, 4, 6 to 11, 13, and 14 were 130 W / kg or less, indicating very good AC magnetic characteristics.

  On the other hand, in each of test numbers 17 to 27, one or more of AC magnetic characteristics, deformability, and deformation resistance were defective. Specifically, in Test No. 17, since the Al content was low and fn1 was small, the total iron loss exceeded 140 W / kg. Since test number 18 had high Si content, the limit compression rate was less than 70%. In Test No. 19, since the Al content was high, the critical compression ratio was less than 70%, and the deformation resistance was 650 MPa or more.

  Test numbers 20 and 21 both had a high Si content. Therefore, the deformation resistance exceeded 650 MPa, and the critical compression rate was less than 70%. Since test number 22 had little Mn content, the total iron loss exceeded 140 W / kg and the limit compression rate was also less than 70%.

  Test No. 23 had a chemical composition within the range of the present invention, but fn1 was low, so that the total iron loss exceeded 140 W / kg. In Test No. 24, although the chemical composition was within the range of the present invention, fn2 was low, so that the critical compression ratio was less than 70% and the deformation resistance exceeded 650 MPa.

  In Test No. 25, since the Ti content was low, the deformation resistance exceeded 650 MPa, and the critical compression ratio was less than 70%. Since test number 26 had high Ti content, the limit compression rate was less than 70%.

  In test number 27, the chemical compositions Al, Ti, fn1, and fn2 were out of the scope of the present invention. Therefore, these critical compression ratios were less than 70%.

  While the embodiments of the present invention have been described above, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

  The soft magnetic steel material according to the present invention can be widely used for electrical parts. In particular, it can be used as a core material for AC magnetic fields in motors, power generation devices, electromagnetic switches, and the like.

It is a figure which shows the relationship between fn1 of a soft magnetic steel material, a total iron loss, and a limit compressibility. It is a figure which shows the upper surface and side surface of a test piece used by the deformability evaluation test in an Example. It is a figure which shows the upper surface and side surface of a test piece used by the deformation resistance evaluation test in an Example.

Claims (4)

In mass%, C: 0.015% or less, Si: 0.005 to 0.10%, Mn: 0.1 to 0.5%, P: 0.02% or less, S: 0.02% or less, Al: more than 0.010 to 1.3%, Ti: 0.02 to 0.20%, N: 0.010% or less, O (oxygen): 0.020% or less, the balance being Fe and impurities And a soft magnetic steel material satisfying the formulas (1) and (2).
0.85 ≦ 0.8−0.57C + 0.82Si + 0.07Mn + 0.78P−3.56S + 0.82Al−1.0N ≦ 2.0 (1)
Ti-3.4N ≧ 0.015 (2)
Here, the symbol in Formula (1) and (2) is content (mass%) of each element. The soft magnetic steel material according to claim 1,
The structure of the soft magnetic steel material is substantially composed of ferrite, and the ferrite particle diameter D (μm) satisfies the formula (3).
80 ≦ D <200 (3)   The soft magnetic steel material according to claim 1 or 2, further comprising B: 0.0005 to 0.005%. The soft magnetic steel material according to any one of claims 1 to 3, further comprising at least one of Te: 0.0005 to 0.01% and Ca: 0.0005 to 0.005%. Soft magnetic steel material characterized by containing.

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