JP5651002B2 - Soft magnetic steel parts having excellent AC magnetic characteristics and manufacturing method thereof - Google Patents

Description

  The present invention relates to a soft magnetic steel part and a method for manufacturing the same, and more particularly to a soft magnetic steel part used in an alternating magnetic field and a method for manufacturing the same.

  Soft magnetic steel parts are used, for example, as parts (for example, core materials) constituting a magnetic circuit of a motor driven by an alternating magnetic field used in automobiles, industrial machines, and the like. Conventionally, this soft magnetic steel part has been manufactured by punching a laminated body in which a plurality of electromagnetic steel sheets are laminated. However, the soft magnetic steel parts obtained in this manner have low strength and rigidity because a plurality of electromagnetic steel sheets are laminated. Moreover, since it was necessary to laminate | stack several electromagnetic steel plates, the manufacturing cost was high.

  In recent years, it has been studied to produce soft magnetic steel parts from steel bars (for example, steel bars and wire rods). If strip steel is used as the material of the soft magnetic steel part, it can be formed into a part shape by cold forging, so that the step of laminating electromagnetic steel sheets can be omitted as described above, and the manufacturing cost can be reduced. Further, when the steel bar is used, since it is not a laminated structure, strength and rigidity can be increased.

  The soft magnetic steel parts are required to have good AC magnetic characteristics. Specifically, reduction of iron loss when used in an alternating magnetic field is required. Iron loss is the sum of hysteresis loss and eddy current loss, but eddy current loss accounts for the majority of iron loss in an alternating magnetic field. In order to reduce this eddy current loss, it is effective to increase the electrical resistance of steel.

  Patent Document 1 proposes a soft magnetic material in which the electric resistance of steel is improved to improve the AC magnetic characteristics. In this document, in order to increase the electric resistance of the soft magnetic material to 40 μΩcm or more, the S value calculated by the relational expression “2 × (Al% + Si%) + Cr%” is adjusted to the range of 4.5-9. Is disclosed.

  By the way, the above bar steel is also required to have good cold forgeability in order to be formed into a part shape. The cold forgeability needs to have low deformation resistance and high deformability. Since the load at the time of forging can be reduced by lowering the deformation resistance, the life of the mold used in cold forging can be improved. In addition, since the deformability is high and cracking hardly occurs even when cold forging, it is possible to reduce the size of the soft magnetic steel part and to complicate the part shape.

  Patent Document 2 proposes a soft magnetic steel material having alternating magnetic properties and high deformability and low deformation resistance. In this document, in order to improve AC magnetic properties and deformability, the content of Si, Mn, Al, C, N, S, and P should be optimized, and AC magnetic properties and deformability are further improved. It is disclosed that Ti may be contained in order to improve and improve deformation resistance. Further, it is described that in order to improve the AC magnetic characteristics, the solid solution amount of Si, Mn, and Al, which has the effect of increasing the electrical resistance of steel, should be increased to reduce the eddy current loss.

Patent Document 3 discloses a magnetic circuit member for an electromagnetic valve that has high electrical resistance, has excellent high-speed response, can be mass-produced, and can reduce product cost. In this document, it is possible to improve the machinability and cold forgeability by using electromagnetic soft iron or low carbon steel as the base material of the magnetic circuit member, and the electrical resistance is increased by containing Al in the magnetic circuit member. It is described that eddy current loss can be reduced. As a method for incorporating Al in the magnetic circuit member, a magnetic circuit member made of electromagnetic soft iron is embedded in a mixture of Al powder and Al ₂ O ₃ powder and NH ₄ Cl added, and 900 ° C. in a hydrogen stream. A method of performing a heat treatment for 3 hours is adopted.

  Patent Document 4 proposes a high silicon steel material excellent in high-frequency magnetic characteristics. In this document, a high silicon steel sheet is used as an electromagnetic steel sheet, and this type of steel sheet has a reduced iron loss as the Si content increases. At Si: 6.5%, the magnetostriction becomes zero, It is described that the maximum magnetic permeability also peaks and exhibits excellent magnetic properties. On the other hand, it is also described that when the Si content is increased, the workability is remarkably deteriorated, so that cold working becomes difficult. As a method for producing a high silicon steel plate, there is exemplified a method in which Si is infiltrated from the surface (low silicidation method) after melting low silicon steel and rolling it into a thin plate. According to this silicidation method, Si can be infiltrated after processing, so that a high silicon steel sheet having excellent high frequency magnetic properties can be produced without causing problems of workability and shape defects.

JP-A-8-134603 JP 2006-328458 A JP-A-63-3318380 Japanese Patent Publication No. 5-49744

  In Patent Document 1 described above, the electrical resistance of the soft magnetic material is increased by adjusting the component composition of the steel material. However, the method of adjusting the component composition of the steel material has a limit in improving the electrical resistance. Further, the soft magnetic steel material disclosed in Patent Document 2 contains Ti as an essential element. When Ti is contained, precipitates such as TiC and TiN are formed in the steel material, and crystal There arises a problem that the magnetic properties are reduced by reducing the size of the grains.

  By the way, in order to reduce the eddy current loss of soft magnetic steel parts and improve the AC magnetic characteristics, it is necessary to increase the electrical resistance in the surface layer portion. As a means for increasing the electrical resistance in the surface layer portion, as proposed in Patent Document 3, a method of impregnating Al on the surface of a member by a powder coating method is known. However, when the surface of the member is impregnated with Al, if a layer having a remarkably high Al concentration (for example, a layer containing 20% by mass or more of Al) is formed, the portion becomes a nonmagnetic phase, and the AC magnetic characteristics are It turns out that it falls. Moreover, in the said patent document 4, an iron loss is reduced and magnetic characteristics are improved by raising Si content. However, the method of diffusing and penetrating Si requires expensive production equipment and advanced technology, and mass production is difficult.

  This invention is made | formed in view of such a condition, It is providing the soft magnetic steel component excellent in the alternating current magnetic characteristic by the method different from the said patent documents 1-4, and its manufacturing method. Another object of the present invention is to provide a soft magnetic steel part having good cold forgeability when formed into a part shape and a method for producing the same.

The soft magnetic steel part excellent in AC magnetic characteristics according to the present invention that has solved the above problems has a chemical composition composition of the parent phase C: 0.002 to 0.20% (meaning mass%. The same applies hereinafter). ), Si: 1.2% or less (excluding 0%), Mn: 0.05 to 2.6%, P: 0.050% or less (not including 0%), S: 0.05% Or less (not including 0%), Cr: 4% or less (not including 0%), Al: 0.002 to 2.2%, N: 0.01% or less (not including 0%), O: 0.03% or less (not including 0%), balance: steel and steel parts that are inevitable impurities. In this steel part, a P diffusion layer containing a P amount (P _D ) satisfying the following formula (1) is formed on the surface layer portion, and the thickness of the P diffusion layer is 20 μm or more. Has a summary.
P _B + 0.1 ≦ P _D ≦ 2.0 (1)

In the above formula (1), P _D represents the amount of P (mass%) contained in the P diffusion layer, and P _B represents the amount of P (mass%) contained in the parent phase of the steel part.

It is recommended that the chemical component composition further satisfies the following formula (2). In the following formula (2), [] indicates the content (% by mass) of each element.
13 × [C] + 2 × [Si] + [Mn] + [Cr] / 5 + [Al] ≦ 2.8 (2)

  The steel part may further contain Cu: 0.5% or less (not including 0%) and / or Ni: 0.5% or less (not including 0%) as other elements. .

  The soft magnetic steel part according to the present invention can be manufactured by heating a steel material having a P film on the surface and processed into a part shape. The P film is preferably formed using phosphate.

  According to the present invention, since the P diffusion layer containing P at a concentration higher than the amount of P contained in the parent phase is formed on the surface layer portion of the soft magnetic steel part with a predetermined thickness, the electrical resistance of the surface layer portion As a result, eddy current loss can be reduced, and as a result, AC magnetic characteristics can be improved. Moreover, in the present invention, the deformation resistance of the steel material is reduced by appropriately adjusting the relationship among the amounts of C, Si, Mn, Cr and Al contained as alloy elements in the steel material as the material of the soft magnetic steel part. Since the performance can be improved, the cold forgeability when forming into a part shape can also be improved.

FIG. 1 is a graph showing the relationship between the thickness of the P diffusion layer and the ratio of the AC maximum magnetic flux density for the test pieces used in the examples. FIG. 2 is a graph showing the relationship between the value (Z value) on the left side of the equation (1) defined in the present invention and the deformation resistance for the test pieces used in the examples.

The present inventor has repeatedly studied to improve the AC magnetic characteristics by increasing the electric resistance in the surface layer portion of the soft magnetic steel part and reducing the eddy current loss by a method different from the above-mentioned Patent Documents 1 to 4. as a result,
(1) When heat treatment is performed on a steel material having a P film on the surface and processed into a part shape, P existing on the surface diffuses and penetrates uniformly into the steel material to form a P diffusion layer;
(2) This P diffusion layer can improve the AC magnetic properties of steel parts in order to increase the electrical resistance of the surface layer,
(3) It has also been found that the effect of improving the AC magnetic properties is enhanced because the position of forming the P diffusion layer is the surface layer portion of the steel part, so that the magnetic moment of the steel can be prevented from being lowered.

  That is, since P diffuses and penetrates uniformly from the surface to the inside of the steel material, a portion where P is excessively concentrated locally is not formed on the surface layer portion of the soft magnetic steel part. Further, P diffuses and concentrates preferentially in the crystal grain boundaries rather than in the crystal grains. Therefore, P that diffuses the crystal grain boundaries diffuses deeper into the steel material than P diffuses in the crystal grains. . P diffused along the crystal grain boundary forms a linear concentrated portion, and this concentrated portion has a high electric resistance, and therefore exhibits an extremely high eddy current suppressing effect. In addition, for example, P is less likely to diffuse in the crystal grains than Al and Sn, so that it does not penetrate deeper into the steel than Al or Sn and concentrates in the vicinity of the outermost surface of the steel. For this reason, the soft magnetic steel part of the present invention has improved AC magnetic characteristics even at high-frequency AC (for example, 10 kHz) (see Examples described later).

  Furthermore, since P diffuses and penetrates uniformly from the steel surface to the inside of the steel material, concentration unevenness hardly occurs and a non-magnetic phase is not easily formed. Therefore, it is possible to prevent the deterioration of AC magnetic characteristics. Further, it is known that when P is added up to about 2%, the magnetic properties of the steel material itself are improved. Accordingly, by diffusing and penetrating P, both the magnetic properties of the substrate itself and the electrical resistance of the surface layer portion can be enhanced. Therefore, P is an element having a high effect of improving AC magnetic properties.

  Conventionally, as disclosed in Patent Document 2, a large amount of alloying elements are added to the steel material, and the amount of this alloying element is optimized to increase the electrical resistance of the steel material and improve the AC magnetic characteristics. It was. On the other hand, according to the present invention, the AC magnetic property improving effect is exhibited by providing the P diffusion layer on the surface layer portion of the steel part. Therefore, the steel material used as the material for the steel part in the present invention can reduce the amount of alloy elements to be contained, so that the deformation resistance can be reduced. By reducing the deformation resistance of the steel material, the deformability is improved, so that the cold forgeability when the steel material is formed into a part shape can also be improved.

Hereinafter, the soft magnetic steel part of the present invention will be described in detail. The soft magnetic steel part of the present invention has a P diffusion layer formed on the surface layer. In the present invention, the P diffusion layer means a region containing a P amount (P _D ) that satisfies the following formula (1). In formula (1), P amount P _D contained in the P diffusion layer (mass%), P _B represents the amount P contained in the matrix of the steel component (mass%).
P _B + 0.1 ≦ P _D ≦ 2.0 (1)

If P _D is less than the value (P _B +0.1) on the left side of the above formula (1), the electrical resistance of the surface layer cannot be increased, so that eddy current loss cannot be reduced and AC magnetic characteristics cannot be improved. On the other hand, when P _D exceeds the value (2.0) on the right side of the above formula (1), the amount of Fe ₃ P generated increases, and the magnetic moment and magnetic permeability are significantly reduced, resulting in AC magnetism. The effect of improving the characteristics is reduced. Therefore, in the present invention, a region containing an amount of P that satisfies the above formula (1) is defined as a P diffusion layer, and the AC magnetic characteristics are improved by forming this P diffusion layer on the surface layer portion of the steel part. doing.

  The surface layer portion means the vicinity of the surface including the outermost surface of the soft magnetic steel part, and specifically refers to a region from the outermost surface to a depth of about 500 μm.

  The P diffusion layer preferably has a P content decreasing from the outermost surface side toward the center. This is because the AC magnetic characteristics can be effectively improved by inclining the P concentration in the surface layer portion.

  By setting the thickness of the P diffusion layer to 20 μm or more, the electrical resistance of the surface layer portion can be increased, so that the eddy current loss is reduced and the AC magnetic characteristics can be improved. The P diffusion layer preferably has a larger thickness, preferably 25 μm or more, more preferably 30 μm or more, and particularly preferably 35 μm or more. As the thickness of the P diffusion layer increases, the AC magnetic characteristics are improved. The upper limit of the thickness of the P diffusion layer is not particularly limited. For example, the P diffusion layer may have a thickness exceeding 250 μm, but may be 500 μm or less from the viewpoint of suppressing an increase in cost due to heat treatment.

The P concentration (P _D ) in the surface layer portion is a region from the outermost surface of the steel part to a depth of 500 μm, for example, an electron probe X-ray Micro Analyzer (EPMA), The thickness of the P diffusion layer may be calculated based on values measured in the crystal grains at regular intervals (for example, at intervals of several μm) in the depth direction.

  Next, the component composition of the steel material (matrix) that is the material of the soft magnetic steel part according to the present invention will be described. Steel materials used in the present invention are: C: 0.002 to 0.20%, Si: 1.2% or less (excluding 0%), Mn: 0.05 to 2.6%, P: 0.050% Or less (excluding 0%), S: 0.05% or less (not including 0%), Cr: 4% or less (not including 0%), Al: 0.002 to 2.2%, N: It contains 0.01% or less (not including 0%), O: 0.03% or less (not including 0%), and the balance: iron and inevitable impurities. The reason for specifying such a range is as follows.

  C is an important element for ensuring the balance between strength and ductility of the steel material. However, if C exceeds 0.20%, the strength becomes too high, the deformation resistance increases, and the cold forgeability deteriorates. In addition, due to the C dissolved in the steel, strain aging occurs at the time of forming the part, and the AC magnetic characteristics also deteriorate. Therefore, C is 0.20% or less, preferably 0.1% or less, more preferably 0.08% or less. The smaller the C, the lower the strength and the better the ductility, so the cold forgeability becomes better. However, if the amount of C is reduced too much, the strength of the steel part will be reduced too much. Therefore, C is 0.002% or more, preferably 0.003% or more.

  Si is an element that contributes to improving the AC magnetic characteristics by increasing the electrical resistance of the steel material by reducing the eddy current loss by solid solution. Moreover, it has the effect | action which ferritizes the metal structure of steel parts and improves an alternating current magnetic characteristic. However, when the content exceeds 1.2%, the deformation resistance increases and the cold forgeability deteriorates. Therefore, Si is 1.2% or less, preferably 1.0% or less, more preferably 0.8% or less. In particular, in order to reduce the deformation resistance of the steel material and improve the cold forgeability, Si is preferably 0.7% or less, more preferably 0.5% or less, still more preferably 0.1% or less. It is.

  Mn is an element used as a deoxidizer during melting, and has an action of binding to S and suppressing embrittlement due to S in steel. In addition, it combines with S in steel to form MnS, or MnS forms a composite precipitate around the oxide in the steel to form a composite precipitate, thereby increasing the electrical resistance of steel parts and alternating current magnetic properties. Has the effect of improving. Therefore, Mn is 0.05% or more, preferably 0.1% or more, more preferably 0.15% or more. However, if Mn exceeds 2.6%, the deformation resistance becomes too large and the cold forgeability deteriorates. Further, when Mn is excessive, the magnetic moment is lowered and the AC magnetic characteristics are deteriorated. Therefore, Mn is 2.6% or less, preferably 2% or less, more preferably 1% or less, and still more preferably 0.5% or less.

  If P contained in the parent phase (base material) segregates at the grain boundaries, the deformability is lowered, which causes cracks during cold forging. Moreover, when it contains excessively, an alternating current magnetic characteristic will also deteriorate. Therefore, P contained in the parent phase is 0.050% or less, preferably 0.02% or less, and more preferably 0.01% or less.

  S combines with Mn or the like to form a sulfide, and this sulfide is precipitated at the grain boundary, so that the deformability is lowered. Therefore, S is 0.05% or less, preferably 0.02% or less, more preferably 0.015% or less.

  Cr is an element that acts to increase the electrical resistance of steel parts, reduce eddy current loss, and improve AC magnetic properties. Moreover, it has the effect | action which ferritizes the metal structure of steel parts and improves an alternating current magnetic characteristic. In order to exhibit such an action effectively, Cr is preferably contained in an amount of 0.005% or more, more preferably 0.008% or more. However, if Cr exceeds 4%, the hardness of the ferrite structure is excessively increased by the solid solution of Cr, so that the deformability is lowered and cracking occurs during cold forging. Therefore, Cr is 4% or less, preferably 2% or less, more preferably 1% or less, and still more preferably 0.5% or less.

  Al is an element that acts to increase the electrical resistance of steel parts, reduce eddy current loss, and improve AC magnetic properties. Al, like Si and Cr, also has the effect of improving the AC magnetic characteristics by ferritizing the metal structure of the steel part. Therefore, Al is contained in an amount of 0.002% or more, preferably 0.003% or more. However, if the content exceeds 2.2%, the deformation resistance of the steel material becomes too large and the cold forgeability deteriorates. Therefore, Al is 2.2% or less, preferably 1% or less, more preferably 0.8% or less, still more preferably 0.5% or less, and particularly preferably 0.1% or less.

  N is an element that age hardens the steel, and if it exceeds 0.01%, the deformability of the steel decreases and causes cracking during cold forging. Therefore, N is 0.01% or less, preferably 0.008% or less, more preferably 0.005% or less. It is desirable to reduce N as much as possible.

  O (oxygen) is an element that forms an oxide in the steel, reduces the deformability of the steel material, and generates cracks during cold forging. Moreover, the oxide formed in steel becomes a cause which degrades an alternating current magnetic characteristic. Therefore, O is 0.03% or less, preferably 0.01% or less, more preferably 0.005% or less. It is desirable to reduce O as much as possible.

  The balance of the steel material is iron and inevitable impurities. As inevitable impurities, elements mixed in depending on the situation of raw materials, materials, manufacturing equipment, etc. are allowed.

  The steel material may further contain Cu: 0.5% or less (not including 0%) and / or Ni: 0.5% or less (not including 0%) as other elements. Cu and Ni are inevitably mixed elements. If Cu or Ni exceeds 0.5% and excessively contained, the magnetic moment decreases and the alternating magnetic flux density decreases. A preferred upper limit was set to 0.5%. Cu is more preferably 0.1% or less, and Ni is more preferably 0.1% or less.

It is recommended that the steel materials used in the present invention satisfy the following formula (2) as well as the chemical component composition satisfying the above range. The following formula (2) shows a relational expression that is extracted based on the influence degree of each element by extracting an element that affects the deformation resistance of the steel material from the alloy elements contained in the steel material. When the value on the left side of the following formula (2) is the Z value, the deformation resistance can be reduced by suppressing the Z value to preferably 2.8 or less, and the cold forgeability can be improved. In addition, in following formula (2), [] has shown content (mass%) of each element.
13 × [C] + 2 × [Si] + [Mn] + [Cr] / 5 + [Al] ≦ 2.8 (2)

  That is, C, Si, Mn, Cr, and Al are elements that act to increase the electrical resistance of the steel material, reduce eddy current loss, and improve AC magnetic characteristics. Therefore, it has been actively added in the past. However, these elements all act as a solid solution in the steel or form precipitates to increase the strength of the steel material and increase the deformation resistance of the steel material. Therefore, the tendency for cold forgeability to deteriorate was recognized when content increased.

  On the other hand, in the present invention, as described above, the AC magnetic characteristics can be improved by forming a P diffusion layer in the surface layer portion of the soft magnetic steel part. Therefore, the contents of C, Si, Mn, Cr and Al are reduced. Can be reduced. Therefore, in this invention, the cold forgeability of steel materials can further be improved by restraining the Z value calculated based on the content of these elements to preferably 2.8 or less. The Z value is more preferably 2.5 or less, still more preferably 2 or less, and particularly preferably 1 or less.

  Next, a method for producing the soft magnetic steel part of the present invention will be described. The soft magnetic steel part can be manufactured by heat-treating a steel material having a P film on the surface. That is, by forming a P film on the surface of the steel material and heat-treating it, P can be diffused and penetrated from the surface of the steel material, and the P diffusion layer can be formed on the surface layer portion of the steel part. Further, P is easily diffused and concentrated in the crystal grain boundaries rather than in the crystal grains, so that P can also be concentrated in a limited line by the heat treatment. As described above, in the present invention, P is uniformly diffused and permeated from the surface of the steel material, so that it is possible to prevent P from locally concentrating in a planar shape on the surface layer portion of the soft magnetic steel part. In addition, as described above, the steel material used in the present invention keeps the Z value calculated based on the amount of alloy elements of C, Si, Mn, Cr, and Al below a predetermined value. The cold forgeability can be further improved.

  The steel material before the heat treatment may have a P film on the surface and be processed into a part shape, and the order of the process of forming the P film on the surface of the steel material and the process of processing the steel material into a part shape is particularly limited. Not. That is, a P film may be formed after the steel material is processed into a part shape, or a P film may be formed on the steel material and then processed into a part shape. The processing to the part shape may be performed by cold forging, for example.

  The P film may be a film containing P element (P-containing film), and the method of forming the P film is not particularly limited. For example, a method of forming by applying a phosphate, solid immersion Examples thereof include a phosphorus method and a liquid immersion phosphorus method.

  The method of forming a P film (phosphate film) by applying a phosphate is a method of applying a phosphate-containing lubricant to the surface of a steel material in order to improve lubrication during wire drawing. This is a method of forming a P film on the surface of a steel material by processing into a part shape without removing the phosphate-containing lubricant later. Thus, the process of forming P film | membrane can be skipped by utilizing the phosphate containing lubricant used as a lubricant. Examples of the phosphate include iron phosphate, zinc phosphate, zinc iron phosphate, zinc calcium phosphate, manganese phosphate, and sodium phosphate.

  The method of forming a P film by the solid immersion phosphorus method is a method of forming a P film on the surface of a steel material by gas reaction by putting the steel material and phosphorous iron in a crucible and heating them (for example, 800 to 1000 ° C.). is there.

  The method of forming a P film by the liquid immersion phosphorus method is a method of forming a P film on the surface of a steel material by immersing the steel material in a molten salt to which sodium phosphate is added.

  In addition, you may form P membrane | film | coat by the said method on the steel material surface after processing into a component shape.

  In the heat treatment, the heating temperature and the heating time may be adjusted so that the thickness of the P diffusion layer is formed on the surface layer portion of the steel part, for example, the heating temperature is 700 ° C. or more, and the heating time is 1 hour or more. It is preferable to adjust within the range. If the heating temperature is lower than 700 ° C. or the heating time is shorter than 1 hour, P does not sufficiently diffuse and penetrate into the steel material, making it difficult to form a desired P diffusion layer. As demonstrated in the examples described later, when the heating temperature is set to 700 ° C., the P diffusion layer can be formed with a thickness of 20 μm by heating for a long time (10 hours in the examples).

  The heating temperature is more preferably 750 ° C. or higher, further preferably 800 ° C. or higher, particularly preferably 850 ° C. or higher, more preferably 900 ° C. or higher, and most preferably 950 ° C. or higher. The heating temperature is desirably set as high as possible in order to diffuse and penetrate P from the surface side toward the inside.

  The heating time is more preferably 2 hours or more, and further preferably 3 hours or more. The heating time is desirably as long as possible in order to diffuse and penetrate P from the surface side toward the inside. However, if the heating time is too long, the productivity will deteriorate, so the upper limit is preferably set to 15 hours, for example.

  In addition, as demonstrated in the examples to be described later, the heat treatment can be performed in a high frequency (frequency 10 kHz in the embodiment) AC magnetic field by setting the heating temperature to 800 ° C. or more and the heating time to 1 hour or more. Soft magnetic steel parts having good AC magnetic properties can be manufactured.

  The heat treatment is preferably performed in a reducing atmosphere. As the reducing gas, for example, hydrogen may be contained.

  What is necessary is just to let the temperature increase rate when heating to the said heating temperature be 100-400 degreeC / hour, for example. Moreover, what is necessary is just to let the temperature fall rate when cooling to room temperature after heat processing be 100-400 degreeC / hour, for example.

  The thus obtained soft magnetic steel part according to the present invention is used, for example, as an iron part of an electric component or an electromagnetic coil that is driven through a magnetic force among steel parts mounted on an automobile or an industrial machine.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

  In Experimental Example 1 below, the AC magnetic properties of the soft magnetic steel parts were evaluated, and in Experimental Example 2 below, the cold forgeability of the steel material used as the material of the soft magnetic steel parts was evaluated.

[Experimental Example 1]
Steel containing chemical components shown in Table 1 below (with the balance being iron and inevitable impurities) was vacuum-melted to prepare 150 kg of melted material. In Table 1 below, the value (Z value) on the left side of the formula (2) is calculated and shown as a reference value.

  The obtained molten material is forged to produce a steel material having a diameter of 40 mm. A ring-shaped test piece is cut out from this steel material, and the AC magnetic characteristics when a P diffusion layer is provided on the test piece are as follows. evaluated. Specifically, a ring-shaped test piece having an outer diameter of 38 mm, an inner diameter of 30 mm, and a thickness of 4 mm is cut out from the steel material (diameter 40 mm), a zinc phosphate film is formed on the surface of the test piece, and then the surface is subjected to heat treatment. P was diffused and penetrated into the test piece. The heat treatment was performed in a hydrogen reduction atmosphere at a temperature rising rate of 300 ° C./hour up to the temperature shown in Table 2 below, and then held at this temperature for the time shown in Table 2 below. After the heat treatment, it was cooled to room temperature at a temperature lowering rate of 300 ° C./hour. Table 2 below shows the heating temperature and holding time during the heat treatment, respectively.

Next, the P concentration in the surface layer portion of the test piece on which the P diffusion layer was formed was measured at 1 μm intervals using EPMA (“JXA-8900RL (device name)” manufactured by JEOL Ltd.) with the beam diameter of EPMA being 1 μm. Then, it was evaluated whether or not a P diffusion layer containing a P amount (P _D ) satisfying the above formula (1) was formed. In addition, according to the EPMA line analysis, the amount of P at the grain boundary may be detected, but even if the amount of P at the grain boundary is detected, the measurement result of EPMA exists around the grain boundary. The amount of P in each grain is also included, and a value obtained by averaging these P amounts is a measured value. Therefore, there is no problem as a value obtained by measuring the EPMA measurement result in the crystal grain.

The P amount (P _B ) of the parent phase was measured by inductively coupled plasma emission spectroscopy after dissolving a columnar material having a diameter of 40 mm × thickness of 5 mm with hydrochloric acid. The measured P amount (P _B ) of the parent phase was consistent with the P amount shown in Table 1 below.

Moreover, the thickness of the P diffusion layer containing the P amount (P _D ) that satisfies the above formula (1) was determined. The results are shown in Table 2 below. In the surface layer portion of the test piece, the amount of P on the outermost surface was the largest, and the amount of P decreased toward the center, indicating that it was a gradient composition.

  Next, the AC magnetic characteristics of the test pieces obtained by heat treatment were evaluated.

<Evaluation of AC magnetic characteristics>
The AC magnetic characteristics were evaluated by measuring the AC maximum magnetic flux density of the test piece. The increase in the value of the AC maximum magnetic flux density means that the formation of the P diffusion layer increases the electrical resistance of the surface layer portion and reduces eddy current loss, resulting in improved AC magnetic characteristics. Show. The detailed measurement method is as follows. A primary coil for applying a magnetic field and a secondary coil for detecting magnetic flux are wound around a heat-treated test piece, and a BH curve is measured using an automatic magnetization measuring device (Iwatsu BH analyzer: SY-8232). The maximum AC magnetic flux density was obtained. In measuring the BH curve, in order to prevent the temperature of the test piece from rising due to heat generated by iron loss, the test piece was subjected to insulation treatment and then measured while immersed in water at 20 ° C. . The AC maximum magnetic flux density was obtained when the magnetic field amplitude was 800 A / m and the frequency was 5 kHz. For reference, the test piece using steel type α was also measured at a frequency of 10 kHz. The results are shown in Table 2 below.

  As a comparative material, a ring-shaped test piece cut out from the above steel type α and steel type β was subjected to magnetic annealing at 850 ° C. for 3 hours, and then a zinc phosphate film was not formed and heat treatment was not performed (that is, P diffusion) In the same manner as above, a primary coil for applying a magnetic field and a secondary coil for detecting a magnetic flux are wound (hereinafter referred to as an unprocessed product), and the BH curve is obtained. The AC maximum magnetic flux density was obtained by measurement. As a result, the AC maximum magnetic flux density of the untreated product using the steel type α was 67 mT when the frequency was 5 kHz, 51 mT when the frequency was 10 kHz, and the AC maximum magnetic flux density of the untreated product using the steel type β was 108 mT. It was.

  In Table 2 below, a ring-shaped test piece cut out from the steel type α and the steel type β was subjected to magnetic annealing at 850 ° C. for 3 hours, and then a zinc phosphate film was formed under the same conditions as above. In the same manner as described above, a heat-treated primary coil and a magnetic flux detection secondary coil are wound, and the BH curve is measured to determine the maximum AC magnetic flux density. The obtained results are shown (Nos. 1 and 12).

  The ratio of the AC maximum magnetic flux density (with P diffusion layer / unprocessed product) when the P diffusion layer is provided with respect to the AC maximum magnetic flux density of the untreated product is calculated and shown in Table 2 below. In Table 2 below, No. 1 and No. For No. 12, the ratio of the AC maximum magnetic flux density without the P diffusion layer to the AC maximum magnetic flux density of the untreated product (no P diffusion layer / unprocessed product) was calculated.

  Based on the ratio value of the AC maximum magnetic flux density, AC magnetic characteristics are evaluated according to the following criteria, and the evaluation results are also shown in Table 2 below. In the present invention, a case where the ratio of the AC maximum magnetic flux density when measured at a frequency of 5 kHz is 1.10 or more (evaluation ○ or evaluation ◎) is evaluated as being excellent in AC magnetic characteristics.

<Evaluation criteria>
◎ (Pass): Ratio of AC maximum magnetic flux density is 1.20 or more (that is, increase by 20% or more with respect to AC maximum magnetic flux density of the comparative material (without P diffusion layer))
○ (Pass): The ratio of the AC maximum magnetic flux density is 1.10 or more and less than 1.20 (that is, in the range of 10% or more and less than 30% with respect to the AC maximum magnetic flux density of the comparative material (without P diffusion layer)). .)
X (failed): AC maximum magnetic flux density ratio is less than 1.10 (that is, the rate of increase of the comparative material (without P diffusion layer) with respect to the AC maximum magnetic flux density is less than 10%.)

  It can be considered as follows from Table 2 below.

  First, the results of measuring the AC maximum magnetic flux density at a frequency of 5 kHz will be considered.

  No. 1 and No. No. 12 is a comparative example in which no heat treatment was performed after the P film was formed, and no P diffusion layer was formed. Therefore, the AC maximum magnetic flux density is comparable to that of the untreated product (No. 12) or lower than that of the untreated product (No. 1).

  No. 2, 3, 13, and 14 are examples that do not satisfy the requirements defined in the present invention, and the P diffusion layer is too thin, so that the AC magnetic characteristics cannot be improved.

  No. Nos. 4 to 11 and 15 to 21 are examples satisfying the requirements defined in the present invention, and a P diffusion layer having a desired thickness can be formed on the surface layer portion of the test piece. The AC magnetic characteristics can be improved compared to a comparative material (untreated product) that is not provided. In particular, when the thickness of the P diffusion layer is 30 μm or more, the ratio of the AC maximum magnetic flux density is 1.20 or more, indicating that the AC magnetic characteristics are particularly excellent (Nos. 7 to 11, 18 to 21). .

  Further, it can be seen from Table 2 that the thickness of the P diffusion layer increases as the heat treatment temperature for forming the P diffusion layer is increased or the heat treatment time is increased.

  Next, the test piece using the steel type α will be considered based on the result of measuring the AC maximum magnetic flux density at a frequency of 5 kHz and the result of measuring the AC maximum magnetic flux density at a frequency of 10 kHz. No. Nos. 5 to 11 are excellent in AC magnetic characteristics even in an AC magnetic field having a frequency of 10 kHz. On the other hand, no. No. 4 is excellent in AC magnetic characteristics when the frequency is 5 kHz, but it can be seen that when the frequency is set to 10 kHz, the effect of improving the AC magnetic characteristics decreases. From this result, it is understood that the thickness of the P diffusion layer is recommended to be 25 μm or more when used in a high-frequency magnetic field.

  Next, FIG. 1 shows the relationship between the thickness of the P diffusion layer and the ratio of the AC maximum magnetic flux density. In FIG. 1, about the test piece (Nos. 1-11) using steel grade (alpha), the result measured at the frequency of 5 kHz is (circle), the result measured at the frequency of 10 kHz is □, and the test piece (No. With respect to 21), the results of measurement at a frequency of 5 kHz are indicated by ▲. As is apparent from FIG. 1, it can be seen that as the thickness of the P diffusion layer increases, the ratio of the AC maximum magnetic flux density tends to increase, and the AC magnetic characteristics can be improved.

[Experiment 2]
Steel containing chemical components shown in Table 3 below (with the balance being iron and inevitable impurities) was vacuum-melted to prepare 150 kg of melted material. In Table 3 below, the value (Z value) on the left side of the above formula (2) is calculated and shown. In addition, No. shown in Table 3 below. The chemical components of the steels 31 and 34 are the same as the steel types α and β shown in Table 1 above.
Z value = 13 × [C] + 2 × [Si] + [Mn] + [Cr] / 5 + [Al]

  The obtained molten material was forged to produce a steel material having a diameter of 40 mm, and the cold forgeability was evaluated by the following procedure.

<Evaluation of cold forgeability>
The cold forgeability of the steel material was evaluated by the deformation resistance when the test piece was 50% compressed and the deformability when the sample was compressed. Specifically, the deformation resistance (N / mm ² ) of the steel material was measured by cutting a test piece having a diameter of 16 mm × a height of 24 mm from the steel material and compressing the test piece so that the height of the test piece was 50%. . The compression process was performed by constraining the end face at a strain rate of 10 / sec. The measured deformation resistance is shown in Table 3 below. In this invention, deformation resistance evaluated less than 580 N / mm < ² > as pass, and evaluated 580 N / mm < ² > or more as failure. FIG. 2 shows the relationship between the Z value and the measured deformation resistance value.

  On the other hand, the deformability of the steel material was evaluated by performing compression processing under the above conditions and then observing the test piece with the naked eye and an optical microscope (observation magnification: 40 times) to check for the presence of cracks. The presence or absence of cracking is shown in Table 3 below. The case where the crack does not occur is passed, and the case where the crack is generated is rejected.

  In the present invention, the case where both the deformation resistance and the deformability satisfy the acceptance criteria is evaluated as "excellent in cold forgeability", and at least one of the cases does not satisfy the acceptance criteria. It was evaluated as “inferior in cold forgeability”.

The following table 3 and FIG. 2 can be considered as follows. No. 31, 32, 34, 36, 40, 42, 49, 50 to 52 are examples in which the chemical composition of the steel material satisfies the requirements defined in the present invention, the deformation resistance is less than 580 N / mm ² , and compression No cracks occur during processing, and it has excellent cold forgeability.

In contrast, no. 33, 35, 37-39, 41, 43-48 are examples in which the chemical composition of the steel material does not satisfy the requirements defined in the present invention, and the deformation resistance is 580 N / mm ² or more, or compression processing Since cracks sometimes occurred, cold forgeability is poor.

Specifically, no. 33, 35, and 37 are examples in which C, Si, and Mn respectively exceed the upper limit values defined in the present invention. Since the Z value is larger than 2.8, the deformation resistance is 580 N / mm ² or more. became. No. No. 38 is an example in which P exceeds the upper limit specified in the present invention. Since the grain boundary segregation amount of P increased, the deformability decreased and cracking occurred during compression processing. No. 39 is an example in which S exceeds the upper limit defined in the present invention. Since a large amount of sulfides precipitated at the grain boundaries, the deformability decreased and cracking occurred during compression processing. No. 41 is an example in which Cr exceeds the upper limit defined in the present invention. Due to the solid solution of Cr, the hardness of the ferrite structure increased too much and the deformability decreased, and cracking occurred during compression processing. No. No. 43 had a deformation resistance of 580 N / mm ² or more because Al exceeded the upper limit defined in the present invention. No. 44 is an example in which N exceeds the upper limit defined in the present invention. Excess N caused age hardening to reduce deformability, and cracking occurred during compression processing. No. 45 is an example in which O (oxygen) exceeds the upper limit defined in the present invention. Excess O produced a large amount of oxide in the steel, and this oxide reduced the deformability of the steel material, and cracking occurred during compression processing. No. In Nos. 46 to 48, the chemical composition of the steel material satisfied the range specified in the present invention, but the Z value exceeded 2.8, so the deformation resistance was 580 N / mm ² or more.

Claims (6)

The chemical composition of the parent phase is
C: 0.002 to 0.20% (meaning mass%, the same shall apply hereinafter),
Si: 1.2% or less (excluding 0%),
Mn: 0.05 to 2.6%,
P: 0.050% or less (excluding 0%),
S: 0.05% or less (excluding 0%),
Cr: 4% or less (excluding 0%),
Al: 0.002 to 2.2%,
N: 0.01% or less (excluding 0%),
O: 0.03% or less (excluding 0%),
Balance: the surface layer of the steel bars is iron and inevitable impurities, the amount P satisfying the following formula (1) (P _D) and P diffusion layer is formed containing, and the thickness of the P diffusion layer than 20μm Soft magnetic steel parts with excellent AC magnetic characteristics characterized by
P _B + 0.1 ≦ P _D ≦ 2.0 (1)
Wherein (1), P _D is the amount P contained in the P diffusion layer (mass%), P _B represents the amount P contained in the matrix of the steel component (mass%). ] The soft magnetic steel part according to claim 1, wherein the chemical component composition further satisfies the following formula (2).
13 × [C] + 2 × [Si] + [Mn] + [Cr] / 5 + [Al] ≦ 2.8 (2)
[In Formula (2), [] has shown content (mass%) of each element. ] The steel part further includes, as other elements,
The soft magnetic steel part according to claim 1 or 2, comprising Cu: 0.5% or less (excluding 0%) and / or Ni: 0.5% or less (excluding 0%). . A method for producing the soft magnetic steel part according to claim 1,
A method for producing a soft magnetic steel part having excellent AC magnetic characteristics, characterized by heating a strip having a P film on its surface and processed into a part shape.   The manufacturing method according to claim 4, wherein the P film is formed using a phosphate. The manufacturing method of Claim 4 or 5 which makes the temperature increase rate when heating the said strip steel 100-400 degreeC / hour.

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