JP5374233B2 - Soft magnetic steel materials, soft magnetic steel parts, and methods for producing them - Google Patents

Description

  The present invention relates to a soft magnetic steel material, a soft magnetic steel part, and a method for producing the same, and in particular, a soft magnetic steel part exhibiting excellent magnetic properties, a soft magnetic steel material used for manufacturing the soft magnetic steel part, And a manufacturing method thereof.

  For example, electrical parts that are driven by magnetic force mounted on automobiles and industrial machines, and steel parts used for the core material of electromagnetic coils, in addition to the characteristics that can be easily magnetized with a low external magnetic field, A small coercive force is required. For this reason, as a material for the steel part, a pure iron-based soft magnetic steel material in which the magnetic flux density inside the part easily responds to an external magnetic field, for example, having a C content of about 0.01% by mass or less is generally used.

Assuming that low carbon steel is used in this way, for example, in Patent Document 1, B is added to steel and solid solution N, which is an unavoidable impurity, is fixed as BN. It has been proposed to improve magnetic properties by suppressing the magnetic properties. In Patent Document 1, for the purpose of improving cold forgeability and suppressing deterioration of magnetic properties, BN having a predetermined size is dispersed and precipitated at a predetermined density and from the viewpoint of suppressing BN coarsening. It is shown that the BN having an average particle diameter of 0.1 to 2 μm in the ferrite crystal grains is set to 120 to 500 pieces / mm ² .

  However, since the steel material described in Patent Document 1 focuses on cold forgeability, the adverse effect on the magnetic properties due to the form of BN is suppressed, but the influence of other inclusions on the magnetic properties. Therefore, it cannot be said that the magnetic properties are sufficiently satisfactory.

Patent Document 2 proposes that the adverse effect on the magnetic properties is suppressed by controlling the precipitate size and density of MnS. Specifically, as MnS precipitates, MnS precipitates having a particle size of 0.2 μm or more are present in the range of 0.02 to 0.5 / μm ² , and the average particle size of the MnS precipitates By setting the thickness to 0.05 to 4 μm, the machinability is improved and the deterioration of the magnetic properties is suppressed.

  However, the technique of Patent Document 2 focuses on improving machinability, and MnS is also dispersed in steel for improving machinability. For this reason, there is a concern about a decrease in magnetic properties due to MnS, and it cannot be said that the magnetic properties are sufficiently satisfactory.

  Further, Patent Document 3 proposes that an excellent saturation magnetic flux density can be obtained by using a component system mainly composed of an Fe—Co alloy. However, since this steel material uses a large amount of rare metal Co, the cost of the steel material is extremely high and the workability is extremely poor, so the manufacturing method is limited to sintering and the mass production of popular products such as automobiles. There is a problem that is not suitable for.

JP 2007-238970 A JP 2003-55745 A JP 2006-336038 A

  The present invention has been made by paying attention to the above-described circumstances, and its purpose is to provide more excellent magnetic characteristics (specifically, a high magnetic flux density in both a low magnetic field region and a high magnetic field region). To establish a soft magnetic steel part exhibiting excellent magnetic flux density characteristics and a low coercive force characteristic), a soft magnetic steel material used for manufacturing the soft magnetic steel part, and a manufacturing method thereof. is there.

The soft magnetic steel material of the present invention capable of solving the above problems is
C: 0.002 to 0.01% (meaning mass%, the same applies to the components below),
Si: 0.1% or less (excluding 0%),
Mn: 0.01 to 0.09%,
P: 0.025% or less (excluding 0%),
S: 0.005% or less (excluding 0%),
Al: 0.005% or less (excluding 0%),
N: 0.0025% or less (excluding 0%),
B: 0.0008 to 0.0025%, and O: 0.006% or less (excluding 0%)
And the balance: iron and inevitable impurities, satisfying the following formula (1),
It is characterized in that the steel structure is a ferrite single phase structure and the area ratio of MnS is 1.2% or less.
−0.0013 ≦ [N] − (10.8 / 14) [B] ≦ 0.0013 (1)
{In Formula (1), [N] represents the N content (mass%) in the steel, and [B] represents the B content (mass%) in the steel}

  The soft magnetic steel material may be included as inevitable impurities, Cu is 0.04% or less (including 0%), Ni is 0.04% or less (including 0%), and Cr is 0.04% or less ( (Including 0%) is preferable.

  The present invention also prescribes a method for producing the soft magnetic steel material, the method comprising: heating the steel having the component composition to 1000 to 1200 ° C. and then hot rolling to 850 ° C. or higher. It is characterized in that the winding is completed at 800 ° C. or higher after the rolling is completed at the temperature (rolling completion temperature).

  Further, the present invention is a soft magnetic steel part obtained by using the soft magnetic steel material, which satisfies the component composition, and the steel structure is a ferrite single phase structure, and is defined by JIS G 0552 (2005). Also included are soft magnetic steel parts characterized by a ferrite grain size number of 4.0 or less.

  Furthermore, the present invention also relates to a method for manufacturing the soft magnetic steel part, characterized in that the soft magnetic steel material is processed into a part shape and then annealed at 850 to 900 ° C. for 2 hours or more. Included in the invention.

  According to the present invention, it is possible to obtain a soft magnetic steel material (for example, a steel bar or a wire) that exhibits excellent magnetic properties after annealing. Excellent magnetic properties when this soft magnetic steel material is used in the manufacture of electrical parts (soft magnetic steel parts) such as solenoids, relays, and iron cores of solenoid valves used in automobiles, trains, ships, various industrial machines, etc. Therefore, it is possible to contribute to high efficiency and light weight of the electrical component.

FIG. 1 is a graph showing the relationship between [N] − (10.8 / 14) [B] and the magnetic flux density (magnetic field strength: 100 A / m) in the prescribed formula (1). FIG. 2 is a graph showing the relationship between [N] − (10.8 / 14) [B] and the coercive force in the prescribed formula (1). FIG. 3 is a graph showing the relationship between the amount of Mn in steel and the magnetic flux density (magnetic field strength: 100 A / m). FIG. 4 is a graph showing the relationship between the amount of Mn in steel and the coercive force.

  In order to establish a soft magnetic steel part exhibiting excellent magnetic properties, a soft magnetic steel material used for manufacturing the soft magnetic steel part, and a manufacturing method thereof, in particular, the present inventor has developed a chemical composition and a steel structure (matrix structure). And the effect of the precipitates) on the magnetic properties were examined and examined from various angles such as component composition and manufacturing method.

  In order to improve the magnetic properties of soft magnetic steel materials, the magnetic flux density can be improved by reducing the impurity elements and increasing the magnetic moment of the substrate, and the dislocations and precipitates can hinder crystal grain coarsening and domain wall motion. In addition, it is possible to suppress the solid solution elements and lattice distortion caused by them, and to easily perform the domain wall movement to improve the magnetic flux density or reduce the coercive force. It has been found that the magnetic flux density can be sufficiently increased and the coercive force can be sufficiently reduced by sufficiently reducing the solid solution N and the solid solution Mn and MnS.

In particular,
(A) Balance the amount of N in the steel and the amount of B in the steel so as to satisfy the following formula (1), and particularly reduce the solute N by the B in the steel; and
(B) The amount of Mn in steel is 0.09% or less, which is sufficiently lower than that of conventional soft magnetic steel materials to reduce the amount of dissolved Mn, and to keep MnS below a certain level;
The present invention has been completed.
−0.0013 ≦ [N] − (10.8 / 14) [B] ≦ 0.0013 (1)
{In Formula (1), [N] represents the amount of N in the steel (mass%, hereinafter referred to as “%”), and [B] represents the amount of B in the steel (mass%, hereinafter referred to as “%”). }

  First, (A) will be described in detail.

  In the present invention, the factor for [N] in steel: [N] (%) and B in steel: [B] (%): [N] − (10.8 / 14) [B] is expressed by the above formula ( As shown in 1), it was found that it should be within a certain range.

FIG. 1 shows the relationship between [N]-(10.8 / 14) [B] and magnetic flux density (magnetic field strength: 100 A / m) using the results of the examples described later. However, in order to achieve magnetic flux density (magnetic field strength: 100 A / m): 0.94 T or more, [N] − (10.8 / 14) [B] should be 0.0013% or less. I understand. This is because when [N]-(10.8 / 14) [B] is 0.0013% or less, solid solution N can be sufficiently fixed as BN, and dislocation can be prevented from sticking. It is considered that the domain wall movement is facilitated and the magnetic flux density can be increased by suppressing the lattice distortion due to N and the fixed dislocation. In order to achieve a higher magnetic flux density, the above [N]-(10.8 / 14) [B] is preferably set to 0.0011% or less. On the other hand, if [N]-(10.8 / 14) [B] becomes too small, Fe ₂ B tends to be precipitated at the crystal grain boundary, and the magnetic flux density of 0.94 T or more cannot be achieved. From such a viewpoint, the above [N]-(10.8 / 14) [B] is set to -0.0013% or more (preferably -0.0011% or more).

FIG. 2 shows the relationship between [N]-(10.8 / 14) [B] and the coercive force using the results of the examples described later. The coercive force is 55 A / m. It can be seen that [N]-(10.8 / 14) [B] may be 0.0013% or less to achieve the following. Also in this case, it is considered that by satisfying the above relationship, the lattice distortion due to the solid solution N and the fixed dislocations can be suppressed, and the coercive force can be suppressed. In order to achieve a lower coercive force, the above [N]-(10.8 / 14) [B] is preferably made 0.0011% or less. On the other hand, when [N]-(10.8 / 14) [B] becomes too small, as described above, the coercive force is likely to increase due to Fe ₂ B precipitated at the crystal grain boundaries. Therefore, the above [N]-(10.8 / 14) [B] is set to -0.0013% or more (preferably -0.0011% or more).

  Next, the above (A) will be described in detail.

  The solid solution Mn reduces the magnetic moment of the substrate and causes the magnetic properties to deteriorate. Further, MnS which is a precipitate also causes a decrease in magnetic properties.

  FIG. 3 is a graph showing the relationship between the amount of Mn in steel and the magnetic flux density (magnetic field strength: 100 A / m) using the results of Examples described later. FIG. 4 is a graph showing the relationship between the amount of Mn in steel and the coercive force using the results of Examples described later. From FIG. 3 and FIG. 4, the magnetic flux density (magnetic field strength: 100 A / m): In order to achieve 0.94T or more and to achieve a coercive force of 55 A / m or less, the amount of Mn in the steel is suppressed to 0.09% or less, and the formation of the above-mentioned solid solution Mn and MnS is suppressed. Can be seen to be effective. In order to achieve a higher magnetic flux density and a lower coercive force, the amount of Mn in steel is preferably 0.06% or less.

  Even if the amount of Mn in the steel is too small, cracks occur due to hot brittleness due to S that does not form MnS. Therefore, the amount of Mn in the steel is 0.01% or more (preferably 0.03%). Above).

  In the present invention, from the viewpoint of suppressing the formation of MnS, the area ratio of MnS (referred to as MnS existing in ferrite crystal grains and ferrite grain boundaries) is suppressed to 1.2% or less. Preferably it is 1.05% or less.

Incidentally, those examples of the MnS, which others sulfide Mn is present alone, MnO, and composite precipitates MgO, an oxide such as Al ₂ O _3, formed as a composite precipitate with nitride Is also included.

  In order to obtain a steel part (soft magnetic steel part) exhibiting excellent magnetic properties by performing magnetic annealing, the structure of the steel part is 4.0 or less in terms of ferrite grain size specified in JIS G 0552 (2005). It is indispensable to use a ferrite single-phase structure with coarse grains and reduce the grain interface area. The magnetic characteristics are related to the magnitude of the spontaneous magnetization of the material and the amount of energy for fixing the magnetic flux moving inside the steel material, and are affected by the size of the ferrite crystal grains. If the ferrite crystal grains are thus coarsened to reduce the grain boundary area, the coercive force can be reduced and the magnetic flux density can be increased, and magnetic characteristics suitable as a component member of the electrical component can be ensured.

  Even if the ferrite crystal grains become too large, the above effect is saturated. From the viewpoint of productivity such as annealing time, the lower limit of the ferrite grain size number is about 0 to 1.

  In order to easily obtain a steel part exhibiting excellent magnetic properties by performing the magnetic annealing, the steel structure of the steel material (soft magnetic steel material) used for manufacturing the steel part is a ferrite single phase structure, preferably The ferrite grain size number specified in JIS G 0552 (2005) is sized to 6.0 or less (a state where the difference in crystal grain size number is within a range of ± 1.5 and the generation of mixed grains is suppressed). Is good. The steel material (rolled material) is processed, and then subjected to magnetic annealing under the conditions described later to promote recrystallization generation and grain growth, thereby obtaining a steel part with coarsened ferrite grains. Can do.

  The “ferrite single phase structure” in the present invention is intended to include the above BN, MnS, and other precipitates that can be unavoidably formed in the manufacturing process, in addition to the ferrite structure.

  The point of the present invention is to balance the amount of N in the steel and the amount of B in the steel, in particular, to reduce the solid solution N by the B in the steel, and to reduce the solid solution Mn and MnS by keeping the amount of Mn in the steel below a certain level. In order to ensure excellent magnetic properties, these functions and effects can be effectively demonstrated, and excellent workability (for example, cold forgeability) in the manufacturing process of steel parts is ensured, and finally In order to secure the characteristics (strength etc.) when used as electrical parts, etc., it is necessary to make components other than Mn in steel materials and steel parts within the following ranges.

[C: 0.002 to 0.01%]
C is a basic element that governs the balance between strength and ductility of the steel material, and as the content decreases, the strength decreases and the ductility improves. Further, C is an element that is easily dissolved in steel and easily causes strain age hardening, so it is desirable to reduce it as much as possible and ensure excellent magnetic properties (satisfying magnetic properties of JIS-SUYB-0 or higher). It is preferable that the amount is extremely low in terms of the surface. Therefore, in the present invention, the upper limit of the C amount is set to 0.01%. Preferably it is 0.007% or less. On the other hand, the lower limit of the amount of C is set to 0.002% from the viewpoint of ensuring the minimum strength as an electrical component and allowing B to exist as a stable carbide when B is excessively present. Preferably it is 0.003% or more.

[Si: 0.1% or less (excluding 0%)]
Si is an element that acts as a deoxidizer during melting and brings about an effect of improving magnetic properties. From the viewpoint of exerting such an effect, Si may be contained in an amount of 0.003% or more. However, if the amount of Si becomes excessive, cold forgeability deteriorates. In the present invention, from the viewpoint of securing cold forgeability during component molding, the upper limit is set to 0.1%. Preferably it is 0.05% or less, More preferably, it is 0.01% or less.

[P: 0.025% or less (excluding 0%)]
P (phosphorus) is an element that causes grain boundary segregation and causes a decrease in cold forgeability and magnetic properties. Therefore, in the present invention, the upper limit of the P content is 0.025%. Preferably it is 0.015% or less.

[S: 0.005% or less (excluding 0%)]
S (sulfur) shows remarkable solidification segregation and decreases hot brittleness. On the other hand, if S is excessive, the magnetic properties are degraded due to the formation of FeS. Therefore, the upper limit of the S amount needs to be 0.005%. Preferably it is 0.003% or less.

[Al: 0.005% or less (excluding 0%)]
Al is an element that fixes solute N in the form of AlN. If the amount of Al becomes excessive and a large amount of AlN is present, the growth of crystal grains is suppressed and the crystal grain boundaries are likely to increase, leading to a decrease in magnetic properties. Therefore, in the present invention, the amount of Al is suppressed to 0.005% or less. Preferably it is 0.003% or less.

[N: 0.0025% or less (excluding 0%)]
N (nitrogen) combines with Ti, B, Al and the like to form nitrides, but N which does not form nitrides with these elements remains in a solid solution N state. When the solid solution N increases, the lattice strain of the ferrite phase increases as described above, and the magnetic properties deteriorate. In order to reduce the solute N amount, it is effective to reduce the total nitrogen amount in the steel, so the N amount is set to 0.0025% or less. Preferably it is 0.0020% or less.

[B: 0.0008 to 0.0025%]
B fixes solute N in the form of BN, and suppresses a decrease in magnetic properties due to lattice distortion of the ferrite phase. In order to exert this effect, 0.0008% or more of B is contained. Preferably it is 0.0010% or more. B not bonded to N forms a stable carbide [Fe ₂₃ (CB) ₆ ], but when the amount of B becomes excessive, it precipitates as Fe ₂ B at the grain boundary, and the hot ductility is significantly reduced. At the same time, the magnetic properties deteriorate. Therefore, the upper limit of the B amount is 0.0025%. Preferably it is 0.0020% or less.

[O: 0.006% or less (excluding 0%)]
O (oxygen) hardly dissolves in steel at room temperature, exists as a hard oxide (Al ₂ O ₃ , SiO _2, etc.), and greatly reduces magnetic properties. Moreover, the increase of the said hard oxide is caused and it becomes a cause which a deformation resistance rises. Therefore, the amount of O should be reduced as much as possible, and is limited to 0.006% or less in the present invention. Preferably it is 0.004% or less.

  The contained elements defined in the present invention are as described above, and the balance is iron and unavoidable impurities. As the unavoidable impurities, mixing of elements brought in depending on the situation of raw materials, materials, production facilities, etc. can be allowed.

  Cu, Ni, and Cr that can be included as inevitable impurities are elements that cause a decrease in magnetic properties. Therefore, it is preferable to suppress any element to 0.04% or less (more preferably 0.02% or less).

  Next, the reason why the method for producing a soft magnetic steel material is specified in the present invention will be described. In order to achieve the steel structure defined in the present invention and obtain a soft magnetic steel material that exhibits excellent magnetic properties by performing magnetic annealing, after melting and casting the steel satisfying the above component composition by a general method It is very effective to perform hot rolling under the following conditions. Hereinafter, each condition will be described in detail.

[Heating temperature during hot rolling: 1000 to 1200 ° C.]
In order to completely dissolve the alloy components in the matrix, it is desirable to heat at as high a temperature as possible. If the heating temperature is too low, different phases are locally generated during rolling, and cracking may occur during rolling. Furthermore, the roll load at the time of rolling increases, and the productivity tends to decrease. From these viewpoints, the heating temperature is set to 1000 ° C. or higher. Preferably it is 1050 degreeC or more. However, if the heating temperature is too high, the coarsening of the ferrite crystal grains becomes partly remarkable, and the cold forgeability at the time of component molding is lowered. Therefore, the upper limit of the heating temperature is set to 1200 ° C. Preferably it is 1150 degrees C or less.

[Rolling end temperature (finish rolling end temperature): 850 ° C. or higher]
If the rolling end temperature in hot rolling is too low, the steel structure (microstructure) tends to become fine grains, and partial abnormal grain growth (GG, mixed grains) may occur in the subsequent cooling process or annealing process during component manufacturing. Incurs outbreaks. Since the GG generating part causes rough skin and variations in magnetic characteristics during cold forging, it is preferable to ensure uniform sizing. From such a viewpoint, the rolling end temperature is set to 850 ° C. or higher. Preferably it is 875 degreeC or more.

[Winding temperature after hot rolling: 800 ° C or higher]
If the coiling temperature after hot rolling is low, the steel structure (microstructure) tends to be fine and the cold forgeability is reduced as in the case where the rolling end temperature is low. Also, the magnetic properties are degraded. Therefore, the winding is completed at 800 ° C. or higher (preferably 850 ° C. or higher). In addition, the cooling method after winding is not particularly limited, and for example, slow cooling or the like may be performed.

  The soft magnetic steel material of the present invention is hot-rolled under the above conditions to obtain, for example, a rod shape or a linear shape, and the size can be appropriately determined according to the electrical component that is the final product.

[About annealing conditions]
In order to produce a soft magnetic steel part that exhibits excellent magnetic properties even in the soft magnetic steel material of the present invention that has not been subjected to magnetic annealing, but exhibits superior magnetic properties of the JIS-SUYB-0 class level, After processing the soft magnetic steel material into a predetermined part shape (for example, cold forging or warm forging (preferably cold forging) or cutting), magnetic annealing is performed under the following conditions, and the steel structure of the steel part Is a ferrite single-phase structure in which the ferrite crystal grain size is 4.0 or less as defined in JIS G 0552 (2005) and the ferrite crystal grains are coarsened.

  When the annealing temperature in magnetic annealing is too low, the existing precipitates such as nitrides inhibit the growth of ferrite crystal grains, so that coarse crystal grains having a ferrite grain size number of 4.0 or less in practical annealing time. It is difficult to do. Therefore, annealing temperature shall be 850 degreeC or more. However, if the annealing temperature becomes too high, the magnetic properties (particularly the coercive force and the magnetic flux density on the low magnetic field side) are reduced due to strain accompanying the phase transformation, so the upper limit is made 900 ° C.

  If the annealing time is too short, the ferrite crystal grains cannot be sufficiently coarsened even if the annealing temperature is set high. Therefore, the annealing time at the annealing temperature is 2 hours or more. Preferably it is 3 hours or more. However, even if the annealing time is too long, the effect of coarsening the crystal grains is saturated. Therefore, the annealing time is preferably 6 hours or less.

  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.

  150 kg each of sample materials having the composition shown in Table 1 were manufactured by vacuum melting. Then, the melted material is hot forged into a bar shape having a cross-sectional size of 155 mm × 155 mm, welded to a dummy billet material, and then hot-rolled under the conditions shown in Table 2 to produce a steel wire material having a diameter of 40 mm (soft magnetic steel material). Got. Using this, the cross-sectional structure was observed, and after magnetic annealing (annealing conditions are as shown in Table 2) for the purpose of improving the magnetic characteristics, the cross-sectional structure was observed and the magnetic characteristics were evaluated. .

  Observation of the cross-sectional structure of the sample before and after magnetic annealing (classification of steel structure and measurement of ferrite crystal grain size) was performed by the following method. That is, using each steel wire before and after magnetic annealing, the steel wire was embedded in a resin in a state where the cross section (cross section perpendicular to the rolling direction) of the steel wire was exposed, and after polishing, 15% to 30% in a 5% picric acid alcohol solution. After immersing and corroding for 2 seconds, the tissue of the D / 4 (D is a diameter, the same applies hereinafter) site was photographed at 10 times with an optical microscope (Nikon EPIPOT 200), and the type of tissue and JIS G 0552 The ferrite grain size number specified in (2005) was established. In all samples, the steel structure before and after magnetic annealing was a ferrite single phase structure.

  The area ratio of MnS was measured as follows. That is, the steel wire was embedded in a resin in a state where the cross section (cross section perpendicular to the rolling direction) of the steel wire was exposed, and the sample surface was polished with emery paper or diamond buff. Next, five fields of view (size of one field of view: 91 mm × 73 mm) were photographed at a magnification of 400 times in the center with an optical microscope. Then, using the particle analysis software (“Particle Analysis III”), the image was binarized under general conditions, and the average value of the area ratio of MnS in the five fields of view was determined with the black portion as MnS.

  The magnetic properties of each sample were evaluated by the following method. That is, after producing a ring-shaped sample having an outer diameter of 38 mm, an inner diameter of 30 mm, and a thickness of 4 mm using the steel wire, and performing magnetic annealing under the conditions of temperature (holding temperature) and time (holding time) shown in Table 2. In addition, a primary coil for magnetic field application and a secondary coil for magnetic flux detection are wound, and an automatic magnetization measuring device [DC magnetization BH characteristic automatic recording device (BHS-40) manufactured by Riken Electronics Co., Ltd.] is installed. And determined by measuring the H-B curve. No. In No. 10, since the test piece was cracked, the magnetic characteristics were not evaluated.

  These results are also shown in Table 2 (note that the evaluation criteria for characteristics in Table 2 are shown in Table 3).

  It can be considered as follows from Tables 1 and 2 (the following No. indicates the experiment No. in Table 2).

  No. Since 1-4, 11, 12, and 26 satisfy | fill the component composition prescribed | regulated by this invention and were manufactured by the method prescribed | regulated by this invention, the obtained steel materials (steel wire) are expecting a high magnetic characteristic. it can. Moreover, it turns out that all the steel parts obtained by giving annealing to this steel material show the outstanding magnetic characteristic more than evaluation criteria.

  In contrast, no. 5 to 10, 13 to 25, and 27 to 29 are steel components that satisfy the magnetic properties of the evaluation criteria because the chemical components of the steel materials deviate from the requirements of the present invention or were not manufactured under the conditions defined in the present invention. Unfavorable results such as not being obtained.

  No. No. 5, because [N]-(10.8 / 14) [B] exceeds the upper limit of the specified range, solid solution N in steel cannot be sufficiently fixed as BN, and lattice distortion due to solid solution N occurs. As a result, the magnetic properties deteriorated.

No. In No. 6, since [N]-(10.8 / 14) [B] was below the lower limit of the specified range, Fe ₂ B was precipitated due to the presence of excess B, and the magnetic properties were deteriorated.

  No. In No. 7, the amount of C exceeds the upper limit value, and the magnetic characteristics are deteriorated due to the effect of lattice distortion due to C.

  No. In Nos. 8 and 9, the amount of Si exceeded the upper limit value, and cracking occurred during part processing. No. As can be seen from FIG. 9, when Si is excessively contained, the magnetic flux density in the low magnetic field is less affected, but the magnetic flux density in the high magnetic field is reduced.

  No. 10, it can be seen that when the amount of Mn is insufficient, the hot brittleness due to S decreases and cracks occur during hot rolling.

  No. From 13 and 14, it can be seen that if the amount of Mn is excessive, the magnetic moment of the substrate is lowered by Mn solid-dissolved in ferrite, and the area ratio of MnS exceeds the specified value, and the magnetic properties are lowered. .

  No. In No. 15, since the amount of P is excessive, P is segregated at the grain boundary and the magnetic properties are deteriorated.

  No. In No. 16, since the amount of S is excessive, segregation of sulfide occurs at the grain boundary, and the magnetic properties are deteriorated.

  No. No. 17 has an excessive amount of Ni. No. 18 has an excessive amount of Cr. In No. 19, since the amount of Cu is excessive, lattice strain is caused by solid solution elements, and the magnetic properties are deteriorated.

  No. In No. 20, since the amount of Al is excessive, the coarsening of the crystal grains is suppressed by the generation of AlN and the crystal grain boundaries are increased, so that the magnetic properties are deteriorated.

  No. No. 21 has an excessive amount of N, and [N]-(10.8 / 14) [B] exceeds the upper limit of the specified range, so that the reduction of solid solution N is not sufficient, and magnetism due to lattice strain The characteristic is deteriorated.

No. In No. 22, since the amount of B is excessive and [N]-(10.8 / 14) [B] is below the lower limit of the specified range, lattice distortion occurs due to excess B, and the magnetic properties are degraded. As a result. Further, B that could not be completely dissolved in the ferrite was precipitated as Fe ₂ B at the grain boundaries, resulting in a decrease in magnetic properties.

No. No. 23 has an excessive amount of O, so that hard oxides (SiO ₂ , Al ₂ O _3, etc.) are increased and the magnetic properties are deteriorated.

  No. In No. 24, since the amount of Mn is excessive, the amount of B is insufficient, and [N]-(10.8 / 14) [B] exceeds the upper limit of the specified range, It can be seen that the magnetic properties are deteriorated due to moment reduction, excessive precipitation of MnS and lattice distortion due to solute N.

  No. 25, Mn, S, Cr, and N are all contained excessively, the amount of B is insufficient, and [N]-(10.8 / 14) [B] exceeds the upper limit of the specified range. Therefore, it can be seen that the magnetic properties of the substrate are reduced due to a decrease in the magnetic moment of the substrate due to solute Mn, excessive precipitation of MnS, and lattice distortion due to solute N.

  No. In Nos. 27 to 29, the component composition of the steel material satisfies the specified requirements of the present invention, but the following problems occur because the manufacturing conditions deviate from the requirements of the present invention. That is, no. No. 27, because the finish rolling temperature and the coiling temperature during hot rolling were both too low, abnormal grain growth (GG) occurred in a part of the structure of the rolled material, resulting in mixed grains, and recrystallization in magnetic annealing and As a result, the crystal growth did not progress uniformly and the magnetic properties deteriorated.

  No. In Nos. 28 and 29, since the magnetic annealing was not performed under the specified conditions, recrystallization did not proceed sufficiently, resulting in a structure with a large grain boundary area, resulting in poor magnetic properties.

Claims (5)

C: 0.002 to 0.01% (meaning mass%, the same applies to the components below),
Si: 0.1% or less (excluding 0%),
Mn: 0.01 to 0.06 %,
P: 0.025% or less (excluding 0%),
S: 0.005% or less (excluding 0%),
Al: 0.005% or less (excluding 0%),
N: 0.0025% or less (excluding 0%),
B: 0.0008 to 0.0025%, and O: 0.006% or less (excluding 0%)
And the balance: iron and inevitable impurities, satisfying the following formula (1),
A soft magnetic steel material characterized in that the steel structure is a ferrite single phase structure and the area ratio of MnS is 1.05 % or less.
−0.0013 ≦ [N] − (10.8 / 14) [B] ≦ 0.0013 (1)
{In Formula (1), [N] represents the N content (mass%) in the steel, and [B] represents the B content (mass%) in the steel}   Furthermore, Cu: 0.04% or less (including 0%), Ni: 0.04% or less (including 0%), and Cr: 0.04% or less (including 0%) The soft magnetic steel described.   A method for producing the soft magnetic steel material according to claim 1 or 2, wherein the steel having the component composition according to claim 1 or 2 is heated to 1000 to 1200 ° C and hot-rolled to obtain 850 ° C. A method for producing a soft magnetic steel material, characterized in that after completion of rolling at the above temperature (rolling end temperature), winding is completed at 800 ° C. or higher. A soft magnetic steel part obtained by annealing using the soft magnetic steel material according to claim 1 or 2, wherein the steel composition satisfies the component composition according to claim 1 or 2, and the steel structure is a ferrite single phase structure And a ferrite magnetic grain size number defined by JIS G 0552 (2005) is 4.0 or less, a soft magnetic steel part.   The method for producing a soft magnetic steel part according to claim 4, wherein the soft magnetic steel material according to claim 1 or 2 is annealed at 850 to 900 ° C for 2 hours or more after being processed into a part shape. To produce soft magnetic steel parts.

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