WO2018088328A1

WO2018088328A1 - Steel material for soft magnetic components and method for producing soft magnetic component using same

Info

Publication number: WO2018088328A1
Application number: PCT/JP2017/039760
Authority: WO
Inventors: 昌之坂田; 千葉　政道
Original assignee: 株式会社神戸製鋼所
Priority date: 2016-11-09
Filing date: 2017-11-02
Publication date: 2018-05-17
Also published as: JP2018076556A; TW201825693A

Abstract

A steel material for soft magnetic components, which exhibits excellent magnetic characteristics after annealing, and which is characterized by being composed of 0.0001 mass% to 0.05 mass% of C, more than 0 mass% but 0.5 mass% or less of Si, 0.1 mass% to 0.5 mass% of Mn, more than 0 mass% but 0.02 mass% or less of P, more than 0 mass% but 0.1 mass% or less of S, more than 0 mass% but 0.05 mass% or less of Al and more than 0.01 mass% but 0.1 mass% or less of N, with the balance made up of Fe and unavoidable impurities, while having an area ratio of the ferrite structure of 95.0% or more. This steel material for soft magnetic components is also characterized by satisfying formula (1). [N] - (1/2[Al]) > 0.01 (1) In the formula, [N] and [Al] represent the contents (mass%) of N and Al, respectively.

Description

Steel material for soft magnetic parts and method for producing soft magnetic parts using the same

The present disclosure relates to a steel material for soft magnetic parts and a method for producing a soft magnetic part using the steel material. In particular, the present disclosure relates to iron core materials or cover materials (so-called soft magnetic materials) used for solenoids, relays, solenoid valves, etc. used for various electrical components in automobiles, trains, ships, construction machinery, industrial machinery, home appliances, etc. The present invention relates to a soft magnetic steel material suitable for manufacturing a component) and a method of manufacturing a soft magnetic component using the soft magnetic steel material.

The soft magnetic parts that constitute the magnetic circuit in automobile electrical parts and the like are required to have excellent soft magnetic characteristics in order to save power and improve responsiveness. For this reason, a soft magnetic material in which the magnetic flux density inside the soft magnetic component easily responds to an external magnetic field is used.

極 Ultra-low carbon steel is used as a steel material for soft magnetic parts with excellent soft magnetic properties. A wire material or a plate-shaped steel material for soft magnetic parts is formed from ultra-low carbon steel, and a soft magnetic part having a desired shape can be manufactured by a processing technique such as cold forging, pressing, and cutting. In order to facilitate such processing, it has been studied to improve the cold forgeability, press workability or cutting workability of the steel for soft magnetic parts.

For example, Patent Document 1 discloses a technique for increasing the local component strength after cold forging while improving the cold forgeability (particularly, deformation resistance) of the entire steel material for a steel material of extremely low carbon steel. . Specifically, the amount of solid solution N (the amount of solid solution nitrogen) in the portion of the steel material whose strength is to be improved is increased to suppress the amount of solid solution N in the other portions. The portion having a large amount of solute N can increase the mechanical component strength more than the normal deformation resistance. On the other hand, since the amount of solute N is relatively low in the other portions, only the ordinary deformation resistance allowance increases as a whole, and cold forgeability can be ensured.

Patent Document 2 discloses a soft magnetic steel sheet that can accurately process a steel material by cold forging and stably obtain excellent magnetic properties. In the soft magnetic steel material, the deformation resistance can be effectively reduced by controlling the ratio of the B amount to the N amount in the steel, fixing the solid solution N as BN, and reducing the solid solution N in the steel. This achieves excellent magnetic property stability and cold forgeability.

Patent Document 3 discloses a soft magnetic steel material having excellent cold forgeability, cutting workability, and magnetic properties. By finely dispersing MnS in the ferrite crystal grains in the steel material, machinability, in particular, burr resistance (an effect of suppressing burr formation on the cut surface) is improved. Moreover, the magnetic characteristics are improved by adding B to the steel material and changing N in the steel material to BN.

Patent Document 4 discloses a BN free-cutting steel excellent in soft magnetism. B and N are positively added to the steel material, and BN is formed as a free-cutting inclusion in the steel material to improve the cutting workability, particularly the tool life. Note that the presence of B or N that does not form BN decreases soft magnetism, so the N / B ratio is set to 0.8 to 2.5.

JP2011-115815A JP2007-238970 JP 2003-55745 A JP 2001-303209 A

When forming a soft magnetic part by cutting a soft magnetic part steel material, productivity can be improved by unmanned and automated cutting work. However, if the chips extend for a long time, they may become entangled with the work material or tool. If chips are entangled in the work material, it may cause wrinkles on the processed product (soft magnetic component). Further, when the work material is entangled in the tool, the tool life may be shortened by deteriorating the heat radiation efficiency from the tool. For this reason, it is necessary to remove the chips when the work material or the like becomes entangled, but if the apparatus is stopped for that purpose, the productivity is lowered. For this reason, the steel material for soft magnetic parts is required to have a characteristic that chips are naturally divided during cutting and are not easily entangled with a work material or the like (that is, chip disposal is good). .

However, the steel materials disclosed in Patent Documents 1 and 2 are only considered for cold forging and not for cutting. In Patent Document 3, burr resistance is studied among cutting workability, but chip disposability is not studied.

In Patent Document 4, the quality judgment of chip disposal is shown in Table 3, but the determination criteria are not described, and a specific explanation is given as to how the chip disposal can be improved. Absent. Further, from Table 3, if the cutting tool life is good, it can be seen that the chip disposal is good, but there are steel materials that have good chip disposal even if the cutting tool life is poor. Therefore, it is impossible to grasp how the chip disposal can be improved.

Embodiments of the present invention have been made in view of such circumstances, and the purpose thereof is a steel material for soft magnetic parts that has excellent machinability while exhibiting excellent magnetic properties after magnetic annealing. Another object of the present invention is to provide a method for producing a soft magnetic component using the steel material.

Aspect 1 of an embodiment of the present invention is:
Steel material for soft magnetic parts with excellent magnetic properties after annealing,
C: 0.0001 mass% to 0.05 mass%
Si: more than 0% by mass to 0.5% by mass,
Mn: 0.1% by mass to 0.5% by mass,
P: more than 0% by mass to 0.02% by mass,
S: more than 0% by mass to 0.1% by mass,
Al: more than 0% by mass to 0.05% by mass, and N: more than 0.01% by mass to 0.1% by mass,
The balance consists of Fe and inevitable impurities,
A steel material for soft magnetic parts, wherein the ferrite structure has an area ratio of 95.0% or more and satisfies the following formula (1).
[N]-(1/2 [Al])> 0.01 (1)
However, [N] and [Al] indicate the content (mass%) of N and Al, respectively.

Aspect 2 of the embodiment of the present invention is:
The steel material for soft magnetic parts according to aspect 1, further comprising any one or more of the following (a) to (c):
(A) One or more of Cu: more than 0% by mass to 0.10% by mass, Ni: more than 0% by mass to 0.10% by mass, and Cr: more than 0% by mass to 0.10% by mass (B) Ti: more than 0% by mass to 0.10% by mass, and Nb: more than 0% by mass to 0.10% by mass, and satisfying the following formula (2) (c) B: Over 0% by mass to 0.0300% by mass and satisfies the following formula (3)

[N] − (1/2 [Al] +1/4 [Ti] +1/7 [Nb])> 0.01 (2)
[N] − (1/2 [Al] +1/4 [Ti] +1/7 [Nb] + [B])> 0.01 (3)
However, [Ti], [Nb] and [B] represent the contents (mass%) of Ti, Nb and B, respectively.

Aspect 3 of the embodiment of the present invention is:
Forming the steel material for soft magnetic parts according to aspect 1 or 2 into a part shape;
An annealing process of annealing the formed steel material for soft magnetic parts so that the amount of solute N in the steel is 90 ppm or less.

Aspect 4 of the embodiment of the present invention provides:
The annealing process is the manufacturing method according to the aspect 3, wherein the annealing step is performed under a hydrogen atmosphere, an inert gas atmosphere, or a reduced pressure of 10 ⁻² Torr or less.

According to an embodiment of the present invention, there is provided a steel material for soft magnetic parts capable of exhibiting excellent magnetic properties after magnetic annealing while having excellent machinability, and a method for producing a soft magnetic part using the steel material. Can be provided.

It is a figure which shows the example of classification | category of the shape of a chip.

Generally, in soft magnetic parts, in order to improve magnetic properties, the amount of alloying elements added to steel materials for soft magnetic parts (hereinafter sometimes simply referred to as “steel materials”) is made small. Since the grain growth of the ferrite crystal is not inhibited by the alloy element during the annealing process, the number of crystal grain boundaries is reduced. Since the crystal grain boundary becomes an obstacle to domain wall movement, it can be said that the steel material with few crystal grain boundaries is excellent in magnetic properties. However, if the added amount of alloying elements in the steel material is small, the toughness of the steel material increases, and the machinability of the steel material, particularly the chip disposal, deteriorates.

Under such circumstances, the present inventor has conducted intensive research. As a result, by increasing the amount of solute N in the steel material, the magnetic properties are low but the chip treatment is high before magnetic annealing. Later, it was found that a steel material for soft magnetic parts with improved magnetic properties could be obtained. When the amount of solute N in the steel material is large, the magnetic properties are greatly deteriorated. Therefore, before the magnetic annealing, the magnetic properties of the steel material for soft magnetic parts are poor. However, by controlling the annealing conditions, particularly the atmosphere during annealing, at least a part of the solid solution N can be released out of the steel during the magnetic annealing. Thereby, in the final product after magnetic annealing, the amount of solute N is reduced, and a final product having good magnetic properties can be obtained.

Thus, the present inventor can obtain a soft magnetic component having good chip disposal before magnetic annealing and having excellent magnetic properties after magnetic annealing by leaving solid solution N in the steel material. The invention of steel material for soft magnetic parts was completed.
Details of a steel material for soft magnetic parts according to an embodiment of the present invention and a method for producing a soft magnetic part using the same will be described below.

1. Component Composition of Steel Material for Soft Magnetic Parts The component composition of the steel material for soft magnetic parts according to the embodiment of the present invention will be described below.
In addition, unit% display of a component composition means the mass% altogether.

[C: 0.0001 to 0.05%]
C is an element that governs the balance between the strength and ductility of the steel material, and the strength decreases and the ductility improves as the amount added is reduced. From the viewpoint of efficiently producing a steel material, the lower limit of the C content is set to 0.0001%. The amount of C is preferably 0.001% or more, and more preferably 0.002% or more. However, the magnetic properties are better as the volume fraction of ferrite, which is a ferromagnetic material, increases. When the amount of C is large, cementite precipitates, the volume fraction of ferrite decreases, and cementite hinders domain wall movement, so that the magnetic properties deteriorate. Therefore, the upper limit of the C amount is set to 0.05%. The amount of C is preferably 0.03% or less, and more preferably 0.015% or less.

[Si: over 0 to 0.5%]
Si is used as a deoxidizer during melting. Furthermore, the effect of improving the magnetic characteristics is brought about. In order to effectively exhibit the above effect, Si is preferably 0.001% or more, more preferably 0.003% or more. However, if Si is excessively contained, the magnetic properties are deteriorated. Therefore, the upper limit of Si content is set to 0.5%. The amount of Si is preferably 0.4% or less, and more preferably 0.3% or less.

[Mn: 0.1 to 0.5%]
Mn acts effectively as a deoxidizer. Further, Mn combines with S contained in the steel material and finely disperses as MnS precipitates, thereby forming a chip breaker for chips generated during the cutting process and contributing to improvement of machinability. In order to exhibit such an action effectively, the amount of Mn was determined to be 0.1% or more. The amount of Mn is preferably 0.15% or more, more preferably 0.20% or more. If the amount of Mn is too large, the magnetic properties are deteriorated. The amount of Mn is preferably 0.45% or less, more preferably 0.4% or less, and still more preferably 0.38% or less.

[P: over 0 to 0.02%]
P (phosphorus) is an element that causes grain boundary segregation in steel and deteriorates magnetic properties. Therefore, the P amount is suppressed to 0.02% or less to improve the magnetic characteristics. The amount of P is preferably 0.015% or less, more preferably 0.010% or less. The smaller the amount of P, the better. However, it is usually contained by about 0.001%.

[S: over 0 to 0.1%]
S (sulfur) forms MnS in steel as described above, and has a function of improving the machinability by becoming a stress concentration spot when stress is applied by cutting. In order to exhibit such an action effectively, S may be contained in an amount of 0.003% or more, and more preferably 0.010% or more. However, if the amount of S is excessively increased, an excessive increase in the number of MnS harmful to the magnetic properties is caused. Therefore, the amount of S is determined to be 0.1% or less. The amount of S is preferably 0.05% or less, more preferably 0.030% or less.

[Al: more than 0 to 0.05%]
Al is an element added as a deoxidizing material, and has an effect of reducing impurities and improving magnetic properties with deoxidation. In order to exert this effect, the Al content is preferably 0.001% or more, more preferably 0.002% or more. Further, Al can combine with N in the steel material to form AlN. The formed AlN acts as a pinning particle that suppresses crystal grain growth in an annealing process to be described later, and therefore increases the crystal grain boundary that hinders domain wall movement, thereby degrading the magnetic properties. Therefore, the Al content is determined to be 0.05% or less. In order to exhibit more excellent magnetic properties, the Al content is preferably 0.04% or less, more preferably 0.03% or less.

[N: more than 0.01 to 0.1%]
N is an element particularly important in the present invention. When N is present as solid solution N in the steel material, the toughness of the steel material is lowered and the chips are easily cut off during the cutting process. In order to sufficiently exhibit the effect of improving chip disposal, solid solution N needs to be present in the steel material in excess of 0.01%. Therefore, the N content is set to more than 0.01%. In order to further improve the chip disposability, the solid solution N amount is preferably 0.015% or more, and more preferably 0.018% or more. In addition, although solid solution N reduces a magnetic characteristic, it can be made harmless by passing through the manufacturing method of the soft-magnetic component mentioned later. If the amount of N is excessive, N ₂ gas is generated during melting, and there is a problem in safety such that the molten steel scatters. Therefore, in the embodiment of the present invention, the upper limit of the amount of N is 0 from the viewpoint of the productivity of the steel material. Set to 1%.

[Relationship between N and Al contents]
The N content and the Al content in the steel material satisfy the following relational expression.
[N]-(1/2 [Al])> 0.01 (1)
However, [N] and [Al] indicate the content (mass%) of N and Al, respectively.
As described above, in order to improve the chip disposability, it is necessary that solute N is present in the steel material in an amount exceeding 0.01%. By satisfy | filling Formula (1), even if all Al in steel materials reacts with N and forms AlN, solid solution N can exist in more than 0.01%.
The right side of the formula (1) is 0.01, but the right side is preferably 0.015 (that is, the solid solution N exceeds 0.015%), more preferably 0.018 (that is, the solid solution). N is more than 0.018%).

[Balance]
In one preferred embodiment, the balance is iron and inevitable impurities. As inevitable impurities, mixing of trace elements (for example, As, Sb, Sn, etc.) brought in depending on the situation of raw materials, materials, manufacturing equipment, etc. is allowed. In addition, for example, like P and S, it is usually preferable that the content is small. Therefore, although it is an unavoidable impurity, there is an element that separately defines the composition range as described above. For this reason, in this specification, the term “inevitable impurities” constituting the balance is a concept that excludes elements whose composition ranges are separately defined.

However, it is not limited to this embodiment. Any other element may be further included as long as the characteristics of the high-strength steel sheet of the present invention can be maintained. Other elements that can be selectively contained as described above are exemplified below.

[One or more of Cu: more than 0 to 0.10%, Ni: more than 0 to 0.10%, and Cr: more than 0 to 0.10%]
Cu increases the electrical resistance of the ferrite phase and is effective in reducing the decay time constant of the eddy current. However, if Cu is contained excessively, the magnetic moment is lowered and the magnetic properties of the soft magnetic component are deteriorated. Therefore, when Cu is contained, the upper limit is set to 0.1%. Preferably it is 0.05% or less.

Ni, like Cu, increases the electrical resistance of the ferrite phase and is effective in reducing the decay time constant of eddy currents. However, if Ni is contained excessively, the magnetic moment is lowered and the magnetic properties of the soft magnetic component are deteriorated. Therefore, when Ni is contained, the upper limit is set to 0.10%. Preferably it is 0.05% or less.
Cr, like Cu and Ni, increases the electrical resistance of the ferrite phase and is effective in reducing the decay time constant of eddy current. Further, since Cr is a strong carbide-forming element, it is effective in forming carbides and reducing solute C. However, if Cr is excessively contained, the magnetic moment is lowered and the magnetic properties of the soft magnetic component are deteriorated. Therefore, when Cr is contained, the upper limit is set to 0.10%. Preferably it is 0.05% or less.

[Ti: more than 0 to 0.10% and Nb: more than 0 to 0.10%, one or two]
Ti forms TiS and may be added because it is effective in improving chip disposal. In order to effectively exhibit the above effects, it is preferable to add more than 0, for example, 0.005% or more. More preferably, it is 0.01% or more. However, in order to reduce the magnetic properties when excessively added, when Ti is included, the upper limit of Ti is set to 0.10%. Preferably it is 0.05% or less, More preferably, it is 0.03% or less.

Nb may be added because it forms NbC and is effective in reducing the amount of dissolved C and improving magnetic properties. However, if Nb is contained excessively, the solid solution Nb that did not form carbides deteriorates the magnetic properties. Therefore, when Nb is contained, the upper limit of Nb is set to 0.10%. Preferably it is 0.05% or less, More preferably, it is 0.03% or less.

[Relationship between N, Al, Ti and Nb]
When adding Ti, Nb or both, the content of each element is adjusted so as to satisfy the following relational expression (2).
[N] − (1/2 [Al] +1/4 [Ti] +1/7 [Nb])> 0.01% (2)
However, [N], [Al], [Ti] and [Nb] indicate the contents (mass%) of N, Al, Ti and Nb, respectively.

As described above, in order to improve the chip disposability, it is necessary that solute N is present in the steel material in an amount exceeding 0.01%. By satisfying the formula (2), even if all of Al, Ti, and Nb in the steel react with N to form nitrides, solid solution N can exist in an amount exceeding 0.01%.
The right side of the formula (2) is 0.01, but the right side is preferably 0.015 (that is, the solid solution N exceeds 0.015%), more preferably 0.018 (that is, the solid solution). N is more than 0.018%).

[B: Over 0 to 0.0300%]
B is an element that forms BN, which is a compound with N, contributes to lubrication during cutting, and is effective in improving cutting workability (such as burr resistance). However, if B is contained excessively, the hot ductility is lowered, so the productivity of continuous casting and hot rolling is lowered. Therefore, when B is included, the upper limit of B is set to 0.0300%. Preferably it is 0.0200% or less, More preferably, it is 0.0150% or less.

[Relationship between N, Al, Ti, Nb and B]
Here, when adding said B, content of each element is adjusted so that the following relational expression (3) may be satisfy | filled.
[N] − (1/2 [Al] +1/4 [Ti] +1/7 [Nb] + [B])> 0.01 (3)
However, [N], [Al], [Ti], [Nb] and [B] indicate the contents (mass%) of N, Al, Ti, Nb and B, respectively.

As described above, in order to improve the chip disposability, it is necessary that solute N is present in the steel material in an amount exceeding 0.01%. By satisfying formula (3), even if all of Al, Ti, Nb and B in the steel material react with N to form nitrides, solid solution N can be present in excess of 0.01%.
Although the right side of the formula (3) is 0.01, the right side is preferably 0.015 (that is, solid solution N exceeds 0.015%), more preferably 0.018 (that is, solid solution). N is more than 0.018%).

2. Metal structure of soft magnetic component steel material The metal structure of the soft magnetic component preferably contains a large amount of ferrite structure as a ferromagnetic material in order to increase the magnetic moment. For this reason, it is preferable that the steel material for manufacturing the soft magnetic component also contains a large amount of ferrite structure. The ratio of the ferrite structure in the steel material was set to 95.0% or more. Preferably it is 97.0% or more, more preferably 99.0% or more.

3. Method for Producing Steel Material for Soft Magnetic Parts A method for producing a steel material for soft magnetic parts according to the present embodiment is a method for producing a steel material for soft magnetic parts according to the conventional method. Rolling or hot forging.

4). Method for Manufacturing Soft Magnetic Component A method for manufacturing a soft magnetic component using steel will be described.
The steel material for soft magnetic parts according to the embodiment of the present invention is formed into a desired part shape. As the forming method, conventional methods such as cold forging, hot forging, pressing and cutting can be adopted. Although the steel material of the present invention is characterized by excellent machinability, soft magnetic parts may be manufactured by other processing methods without performing the cutting processing. For example, cutting and forging may be combined, or molding may be performed only by forging.

Subsequently, magnetic annealing is performed on the steel material (molded product) formed into a part shape so that the amount of solute N in the steel material is 90 ppm or less. Thereby, a soft magnetic component is manufactured. Before the magnetic annealing, solid solution N is contained in the steel material in an amount of more than 0.01% (more than 100 ppm). The magnetic properties of the soft magnetic parts after annealing can be improved by releasing a part of the solute N in the steel out of the steel by magnetic annealing and reducing the amount of solute N in the steel to 90 ppm or less. . The amount of solute N in the steel after annealing is preferably 80 ppm or less, more preferably 70 ppm or less, and even more preferably reduced to 60 ppm or less.

Magnetic annealing can also remove strains that degrade magnetic properties. In addition, the area ratio of the crystal grain boundary that makes the crystal grains coarse and deteriorates the magnetic characteristics can be reduced.

Annealing conditions include control of annealing temperature, annealing time, and annealing atmosphere, but it is important to control the annealing atmosphere from the viewpoint of releasing solid solution N sufficiently outside the steel. Below, each annealing condition is demonstrated.

The annealing temperature is preferably 500 ° C. to 1200 ° C., more preferably 600 ° C. to 1100 ° C., and still more preferably in order to remove strain in the steel material and reduce the area ratio of the grain boundaries. 700 ° C. to 1000 ° C.

The annealing time is preferably 0.5 hours to 10 hours, more preferably 1 hour to 8 hours, and even more preferably, in order to remove strain in the steel material and reduce the area ratio of the grain boundaries. Preferably, it is 2 hours to 5 hours.

The annealing atmosphere is selected such that the solute N in the steel material is easily released out of the steel so that the amount of solute N in the steel is 90 ppm or less. For example, a hydrogen atmosphere, an inert gas atmosphere, or a reduced pressure of 10 ⁻² Torr or less is preferable. Here, the “inert gas” is a gas having low reactivity, and examples thereof include nitrogen and argon.
By performing magnetic annealing in the annealing atmosphere, solid solution N harmful to the magnetic properties is sufficiently released out of the steel, and the magnetic properties of the soft magnetic parts are dramatically improved.

In the case of annealing in a hydrogen atmosphere and an inert gas atmosphere, the moisture content in the atmosphere is preferably 0.5% or less because the effect of releasing solid solution N is improved. The amount of water is more preferably 0.05% or less, and even more preferably 0.005% or less.

Further, when annealing under reduced pressure, it is preferable to reduce the amount of residual oxygen as much as possible in order to effectively exhibit the effect of releasing solid solution N. If the amount of residual oxygen is large, an oxide scale is formed on the surface of the steel material, and it is considered that solute N is difficult to be released out of the steel. In the case of annealing under reduced pressure, the upper limit of the degree of vacuum is set to 10 ⁻² Torr from the viewpoint of reducing the amount of residual oxygen. It is preferably 10 ⁻³ Torr or less, more preferably 10 ⁻⁴ Torr or less.

According to the method for manufacturing a soft magnetic component in the present embodiment, a soft magnetic component having excellent magnetic characteristics can be manufactured even when a steel material having a high solid solution N amount (that is, poor magnetic characteristics) is used.

Hereinafter, the embodiments of the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and may be appropriately changed within the scope applicable to the purpose described above and below. Of course, the present invention can be carried out in addition to those described above, and both are included in the technical scope of the present invention.

1. Cutting test Specimens with the composition shown in Table 1 were melted. Cast pieces of steel types D and E were hot-rolled at 1100 ° C, and cast pieces of steel types A to C and F to O were heated at 1100 ° C. Inter-forging was performed to obtain a bar with a diameter of 42 mm. Thereafter, a wire piece having a length of 1000 mm was cut out from the bar and subjected to a normalizing treatment at 1200 ° C. for 1 hour. The atmosphere of the normalizing treatment was in the air. In addition, since the oxide scale is formed in the surface of the wire piece before the normalization process, it is suppressed by the normalization process that the solid solution N in the wire piece is released into the atmosphere.

A sample for cutting test having a length of 400 mm was cut out from the wire piece after the normalizing treatment. The cutting test was carried out using an LS-N type NC lathe manufactured by Otsuchi Corporation (currently Okuma Corporation). The cutting conditions were a feed rate of 0.04 mm / rev, a cutting depth of 0.2 mm, and a cutting rate of 50 m / min, 75 m / min, 100 m / min, and 150 m / min. Moreover, the chip | tip (model number: SNMA12404 T9005) by Tangaloy Co., Ltd. was used for the cutting tool.

Using the chips produced in the cutting test of each sample, the chip disposal of each sample was evaluated by the following procedure.
Ten chips of each sample were collected at random, and the shapes were classified into the following four levels A to D as shown in FIG. Each level is explained as follows.
A: 1 turn or less with radius R exceeding 10 mm, or irregular connection B: Winding length (length of spiral chip in the central axis direction) is over 40.0 mm C: Winding length is 40.0 mm or less D: 1 roll or less with radius R of 10 mm or less

If the chips extend for a long time, they may become entangled with the work material and the tool, resulting in deterioration of the product quality and damage to the tool. In the embodiment of the present invention, A is the longest chip and is not preferable. B to D are acceptable chips, in particular D is the best, C is the next, and B is the next. Based on these evaluations, the chip disposal index was calculated by the following formula (4) weighted by a coefficient.
(Chip disposal index) = (Number of chips of D) × 10 + (Number of chips of C) × 20/3 + (Number of chips of B) × 10/3 (4)

Table 2 shows the chip disposal index at each cutting speed for each sample. In the “determination” in Table 2, a chip treatment index exceeding 50 at all cutting speeds was accepted (◯), and a chip treatment index at two cutting speeds was 50 or less was rejected (×). did. From this result, it can be considered as follows.

Steel types A, B, G, H, J, K, L, and N are examples that satisfy the requirements defined in the embodiments of the present invention, and the chip treatment index exceeds 50 at all cutting speeds. It turns out that it is a steel material with high processability.
Steel types D, E, and F have a small amount of N and a small amount of solid solution N (does not satisfy formula (1)). However, since there are many other alloy elements (C, Si, Mn, P, S, Al, etc.), chip disposal was high.

Steel type C has a small amount of N and a small amount of solid solution N (does not satisfy equation (1)). Therefore, when the cutting speed is high (75 m / min, 100 m / min, and 150 m / min), the chip treatment index is low, and the chip disposability is not sufficient.

Steel type M has a small amount of solute N (does not satisfy formula (2)). Therefore, when the cutting speed is high (100 m / min and 150 m / min), the chip treatment index is low, and the chip disposability is not sufficient.

Steel type O has a small amount of solute N (does not satisfy formula (3)). Therefore, when the cutting speed is high (75 m / min, 100 m / min, and 150 m / min), the chip treatment index is low, and the chip disposability is not sufficient.

As described above, the steel type having inferior chip disposal has a lower chip disposal index as the cutting speed increases, and the chip disposal has deteriorated. On the other hand, in the steel types satisfying the requirements of the component composition defined in the embodiment of the present invention, the chip treatment index satisfied the acceptance criteria even at a high cutting speed, and the chip disposal was good.

2. Measurement of magnetic properties The measurement of magnetic properties was performed on steel materials (steel types A, B, D to L, and N) that passed the chip disposal evaluation in the cutting test.
The specimens having the composition shown in Table 1 were melted. The cast pieces of steel types D and E were hot-rolled at 1100 ° C., and the cast pieces of steel types A, B, F to L and N were heated at 1100 ° C. Inter-forging was performed to obtain a bar with a diameter of 38 mm. Then, the normalizing process for 1 hour was performed at 1200 degreeC. Thereafter, the rod was cut to prepare a ring-shaped sample having an outer diameter of 38 mm, an inner diameter of 30 mm, and a thickness of 4 mm. The ring-shaped sample was magnetically annealed at an annealing temperature of 850 ° C. and an annealing time of 3 hours. The annealing atmosphere is listed in Table 3. In the annealing atmosphere, in the hydrogen atmosphere, hydrogen gas of 99.99% hydrogen is filled in the annealing furnace, the moisture content in the annealing furnace is controlled to 0.001% or less, and in the nitrogen atmosphere, liquid nitrogen is vaporized and nitrogen is 99.99. % Of nitrogen gas in the annealing furnace, the moisture content in the annealing furnace is controlled to 0.09% or less, and in the argon atmosphere, 99.9% of argon gas is filled in the annealing furnace, and the moisture in the annealing furnace is filled. The amount was controlled to 0.28% or less, and 10 ⁻³ Torr or less under reduced pressure.

About the ring-shaped sample after annealing, the magnetic measurement was performed as follows. After winding the magnetization application coil and magnetic flux detection coil, the HB curve is measured according to JIS C2504 using an automatic magnetization measurement device (DC magnetic measurement device BHS-40CD manufactured by Riken Denshi Co., Ltd.) The relative permeability was determined. The maximum relative magnetic permeability was 4000 or more, and the magnetic properties were acceptable.

Moreover, among the ring-shaped samples after annealing, samples of steel types A, B, G, H, J, K, L, and N were measured for the amount of N in the steel. The amount of N was measured using LECO oxygen / nitrogen analyzer ON836. The N amount to be measured is the total amount of the solute N amount and the N amount fixed as nitride. “Solubility N amount” in Table 3 indicates that alloy elements (Al, Ti, Nb, and B) that can form nitrides among the alloy elements (see Table 1) of the steel material used for the preparation of the ring-shaped sample. It was calculated assuming that all nitrides were formed.
Table 3 shows the measurement results of the magnetic characteristics. In “judgment” in Table 3, a sample having a maximum relative permeability exceeding 4000 was evaluated as acceptable (◯), and a value of 4000 or less was rejected (x). From this result, it can be considered as follows.

Sample No. Reference numerals 1, 7 and 11 to 16 are invention examples in which annealing was performed in a hydrogen atmosphere. The amount of solute N was 90 ppm or less in all samples, and the maximum relative magnetic permeability exceeded 4000 in all cases.

Sample No. 2 and 3 are examples of the invention which were annealed in an inert gas atmosphere. The amount of solute N was 90 ppm or less in all samples, and the maximum relative magnetic permeability exceeded 4000 in all cases.

Sample No. 4 is an example of the invention which was annealed under reduced pressure. The amount of solute N was 90 ppm or less in all samples, and the maximum relative magnetic permeability exceeded 4000 in all cases.

As shown in Table 3, when the solid solution N amount of each sample (sample Nos. 1 to 4, 7, and 11 to 16) annealed under a hydrogen atmosphere, an inert gas atmosphere, and a reduced pressure was compared, It can be seen that the effect of releasing N out of the steel is highest in the hydrogen atmosphere, and decreases in the order of hydrogen atmosphere, inert gas atmosphere, and reduced pressure.

Sample No. In No. 5, since the atmosphere at the time of magnetic annealing was air, the amount of solute N was hardly reduced from the steel material (steel type A) before the magnetic annealing and exceeded 90 ppm. Therefore, the maximum relative permeability was 4000 or less.

Sample No. Although the component composition of steel 6 satisfy | fills the range prescribed | regulated to embodiment of this invention, since annealing was not given, the amount of solute N exceeded 90 ppm and the maximum relative magnetic permeability was 4000 or less.

Sample No. No. 8 is an example in which the amount of C is excessive, and since the ferrite area ratio of the used steel material was less than 95%, the maximum relative permeability of the sample after magnetic annealing was 4000 or less.

Sample No. No. 9 is an example in which Mn, P and S are excessive, and the maximum relative permeability was 4000 or less even after magnetic annealing.

Sample No. No. 10 is an example in which Si and Al are excessive, and the maximum relative permeability was 4000 or less even after magnetic annealing.

This application is accompanied by a priority claim based on Japanese Patent Application No. 2016-219158, whose application date is November 9, 2016. Japanese Patent Application No. 2016-219158 is incorporated herein by reference.

Claims

Steel material for soft magnetic parts with excellent magnetic properties after annealing,
C: 0.0001 mass% to 0.05 mass%
Si: more than 0% by mass to 0.5% by mass,
Mn: 0.1% by mass to 0.5% by mass,
P: more than 0% by mass to 0.02% by mass,
S: more than 0% by mass to 0.1% by mass,
Al: more than 0% by mass to 0.05% by mass, and N: more than 0.01% by mass to 0.1% by mass,
The balance consists of Fe and inevitable impurities,
A steel material for soft magnetic parts, wherein the ferrite structure has an area ratio of 95.0% or more and satisfies the following formula (1).
[N]-(1/2 [Al])> 0.01 (1)
However, [N] and [Al] indicate the content (mass%) of N and Al, respectively.
The steel material for soft magnetic parts according to claim 1, further comprising at least one of the following (a) to (c).
(A) One or more of Cu: more than 0% by mass to 0.10% by mass, Ni: more than 0% by mass to 0.10% by mass, and Cr: more than 0% by mass to 0.10% by mass (B) Ti: more than 0% by mass to 0.10% by mass, and Nb: more than 0% by mass to 0.10% by mass, and satisfying the following formula (2) (c) B: Over 0% by mass to 0.0300% by mass and satisfies the following formula (3)

[N] − (1/2 [Al] +1/4 [Ti] +1/7 [Nb])> 0.01 (2)
[N] − (1/2 [Al] +1/4 [Ti] +1/7 [Nb] + [B])> 0.01 (3)
However, [Ti], [Nb] and [B] represent the contents (mass%) of Ti, Nb and B, respectively.
Forming the steel material for soft magnetic parts according to claim 1 or 2 into a part shape;
An annealing step of annealing the formed steel material for soft magnetic parts so that the amount of solute N in the steel is 90 ppm or less.
The manufacturing method according to claim 3, wherein the annealing step is performed under a hydrogen atmosphere, an inert gas atmosphere, or a reduced pressure of 10 −2 Torr or less.