Electromagnetic soft iron

Abstract

Provided is an electromagnetic soft iron having excellent magnetic properties, particularly suitable for steel bars. This electromagnetic soft iron contains 0.010 mass% or less of C, 0.010 mass% or less of Si, 0.01-0.50 mass% of Mn, 0.050 mass% or less of P, 0.050 mass% or less of S, and 0.021-0.100 mass% of Al, and the N concentration in a steel material satisfies the following formula: Nmat-Nsur > = 0.0010 mass%, where Nmat is the N concentration (mass%) at a position 1 mm below the surface, and Nsur is the N concentration (mass%) at a position 0.1 mm below the surface.

Description

Technical Field

[0001] The present invention relates to electromagnetic soft iron having excellent magnetic properties and used for an iron core of a motor, an electromagnetic valve, and the like. Background Art

[0002] In recent years, with the increasing sophistication of vehicle control technology, such as in automobiles, the importance of electronic and electromagnetic control components has increased significantly. In particular, solenoid valves, used to control hydraulic pressure, utilize electromagnetic soft iron, which has excellent magnetic properties, to ensure rapid and stable control of hydraulic pressure.

[0003] For example, Patent Document 1 proposes a soft magnetic steel material in which magnetic properties and cold forgeability are improved by controlling the crystal grain size number of ferrite to 9.1 or less and controlling the dispersion state of carbonitrides.

[0004] Patent Document 2 proposes a soft magnetic steel material having a ferrite grain size number of 7 or less by controlling the amount of Cu+Cr and Mn / S, and a method for producing a soft magnetic steel part by annealing in vacuum or inert gas atmosphere.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 6262599

[0008] Patent Document 2: Japanese Patent No. 5416452 Summary of the Invention

[0009] However, in recent years, the trend of electrification and electrification of automobiles and the like has become stronger, and therefore further performance improvement of the magnetic properties of electronic and electromagnetically controlled components has been required. In contrast, the technologies described in the above-mentioned patent documents 1 and 2 have a problem of not being able to meet the requirements of the performance of the higher magnetic properties.

[0010] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an electromagnetic soft iron having excellent magnetic properties, and in particular, to provide an electromagnetic soft iron suitable for use in steel bars.

[0011] To achieve the above-mentioned objectives, the inventors conducted extensive research on the influence of magnetic properties and material factors and found that the difference in nitrogen concentration between the surface and the interior of electromagnetic soft iron, particularly electromagnetic soft iron bar steel, is closely related to the magnetic properties.

[0012] The present invention has been completed based on the above findings.

[0013] That is, the gist of the present invention is as follows.

[0014] 1. An electromagnetic soft iron comprising: 0.010 mass % or less of C, 0.010 mass % or less of Si, 0.01 to 0.50 mass % of Mn, 0.050 mass % or less of P, 0.050 mass % or less of S, and 0.021 to 0.100 mass % of Al, wherein the N concentration satisfies the following formula, and the remainder is Fe and unavoidable impurities:

[0015] N mat -N sur ≥0.0010 mass%

[0016] in,

[0017] N mat is the N concentration (mass %) at 1 mm below the surface,

[0018] N sur It is the N concentration (mass %) at a position 0.1 mm below the surface.

[0019] 2. The electromagnetic soft iron according to item 1 above, wherein the composition of the electromagnetic soft iron further contains one or more selected from the group consisting of B: 0.0100 mass % or less, Se: 0.300 mass % or less, Ca: 0.0500 mass % or less, Pb: 0.300 mass % or less, Bi: 0.300 mass % or less, Mg: 0.0500 mass % or less, Zr: 0.2000 mass % or less, REM: 0.010 mass % or less, and O: 0.0250 mass % or less.

[0020] 3. The electromagnetic soft iron according to item 1 or 2 above, wherein the composition of the electromagnetic soft iron further contains one or more elements selected from the group consisting of Cr: 2.0 mass% or less, Mo: 1.00 mass% or less, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Ti: 0.10 mass% or less, Nb: 0.10 mass% or less, and V: 0.30 mass% or less.

[0021] 4. The electromagnetic soft iron according to any one of 1 to 3 above, wherein the composition of the electromagnetic soft iron further contains one or more selected from Sn: 0.1000 mass % or less and Sb: 0.1000 mass % or less.

[0022] According to the present invention, it is possible to provide electromagnetic soft iron having excellent magnetic properties, and in particular, to provide electromagnetic soft iron bar steel, which is extremely useful industrially. DETAILED DESCRIPTION

[0023] Hereinafter, the present invention will be described in detail.

[0024] First, the basic components of the electromagnetic soft iron of the present invention will be described.

[0025] C: 0.010 mass% or less

[0026] If the C content exceeds 0.010 mass%, magnetic aging causes deterioration in iron loss, so the C content is limited to 0.010 mass% or less. On the other hand, the lower limit of the C content is not particularly limited, but is preferably 0.001 mass% or more to suppress an increase in refining costs.

[0027] Si: 0.010 mass% or less

[0028] Si is effective as a deoxidizer, but if it exceeds 0.010 mass%, workability is reduced, so it is limited to 0.010 mass% or less. It is preferably 0.005 mass% or less, and more preferably 0.003 mass% or less. On the other hand, the lower limit of the Si amount is not particularly limited, but excessive reduction leads to increased refining costs, so it is preferably 0.001 mass% or more.

[0029] Mn: 0.01-0.50 mass%

[0030] Mn is an element that improves machinability by combining with sulfur to form sulfides. To achieve this effect, at least 0.01 mass% or more must be added. On the other hand, excessive addition can degrade magnetic properties, so the upper limit of the Mn amount is limited to 0.50 mass%. Furthermore, the Mn content is preferably 0.10 mass% or more, and more preferably 0.20 mass% or more. Furthermore, the content is preferably 0.40 mass% or less, and more preferably 0.35 mass% or less.

[0031] P: 0.050 mass% or less

[0032] P has the effect of improving machinability. It can be added to achieve this effect, but in this case, the effect may not be significant unless 0.001% by mass or more of P is added. On the other hand, adding more than 0.050% by mass reduces the toughness of the steel, so the upper limit of the P amount is 0.050% by mass.

[0033] S: 0.050 mass% or less

[0034] S is an element that exists as a sulfide inclusion and is effective in improving machinability. To achieve this effect, it is preferably added at least 0.001 mass%. On the other hand, adding more than 0.050 mass% will reduce the hot workability of the steel and increase surface cracking during continuous casting.

[0035] Therefore, the S content is limited to a range of 0.050 mass% or less. It should be noted that it is preferably 0.040 mass% or less, and more preferably 0.035 mass% or less. Furthermore, it is preferably 0.005 mass% or more, and more preferably 0.010 mass% or more. It is further preferably 0.021 mass% or more.

[0036] Al: 0.021-0.100 mass%

[0037] Al combines with N to form minute nitrides. These nitrides have a pinning force that hinders the movement of grain boundaries and inhibits grain growth, but by controlling their dispersion, the crystal grain size can be coarsened and excellent magnetic properties can be stably obtained.

[0038] In particular, the present invention is characterized by reducing the nitrogen concentration within 0.1 mm below the surface (on the steel surface side) to a predetermined concentration. To achieve this characteristic, when adding Al, at least 0.021 mass% must be added. This is because increasing the amount of nitride effectively increases the pinning force. On the other hand, even if excessive addition exceeds 0.100 mass%, the effect is saturated.

[0039] Therefore, the Al content is limited to the range of 0.021 to 0.100 mass %, preferably 0.025 mass % or more, more preferably 0.030 mass % or more, and preferably 0.090 mass % or less, more preferably 0.080 mass % or less.

[0040] N mat -N sur ≥0.0010 mass%

[0041] in,

[0042] N mat is the N concentration (mass %) at 1 mm below the surface,

[0043] N sur is the N concentration (mass %) at 0.1 mm below the surface,

[0044] Nitrogen combines with aluminum to form nitrides. Nitrides have a pinning force that inhibits grain boundary movement. The smaller and more dispersed they are, the stronger the pinning force. The strength of this pinning force is proportional to the grain size; the stronger the pinning force, the smaller the grain size.

[0045] Therefore, when there is a difference in N concentration between the surface and the interior of the steel material, there will be a difference in grain size between the surface and the interior of the steel material. In this way, if there is a difference in grain size between the surface and the interior, abnormal grain growth will occur, in which coarse grains will erode fine grains, resulting in the formation of extremely coarse grains, which will help improve magnetic properties.

[0046] To effectively utilize this effect, the difference between the N concentration (mass %) at 1 mm below the surface and the N concentration (mass %) at 0.1 mm below the surface must be at least 0.0010 mass %. Preferably, this difference is 0.0020 mass % or greater. Meanwhile, the upper limit of this difference is not particularly limited, but considering the N concentration that can be added to steel using existing technologies, it is approximately 0.1000 mass % or less.

[0047] The amount of nitrogen in the steel is not particularly limited as long as the concentration difference satisfies the above formula and a difference in grain size occurs between the surface and the interior of the steel material. However, it is preferably within a range of approximately 0.0015 to 0.1000 mass %. It is more preferably 0.0025 mass % or greater. Furthermore, it is more preferably 0.0300 mass % or less.

[0048] Here, in order to reduce the N concentration within 0.1 mm below the surface, a heat treatment may be performed to control the nitrogen potential to a value lower than that of the base material. For example, a heat treatment in vacuum (under reduced pressure) may be applied.

[0049] In the present invention, a position 1 mm below the surface refers to a position 1 mm deep from the steel surface of any electromagnetic soft iron member or component. Furthermore, a position 0.1 mm below the surface refers to a position 0.1 mm deep from the steel surface of any electromagnetic soft iron member or component. It should be noted that in the present invention, either the position 1 mm below the surface or the position 0.1 mm below the surface suffices as long as the depth requirements are met. Positions perpendicular to the depth direction (e.g., along the longitudinal or width direction of a rod-shaped member) may be randomly selected.

[0050] The effects of the present invention can be obtained by measuring and controlling the N concentration at the above-mentioned position.

[0051] Although the basic components of the present invention have been described above, in the present invention, the following components may be further appropriately added as needed.

[0052] B: 0.0100 mass% or less

[0053] B improves machinability by combining with N to form nitrides. However, if the B content exceeds 0.0100 mass%, there is a risk of deteriorating magnetic properties. Therefore, the upper limit of the B content is preferably 0.0100 mass%. It is more preferably 0.0050 mass% or less. Even more preferably, it is 0.0030 mass% or less. On the other hand, the lower limit of the B content is not particularly limited, but to fully achieve the effect of improving machinability, it is preferably 0.0005 mass% or more. It is more preferably 0.0010 mass% or more.

[0054] Se: 0.300 mass% or less

[0055] Se improves machinability by combining with Mn to form Se compounds. However, if the Se content exceeds 0.300 mass%, magnetic properties may be degraded. Therefore, the upper limit of the Se content is preferably 0.300 mass%. It is more preferably 0.100 mass% or less. It is even more preferably 0.070 mass% or less. Meanwhile, the lower limit of the Se content is not particularly limited, but to fully achieve the effect of improving machinability, it is preferably 0.001 mass% or more. It is more preferably 0.005 mass% or more.

[0056] Ca: 0.0500 mass% or less

[0057] Ca improves machinability by combining with S to form sulfides. However, if the amount exceeds 0.0500 mass%, magnetic properties may be degraded. Therefore, the upper limit of the Ca amount is preferably 0.0500 mass%. It is more preferably 0.0300 mass% or less. Even more preferably, it is 0.0150 mass% or less. On the other hand, the lower limit of the Ca amount is not particularly limited, but to fully achieve the effect of improving machinability, it is preferably 0.0005 mass% or more. More preferably, it is 0.0010 mass% or more.

[0058] Pb: 0.300 mass% or less, Bi: 0.300 mass% or less

[0059] Pb and Bi improve machinability by minimizing the chips during cutting. However, excessive addition will saturate the effect, so the upper limit of the Pb and Bi amounts is preferably set to 0.300 mass%. The Pb and Bi amounts are more preferably both 0.250 mass% or less. More preferably, both are 0.150 mass% or less. On the other hand, there is no particular lower limit for the Pb and Bi amounts, but in order to fully achieve the effect of improving machinability, they are preferably both 0.005 mass% or more. More preferably, both are 0.010 mass% or more.

[0060] Mg: 0.0500 mass% or less

[0061] While Mg improves machinability, exceeding 0.0500 mass% can significantly degrade magnetic properties. Therefore, the upper limit of the Mg content is preferably 0.0500 mass%. More preferably, it is 0.0300 mass% or less. Even more preferably, it is 0.0150 mass% or less. Meanwhile, the lower limit of the Mg content is not particularly limited, but to fully achieve the machinability-enhancing effect, it is preferably 0.0010 mass% or more. More preferably, it is 0.0030 mass% or more.

[0062] Zr: 0.2000 mass% or less

[0063] While Zr improves machinability, exceeding 0.2000 mass% can significantly degrade magnetic properties. Therefore, the upper limit of the Zr content is preferably 0.2000 mass%. More preferably, it is 0.1000 mass% or less. Even more preferably, it is 0.0500 mass% or less. On the other hand, the lower limit of the Zr content is not particularly limited, but to fully achieve the effect of improving machinability, it is preferably 0.0010 mass% or more. More preferably, it is 0.0030 mass% or more.

[0064] REM: 0.010 mass% or less

[0065] While REM improves machinability, exceeding 0.010 mass% can significantly degrade magnetic properties. Therefore, the upper limit of the REM content is preferably 0.010 mass%. It is more preferably 0.005 mass% or less. Even more preferably, it is 0.004 mass% or less. Meanwhile, the lower limit of the REM content is not particularly limited, but to fully achieve the effect of improving machinability, it is preferably 0.001 mass% or more. It is more preferably 0.002 mass% or more.

[0066] O: 0.0250 mass% or less

[0067] While O (oxygen) improves machinability by coarsening sulfide inclusions, excessive addition can reduce the toughness of the steel and cause premature failure of structural components. Therefore, the upper limit of the O content is preferably 0.0250 mass%. It is more preferably 0.0230 mass% or less, and even more preferably 0.0200 mass% or less. While the lower limit of the O content is not particularly limited, to fully achieve the machinability-enhancing effect, it is preferably 0.0010 mass% or more, and more preferably 0.0050 mass% or more.

[0068] Cr: 2.0 mass% or less, Mo: 1.00 mass% or less, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Ti: 0.10 mass% or less, Nb: 0.10 mass% or less, and V: 0.30 mass% or less

[0069] Cr, Mo, Cu, Ni, Ti, Nb, and V contribute to improving the strength of steel through solid solution strengthening and precipitation strengthening. These elements may be added to adjust the strength to meet the required characteristics of the component, but even if added in excessive amounts, the effect is saturated, so it is preferred that the upper limit be set to the above amount. On the other hand, the lower limit of these elements is not particularly limited and can be 0 mass %.

[0070] Sb: 0.0100 mass% or less, Sn: 0.1000 mass% or less

[0071] Sb and Sn improve descaling properties during shot peening and pickling prior to cold drawing, and can be added as needed when these steps are included in component manufacturing. However, even if Sb and Sn are added in amounts exceeding 0.0100 mass% and 0.1000 mass%, respectively, the descaling-enhancing effect becomes saturated. Therefore, the upper limits of the Sb and Sn amounts are 0.0100 mass% and 0.1000 mass%, respectively. Meanwhile, the lower limits of the Sb and Sn amounts are not particularly limited and can both be 0.0010 mass%.

[0072] The remainder other than the elements described above is Fe and inevitable impurities. Inevitable impurities refer to impurities that enter from raw materials such as ore and scrap iron or the manufacturing environment during industrial steel production, and are permitted as long as they do not negatively affect the characteristics of this embodiment.

[0073] The electromagnetic soft iron (electromagnetic soft iron steel bar) according to the present invention can be produced by conventional methods.

[0074] For example, after the steel having the above-mentioned composition is melted by continuous casting, it is hot rolled at a heating temperature range of 1250 to 920°C and air-cooled. Then, it is hot rolled again at a heating temperature range of 1250 to 920°C, thereby forming it into a specified shape such as a round bar. Then, the electromagnetic soft iron (electromagnetic soft iron bar steel) according to the present invention can be obtained by performing a heat treatment to control the nitrogen potential to a value smaller than that of the base material. Before performing the heat treatment to control the nitrogen potential to a value smaller than that of the base material, forging, cutting and other processing can be performed as needed. In this way, electromagnetic soft iron with excellent magnetic properties can be obtained, and in particular, electromagnetic soft iron suitable for bar steel can be obtained. It should be noted that for the present invention, the shape is not limited to bar steel, and it can also be a steel plate, etc.

[0075] The electromagnetic soft iron of the present invention is particularly preferably used for steel bars used in electromagnetic soft iron components such as solenoid valves, etc. In addition, it can also be used in solenoid valves, voice coil motors, etc. by taking advantage of its excellent magnetic properties.

[0076] Example

[0077] Hereinafter, according to embodiment, the constitution and effect of the present invention will be further specifically described. It should be noted that the present invention is not limited by the present embodiment and can be appropriately changed within the scope of the present invention's gist, and these are all included in the technical scope of the present invention.

[0078] The steel having the composition shown in Table 1 was hot-rolled into round bars with a diameter of 50 mm. The bars were then cut to produce cylindrical (hereinafter also referred to as ring-shaped) test pieces having a central hollow hole, an outer diameter of 45 mm, an inner diameter of 33 mm, and a height of 30 mm. These pieces were then heat-treated at 850°C for 30 minutes in a heating furnace with a controlled nitrogen potential atmosphere.

[0079] The nitrogen concentration at the outer diameter side of the ring-shaped test piece at 0.1 mm and 1 mm below the surface was measured using soft X-ray spectroscopy. The measurement conditions were: accelerating voltage: 8 kV, probe diameter: 10 μm, measuring current: 0.1 μA, and measuring time: 360 seconds.

[0080] Magnetic properties were measured in accordance with JIS C2504 using an excitation winding (primary winding, 220 turns) and a detection winding (secondary winding, 100 turns). A B-H curve was measured using a DC magnetization measuring device, and the magnetic flux density at 200 A / m during the magnetization process was evaluated at a maximum magnetic field of 10,000 A / m. In this test, a value of 1.45 T or higher was considered excellent.

[0081] Similarly, the coercive force was measured and evaluated using a DC magnetic properties tester with a reversal magnetizing force of ±400 A / m. In this example, a coercive force of 45 A / m or less was considered excellent in magnetic properties.

[0082] The evaluation results of the magnetic properties are also recorded in Table 1.

[0083] [Table 1]

[0084]

[0085]

[0086] ※ The unit of composition is mass %, and the remainder is Fe and inevitable impurities.

[0087] As shown in Table 1, it can be seen that all the inventive examples according to the present invention have excellent magnetic properties.

[0088] In contrast, the magnetic properties of the comparative examples that deviate from the present invention are all inferior.

Claims

1. An electromagnetic soft iron, comprising the following components: C: 0.010 mass % or less, Si: 0.010 mass% or less, Mn: 0.01 to 0.50 mass%, P: 0.050 mass% or less, S: 0.050 mass% or less, and Al: 0.021-0.100 mass% Furthermore, the N concentration satisfies the following formula, with the remainder being Fe and unavoidable impurities, N mat -N sur ≥0.0010% by mass in, N mat is the N concentration in mass % at a position 1 mm below the surface, N sur It is the nitrogen concentration in mass % at a position 0.1 mm below the surface.

2. The electromagnetic soft iron according to claim 1, wherein: The composition of the electromagnetic soft iron further comprises B: 0.0100 mass% or less, Se: 0.300 mass% or less, Ca: 0.0500 mass% or less, Pb: 0.300 mass% or less, Bi: 0.300 mass% or less, Mg: 0.0500 mass% or less, Zr: 0.2000 mass% or less, REM: 0.010 mass% or less and O: 0.0250 mass% or less 1 or more of the .

3. The electromagnetic soft iron according to claim 1 or 2, wherein: The composition of the electromagnetic soft iron further comprises Cr: 2.0 mass% or less, Mo: 1.00 mass% or less, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Ti: 0.10 mass% or less, Nb: 0.10 mass% or less and V: 0.30 mass% or less 1 or more of the .

4. The electromagnetic soft iron according to claim 1 or 2, wherein: The composition of the electromagnetic soft iron further comprises Sn: 0.1000 mass% or less and Sb: 0.1000 mass% or less 1 or more of the .

5. The electromagnetic soft iron according to claim 3, wherein: The composition of the electromagnetic soft iron further comprises Sn: 0.1000 mass% or less and Sb: 0.1000 mass% or less 1 or more of the .

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