Electromagnetic soft iron

Abstract

Provided is electromagnetic soft iron having excellent magnetic properties and machinability, particularly electromagnetic soft iron suitable for use in bar steel. The electromagnetic soft iron according to the present invention contains no more than 0.010 mass% of C, no more than 0.010 mass% of Si, 0.10-0.50 mass% of Mn, 0.010-0.150 mass% of P, and 0.005-0.050 mass% of S, with the remainder comprising Fe and unavoidable impurities.

Description

[Technical Field]

[0001] The present invention relates to an electromagnetic soft iron having excellent machinability and magnetic properties, which is used for the iron cores of motors, solenoid valves, etc. [Background technology]

[0002] In recent years, with the demand for more advanced vehicle control technology in automobiles, etc., the importance of electronic and electromagnetic control parts is increasing. Electromagnetic soft iron, which has excellent magnetic properties, is used in solenoid valves used to control hydraulic pressure, etc., in order to set hydraulic pressure quickly and stably.

[0003] Furthermore, since these parts are primarily formed by cutting, sufficient machinability is also required.

[0004] For example, Patent Document 1 proposes a soft magnetic low-carbon steel material that is excellent in machinability and magnetic properties by controlling the ferrite crystal grain size, the mass ratio of Mn to S, and the dispersion state of MnS.

[0005] Furthermore, Patent Document 2 proposes a soft magnetic steel material that has improved strength and machinability without deteriorating magnetic properties by controlling the grain size number of ferrite and the dispersion state of carbonitrides. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-55745 [Patent Document 2] Patent No. 6262599 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in recent years, with the increasing trend toward electronics and electrification, particularly in automobiles, and in order to improve the performance of electronic and electromagnetic control parts, their shapes have become more complex and their dimensions have become more precise, requiring electromagnetic soft iron to have better machinability than ever before.However, the ferrite grain size and MnS dispersion control technologies described in the above-mentioned Patent Documents 1 and 2 have had the problem that the machinability of the resulting steel materials is insufficient.

[0008] The present invention has been developed in view of the above circumstances, and has as its object to provide electromagnetic soft iron that is excellent in both magnetic properties and machinability, particularly electromagnetic soft iron that is suitable for use in steel bars. [Means for solving the problem]

[0009] In order to achieve the above object, the inventors have conducted extensive research into the effects of alloying elements on machinability and magnetic properties, and have found that the addition of P improves machinability without impairing magnetic properties when used in electromagnetic soft iron, particularly electromagnetic soft iron steel bars.

[0010] The present invention was completed based on the above findings and through further consideration. That is, the gist of the present invention is as follows. 1. Soft magnetic iron having a chemical composition containing C: 0.010% by mass or less, Si: 0.010% by mass or less, Mn: 0.10 to 0.50% by mass, P: 0.010 to 0.150% by mass, and S: 0.005 to 0.050% by mass, with the remainder being Fe and unavoidable impurities.

[0011] 2. The electromagnetic soft iron according to 1 above, wherein the component composition of the electromagnetic soft iron further contains one or more selected from one or more groups consisting of the following groups A to E: Group A: 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, Group B: Cr: 2.0% by mass or less, Mo: 1.00% by mass or less, Cu: 1.0% by mass or less, Ni: 1.0% by mass or less, Ti: 0.10% by mass or less, Nb: 0.10% by mass or less, and V: 0.3% by mass or less, Group C: Sn: 0.1000 mass% or less and Sb: 0.0100 mass% or less, Group D: Al: 0.0300% by mass or less, Group E: N: 0.0100% by mass or less [Effects of the Invention]

[0012] According to the present invention, it is possible to provide electromagnetic soft iron, particularly electromagnetic soft iron steel bar, which has excellent magnetic properties and also excellent machinability. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 10 is a schematic diagram showing the flank wear width (Vb) of the tool of this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be specifically described below. First, the basic components of the electromagnetic soft iron of the present invention will be described. C: 0.010% by mass or less If the C content exceeds 0.010% by mass, the iron loss will deteriorate due to magnetic aging. Therefore, the C content is limited to 0.010% by mass or less. On the other hand, there is no particular lower limit for the C content, but it is preferably 0.001% by mass or more to prevent an increase in refining costs.

[0015] Si: 0.010% by mass or less Although Si is effective as a deoxidizer, if it exceeds 0.010% by mass it reduces workability. Therefore, the Si content is limited to 0.010% by mass or less. Preferably, it is 0.005% by mass or less, and more preferably, it is 0.003% by mass or less. On the other hand, there is no particular lower limit for the Si content, but an excessive reduction leads to an increase in refining costs, so a content of 0.001% by mass or more is preferred.

[0016] Mn:0.10~0.50% by mass Mn is an element that improves machinability by bonding with S to form sulfides, and to achieve this effect, it is necessary to add at least 0.10% by mass. The content is preferably 0.15% by mass or more, and more preferably 0.20% by mass or more. However, excessive addition of Mn reduces magnetic properties, so the upper limit of the Mn content is set to 0.50% by mass. The content is preferably 0.40% by mass or less, and more preferably 0.35% by mass or less.

[0017] P:0.010~0.150% by mass P has the effect of improving machinability. To obtain this effect, it is necessary to add at least 0.010% by mass. On the other hand, even if it is added in excess of 0.150% by mass, the effect of improving machinability saturates. For this reason, the P amount is limited to the range of 0.010 to 0.150% by mass. It is preferably 0.020% by mass or more, and more preferably 0.031% by mass or more. It is also preferably 0.100% by mass or less, and more preferably 0.085% by mass or less.

[0018] S:0.005~0.050% by mass S exists as sulfide-based inclusions and is an element effective in improving machinability. To achieve this effect, an addition of at least 0.005% by mass is necessary. On the other hand, an addition of more than 0.050% by mass reduces the hot workability of the steel and increases surface cracking during continuous casting. Therefore, the S content is limited to the range of 0.005 to 0.050% by mass. It is preferably 0.010% by mass or more, more preferably 0.015% by mass or more, and even more preferably 0.021% by mass or more. It is also preferably 0.040% by mass or less, more preferably 0.035% by mass or less.

[0019] The basic components of the present invention have been described above, but the present invention can further contain, as necessary, one or more components (elements) selected from one or more groups consisting of the following groups A to E. The balance in any case is Fe and inevitable impurities. The inevitable impurities are those that are mixed in from raw materials such as ore and scrap, or the manufacturing environment, during industrial production of steel, and are permissible within a range that does not adversely affect the properties of this embodiment.

[0020] Group A: 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. B: 0.0100% by mass or less B improves machinability by bonding with N to form nitrides. However, if the B content exceeds 0.0100% by mass, there is a risk of degrading magnetic properties, so the upper limit of the B content is preferably 0.0100% by mass. It is more preferably 0.0050% by mass or less, and even more preferably 0.0030% by mass or less. On the other hand, the lower limit of the B content is not particularly limited, but is preferably 0.0005% by mass or more, and more preferably 0.0010% by mass or more.

[0021] Se: 0.300% by mass or less Se improves machinability by combining with Mn to form Se compounds. However, if the Se content exceeds 0.300% by mass, magnetic properties may be reduced, so the upper limit of the Se content is preferably 0.300% by mass. More preferably, it is 0.100% by mass or less, and even more preferably, it is 0.070% by mass or less. On the other hand, the lower limit of the Se content is not particularly limited, but is preferably 0.001% by mass or more, and more preferably, it is 0.005% by mass or more.

[0022] Ca: 0.0500% by mass or less Ca improves machinability by bonding with S to form sulfides. However, if the Ca content exceeds 0.0500% by mass, there is a risk of degrading magnetic properties, so the upper limit of the Ca content is preferably 0.0500% by mass. It is more preferably 0.0300% by mass or less, and even more preferably 0.0150% by mass or less. On the other hand, the lower limit of the Ca content is not particularly limited, but is preferably 0.0005% by mass or more, and more preferably 0.0010% by mass or more.

[0023] Pb: 0.300 mass% or less, Bi: 0.300 mass% or less Pb and Bi improve machinability by reducing the size of chips during cutting. However, excessive addition of these elements will only saturate the effect, so the upper limits for both Pb and Bi are preferably 0.300% by mass. More preferably, each is 0.250% by mass or less, and even more preferably, each is 0.150% by mass or less. While there are no particular lower limits for Pb and Bi, each is preferably 0.005% by mass or more, and more preferably, each is 0.010% by mass or more.

[0024] Mg: 0.0500% by mass or less Mg has the effect of improving machinability, but if the content exceeds 0.0500% by mass, magnetic properties may be degraded. Therefore, the upper limit of the Mg content is preferably 0.0500% by mass. More preferably, it is 0.0300% by mass or less, and even more preferably, it is 0.0150% by mass or less. On the other hand, the lower limit of the Mg content is not particularly limited, but is preferably 0.0010% by mass or more, and more preferably, it is 0.0030% by mass or more.

[0025] Zr: 0.2000 mass% or less Zr has the effect of improving machinability, but if it exceeds 0.2000% by mass, magnetic properties may be reduced. Therefore, the upper limit of the Zr content is preferably 0.2000% by mass. More preferably, it is 0.1000% by mass or less, and even more preferably, it is 0.0500% by mass or less. On the other hand, the lower limit of the Zr content is not particularly limited, but is preferably 0.0010% by mass or more, and more preferably, it is 0.0030% by mass or more.

[0026] REM: 0.010% by mass or less REM has the effect of improving machinability, but if it exceeds 0.010% by mass, magnetic properties may be degraded. Therefore, the upper limit of the REM content is preferably 0.010% by mass. More preferably, it is 0.005% by mass or less, and even more preferably, it is 0.004% by mass or less. On the other hand, the lower limit of the REM content is not particularly limited, but is preferably 0.001% by mass or more, and more preferably, it is 0.002% by mass or more.

[0027] O: 0.0250% by mass or less O (oxygen) has the effect of improving machinability by coarsening sulfide inclusions, but excessive addition can reduce the toughness of the steel and potentially cause premature fracture of structural components. Therefore, the upper limit of the O content is preferably 0.0250% by mass, more preferably 0.0230% by mass or less, and even more preferably 0.0200% by mass or less. On the other hand, the lower limit of the O content is not particularly limited, but is preferably 0.0010% by mass or more, and more preferably 0.0050% by mass or more.

[0028] Group B: 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: 0.3 mass% or less 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 match the required characteristics of the part, but even if added in excess, the effect will saturate. Therefore, it is preferable to set the upper limit of each element to the value listed above. Meanwhile, there are no particular restrictions on the lower limits of the Cr, Mo, Cu, Ni, Ti, Nb, and V contents, and each may be 0 mass%.

[0029] Group C: Sb: 0.0100% by mass or less, Sn: 0.1000% by mass or less Sb: 0.0100 mass% or less, Sn: 0.1000 mass% or less Sb and Sn have the effect of improving descaling properties during shot blasting and pickling, which are performed before cold wiredrawing, and can be added as needed if these processes are included in the part manufacturing process. However, even if Sb and Sn are added in amounts exceeding 0.0100% by mass and 0.1000% by mass, respectively, the effect of improving descaling properties saturates, so the upper limits of the Sb and Sn contents are preferably set to 0.0100% by mass and 0.1000% by mass, respectively. On the other hand, there are no particular restrictions on the lower limits of the Sb and Sn contents, and both can be 0.0010% by mass.

[0030] Group D: Al: 0.0300% by mass or less Al: 0.0300% by mass or less Al bonds with N to form fine nitrides, thereby reducing the crystal grain size and degrading the magnetic properties. To minimize this adverse effect, it is preferable to reduce the Al content to 0.0300% by mass or less, more preferably 0.0015% by mass or less, and even more preferably 0.0010% by mass or less. On the other hand, there is no particular lower limit for the Al content, and it may be 0% by mass. In the present invention, an Al content of up to about 0.0015 mass % can be considered as an unavoidable impurity.

[0031] Group E: N: 0.0100% by mass or less N: 0.0100% by mass or less N deteriorates magnetic properties over time through the aging effect of solute N. To minimize this adverse effect, it is preferable to reduce the N content to 0.0100% by mass or less, more preferably 0.0050% by mass or less, and even more preferably 0.0040% by mass or less. On the other hand, there is no particular lower limit for the N content, and it may be 0% by mass. In the present invention, an N content of up to about 0.0050 mass % can be considered as an unavoidable impurity.

[0032] In the electromagnetic soft iron (electromagnetic soft iron steel bar) and its manufacturing method according to the present invention, items not described in this specification can all be made in accordance with known electromagnetic soft iron or electromagnetic soft iron steel bar and conventional methods. For example, one manufacturing method involves melting steel having the aforementioned chemical composition by continuous casting, hot-rolling it at a heating temperature in the range of 950 to 1250°C, air-cooling it, and then hot-rolling it again at a heating temperature in the range of 950 to 1250°C to form it into a specified shape such as a round bar. This makes it possible to obtain electromagnetic soft iron that has excellent magnetic properties and machinability, and is particularly suitable for use in steel bars, which are often machined into parts by cutting. Note that while the present invention is particularly suitable for steel materials that are machined into parts by cutting, the shape is not limited to steel bars and may be steel plates, etc. [Example]

[0033] The following examples will explain the structure and effects of the present invention in more detail. However, the present invention is not limited to the following examples, and various modifications can be made within the scope of the present invention, and all such modifications are within the technical scope of the present invention.

[0034] Steels having the chemical compositions shown in Table 1 were melted and formed into round bars with a diameter of 25 mm by hot rolling. The magnetic properties and machinability of the obtained round bars were evaluated by the methods described below.

[0035] [Table 1]

[0036] The magnetic properties were measured in accordance with JIS C2504. Specifically, a ring test piece was taken from the round bar and annealed at 750°C for 2 hours. An excitation winding (primary winding: 220 turns) and a detection winding (secondary winding: 100 turns) were then attached to the ring test piece for measurement. The BH curve was measured using a DC magnetization measuring device, and the magnetic flux densities of 100 A / m and 300 A / m were evaluated during the magnetization process at a maximum magnetic field of 10,000 A / m. In this test, magnetic properties can be said to be excellent if the magnetic flux densities are 1.20 T and 1.50 T or higher, respectively. Similarly, using a DC magnetic property tester, the coercive force was measured and evaluated at a reversal magnetization force of ±400 A / m. In this test, if the coercive force was 60 A / m or less, it can be said that the magnetic properties were excellent.

[0037] Next, cutting tests were carried out under the conditions shown in Table 2, and machinability was evaluated by comparing the tool life, surface roughness during cutting, and chip shape.

[0038] [Table 2]

[0039] The tool life was evaluated by the flank wear width of the tool after cutting 5 m of the obtained round bar in the longitudinal direction. As shown in Figure 1, the flank wear width was the flank wear width (Vb) of the average wear area, not the boundary wear area. Under the conditions of this example, a flank wear width of 200 μm or less can be said to have an excellent tool life.

[0040] The surface roughness during cutting was evaluated by cutting the obtained round bar by 1 m in the longitudinal direction, measuring the ten-point average roughness Rz (JIS B 0601) with a stylus roughness meter over a reference length of 4 mm, and then based on the magnitude of the Rz. Under the conditions of this example, it can be said that a surface roughness Rz of 25 μm or less is sufficient to manufacture good-quality parts.

[0041] The chip shape was evaluated based on whether or not three or more rings of chips were formed in the chips generated during cutting in the surface roughness evaluation test. If three or more rings of chips were not formed, the chips were broken into small pieces, and it can be said that the chips are easy to process. Table 3 summarizes the evaluation results for magnetic properties and machinability. Note that when the number in Table 1 is the same as the number in Table 3, it means that the same steel material was used. For example, the composition of the round bar whose evaluation results are shown in No. 1 in Table 3 is the composition shown in No. 1 in Table 1. In addition, in Table 3, ◎ means that the ring of the chips is less than one turn, ○ means that the ring of the chips is one to three turns, and × means that the ring of the chips is three or more turns.

[0042] [Table 3]

[0043] As shown in Table 3, it can be seen that all of the inventive examples according to the present invention have excellent magnetic properties and excellent machinability.

[0044] In contrast, the comparative examples outside the scope of the present invention were inferior in at least one of magnetic properties and machinability.

Claims

1. C: 0.010% by mass or less, Si: 0.010% by mass or less, Mn: 0.10 to 0.50% by mass, P: 0.010 to 0.150 mass% and S: 0.026 to 0.050% by mass and the balance being Fe and unavoidable impurities.

2. The electromagnetic soft iron according to claim 1, wherein the component composition of the electromagnetic soft iron further contains one or more selected from one or more groups consisting of the following groups A to E: Group A: B: 0.0100% by mass or less, Se: 0.300% by mass or less, Ca: 0.0500% by mass or less, Pb: 0.300% by mass or less, Bi: 0.300% by mass or less, Mg: 0.0500% by mass or less, Zr: 0.2000% by mass or less, REM: 0.010% by mass or less and O: 0.0250% by mass or less, Group B: Cr: 2.0% by mass or less, Mo: 1.00% by mass or less, Cu: 1.0% by mass or less, Ni: 1.0% by mass or less, Ti: 0.10% by mass or less, Nb: 0.10% by mass or less and V: 0.3% by mass or less, Group C: Sn: 0.1000 mass% or less and Sb: 0.0100% by mass or less, Group D: Al: 0.0152 to 0.0300% by mass, Group E: N: 0.0100% by mass or less

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