Electromagnetic soft iron

Abstract

Provided is a technique capable of achieving both high-level magnetic performance and machinability, which cannot be achieved only by conventional techniques for improving machinability using MnS or the like. An electromagnetic soft iron having a component composition containing, in mass%, less than 0.02% of C, less than 0.05% of Si, more than 0.03% and 0.50% or less of Mn, 0.002% or more and less than 0.006% of P, 0.013% to 0.050% of S, 0.010% or less of Al, 0.0010% to 0.0100% of N, and 0.0003% to 0.0065% of B, with the balance being iron and unavoidable impurities.

Description

[0001] This application is a divisional application of patent application 202180072305.1 (international application date: October 22, 2021, name of invention: electromagnetic soft iron). Technical Field

[0002] The invention relates to an electromagnetic soft iron with excellent cutting performance and magnetic properties. Background Art

[0003] In recent years, from the perspective of protecting the global environment, there has been a worldwide demand for resource conservation and energy saving. In the field of electrical equipment, efficiency and miniaturization are being actively promoted for the purpose of energy saving. Against this background, electronic components used in automobiles and other applications are also required to save power and increase the speed of response to external magnetic fields.

[0004] Pure iron-based electromagnetic soft iron is usually used as a material that easily responds to external magnetic fields. In this type of electromagnetic soft iron, steel with a carbon content of about 0.01% or less is generally used. After hot rolling, wire drawing is performed to obtain steel bars, which are then forged and cut to make electronic components.

[0005] Among them, in parts processing, it is known that the machinability of the soft ferrite single-phase structure of electromagnetic soft iron is very poor. Therefore, for electromagnetic soft iron, in addition to magnetic properties, excellent machinability has also become important.

[0006] For example, Patent Document 1 discloses a technique for producing a soft magnetic steel material having excellent magnetic properties and cutting performance by controlling the size and number of MnS when dispersed in steel.

[0007] Patent Document 2 discloses a technique for controlling the size and density of FeS precipitates and relating to a soft magnetic steel material having excellent cold forgeability, machinability, and magnetic properties.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Publication No. 2007-51343

[0011] Patent Document 2: Japanese Patent Application Publication No. 2007-46125 Summary of the invention

[0012] The technologies described in Patent Documents 1 and 2 are technologies that utilize the effects of MnS or FeS alone to improve cutting performance. However, an increase in the amount of these precipitates (MnS, FeS) may lead to a deterioration in magnetic properties. Therefore, there are technical limitations for further achieving both high levels of magnetic properties and cutting performance.

[0013] The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technology capable of achieving both high levels of magnetic properties and cutting performance, which cannot be achieved by conventional technologies that use MnS or the like alone to improve cutting performance.

[0014] The inventors have conducted intensive studies to solve the above problems and have newly found that the use of BN can improve the cutting performance without deteriorating the magnetic properties.

[0015] The present invention has been completed through further repeated studies based on the above-mentioned new insights, and its main structure is as follows.

[0016] 1. An electromagnetic soft iron having the following composition: containing, by mass%, C: less than 0.02%, Si: less than 0.05%, Mn: greater than 0.03% and less than 0.50%, P: 0.002% or more and less than 0.006%, S: 0.013% to 0.050%, Al: less than 0.010%, N: 0.0010% to 0.0100% and B: 0.0003% to 0.0065%, and the remainder being iron and unavoidable impurities.

[0017] 2. The electromagnetic soft iron according to item 1 above, further comprising, in the above component composition, in terms of mass %, one or more selected from the group consisting of Cu: 0.20% or less, Ni: 0.30% or less, Cr: 0.30% or less, Mo: 0.10% or less, V: 0.02% or less, Nb: less than 0.015% and Ti: less than 0.010%.

[0018] 3. The electromagnetic soft iron according to item 1 or 2 above, wherein the above component composition further contains, in terms of mass%, one or more selected from the group consisting of Pb: 0.30% or less, Bi: 0.30% or less, Te: 0.30% or less, Se: 0.30% or less, Ca: 0.0100% or less, Mg: less than 0.0050%, Zr: 0.200% or less, and REM: 0.0100% or less.

[0019] According to the present invention, pure iron-based electromagnetic soft iron having excellent magnetic properties and cutting performance can be stably provided. DETAILED DESCRIPTION

[0020] Hereinafter, a pure iron-based electromagnetic soft iron according to an embodiment of the present invention will be described.

[0021] First, the reasons for limiting the components in the composition of pure iron-based electromagnetic soft iron will be described. It should be noted that in this specification, "%" indicating the content of each component element means "mass %" unless otherwise specified.

[0022] C: less than 0.02%

[0023] If the C content is 0.02% or more, the iron loss due to magnetic aging is significantly deteriorated, so it is limited to less than 0.02%. It should be noted that even if the C content is less than 0.001%, the effect on magnetic properties is saturated, but in order to reduce the C content to less than 0.001%, it will increase the refining cost, so the C content is preferably 0.001% or more. It is preferably 0.001% to 0.015%, and more preferably 0.001% to 0.010%.

[0024] Si: less than 0.05%

[0025] Si is an effective deoxidizing element. If the Si content is 0.05% or more, the ferrite is hardened and the cold workability is reduced. Therefore, Si can be contained, but the Si content should be less than 0.05%. It is preferably 0.03% or less. It should be noted that Si can of course be 0%.

[0026] Mn: more than 0.03% and less than 0.50%

[0027] Mn is effective in improving strength by solid solution strengthening. It is also an effective element in improving cutting performance by combining with S to form MnS and dispersing in steel. Therefore, the content is greater than 0.03%. On the other hand, excessive addition deteriorates magnetic properties, so it is less than 0.50%. It is preferably greater than 0.03% and less than 0.40%. It is more preferably greater than 0.03% and less than 0.35%.

[0028] P: 0.002% or more and less than 0.006%

[0029] Even if a relatively small amount of P is added, a significant solid solution strengthening capability can be obtained. Therefore, the content is 0.002% or more. On the other hand, excessive addition will impair cold workability, so the content is less than 0.006%.

[0030] S: 0.013%~0.050%

[0031] S forms MnS in steel, which helps improve cutting performance. In order to show this effect, it is necessary to add 0.013% or more. On the other hand, adding more than 0.050% will deteriorate cold workability. Therefore, the amount of S is 0.013% to 0.050%. It is preferably 0.013% to 0.045%, and more preferably 0.013% to 0.040%.

[0032] Al: 0.010% or less

[0033] Al combines with N in steel to form fine AlN. This fine AlN inhibits the growth of crystal grains and deteriorates magnetic properties, so it is necessary to be 0.010% or less. Of course, Al may be 0%.

[0034] N: 0.0010%~0.0100%

[0035] N helps the cutting performance by combining with B to form BN. In order to produce this effect, it is necessary to add 0.0010% or more. On the other hand, adding more than 0.0100% will deteriorate the cold workability and magnetic properties, so the upper limit is 0.0100%. It is preferably 0.0015% to 0.0090%.

[0036] B: 0.0003%~0.0065%

[0037] B combines with N in steel to form BN. BN has the effect of improving cutting performance. In order to achieve this effect, it is necessary to add 0.0003% or more. On the other hand, addition exceeding 0.0065% will lead to deterioration of magnetism and castability, so the upper limit is 0.0065%. It is preferably 0.0005% to 0.0060%, and more preferably 0.0010% to 0.0055%.

[0038] The basic components of the present invention have been described above. The remainder other than the above components is Fe and inevitable impurities. Further, any one or more of the following elements may be appropriately contained as needed:

[0039] Cu: 0.20% or less,

[0040] Ni: 0.30% or less,

[0041] Cr: 0.30% or less,

[0042] Mo: 0.10% or less,

[0043] V: 0.02% or less,

[0044] Nb: less than 0.015%,

[0045] Ti: less than 0.010%.

[0046] Cu, Ni and Cr contribute to improving strength mainly by solid solution strengthening, and in order to exhibit this effect, it is preferable to add 0.01% or more of each. However, excessive addition deteriorates magnetic properties, so the upper limits are preferably 0.20%, 0.30% and 0.30%, respectively.

[0047] In addition, Mo, V, Nb and Ti contribute to improving strength mainly through precipitation strengthening, and in order to show this effect, it is preferably added 0.001%, 0.0001%, 0.0001% and 0.0001% or more, respectively. However, excessive addition deteriorates magnetic properties, so it is preferably 0.10% or less, 0.02% or less, less than 0.015% and less than 0.010%, respectively.

[0048] In the present invention, any one or more of the following elements may be further contained:

[0049] Pb: 0.30% or less,

[0050] Bi: 0.30% or less,

[0051] Te: 0.30% or less,

[0052] Se: 0.30% or less,

[0053] Ca: 0.0100% or less,

[0054] Mg: less than 0.0050%,

[0055] Zr: 0.200% or less,

[0056] REM: 0.0100% or less.

[0057] Pb, Bi, Te, Se, Ca, Mg, Zr and REM are elements that contribute to improving cutting performance. In order to show the effect, it is preferred to add Pb 0.001% or more, Bi 0.001% or more, Te 0.001% or more, Se 0.001% or more, Ca 0.0001% or more, Mg 0.0001% or more, Zr 0.005% or more and REM 0.0001% or more, respectively. However, excessive addition may cause deterioration of magnetic properties, so it is preferred that Pb is 0.30% or less, Bi is 0.30% or less, Te is 0.30% or less, Se is 0.30% or less, Ca is 0.0100% or less, Mg is less than 0.0050%, Zr is 0.200% or less and REM is 0.0100% or less.

[0058] In the component composition of the present invention, components other than those described above are Fe and unavoidable impurities.

[0059] A suitable method for producing the pure iron-based electromagnetic soft iron according to the present invention will be described.

[0060] The molten steel having the above-mentioned composition is melted by a general smelting method such as a converter or an electric furnace, and then made into steel by a general continuous casting method or a slab-opening method. Then, the steel is heated as required, and then hot-rolled into electromagnetic soft iron by billet rolling, bar rolling, etc. The above-mentioned heating and rolling conditions are not particularly limited and can be appropriately determined according to the required materials. For example, the structure control can be performed to facilitate the subsequent forging and machining of parts. It should be noted that the electromagnetic soft iron of the present invention has excellent machinability, so in the use of cutting processing, its shape is preferably any of a rod, a strip, and a wire.

[0061] In addition, the content of each element can be obtained by spark discharge atomic emission spectrometry, fluorescent X-ray analysis, ICP emission spectrometry, ICP mass spectrometry, combustion method, etc.

[0062] Other manufacturing conditions can be carried out according to the general manufacturing method of steel materials.

[0063] Example

[0064] Next, examples of the present invention will be described. However, the present invention is not limited to the following examples.

[0065] After melting the steel having the composition shown in Table 1, hot forging was performed at about 1200°C, and then annealing was performed at 950°C to produce a steel bar with a diameter of 25 mm. The magnetic properties, cold workability and cutting performance of the obtained steel bar were evaluated according to the following methods. The evaluation results are shown in Table 2.

[0066]

[0067]

[0068] [magnetic]

[0069] The magnetism is measured according to the JIS C2504 standard. That is, an annular test piece is obtained from the above-mentioned steel bar (material) and maintained at 750°C for 2 hours for magnetic annealing. Then, the excitation winding (220 turns of the primary winding) and the detection winding (100 turns of the secondary winding) are wound on the annular test piece for testing. The B-H curve is measured using a DC magnetization measuring device to determine the magnetic flux density. Specifically, the magnetic flux density at 100 and 300 A / m during the magnetization process to reach the maximum magnetic field of 10,000 A / m is determined. If it is 1.20T and 1.50T or more, respectively, it can be said that the magnetism is excellent.

[0070] The coercive force is measured by using a DC magnetic tester under a reverse magnetizing force of ±400 A / m using a ring-shaped test piece with the same winding as above. If the coercive force is 60 A / m or less, the magnetic properties are considered to be excellent.

[0071] [Cold workability]

[0072] Cold workability is evaluated by the limit upsetting rate. That is, a test piece with a diameter of 15 mm and a height of 22.5 mm is obtained from the outer surface of the steel bar at a depth of 1 / 2 of the diameter, and a cut with a depth of 0.8 mm and a bottom of R0.15 is made on the side of the test piece, and the test piece is compressed. The test piece is gradually compressed until a crack with a width of 0.5 mm or more is generated at the bottom. The upsetting rate at this time is set as the limit upsetting rate.

[0073] If the limit upsetting ratio is 55% or more, it can be said that the cold workability is excellent.

[0074] [Cutting performance]

[0075] Cutting performance is evaluated by measuring the amount of flank wear on the tool. Specifically, on an NC lathe, a coated carbide tool is used to perform wet cutting on a 25mm diameter steel bar, with a cutting depth of 0.2mm, a feed rate of 0.15mm / rev, a rotation speed of 300m / min, and a cutting length of 1000m. After processing, the tool flank wear is measured to evaluate. If the flank wear is less than 35μm, the cutting performance is considered excellent.

Claims

1. An electromagnetic soft iron having the following composition: containing, by mass%, C: less than 0.02%, Si: less than 0.05%, Mn: greater than 0.03% and less than 0.50%, P: 0.002% or more and less than 0.006%, S: 0.013% to 0.050%, Al: less than 0.010%, N: 0.003% to 0.0100% and B: 0.0003% to 0.0065%, and the remainder being iron and unavoidable impurities.

2. The electromagnetic soft iron according to claim 1, wherein: Furthermore, in terms of mass%, it contains one or more selected from the group consisting of Cu: 0.20% or less, Ni: 0.30% or less, Cr: 0.30% or less, Mo: 0.10% or less, V: 0.02% or less, Nb: less than 0.015% and Ti: less than 0.010%.

3. The electromagnetic soft iron according to claim 1 or 2, wherein: Furthermore, in terms of mass%, it contains one or more selected from the group consisting of Pb: 0.30% or less, Bi: 0.30% or less, Te: 0.30% or less, Se: 0.30% or less, Ca: 0.0100% or less, Mg: less than 0.0050%, Zr: 0.200% or less, and REM: 0.0100% or less.

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