Electromagnetic soft iron

Abstract

To provide electromagnetic soft iron that is excellent in cold processing property and combines magnetic characteristics and machinability at high level.SOLUTION: The electromagnetic soft iron has a component composition that comprises, in mass%, C: 0.02% or less, Si: 0.05% or less, Mn: 0.010% or more and 0.500% or less, P: 0.002% or more and 0.020% or less, S: 0.001% or more and 0.050% or less, Al: 0.010% or more and 0.050% or less, O: 0.0010% or more and 0.0200% or less, N: 0.0010% or more and 0.0100% or less and B: 0.0003% or more and 0.0065% or less, with the remainder being iron and unavoidable impurities, and the number density of a total amount of precipitates of MnS, BN, and their composite compound (MnS + BN) is 5,000 pieces / mm2 or more, and in the frequency distribution of an equivalent circle diameter of the precipitates observed from a region of 0.2 mm2 or more, a most frequent value is 50 nm or more and 250 nm or less, and a ratio of 600 nm or more is 7% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to soft magnetic iron. [Background technology]

[0002] In recent years, there has been a global demand for resource and energy conservation in order to protect the global environment, and in the field of electrical equipment, efforts are being made to improve efficiency and miniaturization with the aim of saving energy. Against this background, there is also a demand for electrical components used in automobiles and other vehicles to reduce power consumption and improve response speed to external magnetic fields.

[0003] Pure iron-based electromagnetic soft iron is commonly used as a material that responds easily to external magnetic fields. This electromagnetic soft iron is made from steel with a carbon content of approximately 0.01% by mass or less, and is generally manufactured into electrical components by forging and cutting the steel bars obtained by hot rolling and then drawing the wire.

[0004] It is known that the soft ferrite single-phase structure of electromagnetic soft iron has very poor machinability in parts processing, so it is becoming increasingly important for electromagnetic soft iron to have excellent workability, particularly both machinability and cold workability, in addition to magnetic properties.

[0005] For example, Patent Document 1 discloses a technique for producing soft magnetic steel material with excellent magnetic properties and machinability by controlling the size and number of MnS particles when dispersing them in steel.

[0006] Furthermore, Patent Document 2 discloses a technique relating to a soft magnetic steel material that controls the size and density of FeS precipitates and has excellent cold forgeability, machinability, and magnetic properties. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-51343 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-46125 Summary of the Invention [Problem to be solved by the invention]

[0008] The techniques described in Patent Documents 1 and 2 are techniques for improving machinability by utilizing the sole effect of MnS or FeS. However, increasing the amount of these precipitates (MnS, FeS) may lead to a deterioration in magnetic properties. Therefore, there are technical limitations to achieving both higher levels of magnetic properties and machinability.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a steel material that is excellent in cold workability and that also has high levels of magnetic properties and machinability. [Means for solving the problem]

[0010] In order to solve the above problems, the inventors have conducted extensive research and have newly discovered that by adopting the following structure that newly utilizes BN in addition to the conventional single effect of MnS, etc., it is possible to improve machinability and cold workability while maintaining good magnetic properties.

[0011] The present invention was completed after further investigation based on the above-mentioned novel findings, and the gist and configuration of the present invention are as follows.

[0012] [1] In mass%, C: 0.02% or less, Si: 0.05% or less, Mn: 0.010% or more and 0.500% or less, P: 0.002% or more and 0.020% or less, S: 0.001% or more and 0.050% or less, Al: 0.010% or more and 0.050% or less, O: 0.0010% or more and 0.0200% or less, N: 0.0010% or more and 0.0100% or less and B: 0.0003% or more and 0.0065% or less and the balance being iron and unavoidable impurities, The total number density of manganese sulfide (MnS), boron nitride (BN), and their composite compound (MnS+BN) precipitates is 5,000 / mm 2 That's all, 0.2mm 2 Electromagnetic soft iron, characterized in that in a frequency distribution of the circle-equivalent diameters of the precipitates observed from the above region, the mode is 50 nm or more and 250 nm or less, and the proportion of diameters 600 nm or more is 7% or more.

[0013] [2] The component composition further includes, in mass%, Cu: 0.20% or less, Ni: 0.30% or less and Cr:0.30% or less The electromagnetic soft iron according to [1] above, containing one or more selected from the following:

[0014] [3] The component composition further includes, in mass%, Mo: 0.10% or less V: 0.02% or less, Nb: 0.015% or less and Ti: 0.010% or less The electromagnetic soft iron according to [1] or [2] above, containing one or more selected from the following:

[0015] [4] The component composition further includes, in mass%, Sn: 0.10% or less and Sb: 0.10% or less The electromagnetic soft iron according to [1] or [2] above, containing one or two selected from the following:

[0016] [5] The component composition further includes, in mass%, Sn: 0.10% or less and Sb: 0.10% or less The electromagnetic soft iron according to [3] above, containing one or two selected from the following: [Effects of the Invention]

[0017] According to the present invention, it is possible to provide electromagnetic soft iron as a steel material that has excellent cold workability and that also has high levels of magnetic properties and machinability. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an electromagnetic soft iron according to one embodiment of the present invention (sometimes referred to as "electromagnetic soft iron according to this embodiment") will be described.

[0019] In the conventional method of dispersing compounds such as MnS in steel as described above, it has been found that increasing the amount of the compound may cause the compound itself to exert a pinning effect, inhibiting the growth of crystal grains in the steel matrix (reducing the crystal size), and thereby potentially causing deterioration of the magnetic properties.

[0020] To solve these problems, the inventors conducted repeated experiments under various manufacturing conditions to obtain various steel products and investigated the morphology of the compounds in the obtained steel products. As a result, it was found that manganese sulfide (MnS), boron nitride (BN), and their composite compound (MnS+BN) precipitated as inclusions in certain steel products, and that the distribution of their equivalent circle diameters was non-uniform.

[0021] Therefore, in order to establish suitable conditions, the obtained steel material was subjected to mirror polishing. Next, a position near the surface of the steel material where decarburization and oxidation reactions had not occurred was subjected to a 0.2 mm scan at a magnification of 10,000 times using a scanning electron microscope (SEM) and an energy dispersive X-ray analyzer (EDS) attached to the SEM. 2 As a result, the total number density of MnS, BN and their composite compounds (MnS + BN) precipitated in the steel was 5,000 particles / mm 2Furthermore, when the circle-equivalent diameters of the precipitates of MnS, BN, and their composite compounds (MnS+BN) were determined and their frequency distribution was obtained, it was found that when the mode in the frequency distribution obtained was in the range of 50 nm to 250 nm and the proportion (proportion by number) of precipitates of 600 nm or more was 7% or more, the magnetic properties, cold workability, and machinability were balanced at a high level.

[0022] The inventors consider this result as follows. That is, the coarser the crystal grain size in a steel, the better its magnetic properties. However, compounds such as MnS, which contribute to improving machinability, inhibit the growth of crystal grains in the parent phase due to the so-called pinning effect, as mentioned above, resulting in deterioration of magnetic properties. However, the greater the variation in compound size, the more difficult it is for the pinning force to act uniformly within the steel. This non-uniformity of the pinning force leads to the coarse grains and fine grains being mixed (mixed grains). In such cases, if the fine grains are eroded by the coarse grains, abnormal grain growth is likely to occur. As a result, the crystal grain size in the steel becomes coarse. These coarse crystal grains capable of exhibiting excellent magnetic properties are obtained from compounds that contribute to improving machinability. In other words, it is believed that this steel will have excellent magnetic properties and machinability while maintaining good cold workability.

[0023] The present invention was completed based on the above-mentioned novel findings and as a result of further investigations. Note that, hereinafter, the number density of the above-mentioned predetermined precipitates, the mode in the frequency distribution of the circle-equivalent diameters of the precipitates, and the proportion of precipitates with diameters of 600 nm or more may be collectively referred to as the "distribution morphology of precipitates."

[0024] Next, the reasons for limiting each basic component in the component composition of the electromagnetic soft iron of this embodiment will be described. In this specification, "%" representing the content of each component (element) means "% by mass" unless otherwise specified. The content of each component (element) can be measured by spark discharge optical emission spectroscopy, X-ray fluorescence analysis, ICP optical emission spectroscopy, ICP mass spectroscopy, combustion method, or the like.

[0025] C: 0.02% or less If the C content exceeds 0.02%, the magnetic properties deteriorate significantly due to magnetic aging. Therefore, the C content is set to 0.02% or less. From the same viewpoint, the C content is preferably 0.015% or less, and more preferably 0.010% or less. Furthermore, even if the C content is less than 0.001%, the effect on the magnetic properties saturates, while reducing the C content to less than 0.001% increases the refining cost, so the C content is preferably 0.001% or more.

[0026] Si: 0.05% or less Si is an effective deoxidizing element. If the Si content exceeds 0.05%, the ferrite hardens, resulting in a decrease in cold workability. Therefore, the Si content is set to 0.05% or less. From the same viewpoint, the Si content is preferably 0.03% or less. Although the Si content may be 0%, in order to obtain the effect as a deoxidizing element, it is preferably 0.005% or more, and more preferably 0.01% or more.

[0027] Mn: 0.010% or more and 0.500% or less Mn is an element that is effective in improving strength through solid solution strengthening, and also in improving machinability by dispersing MnS bonded to S in the steel. To achieve this effect, the Mn content is set to 0.010% or more. However, excessive addition not only deteriorates magnetic properties but also makes it impossible to obtain the desired precipitate distribution pattern, so the Mn content is set to 0.500% or less. From the same perspective, the Mn content is preferably 0.050% or more, more preferably 0.150% or more, and also preferably 0.400% or less, more preferably 0.350% or less.

[0028] P: 0.002% or more and 0.020% or less P is an element that exerts significant solid solution strengthening ability even when added in a relatively small amount. To obtain this effect, the P content is set to 0.002% or more. On the other hand, excessive addition reduces cold workability, so the P content is set to 0.020% or less. From the same viewpoint, the P content is preferably 0.015% or less.

[0029] S: 0.001% or more and 0.050% or less S forms MnS in steel, contributing to improved machinability. To sufficiently improve machinability and obtain the desired precipitate distribution, the S content is set to 0.001% or more. On the other hand, addition of more than 0.050% not only reduces cold workability but also coarsens the compounds, making it impossible to obtain the desired precipitate distribution. Therefore, the S content is set to 0.050% or less. From the same perspective, the S content is preferably 0.005% or more, more preferably 0.010% or more, and also preferably 0.045% or less, more preferably 0.040% or less.

[0030] Al: 0.010% or more and 0.050% or less Al is an effective element as a deoxidizer. Adding 0.010% or more of Al reduces the amount of oxygen in molten steel, reducing harmful oxides and improving the yield of alloying elements. On the other hand, adding more than 0.050% of Al increases Al oxides, deteriorating workability and magnetic properties. Therefore, the Al content is set to 0.010% or more and 0.050% or less. From the same viewpoint, the Al content is preferably 0.045% or less, and more preferably 0.040% or less.

[0031] O: 0.0010% or more and 0.0200% or less O has the effect of coarsening sulfide-based inclusions by combining with them, thereby improving machinability. To achieve this effect, the O content is set to 0.0010% or more. On the other hand, excessive addition of O leads to a decrease in the toughness of the steel material and causes premature fracture of structural members (components) using the steel material, so the O content is set to 0.0200% or less. From the same perspective, the O content is preferably more than 0.0010%, and is preferably 0.0190% or less, and more preferably 0.0180% or less.

[0032] N: 0.0010% or more and 0.0100% or less N combines with B in the steel to form BN, thereby contributing to improved machinability. To achieve this effect and to obtain the desired precipitate distribution, the N content must be 0.0010% or more. On the other hand, adding more than 0.0100% not only deteriorates cold workability and / or magnetic properties, but also coarsens the compounds, making it impossible to obtain the desired precipitate distribution. Therefore, the N content is set to 0.0100% or less. From the same perspective, the N content is preferably 0.0015% or more and preferably 0.0090% or less.

[0033] B: 0.0003% or more and 0.0065% or less B can contribute to improving machinability by combining with N in the steel to form BN. To achieve this effect and to obtain the desired precipitate distribution, the B content must be 0.0003% or more. On the other hand, adding more than 0.0065% not only deteriorates magnetic properties and / or castability, but also coarsens the compounds, making it impossible to obtain the desired precipitate distribution. Therefore, the B content is set to 0.0065% or less. From the same perspective, the B content is preferably 0.0005% or more, more preferably 0.0010% or more, and preferably 0.0060% or less, more preferably 0.0055% or less.

[0034] The basic components in the composition of electromagnetic soft iron have been explained above. The component composition of the electromagnetic soft iron may further contain one or more of the elements shown below in addition to the components described above, as necessary. Cu:0.20% or less Ni: 0.30% or less Cr:0.30% or less

[0035] Cu, Ni, and Cr contribute to increasing strength mainly through solid solution strengthening. Therefore, in order to obtain the above effects, when Cu is contained, its content is preferably 0.01% or more. Similarly, when Ni is contained, its content is preferably 0.01% or more. Similarly, when Cr is contained, its content is preferably 0.01% or more. On the other hand, excessive addition of Cu, Ni, and Cr each deteriorates the magnetic properties. Therefore, as mentioned above, when Cu is contained, its content is preferably 0.20% or less. Similarly, when Ni is contained, its content is preferably 0.30% or less. Similarly, when Cr is contained, its content is preferably 0.30% or less.

[0036] Furthermore, the component composition of the electromagnetic soft iron may further contain, in addition to the components described above, one or more of the elements shown below, as necessary. Mo: 0.10% or less V:0.02% or less Nb: 0.015% or less Ti: 0.010% or less

[0037] Mo, V, Nb, and Ti contribute to increasing strength mainly through precipitation strengthening. Therefore, in order to obtain the above-mentioned effects, when Mo is contained, its content is preferably 0.001% or more. Similarly, when V is contained, its content is preferably 0.0001% or more. Similarly, when Nb is contained, its content is preferably 0.0001% or more. Similarly, when Ti is contained, its content is preferably 0.0001% or more. On the other hand, excessive addition of Mo, V, Nb, and Ti deteriorates magnetic properties and / or cold workability. Therefore, as described above, when Mo is contained, its content is preferably 0.10% or less. Similarly, when V is contained, its content is preferably 0.02% or less. Similarly, when Nb is contained, its content is preferably 0.015% or less. Similarly, when Ti is contained, its content is preferably 0.010% or less.

[0038] Furthermore, the component composition of the electromagnetic soft iron may further contain, in addition to the components described above, one or more of the elements shown below, as necessary. Sn: 0.10% or less Sb: 0.10% or less

[0039] Sn and Sb have the effect of improving descaling during the shot blasting and pickling processes performed before cold wire drawing, and can be added as needed when these processes are included in the manufacture of parts. To obtain the above effects, when Sn is contained, its content is preferably 0.001% or more. Similarly, when Sb is contained, its content is preferably 0.001% or more. On the other hand, if Sn and Sb are added in excess, not only will the effect of improving descaling be saturated, but magnetic properties will also be deteriorated. Therefore, as mentioned above, when Sn is contained, its content is preferably 0.10% or less. Similarly, when Sb is contained, its content is preferably 0.10% or less.

[0040] In the composition of the electromagnetic soft iron, the components other than those mentioned above (the remainder) are iron (Fe) and inevitable impurities.

[0041] Next, we will discuss the main characteristics of the electromagnetic soft iron of this embodiment as a steel material, particularly its microstructure (distribution of precipitates). In the present invention, it is important to quantitatively understand the number density of specific precipitates in the steel material and the distribution of their diameters (circle-equivalent diameters). When specifying the number density and distribution, it is sufficient to target a position near the surface of the steel material (electromagnetic soft iron) where decarburization and oxidation reactions are not occurring, i.e., a steady-state portion.

[0042] MnS, BN, and their composite compounds (MnS+BN) are inclusions that improve machinability, and by dispersing them at high density in the steel material, the effect of improving machinability is further enhanced. In the steel material (electromagnetic soft iron) of this embodiment, the total number density of dispersed precipitates of MnS, BN, and their composite compounds (MnS+BN) is 5,000 particles / mm 2 As mentioned above, the number density must be 5,000 pieces / mm or more. 2 To achieve a number density of 0.2 mm or more, it is necessary to substantially include compounds of 0.5 μm or less. Therefore, in order to determine the number density of the precipitates, it is necessary to observe images at a relatively high magnification. For example, a scanning electron microscope (SEM) is used to observe images of 0.2 mm or less. 2 By observing the above-mentioned region, the number density of the precipitates can be determined. On the other hand, the number density is not particularly limited, but is preferably 50,000 particles / mm 2 It can be as follows: Considering the detection limit of a general microscope, the precipitates to be measured can typically be precipitates of 50 nm or more.

[0043] In addition, the steel material (electromagnetic soft iron) of this embodiment is 0.2 mm 2 In the frequency distribution of the circle-equivalent diameters of the precipitates observed from the above regions, the mode must be 50 nm or more and 250 nm or less, and the proportion of diameters 600 nm or more must be 7% or more. The proportion of diameters 600 nm or more is not particularly limited, but can be 40% or less. Such a frequency distribution in which the proportion of diameters larger than the mode is equal to or greater than a certain level often has a shape approaching bimodal.

[0044] Here, 0.2 mm 2 The above regions can be observed using a scanning electron microscope (SEM), similar to the number density. The observed precipitates may also include precipitates composed of components other than MnS, BN, and their complex compounds (MnS+BN). Therefore, analysis using an energy dispersive X-ray analyzer (EDS) allows the identification of MnS, BN, and their complex compounds (MnS+BN) precipitates, which can then be used as the subject of a frequency distribution. Furthermore, when determining the mode in a frequency distribution (e.g., a histogram) of equivalent circle diameters, the frequency distribution can be created with a class width of equivalent circle diameters of 50 nm or less.

[0045] As a means for obtaining the above-mentioned desired distribution form of precipitates, for example, the amounts of Mn, S, Al, O, B, and N in the component composition may be appropriately adjusted so that the main oxides formed in the steel material are Al-based oxides.

[0046] The electromagnetic soft iron of this embodiment preferably has a limiting upsetting ratio of 55% or more. If the limiting upsetting ratio is 55% or more, better cold workability can be exhibited. The critical upsetting ratio is defined as the upsetting ratio when a test piece with a diameter of 15 mm, a height of 22.5 mm, and a notch with a depth of 0.8 mm on the side and a notch bottom radius of 0.15 is taken from the peripheral surface of the electromagnetic soft iron bar at a depth of 1 / 2 the diameter, and the test piece is compressed until a crack with a width of 0.5 mm or more appears at the notch bottom.

[0047] Since the electromagnetic soft iron of this embodiment has excellent machinability, it is preferable that it has either a rod shape (straight rod, steel bar, etc.) or a coil shape, which are mainly used in applications where cutting processing is performed.

[0048] Next, a preferred method for manufacturing the electromagnetic soft iron of this embodiment will be described. For example, molten steel having the above-mentioned composition is melted using a conventional converter, electric furnace, or the like, and then processed into a steel material by conventional continuous casting or blooming. The steel material is then heated as needed and subjected to hot rolling, such as billet rolling or bar rolling, to produce magnetic soft iron. In particular, in the above-mentioned manufacturing method, in order to obtain the desired precipitate distribution and thereby improve cold workability, magnetic properties, and machinability, it is preferable to set the thickness of the steel material or the diameter of the steel bar after hot rolling to 10 mm or more, and it is also preferable to allow the steel to cool naturally after hot rolling. Furthermore, in the above-mentioned manufacturing method, in order to obtain the desired precipitate distribution and thereby improve cold workability, magnetic properties, and machinability, it is preferable not to perform an annealing treatment. Other conditions are not particularly limited; for example, the structure may be controlled to be advantageous for subsequent forging and machining for part formation. Other manufacturing conditions may follow those of general steel manufacturing methods. [Example]

[0049] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

[0050] For Steel Nos. 1 to 34, molten steel having the composition shown in Table 1 was obtained, then heated to 1200°C and hot-rolled, with the final rolling temperature set to 900°C to produce steel bars (electromagnetic soft iron) having a diameter of 25 mm. That is, no annealing treatment was performed in the production of Steel Nos. 1 to 34. On the other hand, for Steel Nos. 35 and 36, molten steel having the composition shown in Table 1 was obtained, then heated to 1200°C and hot-forged, followed by intermediate annealing at 950°C to produce steel bars (electromagnetic soft iron) having a diameter of 25 mm.

[0051] [Table 1]

[0052] [Distribution of precipitates] The obtained steel bar (soft magnetic iron) was cut to prepare a cross-sectional sample having a circular cross section, and the cross-sectional sample was mirror-polished to obtain a sample for observing the distribution of precipitates. 2 The above regions were observed using a scanning electron microscope (SEM) under conditions of an accelerating voltage of 15 kV and a magnification of 10,000 times. For the precipitates determined from the observed SEM images, the components that make up the precipitates were identified by analysis using an energy dispersive X-ray analyzer (EDS). The precipitates identified as MnS, BN, or their composite compound (MnS+BN) in this EDS analysis were used as the measurement targets, and the number density per unit area (particles / mm 2 ) was measured. Furthermore, for each of the precipitates identified above, the area was analyzed from the SEM image, and the equivalent circle diameter was calculated from the area. Next, a frequency distribution (histogram) of the calculated equivalent circle diameters was created with a class width of 50 nm, and the mode and the proportion of diameters 600 nm or greater were determined. These results are shown in Table 2.

[0053] Furthermore, the magnetic properties (magnetic flux density and coercive force), cold workability (limiting upsetting ratio) and machinability (amount of flank wear) of the obtained electromagnetic soft iron were evaluated according to the methods described below.

[0054] [Magnetic properties] The magnetic properties were measured in accordance with JIS C2504. Specifically, ring-shaped test specimens were cut from the steel bars (magnetic soft iron) and subjected to magnetic annealing at 750°C for 2 hours. An excitation winding (220 turns of primary winding) and a detection winding (100 turns of secondary winding) were then wound around the ring test specimens for testing. The magnetic flux density was determined by measuring the BH curve using a DC magnetization measurement device. Specifically, the magnetic flux densities were determined at 100 A / m and 300 A / m during the magnetization process, with a maximum magnetic field of 10,000 A / m. The results are shown in Table 2. A magnetic flux density of 1.25 T or higher at 100 A / m and 1.55 T or higher at 300 A / m can be considered to have excellent magnetic properties.

[0055] The coercive force was measured using a DC magnetic property tester with a ring-shaped test piece wound in the same manner as above, at a reversal magnetization force of ±400 A / m. The results are shown in Table 2. A coercive force of 60 A / m or less can be said to have excellent magnetic properties.

[0056] [Cold workability] The cold workability was evaluated by the limiting upsetting ratio. To determine the critical upsetting ratio, a test piece with a diameter of 15 mm, a height of 22.5 mm, and a notch with a depth of 0.8 mm and a notch bottom radius of 0.15 mm on the side was taken from the steel bar at a depth of half the diameter from the circumferential surface. This test piece was then subjected to compression. Sequential compression was continued until a crack with a width of 0.5 mm or more appeared at the notch bottom of the test piece. The upsetting ratio at this point was taken as the critical upsetting ratio. The results are shown in Table 2. If the limiting upsetting rate is 55% or more, it can be said that the cold workability is excellent.

[0057] [Machinability] Machinability was evaluated by measuring the amount of flank wear on the tool. Specifically, using an NC lathe, a 25mm diameter steel bar was cut with a coated tool made of carbide substrate at a depth of cut of 0.2mm, a feed rate of 0.15mm / rev, a peripheral speed of 300m / min, and a cutting length of 1000mm, using a wet cutting method. The amount of flank wear on the tool was then measured. The results are shown in Table 2. If the flank wear amount is 35 μm or less, it can be said that the cutting edge has excellent machinability.

[0058] [Table 2]

[0059] Tables 1 and 2 show that the steel material (electromagnetic soft iron) according to the present invention has excellent cold workability and also achieves high levels of both magnetic properties and machinability. On the other hand, in the comparative examples in which the composition of elements is outside the range of the present invention and / or the distribution form of precipitates is outside the range of the present invention, at least one of the magnetic properties, cold workability, and machinability was not fully satisfied.

Claims

1. In mass%, C: 0.02% or less, Si: 0.05% or less, Mn: 0.010% or more and 0.500% or less, P: 0.002% or more and 0.020% or less, S: 0.001% or more and 0.050% or less, Al: 0.014% or more and 0.050% or less, O: 0.0010% or more and 0.0200% or less, N: 0.0010% or more and 0.0100% or less; B: 0.0003% or more and 0.0065% or less and the balance being iron and unavoidable impurities, The total number density of precipitates of manganese sulfide (MnS), boron nitride (BN) and their composite compound (MnS + BN) is 5,000 pieces / mm ２ That's all, 0.2 mm ２ In a frequency distribution of the circle-equivalent diameters of the precipitates observed from the above region, the mode is 50 nm or more and 250 nm or less, and the proportion (proportion by number) of precipitates of 600 nm or more is 7% or more.

2. The component composition further includes, in mass %, Cu: 0.01% or more and 0.20% or less, Ni: 0.01% or more and 0.30% or less; Cr: 0.01% or more and 0.30% or less 2. The electromagnetic soft iron according to claim 1, comprising one or more selected from the following:

3. The component composition further includes, in mass %, Mo: 0.10% or less, V: 0.02% or less, Nb: 0.015% or less and Ti: 0.010% or less 3. The electromagnetic soft iron according to claim 1, comprising one or more selected from the following:

4. The component composition further includes, in mass %, Sn: 0.10% or less and Sb: 0.10% or less 3. The electromagnetic soft iron according to claim 1, comprising one or two selected from the following:

5. The component composition further includes, in mass %, Sn: 0.10% or less and Sb: 0.10% or less The electromagnetic soft iron according to claim 3, containing one or two selected from the following:

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