Electromagnetic soft iron

Abstract

Provided is an electromagnetic soft iron having excellent cold workability and having both high levels of magnetic characteristics and machinability. The electromagnetic soft iron comprises the following components in percentage by mass: 0.02% or less of C, 0.05% or less of Si, 0.010%-0.500% of Mn, 0.002%-0.020% of P, 0.001%-0.050% of S, 0.010%-0.050% of Al, 0.0010%-0.0200% of O, 0.0010%-0.0100% of N, 0.0003%-0.0065% of B, and the balance of iron and unavoidable impurities. The total number density of precipitates of MnS, BN, and a composite compound thereof (MnS + BN) is 5000 / mm2 or more, and in the frequency distribution of the equivalent circle diameter of the precipitates observed from a region of 0.2 mm2 or more, the mode is 50-250 nm, and the proportion of 600 nm or more is 7% or more.

Description

Technical Field

[0001] The present invention relates to.

[0002] Background technology electromagnetic soft iron

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

[0004] As a material that easily responds to an external magnetic field, pure iron-based electromagnetic soft iron is generally used. In this electromagnetic soft iron, steel with a carbon content of about 0.01 mass% or less is generally used, and the steel bar obtained by wire drawing after hot rolling is subjected to forging, cutting, etc. to make electrical components.

[0005] Here, in component processing, it is known that the machinability of the soft ferrite single-phase structure of electromagnetic soft iron is very poor. Therefore, it is important for electromagnetic soft iron to have excellent machinability, especially both machinability and cold workability, in addition to magnetic properties.

[0006] For example, Patent Document 1 discloses a technique for producing a soft magnetic steel material having excellent magnetic properties and machinability 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 to produce 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 technology described in Patent Documents 1 and 2 is a technology that utilizes the individual effects of MnS or FeS to improve machinability. However, the increase in these precipitates (MnS, FeS) may lead to deterioration of magnetic properties. Therefore, there is a technical limit to achieving both magnetic properties and machinability at a higher level.

[0013] 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 which is excellent in cold workability and has both high-level magnetic properties and machinability.

[0014] The inventors have conducted intensive studies to solve the above problems and have found that in addition to the conventional effects of MnS and the like, the following structure using BN can improve machinability and cold workability while maintaining good magnetic properties.

[0015] The present invention has been completed through further research based on the above-mentioned new findings, and its gist is as follows.

[0016] [1] An electromagnetic soft iron characterized by having the following composition: in terms of mass %, containing C: 0.02% or less, Si: 0.05% or less, Mn: 0.010% to 0.500%, P: 0.002% to 0.020%, S: 0.001% to 0.050%, Al: 0.010% to 0.050%, O: 0.0010% to 0.0200%, N: 0.0010% to 0.0100% and B: 0.0003% to 0.0065%, with the remainder being iron and unavoidable impurities; and the total number density of precipitates of manganese sulfide (MnS), boron nitride (BN) and their composite compound (MnS+BN) is 5000 pieces / mm 2 Above, from 0.2mm 2 In the frequency distribution of the equivalent circle diameters of the precipitates observed in the above region, the mode is 50 nm to 250 nm, and the proportion of 600 nm or more is 7% or more.

[0017] [2] The electromagnetic soft iron according to [1] above, wherein the component composition further contains, in terms of mass %, one or more selected from the group consisting of Cu: 0.20% or less, Ni: 0.30% or less, and Cr: 0.30% or less.

[0018] [3] The electromagnetic soft iron according to [1] or [2], wherein the component composition further contains, in terms of mass %, one or more selected from the group consisting of Mo: 0.10% or less, V: 0.02% or less, Nb: 0.015% or less, and Ti: 0.010% or less.

[0019] [4] The electromagnetic soft iron according to [1] or [2], wherein the component composition further contains, in mass %, one or two selected from Sn: 0.10% or less and Sb: 0.10% or less.

[0020] [5] The electromagnetic soft iron according to [3] above, wherein the component composition further contains, in mass %, one or two selected from Sn: 0.10% or less and Sb: 0.10% or less.

[0021] According to the present invention, it is possible to provide an electromagnetic soft iron which is a steel material having excellent cold workability and having both high-level magnetic properties and machinability. DETAILED DESCRIPTION

[0022] Hereinafter, an electromagnetic soft iron according to an embodiment of the present invention (may be referred to as “electromagnetic soft iron according to the present embodiment”) will be described.

[0023] In the conventional method of dispersing compounds such as MnS in steel materials as described above, it has been found that the increase in the amount of the compound itself exerts a pinning effect, inhibiting the growth of grains in the steel matrix (making the crystals finer), which may lead to deterioration of magnetic properties.

[0024] In order to solve such a problem, the present inventors have repeatedly conducted experiments under various manufacturing conditions, obtained various steel materials, and investigated the morphology of compounds in the obtained steel materials. The results showed that in the characteristic steel materials, manganese sulfide (MnS), boron nitride (BN) and their composite compounds (MnS+BN) were precipitated as inclusions, and the distribution of their equivalent circle diameters was uneven.

[0025] Therefore, in order to establish appropriate conditions, the obtained steel material was subjected to mirror polishing, and then, at the position near the surface of the steel material where no decarburization reaction and oxidation reaction occurred, a scanning electron microscope (SEM) and an energy dispersive X-ray analyzer (EDS) device attached to the SEM were used to analyze the 0.2 mm2 area at a magnification of 10,000 times. 2 The results showed that if the total number density of MnS, BN and their composite compounds (MnS+BN) precipitated in the steel is less than 5000 pieces / mm 2 , at least one of the magnetic properties, cold workability and machinability is insufficient. Furthermore, the equivalent circle diameters of the precipitates of the above-mentioned MnS, BN and their composite compounds (MnS+BN) are calculated to obtain their frequency distribution. If the mode in the obtained frequency distribution is in the range of 50nm to 250nm and the proportion (number ratio) of 600nm or more is 7% or more, it indicates that the magnetic properties, cold workability and machinability are balanced at a high level.

[0026] Regarding this result, the inventors conducted the following investigations.

[0027] That is, the coarser the crystal grain size in the steel, the better its magnetic properties, but the compounds such as MnS that help improve machinability hinder the growth of the grains of the parent phase due to the so-called pinning effect as described above, resulting in the degradation of magnetic properties. However, the greater the deviation of the compound size, the more difficult it is for the pinning force to act evenly in the steel. Such an inhomogeneous pinning force leads to the mixing (mixed graining) of coarse grains and fine grains. In such a case, the fine grains are eroded by the coarse grains, and abnormal grain growth is prone to occur. As a result, the crystal grain size in the steel becomes coarse. The coarse grains that can show this excellent magnetic property are obtained by compounds that help improve machinability, that is, it can be considered to be a steel that is excellent in both magnetic properties and machinability while maintaining good cold workability.

[0028] The present invention was completed after further repeated studies based on the above new knowledge. It should be noted that the number density of the above-mentioned precipitates, the mode in the frequency distribution of the equivalent circle diameter of the precipitates, and the proportion of 600 nm or more are collectively referred to as "distribution form of precipitates".

[0029] Next, the reasons for limiting each basic component in the component composition of the electromagnetic soft iron of the present embodiment will be described. It should be noted that in this specification, "%" indicating the content of each component (element) means "mass %" unless otherwise specified.

[0030] In addition, the content of each component (element) can be measured by spark discharge emission spectrometry, fluorescent X-ray analysis, ICP emission spectrometry, ICP mass spectrometry, combustion method, or the like.

[0031] C: 0.02% or less

[0032] If the C content exceeds 0.02%, the magnetic properties will be significantly deteriorated due to magnetic aging. Therefore, the C content is set to 0.02% or less. From the same point of view, the C content is preferably 0.015% or less, and more preferably 0.010% or less. In addition, even if the C content is less than 0.001%, the effect on the magnetic properties is saturated. On the other hand, reducing it to less than 0.001% will be accompanied by an increase in refining costs, so it is preferably 0.001% or more.

[0033] Si: 0.05% or less

[0034] Si is an element effective as a deoxidizing element. If the Si content exceeds 0.05%, the ferrite is hardened and the cold workability is reduced. Therefore, the Si content is set to 0.05% or less. From the same point of view, the Si content is preferably 0.03% or less. It should be noted that the Si content can also be 0%, and in order to obtain the effect as a deoxidizing element, it is preferably 0.005% or more, and more preferably 0.01% or more.

[0035] Mn: 0.010%~0.500%

[0036] Mn is effective in improving strength by solid solution strengthening. MnS formed by combining with S is dispersed in steel and is also an effective element in improving machinability. In order to obtain such an effect, the content of Mn is set to more than 0.010%. On the other hand, excessive addition not only deteriorates the magnetic properties, but also fails to obtain the desired distribution form of precipitates. Therefore, the content of Mn is set to less than 0.500%. From the same viewpoint, the content of Mn is preferably more than 0.050%, more preferably more than 0.150%, and preferably less than 0.400%, more preferably less than 0.350%.

[0037] P: 0.002% to 0.020% or less

[0038] P is an element that can show significant solid solution strengthening ability even if added in a small amount. In order to obtain such an effect, the content of P is set to 0.002% or more. On the other hand, excessive addition reduces cold workability, so the content of P is set to 0.020% or less. From the same point of view, the content of P is preferably 0.015% or less.

[0039] S: 0.001%~0.050%

[0040] S forms MnS in steel, which helps to improve machinability. In order to fully improve machinability and obtain the desired distribution form of precipitates, the S content is set to 0.001% or more. On the other hand, the addition of more than 0.050% not only reduces the cold workability, but also coarsens the compound, and the desired distribution form of precipitates cannot be obtained. Therefore, the S content is set to 0.050% or less. From the same point of view, the S content is preferably 0.005% or more, more preferably 0.010% or more, and preferably 0.045% or less, more preferably 0.040% or less.

[0041] Al: 0.010%~0.050%

[0042] Al is an element that is effective as a deoxidizing material. By adding 0.010% or more of Al, the amount of oxygen in molten steel can be reduced, harmful oxides can be reduced, and the yield of alloying elements can be improved. On the other hand, if more than 0.050% of Al is added, the workability and magnetic properties will deteriorate due to the increase of Al oxides. Therefore, the Al content is set to 0.010% to 0.050%. From the same point of view, the Al content is preferably 0.045% or less, and more preferably 0.040% or less.

[0043] O: 0.0010%~0.0200%

[0044] O has the effect of improving machinability by compounding with sulfide inclusions to coarsen the inclusions. In order to show such an effect, the content of O is set to 0.0010% or more. On the other hand, excessive addition leads to a decrease in the toughness of the steel material, causing early failure of structural parts (members) using the steel material, so the content of O is set to 0.0200% or less. From the same viewpoint, the content of O is preferably greater than 0.0010%, and is preferably 0.0190% or less, and more preferably 0.0180% or less.

[0045] N: 0.0010%~0.0100%

[0046] N can form BN by combining with B in the steel, which helps to improve the machinability. In order to obtain such an effect, and in order to obtain the desired distribution form of precipitates, it is necessary to set the N content to 0.0010% or more. On the other hand, the addition of more than 0.0100% not only deteriorates the cold workability and / or magnetic properties, but also makes the compound coarse and the desired distribution form of precipitates cannot be obtained. Therefore, the N content is set to 0.0100% or less. From the same point of view, the N content is preferably 0.0015% or more, and preferably 0.0090% or less.

[0047] B.0003%~0.0065%

[0048] B can form BN by combining with N in the steel, which helps to improve the machinability. In order to obtain such an effect, and in order to obtain the desired distribution form of precipitates, the B content needs to be set to 0.0003% or more. On the other hand, the addition of more than 0.0065% not only deteriorates the magnetic properties and / or castability, but also coarsens the compound and cannot obtain the desired distribution form of precipitates. Therefore, the B content is set to 0.0065% or less. From the same point of view, 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.

[0049] The basic components of the composition of electromagnetic soft iron have been described above.

[0050] The component composition of the electromagnetic soft iron may further contain one or more of the following elements in addition to the above components as necessary.

[0051] Cu: 0.20% or less

[0052] Ni: 0.30% or less

[0053] Cr: 0.30% or less

[0054] Cu, Ni and Cr contribute to improving strength mainly through solid solution strengthening. Therefore, in order to obtain the above-mentioned 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.

[0055] On the other hand, if Cu, Ni and Cr are added in excess, the magnetic properties will deteriorate. Therefore, as described 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.

[0056] The component composition of the electromagnetic soft iron may further contain one or more of the following elements in addition to the above components as necessary.

[0057] Mo: 0.10% or less

[0058] V: 0.02% or less

[0059] Nb: 0.015% or less

[0060] Ti: 0.010% or less

[0061] Mo, V, Nb and Ti contribute to improving 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.

[0062] On the other hand, if Mo, V, Nb and Ti are added in excess, the magnetic properties and / or cold workability are deteriorated. 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.

[0063] The component composition of the electromagnetic soft iron may further contain one or more of the following elements in addition to the above components as necessary.

[0064] Sn: 0.10% or less

[0065] Sb: 0.10% or less

[0066] Sn and Sb have the effect of improving the descaling property during the shot peening and pickling steps before cold drawing, and can be added as needed when these steps are included in the production of parts. In addition, in order 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.

[0067] On the other hand, if Sn and Sb are added in excessive amounts, not only will the descaling improvement effect be saturated, but the magnetic properties will also deteriorate. Therefore, as described 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.

[0068] In the component composition of electromagnetic soft iron, components other than the above (balance) are iron (Fe) and inevitable impurities.

[0069] Next, the main characteristics of the steel material as the electromagnetic soft iron of this embodiment, especially the microstructure (distribution form of precipitates) are described. In the present invention, it is important to quantitatively grasp the number density of certain precipitates in the steel material and the distribution of their diameters (equivalent circle diameters). It should be noted that when determining the above number density and distribution, it is sufficient to take the position near the surface of the steel material (electromagnetic soft iron) where no decarburization reaction and oxidation reaction occur, that is, the constant part as the object.

[0070] MnS, BN and their composite compounds (MnS+BN) are inclusions that improve machinability. By dispersing them in the steel material at a high density, the effect of improving machinability can be further exerted. In addition, in the steel material (electromagnetic soft iron) of this embodiment, the total number density of the dispersed precipitates of MnS, BN and their composite compounds (MnS+BN) needs to be 5000 pieces / mm 2 It should be noted that in order to achieve a number density of 5000 pieces / mm 2 Therefore, in order to determine the number density of the above precipitates, it is necessary to observe images with a higher magnification, for example, by using a scanning electron microscope (SEM) to observe 0.2 mm 2 On the other hand, the number density is not particularly limited and can be set to 50,000 pieces / mm 2 the following.

[0071] In addition, according to the detection limit of a general microscope, the precipitate to be measured may typically be a precipitate of 50 nm or more.

[0072] In addition, in the steel material (electromagnetic soft iron) of this embodiment, 2In the frequency distribution of the equivalent circle diameter of the above precipitates observed in the above regions, it is necessary to make the mode 50nm to 250nm and the proportion of 600nm or more be 7% or more. It should be noted that the proportion of 600nm or more is not particularly limited and can be 40% or less. This frequency distribution with a proportion greater than the mode being above a certain value mostly has a shape close to bimodal.

[0073] Here, 0.2 mm 2 The observation in the above region can be carried out using a scanning electron microscope (SEM) in the same manner as number density. In addition, the observed precipitate can also contain the precipitate composed of the components other than MnS, BN and their composite compound (MnS+BN). Therefore, by using an energy dispersive X-ray analysis (EDS) device to analyze, the precipitate of MnS, BN and their composite compound (MnS+BN) can be identified, and they can be used as the object of frequency distribution. In addition, when obtaining the mode in the frequency distribution (for example, histogram) of the equivalent circle diameter, the grade width of the equivalent circle diameter can be set to 50nm or less to make frequency distribution.

[0074] As a method for obtaining the above-mentioned desired distribution form of precipitates, for example, Mn, S, Al, O, B and N in particular are appropriately adjusted in the component composition so that the main oxides generated in the steel material are Al-based oxides.

[0075] The limit upsetting rate of the electromagnetic soft iron of the present embodiment is preferably 55% or more. If the limit upsetting rate is 55% or more, more excellent cold workability can be exhibited.

[0076] It should be noted that the limit upsetting rate is defined as the upsetting rate when a test piece having a diameter of 15 mm and a height of 22.5 mm and a notch having a depth of 0.8 mm and a notch bottom R0.15 on the side is collected from a depth position of 1 / 2 of the diameter of the circumference of the electromagnetic soft iron as a steel bar, and compression processing is performed until a crack with a width of 0.5 mm or more is generated at the notch bottom of the test piece.

[0077] The electromagnetic soft iron of the present embodiment is excellent in machinability, and therefore preferably has any of a rod shape (straight rod, steel rod, etc.) and a coil shape, which are mainly used for cutting.

[0078] Next, a suitable method for manufacturing the electromagnetic soft iron according to the present embodiment will be described.

[0079] For example, the molten steel having the above-mentioned composition is melted by a smelting method using a common converter, electric furnace, etc., and a steel billet is made by a common continuous casting and a slab-opening method. Then, the steel billet is heated as needed, and hot rolling such as steel sheet rolling and bar rolling is performed, thereby making electromagnetic soft iron. In particular, in the above-mentioned manufacturing method, in order to obtain the desired distribution form of precipitates, and then to improve cold workability, magnetic properties and machinability, it is preferred that the thickness of the steel material after hot rolling or the diameter of the steel bar is set to more than 10 mm, and it is also preferred to cool after hot rolling. In addition, in the above-mentioned manufacturing method, in order to obtain the desired distribution form of precipitates, and then to improve cold workability, magnetic properties and machinability, it is preferred not to implement annealing. The conditions other than this are not particularly limited, for example, as long as the organization control is performed in a manner that is conducive to subsequent forging, machining, etc. for component forming. In addition, other manufacturing conditions can be in accordance with the general manufacturing method of steel.

[0080] Example

[0081] Next, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following Examples.

[0082] Regarding steel No. 1 to 34, after obtaining molten steel having the composition shown in Table 1, the steel was heated to 1200°C and hot rolled, and the final finishing temperature of the rolling was set to 900°C to produce steel bars (electromagnetic soft iron) with a diameter of 25 mm. That is, in the production of steel No. 1 to 34, annealing treatment was not performed. On the other hand, regarding steel No. 35 and 36, after obtaining molten steel having the composition shown in Table 1, the steel was heated to 1200°C and hot forged, and then intermediate annealing was performed at 950°C to produce steel bars (electromagnetic soft iron) with a diameter of 25 mm.

[0083]

[0084] [Distribution form of precipitates]

[0085] The obtained steel rod (electromagnetic soft iron) was cut into 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 morphology of the precipitates. Using a scanning electron microscope (SEM), an arbitrary 0.2 mm area near the surface of the sample where no decarburization reaction or oxidation reaction occurred was observed at an acceleration voltage of 15 kV and a magnification of 10,000 times. 2The above areas were observed. Based on the observed SEM images, the objects determined to be precipitates were analyzed using an energy dispersive X-ray analyzer (EDS) to identify the components constituting the precipitates. The EDS analysis was used to measure the number density (pieces / mm2) per unit area of ​​the samples identified as precipitates of MnS, BN or their composite compounds (MnS+BN). 2 ).

[0086] In addition, for the samples identified as the above precipitates, the area was analyzed from the SEM image, and the equivalent circle diameter was calculated from the area. Next, the frequency distribution (histogram) of the calculated equivalent circle diameter was prepared with a step width of 50 nm, and the mode and the proportion of 600 nm or more were obtained.

[0087] Table 2 shows these results.

[0088] Furthermore, the magnetic properties (magnetic flux density and coercive force), cold workability (limiting upsetting ratio), and machinability (flank wear amount) of the obtained electromagnetic soft iron were evaluated by the following methods.

[0089] [Magnetic properties]

[0090] The magnetic properties are measured in accordance with JIS C2504. That is, an annular test piece is collected from the above-mentioned steel bar (electromagnetic soft iron) and subjected to magnetic annealing at 750°C for 2 hours. Then, the excitation winding (220 turns of the primary winding) and the detection winding (100 turns of the pole winding) are wound on the annular test piece for testing. The magnetic flux density is determined by measuring the B-H curve using a DC magnetization measuring device. Specifically, the magnetic flux density at 100 A / m and 300 A / m during the magnetization process when the maximum magnetic field reached is 10,000 A / m is determined. The results are shown in Table 2. If the magnetic flux density at 100 A / m is above 1.25 T and the magnetic flux density at 300 A / m is above 1.55 T, it can be said that the magnetic properties are excellent.

[0091] The coercive force was measured using a ring-shaped test piece wound in the same manner as above, using a DC magnetic property tester at a reverse magnetizing force of ±400 A / m. The results are shown in Table 2. If the coercive force is 60 A / m or less, the magnetic property can be considered to be excellent.

[0092] [Cold workability]

[0093] The cold workability was evaluated by the limit upsetting ratio.

[0094] The limit upset rate is obtained by collecting a test piece with a diameter of 15 mm and a height of 22.5 mm and a notch with a depth of 0.8 mm and a notch bottom R0.15 on the side from a depth position of 1 / 2 of the diameter of the circumference of the above-mentioned steel bar, and using the test piece for compression processing. The compression is performed successively until a crack with a width of 0.5 mm or more is generated at the notch bottom of the test piece. The upset rate at this time is taken as the limit upset rate. The results are shown in Table 2.

[0095] If the limit upsetting ratio is 55% or more, it can be said that the cold workability is excellent.

[0096] [Machinability]

[0097] Cutting performance was evaluated by measuring the amount of flank wear on the tool. Specifically, a 25 mm diameter steel bar was wet cut using a coated carbide tool on an NC lathe. The cut depth was 0.2 mm, the feed rate was 0.15 mm / rev, the circumferential speed was 300 m / min, and the cutting length was 1000 mm. The flank wear of the tool was then measured and evaluated. The results are shown in Table 2.

[0098] If the flank wear amount is 35 μm or less, it can be said that the machinability is excellent.

[0099]

[0100] As can be seen from Tables 1 and 2, the steel material (electromagnetic soft iron) of the present invention has excellent cold workability and has both magnetic properties and machinability at a high level. On the other hand, in the comparative examples whose component compositions are outside the scope of the present invention and / or whose distribution forms of precipitates are outside the scope of the present invention, at least any one of magnetic properties, cold workability and machinability is not fully satisfied.

Claims

1. An electromagnetic soft iron, characterized in that: The invention has the following composition: containing, by mass%, C: 0.02% or less, Si: 0.05% or less, Mn: 0.010% to 0.500%, P: 0.002% to 0.020%, S: 0.001% to 0.050%, Al: 0.010% to 0.050%, O: 0.0010% to 0.0200%, N: 0.0010% to 0.0100% and B: 0.0003% to 0.0065%, and the remainder is iron and unavoidable impurities; The total number density of precipitates of manganese sulfide (MnS), boron nitride (BN), and their composite compound (MnS+BN) is 5000 pieces / mm 2 above, From 0.2mm 2 In the frequency distribution of the equivalent circle diameters of the precipitates observed in the above region, the mode is 50 nm to 250 nm, and the proportion of 600 nm or more is 7% or more.

2. The electromagnetic soft iron according to claim 1, wherein: The component composition further contains, in mass %, one or more selected from the group consisting of Cu: 0.20% or less, Ni: 0.30% or less, and Cr: 0.30% or less.

3. The electromagnetic soft iron according to claim 1 or 2, wherein: The component composition further contains, in mass %, one or more selected from the group consisting of Mo: 0.10% or less, V: 0.02% or less, Nb: 0.015% or less, and Ti: 0.010% or less.

4. The electromagnetic soft iron according to claim 1 or 2, wherein: The above-mentioned component composition further contains, in mass %, one or two selected from the group consisting of Sn: 0.10% or less and Sb: 0.10% or less.

5. The electromagnetic soft iron according to claim 3, wherein: The above-mentioned component composition further contains, in mass %, one or two selected from the group consisting of Sn: 0.10% or less and Sb: 0.10% or less.

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