Non-oriented magnetic steel sheet with excellent punching workability

Abstract

A non-oriented electrical steel sheet with low iron losses and excellent blanking property is provided that has a composition of components including, in mass%, C: 0.0050% or less, Si: 2.5 to 6.5%, Mn: 0.05 to 2.0%, P: 0.10% or less, S: 0.0050% or less, Al: 0.30 to 2.0%, N: 0.010% or less, Pb: 0.00010 to 0.010%, and Zn: 0.0005 to 0.020%, in which the ratio [Zn] / [Pb] of the Zn content (mass%) to the Pb content (mass%) is 1.58 or greater, and provided that the particle size distribution of secondary-phase particles in the particle size range of 0.10 µm or greater but less than 5.00 µm in a cross-section of the steel sheet in the thickness direction that coincides with the rolling direction is represented by a histogram where each class represents the particle size, the frequency represents the number density, and the class interval is 0.10 µm, the force of pinning magnetic domain walls calculated with Expression (3) below: ∑i=1nπdiNSi , where di represents the class value (µm) of a class i, and Nsi represents the frequency (number / µm2) of the class i) from the particle size distribution is 0.0015 or less.

Description

Technical Field

[0001] The present invention relates to a non-oriented electrical steel sheet with low iron losses and excellent blanking property.Background Art

[0002] In recent years, there has been increasing demand for energy saving, and electrical devices have also been strongly required to have higher efficiency. Therefore, non-oriented electrical steel sheets, which are widely used as iron core materials of electrical devices, have also been desired to exhibit further improved characteristics, such as lower iron losses. In response to such demand, several attempts have been made so far, such as adding a large amount of components that increase the specific resistance of steel, like Si and Al, or reducing the sheet thickness, for example.

[0003] Meanwhile, when a laminated iron core, which is formed by laminating steel sheets with core shapes (i.e., core materials), is adopted as an iron core (i.e., core) of a motor, for example, stamping is commonly used as a method of obtaining the core materials from a non-oriented electrical steel sheet. However, it is known that the magnetic properties of the iron core will degrade due to strain introduced into a region around a cut portion during stamping, or due to changes in the shape of a cut end surface, such as shear droops and burrs.

[0004] Therefore, there have been conducted so far numerous studies on improving the blanking property of non-oriented electrical steel sheets. For example, Patent Literature 1 discloses non-oriented electrical steel containing Si: 1.5 mass% or less, Mn: in the range of 0.4 mass% to 1.5 mass%, sol.Al: in the range of 0.01 mass% to 0.04 mass%, Ti: 0.0015 mass% or less, N: 0.0030 mass% or less, S: in the range of 0.0010 mass% to 0.0040 mass%, and B: in the range of 0.5 to 1.5 (in terms of B / N), with the balance being Fe and unavoidable impurities, in which 10% or more (in terms of the number of particles) of sulfide particles containing Mn are formed as complex precipitates with B precipitates, and the crystal grain size is controlled to be an appropriate size so that high blanking property is achieved.

[0005] In addition, Patent Literature 2 discloses non-oriented electrical steel that contains steel components including C: 0.003 mass% or less, Si: in the range of 1.0 mass% to 3.0 mass%, Al: in the range of 0.1 mass% to 3.0 mass%, and Mn: in the range of 0.1 mass% to 1.0 mass%, with the balance being Fe and unavoidable impurities, in which the Al content and the Si content satisfy the relationship of 0.2≤Al / (Si+Al)≤0.6, the yield ratio represented by (yield strength / tensile strength) is 0.6 or greater, and the Vickers hardness is 200 or less, thus exhibiting excellent in magnetic properties and blanking property.Citation ListPatent Literature

[0006] Patent Literature 1: International Publication No. WO 2005 / 100627 Patent Literature 2: Japanese Patent Laid-Open No. 2015-214758 Summary of InventionTechnical Problem

[0007] However, the electrical steel sheet described in Patent Literature 1 above has a Si content of 1.5 mass% or less, and is not directly applicable to a non-oriented electrical steel sheet with a higher Si content. In addition, the electrical steel sheet disclosed in Patent Literature 2 requires a Vickers hardness of 200 or less. Thus, such an electrical steel sheet is not applicable to a non-oriented electrical steel sheet with a high Si content, either. Further, although the non-oriented electrical steel sheet described in Patent Literature 1 relates to a technology for improving blanking property by controlling the crystal grain size, and the non-oriented electrical steel sheet described in Patent Literature 2 relates to a technology for improving blanking property by controlling the mechanical characteristics of a parent phase, it is difficult to achieve a further improvement in blanking property using such these methods alone.

[0008] The present invention has been made in view of the foregoing problems posed by the conventional technologies, and an object of the present invention is to provide a high-Si non-oriented electrical steel sheet having blanking property improved with a method different from the conventional technologies, without degradation in iron loss properties.Solution to Problem

[0009] The inventors have conducted concentrated studies to achieve the foregoing object. Consequently, the inventors have arrived at the present invention as follows. That is, they found that it is possible to improve the blanking property of a steel sheet without causing an increase in iron losses, by adding Pb into a steel material to improve the blanking property of the steel sheet, and also by adding an appropriate amount of Zn thereinto to control the particle size distribution of secondary-phase particles, such as inclusions, in the steel sheet so that this particle size distribution will fall into an appropriate range so as to prevent the degradation in magnetic properties due to the addition of Pb.

[0010] The present invention based on the foregoing findings is a non-oriented electrical steel sheet including a composition of components including C: 0.0050 mass% or less, Si: 2.5 to 6.5 mass%, Mn: 0.05 to 2.0 mass%, P: 0.10 mass% or less, S: 0.0050 mass% or less, Al: 0.30 to 2.0 mass%, N: 0.010 mass% or less, Pb: 0.00010 to 0.010 mass%, Zn: 0.0005 to 0.020 mass%, Ti: 0.0050 mass% or less, Nb: 0.0050 mass% or less, V: 0.0050 mass% or less, and O: 0.0050 mass% or less, with a balance being Fe and unavoidable impurities, characterized in that: provided that contents (mass%) of Pb and Zn are respectively represented by [Pb] and [Zn], [Pb] and [Zn] satisfy Expression (1) below: Zn / Pb ≥ 1.58and provided that a particle size distribution of secondary-phase particles in a particle size range of 0.10 µm or greater but less than 5.00 µm in a cross-section of the steel sheet in a thickness direction that coincides with a rolling direction is represented by a histogram where each class represents a particle size, a frequency represents a number density, and a class interval is 0.10 µm, the particle size distribution satisfies Expression (2) below: ∑ i = 1 n π d i N Si ≦ 0.0015 where d i represents a class value (µm) of a class i, and N si represents a frequency (number / µm 2< ) of the class i.

[0011] In the foregoing non-oriented electrical steel sheet of the present invention, an average particle size of the secondary-phase particles in the particle size range of 0.10 µm or greater but less than 5.00 µm in the cross-section of the steel sheet in the thickness direction that coincides with the rolling direction is 0.40 µm or greater.

[0012] The foregoing non-oriented electrical steel sheet of the present invention further includes, in addition to the composition of components, at least one of Groups A to I of components below: Group A: at least one of Sn and Sb: a total of 0.005 to 0.20 mass%; Group B: at least one of Ca, Mg, and REM: a total of 0.0005 to 0.020 mass%; Group C: at least one of Cr, Cu, and Ni: a total of 0.01 to 1.0 mass%; Group D: at least one of Mo: 0.001 to 0.050 mass% and W: 0.001 to 0.050 mass%; Group E: B: 0.0001 to 0.0040 mass%; Group F: Co: 0.0005 to 0.0200 mass%; Group G: Ta: 0 to 0.0020 mass%; Group H: As: 0 to 0.020 mass%; and Group I: at least one of Ge: 0 to 0.030 mass% and Ga: 0 to 0.030 mass%. Advantageous Effects of Invention

[0013] According to the present invention, it is possible to improve the blanking property of a non-oriented electrical steel sheet with a high Si content without causing degradation in iron loss properties. Thus, it is possible to provide a non-oriented electrical steel sheet that is suitable as an iron core material of a motor or a transformer, for example, that is produced through blanking.Brief Description of Drawings

[0014] [Fig. 1] Fig. 1 is a graph illustrating the influence of the Pb content on the height of a burr on a cut surface resulting from blanking. [Fig. 2] Fig. 2 is a graph illustrating the influence of the Zn content on the force of pinning magnetic domain walls. [Fig. 3] Fig. 3 is a graph illustrating the influence of the force of pinning magnetic domain walls on iron losses. Description of Embodiments

[0015] First, experiments conducted to develop the present invention will be described.(Experiment 1)

[0016] Steel, which has a composition of components including C: 0.0020 mass%, Si: 2.9 mass%, Mn: 0.2 mass%, P: 0.01 mass%, S: 0.0020 mass%, Al: 0.4 mass%, N: 0.0012 mass%, Ti: 0.0010 mass%, Nb: 0.0001 mass%, V: 0.0005 mass%, and O: 0.0010 mass%, and also including Pb with varying content in the range of 0.00001 to 0.022 mass%, with the balance being Fe and unavoidable impurities, was smelted in a vacuum melting furnace, and was then cast to form a steel ingot. Next, the steel ingot was hot-rolled to obtain a hot-rolled sheet with a thickness of 1.8 mm. Then, the hot-rolled sheet was subjected to hot-band annealing at 1000°C × 30 seconds, and was then pickled before being cold-rolled to obtain a cold-rolled sheet with a final thickness of 0.25 mm. The cold-rolled sheet was then subjected to finishing annealing at 1000°C × 10 seconds.

[0017] Next, the steel sheet that had thus been subjected to finishing annealing was subjected to blanking with a clearance set to 5%, thereby allowing a disk-like specimen with a diameter of 10 mm to be collected therefrom. At this time, each steel sheet was stamped with a new die. With respect to each of disk-like specimens obtained through 1,000,000 times of stamping, the heights of burrs generated on two cut end portions at opposite ends of the steel sheet in the rolling direction were measured. Then, the blanking property of the steel sheet was evaluated from the mean value thereof.

[0018] Fig. 1 illustrates the relationship between the Pb content in the steel material and the height of a burr observed after stamping was performed 1,000,000 times. From the graph, it is found that adding 0.00010 mass% or more of Pb can reduce the height of the burr to 30 µm or less, and thus can improve blanking property.

[0019] The reason that adding Pb can improve blanking property is considered as follows. Pb is not dissolved as a solid solution in steel, but is dispersed as fine granular particles (i.e., metal inclusions) in the steel. Thus, when stamping is performed, stress concentrates on the metal inclusions, which promotes the occurrence and propagation of cracking, and thus reduces the wear of a die.

[0020] As a result of the foregoing experiment, it has been confirmed that adding an appropriate amount of Pb can improve blanking property. Meanwhile, it was revealed that a new problem would arise with the addition of Pb such that the crystal grain size would decrease, which results in degradation in magnetic properties, in particular, iron loss properties. In this regard, the inventors have focused on the influence of secondary-phase particles, such as inclusions, on the iron loss properties, and conducted the following experiment to inspect the particle size and particle size distribution of the secondary-phase particles that are required to obtain excellent iron loss properties.(Experiment 2)

[0021] Steel, which has a composition of components including C: 0.0020 mass%, Si: 3.1 mass%, Mn: 0.3 mass%, P: 0.01 mass%, S: 0.0020 mass%, Al: 0.8 mass%, N: 0.0010 mass%, Pb: 0.003 mass%, Ti: 0.0015 mass%, Nb: 0.0002 mass%, V: 0.0010 mass%, and O: 0.0010 mass%, and also including Zn with varying content in the range of 0.0001 to 0.052 mass%, with the balance being Fe and unavoidable impurities, was smelted in a vacuum melting furnace, and was then cast to form a steel ingot. Next, the steel ingot was hot-rolled to obtain a hot-rolled sheet with a thickness of 1.5 mm. Then, the hot-rolled sheet was subjected to hot-band annealing at 1020°C × 30 seconds, and was then pickled before being cold-rolled to obtain a cold-rolled sheet with a final thickness of 0.25 mm. The cold-rolled sheet was then subjected to finishing annealing at 1000°C × 10 seconds.

[0022] Next, two types of specimens each having a width of 30 mm × a length of 280 mm were obtained from the steel sheet, which had been subjected to the finishing annealing, through shearing such that their longitudinal directions respectively coincided with the rolling direction (i.e., L-direction) and the sheet width direction (i.e., C-direction). Then, equal numbers of specimens in the L-direction and in the C-direction were stacked in an Epstein testing machine, so that the iron loss W 10 / 400 was measured with a method described in JIS C 2550.

[0023] In addition, a cross-section of each specimen across its thickness in the rolling direction (i.e., total sheet thickness) was observed in the range of 2 mm 2< or greater, using a scanning microscope (SEM), so that the particle sizes of secondary-phase particles in the range were measured. Herein, the secondary-phase particles refer to inclusions or precipitates forming a phase other than a ferrite phase that is a parent phase. Specifically, the secondary-phase particles refer to oxide-base inclusions, carbonitride, sulfide, boride, and their compounds. In addition, the particle size of each secondary-phase particle refers to the mean value of the Feret's diameter in the rolling direction and the Feret's diameter in the thickness direction. Note that as the secondary-phase particles for the measurement of the particle size, secondary-phase particles with a particle size of 0.10 µm or greater were selected. This is because particles with a particle size of less than 0.10 µm have a low level of interaction with magnetic domain walls, and thus have little effect of pinning the magnetic domain walls. Meanwhile, particles with a particle size of 5.00 µm or greater are also excluded from the measurement target because such particles likewise have a low level of interaction with magnetic domain walls. Although a SEM was used to measure the particle sizes of the secondary-phase particles in the present invention, any method may be used as long as the observation of particles with a particle size of 0.10 µm or greater is possible. However, the use of a SEM is preferable from the perspective that the adjustment of samples is easy and wide-range observation is possible.

[0024] Next, measurement data on the thus measured particle sizes of the secondary-phase particles were separated at a particle size pitch of 0.10 µm, and the number of secondary-phase particles in each section was determined. Then, this value was divided by the measurement area to determine the number density N s (number / µm 2< ) of the secondary-phase particles in each section. Next, the particle size (i.e., class value) of the secondary-phase particles in each section was regarded as the center value of the section (for example, the particle size of particles in a section corresponding to a particle size of 0.10 µm or greater but less than 0.20 µm was regarded as 0.15 µm), and a histogram was created where each class represents the particle size of secondary-phase particles, the frequency represents the number density N si of the secondary-phase particles, and the class interval is 0.10 µm.

[0025] Next, from the thus determined histogram, the index value (particles·µm -1< ) defined by Expression (3) below was determined. ∑ i = 1 n πd i N Si where d i represents the class value (µm) of a class i, and N si represents the frequency (number / µm 2< ) of the class i. The index value represents the magnitude of a force that suppresses the movement of magnetic domain walls. In the present invention, such a force that suppresses the movement of magnetic domain walls shall also be referred to as a "force of pinning magnetic domain walls."

[0026] Fig. 2 illustrates the relationship between the foregoing force of pinning magnetic domain walls and the Zn content. From the graph, it is found that the force of pinning magnetic domain walls will decrease as the Zn content increases. In particular, it is found that when the Zn content is 0.0005 mass% or greater, the force of pinning magnetic domain walls will decrease down to 0.0015 particles·µm -1< or less. In addition, Fig. 3 illustrates the relationship between the foregoing force of pinning magnetic domain walls and the iron loss W 10 / 400 . From the graph, it is found that the iron loss W 10 / 400 will also decrease as the force of pinning magnetic domain walls decreases. In particular, it is found that when the force of pinning magnetic domain walls is 0.0015 particles·µm -1< or less, the iron loss W 10 / 400 is 10.0 W / kg or less, which is a favorable value. From the results, it has been found that to suppress an increase in iron losses due to the addition of Pb, it is important to reduce the "force of pinning magnetic domain walls," which is defined by Expression (3) above, to a predetermined value or less by optimizing the particle size distribution of the secondary-phase particles through the addition of Zn.

[0027] The mechanism that the addition of Zn has influence on the force of pinning magnetic domain walls as described above has not been fully understood so far, but the inventors' reasonings are as follows..

[0028] When the Zn concentration in molten steel is increased, Zn binds to O and S in the molten steel, and thus forms oxide and sulfide. Such oxide and sulfide are discharged to the outside of the system, or grow into coarse particles, which suppresses the formation of fine oxide-base inclusions and fine precipitates. This can decrease the force of pinning magnetic domain walls, and thus can obtain excellent iron loss properties.

[0029] The present invention has been developed based on such new findings with further studies conducted thereon.

[0030] Next, the composition of components of a non-oriented electrical steel sheet of the present invention will be described.C: 0.0050 mass% or less

[0031] C contained in the product sheet is a detrimental element that degrades the iron loss properties by forming and precipitating carbides due to magnetic aging. Therefore, the C content in the steel material is limited to 0.0050 mass% or less. Preferably, the C content is set to 0.0040 mass% or less. Note that the lower limit of the C content is not particularly specified, but it is preferably set to about 0.0001 mass% from the perspective of reducing the decarburization cost of a refining step.Si: 2.5 to 6.5 mass%

[0032] Si is an element effective in increasing the specific resistance of steel, and thus reducing iron losses. Si also has the effect of increasing the strength of steel through solid-solution strengthening. Therefore, in the present invention, the Si content is set to 2.5 mass% or greater. Meanwhile, if the Si content is over 6.5 mass%, it will be difficult to perform rolling for the production. Thus, the upper limit of the Si content is set to 6.5 mass%. Preferably, the Si content is set in the range of 2.8 to 6.0 mass%.Mn: 0.05 to 2.0 mass%

[0033] As with Si, Mn is an element useful in increasing the specific resistance and strength of steel. Mn is also an element that forms sulfide to improve hot workability. Thus, in the present invention, the Mn content is set to 0.05 mass% or greater. Meanwhile, if the Mn content is over 2.0 mass%, cracking of the slab will occur, for example, which will decrease operability in the steelmaking step. Thus, the upper limit of the Mn content is set to 2.0 mass%. Preferably, the Mn content is set in the range of 0.1 to 1.5 mass%.P: 0.10 mass% or less

[0034] P is an element having a great effect of increasing the specific resistance of steel, and thus reducing eddy current losses. P also has the effect of increasing the hardness of steel, and thus improving blanking property. Thus, P may be added in an appropriate amount. However, if P is added excessively, cold-rolling performance will degrade. Thus, the upper limit of the P content is set to 0.10 mass%. Preferably, the P content is set to 0.05 mass% or less.S: 0.0050 mass% or less

[0035] S is a detrimental element that will form sulfide to become precipitates or inclusions, which will degrade manufacturability (i.e., hot-rolling performance) as well as the magnetic properties of the product sheet. Therefore, the S content is preferably minimized. Thus, in the present invention, the upper limit of the S content is set to 0.0050 mass%. Preferably, the S content is set to 0.0030 mass% or less.Al: 0.30 to 2.0 mass%

[0036] As with Si, Al is an element having the effect of reducing iron losses by increasing the specific resistance of steel, and the effect of increasing the strength of steel. However, if the Al content is over 2.0 mass%, the steel will become brittle, and thus will become difficult to roll. Thus, the upper limit of the Al content is set to 2.0 mass%. Meanwhile, if the Al content is less than 0.30 mass%, fine nitride will form and precipitate, which will rather degrade the iron loss properties. Thus, the lower limit of the Al content is set to 0.30 mass%. Preferably, the Al content is set in the range of 0.4 to 1.5 mass%.N: 0.010 mass% or less

[0037] N is a detrimental element that will form nitride as such nitride will precipitate and degrade the magnetic properties. Thus, the N content is limited to 0.010 mass% or less. Preferably, the N content is set to 0.0060 mass% or less.Pb: 0.00010 to 0.010 mass%

[0038] Pb is dispersed as fine granular metal inclusions in steel, and will remain in the steel even after finishing annealing. Accordingly, as Pb becomes the starting point of cracking or promotes the propagation of cracking when stress concentrates thereon during stamping, Pb has the effect of improving blanking property and suppressing the wear of a die. However, if the Pb content is less than 0.00010 mass%, such an effect will not be obtained sufficiently. Meanwhile, if the Pb content is over 0.010 mass%, grain growth will be hindered, which makes it impossible to achieve excellent iron loss properties. Accordingly, the Pb content is set in the range of 0.00010 to 0.010 mass%. Preferably, the Pb content is set in the range of 0.0003 to 0.0050 mass%.Zn: 0.0005 to 0.020 mass%

[0039] Zn forms stable and coarse sulfide or oxide. That is, Zn has the effect of suppressing an increase in iron losses due to the addition of Pb described above by coarsening secondary-phase particles in steel and thus weakening the force of pinning magnetic domain walls with the secondary-phase particles. To obtain such an effect, Zn needs to be added in an amount of 0.0005 mass% or greater. However, if the Zn content is over 0.020 mass%, such an effect will saturate. Accordingly, the Zn content is set in the range of 0.0005 to 0.020 mass%. Preferably, the Zn content is set in the range of 0.001 to 0.010 mass%.Ti: 0.0050 mass% or less, Nb: 0.0050 mass% or less, and V: 0.0050 mass% or less

[0040] Each of Ti, Nb, and V is a detrimental element that will form fine carbonitride as such fine carbonitride will precipitate and increase iron losses. In particular, if the content of each of these elements is over 0.0050 mass%, such an adverse effect will become significant. Thus, the upper limit of the content of each element is limited to 0.0050 mass%. Preferably, the content of each element is set to 0.0030 mass% or less.O: 0.0050 mass% or less

[0041] O is a detrimental element that will form oxide as such oxide will pin the movement of grain boundaries as well as magnetic domain walls, thereby degrading the magnetic properties. Thus, the O content needs to be minimized. Therefore, in the present invention, the O content is limited to 0.0050 mass% or less. Preferably, the O content is set to 0.0040 mass% or less.[Zn] / [Pb]≥1.58

[0042] The non-oriented electrical steel sheet of the present invention contains Pb and Zn in the foregoing ranges. Further, provided that the Pb content (mass%) and the Zn content (mass%) are respectively represented by [Zn] and [Pb], it is necessary that [Zn] and [Pb] satisfy Expression (1) below: Zn / Pb ≥ 1.58

[0043] As is obvious from the results of the foregoing experiments, when Pb is added, an increase in iron losses will occur. However, if Zn is added such that Expression (1) above is satisfied, the force of pinning magnetic domain walls will decrease, so that excellent iron loss properties can be obtained. Preferably, the Zn and Pb contents satisfy [Zn] / [Pb]≥2.5.

[0044] The non-oriented electrical steel sheet of the present invention contains the foregoing components, with the balance being Fe and unavoidable impurities. Further, the non-oriented electrical steel sheet may contain the following components as appropriate in accordance with the characteristics required, in addition to the foregoing components.At least one of Sn and Sb: a total of 0.005 to 0.20 mass%

[0045] Each of Sn and Sb has the effect of improving the recrystallization texture, and thus improving the magnetic flux density and iron loss properties. To obtain such an effect, at least one of such components needs to be added in an amount of 0.005 mass% or greater in total. However, if the total content of such a component(s) is over 0.20 mass%, the foregoing effect will saturate. Accordingly, when Sn and Sb are added, the total content of at least one of them is preferably set in the range of 0.005 to 0.20 mass%. More preferably, the total content of at least one of them is set in the range of 0.010 to 0.10 mass%.At least one of Ca, Mg, and REM: a total of 0.0005 to 0.020 mass%

[0046] Each of Ca, Mg, and REM has the effect of decreasing the force of pinning magnetic domain walls with the secondary-phase particles by forming stable and coarse sulfide or oxide. To obtain such an effect, at least one of Ca, Mg, and REM needs to be added in an amount of 0.0005 mass% or greater in total. However, if the total content of such an element(s) is over 0.020 mass%, the foregoing effect will saturate. Accordingly, when Ca, Mg, and REM are added, the total content of at least one of them is preferably set in the range of 0.0005 to 0.020 mass%. More preferably, the total content of at least one of them is set in the range of 0.0010 to 0.010 mass%.At least one of Cu, Ni, and Cr: a total of 0.01 to 1.0 mass%

[0047] Each of Cu, Ni, and Cr has the effect of reducing iron losses by increasing the specific resistance of steel. To obtain such an effect, at least one of Cu, Ni, and Cr is preferably added in an amount of 0.01 mass% or greater in total. However, if the total content of such an element(s) is over 1.0 mass%, the cost of the raw materials will increase. Accordingly, the total content of at least one of such elements is preferably set in the range of 0.01 to 1.0 mass%. More preferably, the total content of at least one of such elements is set in the range of 0.03 to 0.8 mass%.At least one of Mo: 0.001 to 0.050 mass% and W: 0.001 to 0.050 mass%

[0048] Each of Mo and W is an element effective in reducing surface defects (i.e., scabs) of the steel sheet. In particular, since the steel sheet of the present invention is a high-alloy steel, and the surface thereof is thus easily oxidized, scabs are likely to occur due to surface cracking. However, such cracking can be reduced if Mo and W, which are elements that increase high-temperature strength, are added in a small amount. The foregoing effect will not be obtained sufficiently if each of the Mo content and the W content is less than 0.001 mass%. Meanwhile, even if each of the Mo content and the W content is over 0.050 mass%, the foregoing effect will saturate, resulting in an increased cost of alloying. Accordingly, when Mo and W are added, it is preferred that at least one of them be added in the foregoing range(s) respectively. More preferably, the content of each of these elements is set in the range of 0.0050 to 0.050 mass%.B: 0.0001 to 0.0040 mass%

[0049] B is an element that contributes to improving blanking property by reducing the grain size of the microstructure of the steel sheet. To obtain such an effect, B is preferably added in an amount of 0.0001 mass% or greater. Meanwhile, if the B content is over 0.0040 mass%, not only such an effect will saturate, but an excessive amount of boride will be generated, which will increase iron losses. Thus, the upper limit of the B content is preferably set to 0.0040 mass%. More preferably, the B content is set in the range of 0.0005 to 0.0020 mass%.Co: 0.0005 to 0.0200 mass%

[0050] Co has the effect of suppressing nitridation during finishing annealing. To obtain such an effect, Co is preferably added in an amount of 0.0005 mass% or greater. Meanwhile, if the Co content is over 0.0200 mass%, such an effect will saturate, resulting in an increased cost of alloying. Accordingly, when Co is added, the Co content is preferably set in the range of 0.0005 to 0.0200 mass%. More preferably, the Co content is set in the range of 0.001 to 0.010 mass%.Ta: 0 to 0.0020 mass%

[0051] Ta can be added to improve the workability of steel and increase its strength. To reliably obtain such effects, Ta is preferably added in an amount of 0.0001 mass% or greater. Meanwhile, Ta is also an element that will increase iron losses. In particular, if the Ta content is over 0.0020 mass%, such an adverse effect will become significant. Thus, the upper limit of the Ta content is set to 0.0020 mass%. More preferably, the Ta content is set in the range of 0.0003 to 0.0010 mass%.As: 0 to 0.020 mass%

[0052] As is an element that increases the hardness of steel, and can be added to adjust the mechanical properties. To reliably obtain such an effect, As is preferably added in an amount of 0.001 mass% or greater. Meanwhile, As is also an element that will embrittle steel. In particular, if the As content is over 0.020 mass%, such an adverse effect will become significant. Thus, the upper limit of the As content is set to 0.020 mass%. More preferably, the As content is set in the range of 0.003 to 0.010 mass%.At least one of Ge: 0 to 0.030 mass% and Ga: 0 to 0.030 mass%

[0053] Each of Ge and Ga is an element that improves the texture. To reliably obtain such an effect, each of at least one of such elements is preferably added in an amount of 0.001 mass% or greater. Meanwhile, if the content of each of such elements is over 0.030 mass%, the foregoing effect will saturate. Thus, the upper limit of the content of each of such elements is set to 0.030 mass%. More preferably, the content of each of such elements is set in the range of 0.003 to 0.010 mass%.Next, the non-oriented electrical steel sheet of the present invention will be described.

[0054] Regarding the non-oriented electrical steel sheet of the present invention, the force of pinning magnetic domain walls determined with Expression (3) below from the particle size and the number density of secondary-phase particles in the particle size range of 0.10 µm or greater but less than 5.00 µm in the steel sheet needs to be 0.0015 particles·µm -1< or less. ∑ i = 1 n πd i N Si where d i represents the class value (µm) of a class i, and N si represents the frequency (number / µm 2< ) of the class i. If the force of pinning magnetic domain walls is over 0.0015 particles·µm -1< , the movement of the magnetic domain walls will be hindered. In such a case, it will be not possible to cancel out an increase in iron losses due to the addition of Zn. Preferably, the force of pinning magnetic domain walls is 0.0012 particles·µm -1< or less.

[0055] In addition, regarding the non-oriented electrical steel sheet of the present invention, from the perspective of further decreasing the force of pinning magnetic domain walls, which can cause an increase in iron losses, it is preferable that the mean value of the particle sizes of secondary-phase particles in the particle size range of 0.10 µm or greater but less than 5.00 µm in the steel sheet be 0.40 µm or greater. Further preferably, the mean value is 0.6 µm or greater.

[0056] Next, a method for producing the non-oriented electrical steel sheet of the present invention will be described.

[0057] The non-oriented electrical steel sheet of the present invention may be produced with a known method, and the production method is not limited to a particular one. An example of a preferable production method will be described below.

[0058] First, steel with the foregoing composition of components, which matches the present invention, is smelted through a known refining process that involves the use of a converter or an electric furnace, or a vacuum degassing apparatus, for example. Then, the steel is subjected to a known continuous casting process or ingot making-blooming process so that a steel material (i.e., a slab) is produced. If an electric furnace, for which iron scraps generated as wastes or in factories are used as a raw material, is used in the smelting process, it is possible to utilize as an iron source inexpensive scraps containing Pb and Zn as impurities, which contributes to reducing the cost of the raw materials. To produce the slab, it is also possible to produce a thin slab with a thickness of 200 mm or less with a view to reducing the rolling reduction in a subsequent cold-rolling step, and thus increasing the magnetic flux density.

[0059] When a slab is produced through a continuous casting process, if the cooling rate during solidification is high, finer inclusions will form, which will hinder grain growth, or increase the force of pinning magnetic domain walls. Thus, it is preferable to set the average cooling rate to 1.0°C / s or less for the central portion of the slab in the thickness direction in the temperature range of the solidification temperature to 1400°C. More preferably, the average cooling rate is set to 0.5°C / s or less. Note that the cooling rate during solidification can also be controlled by increasing the thickness of the slab to be cast or by decreasing the casting rate.

[0060] As a method for promoting the elimination of harmful effects by coarsening the particle size of the secondary-phase particles, it is also effective to add Ca, Mg, and REM that will form coarse sulfide or oxide, for example, other than decreasing the cooling rate during the continuous casting process as described above.

[0061] Next, the slab produced with the foregoing method is hot-rolled, and is then subjected to hot-band annealing as appropriate, and further to pickling, cold rolling, and finishing annealing. Then, the resulting sheet is covered with an insulation coating as appropriate so that a non-oriented electrical steel sheet as a product sheet is produced. Such production steps may be performed under conventionally known conditions, and are not limited to particular steps. In addition, the foregoing cold rolling may include one cold-rolling step to obtain a final thickness (i.e., the thickness of the product sheet), or may include two or more cold-rolling steps with intermediate annealing interposed therebetween to obtain a final thickness.Examples

[0062] A steel material (i.e., a slab) having a composition of components including various components illustrated in Table 1, with the balance being Fe and unavoidable impurities was produced through a continuous casting process. Then, the steel material was hot-rolled to obtain a hot-rolled sheet with a thickness of 1.5 mm. Next, the hot-rolled sheet was subjected to hot-band annealing at 1080°C × 30 seconds, and was then pickled before being cold-rolled to obtain a cold-rolled sheet with a final thickness of 0.25 mm. Regarding No. A1 and No. A4, a fracture occurred during cold rolling. Thus, evaluation was not performed in the steps including cold rolling and the following steps. After that, the cold-rolled sheet was subjected to finishing annealing at 1000°C × 15 seconds to obtain a product sheet. [Table 1-1]No.Chemical composition (mass%)RemarksCSiMnPSAlNPbZnTiNbvOOthersZn / Pb10.0083.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001-5.00Comparative steel20.0022.20.30.010.0010.80.0010.00040.0020.0010.00020.00030.001-5.00Comparative steel30.0023.10.030.010.0010.80.0010.00040.0020.0010.00020.00030.001-5.00Comparative steel40.0023.10.30.010.0010.250.0010.00040.0020.0010.00020.00030.001-5.00Comparative steel50.0023.10.30.010.0010.80.0010.000070.0020.0010.00020.00030.001-28.57Comparative steel60.0023.10.30.010.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel70.0023.10.30.010.0010.80.0010.000130.00060.0010.00020.00030.001-4.62Invention steel80.0023.10.30.010.0010.80.0010.00030.0020.0010.00020.00030.001-6.67Invention steel90.0023.10.30.010.0010.80.0010.00090.0020.0010.00020.00030.001-2.22Invention steel100.0023.10.30.010.0010.80.0010.01080.0190.0010.00020.00030.001-1.76Comparative steel110.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.006-5.00Comparative steel120.0023.10.30.010.0010.80.0010.00020.00040.0010.00020.00030.001-2.00Comparative steel130.0023.10.30.010.0010.80.0010.00040.0100.0010.00020.00030.001-25.00Invention steel140.0023.10.30.010.0010.80.0010.00080.0010.0010.00020.00030.001-1.25Comparative steel150.0023.10.30.010.0010.80.0010.00080.00150.0010.00020.00030.001-1.88Invention steel160.0023.10.30.010.0010.80.0010.00040.0020.0070.00020.00030.001-5.00Comparative steel170.0023.10.30.010.0010.80.0010.00040.0020.0010.00600.00030.001-5.00Comparative steel180.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00600.001-5.00Comparative steel190.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001-5.00Invention steel200.0022.50.30.010.0010.80.0010.000130.0020.0010.00020.00030.003-15.38Invention steel210.0024.50.30.030.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel220.0025.50.30.010.0030.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel230.0026.50.30.010.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel240.0026.70.30.010.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Comparative steel250.0023.10.060.050.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel260.0023.11.20.050.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel270.0023.11.90.050.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel280.0023.10.30.120.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Comparative steel [Table 1-2] Chemical composition (mass%)RemarksCSiMnPSAlNPbZnTiNbvOOthersZn / Pb290.0023.12.00.010.0010.80.0010.000130.0020.0010.00020.00100.001-15.38Invention steel300.0023.12.50.010.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Comparative steel310.0023.10.30.010.0010.310.0010.000130.0020.0010.00020.00030.001-15.38Invention steel320.0023.10.30.010.0011.20.0010.000130.0020.0010.00020.00030.001-15.38Invention steel330.0023.10.30.010.0042.00.0010.000130.0020.0010.00020.00030.001-15.38Invention steel340.0023.10.30.010.0062.00.0010.000130.0020.0010.00020.00030.001-15.38Comparative steel350.0023.10.30.010.0012.20.0010.000130.0020.0010.00020.00030.001-15.38Comparative steel360.0023.10.30.10.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel370.0022.50.30.010.0010.80.0010.0100.0190.0010.00020.00030.001-1.90Invention steel380.0022.50.30.010.0010.80.0050.0080.0150.0010.00020.00030.001-1.88Invention steel390.0022.50.30.010.0010.80.0110.0080.0150.0010.00020.00030.001-1.88Comparative steel400.0022.50.30.010.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel410.0022.50.30.010.0010.80.0010.000130.0200.0010.00400.00030.001-153.85Invention steel420.0022.50.30.010.0010.80.0010.000130.00050.0030.00020.00030.001-3.85Invention steel430.0022.50.30.010.0010.80.0010.000130.0090.0010.00020.00400.001-69.23Invention steel440.0022.50.30.010.0010.80.0010.000130.0150.0050.00020.00030.001-115.38Invention steel450.0022.50.30.010.0010.80.0010.000130.0220.0010.00020.00030.001-169.23Comparative steel460.0023.10.30.010.0010.80.0010.00120.00180.0010.00020.00030.001-1.50Comparative steel470.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Sn:0.015.00Invention steel480.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Sn:0.155.00Invention steel490.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Sb:0.025.00Invention steel500.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Sb:0.185.00Invention steel510.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ca:0.00075.00Invention steel520.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ca:0.0185.00Invention steel530.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Mg:0.00065.00Invention steel540.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Mg:0.0195.00Invention steel550.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001REM:0.00065.00Invention steel560.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001REM:0.0185.00Invention steel570.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ca:0.0004, Mg:0.0002, REM:0.00025.00Invention steel [Table 1-3] No.Chemical composition (mass%)RemarksCSiMnPSAlNPbZnTiNbvOOthersZn / Pb580.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Cu:0.055.00Invention steel590.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Cu:0.525.00Invention steel600.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Cr:0.045.00Invention steel610.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Cr:0.345.00Invention steel620.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ni:0.055.00Invention steel630.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ni:0.655.00Invention steel640.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Mo:0.0155.00Invention steel650.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Mo:0.045.00Invention steel660.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001W:0.00155.00Invention steel670.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001W:0.0385.00Invention steel680.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001B:0.000155.00Invention steel690.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001B:0.00375.00Invention steel700.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Co:0.0045.00Invention steel710.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Co:0.0155.00Invention steel720.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Sn:0.03, Sb:0.0025, Cu:0.08, Cr:0.12, Ni:0.08, Mo:0.031, W:0.0021, B:0.0001, Co:0.00585.00Invention steel730.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Sn:0.03, Sb:0.0025, Ca:0.0004, Mg:0.0002, REM:0.0002, Cu:0.08, Cr:0.12, Ni:0.08, Mo:0.031, W:0.0021, B:0.0001, Co:0.00585.00Invention steel740.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ta:0.00185.00Invention steel750.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001As:0.0195.00Invention steel760.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ge:0.0285.00Invention steel770.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ga:0.0295.00Invention steel780.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ge:0.027, Ga:0.0285.00Invention steel790.0023.10.30.010.0010.80.0010.000130.0020.0010.00020.00030.001Sn:0.01, Ca:0.0002, Mg:0.0005, Mo:0.02, B:0.0002, Co:0.004, As:0.003, Ga:0.00215.38Invention steel

[0063] Next, the steel sheet (i.e., the product sheet), which had been subjected to the finishing annealing, was stamped using a die with a clearances set to 5% so that a disk-like specimen with a diameter of 10 mm was obtained. At this time, the stamping die was replaced with a new one for each steel sheet. With respect to each of disk-like specimens obtained through 1,000,000 times of stamping, the heights of burrs in the rolling direction on two stamping end portions at opposite ends of the specimen were measured, and the mean value thereof was calculated.

[0064] In addition, two types of specimens each having a width of 30 mm × a length of 280 mm were cut out of the steel sheet, which had been subjected to the finishing annealing, through shearing such that their longitudinal directions respectively coincided with the rolling direction (i.e., L-direction) and the width direction (i.e., C-direction). Next, equal numbers of specimens in the L-direction and in the C-direction were stacked in an Epstein testing machine, so that the iron loss W 10 / 400 was measured with a method described in JIS C 2550.

[0065] Further, a cross-section of each steel sheet in the rolling direction (i.e., the total sheet thickness × the rolling direction) was observed in the range of 2 mm 2< or greater, using a SEM, so that the particle sizes of all secondary-phase particles in the particle size range of 0.10 µm or greater but less than 5.00 µm in the cross-section were measured. Next, measurement data on the particle sizes were separated at a particle size pitch of 0.10 µm, so that a histogram of a particle size distribution was created. From the histogram, the force of pinning magnetic domain walls defined by Expression (3) below was determined. ∑ i = 1 n πd i N Si where d i represents the class value (µm) of a class i, and N si represents the frequency (number / µm 2< ) of the class i.

[0066] Table 2 illustrates the results of the measurement (i.e., the height of a burr, the iron loss W 10 / 400 , the force of pinning magnetic domain walls with the secondary-phase particles, and the average particle size of the secondary-phase particles after stamping was performed 1,000,000 times). From the results, it is found that each of the steel sheets that satisfy the conditions of the present invention is excellent in both blanking property and iron loss properties. [Table 2-1]No.Height (µm) of burrForce (particles·µm -1< ) of pinning magnetic domain wallsAverage particle size (µm) of secondary-phase particlesIron loss W 10 / 400 (W / kg)Remarks123.20.00120.6811.57Comparative Example226.80.00120.6710.68Comparative Example323.70.00120.6910.79Comparative Example422.70.00180.3810.68Comparative Example538.00.00080.969.58Comparative Example626.70.00100.769.62Invention Example724.70.00110.719.63Invention Example824.60.00140.469.64Invention Example922.60.00140.379.69Invention Example1027.10.00170.3211.26Comparative Example1123.70.00180.4211.35Comparative Example1224.80.00170.4810.87Comparative Example1325.20.00110.649.58Invention Example1423.20.00180.3810.68Comparative Example1523.50.00130.439.84Invention Example1627.50.00190.4111.29Comparative Example1727.20.00210.3411.49Comparative Example1824.10.00210.3811.57Comparative Example1926.40.00110.689.65Invention Example2026.90.00090.589.85Invention Example2126.80.00100.679.21Invention Example2226.90.00120.689.14Invention Example2326.60.00080.719.08Invention Example24----Comparative Example2526.60.00090.789.91Invention Example2626.70.00100.709.54Invention Example2726.40.00110.629.85Invention Example28----Comparative Example [Table 2-2] No.Height (µm) of burrForce (particles·µm -1< ) of pinning magnetic domain wallsAverage particle size (µm) of secondary-phase particlesIron loss W 10 / 400 (W / kg)Remarks2926.80.00120.619.87Invention Example3026.50.00160.6310.89Comparative Example3127.20.00130.539.84Invention Example3226.80.00090.729.34Invention Example3326.80.00130.689.58Invention Example3426.90.00180.6510.12Comparative Example3526.70.00120.6511.06Comparative Example3626.20.00080.679.42Invention Example3722.10.00140.589.92Invention Example3823.50.00130.639.84Invention Example3923.60.00170.6110.08Comparative Example4027.90.00100.769.75Invention Example4127.50.00080.799.85Invention Example4227.60.00120.579.89Invention Example4327.40.00110.759.87Invention Example4427.90.00100.629.88Invention Example4527.50.00080.7810.78Comparative Example4623.40.00100.699.64Comparative Example4726.00.00120.689.54Invention Example4825.70.00130.699.35Invention Example4927.10.00120.679.55Invention Example5025.70.00130.699.38Invention Example5125.00.00090.739.51Invention Example5224.30.00080.899.48Invention Example5324.60.00070.729.52Invention Example5423.50.00080.919.47Invention Example5523.10.00080.739.58Invention Example5625.10.00090.829.52Invention Example5724.70.00050.929.43Invention Example [Table 2-3] NºHeight (µm) of burrForce (particles·µm -1< ) of pinning magnetic domain wallsAverage particle size (µm) of secondary-phase particlesIron loss W 10 / 400 (W / kg)Remarks5825.10.00120.689.61Invention Example5926.20.00110.679.62Invention Example6025.70.00110.699.59Invention Example6124.70.00130.659.57Invention Example6225.70.00120.689.58Invention Example6326.00.00110.699.54Invention Example6424.20.00140.659.68Invention Example6522.90.00140.629.69Invention Example6624.20.00130.689.67Invention Example6726.50.00140.679.72Invention Example6824.60.00110.429.68Invention Example6925.00.00120.419.75Invention Example7024.60.00110.659.61Invention Example7122.70.00100.689.52Invention Example7225.30.00100.719.61Invention Example7325.20.00080.879.49Invention Example7424.40.00130.679.82Invention Example7525.10.00120.689.63Invention Example7625.20.00110.669.45Invention Example7725.30.00110.659.44Invention Example7825.20.00120.669.41Invention Example7924.60.00130.679.49Invention Example

Examples

experiment 1

(Experiment 1)

[0016]Steel, which has a composition of components including C: 0.0020 mass%, Si: 2.9 mass%, Mn: 0.2 mass%, P: 0.01 mass%, S: 0.0020 mass%, Al: 0.4 mass%, N: 0.0012 mass%, Ti: 0.0010 mass%, Nb: 0.0001 mass%, V: 0.0005 mass%, and O: 0.0010 mass%, and also including Pb with varying content in the range of 0.00001 to 0.022 mass%, with the balance being Fe and unavoidable impurities, was smelted in a vacuum melting furnace, and was then cast to form a steel ingot. Next, the steel ingot was hot-rolled to obtain a hot-rolled sheet with a thickness of 1.8 mm. Then, the hot-rolled sheet was subjected to hot-band annealing at 1000°C × 30 seconds, and was then pickled before being cold-rolled to obtain a cold-rolled sheet with a final thickness of 0.25 mm. The cold-rolled sheet was then subjected to finishing annealing at 1000°C × 10 seconds.

[0017]Next, the steel sheet that had thus been subjected to finishing annealing was subjected to blanking with a clearance set to 5%, there...

experiment 2

(Experiment 2)

[0021]Steel, which has a composition of components including C: 0.0020 mass%, Si: 3.1 mass%, Mn: 0.3 mass%, P: 0.01 mass%, S: 0.0020 mass%, Al: 0.8 mass%, N: 0.0010 mass%, Pb: 0.003 mass%, Ti: 0.0015 mass%, Nb: 0.0002 mass%, V: 0.0010 mass%, and O: 0.0010 mass%, and also including Zn with varying content in the range of 0.0001 to 0.052 mass%, with the balance being Fe and unavoidable impurities, was smelted in a vacuum melting furnace, and was then cast to form a steel ingot. Next, the steel ingot was hot-rolled to obtain a hot-rolled sheet with a thickness of 1.5 mm. Then, the hot-rolled sheet was subjected to hot-band annealing at 1020°C × 30 seconds, and was then pickled before being cold-rolled to obtain a cold-rolled sheet with a final thickness of 0.25 mm. The cold-rolled sheet was then subjected to finishing annealing at 1000°C × 10 seconds.

[0022]Next, two types of specimens each having a width of 30 mm × a length of 280 mm were obtained from the steel sheet, wh...

examples

[0062]A steel material (i.e., a slab) having a composition of components including various components illustrated in Table 1, with the balance being Fe and unavoidable impurities was produced through a continuous casting process. Then, the steel material was hot-rolled to obtain a hot-rolled sheet with a thickness of 1.5 mm. Next, the hot-rolled sheet was subjected to hot-band annealing at 1080°C × 30 seconds, and was then pickled before being cold-rolled to obtain a cold-rolled sheet with a final thickness of 0.25 mm. Regarding No. A1 and No. A4, a fracture occurred during cold rolling. Thus, evaluation was not performed in the steps including cold rolling and the following steps. After that, the cold-rolled sheet was subjected to finishing annealing at 1000°C × 15 seconds to obtain a product sheet.

[Table 1-1]

No.Chemical composition (mass%)Remarks

CSiMnPSAlNPbZnTiNbvOOthersZn / Pb

10.0083.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001-5.00Comparative steel

20.0022.20.30.010.001...

Technical Field

[0001] The present invention relates to a non-oriented electrical steel sheet with low iron losses and excellent blanking property.Background Art

[0002] In recent years, there has been increasing demand for energy saving, and electrical devices have also been strongly required to have higher efficiency. Therefore, non-oriented electrical steel sheets, which are widely used as iron core materials of electrical devices, have also been desired to exhibit further improved characteristics, such as lower iron losses. In response to such demand, several attempts have been made so far, such as adding a large amount of components that increase the specific resistance of steel, like Si and Al, or reducing the sheet thickness, for example.

[0003] Meanwhile, when a laminated iron core, which is formed by laminating steel sheets with core shapes (i.e., core materials), is adopted as an iron core (i.e., core) of a motor, for example, stamping is commonly used as a method of obtaining the core materials from a non-oriented electrical steel sheet. However, it is known that the magnetic properties of the iron core will degrade due to strain introduced into a region around a cut portion during stamping, or due to changes in the shape of a cut end surface, such as shear droops and burrs.

[0004] Therefore, there have been conducted so far numerous studies on improving the blanking property of non-oriented electrical steel sheets. For example, Patent Literature 1 discloses non-oriented electrical steel containing Si: 1.5 mass% or less, Mn: in the range of 0.4 mass% to 1.5 mass%, sol.Al: in the range of 0.01 mass% to 0.04 mass%, Ti: 0.0015 mass% or less, N: 0.0030 mass% or less, S: in the range of 0.0010 mass% to 0.0040 mass%, and B: in the range of 0.5 to 1.5 (in terms of B / N), with the balance being Fe and unavoidable impurities, in which 10% or more (in terms of the number of particles) of sulfide particles containing Mn are formed as complex precipitates with B precipitates, and the crystal grain size is controlled to be an appropriate size so that high blanking property is achieved.

[0005] In addition, Patent Literature 2 discloses non-oriented electrical steel that contains steel components including C: 0.003 mass% or less, Si: in the range of 1.0 mass% to 3.0 mass%, Al: in the range of 0.1 mass% to 3.0 mass%, and Mn: in the range of 0.1 mass% to 1.0 mass%, with the balance being Fe and unavoidable impurities, in which the Al content and the Si content satisfy the relationship of 0.2≤Al / (Si+Al)≤0.6, the yield ratio represented by (yield strength / tensile strength) is 0.6 or greater, and the Vickers hardness is 200 or less, thus exhibiting excellent in magnetic properties and blanking property.Citation ListPatent Literature

[0006] Patent Literature 1: International Publication No. WO 2005 / 100627 Patent Literature 2: Japanese Patent Laid-Open No. 2015-214758 Summary of InventionTechnical Problem

[0007] However, the electrical steel sheet described in Patent Literature 1 above has a Si content of 1.5 mass% or less, and is not directly applicable to a non-oriented electrical steel sheet with a higher Si content. In addition, the electrical steel sheet disclosed in Patent Literature 2 requires a Vickers hardness of 200 or less. Thus, such an electrical steel sheet is not applicable to a non-oriented electrical steel sheet with a high Si content, either. Further, although the non-oriented electrical steel sheet described in Patent Literature 1 relates to a technology for improving blanking property by controlling the crystal grain size, and the non-oriented electrical steel sheet described in Patent Literature 2 relates to a technology for improving blanking property by controlling the mechanical characteristics of a parent phase, it is difficult to achieve a further improvement in blanking property using such these methods alone.

[0008] The present invention has been made in view of the foregoing problems posed by the conventional technologies, and an object of the present invention is to provide a high-Si non-oriented electrical steel sheet having blanking property improved with a method different from the conventional technologies, without degradation in iron loss properties.Solution to Problem

[0009] The inventors have conducted concentrated studies to achieve the foregoing object. Consequently, the inventors have arrived at the present invention as follows. That is, they found that it is possible to improve the blanking property of a steel sheet without causing an increase in iron losses, by adding Pb into a steel material to improve the blanking property of the steel sheet, and also by adding an appropriate amount of Zn thereinto to control the particle size distribution of secondary-phase particles, such as inclusions, in the steel sheet so that this particle size distribution will fall into an appropriate range so as to prevent the degradation in magnetic properties due to the addition of Pb.

[0010] The present invention based on the foregoing findings is a non-oriented electrical steel sheet including a composition of components including C: 0.0050 mass% or less, Si: 2.5 to 6.5 mass%, Mn: 0.05 to 2.0 mass%, P: 0.10 mass% or less, S: 0.0050 mass% or less, Al: 0.30 to 2.0 mass%, N: 0.010 mass% or less, Pb: 0.00010 to 0.010 mass%, Zn: 0.0005 to 0.020 mass%, Ti: 0.0050 mass% or less, Nb: 0.0050 mass% or less, V: 0.0050 mass% or less, and O: 0.0050 mass% or less, with a balance being Fe and unavoidable impurities, characterized in that: provided that contents (mass%) of Pb and Zn are respectively represented by [Pb] and [Zn], [Pb] and [Zn] satisfy Expression (1) below: Zn / Pb ≥ 1.58and provided that a particle size distribution of secondary-phase particles in a particle size range of 0.10 µm or greater but less than 5.00 µm in a cross-section of the steel sheet in a thickness direction that coincides with a rolling direction is represented by a histogram where each class represents a particle size, a frequency represents a number density, and a class interval is 0.10 µm, the particle size distribution satisfies Expression (2) below: ∑ i = 1 n π d i N Si ≦ 0.0015 where d i represents a class value (µm) of a class i, and N si represents a frequency (number / µm 2< ) of the class i.

[0011] In the foregoing non-oriented electrical steel sheet of the present invention, an average particle size of the secondary-phase particles in the particle size range of 0.10 µm or greater but less than 5.00 µm in the cross-section of the steel sheet in the thickness direction that coincides with the rolling direction is 0.40 µm or greater.

[0012] The foregoing non-oriented electrical steel sheet of the present invention further includes, in addition to the composition of components, at least one of Groups A to I of components below: Group A: at least one of Sn and Sb: a total of 0.005 to 0.20 mass%; Group B: at least one of Ca, Mg, and REM: a total of 0.0005 to 0.020 mass%; Group C: at least one of Cr, Cu, and Ni: a total of 0.01 to 1.0 mass%; Group D: at least one of Mo: 0.001 to 0.050 mass% and W: 0.001 to 0.050 mass%; Group E: B: 0.0001 to 0.0040 mass%; Group F: Co: 0.0005 to 0.0200 mass%; Group G: Ta: 0 to 0.0020 mass%; Group H: As: 0 to 0.020 mass%; and Group I: at least one of Ge: 0 to 0.030 mass% and Ga: 0 to 0.030 mass%. Advantageous Effects of Invention

[0013] According to the present invention, it is possible to improve the blanking property of a non-oriented electrical steel sheet with a high Si content without causing degradation in iron loss properties. Thus, it is possible to provide a non-oriented electrical steel sheet that is suitable as an iron core material of a motor or a transformer, for example, that is produced through blanking.Brief Description of Drawings

[0014] [Fig. 1] Fig. 1 is a graph illustrating the influence of the Pb content on the height of a burr on a cut surface resulting from blanking. [Fig. 2] Fig. 2 is a graph illustrating the influence of the Zn content on the force of pinning magnetic domain walls. [Fig. 3] Fig. 3 is a graph illustrating the influence of the force of pinning magnetic domain walls on iron losses. Description of Embodiments

[0015] First, experiments conducted to develop the present invention will be described.(Experiment 1)

[0016] Steel, which has a composition of components including C: 0.0020 mass%, Si: 2.9 mass%, Mn: 0.2 mass%, P: 0.01 mass%, S: 0.0020 mass%, Al: 0.4 mass%, N: 0.0012 mass%, Ti: 0.0010 mass%, Nb: 0.0001 mass%, V: 0.0005 mass%, and O: 0.0010 mass%, and also including Pb with varying content in the range of 0.00001 to 0.022 mass%, with the balance being Fe and unavoidable impurities, was smelted in a vacuum melting furnace, and was then cast to form a steel ingot. Next, the steel ingot was hot-rolled to obtain a hot-rolled sheet with a thickness of 1.8 mm. Then, the hot-rolled sheet was subjected to hot-band annealing at 1000°C × 30 seconds, and was then pickled before being cold-rolled to obtain a cold-rolled sheet with a final thickness of 0.25 mm. The cold-rolled sheet was then subjected to finishing annealing at 1000°C × 10 seconds.

[0017] Next, the steel sheet that had thus been subjected to finishing annealing was subjected to blanking with a clearance set to 5%, thereby allowing a disk-like specimen with a diameter of 10 mm to be collected therefrom. At this time, each steel sheet was stamped with a new die. With respect to each of disk-like specimens obtained through 1,000,000 times of stamping, the heights of burrs generated on two cut end portions at opposite ends of the steel sheet in the rolling direction were measured. Then, the blanking property of the steel sheet was evaluated from the mean value thereof.

[0018] Fig. 1 illustrates the relationship between the Pb content in the steel material and the height of a burr observed after stamping was performed 1,000,000 times. From the graph, it is found that adding 0.00010 mass% or more of Pb can reduce the height of the burr to 30 µm or less, and thus can improve blanking property.

[0019] The reason that adding Pb can improve blanking property is considered as follows. Pb is not dissolved as a solid solution in steel, but is dispersed as fine granular particles (i.e., metal inclusions) in the steel. Thus, when stamping is performed, stress concentrates on the metal inclusions, which promotes the occurrence and propagation of cracking, and thus reduces the wear of a die.

[0020] As a result of the foregoing experiment, it has been confirmed that adding an appropriate amount of Pb can improve blanking property. Meanwhile, it was revealed that a new problem would arise with the addition of Pb such that the crystal grain size would decrease, which results in degradation in magnetic properties, in particular, iron loss properties. In this regard, the inventors have focused on the influence of secondary-phase particles, such as inclusions, on the iron loss properties, and conducted the following experiment to inspect the particle size and particle size distribution of the secondary-phase particles that are required to obtain excellent iron loss properties.(Experiment 2)

[0021] Steel, which has a composition of components including C: 0.0020 mass%, Si: 3.1 mass%, Mn: 0.3 mass%, P: 0.01 mass%, S: 0.0020 mass%, Al: 0.8 mass%, N: 0.0010 mass%, Pb: 0.003 mass%, Ti: 0.0015 mass%, Nb: 0.0002 mass%, V: 0.0010 mass%, and O: 0.0010 mass%, and also including Zn with varying content in the range of 0.0001 to 0.052 mass%, with the balance being Fe and unavoidable impurities, was smelted in a vacuum melting furnace, and was then cast to form a steel ingot. Next, the steel ingot was hot-rolled to obtain a hot-rolled sheet with a thickness of 1.5 mm. Then, the hot-rolled sheet was subjected to hot-band annealing at 1020°C × 30 seconds, and was then pickled before being cold-rolled to obtain a cold-rolled sheet with a final thickness of 0.25 mm. The cold-rolled sheet was then subjected to finishing annealing at 1000°C × 10 seconds.

[0022] Next, two types of specimens each having a width of 30 mm × a length of 280 mm were obtained from the steel sheet, which had been subjected to the finishing annealing, through shearing such that their longitudinal directions respectively coincided with the rolling direction (i.e., L-direction) and the sheet width direction (i.e., C-direction). Then, equal numbers of specimens in the L-direction and in the C-direction were stacked in an Epstein testing machine, so that the iron loss W 10 / 400 was measured with a method described in JIS C 2550.

[0023] In addition, a cross-section of each specimen across its thickness in the rolling direction (i.e., total sheet thickness) was observed in the range of 2 mm 2< or greater, using a scanning microscope (SEM), so that the particle sizes of secondary-phase particles in the range were measured. Herein, the secondary-phase particles refer to inclusions or precipitates forming a phase other than a ferrite phase that is a parent phase. Specifically, the secondary-phase particles refer to oxide-base inclusions, carbonitride, sulfide, boride, and their compounds. In addition, the particle size of each secondary-phase particle refers to the mean value of the Feret's diameter in the rolling direction and the Feret's diameter in the thickness direction. Note that as the secondary-phase particles for the measurement of the particle size, secondary-phase particles with a particle size of 0.10 µm or greater were selected. This is because particles with a particle size of less than 0.10 µm have a low level of interaction with magnetic domain walls, and thus have little effect of pinning the magnetic domain walls. Meanwhile, particles with a particle size of 5.00 µm or greater are also excluded from the measurement target because such particles likewise have a low level of interaction with magnetic domain walls. Although a SEM was used to measure the particle sizes of the secondary-phase particles in the present invention, any method may be used as long as the observation of particles with a particle size of 0.10 µm or greater is possible. However, the use of a SEM is preferable from the perspective that the adjustment of samples is easy and wide-range observation is possible.

[0024] Next, measurement data on the thus measured particle sizes of the secondary-phase particles were separated at a particle size pitch of 0.10 µm, and the number of secondary-phase particles in each section was determined. Then, this value was divided by the measurement area to determine the number density N s (number / µm 2< ) of the secondary-phase particles in each section. Next, the particle size (i.e., class value) of the secondary-phase particles in each section was regarded as the center value of the section (for example, the particle size of particles in a section corresponding to a particle size of 0.10 µm or greater but less than 0.20 µm was regarded as 0.15 µm), and a histogram was created where each class represents the particle size of secondary-phase particles, the frequency represents the number density N si of the secondary-phase particles, and the class interval is 0.10 µm.

[0025] Next, from the thus determined histogram, the index value (particles·µm -1< ) defined by Expression (3) below was determined. ∑ i = 1 n πd i N Si where d i represents the class value (µm) of a class i, and N si represents the frequency (number / µm 2< ) of the class i. The index value represents the magnitude of a force that suppresses the movement of magnetic domain walls. In the present invention, such a force that suppresses the movement of magnetic domain walls shall also be referred to as a "force of pinning magnetic domain walls."

[0026] Fig. 2 illustrates the relationship between the foregoing force of pinning magnetic domain walls and the Zn content. From the graph, it is found that the force of pinning magnetic domain walls will decrease as the Zn content increases. In particular, it is found that when the Zn content is 0.0005 mass% or greater, the force of pinning magnetic domain walls will decrease down to 0.0015 particles·µm -1< or less. In addition, Fig. 3 illustrates the relationship between the foregoing force of pinning magnetic domain walls and the iron loss W 10 / 400 . From the graph, it is found that the iron loss W 10 / 400 will also decrease as the force of pinning magnetic domain walls decreases. In particular, it is found that when the force of pinning magnetic domain walls is 0.0015 particles·µm -1< or less, the iron loss W 10 / 400 is 10.0 W / kg or less, which is a favorable value. From the results, it has been found that to suppress an increase in iron losses due to the addition of Pb, it is important to reduce the "force of pinning magnetic domain walls," which is defined by Expression (3) above, to a predetermined value or less by optimizing the particle size distribution of the secondary-phase particles through the addition of Zn.

[0027] The mechanism that the addition of Zn has influence on the force of pinning magnetic domain walls as described above has not been fully understood so far, but the inventors' reasonings are as follows..

[0028] When the Zn concentration in molten steel is increased, Zn binds to O and S in the molten steel, and thus forms oxide and sulfide. Such oxide and sulfide are discharged to the outside of the system, or grow into coarse particles, which suppresses the formation of fine oxide-base inclusions and fine precipitates. This can decrease the force of pinning magnetic domain walls, and thus can obtain excellent iron loss properties.

[0029] The present invention has been developed based on such new findings with further studies conducted thereon.

[0030] Next, the composition of components of a non-oriented electrical steel sheet of the present invention will be described.C: 0.0050 mass% or less

[0031] C contained in the product sheet is a detrimental element that degrades the iron loss properties by forming and precipitating carbides due to magnetic aging. Therefore, the C content in the steel material is limited to 0.0050 mass% or less. Preferably, the C content is set to 0.0040 mass% or less. Note that the lower limit of the C content is not particularly specified, but it is preferably set to about 0.0001 mass% from the perspective of reducing the decarburization cost of a refining step.Si: 2.5 to 6.5 mass%

[0032] Si is an element effective in increasing the specific resistance of steel, and thus reducing iron losses. Si also has the effect of increasing the strength of steel through solid-solution strengthening. Therefore, in the present invention, the Si content is set to 2.5 mass% or greater. Meanwhile, if the Si content is over 6.5 mass%, it will be difficult to perform rolling for the production. Thus, the upper limit of the Si content is set to 6.5 mass%. Preferably, the Si content is set in the range of 2.8 to 6.0 mass%.Mn: 0.05 to 2.0 mass%

[0033] As with Si, Mn is an element useful in increasing the specific resistance and strength of steel. Mn is also an element that forms sulfide to improve hot workability. Thus, in the present invention, the Mn content is set to 0.05 mass% or greater. Meanwhile, if the Mn content is over 2.0 mass%, cracking of the slab will occur, for example, which will decrease operability in the steelmaking step. Thus, the upper limit of the Mn content is set to 2.0 mass%. Preferably, the Mn content is set in the range of 0.1 to 1.5 mass%.P: 0.10 mass% or less

[0034] P is an element having a great effect of increasing the specific resistance of steel, and thus reducing eddy current losses. P also has the effect of increasing the hardness of steel, and thus improving blanking property. Thus, P may be added in an appropriate amount. However, if P is added excessively, cold-rolling performance will degrade. Thus, the upper limit of the P content is set to 0.10 mass%. Preferably, the P content is set to 0.05 mass% or less.S: 0.0050 mass% or less

[0035] S is a detrimental element that will form sulfide to become precipitates or inclusions, which will degrade manufacturability (i.e., hot-rolling performance) as well as the magnetic properties of the product sheet. Therefore, the S content is preferably minimized. Thus, in the present invention, the upper limit of the S content is set to 0.0050 mass%. Preferably, the S content is set to 0.0030 mass% or less.Al: 0.30 to 2.0 mass%

[0036] As with Si, Al is an element having the effect of reducing iron losses by increasing the specific resistance of steel, and the effect of increasing the strength of steel. However, if the Al content is over 2.0 mass%, the steel will become brittle, and thus will become difficult to roll. Thus, the upper limit of the Al content is set to 2.0 mass%. Meanwhile, if the Al content is less than 0.30 mass%, fine nitride will form and precipitate, which will rather degrade the iron loss properties. Thus, the lower limit of the Al content is set to 0.30 mass%. Preferably, the Al content is set in the range of 0.4 to 1.5 mass%.N: 0.010 mass% or less

[0037] N is a detrimental element that will form nitride as such nitride will precipitate and degrade the magnetic properties. Thus, the N content is limited to 0.010 mass% or less. Preferably, the N content is set to 0.0060 mass% or less.Pb: 0.00010 to 0.010 mass%

[0038] Pb is dispersed as fine granular metal inclusions in steel, and will remain in the steel even after finishing annealing. Accordingly, as Pb becomes the starting point of cracking or promotes the propagation of cracking when stress concentrates thereon during stamping, Pb has the effect of improving blanking property and suppressing the wear of a die. However, if the Pb content is less than 0.00010 mass%, such an effect will not be obtained sufficiently. Meanwhile, if the Pb content is over 0.010 mass%, grain growth will be hindered, which makes it impossible to achieve excellent iron loss properties. Accordingly, the Pb content is set in the range of 0.00010 to 0.010 mass%. Preferably, the Pb content is set in the range of 0.0003 to 0.0050 mass%.Zn: 0.0005 to 0.020 mass%

[0039] Zn forms stable and coarse sulfide or oxide. That is, Zn has the effect of suppressing an increase in iron losses due to the addition of Pb described above by coarsening secondary-phase particles in steel and thus weakening the force of pinning magnetic domain walls with the secondary-phase particles. To obtain such an effect, Zn needs to be added in an amount of 0.0005 mass% or greater. However, if the Zn content is over 0.020 mass%, such an effect will saturate. Accordingly, the Zn content is set in the range of 0.0005 to 0.020 mass%. Preferably, the Zn content is set in the range of 0.001 to 0.010 mass%.Ti: 0.0050 mass% or less, Nb: 0.0050 mass% or less, and V: 0.0050 mass% or less

[0040] Each of Ti, Nb, and V is a detrimental element that will form fine carbonitride as such fine carbonitride will precipitate and increase iron losses. In particular, if the content of each of these elements is over 0.0050 mass%, such an adverse effect will become significant. Thus, the upper limit of the content of each element is limited to 0.0050 mass%. Preferably, the content of each element is set to 0.0030 mass% or less.O: 0.0050 mass% or less

[0041] O is a detrimental element that will form oxide as such oxide will pin the movement of grain boundaries as well as magnetic domain walls, thereby degrading the magnetic properties. Thus, the O content needs to be minimized. Therefore, in the present invention, the O content is limited to 0.0050 mass% or less. Preferably, the O content is set to 0.0040 mass% or less.[Zn] / [Pb]≥1.58

[0042] The non-oriented electrical steel sheet of the present invention contains Pb and Zn in the foregoing ranges. Further, provided that the Pb content (mass%) and the Zn content (mass%) are respectively represented by [Zn] and [Pb], it is necessary that [Zn] and [Pb] satisfy Expression (1) below: Zn / Pb ≥ 1.58

[0043] As is obvious from the results of the foregoing experiments, when Pb is added, an increase in iron losses will occur. However, if Zn is added such that Expression (1) above is satisfied, the force of pinning magnetic domain walls will decrease, so that excellent iron loss properties can be obtained. Preferably, the Zn and Pb contents satisfy [Zn] / [Pb]≥2.5.

[0044] The non-oriented electrical steel sheet of the present invention contains the foregoing components, with the balance being Fe and unavoidable impurities. Further, the non-oriented electrical steel sheet may contain the following components as appropriate in accordance with the characteristics required, in addition to the foregoing components.At least one of Sn and Sb: a total of 0.005 to 0.20 mass%

[0045] Each of Sn and Sb has the effect of improving the recrystallization texture, and thus improving the magnetic flux density and iron loss properties. To obtain such an effect, at least one of such components needs to be added in an amount of 0.005 mass% or greater in total. However, if the total content of such a component(s) is over 0.20 mass%, the foregoing effect will saturate. Accordingly, when Sn and Sb are added, the total content of at least one of them is preferably set in the range of 0.005 to 0.20 mass%. More preferably, the total content of at least one of them is set in the range of 0.010 to 0.10 mass%.At least one of Ca, Mg, and REM: a total of 0.0005 to 0.020 mass%

[0046] Each of Ca, Mg, and REM has the effect of decreasing the force of pinning magnetic domain walls with the secondary-phase particles by forming stable and coarse sulfide or oxide. To obtain such an effect, at least one of Ca, Mg, and REM needs to be added in an amount of 0.0005 mass% or greater in total. However, if the total content of such an element(s) is over 0.020 mass%, the foregoing effect will saturate. Accordingly, when Ca, Mg, and REM are added, the total content of at least one of them is preferably set in the range of 0.0005 to 0.020 mass%. More preferably, the total content of at least one of them is set in the range of 0.0010 to 0.010 mass%.At least one of Cu, Ni, and Cr: a total of 0.01 to 1.0 mass%

[0047] Each of Cu, Ni, and Cr has the effect of reducing iron losses by increasing the specific resistance of steel. To obtain such an effect, at least one of Cu, Ni, and Cr is preferably added in an amount of 0.01 mass% or greater in total. However, if the total content of such an element(s) is over 1.0 mass%, the cost of the raw materials will increase. Accordingly, the total content of at least one of such elements is preferably set in the range of 0.01 to 1.0 mass%. More preferably, the total content of at least one of such elements is set in the range of 0.03 to 0.8 mass%.At least one of Mo: 0.001 to 0.050 mass% and W: 0.001 to 0.050 mass%

[0048] Each of Mo and W is an element effective in reducing surface defects (i.e., scabs) of the steel sheet. In particular, since the steel sheet of the present invention is a high-alloy steel, and the surface thereof is thus easily oxidized, scabs are likely to occur due to surface cracking. However, such cracking can be reduced if Mo and W, which are elements that increase high-temperature strength, are added in a small amount. The foregoing effect will not be obtained sufficiently if each of the Mo content and the W content is less than 0.001 mass%. Meanwhile, even if each of the Mo content and the W content is over 0.050 mass%, the foregoing effect will saturate, resulting in an increased cost of alloying. Accordingly, when Mo and W are added, it is preferred that at least one of them be added in the foregoing range(s) respectively. More preferably, the content of each of these elements is set in the range of 0.0050 to 0.050 mass%.B: 0.0001 to 0.0040 mass%

[0049] B is an element that contributes to improving blanking property by reducing the grain size of the microstructure of the steel sheet. To obtain such an effect, B is preferably added in an amount of 0.0001 mass% or greater. Meanwhile, if the B content is over 0.0040 mass%, not only such an effect will saturate, but an excessive amount of boride will be generated, which will increase iron losses. Thus, the upper limit of the B content is preferably set to 0.0040 mass%. More preferably, the B content is set in the range of 0.0005 to 0.0020 mass%.Co: 0.0005 to 0.0200 mass%

[0050] Co has the effect of suppressing nitridation during finishing annealing. To obtain such an effect, Co is preferably added in an amount of 0.0005 mass% or greater. Meanwhile, if the Co content is over 0.0200 mass%, such an effect will saturate, resulting in an increased cost of alloying. Accordingly, when Co is added, the Co content is preferably set in the range of 0.0005 to 0.0200 mass%. More preferably, the Co content is set in the range of 0.001 to 0.010 mass%.Ta: 0 to 0.0020 mass%

[0051] Ta can be added to improve the workability of steel and increase its strength. To reliably obtain such effects, Ta is preferably added in an amount of 0.0001 mass% or greater. Meanwhile, Ta is also an element that will increase iron losses. In particular, if the Ta content is over 0.0020 mass%, such an adverse effect will become significant. Thus, the upper limit of the Ta content is set to 0.0020 mass%. More preferably, the Ta content is set in the range of 0.0003 to 0.0010 mass%.As: 0 to 0.020 mass%

[0052] As is an element that increases the hardness of steel, and can be added to adjust the mechanical properties. To reliably obtain such an effect, As is preferably added in an amount of 0.001 mass% or greater. Meanwhile, As is also an element that will embrittle steel. In particular, if the As content is over 0.020 mass%, such an adverse effect will become significant. Thus, the upper limit of the As content is set to 0.020 mass%. More preferably, the As content is set in the range of 0.003 to 0.010 mass%.At least one of Ge: 0 to 0.030 mass% and Ga: 0 to 0.030 mass%

[0053] Each of Ge and Ga is an element that improves the texture. To reliably obtain such an effect, each of at least one of such elements is preferably added in an amount of 0.001 mass% or greater. Meanwhile, if the content of each of such elements is over 0.030 mass%, the foregoing effect will saturate. Thus, the upper limit of the content of each of such elements is set to 0.030 mass%. More preferably, the content of each of such elements is set in the range of 0.003 to 0.010 mass%.Next, the non-oriented electrical steel sheet of the present invention will be described.

[0054] Regarding the non-oriented electrical steel sheet of the present invention, the force of pinning magnetic domain walls determined with Expression (3) below from the particle size and the number density of secondary-phase particles in the particle size range of 0.10 µm or greater but less than 5.00 µm in the steel sheet needs to be 0.0015 particles·µm -1< or less. ∑ i = 1 n πd i N Si where d i represents the class value (µm) of a class i, and N si represents the frequency (number / µm 2< ) of the class i. If the force of pinning magnetic domain walls is over 0.0015 particles·µm -1< , the movement of the magnetic domain walls will be hindered. In such a case, it will be not possible to cancel out an increase in iron losses due to the addition of Zn. Preferably, the force of pinning magnetic domain walls is 0.0012 particles·µm -1< or less.

[0055] In addition, regarding the non-oriented electrical steel sheet of the present invention, from the perspective of further decreasing the force of pinning magnetic domain walls, which can cause an increase in iron losses, it is preferable that the mean value of the particle sizes of secondary-phase particles in the particle size range of 0.10 µm or greater but less than 5.00 µm in the steel sheet be 0.40 µm or greater. Further preferably, the mean value is 0.6 µm or greater.

[0056] Next, a method for producing the non-oriented electrical steel sheet of the present invention will be described.

[0057] The non-oriented electrical steel sheet of the present invention may be produced with a known method, and the production method is not limited to a particular one. An example of a preferable production method will be described below.

[0058] First, steel with the foregoing composition of components, which matches the present invention, is smelted through a known refining process that involves the use of a converter or an electric furnace, or a vacuum degassing apparatus, for example. Then, the steel is subjected to a known continuous casting process or ingot making-blooming process so that a steel material (i.e., a slab) is produced. If an electric furnace, for which iron scraps generated as wastes or in factories are used as a raw material, is used in the smelting process, it is possible to utilize as an iron source inexpensive scraps containing Pb and Zn as impurities, which contributes to reducing the cost of the raw materials. To produce the slab, it is also possible to produce a thin slab with a thickness of 200 mm or less with a view to reducing the rolling reduction in a subsequent cold-rolling step, and thus increasing the magnetic flux density.

[0059] When a slab is produced through a continuous casting process, if the cooling rate during solidification is high, finer inclusions will form, which will hinder grain growth, or increase the force of pinning magnetic domain walls. Thus, it is preferable to set the average cooling rate to 1.0°C / s or less for the central portion of the slab in the thickness direction in the temperature range of the solidification temperature to 1400°C. More preferably, the average cooling rate is set to 0.5°C / s or less. Note that the cooling rate during solidification can also be controlled by increasing the thickness of the slab to be cast or by decreasing the casting rate.

[0060] As a method for promoting the elimination of harmful effects by coarsening the particle size of the secondary-phase particles, it is also effective to add Ca, Mg, and REM that will form coarse sulfide or oxide, for example, other than decreasing the cooling rate during the continuous casting process as described above.

[0061] Next, the slab produced with the foregoing method is hot-rolled, and is then subjected to hot-band annealing as appropriate, and further to pickling, cold rolling, and finishing annealing. Then, the resulting sheet is covered with an insulation coating as appropriate so that a non-oriented electrical steel sheet as a product sheet is produced. Such production steps may be performed under conventionally known conditions, and are not limited to particular steps. In addition, the foregoing cold rolling may include one cold-rolling step to obtain a final thickness (i.e., the thickness of the product sheet), or may include two or more cold-rolling steps with intermediate annealing interposed therebetween to obtain a final thickness.Examples

[0062] A steel material (i.e., a slab) having a composition of components including various components illustrated in Table 1, with the balance being Fe and unavoidable impurities was produced through a continuous casting process. Then, the steel material was hot-rolled to obtain a hot-rolled sheet with a thickness of 1.5 mm. Next, the hot-rolled sheet was subjected to hot-band annealing at 1080°C × 30 seconds, and was then pickled before being cold-rolled to obtain a cold-rolled sheet with a final thickness of 0.25 mm. Regarding No. A1 and No. A4, a fracture occurred during cold rolling. Thus, evaluation was not performed in the steps including cold rolling and the following steps. After that, the cold-rolled sheet was subjected to finishing annealing at 1000°C × 15 seconds to obtain a product sheet. [Table 1-1]No.Chemical composition (mass%)RemarksCSiMnPSAlNPbZnTiNbvOOthersZn / Pb10.0083.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001-5.00Comparative steel20.0022.20.30.010.0010.80.0010.00040.0020.0010.00020.00030.001-5.00Comparative steel30.0023.10.030.010.0010.80.0010.00040.0020.0010.00020.00030.001-5.00Comparative steel40.0023.10.30.010.0010.250.0010.00040.0020.0010.00020.00030.001-5.00Comparative steel50.0023.10.30.010.0010.80.0010.000070.0020.0010.00020.00030.001-28.57Comparative steel60.0023.10.30.010.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel70.0023.10.30.010.0010.80.0010.000130.00060.0010.00020.00030.001-4.62Invention steel80.0023.10.30.010.0010.80.0010.00030.0020.0010.00020.00030.001-6.67Invention steel90.0023.10.30.010.0010.80.0010.00090.0020.0010.00020.00030.001-2.22Invention steel100.0023.10.30.010.0010.80.0010.01080.0190.0010.00020.00030.001-1.76Comparative steel110.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.006-5.00Comparative steel120.0023.10.30.010.0010.80.0010.00020.00040.0010.00020.00030.001-2.00Comparative steel130.0023.10.30.010.0010.80.0010.00040.0100.0010.00020.00030.001-25.00Invention steel140.0023.10.30.010.0010.80.0010.00080.0010.0010.00020.00030.001-1.25Comparative steel150.0023.10.30.010.0010.80.0010.00080.00150.0010.00020.00030.001-1.88Invention steel160.0023.10.30.010.0010.80.0010.00040.0020.0070.00020.00030.001-5.00Comparative steel170.0023.10.30.010.0010.80.0010.00040.0020.0010.00600.00030.001-5.00Comparative steel180.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00600.001-5.00Comparative steel190.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001-5.00Invention steel200.0022.50.30.010.0010.80.0010.000130.0020.0010.00020.00030.003-15.38Invention steel210.0024.50.30.030.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel220.0025.50.30.010.0030.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel230.0026.50.30.010.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel240.0026.70.30.010.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Comparative steel250.0023.10.060.050.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel260.0023.11.20.050.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel270.0023.11.90.050.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel280.0023.10.30.120.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Comparative steel [Table 1-2] Chemical composition (mass%)RemarksCSiMnPSAlNPbZnTiNbvOOthersZn / Pb290.0023.12.00.010.0010.80.0010.000130.0020.0010.00020.00100.001-15.38Invention steel300.0023.12.50.010.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Comparative steel310.0023.10.30.010.0010.310.0010.000130.0020.0010.00020.00030.001-15.38Invention steel320.0023.10.30.010.0011.20.0010.000130.0020.0010.00020.00030.001-15.38Invention steel330.0023.10.30.010.0042.00.0010.000130.0020.0010.00020.00030.001-15.38Invention steel340.0023.10.30.010.0062.00.0010.000130.0020.0010.00020.00030.001-15.38Comparative steel350.0023.10.30.010.0012.20.0010.000130.0020.0010.00020.00030.001-15.38Comparative steel360.0023.10.30.10.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel370.0022.50.30.010.0010.80.0010.0100.0190.0010.00020.00030.001-1.90Invention steel380.0022.50.30.010.0010.80.0050.0080.0150.0010.00020.00030.001-1.88Invention steel390.0022.50.30.010.0010.80.0110.0080.0150.0010.00020.00030.001-1.88Comparative steel400.0022.50.30.010.0010.80.0010.000130.0020.0010.00020.00030.001-15.38Invention steel410.0022.50.30.010.0010.80.0010.000130.0200.0010.00400.00030.001-153.85Invention steel420.0022.50.30.010.0010.80.0010.000130.00050.0030.00020.00030.001-3.85Invention steel430.0022.50.30.010.0010.80.0010.000130.0090.0010.00020.00400.001-69.23Invention steel440.0022.50.30.010.0010.80.0010.000130.0150.0050.00020.00030.001-115.38Invention steel450.0022.50.30.010.0010.80.0010.000130.0220.0010.00020.00030.001-169.23Comparative steel460.0023.10.30.010.0010.80.0010.00120.00180.0010.00020.00030.001-1.50Comparative steel470.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Sn:0.015.00Invention steel480.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Sn:0.155.00Invention steel490.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Sb:0.025.00Invention steel500.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Sb:0.185.00Invention steel510.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ca:0.00075.00Invention steel520.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ca:0.0185.00Invention steel530.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Mg:0.00065.00Invention steel540.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Mg:0.0195.00Invention steel550.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001REM:0.00065.00Invention steel560.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001REM:0.0185.00Invention steel570.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ca:0.0004, Mg:0.0002, REM:0.00025.00Invention steel [Table 1-3] No.Chemical composition (mass%)RemarksCSiMnPSAlNPbZnTiNbvOOthersZn / Pb580.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Cu:0.055.00Invention steel590.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Cu:0.525.00Invention steel600.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Cr:0.045.00Invention steel610.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Cr:0.345.00Invention steel620.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ni:0.055.00Invention steel630.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ni:0.655.00Invention steel640.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Mo:0.0155.00Invention steel650.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Mo:0.045.00Invention steel660.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001W:0.00155.00Invention steel670.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001W:0.0385.00Invention steel680.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001B:0.000155.00Invention steel690.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001B:0.00375.00Invention steel700.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Co:0.0045.00Invention steel710.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Co:0.0155.00Invention steel720.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Sn:0.03, Sb:0.0025, Cu:0.08, Cr:0.12, Ni:0.08, Mo:0.031, W:0.0021, B:0.0001, Co:0.00585.00Invention steel730.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Sn:0.03, Sb:0.0025, Ca:0.0004, Mg:0.0002, REM:0.0002, Cu:0.08, Cr:0.12, Ni:0.08, Mo:0.031, W:0.0021, B:0.0001, Co:0.00585.00Invention steel740.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ta:0.00185.00Invention steel750.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001As:0.0195.00Invention steel760.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ge:0.0285.00Invention steel770.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ga:0.0295.00Invention steel780.0023.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001Ge:0.027, Ga:0.0285.00Invention steel790.0023.10.30.010.0010.80.0010.000130.0020.0010.00020.00030.001Sn:0.01, Ca:0.0002, Mg:0.0005, Mo:0.02, B:0.0002, Co:0.004, As:0.003, Ga:0.00215.38Invention steel

[0063] Next, the steel sheet (i.e., the product sheet), which had been subjected to the finishing annealing, was stamped using a die with a clearances set to 5% so that a disk-like specimen with a diameter of 10 mm was obtained. At this time, the stamping die was replaced with a new one for each steel sheet. With respect to each of disk-like specimens obtained through 1,000,000 times of stamping, the heights of burrs in the rolling direction on two stamping end portions at opposite ends of the specimen were measured, and the mean value thereof was calculated.

[0064] In addition, two types of specimens each having a width of 30 mm × a length of 280 mm were cut out of the steel sheet, which had been subjected to the finishing annealing, through shearing such that their longitudinal directions respectively coincided with the rolling direction (i.e., L-direction) and the width direction (i.e., C-direction). Next, equal numbers of specimens in the L-direction and in the C-direction were stacked in an Epstein testing machine, so that the iron loss W 10 / 400 was measured with a method described in JIS C 2550.

[0065] Further, a cross-section of each steel sheet in the rolling direction (i.e., the total sheet thickness × the rolling direction) was observed in the range of 2 mm 2< or greater, using a SEM, so that the particle sizes of all secondary-phase particles in the particle size range of 0.10 µm or greater but less than 5.00 µm in the cross-section were measured. Next, measurement data on the particle sizes were separated at a particle size pitch of 0.10 µm, so that a histogram of a particle size distribution was created. From the histogram, the force of pinning magnetic domain walls defined by Expression (3) below was determined. ∑ i = 1 n πd i N Si where d i represents the class value (µm) of a class i, and N si represents the frequency (number / µm 2< ) of the class i.

[0066] Table 2 illustrates the results of the measurement (i.e., the height of a burr, the iron loss W 10 / 400 , the force of pinning magnetic domain walls with the secondary-phase particles, and the average particle size of the secondary-phase particles after stamping was performed 1,000,000 times). From the results, it is found that each of the steel sheets that satisfy the conditions of the present invention is excellent in both blanking property and iron loss properties. [Table 2-1]No.Height (µm) of burrForce (particles·µm -1< ) of pinning magnetic domain wallsAverage particle size (µm) of secondary-phase particlesIron loss W 10 / 400 (W / kg)Remarks123.20.00120.6811.57Comparative Example226.80.00120.6710.68Comparative Example323.70.00120.6910.79Comparative Example422.70.00180.3810.68Comparative Example538.00.00080.969.58Comparative Example626.70.00100.769.62Invention Example724.70.00110.719.63Invention Example824.60.00140.469.64Invention Example922.60.00140.379.69Invention Example1027.10.00170.3211.26Comparative Example1123.70.00180.4211.35Comparative Example1224.80.00170.4810.87Comparative Example1325.20.00110.649.58Invention Example1423.20.00180.3810.68Comparative Example1523.50.00130.439.84Invention Example1627.50.00190.4111.29Comparative Example1727.20.00210.3411.49Comparative Example1824.10.00210.3811.57Comparative Example1926.40.00110.689.65Invention Example2026.90.00090.589.85Invention Example2126.80.00100.679.21Invention Example2226.90.00120.689.14Invention Example2326.60.00080.719.08Invention Example24----Comparative Example2526.60.00090.789.91Invention Example2626.70.00100.709.54Invention Example2726.40.00110.629.85Invention Example28----Comparative Example [Table 2-2] No.Height (µm) of burrForce (particles·µm -1< ) of pinning magnetic domain wallsAverage particle size (µm) of secondary-phase particlesIron loss W 10 / 400 (W / kg)Remarks2926.80.00120.619.87Invention Example3026.50.00160.6310.89Comparative Example3127.20.00130.539.84Invention Example3226.80.00090.729.34Invention Example3326.80.00130.689.58Invention Example3426.90.00180.6510.12Comparative Example3526.70.00120.6511.06Comparative Example3626.20.00080.679.42Invention Example3722.10.00140.589.92Invention Example3823.50.00130.639.84Invention Example3923.60.00170.6110.08Comparative Example4027.90.00100.769.75Invention Example4127.50.00080.799.85Invention Example4227.60.00120.579.89Invention Example4327.40.00110.759.87Invention Example4427.90.00100.629.88Invention Example4527.50.00080.7810.78Comparative Example4623.40.00100.699.64Comparative Example4726.00.00120.689.54Invention Example4825.70.00130.699.35Invention Example4927.10.00120.679.55Invention Example5025.70.00130.699.38Invention Example5125.00.00090.739.51Invention Example5224.30.00080.899.48Invention Example5324.60.00070.729.52Invention Example5423.50.00080.919.47Invention Example5523.10.00080.739.58Invention Example5625.10.00090.829.52Invention Example5724.70.00050.929.43Invention Example [Table 2-3] NºHeight (µm) of burrForce (particles·µm -1< ) of pinning magnetic domain wallsAverage particle size (µm) of secondary-phase particlesIron loss W 10 / 400 (W / kg)Remarks5825.10.00120.689.61Invention Example5926.20.00110.679.62Invention Example6025.70.00110.699.59Invention Example6124.70.00130.659.57Invention Example6225.70.00120.689.58Invention Example6326.00.00110.699.54Invention Example6424.20.00140.659.68Invention Example6522.90.00140.629.69Invention Example6624.20.00130.689.67Invention Example6726.50.00140.679.72Invention Example6824.60.00110.429.68Invention Example6925.00.00120.419.75Invention Example7024.60.00110.659.61Invention Example7122.70.00100.689.52Invention Example7225.30.00100.719.61Invention Example7325.20.00080.879.49Invention Example7424.40.00130.679.82Invention Example7525.10.00120.689.63Invention Example7625.20.00110.669.45Invention Example7725.30.00110.659.44Invention Example7825.20.00120.669.41Invention Example7924.60.00130.679.49Invention Example

Examples

experiment 1

(Experiment 1)

[0016]Steel, which has a composition of components including C: 0.0020 mass%, Si: 2.9 mass%, Mn: 0.2 mass%, P: 0.01 mass%, S: 0.0020 mass%, Al: 0.4 mass%, N: 0.0012 mass%, Ti: 0.0010 mass%, Nb: 0.0001 mass%, V: 0.0005 mass%, and O: 0.0010 mass%, and also including Pb with varying content in the range of 0.00001 to 0.022 mass%, with the balance being Fe and unavoidable impurities, was smelted in a vacuum melting furnace, and was then cast to form a steel ingot. Next, the steel ingot was hot-rolled to obtain a hot-rolled sheet with a thickness of 1.8 mm. Then, the hot-rolled sheet was subjected to hot-band annealing at 1000°C × 30 seconds, and was then pickled before being cold-rolled to obtain a cold-rolled sheet with a final thickness of 0.25 mm. The cold-rolled sheet was then subjected to finishing annealing at 1000°C × 10 seconds.

[0017]Next, the steel sheet that had thus been subjected to finishing annealing was subjected to blanking with a clearance set to 5%, there...

experiment 2

(Experiment 2)

[0021]Steel, which has a composition of components including C: 0.0020 mass%, Si: 3.1 mass%, Mn: 0.3 mass%, P: 0.01 mass%, S: 0.0020 mass%, Al: 0.8 mass%, N: 0.0010 mass%, Pb: 0.003 mass%, Ti: 0.0015 mass%, Nb: 0.0002 mass%, V: 0.0010 mass%, and O: 0.0010 mass%, and also including Zn with varying content in the range of 0.0001 to 0.052 mass%, with the balance being Fe and unavoidable impurities, was smelted in a vacuum melting furnace, and was then cast to form a steel ingot. Next, the steel ingot was hot-rolled to obtain a hot-rolled sheet with a thickness of 1.5 mm. Then, the hot-rolled sheet was subjected to hot-band annealing at 1020°C × 30 seconds, and was then pickled before being cold-rolled to obtain a cold-rolled sheet with a final thickness of 0.25 mm. The cold-rolled sheet was then subjected to finishing annealing at 1000°C × 10 seconds.

[0022]Next, two types of specimens each having a width of 30 mm × a length of 280 mm were obtained from the steel sheet, wh...

examples

[0062]A steel material (i.e., a slab) having a composition of components including various components illustrated in Table 1, with the balance being Fe and unavoidable impurities was produced through a continuous casting process. Then, the steel material was hot-rolled to obtain a hot-rolled sheet with a thickness of 1.5 mm. Next, the hot-rolled sheet was subjected to hot-band annealing at 1080°C × 30 seconds, and was then pickled before being cold-rolled to obtain a cold-rolled sheet with a final thickness of 0.25 mm. Regarding No. A1 and No. A4, a fracture occurred during cold rolling. Thus, evaluation was not performed in the steps including cold rolling and the following steps. After that, the cold-rolled sheet was subjected to finishing annealing at 1000°C × 15 seconds to obtain a product sheet.

[Table 1-1]

No.Chemical composition (mass%)Remarks

CSiMnPSAlNPbZnTiNbvOOthersZn / Pb

10.0083.10.30.010.0010.80.0010.00040.0020.0010.00020.00030.001-5.00Comparative steel

20.0022.20.30.010.001...

Claims

1. A non-oriented electrical steel sheet comprising a composition of components including C: 0.0050 mass% or less, Si: 2.5 to 6.5 mass%, Mn: 0.05 to 2.0 mass%, P: 0.10 mass% or less, S: 0.0050 mass% or less, Al: 0.30 to 2.0 mass%, N: 0.010 mass% or less, Pb: 0.00010 to 0.010 mass%, Zn: 0.0005 to 0.020 mass%, Ti: 0.0050 mass% or less, Nb: 0.0050 mass% or less, V: 0.0050 mass% or less, and O: 0.0050 mass% or less, with a balance being Fe and unavoidable impurities, characterized in that: provided that contents (mass%) of Pb and Zn are respectively represented by [Pb] and [Zn], [Pb] and [Zn] satisfy Expression (1) below, and provided that a particle size distribution of secondary-phase particles in a particle size range of 0.10 µm or greater but less than 5.00 µm in a cross-section of the steel sheet in a thickness direction that coincides with a rolling direction is represented by a histogram where each class represents a particle size, a frequency represents a number density, and a class interval is 0.10 µm, the particle size distribution satisfies Expression (2) below: Zn / Pb ≥ 1.58 ∑ i = 1 n π d i N Si ≦ 0.0015 where di represents a class value (µm) of a class i, and Nsi represents a frequency (number / µm2) of the class i.

2. The non-oriented electrical steel sheet according to claim 1, wherein an average particle size of the secondary-phase particles in the particle size range of 0.10 µm or greater but less than 5.00 µm in the cross-section of the steel sheet in the thickness direction that coincides with the rolling direction is 0.40 µm or greater.

3. The non-oriented electrical steel sheet according to claim 1 or 2, further comprising, in addition to the composition of components, at least one of Groups A to I of components below: - Group A: at least one of Sn and Sb: a total of 0.005 to 0.20 mass%; - Group B: at least one of Ca, Mg, and REM: a total of 0.0005 to 0.020 mass%; - Group C: at least one of Cr, Cu, and Ni: a total of 0.01 to 1.0 mass%; - Group D: at least one of Mo: 0.001 to 0.050 mass% and W: 0.001 to 0.050 mass%; - Group E: B: 0.0001 to 0.0040 mass%; - Group F: Co: 0.0005 to 0.0200 mass%; - Group G: Ta: 0 to 0.0020 mass%; - Group H: As: 0 to 0.020 mass%; and - Group I: at least one of Ge: 0 to 0.030 mass% and Ga: 0 to 0.030 mass%.

Images