Non-oriented electrical steel sheet having excellent punching workability

Abstract

A non-oriented electrical steel sheet having low iron loss and excellent punching workability, the non-oriented electrical steel sheet having a component composition containing, in mass%, 0.0050% or less of C, 2.5-6.5% of Si, 0.05-2.0% of Mn, 0.10% or less of P, 0.0050% or less of S, 0.30-2.0% of Al, 0.010% or less of N, 0.00010-0.010% of Pb, and 0.0005-0.020% of Zn, the ratio [Zn] / [Pb] of the content (mass%) of Pb and Zn being 1.58 or more, when the particle size distribution of second-phase particles having a particle size of 0.10 [mu] m or more and less than 5.00 [mu] m in a plate thickness cross section in the rolling direction is represented by a histogram in which the particle size is grouped, the number density is the frequency number, and the group pitch is 0.10 [mu] m, the pinning force of the domain wall calculated from the particle size distribution by formula (3) is 0.0015 or less: # imgabs0 # Here, di is the group median ([mu] m) of group i, and di is the group pitch ([mu] m) of group i. Nsi is the frequency number (number / [mu] m2) of group i.

Description

Technical Field

[0001] The present invention relates to a non-oriented electromagnetic steel sheet having low iron loss and excellent blanking processability. Background Art

[0002] In recent years, the demand for energy conservation has increased, and high efficiency has been strongly required for electrical equipment. Therefore, for non-oriented electromagnetic steel sheets widely used as core materials for electrical equipment, further improvement in characteristics such as reduction of iron loss is also expected. Conventionally, in response to the above requirements, components that increase the resistivity of steel such as Si and Al are added in large amounts or the plate thickness is reduced.

[0003] On the other hand, in the case of using a laminated core formed by laminating steel sheets (core materials) having a core shape as a core of a motor or the like, blanking is generally used as a method of cutting out the core material from the non-oriented electromagnetic steel sheet. However, it is known that the magnetic characteristics of the core deteriorate due to shape changes of the cut end surface such as strain, burrs, and burrs introduced into the vicinity of the cut portion due to the blanking process.

[0004] Therefore, a great deal of research has been conducted so far on countermeasures for improving the blanking processability of non-oriented electromagnetic steel sheets. For example, Patent Document 1 discloses a non-oriented electromagnetic steel containing Si: 1.5% by mass or less, Mn: 0.4% by mass or more and 1.5% by mass or less, sol.Al: 0.01% by mass or more and 0.04% by mass or less, Ti: 0.0015% by mass or less, N: 0.0030% by mass or less, S: 0.0010% by mass or more and 0.0040% by mass or less, B having a B / N ratio of 0.5 or more and 1.5 or less, and the balance being composed of Fe and inevitable impurities, and causing 10% or more of the sulfides containing Mn to be co-precipitated with B precipitates to form an appropriate crystal grain size, thereby ensuring blanking processability.

[0005] In addition, Patent Document 2 discloses a non-oriented electromagnetic steel having excellent magnetic characteristics and blanking processability, which has a steel composition containing C: 0.003% by mass or less, Si: 1.0% by mass or more and 3.0% by mass or less, Al: 0.1% by mass or more and 3.0% by mass or less, Mn: 0.1% by mass or more and 1.0% by mass or less, and the content of Al and Si satisfies the relationship of 0.2 ≤ Al / (Si + Al) ≤ 0.6, and the balance is composed of Fe and inevitable impurities, and the yield ratio represented by (yield strength / tensile strength) is 0.6 or more and the Vickers hardness is 200 or less.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: WO 2005 / 100627

[0009] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2015-214758 Summary of the Invention

[0010] Problems to be Solved by the Invention

[0011] However, the Si content of the electromagnetic steel sheet described in Patent Document 1 above is 1.5 mass% or less and cannot be directly applied to a non-oriented electromagnetic steel sheet containing a higher Si. In addition, the electromagnetic steel sheet described in Patent Document 2 requires a Vickers hardness of 200 or less, and thus cannot be applied to a non-oriented electromagnetic steel sheet with a high Si content either. Moreover, the non-oriented electromagnetic steel sheet described in Patent Document 1 is a technique for improving blanking processability by controlling the crystal grain size, and the non-oriented electromagnetic steel sheet described in Patent Document 2 is a technique for improving blanking processability by controlling the mechanical properties of the parent phase. However, it is difficult to further improve the blanking processability only by these methods.

[0012] The present invention has been completed in view of the above problems of the prior art, and an object thereof is to provide a high-Si non-oriented electromagnetic steel sheet that improves blanking processability by a method different from the prior art without deteriorating the iron loss characteristics.

[0013] Means for Solving the Problems

[0014] The inventors repeatedly conducted in-depth research to achieve the above object. As a result, it was found that by adding Pb to the steel raw material, it is possible to improve the blanking processability of the steel sheet. Further, with respect to the deterioration of the magnetic properties caused by the addition of Pb, by controlling the particle size distribution of second-phase particles such as inclusions present in the steel sheet within an appropriate range by adding an appropriate amount of Zn, it is possible to improve the blanking processability without deteriorating the iron loss, and thus the present invention was developed.

[0015] The present invention based on the above findings is a non-oriented electromagnetic steel sheet, characterized in that

[0016] It has the following components: containing C: 0.0050 mass% or less, Si: 2.5 - 6.5 mass%, Mn: 0.05 - 2.0 mass%, P: 0.10 mass% or less, S: 0.0050 mass% or less, Al: 0.30 - 2.0 mass%, N: 0.010 mass% or less, Pb: 0.00010 - 0.010 mass%, Zn: 0.0005 - 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. And when expressing the contents (mass%) of Pb and Zn as [Pb] and [Zn] respectively, the above [Pb] and [Zn] satisfy the following formula (1), and the balance is composed of Fe and inevitable impurities.

[0017] [Zn] / [Pb]≥1.58 …(1)

[0018] When representing the particle size distribution of the second-phase particles with a particle size of 0.10 μm or more and less than 5.00 μm existing in the plate thickness cross-section in the rolling direction by a histogram with the particle size as the group, the number density as the frequency, and the class interval as 0.10 μm, the above particle size distribution satisfies the following formula (2).

[0019]

[0020] Here, d i : the class midpoint of group i (μm), N si : the frequency of group i (pieces / μm 2 ).

[0021] The non-oriented electromagnetic steel sheet of the present invention is characterized in that the average particle size of the second-phase particles with a particle size of 0.10 μm or more and less than 5.00 μm existing in the plate thickness cross-section in the rolling direction is 0.40 μm or more.

[0022] In addition, the non-oriented electromagnetic steel sheet of the present invention is characterized in that on the basis of the above component composition, it further contains at least one group of components in the following groups A - I.

[0023] · Group A: at least one of Sn and Sb: total 0.005 - 0.20 mass%

[0024] · Group B: at least one of Ca, Mg, and REM: total 0.0005 - 0.020 mass%

[0025] · Group C: at least one of Cr, Cu, and Ni: total 0.01 - 1.0 mass%

[0026] ·Group D: at least one of Mo: 0.001 to 0.050 mass% and W: 0.001 to 0.050 mass%

[0027] ·Group E: B: 0.0001 to 0.0040 mass%

[0028] ·Group F: Co: 0.0005 to 0.0200 mass%

[0029] ·Group G: Ta: 0 to 0.0020 mass%

[0030] ·Group H: As: 0 to 0.020 mass%

[0031] ·Group I: at least one of Ge: 0 to 0.030 mass% and Ga: 0 to 0.030 mass%

[0032] Advantages of the Invention

[0033] According to the present invention, it is possible to improve the blanking processability of a non-oriented electrical steel sheet with a high Si content without deteriorating the iron loss characteristics. Therefore, it is possible to provide a non-oriented electrical steel sheet suitable as a core material for motors, transformers, etc. manufactured by blanking process. Description of the Drawings

[0034] Figure 1 is a diagram showing the influence of the Pb content on the burr height of the cut surface after blanking process.

[0035] Figure 2 is a diagram showing the influence of the Zn content on the pinning force of magnetic domain walls.

[0036] Figure 3 is a diagram showing the influence of the pinning force of magnetic domain walls on the iron loss. Detailed Description of the Invention

[0037] First, the experiments for developing the present invention will be described.

[0038] (Experiment 1)

[0039] A steel having a composition consisting of 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 further containing Pb in various variations in the range of 0.00001 to 0.022 mass%, with the balance being composed of Fe and inevitable impurities, is melted in a vacuum melting furnace and cast to form an ingot. Then, the above ingot is hot-rolled to form a hot-rolled sheet with a thickness of 1.8 mm. After subjecting this hot-rolled sheet to hot-rolled sheet annealing at 1000 °C for 30 seconds, pickling is carried out, and then cold-rolled to form a cold-rolled sheet with a final thickness of 0.25 mm. The cold-rolled sheet is subjected to final annealing at 1000 °C for 10 seconds.

[0040] Next, a disc-shaped test piece with a diameter of 10 mm is cut from the above steel sheet after the final annealing by blanking with a gap set to 5%. At this time, for each steel sheet, blanking is carried out using a new die. For the disc-shaped test pieces after 1 million blanking operations, the height of the burrs generated at the two cut ends at both ends in the rolling direction is measured, and the blanking workability of the steel sheet is evaluated by their average value.

[0041] Figure 1 The relationship between the Pb content in the steel raw material and the burr height after 1 million blanking operations is shown. From this figure, it can be seen that by adding 0.00010 mass% or more of Pb, the burr height is reduced to 30 μm or less, and the blanking workability is improved.

[0042] Regarding the reason why the blanking workability is improved due to the addition of Pb, the following is considered. Pb is not dissolved in the steel but is dispersed in the steel in the form of fine particles (metallic inclusions). Therefore, during blanking, stress is concentrated on these metallic inclusions, promoting the generation and propagation of cracks, and reducing the wear of the die.

[0043] The results of the above experiment confirmed that the blanking workability is improved by adding an appropriate amount of Pb. However, on the other hand, it was clarified that due to the addition of Pb, the grain refinement occurs, and new problems such as deterioration of magnetic properties, especially iron loss characteristics, arise. Therefore, the inventors focused on the influence of second-phase particles such as inclusions on the iron loss characteristics and conducted the following experiment to investigate the particle size and particle size distribution of the second-phase particles required for good iron loss.

[0044] (Experiment 2)

[0045] A steel having a composition consisting of C: 0.0020% by mass, Si: 3.1% by mass, Mn: 0.3% by mass, P: 0.01% by mass, S: 0.0020% by mass, Al: 0.8% by mass, N: 0.0010% by mass, Pb: 0.003% by mass, Ti: 0.0015% by mass, Nb: 0.0002% by mass, V: 0.0010% by mass, and O: 0.0010% by mass, and further containing Zn in various variations within the range of 0.0001 to 0.052% by mass, with the balance being composed of Fe and unavoidable impurities, is melted in a vacuum melting furnace and cast to form an ingot. Subsequently, the above ingot is hot-rolled to form a hot-rolled sheet with a thickness of 1.5 mm. After subjecting the hot-rolled sheet to hot-rolled sheet annealing at 1020°C for 30 seconds, pickling is performed, and then cold-rolled to form a cold-rolled sheet with a final thickness of 0.25 mm. Then, the cold-rolled sheet is subjected to final annealing at 1000°C for 10 seconds.

[0046] Subsequently, two types of test pieces with a width of 30 mm and a length of 280 mm, where the length direction is the rolling direction (L direction) or the plate width direction (C direction), are cut from the above steel sheet after the final annealing by shearing. The same number of test pieces in the L direction and the C direction are stacked on an Epstein tester, and the iron loss W is measured by the method described in JIS C 2550. 10 / 400 。

[0047] In addition, a scanning electron microscope SEM is used to observe the plate thickness cross-section (total plate thickness) in the rolling direction of the test piece within a range of 2 mm 2 or more, and the particle size of the second-phase particles present within the above range is measured. Here, the above second-phase particles refer to inclusions or precipitates that form a phase other than the ferrite phase as the matrix phase. Specifically, they refer to oxide-based inclusions, carbonitrides, sulfides, borides, and their composites. In addition, the particle size of the above second-phase particles refers to the average value of the Feret diameter in the rolling direction and the Feret diameter in the plate thickness direction. It should be noted that the second-phase particles for which the particle size is measured are those with a particle size of 0.10 μm or more. This is because particles with a particle size less than 0.10 μm have a small interaction with the magnetic domain wall and a small pinning effect on the magnetic domain wall. In addition, particles with a size of 5.00 μm or more are also excluded from the measurement objects due to their small interaction with the magnetic domain wall. It should be noted that although the particle size of the second-phase particles in the present invention is measured using SEM, there is no particular limitation as long as it is a method capable of observing particles of 0.10 μm or more. However, from the perspective of ease of specimen preparation and the ability to perform a wide range of observations, it is preferred to use SEM.

[0048] Next, the measurement data of the particle size of the second-phase particles measured as above is divided at intervals of 0.10 μm in particle size, the number of second-phase particles in each interval is obtained, and this value is divided by the measurement area to obtain the number density N of the second-phase particles present in each interval. s (particles / μm 2 ). Next, a histogram is created in which the particle size (class mid-value) of the second-phase particles in each interval is regarded as the central value of that interval (for example, the particle size of the particles in the interval of 0.10 μm or more and less than 0.20 μm is treated as 0.15 μm), the class is set to the particle size of the second-phase particles, and the frequency is set to the number density N of the second-phase particles. si and the class width is set to 0.10 μm.

[0049] Next, based on the histogram obtained as above, an index value (particle·μm -1 ) defined by the following formula (3) is obtained. This index value represents the magnitude of the force that inhibits the movement of magnetic domain walls. Therefore, in the present invention, the force that inhibits the movement of the above magnetic domain walls is also referred to as the "pinning force of the magnetic domain wall".

[0050]

[0051] Here, d i : class mid-value of class i (μm), N si : frequency of class i (particles / μm 2 ).

[0052] Figure 2 shows the relationship between the pinning force of the above magnetic domain wall and the Zn content. From this figure, it can be seen that as the Zn content increases, the pinning force of the magnetic domain wall decreases. In particular, when the Zn addition amount is 0.0005 mass% or more, the pinning force of the magnetic domain wall decreases to 0.0015 particle·μm -1 or less. In addition, Figure 3 shows the relationship between the pinning force of the above magnetic domain wall and the iron loss W 10 / 400 . From this figure, it can be seen that as the pinning force of the magnetic domain wall decreases, the iron loss W 10 / 400 also decreases. In particular, when the pinning force of the magnetic domain wall is 0.0015 particle·μm -1 or less, the iron loss W 10 / 400 shows a good value of 10.0 W / kg or less. From the above results, it is important to add Zn to make the particle size distribution of the second-phase particles appropriate and reduce the "pinning force of the magnetic domain wall" defined by the above formula (3) to a specified value or less in order to suppress the deterioration of the iron loss caused by the addition of Pb.

[0053] It should be noted that the mechanism by which the addition of Zn as described above affects the pinning force of the magnetic domain wall has not been fully clarified at present, but the inventors speculate as follows.

[0054] When the Zn concentration in the molten steel increases, Zn combines with O and S in the molten steel to form oxides and sulfides, which are discharged out of the system or grow coarsely, and the formation of fine oxide-based inclusions and fine precipitates is suppressed. As a result, the pinning force of the magnetic domain wall is reduced, and good iron loss is obtained.

[0055] The present invention is developed by further studying the above new insights.

[0056] Next, the composition of the non-oriented electromagnetic steel sheet of the present invention will be described.

[0057] C: 0.0050 mass% or less

[0058] C contained in the product sheet is a harmful element that forms carbides and precipitates due to magnetic aging, deteriorating the iron loss characteristics. Therefore, the C contained in the steel raw material is limited to 0.0050 mass% or less. Preferably, it is 0.0040 mass% or less. It should be noted that the lower limit of C is not particularly specified, but from the viewpoint of suppressing the decarburization cost in the refining process, it is preferably about 0.0001 mass%.

[0059] Si: 2.5 - 6.5 mass%

[0060] Si is an element effective in increasing the resistivity of steel and reducing iron loss. In addition, it also has the effect of increasing the strength of steel by solid solution strengthening. Therefore, in the present invention, Si is contained in an amount of 2.5 mass% or more. On the other hand, when Si is more than 6.5 mass%, rolling manufacture becomes difficult, so the upper limit is set at 6.5 mass%. Preferably, it is in the range of 2.8 - 6.0 mass%.

[0061] Mn: 0.05 - 2.0 mass%

[0062] Mn, like Si, is an element useful for increasing the resistivity and strength of steel. In addition, it is also an element that forms sulfides to improve hot workability. Therefore, in the present invention, Mn is contained in an amount of 0.05 mass% or more. On the other hand, the addition of Mn more than 2.0 mass% causes billet cracks and the like, deteriorating the workability in the steelmaking process, so the upper limit is set at 2.0 mass%. Preferably, it is in the range of 0.1 - 1.5 mass%.

[0063] P: 0.10 mass% or less

[0064] P is an element that has a great effect on increasing the resistivity of steel and reducing eddy current loss. In addition, it also has the effect of increasing the hardness of steel and improving blanking workability, so it can be added appropriately. However, the excessive addition of P will cause poor cold rollability, so the upper limit is set at 0.10 mass%. Preferably, it is 0.05 mass% or less.

[0065] S: 0.0050 mass% or less

[0066] S is a harmful element that forms precipitates and inclusions by becoming sulfides, deteriorating the manufacturability (hot rolling property) and magnetic properties of the product sheet. Therefore, it is preferably reduced as much as possible. Accordingly, in the present invention, the upper limit of S is set to 0.0050% by mass. It is preferably 0.0030% by mass or less.

[0067] Al: 0.30 to 2.0% by mass

[0068] Al, like Si, is an element that has the effects of increasing the resistivity of steel, reducing iron loss, and increasing the strength of steel. However, when it is greater than 2.0% by mass, the steel becomes brittle and rolling becomes difficult, so the upper limit is set to 2.0% by mass. On the other hand, when Al is less than 0.30% by mass, fine nitrides are formed and precipitated, which instead deteriorates the iron loss characteristics. Therefore, the lower limit is set to 0.30% by mass. It is preferably in the range of 0.4 to 1.5% by mass.

[0069] N: 0.010% by mass or less

[0070] N is a harmful element that forms nitrides and precipitates, deteriorating the magnetic properties. Therefore, it is limited to 0.010% by mass or less. It is preferably 0.0060% by mass or less.

[0071] Pb: 0.00010 to 0.010% by mass

[0072] Pb is dispersed in the steel in the form of fine granular metal inclusions and remains in the steel even after final annealing. Therefore, during blanking, stress concentration occurs and it becomes the starting point of cracks or promotes the propagation of cracks, thereby having the effect of improving blanking processability or suppressing die wear. However, when Pb is less than 0.00010% by mass, the above effects cannot be obtained sufficiently. On the other hand, when it is greater than 0.010% by mass, it hinders grain growth and good iron loss cannot be obtained. Therefore, the content of Pb is set in the range of 0.00010 to 0.010% by mass. It is preferably in the range of 0.0003 to 0.0050% by mass.

[0073] Zn: 0.0005 to 0.020% by mass

[0074] Zn forms stable and coarse sulfides or oxides, that is, coarsens the second-phase particles in the steel, thereby having the effect of weakening the pinning force of the magnetic domain walls caused by the second-phase particles and suppressing the increase in iron loss caused by the addition of the aforementioned Pb. To obtain the above effects, it is necessary to add 0.0005% by mass or more of Zn. However, even if more than 0.020% by mass is added, the above effects are saturated. Therefore, the content of Zn is set in the range of 0.0005 to 0.020% by mass. It is preferably in the range of 0.001 to 0.010% by mass.

[0075] Ti: 0.0050 mass% or less, Nb: 0.0050 mass% or less, and V: 0.0050 mass% or less

[0076] Ti, Nb, and V are all harmful elements that form fine carbonitrides and precipitate, increasing iron loss. In particular, when each element is greater than 0.0050 mass%, the above-mentioned adverse effects become significant. Therefore, the upper limit of each element is limited to 0.0050 mass%. Preferably, they are each 0.0030 mass% or less.

[0077] O: 0.0050 mass% or less

[0078] O is a harmful element that forms oxides, pins grain boundaries and the movement of magnetic domain walls, and deteriorates magnetic properties. Therefore, it needs to be reduced as much as possible. Therefore, in the present invention, it is limited to 0.0050 mass% or less. Preferably, it is 0.0040 mass% or less.

[0079] [Zn] / [Pb] ≥ 1.58

[0080] In addition to containing Pb and Zn in the above ranges, the non-oriented electrical steel sheet of the present invention also requires that when the contents (mass%) of Pb and Zn are represented by [Zn] and [Pb] respectively, the above [Zn] and [Pb] satisfy the following formula (1): [Zn] / [Pb] ≥ 1.58...(1). It can be clearly known from the above experimental results that when Pb is added, the iron loss deteriorates. However, by adding Zn in a manner that satisfies the above formula (1), the pinning force of the magnetic domain wall is reduced, and good iron loss can be obtained. Preferably, [Zn] / [Pb] ≥ 2.5.

[0081] In the non-oriented electrical steel sheet of the present invention, the balance other than the above components is Fe and unavoidable impurities. However, according to the required characteristics, the following components can be further appropriately contained on the basis of the above components.

[0082] At least one of Sn and Sb: 0.005 - 0.20 mass% in total

[0083] Both Sn and Sb have the effects of improving the recrystallization texture, improving the magnetic flux density, and iron loss characteristics. In order to obtain the above effects, it is necessary to add at least one of the above components in a total amount of 0.005 mass% or more. However, even if more than 0.20 mass% is added, the above effects are saturated. Therefore, when adding Sn and Sb, it is preferably in the range of 0.005 - 0.20 mass% in total for at least one. More preferably, it is in the range of 0.010 - 0.10 mass% in total.

[0084] At least one of Ca, Mg, and REM: 0.0005 - 0.020 mass% in total

[0085] Ca, Mg and REM all have the effect of reducing the pinning force of the magnetic domain wall of the second phase particles by forming stable and coarse sulfides or oxides. In order to obtain the above effect, it is necessary to add at least one of Ca, Mg and REM in an amount of more than 0.0005 mass %. However, even if more than 0.020 mass % is added, the above effect is saturated. Therefore, when adding Ca, Mg and REM, it is preferred to set at least one in the range of 0.0005 to 0.020 mass % in total. More preferably, it is in the range of 0.0010 to 0.010 mass % in total.

[0086] At least one of Cu, Ni and Cr: 0.01-1.0 mass % in total

[0087] Cu, Ni and Cr all have the effect of increasing the resistivity of steel and reducing iron loss. In order to obtain the above effect, it is preferred to add at least one of Cu, Ni and Cr in a total amount of 0.01% by mass or more. However, the addition of more than 1.0% by mass will lead to an increase in raw material costs. Therefore, it is preferred that at least one of the above elements is added in a total range of 0.01 to 1.0% by mass. More preferably, it is in a total range of 0.03 to 0.8% by mass.

[0088] At least one of Mo: 0.001 to 0.050 mass % and W: 0.001 to 0.050 mass %

[0089] Both Mo and W are elements that are effective in suppressing surface defects (scaly folding) of steel plates. In particular, the steel plate of the present invention is a high-alloy steel, and its surface is easily oxidized, so it is easy to produce scaly folding caused by surface cracks, but by adding a trace amount of Mo and W as elements that improve high-temperature strength, the above cracks can be suppressed. When the content of Mo and W is less than 0.001% by mass, the above effect is not sufficient. On the other hand, even if more than 0.050% by mass is added, the above effect is saturated, which only increases the alloy cost. Therefore, when adding Mo and W, it is preferred to set at least one of them to the above range. More preferably, it is in the range of 0.0050 to 0.050% by mass.

[0090] B: 0.0001 to 0.0040 mass%

[0091] B is an element that makes the steel sheet microstructure fine-grained and helps improve the punching workability. In order to obtain this effect, it is preferably added at 0.0001 mass % or more. On the other hand, when it is greater than 0.0040 mass %, not only the above effect is saturated, but also excessive generation of boride increases iron loss, so the upper limit is preferably set to 0.0040 mass %. More preferably, it is in the range of 0.0005 to 0.0020 mass %.

[0092] Co: 0.0005-0.0200 mass%

[0093] Co has the effect of suppressing nitridation during final annealing. To obtain the above effect, it is preferably added in an amount of 0.0005% by mass or more. On the other hand, even if added in an amount exceeding 0.0200% by mass, the above effect saturates, only increasing the alloy cost. Therefore, when adding Co, it is preferably in the range of 0.0005 to 0.0200% by mass. More preferably, it is in the range of 0.001 to 0.010% by mass.

[0094] Ta: 0 to 0.0020% by mass

[0095] Ta can be added for improving the workability and high strength of steel. To reliably obtain the above effects, it is preferably added in an amount of 0.0001% by mass or more. On the other hand, Ta is also an element that increases iron loss. Especially when it is greater than 0.0020% by mass, the above adverse effects become significant, so the upper limit is set at 0.0020% by mass. More preferably, it is in the range of 0.0003 to 0.0010% by mass.

[0096] As: 0 to 0.020% by mass

[0097] As is an element that increases the hardness of steel and can be added for adjusting mechanical properties. To reliably obtain the above effects, it is preferably added in an amount of 0.001% by mass or more. On the other hand, As is also an element that embrittles steel. Especially when it is greater than 0.020% by mass, the above adverse effects become significant, so the upper limit is set at 0.020% by mass. More preferably, it is in the range of 0.003 to 0.010% by mass.

[0098] At least one of Ge: 0 to 0.030% by mass and Ga: 0 to 0.030% by mass

[0099] Both Ge and Ga are elements that improve the texture. To reliably obtain the above effects, it is preferably added at least one of the above elements in an amount of 0.001% by mass or more. On the other hand, even if added in an amount exceeding 0.030% by mass, the above effect saturates, so the upper limit is set at 0.030% by mass respectively. More preferably, the ranges are 0.003 to 0.010% by mass respectively.

[0100] Next, the non-oriented electromagnetic steel sheet of the present invention will be described.

[0101] The non-oriented electromagnetic steel sheet of the present invention requires that the magnetic domain wall pinning force calculated by the following formula (3) based on the particle size and number density of the second-phase particles having a particle size of 0.10 μm or more and less than 5.00 μm present in the steel sheet is 0.0015 pieces·μm -1 Below. If the above magnetic domain wall pinning force is greater than 0.0015 pieces·μm -1, the movement of the magnetic domain wall is hindered, so it is impossible to offset the deterioration of iron loss by adding Zn. It is preferably 0.0012 pieces·μm -1 or less.

[0102]

[0103] Here, d i : the group median value (μm) of group i, N si : the frequency of group i (pieces / μm 2 ).

[0104] In addition, regarding the non-oriented electrical steel sheet of the present invention, from the viewpoint of further reducing the pinning force of the magnetic domain wall that causes an increase in iron loss, the average particle size of the second-phase particles existing in the steel sheet in the range of 0.10 μm or more and less than 5.00 μm is preferably 0.40 μm or more. More preferably, it is 0.6 μm or more.

[0105] Next, a method for manufacturing the non-oriented electrical steel sheet of the present invention will be described.

[0106] The non-oriented electrical steel sheet of the present invention can be manufactured by a known method without particular limitation. Hereinafter, an example of a preferred manufacturing method will be described.

[0107] First, the steel having the composition conforming to the present invention is melted by a known refining process using a converter, an electric furnace, a vacuum degassing device, etc., and then a steel raw material (slab) is manufactured by a known continuous casting method or an ingot - blooming rolling method. In the above-mentioned melting process, by using an electric furnace with iron scrap generated in the market as a raw material, it is possible to effectively utilize low-cost scrap containing Pb and Zn as impurities as an iron source, so it is possible to contribute to the reduction of raw material costs. In addition, in the manufacture of the above slab, for the purpose of reducing the cold rolling reduction rate in subsequent processes and increasing the magnetic flux density, a thin slab with a thickness of 200 mm or less can be manufactured.

[0108] In addition, when manufacturing a slab by continuous casting, if the cooling rate during solidification is large, inclusions are refined, which hinders grain growth or the force pinning the magnetic domain wall becomes large. Therefore, the average cooling rate from the solidification temperature at the center of the slab thickness to 1400 °C is preferably 1.0 °C / s or less. More preferably, it is 0.5 °C / s or less. In addition, the above cooling rate during solidification can also be controlled by increasing the thickness of the cast slab or reducing the casting speed.

[0109] It should be noted that as a method for coarsening the particle size of the second-phase particles to promote harmlessness, in addition to the above-mentioned reduction of the cooling rate during continuous casting, adding Ca, Mg, REM, etc. that form coarse sulfides / oxides is also effective.

[0110] Next, the steel billet manufactured by the above method is hot-rolled, and hot-rolled sheet annealing, pickling, cold rolling, and final annealing are carried out as required. An insulating coating film is applied as required to produce a product sheet of a non-oriented electromagnetic steel sheet. These manufacturing processes can be carried out under the conditions well-known in the past and are not particularly limited. In addition, the above cold rolling can be used to produce the final sheet thickness (product sheet thickness) by one-time cold rolling, or the final sheet thickness can be produced by two or more cold rollings with intermediate annealing in between.

[0111] Examples

[0112] A steel raw material (steel billet) having a composition containing various components shown in Table 1 and the balance composed of Fe and inevitable impurities is manufactured by the continuous casting method and hot-rolled to produce a hot-rolled sheet with a thickness of 1.5 mm. Next, after subjecting the above hot-rolled sheet to hot-rolled sheet annealing at 1080 °C for 30 seconds, pickling and cold rolling are carried out to produce a cold-rolled sheet with a final thickness of 0.25 mm. It should be noted that No. A1 and No. A4 stopped the evaluation after cold rolling because they fractured during cold rolling. Then, the above cold-rolled sheet is subjected to final annealing at 1000 °C for 15 seconds to produce a product sheet.

[0113]

[0114]

[0115]

[0116] Next, a disc-shaped test piece with a diameter of 10 mm is cut out from the above steel sheet after final annealing by blanking with a die having a gap set to 5%. At this time, for the above blanking die, a new die is replaced for each steel sheet, and for the disc-shaped test pieces after 1 million blankings, the heights of the burrs at the two blanking ends at both ends in the rolling direction are measured, and the average value is calculated.

[0117] In addition, two types of test pieces with a width of 30 mm and a length of 280 mm with the length direction as the rolling direction (L direction) or the width direction (C direction) are cut out from the steel sheet after final annealing by shearing. Next, the same number of test pieces in the L direction and the C direction are stacked on an Epstein tester, and the iron loss W is measured by the method described in JIS C 2550. 10 / 400 .

[0118] Furthermore, the cross-section in the rolling direction of the above steel sheet is observed by SEM for 2 mm in terms of (total sheet thickness × rolling direction). 2Above, measure the particle sizes of all the second-phase particles with particle sizes of 0.10 μm or more and less than 5.00 μm present in the above cross-section. Next, group the above particle size measurement data at intervals of 0.10 μm in particle size, create a histogram of the particle size distribution, and obtain the pinning force of the magnetic domain wall defined by the following formula (3) from the above histogram.

[0119]

[0120] Here, d i : the group median (μm) of group i, N si : the frequency of group i (number / μm 2 ).

[0121] Show the above measurement results (burr height after 1 million blanking processes, iron loss W 10 / 400 , the pinning force of the magnetic domain wall caused by the second-phase particles, and the average particle size of the second-phase particles) in Table 2. From this result, it can be seen that the blanking processability of the steel plates that meet the conditions of the present invention is excellent, and the iron loss characteristics are also excellent.

[0122]

[0123]

[0124]

Claims

1. An isotropic electromagnetic steel sheet, characterized in that, It has the following composition: containing C: 0.0050 mass% or less, Si: 2.5 - 6.5 mass%, Mn: 0.05 - 2.0 mass%, P: 0.10 mass% or less, S: 0.0050 mass% or less, Al: 0.30 - 2.0 mass%, N: 0.010 mass% or less, Pb: 0.00010 - 0.010 mass%, Zn: 0.0005 - 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. And when the contents (mass%) of Pb and Zn are represented as [Pb] and [Zn] respectively, the [Pb] and [Zn] satisfy the following formula (1), and the balance is composed of Fe and inevitable impurities. When the particle size distribution of the second-phase particles with a particle size of 0.10 μm or more and less than 5.00 μm existing in the plate thickness cross-section in the rolling direction is represented by a histogram with the particle size as the group, the number density as the frequency, and the class interval as 0.10 μm, the particle size distribution satisfies the following formula (2). [Zn] / [Pb]≥1.58 …(1) Here, d i : the group mid-value of group i (μm), N si : the frequency of group i (number / μm 2 ).

2. The isotropic electromagnetic steel sheet according to claim 1, characterized in that, The average particle size of the second-phase particles with a particle size of 0.10 μm or more and less than 5.00 μm existing in the plate thickness cross-section in the rolling direction is 0.40 μm or more.

3. The isotropic electromagnetic steel sheet according to claim 1 or 2, characterized in that, On the basis of the above composition, it further contains at least one group of components in the following groups A - I. · Group A: At least one of Sn and Sb: total 0.005 - 0.20 mass%. · Group B: At least one of Ca, Mg, and REM: total 0.0005 - 0.020 mass%. · Group C: At least one of Cr, Cu, and Ni: total 0.01 - 1.0 mass%. · Group D: At least one of Mo: 0.001 - 0.050 mass% and W: 0.001 - 0.050 mass%. · Group E: B: 0.0001 - 0.0040 mass%. · Group F: Co: 0.0005 - 0.0200 mass%. · Group G: Ta: 0 - 0.0020 mass%. · Group H: As: 0 - 0.020 mass%. · Group I: At least one of Ge: 0 - 0.030 mass% and Ga: 0 - 0.030 mass%.

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