Method of producing hot-rolled steel sheet for non-oriented electrical steel sheet, method of producing non-oriented electrical steel sheet, and hot-rolled steel sheet for non-oriented electrical steel sheet

Abstract

A method for manufacturing a hot-rolled steel sheet for non-oriented electrical steel sheets, comprising a continuous casting process for manufacturing a steel slab having a predetermined composition and a thickness of 50 mm or more and 200 mm or less by a continuous casting method, a conveying process for conveying the steel slab to a hot-rolling facility while maintaining the surface temperature of the steel slab at 800°C or higher, and a hot-rolling process for sequentially performing rough rolling, reheating treatment, and finish rolling on the steel slab in the hot-rolling facility to produce a hot-rolled steel sheet, wherein the hot-rolling process is performed under conditions satisfying the following (1) to (4). (1) Exit speed of the above rough rolling: 100 mpm or less (2) Reduction rate in the final pass of the above rough rolling: 45% or more (3) Average heating rate in the above reheating treatment: 9℃ / s or more (4) Temperature rise in the above reheating treatment: 30℃ or more

Description

Technology Field

[0001] The present invention relates to a method for manufacturing a hot-rolled steel sheet for a non-oriented electrical steel sheet, a method for manufacturing a non-oriented electrical steel sheet, and a hot-rolled steel sheet for a non-oriented electrical steel sheet. Background Technology

[0002] Non-oriented electrical steel is a material used for the cores of motors and generators. Recently, there has been a strong demand for higher efficiency in electrical equipment from the perspective of CO2 reduction, and further reduction in iron loss is required for non-oriented electrical steel used as a core material. For this reason, efforts are being made to reduce eddy current loss by reducing the sheet thickness or by increasing the content of Si, Al, and Mn, which are elements that increase the electrical resistance of the steel sheet. However, since reducing the sheet thickness and increasing the amount of alloying elements significantly increases the manufacturing cost of non-oriented electrical steel, there is also a growing demand for cost reduction.

[0003] One technology for reducing the cost of non-oriented electrical steel sheets is hot direct rolling. In hot direct rolling, the thermal energy of the continuous casting slab can be effectively utilized, eliminating the need to reheat the slab after it has cooled during hot rolling. Consequently, this enables a significant reduction in energy costs and leads to a reduction in CO2 emissions.

[0004] As an example of utilizing direct rolling, Patent Document 1 proposes a technology for manufacturing hot-rolled steel sheets with a thickness of 0.7 to 4.5 mm by continuously hot-rolling a thin slab with a thickness of 30 to 140 mm obtained by a continuous casting method. Prior art literature

[0005] Japanese Patent Publication No. 2002-206114 The problem to be solved

[0006] Energy saving through direct rolling can be achieved by using equipment that integrates continuous casting and hot rolling mills, known as a thin slab caster. It is believed that the technology of Patent Document 1 can also be implemented by using a thin slab caster.

[0007] However, in some thin slab casters, the continuously cast slab is sent to the hot rolling process without cutting, and by continuously performing hot rolling, the abnormal portion of the hot rolling is minimized to improve the yield. In such cases, the sheet passing speed is limited to the casting speed, so the hot rolling speed, especially the speed of rough hot rolling, is significantly reduced compared to conventional processes that are not direct rolling.

[0008] As a result of examining this low-speed hot rolling process, the inventors found that, particularly in steels containing a large amount of alloying elements such as Si and Al, recrystallization during the annealing of the hot-rolled sheet becomes difficult, and ridging (surface curvature) is prone to occur in the non-oriented electrical steel sheet obtained at the end.

[0009] The present invention aims to solve the above-mentioned problem, and specifically, aims to suppress leaching that occurs when steel contains a large amount of Si and Al as alloying elements in a low-speed hot rolling process. means of solving the problem

[0010] As a result of careful consideration to solve the above problem, the inventors discovered that lagging can be suppressed by increasing the rolling reduction rate in the final pass of rough rolling and controlling the reheating conditions after rough rolling.

[0011] The present invention is completed based on the above recognition, and its gist is as follows.

[0012] 1. In mass %,

[0013] Si: 2.0% or more and 5.0% or less and,

[0014] Al: Contains 3.0% or less,

[0015] It has a component composition in which the total content of Si and Al is 3.5% or more, and

[0016] A continuous casting process for manufacturing steel slabs with a thickness of 50 mm or more and 200 mm or less by a continuous casting method, and

[0017] A conveying process for conveying the above steel slab to a hot rolling facility while maintaining its surface temperature at 800℃ or higher, and

[0018] A method for manufacturing a hot-rolled steel sheet for non-oriented electrical steel sheets, comprising a hot-rolling process in which rough rolling, reheat treatment, and finish rolling are sequentially performed on the steel slab in the above-mentioned hot-rolling facility to produce a hot-rolled steel sheet, wherein

[0019] A method for manufacturing a hot-rolled steel sheet for non-oriented electrical steel sheets, wherein the above hot-rolling process is performed under conditions satisfying (1) to (4) below.

[0020] (1) Exit speed of the above roughing mill: 100 mpm or less

[0021] (2) Reduction rate in the final pass of the above rough rolling: 45% or more

[0022] (3) Average heating rate in the above reheating treatment: 9℃ / s or higher

[0023] (4) Temperature rise in the above reheating treatment: 30℃ or higher

[0024] 2. A method for manufacturing a hot-rolled steel sheet for non-oriented electrical steel sheets described in 1, wherein, in the finishing rolling above, the thickness of the hot-rolled steel sheet is rolled to 1.5 mm or less.

[0025] 3. The composition of the above steel slab is, in mass %,

[0026] C: 0.005% or less,

[0027] Mn: 3.0% or less,

[0028] Cr: 3.0% or less,

[0029] Ni: 2.0% or less,

[0030] Cu: 2.0% or less,

[0031] P: 0.2% or less,

[0032] S: 0.0050% or less,

[0033] N: 0.0050% or less,

[0034] O: 0.0050% or less,

[0035] Ti: 0.0040% or less,

[0036] Sn: 0.20% or less,

[0037] Sb: 0.20% or less,

[0038] Mo: 0.10% or less,

[0039] Ca: 0.01% or less,

[0040] REM: 0.05% or less,

[0041] Mg: 0.01% or less and,

[0042] Zn: additionally contains at least one selected from the group consisting of 0.01% or less, and

[0043] A method for manufacturing a hot-rolled steel sheet for non-oriented electrical steel sheets as described in 1 or 2 above, wherein the remainder is Fe and unavoidable impurities.

[0044] 4. The above component composition, in mass%,

[0045] Nb: 0.005% or less,

[0046] V: 0.02% or less,

[0047] Ta: 0.002% or less,

[0048] B: 0.002% or less,

[0049] Ga: 0.005% or less,

[0050] Pb: 0.002% or less,

[0051] W: 0.05% or less,

[0052] Ge: 0.05% or less,

[0053] As: 0.05% or less and,

[0054] Co: 0.05% or less,

[0055] A method for manufacturing a hot-rolled steel sheet for non-oriented electrical steel sheets described in 3, additionally containing at least one selected from the group consisting of

[0056] 5. A hot-rolled steel sheet manufacturing process for manufacturing a hot-rolled steel sheet by the method for manufacturing a hot-rolled steel sheet for non-oriented electrical steel sheets described in any one of 1 to 4 above, and

[0057] A hot-rolled plate annealing process for performing hot-rolled plate annealing on the above hot-rolled steel plate, and

[0058] A cold rolling process for producing a cold-rolled steel sheet by performing cold rolling on the above hot-rolled steel sheet, and

[0059] A method for manufacturing a non-oriented electrical steel sheet comprising a finishing annealing process for performing finishing annealing on the above cold-rolled steel sheet.

[0060] 6. A hot-rolled steel sheet for non-oriented electrical steel obtained by the method for manufacturing a hot-rolled steel sheet for non-oriented electrical steel described in any one of 1 to 4 above, wherein

[0061] Hot-rolled steel sheet for non-oriented electrical steel sheets, having a number density of inclusions with an equivalent diameter of 0.3㎛ or more and 1.0㎛ or less of 9 or more / mm². Effects of the invention

[0062] According to the present invention, under conditions such as a high total content of Si and Al of 3.5% or more and an exit speed of rough rolling of 100 mpm or less, lagging can be effectively suppressed. Therefore, according to the present invention, it is possible to manufacture non-oriented electrical steel sheets with low iron loss and suppressed lagging by using direct rolling, which is a low-energy consumption process. Accordingly, the present invention is also very effective from the perspective of the Sustainable Development Goals (SDGs). Brief explanation of the drawing

[0063] Figure 1 is a graph showing the correlation between the total content of Si and Al of the slab (mass%) and the arithmetic mean bend Wa (μm) in the width direction of the non-oriented electrical steel sheet. Figure 2 is a graph showing the correlation between the exit speed (mpm) at the final pass of rough rolling and the arithmetic mean bend Wa (μm) in the width direction of the non-oriented electrical steel sheet. Figure 3 is a graph showing the correlation between the average heating rate (°C / s) and the reduction rate (%) of the final pass of rough rolling in the reheating treatment, and the arithmetic mean bending Wa (μm) in the width direction of the non-oriented electrical steel sheet. Figure 4 is a graph showing the correlation between the finished thickness (mm) in hot rolling and the arithmetic mean bend Wa (μm) in the width direction of the non-oriented electrical steel sheet. Figure 5 is a graph showing the correlation between the number density (number / mm²) of inclusions with a circle equivalent diameter of 0.3㎛ or more and 1.0㎛ or less, and the arithmetic mean bending Wa (㎛) in the width direction of a non-oriented electrical steel sheet. Specific details for implementing the invention

[0064] (Form for carrying out the invention)

[0065] The details of the present invention, along with the reasons for its limitation, will be explained below. Furthermore, in this specification and drawings, "%" as a unit of content shall refer to "mass%" unless otherwise specifically stated. Additionally, the unit of throughput speed "mpm" shall refer to meter per minute.

[0066] (Experiment 1)

[0067] First, a slab with a thickness of 130 mm having a composition comprising C: 0.002%, Si: 1.8–4.0%, Al: 0.2–1.1%, Mn: 0.6%, Cr: 0.01%, Ni: 0.01%, Cu: 0.01%, P: 0.01%, S: 0.002%, N: 0.002%, O: 0.001%, and Ti: 0.001%, with the remainder being Fe and unavoidable impurities, was steelmade in a vacuum furnace, removed from the furnace, and transported to an electric furnace so that the surface temperature of the slab did not fall below 800°C. In the above electric furnace, after performing a temperature holding treatment at 1100°C for 30 minutes, the slab was removed from the electric furnace and hot-rolled to become a hot-rolled steel sheet.

[0068] In the above hot rolling, first, the thickness was reduced to 20 mm in 4 passes of hot rolling equivalent to rough rolling, then reheated from 1000°C to 1100°C at 5°C / s using an induction heating device, and then the thickness was reduced to 1.2 mm in 6 passes equivalent to finish rolling.

[0069] In the above hot rolling, the hot rolling speed was set to one of the following two.

[0070] (1) Low-speed rolling:

[0071] To simulate low-speed hot rolling of a thin slab caster, the entry speed of the first rolling pass was set to 5 mpm, and the subsequent rolling speed was set to 130 mm ÷ (entry plate thickness) × 5 mpm. That is, the exit speed at the final pass of rough rolling is 32.5 mpm. The finishing rolling was set to 200 mpm for the entire pass.

[0072] (2) High-speed rolling:

[0073] To simulate typical rough rolling, the rough rolling was set to 120 mpm for all passes. The finish rolling was set to 200 mpm for all passes.

[0074] The obtained hot-rolled steel sheet was subjected to hot-rolled sheet annealing at 1050°C for 20 seconds, followed by cold rolling to obtain a cold-rolled steel sheet with a final thickness of 0.25 mm. The above cold-rolled steel sheet was subjected to finish annealing at 980°C for 15 seconds to obtain a non-oriented electrical steel sheet. Since a leaching pattern was visually observed in a portion of the obtained non-oriented electrical steel sheet, the arithmetic mean bending Wa in the width direction of the above non-oriented electrical steel sheet was measured using a contact roughness meter.

[0075] Figure 1 is a graph showing the relationship between the measured Wa (μm) and the total content of Si and Al in the slab. In addition, in the following description, the Si content of the slab is denoted as [Si], the Al content of the slab as [Al], and the total content of Si and Al in the slab as [Si] + [Al], respectively.

[0076] As shown in Figure 1, when [Si] + [Al] is 3.5% or more, Wa increases significantly under low-speed rolling conditions. This increase in Wa indicates that leaching has occurred. Here, when the microstructure of the sample with leaching after hot-rolled annealing was examined, the recrystallization rate was found to be low. From this result, it can be seen that when a slab containing a large amount of Si and Al is hot-rolled at a low speed, recrystallization does not proceed sufficiently during hot-rolled annealing, and leaching occurs during subsequent cold rolling.

[0077] In addition, Figure 2 shows the results of changing the exit speed in the final pass of rough rolling using a steel slab with [Si] + [Al] = 3.92%. When the exit speed in the final pass of rough rolling was 100 mpm or less, there was a tendency for leaching to occur in the finally obtained non-oriented electrical steel sheet.

[0078] (Experiment 2)

[0079] Next, in order to suppress the leaching that occurs when the exit speed in the final pass of rough rolling is low, the inventors focused on the pass schedule of rough rolling and the heating speed of reheating after rough rolling, and conducted the following experiment.

[0080] A slab with a thickness of 130 mm having a composition containing C: 0.002%, Si: 3.31%, Al: 0.82%, Mn: 0.45%, Cr: 0.05%, Ni: 0.03%, Cu: 0.05%, P: 0.01%, S: 0.002%, N: 0.002%, O: 0.001%, and Ti: 0.001%, with the remainder being Fe and unavoidable impurities, was melted in a vacuum melting furnace and, after being removed from the furnace, transported to an electric furnace so that the surface temperature of the slab did not fall below 800°C. In the electric furnace, after performing a heat retention treatment at 1100°C for 30 minutes, the slab was removed from the electric furnace and hot-rolled to become a hot-rolled steel sheet.

[0081] In the above hot rolling, first, the thickness was reduced to 20 mm in 4 passes equivalent to rough rolling, then reheated from 1000°C to 1100°C using an induction heating device, and subsequently reduced to 1.2 mm in 6 passes equivalent to finish rolling. At that time, the reduction rate in the final pass of the above rough rolling and the average heating rate in the above reheating treatment were varied.

[0082] Here, to simulate low-speed hot rolling of a thin slab caster, the entry speed of the first pass of rough rolling was set to 5 mpm, and the subsequent rolling speed was set to 130 mm ÷ (entry plate thickness) × 5 mpm. The finishing rolling was set to 200 mpm for the entire pass.

[0083] The obtained hot-rolled steel sheet was subjected to hot-rolled sheet annealing at 1040°C for 30 seconds, followed by cold rolling to obtain a cold-rolled steel sheet with a final thickness of 0.25 mm. The cold-rolled steel sheet was subjected to finish annealing at 980°C for 15 seconds to obtain a non-oriented electrical steel sheet. Using a contact roughness meter, the arithmetic mean bending Wa in the width direction of the non-oriented electrical steel sheet was measured.

[0084] Figure 3 shows the effect of the average heating rate and the reduction rate of the final pass of rough rolling on Wa during the above reheating treatment. As can be seen from Figure 3, when the reduction rate of the final pass of rough rolling is 45% or more and the average heating rate during reheating is 9℃ / s or more, the occurrence of leaching is suppressed.

[0085] From the results of experiments 1 and 2 above, it can be seen that leaching can be suppressed by increasing the reduction rate of the final pass of rough rolling and by increasing the average heating rate during reheating after rough rolling.

[0086] The mechanism by which ridging is suppressed is presumed to be as follows. First, by applying a large reduction during the final pass of rough rolling, deformation energy is accumulated within the material. Subsequently, by performing rapid heating, recovery during heating is suppressed, effectively promoting recrystallization, which leads to the randomization of the texture and the refinement of the grain size. It is believed that by refining the microstructure prior to finish rolling, recrystallization and the randomization of the texture are promoted during the finish rolling process. Although the recrystallization of the material cannot be completely finished at the time of hot rolling completion, the coarse cast microstructure, which is the cause of ridging, is destroyed to some extent by the above effect. Consequently, it is believed that the texture becomes randomized, promoting recrystallization during the annealing of the hot-rolled sheet, while simultaneously suppressing the formation of ridging patterns during cold rolling.

[0087] (Experiment 3)

[0088] Next, the inventors focused on the effect of finishing thickness in hot rolling on rising and conducted the following experiment to verify this. Furthermore, "finishing thickness" here refers to the plate thickness at the point when finishing rolling is completed in the hot rolling process, that is, the plate thickness of the obtained hot-rolled steel sheet.

[0089] A slab with a thickness of 120 mm having a composition comprising C: 0.002%, Si: 3.12%, Al: 0.83%, Mn: 0.56%, Cr: 0.01%, Ni: 0.02%, Cu: 0.03%, P: 0.01%, S: 0.002%, N: 0.002%, O: 0.001%, and Ti: 0.001%, with the remainder being Fe and unavoidable impurities, was melted in a vacuum melting furnace and, after being removed from the furnace, transported to an electric furnace so that the surface temperature of the slab did not fall below 800°C. In the electric furnace, after performing a heat retention treatment at 1100°C for 30 minutes, the slab was removed from the electric furnace and hot-rolled to become a hot-rolled steel sheet.

[0090] In the above hot rolling, the thickness was reduced to 15 mm in 4 passes corresponding to rough rolling, then reheated from 990°C to 1100°C using an induction heating device, and subsequently reduced to the target plate thickness in 6 passes corresponding to finish rolling. Here, to simulate low-speed hot rolling of thin slab casters, the entry speed of the first pass of rough rolling was set to 5 mpm, and the subsequent rolling speed was set to 130 mm ÷ (entry plate thickness) × 5 mpm. The finish hot rolling was set to a total of 200 mpm.

[0091] The obtained hot-rolled steel sheet was subjected to hot-rolled sheet annealing at 1010°C for 30 seconds, followed by cold rolling to obtain a cold-rolled steel sheet with a final thickness of 0.25 mm. The cold-rolled steel sheet was subjected to finish annealing at 980°C for 30 seconds to obtain a non-oriented electrical steel sheet. Using a contact roughness meter, the arithmetic mean bending Wa in the width direction of the non-oriented electrical steel sheet was measured.

[0092] Figure 4 shows the effect of the finishing thickness on Wa in hot rolling. From the results shown in Figure 4, it can be seen that when the thickness of the hot-rolled steel sheet is rolled to 1.5 mm or less during finishing rolling, the leaching is further improved.

[0093] (Experiment 4)

[0094] Next, the inventors focused on the effect of inclusions on lising and conducted the following experiments to verify this.

[0095] A slab with a thickness of 120 mm having a composition consisting of C: 0.002%, Si: 3.51%, Al: 1.23%, Mn: 1.02%, Cr: 0.05%, Ni: 0.08%, Cu: 0.11%, P: 0.01%, S: 0.002%, N: 0.002%, O: 0.001%, and Ti: 0.001%, with the remainder being Fe and unavoidable impurities, was melted in a vacuum melting furnace. At that time, by adjusting the time from the addition of alloying elements to tapping and the thickness of the mold, the amount of inclusions floating to the surface or the precipitation density were changed, thereby changing the size and number density of inclusions remaining in the steel.

[0096] After removing the red-hot slab from the furnace, it was transported to an electric furnace so that the surface temperature of the slab would not fall below 800°C. In the electric furnace, after performing a heat retention treatment at 1100°C for 30 minutes, the slab was removed from the electric furnace and hot-rolled to become a hot-rolled steel sheet.

[0097] In the above hot rolling, the thickness was reduced to 10 mm in 4 passes equivalent to rough rolling, then reheated from 980°C to 1100°C using an induction heating device, and subsequently reduced to 1.2 mm in 6 passes equivalent to finish rolling. Here, in order to simulate low-speed hot rolling of a thin slab caster, the entry speed of the first rolling pass was set to 5 mpm, and the subsequent rolling speed was set to 130 mpm ÷ (entry plate thickness) × 5 mpm.

[0098] A portion of the obtained hot-rolled steel sheet was cut and embedded in a carbon mold to create a sample. Using a scanning electron microscope (SEM), the plane perpendicular to the rolling direction of the sample was observed to investigate the size and number of inclusions.

[0099] Next, the obtained hot-rolled steel sheet was subjected to hot-rolled sheet annealing at 1040°C for 30 seconds, followed by cold rolling to obtain a cold-rolled steel sheet with a final thickness of 0.25 mm. The cold-rolled steel sheet was subjected to finish annealing at 980°C for 15 seconds to obtain a non-oriented electrical steel sheet. Using a contact roughness meter, the arithmetic mean bending Wa in the width direction of the non-oriented electrical steel sheet was measured.

[0100] As a result of investigating the relationship between inclusions and lagging, the inventors found that lagging is suppressed when there are many inclusions of relatively small size. Figure 5 shows the relationship between the number density of inclusions with an equivalent diameter of 0.3 μm or more and 1.0 μm or less in hot-rolled steel sheets and Wa. When the number density of the above inclusions is 9 or more / mm², a tendency for lagging to be further improved was observed.

[0101] From the results of experiments 3 and 4 above, it can be seen that lagging can be further suppressed by reducing the finishing thickness of the hot rolling and by including relatively small-sized inclusions.

[0102] It is believed that reducing the finishing thickness of hot rolling introduces shear deformation of the hot-rolled material up to the center of the plate thickness, thereby further promoting recrystallization. Furthermore, regarding relatively small inclusions, it is thought that they serve as nucleation sites during the solidification of molten steel, contributing to the refinement of the slab structure and the randomization of the texture. While most of these small inclusions are oxides, large inclusions are primarily AlN or MnS. Therefore, it is presumed that large inclusions do not precipitate during the solidification of molten steel and do not contribute to the improvement of leaching.

[0103] The present invention is based on the above understanding. Below, embodiments for carrying out the present invention will be described in detail. Furthermore, the present invention is not limited to these embodiments.

[0104] [Ingredient Composition]

[0105] In the present invention, the reason for limiting the composition of the steel slab components is explained.

[0106] Si: 2.0∼5.0%

[0107] Si is an element that increases the intrinsic resistance of steel sheets and has the effect of reducing iron loss. To obtain the above effect, the Si content is set to 2.0% or more, preferably 2.5% or more. On the other hand, since industrial production by cold rolling becomes difficult when the Si content exceeds 5.0%, the Si content is set to 5.0% or less, preferably 4.0% or less.

[0108] Al: 3.0% or less

[0109] Al is an element that increases the intrinsic resistance of steel sheets and has the effect of reducing iron loss. However, if the Al content exceeds 3.0%, cracking becomes more likely to occur during continuous casting. Therefore, the Al content is set to 3.0% or less, preferably 1.5% or less. Meanwhile, although there is no specific lower limit for the Al content, it is desirable to set the Al content to 0.00001% or more, as excessive reduction leads to increased manufacturing costs. From the perspective of magnetic properties, it is desirable to set it to 0.3% or more. However, if magnetic flux density is prioritized, it is desirable to set the Al content to 0.002% or less.

[0110] Total Si and Al content: 3.5% or more

[0111] From the perspective of increasing the intrinsic resistance of the steel sheet and reducing iron loss, it is desirable to increase the Si and Al content; however, as shown in FIG. 1, when the total content of Si and Al is 3.5% or more, recrystallization during hot-rolled sheet annealing is suppressed, making it prone to leaching. However, in the present invention, by performing hot rolling under predetermined conditions, leaching can be suppressed even if the total content of Si and Al is 3.5% or more. Therefore, in the present invention, the total content of Si and Al is set to 3.5% or more.

[0112] In one embodiment of the present invention, the steel slab,

[0113] Si: 2.0% or more and 5.0% or less and,

[0114] Al: Contains 3.0% or less,

[0115] It consists of residual Fe and unavoidable impurities,

[0116] It may have a composition in which the total content of Si and Al is 3.5% or more.

[0117] In another embodiment of the present invention, the composition of the steel slab may additionally contain at least one of the following elements in addition to Si and Al. In that case, the remainder of the composition is Fe and unavoidable impurities. Furthermore, all of the elements listed below are optional additive elements, and therefore the lower limit of their content may be 0%.

[0118] C: 0.005% or less

[0119] When adding C, the C content is kept at 0.005% or less for the purpose of preventing magnetic aging. On the other hand, if the C content is reduced excessively, the magnetic flux density decreases. Therefore, for the purpose of preventing a decrease in magnetic flux density, it is desirable to keep the C content at 0.001% or more.

[0120] Mn: 3.0% or less

[0121] Mn is an element that increases the intrinsic resistance of steel sheets and has the effect of further reducing iron loss. However, if the Mn content exceeds 3.0%, carbides precipitate, which actually increases iron loss. Therefore, when adding Mn, the Mn content should be 3.0% or less, preferably 2.0% or less. On the other hand, from the perspective of avoiding hot brittleness in hot rolling, it is desirable to have a Mn content of 0.05% or more. From the perspective of magnetic properties, it is more desirable to have a Mn content of 0.3% or more.

[0122] Cr: 3.0% or less

[0123] Cr is an element that increases the intrinsic resistance of steel sheets and has the effect of reducing iron loss. However, if the Cr content exceeds 3.0%, carbides precipitate, which actually increases iron loss. Therefore, when adding Cr, the Cr content is kept at 3.0% or less. From the perspective of magnetic properties, it is desirable to keep the Cr content at 1.5% or less. On the other hand, while there is no specific lower limit for the Cr content, it is desirable to keep it at 0.005% or more from the perspective of enhancing the effect of adding Cr.

[0124] Ni: 2.0% or less

[0125] Ni is an element that has the effect of improving the magnetic flux density of steel sheets. However, Ni is an expensive element, and if the Ni content exceeds 2.0%, the cost becomes very high. Therefore, when adding Ni, the Ni content is kept at 2.0% or less. From the perspective of balancing magnetic properties and cost, it is desirable to keep the Ni content at 0.5% or less. On the other hand, while there is no specific lower limit for the Ni content, from the perspective of enhancing the effect of adding Ni, it is desirable to keep it at 0.005% or more.

[0126] Cu: 2.0% or less

[0127] Cu is an element that has the effect of improving the magnetic flux density of steel sheets. However, if the Cu content exceeds 2.0%, it causes hot brittleness and becomes a cause of surface defects. Therefore, when adding Cu, the Cu content is kept at 2.0% or less. From the perspective of balancing magnetic properties and cost, it is desirable to keep the Cu content at 0.5% or less. On the other hand, while there is no specific lower limit for the Cu content, it is desirable to keep it at 0.005% or more from the perspective of enhancing the effect of adding Cu.

[0128] P: 0.2% or less

[0129] P is an element used to adjust the strength of steel sheets. However, if the P content exceeds 0.2%, the steel becomes brittle, making cold rolling difficult. Therefore, when adding P, the P content is kept at 0.2% or less. From the perspective of balancing high strength and embrittlement, it is desirable to keep the P content at 0.1% or less. On the other hand, while there is no specific lower limit for the P content, it is desirable to keep it at 0.005% or more to enhance the effect of adding P.

[0130] S: 0.0050% or less

[0131] S is an element that forms sulfides and increases iron loss. Therefore, when S is included, the S content is set to 0.0050% or less, preferably 0.0020% or less, and more preferably 0.0010% or less. On the other hand, from the perspective of magnetic properties, the lower the S content, the better, so the lower limit of the S content may be 0%. However, since excessive reduction leads to an increase in manufacturing costs, from the perspective of cost, it is desirable to set it to 0.0001% or more.

[0132] N: 0.0050% or less

[0133] N is an element that forms nitrides and increases iron loss. Therefore, when N is included, the N content is set to 0.0050% or less, preferably 0.0030% or less, and more preferably 0.0020% or less. On the other hand, from the perspective of magnetic properties, the lower the N content, the better, so the lower limit of the N content may be 0%. However, since excessive reduction leads to an increase in manufacturing costs, from the perspective of cost, it is desirable to set it to 0.0001% or more.

[0134] O: 0.0050% or less

[0135] O is an element that forms oxides and increases iron loss. Therefore, when O is included, the O content is set to 0.0050% or less, preferably 0.0020% or less, and more preferably 0.0010% or less. On the other hand, from the perspective of magnetic properties, the lower the O content, the better, so the lower limit of the O content may be 0%. However, since excessive reduction leads to an increase in manufacturing costs, from the perspective of cost, it is desirable to set it to 0.0001% or more.

[0136] Ti: 0.0040% or less

[0137] Ti is an element that forms carbonitrides and increases iron loss. Therefore, when Ti is included, the Ti content is set to 0.0040% or less, preferably 0.0020% or less, and more preferably 0.0010% or less. On the other hand, from the perspective of magnetic properties, the lower the Ti content, the better, so the lower limit of the Ti content may be 0%. However, since excessive reduction leads to an increase in manufacturing costs, from the perspective of cost, it is desirable to set it to 0.0001% or more.

[0138] Sn: 0.20% or less

[0139] Sn is an element that has the effect of reducing iron loss by suppressing nitridation and oxidation of the surface layer. However, the effect becomes saturated even if added in an amount exceeding 0.20%. Therefore, when adding Sn, the Sn content is set to 0.20% or less, preferably 0.10% or less. On the other hand, from the perspective of enhancing the effect of adding Sn, it is desirable to set the Sn content to 0.005% or more.

[0140] Sb: 0.20% or less

[0141] Sb is an element that has the effect of reducing iron loss by suppressing nitriding and oxidation of the surface layer. However, the effect becomes saturated even if added in an amount exceeding 0.20%. Therefore, when adding Sb, the Sb content is set to 0.20% or less, preferably 0.10% or less. On the other hand, from the perspective of enhancing the effect of adding Sb, it is desirable to set the Sb content to 0.005% or more.

[0142] Mo: 0.10% or less

[0143] Mo is an element that has the effect of reducing iron loss by suppressing nitridation and oxidation of the surface layer. However, if added in an amount exceeding 0.10%, iron loss actually increases. Therefore, when adding Mo, the Mo content is set to 0.10% or less, preferably 0.05% or less. On the other hand, from the perspective of enhancing the effect of adding Mo, it is desirable to set the Mo content to 0.001% or more.

[0144] Ca: 0.01% or less

[0145] Ca is an element that reduces iron loss by suppressing the formation of fine oxides and sulfides. However, the effect becomes saturated even if added in amounts exceeding 0.01%. Therefore, when adding Ca, the Ca content is set to 0.01% or less, preferably 0.006% or less. On the other hand, from the perspective of enhancing the effect of adding Ca, it is desirable to set the Ca content to 0.001% or more.

[0146] REM: 0.05% or less

[0147] REM (rare earth metal) is a component that reduces iron loss by suppressing the formation of fine sulfides. However, the effect saturates even if added in an amount exceeding 0.05%. Therefore, when adding REM, the REM content is set to 0.05% or less, preferably 0.03% or less. On the other hand, from the perspective of enhancing the effect of adding REM, it is desirable to set the REM content to 0.005% or more.

[0148] Mg: 0.01% or less

[0149] Mg is an element that reduces iron loss by suppressing the formation of fine sulfides. However, the effect becomes saturated even if added in amounts exceeding 0.01%. Therefore, when adding Mg, the Mg content is set to 0.10% or less, preferably 0.006% or less. On the other hand, from the perspective of enhancing the effect of adding Mg, it is desirable to set the Mg content to 0.001% or more.

[0150] Zn: 0.01% or less

[0151] Zn is an element that reduces iron loss by suppressing the formation of fine oxides and sulfides. However, the effect becomes saturated even if added in amounts exceeding 0.01%. Therefore, when adding Zn, the Zn content is set to 0.01% or less, preferably 0.005% or less. On the other hand, from the perspective of enhancing the effect of adding Zn, it is desirable to set the Zn content to 0.001% or more.

[0152] The composition of the above steel slab may additionally optionally contain at least one of the following elements. In addition, all of the following elements are optionally added elements, and therefore, the lower limit of their content may be 0%.

[0153] Nb: 0.005% or less

[0154] Nb is an element that forms fine carbonitrides, which increases iron loss. In particular, adverse effects become significant when the Nb content exceeds 0.005%. Therefore, when adding Nb, the Nb content should be 0.005% or less, preferably 0.002% or less. On the other hand, from the perspective of magnetic properties, the lower the Nb content, the better, so the lower limit of the Nb content may be 0%. However, since excessive reduction leads to an increase in manufacturing costs, it is desirable to keep it at 0.00001% or more from a cost perspective.

[0155] V: 0.02% or less

[0156] V is an element that forms fine carbonitrides, which increases iron loss. In particular, adverse effects become significant when the V content exceeds 0.02%. Therefore, when V is included, the V content should be 0.02% or less, preferably 0.005% or less. On the other hand, from the perspective of magnetic properties, the lower the V content, the better, so the lower limit of the V content may be 0%. However, since excessive reduction leads to an increase in manufacturing costs, it is desirable to keep it 0.0001% or more from a cost perspective.

[0157] Ta: 0.002% or less

[0158] Ta is an element that forms fine carbonitrides, which increases iron loss. In particular, adverse effects become significant when the Ta content exceeds 0.002%. Therefore, when Ta is included, the Ta content is kept at 0.002% or less, preferably 0.001% or less. On the other hand, from the perspective of magnetic properties, the lower the Ta content, the better, so the lower limit of the Ta content may be 0%. However, since excessive reduction leads to an increase in manufacturing costs, from the perspective of cost, it is desirable to keep it at 0.00001% or more.

[0159] B: 0.002% or less

[0160] B is an element that forms fine nitrides, which increases iron loss. In particular, if the B content exceeds 0.002%, the adverse effects become significant. Therefore, when B is included, the B content is set to 0.002% or less, preferably 0.001% or less. On the other hand, from the perspective of magnetic properties, the lower the B content, the better, so the lower limit of the B content may be 0%. However, since excessive reduction leads to an increase in manufacturing costs, from the perspective of cost, it is desirable to set it to 0.00001% or more.

[0161] Ga: 0.005% or less

[0162] Ga is an element that forms fine nitrides, which increases iron loss. In particular, adverse effects become significant when the Ga content exceeds 0.005%. Therefore, when Ga is included, the Ga content is set to 0.005% or less, preferably 0.002% or less. On the other hand, from the perspective of magnetic properties, the lower the Ga content, the better, so the lower limit of the Ga content may be 0%. However, since excessive reduction leads to an increase in manufacturing costs, it is desirable to set it to 0.00001% or more from a cost perspective.

[0163] Pb: 0.002% or less

[0164] Pb is an element that forms fine Pb particles, which increases iron loss. In particular, adverse effects become significant when the Pb content exceeds 0.002%. Therefore, when Pb is included, the Pb content should be 0.002% or less, preferably 0.001% or less. On the other hand, from the perspective of magnetic properties, the lower the Pb content, the better, so the lower limit of the Pb content may be 0%. However, since excessive reduction leads to an increase in manufacturing costs, it is desirable to keep it 0.00001% or more from the perspective of cost.

[0165] W: 0.05% or less

[0166] W is an element that forms fine carbides, thereby increasing iron loss. In particular, adverse effects become significant when the W content exceeds 0.05%. Therefore, when W is included, the W content should be 0.05% or less, preferably 0.02% or less. On the other hand, from the perspective of magnetic properties, the lower the W content, the better, so the lower limit of the W content may be 0%. However, since excessive reduction leads to an increase in manufacturing costs, from the perspective of cost, it is desirable to keep it at 0.00001% or more.

[0167] Ge: 0.05% or less

[0168] Ge is an element that improves magnetic flux density and has the effect of reducing iron loss. However, if the Ge content exceeds 0.05%, the addition effect becomes saturated. Therefore, when adding Ge, the Ge content is set to 0.05% or less, preferably 0.01% or less. Meanwhile, although the lower limit of the Ge content is not particularly limited, it is desirable to set it to 0.0001% or more from the perspective of enhancing the addition effect of Ge.

[0169] As: 0.05% or less

[0170] As is an element that improves magnetic flux density and has the effect of reducing iron loss. However, if the As content exceeds 0.05%, the addition effect becomes saturated. Therefore, when adding As, the As content is set to 0.05% or less, preferably 0.01% or less. On the other hand, while the lower limit of the As content is not particularly limited, it is desirable to set it to 0.0001% or more from the perspective of enhancing the addition effect of As.

[0171] Co: 0.05% or less

[0172] Co is an element that improves magnetic flux density and has the effect of reducing iron loss. However, if the Co content exceeds 0.05%, the addition effect becomes saturated. Therefore, when adding Co, the Co content is set to 0.05% or less, preferably 0.01% or less. Meanwhile, although the lower limit of the Co content is not particularly limited, it is desirable to set it to 0.0001% or more from the perspective of enhancing the addition effect of Co.

[0173] [Manufacturing Conditions for Hot-Rolled Steel Sheets for Non-Oriented Electrical Steel Sheets]

[0174] Next, the manufacturing conditions for producing hot-rolled steel sheets for non-oriented electrical steel sheets using a steel slab having the above-mentioned composition will be explained.

[0175] A method for manufacturing a hot-rolled steel sheet for non-oriented electrical steel sheets in one embodiment of the present invention comprises a continuous casting process for manufacturing a steel slab by a continuous casting method, a conveying process for conveying the steel slab to a hot-rolling facility while maintaining the surface temperature of the steel slab at 800°C or higher, and a hot-rolling process for producing a hot-rolled steel sheet by sequentially performing rough rolling, reheating treatment, and finish rolling on the steel slab in the hot-rolling facility. Each process is described below.

[0176] · Continuous casting process

[0177] First, a steel slab having the aforementioned composition is manufactured by a continuous casting method (continuous casting process). The method of performing continuous casting is not particularly limited and can be carried out according to conventional methods. The method of adjusting the composition of the molten steel used for continuous casting is also not particularly limited and can be carried out by any method. For example, a converter, an electric furnace, a vacuum degasser, and other devices and methods may be used to adjust the composition of the molten steel.

[0178] Steel slab thickness: 50–200 mm

[0179] In the above continuous casting process, a steel slab with a thickness of 50 mm or more and 200 mm or less is manufactured. If the thickness of the steel slab is less than 50 mm, the reduction rate in the hot rolling process becomes excessively low, so recrystallization cannot be sufficiently promoted. On the other hand, if the thickness of the steel slab is thicker than 200 mm, the equipment cost increases.

[0180] · Return process

[0181] Next, the steel slab produced in the above continuous casting process is conveyed to the hot rolling facility (conveying process). The present invention is intended for so-called direct rolling, and in this conveying process, the steel slab is conveyed to the hot rolling facility while maintaining its surface temperature at 800°C or higher. In other words, in the present invention, conveying is performed so that the surface temperature of the steel slab does not fall below 800°C between the time it is produced in the continuous casting process and the time it reaches the hot rolling facility.

[0182] In the present invention, a steel slab obtained from a continuous casting process is provided to a hot rolling process while maintaining its temperature at a high temperature of 800°C or higher. Therefore, there is no need to reheat the steel slab before hot rolling, which can significantly reduce energy costs. Although the occurrence of leaching is a problem in such direct rolling, the present invention can suppress the occurrence of leaching by controlling the hot rolling conditions as described below.

[0183] In addition, prior to hot rolling, a heat retention treatment may be performed by maintaining the steel slab at a temperature of 1000°C or higher and 1300°C or lower for at least 60 seconds. By performing the above heat retention treatment, MnS or AlN can be coarsened, thereby further improving iron loss. The heating method in the above heat retention treatment is not particularly limited, and any method such as induction heating, gas furnace, or electric furnace may be used.

[0184] Hot rolling

[0185] Next, in the above-described hot rolling facility, the steel slab is sequentially subjected to rough rolling, reheating treatment, and finish rolling to form a hot-rolled steel sheet (hot rolling process). In the present invention, it is important to perform the hot rolling process under conditions that satisfy the following (1) to (4).

[0186] (1) Exit speed of the above roughing mill: 100 mpm or less

[0187] (2) Reduction rate in the final pass of the above rough rolling: 45% or more

[0188] (3) Average heating rate in the above reheating treatment: 9℃ / s or higher

[0189] (4) Temperature rise in the above reheating treatment: 30℃ or higher

[0190] Exit speed of rough rolling: 100 mpm or less

[0191] As mentioned above, although direct rolling is superior in terms of energy saving, the rate of passing the sheet is limited to the casting speed, which reduces the hot rolling speed. Furthermore, as shown in Experiment 1 above, if the exit speed of the final pass of rough rolling is 100 mpm or less, the occurrence of lagging becomes significant. However, in the present invention, by controlling the reduction rate and reheating treatment conditions in the final pass of rough rolling, lagging can be suppressed even if the exit speed of rough rolling is 100 mpm or less. Therefore, in the present invention, the exit speed of rough rolling is set to 100 mpm or less, preferably 70 mpm or less. Accordingly, the present invention can achieve both a reduction in energy consumption and the suppression of lagging.

[0192] In addition, such an output speed is realized, for example, when a cast steel slab is continuously hot-rolled without being cut. This is because the rate of hot rolling is limited by the rate of casting. In contrast, in the conventional process of cutting the steel slab before hot rolling, the rate of hot rolling generally exceeds 100 mpm from the perspective of manufacturing efficiency.

[0193] Meanwhile, although the lower limit of the above-mentioned output speed is not specifically limited, productivity decreases if the output speed is excessively slow. Therefore, it is preferable that the above-mentioned output speed be 10 mpm or higher, and more preferable that it be 15 mpm or higher.

[0194] Reduction rate in the final pass of rough rolling: 45% or more

[0195] Setting the reduction rate in the final pass of rough rolling to 45% or more is effective in suppressing lagging. If the above reduction rate is less than 45%, sufficient deformation energy is not accumulated in the material, and recrystallization is not sufficiently promoted. Therefore, the reduction rate in the final pass of rough rolling is set to 45% or more, preferably 55% or more. Meanwhile, the upper limit of the above reduction rate is not particularly limited, but, for example, it may be 80% or less, 75% or less, or 70% or less.

[0196] In addition, the exit temperature of the above rough rolling is not particularly limited, but it is preferable to set it to 850℃ to 1000℃, and more preferable to set it to 900℃ to 950℃.

[0197] After the above rough rolling, a reheating treatment is performed prior to the finishing hot rolling. By performing the above reheating treatment, the temperature of the material can be raised, and the deformation resistance during finishing rolling can be lowered. The heating method for the above reheating treatment is not particularly limited, and any method such as induction heating, gas furnace, or electric furnace may be used.

[0198] Average heating rate during reheating treatment: 9℃ / s or higher

[0199] To suppress lizing, the average heating rate in the above reheating treatment is set to 9°C / s or higher, preferably 12°C / s or higher. If the average heating rate is less than 9°C / s, the deformation accumulated in the material during rough rolling is recovered during heating, so recrystallization is not sufficiently promoted, and significant lizing cannot be suppressed. Meanwhile, although the upper limit of the average heating rate is not particularly limited, if the average heating rate is excessively high, high-output heating equipment becomes required, which increases equipment costs. Therefore, from the perspective of equipment costs, it is desirable to set it to 100°C / s or lower, more desirable to set it to 50°C / s or lower, and even more desirable to set it to 20°C / s or lower.

[0200] Temperature rise during reheating treatment: 30℃ or more

[0201] If the temperature rise caused by reheating is less than 30°C, recrystallization is not sufficiently promoted, and thus, leaching cannot be suppressed. Therefore, in the above reheating treatment, the temperature is raised to 30°C or higher, preferably 50°C or higher. Although there is no specific upper limit for the temperature rise, if the temperature rise is greater than 200°C, the increase in manufacturing costs becomes significant. Therefore, from a cost perspective, it is desirable to keep the temperature rise at 200°C or lower.

[0202] The heating temperature (reached temperature) in the above reheating treatment is not particularly limited, but from the perspective of further suppressing leaching, it is preferable to set it to 1000 to 1200°C.

[0203] After the above reheating treatment, finish rolling is performed. The conditions for finish rolling are not particularly limited and can be performed in accordance with commercial methods.

[0204] The finishing temperature in the above hot rolling is not particularly limited, but from the perspective of stabilizing the shape or suppressing oxidation, it is preferable to set the finishing temperature to 900°C or lower. Meanwhile, the lower limit of the finishing temperature is not particularly limited, but it is preferable to set it to 600°C or higher.

[0205] Finish thickness: 1.5 mm or less

[0206] In addition, regarding the above-mentioned finishing rolling, it is preferable to perform rolling such that the final thickness (finishing thickness) of the hot-rolled steel sheet obtained is 1.5 mm or less. By making the finishing thickness 1.5 mm or less, sufficient shear deformation is introduced to the center of the sheet thickness during hot rolling, which further promotes recrystallization and thereby further suppresses leaching. It is more preferable to make the finishing thickness 1.3 mm or less. Meanwhile, although there is no particular limit regarding the lower limit of the finishing thickness, if the finishing thickness is excessively thin, the hot-rolled coil becomes excessively long, which increases the cost of passing through the hot-rolled sheet annealing or acid cleaning line. Therefore, it is preferable to make the finishing thickness 0.4 mm or more.

[0207] By the above sequence, a hot-rolled steel sheet for non-oriented electrical steel can be obtained. Additionally, after the hot rolling process, it is also desirable to wind the obtained hot-rolled steel sheet into a coil shape. At that time, the winding temperature is not particularly limited, but from the perspective of stabilizing the shape and suppressing oxidation, it is desirable to keep the winding temperature at 700°C or lower. Meanwhile, the lower limit of the winding temperature is not particularly limited, but it is desirable to keep it at 400°C or higher.

[0208] Inclusion density: 9 or more / mm²

[0209] In the above hot-rolled steel sheet, additionally, lagging can be suppressed by making the number density of inclusions with an equivalent circular diameter of 0.3 μm or more and 1.0 μm or less 9 or more / mm² or more. Here, the number density of the inclusions is measured by observing a cross-section perpendicular to the rolling direction of the hot-rolled steel sheet using SEM. In the above measurement, the equivalent circular diameter (diameter) is calculated from the area of ​​the observed inclusions. It is preferable that the area of ​​the observation field be 10 mm² or more.

[0210] Inclusions that are relatively small, with an equivalent diameter of 0.3㎛ or more and 1.0㎛ or less, are thought to serve as nucleation sites during the solidification of molten steel, contributing to the refinement of the slab structure and the randomization of the texture. Inclusions with an equivalent diameter greater than 1.0㎛ do not have the effect of inhibiting lagging. Additionally, inclusions with an equivalent diameter of less than 0.3㎛ are excluded because they are difficult to observe and quantify using SEM. Furthermore, since inclusions with an equivalent diameter of less than 0.3㎛ are generally thought to strongly inhibit grain boundary migration, it is desirable to reduce them as much as possible from the perspective of reducing iron loss.

[0211] It is more preferable to have the above number density at least 12 pieces / mm². Meanwhile, although the upper limit of the above number density is not specifically limited, it is preferable to have it at least 1,000 pieces / mm² and more preferable to have it at least 600 pieces / mm² from the perspective of suppressing adverse effects on iron loss.

[0212] [Manufacturing Conditions for Non-Oriented Electrical Steel Sheets]

[0213] A method for manufacturing a non-oriented electrical steel sheet in one embodiment of the present invention comprises a hot-rolled steel sheet manufacturing process for manufacturing a hot-rolled steel sheet by the manufacturing method, a hot-rolled steel sheet annealing process for performing hot-rolled steel sheet annealing on the hot-rolled steel sheet, a cold-rolling process for performing cold-rolling on the hot-rolled steel sheet to form a cold-rolled steel sheet, and a finishing annealing process for performing finishing annealing on the cold-rolled steel sheet.

[0214] Each of the above processes of hot-rolled plate annealing, cold rolling, and finish annealing is not particularly limited and can be performed in accordance with commercial methods.

[0215] The cracking temperature in the above-mentioned hot-rolled plate annealing is not particularly limited, but it is preferable to set it to 900 to 1100°C. Similarly, the cracking time is not particularly limited, but it is preferable to set it to 1 to 300 seconds. The atmosphere of the above-mentioned hot-rolled plate annealing is not specifically defined and can be performed in any atmosphere. As for the above-mentioned atmosphere, for example, it is preferable to use an atmosphere containing at least one selected from the group consisting of N2, H2, Ar, CO, CO2, and H2O, and it is more preferable to use an atmosphere consisting of at least one selected from the group consisting of N2, H2, Ar, CO, CO2, and H2O.

[0216] For the above cold rolling, any rolling mill may be used without any particular limitations. As the rolling mill, either a tandem mill or a reverse mill may be used. In the above cold rolling, it is preferable that the thickness of the plate at the entry side be 0.5 to 3 mm. In addition, it is preferable that the thickness of the plate at the exit side be 0.1 to 0.5 mm. From the perspective of improving magnetic properties or preventing breakage, warm rolling may be applied. For example, it is advantageous to keep the material temperature during rolling 100 to 300°C or lower.

[0217] The cracking temperature in the above finishing annealing is not particularly limited, but it is preferable to set it to 800 to 1100°C. Similarly, the cracking time is not particularly limited, but it is preferable to set it to 1 to 300 seconds. From the perspective of suppressing oxidation of the material, it is preferable to perform the above finishing annealing in a non-oxidizing atmosphere. As the above non-oxidizing atmosphere, it is preferable to use an atmosphere composed of at least one selected from the group consisting of H2, N2, and Ar. In addition, it is preferable to manage the dew point of the atmosphere to -30°C or lower.

[0218] It is also desirable to perform acid cleaning after the annealing of the hot-rolled sheet and prior to the cold rolling. Furthermore, it is desirable to form an insulating coating on the surface of the obtained non-oriented electrical steel sheet after the finishing annealing. The acid cleaning and the formation of the insulating coating are not particularly limited and can be performed according to commercial methods.

[0219] Examples

[0220] (Example 1)

[0221] A steel slab with a thickness of 150 mm was manufactured by a continuous casting method having a compositional composition containing C: 0.0011%, Si: 3.34%, Al: 0.82%, Mn: 0.45%, Cr: 0.10%, Ni: 0.01%, Cu: 0.03%, P: 0.01%, S: 0.0005%, N: 0.0012%, O: 0.001%, and Ti: 0.0005%, with the remainder being Fe and unavoidable impurities. In the manufacture of the steel slab, the number and size of inclusions were controlled by adjusting the time from the addition of a deoxidizing element to the molten steel until the pouring, and the cooling rate of the slab immediately after solidification.

[0222] Afterward, the steel slab was conveyed to the hot rolling facility. During the conveyance, a tunnel-type gas furnace was used, and heat retention treatment was performed under the conditions shown in Table 1. Immediately before being introduced into the gas furnace, the surface temperature of the steel slab was 980°C, and the line speed was 4 mpm. In addition, in some examples, heat retention treatment was not performed for comparison. In all examples, the surface temperature of the steel slab was maintained at 800°C or higher until it was conveyed to the hot rolling facility.

[0223] Next, in the above-mentioned hot rolling facility, the steel slab was sequentially subjected to rough rolling, reheating treatment, and finish rolling to produce a hot-rolled steel sheet. Specifically, first, the thickness was reduced to the exit plate thickness shown in Table 1 during 4-pass rough rolling. The exit speed of the rough rolling and the reduction rate in the final pass were as shown in Table 1. Next, the sheet was reheated to 1120°C using an induction heating device. The average heating rate and temperature rise during the reheating were as shown in Table 1. Subsequently, 5-pass finish rolling was performed to reduce the thickness to the finish thickness shown in Table 1. After that, the obtained hot-rolled steel sheet was wound into a coil shape.

[0224] During the period from the hot rolling to the completion of coiling in the above continuous casting, the material was not cut and was continuously passed through. Under any conditions, the cooling conditions were adjusted so that the hot rolling finishing temperature was 900°C or lower and the coiling temperature was 700°C or lower.

[0225] (Inclusion count density)

[0226] The number density of inclusions with an equivalent circular diameter of 0.3 μm or more and 1.0 μm or less in the obtained hot-rolled steel sheet was measured. Specifically, first, the hot-rolled steel sheet was cut to obtain a test specimen. Subsequently, the test specimen was embedded in a carbon mold, and the plane perpendicular to the rolling direction was observed using SEM to investigate the size and number of inclusions. The equivalent circular diameter was calculated from the area of ​​each observed inclusion, and the number density of inclusions with an equivalent circular diameter of 0.3 μm or more and 1.0 μm or less was determined. The measurement results are shown in Table 1.

[0227] Next, a non-oriented electrical steel sheet was manufactured using the above hot-rolled steel sheet. Specifically, the above hot-rolled steel sheet was first subjected to hot-rolled annealing at 1010°C for 20 seconds to obtain a hot-rolled annealed sheet. Subsequently, the above hot-rolled annealed sheet was cold-rolled to obtain a cold-rolled steel sheet with a final thickness of 0.20 mm. The above cold-rolled steel sheet was subjected to finishing annealing at 1000°C for 20 seconds to obtain a non-oriented electrical steel sheet (finishing annealed sheet).

[0228] To evaluate the occurrence of lagging, the arithmetic mean bending Wa in the width direction of the above non-oriented electrical steel sheet was measured using a contact roughness meter. In addition, to evaluate magnetic properties, the iron loss W at a magnetic flux density of 1.0 T and a frequency of 400 Hz was measured by the Epstein test. 10 / 400 (W / kg) was measured. The measurement results are listed in Table 1.

[0229] As can be seen from the results shown in Table 1, in the embodiments satisfying the conditions of the present invention, iron loss was good, Wa was low at 1.0 μm or less, and lagging was suppressed. In addition, here, iron loss W 10 / 400 It was said that iron loss is good when (W / kg) is 28 × final plate thickness (mm) + 5.5 or less.

[0230]

[0231] (Example 2)

[0232] Steel slabs having the compositions shown in Tables 2 to 4 were manufactured by a continuous casting method. In the manufacture of the above steel slabs, the number and size of inclusions were controlled by adjusting the time from the addition of deoxidizing elements to the molten steel until the pouring, and the cooling rate of the slab immediately after solidification.

[0233] Afterward, the steel slab was conveyed to the hot rolling facility. During the conveyance, a tunnel-type electric furnace was used to perform a heat retention treatment of 1100°C × 15 min. Immediately before being introduced into the electric furnace, the surface temperature of the steel slab was 1050°C and the line speed was 3 mpm. In all embodiments, the surface temperature of the steel slab was maintained at 800°C or higher until it was conveyed to the hot rolling facility.

[0234] Next, in the above-mentioned hot rolling facility, the steel slab was sequentially subjected to rough rolling, reheating treatment, and finish rolling to produce a hot-rolled steel sheet. Specifically, first, the thickness was reduced to 10 mm in four passes of rough rolling. The reduction rate in the final pass of the rough rolling was set to 58%. Subsequently, a reheating treatment was performed using an induction heating device. During the reheating treatment, the average heating rate in the temperature range from 1010°C to 1080°C was 14°C / s. Subsequently, six passes of finish rolling were performed to reduce the thickness to 1.2 mm. Afterward, the obtained hot-rolled steel sheet was wound into a coil shape.

[0235] During the period from the above continuous casting until the completion of coiling after hot rolling, the material was not cut and was continuously passed through. Under any conditions, the cooling conditions were adjusted so that the hot rolling finishing temperature was 900°C or lower and the coiling temperature was 700°C or lower.

[0236] The number density of inclusions with an equivalent diameter of 0.3 μm or more and 1.0 μm or less in the obtained hot-rolled steel sheet was determined in the same manner as in Example 1. The measurement results are shown in Tables 2 to 4.

[0237] Next, a non-oriented electrical steel sheet was manufactured using the above hot-rolled sheet annealing. Specifically, the above hot-rolled steel sheet was first subjected to hot-rolled sheet annealing at 1040°C for 40 seconds to obtain a hot-rolled annealed sheet. Subsequently, the above hot-rolled annealed sheet was cold-rolled to obtain a cold-rolled steel sheet with a final thickness of 0.25 mm. The above cold-rolled steel sheet was subjected to finish annealing at 980°C for 10 seconds to obtain a non-oriented electrical steel sheet (finish annealed sheet).

[0238] Arithmetic mean bending Wa and iron loss W in the obtained non-oriented electrical steel sheet 10 / 400 ...was measured in the same manner as in Example 1. The measurement results are shown in Tables 2 to 4.

[0239] As can be seen from the results shown in Tables 2 to 4, in the embodiments satisfying the conditions of the present invention, iron loss was good, and Wa was low at 1.0 μm or less, so lagging was suppressed. In addition, here, iron loss W 10 / 400 It was stated that iron loss is good when (W / kg) is 28 × final plate thickness (mm) + 5.5 or less. In addition, Comparative Example No. 58 could not be obtained as it fractured during the cold rolling process because the Si content was excessively high. In addition, Comparative Example No. 59 could not be obtained as it broke out during continuous casting because the Al content was excessively high.

[0240]

[0241]

[0242]

Claims

Claim 1 In mass%, it contains Si: 2.0% or more and 5.0% or less and Al: 3.0% or less, with a total content of Si and Al of 3.5% or more, and additionally contains at least one element selected from the group consisting of C: 0.005% or less, Mn: 3.0% or less, Cr: 3.0% or less, Ni: 2.0% or less, Cu: 2.0% or less, P: 0.2% or less, S: 0.0050% or less, N: 0.0050% or less, O: 0.0050% or less, Ti: 0.0040% or less, Sn: 0.20% or less, Sb: 0.20% or less, Mo: 0.10% or less, Ca: 0.01% or less, REM: 0.05% or less, Mg: 0.01% or less, and Zn: 0.01% or less. A method for manufacturing a hot-rolled steel sheet for non-oriented electrical steel sheets, comprising: a continuous casting process for manufacturing a steel slab having a thickness of 50 mm or more and 200 mm or less, having a composition in which the remainder is Fe and unavoidable impurities, by a continuous casting method; a conveying process for conveying the steel slab to a hot rolling facility while maintaining the surface temperature of the steel slab at 800°C or higher; and a hot rolling process in which, in the hot rolling facility, the steel slab is sequentially subjected to rough rolling, reheat treatment, and finish rolling to form a hot-rolled steel sheet, wherein the hot rolling process is performed under conditions satisfying (1) to (4) below. (1) Exit speed of the above rough rolling: 100 mpm or less (2) Reduction rate in the final pass of the above rough rolling: 45% or more (3) Average heating rate in the above reheating treatment: 9℃ / s or more (4) Temperature rise in the above reheating treatment: 30℃ or more Claim 2 A method for manufacturing a hot-rolled steel sheet for non-oriented electrical steel sheets, wherein, in the finishing rolling of claim 1, the thickness of the hot-rolled steel sheet is rolled to 1.5 mm or less. Claim 3 A method for manufacturing a hot-rolled steel sheet for non-oriented electrical steel sheets according to claim 1, wherein the composition of the above components further comprises, in mass%, at least one selected from the group consisting of Nb: 0.005% or less, V: 0.02% or less, Ta: 0.002% or less, B: 0.002% or less, Ga: 0.005% or less, Pb: 0.002% or less, W: 0.05% or less, Ge: 0.05% or less, As: 0.05% or less, and Co: 0.05% or less. Claim 4 A method for manufacturing a hot-rolled steel sheet for non-oriented electrical steel sheets according to claim 2, wherein the above composition of components further contains at least one selected from the group consisting of, in mass%, Nb: 0.005% or less, V: 0.02% or less, Ta: 0.002% or less, B: 0.002% or less, Ga: 0.005% or less, Pb: 0.002% or less, W: 0.05% or less, Ge: 0.05% or less, As: 0.05% or less, and Co: 0.05% or less. Claim 5 A method for manufacturing a non-oriented electrical steel sheet comprising: a hot-rolled steel sheet manufacturing process for manufacturing a hot-rolled steel sheet according to the method for manufacturing a hot-rolled steel sheet for a non-oriented electrical steel sheet described in any one of claims 1 to 4; a hot-rolled steel sheet annealing process for performing hot-rolled steel sheet annealing on the hot-rolled steel sheet; a cold-rolling process for performing cold-rolling on the hot-rolled steel sheet to form a cold-rolled steel sheet; and a finishing annealing process for performing finishing annealing on the cold-rolled steel sheet. Claim 6 A hot-rolled steel sheet for non-oriented electrical steel obtained by a method for manufacturing a hot-rolled steel sheet for non-oriented electrical steel described in any one of claims 1 to 4, wherein the sheet thickness is 1.5 mm or less and the number density of inclusions having an equivalent diameter of 0.3 μm or more and 1.0 μm or less is 9 or more / mm² or more.

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