Manufacturing method of hot-rolled steel sheet for non-oriented electrical steel sheet and manufacturing method of non-oriented electrical steel sheet

Abstract

The purpose of the present invention is to suppress ridging, which presents a problem when handling steel containing a large amount of alloy elements such as Si and Al in a slow hot-rolling process. Provided is a method for manufacturing a hot-rolled steel sheet for a non-oriented electrical steel sheet including: a continuous casting step for producing a steel slab having a predetermined component composition and a thickness of 50-200 mm inclusive by a continuous casting method; a transportation step for transporting the steel slab to hot-rolling equipment while maintaining the surface temperature of the steel slab at 800°C or above; and a hot-rolling step for sequentially performing, in the hot-rolling equipment, rough rolling, a reheating treatment, and finishing rolling on the steel slab to produce a hot-rolled steel sheet, the hot-rolling step being carried out under conditions satisfying the following (1)-(4). (1) Outlet-side speed of the hot rolling: 100 mpm or below. (2) Draft in the final pass of the rough rolling: 45% or above. (3) Average temperate increase speed in the reheating treatment: 9°C / s or above. (4) Temperature increase in the reheating treatment: 30°C or above.

Description

[Technical field]

[0001] The present invention relates to a manufacturing method of a hot-rolled steel sheet for a non-oriented electrical steel sheet, a manufacturing method of 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 sheets are materials used in the iron cores of motors and generators. In recent years, there has been a strong demand for higher efficiency in electrical equipment in order to reduce CO2 emissions, and non-oriented electrical steel sheets, which are used as iron core materials, are required to have even lower iron loss. For this reason, efforts are being made to reduce eddy current loss by reducing the sheet thickness and increasing the content of Si, Al, and Mn, elements that increase the electrical resistance of steel sheets. However, reducing the sheet thickness and increasing the amount of alloy elements significantly increases the manufacturing cost of non-oriented electrical steel sheets, so there is also an increasing demand for cost reduction.

[0003] One example of a technology for reducing the cost of non-oriented electrical steel sheets is direct rolling. Direct rolling makes it possible to effectively utilize the thermal energy contained in the continuous cast slab, and there is no need to reheat the cooled slab during hot rolling. This allows for a significant reduction in energy costs and also leads to a reduction in CO2 emissions.

[0004] As an example of utilizing direct rolling, Patent Document 1 proposes a technology in which a thin slab having a thickness of 30 to 140 mm obtained by a continuous casting method is subsequently hot rolled to produce a hot-rolled steel sheet having a thickness of 0.7 to 4.5 mm. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-206114 A Summary of the Invention [Problem to be solved by the invention]

[0006] Energy saving by direct rolling can be realized by using equipment that integrates continuous casting and hot rolling mills, so-called thin slab casters. It is considered that the technology of Patent Document 1 can also be implemented by using a thin slab caster.

[0007] However, some thin slab casters send the continuously cast slab to the hot rolling process without cutting it, and perform continuous hot rolling to minimize the non-steady part of the hot rolling and improve the yield. In such cases, the threading speed is determined by the casting speed, so the hot rolling speed, especially the rough hot rolling speed, is significantly reduced compared to conventional processes that are not direct rolling.

[0008] When the inventors investigated such a low-speed hot rolling process, they found that recrystallization during hot-rolled sheet annealing becomes difficult, particularly in steels containing large amounts of alloying elements such as Si and Al, and that ridging (a wavy pattern on the surface) is likely to occur in the final non-oriented electrical steel sheet.

[0009] The present invention aims to solve the above problems, and specifically aims to suppress ridging that occurs in a low-speed hot rolling process when steel contains large amounts of Si and Al as alloy elements. [Means for solving the problem]

[0010] As a result of intensive research to solve the above problems, the present inventors have found that ridging can be suppressed by increasing the rolling reduction in the final pass of rough rolling and controlling the reheating conditions after rough rolling.

[0011] The present invention has been completed based on the above findings, and the gist of the present invention is as follows.

[0012] 1. In mass percent, Si: 2.0% or more and 5.0% or less, and Al: 3.0% or less; The total content of Si and Al is 3.5% or more. a continuous casting process for producing a steel slab having a thickness of 50 mm or more and 200 mm or less by a continuous casting method; A transporting step of transporting the steel slab to a hot rolling facility while maintaining the surface temperature of the steel slab at 800°C or higher; A method for producing a hot-rolled steel sheet for a non-oriented electrical steel sheet, comprising: a hot rolling step in which the steel slab is subjected to rough rolling, reheating treatment, and finish rolling in the hot rolling equipment in sequence to produce a hot-rolled steel sheet, The method for producing a hot-rolled steel sheet for a non-oriented electrical steel sheet, wherein the hot-rolling step is carried out under conditions that satisfy the following (1) to (4): (1) The speed at the delivery side of the rough rolling: 100 mpm or less (2) Reduction ratio in the final pass of the rough rolling: 45% or more (3) Average heating rate in the reheating treatment: 9°C / s or more (4) Temperature rise during the reheating process: 30°C or more

[0013] 2. The method for producing a hot-rolled steel sheet for use as a non-oriented electrical steel sheet according to 1 above, wherein in the finish rolling, the hot-rolled steel sheet is rolled to a thickness of 1.5 mm or less.

[0014] 3. The composition of the steel slab is, in mass%, 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; 3. The method for producing a hot-rolled steel sheet for use in a non-oriented electrical steel sheet according to 1 or 2 above, wherein the balance is Fe and unavoidable impurities.

[0015] 4. The composition of the components is, 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, 4. The method for producing a hot-rolled steel sheet for use in a non-oriented electrical steel sheet according to 3 above, further comprising at least one selected from the group consisting of:

[0016] 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 sheet according to any one of 1 to 4 above; A hot-rolled sheet annealing process for subjecting the hot-rolled steel sheet to hot-rolled sheet annealing; A cold rolling process in which the hot-rolled steel sheet is cold-rolled to obtain a cold-rolled steel sheet; and a finish annealing step of subjecting the cold-rolled steel sheet to finish annealing.

[0017] 6. A hot-rolled steel sheet for non-oriented electrical steel sheet obtained by the method for producing a hot-rolled steel sheet for non-oriented electrical steel sheet according to any one of 1 to 4 above, The number density of inclusions with a circle equivalent diameter of 0.3 μm to 1.0 μm is 9 pieces / mm 2 The above is the hot-rolled steel sheet for non-oriented electrical steel sheet. Effect of the Invention

[0018] According to the present invention, ridging can be effectively suppressed under conditions where the total content of Si and Al is high at 3.5% or more and the delivery speed of rough rolling is 100 mpm or less. Therefore, according to the present invention, it is possible to manufacture a non-oriented electrical steel sheet with low iron loss and suppressed ridging by using direct rolling, which is a low-energy consumption process. Therefore, the present invention is extremely effective from the viewpoint of the Sustainable Development Goals (SDGs). [Brief description of the drawings]

[0019] [Figure 1] 1 is a graph showing the correlation between the total content (mass%) of Si and Al in a slab and the arithmetic mean waviness Wa (μm) in the width direction of a non-oriented electrical steel sheet. [Diagram 2] 1 is a graph showing the correlation between the delivery speed (mpm) in the final pass of rough rolling and the arithmetic mean waviness Wa (μm) in the width direction of a non-oriented electrical steel sheet. [Diagram 3] 1 is a graph showing the correlation between the average heating rate (° C. / s) in the reheating treatment and the reduction rate (%) in the final pass of rough rolling, and the arithmetic mean waviness Wa (μm) in the width direction of the non-oriented electrical steel sheet. [Figure 4] 1 is a graph showing the correlation between the finish thickness (mm) in hot rolling and the arithmetic mean waviness Wa (μm) in the width direction of a non-oriented electrical steel sheet. [Diagram 5] 1 is a graph showing the correlation between the number density (pieces / mm2) of inclusions having an equivalent circle diameter of 0.3 μm or more and 1.0 μm or less and the arithmetic mean waviness Wa (μm) in the width direction of a non-oriented electrical steel sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The details of the present invention will be described below together with the reasons for the limitations. In this specification and drawings, the unit of content "%" refers to "mass%" unless otherwise specified. In addition, the unit of strip threading speed "mpm" refers to meter per minute.

[0021] (Experiment 1) First, a 130 mm thick slab containing 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 balance being Fe and unavoidable impurities, was melted in a vacuum melting furnace, removed from the furnace, and transported to an electric furnace so that the slab surface temperature did not become less than 800 ° C. In the electric furnace, a heat retention treatment was performed at 1100 ° C. for 30 minutes, and then the slab was removed from the electric furnace and hot-rolled to obtain a hot-rolled steel sheet.

[0022] In the hot rolling, the sheet was first reduced in thickness to 20 mm by four passes of hot rolling, which corresponds to rough rolling, and then reheated from 1000°C to 1100°C at 5°C / s using an induction heating device, and then reduced in thickness to 1.2 mm by six passes, which corresponds to finish rolling.

[0023] In the above hot rolling, the hot rolling speed was set to one of the following two speeds. (1) Low speed rolling: To simulate the low-speed hot rolling of a thin slab caster, the entry speed in the first rolling pass was 5 mpm, and the rolling speed thereafter was 130 mm ÷ (entry plate thickness) × 5 mpm. In other words, the exit speed in the final pass of rough rolling was 32.5 mpm. The finish rolling was performed at 200 mpm for all passes. (2) High-speed rolling: In order to simulate typical rough hot rolling, the rough rolling was performed at 120 mpm for all passes, and the finish rolling was performed at 200 mpm for all passes.

[0024] The obtained hot-rolled steel sheet was subjected to hot-rolled sheet annealing at 1050°C for 20 seconds, and then cold rolling to obtain a cold-rolled steel sheet with a final sheet 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. Since a ridging pattern was visually observed in a part of the obtained non-oriented electrical steel sheet, the arithmetic mean waviness Wa of the non-oriented electrical steel sheet in the width direction was measured using a contact roughness meter.

[0025] 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 the following description, the Si content in the slab is represented as [Si], the Al content in the slab as [Al], and the total content of Si and Al in the slab as [Si] + [Al].

[0026] 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 the occurrence of ridging. When the structure of the samples with ridging after hot-rolled sheet annealing was checked, the recrystallization rate was found to be low. This result shows that when a slab containing a large amount of Si and Al is hot-rolled at a low speed, recrystallization does not progress sufficiently during hot-rolled sheet annealing, and ridging occurs during the subsequent cold rolling.

[0027] Moreover, using a steel slab with [Si] + [Al] = 3.92%, the results of changing the delivery speed in the final pass of rough rolling are shown in Figure 2. When the delivery speed in the final pass of rough rolling was 100 mpm or less, ridging tended to occur in the finally obtained non-oriented electrical steel sheet.

[0028] (Experiment 2) Next, in order to suppress ridging that occurs when the delivery speed in the final pass of rough rolling is low, the inventors focused on the pass schedule of rough rolling and the heating rate of reheating after rough rolling and conducted the following experiment.

[0029] A 130 mm thick slab 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 balance being Fe and unavoidable impurities, was melted in a vacuum melting furnace, removed from the furnace, and transported to an electric furnace so that the slab surface temperature did not fall below 800 ° C. In the electric furnace, a heat retention treatment was performed at 1100 ° C. for 30 minutes, after which the slab was removed from the electric furnace and hot rolled to obtain a hot-rolled steel sheet.

[0030] In the hot rolling, the thickness was first reduced to 20 mm in four passes corresponding to rough rolling, then reheated to 1000°C to 1100°C using an induction heating device, and then reduced to 1.2 mm in six passes corresponding to finish rolling. At that time, the rolling reduction in the final pass of the rough rolling and the average heating rate in the reheating treatment were variously changed.

[0031] In order to simulate the 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 rolling speed thereafter was set to 130 mm ÷ (entry plate thickness) × 5 mpm. Finish rolling was performed at 200 mpm for all passes.

[0032] The obtained hot-rolled steel sheet was subjected to hot-rolled sheet annealing at 1040°C for 30 seconds, and then cold-rolled to obtain a cold-rolled steel sheet with a final sheet 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. The arithmetic mean waviness Wa in the width direction of the non-oriented electrical steel sheet was measured using a contact roughness meter.

[0033] The influence of the average heating rate in the reheating treatment and the reduction rate in the final pass of rough rolling on Wa is shown in Figure 3. As can be seen from Figure 3, when the reduction rate in the final pass of rough rolling is 45% or more and the average heating rate during reheating is 9°C / s or more, the occurrence of ridging is suppressed.

[0034] From the results of Experiments 1 and 2 above, it is clear that ridging can be suppressed by increasing the reduction rate in the final pass of rough rolling and by increasing the average heating rate in reheating after rough rolling.

[0035] The mechanism by which ridging is suppressed is presumed to be as follows. First, strain energy is accumulated in the material by performing large reduction in the final pass of rough rolling. Then, rapid heating is performed to suppress recovery during heating, and recrystallization is effectively promoted, randomizing the texture and fine grains. It is believed that recrystallization and randomization of the texture are promoted during finish rolling by refining the texture before finish rolling. Although it is not possible to completely complete the recrystallization of the material at the completion of hot rolling, the above effect destroys the coarse cast texture that causes ridging to a certain extent. As a result, it is believed that the texture is randomized, recrystallization during hot-rolled sheet annealing is promoted, and the formation of ridging patterns during cold rolling is suppressed.

[0036] (Experiment 3) Next, the inventors focused on the effect of the finish thickness in hot rolling on ridging, and conducted the following experiment to confirm this effect. Note that the "finish thickness" here refers to the plate thickness at the time when the finish rolling is completed in the hot rolling process, that is, the plate thickness of the obtained hot-rolled steel plate.

[0037] A 120 mm thick slab containing 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 balance being Fe and unavoidable impurities, was melted in a vacuum melting furnace, removed from the furnace, and transported to an electric furnace so that the slab surface temperature did not become less than 800 ° C. In the electric furnace, a heat retention treatment was performed at 1100 ° C. for 30 minutes, and then the slab was removed from the electric furnace and hot rolled to obtain a hot-rolled steel sheet.

[0038] In the hot rolling, the thickness was reduced to 15 mm in four passes equivalent to rough rolling, and then the plate was reheated from 990°C to 1100°C using an induction heating device, and then reduced to the target plate thickness in six passes equivalent to finish rolling. Here, in order to simulate the low-speed hot rolling of a thin slab caster, the entry speed of the first pass of rough rolling was 5 mpm, and the rolling speed thereafter was 130 mm ÷ (entry plate thickness) × 5 mpm. The finish hot rolling was performed at 200 mpm for all passes.

[0039] The obtained hot-rolled steel sheet was subjected to hot-rolled sheet annealing at 1010°C for 30 seconds, and then cold-rolled to obtain a cold-rolled steel sheet with a final sheet 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. The arithmetic mean waviness Wa in the width direction of the non-oriented electrical steel sheet was measured using a contact roughness meter.

[0040] The effect of the finish thickness in hot rolling on Wa is shown in Fig. 4. From the results shown in Fig. 4, it can be seen that ridging is further improved when the plate thickness of the hot rolled steel plate is rolled to 1.5 mm or less in finish rolling.

[0041] (Experiment 4) Next, the inventors paid attention to the effect of inclusions on ridging, and carried out the following experiment to confirm this effect.

[0042] A 120mm thick slab containing 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 balance being Fe and unavoidable impurities, was melted in a vacuum melting furnace. The amount of inclusions that floated and the precipitation density were changed by adjusting the time from adding the alloying elements to tapping and the thickness of the mold, and the size and number density of the inclusions remaining in the steel were changed.

[0043] The red-hot slab was removed from the furnace and then transported to an electric furnace so that the surface temperature of the slab did not fall below 800° C. In the electric furnace, the slab was subjected to a heat retention treatment at 1100° C. for 30 minutes, after which the slab was removed from the electric furnace and hot-rolled to obtain a hot-rolled steel sheet.

[0044] In the 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 then reduced to 1.2 mm in 6 passes equivalent to finish rolling. Here, in order to simulate the low-speed hot rolling of a thin slab caster, the entry speed in the first rolling pass was 5 mpm, and the rolling speed thereafter was 130 mpm ÷ (entry plate thickness) × 5 mpm.

[0045] A part of the obtained hot-rolled steel sheet was cut and embedded in a carbon mold to prepare a sample. The surface of the sample perpendicular to the rolling direction was observed using a scanning electron microscope (SEM) to investigate the size and number of inclusions.

[0046] The hot-rolled steel sheet was then annealed at 1040°C for 30 seconds, and then cold-rolled to obtain a cold-rolled steel sheet with a final thickness of 0.25 mm. The cold-rolled steel sheet was then finish-annealed at 980°C for 15 seconds to obtain a non-oriented electrical steel sheet. The arithmetic mean waviness (Wa) of the non-oriented electrical steel sheet in the width direction was measured using a contact roughness meter.

[0047] The inventors of the present invention have investigated the relationship between inclusions and ridging and found that the occurrence of ridging is suppressed when there are many inclusions of relatively small size. The relationship between the number density of inclusions having a circle equivalent diameter of 0.3 μm to 1.0 μm in a hot-rolled steel sheet and Wa is shown in Figure 5. When the number density of the inclusions is 9 pieces / mm 2 In the above cases, there was a tendency for the ridging to be further improved.

[0048] The results of Experiments 3 and 4 above show that ridging can be further suppressed by reducing the finish thickness of hot rolling and by containing inclusions of relatively small size.

[0049] It is believed that reducing the finishing thickness of hot rolling introduces shear strain from hot rolling to the center of the plate thickness, which has the effect of further promoting recrystallization. In addition, it is believed that relatively small inclusions become nucleation sites when the molten steel solidifies, contributing to the refinement of the slab structure and the randomization of the texture. While most of these small inclusions are oxides, the larger inclusions are mainly AlN and MnS. Therefore, it is presumed that the large inclusions do not precipitate when the molten steel solidifies, and do not contribute to the improvement of ridging.

[0050] The present invention is based on the above findings. Hereinafter, the embodiment for carrying out the present invention will be specifically described. However, the present invention is not limited to this embodiment.

[0051] [Component composition] In the present invention, the reasons for limiting the composition of the steel slab will be explained.

[0052] Si: 2.0~5.0% Silicon is an element that has the effect of increasing the resistivity of a steel sheet and reducing iron loss. To obtain this effect, the silicon content is set to 2.0% or more, preferably 2.5% or more. On the other hand, if the silicon content exceeds 5.0%, industrial production by cold rolling becomes difficult, so the silicon content is set to 5.0% or less, preferably 4.0% or less.

[0053] Al: 3.0% or less Al is an element that has the effect of increasing the resistivity of a steel sheet and reducing iron loss. However, if the Al content exceeds 3.0%, cracks are likely to occur during continuous casting. Therefore, the Al content is set to 3.0% or less, preferably 1.5% or less. On the other hand, although there is no particular lower limit for the Al content, since an excessive reduction leads to an increase in manufacturing costs, the Al content is preferably set to 0.00001% or more. From the viewpoint of magnetic properties, it is preferably set to 0.3% or more. However, when importance is placed on magnetic flux density, it is preferable that the Al content be set to 0.002% or less.

[0054] Total content of Si and Al: 3.5% or more From the viewpoint of increasing the resistivity of the steel sheet and reducing iron loss, it is desirable to increase the Si content and Al content, but 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 and ridging is likely to occur. However, in the present invention, by performing hot rolling under specified conditions, ridging can be suppressed even when 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.

[0055] In one embodiment of the present invention, the steel slab comprises: Si: 2.0% or more and 5.0% or less, and Al: 3.0% or less; The balance is Fe and unavoidable impurities. The composition may have a total content of Si and Al of 3.5% or more.

[0056] In another embodiment of the present invention, the composition of the steel slab may optionally contain at least one of the following elements in addition to Si and Al. In this case, the balance of the composition is Fe and inevitable impurities. Note that all of the following elements are optional elements, and therefore the lower limit of their content may be 0%.

[0057] C: 0.005% or less When C is added, the C content is set to 0.005% or less from the viewpoint of preventing magnetic aging. On the other hand, if the C content is reduced too much, the magnetic flux density decreases. Therefore, from the viewpoint of preventing the decrease in magnetic flux density, it is preferable that the C content is set to 0.001% or more.

[0058] Mn:3.0% or less Mn is an element that has the effect of increasing the resistivity of the steel sheet and further reducing iron loss. However, if the Mn content exceeds 3.0%, carbides are precipitated, and iron loss increases. Therefore, when Mn is added, the Mn content is set to 3.0% or less, preferably 2.0% or less. On the other hand, from the viewpoint of avoiding hot brittleness during hot rolling, the Mn content is preferably set to 0.05% or more. From the viewpoint of magnetic properties, the Mn content is more preferably set to 0.3% or more.

[0059] Cr:3.0% or less Cr is an element that has the effect of increasing the resistivity of steel sheet and reducing iron loss. However, if the Cr content exceeds 3.0%, carbides are precipitated, and iron loss increases. Therefore, when Cr is added, the Cr content is set to 3.0% or less. From the viewpoint of magnetic properties, the Cr content is preferably set to 1.5% or less. On the other hand, although there is no particular lower limit for the Cr content, from the viewpoint of enhancing the effect of adding Cr, it is preferably set to 0.005% or more.

[0060] Ni: 2.0% or less Ni is an element that has the effect of improving the magnetic flux density of a steel sheet. However, Ni is an expensive element, and if the Ni content exceeds 2.0%, the cost becomes very high. Therefore, when Ni is added, the Ni content is set to 2.0% or less. From the viewpoint of the balance between magnetic properties and cost, it is preferable that the Ni content is set to 0.5% or less. On the other hand, although there is no particular lower limit for the Ni content, it is preferable that it is set to 0.005% or more from the viewpoint of enhancing the effect of adding Ni.

[0061] Cu:2.0% or less Cu is an element that has the effect of improving the magnetic flux density of a steel sheet. However, if the Cu content exceeds 2.0%, it causes hot brittleness and is the cause of surface defects. Therefore, when Cu is added, the Cu content is set to 2.0% or less. From the viewpoint of the balance between magnetic properties and cost, it is preferable that the Cu content is set to 0.5% or less. On the other hand, although there is no particular limit to the lower limit of the Cu content, it is preferable that it is set to 0.005% or more from the viewpoint of enhancing the effect of adding Cu.

[0062] P:0.2% or less P is an element used to adjust the strength of steel sheets. However, if the P content exceeds 0.2%, the steel becomes brittle and cold rolling becomes difficult. Therefore, when P is added, the P content is set to 0.2% or less. From the viewpoint of the balance between high strength and brittleness, it is preferable that the P content be 0.1% or less. On the other hand, although there is no particular limit to the lower limit of the P content, it is preferable that it be 0.005% or more from the viewpoint of enhancing the effect of adding P.

[0063] S: 0.0050% or less S is an element that forms sulfides and increases iron loss. Therefore, when S is contained, 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 viewpoint of magnetic properties, the lower the S content, the better, so the lower limit of the S content may be 0%. However, excessive reduction leads to an increase in manufacturing costs, so from the viewpoint of cost, it is preferable to set the S content to 0.0001% or more.

[0064] N: 0.0050% or less N is an element that forms nitrides and increases iron loss. Therefore, when N is contained, 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 viewpoint of magnetic properties, the lower the N content, the better, so the lower limit of the N content may be 0%. However, excessive reduction leads to an increase in manufacturing costs, so from the viewpoint of cost, it is preferable to set the N content to 0.0001% or more.

[0065] O: 0.0050% or less O is an element that forms oxides and increases iron loss. Therefore, when O is contained, 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 viewpoint of magnetic properties, the lower the O content, the better, so the lower limit of the O content may be 0%. However, excessive reduction leads to an increase in manufacturing costs, so from the viewpoint of cost, it is preferable to set the O content to 0.0001% or more.

[0066] Ti:0.0040% or less Ti is an element that forms carbonitrides and increases iron loss. Therefore, when Ti is contained, 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 viewpoint of magnetic properties, the lower the Ti content, the better, so the lower limit of the Ti content may be 0%. However, excessive reduction leads to an increase in manufacturing costs, so from the viewpoint of cost, it is preferable to set the Ti content to 0.0001% or more.

[0067] Sn: 0.20% or less Sn is an element that has the effect of suppressing nitridation and oxidation of the surface layer and reducing iron loss. However, even if it is added in an amount exceeding 0.20%, the effect is saturated. Therefore, when Sn is added, the Sn content is set to 0.20% or less, preferably 0.10% or less. On the other hand, from the viewpoint of enhancing the effect of adding Sn, the Sn content is preferably set to 0.005% or more.

[0068] Sb: 0.20% or less Sb is an element that has the effect of suppressing nitridation and oxidation of the surface layer and reducing iron loss. However, even if added in an amount exceeding 0.20%, the effect is saturated. Therefore, when Sb is added, the Sb content is set to 0.20% or less, preferably 0.10% or less. On the other hand, from the viewpoint of enhancing the effect of adding Sb, the Sb content is preferably set to 0.005% or more.

[0069] Mo: 0.10% or less Mo is an element that has the effect of suppressing nitridation and oxidation of the surface layer and reducing iron loss. However, if added in an amount exceeding 0.10%, iron loss increases. Therefore, when Mo is added, the Mo content is set to 0.10% or less, preferably 0.05% or less. On the other hand, from the viewpoint of enhancing the effect of adding Mo, it is preferable that the Mo content is set to 0.001% or more.

[0070] Ca: 0.01% or less Ca is an element that suppresses the generation of fine oxides and sulfides and reduces iron loss. However, even if it is added in an amount exceeding 0.01%, the effect is saturated. Therefore, when Ca is added, the Ca content is set to 0.01% or less, preferably 0.006% or less. On the other hand, from the viewpoint of enhancing the effect of adding Ca, it is preferable that the Ca content is set to 0.001% or more.

[0071] REM: 0.05% or less REM (rare earth metal) is a component that suppresses the generation of fine sulfides and reduces iron loss. However, even if added in an amount exceeding 0.05%, the effect is saturated. Therefore, when REM is added, the REM content is set to 0.05% or less, preferably 0.03% or less. On the other hand, from the viewpoint of increasing the effect of adding REM, the REM content is preferably set to 0.005% or more.

[0072] Mg: 0.01% or less Mg is an element that suppresses the generation of fine sulfides and reduces iron loss. However, even if added in an amount exceeding 0.01%, the effect is saturated. Therefore, when Mg is added, the Mg content is set to 0.10% or less, preferably 0.006% or less. On the other hand, from the viewpoint of enhancing the effect of adding Mg, the Mg content is preferably set to 0.001% or more.

[0073] Zn: 0.01% or less Zn is an element that suppresses the generation of fine oxides and sulfides and reduces iron loss. However, even if added in an amount exceeding 0.01%, the effect is saturated. Therefore, when Zn is added, the Zn content is set to 0.01% or less, preferably 0.005% or less. On the other hand, from the viewpoint of enhancing the effect of adding Zn, the Zn content is preferably set to 0.001% or more.

[0074] The composition of the steel slab may further contain at least one of the following elements. Note that all of the following elements are optional elements, and therefore the lower limit of their content may be 0%.

[0075] Nb: 0.005% or less Nb is an element that forms fine carbonitrides and increases iron loss. In particular, when the Nb content exceeds 0.005%, the adverse effects become significant. Therefore, when Nb is added, the Nb content is set to 0.005% or less, preferably 0.002% or less. On the other hand, from the viewpoint of magnetic properties, the lower the Nb content, the better, so the lower limit of the Nb content may be 0%. However, excessive reduction leads to an increase in manufacturing costs, so from the viewpoint of cost, it is preferable to set the Nb content to 0.00001% or more.

[0076] V:0.02% or less V is an element that forms fine carbonitrides and increases iron loss. In particular, when the V content exceeds 0.02%, the adverse effects become significant. Therefore, when V is contained, the V content is set to 0.02% or less, preferably 0.005% or less. On the other hand, from the viewpoint of magnetic properties, the lower the V content, the better, so the lower limit of the V content may be 0%. However, excessive reduction leads to an increase in manufacturing costs, so from the viewpoint of cost, it is preferable to set the V content to 0.0001% or more.

[0077] Ta: 0.002% or less Ta is an element that forms fine carbonitrides and increases iron loss. In particular, when the Ta content exceeds 0.002%, the adverse effects become significant. Therefore, when Ta is contained, the Ta content is set to 0.002% or less, preferably 0.001% or less. On the other hand, from the viewpoint of magnetic properties, the lower the Ta content, the better, so the lower limit of the Ta content may be 0%. However, excessive reduction leads to an increase in manufacturing costs, so from the viewpoint of cost, it is preferable to set the Ta content to 0.00001% or more.

[0078] B: 0.002% or less B is an element that forms fine nitrides and increases iron loss. In particular, if the B content exceeds 0.002%, the adverse effects become significant. Therefore, when B is contained, the B content is set to 0.002% or less, preferably 0.001% or less. On the other hand, from the viewpoint of magnetic properties, the lower the B content, the better, so the lower limit of the B content may be 0%. However, excessive reduction leads to an increase in manufacturing costs, so from the viewpoint of cost, it is preferable to set the B content to 0.00001% or more.

[0079] Ga: 0.005% or less Ga is an element that forms fine nitrides and increases iron loss. In particular, when the Ga content exceeds 0.005%, the adverse effects become significant. Therefore, when Ga is contained, the Ga content is set to 0.005% or less, preferably 0.002% or less. On the other hand, from the viewpoint of magnetic properties, the lower the Ga content, the better, so the lower limit of the Ga content may be 0%. However, excessive reduction leads to an increase in manufacturing costs, so from the viewpoint of cost, it is preferable to set the Ga content to 0.00001% or more.

[0080] Pb: 0.002% or less Pb is an element that forms fine Pb particles and increases iron loss. In particular, when the Pb content exceeds 0.002%, the adverse effects become significant. Therefore, when Pb is contained, the Pb content is set to 0.002% or less, preferably 0.001% or less. On the other hand, from the viewpoint of magnetic properties, the lower the Pb content, the better, so the lower limit of the Pb content may be 0%. However, excessive reduction leads to an increase in manufacturing costs, so from the viewpoint of cost, it is preferable to set the Pb content to 0.00001% or more.

[0081] W: 0.05% or less W is an element that forms fine carbides and increases iron loss. In particular, when the W content exceeds 0.05%, the adverse effects become significant. Therefore, when W is contained, the W content is set to 0.05% or less, preferably 0.02% or less. On the other hand, from the viewpoint of magnetic properties, the lower the W content, the better, so the lower limit of the W content may be 0%. However, excessive reduction leads to an increase in manufacturing costs, so from the viewpoint of cost, it is preferable to set the W content to 0.00001% or more.

[0082] Ge: 0.05% or less Ge is an element that has the effect of improving magnetic flux density and reducing iron loss. However, when the Ge content exceeds 0.05%, the effect of adding the Ge is saturated. Therefore, when Ge is added, the Ge content is set to 0.05% or less, preferably 0.01% or less. On the other hand, the lower limit of the Ge content is not particularly limited, but from the viewpoint of enhancing the effect of adding Ge, it is preferably set to 0.0001% or more.

[0083] As: 0.05% or less As is an element that has the effect of improving magnetic flux density and reducing iron loss. However, when the As content exceeds 0.05%, the effect of adding As is saturated. Therefore, when As is added, the As content is set to 0.05% or less, preferably 0.01% or less. On the other hand, although there is no particular limit to the lower limit of the As content, it is preferable to set it to 0.0001% or more from the viewpoint of enhancing the effect of adding As.

[0084] Co:0.05% or less Co is an element that has the effect of improving magnetic flux density and reducing iron loss. However, when the Co content exceeds 0.05%, the effect of adding Co is saturated. Therefore, when Co is added, the Co content is set to 0.05% or less, preferably 0.01% or less. On the other hand, the lower limit of the Co content is not particularly limited, but from the viewpoint of enhancing the effect of adding Co, it is preferable to set it to 0.0001% or more.

[0085] [Manufacturing conditions for hot-rolled steel sheets for non-oriented electrical steel sheets] Next, the manufacturing conditions for manufacturing a hot-rolled steel sheet for non-oriented electrical steel sheet using a steel slab having the above-mentioned composition will be described.

[0086] A method for producing a hot-rolled steel sheet for a non-oriented electrical steel sheet in one embodiment of the present invention includes a continuous casting step of producing a steel slab by a continuous casting method, a transport step of transporting 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 step of subjecting the steel slab to rough rolling, reheating treatment, and finish rolling in the hot rolling facility in that order to produce a hot-rolled steel sheet. Each step will be described below.

[0087] ·Continuous casting process First, a steel slab having the above-mentioned composition is produced by a continuous casting method (continuous casting process). The method for performing continuous casting is not particularly limited, and can be performed according to a conventional method. The method for adjusting the composition of the molten steel used in continuous casting is also not particularly limited, and can be performed by any method. For example, a converter, an electric furnace, a vacuum degassing device, and other devices and methods can be used to adjust the composition of the molten steel.

[0088] Steel slab thickness: 50~200mm In the above continuous casting process, a steel slab having a thickness of 50 mm to 200 mm is produced. If the thickness of the steel slab is less than 50 mm, the reduction ratio in the hot rolling process becomes too low, and recrystallization cannot be sufficiently promoted. On the other hand, if the thickness of the steel slab is more than 200 mm, the equipment cost becomes high.

[0089] ·Transportation process Next, the steel slab produced in the continuous casting process is transported to a hot rolling facility (transportation process). The present invention is directed to so-called direct rolling, and in this transport process, the steel slab is transported to the hot rolling facility while maintaining its surface temperature at 800°C or higher. In other words, in the present invention, the steel slab is transported so that its surface temperature does not become lower than 800°C between the time it is produced in the continuous casting process and the time it arrives at the hot rolling facility.

[0090] In the present invention, the steel slab obtained in the continuous casting process is subjected to the hot rolling process while being kept at a high temperature of 800°C or more. Therefore, there is no need to reheat the steel slab before hot rolling, and energy costs can be significantly reduced. In such direct rolling, the occurrence of ridging is a problem, but in the present invention, the occurrence of ridging can be suppressed by controlling the hot rolling conditions, as described later.

[0091] Before hot rolling, the steel slab may be subjected to a heat-holding treatment in which the steel slab is held at a temperature of 1000°C or more and 1300°C or less for 60 seconds or more. By performing the heat-holding treatment, MnS and AlN can be coarsened, and iron loss can be further improved. The heating method in the heat-holding treatment is not particularly limited, and any method such as induction heating, a gas furnace, or an electric furnace can be used.

[0092] Hot rolling Next, in the hot rolling equipment, the steel slab is subjected to rough rolling, reheating, and finish rolling in this order to obtain a hot-rolled steel sheet (hot rolling step). In the present invention, it is important to carry out the hot rolling step under conditions that satisfy the following (1) to (4). (1) The speed at the delivery side of the rough rolling: 100 mpm or less (2) Reduction ratio in the final pass of the rough rolling: 45% or more (3) Average heating rate in the reheating treatment: 9°C / s or more (4) Temperature rise during the reheating process: 30°C or more

[0093] Rough rolling exit speed: 100mpm or less As described above, direct rolling is excellent in terms of energy saving, but the hot rolling speed is reduced because the sheet threading speed is limited by the casting speed. As shown in the above experiment 1, when the delivery speed in the final pass of rough rolling is 100 mpm or less, the occurrence of ridging becomes significant. However, in the present invention, by controlling the reduction rate and the reheating treatment conditions in the final pass of rough rolling, ridging can be suppressed even when the delivery speed of rough rolling is 100 mpm or less. Therefore, in the present invention, the delivery speed of rough rolling is set to 100 mpm or less, preferably 70 mpm or less. As a result, in the present invention, it is possible to achieve both reduction in energy consumption and suppression of ridging.

[0094] Such an exit speed is realized, for example, when a cast steel slab is continuously hot-rolled without being cut. This is because the hot-rolling speed is determined by the casting speed. In contrast, in a conventional process in which a steel slab is cut and then hot-rolled, the rough hot-rolling speed is generally set to be more than 100 mpm from the viewpoint of manufacturing efficiency.

[0095] On the other hand, although there is no particular lower limit to the outlet speed, if the outlet speed is too slow, the productivity decreases, so the outlet speed is preferably 10 mpm or more, and more preferably 15 mpm or more.

[0096] Reduction rate in the final pass of rough rolling: 45% or more Setting the reduction rate in the final pass of rough rolling to 45% or more is effective in suppressing ridging. If the reduction rate is less than 45%, sufficient strain 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. On the other hand, the upper limit of the reduction rate is not particularly limited, and may be, for example, 80% or less, 75% or less, or 70% or less.

[0097] The delivery temperature of the rough rolling is not particularly limited, but is preferably 850°C to 1000°C, and more preferably 900°C to 950°C.

[0098] After the rough rolling, a reheating treatment is performed prior to the finish hot rolling. By performing the reheating treatment, the temperature of the material can be increased, and the deformation resistance during the finish rolling can be reduced. The heating method in the reheating treatment is not particularly limited, and any method such as induction heating, gas furnace, or electric furnace can be used.

[0099] Average heating rate during reheating: 9℃ / s or more In order to suppress ridging, the average heating rate in the reheating treatment is set to 9 ° C. / s or more, preferably 12 ° C. / s or more. If the average heating rate is less than 9 ° C. / s, the strain accumulated in the material during rough rolling is restored during heating, so that recrystallization is not sufficiently promoted and ridging cannot be significantly suppressed. On the other hand, the upper limit of the average heating rate is not particularly limited, but if the average heating rate is excessively increased, a high-output heating facility is required, which increases the facility cost. Therefore, from the viewpoint of facility cost, it is preferably set to 100 ° C. / s or less, more preferably set to 50 ° C. / s or less, and even more preferably set to 20 ° C. / s or less.

[0100] Temperature rise during reheating: 30℃ or more If the temperature rise due to reheating is less than 30°C, recrystallization is not sufficiently promoted and ridging cannot be suppressed. Therefore, in the reheating treatment, the temperature is raised by 30°C or more, preferably 50°C or more. There is no particular upper limit to the temperature rise, but if the temperature rise is more than 200°C, the increase in production costs becomes significant. Therefore, from the viewpoint of cost, it is preferable to set the temperature rise to 200°C or less.

[0101] The heating temperature (ultimate temperature) in the reheating treatment is not particularly limited, but is preferably set to 1000 to 1200° C. from the viewpoint of further suppressing ridging.

[0102] After the reheating treatment, the steel sheet is subjected to finish rolling. The conditions for the finish rolling are not particularly limited, and the finish rolling can be performed according to a conventional method.

[0103] The finishing temperature in the hot rolling is not particularly limited, but from the viewpoint of stabilizing the shape and suppressing oxidation, the finishing temperature is preferably 900° C. or less. On the other hand, the lower limit of the finishing temperature is not particularly limited, but it is preferably 600° C. or more.

[0104] Finish thickness: 1.5mm or less In addition, in the above finish rolling, it is preferable to perform rolling so that the thickness (finishing thickness) of the finally obtained hot-rolled steel sheet is 1.5 mm or less. By setting the finishing thickness to 1.5 mm or less, sufficient shear strain is introduced to the center of the sheet thickness during hot rolling, and recrystallization is further promoted, so that ridging can be further suppressed. It is more preferable that the finishing thickness is 1.3 mm or less. On the other hand, although there is no particular limit to the lower limit of the finishing thickness, if the finishing thickness is excessively thin, the hot-rolled coil becomes too long, and the cost of passing the hot-rolled sheet through the annealing and pickling lines increases. Therefore, it is preferable that the finishing thickness is 0.4 mm or more.

[0105] The above procedure can produce a hot-rolled steel sheet for non-oriented electrical steel sheet. After the hot rolling process, it is also preferable to wind the obtained hot-rolled steel sheet into a coil. In this case, the coiling temperature is not particularly limited, but from the viewpoint of stabilizing the shape and suppressing oxidation, the coiling temperature is preferably 700°C or less. On the other hand, the lower limit of the coiling temperature is not particularly limited, but it is preferably 400°C or more.

[0106] Inclusion density: 9 pieces / mm 2 End In the above hot-rolled steel sheet, the number density of inclusions having a circle equivalent diameter of 0.3 μm or more and 1.0 μm or less is set to 9 pieces / mm 2 By setting the density to the above value, ridging can be further suppressed. 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 with a SEM. In the measurement, the circle equivalent diameter (diameter) is calculated from the area of ​​the observed inclusions. The area of ​​the observation field is 10 mm 2 It is desirable to have more than this.

[0107] Inclusions with a relatively small equivalent circle diameter of 0.3 μm to 1.0 μm are considered to be nucleation sites when molten steel solidifies, and contribute to the refinement of the slab structure and the randomization of the texture. Inclusions with an equivalent circle diameter of more than 1.0 μm do not have the effect of suppressing ridging. Inclusions with an equivalent circle diameter of less than 0.3 μm are excluded because they are difficult to observe and quantify using SEM. In general, inclusions with an equivalent circle diameter of less than 0.3 μm are considered to strongly suppress grain boundary migration, so it is desirable to reduce them as much as possible from the perspective of reducing iron loss.

[0108] The density is 12 pieces / mm 2 On the other hand, the upper limit of the number density is not particularly limited, but it is preferably 1000 pieces / mm from the viewpoint of suppressing adverse effects on iron loss. 2 It is preferable to set the number of pieces per mm or less to 600 pieces / mm 2 It is more preferable to set it as follows:

[0109] [Manufacturing conditions for non-oriented electrical steel sheets] A method for producing a non-oriented electrical steel sheet in one embodiment of the present invention includes a hot-rolled steel sheet production process for producing a hot-rolled steel sheet by the above-mentioned production method, a hot-rolled sheet annealing process for subjecting the hot-rolled steel sheet to hot-rolled sheet annealing, a cold rolling process for cold-rolling the hot-rolled steel sheet to obtain a cold-rolled steel sheet, and a finish annealing process for subjecting the cold-rolled steel sheet to finish annealing.

[0110] The steps of hot-rolled sheet annealing, cold rolling, and finish annealing are not particularly limited and can be carried out according to a conventional method.

[0111] The soaking temperature in the hot-rolled sheet annealing is not particularly limited, but is preferably 900 to 1100°C. Similarly, the soaking time is not particularly limited, but is preferably 1 to 300 seconds. The atmosphere in the hot-rolled sheet annealing is not particularly specified, and the annealing can be performed in any atmosphere. As the 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.

[0112] The cold rolling can be performed using any rolling mill without any particular limitations. As the rolling mill, either a tandem rolling mill or a reverse rolling mill can be used. The sheet thickness at the entry side in the cold rolling is preferably 0.5 to 3 mm. Also, the sheet thickness at the exit side is preferably 0.1 to 0.5 mm. From the viewpoint of improving magnetic properties and preventing breakage, warm rolling may be applied. For example, it is advantageous to set the material temperature during rolling to 100 to 300°C or less.

[0113] The soaking temperature in the final annealing is not particularly limited, but is preferably 800 to 1100°C. Similarly, the soaking time is not particularly limited, but is preferably 1 to 300 seconds. The final annealing is preferably performed in a non-oxidizing atmosphere from the viewpoint of suppressing oxidation of the material. As the non-oxidizing atmosphere, for example, an atmosphere consisting of at least one selected from the group consisting of H2, N2, and Ar is preferably used. In addition, the dew point of the atmosphere is preferably controlled to be -30°C or less.

[0114] It is also preferable to carry out pickling after the hot-rolled sheet annealing and before the cold rolling. It is also preferable to form an insulating coating on the surface of the obtained non-oriented electrical steel sheet after the finish annealing. The pickling and the formation of the insulating coating are not particularly limited and can be carried out according to a conventional method. EXAMPLES

[0115] Example 1 A 150 mm thick steel slab 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 balance being Fe and unavoidable impurities, was produced by continuous casting. In producing the steel slab, the number and size of inclusions were adjusted by adjusting the time from adding a deoxidizing element to the molten steel until casting and the cooling rate of the slab immediately after solidification.

[0116] The steel slab was then transported to a hot rolling facility. In the transport, a tunnel-type gas furnace was used, and heat retention treatment was performed under the conditions shown in Table 1. The surface temperature of the steel slab immediately before being introduced into the gas furnace was 980°C, and the line speed was 4 mpm. In some examples, the 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 transported to the hot rolling facility.

[0117] Next, in the hot rolling equipment, the steel slab was subjected to rough rolling, reheating, and finish rolling in sequence to obtain a hot-rolled steel sheet. Specifically, first, the thickness was reduced to the delivery thickness shown in Table 1 by four passes of rough rolling. The delivery speed of the rough rolling and the reduction ratio in the final pass were as shown in Table 1. Next, the steel slab was reheated to 1120°C using an induction heating device. The average heating rate and temperature rise in the reheating were as shown in Table 1. Next, five passes of finish rolling were performed to reduce the thickness to the finish thickness shown in Table 1. The obtained hot-rolled steel sheet was then wound into a coil.

[0118] From the above continuous casting to the completion of coiling after hot rolling, the material was not cut and was continuously threaded. In all conditions, the cooling conditions were adjusted so that the hot rolling finishing temperature was 900°C or less and the coiling temperature was 700°C or less.

[0119] (Inclusion number density) The number density of inclusions having a circle-equivalent diameter of 0.3 μm or more and 1.0 μm or less in the obtained hot-rolled steel sheet was measured. Specifically, the hot-rolled steel sheet was first cut to obtain a test piece. The test piece was then embedded in a carbon mold, and a surface perpendicular to the rolling direction was observed with an SEM to investigate the size and number of inclusions. The circle-equivalent diameter was calculated from the area of ​​each observed inclusion, and the number density of inclusions having a circle-equivalent diameter of 0.3 μm or more and 1.0 μm or less was obtained. The measurement results were as shown in Table 1.

[0120] Next, a non-oriented electrical steel sheet was manufactured using the above-mentioned hot-rolled steel sheet. Specifically, the hot-rolled steel sheet was first subjected to hot-rolled sheet annealing at 1010°C for 20 seconds to obtain a hot-rolled annealed sheet. The hot-rolled annealed sheet was then cold-rolled to obtain a cold-rolled steel sheet with a final sheet thickness of 0.20 mm. The cold-rolled steel sheet was then subjected to finish annealing at 1000°C for 20 seconds to obtain a non-oriented electrical steel sheet (finish annealed sheet).

[0121] In order to evaluate the occurrence of ridging, the arithmetic mean waviness (Wa) in the width direction of the non-oriented electrical steel sheet was measured using a contact roughness meter. In addition, in order to evaluate the magnetic properties, the iron loss (W) at a magnetic flux density of 1.0 T and a frequency of 400 Hz was measured using an Epstein test. 10 / 400 (W / kg) was measured. The measurement results are shown in Table 1.

[0122] As can be seen from the results shown in Table 1, in the examples that satisfy the conditions of the present invention, the iron loss was good, Wa was low at 1.0 μm or less, and ridging was suppressed. 10 / 400 When (W / kg) is 28 × final plate thickness (mm) + 5.5 or less, the iron loss is considered to be good.

[0123] [Table 1]

[0124] Example 2 Steel slabs having the compositions shown in Tables 2 to 4 were produced by a continuous casting method. In producing the steel slabs, the number and size of inclusions were adjusted by adjusting the time from adding a deoxidizing element to molten steel until casting and the cooling rate of the slab immediately after solidification.

[0125] The steel slab was then transported to a hot rolling facility. In the transport, a tunnel-type electric furnace was used, and a heat retention treatment was performed at 1100°C for 15 minutes. The surface temperature of the steel slab immediately before being introduced into the electric furnace was 1050°C, and the line speed was 3 mpm. In all examples, the surface temperature of the steel slab was maintained at 800°C or higher until it was transported to the hot rolling facility.

[0126] Next, in the hot rolling equipment, the steel slab was subjected to rough rolling, reheating treatment, and finish rolling in sequence to obtain a hot-rolled steel sheet. Specifically, the steel slab was first reduced in thickness to 10 mm by four passes of rough rolling. The rolling reduction in the final pass of the rough rolling was 58%. Then, a reheating treatment was performed using an induction heating device. In the reheating treatment, the average heating rate in the temperature range from 1010°C to 1080°C was 14°C / s. Next, six passes of finish rolling were performed to reduce the thickness to a finish thickness of 1.2 mm. The obtained hot-rolled steel sheet was then wound into a coil.

[0127] From the above continuous casting to the completion of coiling after hot rolling, the material was not cut and was continuously threaded. In all conditions, the cooling conditions were adjusted so that the hot rolling finishing temperature was 900°C or less and the coiling temperature was 700°C or less.

[0128] The number density of inclusions having an equivalent circle 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.

[0129] Next, a non-oriented electrical steel sheet was manufactured using the above-mentioned hot-rolled sheet annealing. Specifically, the 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. The hot-rolled annealed sheet was then cold-rolled to obtain a cold-rolled steel sheet with a final sheet thickness of 0.25 mm. The cold-rolled steel sheet was then subjected to finish annealing at 980°C for 10 seconds to obtain a non-oriented electrical steel sheet (finish annealed sheet).

[0130] The arithmetic mean waviness Wa and core 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.

[0131] As can be seen from the results shown in Tables 2 to 4, in the examples that satisfy the conditions of the present invention, the iron loss was good, Wa was low at 1.0 μm or less, and ridging was suppressed. 10 / 400 When the iron loss coefficient (W / kg) was 28 × final sheet thickness (mm) + 5.5 or less, the iron loss was determined to be good. In addition, since the Si content of Comparative Example No. 58 was too high, it broke during the cold rolling process, and a non-oriented electrical steel sheet could not be obtained. In addition, since the Al content of Comparative Example No. 59 was too high, breakout occurred during continuous casting, and a non-oriented electrical steel sheet could not be obtained.

[0132] [Table 2]

[0133] [Table 3]

[0134] [Table 4]

Claims

1. In mass percent, Si: 2.0% or more and 5.0% or less, and Al: 3.0% or less; The total content of Si and Al is 3.5% or more, and, 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; The balance is Fe and unavoidable impurities, A continuous casting process for producing a steel slab having a thickness of 50 mm or more and 200 mm or less by a continuous casting method; A transporting step of transporting the steel slab to a hot rolling facility while maintaining the surface temperature of the steel slab at 800°C or higher; A method for producing a hot-rolled steel sheet for a non-oriented electrical steel sheet, comprising: a hot rolling step in which the steel slab is subjected to rough rolling, reheating treatment, and finish rolling in the hot rolling equipment in sequence to produce a hot-rolled steel sheet, The method for producing a hot-rolled steel sheet for a non-oriented electrical steel sheet, wherein the hot-rolling step is carried out under conditions that satisfy the following (1) to (4). (1) The delivery speed of the rough rolling: 100 mpm or less (2) Reduction ratio in the final pass of the rough rolling: 45% or more (3) Average heating rate in the reheating treatment: 9° C. / s or more (4) Temperature rise in the reheating treatment: 30° C. or more

2. The method for producing a hot-rolled steel sheet for a non-oriented electrical steel sheet according to claim 1, wherein the hot-rolled steel sheet is rolled to a thickness of 1.5 mm or less in the finish rolling.

3. The composition of the components is, 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, The method for producing a hot-rolled steel sheet for a non-oriented electrical steel sheet according to claim 1, further comprising at least one selected from the group consisting of:

4. The composition of the components is, 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, The method for producing a hot-rolled steel sheet for a non-oriented electrical steel sheet according to claim 2, further comprising at least one selected from the group consisting of:

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 sheet according to any one of claims 1 to 4; A hot-rolled sheet annealing process for subjecting the hot-rolled steel sheet to hot-rolled sheet annealing; A cold rolling process in which the hot-rolled steel sheet is cold-rolled to obtain a cold-rolled steel sheet; and a finish annealing step of subjecting the cold-rolled steel sheet to finish annealing.

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