Method for manufacturing hot-rolled steel sheet for non-oriented electromagnetic steel sheet and method for manufacturing non-oriented electromagnetic steel sheet

Abstract

This invention addresses the problem of wrinkling when processing steel containing large amounts of Si, Al, and Mn alloying elements in a thin slab process. A method for manufacturing a hot-rolled steel sheet for non-oriented electromagnetic steel sheets includes the following steps: a continuous casting step, in which a steel billet with a specified composition and a thickness of 50 mm to 200 mm is manufactured by continuous casting; a conveying step, in which the steel billet is conveyed into a furnace while maintaining its surface temperature at 800°C or higher; a holding step, in which the steel billet is held in the furnace at a holding temperature of 1100°C to 1300°C for a holding time of 60 seconds or higher; and a hot rolling step, in which the steel billet is sequentially subjected to rough rolling, reheating treatment, and finish rolling to produce a hot-rolled steel sheet; and the hot rolling step is performed under the following conditions (1) and (2): (1) Total reduction rate of the rough rolling: 80% or higher; (2) Total reduction rate of the finish rolling: 80% or higher.

Description

Technical Field

[0001] This invention relates to a method for manufacturing hot-rolled steel sheets for non-oriented electromagnetic steel sheets and a method for manufacturing non-oriented electromagnetic steel sheets. Background Technology

[0002] Non-oriented electromagnetic steel sheets are used as core materials for motors and generators. In recent years, from the perspective of reducing CO2, there is a strong need for higher efficiency in electrical equipment, which in turn requires further reduction of iron loss in non-oriented electromagnetic steel sheets as core materials.

[0003] To reduce iron loss in non-oriented electromagnetic steel sheets, adding alloying elements such as Si, Al, and Mn to increase resistivity and reduce sheet thickness is effective. However, high alloying and thinning increase the load during cold rolling, thus increasing the risk of breakage. While thinning the hot-rolled steel sheet supplied for cold rolling can reduce the load, this increases the load during hot rolling and makes shape control difficult.

[0004] To address this, a method for manufacturing non-oriented electromagnetic steel sheets using thinner steel billets (thin slabs) has been proposed. In this method, a continuous casting machine, known as a thin slab casting machine, is used to manufacture the thin slab, which is then fed into rolling. By reducing the slab thickness, the load on both hot and cold rolling processes can be reduced. Furthermore, in the method using thin slabs, the continuous casting machine (thin slab casting machine) is typically directly connected to the hot rolling mill, eliminating the need for slab reheating and thus significantly reducing energy costs.

[0005] As a method for manufacturing non-oriented electromagnetic steel sheets using thin slabs, the methods disclosed in Patent Documents 1 and 2 can be cited as examples. Patent Document 1 discloses a technique for hot-rolling a thin slab with a thickness of 20 to 100 mm to produce a hot-rolled steel strip with a thickness of 1.0 to 4 mm. Patent Document 2 discloses a technique for hot-rolling a thin slab with a thickness of 30 to 140 mm to produce a hot-rolled steel strip with a thickness of 0.7 to 4.5 mm.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2010-047785

[0009] Patent Document 2: Japanese Patent Application Publication No. 2002-206114 Summary of the Invention

[0010] However, it is known that in the prior art described in Patent Documents 1 and 2, if the amount of Si, Al, and Mn as alloying elements is increased, recrystallization during the annealing of hot-rolled plates becomes difficult, and wrinkling (wavy patterns) easily occur on the surface of the final non-oriented electromagnetic steel sheet.

[0011] The purpose of this invention is to solve the above-mentioned problems. Specifically, the purpose is to suppress wrinkling when processing steel containing a large amount of alloying elements such as Si, Al, and Mn in the process of using thin slabs.

[0012] Through in-depth research, the inventors discovered that by holding the hot rolling process at a high temperature before the hot rolling process, dividing the hot rolling into roughing and finishing rolling, and then reheating the process between the two, and by increasing the reduction rate of the roughing and finishing rolling processes, wrinkling can be effectively suppressed.

[0013] This invention is based on the above insights, and its main points are as follows.

[0014] 1. A method for manufacturing a hot-rolled steel sheet for non-oriented electromagnetic steel sheets, comprising the following steps:

[0015] The continuous casting process manufactures steel billets with a thickness of 50 mm to 200 mm by continuous casting, wherein the composition, by mass%, contains Si: 2.0% to 5.0%, Al: less than 3.0%, and Mn: less than 3.0%, and the combined content of Al and Mn is more than 0.40%.

[0016] In the conveying process, the steel billet is conveyed into the furnace while maintaining its surface temperature above 800°C.

[0017] The heat preservation process involves holding the steel billet in the aforementioned furnace at a temperature of 1100℃ to 1300℃ for at least 60 seconds.

[0018] In the hot rolling process, the above-mentioned steel billet is subjected to rough rolling, reheating treatment and finish rolling in sequence to produce hot-rolled steel plate;

[0019] Furthermore, the above-mentioned hot rolling process is carried out under the conditions of satisfying (1) and (2) below;

[0020] (1) The total reduction rate of the above rough rolling: 80% or more.

[0021] (2) The total reduction rate of the above finishing rolling is 80% or more.

[0022] 2. The manufacturing method of hot-rolled steel sheet for non-oriented electromagnetic steel sheet as described in 1 above, wherein the thickness of the exit side plate in the finishing rolling process is set to 0.4 mm to 2.0 mm.

[0023] 3. The method for manufacturing hot-rolled steel sheet for non-oriented electromagnetic steel sheet as described in 1 or 2 above, wherein the hot rolling process is performed under the condition that at least one of (1') and (2') below is satisfied.

[0024] (1') The total reduction rate of the above rough rolling is 88% or more.

[0025] (2') The total reduction rate of the above finishing rolling is 88% or more.

[0026] 4. The method for manufacturing hot-rolled steel sheet for non-oriented electromagnetic steel sheet according to any one of 1 to 3 above, wherein the total reduction rate of the rough rolling is greater than the total reduction rate of the finish rolling.

[0027] 5. A method for manufacturing a hot-rolled steel sheet for non-oriented electromagnetic steel sheet according to any one of 1 to 4 above, wherein the composition of the billet further comprises, by mass %, at least one selected from C: 0.005% 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.

[0028] 6. A method for manufacturing a non-oriented electromagnetic steel sheet, comprising the following steps:

[0029] The hot-rolled steel sheet manufacturing process involves manufacturing a hot-rolled steel sheet using the manufacturing method for non-oriented electromagnetic steel sheets described in any of the above 1 to 5.

[0030] The annealing process involves hot-rolled steel sheet annealing as described above.

[0031] The cold rolling process involves cold rolling the aforementioned hot-rolled steel sheet to produce cold-rolled steel sheet.

[0032] The final annealing process involves performing a final annealing on the aforementioned cold-rolled steel sheet.

[0033] According to the present invention, it is possible to manufacture thin-walled, alloy-rich non-oriented electromagnetic steel sheets at low cost and without wrinkling. Attached Figure Description

[0034] Figure 1 This is a graph showing the correlation between the total content (mass%) of Al and Mn in the billet and the arithmetic mean waviness Wa (μm) in the width direction of the non-oriented electromagnetic steel sheet.

[0035] Figure 2This is a graph showing the correlation between the insulation temperature (°C) and insulation time (seconds) in the insulation process and the arithmetic mean waviness Wa (μm) in the width direction of the non-oriented electromagnetic steel sheet.

[0036] Figure 3 This is a graph showing the correlation between the total reduction rate (%) in roughing and finishing rolling and the arithmetic mean waviness Wa (μm). Detailed Implementation

[0037] First, the experiments that led to the development of this invention will be described. It should be noted that, unless otherwise stated, in this specification, the unit "%" for content refers to "mass %".

[0038] (Experiment 1)

[0039] A 160 mm thick steel billet with the following composition is melted in a vacuum melting furnace: C: 0.002%, Si: 3.0%, Al: 0.05–2.0%, Mn: 0.05–1.0%, Cr: 0.01%, Ni: 0.01%, Cu: 0.01%, P: 0.01%, N: 0.003%, S: 0.002%, O: 0.001%, and Ti: 0.001%, with the remainder consisting of Fe and unavoidable impurities. The resulting steel billet is then hot-rolled using either of the following two methods.

[0040] (1) Reheating and rolling:

[0041] After the steel billet is removed from the vacuum melting furnace, it is cooled to room temperature in the atmosphere. Next, the steel billet is inserted into an electric furnace and reheated at 1100°C for 30 minutes. After that, the steel billet is removed from the electric furnace and inserted into a hot rolling mill.

[0042] (2) Direct feeding rolling:

[0043] After the steel billet is removed from the vacuum melting furnace, it is inserted into the hot rolling mill with the surface temperature not below 900°C.

[0044] In any of the above methods, the steel billet is rough rolled to a thickness of 15 mm in hot rolling, then reheated to 1100°C by an induction heating device, and then finished rolled to a thickness of 1.5 mm to produce a hot-rolled steel plate.

[0045] After hot-rolled steel sheets were annealed at 1000°C for 40 seconds, they were cold-rolled to produce cold-rolled steel sheets with a thickness of 0.3 mm. Next, the cold-rolled steel sheets were subjected to a final annealing at 980°C for 20 seconds to obtain non-oriented electromagnetic steel sheets.

[0046] To evaluate the wrinkling of the surface of the obtained non-oriented electromagnetic steel sheet, the arithmetic mean waviness Wa of the surface of the non-oriented electromagnetic steel sheet was measured. In the above measurement of the arithmetic mean waviness Wa, a stylus-type surface roughness tester was used to measure the steel sheet surface in the width direction with a measurement length of 16 mm, and the arithmetic mean waviness Wa was calculated based on the obtained waviness curve.

[0047] The relationship between the total Al and Mn content (mass%) of the steel billet used and the measured Wa (μm) is shown in the figure. Figure 1 It should be noted that in the following description, the Al content of the billet is denoted as [Al], the Mn content of the billet is denoted as [Mn], and the total Al and Mn content of the billet is denoted as [Al]+[Mn].

[0048] according to Figure 1 The results show that wrinkling does not occur in reheat rolling regardless of the [Al]+[Mn] content, but wrinkling occurs in direct rolling if the [Al]+[Mn] content exceeds 0.4%. Microstructure observation of hot-rolled steel sheets obtained using the direct rolling process revealed the presence of unrecrystallized structures in hot-rolled steel sheets with [Al]+[Mn] content above 0.4%.

[0049] Based on the above experimental results, the inventors hypothesize that the wrinkling observed during direct-feed rolling is caused by residual unrecrystallized structures from the annealing of hot-rolled plates. Therefore, further research was conducted on methods to promote recrystallization during the annealing of hot-rolled plates.

[0050] (Experiment 2)

[0051] The inventors hypothesized that fine precipitates such as MnS and AlN are finely precipitated during direct rolling, and these fine precipitates hinder recrystallization during the annealing of hot-rolled plates. Therefore, they investigated the conditions required for heat treatment before the hot rolling process to induce precipitate formation and growth, thereby reducing the fine precipitates.

[0052] A 120mm thick steel billet with the following composition is melted in a vacuum melting furnace: C: 0.002%, Si: 3.0%, Al: 0.5%, Mn: 0.2%, Cr: 0.01%, Ni: 0.01%, Cu: 0.01%, P: 0.01%, N: 0.003%, S: 0.002%, O: 0.001%, and Ti: 0.001%, with the remainder consisting of Fe and unavoidable impurities. The billet is then conveyed and inserted into an electric furnace while maintaining a surface temperature above 800°C, and subjected to a holding process at 1000–1350°C for 30–600 seconds. The billet is then removed from the electric furnace and inserted into a hot rolling mill for hot rolling. In the above hot rolling process, the steel billet is rough rolled to a plate thickness of 10 mm, then reheated to 1100°C by an induction heating device, and then finished rolled to a plate thickness of 1.2 mm to produce a hot-rolled steel plate.

[0053] After hot-rolled steel sheets were annealed at 1000°C for 40 seconds, they were cold-rolled to produce cold-rolled steel sheets with a thickness of 0.3 mm. Next, the cold-rolled steel sheets were subjected to a final annealing at 980°C for 20 seconds to obtain non-oriented electromagnetic steel sheets.

[0054] The arithmetic mean waviness Wa of the obtained non-oriented electromagnetic steel sheet was measured using the same steps as in Experiment 1 above.

[0055] The relationship between the insulation temperature and insulation time in the above insulation process and the arithmetic mean waviness Wa is shown in the figure. Figure 2 .according to Figure 2 The results show that wrinkling occurs at any holding temperature when the holding time is less than 60 seconds. On the other hand, wrinkling is suppressed when the holding time is more than 60 seconds and the holding temperature is between 1100℃ and 1300℃.

[0056] (Experiment 3)

[0057] Next, in order to study the distribution of reduction rates in roughing hot rolling and finishing hot rolling in direct feeding rolling, the inventors conducted the following experiments.

[0058] A 160 mm thick steel billet with the following composition is melted in a vacuum melting furnace: C: 0.002%, Si: 3.0%, Al: 0.5%, Mn: 0.2%, Cr: 0.01%, Ni: 0.01%, Cu: 0.01%, P: 0.01%, N: 0.003%, S: 0.002%, O: 0.001%, and Ti: 0.001%, with the remainder consisting of Fe and unavoidable impurities. The billet is then conveyed and inserted into an electric furnace while maintaining a surface temperature above 800°C, and held at 1150°C for 300 seconds. The billet is then removed from the electric furnace and inserted into a hot rolling mill for hot rolling.

[0059] In the aforementioned hot rolling process, the steel billet is sequentially subjected to rough rolling, reheating treatment, and finish rolling to produce hot-rolled steel plates with thicknesses of 0.6 mm, 1.0 mm, or 1.8 mm. The total reduction rate in the rough rolling process is set to 70.0%–98.0%, and the total reduction rate in the finish rolling process is set to 43.8%–98.8%. Furthermore, the reheating treatment utilizes an induction heating device to heat the sheet steel (steel after rough rolling) to 1100°C.

[0060] After hot-rolled steel sheets were annealed at 1000°C for 25 seconds, they were cold-rolled with a cold-rolling reduction of 80% to produce cold-rolled steel sheets. The cold-rolled steel sheets were then subjected to a final annealing at 980°C for 20 seconds to obtain non-oriented electromagnetic steel sheets.

[0061] The arithmetic mean waviness Wa of the obtained non-oriented electromagnetic steel sheet was measured using the same steps as in Experiment 1 above.

[0062] The relationship between the total reduction rate in roughing and finishing rolling and the arithmetic mean waviness Wa is shown in the figure. Figure 3 . Figure 3 The three lines correspond to the exit side plate thicknesses (final plate thickness in the hot rolling process) in each finishing mill: 0.6mm, 1.0mm, and 1.8mm. Additionally, the values ​​marked at each point represent the total reduction rate (%) in the finishing mill.

[0063] according to Figure 3 The results show that wrinkling was suppressed when both the total reduction rate in roughing and finishing rolling were above 80%. Furthermore, wrinkling was further suppressed when both the total reduction rate in roughing and finishing rolling were above 88%.

[0064] Based on the results of experiments 1 to 3 above, it can be seen that even when the billet has high Al and Mn content and uses a process that includes direct rolling, wrinkling can be suppressed by holding the billet at a temperature of 1100℃ to 1300℃ for more than 60 seconds, and by setting the total reduction rate in roughing and finishing rolling to more than 80% respectively.

[0065] Regarding this reasoning, the inventors considered the following: First, in steel containing N and S as impurities, if Al and Mn increase, the precipitation temperature of MnS and AlN increases, while the precipitation rate of these precipitates decreases. Therefore, by increasing the holding temperature, the precipitation rate is increased, and the holding time is extended, allowing the precipitates to grow larger.

[0066] Furthermore, by increasing the total reduction rate in rough rolling, the dislocation quantity in thin sheet steel increases, and the rolled microstructure of thin sheet steel becomes finer, with an increased grain boundary density. These dislocations and grain boundaries become precipitation sites for unprecipitated MnS and AlN during the heat treatment, promoting precipitation, and the precipitates grow coarsely during subsequent reheating. In addition, by increasing the total reduction rate in finish rolling, the hot-rolled microstructure becomes finer, and the grain boundary density, serving as recrystallization sites, increases.

[0067] Thus, it is believed that the increase in recrystallization sites caused by the coarsening of precipitates and the refinement of hot-rolled microstructure promotes recrystallization during the annealing of hot-rolled plates and inhibits the formation of wrinkles.

[0068] This invention is based on the above-described understanding. Hereinafter, specific descriptions will be provided of methods for carrying out this invention. It should be noted that this invention is not limited to these embodiments.

[0069] [Ingredients]

[0070] In this invention, the reasons for limiting the composition of the steel billet are explained.

[0071] Si: 2.0–5.0%

[0072] Si is an element that increases the inherent resistivity of steel sheets and reduces iron loss. To achieve these effects, the Si content is set to 2.0% or more. On the other hand, if the Si content exceeds 5.0%, rolling becomes difficult, so the Si content is set to 5.0% or less. From the viewpoint of balancing inherent resistivity and workability, the Si content is preferably 2.5% or more, more preferably 2.8% or more. For the same reason, the Si content is preferably 4.5% or less, more preferably 4.0% or less.

[0073] Al: below 3.0%

[0074] Al is an element that increases the inherent resistance of steel sheets and reduces iron loss. However, if the Al content exceeds 3.0%, rolling becomes difficult. Therefore, the Al content is set to 3.0% or less. From the viewpoint of good castability, the Al content is preferably 1.5% or less. On the other hand, there is no particular limitation on the lower limit of the Al content, but from the viewpoint of balancing iron loss and manufacturability, the Al content is preferably 0.2% or more, more preferably 0.3% or more, and even more preferably 0.5% or more.

[0075] Mn: below 3.0%

[0076] Mn is an element that increases the inherent resistivity of steel sheets and further reduces iron loss. However, if the Mn content exceeds 3.0%, slab cracks and other defects occur, leading to poor workability. Therefore, the Mn content is set to 3.0% or less. From the viewpoint of suppressing the precipitation of fine MnS, the Mn content is more preferably 1.5% or less. On the other hand, there is no lower limit for the Mn content, but from the viewpoint of further suppressing the precipitation of fine MnS, it is preferably 0.20% or more.

[0077] Total content of Al and Mn: ≥0.40%

[0078] If the combined content of Al and Mn is less than 0.40%, the precipitation temperature of the precipitates decreases. If the feature of this invention, namely the high-temperature heat treatment, is applied, precipitation does not occur during the heat treatment, but wrinkling occurs in subsequent hot rolling due to fine precipitation. Therefore, the combined content of Al and Mn is set to 0.40% or more, preferably 1.00% or more, and more preferably 1.50% or more. On the other hand, there is no particular upper limit to the combined content of Al and Mn. However, as mentioned above, the Al content is 3.0% or less, and the Mn content is 3.0% or less, so the maximum combined content of Al and Mn is 6.00%.

[0079] In one embodiment of the present invention, the steel billet may also have the following composition: containing Si: 2.0% to 5.0%, Al: less than 3.0%, Mn: less than 3.0%, with the remainder consisting of Fe and unavoidable impurities, and the total content of Al and Mn being 0.40% or more.

[0080] In another embodiment of the present invention, the composition of the steel billet may further arbitrarily contain at least one of the following elements.

[0081] C: Below 0.005%

[0082] Carbon (C) in non-oriented electromagnetic steel sheets is a harmful element that forms carbides, causing magnetic aging and deteriorating iron loss characteristics. Therefore, when the billet contains C, the C content should be set to 0.005% or less, preferably 0.004% or less. On the other hand, there is no particular limitation on the lower limit of the C content, but from the viewpoint of suppressing decarburization costs in the refining process, the C content is preferably 0.0001% or more.

[0083] Cr: less than 3.0%

[0084] Cr is an element that increases the inherent electrical resistance of steel plates and reduces iron loss. However, if the Cr content exceeds 3.0%, carbides precipitate, and iron loss actually increases. Therefore, when adding Cr, the Cr content is set to 3.0% or less. From the viewpoint of magnetic properties, the Cr content is preferably 1.5% or less. On the other hand, there is no lower limit to the Cr content, but from the viewpoint of improving the effect of adding Cr, the Cr content is preferably 0.001% or more, more preferably 0.005% or more, and even more preferably 0.01% or more.

[0085] Ni: below 2.0%

[0086] Ni is an element that can increase the magnetic flux density of steel sheets. However, Ni is an expensive element, and the cost becomes very high if the Ni content exceeds 2.0%. Therefore, when adding Ni, the Ni content is set to 2.0% or less. From the viewpoint of balancing magnetic properties and cost, the Ni content is preferably 0.5% or less. On the other hand, there is no limit to the lower limit of the Ni content, but from the viewpoint of improving the effect of adding Ni, the Ni content is preferably 0.001% or more, more preferably 0.005% or more, and even more preferably 0.01% or more.

[0087] Cu: below 2.0%

[0088] Cu is an element that can increase the magnetic flux density of steel sheets. However, if the Cu content exceeds 2.0%, it causes hot brittleness, leading to surface defects. Therefore, when adding Cu, the Cu content is set to 2.0% or less. From the viewpoint of balancing magnetic properties and cost, the Cu content is preferably 0.5% or less. On the other hand, there is no limit to the lower limit of Cu content, but from the viewpoint of improving the effect of Cu addition, the Cu content is preferably 0.005% or more, more preferably 0.01% or more, and even more preferably 0.05% or more.

[0089] P: below 0.2%

[0090] Phosphorus (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 set to 0.2% or less. From the viewpoint of balancing strength and brittleness, the P content is preferably 0.1% or less. On the other hand, there is no lower limit to the P content, but from the viewpoint of improving the effect of adding P, the P content is preferably 0.001% or more, more preferably 0.005% or more, and even more preferably 0.01% or more.

[0091] S: below 0.0050%

[0092] Sulfur (S) is an element that forms sulfides and increases iron loss. Therefore, when S is present, 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 iron loss, the lower the S content, the better; therefore, there is no lower limit for the S content, and it can be 0%. However, S is an element that inevitably mixes into steel as an impurity, and excessive reduction will lead to an increase in manufacturing costs. Therefore, from a cost perspective, the S content is preferably 0.0001% or more, and more preferably 0.0005% or more.

[0093] N: below 0.0050%

[0094] Nitrogen (N) is an element that forms nitrides and increases iron loss. Therefore, when N is present, 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 iron loss, the lower the N content, the better; therefore, there is no lower limit to the N content, and it can be 0%. However, N is an element that inevitably mixes into the steel as an impurity, and excessive reduction will lead to an increase in manufacturing costs. Therefore, from the viewpoint of cost, the N content is preferably 0.0001% or more, and more preferably 0.0005% or more.

[0095] O: below 0.0050%

[0096] O is an element that forms oxides and increases iron loss. Therefore, when O is present, 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 iron loss, the lower the O content, the better; therefore, there is no lower limit to the O content, and it can be 0%. However, O is an element that inevitably mixes into steel as an impurity, and excessive reduction will lead to an increase in manufacturing costs. Therefore, from a cost perspective, the O content is preferably 0.0005% or more, and more preferably 0.001% or more.

[0097] Ti: below 0.0040%

[0098] Ti is an element that forms carbonitrides and increases iron loss. Therefore, when Ti is present, 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 iron loss, the lower the Ti content, the better; therefore, there is no lower limit for the Ti content, and it can be 0%. However, Ti is an element that inevitably mixes into steel as an impurity, and excessive reduction will lead to an increase in manufacturing costs. Therefore, from the viewpoint of cost, the Ti content is preferably 0.0001% or more, and more preferably 0.0005% or more.

[0099] Sn: below 0.20%

[0100] Sn is an element that inhibits surface nitriding and oxidation, and reduces iron loss. However, even when added to levels exceeding 0.20%, the effect becomes saturated. Therefore, when adding Sn, the Sn content should be set to 0.20% or less, preferably 0.10% or less. On the other hand, from the viewpoint of improving the aforementioned effects, the Sn content is preferably 0.005% or more.

[0101] Sb: below 0.20%

[0102] Sb is an element that inhibits surface nitriding and oxidation, and reduces iron loss. However, even when added to levels exceeding 0.20%, the effect becomes saturated. 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 viewpoint of improving the aforementioned effects, the Sb content is preferably 0.005% or more.

[0103] Mo: 0.10% or less

[0104] Mo is an element that inhibits surface nitriding and oxidation, and reduces iron loss. However, if it is added to a level exceeding 0.10%, iron loss actually increases. Therefore, when adding Mo, the Mo content should be set to 0.10% or less, preferably 0.05% or less. On the other hand, from the viewpoint of improving the above-mentioned effects, the Mo content is preferably 0.001% or more.

[0105] Ca: below 0.01%

[0106] Ca is an element that inhibits the formation of fine oxides and sulfides and reduces iron loss. However, even when added to more than 0.01%, the effect becomes saturated. 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 viewpoint of improving the above-mentioned effects, the Ca content is preferably 0.001% or more.

[0107] REM: below 0.05%

[0108] Rare earth metals (REMs) are elements that suppress the formation of fine sulfides and reduce iron loss. However, even when added to levels exceeding 0.05%, the effect becomes saturated. Therefore, when adding REMs, the REM content should be set to 0.10% or less, preferably 0.03% or less. On the other hand, from the viewpoint of improving the aforementioned effects, the REM content is preferably 0.005% or more.

[0109] Mg: less than 0.01%

[0110] Mg is an element that inhibits the formation of fine sulfides and reduces iron loss. However, even when added to levels exceeding 0.01%, the effect becomes saturated. 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 viewpoint of improving the aforementioned effect, the Mg content is preferably 0.001% or more.

[0111] Zn: below 0.01%

[0112] Zinc (Zn) is an element that inhibits the formation of fine oxides and sulfides and reduces iron loss. However, even when added to levels exceeding 0.01%, the effect becomes saturated. 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 viewpoint of improving the aforementioned effects, the Zn content is preferably 0.001% or more.

[0113] [Manufacturing conditions for hot-rolled steel sheets for non-oriented electromagnetic steel sheets]

[0114] Next, the manufacturing conditions for manufacturing hot-rolled steel sheets for non-oriented electromagnetic steel sheets using steel billets with the above-mentioned composition will be explained.

[0115] A method for manufacturing a hot-rolled steel sheet for non-oriented electromagnetic steel sheets according to one embodiment of the present invention includes the following steps: a continuous casting step, in which a steel billet is manufactured by continuous casting; a conveying step, in which the steel billet is conveyed into a furnace while maintaining its surface temperature at or above 800°C; a holding step, in which the steel billet is held in the furnace at a holding temperature of 1100°C to 1300°C for a holding time of 60 seconds or more; and a hot rolling step, in which the steel billet is sequentially subjected to rough rolling, reheating treatment, and finish rolling to produce a hot-rolled steel sheet. Each step is described below.

[0116] Continuous casting process

[0117] First, a steel billet with the above-mentioned composition is manufactured by continuous casting (continuous casting process). There are no particular limitations on the method of continuous casting; conventional methods can be used. There are also no particular limitations on the method of adjusting the composition of the molten steel used in continuous casting; any method can be used. For example, the above-mentioned adjustment of the molten steel composition can be performed using a converter, electric furnace, vacuum degassing device, and other devices and methods.

[0118] Steel billet thickness: 50–200 mm

[0119] In the aforementioned continuous casting process, steel billets with a thickness of 50 mm to 200 mm are manufactured. If the billet thickness is less than 50 mm, the reduction rate in the roughing and finishing rolling processes in the hot rolling process cannot be sufficiently obtained, and recrystallization during the annealing of the hot-rolled sheet is hindered. Therefore, the billet thickness is set to 50 mm or more. From the viewpoint of suppressing the drop in slab temperature between the continuous casting process and the holding process, the billet thickness is preferably 100 mm or more. Furthermore, from the viewpoint of ensuring a sufficient reduction rate in roughing and finishing rolling, the billet thickness is more preferably 140 mm or more. On the other hand, if the billet thickness exceeds 200 mm, the rolling load in the hot rolling process increases, leading to larger rolling equipment and increased equipment costs. Therefore, the billet thickness is set to 200 mm or less.

[0120] • Conveying process

[0121] Next, the steel billet manufactured in the continuous casting process is conveyed to a furnace for heat treatment (conveyance process). In this conveyance process, it is important to convey the billet while maintaining its surface temperature at 800°C or higher. In other words, in this invention, the billet is conveyed from its manufacture in the continuous casting process until it reaches the furnace to ensure that its surface temperature does not fall below 800°C. If the surface temperature of the billet falls below 800°C, the energy required for reheating the billet increases, and the energy-saving effect is not achieved.

[0122] There is no particular limitation on the method used to suppress the decrease in surface temperature of the steel billet during the above-mentioned conveying process, but for example, the decrease in surface temperature can be suppressed by increasing the casting speed or increasing the slab thickness.

[0123] In the aforementioned conveying process, the billet can also be cut and then conveyed into the furnace. However, from the viewpoint of suppressing the temperature drop of the slab, it is preferable to convey the billet directly into the furnace (heating equipment) without cutting.

[0124] Insulation process

[0125] Next, the steel billet is held in the furnace at a temperature of 1100℃~1300℃ for a holding time of 60 seconds or more (holding process). The holding treatment promotes the precipitation and coarsening of MnS and AlN, thereby promoting recrystallization in the hot-rolled sheet annealing process when manufacturing non-oriented electromagnetic steel sheets.

[0126] Insulation temperature: 1100~1300℃

[0127] If the holding temperature is below 1100°C, the precipitates will not coarsen and will remain in the slab in a fine state. Furthermore, recrystallization during the annealing of the hot-rolled sheet is hindered, making wrinkling more likely. Therefore, the holding temperature is set to 1100°C or higher, preferably 1150°C or higher. On the other hand, if the holding temperature is above 1300°C, the precipitation of precipitates will not occur, resulting in fine precipitation of MnS and AlN during the hot rolling process after holding. Furthermore, recrystallization during the annealing of the hot-rolled sheet is hindered, making wrinkling more likely. Therefore, the holding temperature is set to 1300°C or lower, preferably 1250°C or lower.

[0128] Heat retention time: 60 seconds or more

[0129] Furthermore, if the holding time is less than 60 seconds, the precipitation and coarsening of MnS and AlN will not occur, so wrinkling is still likely to occur. Therefore, the holding time is set to 60 seconds or more, preferably 300 seconds or more. On the other hand, there is no particular upper limit to the holding time, but if it exceeds 3600 seconds, in addition to the effect saturation, the construction cost of the equipment increases. Therefore, the above-mentioned holding time is preferably 3600 seconds or less, more preferably 2400 seconds or less, and even more preferably 2000 seconds or less.

[0130] The heating method used in the above-mentioned heat preservation treatment is not particularly limited; any method such as induction heating, gas furnace, or electric furnace can be used. However, when using a gas furnace, oxide scale is generated on the surface of the steel plate due to the combustion gases. Therefore, from the viewpoint of suppressing oxide scale formation and CO2 emission, it is preferable to use an electric heating method, i.e., induction heating or an electric furnace. Among these, electric furnaces are suitable for heating steel billets continuously for long periods of time and have lower construction costs. Therefore, the above-mentioned heat preservation treatment further preferably uses an electric furnace.

[0131] Hot-rolled

[0132] Next, the steel billet is subjected to rough rolling, reheating treatment and finish rolling in sequence to produce hot-rolled steel plate (hot rolling process). In this invention, it is important to carry out the above hot rolling process under the conditions of satisfying (1) and (2) below.

[0133] (1) Total reduction rate of rough rolling: 80% or more

[0134] (2) Total reduction rate of finishing rolling: 80% or more

[0135] Total reduction rate in rough rolling: 80% or more

[0136] If the total reduction rate of rough rolling is less than 80%, the dislocation introduction does not sufficiently promote the precipitation of MnS and AlN, and the precipitates do not coarsen during subsequent reheating. Furthermore, the grain boundary density after hot rolling is not sufficiently refined. As a result, recrystallization is not promoted during the annealing of hot-rolled sheets in the manufacture of non-oriented electromagnetic steel sheets, and wrinkling is easily generated. Therefore, the total reduction rate of rough rolling is set to 80% or more, preferably 88% or more, and more preferably 91% or more. In particular, if the total reduction rate of rough rolling is 91%, the width of the processed microstructure after rough rolling becomes extremely fine, and the density of grain boundaries, which serve as precipitation sites for MnS and AlN, increases significantly in the thickness direction. Moreover, this results in extremely effective promotion of MnS and AlN precipitation. Here, the total reduction rate of rough rolling refers to the reduction rate calculated based on the sheet thickness before rough rolling (the thickness of the billet) and the sheet thickness after rough rolling (the thickness on the exit side). It should be noted that there is no particular limitation on the number of passes in the roughing process mentioned above; it can be set to any number of passes, more than one.

[0137] Total reduction rate in finishing rolling: 80% or more

[0138] Furthermore, if the total reduction rate of finishing rolling is less than 80%, the grain boundary density after hot rolling is not sufficiently refined, thus failing to promote recrystallization during hot-rolled sheet annealing and easily leading to wrinkling. Therefore, the total reduction rate of finishing rolling is set to 80% or more, preferably 88% or more, and more preferably 91% or more. In particular, if the total reduction rate of finishing rolling is 91% or more, not only does the grain boundary density after hot rolling increase significantly, but the number of dislocations remaining in the steel sheet after hot rolling also increases significantly. Moreover, this results in easier recrystallization during hot-rolled sheet annealing, which can more effectively suppress wrinkling. It should be noted that here, the total reduction rate of finishing rolling refers to the reduction rate calculated based on the sheet thickness before finishing rolling and the sheet thickness after finishing rolling (exit side sheet thickness). It should also be noted that the number of finishing rolling passes is not particularly limited and can be any number of passes, one or more.

[0139] Furthermore, from the viewpoint of further promoting the precipitation of MnS and AlN and further improving the wrinkling suppression effect, it is preferable that the total reduction rate of rough rolling is greater than that of finish rolling.

[0140] It should be noted that in conventional reheat rolling processes, the large undercooling caused by temporarily cooling the cast steel billet to near room temperature leads to the precipitation of AlN and MnS during cooling or reheating, with the precipitates becoming coarser during reheating. Therefore, in reheat rolling, it is not necessary to control the reduction rate during hot rolling to suppress wrinkling.

[0141] On the other hand, in processes like the present invention where cast steel billets are fed to hot rolling at a maintained high temperature (direct feeding rolling), AlN and MnS do not precipitate or coarsen during the transition from casting to hot rolling. Therefore, even with heat treatment, sufficient wrinkling suppression cannot be achieved without increasing the reduction rate in roughing and finishing rolling to promote recrystallization during hot-rolled sheet annealing. In other words, the reduction rate limitation in the present invention is designed to address the wrinkling problem unique to direct feeding rolling and is based on a novel concept entirely different from the control of reduction rate in conventional reheat rolling.

[0142] A reheating treatment is performed between the roughing and finishing rolling processes. During roughing, this reheating treatment is necessary to coarsen the finely precipitated material and suppress wrinkling. Furthermore, this reheating treatment increases the material temperature and reduces the deformation resistance during finishing rolling.

[0143] The heating temperature in the above-mentioned reheating treatment is not particularly limited, but is preferably 950°C or higher, more preferably 1050°C or higher. On the other hand, there is no particular limit to the upper limit of the heating temperature, but if the heating temperature is too high, the effect will saturate, and energy efficiency will also decrease. Therefore, the heating temperature in the above-mentioned reheating treatment is preferably 1300°C or lower, more preferably 1200°C or lower. The heating method in the above-mentioned reheating treatment is not particularly limited, and any method such as induction heating, gas furnace, or electric furnace can be used.

[0144] It should be noted that the thickness of the exit side plate in the finishing rolling process (the thickness of the final hot-rolled steel sheet) is not particularly limited and can be any thickness. However, if the exit side plate thickness is less than 0.4 mm, the overall length of the steel sheet becomes too long, and productivity decreases. Therefore, from the viewpoint of productivity, the exit side plate thickness in the finishing rolling process is preferably 0.4 mm or more. On the other hand, if the exit side plate thickness exceeds 2.0 mm, the cold rolling load increases. Therefore, from the viewpoint of reducing the load in cold rolling, the exit side plate thickness in the finishing rolling process is preferably 2.0 mm or less. From the viewpoint of reducing the cold rolling load even when the final sheet thickness after cold rolling is thin, the exit side plate thickness is more preferably 1.5 mm or less.

[0145] Manufacturing conditions for non-oriented electromagnetic steel sheets

[0146] A method for manufacturing a non-oriented electromagnetic steel sheet according to one embodiment of the present invention includes: a hot-rolled steel sheet manufacturing process for manufacturing a hot-rolled steel sheet by the above manufacturing method; a hot-rolled steel sheet annealing process for hot-rolled steel sheet; a cold-rolling process for cold-rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet; and a final annealing process for cold-rolled steel sheet.

[0147] There are no special limitations on the above-mentioned hot-rolled plate annealing, cold rolling and final annealing processes, and they can be carried out according to conventional methods.

[0148] Pickling is preferably performed after the hot-rolled sheet annealing and before the cold rolling. Furthermore, it is also preferable to form an insulating coating on the surface of the obtained non-oriented electromagnetic steel sheet after the final annealing. There are no particular limitations on the pickling and the formation of the insulating coating; conventional methods can be followed.

[0149] Example

[0150] (Example 1)

[0151] A 60mm thick steel billet was manufactured using a continuous casting method. The billet composition included C: 0.002%, Si: 3.2%, Al: 0.60%, Mn: 0.50%, S: 0.0010%, N: 0.0015%, O: 0.0010%, Cr: 0.02%, Ni: 0.01%, Cu: 0.02%, P: 0.01%, and Ti: 0.001%, with the remainder consisting of Fe and unavoidable impurities. The billet was not cut and was conveyed to a tunnel furnace while maintaining a surface temperature above 800°C for heat treatment. The heat treatment temperature and time are shown in Table 1. It should be noted that, for comparison purposes, some embodiments did not include heat treatment.

[0152] Next, the steel billet is subjected to hot rolling under the conditions shown in Table 1, consisting of three passes of rough rolling, reheating, and four passes of finish rolling, to produce hot-rolled steel sheet. In the reheating process, the slab immediately after rough rolling is heated by induction heating. It should be noted that, for comparison purposes, the reheating process is omitted in some embodiments.

[0153] Hot-rolled steel sheets, after precision rolling, are continuously coiled to form hot-rolled coils. These hot-rolled coils are then subjected to hot-rolled annealing at 1030°C for 40 seconds to produce hot-rolled annealed sheets. Next, the hot-rolled annealed sheets are cold-rolled with a reduction rate of 85% to produce cold-rolled steel sheets. Finally, the cold-rolled steel sheets are subjected to a final annealing at 1000°C for 15 seconds to obtain non-oriented electromagnetic steel sheets.

[0154] To evaluate the surface wrinkling of the obtained non-oriented electromagnetic steel sheet, the arithmetic mean waviness Wa of the non-oriented electromagnetic steel sheet surface was measured. In the above measurement of the arithmetic mean waviness Wa, a stylus-type surface roughness tester was used to measure the steel sheet surface along the width direction with a measurement length of 16 mm. The arithmetic mean waviness Wa was calculated based on the obtained waviness curve. The measurement results are recorded in Table 1.

[0155] As shown in Table 1, in embodiments that meet the conditions of the present invention, the arithmetic mean waviness Wa is reduced, which can suppress wrinkling.

[0156] Table 1

[0157] [surface

[0158]

[0159] (Example 2)

[0160] A 160mm thick steel billet was manufactured using a continuous casting method. The billet composition included C: 0.002%, Si: 3.0%, Al: 1.3%, Mn: 0.40%, S: 0.0005%, N: 0.0015%, O: 0.0010%, Cr: 0.10%, Ni: 0.15%, Cu: 0.18%, P: 0.02%, and Ti: 0.0015%, with the remainder consisting of Fe and unavoidable impurities. The billet was not cut and was conveyed to a tunnel-type gas furnace while maintaining its surface temperature above 800°C for heat treatment. The heat treatment temperature and time are shown in Table 2. It should be noted that, for comparison purposes, some embodiments did not include heat treatment.

[0161] Next, under the conditions shown in Table 2, the above-mentioned steel billet is subjected to hot rolling consisting of 4 passes of rough rolling, reheating treatment, and 5 passes of finish rolling to produce hot-rolled steel sheet. In the above-mentioned reheating treatment, the slab immediately after rough rolling is heated by induction heating. It should be noted that, for comparison purposes, the reheating treatment is omitted in some embodiments.

[0162] Hot-rolled steel sheets, after precision rolling, are continuously coiled to form hot-rolled coils. These hot-rolled coils are then subjected to hot-rolled annealing at 1020°C for 30 seconds to produce hot-rolled annealed sheets. Next, the hot-rolled annealed sheets are cold-rolled with a reduction rate of 85% to produce cold-rolled steel sheets. Finally, the cold-rolled steel sheets are subjected to a final annealing at 1000°C for 15 seconds to obtain non-oriented electromagnetic steel sheets.

[0163] To evaluate the surface wrinkling of the obtained non-oriented electromagnetic steel sheet, the arithmetic mean waviness Wa of the surface of the non-oriented electromagnetic steel sheet was measured using the same method as in Example 1 above. The measurement results are recorded in Table 2.

[0164] As shown in Table 2, in embodiments that meet the conditions of the present invention, the arithmetic mean waviness Wa is reduced, which can suppress wrinkling.

[0165] [Table 2]

[0166] [surface

[0167]

[0168] (Example 3)

[0169] A 190 mm thick steel billet was manufactured using a continuous casting method. The billet composition included C: 0.002%, Si: 3.4%, Al: 0.3%, Mn: 0.60%, S: 0.0008%, N: 0.010%, O: 0.0010%, Cr: 0.015%, Ni: 0.015%, Cu: 0.03%, P: 0.015%, and Ti: 0.0015%, with the remainder consisting of Fe and unavoidable impurities. The billet was not cut and was conveyed to a tunnel-type gas furnace while maintaining its surface temperature above 800°C for heat treatment. The heat treatment temperature and time are shown in Table 3. It should be noted that, for comparison purposes, some embodiments did not include heat treatment.

[0170] Next, under the conditions shown in Table 3, the above-mentioned steel billet is subjected to hot rolling consisting of 4 passes of rough rolling, reheating treatment, and 5 passes of finish rolling to produce hot-rolled steel sheet. In the above-mentioned reheating treatment, the slab immediately after rough rolling is heated by induction heating. It should be noted that, for comparison purposes, the reheating treatment is omitted in some embodiments.

[0171] Hot-rolled steel sheets, after precision rolling, are continuously coiled to form hot-rolled coils. These hot-rolled coils are then subjected to hot-rolled annealing at 1050°C for 20 seconds to produce hot-rolled annealed sheets. Next, the hot-rolled annealed sheets are cold-rolled with a reduction of 85% to produce cold-rolled steel sheets. Finally, the cold-rolled steel sheets are subjected to a final annealing at 1000°C for 15 seconds to obtain non-oriented electromagnetic steel sheets.

[0172] To evaluate the surface wrinkling of the obtained non-oriented electromagnetic steel sheet, the arithmetic mean waviness Wa of the surface of the non-oriented electromagnetic steel sheet was measured using the same method as in Example 1 above. The measurement results are recorded in Table 3.

[0173] As shown in Table 3, in embodiments that meet the conditions of the present invention, the arithmetic mean waviness Wa is reduced, which can suppress wrinkling.

[0174] [Table 3]

[0175] [surface

[0176]

[0177] (Example 4)

[0178] Steel billets with a thickness of 150 mm and the composition shown in Tables 4-6 are manufactured by continuous casting. Without cutting, the billets are fed into a tunnel-type gas furnace while maintaining a surface temperature above 800°C, where they undergo a heat treatment. The heat treatment temperature is 1150°C, and the heat treatment time is 1500 seconds.

[0179] Next, the steel billet is subjected to hot rolling consisting of four passes of rough rolling, reheating treatment, and five passes of finish rolling to produce a hot-rolled steel plate. The total reduction rate in the rough rolling is set to 90%, and the total reduction rate in the finish rolling is set to 93.3%. In the reheating treatment, the slab immediately after rough rolling is heated to 1100°C by induction heating.

[0180] Hot-rolled steel sheets, after precision rolling, are continuously coiled to form hot-rolled coils. These coils are then subjected to hot-rolled annealing at 1050°C for 20 seconds to produce hot-rolled annealed sheets. Next, the hot-rolled annealed sheets are cold-rolled with a reduction of 80% to produce cold-rolled steel sheets with a thickness of 0.20 mm. Finally, the cold-rolled steel sheets are subjected to a final annealing at 1000°C for 20 seconds to obtain non-oriented electromagnetic steel sheets.

[0181] To evaluate the surface wrinkling of the obtained non-oriented electromagnetic steel sheet, the arithmetic mean waviness Wa of the surface of the non-oriented electromagnetic steel sheet was measured using the same method as in Example 1 above. The measurement results are recorded in Tables 4 to 6.

[0182] As shown in Tables 4-6, in embodiments that meet the conditions of the present invention, the arithmetic mean waviness Wa is reduced, which can suppress wrinkling.

[0183]

[0184]

[0185]

[0186] (Example 5)

[0187] Steel billets with a thickness of 150 mm and the composition shown in Tables 7-9 are manufactured by continuous casting. Without cutting, the billets are fed into a tunnel-type gas furnace while maintaining a surface temperature above 800°C, where they undergo a heat treatment. The heat treatment temperature is 1150°C, and the heat treatment time is 500 seconds.

[0188] Next, the steel billet is subjected to hot rolling consisting of four passes of rough rolling, reheating treatment, and five passes of finish rolling to produce a hot-rolled steel plate. The total reduction rate in the rough rolling is set to 92%, and the total reduction rate in the finish rolling is set to 91.7%. In the reheating treatment, the slab immediately after rough rolling is heated to 1100°C by induction heating.

[0189] Hot-rolled steel sheets, after precision rolling, are continuously coiled to form hot-rolled coils. These coils are then subjected to hot-rolled annealing at 1050°C for 20 seconds to produce hot-rolled annealed sheets. Next, the hot-rolled annealed sheets are cold-rolled with a reduction of 80% to produce cold-rolled steel sheets with a thickness of 0.20 mm. Finally, the cold-rolled steel sheets are subjected to a final annealing at 1000°C for 20 seconds to obtain non-oriented electromagnetic steel sheets.

[0190] To evaluate the surface wrinkling of the obtained non-oriented electromagnetic steel sheet, the arithmetic mean waviness Wa of the surface of the non-oriented electromagnetic steel sheet was measured using the same method as in Example 1 above. The measurement results are recorded in Tables 4 to 6.

[0191] As shown in Tables 7-9, in embodiments that satisfy the preferred roughing conditions of the present invention, the arithmetic mean waviness Wa is further reduced, which can suppress wrinkling.

[0192]

[0193]

[0194]

Claims

1. A method for manufacturing a hot-rolled steel sheet for non-oriented electromagnetic steel sheets, comprising the following steps: The continuous casting process manufactures steel billets with a thickness of 50 mm to 200 mm by continuous casting, wherein the composition, by mass%, contains Si: 2.0% to 5.0%, Al: less than 3.0%, and Mn: less than 3.0%, and the combined content of Al and Mn is more than 0.40%. In the conveying process, the steel billet is conveyed into the furnace while maintaining its surface temperature above 800°C. The heat preservation process involves holding the steel billet in the furnace at a temperature of 1100℃ to 1300℃ for at least 60 seconds. In the hot rolling process, the steel billet is sequentially subjected to rough rolling, reheating treatment, and finish rolling to produce hot-rolled steel plates. The hot rolling process is carried out under the conditions that (1) and (2) below are met. (1) The total reduction rate of the rough rolling: 80% or more, (2) The total reduction rate of the finishing mill is 80% or more.

2. The method for manufacturing hot-rolled steel sheet for non-oriented electromagnetic steel sheet according to claim 1, wherein, The thickness of the exit side plate in the finishing mill is set to 0.4mm to 2.0mm.

3. The method of producing a hot-rolled steel sheet for non-oriented electromagnetic steel sheets according to claim 1 or 2, wherein The hot rolling process is carried out under the condition that at least one of (1') and (2') below is satisfied. (1') The total reduction rate of the rough rolling is 88% or more. (2') The total reduction rate of the finishing mill is 88% or more.

4. The method of producing a hot-rolled steel sheet for non-oriented electromagnetic steel sheets according to any one of claims 1 to 3, wherein The total reduction rate of the roughing mill is greater than the total reduction rate of the finishing mill.

5. The method of producing a hot-rolled steel sheet for non-oriented electromagnetic steel sheets according to any one of claims 1 to 4, wherein The steel billet further comprises, by mass %, at least one selected from the following: C: less than 0.005%, Cr: less than 3.0%, Ni: less than 2.0%, Cu: less than 2.0%, P: less than 0.2%, S: less than 0.0050%, N: less than 0.0050%, O: less than 0.0050%, Ti: less than 0.0040%, Sn: less than 0.20%, Sb: less than 0.20%, Mo: less than 0.10%, Ca: less than 0.01%, REM: less than 0.05%, Mg: less than 0.01%, and Zn: less than 0.01%.

6. A method for manufacturing a non-oriented electromagnetic steel sheet, comprising the following steps: The hot-rolled steel sheet manufacturing process involves manufacturing the hot-rolled steel sheet using the manufacturing method for non-oriented electromagnetic steel sheets as described in any one of claims 1 to 5. The annealing process involves hot-rolled steel sheet annealing. The cold rolling process involves cold rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet. The final annealing process involves performing a final annealing on the cold-rolled steel sheet.

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