TW202532661A - Method for manufacturing hot-rolled steel sheet for non-oriented electromagnetic steel sheet and method for manufacturing non-oriented electromagnetic steel sheet - Google Patents

Abstract

Proposed is a method for producing a hot-rolled steel sheet for a non-oriented electromagnetic steel sheet, the hot-rolled steel sheet being excellent in magnetic characteristics. In the method, a thin slab is hot-rolled. This production method comprises: casting molten steel containing, in mass%, C: ≤ 0.010%, Si: 2.50-5.00%, Mn: 0.10-3.00%, P: ≤ 0.100%, S: 0.0010-0.0050%, Al: ≤ 2.00%, N: ≤ 0.0080%, Cu: ≤ 1.00%, Mo: ≤ 0.050%, Zn: ≤ 0.010%, and Ti: ≤ 0.010%, with the balance being Fe and unavoidable impurities, into a steel slab having a prescribed thickness; subsequently heating the steel slab in a tunnel furnace, with the surface temperature of the steel slab at the exit of the tunnel furnace, the heating time in the tunnel furnace, and the cooling rate of the steel slab from the exit of the tunnel furnace to the entrance of the hot-rolling mill being within predetermined ranges; and subjecting the steel slab to hot-rolling, with the entrance temperature, exit temperature, strain rate during the first pass of the hot-rolling, and coil winding temperature for the hot-rolling mill being within predetermined ranges.

Description

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

The present invention relates to a method for manufacturing a hot-rolled steel plate for non-oriented electromagnetic steel and a method for manufacturing non-oriented electromagnetic steel.

Non-oriented electromagnetic steel sheets are used as the core material for motors and generators. In recent years, there has been a strong demand for higher efficiency in electrical equipment to reduce _CO2 emissions. Consequently, there is a demand for further reduction in the iron loss of non-oriented electromagnetic steel sheets used as core materials.

Effective methods for reducing the iron loss of non-oriented electromagnetic steel sheets include increasing the specific resistivity by adding alloying elements such as Si, Al, and Mn, or reducing the sheet thickness. However, high alloying and thinning increase the rolling load during cold rolling, making the steel more susceptible to cracking during cold rolling. Thinning the hot-rolled steel sheets used for cold rolling can reduce the cold rolling load. However, this increases the rolling load during hot rolling, making shape control more difficult.

Therefore, a method has been proposed for producing non-oriented electromagnetic steel using thinner steel billets (hereinafter referred to as thin slabs) than previously used. In this method, thin slabs are produced using a continuous casting machine called a thin slab mill, which is then rolled. Reducing the thickness of the billet reduces the rolling load during both hot and cold rolling. Furthermore, in many cases, the thin slab method eliminates the need for slab reheating by directly connecting the continuous casting machine (thin slab mill) to the hot rolling mill. This significantly reduces energy costs.

An example of a method for producing non-oriented electromagnetic steel using thin slabs is the method disclosed in Patent Document 1. Patent Document 1 discloses a technique for producing hot-rolled steel sheets having a thickness of 0.4 mm to 2.0 mm by holding a slab having a thickness of 50 mm to 200 mm at room temperature. [Prior Art Document] [Patent Document]

Patent Document 1: International Publication No. 2023/095637

[Problems to be Solved by the Invention] However, each of the aforementioned prior arts presents the following issues that must be addressed. In the method disclosed in Patent Document 1, the steel slab is hot-rolled while being maintained at a high temperature. Consequently, precipitates in the steel prior to hot-rolling may not fully precipitate and coarsen, but instead precipitate finely during hot-rolling. Furthermore, these fine precipitates refine the steel structure, increasing the iron loss of the resulting non-oriented electromagnetic steel sheet.

To address the aforementioned issues with the prior art, the present invention specifically aims to provide a hot-rolled steel sheet in which the formation of fine precipitates is suppressed during hot rolling by subjecting a thin slab to a heat-insulating treatment and maintaining it at a high temperature. Furthermore, the present invention aims to use this hot-rolled steel sheet to produce a non-oriented electromagnetic steel sheet with suppressed iron loss. [Means for Solving the Problem]

The inventors conducted extensive research and discovered that by controlling the S content and keeping the hot rolling conditions within an appropriate range, the fine precipitation of precipitates can be suppressed, thereby suppressing the increase in iron loss in non-oriented electromagnetic steel sheets produced using thin slabs.

That is, the method for producing a hot-rolled steel plate for non-oriented electromagnetic steel of the present invention, which advantageously solves the above-mentioned problem, comprises: a heat-holding step of casting molten steel into a steel billet having a thickness in the range of 30 mm to 180 mm, and then heat-holding the steel billet in a tunnel furnace; and a hot-rolling step of hot-rolling the steel billet, wherein the molten steel has the following composition, which contains, in mass%, C: 0.010% or less, Si: 2.50% or more and 5.00% or less, Mn: 0.10% or more and 3.00% or less, P: 0.100% or less, S: 0.0010% or more and 0.0050% or less, Al: 2. 00% or less, N: 0.0080% or less, Cu: 1.00% or less, Mo: 0.050% or less, Zn: 0.010% or less, and Ti: 0.010% or less, and optionally further containing at least one element selected from the following groups: Group A is at least one element selected from Sn: 0.20% or less and Sb: 0.20% or less; Group B is at least one element selected from Mg: 0.0001% or more and 0.10% or less and rare earth metals ( Metals (REM): at least one selected from 0.0001% to 0.10%; Group C: B: 0.002% to 0.01%; Group D: Ni: 0.01% to 1.0%; Group E: Cr: 0.1% to 5.0%; Group F: at least one selected from V: 0.001% to 0.050%, Nb: 0.001% to 0.005%, Ta: 0.0001% to 0.0020%, W: 0.001% to 0.050% and Pb: 0.0001% to 0.0020%; Group G: Co: 0.00 1% or more and 0.100% or less; H group is at least one selected from Ga: 0.0005% or more and 0.0300% or less and Ge: 0.0005% or more and 0.0300% or less; and I group is As: 0.001% or more and 0.020% or less, and the remainder contains Fe and inevitable impurities. The manufacturing method of the hot-rolled steel plate for non-oriented electromagnetic steel plate is characterized in that, in the holding step, the surface temperature of the steel billet at the entrance side of the tunnel furnace is set to 850°C or more, the surface temperature of the steel billet at the exit side of the tunnel furnace is set to a range of 1050°C or more and 1200°C or less, and the holding time in the tunnel furnace is set to 8 min or more, and in the hot rolling step, the cooling rate of the steel billet from the outlet side of the tunnel furnace to the inlet side of the hot rolling mill is set to 4°C/s or less, the inlet side temperature of the hot rolling mill is set to 950°C or more, the outlet side temperature of the hot rolling mill is set to 800°C or more, the strain rate in the first pass of hot rolling is set to 1.5/s or more, and the coil winding temperature is met under the conditions of 500°C or more.

Furthermore, in a more preferred embodiment of the method for producing a hot-rolled steel plate for non-oriented electromagnetic steel of the present invention, the molten steel is tapped from an electric furnace or a converter.

Furthermore, the method for manufacturing a non-oriented electromagnetic steel sheet of the present invention, which advantageously solves the aforementioned problem, is characterized by comprising: a hot-rolled steel sheet manufacturing step of manufacturing a hot-rolled steel sheet using any of the aforementioned methods for manufacturing a hot-rolled steel sheet for non-oriented electromagnetic steel; a hot-rolled steel sheet annealing step of annealing the hot-rolled steel sheet to produce a hot-rolled annealed steel sheet; a cold-rolling step of cold-rolling the hot-rolled annealed steel sheet to produce a cold-rolled steel sheet; and a finish annealing step of finish annealing the cold-rolled steel sheet. [Effects of the Invention]

The present invention provides a hot-rolled steel sheet obtained by hot-rolling a thin slab while maintaining it at a high temperature through a heat treatment process, thereby suppressing the formation of fine precipitates. This hot-rolled steel sheet can be used to produce non-oriented electromagnetic steel sheets with excellent magnetic properties.

Before describing the embodiments of the present invention, we will first describe the experiments that led to its development. In the following description, "%" representing chemical compositions is based on mass unless otherwise specified. <Experiment 1> The inventors focused on controlling MnS, which precipitates finely in steel and increases steel losses, and measured steel losses. A basic steel composition was used: 0.002% C, 3.00% Si, 0.50% Mn, 0.01% P, 0.50% Al, 0.0020% N, 0.01% Cu, 0.010% Mo, 0.001% Zn, 0.002% Ti, with the remainder being Fe and unavoidable impurities. The molten steel, to which S was added in varying amounts ranging from 0.0001% to 0.0070%, was cast into 60 mm thick ingots. The ingots were then held at 1100°C in a tunnel furnace. They were then hot-rolled into 1.6 mm thick plates at a 960°C inlet temperature, a 5.0/s strain rate in the first hot-rolling pass, and a 520°C coiling temperature. The plates were then annealed at an ambient temperature of 980°C for 30 seconds. Afterwards, the steel was cold-rolled to produce 0.30 mm thick cold-rolled steel plates. Finally, a finish annealing process was performed at 960°C for 10 seconds in a dry atmosphere with a vol% _H₂ : _N₂ ratio of 25:75. Epstein specimens measuring 30 mm wide by 280 mm long were cut from the resulting steel plates in both the rolling and width directions, and the steel loss (W _10/400) was measured using an Epstein tester.

Figure 1 shows the relationship between the S content in steel sheets and the iron loss (W _10/400) . As shown in Figure 1, iron loss is reduced by controlling the S content within the range of 0.0010% to 0.0050%. Furthermore, the grain size of the steel sheets observed with an optical microscope coarsens within the range where iron loss is reduced.

Based on these experimental results, the inventors speculate that when the S content is within the stated range, the effects of precipitates on grain growth degradation are suppressed. Specifically, when the S content is less than 0.0010%, the number of precipitated MnS is small. Therefore, precipitates such as TiN and TiC, which have a lower precipitation temperature than MnS, cannot precipitate using MnS as nuclei. As a result, these precipitates are finely dispersed, reducing grain growth. When the S content exceeds 0.0050%, the number of MnS increases, reducing grain growth.

<Experiment 2> Based on the above results, we investigated the necessary conditions for controlling the hot rolling process to achieve coarse precipitates and reduce fine precipitates. A steel composition containing 0.002% C, 3.00% Si, 0.50% Mn, 0.01% P, 0.50% Al, 0.0020% N, 0.01% Cu, 0.010% Mo, 0.001% Zn, 0.002% Ti, 0.0020% S, with the remainder being Fe and unavoidable impurities, was used as a base. The molten steel was then cast into 60 mm thick billets. The billets were then held at 1100°C in a tunnel furnace. Next, hot-rolled steel plates with a thickness of 1.6 mm were produced under the following conditions: the hot-rolling inlet temperature was varied between 875°C and 1025°C, the strain rate in the first hot-rolling pass was set to 5.0/s, and the coil winding temperature was set to 520°C. The resulting hot-rolled steel plates were subjected to the same procedures as in Experiment 1, and the steel loss was measured.

Figure 2 shows the relationship between the hot rolling inlet temperature and the steel loss (W _10/400) . Figure 2 shows that steel loss increases when the hot rolling inlet temperature is below 950°C. The inventors speculate that this is because the strain introduced during rolling increases the driving force for precipitate formation. Low steel plate temperatures cause precipitates such as TiN and TiC to precipitate simultaneously with MnS and become finely dispersed. Furthermore, it is speculated that low steel plate temperatures also suppress precipitate grain growth, resulting in finer precipitates.

<Experiment 3> Next, we investigated the effect of strain rate on the morphology of precipitates during the first pass of hot rolling. A steel composition containing 0.002% C, 3.00% Si, 0.50% Mn, 0.01% P, 0.50% Al, 0.0020% N, 0.01% Cu, 0.010% Mo, 0.001% Zn, 0.002% Ti, 0.0020% S, with the remainder being Fe and unavoidable impurities, was used as a base. The molten steel was then cast into 60 mm thick billets. These billets were then held at 1100°C in a tunnel furnace. Next, hot-rolled steel sheets with a thickness of 1.6 mm were produced at a hot-rolling inlet temperature of 960°C, a strain rate in the first hot-rolling pass varying from 0.2/s to 4.2/s, and a coil winding temperature of 520°C. The same procedures as in Experiment 1 were applied to the resulting hot-rolled steel sheets, and steel loss was measured.

Figure 3 shows the relationship between the strain rate in the first pass of hot rolling and the steel loss (W _10/400 ). Figure 3 shows that if the strain rate in the first pass of hot rolling is less than 1.5/s, the steel loss increases. The inventors speculate that at low strain rates, the driving force for precipitation decreases, resulting in insufficient precipitation of MnS in the first pass of hot rolling. Precipitation occurs in later passes at lower rolling temperatures, preventing fine precipitates such as TiN and TiC from precipitating around the MnS.

The results of Experiments 1 to 3 demonstrate that even when using a thin slab continuous casting machine, by setting the S content to 0.0010% to 0.0050%, setting the hot rolling inlet temperature to 950°C or higher, and setting the strain rate in the first hot rolling pass to 1.5/s, the increase in steel loss can be suppressed. The present invention is based on this finding. The following describes a specific embodiment of the present invention. However, the present invention is not limited to this embodiment.

<Composition> The following explains the reasons for limiting the composition of the molten steel in this embodiment. The cast thin slab also has the same composition as the molten steel.

C: 0.010% or less C is a harmful element that causes magnetic aging in the finished steel sheet, forming carbides and degrading the steel. Therefore, in this embodiment, to suppress magnetic aging, the C content is set to 0.010% or less. A C content of 0.005% or less is preferred. While there is no specific lower limit, from the perspective of reducing decarburization costs, the lower limit of the C content is preferably set to approximately 0.0001%.

Si: 2.50% or more and 5.00% or less To increase the electrical resistance of the steel sheet and sufficiently reduce iron loss, it is necessary to add 2.50% or more of Si. Therefore, in this embodiment, the Si content is set to 2.50% or more. On the other hand, if the Si content exceeds 5.00%, rolling becomes difficult. Therefore, the Si content is set to 5.00% or less. Furthermore, from the perspective of manufacturability, the Si content is preferably 4.00% or less.

Mn: 0.10% or more to 3.00% or less Mn, like Si and Al, increases the electrical resistance of the steel sheet and reduces steel damage. Therefore, in this embodiment, the Mn content is set to 0.10% or more. On the other hand, if the Mn content exceeds 3.00%, Mn carbides precipitate, worsening steel damage. Therefore, the Mn content is set to 3.00% or less. A range of 0.20% or more to 1.00% is preferred.

P: 0.100% or less P increases the strength of steel and is used for strength adjustment. However, if the P content exceeds 0.100%, the steel becomes brittle, reducing manufacturability. Therefore, the P content is kept to 0.100% or less. While there is no specific lower limit, a P content of 0.001% or more is preferred to reduce P removal costs. Furthermore, to enhance the effectiveness of P addition, a P content of 0.005% or more is more preferred, and 0.010% or more is even more preferred.

S: 0.0010% or more and 0.0050% or less S exists primarily in the form of MnS in steel. It can be detoxified by complex precipitation with precipitates such as TiC and TiN, which would adversely affect magnetic properties if precipitated alone. Therefore, in this embodiment, the S content is set to 0.0010% or more. On the other hand, if the S content exceeds 0.0050%, the amount of MnS precipitation increases, hindering grain growth and increasing iron damage. Therefore, the S content is set to 0.0050% or less. A S content of 0.0010% or more and 0.0040% or less is preferred.

Al: 2.00% or less Like Si, Al has the effect of increasing the electrical resistance of steel sheets and reducing iron loss. However, if the Al content exceeds 2.00%, rolling becomes difficult. Therefore, the Al content is set to 2.00% or less. To ensure good castability, the Al content is preferably set to 1.50% or less. While there is no specific lower limit for the Al content, from the perspective of balancing iron loss and manufacturability, the Al content is preferably 0.20% or more, more preferably 0.30% or more, and even more preferably 0.50% or more.

N: 0.0080% or less N is a harmful element that forms fine nitrides, inhibiting grain growth and increasing steel loss, so it is best to minimize its content. In particular, if the N content exceeds 0.0080%, these adverse effects become significant. Therefore, the N content should be kept to 0.0080% or less. A content of 0.0030% or less is preferred. On the other hand, from the perspective of steel loss, the lower the N content, the better. Therefore, the lower limit of the N content is not specific and can be 0%. However, N is an element that inevitably enters the steel as an impurity, and excessive reduction in N content can lead to increased manufacturing costs. Therefore, from a cost perspective, the N content is preferably kept to 0.0001% or more, and more preferably to 0.0005% or more.

Cu: 1.00% or less Cu is an element that increases the magnetic flux density of steel sheets. However, if the Cu content exceeds 1.00%, it can cause hot brittleness and surface defects. Therefore, when adding Cu, the Cu content should be kept to 1.00% or less. From the perspective of balancing magnetic properties and cost, the Cu content is preferably set to 0.1% or less. While there is no lower limit for the Cu content, a Cu content of 0.01% or more is preferred to maximize the effect of Cu addition.

Mo: 0.050% or less Mo reacts with carbon to form carbides at grain boundaries, which improves strength. However, if the Mo content exceeds 0.050%, iron losses tend to increase. Therefore, when adding Mo, the Mo content should be kept to 0.050% or less. While there is no lower limit for the Mo content, a Mo content of 0.010% or more is preferred from the perspective of strength.

Zn: 0.010% or less Zn reacts with sulfur to form coarse sulfides, which inhibit the precipitation of fine sulfides such as MnS and reduce steel damage. However, if the content exceeds 0.010%, the amount of these sulfides increases, hindering grain growth and increasing steel damage. Therefore, the Zn content is set to 0.010% or less. While there is no lower limit for the Zn content, a Zn content of 0.001% or more is preferred from the perspective of reducing steel damage.

Ti: 0.010% or less Ti reacts with carbon or nitrogen to form carbides and nitrides at grain boundaries, thus increasing strength, similar to Mo. However, if the Ti content exceeds 0.010%, the amount of these carbides and nitrides increases, hindering grain growth and increasing steel loss. Therefore, the Ti content is kept to 0.010% or less. While there is no lower limit for the Ti content, a Ti content of 0.002% or more is preferred from the perspective of strength.

In the present embodiment, the molten steel has a composition comprising C: 0.010% or less, Si: 2.50% to 5.00%, Mn: 0.10% to 3.00%, P: 0.100% or less, S: 0.0010% to 0.0050%, Al: 2.00% or less, N: 0.0080% or less, Cu: 1.00% or less, Mo: 0.050% or less, Zn: 0.010% or less, and Ti: 0.010% or less, with the remainder consisting of Fe and inevitable impurities.

In this embodiment, the composition of the molten steel may optionally further contain elements from at least one group selected from the following Groups A to I.

Group A is at least one selected from Sn: 0.20% or less and Sb: 0.20% or less. Sn: 0.20% or less Sn is an element that inhibits nitridation or oxidation of the surface layer and reduces steel damage. However, even if added in amounts exceeding 0.20%, the effect is saturated. Therefore, when adding Sn, it is preferably kept to 0.20% or less, more preferably 0.10% or less. On the other hand, to enhance the aforementioned effect, a Sn content of 0.005% or more is preferred.

Sb: 0.20% or less Sb is an element that inhibits nitridation and oxidation of the surface layer and reduces steel damage. However, even if added in amounts exceeding 0.20%, these effects are saturated. Therefore, when adding Sb, the Sb content is preferably kept to 0.20% or less, more preferably 0.10% or less. On the other hand, to enhance these effects, an Sb content of 0.005% or more is preferred.

Group B is at least one element selected from Mg: 0.0001% to 0.10% and REM: 0.0001% to 0.10% Mg: 0.0001% to 0.10% Mg is an element that helps reduce iron losses by fixing sulfur in the form of sulfides. To achieve this effect, the Mg content should be 0.0001% or higher. On the other hand, if the Mg content exceeds 0.10%, the effect is saturated, resulting in unnecessary cost increases. Therefore, the upper limit is set to 0.10%. Therefore, the Mg content is preferably within the range of 0.0001% to 0.10%.

REM: 0.0001% or more and 0.10% or less REM (rare earth metals) are a group of elements that help reduce iron losses by fixing sulfur in the form of sulfides. To achieve this effect, the REM content should be at least 0.0001%. On the other hand, if the REM content exceeds 0.10%, the effect is saturated, resulting in unnecessary cost increases. Therefore, the upper limit is set at 0.10%. Therefore, the REM content is preferably within the range of 0.0001% or more and 0.10% or less. REM is a general term for Sc, Y, and the 17 elements of the lanthanide series.

Group C: B: 0.002% or more to 0.01% or less B forms fine carbides in steel, increasing the strength of the steel sheet. To achieve this effect, a B content of 0.002% or more is sufficient. On the other hand, if the B content exceeds 0.01%, excessive carbides form, causing steel damage and deterioration. Therefore, the upper limit is set at 0.01%. Therefore, the B content is preferably within the range of 0.002% or more to 0.01% or less.

D Group: Ni: 0.01% or more to 1.0% or less Nitride is an element that improves the toughness of steel and can be added as needed. To achieve this effect, the Ni content only needs to be at least 0.01%. However, if the Ni content exceeds 1.0%, the effect is saturated, so the upper limit of the Ni content is set at 1.0%. Therefore, the Ni content is preferably within the range of 0.01% or more to 1.0%.

Group E: Cr: 0.1% or more to 5.0% or less Cr increases the intrinsic resistivity of steel and reduces iron loss. To achieve this effect, a Cr content of 0.1% or more is sufficient. On the other hand, a Cr content exceeding 5.0% significantly reduces the saturated magnetic flux density, leading to a significant decrease in magnetic flux density. Therefore, the upper limit is set at 5.0%. Therefore, the Cr content is preferably within the range of 0.1% to 5.0%.

The F group is at least one element selected from V: 0.001% to 0.050%, Nb: 0.001% to 0.005%, Ta: 0.0001% to 0.0020%, W: 0.001% to 0.050%, and Pb: 0.0001% to 0.0020%. V: 0.001% to 0.050%. V is an element that increases the strength of the steel sheet and can be added as appropriate. To achieve this effect, the V content should be 0.001% or more. However, if the V content exceeds 0.050%, fine precipitates will form in the steel sheet, increasing iron losses. Therefore, the upper limit of the V content is set to 0.050%.

Nb: 0.001% or more and 0.005% or less Nb is an element that increases the strength of steel sheets and can be added as needed. To achieve this effect, the Nb content should be at least 0.001%. However, if the Nb content exceeds 0.005%, fine precipitates will form in the steel sheet, increasing iron losses. Therefore, the upper limit of the Nb content is set at 0.005%.

Ta: 0.0001% or more and 0.0020% or less Ta is an element that increases the strength of steel sheets and can be added as needed. To achieve this effect, the Ta content should be at least 0.0001%. However, if the Ta content exceeds 0.0020%, fine precipitates will form in the steel sheet, increasing iron losses. Therefore, the upper limit of the Ta content is set at 0.0020%.

W: 0.001% or more and 0.050% or less W is an element that increases the strength of steel sheets and can be added as needed. To achieve this effect, the W content should be at least 0.001%. However, if the W content exceeds 0.050%, fine precipitates will form in the steel sheet, increasing iron losses. Therefore, the upper limit of the W content is set at 0.050%.

Pb: 0.0001% or more and 0.0020% or less Pb is an element that increases the strength of steel sheets and can be added as needed. To achieve this effect, the Pb content should be at least 0.0001%. However, if the Pb content exceeds 0.0020%, fine precipitates will form in the steel sheet, increasing iron losses. Therefore, the upper limit of the Pb content is set at 0.0020%.

Group G: Co: 0.001% or more to 0.100% or less Co is an element that increases the magnetic flux density of steel sheets and can be added as needed. To achieve this effect, the Co content should be at least 0.001%. However, adding large amounts of Co increases alloy costs, so the upper limit is set at 0.100%.

Group H is at least one selected from Ga: 0.0005% to 0.0300% and Ge: 0.0005% to 0.0300% Ga: 0.0005% to 0.0300% Ga is an element that improves the steel sheet's texture and increases magnetic flux density, and can be added as appropriate. To achieve these effects, the Ga content should be at least 0.0005%. However, adding large amounts of Ga not only diminishes the effect but also increases alloy costs. Therefore, the upper limit of the Ga content is set at 0.0300%.

Ge: 0.0005% or more to 0.0300% or less Ge is an element that improves the steel sheet's structure and increases magnetic flux density, making it a suitable addition. To achieve these effects, the Ge content should be at least 0.0005%. However, adding large amounts of Ge diminishes the effect and increases alloy costs, so the upper limit of the Ge content is set at 0.0300%.

Group I: As: 0.001% or more and 0.020% or less As is an element that increases the strength of steel sheets and can be added appropriately. To achieve this effect, the As content should be at least 0.001%. However, if the As content exceeds 0.020%, the risk of cracking during cold rolling increases. Therefore, the upper limit of the As content is set at 0.020%.

Furthermore, unavoidable impurities such as O (oxygen) are permitted up to 0.0050%. Contents below the effective range for these elements do not affect the magnetic properties of the product and are therefore permitted as unavoidable impurities.

[Manufacturing Conditions for Hot-Rolled Steel Sheets for Non-Oriented Electromagnetic Steel] Next, we will explain the manufacturing conditions for hot-rolled steel sheets for non-oriented electromagnetic steel sheets using molten steel having the aforementioned composition.

The method for producing hot-rolled steel for non-oriented electromagnetic steel according to this embodiment includes: a holding step of casting molten steel having the aforementioned composition into a billet having a thickness ranging from 30 mm to 180 mm, followed by holding the billet in a tunnel furnace; and a hot rolling step of hot rolling. During the holding step, the billet surface temperature at the tunnel furnace entrance is set to 850°C or higher, and the billet surface temperature at the tunnel furnace exit is set to 1050°C to 1200°C or lower. The holding time in the tunnel furnace is set to 8 minutes or longer, and the cooling rate of the billet from the tunnel furnace exit to the hot rolling mill entrance is set to 4°C/s or lower. In the hot rolling step, the hot rolled steel sheet is manufactured under the following conditions: the inlet side temperature of the hot rolling machine is set to 950°C or higher, the outlet side temperature of the hot rolling machine is set to 800°C or higher, the strain rate in the first pass of hot rolling is set to 1.5/s or higher, and the coil winding temperature is met under the conditions of 500°C or higher.

[Molten Steel Melting Step] The method for adjusting the composition of the molten steel is not particularly limited and may be performed using any method. For example, a rotary furnace, electric furnace, vacuum degassing equipment, or other equipment and methods may be used to adjust the composition of the molten steel. It is preferred to tap the molten steel from a rotary furnace or electric furnace. For example, melting and smelting reduced iron or scrap in an electric furnace is preferred because it contributes to reducing _CO2 emissions.

[Continuous Casting Step] The molten steel, after adjusting its composition, is then continuously cast to produce a steel billet. The continuous casting method is not particularly limited and can be performed using conventional methods.

Billet Thickness: 30 mm or more and 180 mm or less In the continuous casting step, billets with a thickness of 30 mm or more and 180 mm or less are produced. If the billet thickness is less than 30 mm, the surface area relative to the slab volume increases, resulting in a faster cooling rate. Consequently, the billet temperature cannot be maintained during the hot rolling step. Therefore, the billet thickness is set to 30 mm or more. On the other hand, if the billet thickness exceeds 180 mm, the rolling load during the hot rolling step increases, thereby increasing the risk of steel strip fracture. Therefore, the billet thickness is set to 180 mm or less.

[Transportation Step] Next, the steel slabs produced in the continuous casting step are transported to a tunnel furnace for heat preservation. During this transport step, it is crucial to maintain the surface temperature of the steel slabs at or above 850°C during transport to the tunnel furnace entrance. In other words, in this embodiment, the surface temperature of the steel slabs does not drop below 850°C from the time they are produced in the continuous casting step until they reach the furnace. If the surface temperature of the steel slabs falls below 850°C, the energy required for reheating increases, preventing the energy savings from being achieved. Therefore, the surface temperature of the steel slabs at the tunnel furnace entrance is maintained at or above 850°C, preferably at or above 900°C. There is no upper limit, but considering that cooling is performed during continuous casting to achieve complete solidification, the upper limit of the billet surface temperature is preferably around 1200°C.

In the transfer step, the slab can be cut and then transferred to the tunnel furnace. However, from the perspective of suppressing the temperature drop of the slab, it is more preferable to transfer the slab directly to the tunnel furnace without cutting it.

[Hot-Standing Step] Next, a hot-holding treatment is performed at the exit of the tunnel furnace, maintaining the billet surface temperature at 1050°C to 1200°C for at least 8 minutes. This hot-holding treatment promotes the precipitation and coarsening of precipitates such as MnS and AlN. This degrades the fine precipitates that hinder grain growth during the hot-rolled and finish annealing steps during the production of non-oriented electromagnetic steel sheets.

Surface temperature of the steel slab at the tunnel furnace exit: 1050°C or higher and 1200°C or lower If the slab temperature is lower than 1050°C, the precipitates will not coarsen sufficiently. Consequently, fine precipitates remain on the slab, hindering grain growth during hot-rolled annealing and finish annealing. This increases iron loss in the product. Therefore, the surface temperature of the steel slab at the tunnel furnace exit, or the holding temperature, is set to 1050°C or higher, preferably 1100°C or higher. On the other hand, if the holding temperature is higher than 1200°C, precipitates will not form. Consequently, fine precipitates form during hot rolling after the holding treatment. As a result, grain growth is hindered during the hot rolled sheet annealing and finish annealing steps, increasing iron loss in the product. Therefore, the holding temperature should be set below 1200°C, preferably below 1150°C.

Holding Time: 8 minutes or longer If the holding time in the tunnel furnace is less than 8 minutes, precipitation and coarsening of precipitates will not proceed sufficiently. Consequently, grain growth during hot-rolled plate annealing and finish annealing is impaired, increasing iron loss in the product. Therefore, the holding time should be set to 8 minutes or longer. While there is no specific upper limit for the holding time, if it exceeds 30 minutes, the effect will be saturated and the tunnel furnace will be longer, increasing equipment costs. Therefore, the holding time is preferably set to 30 minutes or less, and more preferably 15 minutes or less.

The heating method used in the heat treatment is not particularly limited; for example, any method can be used, such as induction heating, a gas furnace, or an electric furnace. However, when using a gas furnace, the combustion of gas forms a large amount of scale on the surface of the steel plate. Consequently, during the hot rolling step described later, water is sprayed vigorously to remove the scale, accelerating the cooling rate of the steel slab. Therefore, from the perspective of maintaining a high temperature, induction heating or an electric furnace, which utilize electrical energy, are preferred.

[Hot rolling step] Next, a hot rolling step is performed, in which the steel billet is transferred to a hot rolling mill, hot rolled, and wound around a coil to produce a hot rolled steel plate. In this embodiment, the hot rolling step is performed under the following conditions (1) to (5). It is important to reduce the iron loss by complex precipitation of fine precipitates such as TiC and TiN with MnS as the core. (1) Cooling rate of the steel billet from the tunnel furnace outlet to the hot rolling mill inlet: 4°C/s or less (2) Surface temperature of the steel billet at the hot rolling mill inlet: 950°C or higher (3) Strain rate in the first pass of hot rolling: 1.5/s or higher (4) Temperature of the steel plate at the hot rolling mill outlet: 800°C or higher (5) Coil winding temperature: 500°C or higher

Billet Cooling Rate: 4°C/s or less After the holding step, the billet reacts with oxygen in the air, forming scale on the surface. When hot rolling is performed with scale remaining, the scale is entangled, causing surface defects. Therefore, after leaving the tunnel furnace, the billet is descaled using high-pressure water. This removes the surface scale and allows the billet to cool. However, if the cooling rate exceeds 4°C/s, the areas of the billet exposed to the high-pressure water will cool rapidly. This significantly reduces the temperature below which MnS precipitates, causing fine precipitates such as TiC and TiN to form, increasing iron loss in the product. Therefore, the cooling rate is set to 4°C/s or less. On the other hand, from the perspective of scale removal, a faster cooling rate is preferred. Therefore, the cooling rate of the steel slab is preferably set to 2°C/s or higher.

Billet Surface Temperature at the Hot Rolling Mill Inlet: 950°C or Higher If the billet surface temperature at the hot rolling mill inlet, i.e., the inlet-side temperature, is less than 950°C, the precipitation driving force increases. Consequently, fine precipitates such as TiC and TiN precipitate simultaneously with MnS, preventing complex precipitation with MnS as the nucleus. Therefore, the hot rolling mill inlet-side temperature is set to 950°C or higher. While there is no specific upper limit for the hot rolling mill inlet-side temperature, a billet surface temperature closer to the tunnel furnace outlet is preferred because it suppresses TiC and TiN precipitation.

Strain rate in the first pass of hot rolling: 1.5/s or more If the strain rate in the first pass of hot rolling is less than 1.5/s, the rate of dislocation recovery exceeds the rate of dislocation introduction, which is the driving force for precipitation. Therefore, MnS precipitation does not proceed sufficiently during hot rolling. Therefore, the strain rate in the first pass of hot rolling is set to 1.5/s or more. On the other hand, there is no particular upper limit for the strain rate in the first pass of hot rolling, but if the strain rate is too high, fine precipitates such as TiC and TiN may precipitate. Therefore, the strain rate in the first pass of hot rolling is preferably 4.0/s or less. Here, the strain rate is calculated according to equations (1) and (2) of the following formula 1.

[Number 1]

Here, ε (circled point) represents the strain rate in the first hot rolling pass (1/s), _h0 represents the thickness of the steel billet before hot rolling (m), _h1 represents the thickness of the rolled material after the first hot rolling pass (m), _tc represents the rolling time required for the first hot rolling pass (s), R represents the roll diameter in the first hot rolling pass (m), and _ν0 represents the sheet feed speed of the rolled material (m/min).

Steel Sheet Temperature at the Hot Rolling Mill Exit: 800°C or Higher If the hot-rolled steel sheet temperature at the hot-rolling mill exit is less than 800°C, the precipitation driving force increases. This causes fine precipitates such as TiC and TiN to precipitate simultaneously with MnS, preventing complex precipitation with MnS as the nucleus. Therefore, the hot-rolled steel sheet temperature at the hot-rolling mill exit is set to 800°C or higher. While there is no specific upper limit for the hot-rolled steel sheet temperature at the hot-rolling mill exit, a temperature closer to the rolled material temperature at the hot-rolling mill entrance is preferred, as precipitation of TiC and TiN is more suppressed.

Furthermore, the number of passes in the hot rolling is not particularly limited and can be set to any number of passes greater than 1.

Furthermore, the thickness of the exit side of the hot-rolled steel plate during the hot-rolled finishing process, that is, the thickness of the final hot-rolled steel plate, is not particularly limited and can be any thickness. However, if the exit side thickness is less than 0.4 mm, the total length of the steel plate will be too long, which may reduce productivity. Therefore, from the perspective of productivity, it is preferable to set the exit side thickness during finishing to 0.4 mm or more. On the other hand, if the exit side thickness exceeds 2.0 mm, there is a risk that the load during cold rolling will become too large. Therefore, from the perspective of reducing the load during cold rolling, it is preferable to set the exit side thickness during finishing to 2.0 mm or less.

Coil Winding Temperature: 500°C or Higher If the coil winding temperature is below 500°C, the precipitation driving force for TiC and TiN decreases. Consequently, aging precipitation cannot occur in the coiled state. Consequently, fine precipitation occurs after the next step, increasing iron loss. Therefore, the coil winding temperature should be set above 500°C. While there is no specific upper limit for the coil winding temperature, winding at high temperatures may cause coil deformation. Therefore, the coil winding temperature is preferably set below 550°C.

[Non-Oriented Electromagnetic Steel Sheet Manufacturing Conditions] The non-oriented electromagnetic steel sheet manufacturing method in this embodiment includes: a hot-rolled steel sheet manufacturing step, in which a hot-rolled steel sheet is manufactured using the manufacturing method; a hot-rolled steel sheet annealing step, in which the hot-rolled steel sheet is subjected to hot-rolled steel sheet annealing to produce a hot-rolled annealed steel sheet; a cold-rolling step, in which the hot-rolled annealed steel sheet is cold-rolled to produce a cold-rolled steel sheet; and a finish annealing step, in which the cold-rolled steel sheet is subjected to finish annealing. The hot-rolled steel sheet annealing, cold-rolling, and finish annealing steps are not particularly limited and can be performed according to conventional methods.

It is also preferred to perform pickling after annealing the hot-rolled sheet and before cold rolling. Furthermore, it is preferred to form an insulating coating on the surface of the resulting non-oriented electromagnetic steel sheet after finish annealing. The pickling and insulating coating formation are not particularly limited and can be performed according to conventional methods. [Examples]

<Example 1> A 60 mm thick steel slab with the composition shown in Table 1 was produced using a continuous casting method. Without cutting, the slab was transferred to a tunnel-type electric furnace while maintaining a surface temperature above 850°C, where it was held at a high temperature. The surface temperature of the slab at the tunnel furnace exit was set at approximately 1100°C, and the holding time was set for 10 minutes. The slab was then descaled using high-pressure water, followed by five passes of hot rolling and wound around a coil to produce hot-rolled steel plate. During the hot rolling process, the cooling rate from the tunnel furnace exit to the hot rolling mill was set at 3°C/s, and the surface temperature of the steel billet at the hot rolling mill entrance was set at 1000°C. The strain rate during the first hot rolling pass was set at 3.0°C/s, the temperature of the steel plate at the hot rolling mill exit was set at 900°C, and the coil winding temperature was set at 520°C.

The resulting hot-rolled steel sheet was annealed at 1000°C for 30 seconds to produce a hot-rolled annealed sheet. The hot-rolled annealed sheet was then cold-rolled to produce a 0.30 mm thick cold-rolled steel sheet. The cold-rolled steel sheet was then finish-annealed at 1000°C for 10 seconds to produce a non-oriented electromagnetic steel sheet.

Epstein samples measuring 30 mm wide and 280 mm long were cut from the resulting non-oriented electromagnetic steel sheet in both the rolling and width directions. The steel loss W10 _/400 was measured using an Epstein tester. For a sheet thickness of 0.30 mm, a W10 _/400 of 13.50 W/kg or less was considered acceptable.

As shown in Table 1, non-oriented electromagnetic steel sheets with excellent iron loss can be obtained with a composition that meets the requirements of the present invention. Tests No. 7, No. 13, No. 19, and No. 23 fractured during production and could not be evaluated. "-" in the composition column indicates that the component was not added or was present as an unavoidable impurity.

[Table 1] No. Ingredient composition (mass%) W _10/400 (W/kg) Remarks C Si Mn P S Al N Cu Mo Zn Ti other 1 0.0001 3.06 0.51 0.010 0.0035 0.49 0.0028 0.01 0.011 0.001 0.003 - 13.23 Invention Example 2 0.010 3.05 0.49 0.001 0.0035 0.50 0.0028 0.01 0.011 0.001 0.002 - 13.42 Invention Example 3 0.011 2.90 0.50 0.010 0.0031 0.50 0.0032 0.01 0.010 0.001 0.003 - 13.55 Comparative example 4 0.002 2.42 0.50 0.009 0.0033 0.49 0.0026 0.01 0.011 0.001 0.003 - 13.55 Comparative example 5 0.002 2.51 0.50 0.009 0.0026 0.49 0.0032 0.01 0.010 0.001 0.002 - 13.45 Invention Example 6 0.002 4.85 0.50 0.009 0.0033 0.50 0.0001 0.01 0.010 0.001 0.003 - 13.12 Invention Example 7 0.002 5.04 0.50 0.010 0.0033 0.49 0.0031 0.01 0.011 0.001 0.003 - - Comparative example 8 0.002 2.99 0.09 0.011 0.0032 0.50 0.0025 0.01 0.010 0.001 0.002 - 13.64 Comparative example 9 0.002 3.01 0.10 0.011 0.0033 0.50 0.0025 0.01 0.010 0.001 0.003 - 13.42 Invention Example 10 0.002 3.05 2.96 0.011 0.0034 0.51 0.0030 0.01 0.010 0.001 0.002 - 13.46 Invention Example 11 0.002 2.98 3.01 0.011 0.0034 0.49 0.0030 0.01 0.011 0.001 0.002 - 13.56 Comparative example 12 0.002 2.90 0.50 0.095 0.0027 0.50 0.0033 0.01 0.011 0.001 0.003 - 13.35 Invention Example 13 0.002 3.08 0.49 0.106 0.0032 0.49 0.0026 0.01 0.010 0.001 0.003 - - Comparative example 14 0.002 2.99 0.50 0.011 0.0009 0.50 0.0033 0.01 0.010 0.001 0.002 - 13.74 Comparative example 15 0.002 3.07 0.50 0.009 0.0011 0.50 0.0030 0.01 0.011 0.001 0.002 - 13.42 Invention Example 16 0.002 3.10 0.49 0.009 0.0049 0.51 0.0025 0.01 0.010 0.001 0.003 - 13.45 Invention Example 17 0.002 3.08 0.50 0.009 0.0053 0.20 0.0035 0.01 0.011 0.001 0.003 - 13.67 Comparative example 18 0.002 3.06 0.50 0.010 0.0035 1.99 0.0027 0.01 0.011 0.001 0.003 - 13.23 Invention Example 19 0.002 3.05 0.49 0.010 0.0032 2.01 0.0031 0.01 0.011 0.001 0.003 - - Comparative example 20 0.002 3.03 0.51 0.011 0.0033 0.50 0.0078 0.01 0.010 0.001 0.003 - 13.45 Invention Example twenty one 0.002 3.05 0.51 0.010 0.0029 0.51 0.0082 0.01 0.011 0.001 0.002 - 13.74 Comparative example twenty two 0.002 3.09 0.51 0.010 0.0030 0.49 0.0025 0.98 0.010 0.001 0.002 - 13.44 Invention Example twenty three 0.002 3.00 0.50 0.009 0.0027 0.50 0.0033 1.05 0.010 0.001 0.003 - - Comparative example twenty four 0.002 2.94 0.51 0.010 0.0031 0.50 0.0035 0.01 0.045 0.001 0.002 - 13.34 Invention Example 25 0.002 2.94 0.49 0.009 0.0029 0.30 0.0033 0.01 0.053 0.001 0.002 - 13.61 Comparative example 26 0.002 2.94 0.49 0.010 0.0031 0.50 0.0032 0.01 0.010 0.010 0.002 - 13.49 Invention Example 27 0.002 2.92 0.50 0.011 0.0033 0.50 0.0027 0.01 0.011 0.013 0.003 - 13.56 Comparative example 28 0.002 2.95 0.49 0.010 0.0033 0.50 0.0031 0.01 0.010 0.001 0.009 - 13.48 Invention Example 29 0.002 3.04 0.51 0.011 0.0027 0.50 0.0028 0.01 0.010 0.001 0.012 - 13.59 Comparative example 30 0.002 2.99 0.50 0.011 0.0027 0.50 0.0032 0.01 0.010 0.001 0.002 Sn: 0.19 13.35 Invention Example 31 0.002 3.10 0.51 0.009 0.0034 0.50 0.0030 0.01 0.011 0.001 0.003 Sn: 0.21 13.46 Invention Example 32 0.002 2.98 0.50 0.009 0.0033 0.50 0.0029 0.01 0.011 0.001 0.002 Sb：0.19 13.31 Invention Example 33 0.002 3.02 0.49 0.010 0.0031 0.50 0.0027 0.01 0.010 0.001 0.002 Sb：0.21 13.45 Invention Example 34 0.002 3.10 0.49 0.01 0.0032 0.50 0.0025 0.01 0.010 0.001 0.002 Mg: 0.01, REM: 0.01, B: 0.005, Ni: 0.1, Cr: 0.5, V: 0.01, Nb: 0.002, Ta: 0.001, W: 0.03, Pb: 0.001, Co: 0.05, Ga: 0.01, Ge: 0.01, As: 0.01 13.42 Invention Example

<Example 2> Steel having a composition comprising 0.002% C, 3.00% Si, 0.50% Mn, 0.01% P, 0.0030% S, 0.50% Al, 0.0020% N, 0.01% Cu, 0.010% Mo, 0.001% Zn, and 0.002% Ti, with the remainder consisting of Fe and inevitable impurities, was melted and continuously cast into steel slabs. Hot-rolled steel sheets for non-oriented electromagnetic steel were produced under the conditions shown in Table 2.

The resulting hot-rolled steel sheet was annealed at 1000°C for 30 seconds to produce a hot-rolled annealed sheet. The hot-rolled annealed sheet was then cold-rolled to produce a 0.30 mm thick cold-rolled steel sheet. The cold-rolled steel sheet was then finish-annealed at 1000°C for 10 seconds to produce a non-oriented electromagnetic steel sheet.

Epstein samples measuring 30 mm wide and 280 mm long were cut from the resulting non-oriented electromagnetic steel sheet in both the rolling and width directions. The steel loss W10 _/400 was measured using an Epstein tester. For a sheet thickness of 0.30 mm, a W10 _/400 of 13.50 W/kg or less was considered acceptable.

As can be seen from the results shown in Table 2, under manufacturing conditions that meet the requirements of the present invention, a non-oriented electromagnetic steel sheet with good iron loss can be obtained.

[Table 2] No. Slab thickness Tunnel furnace Hot rolling W _10/400 Remarks Inlet temperature Outlet temperature Keep warm time Cooling speed Inlet temperature Outlet temperature strain speed Winding temperature mm ℃ ℃ min ℃/s ℃ ℃ 1/s ℃ W/kg 35 60 903 1093 10 2.7 990 836 3.4 527 13.21 Invention Example 36 25 908 1086 11 2.6 980 836 3.0 540 13.64 Comparative example 37 30 916 1097 11 2.1 988 833 3.0 526 13.45 Invention Example 38 175 912 1102 10 2.7 984 832 3.1 533 13.42 Invention Example 39 60 842 1109 9 2.3 976 830 3.0 520 13.67 Comparative example 40 60 855 1108 10 2.3 981 847 3.3 521 13.49 Invention Example 41 60 900 1035 10 2.5 970 846 2.6 527 13.56 Comparative example 42 60 894 1052 11 2.5 984 849 3.2 528 13.41 Invention Example 43 60 897 1193 10 2.2 986 839 3.2 533 13.38 Invention Example 44 60 896 1211 10 2.8 987 846 3.3 520 13.52 Comparative example 45 60 891 1115 7 2.4 983 835 3.4 534 13.59 Comparative example 46 60 919 1105 8 2.2 978 837 3.2 530 13.47 Invention Example 47 60 900 1117 9 4.3 984 832 2.8 526 13.61 Comparative example 48 60 908 1086 10 3.9 988 844 3.1 538 13.45 Invention Example 49 60 899 1088 11 2.5 934 848 2.9 530 13.56 Comparative example 50 60 897 1105 11 2.5 955 838 2.8 527 13.49 Invention Example 51 60 911 1097 10 2.7 980 786 3.2 523 13.58 Comparative example 52 60 912 1120 11 2.2 978 805 2.7 536 13.42 Invention Example 53 60 910 1089 10 2.4 980 839 1.4 520 13.55 Comparative example 54 60 894 1115 9 2.5 984 836 1.6 534 13.45 Invention Example 55 60 907 1092 11 2.9 988 836 3.5 492 13.57 Comparative example 56 60 899 1094 9 2.2 974 844 2.6 503 13.41 Invention Example

Figure 1 is a graph showing the relationship between the S content and the steel loss W10 _/400 in the non-oriented electromagnetic steel sheet in Experiment 1. Figure 2 is a graph showing the relationship between the steel billet inlet temperature to the hot rolling mill and the steel loss W10 _/400 in hot rolling of the non-oriented electromagnetic steel sheet in Experiment 2. Figure 3 is a graph showing the relationship between the strain rate in the first pass and the steel loss W10 _/400 in hot rolling of the non-oriented electromagnetic steel sheet in Experiment 3.

Claims (3)

A method for manufacturing a hot-rolled steel plate for use as a non-oriented electromagnetic steel plate comprises: a heat-holding step of casting molten steel into a steel billet having a thickness ranging from 30 mm to 180 mm, and then heat-holding the steel billet in a tunnel furnace; and a hot-rolling step of hot-rolling the steel billet, wherein the molten steel has the following composition, which comprises, by mass%, the following: C: 0.010% or less, Si: 2.50% or more and 5.00% or less, Mn: 0.10% or more and 3.00% or less, P: 0.100% or less, S: 0.0010% or more and 0.0050% or less, Al: 2.00% or less, N: 0.0080% or less, Cu: 1.00% or less, Mo: 0.050% or less, Zn: 0.010% or less, and Ti: 0.010% or less, optionally further containing at least one element selected from the following groups: Group A: at least one element selected from Sn: 0.20% or less and Sb: 0.20% or less; Group B: at least one element selected from Mg: 0.0001% or more and 0.10% or less and rare earth metals: 0.0001% or more and 0.10% or less; Group C: B: 0.002% or more and 0.01% or less; Group D: Ni: 0.01% or more and 1.0% or less; Group E: Cr: 0.1% or more and 5.0% or less; The F group is at least one selected from V: 0.001% to 0.050%, Nb: 0.001% to 0.005%, Ta: 0.0001% to 0.0020%, W: 0.001% to 0.050%, and Pb: 0.0001% to 0.0020%. The G group is Co: 0.001% to 0.100%. The H group is at least one selected from Ga: 0.0005% to 0.0300%, and Ge: 0.0005% to 0.0300%. The I group is As: 0.001% to 0.020%. The remainder consists of Fe and unavoidable impurities. In the method for manufacturing hot-rolled steel sheets for non-oriented electromagnetic steel, During the holding step, the surface temperature of the steel slab at the inlet side of the tunnel furnace is set to 850°C or higher, and the surface temperature of the steel slab at the outlet side of the tunnel furnace is set to a range of 1050°C or higher and 1200°C or lower. The holding time in the tunnel furnace is set to 8 minutes or longer. The hot rolling step is carried out under the following conditions: the cooling rate of the steel billet from the exit of the tunnel furnace to the entrance of the hot rolling mill is set to 4°C/s or less, the temperature at the entrance of the hot rolling mill is set to 950°C or above, the temperature at the exit of the hot rolling mill is set to 800°C or above, the strain rate in the first pass of hot rolling is set to 1.5/s or above, and the coil winding temperature is set to 500°C or above. The method for producing a hot-rolled steel plate for non-oriented electromagnetic steel according to claim 1, wherein the molten steel is tapped from an electric furnace or a converter. A method for manufacturing a non-oriented electromagnetic steel sheet comprises: a hot-rolled steel sheet manufacturing step of manufacturing a hot-rolled steel sheet using the method for manufacturing a hot-rolled steel sheet for a non-oriented electromagnetic steel sheet as claimed in claim 1 or 2; a hot-rolled steel sheet annealing step of annealing the hot-rolled steel sheet to produce a hot-rolled annealed steel sheet; a cold-rolling step of cold-rolling the hot-rolled annealed steel sheet to produce a cold-rolled steel sheet; and a finish annealing step of finish annealing the cold-rolled steel sheet.