JP6879341B2 - Manufacturing method of non-oriented electrical steel sheet - Google Patents

Description

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet, specifically, a method for manufacturing a high-grade grain-oriented electrical steel sheet having excellent magnetic properties and surface properties without subjecting high-temperature hot-rolled sheet annealing. Is.

In recent years, energy saving has been aimed at from the viewpoint of protecting the global environment, and along with this, high efficiency and miniaturization of electrical equipment have been actively promoted. Therefore, non-oriented electrical steel sheets, which are widely used as iron core materials for electrical equipment, are strongly required to have high magnetic flux density and low iron loss. Further, from the viewpoint of improving the space factor and improving the dimensional accuracy of the core, it is also required to suppress the waviness of the steel sheet surface called rigging.

In the production of high-grade non-oriented electrical steel sheets containing about 3 mass% of Si, it is common practice to annead the hot-rolled steel sheets (hot-rolled sheets) at a high temperature of about 1000 ° C. ing. This is because the steel containing about 3 mass% of Si is a ferrite single-phase steel, and deformation does not occur during hot rolling. Therefore, the steel sheet structure after hot rolling is mainly unrecrystallized, and hot-rolled sheet annealing is performed. This is because if it is not recrystallized and recrystallized, the magnetic properties will deteriorate and rigging will occur. However, performing hot-rolled sheet annealing inevitably leads to a decrease in manufacturing capacity due to an increase in processes and an increase in manufacturing costs due to an increase in the load of process control.

Therefore, as a method of omitting hot-rolled sheet annealing, Patent Document 1 and Patent Document 2 propose a technique of raising the finish rolling end temperature in hot rolling to promote recrystallization by self-annealing.

Japanese Unexamined Patent Publication No. 62-054023 Japanese Unexamined Patent Publication No. 2007-154271

However, the techniques of Patent Documents 1 and 2 have been studied only mainly for steels containing about 2 mass% of Si. Therefore, in high-grade steel having a higher Si content, recrystallization is more difficult to proceed, and there is a problem that the effect of suppressing rigging cannot be stably obtained. Further, when the finish rolling end temperature of hot rolling is raised, there is a problem that it becomes difficult to control the shape of the hot rolled plate.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to obtain magnetic properties without performing hot-rolled sheet annealing at a high temperature or without performing hot-rolled sheet annealing. The purpose of the present invention is to propose a method for manufacturing a high-grade non-oriented electrical steel sheet which is excellent and does not cause rigging.

In order to achieve the above problems, the inventors have made extensive studies focusing on the finish rolling conditions of hot rolling. As a result, by optimizing the rolling conditions of the first pass in the finish rolling of hot rolling, the magnetic properties are excellent without subjecting hot-rolled sheet annealing at high temperature or without performing hot-rolled sheet annealing. Moreover, they have found that it is possible to manufacture a high-grade non-oriented electrical steel sheet that does not cause rigging, and have completed the present invention.

That is, in the present invention, C: 0.0050 mass% or less, Si: 2.0 to 5.0 mass%, Mn: 3.0 mass% or less, P: 0.20 mass% or less, S: 0.0050 mass% or less, Al. : 3.0 mass% or less, N: 0.0050 mass% or less and O: 0.010 mass% or less, and the balance is hot-rolled with a component composition of Fe and unavoidable impurities, and the soaking temperature is 900 ° C. Hereinafter, a non-directional electromagnetic steel sheet that is subjected to cold rolling once or two or more times with an intermediate annealing sandwiched between them without performing hot-rolled sheet annealing or hot-rolled sheet annealing within a soaking time of 5 min or less to finish annealing. In the manufacturing method
The entry-side temperature FET in the first pass of finish rolling in the hot rolling is set to 970 ° C. or higher, and
The first pass of the finish rolling is the following formula (1);
α = FET + 43.4 × ln (SR) ・ ・ ・ (1)
Here, FET: entry side temperature (° C.) in the first pass of finish rolling.
SR: Strain rate of the first pass of finish rolling (s ^-1 )
We propose a method for manufacturing non-oriented electrical steel sheets, which is characterized by rolling under the condition that α defined in 1 is 1070 or more.

The method for producing a non-oriented electrical steel sheet of the present invention is characterized in that the steel sheet is reheated before the finish rolling of the hot rolling.

Further, the method for manufacturing a non-oriented electrical steel sheet of the present invention is characterized in that the finish rolling end temperature FDT in the hot rolling is 900 ° C. or higher and the coil winding temperature CT is 700 ° C. or lower.

Further, the slab used in the method for producing a non-oriented electrical steel sheet of the present invention has, in addition to the above component composition, Sn: 0.005 to 0.20 mass% and Sb: 0.005 to 0.20 mass%. It is characterized by containing one or two kinds selected from.

Further, in the slab used in the method for producing a non-oriented electrical steel sheet of the present invention, in addition to the above component composition, Ca: 0.0005 to 0.020 mass%, Mg: 0.0005 to 0.020 mass% and REM. : It is characterized by containing one or more selected from 0.0005 to 0.020 mass%.

According to the present invention, it is possible to manufacture a high-grade non-directional electromagnetic steel plate having excellent magnetic properties and no rigging without subjecting hot-rolled sheet annealing at a high temperature or without subjecting hot-rolled sheet annealing. This not only makes it possible to shorten or reduce the manufacturing process, but also greatly contributes to improving product quality and reducing manufacturing costs.

It is a graph which shows the influence which the entry-side temperature FET and the strain rate SR of the 1st pass of finish rolling have on rigging.

First, the experiment that triggered the development of the present invention will be described.
C: 0.0016 mass%, Si: 3.11 mass%, Mn: 0.46 mass%, P: 0.01 mass%, S: 0.0015 mass%, Al: 1.12 mass%, N: 0.0017 mass%, Ni : 0.01 mass%, Cr: 0.01 mass%, Ti: 0.0005 mass%, Nb: 0.0001 mass% and O: 0.0028 mass%, and the balance is Fe and unavoidable impurities. It was melted in a vacuum melting furnace to obtain a 50 kg ingot.

Next, the ingot was reheated to a temperature of 1150 ° C. for 30 minutes and then roughly rolled to obtain a sheet bar having a thickness of 50 mm. Next, the sheet bar was cooled to room temperature, reheated to a temperature of 1150 ° C. and held for 30 minutes, and then the finish rolling of the actual machine was simulated using a 5-stand hot rolling mill having a work roll diameter of 300 mmφ. Hot rolling (finish rolling) was carried out to obtain a hot-rolled plate having a plate thickness of 2.3 mm. At this time, the temperature of the steel plate on the exit side of the rolling mill of 5 stands, that is, the finish rolling end temperature FDT is set to 840 ° C. (constant), and the inlet temperature FET and strain rate SR of the first pass of finish rolling are variously changed for rolling. Was done.
Next, the steel sheet (hot-rolled sheet) after the hot-rolling was pickled and cold-rolled to obtain a cold-rolled sheet having a final plate thickness of 0.3 mm, and then finish annealing at 980 ° C. × 10 s was performed.
The surface of the steel sheet after finish annealing thus obtained was visually observed, and the state of occurrence of rigging was evaluated.

The results of the above experiment are shown in FIG. From this figure, the entry-side temperature FET of the first pass of the finish rolling of hot rolling is set to 970 ° C. or higher, and the first pass of the finish rolling is defined by the following equation (1);
α = FET + 43.4 × ln (SR) ・ ・ ・ (1)
Here, FET: entry side temperature (° C.) in the first pass of finish rolling.
SR: Strain rate of the first pass of finish rolling (s ^-1 )
It was found that the occurrence of rigging was suppressed by rolling under the condition that α defined in 1 was 1070 or more.

The inventors think of this reason as follows.
When the first pass of finish rolling is rolled at a high temperature and a high strain rate, static recrystallization after the first pass is promoted, so that the texture can be randomized and the structure can be miniaturized. Achieved. Further, since the structure recrystallized and refined after the first pass of rolling is promoted to be recrystallized even after the second pass, the randomization of the texture is further promoted and the rigging is suppressed.

In addition, all the hot-rolled plates obtained in this experiment had an unrecrystallized structure (processed structure) except for the surface layer portion. From now on, in order to suppress rigging, it is not always necessary to recrystallize the hot-rolled sheet structure after hot-rolling, and the texture may be randomized by the recrystallization during the finish rolling of hot-rolling described above. It was also found that, in that case, the steel sheet structure after the completion of hot rolling may be an unrecrystallized structure. Therefore, if the temperature of the steel sheet on the entry side of the finish rolling mill, that is, the rolling conditions of the first pass of the finish rolling is optimized, rigging can be suppressed without unnecessarily increasing the finish rolling end temperature FDT. It turned out that there was.
The present invention has been developed based on the above new findings.

Next, the composition of the steel material (slab) used in the production of the non-oriented electrical steel sheet of the present invention will be described.
C: 0.0050 mass% or less C is a harmful element that causes magnetic aging in the product plate to form carbides and deteriorates iron loss. Therefore, in the present invention, the C content is limited to 0.0050 mass% or less in order to suppress the magnetic aging. It is preferably 0.0030 mass% or less.

Si: 2.0-5.0 mass%
Si is an effective component for increasing the specific resistance of steel and reducing iron loss. However, if Si is less than 2.0 mass%, the above effect is small, while if it exceeds 5.0 mass%, rolling becomes difficult. Therefore, the Si content is in the range of 2.0 to 5.0 mass%. Since the present invention is intended for high-grade steels that are unlikely to undergo recrystallization, it is preferably applied to steels having a Si: 2.5 mass% or more in which the effects of the present invention are remarkable. Further, the upper limit of Si is preferably 4.5 mass% or less in consideration of manufacturability.

Mn: 3.0 mass% or less Mn has the effect of improving hot workability by fixing S as MnS, reduces fine sulfides, improves grain growth and reduces iron loss. effective. Furthermore, by adding a large amount of Mn, the solid solution temperature of MnS rises and resolid solution and the accompanying fine precipitation are suppressed, so that deterioration of iron loss characteristics due to an increase in the slab heating temperature, which will be described later, is suppressed. You can also do it. However, when the Mn content exceeds 3.0 mass%, Mn carbonitride is precipitated, and iron loss is worsened. Therefore, the Mn content is set to 3.0 mass% or less. In addition, in order to obtain the above-mentioned iron loss reducing effect, it is preferable to add 0.4 mass% or more. The upper limit of Mn is preferably 2.0 mass%.

P: 0.20 mass% or less P is an element used for adjusting the strength of steel because it has a large solid solution hardening ability, and can be added as appropriate. However, if it exceeds 0.20 mass%, the steel becomes brittle and it becomes difficult to perform cold rolling. Therefore, the upper limit of P is set to 0.20 mass%. Preferably, it is 0.08 mass% or less.

S: 0.0050 mass% or less S is a harmful element that forms fine sulfides, inhibits grain growth, and increases iron loss, so it is desirable to reduce it as much as possible. In particular, when the S content exceeds 0.0050 mass%, the above adverse effect becomes remarkable, so the upper limit is set to 0.0050 mass%. By reducing S to 0.0010 mass% or less, deterioration of iron loss characteristics due to an increase in the slab heating temperature, which will be described later, can be suppressed. Therefore, it is preferably 0.0025 mass% or less, more preferably 0. It is 0010 mass% or less.

Al: 3.0 mass% or less Al has the effect of increasing the specific resistance of steel and reducing iron loss, similar to Si. Further, by fixing N as AlN, there is an effect of reducing the precipitation of fine AlN, improving the grain growth property, and reducing the iron loss. Furthermore, by adding a large amount of Al, the solid solution temperature of AlN rises and resolid solution and the accompanying fine precipitation are suppressed, so that deterioration of iron loss characteristics due to an increase in the slab heating temperature, which will be described later, is suppressed. You can also do it. However, if the Al content exceeds 3.0 mass%, rolling becomes difficult. Therefore, Al is set to 3.0 mass% or less. It is preferably 2.0 mass% or less. If the Al content is less than 0.5 mass%, the above-mentioned iron loss improving effect is small, so that the Al content is preferably 0.5 mass% or more.

Al is also an element that forms fine AlN, inhibits grain growth, and adversely affects iron loss characteristics. Therefore, by reducing the Al content as much as possible and reducing the amount of AlN precipitated, grain growth can be promoted and iron loss can be improved. In order to obtain this effect, Al is preferably reduced to 0.05 mass% or less. It is more preferably 0.01 mass% or less, still more preferably 0.005 mass% or less. When Al is reduced, the effect of improving the magnetic flux density by improving the texture can be expected, so that it is particularly suitable for the present invention for high-grade steel in which the magnetic flux density tends to decrease due to omission of hot-rolled sheet annealing. Is.

N: 0.0050 mass% or less N is a harmful element that forms fine nitrides, inhibits grain growth, and increases iron loss. In particular, when the N content exceeds 0.0050 mass%, the above adverse effect becomes remarkable, so the upper limit is set to 0.0050 mass%. By reducing N to 0.0010 mass% or less, deterioration of iron loss characteristics due to an increase in the slab heating temperature, which will be described later, can be suppressed, so that it is more preferably 0.0010 mass% or less.

The steel material used for producing the non-oriented electrical steel sheet of the present invention can appropriately contain the following components in addition to the above components.
Sn: 0.005 to 0.20 mass%, Sb: 0.005 to 0.20 mass%
Sn and Sb have the effect of improving the recrystallization texture and improving the magnetic flux density and iron loss. The above effect cannot be sufficiently obtained when the Sn and Sb contents are less than 0.005 mass%, respectively. On the other hand, even if Sn and Sb are added in an amount of 0.20 mass% or more, the above effect is saturated. Therefore, it is preferable to add Sn and Sb in the range of 0.005 to 0.20 mass%, respectively.

Ca: 0.0001 to 0.020 mass%, Mg: 0.0001 to 0.020 mass%, REM: 0.0001 to 0.020 mass%
Ca, Mg and REM form stable sulfides and selenium compounds and have the effect of improving grain growth. Further, Ca, Mg and REM also have an effect of suppressing deterioration of iron loss characteristics due to an increase in the slab heating temperature, which will be described later, by fixing S that forms a precipitate that inhibits grain growth. The above effect cannot be sufficiently obtained when the content of one or more of Ca, Mg and REM is less than 0.0001 mass%, respectively. On the other hand, when the content of one or more of Ca, Mg and REM exceeds 0.020 mass%, inclusions (compounds of Ca, Mg and REM) increase, and iron loss increases on the contrary. become. Therefore, it is preferable to add Ca, Mg and REM in the range of 0.0001 to 0.020 mass%, respectively. More preferably, they are in the range of 0.0005 to 0.010 mass%, respectively.

In the steel material used for producing the non-oriented electrical steel sheet of the present invention, the balance other than the above components is Fe and unavoidable impurities. However, elements such as Cr, Ni and Cu have the effect of improving iron loss and strength without adversely affecting the effects of the present invention as long as they are within an appropriate range, and can be added as appropriate, but they are raw materials. From the viewpoint of cost reduction, it is desirable that each of these elements is 1 mass% or less. Further, since the elements forming carbonitrides and sulfides such as Ti, Nb, V and Zr are harmful to the magnetic properties, it is desirable to reduce these elements as much as possible, and specifically, each of them. It is preferably 0.002 mass% or less.

Next, the method for manufacturing the non-oriented electrical steel sheet of the present invention will be described.
The non-directional electromagnetic steel sheet of the present invention is obtained by heating a steel material (slab) having a composition suitable for the present invention to a predetermined temperature and then hot rolling to obtain a hot-rolled plate, and the hot-rolled plate is heated. By performing cold rolling once or two or more times with intermediate annealing sandwiched between them to obtain the final plate thickness, finish annealing, and if necessary, an insulating film is applied, with or without rolling sheet annealing. Can be manufactured.

Here, for the steel material (slab), steel having a component composition suitable for the present invention is melted by a conventional refining process consisting of a converter, vacuum degassing, etc., and a conventional continuous casting method or ingot formation is performed. -Can be manufactured by using a bulk rolling method or the like. A thin slab caster in which continuous casting and hot rolling are directly connected may be used as a steel material.

The slab is heated to a predetermined temperature and then subjected to hot rolling, but the slab heating is not essential and may be omitted. For example, in the case of direct rolling HDR in which hot rolling is performed immediately after continuous casting, or in the case of the thin slab. When slab heating is performed, the heating temperature is preferably in the range of 1000 to 1300 ° C. When the slab heating temperature exceeds 1300 ° C., precipitate-forming elements such as AlN and MnS are solid-solved in the steel and reprecipitated in the subsequent process to inhibit grain growth and adversely affect the iron loss characteristics. .. On the other hand, if the temperature is lower than 1000 ° C., not only the load of hot rolling increases, but also the finish rolling inlet side temperature FET and the finish rolling end temperature FDT cannot be secured.

Hot rolling is performed by a plurality of single-stand rolling mills for rough rolling in which a slab is used as a sheet bar having a predetermined plate thickness, and a finishing rolling mill consisting of a plurality of stands following the above-mentioned rough rolling to continuously reach a target plate thickness. It is generally composed of finish rolling, which involves rolling. For rough rolling, it is industrially difficult to control the strain rate, so no particular conditions are specified. Further, in the case of producing a thin slab with the above-mentioned thin slab casters, rough rolling may be omitted. The slab thickness in this case is preferably in the range of 10 to 100 mm.

In the finish rolling following the rough rolling, the temperature of the steel plate on the entry side of the first pass, that is, the temperature FET (° C.) on the entry side of the finish rolling is set to 970 ° C. or higher, and the first pass of the finish rolling is defined by the following equation (1);
α = FET + 43.4 × ln (SR) ・ ・ ・ (1)
Here, FET: entry side temperature (° C.) in the first pass of finish rolling.
SR: Strain rate of the first pass of finish rolling (s ^-1 )
It is important to roll under the condition that α defined in is 1070 or more. As a result, static recrystallization in finish rolling is promoted, and rigging can be suppressed. If the FET is lower than 970 ° C., it becomes difficult to promote recrystallization even if the strain rate is increased within a range of realistic hot rolling conditions. Therefore, the lower limit of the FET needs to be set to 970 ° C. The preferred FET is 1030 ° C. or higher, and α is 1100 or higher.

Various calculation formulas have been proposed for the strain rate SR (s ^-1 ), but in the present invention, the following formula known as the Sims formula is used.

Further, the temperature of the steel sheet on the side of the final pass of the finish rolling of hot rolling, that is, the finish rolling end temperature FDT is preferably 900 ° C. or higher, more preferably 940 ° C. or higher, from the viewpoint of improving the magnetic characteristics. .. As a result, the recrystallization and grain growth of the hot-rolled sheet are promoted, and the magnetic properties can be further improved. The high temperature of the FDT can be achieved by raising the slab heating temperature, optimizing the path schedule, reheating during hot rolling, adjusting the amount of strip coolant, and the like. On the other hand, when the FDT becomes equal to or higher than the solid solution temperature of MnS or AlN, the precipitate may become finer and the iron loss may increase. Therefore, the FDT is preferably set to 1100 ° C. or lower.

Here, the purpose of reheating during the hot rolling is to raise the rolling temperature in the finish rolling and promote recrystallization during the hot rolling of the finish. Therefore, the reheating is preferably performed on the seat bar after rough rolling and before finish rolling, and as a means for reheating, for example, a conventionally known induction heating type seat bar heater is used. Is preferable. When the seat bar is reheated, the temperature is preferably equal to or lower than the slab heating temperature. As a result, the resolidification of precipitates such as AlN and MnS is suppressed, so that adverse effects on grain growth due to reprecipitation of AlN and MnS, and thus adverse effects on iron loss can be avoided. When the reheating temperature is higher than the slab heating temperature or 1150 ° C. or higher, Ca, REM, Mg, etc. are added to fix S as a coarse inclusion and suppress the formation of fine MnS. Is preferable. When slab heating is omitted by using a thin slab caster or the like, the reheating temperature of the seat bar is not particularly limited, but it is still preferable to add Ca, REM, Mg or the like.

On the other hand, when the temperature of the FDT is increased, it becomes difficult to control the shape of the steel sheet after hot rolling. Therefore, in order to achieve both magnetic properties and steel plate shape, the upper limit of FDT is preferably about 1000 ° C. If the temperature of the FDT is not increased, the magnetic flux density tends to decrease, but a steel material in which the Al content is reduced to a very small amount is used, or a steel material to which a small amount of grain boundary segregation elements such as Sn and Sb are added. The above-mentioned adverse effects can be alleviated by using.

Further, the coil winding temperature CT after hot rolling is preferably 700 ° C. or lower because the descalability deteriorates when it exceeds 700 ° C.

The steel sheet (hot-rolled sheet) after the hot-rolling can be subjected to cold-rolling without subjecting the hot-rolled sheet to annealing, but the hot-rolled sheet is annealed for the purpose of further improving the magnetic properties and surface properties. May be good. However, when hot-rolled sheet is annealed, in the present invention, rigging can be suppressed by optimizing the hot rolling conditions, so that the annealing conditions at low temperature for a short time, specifically, the soaking temperature is 900 ° C. or less. Even under annealing conditions where the soaking time is 5 min or less, excellent magnetic properties and surface properties can be obtained.

Next, the steel sheet after the hot rolling or hot rolling sheet annealing was subjected to one cold rolling or two or more cold rollings sandwiching the intermediate annealing to obtain a predetermined final sheet thickness (product sheet thickness). After that, finish annealing is performed. In the finish annealing, the annealing temperature is preferably in the range of 900 to 1100 ° C. from the viewpoint of reducing iron loss and reducing defects by pickup. The finish annealing atmosphere is preferably a non-oxidizing atmosphere or a reducing atmosphere, for example, a dry N ₂ atmosphere or _{an H 2-} N ₂ mixed atmosphere having an _{oxygen potential PH2O} / _PH2 of 0.1 or less. It is preferable to do so. Further, after finish annealing, an insulating film may be applied if necessary, and a known organic, inorganic, or organic / inorganic mixed film can be applied depending on the purpose.

C: 0.0013 to 0.0025 mass%, Si: 2.8 mass%, Mn: 0.4 mass%, P: 0.01 mass%, S: 0.0009 to 0.0015 mass%, Al: 0.9 mass%, N: 0.0012 to 0.0017 mass%, Ni: 0.01 mass%, Cr: 0.01 mass%, Ti: 0.0005 mass% or less, Nb: 0.0002 mass% or less and O: 0.0011 to 0.0023 mass %, Further, other elements shown in Table 1, and a steel having a component composition in which the balance is composed of Fe and unavoidable impurities, by a conventional refining process consisting of a converter, a vacuum degassing device, etc. After melting, a steel material (slab) having a thickness of 200 mm was obtained by a continuous casting method. Next, as shown in Table 1, the slab was heated to various slab heating temperatures, soaked for 30 minutes, and then hot-rolled at the finish rolling end temperature FDT shown in Table 1 to obtain a plate thickness of 2. After forming a 0.0 mm hot-rolled plate, the coil was wound at a coil winding temperature of 590 ° C. At this time, in the first pass of the finish rolling in the hot rolling, a work roll having a diameter of 800 mmφ is used, and the entry side thickness (sheet bar thickness), the roll peripheral speed (rolling speed) and the rolling reduction of the first pass of the finish rolling are determined. By changing the strain rate SR in the first pass of finish rolling, the strain rate SR was changed in various ways. Further, under some conditions, the sheet bar after rough rolling was reheated to the temperature shown in Table 1 by an induction heating type sheet bar heater installed in front of the finish rolling mill, and then finish rolling was performed.
Next, the hot-rolled sheet is subjected to hot-rolled sheet annealing, which is held at the same temperature shown in Table 1 for 30 seconds, or without being pickled, descaled, and then cold-rolled. A cold rolled plate with a final plate thickness of 0.3 mm was used.
Next, the cold-rolled sheet was subjected to finish annealing at a soaking temperature of 990 ° C. and a soaking time of 10 sec in a dry atmosphere _{of H 2} : N _{2 = 25: 75 in a vol% ratio, and then an insulating film was applied.} It was made into a product board.

From the rolling direction and the plate width direction of the product plate thus obtained, a test piece having a width of 30 mm and a length of 280 mm was collected and subjected to an Epstein test in accordance with JIS C 2550-1 (2011) to obtain a magnetic flux density. B ₅₀ and iron loss W _10/400 were measured. In addition, the presence or absence of rigging and the level were visually evaluated.
The above results are shown in Table 1 together with the manufacturing conditions. The steel sheet No. which was annealed by hot rolling at 1000 ° C. Reference numeral 3 denotes a reference example showing the prior art. From this result, the steel sheets hot-rolled under the conditions suitable for the present invention can obtain excellent surface properties and magnetic properties at the same level as the steel sheets subjected to hot-rolled sheet annealing without subjecting hot-rolled sheet annealing. You can see that it has been rolled.
Further, the magnetic flux density B ₅₀ tends to be slightly inferior to that when the hot-rolled plate is not annealed, but can be improved by increasing the temperature of the FDT and adding Sn and Sb, and also the FET and FDT. When the slab heating temperature is raised to increase the temperature of the slab, the iron loss tends to increase, but it can be seen that the increase in iron loss can be suppressed by adding Ca, REM, and Mg.

Steels having the composition of A to E shown in Table 2 are melted by a conventional refining process to obtain a steel material (slab) having a thickness of 240 mm by a continuous casting method, and then shown in Table 3 in a soaking furnace. After heating to the indicated temperature and soaking for 40 minutes, hot rolling is performed at the finish rolling end temperature FDT shown in Table 3 to obtain a hot-rolled plate having a plate thickness of 2.3 mm, and then a coil winding temperature of 560 ° C. I rolled it up with. At this time, for the first pass of the finish rolling, a work roll diameter of 600 mmφ is used, and the entry side thickness (seat bar thickness), the roll peripheral speed (rolling speed) and the rolling rate of the first pass of the finish rolling are changed to change the first pass. The strain rate SR of was changed in various ways. Further, under some conditions, the sheet bar after rough rolling was reheated to the temperature shown in Table 3 by an induction heating type sheet bar heater installed in front of the finish rolling mill, and then finish rolling was performed.
Next, the hot-rolled sheet is subjected to hot-rolled sheet annealing, which is also maintained at the temperature shown in Table 3 for 30 seconds, or without being pickled, descaled, and then cold-rolled. A cold rolled plate with a final plate thickness of 0.3 mm was used.
Next, the cold-rolled sheet is subjected to finish annealing at a soaking temperature of 1010 ° C. and a soaking time of 20 sec in a dry atmosphere _{of H 2} : N _{2 = 20: 80 in a vol% ratio, and then an insulating film is applied.} It was made into a product board.

From the rolling direction and the plate width direction of the product plate thus obtained, a test piece having a width of 30 mm and a length of 280 mm was collected and subjected to an Epstein test in accordance with JIS C 2550-1 (2011) to obtain a magnetic flux density. B ₅₀ and iron loss W _10/400 were measured. In addition, the presence or absence of rigging and the level were visually evaluated.

The above results are shown in Table 3 together with the manufacturing conditions. The steel sheet No. which was annealed by hot rolling at 980 ° C. or higher. 1, 5, 9, 13 and 17 are reference examples showing the prior art. From this result, all of the hot-rolled steel sheets under the conditions suitable for the present invention have excellent surface properties equivalent to those of the hot-rolled sheet annealed steel sheets, even if they are not hot-rolled sheet annealed. It can be seen that not only is it excellent in magnetic properties. Further, it can be seen that the steel A having a low Al content has a larger increase in iron loss when the slab heating temperature is raised than the steel B having a high Al content, and it is advantageous to increase the Al content. .. On the contrary, steel C having a very low Al content also has a small increase in iron loss when the slab heating temperature is raised. Further, the steel D having a low Si content is a so-called transformed steel that undergoes transformation during hot rolling, but excellent surface properties and magnetic properties are obtained by satisfying the production conditions of the present invention.

Claims (5)

C: 0.0050 mass% or less, Si: 2.0 to 5.0 mass%, Mn: 3.0 mass% or less, P: 0.20 mass% or less, S: 0.0050 mass% or less, Al: 3.0 mass% or less , N: 0.0050 mass% or less and O: 0.010 mass% or less, and the balance is composed of Fe and unavoidable impurities. In the method for producing a non-directional electromagnetic steel sheet, which is subjected to one cold rolling or two or more times of cold rolling with an intermediate annealing sandwiched in between, and finish annealing without subjecting hot-rolled sheet annealing or hot-rolled sheet annealing below.
The entry-side temperature FET in the first pass of finish rolling in the hot rolling is set to 970 ° C. or higher and 1040 ° C. or lower , and
A method for producing a non-oriented electrical steel sheet, which comprises rolling the first pass of finish rolling under the condition that α defined by the following equation (1) is 1070 or more.
Description α = FET + 43.4 × ln (SR) ・ ・ ・ (1)
Here, FET: entry side temperature (° C.) in the first pass of finish rolling.
SR: Strain rate of the first pass of finish rolling (s ^-1 ) The method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the steel sheet is reheated before the finish rolling of the hot rolling. The method for manufacturing a non-oriented electrical steel sheet according to claim 1 or 2, wherein the finish rolling end temperature FDT in the hot rolling is 900 ° C. or higher, and the coil winding temperature CT is 700 ° C. or lower. The slab is characterized by further containing one or two selected from Sn: 0.005 to 0.20 mass% and Sb: 0.005 to 0.20 mass% in addition to the component composition. The method for manufacturing a non-oriented electrical steel sheet according to any one of claims 1 to 3. The slab is further selected from Ca: 0.0001 to 0.020 mass%, Mg: 0.0001 to 0.020 mass% and REM: 0.0001 to 0.020 mass% in addition to the above component composition1 The method for producing a non-oriented electrical steel sheet according to any one of claims 1 to 4, which comprises seeds or two or more kinds.

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