JP2020033640A - Production method of non-oriented electromagnetic steel sheet - Google Patents

Abstract

To provide a production method of a high-level non-oriented electromagnetic steel sheet having excellent magnetic properties and no ridging without performing hot-rolled sheet annealing at high temperatures or without performing hot-rolled sheet annealing.SOLUTION: The non-oriented electromagnetic steel sheet is manufactured by hot rolling a slab containing C: 0.0050% or less, Si: 2.0-5.0%, Mn: 3.0% or less, P: 0.20% or less, S: 0.0050% or less, Al: 3.0% or less, N: 0.0050% or less, and O: 0.010% or less, and performing hot-rolled sheet annealing at a soaking temperature of 900°C or lower, a soaking time period of 5 min or shorter, or alternatively cold rolling and finish rolling without performing hot-rolling sheet annealing. In this manufacturing method, an entry temperature FET (°C) of a first pass of the finish rolling in the hot rolling is set to 970°C or higher, and the first pass of the finish rolling is performed under a condition that α defined by the following formula: α=FET+43.4×ln(SR) (where SR: the strain rate (s) of the first pass of the finish rolling) is 1070 or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a non-oriented electrical steel sheet, specifically, a method for producing a high-grade non-oriented electrical steel sheet having excellent magnetic properties and surface properties without performing high-temperature hot-rolled sheet annealing. It is.

  In recent years, energy conservation has been pursued from the viewpoint of protecting the global environment, and accordingly, the efficiency and size of electric devices have been actively promoted. For this reason, non-oriented electrical steel sheets that are widely used as iron core materials for electrical equipment have been strongly required to have high magnetic flux density and low iron loss. In addition, from the viewpoint of improving the space factor and improving the dimensional accuracy of the core, it is also required to suppress undulation of the steel sheet surface, which is called ridging.

  In the production of high-grade non-oriented electrical steel sheets containing about 3 mass% of Si, hot-rolled steel sheets (hot-rolled sheets) are generally subjected to hot-rolled sheet annealing at a high temperature of about 1000 ° C. ing. This is because a steel containing about 3 mass% of Si is a ferritic single-phase steel and does not undergo transformation during hot rolling. If the recrystallization is not performed to form a recrystallized structure, the magnetic properties are reduced and ridging is caused. However, performing hot-rolled sheet annealing inevitably causes a decrease in manufacturing capacity due to an increase in the number of steps and an increase in manufacturing cost due to an increase in the load of step management.

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

JP-A-62-054023 JP 2007-154271 A

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

  The present invention has been made in view of the above-mentioned problems of the related art, and has as its object to perform magnetic properties without performing hot-rolled sheet annealing at a high temperature or without performing hot-rolled sheet annealing. An object of the present invention is to propose a method for manufacturing a high-grade non-oriented electrical steel sheet which is excellent in ridging and excellent in ridging.

  In order to achieve the above-mentioned subject, the inventors focused on finishing rolling conditions of hot rolling and made intensive studies. As a result, by optimizing the rolling conditions in the first pass in the finish rolling of the hot rolling, the magnetic properties are excellent without performing the hot-rolled sheet annealing at a high temperature or without performing the hot-rolled sheet annealing. The inventors have found that a high-grade non-oriented electrical steel sheet free of ridging can be manufactured, 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 remainder is a hot rolled slab having a component composition of Fe and unavoidable impurities, and a soaking temperature of 900 ° C. Hereinafter, without subjecting the hot-rolled sheet annealing or hot-rolled sheet annealing to a soaking time of 5 min or less, the non-oriented electrical steel sheet is subjected to one or two or more cold rolling steps including intermediate annealing to finish annealing. In the manufacturing method,
The entry side temperature FET of the first pass of the finish rolling in the hot rolling is set to 970 ° C. or higher, and
The first pass of the finish rolling is represented by the following formula (1):
α = FET + 43.4 × ln (SR) (1)
Here, FET: entry temperature (° C.) in the first pass of finish rolling
SR: strain rate in the first pass of finish rolling (s ^-1 )
The present invention proposes a method for producing a non-oriented electrical steel sheet, characterized in that rolling is performed under the condition that α defined by (1) is 1070 or more.

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

  Further, the method for producing a non-oriented electrical steel sheet according to 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 further includes Sn: 0.005 to 0.20 mass% and Sb: 0.005 to 0.20 mass% in addition to the above component composition. Characterized by containing one or two selected from the group consisting of:

  The slab used in the method for producing a non-oriented electrical steel sheet according to the present invention further comprises Ca: 0.0005 to 0.020 mass%, Mg: 0.0005 to 0.020 mass%, and REM, in addition to the above component composition. : Characterized by containing one or more selected from 0.0005 to 0.020 mass%.

  According to the present invention, it is possible to produce a high-grade non-oriented electrical steel sheet having excellent magnetic properties and no ridging without hot-rolled sheet annealing at a high temperature or without hot-rolled sheet annealing. This not only shortens or reduces the number of manufacturing steps, but also greatly contributes to improving product quality and reducing manufacturing costs.

It is a graph which shows the influence which entrance temperature FET of the 1st pass of finish rolling and strain rate SR have on ridging.

First, an 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%, the balance being steel having a component composition of Fe and unavoidable impurities. It was melted in a vacuum melting furnace to form 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., held for 30 minutes, and simulated finish rolling of an actual machine using a 5-stand hot roll mill having a work roll diameter of 300 mmφ. Hot rolling (finish rolling) was performed to obtain a hot-rolled sheet having a sheet thickness of 2.3 mm. At this time, the temperature of the steel sheet on the exit side of the five-stand rolling mill, that is, the finish rolling end temperature FDT is 840 ° C. (constant), and the entrance temperature FET and the strain rate SR in the first pass of finish rolling are variously changed to perform rolling. Was done.
Next, the steel sheet (hot-rolled sheet) after the hot rolling was pickled, cold-rolled to a cold-rolled sheet having a final thickness of 0.3 mm, and then subjected to finish annealing at 980 ° C. × 10 s.
The surface of the steel sheet after the finish annealing thus obtained was visually observed to evaluate the occurrence of ridging.

The results of the above experiment are shown in FIG. From this figure, the entry 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 represented by the following formula (1);
α = FET + 43.4 × ln (SR) (1)
Here, FET: entry temperature (° C.) in the first pass of finish rolling
SR: strain rate in the first pass of finish rolling (s ^-1 )
It has been found that the occurrence of ridging is suppressed by rolling under the condition that α defined by the formula is 1070 or more.

For this reason, the inventors consider as follows.
When the first pass of finish rolling is performed at a high temperature and a high strain rate, static recrystallization after the first pass of rolling is promoted, so that the texture is randomized and the structure is refined. Achieved. Further, the microstructure recrystallized and refined after rolling in the first pass promotes recrystallization in the second and subsequent passes, so that the texture is further randomized and ridging is suppressed.

All the hot rolled sheets obtained in this experiment had an unrecrystallized structure (processed structure) except for the surface layer. From this, in order to suppress the ridging, it is not always necessary to make the hot-rolled sheet structure after hot rolling into a recrystallized state, and it is only necessary to randomize the texture by recrystallization during the finish rolling of the above-mentioned hot rolling. In that case, it was also found that the steel sheet structure after the completion of hot rolling may be an unrecrystallized structure. Therefore, by optimizing the temperature of the steel sheet on the entrance side of the finishing mill, that is, the rolling conditions in the first pass of the finishing rolling, it is possible to suppress ridging without unnecessarily increasing the finishing rolling end temperature FDT. I found it.
The present invention has been developed based on the above new findings.

Next, the component composition of the steel material (slab) used for manufacturing 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 a product plate to form carbides and deteriorate iron loss. Therefore, in the present invention, in order to suppress the magnetic aging, the content of C is limited to 0.0050 mass% or less. Preferably it is 0.0030 mass% or less.

Si: 2.0 to 5.0 mass%
Si is an effective component for increasing the specific resistance of steel and reducing iron loss. However, when the content of Si is less than 2.0 mass%, the above effect is small. On the other hand, when the content of Si exceeds 5.0 mass%, it becomes difficult to perform rolling. Therefore, the content of Si is set in the range of 2.0 to 5.0 mass%. In addition, since the present invention is intended for high-grade steel in which recrystallization is unlikely to occur, it is preferable to apply the present invention to steel of 2.5 mass% or more of Si in which the effect of the present invention is 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 an effect of improving hot workability by fixing S as MnS, and also reduces fine sulfides, improves grain growth, and reduces iron loss. effective. Further, by adding a large amount of Mn, the solid solution temperature of MnS is increased, and re-solid solution and accompanying fine precipitation are suppressed, so that deterioration of iron loss characteristics due to a higher slab heating temperature described later is suppressed. You can also. However, if the Mn content exceeds 3.0 mass%, Mn carbonitride precipitates and iron loss worsens. Therefore, the content of Mn is set to 3.0 mass% or less. In order to obtain the above-mentioned iron loss reduction effect, it is preferable to add 0.4 mass% or more. Further, 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 high 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. Therefore, it is desirable to reduce S as much as possible. In particular, when the content of S exceeds 0.0050 mass%, the above-mentioned adverse effect becomes remarkable, so the upper limit is made 0.0050 mass%. In addition, by reducing S to 0.0010 mass% or less, deterioration of iron loss characteristics due to an increase in slab heating temperature described later can be suppressed, and therefore preferably 0.0025 mass% or less, more preferably 0.1 mass% or less. 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, like Si. Further, by fixing N as AlN, there is an effect that precipitation of fine AlN is reduced, grain growth is improved, and iron loss is reduced. Further, by adding a large amount of Al, the solid solution temperature of AlN is increased and re-solid solution and accompanying fine precipitation are suppressed, so that deterioration of iron loss characteristics due to a higher slab heating temperature described later is suppressed. You can also. However, when the Al content exceeds 3.0 mass%, it becomes difficult to perform rolling. Therefore, Al is set to 3.0 mass% or less. Preferably it is 2.0 mass% or less. If the Al content is less than 0.5 mass%, the effect of improving iron loss described above is small, so that the Al content is preferably 0.5 mass% or more.

  Note that 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 to reduce the amount of AlN precipitated, it is possible to promote grain growth and improve iron loss. In order to obtain this effect, it is preferable to reduce Al to 0.05 mass% or less. More preferably, it is 0.01 mass% or less, and still more preferably 0.005 mass% or less. In addition, when Al is reduced, the effect of improving the magnetic flux density by improving the texture can also be expected, so that the present invention is particularly suitable for the present invention, which is intended for high-grade steel whose magnetic flux density is easily reduced by omitting the hot-rolled sheet annealing. It 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-mentioned adverse effects become remarkable, so the upper limit is made 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 described later can be suppressed. Therefore, 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 may further 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 effects cannot be sufficiently obtained when the contents of Sn and Sb are less than 0.005 mass%, respectively. On the other hand, even if Sn and Sb are added in amounts of 0.20 mass% or more, the above effects are saturated. Therefore, Sn and Sb are preferably added 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 have the effect of forming stable sulfides and selenides and improving grain growth. Ca, Mg and REM also have an effect of suppressing the deterioration of iron loss characteristics due to a higher slab heating temperature, which will be described later, by fixing S which forms a precipitate that inhibits grain growth. The above effects 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. become. Therefore, Ca, Mg, and REM are preferably added in the range of 0.0001 to 0.020 mass%, respectively. More preferably, they are each in the range of 0.0005 to 0.010 mass%.

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

Next, a method for producing a non-oriented electrical steel sheet according to the present invention will be described.
The non-oriented electrical steel sheet of the present invention is obtained by heating a steel material (slab) having a component composition suitable for the present invention as described above to a predetermined temperature, and then hot-rolling the steel material to form a hot-rolled sheet. By performing cold rolling once or twice or more with or without intermediate annealing, with or without performing rolled sheet annealing, after finishing to the final sheet thickness, finish annealing, and forming an insulating coating as necessary Can be manufactured.

  Here, the steel material (slab) is produced by melting a steel having a component composition compatible with the present invention by a conventional refining process including a converter and a vacuum degassing process, and using a conventional continuous casting method or ingot forming method. -It can be manufactured using a slab rolling method or the like. Note that a steel material may be used by using a thin slab caster directly connecting continuous casting and hot rolling.

  The slab is heated to a predetermined temperature and then subjected to hot rolling. However, the slab heating is not essential and may be omitted. For example, there is a case of direct-feed rolling HDR in which hot rolling is performed immediately after continuous casting, or a 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 dissolve in the steel, and re-precipitate in a later process to hinder grain growth and adversely affect iron loss characteristics. . On the other hand, when the temperature is lower than 1000 ° C., not only the load of the hot rolling increases, but also the finish rolling entrance temperature FET and the finish rolling end temperature FDT cannot be secured.

  Hot rolling is a plurality of single-stand rolling mills, rough rolling to make the slab a sheet bar of a predetermined thickness, and subsequent to the above-described rough rolling, a finishing rolling mill comprising a plurality of stands and continuously to a target thickness. Generally, it is composed of finish rolling for performing rolling. For the rough rolling, since it is industrially difficult to control the strain rate, no particular conditions are defined. In the case where a thin slab is manufactured using the above-described thin slab caster, 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 sheet on the entry side of the first pass, that is, the finish-rolling entry-side temperature FET (° C.) is set to 970 ° C. or higher, and the first pass of the finish rolling is represented by the following formula (1);
α = FET + 43.4 × ln (SR) (1)
Here, FET: entry temperature (° C.) in the first pass of finish rolling
SR: strain rate in the first pass of finish rolling (s ^-1 )
It is important to perform rolling under the condition that α defined by the above is 1070 or more. Thereby, static recrystallization in finish rolling is promoted, and ridging can be suppressed. If the temperature of the FET is lower than 970 ° C., it is 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 970 ° C. The preferred FET has a temperature of 1030 ° C. or higher and α is 1100 or higher.

Although various calculation formulas have been proposed for the strain rate SR (s ^-1 ), the present invention uses the following formula known as the Sims formula.

  Further, the temperature of the steel sheet on the exit side of the final rolling final pass of hot rolling, that is, the finish rolling end temperature FDT is preferably 900 ° C. or higher, and more preferably 940 ° C. or higher, from the viewpoint of improving magnetic properties. . Thereby, recrystallization and grain growth of the hot rolled sheet are promoted, and the magnetic properties can be further improved. The increase in the temperature of the FDT can be achieved by increasing the slab heating temperature, optimizing the pass schedule, reheating during hot rolling, adjusting the amount of strip coolant, and the like. On the other hand, when the temperature of FDT is equal to or higher than the solid solution temperature of MnS or AlN, the precipitates may be refined and iron loss may increase. Therefore, the FDT is preferably 1100 ° C. or lower.

  Here, the purpose of the reheating during the hot rolling is to increase the rolling temperature in the finish rolling to promote recrystallization during the hot rolling in the finish. Therefore, it is preferable that the reheating is performed on the sheet bar after the rough rolling and before the finish rolling, and as the means for reheating, for example, a conventionally known induction heating type sheet bar heater is used. Is preferred. When the sheet bar is reheated, it is preferable that the temperature be equal to or lower than the slab heating temperature. This suppresses the re-dissolution of precipitates such as AlN and MnS, so that the re-precipitation of AlN and MnS and the like can be prevented from adversely affecting the grain growth and, consequently, the iron loss. When the reheating temperature is higher than the slab heating temperature or higher than 1150 ° C., Ca, REM, Mg or the like is added to fix S as coarse inclusions and suppress the generation of fine MnS. Is preferred. When the slab heating is omitted by using a thin slab caster or the like, the reheating temperature of the sheet bar is not particularly limited, but it is preferable to add Ca, REM, Mg, and the like.

  On the other hand, when the FDT is heated to a high temperature, it becomes difficult to control the shape of the steel sheet after hot rolling. Therefore, the upper limit of the FDT is preferably set to about 1000 ° C. in order to achieve both the magnetic characteristics and the shape of the steel sheet. When the temperature of the FDT is not increased, the magnetic flux density tends to decrease. However, a steel material in which the Al content is reduced to an extremely small amount or a steel material in which a small amount of grain boundary segregation elements such as Sn and Sb are added. Or the like can reduce the above adverse effects.

  Further, if the coil winding temperature CT after hot rolling exceeds 700 ° C., the descaling property deteriorates. Therefore, the coil winding temperature CT is preferably set to 700 ° C. or less.

  The hot-rolled steel sheet (hot-rolled sheet) can be subjected to cold rolling without performing hot-rolled sheet annealing, but is subjected to hot-rolled sheet annealing for the purpose of further improving magnetic properties and surface properties. Is also good. However, in the case of performing hot-rolled sheet annealing, in the present invention, ridging can be suppressed by optimizing the hot-rolling conditions. Therefore, the annealing conditions at low temperature and short time, specifically, the soaking temperature is 900 ° C or less. Excellent magnetic properties and surface properties can be obtained even under the annealing condition in which the soaking time is 5 minutes or less.

Next, the steel sheet after the hot rolling or the hot-rolled sheet annealing has a predetermined final sheet thickness (product sheet thickness) by one cold rolling or two or more cold rollings sandwiching the intermediate annealing. Then, finish annealing is performed. In the finish annealing, the annealing temperature is desirably in the range of 900 to 1100 ° C. from the viewpoint of reducing iron loss and reducing defects due to pickup. The atmosphere for the finish annealing 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 P _H2O / P _H2 of 0.1 or less may be used. Is preferred. After the finish annealing, an insulating film may be formed as necessary, and a known organic, inorganic, or mixed organic / inorganic film can be applied according to 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 %, And further containing other elements shown in Table 1, the balance being Fe and a component composition consisting of unavoidable impurities, by a conventional refining process comprising a converter, a vacuum degassing apparatus, and the like. After smelting, a steel material (slab) having a thickness of 200 mm was formed 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 sheet thickness 2. After forming a hot-rolled sheet having a thickness of 0.0 mm, the sheet 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 mm was used, and the entry side thickness (sheet bar thickness), roll peripheral speed (rolling speed) and rolling reduction in the first pass of the finish rolling were determined. By changing the strain rate, the strain rate SR in the first pass of finish rolling was variously changed. Further, under some conditions, the sheet bar after the rough rolling was reheated to the temperature shown in Table 1 by a sheet bar heater of the induction heating type installed in front of the finishing mill, and then the finish rolling was performed.
Next, the hot-rolled sheet was subjected to hot-rolled sheet annealing at the same temperature shown in Table 1 for 30 seconds, or without pickling, descaling by pickling, and then cold rolling. Thus, a cold-rolled sheet having a final sheet thickness of 0.3 mm was obtained.
Next, the cold-rolled sheet is subjected to finish annealing at a soaking temperature of 990 ° C. × soaking time of 10 sec in a dry atmosphere of H ₂ : N ₂ = 25: 75 at a vol% ratio, and then an insulating film is applied. To make a product plate.

From the rolling direction and the sheet width direction of the product sheet thus obtained, a test piece having a width of 30 mm × length: 280 mm was sampled and subjected to an Epstein test in accordance with JIS C 2550-1 (2011), and a magnetic flux density was obtained. the B ₅₀ and iron loss _{W 10/400} was measured. The presence and level of ridging were visually evaluated.
The above results are shown in Table 1 together with the manufacturing conditions. In addition, the steel sheet No. which performed the hot-rolled sheet annealing at 1000 degreeC. Reference numeral 3 is a reference example showing the prior art. From these results, the steel sheets hot-rolled under the conditions suitable for the present invention can obtain the same excellent surface properties and magnetic properties as the steel sheets subjected to the hot-rolled sheet annealing without any hot-rolled sheet annealing. You can see that it is done.
The magnetic flux density B ₅₀ tends to be slightly inferior to the case where the hot-rolled sheet annealing is not performed, but it can be improved by increasing the temperature of the FDT or adding Sn and Sb. When the slab heating temperature is increased to increase the temperature of iron, 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 component compositions of A to E shown in Table 2 were smelted by a conventional refining process and made into a steel material (slab) having a thickness of 240 mm by a continuous casting method. After heating to the indicated temperature and soaking for 40 minutes, hot rolling was performed at the finish rolling end temperature FDT shown in Table 3 to obtain a hot-rolled sheet having a thickness of 2.3 mm, and a coil winding temperature of 560 ° C. Rolled up. At this time, in the first pass of the finish rolling, a work roll diameter of 600 mmφ is used, and the thickness on the entry side (sheet bar thickness), the peripheral speed of the roll (rolling speed), and the rolling reduction in the first pass of the finish rolling are changed, and the first pass is performed. Was varied in various ways. Further, under some conditions, the sheet bar after the rough rolling was reheated to the temperature shown in Table 3 by an induction heating type sheet bar heater installed before the finishing mill, and then the finish rolling was performed.
Then, the hot-rolled sheet was subjected to pickling and descaling after or after being subjected to hot-rolled sheet annealing maintained at the same temperature shown in Table 3 for 30 seconds, and then cold-rolled. Thus, a cold-rolled sheet having a final sheet thickness of 0.3 mm was obtained.
Next, the cold-rolled sheet is subjected to finish annealing at a soaking temperature of 1010 ° C. × soaking time of 20 sec in a dry atmosphere of H ₂ : N ₂ = 20: 80 at a vol% ratio, and then an insulating film is applied. To make a product plate.

From the rolling direction and the sheet width direction of the product sheet thus obtained, a test piece having a width of 30 mm × length: 280 mm was sampled and subjected to an Epstein test in accordance with JIS C 2550-1 (2011), and a magnetic flux density was obtained. the B ₅₀ and iron loss _{W 10/400} was measured. The presence and level of ridging were visually evaluated.

  The above results are shown in Table 3 together with the production conditions. In addition, the steel sheet No. Reference numerals 1, 5, 9, 13 and 17 are reference examples showing the prior art. From these results, the steel sheet hot-rolled under the conditions suitable for the present invention has excellent surface properties equivalent to that of the steel sheet annealed with hot rolled sheet without any hot-rolled sheet annealing. Not only that, but also the magnetic properties are excellent. In addition, it can be seen that steel A having a low Al content has a large increase in iron loss when the slab heating temperature is increased, as compared with steel B having a high Al content, and it is advantageous to increase the Al content. . Conversely, steel C having a very low Al content also has a small increase in iron loss when the slab heating temperature is increased. 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 a slab having a component composition consisting of Fe and inevitable impurities is hot-rolled, soaking temperature 900 ° C or less, soaking time 5 min. In the method for producing a non-oriented electrical steel sheet to be subjected to hot rolling sheet annealing or hot rolling sheet annealing without being subjected to one or two or more cold rollings sandwiching intermediate annealing, and finish annealing,
The entry side temperature FET of the first pass of the finish rolling in the hot rolling is set to 970 ° C. or higher, and
A method for producing a non-oriented electrical steel sheet, wherein the first pass of finish rolling is rolled under conditions where α defined by the following equation (1) is 1070 or more.
Note that α = FET + 43.4 × ln (SR) (1)
Here, FET: entry temperature (° C.) in the first pass of finish rolling
SR: strain rate in the first pass of finish rolling (s ^-1 ) The method for producing a non-oriented electrical steel sheet according to claim 1, wherein the steel sheet is reheated before finish rolling in the hot rolling. The method for producing a non-oriented electrical steel sheet according to claim 1, wherein the finish rolling end temperature FDT in the hot rolling is 900 ° C. or more and the coil winding temperature CT is 700 ° C. or less. The slab further comprises 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 producing a non-oriented electrical steel sheet according to any one of claims 1 to 3. The slab is one 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 composition. The method for producing a non-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the method comprises one or more kinds.

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