JP5088144B2 - Non-oriented electrical steel sheet for aging heat treatment, non-oriented electrical steel sheet and method for producing the same - Google Patents

Description

  The present invention relates to a non-oriented electrical steel sheet for aging heat treatment, a non-oriented electrical steel sheet and a method for producing the same for obtaining a non-oriented electrical steel sheet suitable as a material for a rotor core of a motor rotating at high speed. In particular, the present invention can withstand stress during rotation or stress variation during acceleration / deceleration, and requires excellent strength characteristics and magnetic characteristics, such as an embedded magnet motor (IPM motor) and salient pole type surface magnet motor (saliency pole). The present invention relates to a non-oriented electrical steel sheet for aging heat treatment, a non-oriented electrical steel sheet and a method for producing the same for obtaining a non-oriented electrical steel sheet suitable as a material for a rotor core of a type SRM motor.

  In order to reduce greenhouse gases, new products that consume less energy are required in the fields of automobiles and home appliances. For example, in the automobile field, there are a hybrid drive vehicle (HEV) of a gasoline engine and a motor or a motor drive electric vehicle in order to reduce fuel consumption. In the home appliance field, there are high-efficiency air conditioners and refrigerators with low annual electricity consumption. These common technologies are motors, and high efficiency of the motors is an important technology. In the process of increasing motor efficiency, motor drive systems have become more sophisticated and various rotational drive controls have become possible. That is, the number of motors capable of variable speed operation and high speed operation at commercial frequency or higher has been increased by frequency control of the drive power source.

  In order to realize such a high-speed rotating machine, it is necessary to develop a rotor that can withstand high-speed rotation. In general, the centrifugal force acting on the rotor is proportional to the rotational radius and proportional to the square of the rotational speed. For this reason, when operating at high speed rotation, the force acting on the rotor may exceed 500 MPa, for example. Therefore, a material with high yield strength is required for the rotor. Furthermore, during rotor high-speed rotation operation, repeated stresses such as external vibration and frequent acceleration / deceleration may occur, so the rotor material must not only have high yield strength but also high fatigue strength. Is also needed. Since it is most effective to increase the tensile strength as a means for increasing the fatigue strength, it can be said that a high yield strength and a high tensile strength are necessary for the material of the rotor rotating at high speed.

  Usually, a laminated non-oriented electrical steel sheet is used for the motor rotor, but the motor that rotates at high speed as described above may not satisfy the required strength. In that case, high strength cast steel or the like is used as a rotor material. However, since the motor rotor uses magnetic properties at the time of rotation, the material is required to have excellent magnetic properties as well as mechanical properties as described above. In other words, an integral cast steel rotor has a problem that the eddy current loss becomes very large and the efficiency of the motor decreases. Further, in the case of an IPM motor, there arises a problem that magnet characteristics deteriorate due to heat generated by loss in the rotor.

  As described above, the rotor core material of the motor rotating at high speed as described above must have high mechanical strength and magnetically have high frequency and low iron loss. As means for increasing the strength of steel sheets, in the field of cold-rolled steel sheets, methods such as solid solution strengthening, precipitation strengthening, grain refinement strengthening, transformation strengthening are generally used, but excellent magnetic properties such as high strength and high frequency low iron loss are used. In general, there is a contradictory relationship, and it has been extremely difficult to satisfy these simultaneously.

  In order to solve such a problem, several proposals have recently been made regarding non-oriented electrical steel sheets having high tensile strength. For example, Patent Document 1 proposes a method in which the Si content is increased to 3.5 to 7.0%, an element having a large solid solution hardening is added thereto, and the tensile strength is increased. In Patent Document 2, a normal non-oriented electrical steel sheet contains 2.0% or more and less than 4.0% Si, and at the same time, one or two of Nb and Zr, or one or two of Ti and V, or 2 A method has been proposed for producing non-oriented electrical steel sheets with high yield strength that combine mechanical and magnetic properties by utilizing various carbonitrides and also controlling hot rolling conditions and finish annealing conditions. Yes. Patent Document 3 proposes a method of increasing the tensile strength by including a metal phase made of Cu having a diameter of 1.0 μm or less in the steel material. Patent Document 4 proposes a method for increasing the tensile strength by dispersing a fine Cu precipitate phase, and Patent Document 5 and Patent Document 6 by dispersing a Cu precipitate phase and a carbonitride phase containing Ti and Nb. Has been.

JP 60-238421 A JP-A-6-330255 JP 2004-84053 A JP 2004-3000535 A JP 2005-344156 A JP 2007-31754 A

However, since the steel sheet obtained by the invention described in Patent Document 1 is very brittle, there is a problem that it is easily broken during cold rolling and the yield is very low.
In the invention described in Patent Document 2, since the finish annealing temperature is low, there is a problem that the crystal grain size of the steel sheet is very small and the iron loss is very inferior.
In the invention described in Patent Document 3, since the finish annealing conditions are not optimized, there is room for further improving the strength. Further, since the hot rolled steel sheet is not annealed or annealed at a high temperature of 980 ° C., Cu is finely dispersed inside the hot rolled steel sheet, and the hot rolled steel sheet becomes very hard. Therefore, subsequent cold rolling becomes difficult, and there is a problem inferior in productivity.
In the inventions described in Patent Document 4, Patent Document 5, and Patent Document 6, a non-oriented electrical steel sheet having excellent strength and magnetic properties can be produced, but the process after hot rolling, for example, temper rolling, In the pickling, annealing, and cold rolling, the hot-rolled steel sheet may be broken to reduce the yield. Furthermore, in the invention described in Patent Document 4, since Ni is an indispensable component for improving strength and suppressing surface defects, a significant increase in raw material cost is inevitable.

  The present invention has been made in view of the above problems, and can be used for aging heat treatment that can increase strength by aging heat treatment, has low iron loss at high frequencies, is excellent in manufacturability, and can reduce raw material costs. The main object is to provide a non-oriented electrical steel sheet, a non-oriented electrical steel sheet and a method for producing the same.

  As a result of intensive research from the viewpoint of whether a steel sheet having excellent magnetic properties can be obtained by increasing the strength by precipitation strengthening by aging heat treatment, the present inventors have obtained Si, Al advantageous in both magnetic properties and strength properties. Based on the contained steel, Cu is used as a precipitation strengthening element, Ti, Nb, V, and Zr carbides are also used as required, and the final annealing conditions are optimized to improve strength and magnetic properties. It has been found that a non-oriented electrical steel sheet having both of the above can be obtained (see Patent Document 5 and Patent Document 6).

However, since the hot-rolled steel sheet is very hard, it has been found that the hot-rolled steel sheet may be broken in the manufacturing process after hot rolling, which may reduce the yield. Further, it has been found that in some cases, surface defects may occur, and it may be necessary to contain Ni which is an expensive element in order to suppress this. Therefore, the present inventors have conducted further earnest research in order to develop a non-oriented electrical steel sheet having excellent strength characteristics and magnetic characteristics as a product while considering the fracture of the hot-rolled steel sheet and raw material costs. , as much as possible reduce the amount of useful Si to the magnetic properties improve, enhance Al content, and by utilizing the precipitation of T i, excellent manufacturability, dominant high strength non-oriented in terms of raw material cost It discovered that an electromagnetic steel plate was obtained and completed this invention.

That is, the present invention is, in mass%, C: 0.02% or less, Si: 1% or less, Mn: 1% or less, P: 0.2% or less, S: 0.03% or less, Al: 2% 4% or less, Ni: less than 0.10%, Cu: more than 1% and 3% or less, and Ti : 0.001% or more and 0.1% or less , with the balance being Fe and impurities. A non-oriented electrical steel sheet for aging heat treatment is provided.

  ADVANTAGE OF THE INVENTION According to this invention, it can be set as the non-oriented electrical steel sheet for aging heat processing by which productivity and a magnetic characteristic are favorable and the raw material cost can be reduced by controlling appropriately the steel composition of a steel plate. Moreover, the non-oriented electrical steel sheet with improved strength characteristics can be obtained by subjecting the non-oriented electrical steel sheet for aging heat treatment of the present invention to aging heat treatment. As described above, by using the non-oriented electrical steel sheet for aging heat treatment of the present invention, it is possible to provide a non-oriented electrical steel sheet suitable for a motor rotor that can be used stably without causing deformation or breakage during operation. It is.

The present invention also provides a non-oriented electrical steel sheet having the above steel composition and having a yield strength of 500 MPa or more.
ADVANTAGE OF THE INVENTION According to this invention, it can be set as the non-oriented electrical steel sheet which has the outstanding magnetic characteristic and intensity | strength characteristic, and whose productivity and cost were improved.

Furthermore, the present invention provides a method for producing the non-oriented electrical steel sheet, characterized in that the non-oriented electrical steel sheet for aging heat treatment is subjected to aging heat treatment. .
ADVANTAGE OF THE INVENTION According to this invention, the non-oriented electrical steel sheet excellent in the magnetic characteristic and intensity | strength characteristic can be manufactured with a sufficient yield, without being accompanied by the increase in cost.

  According to the present invention, a non-oriented electrical steel sheet for aging heat treatment with low iron loss at high frequencies can be obtained, and when the aging heat treatment is applied to the non-oriented electrical steel sheet for aging heat treatment, the iron loss is low. In addition, it is possible to efficiently produce a non-oriented electrical steel sheet having high strength. If an iron core manufactured using such a non-oriented electrical steel sheet is incorporated into a motor rotor that rotates at high speed, the motor efficiency will not only increase, but it can be used stably for a long time without being deformed or broken during operation. It becomes. Such energy-saving effects can contribute to the creation of a future society with less impact on the global environment.

  Hereinafter, the non-oriented electrical steel sheet for aging heat treatment, the non-oriented electrical steel sheet and the manufacturing method thereof according to the present invention will be described in detail.

A. Non-oriented electrical steel sheet for aging heat treatment The non-oriented electrical steel sheet for aging heat treatment of the present invention is in mass%, C: 0.02% or less, Si: 1% or less, Mn: 1% or less, P: 0.2. %: S: 0.03% or less, Al: 2% or more and 4% or less, Ni: less than 0.10%, Cu: more than 1%, 3% or less, and Ti : 0.001% or more and 0.1% or less And the balance has a steel composition comprising Fe and impurities.
“%” Indicating the content of each element means “mass%” unless otherwise specified.

According to the present invention, by appropriately controlling the steel composition of the steel sheet, in particular Si content, Al content and, by appropriately controlling the T i including chromatic amount, improvement of productivity and the raw material cost reduction And excellent magnetic properties can be obtained. In addition, the non-oriented electrical steel sheet for aging heat treatment of the present invention is a non-oriented electrical steel sheet subjected to aging heat treatment, so that strength characteristics can be obtained by subjecting the non-oriented electrical steel sheet for aging heat treatment of the present invention to aging heat treatment. Can also be excellent.
Hereinafter, the steel composition and manufacturing method of the non-oriented electrical steel sheet for aging heat treatment of the present invention will be described.

1. Steel composition (1) C
C is an element effective for increasing the strength of the steel sheet. However, if the C content exceeds 0.02%, carbides such as cementite and ε-carbide precipitate, and the magnetic property deterioration may become remarkable. Therefore, the C content is 0.02% or less. In order to further improve the magnetic properties, particularly to improve the iron loss, the upper limit of the C content is preferably 0.005%. On the other hand, when Ti is contained in an amount of 0.01% or more to enhance precipitation strengthening, the C content is preferably controlled to 0.005% to 0.02%.

(2) Si
Si is an effective element for increasing the strength of the steel sheet and improving the magnetic properties. However, in the steel sheet that must contain Cu as in the present invention, the hot-rolled steel sheet is a material after hot rolling. There is a possibility of breaking in the manufacturing process. If the Si content exceeds 1%, the toughness of the hot-rolled steel sheet is deteriorated, and the hot-rolled steel sheet may be broken to reduce the product yield. Therefore, the Si content is 1% or less. Furthermore, in order to suppress surface defects, it is preferable that the Si content is 0.2% or less. Si is an element contained as an unavoidable impurity, but the lower the content, the better. Therefore, there is no need to specifically limit the lower limit.

(3) Mn
Mn is an unavoidable impurity and need not be added. However, Mn increases the specific resistance of steel and is effective in reducing iron loss. In order to acquire the effect, it is preferable to make it contain 0.1% or more. On the other hand, if the Mn content exceeds 1%, the raw material cost may increase. Therefore, the Mn content is limited to 1% or less.

(4) P
P is an unavoidable impurity and need not be added. However, P is an element effective for increasing the strength of the steel sheet by solid solution strengthening, and 0.05% or more is preferably contained in order to obtain the effect. On the other hand, if the P content exceeds 0.2%, the toughness of the steel sheet deteriorates and the hot-rolled steel sheet may be broken. Therefore, the P content is limited to 0.2% or less.

(5) S
S is an unavoidable impurity and does not need to be added. If the S content exceeds 0.03%, coarse Mn and Cu-containing sulfides are formed, the toughness of the steel deteriorates, and there is a risk of fracture during cold rolling. Therefore, the S content is limited to 0.03% or less. In order to improve magnetic properties, the S content is preferably 0.006% or less.

(6) Al
Al increases the specific resistance of steel and is effective in reducing iron loss. In the present invention, since the Si content having the same effect is reduced, it is necessary to actively add it. However, if the Al content exceeds 4%, the saturation magnetic flux density is remarkably lowered, and the core performance may be deteriorated. On the other hand, it is necessary to contain 2% or more of Al in order to reduce high-frequency iron loss. Therefore, the Al content is limited to 2% or more and 4% or less. More preferably, it is 2.5% or more and 3.5% or less.

(7) Ni
Ni is effective in preventing surface defects of the steel sheet. However, in the present invention, surface defects are suppressed by reducing the Si content as much as possible and increasing the Al content, so that it is necessary to contain a considerable amount of Ni as in the prior art. Absent. In particular, when the Si content is 0.2% or less, it is not necessary to add Ni from the viewpoint of suppressing surface defects, and the Ni content may be at the impurity level. On the other hand, Ni is effective in increasing the strength of the steel sheet by solid solution strengthening, so Ni may be added. However, since Ni is an expensive element, its content is made less than 0.10% from the viewpoint of manufacturing cost. Of course, even if the Ni content is 0.10% or more, the strength and magnetic properties are not impaired.

(8) Cu
Cu is an essential element in the present invention. As described above, when the Cu precipitate is very fine, there is an effect of improving the strength characteristics without substantially degrading the magnetic characteristics. However, when the Cu content is 1% or less, there is a possibility that a sufficient strength increase due to Cu precipitation cannot be obtained. On the other hand, the amount of age hardening increases as the Cu content increases, but if it exceeds 3%, Cu precipitates are unevenly dispersed during finish annealing, resulting in a decrease in strength after aging heat treatment, and also the magnetic flux density of the steel sheet. May decrease. Therefore, the Cu content is limited to more than 1% and 3% or less.

(9) T i
T i forms a nitride or a sulfide, and hot-rolled steel sheet, steel sheet further subjected to annealing hot-rolled steel sheet (hereinafter sometimes referred to as hot-rolled annealed steel sheet.) Important for improving the toughness of the It is an element. Here, it is assumed that the toughness is improved because the steel structure is refined by the nitrides and sulfides. Since T i containing chromatic amount is difficult to ensure a sufficient toughness is less than 0.001%, the T i containing chromatic amount is 0.001% or more. On the other hand, T i containing chromatic weight there is a possibility that the precipitates exceeds 0.1% deteriorates the toughness is remarkably coarse dispersed hot-rolled steel sheets. Thus, T i containing Yuryou is 0.1% or less than 0.001%. Preferably, it is 0.01% or more and 0.1% or less.
Further, T i also has effects of improving the strength by forming a carbide. To obtain the effect of this action to ensure the T i containing chromatic amount is preferably 0.1% or less than 0.01%.

2. Manufacturing method of non-oriented electrical steel sheet for aging heat treatment The non-oriented electrical steel sheet for aging heat treatment of the present invention is, for example, a hot-rolled steel sheet having the above-described steel composition in a temperature range of 600 ° C to 900 ° C for 10 seconds or more. A hot-rolled sheet annealing process for performing hot-rolled sheet annealing, a cold-rolling process for performing cold rolling on the hot-rolled steel sheet subjected to hot-rolled sheet annealing to form a cold-rolled steel sheet, and the cold It is preferable to manufacture by the manufacturing method which has the finish annealing process which performs finish annealing to a rolled steel plate.

  According to the manufacturing method described above, the steel composition of the steel sheet is appropriately controlled, and further subjected to hot-rolled sheet annealing under predetermined conditions, thereby improving the ductility of the steel sheet and effectively suppressing breakage in the cold rolling process. Therefore, it is possible to produce a non-oriented electrical steel sheet for aging heat treatment that has excellent magnetic properties and can be strengthened by aging heat treatment with a high yield.

In the above manufacturing method, the hot rolled steel sheet is usually hot rolled after hot rolling after a steel ingot or steel slab having the above-described steel composition (hereinafter also referred to as slab) is set to a predetermined temperature. Obtained by the process.
Hereinafter, each process in the said manufacturing method is demonstrated.

(1) Hot rolling process In the said manufacturing method, after making the slab which has the steel composition mentioned above into predetermined temperature, you may perform the hot rolling process which hot-rolls. The hot-rolled steel sheet obtained by this step is a material for a cold-rolled steel sheet to be described later.

  A general method can be used as hot rolling. Conditions such as the slab temperature, the finishing temperature in hot rolling, and the coiling temperature are appropriately selected depending on the steel composition of the slab, the thickness of the target steel sheet, and the like. In order to improve the surface properties of the steel sheet, it is preferable that the temperature in the slab heating furnace (approximately equal to the slab surface temperature) be 1200 ° C. or lower. Moreover, in order to improve the toughness of a hot-rolled steel plate, it is preferable that a coiling temperature shall be 550 degreeC or more.

(2) Hot-rolled sheet annealing process The hot-rolled sheet annealing process in the manufacturing method described above is performed on a hot-rolled steel sheet having the above-described steel composition by holding a hot-rolled sheet annealed at a temperature of 600 ° C or higher and 900 ° C or lower for 10 seconds or longer. It is a process to apply. The hot-rolled sheet annealing process is a process useful for making it possible to increase the efficiency of the subsequent cold rolling.

  The annealing temperature in the hot-rolled sheet annealing is 600 ° C. or more and 900 ° C. or less. If the annealing temperature is less than the above range, the strength of the steel sheet may be too high, and cold rolling may be difficult. On the other hand, even if the annealing temperature exceeds the above range, solid solution / reprecipitation of Cu occurs, the strength of the steel sheet increases, and cold rolling may become difficult. A more preferable annealing temperature is 650 ° C. or higher and 850 ° C. or lower.

  The holding time at the annealing temperature is 10 seconds or longer. When holding time is less than the said range, the intensity | strength of a hot-rolled steel plate becomes high and cold rolling may become difficult. The holding time is more preferably 2 hours or more. On the other hand, the upper limit of the holding time is not particularly limited, but is preferably 48 hours or less from the viewpoint of economy.

  A hot-rolled steel sheet is usually subjected to cold rolling after removing scales generated on the surface of the steel sheet during hot rolling by pickling. Pickling may be performed either before or after hot-rolled sheet annealing.

(3) Cold rolling process The cold rolling process in the said manufacturing method is a process which cold-rolls the said hot-rolled steel plate in which hot-rolled sheet annealing was given, and makes it a cold-rolled steel plate.

This step may be a step of performing cold rolling two or more times with intermediate annealing on the hot-rolled steel sheet. Although the intermediate annealing is not necessarily essential, the intermediate annealing has the advantage that the ductility of the steel sheet is improved and the breakage in cold rolling is reduced.
Conditions such as the annealing temperature in the intermediate annealing are preferably the same as those in the hot-rolled sheet annealing.

(4) Finish annealing process The finish annealing process in the said manufacturing method is a process of finishing annealing the said cold-rolled steel plate.

In order to further improve the strength and magnetic properties after the aging heat treatment, it is preferable to appropriately control the finish annealing conditions.
The finish annealing temperature is preferably 900 ° C. or higher and 1100 ° C. or lower. If the finish annealing temperature is less than the above range, recrystallization grain growth is insufficient and the magnetic properties may be significantly deteriorated. On the other hand, when the finish annealing temperature exceeds the above range, the particle size of the steel sheet becomes extremely coarse, Cu precipitates after the aging heat treatment are dispersed unevenly, and the strength may be lowered. In order to further reduce the iron loss, the higher the finish annealing temperature, the better. It is more preferable to set the temperature to 950 ° C. or higher.

(5) Other steps In the manufacturing method, after the finish annealing step, according to a general method, a coating step of applying an insulating film consisting of only an organic component, only an inorganic component, or an organic-inorganic composite to the steel sheet surface. May be performed. Further, the coating process may be a process of applying an insulating coating that exhibits adhesive ability by heating and pressurizing. As a coating material exhibiting adhesive ability, an acrylic resin, a phenol resin, an epoxy resin, a melamine resin, or the like can be used.

  Moreover, a non-oriented electrical steel sheet can be manufactured by performing an aging heat processing on the non-oriented electrical steel sheet for aging heat processing manufactured with the said manufacturing method.

B. Non-oriented electrical steel sheet The non-oriented electrical steel sheet of the present invention has the above-described steel composition and has a yield strength of 500 MPa or more.
The non-oriented electrical steel sheet of the present invention has the same steel composition as the above-mentioned non-oriented electrical steel sheet for aging heat treatment, and since the yield strength is 500 MPa or more, the magnetic properties, strength properties and manufacturability are good. Further, the manufacturing cost can be reduced.

The yield strength is 500 MPa or more, preferably 600 MPa or more. By setting the yield strength to the above range, when the non-oriented electrical steel sheet of the present invention is used, for example, as a motor rotor, it can be used stably without causing deformation or breakage during operation. It is. The upper limit of the yield strength is not particularly limited, but is preferably 1500 MPa or less from the viewpoint of suppressing delayed fracture.
Here, the yield strength can be measured by a method defined in JIS-Z-2241.

  The steel composition is described in “A. Non-oriented electrical steel sheet for aging heat treatment”, and the description is omitted here.

C. Manufacturing method of non-oriented electrical steel sheet The manufacturing method of the non-oriented electrical steel sheet according to the present invention is a manufacturing method of the above-mentioned non-oriented electrical steel sheet, and the aging heat treatment is performed on the non-oriented electrical steel sheet for aging heat treatment. It is characterized by.

  According to the present invention, since the non-oriented electrical steel sheet for aging heat treatment is used, the non-oriented electrical steel sheet having excellent magnetic properties and strength properties can be efficiently produced.

Aging heat treatment is effective for increasing the strength of the non-oriented electrical steel sheet.
Conditions such as temperature, time, and atmosphere in the aging heat treatment are not particularly limited as long as a predetermined yield strength can be obtained, and are appropriately selected depending on the steel composition, the intended strength, and the like.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

Hereinafter, the present invention will be described specifically by way of examples.
A slab having a steel composition shown in Table 1 below was heated to 1200 ° C. in a heating furnace, hot-rolled to a thickness of 2.4 mm, and gradually cooled from 600 ° C. to obtain a hot-rolled steel plate. The hot-rolled steel sheet was subjected to temper rolling with an elongation of 1%, descaling by pickling, and annealing at 800 ° C. for 10 hours. Charpy test pieces (2 mm V-notch in the direction perpendicular to the rolling direction) were collected from the hot-rolled steel sheet and hot-rolled annealed steel sheet thus obtained, and subjected to a Charpy impact test at 25 ° C. It was. The evaluation of the toughness, the impact value 100 J / cm ² than ○, impact value 70 J / cm ² or more 100 J / cm ² or less △, less than the impact value 70 J / cm ² was ×. Furthermore, the presence or absence of wrinkles was investigated by observing the surface of the steel plate after pickling.

Further, the hot-rolled annealed steel sheet was cold-rolled to a thickness of 0.35 mm and finish-annealed at 1000 ° C. A 55 mm square single-plate magnetic test piece was collected from the steel plate thus obtained, and subjected to aging heat treatment at 500 ° C. for 2 hours, and then the iron loss W _10/400 and the magnetic flux density B ₅₀ were measured. Their magnetic properties were average values in the rolling direction and the direction perpendicular thereto. Further, a JIS 13B tensile test piece was collected from the steel plate after the aging heat treatment, and after the same aging heat treatment as described above, a prescribed tensile test was performed on JIS-Z-2241 to measure the yield strength YS and the tensile strength TS.
Table 2 below shows the strength, magnetic properties, toughness data of the hot-rolled steel sheet and hot-rolled annealed steel sheet, and evaluation results for the presence or absence of surface defects.

The steel sheet of the present invention is not only excellent in strength and magnetic properties, but also the impact value of the hot-rolled steel sheet is equivalent to that of the conventional steel (mark G) of Cu trace, and the possibility of breakage is small. On the other hand, comparative steels (marks E and F) having a high Si content are excellent in strength and magnetic properties as in the conventional patent documents, but the impact properties of hot-rolled steel sheets are low and are easily broken. Furthermore, many surface defects were observed on the surface after pickling the hot-rolled steel sheet having a high Si content.
FIG. 1 shows a surface defect (FIG. 1 (a)) and a cross-sectional photograph (FIG. 1 (b)) of a comparative steel (mark E). Since metal Cu is embedded in this surface defect, it is presumed that molten Cu generated during slab heating induced a surface defect during hot rolling. The reason why surface defects did not occur in the steel of the present invention containing almost no Si is not clear, but the inventors infer from the observation of the scale after slab heating as follows. It is inferred that it was difficult to induce surface defects by hot rolling because there was no Si-based low melting point oxide in the scale formed during slab heating and molten Cu did not contact the surface of the slab. A comparative steel (mark D) containing a small amount of Si but hardly containing Ti is excellent in strength and magnetic properties, but is low in toughness after hot-rolled sheet annealing and easily breaks. Since this steel plate has almost no Ti precipitate dispersed therein, it is presumed that the microstructure after annealing is coarsened and the toughness is lowered.

It is a photograph of the surface defect of the hot rolled steel plate in an Example, and its cross section.

Claims (3)

In mass%, C: 0.02% or less, Si: 1% or less, Mn: 1% or less, P: 0.2% or less, S: 0.03% or less, Al: 2% or more and 4% or less, Ni : Less than 0.10%, Cu: more than 1% and 3% or less, and Ti : 0.001% or more and 0.1% or less , with the balance being a steel composition comprising Fe and impurities. Non-oriented electrical steel sheet for heat treatment.   A non-oriented electrical steel sheet having the steel composition according to claim 1 and having a yield strength of 500 MPa or more.   A method for producing a non-oriented electrical steel sheet according to claim 2, wherein the non-oriented electrical steel sheet for aging heat treatment according to claim 1 is subjected to aging heat treatment. .