JP4929484B2 - Non-oriented electrical steel sheet and manufacturing method thereof - Google Patents

Description

  The present invention is a non-oriented electrical steel sheet, particularly a component subjected to a large stress such as a rotor of a high-speed rotating machine, such as a drive motor of a turbine generator, an electric vehicle and a hybrid vehicle, or a servo motor of a robot or a machine tool. The present invention provides a non-oriented electrical steel sheet having a high strength, excellent fatigue properties, and excellent magnetic properties, and a method for producing the same, at a lower cost than in the past.

  In recent years, with the development of motor drive systems, it is possible to control the frequency of the drive power supply, and motors that perform variable speed operation and motors that rotate at a higher speed than the commercial frequency are increasing. In motors that perform such high-speed rotation, the centrifugal force acting on the rotating body is proportional to the radius of rotation and increases in proportion to the square of the rotational speed. Strength is required.

  Further, in recent years, in the embedded magnet type DC inverter control motor (IPM), which is increasingly used in drive motors and compressor motors of hybrid vehicles, between the magnet embedding groove in the rotor and the outer periphery of the rotor, and in the magnet Stress concentrates in a narrow bridge portion with a width of several millimeters between the buried grooves. Since motors can be reduced in size by high-speed rotation, drive motors for hybrid vehicles with space and weight constraints are aimed at high-speed rotation of the motor, and the core material used for high-speed rotation rotors For this, a high strength material is advantageous.

  On the other hand, rotating devices such as motors and generators use an electromagnetic phenomenon, and therefore, the iron core material is required to have excellent magnetic properties. In particular, in the rotor of a high-speed rotary motor, the core temperature rises due to eddy currents generated by high-frequency magnetic flux, which may cause thermal demagnetization of the embedded permanent magnet, or may cause the motor efficiency to decrease. There is a demand for low iron loss at high frequencies. Therefore, there is a demand for a magnetic steel sheet having high strength and excellent magnetic properties as a rotor material.

Steel strengthening mechanisms include solid solution strengthening, precipitation strengthening, grain refinement, and work hardening, and so far, several high-strength non-oriented electrical steel sheets that meet these needs have been studied, and Proposed.
Here, for example, in Patent Document 1, the use of solid solution strengthening is based on increasing the Si content to 3.5 to 7.0%, and for further solid solution strengthening, Ti, W, Mo, Mn, Ni. A method of increasing the strength by adding elements such as Co, Al and Al has been proposed. Furthermore, Patent Document 2 proposes a method for improving magnetic properties by controlling the crystal grain size to 0.01 to 5.0 mm by devising finish annealing conditions in addition to the above-described strengthening method.

  However, when these methods are applied to factory production, troubles such as plate breakage in a rolling line after hot rolling are likely to occur, and yield reduction and line stoppage may be forced. In addition, if cold rolling is performed at a plate temperature of several hundreds of degrees Celsius, the plate breakage is reduced, but it is necessary to deal with equipment for warm rolling, and restrictions on production increase. Process management problems cannot be ignored.

In addition, as a technique using precipitation of carbonitride, Patent Document 3 discloses that in a steel having an Si content of 2.0% or more and less than 4.0%, C is set to 0.05% or less, and among Nb, Zr, Ti, and V, Carbonitride containing 1 or 2 in the range of 0.1 <(Nb + Zr) / 8 (C + N) <1.0, 0.4 <(Ti + V) / 4 (C + N) <4.0 Techniques have been proposed that utilize the precipitation hardening and grain refining effects produced by the process.
Similarly, in Patent Document 4, in addition to the matters described in Patent Document 3, Ni and Mn are added in a total solution of 0.3% or more and 10% or less to enhance the solid solution, and then described in Patent Document 3. A technique has been proposed in which Nb, Zr, Ti and V are added in the same ratio as described above to achieve both high strength and magnetic properties.

  However, when high strength is obtained by these methods, in addition to inevitable deterioration of magnetic properties, surface defects such as heges and internal defects due to precipitates are likely to occur, resulting in a decrease in product quality. There is a problem in that the cost is high because a yield drop for defect removal and a rupture trouble at the time of manufacturing a steel sheet are likely to occur. Moreover, in the technique described in Patent Document 4, since an expensive solid solution strengthening element such as Ni is added, the cost is further increased.

  Furthermore, as a technique using work hardening, Patent Document 5 proposes a technique for increasing the strength of steel containing 0.2 to 3.5% Si by leaving a processed structure inside the steel material. Yes. Specifically, no heat treatment is performed after cold rolling, or even if it does not exceed the extent corresponding to holding at 750 ° C. for 30 seconds, preferably 700 ° C. or less, more preferably 650 ° C. or less, 600 ° C. or less , 550 ° C. or lower and 500 ° C. or lower are disclosed. Here, as a result, annealing is performed at 750 ° C. × 30 seconds, and the work structure ratio is 5%, 700% × 30 seconds is 20%, and 600 ° C. × 30 seconds is 50%. In this case, since the annealing temperature is low, there has been a problem that shape correction of the rolled strip is not sufficiently performed. If the shape of the steel plate is poor, problems such as a decrease in the space factor after lamination processing on a motor core or the like, and a non-uniform stress distribution when rotating as a rotor at high speeds arise. In addition, since the ratio of processed grains and recrystallized grains varies greatly depending on the steel composition and annealing temperature, there is a problem that it is difficult to obtain stable characteristics. Furthermore, in general, finish annealing of non-oriented electrical steel sheets is performed using a continuous annealing furnace, and the inside of the furnace is adjusted to an atmosphere containing hydrogen gas of several percent or more in order to suppress oxidation of the steel sheet surface. Is customary. In such continuous annealing equipment, in order to perform low-temperature annealing below 700 ° C, it takes time to switch the furnace temperature setting, and it is necessary to replace the furnace atmosphere to avoid a hydrogen explosion, etc. As a result, there will be great operational restrictions.

  Inventors have raised the recrystallization temperature of silicon steel by adding Ti excessively with respect to C and N in the silicon steel which reduced C and N in patent document 6 from the above technical background, We proposed a high-strength electrical steel sheet that combines steel plate shape correction in finish annealing and strengthening by non-recrystallized structure. This method had problems such as high alloying costs due to the relatively high amount of Ti added, and mechanical properties may vary due to the remaining non-recrystallized structure. .

JP-A-60-238421 JP-A-62-112723 JP-A-6-330255 Japanese Patent Laid-Open No. 2-8346 JP 2005-113185 A JP 2007-186790 A

  Although several proposals have been made regarding high-strength non-oriented electrical steel sheets, previous proposals have good magnetic properties in addition to high tensile strength and high fatigue strength, and surface defects. It is also possible to manufacture high-strength non-oriented electrical steel sheets that satisfy steel plate quality issues such as internal defects and plate shapes, industrially stable with normal electromagnetic steel sheet manufacturing equipment, with good yield and low cost. The current situation has not been achieved. In particular, high-strength electrical steel sheets that have been provided for high-speed rotors so far have a high magnetic property, that is, high-frequency iron loss, so heat generation of the rotor is unavoidable, and the motor design specifications must be restricted. It was in.

Accordingly, an object of the present invention is to provide a non-oriented electrical steel sheet having excellent magnetic properties and steel sheet quality and a manufacturing method thereof at a low cost, specifically, a tensile strength of 650 MPa or more, preferably 700 MPa or more. , Non-oriented electrical steel sheet with good high frequency and low iron loss characteristics, for example, _W10 / ₄₀₀ value of 0.35mm thickness material is 40W / kg or less, preferably 35W / kg or less, industrially stable Moreover, it is to provide a means for manufacturing at low cost.

The inventors conducted various studies on a high-strength electrical steel sheet that can achieve the above-described object at a high level and a method for manufacturing the same. As a result, it has been found that the addition amount and addition ratio of Ti and C are deeply involved in the balance of strength and magnetic properties of the electrical steel sheet, and by optimizing the precipitation amount of Ti carbide, high strength with excellent properties It was found that electrical steel sheets can be manufactured stably and at low cost.
That is, the present invention is based on the following knowledge.
(A) The presence of a relatively small amount of Ti carbide can suppress the growth of crystal grains in the final annealing of electrical steel sheets, and can be strengthened by refinement of crystal grains.
(B) Too much Ti carbide not only contributes to the effect of suppressing grain growth, but also causes adverse effects such as increased surface defects and internal defects, resulting in decreased steel sheet quality and a starting point for fracture. . On the other hand, by controlling the addition of Ti to an appropriate range, surface defects such as scabs and internal defects should be greatly reduced.
On the other hand, since Ti nitride is produced at a higher temperature than Ti carbide, the effect of suppressing crystal grain growth is weak, and it is not useful for controlling grain refinement, which is the object of the present invention. Therefore, it is desirable that N is stably reduced in a method for suppressing grain growth by controlling the amount of Ti carbide. This is different from conventional precipitation strengthening techniques in which the effects of C and N are treated similarly.
(C) In a steel plate with refined crystal grains, the solid solution C not only increases the tensile strength, but also has the effect of improving the fatigue characteristics that are essentially necessary for a rotor material that rotates at high speed.
(D) The main alloy components usually added for the purpose of increasing the electric resistance of the electrical steel sheet and reducing the iron loss are three elements of Si, Al and Mn. There is also an effect of strengthening solid solution. Therefore, in order to achieve both high strength and low iron loss, it is effective to base on solid solution strengthening with these elements. On the other hand, excessive addition of these elements embrittles steel and makes it difficult to manufacture. Therefore, there is a limit to the addition, and the three points of solid solution strengthening, low iron loss and manufacturability are most efficiently satisfied. It is desirable to add mainly Si.

  From these findings, by utilizing in a well-balanced manner, solid solution strengthening with substitutional alloy elements mainly composed of Si, grain refinement with Ti carbide, and solid solution strengthening with C, an interstitial element, Non-directional electromagnetics that have high strength, excellent fatigue properties under operating conditions, and excellent magnetic properties and steel plate quality without substantially adding restrictions and new processes to the production of ordinary non-oriented electrical steel plates While finding that a steel plate can be obtained, the inventors have found a manufacturing method necessary for this purpose, and have completed the present invention.

That is, the gist of the present invention is as follows.
(I)% by mass
Si: 5.0% or less,
Mn: 2.0% or less,
Al: 2.0% or less and P: 0.05% or less are included within the range satisfying the following formula (1), and C: 0.008% or more and 0.040% or less,
N: 0.003% or less and
A non-oriented electrical steel sheet comprising Ti: 0.04% or less in a range satisfying the following formula (2) and comprising the balance Fe and inevitable impurities.
Record
300 ≦ 85 [Si%] + 16 [Mn%] + 40 [Al%] + 490 [P%] ≦ 430 (1)
0.008 ≦ Ti * <1.2 [C%] (2)
However, Ti * = Ti-3.4 [N%]
Here, [Si%], [Mn%], [Al%], [P%], [C%], and [N%] each indicate the content (% by mass) of the display element.

(Ii) In the above (i), the contents of Si, Mn, Al and P are mass%,
Si: more than 3.5% and less than 5.0%
Mn: 0.3% or less,
A non-oriented electrical steel sheet characterized by Al: 0.1% or less and P: 0.05% or less.

(Iii) In the above (i) or (ii),
Sb: 0.0005% or more and 0.1% or less,
Sn: 0.0005% to 0.1%,
B: 0.0005% or more and 0.01% or less,
Ca: 0.001% to 0.01%,
REM: 0.001% to 0.01%,
Co: 0.05% or more and 5% or less,
Ni: 0.05% to 5% and
Cu: A non-oriented electrical steel sheet comprising one or more of 0.2% to 4%.

(Iv)% by mass
Si: 5.0% or less,
Mn: 2.0% or less,
Al: 2.0% or less and P: 0.05% or less are included within the range satisfying the following formula (1), and C: 0.008% or more and 0.040% or less,
N: 0.003% or less and
Ti: 0.04% or less is contained in a range satisfying the following formula (2), and the steel slab consisting of the remaining Fe and inevitable impurities is soaked at 1000 to 1200 ° C. and then hot-rolled, and then 1 After finishing the final thickness by cold rolling or warm rolling at least twice with intermediate or intermediate annealing, prior to the final annealing, the final annealing is performed at a temperature of 800 ° C or higher and 950 ° C or lower for 30 seconds or longer. A method for producing a non-oriented electrical steel sheet, wherein the holding heat treatment is performed at least once, and then finish annealing is performed at 700 ° C. or higher and 850 ° C. or lower.
Record
300 ≦ 85 [Si%] + 16 [Mn%] + 40 [Al%] + 490 [P%] ≦ 430 (1)
0.008 ≦ Ti * <1.2 [C%] (2)
However, Ti * = Ti-3.4 [N%]

(V) In (iv), the contents of Si, Mn, Al, and P are mass%,
Si: more than 3.5% and less than 5.0%
Mn: 0.3% or less,
A method for producing a non-oriented electrical steel sheet, wherein Al: 0.1% or less and P: 0.05% or less.

(Vi) In the above (iv) or (v),
Sb: 0.0005% or more and 0.1% or less,
Sn: 0.0005% to 0.1%,
B: 0.0005% or more and 0.01% or less,
Ca: 0.001% to 0.01%,
REM: 0.001% to 0.01%,
Co: 0.05% or more and 5% or less,
Ni: 0.05% to 5% and
Cu: The manufacturing method of the non-oriented electrical steel sheet characterized by including 1 type or 2 types or more of 0.2% or more and 4% or less.

  ADVANTAGE OF THE INVENTION According to this invention, the non-oriented electrical steel sheet which has the outstanding mechanical characteristic and magnetic characteristic required as a rotor material of the motor which rotates at high speed, and was excellent also in steel plate quality, such as a baldness and plate shape, can be provided. Further, as compared with the production of a normal non-oriented electrical steel sheet, it is possible to stably produce with a high yield without adding much cost, severe manufacturing restrictions, and new processes. Therefore, it can be adapted to fields that require higher speed rotation in the future, such as drive motors for electric vehicles and hybrid vehicles, or servo motors for robots and machine tools, and its industrial value and contribution to the industry are high.

It is a graph which shows the relationship between Ti amount and tensile strength. It is a graph which shows the relationship between Ti amount and iron loss. It is a graph which shows the relationship between the amount of Ti and the surface hege defect rate.

Hereinafter, the experiment that led to the present invention will be described in detail.
That is, the inventors examined in detail the influence of Ti, which is the main carbonitride-forming element, on the steel plate quality such as precipitation strengthening, recrystallization, grain growth behavior, and baldness. As a result, these elements are greatly different in the effect when added in a range of atomic equivalents or less with respect to C and N in particular, and there is an optimum addition range for satisfying magnetic properties and steel plate quality at a high level as well as high strength. I found it. The main experimental results are shown. In addition, unless otherwise indicated, the display of "%" shown below means "mass%".

<Experiment 1>
Si: 4.0-4.1%, Mn: 0.03-0.05%, Al: 0.001% or less, P: 0.007-0.009% and S: 0.001-0.002% as main components, C amount is 0.024-0.026%, N amount is 0.001 Steel composition with a constant content of ~ 0.002%, steel with various amounts of Ti changed to a range of 0.001 ~ 0.36% was melted in a vacuum melting furnace, heated to 1100 ° C and hot rolled to 2.1mm thickness did. Thereafter, hot-rolled sheet annealing was performed at 900 ° C. for 90 seconds, and the thickness was further reduced to 0.35 mm by cold rolling, and then the state of occurrence of shave defects on the surface of the steel sheet (shave length per unit area) was evaluated. Then, finish annealing is performed at 800 ° C for 30 seconds, and mechanical characteristics (JIS5 test piece is cut out in parallel with the rolling direction and evaluated) and magnetic properties (Epstein test piece are cut out in the rolling parallel direction and perpendicular to the rolling direction). T, iron loss W _10/400 at a frequency of 400 Hz was measured). The investigation results on the Ti content, tensile strength, magnetic properties, and surface bald defects are shown in FIG. 1, FIG. 2 and FIG.

  First, as shown in FIG. 1, the tensile strength increases with the addition of Ti, but the effect is small in the region A in FIG. 1 where the addition amount is small, and stable in the Ti amount range shown in the region B in the drawing. As a result, the strength was improved. Further, in the region C in the figure where the Ti amount is high, the strength further increases. When the steel structure in these regions was observed, the steel structure in region B had a uniform microstructure with a crystal grain size of 10 μm or less, whereas the crystal grains in the steel structure in region A grew from region B. In particular, it exhibited a mixed grain structure in which partial grain growth was observed. On the other hand, in the region C, a composite structure of non-recrystallized grains and recrystallized grains was exhibited.

FIG. 2 shows the relationship between the Ti addition amount and the iron loss W _10/400 . In the region A in the figure, the iron loss is the lowest and good, but as shown in FIG. 1, the region A has a low strength level. On the other hand, in regions C and D in the figure, a high-strength material is obtained, but the iron loss is also high. On the other hand, in the region B, a material that has a strength comparable to that of the region C and has good iron loss close to that of the region A is obtained.

On the other hand, as shown in FIG. 3, hege defects begin to increase when the Ti addition amount exceeds 0.04%, and increases until the element equivalent ratio of Ti, C, and N becomes 1, and there is a substantially constant hege defect. It has reached the amount of galling. If the C and N contents are constant, the precipitation amount of Ti carbonitride increases until the element equivalent ratio becomes 1, and thereafter, the precipitation amount becomes constant. The amount is considered to be related to the amount of balding.
From these results, by controlling the amount of Ti added to the range of region B, high strength and low iron are achieved while suppressing whisker defects that directly cause an increase in manufacturing cost which causes a decrease in yield and troubles in sheet breakage. It became clear that it was possible to balance losses. That is, it is understood that Ti needs an amount to form a certain amount of Ti carbonitride, but it is advantageous to contain Ti at 0.04% or less from the viewpoint of suppressing hege defects.

  Moreover, as a component other than the steel and the N amount, when the N amount contained was changed and investigated, it was clear that the lower limit of the Ti amount at which high strength was obtained increased with an increase in the N amount. became. As a result of further investigation, it was found that 0.008 ≦ Ti * (where Ti * = Ti−3.4 [N%]) must be satisfied. For this reason, Ti carbide is considered to have a greater contribution to higher strength and Ti nitride contributes less, and control of Ti carbide becomes more important.

  From these results, by controlling the amount of Ti added to the level of region B, high strength and low iron are achieved while suppressing the whisker defects that directly cause an increase in manufacturing cost that causes a decrease in yield and troubles in sheet breakage. It became clear that it was possible to balance losses.

<Experiment 2>
Next, in order to investigate the influence of Ti carbonitride in detail, steel having the composition shown in Table 1 was melted in a vacuum melting furnace, and a steel plate having a thickness of 0.35 mm was produced in the same procedure as in Experiment 1. The amount of C and N was changed based on steel a having a small amount of C and N. Steels c and d are added so that the amount of C + N is constant. Table 2 shows the surface bald defect rate, iron loss, and tensile strength of the obtained sample. Compared to steel a, steels b, c, and d have increased strength, but by comparing steels c and d in which the total amount of C and N is approximately the same, the effect of addition of C and N is The steel c having a lower amount has higher strength. When the structure was observed, the order of crystal grain size was steel a>d>b> c, corresponding to the order of tensile strength.

  Furthermore, the fatigue properties of these samples were investigated. The test conditions were the stress limit 0.1, the stress which was performed in the tension-tensile mode with a stress ratio of 0.1 and the cycle of 20 Hz and did not break at the amplitude of 10 million times. The results are also shown in Table 2. The material with higher tensile strength TS tends to have higher fatigue limit strength FS, but the ratio FS / TS is different, and steel c is the most excellent result. On the other hand, steel d has a small improvement margin for fatigue limit strength although its tensile strength is high. Therefore, when the structure of steel d was investigated in detail, it was presumed that precipitates thought to be TiN exceeding a particle size of 5 μm were scattered, and this was the starting point of fatigue fracture. Here, nitrogen reacts with Ti at a relatively high temperature of 1100 ° C. or higher and easily precipitates coarsely as TiN, so it is likely to become a starting point of fatigue fracture, and compared with Ti carbide, crystal grains are one of the aims of the present invention. It was thought that the growth suppression effect was small.

  On the other hand, in comparison between steels b and c, steel c is superior in both tensile strength and fatigue limit strength, but in particular, fatigue limit strength is relatively high and strength ratio FS / TS is high. It is characteristic. Since the Ti and N contents of steels b and c are almost the same, the precipitation of Ti nitride and Ti carbide is the same, and the difference between the two is considered to be due to the difference in the amount of solute carbon. . Therefore, it is presumed that the presence of solute carbon suppresses the generation and propagation of cracks and increases the fatigue limit strength by fixing dislocations introduced under repeated stress as in a fatigue test. Therefore, it is important to secure solid solution carbon.

  Based on the above experimental results, further study on the effects of factors such as Ti carbide, Ti nitride, and solute carbon due to the addition of a relatively small amount of Ti on steel structure, steel plate surface quality, steel plate mechanical properties and magnetic properties As a result, the present inventors have found a rule encompassing these factors and have completed the present invention.

Next, the present invention will be described in detail for each requirement.
First, the reasons for limiting the main steel components will be described.
Si: 5.0% or less, Mn: 2.0% or less, Al: 2.0% or less, and P: 0.05% or less are contained within a range satisfying the following formula (1).
Record
300 ≦ 85 [Si%] + 16 [Mn%] + 40 [Al%] + 490 [P%] ≦ 430 (1)

  The purpose of the present invention is to provide a magnetic steel sheet having high strength and excellent magnetic properties at low cost, and for this purpose, the amount of solid solution strengthening by the above four main alloy components needs to be a certain level or more. Therefore, in addition to defining the individual contents of the main four alloy components as described below, the total amount of the main four alloy components is as described above in consideration of the contribution to the individual solid solution strengthening amounts. It is important to add in a range satisfying the formula (1). That is, if the formula (1) is less than 300, the resulting material strength is insufficient. On the other hand, if it exceeds 430, troubles in plate cracking at the time of steel plate production increase, resulting in a decrease in productivity and a significant increase in production cost.

Next, the reason for limiting the content of each of the four main alloy components will be described.
Si: 5.0% or less
In addition to being generally used as a deoxidizer, Si is a main element that constitutes a non-oriented electrical steel sheet that has the effect of increasing the electrical resistance of steel and reducing iron loss. Furthermore, it has a high solid solution strengthening ability. In other words, compared to other solid solution strengthening elements such as Mn, Al, and Ni added to non-oriented electrical steel sheets, it is possible to achieve both high tensile strength, high fatigue strength and low iron loss in the most balanced manner. Since it is an element that can be produced, it is an element that is actively added. For that purpose, it is advantageous to contain it at 3.0% or more, more preferably more than 3.5%. However, if it exceeds 5.0%, toughness deterioration becomes remarkable, and advanced control is required at the time of sheet passing and rolling, and productivity is also lowered. Therefore, the upper limit is 5.0% or less.

Mn: 2.0% or less
In addition to being effective in improving hot brittleness, Mn also has the effect of increasing the electric resistance of steel to reduce iron loss and the effect of improving strength by solid solution strengthening. However, Mn has a lower strength improvement effect than Si, and excessive addition causes embrittlement of the steel, so the Mn content is 2.0% or less.

Al: 2.0% or less
Al is an element commonly used in steel refining as a powerful deoxidizer. Furthermore, like Si and Mn, it has the effect of increasing the electrical resistance of steel to reduce iron loss and the effect of improving strength by solid solution strengthening. However, Al has a smaller strength improvement effect than Si, and excessive addition causes embrittlement of the steel, so the Al content is 2.0% or less.

P: 0.05% or less P is extremely effective for increasing the strength because a significant solid solution strengthening ability can be obtained even when added in a relatively small amount, and is preferably contained at 0.005% or more. However, excessive addition leads to grain boundary cracking and rollability deterioration due to embrittlement due to segregation, so the addition amount is limited to 0.05% or less.

  Of these main alloy elements Si, Mn, Al and P, an alloy design mainly composed of Si is advantageous in order to achieve the most efficient balance between solid solution strengthening, low iron loss and manufacturability. That is, it is advantageous to contain Si in the range of more than 3.5% in order to optimize the characteristic balance of the non-oriented electrical steel sheet. In this case, the remaining three components are Mn: 0.3% or less and Al: It is preferable to regulate to 0.1% or less and P: 0.05% or less. The reason for this upper limit is the same as described above.

C, N and Ti are also important elements in the present invention. This is because it is important to suppress the grain growth during annealing of the steel sheet by using an appropriate amount of fine Ti carbide to develop the strengthening of grain refinement. For that purpose, it is necessary to contain C: 0.008% or more and 0.040% or less, N: 0.003% or less, and Ti: 0.04% or less in a range satisfying the following formula (2).
Record
0.008 ≦ Ti * <1.2 [C%] (2)
However, Ti * = Ti-3.4 [N%]

C: 0.008% or more and 0.040% or less C needs to be 0.008% or more. That is, if it is less than 0.008%, it becomes difficult to precipitate fine Ti carbide stably, and since the amount of solute C is insufficient, further improvement in fatigue strength cannot be expected. On the other hand, excessive addition leads to deterioration of magnetic characteristics, and work hardening during cold rolling becomes significant, causing plate breakage, and increased rolling load due to increased rolling load. This limits the upper limit to 0.04%.

N: 0.003% or less N forms Ti and nitride, but is not so effective for refinement of crystal grains because it is produced at a higher temperature than Ti carbide and has a weak effect of suppressing crystal grain growth. Rather, it may be adversely affected such as starting from fatigue failure, so it is limited to 0.003% or less. The lower limit is not particularly limited, but is preferably about 0.0005% from the viewpoint of steelmaking degassing ability and productivity reduction due to long-time refining.

Ti: 0.04% or less In the present invention, it is important to control Ti carbide. Since Ti tends to form nitride at a higher temperature than that of carbide, it is necessary to control the amount of Ti that forms carbide. Here, when the Ti amount capable of forming carbide is expressed as Ti *, this Ti * is the amount obtained by subtracting the atomic equivalent of N from the Ti content, that is,
Ti * = Ti-3.4 [N%]
It is expressed. In order to prevent the increase of iron loss by suppressing the grain growth while precipitating Ti to be added as Ti carbide to increase the strength, Ti ^* ≧ 0.008 is necessary together with an appropriate amount of C. On the other hand, if the Ti addition amount is increased with respect to the C amount, the solid solution C decreases and the effect of improving the fatigue strength cannot be expected. Therefore, it is necessary to satisfy Ti * <1.2 [C%] at the same time.

  Further, if the Ti amount exceeds 0.04%, as shown in FIG. 3 above, the number of whisker defects increases, and the steel sheet quality and yield decrease, resulting in an increase in cost. Therefore, 0.04% is made the upper limit.

  In the present invention, it is possible to contain elements other than the elements described above as long as the effects of the invention are not impaired. For example, Sb and Sn, which have the effect of improving magnetic properties, are 0.0005 to 0.1%, and B, which is effective to increase the grain boundary strength, are 0.0005 to 0.01%, improving the magnetic properties by controlling the form of oxides and sulfides. Ca and REM have an effect of 0.001 to 0.01%, Co and Ni have an effect of improving magnetic flux density 0.05 to 5%, and Cu that can be expected to strengthen due to aging precipitation is added in a range of 0.2 to 4%. It is possible.

Next, the reasons for limiting the manufacturing method will be described.
In this invention, the manufacturing process from steel melting to cold rolling can be implemented according to the method currently performed with the general non-oriented electrical steel sheet. For example, steel that has been melted and refined to a specified component in a converter or electric furnace is made into a steel slab by continuous casting or ingot rolling after ingot forming, hot rolling, hot-rolled sheet annealing as needed, cold It can be manufactured through processes such as cold rolling, finish annealing, and insulating film coating and baking. In these steps, the conditions for properly controlling the precipitation state are as follows. In addition, after hot rolling, it is possible to perform hot-rolled sheet annealing as necessary, and cold rolling may be performed once or twice or more with intermediate annealing interposed therebetween.

  The slab heating temperature at the time of hot rolling the steel slab having the component composition described above is set to 1000 ° C. or more and 1200 ° C. or less. That is, when the temperature is lower than 1000 ° C., Ti carbide precipitates and grows during slab heating, so that the effect of suppressing crystal grain growth during finish annealing cannot be sufficiently exhibited. On the other hand, if it exceeds 1200 ° C, in addition to being disadvantageous in terms of cost, the operability is deteriorated, for example, the high-temperature strength is lowered and the slab is deformed to hinder extraction from the heating furnace. Accordingly, the slab heating temperature is set to 1000 ° C. or more and 1200 ° C. or less. In addition, hot rolling itself is not specifically limited, For example, hot-rolling finishing temperature can be 700-950 degreeC, and coiling temperature can be made into the conditions of 750 degrees C or less.

  Then, if necessary, hot-rolled sheet annealing is performed, and after final thickness is obtained by cold rolling or warm rolling two or more times with one or more intermediate annealings, finish annealing is performed. Prior to this, it is important to perform at least one heat treatment for holding at a temperature of 800 ° C. or higher and 950 ° C. or lower for 30 seconds or longer. By this heat treatment, Ti carbide can be precipitated in the structure before the finish annealing, and the growth of crystal grains during the finish annealing can be suppressed.

  That is, if the heat treatment is less than 800 ° C., sufficient precipitation may not occur. On the other hand, if the heat treatment exceeds 950 ° C., precipitates grow and the effect of suppressing crystal grain growth during finish annealing becomes insufficient.

  In addition, it is preferable to perform the said heat processing to serve as either hot-rolled sheet annealing or intermediate annealing prior to finish annealing.

  Subsequent finish annealing is performed at 700 ° C. or higher and 850 ° C. or lower, whereby a recrystallized grain structure can be controlled uniformly and finely to obtain an electrical steel sheet having high strength and excellent magnetic properties. When the finish annealing temperature is less than 700 ° C., recrystallization becomes insufficient. On the other hand, when it exceeds 850 ° C., crystal grains are likely to grow even when the present invention is applied, and the strength is lowered. Subsequent to this finish annealing, an insulating film is applied and baked to obtain a final product.

  Steel having the composition shown in Table 3 was melted in a vacuum melting furnace, heated to 1100 ° C., and then hot rolled to a thickness of 2.1 mm. Thereafter, hot-rolled sheet annealing was performed at 900 ° C. for 90 seconds, and the thickness was further reduced to 0.35 mm by cold rolling. The state of occurrence of shave defects on the steel sheet surface obtained here was evaluated using the shave length per unit area as an index. Thereafter, finish annealing was performed for 30 seconds under two conditions of 750 ° C. and 800 ° C., and a test piece was cut out in parallel to the rolling direction for the obtained sample, and a tensile test and a fatigue test were performed. Further, the magnetic properties were evaluated by iron loss at an excitation magnetic flux density of 1.0 T and a frequency of 400 Hz after cutting out Epstein test pieces in the rolling parallel direction and the rolling perpendicular direction. The results are shown in Table 4.

  From Table 4, it can be seen that the steel 1 whose Ti * amount is out of the range of the present invention has a large characteristic difference due to the difference in the finish annealing temperature and has a problem in quality control. On the other hand, when Ti is added appropriately, the difference in characteristics depending on the finish annealing temperature is reduced, and high tensile strength is stably obtained. However, compared with steels 2 and 3 in the steel composition range of the present invention, steels 4, 5 and 6 whose Ti amount is outside the scope of the invention are not high in fatigue limit strength although they show high tensile strength. The incidence and magnetic properties are also poor.

Steels having the compositions shown in Table 5 were melted in a vacuum melting furnace, heated to 1050 ° C. and hot-rolled to a thickness of 2.1 mm. Thereafter, hot-rolled sheet annealing was performed at 850 ° C. for 120 seconds, and the thickness was further reduced to 0.35 mm by cold rolling. The state of occurrence of shave defects on the steel sheet surface obtained here was evaluated using the shave length per unit area as an index. Thereafter, finish annealing was performed at 800 ° C. for 30 seconds, and a test piece was cut out in parallel to the rolling direction for the obtained sample, and a tensile test and a fatigue test were performed. Further, the magnetic properties were evaluated by iron loss at an excitation magnetic flux density of 1.0 T and a frequency of 400 Hz after cutting out Epstein test pieces in the rolling parallel direction and the rolling perpendicular direction. The results are also shown in Table 6.
In addition, since the steel 18 which the value of Formula (1) remove | deviates from the range of this invention has produced the plate crack by cold rolling, subsequent evaluation is not performed.

  From Table 6, it can be seen that the steel sheet according to the present invention is less prone to baldness and has both good iron loss, high tensile strength, and high fatigue limit strength.

Claims (6)

% By mass
Si: 5.0% or less,
Mn: 2.0% or less,
Al: 2.0% or less and P: 0.05% or less are included within the range satisfying the following formula (1), and C: 0.008% or more and 0.040% or less,
N: 0.003% or less and
A non-oriented electrical steel sheet comprising Ti: 0.04% or less in a range satisfying the following formula (2) and comprising the balance Fe and inevitable impurities.
Record
300 ≦ 85 [Si%] + 16 [Mn%] + 40 [Al%] + 490 [P%] ≦ 430 (1)
0.008 ≦ Ti * <1.2 [C%] (2)
However, Ti * = Ti-3.4 [N%] In Claim 1, content of Si, Mn, Al, and P is the mass%,
Si: more than 3.5% and less than 5.0%
Mn: 0.3% or less,
A non-oriented electrical steel sheet characterized by Al: 0.1% or less and P: 0.05% or less. 3. The method according to claim 1, further comprising:
Sb: 0.0005% or more and 0.1% or less,
Sn: 0.0005% to 0.1%,
B: 0.0005% or more and 0.01% or less,
Ca: 0.001% to 0.01%,
REM: 0.001% to 0.01%,
Co: 0.05% or more and 5% or less,
Ni: 0.05% to 5% and
Cu: A non-oriented electrical steel sheet comprising one or more of 0.2% to 4%. % By mass
Si: 5.0% or less,
Mn: 2.0% or less,
Al: 2.0% or less and P: 0.05% or less are included within the range satisfying the following formula (1), and C: 0.008% or more and 0.040% or less,
N: 0.003% or less and
Ti: 0.04% or less is contained in a range satisfying the following formula (2), and the steel slab consisting of the remaining Fe and inevitable impurities is soaked at 1000 to 1200 ° C. and then hot-rolled, and then 1 After finishing the final thickness by cold rolling or warm rolling at least twice with intermediate or intermediate annealing, prior to the final annealing, the final annealing is performed at a temperature of 800 ° C or higher and 950 ° C or lower for 30 seconds or longer. A method for producing a non-oriented electrical steel sheet, wherein the holding heat treatment is performed at least once, and then finish annealing is performed at 700 ° C. or higher and 850 ° C. or lower.
Record
300 ≦ 85 [Si%] + 16 [Mn%] + 40 [Al%] + 490 [P%] ≦ 430 (1)
0.008 ≦ Ti * <1.2 [C%] (2)
However, Ti * = Ti-3.4 [N%] In Claim 4, content of Si, Mn, Al, and P is the mass%,
Si: more than 3.5% and less than 5.0%
Mn: 0.3% or less,
A method for producing a non-oriented electrical steel sheet, wherein Al: 0.1% or less and P: 0.05% or less. 6. The method according to claim 4, further comprising:
Sb: 0.0005% or more and 0.1% or less,
Sn: 0.0005% to 0.1%,
B: 0.0005% or more and 0.01% or less,
Ca: 0.001% to 0.01%,
REM: 0.001% to 0.01%,
Co: 0.05% or more and 5% or less,
Ni: 0.05% to 5% and
Cu: The manufacturing method of the non-oriented electrical steel sheet characterized by including 1 type or 2 types or more of 0.2% or more and 4% or less.

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