KR101412363B1 - Non-oriented electrical steel sheet and method for manufacturing the same - Google Patents

Abstract

According to the present invention, there is provided a steel sheet comprising, in terms of mass%, Si: 5.0% or less, Mn: 2.0% or less, Al: 2.0% : 0.008% or more to 0.040% or less, N: 0.003% or less, and Ti: 0.04% or less in the range satisfying the following formula (2), and the balance being Fe and inevitable impurities, It is possible to obtain a non-oriented electrical steel sheet excellent in mechanical properties and further superior in steel sheet quality at low cost.
300 ≦ 85 [Si%] + 16 [Mn%] + 40 [Al%] + 490 [P%] ≦ 430 (One)
0.008? Ti * < 1.2 [C%] ... (2)
Ti * = Ti - 3.4 [N%],

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a non-oriented electrical steel sheet,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-oriented electrical steel sheet, particularly to a component subjected to a large stress, such as a turbine generator, a drive motor for an electric vehicle and a hybrid automobile, or a servo motor for a robot or a machine tool, Oriented electric steel sheet having excellent strength and fatigue characteristics, and further having excellent magnetic properties, and a method for producing the same.

The present invention is to provide the non-oriented electrical steel sheet at a lower cost than conventional ones.

BACKGROUND ART [0002] Recent development of a motor drive system has enabled frequency control of a drive power source, and motors that perform variable speed operation and motors that perform high-speed rotation above a commercial frequency have been increasing. In such a high-speed motor, the centrifugal force acting on the rotating body is proportional to the turning radius, and increases in proportion to the square of the rotating speed.

In a land magnet type DC inverter control motor (IPM), which is increasingly employed in a drive motor or a compressor motor of a hybrid car in recent years, it has been known that the magnetic flux- The stress concentrates on a narrow bridge portion having a width of several millimeters between them. Since the motor can be miniaturized by high-speed rotation, high-speed rotation of the motor is intended for a drive motor of a hybrid automobile having a space or a weight restriction, and high strength material is advantageous for the core material used for the rotor of the high- .

On the other hand, since such a rotating machine such as a motor or a generator uses electromagnetic phenomenon, the iron core material is also required to have excellent magnetic properties. Particularly, in the rotor of the high-speed rotation motor, the core temperature rises due to the eddy current generated by the high-frequency magnetic flux, which causes the thermal demagnetization of the buried permanent magnet, It is required to have low iron loss at high frequencies. Therefore, an electric steel sheet having high strength and excellent magnetic properties is desired as a material for a rotor.

Steel strengthening mechanisms include solidification of reinforcement, precipitation strengthening, grain refinement, and work hardening. Up to now, several high strength non-oriented electrical steel sheets have been proposed and proposed to meet the needs of rotors of high-speed rotating motors.

W, Mo, Mn, Ni, Co, and Al, for example, in order to further enhance the solubility, based on increasing the Si content to 3.5 to 7.0% Or the like is added to the surface of the substrate to increase the strength. Patent Document 2 proposes a method of improving magnetic properties by controlling the crystal grain size to 0.01 to 5.0 mm by studying finish annealing conditions in addition to the above strengthening method.

However, when these methods are applied to factory production, troubles such as plate breakage in the rolling line after hot rolling are likely to occur, resulting in a reduction in yield and inevitable line stoppage. If the cold rolling is carried out at a temperature of several hundreds of degrees Celsius, it is possible to reduce the plate breakage, but it is impossible to ignore the problems in process control such as the necessity of facility response for warm rolling and the restriction of production.

Patent Document 3 discloses a technique of using carbonitride precipitation. In a steel having a Si content of 2.0% or more and less than 4.0%, C is 0.05% or less and one or two of Nb, Zr, Ti, and V In the range of 0.1 <(Nb + Zr) / 8 (C + N) <1.0 and 0.4 <(Ti + V) / 4 (C + N) <4.0.

Likewise, in Patent Document 4, in addition to the matters described in Patent Document 3, addition of 0.3% or more and 10% or less of Ni and Mn in total in order to enhance solidification is performed. Then, Nb, Zr, There has been proposed a technique of adding Ti and V to achieve both high strength and magnetic properties.

However, when a high strength is obtained by these methods, deterioration of magnetic properties can not be avoided, and surface defects such as spots caused by precipitates and internal defects tend to occur, resulting in deterioration of product quality, There is a problem that the yield is lowered or the cost is increased because the steel is liable to cause breakage trouble in the production of the steel sheet. In addition, in the technique described in Patent Document 4, since a high-priced solid solution strengthening element such as Ni is added, the cost is further increased.

As a technique using work hardening, Patent Document 5 proposes a technique for achieving a high strength by retaining a machined structure in a steel containing 0.2 to 3.5% of Si. Concretely, the heat treatment is not carried out after the cold rolling, and the heat treatment is not conducted to a degree equivalent to the holding at 750 ° C for 30 seconds but is preferably 700 ° C or less, more preferably 650 ° C or less, 550 DEG C or lower and 500 DEG C or lower. In this example, the results are shown as results at a processing organization rate of 5% at 750 ° C for 30 seconds, 20% at 700 ° C for 30 seconds, and 50% at 600 ° C for 30 seconds. In this case, there is a problem that the shape of the rolled strip can not be sufficiently corrected because the annealing temperature is low. If the shape of the steel sheet is defective, there is a problem that the drop rate after lamination with a core for motor or the like is lowered, and the stress distribution at the time of high-speed rotation as a rotor becomes uneven. In addition, there is also a problem that it is difficult to obtain stable characteristics because the ratio of the processed lips to the recrystallized lobes varies greatly depending on the steel composition and the annealing temperature. Further, in general, the finish annealing of the non-oriented electrical steel sheet is performed by using a continuous annealing furnace. In order to suppress oxidation of the surface of the steel sheet, the inside of the furnace is usually adjusted to an atmosphere containing hydrogen gas of several percent or more. In order to perform the low-temperature annealing below 700 ° C in such a continuous annealing facility, it takes time to change the furnace temperature setting, and it is necessary to replace the furnace atmosphere in order to avoid hydrogen explosion. .

From the above technical background, the inventors of the present invention have found that, in the silicon steel in which C and N are reduced in the Patent Document 6, the recrystallization temperature of the silicon steel is increased by adding Ti excessively to C and N, High strength steel sheet with both reinforced and non - recrystallized structure. This method has a problem in that the alloy cost is high because the addition amount of Ti is relatively high, and there is a possibility that there is a deviation in mechanical characteristics because an unrecrystallized structure remains.

Japanese Patent Application Laid-Open No. 60-238421 Japanese Patent Application Laid-Open No. 62-112723 Japanese Patent Application Laid-Open No. 6-330255 Japanese Unexamined Patent Publication No. 2-8346 Japanese Patent Application Laid-Open No. 2005-113185 Japanese Patent Application Laid-Open No. 2007-186790

Several proposals have been made regarding the high strength nonoriented electrical steel sheet. However, in the proposals so far, a high-strength non-oriented electrical steel sheet having good magnetic properties in addition to high tensile strength and high fatigue strength and satisfying the problems of surface defects and defects such as internal defects and plate form, It is a reality that industrially stable production using an electric steel sheet manufacturing facility at low cost with a good yield has not been achieved. Especially, in the high-strength electric steel sheet which has been provided for the rotor of the high-speed rotary motor up to now, since the magnetic property, that is, the high-frequency iron loss is high, the heat generation of the rotor can not be avoided and the design specifications of the motor are inevitably limited.

Therefore, an object of the present invention is to provide a high strength non-oriented electrical steel sheet excellent in magnetic properties and steel sheet quality and a manufacturing method thereof at low cost. An object of the present invention, specifically, a tensile strength more than 650 ㎫, preferably at least 700 ㎫, good high-frequency low iron loss properties, such as W _10/400 value of the plate thickness 0.35 ㎜ material (材) is 40 W / Kg or less, preferably 35 W / kg or less, in an industrially stable manner and at a low cost.

The inventors of the present invention have conducted various studies on a high strength electrical steel sheet capable of achieving the above object at a high level and a manufacturing method thereof. As a result, it has been found out that the addition amounts and the addition ratios of Ti and C are deeply involved in the balance between the strength characteristics and the magnetic properties of the electrical steel sheet, and by appropriately adjusting the precipitation amount of Ti carbide, a high strength electrical steel sheet having excellent properties is stably and inexpensively And found that it can be manufactured.

That is, the present invention is based on the following findings.

(A) The presence of a relatively small amount of Ti carbide can suppress the growth of crystal grains in the finish annealing of the electric steel sheet, and enhancement by the refinement of the crystal grains can be achieved.

(B) Even if the amount of Ti carbide is excessively large, not only does it not contribute to the effect of suppressing grain growth but also adversely affects such as surface defects and internal defects are increased to deteriorate the quality of the steel sheet or to become a starting point of fracture. In this respect, surface defects such as scabs and internal defects are greatly reduced by controlling the addition of Ti to an appropriate range.

On the other hand, since the Ti nitride is generated at a higher temperature than the Ti carbide, the effect of suppressing the grain growth is weak, so that it is not useful for controlling the grain refinement of the present invention. Therefore, in the method of suppressing crystal grain growth by controlling the amount of Ti carbide, N is preferably reduced stably. This is totally different from the conventional precipitation strengthening method in which the effects of C and N are treated equally.

(C) In a steel sheet obtained by refining crystal grains, the solid solution C not only enhances the tensile strength, but also has an effect of improving the fatigue characteristics inherently required for a rotor material rotating at a high speed.

(D) The main alloying elements which are usually added for the purpose of increasing the electrical resistance of the electric steel sheet to achieve low iron loss are Si, Al, and Mn. These substitutional alloying elements have an effect have. Therefore, in order to make both high strength and low iron loss compatible, it is effective to base on solid solution strengthening by these elements. On the other hand, in the case of excessive addition of these elements, it is difficult to manufacture due to embrittlement of the steel, so that the addition is limited. In order to satisfy the three points of hardening of hardeness, low iron loss and productivity most efficiently, The addition is preferable.

From these findings, it can be seen that constraint and new processes in the production of steel sheet can be carried out in a conventional manner by using a balance of solid solution strengthening by substitutional alloy element mainly composed of Si, grain refinement by Ti carbide and solid solution strengthening by interstitial element C It is possible to obtain a non-oriented electrical steel sheet having high strength, excellent fatigue properties under the use conditions, and superior magnetic properties and steel sheet quality, without substantially adding to the production of the non-oriented electrical steel sheet. And have accomplished 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: not more than 0.05%

In the range satisfying the following formula (1), and further contains

  C: not less than 0.008% and not more than 0.040%

  N: 0.003% or less and

  Ti: not more than 0.04%

In the range satisfying the following formula (2), and the balance of Fe and unavoidable impurities.

300 ≦ 85 [Si%] + 16 [Mn%] + 40 [Al%] + 490 [P%] ≦ 430 (One)

0.008? Ti * &lt; 1.2 [C%] ... (2)

Ti * = Ti - 3.4 [N%],

Here, [Si%], [Mn%], [Al%], [P%], [C%] and [N%] represent the content (mass%) of the display element, respectively.

(ii) In the above (i), the content of Si, Mn, Al and P is in% by mass

  Si: more than 3.5% and not more than 5.0%

  Mn: 0.3% or less,

  Al: 0.1% or less and

  P: not more than 0.05%

Wherein the non-oriented electrical steel sheet is a non-oriented electrical steel sheet.

(iii) In the above (i) or (ii), further, in mass%

  Sb: not less than 0.0005% and not more than 0.1%

  Sn: not less than 0.0005% and not more than 0.1%

  B: not less than 0.0005% and not more than 0.01%

  Ca: 0.001% or more and 0.01% or less,

  REM: 0.001% or more and 0.01% or less,

  Co: 0.05% or more and 5% or less,

  Ni: not less than 0.05% and not more than 5%

  Cu: not less than 0.2% and not more than 4%

Of the non-oriented electrical steel sheet.

(iv) in mass%

  Si: 5.0% or less,

  Mn: 2.0% or less,

  Al: 2.0% or less and

  P: not more than 0.05%

In the range satisfying the following formula (1), and further contains

  C: not less than 0.008% and not more than 0.040%

  N: 0.003% or less and

  Ti: not more than 0.04%

In a range satisfying the following formula (2) is maintained at a temperature of 1000 to 1200 DEG C and then hot-rolled, and then the steel slab is subjected to two or more cold rolling Or heat-rolling to a final thickness, and then performing finish annealing, a heat treatment is performed at least once for at least 30 seconds at a temperature of 800 ° C to 950 ° C prior to the finish annealing, Wherein the annealing is carried out at a temperature of 700 ° C or more and 850 ° C or less.

300 ≦ 85 [Si%] + 16 [Mn%] + 40 [Al%] + 490 [P%] ≦ 430 (One)

0.008? Ti * &lt; 1.2 [C%] ... (2)

Ti * = Ti - 3.4 [N%],

(v) In the above (iv), the content of Si, Mn, Al and P is in% by mass

  Si: more than 3.5% and not more than 5.0%

  Mn: 0.3% or less,

  Al: 0.1% or less and

  P: not more than 0.05%

Wherein the non-oriented electrical steel sheet is produced by the method.

(vi) In (iv) or (v), further, in terms of mass%

  Sb: not less than 0.0005% and not more than 0.1%

  Sn: not less than 0.0005% and not more than 0.1%

  B: not less than 0.0005% and not more than 0.01%

  Ca: 0.001% or more and 0.01% or less,

  REM: 0.001% or more and 0.01% or less,

  Co: 0.05% or more and 5% or less,

  Ni: not less than 0.05% and not more than 5%

  Cu: not less than 0.2% and not more than 4%

Wherein the non-oriented electrical steel sheet comprises one or more of the following.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a non-oriented electrical steel sheet which has excellent mechanical properties and magnetic properties required for a rotor material of a motor rotating at high speed and which is also excellent in steel sheet quality such as a scap or plate shape. Further, it is possible to stably manufacture the steel sheet at a high yield, without adding a significant increase in cost, strict manufacturing constraints, or a new process as compared with the conventional production of a non-oriented electrical steel sheet. Therefore, the present invention is suitable for fields requiring higher speed dialing such as driving motors for electric vehicles and hybrid vehicles, or servo motors for robots and machine tools, and its contribution to industrial value and industry is high.

1 is a graph showing the relationship between the amount of Ti and the tensile strength.
2 is a graph showing the relationship between the amount of Ti and iron loss.
3 is a graph showing the relationship between the amount of Ti and the surface scap defect rate.

Hereinafter, experiments leading to the present invention will be described in detail.

That is, the inventors have studied in detail the effect of Ti, which is a main carbonitride-forming element, on steel sheet quality such as precipitation strengthening, recrystallization, grain growth behavior and scap. As a result, it can be seen that the effect of adding Ti in the range of not more than atomic equivalents relative to C or N is greatly different, and it is found that there is an optimum range of addition for satisfying magnetic properties and steel sheet quality at high level there was. The main experimental results are shown. In the following description, &quot;% &quot; means &quot; mass% &quot;

<Experiment 1>

Wherein the main component is Si: 4.0 to 4.1%, Mn: 0.03 to 0.05%, Al: 0.001% or less, P: 0.007 to 0.009% and S: 0.001 to 0.002% The steel in which the amount of Ti is varied in the range of 0.001 to 0.002% in an almost constant amount and the amount of Ti is varied in the range of 0.001 to 0.36% is variously dissolved in a vacuum melting furnace and heated to 1100 캜 and hot rolled to a thickness of 2.1 mm Respectively. Thereafter, hot rolled sheet annealing was performed at 900 占 폚 for 90 seconds and cold rolled to a thickness of 0.35 mm. Thereafter, the occurrence of scap defects (scap length per unit area) on the surface of the steel sheet was evaluated. Then, finish annealing at 800 ° C for 30 seconds was carried out to measure mechanical properties (cutting JIS No. 5 specimen in parallel with the rolling direction) and magnetic properties (cutting the Epstein specimens in the direction parallel to the rolling direction and rolling direction, the T, the iron loss W _10/400 at the frequency of 400 Hz were evaluated for measurement). Fig. 1, Fig. 2 and Fig. 3 show the results of investigation on the amount of Ti, the tensile strength, the magnetic properties, and the occurrence of surface scap defects.

First, as shown in Fig. 1, the tensile strength increases with Ti addition, but the effect is small in the region A in Fig. 1 where the addition amount is small, and in the range of Ti shown in the region B in the figure, It looked. Further, in the region C where the amount of Ti is high, the strength is further increased. As a result of observation of the steel structure in these regions, it was found that the steel structure of the region B had a uniform microstructure at a crystal grain size of 10 탆 or less, while the grain of the steel structure of the region A was grown more than the region B, Indicating the texture of the grain. On the other hand, region C shows a composite structure of unrefined and recrystallized grains.

In Figure 2, it shows the relationship between the Ti content and iron loss W _10/400. The iron loss in the region A in the figure becomes the lowest and becomes good, but as shown in Fig. 1, the region A has a low level of strength. 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 having a strength comparable to the region C and a good core loss close to the region A is obtained.

On the other hand, as shown in Fig. 3, the scab defect starts to increase when the Ti addition amount exceeds 0.04%, and rises to the vicinity where the element equivalent ratio of Ti, C, and N becomes 1, . When the contents of C and N are constant, the precipitation amount of the Ti carbonitride is increased up to the vicinity of the element equivalent ratio of 1, and after that, the precipitation amount becomes constant, so that the precipitation amount of the Ti carbonitride is considered to be related to the scap generation amount .

From these results, it has become clear that by controlling the amount of Ti to be in the range of the region B, it is possible to achieve high yield and low iron loss while suppressing scab defects that directly lead to an increase in production cost, which is a cause of reduction in yield or plate breakage trouble. In other words, Ti is required to have a certain amount of Ti carbonitride to be formed, but it is advantageous to contain Ti in an amount of 0.04% or less from the viewpoint of suppressing scap defects.

Further, it was found that the same amount of the components other than the steel and N amount was changed and the amount of N contained was changed. As a result, it was found that the lower limit of the amount of Ti to obtain high strength was increased by increasing the amount of N. Further, as a result of further investigation, it was found that 0.008? Ti * (however, Ti * = Ti-3.4 [N%]) must be satisfied. At this point, the contribution of Ti carbide to high strength is large, and the contribution of Ti nitride is considered to be small, so that control of Ti carbide becomes more important.

From these results, it has become clear that by controlling the amount of Ti added to the level of the region B, it is possible to achieve both high strength and low iron loss while suppressing scab defects that directly lead to reduction in yield or plate breakage trouble and increase in manufacturing cost.

<Experiment 2>

Next, in order to investigate the influence of Ti carbonitride in detail, a steel having the composition shown in Table 1 was dissolved in a vacuum melting furnace, and a steel sheet having a thickness of 0.35 mm was produced in the same manner as in Experiment 1. [ The amounts of C and N were varied on the basis of the steel a having a small amount of C and N as a base. Strengths c and d are added so that the amount of C + N becomes constant. Table 2 shows the surface scap defect rate, iron loss and tensile strength of the obtained sample. The strengths b, c and d of the steel b are increased with respect to the steel a, but by the comparison of the strengths c and d in which the total amounts of C and N are substantially equal, It is higher strength than this. As a result of the observation of the structure, the crystal grain size was in the order of the steel a> d> b> c, corresponding to the order of the tensile strength.

Then, the fatigue characteristics of these samples were examined. The test conditions were a tensile-tensile mode with a stress ratio of 0.1, and a stress that was not broken at an amplitude of 10 million cycles at a cycle of 20 Hz as the fatigue limit strength. The results are also shown in Table 2. The fatigue limit strength (FS) of the material with higher tensile strength (TS) also showed a higher tendency. The ratio (FS / TS) was different and the steel c had the best result. On the other hand, the value of the improvement of the fatigue limit strength of the steel d is smaller than that of the steel having a higher tensile strength. Therefore, as a result of detailed examination of the structure of the steel d, precipitates considered to be TiN exceeding 5 탆 in diameter were dispersed, and it was assumed that this became the starting point of fatigue fracture. Here, nitrogen reacts with Ti at a relatively high temperature of 1100 占 폚 or more, and is liable to precipitate as TiN as a host. Therefore, TiN tends to be a starting point of fatigue fracture, and it is considered that the effect of suppressing grain growth, which is one of the goals of the present invention, is smaller than that of Ti carbide.

On the other hand, also in the comparison of the strengths b and c, the strength c and the fatigue limit strength are both excellent, but the fatigue limit strength is relatively high and the strength ratio (FS / TS) is high. Since the amounts of Ti and N in the steel b and the steel c are almost equal to each other, the deposition states of Ti nitride and Ti carbide are the same, and it is considered that the difference between the two is caused by the difference in the amount of dissolved carbon. Therefore, it is presumed that the presence of the solid carbon has increased the fatigue limit strength by restraining generation and propagation of cracks by fixing the introduced electric potential under cyclic stress such as fatigue test. Therefore, securing employment carbon is also important.

On the basis of the above experimental results, the influence of factors such as Ti carbide, Ti nitride, and Hardened carbon due to the addition of a relatively small amount of Ti on the steel texture, the steel surface quality, and the mechanical and magnetic properties of the steel sheet is further investigated As a result, the present inventors have found a regulation covering these factors and have completed the present invention.

Next, the present invention will be described in detail by requirements.

First, the reason for limiting the main steel components will be described.

Not more than 5.0% of Si, not more than 2.0% of Mn, not more than 2.0% of Al and not more than 0.05% of P in a range satisfying the following formula (1).

300 ≦ 85 [Si%] + 16 [Mn%] + 40 [Al%] + 490 [P%] ≦ 430 (One)

The object of the present invention is to provide an electric steel sheet having high strength and excellent magnetic properties at low cost. To achieve this, it is necessary to increase the amount of solid solution strengthened by the main four alloy component to a certain level or more. It is important to add the total amount of the main four alloy components within the range satisfying the above-mentioned formula (1), taking into account the individual content of the alloy components as described below and the contribution to the respective solid solution strengthening amounts Do. That is, when the value of the formula (1) is less than 300, the obtained material strength is insufficient. On the other hand, if the value exceeds 430, the plate cleavage trouble during the production of the steel sheet increases, leading to a decrease in productivity and a remarkable increase in the production cost.

Next, reasons for limiting the content of each of the four major alloy components will be described.

Si: not more than 5.0%

Si is a main element constituting a non-oriented electrical steel sheet which is generally used as a deoxidizing agent and has an effect of increasing the electrical resistance of the steel to reduce iron loss. It also has a high employment enhancement ability. That is, since it is an element that can balance both high tensile strength, high fatigue strength and low iron loss in comparison with other solid strengthening elements such as Mn, Al and Ni added to the nonoriented electric steel sheet, . For this purpose, it is advantageous to contain at least 3.0%, more preferably more than 3.5%. However, if it exceeds 5.0%, deterioration of toughness becomes remarkable, and high control is required at the time of plate passing and rolling, and productivity is lowered. Therefore, the upper limit is 5.0% or less.

Mn: 2.0% or less

Mn is effective for improvement of hot brittleness. In addition, it has an effect of reducing the iron loss by increasing the electrical resistance of the steel and also enhancing the strength by solid solution strengthening. Therefore, Mn is preferably contained in an amount of 0.01% or more. However, the effect of improving the strength is small compared with that of Si, and excessive addition of Mn causes brittleness of steel, so that the Mn content is 2.0% or less.

Al: 2.0% or less

Al is a strong deoxidizer and is a commonly used element for steel scouring. In addition, like Si and Mn, it also has an effect of reducing the iron loss by increasing the electrical resistance of steel and enhancing the strength by solid solution strengthening. Therefore, Al is preferably contained in an amount of 0.0001% or more. However, the effect of improving the strength is small compared with that of Si, and excessive addition of Al causes embrittlement of steel, so that the Al content is 2.0% or less.

P: not more than 0.05%

P is very effective for increasing the strength because a large amount of solubility-enhancing ability can be obtained even by adding a relatively small amount, and is preferably contained in an amount of 0.005% or more. However, since excessive addition invites reduction in grain size and rolling property due to embrittlement caused by segregation, the addition amount is limited to 0.05% or less.

Further, among the main alloying elements Si, Mn, Al and P, the alloying design mainly composed of Si is advantageous in order to achieve the most efficient combination of solid solution strengthening and low iron loss and fabrication. That is, it is advantageous to optimize the balance of the characteristics of the non-oriented electrical steel sheet by containing Si in the range of more than 3.5%. At that time, the remaining three components are Mn: not more than 0.3%, Al: not more than 0.1% P: 0.05% or less. The reason for the 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 crystal grain growth at the time of annealing the steel sheet with a suitable fine Ti carbide and to express grain refinement enhancement. In order to do so, it is necessary to contain C in an amount not less than 0.008% and not more than 0.040%, N: not more than 0.003%, and Ti: not more than 0.04% in the range satisfying the following formula (2).

0.008? Ti * &lt; 1.2 [C%] ... (2)

Ti * = Ti - 3.4 [N%],

C: not less than 0.008% and not more than 0.040%

C is required to be 0.008% or more. That is, when the content is less than 0.008%, it is difficult to stably deposit fine Ti carbide and the amount of solid solution C becomes insufficient, so that the fatigue strength can not be further improved. On the other hand, excessive addition leads to deterioration of the magnetic properties, resulting in remarkable work hardening during cold rolling, leading to plate breakage, or an increase in the number of rolling due to an increase in rolling load, , And the upper limit is 0.04%.

N: not more than 0.003%

N forms nitrides with Ti, which is generated at a higher temperature than Ti carbide and has a weak effect of suppressing crystal grain growth, and thus is not effective for finer crystal grains. It may cause adverse effects such as becoming a starting point of fatigue fracture. Therefore, 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 the steelmaking degassing ability and the productivity deterioration due to refining for a long time.

Ti: not more than 0.04%

In the present invention, it is important to control the Ti carbide. Ti is liable to form a nitride at a higher temperature than that of forming a carbide, and therefore it is necessary to control the amount of Ti forming carbide. If the amount of Ti capable of forming carbide is represented by Ti *, Ti * is an amount obtained by subtracting the atomic equivalent of N from the Ti content, that is,

Ti * = Ti - 3.4 [N%]

. Ti * ≥ 0.008 is required together with an appropriate amount of C in order to suppress the increase of the iron loss by suppressing the grain growth while making the added Ti precipitate as the Ti carbide to increase the strength. On the other hand, if the amount of Ti added to the amount of C increases, the effect of improving the fatigue strength can not be expected because the solid solution C decreases, so that Ti * <1.2 [C%] must also be satisfied at the same time.

If the amount of Ti exceeds 0.04%, as shown in Fig. 3, the scall-defect increases and the steel plate quality and yield decrease and the cost increases. Therefore, the upper limit is set to 0.04%.

In the present invention, it is possible to contain an element other than the above-described element within a range not to impair the effect of the present invention. For example, the effect of improving the magnetic properties by controlling the shape of the oxide or the sulphide is improved by improving the magnetic properties by adding 0.0005 to 0.1% of Sb and Sn which have the effect of improving magnetic properties, and 0.0005 to 0.01% Of Ca and REM is 0.001 to 0.01%, that of Co and Ni having an effect of improving magnetic flux density is 0.05 to 5%, and that of precipitation strengthening due to aging precipitation is expected to be 0.2 to 4% It is possible.

Next, the reason for limiting the manufacturing method is referred to.

In the present invention, the manufacturing process from the strong solvent to the cold rolling can be carried out according to the method performed in a general non-oriented electrical steel sheet. For example, a steel slab may be made of a steel slab by continuous casting or granular rolling after the steel ingot is refined into a predetermined component in a converter or an electric furnace, and subjected to hot rolling and, if necessary, hot rolling annealing, cold rolling, Annealing, and insulating film coating baking. In these processes, the conditions for appropriately controlling the precipitation state are as follows. It is also possible to perform hot-rolled sheet annealing after hot-rolling, if necessary, and cold-rolling may be carried out twice or more with intermediate or intermediate annealing in between.

The slab heating temperature at the time of hot rolling the steel slab having the above-described composition is set to 1000 deg. C or more and 1200 deg. C or less. That is, when it is less than 1000 占 폚, since the carbide of Ti precipitates and grows during the heating of the slab, the effect of suppressing grain growth during finish annealing can not be sufficiently exhibited. On the other hand, if it exceeds 1200 ° C., not only the cost is deteriorated but also the high-temperature strength is lowered and the slab is deformed and the extraction from the heating furnace is hindered. Therefore, the slab heating temperature is set to 1000 deg. C or higher and 1200 deg. C or lower. The hot rolling itself is not particularly limited. For example, the hot rolling finishing temperature may be 700 to 950 占 폚, and the coiling temperature may be 750 占 폚 or less.

Then, if necessary, hot-rolled sheet annealing is carried out, and after finishing annealing is carried out after making the final sheet thickness by two or more cold rolling or warm rolling with one or intermediate annealing in between, It is important to carry out the heat treatment at least once at a temperature of not lower than 950 占 폚 for at least 30 seconds. By this heat treatment, Ti carbide can be precipitated in the structure before the finish annealing, and growth of crystal grains during finish annealing can be suppressed.

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

It is also preferable that the above-mentioned heat treatment is performed in addition to either the hot-rolled sheet annealing or the intermediate annealing prior to the finish annealing.

The subsequent finish annealing is performed at a temperature of 700 캜 or higher and 850 캜 or lower, whereby an electric steel sheet having high strength and excellent magnetic properties can be obtained by uniformly and finely controlling the recrystallized grain structure. When the temperature of the finish annealing is less than 700 캜, recrystallization becomes insufficient. On the other hand, when the temperature exceeds 850 캜, the crystal grains are easily grown by application of the present invention, and the strength is lowered. Subsequent to the finish annealing, an insulating coating is applied and baking treatment is performed to obtain a final product.

Example 1

Steels having the compositions shown in Table 3 were dissolved in a vacuum melting furnace and heated to 1100 캜 and hot rolled to a thickness of 2.1 mm. Thereafter, the hot-rolled sheet was annealed at 900 ° C for 90 seconds, and then cold-rolled to 0.35 mm thick. The occurrence status of the scap defects on the steel sheet surface obtained here was evaluated with the scall length per unit area as an index. Thereafter, finishing annealing was performed for 30 seconds under two conditions of 750 ° C and 800 ° C, and a tensile test and a fatigue test were performed on the obtained sample by cutting the test piece parallel to the rolling direction. The magnetic properties were evaluated by cutting the Epstein specimens in the rolling parallel direction and in the direction perpendicular to the rolling direction and by iron loss at an excitation flux density of 1.0 T and a frequency of 400 Hz. These results are shown in Table 4.

From Table 4, it can be seen that the steel 1 with the amount of Ti * deviated from the range of the present invention has a problem in quality control due to a large difference in characteristics depending on the difference in finish annealing temperature. On the other hand, when Ti is adequately added, the characteristic difference due to the annealing temperature is reduced, and a high tensile strength is stably obtained. However, compared to steels 2 and 3 in the steel composition range of the present invention, steels 4, 5 and 6 having a Ti amount outside the scope of the invention show high tensile strength, while fatigue limit strength is not high, Characteristics also fell.

Example 2

Steels having the compositions shown in Table 5 were dissolved in a vacuum melting furnace, heated to 1050 占 폚 and hot-rolled to a thickness of 2.1 mm. Thereafter, the hot-rolled sheet was annealed at 850 ° C for 120 seconds, and then cold-rolled to a thickness of 0.35 mm. The occurrence status of the scap defects on the steel sheet surface obtained here was evaluated with the scall length per unit area as an index. Thereafter, finishing annealing was performed at 800 DEG C for 30 seconds, and a test piece was cut in parallel with the rolling direction with respect to the obtained sample, and a tensile test and a fatigue test were carried out. The magnetic properties were evaluated by cutting the Epstein specimens in the rolling parallel direction and in the direction perpendicular to the rolling direction and by iron loss at an excitation flux density of 1.0 T and a frequency of 400 Hz. The results are also shown in Table 6.

Steel 18 in which the value of the formula (1) deviates from the range of the present invention was not subjected to the subsequent evaluation because the steel sheet cracking occurred in the cold rolling.

It can be seen from Table 6 that all of the steel sheets according to the present invention have less scar occurrence, have good iron loss, high tensile strength and high fatigue limit strength.

Claims (6)

In terms of% by mass,
Si: more than 0% and not more than 5.0%
Mn: more than 0% and not more than 2.0%
Al: more than 0% and not more than 2.0%
P: more than 0% and less than 0.05%
In the range satisfying the following formula (1), and further contains
C: not less than 0.008% and not more than 0.040%
N: more than 0% and not more than 0.003%
Ti: more than 0% and not more than 0.04%
In the range satisfying the following formula (2), and the balance of Fe and unavoidable impurities.
300 ≦ 85 [Si%] + 16 [Mn%] + 40 [Al%] + 490 [P%] ≦ 430 (One)
0.008? Ti * &lt; 1.2 [C%] ... (2)
Ti * = Ti - 3.4 [N%], The method according to claim 1,
When the content of Si, Mn, Al and P is in a mass%
Si: more than 3.5% and not more than 5.0%
Mn: more than 0% and not more than 0.3%
Al: more than 0% and not more than 0.1%
P: more than 0% and less than 0.05%
Wherein the non-oriented electrical steel sheet is a non-oriented electrical steel sheet. 3. The method according to claim 1 or 2,
In addition, by mass%
Sb: not less than 0.0005% and not more than 0.1%
Sn: not less than 0.0005% and not more than 0.1%
B: not less than 0.0005% and not more than 0.01%
Ca: 0.001% or more and 0.01% or less,
REM: 0.001% or more and 0.01% or less,
Co: 0.05% or more and 5% or less,
Ni: not less than 0.05% and not more than 5%
Cu: not less than 0.2% and not more than 4%
Of the non-oriented electrical steel sheet. In terms of% by mass,
Si: more than 0% and not more than 5.0%
Mn: more than 0% and not more than 2.0%
Al: more than 0% and not more than 2.0%
P: more than 0% and less than 0.05%
In the range satisfying the following formula (1), and further contains
C: not less than 0.008% and not more than 0.040%
N: more than 0% and not more than 0.003%
Ti: more than 0% and not more than 0.04%
Of the steel slab in the range satisfying the following formula (2), and the remainder being Fe and inevitable impurities is heated to a temperature of 1000 to 1200 DEG C and then hot-rolled, The annealing is carried out at a temperature of 800 DEG C or more and 950 DEG C or less for 30 seconds or more prior to the finish annealing in the case of carrying out the final annealing after the annealing is performed twice or more by cold rolling or warm rolling, And the finish annealing is performed at 700 ° C or more and 850 ° C or less.
300 ≦ 85 [Si%] + 16 [Mn%] + 40 [Al%] + 490 [P%] ≦ 430 (One)
0.008? Ti * &lt; 1.2 [C%] ... (2)
Ti * = Ti - 3.4 [N%], 5. The method of claim 4,
When the content of Si, Mn, Al and P is in a mass%
Si: more than 3.5% and not more than 5.0%
Mn: more than 0% and not more than 0.3%
Al: more than 0% and not more than 0.1%
P: more than 0% and less than 0.05%
Wherein the non-oriented electrical steel sheet is produced by the method. The method according to claim 4 or 5,
In addition, by mass%
Sb: not less than 0.0005% and not more than 0.1%
Sn: not less than 0.0005% and not more than 0.1%
B: not less than 0.0005% and not more than 0.01%
Ca: 0.001% or more and 0.01% or less,
REM: 0.001% or more and 0.01% or less,
Co: 0.05% or more and 5% or less,
Ni: not less than 0.05% and not more than 5%
Cu: not less than 0.2% and not more than 4%
Wherein the non-oriented electrical steel sheet comprises one or more of the following.

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