TWI767210B - Non-oriented electrical steel sheet and method for producing the same - Google Patents

Abstract

[Subject] To provide a non-oriented electrical steel sheet with high strength and excellent magnetic properties. [Solution] A non-oriented electrical steel sheet, the chemical composition of the base metal is: in mass %, C: 0.0050% or less, Si: 3.8~5.0%, Mn: more than 0.2% and less than 2.0%, P: 0.030 % or less, S: 0.0030% or less, Al: 0.005% or more and less than 0.050%, N: 0.0005~0.0030%, Ti: less than 0.0050%, Nb: less than 0.0050%, Zr: less than 0.0050%, V: less than 0.0050%, Cu: less than 0.20%, Ni: less than 0.50%, Sn: 0~0.10%, Sb: 0~0.10% and the remainder: Fe and impurities, and satisfy [Si+0.5×Mn≧4.3]; and the average of the base metal The crystal grain size is 10~80µm.

Description

Non-oriented electrical steel sheet and method for producing the same

The present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof.

In recent years, due to the development of the drive system of the motor, the frequency of the drive power can be gradually controlled. Accordingly, there is an increasing demand for motors that perform variable-speed operation or high-speed rotation above the commercial frequency. The centrifugal force acting on the rotor constituting the motor that rotates at high speed increases in proportion to the square of the rotational speed. Therefore, higher strength is required for the steel used as the rotor of the high-speed motor.

In addition, in a drive motor of a hybrid vehicle or an electric vehicle, or an embedded-magnet-type inverter-controlled motor used in a compressor motor of an air conditioner, etc., a slit is provided in the outer peripheral portion of the rotor and a magnet is embedded. Therefore, due to the centrifugal force when the motor rotates at a high speed, the stress is concentrated on the narrow bridge portion such as between the outer periphery of the rotor and the slit. Therefore, the core material used for the rotor is required to have the strength not to be deformed or damaged by centrifugal force.

In addition, eddy currents are generated by high-frequency magnetic fluxes in high-speed rotating motors, resulting in reduced motor efficiency and heat generation. If the amount of heat generated increases, the magnets embedded in the rotor will be demagnetized, so that the iron loss in the high frequency region is also required to be low.

As a method of increasing the strength of a steel sheet, there are known methods utilizing solid solution strengthening, precipitation strengthening, grain refinement strengthening, composite structure strengthening, and the like. However, in many of these methods, the magnetic properties are degraded or the workability of the cold rolling delay is degraded. Therefore, it is generally extremely difficult to achieve a high degree of compatibility between the strength and the magnetic properties.

Against the background of the foregoing, for example, in Patent Documents 1 to 3, attempts have been made to achieve excellent magnetic properties and high strength.

prior art literature Patent Literature Patent Document 1: Japanese Patent Laid-Open No. 2004-300535 Patent Document 2: Japanese Patent Laid-Open No. 2007-186791 Patent Document 3: Japanese Patent Laid-Open No. 2012-140676

The problem to be solved by the invention However, in order to realize the energy-saving characteristics required for the motors of electric vehicles and hybrid vehicles in recent years, the technologies disclosed in Patent Documents 1 to 3 are insufficient to reduce iron loss, and the cost is high.

The present invention was made in order to solve the above-mentioned problems, and an object thereof is to provide a non-oriented electrical steel sheet having high strength and excellent magnetic properties at low cost and in a stable manner.

means of solving problems The gist of the present invention is the following non-oriented electrical steel sheet and a method for producing the same.

(1) A non-oriented electrical steel sheet, the chemical composition of its base metal is: In mass %, C: 0.0050% or less, Si: 3.8~5.0%, Mn: more than 0.2% and less than 2.0%, P: 0.030% or less, S: 0.0030% or less, Al: 0.005 or more and less than 0.050%, N: 0.0005~0.0030%, Ti: less than 0.0050%, Nb: less than 0.0050%, Zr: less than 0.0050%, V: less than 0.0050%, Cu: less than 0.20%, Ni: less than 0.50%, Sn: 0~0.10%, Sb: 0~0.10% and The remainder: Fe and impurities, and satisfy the following formula (i); and The average crystal grain size of the aforementioned base material is 10 to 80 µm. Si+0.5×Mn≧4.3・・・(i) However, the element symbol in the above formula is the content (mass %) of each element.

(2) The non-oriented electrical steel sheet according to the above (1), wherein the tensile strength is 650 MPa or more.

(3) The non-oriented electrical steel sheet according to (1) or (2) above, wherein the chemical composition contains one or two elements selected from the following: In mass %, Sn: 0.005~0.10% and Sb: 0.005~0.10%.

(4) The non-oriented electrical steel sheet according to any one of (1) to (3) above, which has an insulating coating on the surface of the base material.

(5) A method for producing a non-oriented electrical steel sheet, which is a method for producing the non-oriented electrical steel sheet according to any one of (1) to (4) above; The method is to perform hot rolling on a steel block having the chemical composition of any one of the above (1) to (3), followed by the following step 1 or step 2: (step 1) cold rolling and finish annealing are performed sequentially without annealing the hot-rolled sheet; (Step 2) annealing the hot-rolled sheet at a temperature below 950° C., and then performing the aforementioned cold rolling and the aforementioned finish annealing in sequence; However, the above-mentioned finish annealing is performed with a soaking temperature of 750 to 1000° C. and a soaking time of 1 to 300 seconds.

Invention effect According to the present invention, a non-oriented electrical steel sheet having high strength and excellent magnetic properties can be obtained in a low-cost and stable manner.

The inventors of the present invention have conducted intensive studies in order to solve the above-mentioned problems, and as a result, they have finally obtained the following knowledge.

Si, Mn, and Al are elements that have the effect of increasing the electrical resistance of steel and reducing eddy current loss. In addition, these elements are also elements that contribute to the high strength of steel.

Among the above-mentioned elements, Si is the element that most effectively contributes to the increase in resistance, and is also the element that most effectively contributes to the increase of strength. Like Si, Al also has the effect of effectively increasing the resistance. However, when Al and Si are added in large amounts at the same time, there is a problem that the toughness of the steel is lowered and the workability is deteriorated. On the other hand, although Mn has a lower effect of increasing the resistance than Si and Al, it has an advantage that the deterioration of workability is less likely to occur.

Based on the above, in the present embodiment, by adjusting the content of Si and Mn within an appropriate range, high strength and improved magnetic properties are achieved, and workability is ensured.

In addition, in order to increase the strength and improve the magnetic properties, it is also important to control the crystal grain size. From the viewpoint of high strength, the crystals in the steel are preferably fine grains.

In addition, in terms of the magnetic properties of non-oriented electrical steel sheets used as iron core materials for drive motors for electric vehicles and hybrid vehicles, and for compressor motors for air conditioners, it is necessary to improve iron loss, especially at high frequencies. iron loss in the area. Iron loss is mainly composed of hysteresis loss and eddy current loss. Here, in order to reduce the hysteresis loss, it is preferable to coarsen the crystal grains, and to reduce the eddy current loss, it is preferable to make the crystal grains finer. That is, there is a trade-off relationship between the two.

Therefore, the inventors of the present invention conducted further research and found that there is a preferable particle size range for achieving high strength and reducing high-frequency iron loss, and it is necessary to adjust the content of Al and N to an appropriate range.

The non-oriented electrical steel sheet of the present embodiment was prepared based on the above knowledge. Hereinafter, each requirement of the non-oriented electrical steel sheet of the present embodiment will be described in detail.

1. Overall composition The non-oriented electrical steel sheet of the present invention has a particularly high strength and is therefore suitable for a rotor, and also for a stator because of its excellent magnetic properties. In addition, the non-oriented electrical steel sheet of the present invention preferably includes an insulating coating on the surface of the base material described below.

2. Chemical composition of base material The reason for limiting each element is as follows. In addition, "%" concerning content in the following description means "mass %". In addition, in this embodiment, the numerical range represented using "~" means the range which includes the numerical value described before and after "~" as a lower limit value and an upper limit value.

C: 0.0050% or less C (carbon) is an element that causes deterioration of iron loss. If the C content exceeds 0.0050%, iron loss deterioration occurs in the non-oriented electrical steel sheet, and good magnetic properties cannot be obtained. Therefore, the C content is made 0.0050% or less. The C content is preferably 0.0040% or less, and preferably 0.0035% or less. In addition, C contributes to the high strength of the steel sheet, so to obtain this effect, the C content is preferably 0.0005% or more, and more preferably 0.0010% or more.

Si: 3.8~5.0% Si (silicon) is an element that increases the resistance of steel to reduce eddy current loss and improve high-frequency iron loss. In addition, since Si has a large solid solution strengthening ability, it is also an effective element in increasing the strength of the steel sheet. On the other hand, when the Si content is too large, the workability deteriorates remarkably, and it becomes difficult to perform cold rolling. Therefore, the Si content is set to 3.8 to 5.0%. The Si content is preferably above 3.9%, preferably above 4.0%. In addition, the Si content is preferably 4.8% or less, more preferably 4.5% or less.

Mn: more than 0.2% and less than 2.0% Mn (manganese) is an effective element for reducing eddy current loss and improving high-frequency iron loss by increasing the electrical resistance of steel. However, if the Mn content is too large, the magnetic flux density is significantly reduced. Therefore, the Mn content is set to be more than 0.2% and less than 2.0%. The Mn content is preferably more than 0.3%, more preferably more than 0.4%, more preferably more than 0.5%, and more preferably more than 0.6%. Moreover, the Mn content is preferably 1.8% or less, preferably 1.7% or less, more preferably less than 1.5%, still more preferably 1.4% or less, still more preferably 1.2% or less, and still more preferably 1.0% or less.

In the present invention, the electrical resistance of the steel is ensured by appropriately controlling the Si and Mn contents. Therefore, the following formula (i) must be satisfied in addition to the Si and Mn contents being within the above ranges, respectively. The left-hand value of the formula (i) is preferably 4.4 or more, and preferably 4.5 or more. Si+0.5×Mn≧4.3・・・(i) However, the element symbol in the above formula is the content (mass %) of each element. The gist of formula (i) is as follows. As described above, in the present embodiment, by adjusting the content of Si and Mn within an appropriate range, the enhancement of strength and the improvement of magnetic properties are achieved, and the workability is ensured. First, if attention is paid to Si, Si is an element that increases the electrical resistance of steel, reduces eddy current loss, and improves high-frequency iron loss. In addition, since Si has a large solid solution strengthening ability, it is also an effective element in increasing the strength of the steel sheet. On the other hand, when the Si content is too large, the workability deteriorates remarkably, and it becomes difficult to perform cold rolling. From the above viewpoints, the Si content is set to 3.8 to 5.0%.

If the Si content range is compared with the formula (i), when the Si content reaches 4.3 to 5.0%, the formula (i) is satisfied regardless of the Mn content. Therefore, in this case (provided that the other requirements of the non-oriented electrical steel sheet of the present embodiment are satisfied), good magnetic properties can be obtained. In addition, since the Si content satisfies the requirements of the present embodiment, the non-oriented electrical steel sheet exhibits high strength. On the other hand, although Si is an unfavorable element from the viewpoint of workability, the workability is also good when the Si content is at least 5.0% or less.

On the other hand, when the Si content is 3.8% or more and less than 4.3%, the formula (i) cannot be satisfied only by the Si content. That is, desired magnetic properties may not be obtained with Si alone. Therefore, Mn is used to supplement the insufficient magnetic properties. That is, the Mn content is increased within a range of more than 0.2% and less than 2.0% to satisfy the formula (i). Thereby, the magnetic properties of the non-oriented electrical steel sheet are improved. On the other hand, since Si is 3.8% or more, the strength of the non-oriented electrical steel sheet is also increased. Regarding workability, since the Si content is less than 4.3%, the workability tends to be improved compared to the above-mentioned case (that is, when the Si content is 4.3% or more). Here, since Mn hardly affects the workability, even if the Mn content is increased to satisfy the formula (i), the workability is not easily reduced. In addition, the action of increasing the Mn content is not as good as Si but still has the effect of increasing the strength.

As described above, in the present embodiment, the Si content and the Mn content are set to be within the above numerical ranges and satisfy the formula (i), so that the non-oriented electrical steel sheet can be increased in strength and magnetic properties can be improved. And can ensure the processability.

P: 0.030% or less P (phosphorus) is contained in steel as an impurity, and when the content is too large, the ductility of the steel sheet is significantly reduced. Therefore, the P content is made 0.030% or less. The P content is preferably below 0.025%, preferably below 0.020%.

S: 0.0030% or less S (sulfur) is an element that increases the iron loss by forming fine precipitates of MnS, thereby deteriorating the magnetic properties of the steel sheet. Therefore, the S content is made 0.0030% or less. The S content is preferably 0.0025% or less, and preferably 0.0020% or less. In addition, an extreme reduction in the S content may lead to an increase in manufacturing cost, so the S content is preferably 0.0001% or more, more preferably 0.0003% or more, and more preferably 0.0005% or more.

Al: 0.005% or more and less than 0.050% Al (aluminum) bonds with N to form AlN, and is an effective element for stable grain refinement. In order to exhibit this effect, 0.005% or more must be contained. On the other hand, when 0.050% or more is contained, the effect of refining crystal grains is reduced. Therefore, the Al content is set to 0.005% or more and less than 0.050%. The Al content is preferably more than 0.008%, more preferably more than 0.010%, more preferably more than 0.015%, and more preferably more than 0.020%. In addition, the Al content is preferably 0.048% or less, and preferably 0.045% or less. In addition, in this specification, Al content means the total content of Al contained in a base material.

N: 0.0005～0.0030% N (nitrogen) bonds with Al to form AlN, and is an effective element for stable grain refinement. On the other hand, when a large amount is contained, too much AlN is formed, and iron loss is deteriorated. Therefore, the N content is set to 0.0005 to 0.0030%. The N content is preferably 0.0007% or more, and preferably 0.0010% or more. In addition, the N content is preferably 0.0027% or less, and preferably 0.0025% or less.

Ti: less than 0.0050% Ti (titanium) is an unavoidably mixed element, and bonds with carbon or nitrogen to form precipitates (carbides, nitrides). When carbides or nitrides are formed, the precipitates themselves may degrade magnetic properties. Furthermore, grain growth during finish annealing is hindered, resulting in deterioration of magnetic properties. Therefore, the Ti content is set to be less than 0.0050%. The Ti content is preferably below 0.0040%, preferably below 0.0030%, and more preferably below 0.0020%. Further, if the Ti content is extremely reduced, the manufacturing cost may increase, so the Ti content is preferably 0.0005% or more.

Nb: less than 0.0050% Nb (niobium) is an element that bonds with carbon or nitrogen to form precipitates (carbides, nitrides) and thereby contributes to high strength, but these precipitates themselves degrade magnetic properties. Therefore, the Nb content is set to be less than 0.0050%. The Nb content is preferably below 0.0040%, preferably below 0.0030%, and more preferably below 0.0020%. And the lower the Nb content, the better, and it is better to be below the determination limit.

Zr: less than 0.0050% Zr (zirconium) is an element that bonds with carbon or nitrogen to form precipitates (carbides, nitrides) and thereby contributes to high strength, but these precipitates themselves degrade magnetic properties. Therefore, the Zr content is made less than 0.0050%. The Zr content is preferably below 0.0040%, preferably below 0.0030%, more preferably below 0.0020%. In addition, the lower the Zr content, the better, and preferably below the measurement limit.

V: less than 0.0050% V (vanadium) is an element that bonds with carbon or nitrogen to form precipitates (carbides, nitrides) and thereby contributes to high strength, but these precipitates themselves degrade magnetic properties. Therefore, the V content is set to be less than 0.0050%. The V content is preferably 0.0040% or less, preferably 0.0030% or less, and more preferably 0.0020% or less. In addition, the lower the V content, the better, and it is better to be below the measurement limit.

Cu: less than 0.20% Cu (copper) is an element that inevitably mixes. Deliberate addition of Cu increases the manufacturing cost of the steel sheet. Therefore, in the present invention, it is not necessary to actively add it, and it is sufficient to be an impurity grade. The Cu content is set to the maximum value that inevitably mixes in the production process, that is, less than 0.20%. The Cu content is preferably below 0.15%, preferably below 0.10%. In addition, the lower limit value of the Cu content is not particularly limited, but extremely reducing the Cu content may lead to an increase in manufacturing cost. Therefore, the Cu content is preferably 0.001% or more, more preferably 0.003% or more, and more preferably 0.005% or more.

Ni: less than 0.50% Ni (nickel) is an element that inevitably mixes. However, since Ni is also an element that can increase the strength of the steel sheet, it can also be added deliberately. However, since Ni is expensive, when it is intentionally added, its content is made less than 0.50%. The Ni content is preferably 0.40% or less, preferably 0.30% or less. In addition, the lower limit value of the Ni content is not particularly limited, but extremely reducing the Ni content may lead to an increase in manufacturing cost. Therefore, the Ni content is preferably 0.001% or more, more preferably 0.003% or more, and more preferably 0.005% or more.

Sn: 0~0.10% Sb: 0~0.10% Sn (tin) and Sb (antimony) segregate on the surface to suppress oxidation and nitridation during annealing, and are therefore useful elements for securing low iron loss. In addition, it segregates at the crystal grain boundary to improve the aggregate structure, and also has the effect of increasing the magnetic flux density. Therefore, at least one of Sn and Sb may also be contained as required. However, if the content of these elements is too large, the toughness of the steel is lowered and cold rolling may be difficult. Therefore, the contents of Sn and Sb are each made 0.10% or less. The content of Sn and Sb is preferably 0.06% or less, respectively. In addition, in order to obtain the above-mentioned effects, the content of at least one of Sn and Sb is preferably 0.005% or more, more preferably 0.010% or more.

In the chemical composition of the base material of the non-oriented electrical steel sheet of the present invention, the remainder is Fe and impurities. The "impurities" referred to here refer to components mixed with raw materials such as ore, scraps, or various factors in the production process during industrial steel production, and are allowed within the range that does not adversely affect the present invention. thing.

In addition, as an impurity element, the content of Cr and Mo is not specifically prescribed|regulated. In the non-oriented electrical steel sheet of the present embodiment, even if these elements are contained in an amount of 0.5% or less, the effect of the present invention is not particularly affected. In addition, even if Ca and Mg are contained in the range of 0.002% or less, the effect of the present invention is not particularly affected, and even if the rare earth element (REM) is contained in the range of 0.004% or less, the effect of the present invention is not particularly affected.

O is also an impurity element, but even if it is contained in a range of 0.05% or less, it does not affect the effect of the present invention. O may be mixed in the annealing step, so even if it is contained in the range of 0.01% or less in the content of the flat embryo stage (that is, the analysis value of the ladle sampling), the effect of the present invention is not particularly affected.

In addition to the above elements, elements such as Pb, Bi, As, B, and Se may be contained, and the effects of the present invention are not impaired as long as the respective contents are in the range of 0.0050% or less.

The chemical composition of the above-mentioned base material may be measured by a general analytical method. For example, the steel composition may be measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry)). In addition, C and S may be measured by a combustion-infrared absorption method, N by an inert gas fusion-thermal conductivity method, and O by an inert gas fusion-non-dispersive infrared absorption method.

3. Crystal particle size As described above, from the viewpoint of high strength, the crystals in the steel are preferably fine grains. In addition, in order to reduce the hysteresis loss, it is preferable to coarsen the crystal grains, and to reduce the eddy current loss, it is preferable to make the crystal grains finer.

When the average crystal grain size of the base material is less than 10 µm, the hysteresis loss is significantly deteriorated, and it is difficult to improve the magnetic properties. On the other hand, if the average grain size is larger than 80 µm, the strength of the steel will decrease. Therefore, the average crystal grain size of the base material is set to 10 to 80 µm. The average crystal grain size is preferably 12 µm or more, and more preferably 14 µm or more. In addition, the average crystal grain size is preferably 70 µm or less, more preferably 60 µm or less.

In addition, in the present invention, the average grain size of the base material is determined in accordance with JIS G 0551 (2013) "Steel - Microscopic test method for grain size".

4. Magnetic properties In the non-oriented electrical steel sheet of the present invention, the term "excellent magnetic properties" means that the iron loss W _10/400 is low and the magnetic flux density B ₅₀ is high. Here, the above-mentioned magnetic properties are measured in accordance with the Epstein method defined in JIS C 2550-1 (2011).

5. Mechanical properties In the non-oriented electrical steel sheet of the present invention, having high strength means that the tensile strength is 650 MPa or more. In addition, the tensile strength is preferably 660 MPa or more. Here, the tensile strength shall be measured by performing a tensile test based on JIS Z 2241 (2011).

6. Insulating film As described above, in the non-oriented electrical steel sheet of the present invention, it is preferable that an insulating coating is formed on the surface of the base material. The non-oriented electromagnetic steel sheet is used after being punched out of the iron core blank and then laminated. Therefore, by providing an insulating film on the surface of the base material, the eddy current between the plates can be reduced, thereby reducing the eddy current as an iron core. loss.

The type of the insulating film is not particularly limited, and a well-known insulating film used as an insulating film of a non-oriented electrical steel sheet can be used. The above-mentioned insulating film includes, for example, a composite insulating film mainly composed of an inorganic substance and further containing an organic substance. Here, the composite insulating film is, for example, an insulating film mainly composed of at least one of inorganic substances such as metal chromate, metal phosphate, colloidal silicon oxide, Zr compound, and Ti compound, in which fine organic resin particles are dispersed. insulating film. In particular, from the viewpoint of reducing the environmental load at the time of production, which has been gradually increasing in demand in recent years, it is preferable to use an insulating film using a coupling agent of metal phosphate, Zr or Ti, or a carbonate or ammonium salt of these as a starting material. .

Here, the adhesion amount of the insulating film is not particularly limited, but is preferably about 200 to 1500 mg/m ² per single side, and preferably 300 to 1200 mg/m ² per single side, for example. Excellent uniformity can be maintained by forming the insulating film so as to have an adhesion amount within the above-mentioned range. In addition, when measuring the adhesion amount of the insulating film afterwards, various well-known measuring methods can be used. For example, a method of measuring the mass difference between before and after immersion in an aqueous sodium hydroxide solution, or a fluorescence method using a calibration curve method can be appropriately used. X-ray method etc. may be sufficient.

7. Manufacturing method The manufacturing method of the non-oriented electrical steel sheet of the present invention is not particularly limited. For example, it can be manufactured by performing hot rolling on a steel block having the above-mentioned chemical composition, and then performing the following step 1 or step 2. (Step 1) Cold rolling and finish annealing are sequentially performed without performing annealing of the hot-rolled sheet. (Step 2) Hot-rolled sheet annealing is performed at a temperature of 950° C. or lower, followed by cold rolling and finish annealing in this order. In addition, when an insulating film is to be formed on the surface of the base material, the insulating film is formed after the above-mentioned finish annealing. Hereinafter, each step will be described in detail.

<Hot rolling step> A steel block (flat blank) having the above chemical composition is heated, and the heated steel block is hot-rolled to obtain a hot-rolled sheet. Here, the heating temperature of the steel ingot for the delayed hot rolling is not particularly specified, but it is preferably set to, for example, 1050 to 1250°C. In addition, the thickness of the hot-rolled sheet after hot rolling is not particularly specified, but the final sheet thickness of the base material is preferably set to, for example, about 1.5 to 3.0 mm.

<Hot-rolled sheet annealing step> Then, for the purpose of increasing the magnetic flux density of the steel sheet, hot-rolled sheet annealing may be performed. That is, in step 1, the hot-rolled sheet annealing step is omitted. Whereas, in step 2, the hot-rolled sheet annealing step is performed. During the annealing step of the hot-rolled sheet, if annealing at a high temperature higher than 950° C. is performed, fracture may occur during the cold rolling delay. Therefore, the annealing temperature is set to 950°C or lower. In the case of continuous annealing, the hot-rolled steel sheet should be annealed by soaking at 700-950°C for 10-150 seconds. The soaking conditions are preferably set at 800 to 930° C. for 10 to 150 seconds.

Furthermore, in the case of box annealing, it is preferable to anneal the hot-rolled steel sheet by soaking at 600 to 850° C. for 30 minutes to 24 hours. Preferably, soaking is performed at 650-800°C for 1-20 hours. In addition, although the magnetic properties are inferior compared with the case where the hot-rolled sheet annealing step is performed, the above-mentioned hot-rolled sheet annealing step (step 1) may be omitted in order to reduce costs.

＜Pickling step＞ After the above-mentioned hot-rolled sheet annealing, pickling may also be performed. By this pickling, the rust layer formed on the surface of the base material can be removed. Here, the pickling conditions such as the concentration of the acid used for pickling, the concentration of the accelerator used for pickling, and the temperature of the pickling solution are not particularly limited, and known pickling conditions can be used. In addition, when the annealing of the hot-rolled sheet is box annealing, the pickling step is preferably performed before the annealing of the hot-rolled sheet from the viewpoint of descaling properties. In this case, it is not necessary to perform pickling after annealing of the hot-rolled sheet. When the annealing of the hot-rolled sheet is omitted, the above-mentioned pickling may also be performed on the hot-rolled sheet for the purpose of removing the scale layer from the hot-rolled sheet after hot rolling.

<Cold rolling step> In step 1, after the hot rolling step, in step 2, cold rolling is performed after the above-mentioned pickling (when the hot-rolled sheet annealing is performed by box annealing, the cold rolling may be performed after the hot-rolled sheet annealing step). . In cold rolling, for example, the pickling sheet from which the scale layer has been removed is rolled at a reduction ratio such that the final sheet thickness of the base material is 0.10 to 0.35 mm.

<Finish annealing step> Finish annealing is performed after the above-mentioned cold rolling. In the method for producing a non-oriented electrical steel sheet according to the present embodiment, a continuous annealing furnace is preferably used for finish annealing. The finish annealing step is an important step for controlling the average crystal grain size of the base metal.

Here, as for the finish annealing conditions, the soaking temperature is preferably 750 to 1000°C, the soaking time is 1 to 300 seconds, and the gas atmosphere is preferably H ₂ and N with a H ₂ ratio of 10 to 100 vol %. The mixed gas environment of ₂ (ie, H ₂ +N ₂ =100% by volume), and the dew point of the gas environment is set to 30°C or less.

When the soaking temperature is lower than 750°C, the unrecrystallized structure increases and the iron loss is deteriorated, which is not good. When the soaking temperature is higher than 1000°C, the strength is insufficient and the iron loss is also deteriorated, so it is not good. The soaking temperature is preferably 760-980°C, more preferably 770-960°C. The H ₂ ratio in the gas environment is preferably 15-90 vol%. The dew point of the gas environment is preferably below 20°C, more preferably below 10°C.

<Insulating film formation step> After the above-mentioned finish annealing, the step of forming an insulating film may be performed. Here, the step of forming the insulating film is not particularly limited, and the treatment liquid may be applied and dried by a known method using the known insulating film treatment liquid as described above.

In addition, any pretreatment such as degreasing treatment with alkali or the like, or pickling treatment with hydrochloric acid, sulfuric acid, phosphoric acid, etc., may be applied to the surface of the base material to be formed into the insulating film before applying the treatment liquid, or it may not be applied. Such pre-treated surfaces remain in their finish annealed state.

As described above, according to the present embodiment, by adjusting the content of Si and Mn to an appropriate range (that is, the range represented by the formula (i)), the enhancement of the strength of the non-oriented electrical steel sheet and the improvement of the magnetic properties can be achieved. , and ensure processability. In addition, since the average crystal grain size of the base material is 10 to 80 µm, the strength of the non-oriented electrical steel sheet can also be improved from this point of view, and the magnetic properties can also be improved. In this way, in this embodiment, non-directionality can be achieved without adding a large amount of expensive special elements such as Ni and Cu in Patent Document 1, Ti and V in Patent Document 2, and Ca in Patent Document 3. Enhance the strength of the electrical steel sheet, improve the magnetic properties, and ensure the workability. In addition, in the present embodiment, by adding an appropriate amount of low-cost Al, it is easy to ensure the workability of cold rolling delay and control the crystal grain size at the time of finish annealing, so that the product yield is improved. Therefore, a non-oriented electrical steel sheet having high strength and excellent magnetic properties can be provided in a low-cost and stable manner. Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples. Example

After heating the slab having the chemical composition shown in Table 1 to 1150°C, hot rolling was performed at a finish temperature of 850°C and a finished sheet thickness of 2.0 mm, and coiled at 650°C to obtain a hot-rolled steel sheet. In some test numbers, the obtained hot-rolled steel sheets were subjected to hot-rolled sheet annealing at the annealing temperature shown in Table 2, and the surface scale was removed by pickling. The soaking time in the annealing of the hot-rolled sheet was all set to 30 seconds. The pickled sheet obtained in the above-mentioned manner (when annealing of the hot-rolled sheet is omitted, it is a pickled sheet from which the scale of the hot-rolled steel sheet has been removed) is cold-rolled into a cold-rolled steel sheet with a sheet thickness of 0.25 mm.

In addition, in a mixed gas environment of H ₂ : 25%, N ₂ : 75% and a dew point of 0° C., the finish annealing conditions (soaking temperature (annealing temperature) and soaking time) for annealing. Specifically, when controlling the average crystal grain size to increase, the soaking temperature and/or soaking time are increased. In addition, in order to control so that an average crystal grain size may become small, it is made the opposite to the above. The specific soaking temperature (annealing temperature) and soaking time are listed in Table 2. Then, an insulating film was applied, and a non-oriented electrical steel sheet was prepared to prepare a test material.

In addition, the above-mentioned insulating film is formed by applying an insulating film so as to have a predetermined adhesion amount, and then firing at 350° C. in the atmosphere. It is composed of resin emulsion.

[Table 1]

[Table 2]

The chemical composition of each obtained test material was confirmed by the above-mentioned measurement method, and as a result, it was confirmed that the chemical composition of the line and the flat embryo were almost the same. In addition, the average crystal grain size of the base material was measured according to JIS G 0551 (2013) "Steel - Microscopic test method for grain size". Furthermore, Epstein test pieces were taken from the rolling direction and the width direction of each test material, and the magnetic properties (iron loss W _10/400 , magnetic flux) were evaluated by the Epstein test in accordance with JIS C 2550-1 (2011). density B ₅₀ ). For the magnetic flux density B ₅₀ series, the qualified grade is 1.60T or more, and the iron loss W _10/400 series is qualified as 22.0W/kg or less. In addition, according to JIS Z 2241 (2011), JIS No. 5 tensile test pieces were collected from each test material so that the longitudinal direction was aligned with the rolling direction of the steel sheet. Then, the tensile test was performed according to JIS Z 2241 (2011) using the above-mentioned test piece, and the tensile strength was measured. The tensile strength is above 650MPa as the qualified grade. The above results are shown in Table 2 together.

It is known that in test numbers 3, 4, 6, 7, 9, 10, 13 to 17, 20, 22 to 30, and 37 where the chemical composition of the steel sheet and the average grain size after finish annealing satisfy the requirements of the present invention, the iron loss is It has excellent magnetic flux density, especially low iron loss, and has a high tensile strength of 650 MPa or more. In particular, when the content of each chemical component is a value within an ideal range, any of these properties tends to become more favorable.

On the other hand, in the test numbers 1, 2, 5, 8, 11 to 12, 18, 19, 21, 31 to 36 of the comparative examples, at least one of the magnetic properties and the strength was poor, or the toughness was significantly deteriorated, making it difficult to manufacture.

Specifically, in Test No. 1, since the Si content was lower than the predetermined range, the tensile strength was poor. In addition, when comparing Test Nos. 2 to 5 whose chemical compositions satisfy the requirements, in No. 2, the average crystal grain size was smaller than the predetermined, resulting in poor iron loss, and in Test Nos. 5, 35, and 36, the average crystal grain size was less than the predetermined value. larger and as a result of poor tensile strength.

In addition, in Test No. 8, the Si content was out of the specified range, in Test No. 12, the P content was out of the specified range, and in Test No. 18, the annealing temperature of the hot-rolled sheet was out of the specified range, so that the toughness was deteriorated and the fracture was delayed by cold rolling, and it was impossible to implement Determination of average crystal grain size, tensile strength and magnetic properties. In addition, in Test Nos. 11 and 34, the Mn content was out of the predetermined range, resulting in a difference in magnetic flux density. In Test No. 32, the iron loss was poor because the Mn content was below the predetermined range.

In Test No. 19, the Al content was below the predetermined range, and in Test Nos. 21 and 33, the Al content exceeded the predetermined range, and it was difficult to adjust the average crystal grain size, resulting in poor tensile strength. In Test No. 31, the iron loss was poor because the formula (i) was not satisfied.

industrial availability As described above, according to the present invention, a non-oriented electrical steel sheet having high strength and excellent magnetic properties can be obtained in a low-cost and stable manner.

(none)

Claims (6)

A non-oriented electrical steel sheet, the chemical composition of the base metal is: in mass %, C: 0.0050% or less, Si: 3.8~5.0%, Mn: more than 0.2% and less than 2.0%, P: 0.030% or less, S : 0.0030% or less, Al: 0.005% or more and less than 0.050%, N: 0.0005~0.0030%, Ti: less than 0.0050%, Nb: less than 0.0050%, Zr: less than 0.0050%, V: less than 0.0050%, Cu: less than 0.20 %, Ni: less than 0.50%, Sn: 0~0.10%, Sb: 0~0.10% and the remainder: Fe and impurities, and satisfy the following formula (i); and the average grain size of the base metal is 10~ 80μm; Si+0.5×Mn≧4.3‧‧‧(i) However, the element symbol in the above formula is the content (mass %) of each element. The non-oriented electrical steel sheet of claim 1 has a tensile strength of 650 MPa or more. The non-oriented electrical steel sheet of claim 1 or claim 2, wherein the aforementioned chemical composition contains one or two elements selected from the following: in mass %, Sn: 0.005~0.10% and Sb: 0.005~0.10 %. The non-oriented electrical steel sheet according to claim 1 or claim 2, which has an insulating coating on the surface of the base material. The non-oriented electrical steel sheet according to claim 3, which has an insulating coating on the surface of the base material. A method for manufacturing a non-oriented electrical steel sheet, which is a method for manufacturing a non-oriented electrical steel sheet as claimed in any one of claim 1 to claim 5; The chemical composition of the steel ingot is subjected to hot rolling, followed by the following steps 1 or 2: (step 1) do not perform hot-rolled sheet annealing, but sequentially perform cold rolling and finish annealing; (step 2) below 950 ℃ The hot-rolled sheet is annealed at the temperature, and then the cold rolling and the finishing annealing are sequentially performed; wherein, the finishing annealing is performed by setting the soaking temperature to 750-1000° C., and setting the soaking time to 1-300 seconds. conduct.