Non-oriented electrical steel sheet and method for producing same

Abstract

When a steel slab containing 0.0005-0.0100% by mass of C, 2.0-4.5% by mass of Si, 0.1-2.0% by mass of Mn, and further containing 0.01-0.20% by mass of Sn and / or Sb in total is hot-rolled, hot-rolled sheet annealing, cold rolling, and final annealing are performed to produce the steel slab, the soaking temperature of the final annealing is set to 700-1100 DEG C, the soaking time is set to 2 s or more, and the temperature of the final annealing is set to 700-1100 DEG C. A non-oriented electromagnetic steel sheet having a yield strength of 300 MPa or more at 150 DEG C and a fluctuation in the sheet width direction of 30 MPa or less at 150 DEG C is obtained by controlling the cooling rate, the composition and dew point of the atmosphere gas, and the fluctuation in the sheet width direction temperature during the cooling process from the soaking temperature of the final annealing to 200 DEG C so as to satisfy prescribed conditions.

Description

Technical Field

[0001] The present invention relates to a non-oriented electrical steel sheet having low iron loss and high strength at practical temperature and a method for producing the same. Background Art

[0002] In recent years, the demand for energy saving and reduction of carbon dioxide emissions has become higher, and high efficiency is also strongly required in the fields of various automobiles and electrical equipment. Therefore, for non-oriented electromagnetic steel sheets used for the iron core of electric motors, in addition to excellent iron loss characteristics, high strength is also required from the perspective of durability. In addition, if there is a fluctuation in strength within the steel sheet, the risk of breakage of the weak part of the iron core during use increases, so uniform strength is also required within the steel sheet. In addition, the driving motor of the automobile is required to be small and have a large output. Therefore, the temperature of the motor during use is high, and high strength is required even at the level of 150°C. As mentioned above, for non-oriented electromagnetic steel sheets used for iron cores, it is not only important to have excellent magnetic properties, but it is also important to have a high yield strength in a high temperature range and small fluctuations.

[0003] As a non-oriented electrical steel sheet having high yield strength, for example, Patent Document 1 proposes a non-oriented electrical steel sheet having high yield strength, characterized in that it has a component composition containing Si: 1.5 mass % or more and 3.5 mass % or less, Mn: 1.5 mass % or less, Al: 0.2 mass % or more and 3.0 mass % or less, Mg: 0.0003 mass % or more and 0.0050 mass % or less, and the remainder is Fe and unavoidable impurities, and the grain size d is 5 μm or more and 40 μm or less, and satisfies the relationship of d≤50×(Si+0.5Al-2).

[0004] In addition, as a method for manufacturing a non-oriented electromagnetic steel sheet that makes the iron loss in the plate width direction uniform, for example, in Patent Document 2, a method for manufacturing a low iron loss non-oriented electromagnetic steel sheet is proposed, which is characterized in that a silicon steel billet containing C: 0.005 mass% or less, Si: 2.5-4.0 mass%, S: 0.005 mass% or less, Al: 0.3-1.5 mass% and N: 0.004 mass% or less is hot rolled, and then annealed for the hot rolled sheet, and the sheet is made into a final sheet thickness by cold rolling once or by cold rolling twice or more with intermediate annealing, and then soaked at 900-1200°C for 5 seconds to 15 minutes, and then, while keeping the temperature of the entire width in the plate width direction within (plate width center temperature ±20°C), the sheet is cooled until the temperature of the plate width center is cooled to 600°C for final annealing, and then insulation treatment is performed.

[0005] In addition, as a method for manufacturing a non-oriented electrical steel sheet having good magnetic properties, for example, Patent Document 3 proposes a method for manufacturing a non-oriented electrical steel sheet having excellent low magnetic field properties, characterized in that: (1) a steel sheet containing C: 0.01 mass % or less, Si: 4 mass % or less, Mn: 0.1 to 0.8 mass %, Al: 0.004 mass % or less or 0.1 to 1 mass %, Cu: 0.05 mass % or less (including 0), S: 0.015 mass % or less (including 0), N: 0.005 mass % or less (including 0), P: 0.2 mass % or less, and a non-oriented electrical steel sheet having good magnetic properties is prepared. % or less (including 0), and the remainder being substantially Fe and inevitable impurities, to produce a hot-rolled steel sheet; (2) the process of subjecting the hot-rolled steel sheet to one or more cold rolling to produce a cold-rolled steel sheet; (3) the process of subjecting the cold-rolled steel sheet to final annealing, cooling the steel sheet at an average cooling rate VS of less than 10°C / s from the soaking temperature to a rapid cooling start temperature TS in the temperature range of 600°C to 500°C, and rapidly cooling the steel sheet at an average cooling rate VQ of 10 to 50°C / s from the rapid cooling start temperature TS to 300°C.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2005-113158

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 63-047333

[0010] Patent Document 3: Japanese Patent Application Laid-Open No. 09-302414 Summary of the invention

[0011] Problems to be solved by the invention

[0012] However, according to the results of the investigation by the inventors, it has been clarified that the above-mentioned prior art has the following problems. For the technology disclosed in Patent Document 1, although the yield strength at room temperature is sufficiently high, the yield strength at 150°C may not be sufficient, and good iron loss cannot be obtained. In addition, for the technology disclosed in Patent Document 2, although the fluctuation of iron loss in the plate width direction can be reduced, the yield strength at 150°C is prone to fluctuation. In addition, for the technology disclosed in Patent Document 3, although good magnetic properties can be obtained, the yield strength at 150°C is reduced.

[0013] The present invention has been made in view of the above-mentioned problems existing in the prior art, and its object is to provide a non-oriented electromagnetic steel sheet which has not only good magnetic properties but also high yield strength at practical temperature of electric motors and small fluctuation of the yield strength, and to propose an advantageous manufacturing method thereof.

[0014] Methods used to solve problems

[0015] In order to solve the above problems, the inventors have repeatedly conducted in-depth studies focusing on the component composition of steel sheets and their manufacturing methods, especially carbon C, which is generally considered to be required to be reduced because it deteriorates iron loss. As a result, they found that in the cooling process of the final annealing step, the cooling rate within a specified temperature range and the composition and dew point of the atmosphere gas in the furnace are appropriately controlled to uniformly cool the steel sheet over the entire width, so that the solid solution carbon remains uniformly in the width direction of the steel sheet, thereby not only having good iron loss, but also being able to improve the yield strength at 150°C, which is a practical temperature for electric motors, and reduce the fluctuation in the width direction of the steel sheet, and thus developed the present invention.

[0016] That is, the present invention is a non-oriented electrical steel sheet having a component composition containing C: 0.0005-0.0100 mass %, Si: 2.0-4.5 mass %, Mn: 0.1-2.0 mass %, P: 0.050 mass % or less, S: 0.0050 mass % or less, Al: 0.20-2.50 mass %, N: 0.0050 mass % or less and O: 0.0050 mass % or less, further containing at least one of Sn and Sb in an amount of 0.01-0.20 mass % in total, and the balance consisting of Fe and inevitable impurities, wherein the minimum value of the yield strength in the plate width direction at 150° C. is 300 MPa or more, and the fluctuation of the yield strength in the plate width direction is 30 MPa or less.

[0017] The non-oriented electrical steel sheet of the present invention is characterized by containing at least one component of the following groups A to F in addition to the above-mentioned component composition:

[0018] Group A: at least one of Ca, Mg and REM: 0.0010-0.0080% by mass in total;

[0019] Group B: at least one of Cr, Mo, Cu and Ni: 0.01 to 0.60% by mass in total;

[0020] Group C: at least one of Ti, Nb and V: 0.0005 to 0.0050% by mass in total;

[0021] Group D: at least one of B: 0.0001 to 0.0020 mass %, Pb: 0.0001 to 0.0010 mass %, and W: 0.0005 to 0.0050 mass %;

[0022] · Group E: Zn: 0.001-0.010% by mass;

[0023] · Group F: Co: 0.0010 to 0.0500 mass %.

[0024] In addition, the present invention provides a method for producing a non-oriented electrical steel sheet, characterized in that a steel sheet containing 0.0005-0.0100 mass% of C, 2.0-4.5 mass% of Si, 0.1-2.0 mass% of Mn, 0.050 mass% or less of P, 0.0050 mass% or less of S, 0.20-2.50 mass% of Al, 0.0050 mass% or less of N and 0.0050 mass% or less of O, and a total of A non-oriented electrical steel sheet is produced by hot rolling, hot rolled sheet annealing, cold rolling and final annealing of a steel billet containing at least one of Sn and Sb in an amount of 0.01 to 0.20 mass % and the balance being Fe and inevitable impurities. In this method, the soaking temperature of the final annealing is set to 700 to 1100° C., the soaking time is set to 2 s or more, and the steel billet is cooled from the soaking temperature of the final annealing to 200° C. under the following conditions (1) to (3):

[0025] (1) Average cooling rate in the temperature range from 700°C to 200°C: above 10°C / s;

[0026] (2) Hydrogen concentration in the furnace atmosphere from the soaking temperature to 700°C: 1% by volume or more;

[0027] (3) Dew point of the atmosphere gas in the furnace within the temperature range from the soaking temperature to 300°C: below -30°C;

[0028] (4) Fluctuation of the steel plate temperature in the plate width direction within the temperature range from 500°C to 200°C: 40°C or less.

[0029] The method for producing the nonoriented electrical steel sheet of the present invention is characterized by cooling the sheet so that the difference between the maximum and minimum values ​​of the average cooling rate per 100°C in the temperature range of 700°C to 200°C in the final annealing is 20°C / s or less.

[0030] Furthermore, the steel slab used in the method for producing the non-oriented electrical steel sheet of the present invention is characterized by containing, in addition to the above-mentioned component composition, at least one component of the following groups A to F:

[0031] Group A: at least one of Ca, Mg and REM: 0.0010-0.0080% by mass in total;

[0032] Group B: at least one of Cr, Mo, Cu and Ni: 0.01 to 0.60% by mass in total;

[0033] Group C: at least one of Ti, Nb and V: 0.0005 to 0.0050% by mass in total;

[0034] Group D: at least one of B: 0.0001 to 0.0020 mass %, Pb: 0.0001 to 0.0010 mass %, and W: 0.0005 to 0.0050 mass %;

[0035] · Group E: Zn: 0.001-0.010% by mass;

[0036] · Group F: Co: 0.0010 to 0.0500 mass %.

[0037] Effects of the Invention

[0038] According to the present invention, a non-oriented electromagnetic steel sheet having not only good magnetic properties but also high yield strength over the entire width of the steel sheet at practical temperature of an electric motor can be stably provided. Therefore, according to the present invention, a material suitable for an iron core of an electric motor requiring high efficiency and high durability can be provided. DETAILED DESCRIPTION

[0039] First, the reasons for limiting the component composition that the non-oriented electrical steel sheet of the present invention should have will be described.

[0040] C: 0.0005 to 0.0100 mass%

[0041] C is an essential element for obtaining high yield strength at 150°C, which is a practical temperature for electric motors, in the present invention. By existing in the product steel plate in the form of solid solution C, when heated to 150°C, dislocations and grain boundary segregation in the steel plate contribute to improving the yield strength. In order to obtain the above effect, C needs to contain 0.0005% by mass or more. On the other hand, when contained in excess, the fluctuation of yield strength becomes larger or the iron loss deteriorates, so it is limited to less than 0.0100% by mass. Preferably, it is in the range of 0.0008 to 0.0060% by mass.

[0042] Si: 2.0-4.5 mass%

[0043] Si has the effect of increasing the resistivity of steel and reducing iron loss, so it contains more than 2.0 mass % in the present invention. It should be noted that Si also has the effect of increasing yield strength, and in order to obtain this effect, it is preferably added more than 2.7 mass %. Furthermore, in high-grade materials with strong demand for low iron loss, it is preferably added more than 3.0 mass %. However, when adding more than 4.5 mass % of Si, not only the fluctuation of yield strength becomes larger, but also the steel hardens and becomes difficult to roll, so the upper limit is set to 4.5 mass %. The upper limit of the preferred Si content is 4.0 mass %.

[0044] Mn: 0.1-2.0 mass%

[0045] Mn, like Si, is an element effective in increasing the resistivity of steel and reducing iron loss, so it is added at 0.1% by mass or more. Preferably, it is added at 0.3% by mass or more. On the other hand, when Mn exceeds 2.0% by mass, fine Mn carbides are formed and the solid solution C decreases, so the yield strength at 150°C decreases. Therefore, Mn is set to 2.0% by mass or less. Preferably, it is added at 1.0% by mass or less.

[0046] P: 0.050 mass % or less

[0047] P segregates at grain boundaries and makes steel embrittled, reduces rollability, or increases yield strength fluctuation, so it is limited to 0.050 mass % or less. It is preferably 0.030 mass % or less, and more preferably 0.015 mass % or less. It should be noted that the lower limit of P is not particularly specified, but is preferably set to about 0.004 mass % from the viewpoint of suppressing the increase in P removal cost in the steelmaking process.

[0048] S: 0.0050 mass % or less

[0049] S is a harmful element that impairs the hot workability of steel, forms fine sulfides to refine grains and increase yield strength fluctuations, or deteriorates iron loss. Therefore, S is limited to 0.0050 mass % or less, preferably 0.0020 mass % or less.

[0050] Al: 0.20-2.50 mass%

[0051] Al, like Si, has the effect of increasing the resistivity of steel and reducing iron loss, and also has the effect of increasing yield strength. Therefore, in the present invention, 0.20% by mass or more of Al is added. Preferably, 0.50% by mass or more. On the other hand, when Al is added excessively, the fluctuation of yield strength becomes larger, or a large amount of aluminum oxide is generated to induce surface defects, so the upper limit of Al is set to 2.50% by mass. Preferably, it is less than 2.20% by mass.

[0052] N: 0.0050 mass % or less

[0053] N is a harmful element that forms fine nitrides such as AlN and increases the fluctuation of yield strength or deteriorates iron loss, so it is limited to 0.0050 mass % or less. Preferably, it is 0.0030 mass % or less. It should be noted that the lower limit is not particularly limited, and from the viewpoint of suppressing the increase in steelmaking costs, it is preferably set to about 0.0005 mass %.

[0054] O: 0.0050 mass % or less

[0055] O is a harmful element that forms fine oxides and hinders the growth of crystal grains and deteriorates iron loss. In addition, the fine oxides refine the crystal grains and also cause fluctuations in yield strength. Therefore, O is limited to 0.0050 mass % or less. Preferably, it is 0.0025 mass % or less.

[0056] At least one of Sn and Sb: 0.01 to 0.20 mass % in total

[0057] Sn and Sb are elements effective in improving the texture of the steel sheet after final annealing and thus improving the magnetic properties. Therefore, at least one of Sn and Sb is added in a total of 0.01 mass % or more. On the other hand, even if Sn and Sb are added excessively, the above effect is saturated, so at least one is limited to a total of 0.20 mass % or less. Preferably, it is in the range of 0.02 to 0.05 mass %.

[0058] In the non-oriented electrical steel sheet of the present invention, the balance other than the above components is Fe and inevitable impurities. However, in order to further improve magnetic properties and strength properties, at least one component selected from the following groups A to F may be contained.

[0059] Group A: at least one of Ca, Mg and REM: 0.0010 to 0.0080 mass % in total

[0060] Ca, Mg and REM have the effect of fixing S in the form of sulfide and improving iron loss. Therefore, it is preferred to add at least one of Ca, Mg and REM in a total of 0.0010 mass % or more. On the other hand, when Ca, Mg and REM are added excessively, inclusions are formed and manufacturability is reduced. Therefore, the content of Ca, Mg and REM is preferably set to a total of 0.0080 mass % or less. More preferably, the total is in the range of 0.0015 to 0.0060 mass %.

[0061] Group B: at least one of Cr, Mo, Cu and Ni: 0.01 to 0.60 mass % in total

[0062] Cr, Mo, Cu and Ni have the effect of increasing the resistivity of steel and improving iron loss. Therefore, it is preferred to add at least one of Cr, Mo, Cu and Ni in an amount of 0.01% by mass or more. On the other hand, when Cr, Mo, Cu and Ni are added excessively, the surface properties deteriorate. Therefore, it is preferred to limit at least one of Cr, Mo, Cu and Ni to a total of 0.60% by mass or less. A total range of 0.03 to 0.50% by mass is more preferred. It should be noted that, with respect to Cu, due to the large influence on the surface properties, it is preferably set to 0.50% by mass or less, and in the case of strict surface properties, it is more preferably set to 0.10% by mass or less.

[0063] C group: at least one of Ti, Nb and V: 0.0005 to 0.0050 mass % in total

[0064] Ti, Nb and V have the effect of forming precipitates and improving yield strength. Therefore, it is preferred to add at least one of Ti, Nb and V in a total of 0.0005 mass % or more. On the other hand, when the addition amount of Ti, Nb and V is excessive, the growth of grains is significantly hindered and the iron loss is deteriorated. Therefore, it is preferred to limit at least one of Ti, Nb and V to a total of 0.0050 mass % or less. More preferably, the total is in the range of 0.0010 to 0.0025 mass %.

[0065] Group D: at least one of B: 0.0001 to 0.0020 mass %, Pb: 0.0001 to 0.0010 mass %, and W: 0.0005 to 0.0050 mass %

[0066] B, Pb and W all have the effect of making the steel sheet structure after final annealing fine-grained and improving the yield strength. In order to obtain this effect, B and Pb are preferably added at 0.0001% by mass or more, and W is preferably added at 0.0005% by mass or more. On the other hand, when the content of the above elements is excessive, not only the above effects are saturated, but also the iron loss deteriorates. Therefore, in the case of addition, it is preferred that B is set to less than 0.0020% by mass, Pb is set to less than 0.0010% by mass, and W is set to less than 0.0050% by mass. More preferably, it is in the range of B: 0.0003-0.0010% by mass, Pb: 0.0002-0.0006% by mass, and W: 0.0020-0.0035% by mass.

[0067] E group: Zn: 0.001 to 0.010 mass%

[0068] Zn has the effect of forming oxides or sulfides, making the steel sheet microstructure finer and improving the yield strength. In order to obtain this effect, Zn is preferably added in an amount of 0.001 mass % or more. On the other hand, when Zn is added excessively, the iron loss is reduced. Therefore, when Zn is added, it is preferably set to 0.010 mass % or less. More preferably, it is in the range of 0.003 to 0.006 mass %.

[0069] F group: Co: 0.0010 to 0.0500 mass%

[0070] Co has the effect of increasing the resistivity of steel and reducing iron loss, or increasing yield strength. In order to obtain these effects, it is preferably added 0.0010 mass % or more. On the other hand, even if Co is added excessively, only the above effects are saturated, so when added, it is preferably set to 0.0500 mass % or less. More preferably, it is in the range of 0.0040 to 0.0200 mass %.

[0071] Next, the mechanical strength characteristics of the non-oriented electrical steel sheet of the present invention will be described.

[0072] · Minimum value of yield strength in the plate width direction at 150°C: 300 MPa or more

[0073] In recent years, the temperature (practical temperature) when the motor is used has become higher, and durability at the level of 150°C has become important. Therefore, it is necessary to maintain a high yield strength even at the above temperature. From this point of view, the yield strength at 150°C is specified to be 300 MPa or more in the present invention. Preferably, it is 340 MPa or more. Here, the yield strength at 150°C refers to the minimum value of the yield strength (upper yield point, 0.2% yield strength when there is no upper yield point) measured in accordance with JIS Z 2241 by cutting test pieces from more than 10 locations in the plate width direction of the steel plate.

[0074] · Fluctuation of yield strength in the plate width direction at 150°C: 30 MPa or less

[0075] In addition, even if the minimum value of the yield strength in the plate width direction is high, if the fluctuation of the yield strength is large, the part with weak yield strength may become the starting point of damage. Therefore, in the present invention, the fluctuation of the yield strength in the plate width direction at 150°C is limited to 30 MPa or less. Here, the fluctuation in the plate width direction refers to the difference between the maximum value and the minimum value when the yield strength is measured at more than 10 parts in the steel plate width direction.

[0076] Next, a method for producing a non-oriented electrical steel sheet according to the present invention will be described.

[0077] Steel raw materials (steel billets)

[0078] The steel raw material (steel billet) used to manufacture the non-oriented electromagnetic steel sheet of the present invention needs to adjust the steel composition to meet the above-mentioned composition. As a smelting method for steel having the above-mentioned composition, a known refining process using a converter, an electric furnace or a secondary refining device such as a vacuum degassing device can be used, without particular limitation. In addition, the manufacturing method of the above-mentioned steel billet is preferably a continuous casting method, and an ingot casting-blowing rolling method, a thin slab continuous casting method, etc. can also be used. In addition, scrap iron and direct reduced iron can be used as raw materials.

[0079] Hot Rolling

[0080] After the steel slab is heated to a predetermined temperature, hot rolling is performed to form a hot rolled plate of a predetermined thickness. The conditions for the hot rolling are not particularly limited, but the heating temperature of the steel slab is preferably set to a range of 1000°C to 1160°C. It should be noted that direct rolling can be adopted in which the steel slab after continuous casting is directly hot rolled without being heated. The coiling temperature of the hot rolled coil is preferably set to 500°C to 650°C.

[0081] Hot rolled sheet annealing

[0082] Then, the hot rolled steel sheet (hot rolled sheet) is subjected to hot rolled sheet annealing. The conditions for the hot rolled sheet annealing are not particularly limited, but the annealing temperature is preferably set in the range of 800 to 1000°C. In addition, it is preferred to perform pickling in the pre-process or post-process of the hot rolled sheet annealing to remove the oxide scale formed on the surface of the steel sheet. The pickling conditions can be in accordance with conventional methods and are not particularly specified.

[0083] Cold Rolling

[0084] Next, the steel sheet after the hot-rolled sheet annealing is subjected to one cold rolling or two or more cold rollings with intermediate annealing to form a cold-rolled sheet with a final sheet thickness (product sheet thickness). As long as the final sheet thickness can be obtained, the cold rolling conditions are not particularly limited. It should be noted that, from the perspective of reducing iron loss, the final sheet thickness is preferably set to be less than 0.35 mm.

[0085] Final annealing

[0086] Next, the cold-rolled sheet having the final sheet thickness is subjected to final annealing for imparting desired magnetic properties and strength properties. This final annealing step is the most important step in the present invention and needs to be performed under the following conditions.

[0087] Soaking temperature: 700~1100℃, Soaking time: more than 2s

[0088] When the soaking temperature of the final annealing is lower than 700°C, recrystallization cannot occur sufficiently and good magnetic properties cannot be obtained. It is preferably above 800°C. On the other hand, when it exceeds 1100°C, the steel plate structure coarsens, the yield strength decreases and the desired strength cannot be obtained. It is preferably below 1050°C. In addition, in order to heat the plate width direction uniformly, the soaking time maintained at the above-mentioned soaking temperature needs to be set to more than 2s. It is preferably more than 5s, and more preferably more than 10s. It should be noted that from the viewpoint of preventing the reduction of yield strength caused by the coarsening of the steel plate structure, the upper limit of the soaking time is preferably set to about 60s.

[0089] Cooling rate from 700°C to 200°C: 10°C / s or more

[0090] In the cooling process after equalization, the steel plate is cooled uniformly in the plate width direction at a prescribed cooling rate so that the solid solution C remains uniformly in the plate width direction as a whole, thereby reducing the yield strength at 150°C and reducing the fluctuation in the plate width direction. However, when the cooling rate from 700°C to 200°C is less than 10°C / s, C precipitates in the form of Fe carbides during cooling and the amount of solid solution C decreases, so high yield strength cannot be obtained at 150°C. Therefore, the cooling rate from 700°C to 200°C needs to be set to 10°C / s or more. It should be noted that in order to further increase the yield strength at 150°C, it is preferably set to 15°C / s or more. On the other hand, when the cooling rate is too large, it is difficult to uniformly control the temperature in the plate width direction, the fluctuation of the yield strength in the plate width direction becomes larger, or the magnetic properties deteriorate due to cooling strain, so the upper limit is preferably set to about 50°C / s.

[0091] · Hydrogen concentration in the furnace atmosphere from the soaking temperature to 700°C: 1% by volume or more

[0092] In addition, when the temperature of the steel plate is in the high temperature range from the soaking temperature to 700°C and the hydrogen concentration in the furnace atmosphere gas is less than 1% by volume, the surface of the steel plate is unevenly oxidized to form an oxide film, so that the heat exchange with the cooling gas is different, which promotes the temperature fluctuation in the width direction of the plate. From this point of view, in the present invention, the hydrogen concentration in the furnace atmosphere gas from the soaking temperature to 700°C needs to be set to 1% by volume or more. From the perspective of increasing the thermal conductivity of the atmosphere gas and reducing the temperature fluctuation in the width direction of the steel plate, it is preferably set to 5% by volume or more, and more preferably set to 8% by volume or more. However, even if the hydrogen concentration is increased excessively, not only the above effect is saturated, but the cost of the atmosphere gas increases, so the upper limit is preferably set to about 30% by volume.

[0093] · Dew point of furnace atmosphere gas within the temperature range from soaking temperature to 300°C: below -30°C

[0094] When the dew point of the furnace atmosphere gas in the temperature range from the soaking temperature to 300°C is high, the surface of the steel plate is unevenly oxidized to form an oxide film, so that the heat exchange with the cooling gas is different, which promotes the temperature fluctuation in the width direction of the plate. Therefore, the dew point of the furnace atmosphere gas in the temperature range from the soaking temperature to 300°C needs to be set to -30°C or less. Preferably, it is -40°C or less. It should be noted that even if the lower limit of the dew point of the furnace atmosphere gas is too low, the above effect is saturated. Considering the dew point of the atmosphere gas that can be used industrially, it is preferably set to about -70°C.

[0095] · Fluctuation of steel plate temperature in the width direction within the temperature range from 500°C to 200°C: 40°C or less

[0096] When the fluctuation of the steel plate temperature in the plate width direction in the temperature range of 500-200°C is large, the amount of dissolved C changes in the plate width direction, and as a result, the fluctuation of the yield strength at 150°C in the plate width direction may become large. Therefore, the fluctuation of the steel plate temperature in the plate width direction between 500-200°C needs to be limited to 40°C or less. Preferably, it is 30°C or less. Here, the fluctuation of the steel plate temperature in the plate width direction refers to the difference between the maximum and minimum values ​​of the steel plate temperature in the plate width direction of the portion of the steel plate other than the plate width edge 10mm.

[0097] ·Difference between the maximum and minimum average cooling rate per 100°C in the temperature range from 700°C to 200°C: 20°C / s or less

[0098] In addition, if the average cooling rate per 100°C changes significantly during the cooling process after soaking in the final annealing, it is possible to promote temperature fluctuations in the width direction of the plate. Therefore, the cooling rate during the cooling process between 700 and 200°C is preferably as uniform as possible. Specifically, the difference between the maximum and minimum values ​​of the average cooling rate per 100°C in the temperature range of the steel plate temperature from 700°C to 200°C is preferably controlled to be less than 20°C / s. More preferably, it is less than 10°C / s.

[0099] The steel sheet subjected to the final annealing as described above may be coated with an insulating film as necessary to obtain a finished steel sheet. The insulating film may be inorganic, organic, or a mixture of inorganic and organic, and is not particularly limited.

[0100] Example

[0101] After steel having a composition containing various components shown in Table 1 and the balance consisting of Fe and inevitable impurities was melted by a conventional refining process, it was made into a steel raw material (steel billet) by a continuous casting method. Next, the above-mentioned steel billet was heated at a temperature of 1130°C in a heating furnace for 60 minutes, and then hot-rolled by rough rolling and finish rolling to form a hot-rolled plate with a plate thickness of 1.8 mm, and then coiled at 550°C to form a coil. The hot-rolled plate was annealed at a soaking temperature of 960°C, cold-rolled to form a cold-rolled plate with a final plate thickness of 0.30 mm, and finally annealed under the various conditions shown in Table 2 to form a finished plate.

[0102]

[0103]

[0104] Sample materials were cut out from the thus obtained product sheets and subjected to the following evaluation tests.

[0105] <Magnetic properties>

[0106] A test piece of 30 mm in width and 280 mm in length was cut from the center of the plate width of the sample material, with the longitudinal directions being the L direction (rolling direction) and the C direction (direction perpendicular to the rolling direction), and the iron loss W was measured in accordance with JIS C 2550-1. 10 / 400 .

[0107] <Yield strength at 150℃>

[0108] 20 JIS No. 5 test pieces with the L direction (rolling direction) as the tensile direction were cut from the plate width direction of the above sample material, heated to 150°C in a thermostatic chamber set in a tensile testing machine, and kept for 10 minutes. Then, a tensile test was performed in accordance with JIS Z 2241 to measure the yield strength at 150°C. For the test piece showing the upper yield point, the upper yield point was used as the yield strength, and for the test piece not showing the upper yield point, the 0.2% yield strength was used as the yield strength, and the minimum value of the 20 test pieces was used as the yield strength of the steel plate. In the determination of strain (elongation) in the tensile test, a video extensometer was used. In addition, the difference between the maximum and minimum values ​​of the yield strength of the 20 test pieces was used as the fluctuation of the yield strength in the plate width direction.

[0109] The results of the above evaluation tests are also shown in Table 2. According to the results, the steel plates of the invention examples manufactured under the conditions suitable for the present invention all have a yield strength of 300 MPa or more at 150°C, a fluctuation of the yield strength in the plate width direction of 30 MPa or less, and an iron loss W of 1.344 W / cm3. 10 / 400 The magnetic properties are good, being 15.0 W / kg or less.

[0110]

[0111]

Claims

1. A non-oriented electrical steel sheet having a composition comprising 0.0005-0.0100 mass % of C, 2.0-4.5 mass % of Si, 0.1-2.0 mass % of Mn, 0.050 mass % or less of P, 0.0050 mass % or less of S, 0.20-2.50 mass % of Al, 0.0050 mass % or less of N, and 0.0050 mass % or less of O, further comprising 0.01-0.20 mass % of at least one of Sn and Sb in total, and the balance consisting of Fe and inevitable impurities, The minimum value of the yield strength in the plate width direction at 150°C is 300 MPa or more. The fluctuation of the yield strength in the plate width direction is 30 MPa or less.

2. The non-oriented electrical steel sheet according to claim 1, characterized in that: In addition to the above composition, it also contains at least one of the following groups A to F. Group A: at least one of Ca, Mg and REM: 0.0010-0.0080% by mass in total; Group B: at least one of Cr, Mo, Cu and Ni: 0.01 to 0.60% by mass in total; Group C: at least one of Ti, Nb and V: 0.0005 to 0.0050% by mass in total; Group D: at least one of B: 0.0001 to 0.0020 mass %, Pb: 0.0001 to 0.0010 mass %, and W: 0.0005 to 0.0050 mass %; · Group E: Zn: 0.001-0.010% by mass; · Group F: Co: 0.0010 to 0.0500 mass %.

3. A method for manufacturing a non-oriented electromagnetic steel sheet, characterized in that: A non-oriented electrical steel sheet is produced by hot rolling, hot rolled sheet annealing, cold rolling and final annealing a steel billet having a component composition containing 0.0005-0.0100 mass % of C, 2.0-4.5 mass % of Si, 0.1-2.0 mass % of Mn, 0.050 mass % or less of P, 0.0050 mass % or less of S, 0.20-2.50 mass % of Al, 0.0050 mass % or less of N and 0.0050 mass % or less of O, further containing 0.01-0.20 mass % of at least one of Sn and Sb in total, and the balance consisting of Fe and inevitable impurities. In this method, The soaking temperature of the final annealing is set to 700-1100°C, and the soaking time is set to more than 2 seconds. Cooling from the soaking temperature of the final annealing to 200° C. under the following conditions (1) to (3), (1) Average cooling rate in the temperature range from 700°C to 200°C: above 10°C / s; (2) Hydrogen concentration in the furnace atmosphere from the soaking temperature to 700°C: 1% by volume or more; (3) Dew point of the atmosphere gas in the furnace within the temperature range from the soaking temperature to 300°C: below -30°C; (4) Fluctuation of the steel plate temperature in the plate width direction within the temperature range from 500°C to 200°C: 40°C or less.

4. The method for manufacturing a non-oriented electrical steel sheet according to claim 3, wherein: The cooling is performed so that the difference between the maximum value and the minimum value of the average cooling rate per 100° C. in the temperature range from 700° C. to 200° C. in the final annealing is 20° C. / s or less.

5. The method for producing a non-oriented electrical steel sheet according to claim 3 or 4, wherein: The steel slab further contains at least one component of the following groups A to F in addition to the above component composition. Group A: at least one of Ca, Mg and REM: 0.0010-0.0080% by mass in total; Group B: at least one of Cr, Mo, Cu and Ni: 0.01 to 0.60% by mass in total; Group C: at least one of Ti, Nb and V: 0.0005 to 0.0050% by mass in total; Group D: at least one of B: 0.0001 to 0.0020 mass %, Pb: 0.0001 to 0.0010 mass %, and W: 0.0005 to 0.0050 mass %; · Group E: Zn: 0.001-0.010% by mass; · Group F: Co: 0.0010 to 0.0500 mass %.

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