JP2006131939A - Non-oriented electromagnetic steel sheet with excellently low iron loss - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-oriented electromagnetic steel sheet which adequately grows its crystal grain and decreases an iron loss, even when annealed at a low temperature and for a short period of time, after having been stamped. <P>SOLUTION: The non-oriented electromagnetic steel sheet with the excellently low iron loss comprises, by mass%, 0.01% or less C, 0.1% to 7.0% Si, 0.1% to 3.0% Al, 0.1% to 2.0% Mn, 0.005% or less N, 0.02% or less Ti, 0.05% or less REM, 0.005% or less S, 0.005% or less O, and the balance iron with unavoidable impurities, wherein the mass% of S represented by [S], the mass% of O represented by [O], the mass% of REM represented by [REM], the mass% of Ti represented by [Ti] and the mass% of N represented by [N] satisfy expression 1: [REM]<SP>2</SP>×[O]<SP>2</SP>×[S]≥1×10<SP>-15</SP>, and expression 2: ([REM]<SP>2</SP>×[O]<SP>2</SP>×[S])/([Ti]×[N])≥1×10<SP>-10</SP>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention reduces the iron loss of non-oriented electrical steel sheets used for motor iron cores, etc., reduces energy loss, increases the efficiency of electrical equipment, and contributes to energy saving. Provided is a non-oriented electrical steel sheet excellent in later iron loss.

  Non-oriented electrical steel sheets are known to have a minimum iron loss when the crystal grain size is about 150 μm. For this reason, from the viewpoint of product characteristics, or from the viewpoint of simplification of production and high productivity, a steel plate with better crystal grain growth in finish annealing is desired.

  Furthermore, when the iron core is punched by a customer, the punching accuracy in the punching is better as the crystal grains are finer, and the crystal grain size is preferably, for example, 40 μm or less. As described above, there is a case where the iron loss with respect to the crystal grain size and the requirement of the punching accuracy are contradictory.

  In particular, when satisfying this conflicting requirement, the product is shipped with the crystal grain size of the product plate kept fine, and after the punching process by the customer, for example, 750 ° C. × 2 hours of strain relief annealing is performed to grow the crystal grains Measures to be taken are selected.

  In recent years, demands for low iron loss materials have been stronger than customers, and the improvement of customer productivity has been aimed at reducing the temperature and time of stress relief annealing. The need for good product boards has increased.

  One of the main factors that hinders grain growth is inclusions that are finely dispersed in the steel. It is known that as the number of inclusions contained in a product increases and the size decreases, crystal grain growth is inhibited.

  That is, as suggested by Zener, the smaller the r / f value represented by the sphere equivalent radius r of inclusions and the volume occupancy f of inclusions in the steel, the worse the grain growth. To do. Therefore, in order to improve the crystal grain growth, it is important not only to reduce the number of inclusions but also to increase the size of the inclusions.

  As fine inclusions that inhibit crystal grain growth of non-oriented electrical steel sheets, oxides such as silica and alumina, sulfides such as manganese sulfide, and nitrides such as aluminum nitride and titanium nitride are known.

  In order to remove these fine inclusions or reduce them to a necessary and sufficient level, it is obvious that high purity should be achieved at the molten steel stage. However, it is not preferable to increase the purity in the molten steel stage in order to remove fine inclusions or reduce them to a necessary and sufficient level, because an increase in steelmaking costs cannot be avoided.

  Therefore, as another method, several methods are known in which various elements are added to steel to make inclusions harmless.

  Regarding oxides, it is possible to remove the oxides at the molten steel stage and make them harmless by adding a sufficient amount of Al, which is a strong deoxidizing element, and taking sufficient time to lift and remove the oxides. It has become.

  With respect to sulfides, for example, as disclosed in (Patent Document 1), (Patent Document 2), (Patent Document 3), (Patent Document 4) and the like, a rare earth element that is a desulfurization element (hereinafter referred to as REM). A method of fixing S by adding such as is known.

  As for nitrides, as disclosed in (Patent Document 5) or (Patent Document 6), a method of fixing N as coarse inclusions by adding B is known.

JP 51-62115 A JP 56-102550 A JP 59-74212 A Japanese Patent No. 3037878 Japanese Patent No. 11678896 Japanese Patent No. 1245901

  When the oxides, sulfides and nitrides are rendered harmless by the above-mentioned method and the product plate is subjected to finish annealing or stress relief annealing after punching, the crystal grain growth partially varies, resulting in fine crystals. Grains and coarse crystal grains are mixed, and iron loss sometimes becomes poor.

  The reason for this is that fine titanium carbide (hereinafter referred to as TiC) is formed in a part of the product plate in the annealing stage and inhibits the growth of crystal grains, as will be described in detail below. Met.

  Finish annealing of product plates or strain relief annealing after punching is usually processed at a relatively low temperature of 1000 ° C or less, and in particular, strain relief annealing is used to prevent wear on the surface coating of product plates. The temperature is as low as about 750 ° C., and in order to sufficiently grow crystal grains at such a low temperature, annealing for a long time of 1 hour or more is forced.

  In such low temperature and long time annealing, it is extremely rare that the temperature of the product plate is always constant over the entire surface, some become lower temperature, and another part becomes higher temperature, and variation is inevitable. .

  By the way, in the electromagnetic steel, it is clear by separate examination that the generation temperature of TiC is in the range of 700 to 800 ° C. In the annealing at low temperature for a long time, the portion where the temperature is high among the variations exceeds the generation temperature of TiC, so TiC is not generated, and because of the high temperature, the crystal grain growth rate is fast, so the crystal grains become coarse To do.

  On the other hand, the portion of the variation that was at a low temperature becomes lower than the TiC generation temperature, and TiC may be generated during annealing. TiC produced at a low temperature cannot grow to a sufficient size due to the low temperature, becomes fine, and hinders crystal grain growth during long-time annealing.

  Since TiC to be produced is fine, even if the amount of Ti and C contained in the steel is at most about several ppm, TiC is produced in a number sufficient to inhibit crystal grain growth. Further, since the growth rate of the crystal grains is slow because of the low temperature, the effect of inhibiting the crystal grain growth by the fine TiC becomes stronger, so that the crystal grains do not grow and become fine.

  As described above, due to the inevitable variation in the annealing temperature, variation in the presence or absence of TiC occurs, and as a result, variation in crystal grain growth occurs.

  An object of the present invention is to provide a non-oriented electrical steel sheet capable of sufficiently growing crystal grains and reducing iron loss by preventing the precipitation of fine TiC during annealing. .

The gist of the present invention is as follows.
(1) By mass%, C: 0.01% or less, Si: 0.1% to 7.0%, Al: 0.1% to 3.0%, Mn: 0.1% to 2. 0% or less, N: 0.005% or less, Ti: 0.02% or less, REM: 0.05% or less, S: 0.005% or less, O: 0.005% or less, with the balance being iron And an inevitable impurity, and the mass% of S indicated by [S], the mass% of O indicated by [O], the mass% of REM indicated by [REM], and [Ti The non-oriented electrical steel sheet excellent in iron loss, wherein the mass% of Ti shown by [N] and the mass% of N shown by [N] satisfy [Formula 1] and [Formula 2]. .
[REM] ² × [O] ² × [S] ≧ 1 × 10 ⁻¹⁵ [1 set]
([REM] ² × [O] ² × [S]) ÷ ([Ti] × [N]) ≧ 1 × 10 ⁻¹⁰ [2 formulas]

  (2) Further, in mass%, P: 0.1% or less, Cu: 0.5% or less, Ca or Mg: 0.05% or less, Cr: 20% or less, Ni: 1.0% or less, Sn And one or more of Sb: 0.3% or less, Zr: 0.01% or less, V: 0.01% or less, B: 0.005% or less, The non-oriented electrical steel sheet excellent in iron loss according to (1).

  According to the present invention, fine TiC precipitated in the non-oriented electrical steel sheet can be sufficiently suppressed, and it becomes possible to improve the crystal grain growth at the stage of finish annealing and strain relief annealing, thereby obtaining sufficiently good magnetic properties. It can contribute to energy saving while meeting the needs of consumers.

  Below, the action mechanism of this invention is demonstrated in detail. As described above, a technique using REM for detoxifying sulfides in electromagnetic steel, that is, a technique for reducing sulfide inclusions by fixing S by adding REM is conventionally known.

  Here, REM is a generic name for a total of 17 elements including 15 elements from lanthanum having an atomic number of 57 to lutesium having an atomic number of 57 plus scandium having an atomic number of 21 and yttrium having an atomic number of 39.

  As a result of careful study of the phenomenon caused by the addition of REM to electromagnetic steel, the inventor has revealed the following facts. That is, by setting the component values of REM, O, S, Ti and N in the steel within an appropriate range, REM oxysulfide is formed in the steel, and TiN is compositely precipitated on the surface of the REM oxysulfide. Thus, it has been found that there is an appropriate range of each component value that can fix Ti and prevent the formation of TiC during annealing.

  This will be described in detail below. REM reacts with various elements in steel to form inclusions, and examples thereof include REM oxysulfide, REM sulfide, and REM oxide. Since there are many similarities between these crystal structures and the crystal structure of TiN, when these REM inclusions are present in the steel, they are geometrically arranged with respect to the REM inclusions as shown in FIG. In some cases, TiN may be compositely deposited.

  Since it is clear from examination that the TiN production start temperature is in the range of 1200 to 1300 ° C and the TiC production start temperature is in the range of 700 to 800 ° C, Ti is once fixed as TiN. In this case, TiN is not dissolved and TiC is not generated in finish annealing of the product plate or strain relief annealing after punching.

  By the way, among the REM inclusions, the crystal lattice structure of REM oxysulfide and the crystal lattice structure of TiN have many similarities in particular, so this composite precipitation becomes stronger and Ti can be more firmly fixed. . Therefore, it is important to selectively generate REM oxysulfide in steel in order to more reliably prevent the generation of TiC during annealing.

  The requirements that govern the generation of REM oxysulfide are considered to be related to the solubility product of REM and O and S, which are constituent elements, and the values expressed in the form of the product of REM, O and S in steel are as follows: It is inferred that it is necessary to exceed a predetermined value.

  On the other hand, regarding Ti, it is necessary that TiN is generated and sufficiently grown. In particular, Ti and N sufficient for TiN growth are sufficiently contained in the steel in order to fix Ti in the steel as TiN. It is necessary. Here, it is considered that the requirement that affects the generation of TiN is related to the solubility product of Ti and N as constituent elements.

  However, if the amount of Ti or N in the steel is excessive, not all Ti and N in the steel are fixed on the REM oxysulfide as TiN, and excess Ti that failed to form TiN remains. Thus, TiC can be generated. Accordingly, the solubility product of Ti and N needs to be suppressed to a certain ratio or less with respect to the solubility product of REM, O, and S.

In view of the above, as a result of intensive studies by the inventors, the mass% of S indicated by [S], the mass% of O indicated by [O], and the mass% of REM indicated by [REM] , REM oxysulfide is produced in the steel when the mass% of Ti shown by [Ti] and the mass% of N shown by [N] satisfy [Formula 1] and [Formula 2]. And it discovered that TiN compound-deposited on the surface of REM oxysulfide, Ti was fixed as TiN, and the production | generation of TiC was suppressed.
[REM] ² × [O] ² × [S] ≧ 1 × 10 ⁻¹⁵ [1 set]
([REM] ² × [O] ² × [S]) ÷ ([Ti] × [N]) ≧ 1 × 10 ⁻¹⁰ [2 formulas]

  Hereinafter, the appropriate component ranges described above will be specifically described with reference to Table 1 and FIG.

  In mass%, C: 0.0026%, Si: 3.0%, Al: 0.59%, Mn: 0.21%, and contents of O, S, Ti, N and REM are shown in Table 1. As shown in Fig. 3, variously modified steels are continuously cast, hot-rolled, hot-rolled sheet annealed, cold-rolled to a thickness of 0.35 mm, finish annealed at 850 ° C for 30 seconds, and an insulating film is applied. And made a product board. The crystal grain size of the product plate at this time was in the range of 30 to 33 μm.

  Next, these product plates were subjected to strain relief annealing at 750 ° C. for 1.5 hours, which is shorter than conventionally performed. Thereafter, the inclusions, crystal grain size and magnetic properties were investigated. The results are shown in Table 1 and FIG.

No. 1 to No. As shown in FIG. 4, the [REM] ² × [O] ² × [S] value of the steel is in the range of [1 formula], and ([REM] ² × [O] ² × [S]) ÷ ([Ti] × [N]) When the value is in the range of [Formula 2], the crystal grain size after the strain relief annealing is sufficiently grown as 59 to 72 μm, and the magnetic properties ( The iron loss (W15 / 50) was as good as 1.87 to 1.94 W / kg.

  In these steels, REM oxysulfide was present, and as shown in FIG. 2, TiN was compositely precipitated on the surface of REM oxysulfide. Further, TiC was not generated after annealing. From the above results, when the component value of the product is within the range of the present invention, REM in the steel forms REM oxysulfide, and TiN is compound-deposited thereon to fix Ti. It was clear that the formation of TiC was prevented.

No. 5 to No. The example shown in 7 is a case where the [REM] ² × [O] ² × [S] value is outside the range of [Formula 1]. REM oxysulfide was not observed in these steels. Further, TiC was observed, which inhibited the crystal grain growth, the crystal grain size after strain relief annealing remained at 34 to 36 μm, and the W15 / 50 value was around 2.3 W / kg, which was poor. It was.

In this case, REM oxysulfide is not generated in the steel, and thus TiN does not precipitate on the surface of REM oxysulfide to fix Ti, and Ti is generated during strain relief annealing as TiC. Inhibited grain growth. From the above, it has become clear that the [REM] ² × [O] ² × [S] value needs to be within the range of [Formula 1].

No. 8 to No. In the example shown in FIG. 10, the [REM] ² × [O] ² × [S] value is in the range of [Expression 1], and ([REM] ² × [O] ² × [S]) ÷ ( [Ti] × [N]) The value is out of the range of [Formula 2]. REM oxysulfide was observed in these steels. However, TiN was not observed on the surface of REM oxysulfide. In addition, TiC is observed, which inhibits crystal grain growth, and the crystal grain size after strain relief annealing remains at 37 to 41 μm, and the W15 / 50 value is about 2.2 to 2.3 W / kg. It was bad.

In this case, although REM oxysulfide was generated in the steel, TiN was not deposited on the surface by complex precipitation of TiN, and Ti was not fixed as TiC, and Ti was generated during strain relief annealing and inhibited grain growth. . As described above, the [REM] ² × [O] ² × [S] value is within the range of [Expression 1], and ([REM] ² × [O] ² × [S]) ÷ ([Ti] It became clear that the value of [× [N]) needs to be within the range of [Expression 2].

  It should be noted that, for example, Comparative Example No. In other words, TiC may be generated when the amount of Ti is small, such as 5. According to the conventional knowledge, it is preferable that the amount of Ti is as small as possible. Therefore, even if a great deal of effort is required, it is necessary to prevent Ti from being mixed into the steel. TiN is actively added on the surface of REM oxysulfide by adding Ti in some cases and increasing the amount of Ti in steel rather than the amount of Ti inevitably mixed. Thus, it is possible to perform composite precipitation, thereby fixing Ti, eliminating TiC precipitation during annealing, and stably obtaining good product characteristics.

  Note that the above results are the results of performing strain relief annealing in a shorter time than is conventionally performed, but when conventional strain relief annealing is performed, the pinning action of fine inclusions Needless to say, the above-described crystal grain growth property and the suitability of iron loss are further clarified.

  Moreover, even if it uses only 1 type, or it uses it combining 2 or more types of elements if it is an element of REM, said effect will be exhibited if it is in the range of this invention.

Next, the reason for limiting the preferable content of the component composition in the present invention will be described.
[C]: C is not only harmful to magnetic properties, but also magnetic aging due to precipitation of C becomes remarkable, so the upper limit was made 0.01 mass%. The lower limit includes 0% by mass.

  [Si]: Si is an element that reduces iron loss. When less than the lower limit of 0.1% by mass, the iron loss is worsened. Further, if the upper limit of 7.0% by mass is exceeded, the workability becomes extremely poor, so the upper limit was set to 7.0% by mass.

  Since Si has the effect of increasing the activity of Ti in the steel, the lower limit of the Si amount is that the higher the Si, the more active the formation of Ti precipitates, and the combined precipitation of TiN on REM oxysulfide. Is promoted, the amount of Ti fixed per REM oxysulfide increases, and the number density of fine Ti precipitates in the steel further decreases. Since this effect is approximately proportional to the square of the Si amount, it is preferable that the Si amount be higher.

Specifically, the number density of fine Ti precipitates having a diameter of 100 nm or less in steel is 1 × 10 ⁹ pieces / mm ³ or less when the Si amount is 2.2 mass%, and the Si amount is 2.5 mass. %, 5 × 10 ⁸ pieces / mm ³ or less. Therefore, the lower limit of the Si amount is preferably 2.2% by mass or more, and more preferably 2.5% by mass or more.

  Further, a more preferable value as the upper limit of the Si amount is 4.0% by mass with better cold rolling properties. If the upper limit is 3.5% by mass, the cold rolling property is further improved, which is more preferable.

  [Al]: Al is an element that reduces iron loss in the same manner as Si. If the lower limit is less than 0.1% by mass, the iron loss deteriorates, and if it exceeds the upper limit of 3.0% by mass, the cost increases remarkably. The lower limit of Al is preferably 0.2% by mass, more preferably 0.3% by mass, and still more preferably 0.6% by mass from the viewpoint of iron loss.

  [Mn]: Mn is added in an amount of 0.1% by mass or more in order to increase the hardness of the steel sheet and improve the punchability. The upper limit of 2.0% by mass is due to economic reasons.

  [N]: N becomes a nitride such as AlN or TiN and deteriorates the iron loss. Although it is fixed as TiN to the REM inclusion according to the present invention, the practical upper limit is set to 0.005 mass%. For the above reason, the upper limit is preferably 0.003% by mass, more preferably 0.0025% by mass, and still more preferably 0.002% by mass.

  For the above reasons, it is preferable that N is as small as possible. However, since there are large industrial restrictions to make it as close as possible to 0% by mass, the lower limit is made more than 0% by mass. As a practical lower limit, 0.001% by mass is taken as a guide, and if it is reduced to 0.0005% by mass, nitride is suppressed, more preferably, and if it is reduced to 0.0001% by mass, it is more preferable.

  [Ti]: Ti produces fine inclusions such as TiC, which deteriorates grain growth and iron loss. According to the present invention, although TiN is fixed to REM oxysulfide, the practical upper limit is 0.02% by mass. For the above reason, the upper limit is preferably 0.01% by mass, more preferably 0.005% by mass.

  In addition, since Ti is an element that deteriorates the grain growth property, it is preferable that the amount is small. The lower limit is more than 0% by mass. However, as described above, when the amount of Ti is too small, the effect of fixing to REM oxysulfide has an effect. It may not be demonstrated.

  Therefore, when the amount of Ti satisfies the above-described evaluation formula [Formula 2], it is preferable that the amount of Ti exceeds 0.0012% by mass because the effect of fixing to REM oxysulfide becomes more reliable, and further 0.0015 More preferably, it is more preferably 0.002% by mass or more, and even more preferably 0.0025% by mass or more.

  [REM]: REM forms oxysulfide to fix S, and prevents or suppresses the formation of fine sulfide. Moreover, it becomes a TiN composite production site and exerts a Ti fixing effect. For this reason, a content exceeding the prescribed amount according to the amount of Ti is required. However, if it is 0.001% by mass or more, the above-mentioned effect is more surely preferable, and 0.002% by mass or more is more preferable. 0.0025% by mass or more is more preferable, and 0.003% by mass or more is more preferable. The upper limit of 0.05% by mass is due to economic reasons.

  [S]: S becomes a sulfide such as MnS, which deteriorates grain growth and iron loss. Although fixed as REM oxysulfide according to the present invention, the practical upper limit was set to 0.005 mass%.

  For the above reasons, it is preferable that S is as small as possible. However, industrial restrictions are large to bring it as close as possible to 0% by mass, and since it is necessary for the formation of REM oxysulfide, the lower limit is more than 0% by mass. As a practical lower limit in consideration of economy and the like, 0.0005% by mass is a guide.

  [O]: When O is contained in an amount of more than 0.005% by mass, a large number of oxides are generated, and domain wall movement and crystal grain growth are inhibited by the oxides. Therefore, it is preferable to set it as 0.005 mass% or less.

  For the reasons described above, it is preferable that O be as small as possible. However, industrial restrictions are large in order to make it as close as possible to 0% by mass, and since it is necessary for the formation of REM oxysulfide, the lower limit is more than 0% by mass. As a practical lower limit in consideration of economy and the like, 0.0005% by mass is a guide.

  As long as it is an element other than the components described above and does not greatly interfere with the effect of the steel of the present application, it may be contained.

  Below, a selective element is demonstrated. In addition, all the lower limits of these content shall be over 0 mass%.

  [P]: P increases the strength of the material and improves workability. However, if excessive, the cold rolling property is impaired, so 0.1% by mass or less is preferable.

  [Cu]: Cu improves corrosion resistance and increases specific resistance to improve iron loss. However, if the amount is excessive, scabs or the like are generated on the surface of the product plate and the surface quality is impaired, so 0.5 mass% or less is preferable.

  [Ca] and [Mg]: Ca and Mg are desulfurization elements, react with S in steel to form sulfide, and fix S. However, unlike REM, the effect of compounding and depositing TiN is small. If the addition amount is increased, the desulfurization effect is enhanced, but if the upper limit of 0.05% by mass is exceeded, grain growth is hindered by excess Ca and Mg sulfide. Therefore, 0.05 mass% or less is preferable.

  [Cr]: Cr improves the corrosion resistance and increases the specific resistance to improve the iron loss. However, excessive addition increases the cost, so 20 mass% was made the upper limit.

  [Ni]: Ni develops a texture favorable to magnetic properties and improves iron loss. However, excessive addition increases the cost, so 1.0 mass% was made the upper limit.

  [Sn] and [Sb]: Sn or Sb is a segregating element, which inhibits the texture of the (111) plane that deteriorates the magnetic properties and improves the magnetic properties. Even if these are used alone or in combination of the two, the above-described effects can be exhibited. However, if it exceeds 0.3% by mass, the cold rollability deteriorates, so 0.3% by mass was made the upper limit.

  [Zr]: Zr inhibits crystal grain growth even in a small amount, and worsens iron loss after strain relief annealing. Therefore, it is preferable to reduce it as much as possible to 0.01% by mass or less.

  [V]: V forms nitrides or carbides and inhibits domain wall movement and crystal grain growth. For this reason, it is preferable to set it as 0.01 mass% or less.

  [B]: B is a grain boundary segregation element and forms a nitride. Grain boundary movement is hindered by this nitride, and iron loss deteriorates. Therefore, it is preferable to reduce as much as possible to 0.005 mass% or less.

  In addition to the above, known elements can be added. For example, Bi, Ge, or the like can be used as an element for improving magnetic characteristics, and these may be appropriately selected according to required magnetic characteristics. .

  Next, preferable manufacturing conditions and the reason for the definition in the present invention will be described. First, at the steelmaking stage, when refining by a conventional method such as a converter or secondary refining furnace, the oxidation degree of slag, that is, the mass ratio of FeO + MnO in the slag should be in the range of 1.0 to 3.0%. Is preferred.

  The reason for this is that if the degree of oxidation of the slag is less than 1.0%, within the Si range of the electromagnetic steel, the activity of Ti rises due to the influence of Si, so it is difficult to effectively prevent the covered Ti from the slag, If the amount of Ti in the steel rises unnecessarily, and if the oxidation degree of the slag exceeds 3.0%, the REM oxysulfide in the molten steel is unnecessarily oxidized to REM oxide by supplying oxygen from the slag, This is because the fixing of S in the steel becomes insufficient.

  Furthermore, in the steelmaking stage, the basicity of the slag, that is, the ratio of the mass% of CaO to the mass% of SiO2 in the slag is preferably in the range of 0.5 to 5.

  The reason for this is that if the basicity of the slag is less than 0.5, the amount of Ti covered from the slag increases, and the amount of Ti in the steel tends to rise unnecessarily. Therefore, the REM required for fixing Ti is required. When the amount of addition increases and the basicity of the slag exceeds 5, the cover S from the slag increases, and the amount of S in the steel tends to increase unnecessarily, so that it is necessary to fix S. This is because the amount of REM added is increased and both are economically disadvantageous.

  Furthermore, it is also important to examine the furnace material refractories and the like to eliminate foreign oxidation sources as much as possible. Furthermore, in order to maintain a sufficient time for the REM oxide that is inevitably generated when REM is added, the time from REM addition to casting is preferably 10 minutes or more. After the molten steel in the desired composition range is melted by the measures described above, a slab or other slab is cast by continuous casting or ingot casting.

  After this, it is further hot-rolled, hot-rolled sheet annealed as necessary, finished to product thickness by one or more cold rollings sandwiching intermediate annealing, then finish-annealed and coated with insulating film To do. By the method described above, the inclusions in the product plate can be controlled within the scope of the present invention.

  In mass%, C: 0.0026%, Si: 3.0%, Al: 0.59%, Mn: 0.21%, and contents of O, S, Ti, N and REM are shown in Table 1. As shown in Fig. 4, continuously changed steel was continuously cast, hot-rolled, hot-rolled sheet annealed, and cold-rolled to a thickness of 0.35 mm.

  Next, finish annealing at 850 ° C. × 30 seconds is applied and an insulating film is applied to produce a product plate. Further, after 750 ° C. × 1.5 hours of strain relief annealing, investigation of inclusions in the product plate, A crystal grain size survey and a magnetic property survey by 25 cm Epstein method were conducted. The inclusion investigation was conducted by extracting the inclusions by the replica method and observing them using a TEM. The crystal grain size was determined by mirror polishing the plate thickness cross section and performing nital etching to reveal the crystal grains. The diameter was measured.

  As apparent from Table 1 above, the product plate according to the present invention has obtained good results with respect to crystal grain growth and iron loss values. On the other hand, the product plate outside the range of the present invention was inferior in crystal grain growth and iron loss value.

  As explained above, by properly controlling the inclusions contained in the non-oriented electrical steel sheet, good magnetic properties can be obtained stably even with simple annealing, and particularly stable even with simple strain relief annealing. This makes it possible to obtain good magnetic properties and contribute to energy saving while meeting the needs of consumers.

Correlation between values calculated from REM content, S content, O content, Ti content and N content in steel using [Formula 1] of the present invention, and crystal grain size and iron loss value after strain relief annealing FIG. It is a figure which shows the inclusion which TiN compounded on the surface of REM oxysulfide.

Claims (2)

In mass%, C: 0.01% or less, Si: 0.1% to 7.0%, Al: 0.1% to 3.0%, Mn: 0.1% to 2.0% N: 0.005% or less, Ti: 0.02% or less, REM: 0.05% or less, S: 0.005% or less, O: 0.005% or less, the balance being iron and inevitable It consists of impurities and is represented by the mass% of S indicated by [S], the mass% of O indicated by [O], the mass% of REM indicated by [REM], and indicated by [Ti]. A non-oriented electrical steel sheet excellent in iron loss, characterized in that the mass% of Ti and the mass% of N indicated by [N] satisfy [Formula 1] and [Formula 2].
[REM] ² × [O] ² × [S] ≧ 1 × 10 ⁻¹⁵ [1 set]
([REM] ² × [O] ² × [S]) ÷ ([Ti] × [N]) ≧ 1 × 10 ⁻¹⁰ [2 formulas]   Further, by mass%, P: 0.1% or less, Cu: 0.5% or less, Ca or Mg: 0.05% or less, Cr: 20% or less, Ni: 1.0% or less, Sn and Sb One or more of one or two types: 0.3% or less, Zr: 0.01% or less, V: 0.01% or less, B: 0.005% or less, 1. A non-oriented electrical steel sheet excellent in iron loss according to 1.