WO2005100627A1 - Nonoriented electromagnetic steel sheet excellent in blankability and magnetic characteristics after strain removal annealing, and method for production thereof - Google Patents

Abstract

A nonoriented electromagnetic steel exhibiting excellent blankability and also exhibiting good and stable iron loss after the annealing for strain removal, which has a chemical composition, in mass %, that Si: 1.5 % or less, Mn: 0.4 to 1.5 %, Sol.Al: 0.01 to 0.04 %, Ti: 0.0015% or less, N: 0.0030 % or less, S: 0.0010 to 0.0040%, Sn: 0.01 to 0.50%, B: an amount satisfying 0.5 ≤ B/N ≤1.5, and the balance: Fe and inevitable impurities, wherein 10 % or more, in terms of the number of pieces, of the sulfide containing Mn precipitates in a composite form with a B precipitate, and wherein it has a crystal grain diameter of 30 µm or less and exhibits a crystal grain diameter of 50 µm or more after the annealing for strain removal at 750°C for 2 hours; and a method for producing the above nonoriented magnetic steel which comprises holding a slab for hot rolling at a temperature of 1150 to 1250°C for five minutes or more, subsequently holding it at a temperature of 1050°C or higher and lower than 1150°C for 15 minutes or more, and immediately thereafter, subjecting the resultant slab to a hot rolling with a finishing output temperature T (°C) of T ≥ 900 - 1000 x Sn [mass %].

Description

 • Description Non-oriented electrical steel sheet with excellent punching workability and magnetic properties after strain relief annealing and its manufacturing method

 The present invention relates to a non-oriented electrical steel sheet used as an iron core material of electrical equipment and a method for producing the same, and particularly to a non-oriented electrical steel sheet excellent in punching workability and magnetic properties after strain relief annealing. And its manufacturing method. Background art

 In recent years, with the increasing energy conservation of electrical equipment worldwide, non-oriented electrical steel sheets used as core materials for rotating machines have been required to have even higher performance characteristics. For motors, high-grade materials with increased Si and A1 content to increase the specific resistance and crystal grain size have come to be used. On the other hand, motors of general-purpose models are also required to improve their performance, but it is difficult to switch to high-quality materials like high-efficiency models due to severe cost constraints.

 For steel sheets required for general-purpose models, iron loss is dramatic because S i is 1.5% or less and crystal growth during strain relief annealing performed after punching of motor cores is promoted. It is a material that improves. More recently, the number of consumers who use scrap generated during core punching as a raw material for raw materials has increased, and the A1 content of steel sheets has been reduced to less than 0.05% from the viewpoint of ensuring the creativity of scrap. The need has arisen.

In order to improve crystal grain growth during strain relief annealing, unavoidable mixing in steel It is important to reduce or make harmless precipitates, but the material design of non-oriented electrical steel sheets with Al: less than 0.05% is largely divided into two, one of which is Japanese Patent Application Laid-Open No. 54-163720. As shown in Fig. 1, B is added to A1 deoxidized steel (Sol. A1: about 0.02%) at about 0.002% to form BN as nitrides, and A1N harmful to grain growth. This is a method of suppressing the precipitation of.

The other as seen in JP-A-7-150248, and controls the S i deoxidation and steel (S ol. A1≤0. 001% ) S i0 2 and MnO ratio of oxides contained in grain Japanese Patent Application Laid-Open No. Hei 6-73510 discloses a method of controlling extensible inclusions that are harmful to growth, and controlling the Mn / Si of steel components to 0.2 to 1.0. I have.

 As described above, Japanese Patent Application Laid-Open No. 58-117828 discloses a method of appropriately controlling nitrides or oxides generated during deoxidation and further reducing or detoxifying sulfides to improve magnetism. In the gazette, a method of defining S to be 0.005% or less in order to obtain a magnetic improvement effect.In Japanese Patent Application Laid-Open No. 58-164724, when S: 0.01 to 02% is contained, Ca fe or rare earth element is used. In addition, Japanese Patent Application Laid-Open No. 4-63228 discloses a method of fixing S by setting S to not more than 0.0050% and setting the heating temperature of the slab to 1100 ° C or less. A method for preventing fine precipitation is disclosed. Disclosure of Invention ·

 In a situation where further reduction of iron loss is required, it is becoming difficult to produce a sufficient and stable method using the above method. The present invention has been made in view of such a problem, and an improvement measure focusing on B added for the purpose of suppressing the precipitation of A1N and S, which is an unavoidable element contained in steel, is used after the strain relief annealing. An object of the present invention is to provide a steel sheet having good crystal grain growth, low iron loss, and high magnetic flux density.

The present invention has been made to solve the above-mentioned problems, and the The effect is as follows. ,

 (1) In mass%, Si: 1.5% or less, Mn: 0.4% or more and 1.5% or less, Sol.Al: 0.01% or more and 0.04% or less, Ti: 0.0015% or less, N: 0.0030% or less, S: 0.0010% or less 0.0040% or less, B in B / N 0.5 to 1.5, and the balance consists of Fe and unavoidable impurities. Non-oriented electrical steel sheet.

 (2) In mass%, Si: 1.5% or less, Mn: 0.4% or more and 1.5% or less, Sol.A1: 0.01% or more and 0.04% or less, Ti: 0.0015% or less, N: 0.0030% or less, S: 0.0010% or less 0.0040% or less, B in B / N of 0.5 or more and 1.5 or less, the balance of the steel sheet composed of Fe and unavoidable impurities is 30 μm or less, and after strain relief annealing at 750 ° C X2 hours Non-oriented electrical steel sheet having a crystal grain size of 50 m or more.

(3) The non-oriented electrical steel sheet according to (1) or (2), wherein the total distribution density of MnS, Cu ₂ S and its composite sulfide is not more than 3.0 × 10 ⁵ / mm ² .

(4) Further, the distribution density of Ti precipitates having a diameter of less than 0.1 μm is 1.0 × 10 ³ / mm ² or less. Grain-oriented electrical steel sheet.

 (5) In addition, one or more of Sn, Cu, and Ni are added in a total of 0.01% or more and 0.50% or less by mass%, and / or one or more of RM, Ca, and Mg are 0.001 to 0.001%. The non-oriented electrical steel sheet according to any one of (1) to (4), characterized by containing 0.5%.

(6) As a method for producing the steel sheet according to any one of (1) to (5), the steel sheet, hot-rolled, pickled, cold-rolled, and then subjected to finish annealing followed by hot-rolled slab. With regard to heating, it is characterized in that it is retained for 5 minutes or more in the range of 1150 ° C or more and 1250 ° C or less, then continuously for 15 minutes or more in the range of 1050 ° C or more and less than 1150 ° C, and then hot-rolled immediately. Of non-oriented electrical steel sheet Construction method.

 (7) As a method for producing the steel sheet according to any one of (1) to (6), the steel sheet, hot rolling, pickling, and cold rolling are subjected to finish annealing, followed by finishing of hot rolling. A method for producing a non-oriented electrical steel sheet, wherein the exit temperature of rolling is 800 ° C or higher.

 (8) The non-oriented electrical steel sheet according to (6), wherein the finish outlet temperature (TC) of the hot-rolled steel sheet is set to T≥900-lOO X Sn [mass%] in the steel sheet containing Sn. Production method. BEST MODE FOR CARRYING OUT THE INVENTION

The inventors of the present invention have reduced the inevitable contamination element S to about 0.0010% in steels with Si of 1.5% or less, and have been using slab heating as disclosed in JP-A-4-63228. Even if the temperature was lowered to 1100 ° C or less, the iron loss after strain relief annealing varied and it was not stabilized. Investigation of the cause revealed that despite the low S content and slab heating temperature, MnS, Cu ₂ S and its complex sulfide were finely and abundantly dispersed in the steel, and the crystal after strain relief annealing It was found that grain growth was significantly suppressed. Further observations show that these sulfides are spherical with a diameter of about 0.1 to 0.3 μm, but contain Ti precipitates with a diameter equivalent to about 0.05 μιη at the center. It turned out that. The reason why the sulfide takes such a precipitation form is that TiN, which is initially deposited after sintering and heated by hot rolling slab, is finely dispersed, and sulfide is deposited on the nucleus. I understand.

In order to overcome this situation, the present inventors have focused on sulfides that have a higher growth rate than TiN and are likely to become coarse. In other words, contrary to the current situation in which sulfide is complex-precipitated with TiN as a nucleus, it was found that as a result of attempting to precipitate TiN with sulfide as a nucleus, stable and low iron loss can be obtained. . In addition, the present inventors have found that a low iron loss can be stably obtained by complex precipitation of a sulfide with respect to BN generated as a fixation of excess N, which will be described later, and completed the present invention. Hereinafter, the experimental results that led to the present invention will be described.

 (Experiment 1)

 In a laboratory vacuum melting furnace, in mass%, C: 0.003%, Si: 0.6%, Mn: 0.1 to 0.8%, Sol. Al: 0.03%, Ti: 0.0012%, N: 0.0021%, S : 0.0005 to 0.0025%, B: 0.0020%, and Sn: 0.08%. These slabs are kept at 1200 ° C for 20 minutes, cooled to 1100 ° C over 10 minutes, kept for 30 minutes, hot-rolled to a thickness of 2.5 mm, and pickled to a thickness of 0.50 mm. Cold rolled.

 The cold-rolled sheet thus obtained was subjected to finish annealing at 800 ° C for 10 seconds, and then subjected to strain annealing at 750 ° C for 2 hours, and the crystal grain size and iron loss were measured. As a result, as shown in Table 1, in Samples 8, 9, 11, and 12 with Mn of 0.4% or more and S of 0.0012, 0.025%, the crystal grain size after strain relief annealing was good at 50 μm or more. Iron loss was obtained.

 Next, precipitates were observed on the samples after strain relief annealing, and in 8, 9, 11, and 12 samples with good iron loss, the number ratio of sulfide containing Mn was 10% or more. Complex precipitation with B precipitate was observed. On the other hand, in the other samples with poor iron loss, many fine precipitates less than 0.1 μm in diameter, which are considered to be B precipitates, were observed.

As described above, the grain growth after strain relief annealing and the effect of improving iron loss at Μη · 0.4% or more and at S: 0.0012, 0.0025% are considered as follows. First, increasing the Mn raises the MnS precipitation start temperature. As a result, MnS comes to precede BN at the time of hot-rolling heating, and the BN that subsequently precipitates becomes compositely precipitated with MnS as nuclei. As a result, the formation of fine precipitates of B can be suppressed. It is considered that crystal grain growth and iron loss after the strain relief annealing are obtained.

On the other hand, when Mn is less than 0.4%, the precipitation of MnS is not sufficient at the stage of BN precipitation, and when S is 0.0005%, the amount of MnS precipitated itself is small, so that the nuclei of BN precipitation are insufficient in all cases. It is considered that the properties after strain relief annealing are not improved by single and fine precipitation of B.

 table 1

(Experiment 2)

 In a laboratory vacuum melting furnace, in mass%, C: 0.0034%, Si: 0.75%, Mn: 0.15 to 0.72%, Sol. A1: 0.019%, Ti: 0.0008 to 0.0017%, N: 0.0018% A slab containing 0.0023% of S, 0.0025% of B, 0.03% of Sn, 0.01% of Cu, and 0.02% of Ni was prepared. These slabs were kept at 1200 ° C for 5 minutes, cooled to 1100 ° C and kept for 30 minutes, then hot-rolled to a thickness of 2.7 mm, and cooled to 0.50 mm in thickness through pickling. Delayed. The cold-rolled sheet thus obtained was subjected to a finish annealing at 800 ° C for 10 seconds, followed by a strain relief annealing at 750 ° C for 2 hours to observe the precipitates and crystal grain size of the steel sheet. Iron loss was measured.

As a result, as shown in Table 2, Mn was 0.4% or more and Ti was 0.0015% or less. In Sample 4, 5, 7, 8 is, sulfides density after stress relief annealing is 3. 0 X 10 ⁵ or less, the average crystal grain size becomes more 50 // m, good iron loss was obtained. In these samples, there are many spherical sulfides with a diameter of 0.2 to 0.3 μm, and on the outer periphery, multiple fine Ti precipitates equivalent to the diameter of less than 0.1 μm are precipitated. Many were confirmed. On the other hand, in samples 1 to 3 in which Mn is as low as 0.15%, the sulfide density after strain relief annealing is as high as ^4.5 × 10 ⁵ / mm ² or more, and the average crystal grain size is as small as 35 μιη or less. Small and bad iron loss. The sulfides found in these samples were as small as 0.1 m or less in diameter, and many of the sulfides contained Ti precipitates at the center. The Mn is at 0.4% or more, as high as Ti sulfide density after stress relief annealing also samples 6, 9 is greater than 0, 0015% is 3. 8 X 10 ⁵ cells / ² or more The average grain size was less than 45 μιη, and the iron loss was relatively poor. In these samples, the sulfides were distributed over a wide range from 0.05 to 0.3 μm in diameter, and the morphology of the sulfides with the Ti precipitates was also different at the outer periphery or the center. Note that the distribution density of Ti precipitates less than 0.1 μm in diameter was as low as less than 1,0 × 10 ³ / mm ^{2 in} all samples.

We consider the effect of increasing Mn to 0.4% or more and Ti to 0.0015% or less as follows. First, increasing the Mn raises the MnS precipitation onset temperature, while decreasing Ti reduces the TiN precipitation onset temperature. As a result, the order of precipitation is reversed, and MnS precipitates before TiN. Next, the MnS whose precipitation initiation temperature has risen precipitates and grows at 1200 ° C before the hot rolling. On the other hand, it is probable that TiN, whose precipitation starting temperature was lowered, had already coarsened MnS precipitated at the nucleus at 1100 ° C after the hot rolling. Table 2

(Experiment 3)

Next, in order to investigate the effect of heating conditions on hot rolling, using a steel slab of Mn: 0.4% and S: 0.0025% in Experiment 1, holding the hot rolling at 1200 ° C for 60 minutes, 1100 ° Two levels of 60 minutes were added at C, and after pickling, samples were prepared in the same process as in Experiment 1 and compared and evaluated. As a result, as shown in Table 3, the ratio of composite precipitation in Sample 2 kept at 1200 ° C was almost single and fine B in Sample 2 where the result was good (Sample 9 in Experiment 1). Many precipitates were observed, and the crystal grain size and iron loss after strain relief annealing were the worst. On the other hand, in sample 3 kept at 1100 ° C, although not as high as the 1200 ° C heating material (sample 2), the ratio of multiple precipitation was as low as 5%, and neither the crystal grain size nor the iron loss was even better. This result is considered as follows. First, when held at 1200 ° C, MnS is precipitated due to the high Mn of 0.42%, but B is hot-rolled as it is undeposited. Occasionally, single and fine B precipitates are formed, and crystal grain growth and iron loss are significantly deteriorated. Next, if the temperature is kept at 1100 ° C, the distribution of MnS becomes coarse and the number of nuclei in which BN is compositely precipitated becomes insufficient. It is considered that the diameter and iron loss could not be obtained. Table 3

(Experiment 4)

Next, in order to investigate the effect of the heating cycle of hot rolling, using a steel slab with Mn: 0.42% and Ti: 0.0013% in Experiment 2, holding the hot rolling at 1200 ° C for 60 minutes, 1100 ° The sample was hot-rolled by adding two levels of 60 minutes retention at C, and after pickling, samples were prepared in the same process as in Experiment 2 and compared. As shown in Table 4, as shown in Table 4, Sample 1 which had good results (Sample 5 in Experiment 2) had a low sulfide density but a high distribution density of Ti precipitates in Sample 2 kept at 1200 ° C. The crystal grain size and iron loss after strain relief annealing were the worst. On the other hand, in Sample 3, which was maintained at 1100 ° C, the Ti precipitate density was low, but the sulfide density was high, and neither the crystal grain size nor the iron loss was excellent. This result is considered as follows. First, when the temperature is kept at 1200 ° C, MnS coarsens in combination with the high Mn of 0.42% .However, since TiN is hot-rolled without precipitation, it is used during hot rolling and strain relief annealing. Occasionally, single and fine Ti precipitates are formed, and crystal grain growth and iron loss are significantly deteriorated. Next, when the temperature was kept at 1100 ° C, it is probable that the growth of MnS was insufficient, and the number of sulfides increased, resulting in no good crystal grain size and iron loss. Table 4

以上を総括すると、 本発明は Mn量と熱延の加熱サイクルの最適化 によ り、 MnSを優先かつ最適に析出させると同時に、 微細な BNを複 合析出させることで MnSおよび BNの双方を同時に無害化し、 結晶粒 成長および鉄損を改善する方策を知見したものである。 これを実現 するためには Mn量を高めると同時に A1量を低減させなければならな い。 なぜなら A1は A1Nと して Nを消費すると ともに、 A1N自身によつ て結晶粒成長が妨げられるからである。 一方、 A1を全く添加しない 製法では A1量は極めて低く抑えられるため、 BNの生成には好都合で あるが、 鋼中に多数残存する S i0₂ · MnOの介在物が Mn量の増加に伴 なって延伸化し、 かえって粒成長を悪化させてしまう。 そこで本発 明では介在物の改質による延伸抑制と、 BNの析出が優先する A1の最 適範囲として 0. 01%〜0. 04%を見出したのである。

To summarize the above, the present invention preferentially and optimally precipitates MnS by optimizing the amount of Mn and the heating cycle of hot rolling, and simultaneously precipitates both MnS and BN by multiple precipitation of fine BN. At the same time, they found measures to detoxify and improve crystal grain growth and iron loss. To achieve this, the amount of Mn must be increased and the amount of A1 must be reduced. This is because A1 consumes N as A1N, and the grain growth is prevented by A1N itself. Meanwhile, since it is extremely low in the amount of A1 in process without the addition of A1 at all, but it is convenient to generate the BN, inclusions S i0 ₂ · MnO which many remain in the steel becomes with the increase of the Mn amount In this case, the grain growth is worsened. Therefore, in the present invention, 0.011% to 0.04% was found as the optimum range of A1 in which the suppression of stretching by modifying the inclusions and the priority of BN precipitation are A1.

 In addition, the present invention optimizes the precipitation temperature of MnS and TiN, and optimizes the heating cycle of hot rolling, so that first, MnS is coarsely deposited, and then, fine TiN is compositely precipitated. They found a way to render the precipitates harmless and improve crystal grain growth and iron loss.

To achieve this, it is necessary to increase the Mn content to raise the MnS deposition temperature, and further reduce the A1 content to suppress the generation of A1N and promote the deposition of TiN. As a method for keeping the A1 content extremely low, there is a method using Si for deoxidation in steelmaking.In this case, if the Mn content is increased, inclusions are elongated and the iron loss is worsened. Find out It was. Therefore, in the present invention, by controlling the amount of Al to a relatively small range of 0.01 to 0.04%, it has become possible to increase the amount of Mn by modifying the inclusions while maintaining the precipitation of TiN. Furthermore, in this A1 content range, surplus N after TiN precipitation causes fine precipitation of A1N which is harmful to grain growth, so this was avoided by adding a small amount of B to BN.

 Such a technical idea was first discovered in the present invention. For example, in Japanese Patent Application Laid-Open No. 58-117828, Si: 0.1 to: L. 0%, Al: less than 0.1%, Mn to 0.75 to: L5%, N / B: 0.7 to 1.2 B content is stipulated, but there is no specification on the complex precipitation of MnS and BN and the amount of Sol.A1 to achieve it and the heating temperature of hot rolling. However, the technical idea is completely different from the present invention, and the present invention can not be inferred. Japanese Patent Application Laid-Open No. 2000-248344 specifies that Si: l.8% or less, Sol. A1: 0.05 to 0.20%, and Mn: 0.05 to 1.5%, but Sol. Since A1 析出 is preferentially precipitated rather than と and ΒΝ, the technical idea of the present invention of precipitating に with MnS as a nucleus does not hold.

 Next, the reasons for limiting the numerical values of the components and products in the present invention will be described.

 Si is an effective element for increasing electric resistance, but if added in excess of 1.5%, hardness increases, magnetic flux density decreases, and cost increases, so the upper limit was 1.5%.

Mn is an important element for expressing the present invention. The purpose of the present invention is to precipitate BN and / or TiN using sulfides containing MnS as nuclei, and for that purpose, MnS must be sufficiently precipitated before the deposition temperature of and / or TiN. . In the present invention in which Ti: 0.0015% or less, N: 0.0030% or less, and B / N of 0.5 or more and 1.5 or less, the object is achieved by setting Mn to 0.4% or more. You. If the content exceeds 1.5%, the saturation magnetic flux density is significantly reduced. The upper limit of 1.5% was set because the lowering of the γ → a transformation temperature made it difficult to control the structure of the hot-rolled sheet.

A1 is an element required for steel deoxidation. Oxygen non-deoxidized with less than Sol.0.01% is left in the steel to form oxides of Si0 ₂ · MnO, grain growth which was combined stretching of the effect of Mn which is added over 0.4% Therefore, the lower limit of Sol. A1 was set at 0.01%. If Sol. A1 exceeds 0.04%, A1N will precipitate instead of BN, making it difficult to realize the present invention. In addition, ensuring precipitation of TiN and utilizing scrap at customers Therefore, the upper limit of Sol. A1 was set to 0.04%.

Although Ti forms TiN and significantly deteriorates grain growth, it is industrially difficult to reduce it to zero because it is an unavoidable element. In the present invention, the upper limit is defined as 0.0015% as an allowable amount that can be rendered harmless by Mn S, Cu ₂ S, a composite sulfide thereof, and a composite precipitation. If the Ti content exceeds 0.0015%, the temperature at which TiN starts to precipitate becomes too high to control the preferential precipitation of MnS.

 N produces TiN and A1N in addition to BN. S. l. A1: In the present invention containing 0.01 to 0.04%, when A1N is formed, crystal grain growth is significantly deteriorated. Therefore, it is necessary to add B to suppress the formation of A1N. Therefore, the amount of B to be added must be increased as N becomes higher. However, excessive addition of B causes embrittlement of the steel sheet and lowers productivity, so the upper limit of N was set to 0.0030%.

 S is necessary for generating sulfide that becomes a precipitation nucleus of BN and / or TiN, and the object of the present invention is achieved by containing 0.0010% or more. However, if it exceeds 0.0040%, the amount of sulfide precipitation itself increases, and the grain growth is hindered, so the upper limit was made 0.0040%.

B is an element that must be added to suppress the generation of A1N that is harmful to crystal grain growth, but for that purpose it is necessary to add B / N of 0.5 or more. The effect is saturated even if it is added excessively to N, so the upper limit is B / N 1. It was set to 5.

Sn, Cu, Ni is annealed, particularly is effective in suppressing nitride Ya oxidation of the steel sheet surface during stress relief annealing, 3 ₀ 1.1: In the steel of the present invention containing 0.01 to 0 04%. Is particularly preferable because it is easily nitrided. If the addition amount is less than 0.01%, there is no effect, and if it exceeds 0.50%, the effect is saturated and the cost increases, so the addition amount range is 0.01% or more. 0.50% or less. Since the nitriding and oxidation inhibiting effects of Sn, Cu, and Ni are equivalent, it is sufficient that the above-mentioned addition amount range is satisfied by a single or a composite. In addition, it is also possible to add 0.001 to 0.5% of one or more of REM, Ca, and Mg.

 In particular, Sn is an extremely effective element for improving the magnetic flux density in the present invention. This is because, in the present invention, since the Mn is increased, the γ → transformation temperature is inevitably lowered, and the grain growth of the hot-rolled sheet cannot be sufficiently promoted. . If the amount of addition is less than 0.01%, there is no effect, and if it exceeds 0.50%, the effect will be saturated and the cost will increase, so the range of addition is 0.01% or more 0 50% or less. Furthermore, Sn also has the effect of suppressing nitriding and oxidation of the steel sheet surface during strain relief annealing, and it is desirable to add Sn also from that viewpoint.

 Regarding the composite precipitation characterized by the present invention, the number ratio of the sulfide containing Mn in which the B precipitate is compositely deposited is specified to be 10% or more. This is based on the results of observations on a single sample with almost no fine B precipitates.

The crystal grain size is an important factor for achieving both punching workability and magnetism. For steel sheets subjected to stamping, if the grain size exceeds 30 μιη, the punching workability deteriorates, so the crystal grain size was set to 30 μηι or less. For electrical products, the required iron loss cannot be satisfied if the grain size is less than 50 m, so the crystal grain size after 750 ° C x 2 hours of strain relief annealing, which is commonly used Was defined as 50 μm or more.

If MnS, Cu ₂ S and its complex sulfide are too large, they inhibit the grain growth. In order to obtain a crystal grain size of 50 μιη or more after strain relief annealing, the distribution density must be 3.0 X 10 ⁵ grains / mm ² or less. The distribution density described here refers to the number of precipitates in which Mn, S or Cu, S, or Mn, Cu, S is detected by observing a chemically polished sample after mirror polishing with a scanning or transmission electron microscope. It is divided by the observation visual field area (or the total area when multiple visual fields are observed).

The Ti precipitates can be rendered harmless by complex precipitation of sulfides as nuclei, even though they are fine enough to be less than 直径 .ΐμιη in diameter. Those with a grain size of 50 / m or more after strain relief annealing and good iron loss have a distribution density of Ti precipitates less than 0.1 μιη in diameter equivalent to 1.0 X 10 ³ / Since it was nun ² or less, this was set as the upper limit.

 Next, the reasons for limiting the manufacturing conditions in the present invention will be described.

The slab heating of hot rolling must be performed in two continuous cycles to detoxify BN and / or TiN using sulfides including MnS, Cu ₂ S and their composite sulfides as nuclei. In the steel of the present invention in which Mn is increased to 0.4% or more, precipitation and growth of MnS become remarkable in a temperature range of 1150 ° C or more, but solid solution progresses when the temperature exceeds 1250 ° C. Therefore, the heating temperature in the former stage was set to 1150 ° C or higher and 1250 ° C or lower. Since the growth rate of MnS is high, a residence time of 5 minutes or more in this temperature range is sufficient. Next, since the precipitation of TiN and BN on MnS proceeds at a temperature of less than 1150 ° C, the heating temperature in the subsequent stage is set to less than 1150 ° C, and the lower limit temperature is set to 1050 ° from the viewpoint of ensuring rollability. C. If the subsequent heating temperature is lower than 1050 ° C, the precipitation of TiN proceeds, but the formation of single and fine precipitates increases during hot rolling due to insufficient compounding with sulfides. The heating time in the latter stage was set to 15 minutes or more in consideration of the precipitation time of TiN and BN. Even better The magus lasts more than 30 minutes.

 The exit temperature of the finish rolling of hot rolling is higher than 800 ° C as much as possible at temperatures below γ → α transformation.Higher magnetic flux density results in higher magnetic flux density, but the temperature is moderated by the amount of Sn added Therefore, when Sn was added, it was specified as T≥900_1000XSn [% by mass] in consideration of the degree of relaxation.

Example 1

In a laboratory vacuum melting furnace, in mass%, C: 0.003%, Si: 0.55%, Mn: 0.12-0.96%, Sol. A1: 0.033%, Ti: 0.0008%, N: 0.0025%, S : 0.0032%, B: 0.0017%, Sn: 0.02 to 0.09%. These slabs were heated to 1230 ° C and held for 10 minutes, then cooled to 1120 ° C and held for 30 minutes, and then hot-rolled to a thickness of 2.5 mm. The exit temperature of the finish rolling was 855 ° C. The hot rolled sheet was pickled, cold rolled to a sheet thickness of 0.50 mm, subjected to finish annealing at 825 ° C for 10 seconds, and then subjected to strain relief annealing at 750 ° C for 2 hours. The crystal grain size, iron loss and magnetic flux density of the sample thus obtained were measured, and the precipitate was observed with a transmission electron microscope. As a result, as shown in Table 5, in Samples 7 to 12 with Mn of 0.4% or more, good iron loss was obtained when the average crystal grain size after strain relief annealing was 50 μιη or more, and the number ratio of composite precipitation Also exceeded 10%. In samples 8, 9, 11, and 12, which satisfy 855 ≥ 900-1000 XSn, a magnetic flux density about 0.02T higher was obtained.

Table 5

Example 2

In a laboratory vacuum melting furnace, in mass%, C: 0.003%, Si: 1.3%, Mn: 0.29 ~: 1.08%, Al: 0.027%, Ti: 0.0013%, N: 0.0019%, S: 0.0026 %, B: 0.0024%, and Sn: 0.07%. After heating these slabs to 1230 ° C, they were immediately cooled to 1090 ° C, held for 30 minutes, and then hot-rolled. During this heating, the slab stayed at a temperature of 1150 ° C or more for 15 minutes, and the exit temperature of finish rolling was 840 ° C. In addition, a test was conducted in which the steel sheet was heated at a constant temperature of 1230 ° C or 1090 ° C for 60 minutes and then immediately hot-rolled. The hot-rolled sheet thus obtained was pickled, cold-rolled to a sheet thickness of 0.50 mm, subjected to finish annealing at 850 ° C for 10 seconds, and then subjected to strain relief annealing at 750 ° C for 2 hours. After that, the crystal grain size, iron loss, and magnetic flux density were measured, and the precipitates were observed with a transmission electron microscope. As a result, as shown in Table 6, in samples 10 to 12 where Mn was 0.4% or more and the hot rolling temperature was a two-stage cycle from 1230 to 1090 ° C, the average grain size after strain relief annealing However, good iron loss was obtained when the particle size was 50 μm or more, and the number ratio of composite precipitates was 10% or more. In addition, each of them satisfies 840 ≥ 900-1000 XSn (= 0.07%) and has high magnetic flux density Degree was obtained. Table 6

Example 3

 In a laboratory vacuum melting furnace, 0.0038% by mass, Si: 0.51%, Mn: 0.12 to 0.84%, Sol. A1: 0.025%, Ti: 0.0008 to 0.0024%, N: 0.0025%, S : 0.0035% and B: 0.0016%. Immediately after the temperature of the steel slabs was raised to 1240 ° C, the temperature was lowered to 1120 ° C, held for 30 minutes, and hot-rolled to a sheet thickness of 2.7 mm. During this heating, the slab stayed at a temperature of 1150 ° C or more for 22 minutes, and the exit temperature of the finish rolling was 820 ° C. The hot-rolled sheet is pickled, cold-rolled to a sheet thickness of 0.50 mm, subjected to finish annealing at 825 ° C for 10 seconds, and then subjected to strain relief annealing at 750 ° C for 2 hours to obtain precipitates and grains of the steel sheet. The diameter was observed and the iron loss was measured.

As a result, samples 7 and 8 as shown in Table 7, Mn is the and Ti at 0.4% or more and 0.0015% or less, at 10, 11, sulfide density after stress relief annealing is 3.0 X10 ⁵ or less, the average crystal grain Good iron loss was obtained when the diameter was 50 / xm or more. In these samples, a large amount of spherical sulfides with a diameter of 0.2 to 0.3 μιη A large number of Ti precipitates were found on the outer periphery of the material. On the other hand, in samples with low Mn of 0.12 and 0.25%:! To 6, the sulfide density after strain relief annealing was high, the average crystal grain size was small, and iron loss was poor. The sulfides found in these samples were as small as 0.1 m or less in diameter, and many sulfides contained fine Ti precipitates. Samples 9 and 12 with Mn values of 0.4% or more, but with a content of more than 0015% also had a high sulfide density after strain relief annealing, a small average crystal grain size, and relatively poor iron loss. In these samples, the sulfides varied widely in the range of 0.05 to 0.3 m in diameter, and the composite morphology with Ti precipitates also varied at the outer or center of the sulfides. Note that the distribution density of Ti precipitates having a diameter less than 0.1 μμπι was as low as less than 1.0 × 10 ³ / mm ^{2 in} all samples.

 Table 7

Example 4

In a laboratory vacuum melting furnace, in mass%, C: 0.0022%, Si: 1.2%, Mn: 0.31 to 1.44%, Sol. Al: 0.03%, Ti: 0.0013%, N: 0.0016%, S : 0.0031%, B: 0.0021%, and Sn: 0.02%. Add these billets to 12 After the temperature was raised to 20 ° C, the temperature was immediately lowered to 1070 ° C, held for 20 minutes, and then hot rolled. In this heating, the slab stayed at a temperature of 1150 ° C or more for 15 minutes. In addition, a test was conducted in which hot rolling was performed immediately after heating at a constant temperature of 1220 ° C or 1070 ° C for 45 minutes. The hot-rolled sheet thus obtained was pickled, cold-rolled to a sheet thickness of 0.50 mm, subjected to finish annealing at 850 ° C for 5 seconds, and then subjected to strain relief annealing at 750 ° C for 2 hours. The precipitate and the crystal grain size were observed, and the iron loss was measured. As a result, as shown in Table 8, in Samples 12 to 15 where Mn was 0.4% or more and the heating temperature of hot rolling was 1220 → 1070 ° C, the sulfide density after strain relief annealing was 3.0 × 10 ⁵ Thereafter, the average crystal grain size became 50 μm or more, and good iron loss was obtained. In these samples, spherical sulfides with a diameter of 0.2 to 0.3 μιη were predominant, and many Ti precipitates were found on the outer periphery of the sulfides. In other samples, the sulfide density after strain relief annealing was high, or the Ti precipitate density was high, and the average crystal grain size was small, resulting in poor iron loss. Table 8

 Mn Sulfur density T Zelide density Crystal grain size W15 / 50

(%) ((Hi / ram ² ) (pcs / band ² ) (μηι) (Wkg) m

1 0.31 4.0X10 ⁵ ku 1.0X10 ³ 44 4.10

2 0.45 4.1X10 ⁵ 〈1.0 XI 40 4.05

3 1070. C 0.68 3.7X10 ⁵く L0X10 ³ 42 4.07 贿 row

4 1.03 3.4X10 ⁵ wards 1.0X10 ³ 44 4.04纖列

5 1.44 3.3X10 ⁵ οχι 41 4.03

6 0.31 4.7X10 ⁵ 5.5X10 ³ 32 4.64

7 0.45 2.7X10 ⁵ 5.7X10 ³ 30 4.51 Customer

8 1220 ° C 0.68 1.8X10 ⁵ 6.1X10 ³ 32 4.45 1: Read

9 1.03 1.3X10 ⁵ 7.7X1 33 4.36

10 1.44 1.2X10 ⁵ 7.2X10 ³ 34 4.41 ghost

11 0.31 3.5X10 ⁵ ku 1.0X10 ³ 44 4.02: 麵

12 0.45 2.6X1 οχιο ³ 57 3.71 Invention example

13 1220 → 1070 ° C 0.68 2.2X10 5 wards 1.0 XI 59 3.65 invention Example

14 1.03 1.8x10 ⁵ ° 1.0 × 10 ³ 64 3.54 invention Example

15 1.44 1.4 × 10 ⁵ ° 1.0 × 10 ³ 67 3.42 invention Example

Claims

The scope of the claims 1.% by mass, Si: 1.5% or less, Mn: 0.4% or more and 1.5% or less, Sol.Al: 0.01% or more and 0.04% or less, Ti: 0.0015% or less, N: 0.0030% or less, S: 0.0010% or more 0.0040% or less, B is 0.5 to 1.5 in B / N, the balance consists of Fe and unavoidable impurities, and at least 10% of the sulfides containing Mn are precipitated with B precipitates by number ratio. Non-oriented electrical steel sheet characterized by the above-mentioned.  2. By mass%, Si: 1.5% or less, Mn: 0.4% or more and 1.5% or less, Sol. A1: 0.01% or more and 0.04% or less, Ti: 0.0015% or less, N: 0.0030% or less, S: 0.0010% or more 0.0040% or less, B in B / N 0.5 or more and 1.5 or less, and the grain size of the steel sheet consisting of the balance of Fe and unavoidable impurities is 30 μm or less and after strain relief annealing at 750 ° C X2 hours Non-oriented electrical steel sheet having a crystal grain size of 50 μπι or more. 3. The non-oriented electrical steel sheet according to claim 1, wherein the total distribution density of MnS, Cu ₂ S and its composite sulfide is 3.0 × 10 ⁵ / mm ² or less. 4. Furthermore, the non-oriented electrical according to any one of claims 1-3, characterized in that the fabric density of Ti precipitates of less than the diameter Ο.ΐμπι is 1.0 × 10 ³ cells / mm ² or less steel sheet. 5. In addition, 0.001 to Sn, Cu, 0.50% 0.0 1% or more of one or two or more kinds in a total mass% of Ni or less, and / or REM, Ca, over one or more kinds of M _g The non-oriented electrical steel sheet according to any one of claims 1 to 4, characterized by containing 0.1%. 6. As a method for producing the steel sheet according to any one of claims 1 to 5, a steel sheet, hot rolling, pickling, and cold rolling are performed, followed by finish annealing. Regarding heating, keep for 5 minutes or more in the range of 1150 ° C or more and 1250 ° C or less, and continuously for 15 minutes in the range of 1050 ° C or more and less than A method for producing non-oriented electrical steel sheets, comprising hot rolling immediately after residence for at least one minute.  7. As a method for producing the steel sheet according to any one of claims 1 to 6, the steel sheet, hot rolling, pickling, and cold rolling are subjected to finish annealing, followed by finishing of hot rolling. A method for producing a non-oriented electrical steel sheet, wherein the outlet temperature of rolling is 800 ° C or higher.  8. The non-directional electromagnetic device according to claim 6, wherein the finishing outlet temperature T (° C.) of the hot rolling is set to T 900-1000 X Sn [mass%] in the steel sheet containing Sn. Steel plate manufacturing method.