JP3873300B2 - Method for producing grain-oriented silicon steel sheets with excellent magnetic properties - Google Patents

Description

【００６６】
これらのコイルは、３％のTiO₂および２％の Sr(OH)₂・8H₂Oを含有しMgO を主成分とする焼鈍分離剤を鋼板表面に塗布した後、コイル状に巻き取り、N₂中で 840℃45ｈの保持を行った後、15℃/hの昇温速度で25％N₂および75％H₂の雰囲気で1200℃まで昇温し、H₂中で1200℃，10ｈ保持した後降温する、最終仕上焼鈍を施した。その後、未反応の焼鈍分離剤を除去した後、平坦化処理を兼ねて張力コーティングを塗布焼付けて製品とした。かくして得られた製品の磁気特性を、表２に併記する。
【００６７】
【表２】

【００６８】
実施例２
表１に記載した鋼スラブＣを熱間圧延後、1150℃で１分間の熱延板焼鈍を施した後、ミスト水を用いて40℃/sの冷却速度で室温まで冷却した。その後、18％のHCl 水溶液で酸洗してから、 120mm径のワークロールを有するセンジミア圧延機を用いて、0.26mmの最終板厚とした。ここで、コイル表面の酸化物量は0.25〜0.32 g/m² であった。
【００６９】
次に、脱炭焼鈍の前処理として、オルソ珪酸ソーダ浴を用いて電解脱脂し、Siを含有する電着物を 0.9〜1.2 mg/m² で付着させた。このコイルに、50％H₂および残余N₂バランスの雰囲気（露点60℃，Ｐ(H₂O) ／Ｐ(H₂)：0.47）で 850℃，２分間の脱炭焼鈍を行った後、２分割し、一方をN₂雰囲気（露点−10℃， H₂O分圧：0.25％）で 890℃において15秒間の酸化物の分解再生成高密度化処理を施した。残る一方は、そのまま次工程の処理へ廻した。
【００７０】
これらのコイルは、10％TiO₂および２％の Sr(OH)₂・8H₂Oを含有しMgO を主成分とする焼鈍分離剤を鋼板表面に塗布した後、コイル状に巻き取り、25％N₂および75％H₂雰囲気で 850℃まで25℃/h 850℃から1200℃まで12℃/hの昇温速度で昇温し、H₂中1200℃, 10ｈの保持を行った後、降温する最終仕上焼鈍を施した。
その後、未反応の焼鈍分離剤を除去した後、平坦化処理を兼ねて張力コーティングを塗布焼付け、さらに６mm間隔で圧延方向と直角の向きに線状微小歪みをプラズマジェットによって導入し、製品とした。かくして得られた製品の磁気特性を表３に示す。
【００７１】
【表３】

【００７２】
実施例３
Ｃ：0.043 重量％, Si：3.32重量％, Mn：0.07重量％, Ｐ：0.007 重量％, Al：0.001 重量％, Ｓ：0.003 重量％, Se：0.018 重量％, Mo：0.012 重量％およびSb：0.025 重量％を含有し、残部Feと不可避的不純物からなるけい素鋼スラブ２本を熱間圧延し、1000℃, 30秒間の熱延板焼鈍を施した後、0.64mmの板厚とした。その後、75％H₂および残余N₂バランスの雰囲気（露点35℃）で975 ℃，30秒間の中間焼鈍を行い、冷却後表面を研削した。このとき、一方のコイルは軽い研削を行って表面スケールを若干残存させ、他方のコイルは強い研削を行って表面スケールを完全に除去した。その後、双方のコイルとも、タンデム圧延機で低粘度油を用いて0.20mmの最終板厚とした。このとき、鋼板表面に残存する酸化物の量を酸素目付量によって測定したところ、軽研削のコイルは鋼板両面で0.12〜0.23 g/m² 、強研削のコイルは鋼板両面で0.01〜0.02 g/m² であった。
【００７３】
次に、脱炭焼鈍の前処理として、オルソ珪酸ソーダ浴を用いて電解脱脂し、Siを含有する電着物を 1.5〜2.3 g/m²付着させた。これらのコイルを２分割し、一方は55％H₂および残余N₂バランスの雰囲気（露点63℃，Ｐ(H₂O) ／Ｐ(H₂)：0.50）で820 ℃，２分間の前期脱炭焼鈍を行い、引続いて10％H₂および残余N₂バランスの雰囲気（露点５℃，H₂0 分圧：0.86％）下で 980℃，10秒間の酸化物の分解再生成高密度化処理を施した。
他方のコイルは、比較として、同じく55％H₂および残余N₂バランス（露点63℃，Ｐ(H₂O) ／Ｐ(H₂)：0.50）の雰囲気で 820℃，２分間の前期脱炭焼鈍を行い、引続いて 100％H₂の雰囲気（露点−40℃， H₂O分圧：0.01％) 下で1000℃，10秒間の酸化物の分解再生成高密度化処理を施した。
【００７４】
これら４つのコイルは、 1.5％のTiO₂および 1.5％の SrSO₄を含有しMgO を主成分とする焼鈍分離剤を鋼板表面に塗布した後、コイル状に巻き取り、N₂中で 850℃，50ｈ保持後、25％N₂および75％H₂雰囲気で20℃/hの昇温速度で1200℃まで昇温し、H₂中で1200℃, 10ｈ保持した後降温する、最終仕上焼鈍を施した。
その後、未反応の焼鈍分離剤を除去した後、平坦化処理を兼ねて張力コーティングを塗布焼付けて製品とした。かくして得られた製品の磁気特性を表４に示す。
【００７５】
【表４】

【００７６】
【発明の効果】
この発明によれば、磁束密度の高い方向性けい素鋼板を安定して製造することができ、とりわけ方向性けい素鋼板の工業的規模での生産における効果は極めて大きい。
【図面の簡単な説明】
【図１】脱炭焼鈍の前処理法および鋼板表面へのSi含有電着物の付着量と磁気特性との関係を示した図である。
【図２】脱炭焼鈍の前処理条件と脱炭焼鈍板の耐酸化性および耐窒化性との関係を示した図である。
【図３】最終冷間圧延後の鋼板表面に残留する酸化物量を示す酸素目付量と磁気特性との関係を示した図である。
【図４】脱炭焼鈍前期の雰囲気のＰ(H₂O) ／Ｐ(H₂)と磁気特性との関係を示した図である。
【図５】脱炭焼鈍後期処理の雰囲気と磁気特性との関係を示した図である。
【図６】脱炭焼鈍後期処理の温度および時間と磁気特性との関係を示した図である。
【図７】鋼板表面の酸化物の分解再生成高密度化処理によって酸化物の組成と酸化物粒子分布が変化する状態を示した模式図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a grain-oriented silicon steel sheet having excellent magnetic properties, and more particularly to a production method advantageous for improving magnetic flux density.
[0002]
Oriented silicon steel sheets are used as iron cores for transformers, generators, etc. As magnetic properties, magnetic flux density (magnetic flux B at a magnetizing force of 800 A / m₈ Iron loss (maximum magnetic flux density 1.7 T and frequency 50 Hz, iron loss W / kg)_17/50(Indicated by the value) is required to be low.
[0003]
[Prior art]
In recent years, in order to reduce the magnetic properties of grain-oriented silicon steel sheets, especially iron loss, a technology has been developed to subdivide magnetic domains by introducing local strains or forming grooves on the steel sheet surface. Iron loss can be improved. In particular, this technique is extremely effective when applied to a steel plate having a high magnetic flux density, and a reduction in iron loss is achieved in conjunction with an increase in magnetic flux density.
[0004]
In order to improve the magnetic flux density of grain-oriented silicon steel sheets, it is necessary to highly accumulate the crystal orientation of the product in the (110) [001] orientation, the so-called Goth orientation. In the secondary recrystallization phenomenon.
Therefore, in secondary recrystallization, it is necessary to preferentially grow crystal grains close to the (110) 001 orientation and suppress the growth of crystal grains in other orientations. It is essential to add an inhibitor that suppresses growth. This inhibitor contributes to the improvement of the magnetic flux density by forming a precipitated dispersed phase in steel and suppressing the growth of primary recrystallized grains (normal grain growth) until immediately before secondary recrystallization. However, in the actual manufacturing process, it has often been a problem that grains whose crystal orientation is deviated from the (110) 001 orientation are secondarily recrystallized to produce a steel sheet having a deteriorated magnetic flux density.
[0005]
According to the investigation conducted by the inventors about this problem, the surface of the steel sheet is oxidized in the annealing for secondary recrystallization (final finish annealing), and the inhibitors on the surface layer of the steel sheet are decomposed and disappeared. It was found that the normal grain growth inhibitory power in the steel sheet surface layer was insufficient before recrystallization.
[0006]
In order to suppress the decomposition and disappearance of the inhibitor in the steel plate surface layer during the final finish annealing, use the oxide layer (subscale) formed on the steel plate surface in the decarburization annealing, which is the pre-process of the final finish annealing. Can be considered. That is, when an oxide layer is present on the steel sheet surface, if this oxide layer becomes an obstacle to the diffusion of elements such as O, Mn, Al, etc., the oxidation of these elements can be suppressed, resulting in the decomposition of the inhibitor. And disappearance is also suppressed.
[0007]
Based on this technical idea, as a result of intensive studies on the composition of the oxide layer that can contribute to the suppression of oxidation, we developed a technology to control the ratio of firelite and silica within a certain range as the composition of the oxide layer on the steel sheet surface. This is proposed in Japanese Patent Laid-Open No. 4-20271.
[0008]
[Problems to be solved by the invention]
However, even with this technique, it is difficult to stabilize the magnetic properties in industrial production, and in particular, it has been difficult to stably produce a directional silicon steel sheet having a high magnetic flux density.
Accordingly, an object of the present invention is to propose a novel method for producing a grain-oriented silicon steel sheet capable of stably obtaining a high magnetic flux density product even in industrial production.
[0009]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the inventors have adjusted the amount of oxide present on the steel sheet surface after the final cold rolling to a specific range, an electrolytic degreasing method prior to decarburization annealing. To obtain knowledge that stable improvement of magnetic flux density can be realized by applying a predetermined amount of electrodeposits containing Si to the steel plate surface by controlling the atmosphere of decarburization annealing. It was. The present invention is based on the above findings.
[0010]
That is, in the present invention, hot rolling is applied to a silicon-containing steel slab, and then a final sheet thickness is obtained by one or a plurality of cold rolling sandwiching intermediate annealing, followed by decarburization annealing and application of an annealing separator. In producing a grain-oriented silicon steel sheet by a series of processes for final finishing annealing, the amount of oxide on the steel sheet surface after the final cold rolling is 0.05 to 0.35 g / m in terms of oxygen basis weight.²Before the decarburization annealing, the electrodeposit containing Si is 0.1 mg / m on the steel sheet surface by electrolytic degreasing.²The adhering cleaning process is performed, and then the ratio of the water vapor partial pressure to the hydrogen partial pressure in the atmosphere (hereinafter referred to as P (H₂O) / P (H₂) Is adjusted to 0.30 to 0.65, and the temperature in the atmosphere is adjusted to 850 to 950 ° C. and the partial pressure of water vapor is adjusted to 0.05 to 3.0% to decompose and regenerate the oxide on the steel sheet surface. It is the manufacturing method of the grain-oriented silicon steel plate excellent in the magnetic characteristic characterized by performing the decarburization annealing which consists of the latter stage which performs.
[0011]
Next, various experimental results on which the present invention is based will be described.
In addition, the material used for the experiment contained C, Si, and Al as essential components. This is because C is a component useful for improving the structure in hot rolling and cold rolling, Si is a component useful for increasing electrical resistance and improving iron loss, and Al is an inhibitor component. This is because it is a component useful for improving the next recrystallized grain orientation, that is, improving the magnetic flux density.
[0012]
Experiment 1
C: Hot rolling on three steel slabs containing 0.065 wt%, Si: 3.25 wt%, Mn: 0.070 wt%, Al: 0.025 wt%, Se: 0.020 wt% and Sb: 0.025 wt%, respectively After that, hot-rolled sheet annealing is performed at 1000 ° C. for 1 minute, and the thickness is 1.50 mm by the first cold rolling.₂ After annealing at 1100 ° C for 60 seconds in an atmosphere (dew point of 40 ° C) and using mist water to rapidly cool to 350 ° C at a cooling rate of 40 ° C / s, hold at 350 ° C for 20 seconds, then to room temperature Cooled down.
[0013]
Next, after intermediate annealing, the scale on the steel plate surface was lightly removed with a grinding brush, and a final plate thickness of 0.22 mm was obtained using a Sendzimir rolling mill equipped with a 210 mm diameter roll. The amount of oxide on the steel sheet surface on both sides of the coil after the final cold rolling is 0.15 g / m in terms of oxygen basis weight.²Met.
[0014]
Thereafter, as a pretreatment for decarburization annealing, the surface of the steel sheet was cleaned. That is, the first coil was passed through a 15% NaOH aqueous solution and brushed, then rinsed with pure water and dried. Similarly, the second coil was passed through a 15% NaOH aqueous solution and brushed, then passed through a 20% aqueous HCl solution, then rinsed with pure water and dried. The third coil was divided into 10 to a to j, and each divided coil was passed through a sodium orthosilicate bath, rinsed with pure water and dried. Here, when passing through the orthosilicate sodium bath, an alternating current was applied to the split coils other than the split coil a, and the surface of the steel sheet was cleaned by electrolytic degreasing. The split coil b has 1.0 A / dm²− + Alternating current is added, and the divided coils c to j are respectively 0.01, 0.1, 0.5, 1.0, 3.0, 5.0, 8.0, 15 A / dm.²A + − alternating current was added.
[0015]
As a result of these pretreatments, the surface of the steel plate was clean, but the second coil was melted over the thickness of 0.2 μm in the steel plate surface, and the third coil had split coils c to j. The electrodeposit containing Si adheres to the surface of the steel sheet, and the adhesion amount is 0.03 mg / m in the split coil c.² In the same d, 0.06mg / m²In the same e, 0.10mg / m²In the same f, 0.34mg / m²In the same g, 0.54mg / m²In the same h, 1.36mg / m²In the case of i, 2.4 mg / m²In the same j, 4.0 mg / m²Met.
[0016]
Furthermore, each of the 12 types of coils is divided into 2 groups and divided into 2 groups.₂And residual N₂Balance atmosphere (dew point 60 ° C, P (H₂O) / P (H₂): 0.39) Continuous decarburization annealing was performed at 840 ° C. for 2 minutes. For the remaining 12 types of coils, 50% H₂And residual N₂After performing continuous decarburization annealing at 840 ° C for 2 minutes in a balanced atmosphere (dew point 60 ° C), dew point -10 to -4 ° C (H for 10 seconds at 880 ° C)₂O partial pressure: 0.25 to 0.43%) dry N₂Heat treatment was performed under an atmosphere.
[0017]
These coils are then 5% TiO₂And 2% Sr (OH)₂・ 8H₂An annealing separator containing O2 and MgO as the main component was applied to the surface of the steel sheet, wound up in a coil, and heated up to 1200 ° C at a rate of 15 ° C / h with 25% N₂And 75% H₂The temperature was increased in a mixed atmosphere of₂After being held at 1200 ° C. for 10 hours in the atmosphere of the above, final finish annealing for lowering the temperature was performed. Then, after removing the unreacted annealing separator in each coil, a tension coating that also serves as a flattening treatment was applied to the surface of the steel sheet and baked to obtain a product. The magnetic properties of the product coil thus obtained are shown in FIG.
[0018]
As shown in FIG. 1, as a pretreatment for decarburization annealing, an electrolytic degreasing method is adopted and an electrodeposit containing Si on the steel sheet surface is 0.1 mg / m 2.²A product with excellent magnetic properties with a high magnetic flux density was obtained when it was attached as described above and further subjected to heat treatment after decarburization annealing.
[0019]
In addition, in order to elucidate the reason why these excellent magnetic properties were obtained, each decarburized annealed plate was treated with 25% N₂And 75% H₂In the mixed atmosphere (dew point 20 ° C), heat treatment was performed at 900 ° C for 30 minutes, and the oxidation behavior and nitridation behavior were investigated. As a result, as shown in FIG. 2, it was found that oxidation and nitridation of the steel sheet were suppressed under the condition that a material having a high magnetic flux density was obtained.
That is, if oxidation and nitridation at the steel sheet surface layer portion are suppressed, the inhibitor of the steel sheet surface layer portion is maintained in a good state in the final finish annealing, and it is estimated that appropriate secondary recrystallization was obtained. Is done.
[0020]
Furthermore, the heat treatment performed after decarburization annealing decomposes oxides on the surface of the steel sheet, and then regenerates fine oxide particles so that the oxide particles on the surface of the steel sheet are dispersed and generated at a high density, as will be described later. Therefore, since it has an action of suppressing diffusion of oxygen and nitrogen, it is referred to as a decomposition / regeneration / densification treatment of oxides on the surface of the steel sheet.
[0021]
Experiment 2
Sixteen steel slabs with the same composition as in Experiment 1 were each hot-rolled, then hot-rolled sheet annealed at 1000 ° C for 1 minute, and the first cold-rolled thickness was 1.80 mm. And then 25% N₂And 75% H₂In the mixed atmosphere (dew point 45 ° C), the intermediate annealing was performed at 1100 ° C for 60 seconds, quenched with mist water at a cooling rate of 45 ° C / s to 350 ° C, and then held at 350 ° C for 120 seconds. Cooled to room temperature.
[0022]
Subsequently, after passing through an aqueous HCl solution of various concentrations and temperatures to remove the oxide surface layer, cold rolling was performed to obtain a final thickness of 0.19 mm. Cold rolling was performed using the same Sendzimer mill as in Experiment 1. The amount of oxide on the steel sheet surface on both sides of the coil after the final cold rolling is 0.012, 0.022, 0.031, 0.054, 0.073, 0.103, 0.150, 0.205, 0.248, 0.280, 0.298, 0.350, 0.381, respectively. 0.400, 0.423, 0.430 mg / m²Met.
[0023]
These 16 types of coils are further divided into 2 groups and divided into 2 groups. As a pretreatment for decarburization annealing, 16 types of coils are rinsed with pure water after alkaline degreasing in 15% NaOH aqueous solution. The remaining 16 sets of coils were subjected to electrolytic degreasing by passing an alternating current of − ++ − + when passing through the sodium orthosilicate bath, and 1.0 to 2.5 mg / m 2²After depositing an electrodeposit containing Si, the surface of the steel sheet was rinsed with pure water.
[0024]
After that, each coil is 45% H₂And residual N₂Decarburization annealing at 850 ° C for 2 minutes under a balanced atmosphere (dew point 60 ° C), followed by 65% H in the same continuous annealing furnace₂And residual N₂Balance atmosphere (dew point -5-5 ℃, H₂O partial pressure: 0.46 to 0.86%) and continuous annealing at 860 ° C for 15 seconds.
[0025]
These coils are then 10% TiO₂And 3% Sr (OH)₂・ 8H₂An annealing separator containing O and MgO as the main component was applied to the surface of the steel sheet, and then wound up in a coil shape and N for 35 hours at 850 ° C.₂25% N at a rate of 15 ° C / h after holding in₂And 75% H₂The temperature is raised to 1200 ° C in a mixed atmosphere of₂After being held at 1200 ° C. for 10 hours in the atmosphere of the above, final finish annealing for lowering the temperature was performed. Then, after removing the unreacted annealing separator in each coil, a tension coating that also serves as a flattening treatment was applied to the surface of the steel sheet and baked to obtain a product. The magnetic characteristics of the product coil thus obtained are shown in FIG.
[0026]
From FIG. 3, 0.05 to 0.35 g / m in terms of the oxygen basis weight on the surface of the steel sheet after the final cold rolling.²When the electrolytic degreasing method is used as a pretreatment for decarburization annealing and an electrodeposit containing Si is attached to the steel sheet surface, a product with high magnetic flux density and excellent magnetic properties can be obtained. You can see that
[0027]
In addition, in order to elucidate the reason why excellent magnetic properties were obtained, each decarburized annealed plate was treated with 25% N₂And 75% H₂In a mixed atmosphere (dew point 20 ° C), heat treatment was performed at 900 ° C for 30 minutes to investigate the oxidation behavior and nitridation behavior. Oxidation and nitridation were suppressed.
[0028]
Experiment 3
A steel slab having the same composition as in Experiment 1 was hot-rolled, then subjected to hot-rolled sheet annealing at 1050 ° C. for 1 minute, and after the first cold rolling to a thickness of 1.40 mm, 25 % N₂And 75% H₂In the mixed atmosphere (dew point 45 ° C), intermediate annealing was performed at 1050 ° C for 60 seconds, quenched with mist water at a cooling rate of 40 ° C / s to 300 ° C, and then held at 300 ° C for 60 seconds. Cooled to room temperature. Thereafter, the outer scale of the steel sheet was removed by pickling with a 15% HCl aqueous solution. Thereafter, a final thickness of 0.19 mm was obtained using a Sendzimir rolling mill equipped with 200 mm diameter rolls. In addition, the amount of oxide on the steel sheet surface on both sides of the coil after the final cold rolling is 0.12 g / m in oxygen basis weight.²Met.
[0029]
Next, as a pretreatment for decarburization annealing, electrolytic degreasing is performed in a sodium orthosilicate aqueous solution, and an electrodeposit containing Si is 0.8 to 1.2 mg / m 2.²After adhering, this coil is divided into 8 parts and P (H₂O) / P (H₂) Was decarburized and annealed at 850 ° C. for 2 minutes.
[0030]
That is, H₂And N₂By changing the mixing ratio and changing the dew point of the atmosphere, P (H₂O) / P (H₂) Was decarburized and annealed in an atmosphere of 0.05, 0.15, 0.20, 0.30, 0.45, 0.55, 0.65, 0.70, and 0.75, respectively. These 8 types of coils are 60% H₂And residual N₂Balance atmosphere (dew point 2-4 ° C, H₂(O partial pressure 0.70 to 0.92%) Continuous annealing was performed at 870 ° C for 20 seconds.
[0031]
Then these coils are 10% TiO₂And 3% Sr (OH)₂・ 8H₂After coating MgO containing O as an annealing separator on the surface of the steel sheet, it was wound up in a coil and N for 15 hours at 850 ° C.₂25% N at a rate of 15 ° C / h after holding in₂And 75% H₂The temperature is raised to 1200 ° C in a mixed atmosphere of₂A final finish annealing was performed in which the temperature was lowered after holding at 1200 ° C. for 10 hours. Then, after removing the unreacted annealing separator in each coil, a tension coating that also serves as a flattening treatment was applied to the surface of the steel sheet and baked to obtain a product. As shown in FIG. 4, the magnetic properties of the product coil thus obtained are shown in FIG.₂O) / P (H₂) Between 0.30 and 0.65, excellent magnetic properties with high magnetic flux density were obtained.
[0032]
In addition, in order to elucidate the reason why these excellent magnetic properties were obtained, each decarburized annealed plate was treated with 25% N₂And 75% H₂In a mixed atmosphere (dew point 20 ° C), heat treatment was performed at 900 ° C for 30 minutes to investigate the oxidation behavior and nitridation behavior. Oxidation and nitridation were suppressed.
[0033]
Experiment 4
Next, the optimum condition was investigated about the decomposition regeneration density densification process with respect to the oxide of the steel plate surface following decarburization annealing.
A steel slab with the same composition as in Experiment 1 was hot rolled into a 2.0 mm thick coil and wet N₂Hot-rolled sheet annealing was performed at 1150 ° C for 1 minute in an atmosphere (dew point 35 ° C), then cooled to room temperature with an average cooling rate of 40 ° C / s using mist water, and then pickled with 15% HCl aqueous solution Thus, the oxide surface layer of the steel sheet was removed.
[0034]
  This coil was cold-rolled to a final sheet thickness of 0.26 mm by a Sendzimir mill having a 200 mm diameter work roll. The oxide present on the surface of the steel sheet after cold rolling should have an oxygen basis weight.0.12 ~ 0.15g / m²Met.
[0035]
Next, as a pretreatment for decarburization annealing, electrolytic degreasing in an aqueous sodium orthosilicate solution is performed, and an electrodeposit containing Si is 0.5 to 0.8 mg / m 2.²After attaching, 55% H₂And residual N₂Was decarburized and annealed at 850 ° C for 100 seconds under the above conditions (dew point 65 ° C).
This coil was divided into 126 parts, and each coil was subjected to various heat treatments shown below.
[0036]
[Heat treatment atmosphere conditions]
Of the divided coils, 35 coils were heat treated for 20 seconds at 870 ° C and 100% H each.₂H to gas₂O 2, 75% H₂And 25% N₂H to gas₂O-containing, 50% H₂And 50% N₂H to gas₂Containing O 2 and 25% H₂And 75% N₂H to gas₂O-containing, 100% N₂H to gas₂Performed in an atmosphere containing O 2. In addition, it contains H₂The amount of O was 0.1%, 0.3%, 1.5%, 3.8%, 8.5%, 13.5%, and 18.2% in terms of gas partial pressure.
[0037]
After this heat treatment, 10% TiO was obtained for 41 coils including one coil that was not subjected to this heat treatment.₂And 4% Sr (OH)₂・ 8H₂An annealing separator containing MgO containing O as the main component is applied to the surface of the steel sheet, and then wound into a coil shape.₂After holding at 840 ° C for 40 hours, 25% N at a temperature rise rate of 15 ° C / h₂And 75% H₂The temperature is raised to 1200 ° C in a mixed atmosphere of₂A final finish annealing was performed in which the temperature was lowered after being maintained at 1200 ° C. for 10 hours in the atmosphere.
[0038]
Then, after removing the unreacted annealing separator in each coil, a tension coating that also serves as a flattening treatment was applied to the surface of the steel sheet and baked to obtain a product. The magnetic characteristics of the product coil thus obtained are shown in FIG. In addition, the magnetic flux density of the product which did not perform this heat processing is B₈The value was 1.865 T.
To obtain a product with high magnetic flux density from FIG.₂And H₂Regardless of the mixing ratio with₂It can be seen that the O 2 content needs to be 0.05-3.0%.
[0039]
[Heat treatment temperature and time conditions]
Using the remaining 90 coils, 40% N₂And 60% H₂H in a mixed atmosphere₂Heat treatment was performed in an atmosphere containing 1.8% O 2. Here, the heat treatment is performed at a temperature of 800, 825, 850, 875, 900, 925, 950, 975, 1000 ° C. and a time of 2, 3, 5, 10, 15, 20, 30, 40, 50, 60. These were combined in 10 levels per second.
[0040]
After such heat treatment, these 90 kinds of split coils are 10% TiO₂And 4% Sr (OH)₂・ 8H₂An annealing separator containing MgO containing O as the main component is applied to the surface of the steel sheet, and then wound into a coil shape.₂After holding at 840 ° C for 40 hours, 25% N at a temperature rise rate of 15 ° C / h₂And 75% H₂The temperature was raised to 1200 ° C in a mixed atmosphere of₂The temperature was raised to 1200 ° C in an atmosphere of₂A final finish annealing was performed in which the temperature was lowered after holding at 1200 ° C. for 110 hours in the above atmosphere.
[0041]
Then, after removing the unreacted annealing separator in each coil, a tension coating that also serves as a flattening treatment was applied to the surface of the steel sheet and baked to obtain a product. As shown in FIG. 6 for the magnetic properties of the product coil thus obtained, it can be seen that the optimum conditions for temperature and time are in the range of 850 to 950 ° C. for 5 to 40 seconds.
[0042]
Each decarburized annealed plate is 25% N₂And 75% H₂In a mixed atmosphere (dew point 20 ° C), heat treatment was performed at 900 ° C for 30 minutes to investigate the oxidation and nitriding behavior. As in Experiments 1 and 2, the conditions under which a material with a high magnetic flux density was obtained The oxidation and nitridation of the steel sheet were suppressed.
[0043]
In addition, 0.05% to 0.35% H₂In order to investigate in detail the reason why oxidation and nitridation are suppressed when heat treatment is performed in an O partial pressure atmosphere, a SEM photograph of the cross section of the steel sheet was observed.₂SiO_Four) Is decomposed according to the reaction represented by the following formula (1), and silica (SiO₂It was found that fine grains of) were formed at high density.
[Expression 1]
Fe₂SiO_Four+Si  → 2SiO₂+2Fe            ----- (1)
[0044]
That is, as shown in FIG. 7 (a), the oxide produced on the decarburized annealed plate generally produces firelite on the surface side and silica on the ground iron side. In particular, since firelite is generated on the surface side having a high oxygen partial pressure, it is formed as coarse particles as shown in FIG.
[0045]
Where H₂When heat treatment is performed in an atmosphere with an O partial pressure of 0.05 to 3.0%, as shown in FIG. 7 (b), a part of the firelite is decomposed into silica, iron and oxygen, and a small amount of Si in which oxygen is dissolved in iron. To form more silica. Silica produced by decomposition and silica combined with trace amounts of Si dissolved in iron are extremely fine particles and are present in the subscale at a high density. It has a great effect of preventing the diffusion of nitrogen and nitrogen. For this reason, the steel sheet is protected from oxidation and nitriding during the final finish annealing, and the initial state of the inhibitor is maintained until the secondary recrystallization, and good magnetic properties are obtained. Therefore, this heat treatment is referred to as a decomposition / regeneration / densification treatment of oxides on the steel sheet surface.
[0046]
  In order to generate fine silica particles in the oxide at a high density by the decomposition, regeneration, and densification of the oxide on the surface of the steel sheet, it is necessary that sufficient firelite particles exist before the treatment. .
  That is, the oxide existing on the surface of the steel sheet after the final cold rolling is made an oxygen basis weight.0.05 ~ 0.35g / m²As a pretreatment for decarburization annealing, an electrodeposit containing Si on the steel sheet surface is 0.1 mg / m2 by electrolytic degreasing.²In the first stage of the decarburization annealing and the cleaning treatment adhering to P (H₂O) / P (H₂It has been newly found out that setting 0.3) to 0.30 to 0.65 has an effect of increasing the firelite in the oxide formed by decarburization annealing.
[0047]
In addition, when the temperature is too low or the time is too short as a condition for the oxide regenerating / densifying and densifying treatment, the progress of the reaction of decomposition of firelite and regeneration of fine silica is slow, When the temperature is too high, the particle size of silica regenerated by the decomposition of the firelite becomes coarse, and the subscale oxidation and nitridation suppression functions do not function sufficiently. On the other hand, if the treatment time is too long, the firelite is completely decomposed and disappears. It will be suppressed and the magnetic properties will deteriorate.
[Expression 2]
2x MgO + Fe₂SiO_Four  → (Mg_xFe_1-x)₂SiO_Four+ 2xFeO ----- (2)
[0048]
In addition, a technique for performing a heat annealing treatment on a decarburized annealed plate at 890 to 1050 ° C. in a non-oxidizing raw atmosphere is disclosed in Japanese Examined Patent Publication No. 54-24686. Is non-oxidizing and H₂O Partial pressure is 0.01% or less. Also, the heat treatment temperature is as high as 890 ° C or higher, and there is no description about firelite and silica which are oxides in the subscale, so fine SiO₂This is a technique different from the present invention, which is a technique for distributing and regenerating the image.
[0049]
In Japanese Patent Publication No.57-1575, decarburization annealing is divided into the first half and the second half, and P (H₂O) / P (H₂) Is decarburized annealing technology that lowers the first half, but this is a P (H₂O) / P (H₂) To change the generated oxide, and therefore H₂And H₂The ratio of O partial pressure is a problem. That is, H₂This is essentially different from the present invention, in which the partial pressure of O is controlled to a certain value or less to decompose the firelite to regenerate silica, and the difference between them is, for example, 100% N₂Trace amounts of H in the atmosphere₂It is clear if the suitability for the case where O is contained is evaluated. Furthermore, the publication does not describe firelite and silica which are oxides in the subscale, and there is no suggestion of a treatment for increasing the firelite and fine dispersion of silica.
[0050]
As described above, in the manufacturing process of the grain-oriented silicon steel sheet, the present invention appropriately adjusts the amount of residual oxide on the steel sheet surface after the final cold rolling, and then, as a pretreatment for decarburization annealing, an electrolytic degreasing method The electrodeposit containing Si on the steel sheet surface is 0.1mg / m²After the cleaning treatment to adhere to the above, P (H₂O) / P (H₂) Within the prescribed range and H in the latter atmosphere₂O By setting the partial pressure to a predetermined amount or less and the temperature within the predetermined temperature range, the decomposition and fine dispersion regeneration of the oxide on the steel sheet surface after decarburization annealing is promoted, and the oxidation and nitridation of the steel sheet during the final finish annealing And finally improve the magnetic flux density of the product.
[0051]
Here, the raw material component of the present invention generally follows that of grain-oriented silicon steel, and, for example, the following component composition is advantageously adapted.
C: 0.020 to 0.10% by weight
C is a component useful for improving the structure in hot rolling and cold rolling, and this effect cannot be obtained unless the content is less than 0.020% by weight. On the other hand, if the amount exceeds 0.10% by weight, decarburization is poor and magnetic properties are deteriorated, so the C content is limited to a range of 0.020 to 0.10% by weight.
Si: 1.0-5.0 wt%
Si is a heavy component in increasing the electrical resistance of the product and reducing eddy current loss. For this purpose, 1.0% by weight or more is necessary. On the other hand, if it exceeds 5.0%, cold rollability deteriorates. Therefore, it is limited to the range of 1.0 to 5.0% by weight.
Mn: 0.05-2.5% by weight
Mn is an inhibitor forming component which will be described later, and is also a component necessary for improving the hot rolling property. For this purpose, 0.05% by weight or more is required. On the other hand, if the amount exceeds 2.5% by weight, decarburization will occur. Since it becomes difficult, it was limited to the range of 0.05 to 2.5% by weight.
[0052]
Next, as an inhibitor-forming component, in addition to the above Mn, Al, S or Se is contained in the range of 0.005 to 0.04% by weight.
That is, Al, S, or Se is necessary to form an inhibitor by fine precipitation in steel as AlN, MnS, or MnSe, and one or more of these must be contained. For this purpose, it is necessary to contain 0.005% by weight or more, but if it exceeds 0.04% by weight, it becomes difficult to finely disperse and precipitate, and the function of the inhibitor is lowered. In the range of. In addition, when it contains 2 or more types, it is preferable to restrict | limit individual components to the range of 0.005 to 0.04 weight%.
[0053]
In addition, Ge, P, V, Sn, Sb, Bi, B, and N are 0.005 to 0.040 wt%, Sn and Sb are 0.005 to 0.2 wt%, and Bi and B are 0.0003 to 0.0100 as an inhibitor component, if necessary. It is preferable to add in the range of% by weight. Note that N can be added by nitriding during the manufacturing process. Furthermore, in order to improve hot rollability, Mo can be contained in a range of up to 0.05% by weight.
[0054]
DETAILED DESCRIPTION OF THE INVENTION
Next, the manufacturing method according to the present invention will be described in detail.
The steel slab having the above preferred component composition is obtained by casting steel obtained by a conventionally used steel making method, re-rolled as necessary, and then hot-rolled into a hot-rolled coil. Such a hot-rolled coil has a final plate thickness by one or a plurality of cold rollings with intermediate annealing interposed therebetween. The amount of oxide on the surface of the steel plate after the final cold rolling is converted to an oxygen basis weight on both sides of the steel plate. 0.05 ~ 0.35g / m²It is an essential requirement of the present invention to adjust to. This can be achieved by changing the amount of scale removal on the surface of the steel sheet before cold rolling.
[0055]
The amount of oxygen per unit area of steel sheet (g / m²) Can be obtained according to the following equation (3).
[Equation 3]
7.65 × t × (W−W₀) × 10^-3---- (3)
t: Steel plate thickness (mm)
W: Steel sheet oxygen concentration (PPM) including surface oxide
W₀: Oxygen concentration in steel plate after removal of surface oxide (PPM)
[0056]
Here, the oxygen basis weight of the steel sheet is 0.05 g / m² If it is less, the content of firelite in the oxide on the surface of the steel sheet formed in the first stage of decarburization annealing is reduced, and the effect of densification / regeneration / densification treatment of oxide in the latter stage of decarburization annealing is obtained. Absent. Conversely, the oxygen basis weight is 0.35 g / m²In the case of exceeding the above, the amount of firelite in the oxide formed in the first stage of the decarburization annealing becomes excessive, and point defects are inherent in the forsterite film formed during the final finish annealing.
[0057]
The oxide on the surface of the steel sheet after the final cold rolling is performed by changing the removal amount when removing the surface scale after the annealing before the final cold rolling. Moreover, conventionally known methods such as pickling and grinding can be used as the removing means.
The coil after the final cold rolling is then subjected to decarburization annealing, and as a pretreatment for this decarburization annealing, it is necessary to perform a cleaning process by an electrolytic degreasing method. That is, the electrolytic degreasing method is a technique in which the steel sheet surface is cleaned by immersing the steel sheet in a bath and passing a positive or negative current from the steel sheet surface into the bath. In such electrolytic degreasing cleaning, an electrodeposit containing Si is finally added to the steel sheet surface at 0.1 mg / m 2.² It is important to attach them as described above. Because the deposition amount of electrodeposits containing Si is 0.1 mg / m²If less, the content of firelite in the oxide on the surface of the steel sheet formed in the first stage of subsequent decarburization annealing is reduced, and the effect of densification / regeneration / densification treatment of oxide is obtained in the latter stage of decarburization annealing. I can't.
[0058]
In addition, the detection of the adhesion amount of the electrodeposit containing Si can be performed using the number of counts per unit time of Si intensity by fluorescent X-rays. In other words, the deposited electrodeposits are washed off with extremely low concentration of HCl and the change in weight before and after that is measured. The change in weight is correlated with the change in the Si intensity count due to fluorescent X-rays, and a calibration curve is created in advance. By doing so, the measurement of the amount of adhesion is made simple.
[0059]
Further, decarburization annealing may be performed in the same continuous furnace in the first and second periods from the viewpoint of operability, or the first and second periods may be performed as separate annealing treatments.
The first stage of the decarburization annealing is a decarburization annealing that is normally performed. In order to increase the composition ratio of the firelite in the oxide formed on the steel sheet surface, the P (H₂O) / P (H₂) In the range of 0.30 to 0.65. That is, P (H₂O) / P (H₂) Is less than 0.30, the formation of firelite is insufficient, and the generation of fine silica is insufficient in the decomposition regeneration densification treatment for the oxide on the steel sheet surface in the late stage of decarburization annealing. On the other hand, P (H₂O) / P (H₂) Exceeds 0.65, wustite is produced, and it becomes difficult to produce fine silica in the decomposition / regeneration / densification treatment for the oxide. Therefore, P (H₂O) / P (H₂) Is set to 0.30 to 0.65.
[0060]
In the latter stage of decarburization annealing, H in the annealing atmosphere₂It is necessary that the O partial pressure is 0.05 to 3.0% and the annealing temperature is in the range of 850 to 950 ° C. That is, H₂When the partial pressure of O is 0.05% or less, Fe, O and SiO as regenerated products decomposed from firelite₂And does not result in a fine and fine silica dispersion, whereas if it exceeds 3.0%, the decomposition of firelite is inhibited.
Furthermore, if the annealing temperature is less than 850 ° C., the progress of the decomposition reaction of the firelite becomes insufficient. Therefore, H in the annealing atmosphere₂The O partial pressure is 0.05 to 3.0%, and the annealing temperature is limited to the range of 850 to 950 ° C.
[0061]
Such oxide decomposition / regeneration / densification treatment is slightly insufficient for less than 5 seconds, and if it exceeds 40 seconds, the firelite is excessively decomposed, resulting in deterioration of magnetic properties. A range is preferred.
[0062]
After decarburization annealing, an annealing separator is applied, and then final finish annealing is performed at a temperature of about 1200 ° C. to obtain a final product. Then, if necessary, an insulating coating can be applied and a flattening process can be performed to obtain a product. Further, it is possible to provide a groove on the surface of the steel plate or to irradiate a plasma jet or a laser to locally strain the magnetic domain to perform magnetic domain refinement treatment.
[0063]
【Example】
Example 1
  Steel slabs A to P having the composition according to Table 1 were hot-rolled and then subjected to hot-rolled sheet annealing at 1000 ° C. for 1 minute. After the intermediate plate thickness of mm, as intermediate annealing, A to L is 1100 ° C and MP is 1000 ° C for 40 seconds, 25% wet N₂And 75% H₂After annealing in atmosphere (dew point 40 ° C), quench with mist water at a cooling rate of 40 ° C / s to 350 ° C, then A to L 350 ° C and MP to 200 ° C 20 seconds After holding, it was gradually cooled in the air to room temperature. The coil after intermediate annealing is ground on the surface with a grinding brush roll and then has a 180 mm diameter work roll.ZEA final plate thickness of 0.22 mm was obtained with a Nemia rolling mill. The oxygen basis weight of these coils is, 0.15 ~ 0.26 g / m² Met.
[0064]
Next, these coils were divided into two, and one of them was passed through an alkaline degreasing bath as a pretreatment for decarburization annealing, rinsed with pure water and washed. The other is electrolytic degreasing using a sodium orthosilicate bath as a pretreatment for decarburization annealing, and an electrodeposit containing Si is 1.4 to 2.8 mg / mm.²Attached. Then coil 50% H₂And residual N₂Balance atmosphere (dew point 60 ° C, P (H₂O) / P (H₂): Decarburization annealing in the first half of the period at 840 ° C for 2 minutes at 0.39), followed by 50% H in the latter half of the decarburization annealing.₂And balance N₂Balance atmosphere (dew point 5 ° C, H₂O partial pressure: 0.9%) was subjected to decomposition / regeneration / densification of oxide for 20 seconds at 880 ° C.
[0065]
[Table 1]

[0066]
These coils are 3% TiO₂And 2% Sr (OH)₂・ 8H₂After applying an annealing separator containing O and MgO as the main component to the steel sheet surface, it is wound into a coil shape and N₂After holding at 840 ℃ for 45h, 25% N at 15 ℃ / h heating rate₂And 75% H₂The temperature is raised to 1200 ° C in an atmosphere of₂A final finish annealing was performed in which the temperature was lowered after holding at 1200 ° C. for 10 hours. Then, after removing the unreacted annealing separation agent, a tension coating was applied and baked to serve as a flattening process to obtain a product. The magnetic properties of the products thus obtained are also shown in Table 2.
[0067]
[Table 2]

[0068]
Example 2
The steel slab C shown in Table 1 was hot-rolled, subjected to hot-rolled sheet annealing at 1150 ° C. for 1 minute, and then cooled to room temperature at a cooling rate of 40 ° C./s using mist water. Then, after pickling with an 18% HCl aqueous solution, a final thickness of 0.26 mm was obtained using a Sendia mill with a 120 mm diameter work roll. Here, the amount of oxide on the coil surface is 0.25 to 0.32 g / m²Met.
[0069]
Next, as a pretreatment for decarburization annealing, electrolytic degreasing using an orthosilicate sodium bath is performed, and an electrodeposit containing Si is 0.9 to 1.2 mg / m 2.² It was made to adhere with. 50% H in this coil₂And residual N₂Balance atmosphere (dew point 60 ° C, P (H₂O) / P (H₂): After decarburization annealing at 850 ° C for 2 minutes in 0.47), it was divided into two parts, one of which was N₂Atmosphere (dew point -10 ℃, H₂O partial pressure: 0.25%) was applied at 890 ° C. for 15 seconds to decompose and regenerate the oxide for densification. The remaining one was transferred to the next process.
[0070]
These coils are 10% TiO₂And 2% Sr (OH)₂・ 8H₂An annealing separator containing O and MgO as the main component is applied to the surface of the steel sheet, and then wound into a coil shape.₂And 75% H₂Increase the temperature from 850 ° C to 1200 ° C at a rate of 12 ° C / h up to 850 ° C at a rate of 12 ° C / h.₂After holding at 1200 ° C for 10 hours, final finish annealing was performed to lower the temperature.
Then, after removing the unreacted annealing separator, a tension coating is applied and baked also as a flattening treatment, and linear micro-strain is introduced by a plasma jet in a direction perpendicular to the rolling direction at intervals of 6 mm to obtain a product. . Table 3 shows the magnetic properties of the products thus obtained.
[0071]
[Table 3]

[0072]
Example 3
C: 0.043 wt%, Si: 3.32 wt%, Mn: 0.07 wt%, P: 0.007 wt%, Al: 0.001 wt%, S: 0.003 wt%, Se: 0.018 wt%, Mo: 0.012 wt% and Sb: Two silicon steel slabs containing 0.025% by weight and the balance Fe and inevitable impurities were hot-rolled and subjected to hot-rolled sheet annealing at 1000 ° C. for 30 seconds, and then a thickness of 0.64 mm was obtained. Then 75% H₂And residual N₂Intermediate annealing was performed at 975 ° C for 30 seconds in a balanced atmosphere (dew point 35 ° C), and the surface was ground after cooling. At this time, one coil was lightly ground to leave some surface scale, and the other coil was subjected to strong grinding to completely remove the surface scale. Thereafter, both coils were made to have a final thickness of 0.20 mm using low viscosity oil in a tandem rolling mill. At this time, when the amount of oxide remaining on the surface of the steel sheet was measured by the amount of oxygen per unit area, the lightly ground coil was 0.12 to 0.23 g / m on both sides of the steel sheet.² , Strong grinding coil is 0.01 ~ 0.02 g / m on both sides of steel plate² Met.
[0073]
Next, as a pretreatment for decarburization annealing, electrolytic degreasing using an orthosilicate sodium bath is performed, and an electrodeposit containing Si is added to 1.5 to 2.3 g / m.²Attached. These coils are divided into two, one is 55% H₂And residual N₂Balance atmosphere (dew point 63 ℃, P (H₂O) / P (H₂): 0.50), decarburization annealing at 820 ° C for 2 minutes, followed by 10% H₂And residual N₂Balance atmosphere (dew point 5 ° C, H₂The oxide was regenerated and densified and densified at 980 ° C for 10 seconds under 0 partial pressure (0.86%).
The other coil is also 55% H for comparison.₂And residual N₂Balance (dew point 63 ℃, P (H₂O) / P (H₂): 0.50) atmosphere at 820 ° C for 2 minutes, followed by 100% H₂Atmosphere (dew point -40 ℃, H₂O partial pressure: 0.01%) The oxide was decomposed and regenerated and densified at 1000 ° C. for 10 seconds.
[0074]
These four coils are 1.5% TiO₂And 1.5% SrSO_FourAfter applying an annealing separator containing MgO as a main component to the surface of the steel sheet, it is wound into a coil shape and N₂25% N after holding at 850 ℃ for 50h₂And 75% H₂The temperature is raised to 1200 ° C at a rate of 20 ° C / h in the atmosphere,₂A final finish annealing was performed in which the temperature was lowered after holding at 1200 ° C. for 10 hours.
Then, after removing the unreacted annealing separation agent, a tension coating was applied and baked to serve as a flattening process to obtain a product. Table 4 shows the magnetic properties of the products thus obtained.
[0075]
[Table 4]

[0076]
【The invention's effect】
According to the present invention, a grain-oriented silicon steel sheet having a high magnetic flux density can be stably produced, and in particular, the effect in production of the grain-oriented silicon steel sheet on an industrial scale is extremely large.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing a relationship between a pretreatment method for decarburization annealing and an adhesion amount of an Si-containing electrodeposit on a steel sheet surface and magnetic properties.
FIG. 2 is a diagram showing a relationship between pretreatment conditions for decarburization annealing and oxidation resistance and nitridation resistance of a decarburized annealing plate.
FIG. 3 is a diagram showing the relationship between the amount of oxygen per unit area indicating the amount of oxide remaining on the steel sheet surface after the final cold rolling and the magnetic properties.
[Figure 4] P (H₂O) / P (H₂) And the magnetic characteristics.
FIG. 5 is a diagram showing the relationship between the atmosphere of the decarburization annealing late treatment and the magnetic properties.
FIG. 6 is a diagram showing the relationship between the temperature and time of the decarburization annealing late treatment and the magnetic properties.
FIG. 7 is a schematic view showing a state in which the oxide composition and the oxide particle distribution are changed by the decomposition / regeneration / densification treatment of the oxide on the steel sheet surface.

Claims (2)

Hot rolling is applied to silicon-containing steel slabs, and then the final sheet thickness is obtained by cold rolling multiple times with one or more intermediate sandwiches, followed by decarburization annealing and final finish annealing by applying an annealing separator. In producing a grain-oriented silicon steel sheet by a series of applied processes, the amount of oxide on the steel sheet surface after the final cold rolling is adjusted to 0.05 to 0.35 g / m ² in terms of oxygen basis weight, and then prior to decarburization annealing, A cleaning process is performed in which the electrodeposit containing Si adheres to the steel sheet surface at 0.1 mg / m ² or more by electrolytic degreasing, and then the ratio of the water vapor partial pressure to the hydrogen partial pressure in the atmosphere is adjusted to 0.30 to 0.65. Decarburization annealing is performed in the first period and in the second period in which the temperature in the atmosphere is adjusted to 850 to 950 ° C. and the partial pressure of water vapor is adjusted to 0.05 to 3.0%, and the oxide surface decomposition and regeneration densification treatment is performed. method of manufacturing a tropic silicon steel sheet who shall be the feature.   The method for producing a grain-oriented silicon steel sheet according to claim 1, wherein the decomposition / regeneration / densification treatment is performed for 5 to 40 seconds.

Images