JP4207817B2 - Dehydrogenation treatment method for molten steel - Google Patents
Dehydrogenation treatment method for molten steel Download PDFInfo
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- JP4207817B2 JP4207817B2 JP2004087655A JP2004087655A JP4207817B2 JP 4207817 B2 JP4207817 B2 JP 4207817B2 JP 2004087655 A JP2004087655 A JP 2004087655A JP 2004087655 A JP2004087655 A JP 2004087655A JP 4207817 B2 JP4207817 B2 JP 4207817B2
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本発明は、溶鋼の脱水素処理方法に関する。本発明により、短い操業時間で確実に鋼中の水素の量が減少し、溶存水素量のバラツキが小さい溶鋼を得ることができる。 The present invention relates to a method for dehydrogenating molten steel. According to the present invention, it is possible to obtain a molten steel in which the amount of hydrogen in the steel is surely reduced and the variation in dissolved hydrogen amount is small in a short operation time.
鋼の精錬において行なう脱ガス処理は、許容される溶鋼の温度低下には限界があることから、処理時間が制限されてしまう。脱ガスのうち、脱水素が不十分であると、溶鋼をインゴットまたは鋳片（以下、インゴットで代表させる）に鋳造したときに、その内部に、放射状に分布して軸方向に走る微細なクラック（「毛割れ」と呼ばれる）が生じ、圧延製品の欠陥になることがある。 In the degassing process performed in the refining of steel, there is a limit to the allowable temperature drop of molten steel, so that the processing time is limited. Among the degassing, if the dehydrogenation is inadequate, when the molten steel is cast into an ingot or slab (hereinafter referred to as an ingot), fine cracks that run radially in the radial direction are distributed inside (Referred to as “hair cracking”) can result in defects in the rolled product.
したがって、水素を十分に脱ガスすることが、製鋼作業において肝要である。ところが、従来の真空脱ガス処理によるときは、脱ガスの程度にかなりバラツキがでることが避けられないという問題があった。 Therefore, sufficient degassing of hydrogen is essential in steelmaking operations. However, when the conventional vacuum degassing process is used, there is a problem that it is inevitable that the degree of degassing varies considerably.
溶鋼の簡易な脱水素法として、５０〜３００Torrの減圧下にさらされた溶鋼の単位重量あたりの静止面積を０．００６ｍ2／ｔ以上とし、その溶鋼面を通過するように、炉底から不活性ガスを溶鋼静止表面あたり４５０Ｎｌ／min／ｍ2吹き込み、単位静止溶鋼表面積あたりの撹拌エネルギーを０．５Ｗ／ｍ2以上の条件で脱ガス処理を行なうことが開示された（特許文献１）。 As a simple dehydrogenation method for molten steel, the static area per unit weight of molten steel exposed to a reduced pressure of 50 to 300 Torr is set to 0.006 m 2 / t or more, so that it passes through the molten steel surface. It has been disclosed that the active gas is blown at 450 Nl / min / m 2 per molten steel stationary surface and the degassing treatment is performed under the condition that the stirring energy per unit stationary molten steel surface area is 0.5 W / m 2 or more (Patent Document 1).
この発明は、従来の真空脱ガスが、ガス側の物質移動を促進する方法として高真空を利用するものであったのに対し、溶鋼側の物質移動速度を十分高めておくと同時に、溶鋼−ガス界面に不活性ガスを通過させてガス側の物質移動を高めることによって、１００〜３００Torr程度の低真空で脱水素を可能にする、というものである。 In the present invention, the conventional vacuum degassing uses a high vacuum as a method for promoting the mass transfer on the gas side, while the mass transfer rate on the molten steel side is sufficiently increased, The dehydrogenation is possible at a low vacuum of about 100 to 300 Torr by passing an inert gas through the gas interface to enhance the mass transfer on the gas side.
溶鋼の脱水素速度に関する研究報告（非特許文献１）によれば、脱水素に及ぼす影響としては、圧力８７５Ｐａ以下では溶鋼側の物質移動が、これより高い圧力ではガス側の物質移動が、それぞれ支配的であるという。ガス側の物質移動を促進する手段としては、溶鋼表面にガスを吹き付けて水素ガスの分圧を下げることが考えられ、この研究報告においても検討されている。吹き付けるガス量を増大するにつれて脱水素が進むことが確認されているが、この効果に関しては、大気圧下の実験データしか示されていない。
発明者らは、真空脱ガスによる脱水素において、ある真空度を境にして低真空域ではガス側の物質移動が支配的であり、高真空域では溶鋼側の物質移動が支配的になる、という知見と、溶鋼表面へのガスの吹き付けによる水素ガス分圧低下とを組み合わせることを着想し、実験の結果、この組み合わせが、とくに低真空域でガスの吹き付けを行なうのが効果的であることを見出した。 In the dehydrogenation by vacuum degassing, the inventors have a dominant role of mass transfer on the gas side in the low vacuum region at a certain degree of vacuum, and dominant mass transfer on the molten steel side in the high vacuum region. The combination of this knowledge and the reduction of the hydrogen gas partial pressure due to the gas blowing to the molten steel surface, and as a result of the experiment, it is effective to blow the gas especially in the low vacuum region. I found.
本発明の目的は、短い操業時間で確実に溶鋼の脱水素を実現し、低水素量であり、かつ水素量のバラツキが小さいインゴットが得られる溶鋼の脱水素処理方法を提供することにある。 An object of the present invention is to provide a method for dehydrogenating a molten steel that reliably realizes the dehydrogenation of the molten steel in a short operation time, and obtains an ingot having a low hydrogen content and a small variation in the hydrogen content.
上記の目的を達成する本発明の方法は、鋼の精錬過程において行なう溶鋼の脱水素処理の方法であって、真空吸引−不活性ガス底吹きからなる脱ガス工程において、真空吸引を、真空度が大気圧から６．６Torrに至る低真空域を経て６．６Torr未満から１．０Torr以下に達する高真空域にわたって行ない、低真空域にある間は、溶鋼の底から不活性ガスを吹き込んで撹拌するとともに、溶鋼表面に不活性ガスを吹き付けて溶鋼に接している気相の水素ガス分圧を低下させることにより脱水素の速度を高め、高真空域においては、不活性ガスの吹き付けを停止し吹き込みだけを継続することを特徴とする処理方法である。 The method of the present invention that achieves the above object is a method for dehydrogenating a molten steel in a steel refining process, and in the degassing step comprising vacuum suction-inert gas bottom blowing, vacuum suction is performed at a degree of vacuum. Is carried out over a high vacuum range from less than 6.6 Torr to 1.0 Torr or less through a low vacuum range from atmospheric pressure to 6.6 Torr. While in the low vacuum range, an inert gas is blown from the bottom of the molten steel and stirred. In addition, the inert gas is sprayed onto the molten steel surface to reduce the hydrogen gas partial pressure in the gas phase in contact with the molten steel, thereby increasing the dehydrogenation rate. This is a processing method characterized in that only blowing is continued.
本発明の溶鋼の脱水素処理方法は、ガス側の物質移動が律速である圧力が６．６Torrまでの低真空域においては、不活性ガスの吹き付けによって溶鋼表面の水素ガス分圧を低下させて拡散を促進し、溶鋼内部の物質移動が律速となる圧力が６．６Torrより低い高真空域においては、吹き付けを停止して高い真空度への到達を容易にすることにより、後記する実施例にみるように、溶鋼中の水素量を低減するとともに、そのバラツキを小さくする効果が得られる。その結果、前記したインゴットの「毛割れ」トラブルを画期的に低減することができる。 In the method for dehydrogenating molten steel according to the present invention, in the low vacuum region where the gas-side mass transfer rate is limited to 6.6 Torr, the hydrogen gas partial pressure on the molten steel surface is reduced by blowing an inert gas. In the high vacuum region where the diffusion is promoted and the pressure at which the mass transfer inside the molten steel is rate-limiting is lower than 6.6 Torr, the spraying is stopped to easily reach a high degree of vacuum. As can be seen, the effect of reducing the amount of hydrogen in the molten steel and reducing the variation is obtained. As a result, the above-mentioned “hair cracking” trouble of the ingot can be remarkably reduced.
本発明の脱ガス処理方法を実施しているところを図示すれば、図１にみるとおりである。排気ダクト（４）を備えた真空容器（３）内に、溶鋼（１）を入れた取鍋精錬炉（２）をセットし、取鍋の底からＡｒガスを吹き込みながら真空吸引するとともに、作業孔を通るランス（５）からもＡｒガスを溶鋼表面に吹き付ける。吹き付けるＡｒガスの流量は、流量計とバルブにより調節する。真空吸引が進んで圧力計（６）の読みが６．６Torrに達したところで、Ａｒガスの吹き付けを停止して、真空容器内が、速やかに高真空に達するようにはかる。 The place where the degassing treatment method of the present invention is carried out is illustrated in FIG. A ladle refining furnace (2) containing molten steel (1) is set in a vacuum vessel (3) equipped with an exhaust duct (4), and vacuum suction is performed while Ar gas is blown from the bottom of the ladle. Ar gas is also blown onto the surface of the molten steel from the lance (5) passing through the hole. The flow rate of Ar gas to be blown is adjusted by a flow meter and a valve. When the vacuum suction progresses and the reading of the pressure gauge (6) reaches 6.6 Torr, the Ar gas blowing is stopped so that the inside of the vacuum vessel quickly reaches a high vacuum.
脱水素は、溶鋼中の水素を［Ｈ］とすると、一般に次式であらわされる。
［Ｈ］→１／２Ｈ２（ｇ）
高温の溶鋼表面においては水素原子の拡散が律速段階であると考えられるので、それを前提として、気相との界面付近で、溶鋼中の［Ｈ］i（％）と気相中のＰH2（atm）との間に平衡が成立しているとすると、次の式が得られる。
［Ｈ］＝ｋ√ＰH2＋（［Ｈ］s−ｋ√ＰH2）・exp（−ｋａ・ｔ）
logｋ＝−１９０５／Ｔ−１．５９１
ここで、［Ｈ］：脱ガス処理中、ｔ時間後の［Ｈ］値（％）
［Ｈ］i：気相との界面における溶鋼中の［Ｈ］濃度（％）
ＰH2：気相中の水素ガス分圧（≒真空度atm）
［Ｈ］s：脱ガス処理前の［Ｈ］値（％）
ｔ：真空保持時間
ｋａ：反応容量係数 ｋａ＝（Ａ／Ｖ）・ｋ
Ａ：反応界面面積 Ｖ：容積 ｋ：物質移動係数
Dehydrogenation is generally expressed by the following formula, where hydrogen in the molten steel is [H].
[H] → 1 / 2H 2 (g)
Since in the high-temperature molten steel surface is considered that diffusion of the hydrogen atom is the rate limiting step, assuming it, in the vicinity of the interface between the gas phase, in the molten steel [H] i (%) and in the gas phase P H2 If an equilibrium is established with (atm), the following equation is obtained.
[H] = k√P H2 + ([H] s−k√P H2 ) · exp (−ka · t)
logk = -1905 / T-1.591
Here, [H]: [H] value (%) after t time during the degassing process
[H] i: [H] concentration (%) in molten steel at the interface with the gas phase
P H2 : Hydrogen gas partial pressure in the gas phase (≒ degree of vacuum atm)
[H] s: [H] value (%) before degassing
t: Vacuum holding time ka: Reaction volume coefficient ka = (A / V) · k
A: Reaction interface area V: Volume k: Mass transfer coefficient
アーク炉で溶製した肌焼鋼の溶湯２５トンを取鍋精錬炉に受け、図１に示した装置を用いて真空脱ガス処理を行ない、水素ガスの減量をはかった。炉底からＡｒガスを吹き込んで溶湯を撹拌しながら、真空ブースターの稼動状態をほぼ一定にして、下記３種の操業態様を実施した。カッコ内はｎ数である。
通常チャージ：Ａｒガスの吹き付けを行なわない（３１チャージ）
Ａｒブロー１：真空吸引の間、Ａｒガスの吹き付けを継続した（４チャージ）
Ａｒブロー２：６．６Torr以上の低真空域でＡｒガスの吹き付けを行ない、６．６Torr未満の高真空域では吹き付けを停止した（３チャージ）
25 tons of case-hardened steel melted in an arc furnace was taken into a ladle refining furnace and subjected to vacuum degassing using the apparatus shown in FIG. 1 to reduce the amount of hydrogen gas. While the molten metal was stirred by blowing Ar gas from the furnace bottom, the operation state of the vacuum booster was made substantially constant, and the following three operation modes were carried out. The number in parentheses is n.
Normal charge: Ar gas is not sprayed (31 charges)
Ar blow 1: Ar gas was continuously blown during vacuum suction (4 charges)
Ar blow 2: Ar gas was blown in a low vacuum range of 6.6 Torr or higher, and was stopped in a high vacuum range of less than 6.6 Torr (3 charges)
上記３種の操業条件のもとで、真空容器内の真空度が処理時間の進行に伴ってどのように変化するかをしらべて、図２のグラフを得た。Ａｒガスの吹き付けを行なわない場合および吹き付けを途中で停止した場合は、最終的には０．３２Torrという高真空度に到達したのに対し、真空吸引のあいだ継続してＡｒガスの吹き付けを行なった場合には、到達し他真空度は０．６１Torrまでであった。 The graph of FIG. 2 was obtained by examining how the degree of vacuum in the vacuum vessel changed with the progress of the processing time under the above three operating conditions. When Ar gas was not sprayed and when the spray was stopped halfway, the final vacuum reached 0.32 Torr, whereas Ar gas was continuously sprayed during vacuum suction. In some cases, the reached vacuum was up to 0.61 Torr.
各チャージにおいて、脱ガス処理後の溶鋼中の水素含有量を測定した。その結果を、操業の条件とともに、表１に示す。範囲で示した数値は最小値と最大値であり、その前に示した数値は平均値である。脱ガス処理後の溶鋼中に含有されていた水素量の最小値〜最大値と平均値とを、３種の操業条件についてグラフにすると、図３に示すとおりである。 At each charge, the hydrogen content in the molten steel after degassing was measured. The results are shown in Table 1 together with the operating conditions. The numerical values shown in the range are the minimum value and the maximum value, and the numerical values shown before are the average values. When the minimum value to the maximum value and the average value of the hydrogen content contained in the molten steel after the degassing treatment are graphed with respect to three kinds of operation conditions, they are as shown in FIG.
本発明の方法に従って溶鋼の真空脱ガス処理を行なった場合、不活性ガスの吹き付けを行なわなかった場合と比べればもちろんのこと、不活性ガスの吹き付けを真空処理の間一貫して行なった場合よりも、脱ガス処理後の溶鋼中の水素含有量が減少し、かつ、チャージごとのバラツキが小さくなることが、表１および図３から明らかである。 When vacuum degassing of molten steel is performed according to the method of the present invention, as compared with the case where inert gas is not sprayed, as compared with the case where inert gas is sprayed consistently during vacuum processing. However, it is clear from Table 1 and FIG. 3 that the hydrogen content in the molten steel after the degassing treatment is reduced and the variation for each charge is reduced.
本発明の実施態様およびその効果を、肌焼鋼を例にとって説明したが、本発明はこれに限らず、炭素鋼、マンガン鋼そのほか、鋼中に溶存する水素に起因する「毛割れ」トラブルが問題になる鋼種のすべてに適用することができる。 The embodiment of the present invention and the effects thereof have been described by taking the case-hardened steel as an example, but the present invention is not limited to this, and carbon steel, manganese steel, and other problems such as “hair cracking” caused by hydrogen dissolved in the steel. It can be applied to all of the steel types in question.
１ 溶鋼
２ 溶鋼精錬炉
３ 真空容器
４ 排気ダクト
５ ランス
６ 圧力計
1
Claims (2)
The dehydrogenation treatment method according to claim 1, wherein argon gas or nitrogen gas is used as the inert gas.
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