JP2007031807A - Method for manufacturing ultra-low carbon steel - Google Patents

Method for manufacturing ultra-low carbon steel Download PDF

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JP2007031807A
JP2007031807A JP2005220250A JP2005220250A JP2007031807A JP 2007031807 A JP2007031807 A JP 2007031807A JP 2005220250 A JP2005220250 A JP 2005220250A JP 2005220250 A JP2005220250 A JP 2005220250A JP 2007031807 A JP2007031807 A JP 2007031807A
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molten steel
decarburization
steel
refining
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Takayuki Koyanagi
貴幸 小柳
Yoshiyuki Tanaka
芳幸 田中
Takeshi Asahina
健 朝比奈
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JFE Steel Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an ultra-low carbon steel, which method can rapidly perform decarburization refining under reduced pressure and producing a molten steel with a very low carbon content by effecting the decarburization refining of molten steel obtained by decarburization refining using a converter under a reduced pressure in a vacuum degasifier. <P>SOLUTION: When the ultra-low carbon steel is manufactured by effecting the decarburization refining of molten steel obtained by decarburization refining using a converter under reduced pressure in a vacuum degasifier, the composition of the molten steel is previously adjusted such that the carbon content of the molten steel before the start of the decarburization refining in the vacuum degasifier falls in the range of 0.02 to 0.06 mass%, the dissolved oxygen content of the molten steel is 0.04 mass% or higher, and the ratio of the dissolved oxygen content to the carbon content (dissolved oxygen content/carbon content) is 1.34 or larger and that the decarburization refining is performed without feeding any oxygen gas into the molten steel under reduced pressure in the vacuum degasifier. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、転炉における脱炭精錬によって得た溶鋼に、真空脱ガス設備の大気圧よりも低い減圧下において再度脱炭精錬を施して、極低炭素鋼を溶製する方法に関するものである。   The present invention relates to a method of melting ultra-low carbon steel by subjecting molten steel obtained by decarburization refining in a converter to decarburization refining again under reduced pressure lower than the atmospheric pressure of vacuum degassing equipment. .

自動車外装用薄鋼板、缶用薄鋼板、家庭電化製品用薄鋼板など、多くの用途に使用されている薄鋼板に対して、年々その加工性の向上がユーザーから要求されている。一方、製造過程においては、冷間圧延後の薄鋼板に施される焼鈍は、従来のバッチ焼鈍から連続焼鈍へと急速に転換されている。このような状況から、薄鋼板用の鋼は、炭素含有量が0.01〜0.1質量%の低炭素鋼から、炭素含有量が0.01質量%以下の加工性に優れた極低炭素鋼に急激に転換されつつある。   Users have been required to improve their workability year after year for thin steel sheets used in many applications such as thin steel sheets for automobile exteriors, thin steel sheets for cans, and thin steel sheets for home appliances. On the other hand, in the manufacturing process, the annealing applied to the thin steel sheet after the cold rolling is rapidly changed from the conventional batch annealing to the continuous annealing. Under such circumstances, the steel for thin steel sheets is extremely low in excellent workability with a carbon content of 0.01% by mass or less from a low carbon steel with a carbon content of 0.01-0.1% by mass. It is rapidly changing to carbon steel.

高炉で溶製された溶銑から極低炭素鋼を溶製するには、先ず、転炉で溶銑に脱炭精錬を施して溶銑から溶鋼を溶製し、次いで、この溶鋼に真空脱ガス設備による減圧下での脱炭精錬を施して溶製している。これら溶鉄及び溶鋼の脱炭反応は、下記の(1)式によって表され、この脱炭反応の平衡定数Kは下記の(2)式及び(3)式によって表されることが知られている。尚、(2)式において、PCOはCOガスの分圧、aC は炭素の活量、aO は酸素の活量、[%C]は溶鋼中の炭素濃度(質量%)、[%O]は溶鋼中の酸素濃度(質量%)であり、(3)式におけるTは絶対温度(K)である。また、ここに示す酸素は、溶銑或いは溶鋼に溶解した状態の酸素であり、溶存酸素または溶解酸素と呼ばれている。 In order to smelt ultra-low carbon steel from hot metal melted in a blast furnace, first, decarburization refining is performed on the hot metal in the converter, and then molten steel is melted from the hot metal, and then the molten steel is subjected to vacuum degassing equipment. It is made by decarburization refining under reduced pressure. It is known that the decarburization reaction of these molten iron and molten steel is represented by the following equation (1), and the equilibrium constant K of this decarburization reaction is represented by the following equations (2) and (3). . In the equation (2), P CO is the partial pressure of CO gas, a C is the carbon activity, a O is the oxygen activity, [% C] is the carbon concentration (mass%) in the molten steel, [% O] is the oxygen concentration (mass%) in the molten steel, and T in equation (3) is the absolute temperature (K). The oxygen shown here is oxygen in a state of being dissolved in molten iron or molten steel, and is called dissolved oxygen or dissolved oxygen.

Figure 2007031807
Figure 2007031807

これらの(1)式〜(3)式からも明らかなように、脱炭反応によって生成するCOガス分圧(PCO)が1気圧(1013hPa)の状態では、換言すれば転炉における大気圧下での脱炭精錬では、炭素濃度を0.01質量%以下にまで脱炭しようとする場合には、溶存酸素濃度をおよそ0.24質量%以上にする必要がある。溶存酸素をこのような高い濃度レベルにすると、鉄の酸化が激しくなり、転炉における鉄歩留まりは大幅に低下してしまう。また、供給する酸素と鉄とが反応して鉄酸化物が形成されることから、転炉において溶存酸素濃度をこのような高い濃度にすることは、実際には極めて困難である。 These (1) to (3) As is apparent from the equation, in the state of the CO gas partial pressure produced by decarburization (P CO) is 1 atm (1013 hPa), atmospheric pressure in the converter in other words In the decarburization refining below, when the carbon concentration is to be decarburized to 0.01% by mass or less, the dissolved oxygen concentration needs to be about 0.24% by mass or more. When dissolved oxygen is brought to such a high concentration level, iron oxidation becomes intense, and the iron yield in the converter is greatly reduced. Further, since the supplied oxygen and iron react to form iron oxide, it is actually very difficult to make the dissolved oxygen concentration such a high concentration in the converter.

そこで、極低炭素鋼を溶製する場合には、前述したように脱ガス設備を利用し、生成するCOガス分圧(PCO)を下げ、上記(1)式の反応を進行させている。この場合には、溶存酸素濃度を過剰に高くしなくても上記(1)式の反応は進行する。 Therefore, when melting ultra-low carbon steel, the degassing equipment is used as described above, the generated CO gas partial pressure (P CO ) is lowered, and the reaction of the above formula (1) is advanced. . In this case, the reaction of the above formula (1) proceeds without increasing the dissolved oxygen concentration excessively.

このように、脱ガス設備における溶鋼の脱炭精錬では、溶存酸素を有する溶鋼を減圧下に曝せば(1)式に示す脱炭反応が進行するが、脱炭反応を促進させるために、例えばRH真空脱ガス装置においては、浸漬管口径の拡大、環流用Arガス吹き込み量の増大などの溶鋼の環流量を増大させる対策が実施されていた(例えば特許文献1参照)。しかしながら、浸漬管口径を拡大した場合には、浸漬管の寿命が短くなり、また、環流用Arガスの吹き込み量を増大した場合には、スプラッシュの発生が激しく、真空槽内でのスプラッシュの付着により操業性が損なわれるなどといった問題があった。   Thus, in the decarburization refining of the molten steel in the degassing equipment, if the molten steel having dissolved oxygen is exposed under reduced pressure, the decarburization reaction shown in the formula (1) proceeds, but in order to promote the decarburization reaction, for example, In the RH vacuum degassing apparatus, measures for increasing the flow rate of the molten steel, such as increasing the diameter of the dip tube and increasing the amount of Ar gas blow-in for reflux, have been implemented (see, for example, Patent Document 1). However, when the diameter of the dip tube is increased, the life of the dip tube is shortened, and when the amount of Ar gas blown in is increased, splashing is severe and the splash adheres in the vacuum chamber. As a result, there was a problem that the operability was impaired.

そこで、これらの問題を解決するために、真空槽内に設置した上吹きランスから酸素ガスを減圧下の溶鋼湯面に向けて吹き付けて、脱炭精錬する方法が提案された(例えば特許文献2参照)。酸素ガスを供給することにより、溶鋼中の溶存酸素が確保され、脱炭反応は促進される。また、脱炭反応により生成するCOガスが、上吹きランスから供給される酸素ガスによって燃焼してCO2 ガスとなり、この燃焼熱によってスプラッシュの付着が抑制されるという効果も発揮される。 Therefore, in order to solve these problems, a method of decarburizing and refining by blowing oxygen gas from the upper blowing lance installed in the vacuum chamber toward the molten steel surface under reduced pressure has been proposed (for example, Patent Document 2). reference). By supplying oxygen gas, dissolved oxygen in the molten steel is secured, and the decarburization reaction is promoted. In addition, the CO gas produced by the decarburization reaction is burned by the oxygen gas supplied from the top blowing lance to become CO 2 gas, and the effect of suppressing the adhesion of splash by this combustion heat is also exhibited.

しかしながら、近年の高生産性を目的とする操業形態においては、特許文献2の方法でも問題のあることが分かった。つまり、酸素ガスを減圧下の溶鋼湯面に供給する必要があることから、雰囲気圧力の真空度が余り高くならないという点である。酸素ガスの供給を必要としない脱炭精錬の末期でも、スプラッシュによる上吹きランス噴射孔の閉塞を防止するために不活性ガスをパージ用ガスとして連続的に供給する必要があり(例えば特許文献3参照)、特に、脱炭速度が遅くなる脱炭精錬末期において所望する真空度が得られず、脱炭速度が遅くなり、処理時間が延長する、或いは、脱炭精錬終了時の炭素濃度が極限まで低下しないといった問題が発生した。
特開昭58−11721号公報 特開平1−246314号公報 特開平7−316634号公報
However, it has been found that the method of Patent Document 2 has a problem in the operation mode aiming at high productivity in recent years. In other words, since the oxygen gas needs to be supplied to the molten steel surface under reduced pressure, the degree of vacuum of the atmospheric pressure is not so high. Even in the final stage of decarburization refining that does not require the supply of oxygen gas, it is necessary to continuously supply an inert gas as a purge gas in order to prevent the upper blow lance injection hole from being blocked by splash (for example, Patent Document 3). In particular, the desired degree of vacuum cannot be obtained at the end of decarburization and refining when the decarburization rate is slow, the decarburization rate is slowed, the processing time is extended, or the carbon concentration at the end of decarburization and refining is extreme There was a problem that it did not decrease until.
JP 58-11721 A JP-A-1-246314 JP 7-316634 A

本発明は上記事情に鑑みてなされたもので、その目的とするところは、転炉における大気圧下での脱炭精錬によって得た溶鋼を、真空脱ガス設備の大気圧よりも低い減圧下において脱炭精錬して極低炭素鋼を溶製するに当たり、減圧下での脱炭精錬を迅速に行うことができると同時に、炭素濃度の極めて低い溶鋼を溶製することのできる極低炭素鋼の溶製方法を提供することである。   The present invention has been made in view of the above circumstances, and the object of the present invention is to provide molten steel obtained by decarburization and refining under atmospheric pressure in a converter under reduced pressure lower than the atmospheric pressure of vacuum degassing equipment. When melting ultra-low carbon steel by decarburization and refining, it is possible to quickly perform decarburization under reduced pressure, and at the same time, ultra-low carbon steel that can melt molten steel with extremely low carbon concentration. It is to provide a melting method.

上記課題を解決するための第1の発明に係る極低炭素鋼の溶製方法は、転炉における脱炭精錬によって得た溶鋼を、真空脱ガス設備の大気圧よりも低い減圧下において脱炭精錬して極低炭素鋼を溶製するに際し、前記真空脱ガス設備における脱炭精錬開始前の溶鋼の炭素濃度が0.02〜0.06質量%の範囲で、溶鋼の溶存酸素濃度が0.04質量%以上であり、且つ、該溶存酸素濃度と前記炭素濃度との比(溶存酸素濃度/炭素濃度)が1.34以上になるように予め溶鋼の成分を調整するとともに、真空脱ガス設備では減圧下の溶鋼に酸素ガスを供給せずに脱炭精錬することを特徴とするものである。   The method for melting ultra-low carbon steel according to the first invention for solving the above-mentioned problem is to decarburize molten steel obtained by decarburization refining in a converter under a reduced pressure lower than the atmospheric pressure of a vacuum degassing facility. When refining and melting ultra-low carbon steel, the carbon concentration of the molten steel before the start of decarburization refining in the vacuum degassing facility is in the range of 0.02 to 0.06 mass%, and the dissolved oxygen concentration of the molten steel is 0. The components of the molten steel are adjusted in advance so that the ratio (dissolved oxygen concentration / carbon concentration) of the dissolved oxygen concentration to the carbon concentration (dissolved oxygen concentration / carbon concentration) is 1.34 or more. The equipment is characterized by decarburizing and refining the molten steel under reduced pressure without supplying oxygen gas.

第2の発明に係る極低炭素鋼の溶製方法は、第1の発明において、前記転炉における脱炭精錬の末期に、転炉内に供給する酸素ガスの供給流量を低下する、上吹き酸素ランスの高さ位置を上昇する、転炉内溶鋼の攪拌強度を低下する、のうちの何れか1つの対策または何れか2つ以上の対策を実施して、前記溶存酸素濃度を調整することを特徴とするものである。   The ultra-low carbon steel melting method according to the second aspect of the present invention is the first aspect of the present invention, wherein the flow rate of oxygen gas supplied into the converter is reduced at the end of decarburization and refining in the converter. Adjusting the dissolved oxygen concentration by implementing any one measure or any two or more measures of raising the oxygen lance height position and lowering the stirring strength of the molten steel in the converter It is characterized by.

第3の発明に係る極低炭素鋼の溶製方法は、第1の発明において、前記転炉から取鍋への溶鋼の出鋼時に出鋼流に向けて酸素ガスを吹き付ける、出鋼後の取鍋内の溶鋼に酸素ガスを吹き込む、のうちの何れか1つの対策または双方の対策を実施して、前記溶存酸素濃度を調整することを特徴とするものである。   A method for melting ultra-low carbon steel according to a third aspect of the present invention is the method according to the first aspect, wherein oxygen gas is blown toward the outgoing steel flow at the time of outgoing steel from the converter to the ladle. One of the measures of blowing oxygen gas into the molten steel in the ladle or both measures are implemented to adjust the dissolved oxygen concentration.

本発明によれば、真空脱ガス設備における脱炭精錬の前までに、溶鋼中の炭素濃度を0.02〜0.06質量%の範囲とし、同時に、溶鋼中の溶存酸素濃度を、0.04質量%以上で且つ溶鋼中の炭素濃度に応じて溶存酸素濃度と炭素濃度との比(溶存酸素濃度/炭素濃度)が1.34以上になるように調整するので、真空脱ガス設備における脱炭反応に必要な酸素は溶存酸素として確保され、真空脱ガス設備では外部から酸素ガスを供給する必要がなく、また、酸素ガスを供給する必要がないことから酸素ガス供給用上吹きランスのパージ用ガスも自ずと必要とせず、従って、減圧雰囲気の真空度を設備の上限値にまで高めることができる。その結果、真空脱ガス設備における脱炭速度が促進され、短時間で脱炭精錬を完了することができると同時に、炭素濃度の極めて低い溶鋼を溶製することが可能となり、工業上有益な効果がもたらされる。   According to the present invention, before the decarburization refining in the vacuum degassing equipment, the carbon concentration in the molten steel is set in the range of 0.02 to 0.06 mass%, and at the same time, the dissolved oxygen concentration in the molten steel is set to 0. Since the ratio of dissolved oxygen concentration to carbon concentration (dissolved oxygen concentration / carbon concentration) is adjusted to 1.34 or more according to the carbon concentration in the molten steel, the degassing in the vacuum degassing equipment The oxygen required for the charcoal reaction is secured as dissolved oxygen, and it is not necessary to supply oxygen gas from the outside in the vacuum degassing equipment, and it is not necessary to supply oxygen gas. The working gas is not necessarily required, and therefore the vacuum degree of the reduced pressure atmosphere can be increased to the upper limit value of the equipment. As a result, the decarburization speed in the vacuum degassing equipment is accelerated, and decarburization and refining can be completed in a short time. At the same time, it is possible to produce molten steel with extremely low carbon concentration, which is an industrially beneficial effect. Is brought about.

以下、本発明の実施の形態を説明する。   Embodiments of the present invention will be described below.

高炉から出銑された溶銑をトーピードカーや溶銑鍋などの溶銑保持・搬送用容器で受銑し、大気圧下で脱炭精錬を行う次工程の転炉に搬送する。この搬送途中で、予備脱硫処理や予備脱燐処理などの溶銑予備処理が施されることもあるが、本発明においては実施しても実施しなくても、どちらでも構わない。   The hot metal discharged from the blast furnace is received in a hot metal holding / conveying vessel such as a torpedo car or hot metal ladle and transferred to the next converter where decarburization and refining is performed under atmospheric pressure. During this conveyance, hot metal pretreatment such as predesulfurization treatment or predephosphorization treatment may be performed, but in the present invention, it may be performed or not performed.

転炉における溶銑の脱炭精錬は、生石灰などを媒溶剤として用いた通常の精錬を実施する。但し、この媒溶剤の添加量は、溶銑の予備脱燐処理に応じて設定する。即ち、予備脱燐処理によって溶銑中燐濃度が極低炭素鋼鋼材の製品レベルまで低下している場合には生石灰の添加量を少なくし、溶銑中燐濃度が高い場合には生石灰の添加量を多くする。そして、脱炭用の酸素ガスを上吹きまたは底吹き、若しくは上底吹きして、脱炭精錬を行う。また、転炉底部に設けた羽口から攪拌用ガスを吹き込んで、炉内の溶銑或いは溶鋼を攪拌する。   For decarburization refining of hot metal in the converter, normal refining using quick lime or the like as a solvent is carried out. However, the addition amount of this solvent is set according to the preliminary dephosphorization treatment of the hot metal. That is, when the phosphorus concentration in hot metal is reduced to the level of extremely low carbon steel due to preliminary dephosphorization, the amount of quick lime added is reduced, and when the phosphorus concentration in hot metal is high, the amount of quick lime added is reduced. Do more. Then, decarburization refining is performed by blowing up, bottom blowing, or top blowing oxygen gas for decarburization. Moreover, the gas for stirring is blown in from the tuyere provided in the bottom part of the converter, and the hot metal or molten steel in the furnace is stirred.

転炉における脱炭精錬終了時の溶鋼中炭素濃度は、0.02〜0.06質量%とする。0.02質量%未満まで脱炭精錬した場合には、鉄及びマンガンの酸化が著しくなり、鉄及びマンガンの歩留まりが低下して製造コストの上昇を招くので好ましくない。一方、脱炭精錬終了時の溶鋼中炭素濃度が0.06質量%を超える場合には、次工程の真空脱ガス設備における脱炭精錬の負担が重くなり、処理時間が延長するなどして製造コストの上昇を招くので好ましくない。脱炭精錬終了時の溶鋼中炭素濃度の前記成分範囲への調整は、転炉内への脱炭用酸素ガスの供給量の調整によって実施する。   The carbon concentration in the molten steel at the end of decarburization refining in the converter is 0.02 to 0.06% by mass. When decarburizing and refining to less than 0.02% by mass, oxidation of iron and manganese becomes remarkable, and the yield of iron and manganese decreases, leading to an increase in production cost, which is not preferable. On the other hand, when the carbon concentration in the molten steel at the end of decarburization refining exceeds 0.06% by mass, the burden of decarburization refining in the vacuum degassing facility in the next process becomes heavy and the processing time is extended, etc. This is not preferable because it causes an increase in cost. Adjustment to the said component range of the carbon concentration in molten steel at the time of completion | finish of decarburization refining is implemented by adjustment of the supply amount of the oxygen gas for decarburization in a converter.

また、本発明では、次工程の真空脱ガス設備における脱炭精錬(「真空脱炭精錬」とも記す)の開始時には、溶鋼中の溶存酸素が0.04質量%以上であり、且つ、溶存酸素濃度と溶鋼中の炭素濃度との比(溶存酸素濃度/炭素濃度)が溶鋼中炭素濃度に応じて1.34以上になるように調整する必要がある。つまり、高い濃度の溶存酸素を確保する必要がある。溶鋼中の溶存酸素濃度が0.04質量%未満では、溶存酸素濃度が低いために脱炭速度が遅く、処理時間が長くなり、好ましくない。また、比(溶存酸素濃度/炭素濃度)が1.34未満の場合には、酸素と炭素との化学当量的に酸素が不足し、数ppm程度の極めて低い濃度までは脱炭できないことから好ましくない。   In the present invention, at the start of decarburization refining (also referred to as “vacuum decarburization refining”) in the vacuum degassing facility in the next step, the dissolved oxygen in the molten steel is 0.04 mass% or more, and the dissolved oxygen It is necessary to adjust the ratio of the concentration and the carbon concentration in the molten steel (dissolved oxygen concentration / carbon concentration) to be 1.34 or more according to the carbon concentration in the molten steel. That is, it is necessary to ensure a high concentration of dissolved oxygen. If the dissolved oxygen concentration in the molten steel is less than 0.04% by mass, the dissolved oxygen concentration is low, so the decarburization rate is slow and the treatment time is long, which is not preferable. Moreover, when the ratio (dissolved oxygen concentration / carbon concentration) is less than 1.34, oxygen is insufficient in terms of chemical equivalent of oxygen and carbon, and it is preferable because decarburization is not possible up to a very low concentration of about several ppm. Absent.

溶存酸素濃度の調整は、次のようにして実施する。1つの方法は、転炉における脱炭精錬末期に、意図的に溶存酸素濃度が高くなるような操業を実施する方法である。転炉脱炭精錬において、脱炭用酸素ガスの供給流量を低下した操業或いは供給圧力を低下した操業、所謂「ソフトブロー」の操業では、溶鋼中の炭素と供給する酸素との反応が遅れ、換言すれば脱炭酸素効率が低下して、供給した酸素ガスのうちで鉄の酸化反応に費やされる酸素ガスが多くなり、溶存酸素濃度が上昇することが知られている。つまり、溶鋼中の溶存酸素濃度を意図的に上昇させることが可能であることが知られている。従って、脱炭精錬末期をソフトブロー操業とするために、転炉内に供給する脱炭用酸素ガスの供給流量を低下する、或いは、上吹き酸素ランスの高さ位置(「ランス高さ」という)を上昇させる。脱炭用酸素ガスの供給流量を低下することにより、上吹き酸素ジェットの噴出速度が低下して脱炭酸素効率が低下し、同様に、ランス高さを大きくすることで、上吹き酸素ジェトの減衰が大きくなり、脱炭酸素効率が低下する。また、転炉脱炭精錬の末期に、溶鋼攪拌用の攪拌用ガス流量を低下することによっても、溶存酸素濃度を高くすることができる。これは、溶鋼の攪拌を弱くすることで溶鋼中炭素の反応サイトへの移動が遅れ、脱炭反応が阻害されて鉄の酸化が増加するためである。   The dissolved oxygen concentration is adjusted as follows. One method is a method in which an operation in which the dissolved oxygen concentration is intentionally increased at the end of decarburization and refining in the converter is performed. In converter decarburization refining, the operation of reducing the supply flow rate of oxygen gas for decarburization or the operation of reducing the supply pressure, so-called `` soft blow '' operation, delays the reaction between carbon in molten steel and the supplied oxygen, In other words, it is known that the decarbonation efficiency is lowered, the oxygen gas consumed for the iron oxidation reaction is increased in the supplied oxygen gas, and the dissolved oxygen concentration is increased. That is, it is known that the dissolved oxygen concentration in molten steel can be increased intentionally. Therefore, in order to set the end of decarburization refining to soft blow operation, the supply flow rate of decarburization oxygen gas supplied into the converter is reduced, or the height position of the top blown oxygen lance (referred to as “lance height”) ). By reducing the supply flow rate of the decarburization oxygen gas, the jet speed of the top blown oxygen jet is lowered and the decarbonation efficiency is lowered. Similarly, by increasing the lance height, the top blown oxygen jet Attenuation increases and decarbonation efficiency decreases. Also, the dissolved oxygen concentration can be increased by reducing the stirring gas flow rate for stirring molten steel at the end of converter decarburization refining. This is because by weakening the stirring of the molten steel, the movement of carbon in the molten steel to the reaction site is delayed, the decarburization reaction is inhibited, and iron oxidation increases.

溶存酸素濃度を調整する他の1つの方法は、転炉で精錬された溶鋼に酸素ガスを供給して溶存酸素濃度を強制的に上昇させる方法である。この方法としては、例えば、転炉から取鍋に出鋼される出鋼流に向けて酸素ガスを吹き付け、吹き付けた酸素ガスを溶鋼中に溶解させる方法や、出鋼後の取鍋内の溶鋼に吹き込みランスなどを介して酸素ガスを吹き込み、吹き込んだ酸素ガスを溶鋼中に溶解させる方法を用いることができる。   Another method for adjusting the dissolved oxygen concentration is a method of forcibly increasing the dissolved oxygen concentration by supplying oxygen gas to the molten steel refined in the converter. As this method, for example, a method in which oxygen gas is sprayed toward a steel flow to be steeled from a converter to a ladle and the sprayed oxygen gas is dissolved in the molten steel, or a molten steel in the ladle after the steel is delivered. A method can be used in which oxygen gas is blown into the steel through a blow lance and the blown oxygen gas is dissolved in the molten steel.

これらのうちの何れか1つの方法、或いは、複数の方法の組み合わせによって、溶存酸素濃度を0.04質量%以上で、且つ溶鋼中の炭素濃度に応じて溶存酸素濃度と炭素濃度との比(溶存酸素濃度/炭素濃度)が1.34以上になるように調整する。転炉内で調整する場合には、転炉からの出鋼時の溶鋼温度の低下に起因して溶存酸素濃度が低下することもあるので、この点に留意して溶存酸素濃度を調整する。   By any one of these methods or a combination of a plurality of methods, the dissolved oxygen concentration is 0.04% by mass or more, and the ratio between the dissolved oxygen concentration and the carbon concentration according to the carbon concentration in the molten steel ( (Dissolved oxygen concentration / carbon concentration) is adjusted to 1.34 or more. When adjusting in the converter, the dissolved oxygen concentration may decrease due to a decrease in the molten steel temperature at the time of steel output from the converter. Therefore, the dissolved oxygen concentration is adjusted in consideration of this point.

転炉での脱炭精錬終了後、溶鋼を転炉から取鍋に出鋼する。出鋼時、溶鋼に巻き込まれて炉内スラグの一部が取鍋内に流出し、取鍋内の溶鋼上に滞留する。取鍋内に滞留するスラグは次工程の真空脱ガス設備における脱酸処理後に溶鋼中のAlなどの脱酸剤と反応して溶鋼の清浄性を損なうこともあるので、スラグ中に金属Alなどのスラグ改質剤を取鍋上方から添加してスラグを脱酸してもよい。尚、本発明においては、出鋼時、AlやSiなどの強脱酸元素による脱酸処理は当然ながら実施しない。   After decarburization refining in the converter, the molten steel is discharged from the converter into a ladle. At the time of steel removal, a part of the slag in the furnace flows into the ladle and is retained on the molten steel in the ladle. Since the slag staying in the ladle may react with a deoxidizer such as Al in the molten steel after deoxidation treatment in the vacuum degassing facility in the next process, it may impair the cleanliness of the molten steel. The slag modifier may be added from above the pan to deoxidize the slag. In the present invention, the deoxidation treatment with a strong deoxidation element such as Al or Si is naturally not performed at the time of steel output.

次いで、溶鋼を収容した取鍋を真空脱ガス設備に搬送し、真空脱ガス設備において真空脱炭精錬を実施する。溶鋼を処理する真空脱ガス設備としてはRH真空脱ガス装置が広く使用されているので、RH真空脱ガス装置を使用した例で本発明を説明する。   Next, the ladle containing the molten steel is transported to a vacuum degassing facility, and vacuum decarburization refining is performed in the vacuum degassing facility. Since an RH vacuum degassing apparatus is widely used as a vacuum degassing facility for processing molten steel, the present invention will be described using an example in which an RH vacuum degassing apparatus is used.

図1に、本発明を実施する際に用いたRH真空脱ガス装置の例を縦断面概略図で示す。図1に示すように、RH真空脱ガス装置1は、上部槽6及び下部槽7からなる真空槽5と、下部槽7の下部に設けられた上昇側浸漬管8及び下降側浸漬管9とを備え、上部槽6には、排気装置(図示せず)と接続するダクト11と原料投入口12とが備えられ、また、上昇側浸漬管8には環流用ガス吹込管10が設けられている。環流用ガス吹込管10からは環流用ガスとしてArガスが上昇側浸漬管8の内部に吹き込まれる構造となっている。   In FIG. 1, the example of the RH vacuum degassing apparatus used when implementing this invention is shown with a longitudinal cross-sectional schematic diagram. As shown in FIG. 1, the RH vacuum degassing apparatus 1 includes a vacuum tank 5 including an upper tank 6 and a lower tank 7, an ascending-side dip pipe 8 and a descending-side dip pipe 9 provided below the lower tank 7. The upper tank 6 is provided with a duct 11 connected to an exhaust device (not shown) and a raw material inlet 12, and the rising side dip pipe 8 is provided with a reflux gas blowing pipe 10. Yes. From the reflux gas blowing tube 10, Ar gas is blown into the rising side immersion tube 8 as the reflux gas.

このように構成されているRH真空脱ガス装置1において、先ず、溶鋼3を収納する取鍋2を真空槽5の直下に搬送し、取鍋2を昇降装置(図示せず)によって上昇させ、上昇側浸漬管8及び下降側浸漬管9を取鍋2に収容された溶鋼3に浸漬させる。次いで、環流用ガス吹込管10から上昇側浸漬管8の内部にArガスを環流用ガスとして吹き込むとともに、真空槽5の内部をダクト11に連結される排気装置にて排気して真空槽5の内部を減圧する。真空槽5の内部が減圧されると、取鍋2に収容された溶鋼3は、環流用ガス吹込管10から吹き込まれるArガスとともに上昇側浸漬管8を上昇して真空槽5の内部に流入し、その後、下降側浸漬管9を介して取鍋2に戻る流れ、所謂、環流を形成してRH真空脱ガス精錬が施される。   In the RH vacuum degassing apparatus 1 configured in this way, first, the ladle 2 that stores the molten steel 3 is conveyed directly under the vacuum tank 5, and the ladle 2 is raised by an elevating device (not shown), The ascending side dip tube 8 and the descending side dip tube 9 are immersed in the molten steel 3 accommodated in the pan 2. Next, Ar gas is blown into the ascending-side dip tube 8 from the reflux gas blowing tube 10 as a reflux gas, and the inside of the vacuum chamber 5 is evacuated by an exhaust device connected to the duct 11. Depressurize the inside. When the inside of the vacuum chamber 5 is depressurized, the molten steel 3 accommodated in the ladle 2 ascends the rising side dip tube 8 together with Ar gas blown from the reflux gas blowing tube 10 and flows into the vacuum chamber 5. Then, a flow returning to the ladle 2 via the descending side dip tube 9, that is, a so-called recirculation is formed, and RH vacuum degassing is performed.

溶鋼3の環流が形成され、溶鋼3が真空槽5の減圧雰囲気に曝されると、前述した(2)式におけるPCOが大気圧下で実施した転炉脱炭精錬時に比べて大幅に小さくなり、溶鋼中の炭素と溶存酸素との反応が発生する。つまり、脱炭反応が発生し、溶鋼3に含まれる炭素はCOガスとなって排ガスとともに真空槽5からダクト11を介して排出され、溶鋼3に真空脱炭精錬が施される。この場合に、溶鋼3は脱炭反応に必要な酸素を溶存酸素として有しているため、真空槽5を環流する溶鋼3に酸素ガスのみならず、鉄鉱石などの固体酸素源を添加しなくても、極低炭素域まで脱炭することができる。 Formed reflux of molten steel 3, the molten steel 3 is exposed to a reduced-pressure atmosphere of the vacuum chamber 5, significantly lower than in the embodiment the converter decarburization refining P CO in the aforementioned equation (2) is under atmospheric pressure Thus, the reaction between carbon in the molten steel and dissolved oxygen occurs. That is, decarburization reaction occurs, carbon contained in the molten steel 3 becomes CO gas and is discharged together with the exhaust gas from the vacuum tank 5 through the duct 11, and the molten steel 3 is subjected to vacuum decarburization refining. In this case, since the molten steel 3 has oxygen necessary for the decarburization reaction as dissolved oxygen, not only oxygen gas but also a solid oxygen source such as iron ore is not added to the molten steel 3 circulating in the vacuum tank 5. However, it can be decarburized to an extremely low carbon range.

このようにして真空脱炭精錬を継続し、溶鋼3の炭素濃度が0.01質量%以下の所定の値となったなら、原料投入口12から溶鋼3にAlなどの脱酸剤を添加して溶鋼3を脱酸処理する。Alなどの脱酸剤の添加により溶鋼3の溶存酸素は急激に減少し、脱炭反応が終了する。Alなどの脱酸剤を添加した後、溶鋼3の清浄性を確保するために、必要に応じて、溶鋼3の上に存在するスラグ4に金属Alなどからなるスラグ改質剤を添加してもよい。   In this way, vacuum decarburization refining is continued, and when the carbon concentration of the molten steel 3 reaches a predetermined value of 0.01% by mass or less, a deoxidizer such as Al is added to the molten steel 3 from the raw material inlet 12. The molten steel 3 is deoxidized. By adding a deoxidizing agent such as Al, the dissolved oxygen in the molten steel 3 rapidly decreases, and the decarburization reaction ends. In order to ensure the cleanliness of the molten steel 3 after adding a deoxidizer such as Al, a slag modifier made of metal Al or the like is added to the slag 4 existing on the molten steel 3 as necessary. Also good.

そして、脱酸剤添加後も更に数分間程度の環流を継続し、必要に応じてAl、Si、Mn、Nb、Ti、V、Bなどの成分調整剤を原料投入口12から溶鋼3に投入して溶鋼3の成分を調整する。成分調整後、真空槽5を大気圧に戻してRH真空脱ガス精錬を終了する。   Then, after the deoxidizer is added, the recirculation is continued for about several minutes, and component adjusters such as Al, Si, Mn, Nb, Ti, V, and B are added to the molten steel 3 from the raw material inlet 12 as necessary. Then, the components of the molten steel 3 are adjusted. After the component adjustment, the vacuum chamber 5 is returned to atmospheric pressure, and the RH vacuum degassing refining is completed.

以上説明したように、本発明では、RH真空脱ガス装置1における脱炭精錬の前までに、溶鋼中の炭素濃度を0.02〜0.06質量%の範囲とし、同時に、溶鋼中の溶存酸素濃度を、0.04質量%以上で且つ溶鋼中の炭素濃度に応じて溶存酸素濃度と炭素濃度との比(溶存酸素濃度/炭素濃度)が1.34以上になるように調整するので、RH真空脱ガス装置1における脱炭反応に必要な酸素は溶存酸素として確保され、RH真空脱ガス装置1では酸素ガスを供給する必要がなく、また、酸素ガスを供給する必要がなくなることから酸素ガス供給用上吹きランスのパージ用ガスも自ずと必要とせず、従って、真空槽5の内部の真空度を設備の上限値にまで高めることができ、その結果、真空脱炭精錬時の脱炭反応が促進され、短時間で真空脱炭精錬を完了することができると同時に、炭素濃度の極めて低い溶鋼を溶製することが可能となる。   As explained above, in the present invention, before the decarburization refining in the RH vacuum degassing apparatus 1, the carbon concentration in the molten steel is set in the range of 0.02 to 0.06% by mass, and at the same time, dissolved in the molten steel. Since the oxygen concentration is adjusted to 0.04% by mass or more and the ratio of dissolved oxygen concentration to carbon concentration (dissolved oxygen concentration / carbon concentration) is 1.34 or more according to the carbon concentration in the molten steel. Oxygen necessary for the decarburization reaction in the RH vacuum degassing apparatus 1 is ensured as dissolved oxygen, and the RH vacuum degassing apparatus 1 does not need to supply oxygen gas and does not need to supply oxygen gas. The purge gas of the upper blowing lance for gas supply is not necessarily required, so the vacuum inside the vacuum chamber 5 can be increased to the upper limit of the equipment, and as a result, the decarburization reaction during vacuum decarburization refining. Is promoted and true in a short time At the same time it is possible to complete the decarburization refining, it is possible to melting the very low molten steel carbon concentration.

尚、上記説明はRH真空脱ガス装置1を用いた例で説明したが、本発明はRH真空脱ガス装置1を用いることに限られるものではなく、DH真空脱ガス装置やVAD炉などの他の真空脱ガス設備を用いても、上記に沿って実施することができる。   Although the above description has been given with an example using the RH vacuum degassing apparatus 1, the present invention is not limited to the use of the RH vacuum degassing apparatus 1, and other devices such as a DH vacuum degassing apparatus and a VAD furnace. Even if it uses the vacuum degassing equipment, it can implement along the above.

高炉で溶製した溶銑をトーピードカーで受銑し、トーピードカーで脱燐処理及び脱硫処理の溶銑予備処理を施した後、酸素ガスを上底吹きする転炉に装入して脱炭精錬を実施した。この脱炭精錬の末期、上吹き及び底吹の酸素ガスの供給流量を減少させて、溶鋼中の溶存酸素濃度が0.04質量%以上で且つ比(溶存酸素濃度/炭素濃度)が1.34以上になるように調整した。転炉から取鍋への出鋼後の溶鋼成分は、C:0.02〜0.06質量%、Si:0.05質量%以下、Mn:0.3質量%以下、P:0.02質量%以下、S:0.003質量%以下、溶存酸素濃度は0.04質量%以上で、比(溶存酸素濃度/炭素濃度)は1.34〜2.75であった。   The hot metal melted in the blast furnace was received by a torpedo car, and after the hot metal pretreatment of the dephosphorization treatment and the desulfurization treatment was carried out by the torpedo car, the decarburization and refining was carried out by charging it into a converter where oxygen gas was blown into the bottom. . At the end of this decarburization refining, the supply flow rate of oxygen gas for top blowing and bottom blowing is decreased so that the dissolved oxygen concentration in the molten steel is 0.04% by mass or more and the ratio (dissolved oxygen concentration / carbon concentration) is 1. Adjustment was made to be 34 or more. The molten steel components after the steel from the converter to the ladle are C: 0.02 to 0.06 mass%, Si: 0.05 mass% or less, Mn: 0.3 mass% or less, P: 0.02 Mass% or less, S: 0.003 mass% or less, dissolved oxygen concentration was 0.04 mass% or more, and the ratio (dissolved oxygen concentration / carbon concentration) was 1.34 to 2.75.

この溶鋼を真空槽内の到達真空度が1torr(133Pa)以下である、図1に示すRH真空脱ガス装置に搬送して真空脱炭精錬を施し、極低炭素鋼を溶製した(「本発明例」という)。RH真空脱ガス装置では、酸素ガスも鉄鉱石などの固体酸素源も添加せずに真空脱炭精錬を実施した。この真空脱炭精錬の末期には、真空槽内の真空度は0.25torr程度まで低下した。そして、真空脱炭処理時間(t)と真空脱炭処理前の溶鋼中炭素濃度(Ci)と真空脱炭処理後の溶鋼中炭素濃度(Cf)とから、「脱炭速度=[ln(Ci/Cf)]/t」からなる式で脱炭速度を求めた。   This molten steel is transported to the RH vacuum degassing apparatus shown in FIG. 1 whose ultimate vacuum in the vacuum chamber is 1 torr (133 Pa) or less and subjected to vacuum decarburization refining to melt ultra-low carbon steel (“this” Invention examples)). In the RH vacuum degassing apparatus, vacuum decarburization refining was performed without adding oxygen gas or solid oxygen source such as iron ore. At the end of this vacuum decarburization refining, the degree of vacuum in the vacuum chamber decreased to about 0.25 torr. Then, from the vacuum decarburization time (t), the carbon concentration (Ci) in the molten steel before the vacuum decarburization treatment, and the carbon concentration (Cf) in the molten steel after the vacuum decarburization treatment, “decarburization rate = [ln (Ci / Cf)] / t ”was used to determine the decarburization rate.

また、比較のために、上記と同一の条件で溶製した溶鋼を、上吹きランスの設置されたRH真空脱ガス装置に搬送して真空脱炭精錬を実施し、極低炭素鋼を溶製した(「比較例」という)。この場合、真空脱炭精錬に必要な酸素は溶鋼が溶存酸素として保有していることから、上吹きランスからは酸素ガスを供給しないで真空脱炭精錬を実施したが、上吹きランスのパージ用ガスとしてArガスを700〜900L(標準状態)/分程度上吹きランスから真空槽内に吹き込んだ。比較例においては、真空槽内の真空度は、真空脱炭精錬の末期においても0.5torr程度であった。この比較例においても上記の式を用いて脱炭速度を求めた。   For comparison, molten steel melted under the same conditions as described above is transported to an RH vacuum degassing device equipped with an upper blowing lance and subjected to vacuum decarburization and refining to produce ultra-low carbon steel. (Referred to as “comparative example”). In this case, the oxygen required for the vacuum decarburization refining is held in the molten steel as dissolved oxygen, so vacuum decarburization refining was carried out without supplying oxygen gas from the top blowing lance. Ar gas was blown into the vacuum chamber from the upper blow lance as a gas at a rate of 700 to 900 L (standard state) / min. In the comparative example, the degree of vacuum in the vacuum chamber was about 0.5 torr even in the final stage of vacuum decarburization refining. Also in this comparative example, the decarburization rate was calculated | required using said formula.

その結果、本発明例における脱炭速度の平均値は、比較例における脱炭速度の平均値に比べて約20%向上することが確認できた。つまり、本発明によって、真空脱炭処理時間を約20%短縮することができた。   As a result, it was confirmed that the average value of the decarburization rate in the present invention example was improved by about 20% as compared with the average value of the decarburization rate in the comparative example. That is, according to the present invention, the vacuum decarburization processing time could be shortened by about 20%.

本発明を実施する際に用いたRH真空脱ガス装置の縦断面概略図である。It is the longitudinal cross-sectional schematic of the RH vacuum degassing apparatus used when implementing this invention.

符号の説明Explanation of symbols

1 RH真空脱ガス装置
2 取鍋
3 溶鋼
4 スラグ
5 真空槽
6 上部槽
7 下部槽
8 上昇側浸漬管
9 下降側浸漬管
10 環流用ガス吹込管
11 ダクト
12 原料投入口
DESCRIPTION OF SYMBOLS 1 RH vacuum degassing apparatus 2 Ladle 3 Molten steel 4 Slag 5 Vacuum tank 6 Upper tank 7 Lower tank 8 Rising side immersion pipe 9 Lowering side immersion pipe 10 Recirculation gas blowing pipe 11 Duct 12 Raw material inlet

Claims (3)

転炉における脱炭精錬によって得た溶鋼を、真空脱ガス設備の大気圧よりも低い減圧下において脱炭精錬して極低炭素鋼を溶製するに際し、前記真空脱ガス設備における脱炭精錬開始前の溶鋼の炭素濃度が0.02〜0.06質量%の範囲で、溶鋼の溶存酸素濃度が0.04質量%以上であり、且つ、該溶存酸素濃度と前記炭素濃度との比(溶存酸素濃度/炭素濃度)が1.34以上になるように予め溶鋼の成分を調整するとともに、真空脱ガス設備では減圧下の溶鋼に酸素ガスを供給せずに脱炭精錬することを特徴とする、極低炭素鋼の溶製方法。   When decarburizing and refining the molten steel obtained by decarburizing and refining in the converter under a reduced pressure lower than the atmospheric pressure of the vacuum degassing facility, decarburization and refining at the vacuum degassing facility is started. The carbon concentration of the previous molten steel is in the range of 0.02 to 0.06 mass%, the dissolved oxygen concentration of the molten steel is 0.04 mass% or more, and the ratio between the dissolved oxygen concentration and the carbon concentration (dissolved The components of the molten steel are adjusted in advance so that (oxygen concentration / carbon concentration) is 1.34 or more, and the vacuum degassing equipment is decarburized and refined without supplying oxygen gas to the molten steel under reduced pressure. , Method for melting ultra-low carbon steel. 前記転炉における脱炭精錬の末期に、転炉内に供給する酸素ガスの供給流量を低下する、上吹き酸素ランスの高さ位置を上昇する、転炉内溶鋼の攪拌強度を低下する、のうちの何れか1つの対策または何れか2つ以上の対策を実施して、前記溶存酸素濃度を調整することを特徴とする、請求項1に記載の極低炭素鋼の溶製方法。   In the final stage of decarburization and refining in the converter, the supply flow rate of oxygen gas supplied into the converter is decreased, the height position of the top blown oxygen lance is increased, and the stirring strength of the molten steel in the converter is decreased, The method for melting ultra-low carbon steel according to claim 1, wherein the dissolved oxygen concentration is adjusted by implementing any one of the measures or any two or more measures. 前記転炉から取鍋への溶鋼の出鋼時に出鋼流に向けて酸素ガスを吹き付ける、出鋼後の取鍋内の溶鋼に酸素ガスを吹き込む、のうちの何れか1つの対策または双方の対策を実施して、前記溶存酸素濃度を調整することを特徴とする、請求項1に記載の極低炭素鋼の溶製方法。   Either one of the countermeasures or both of blowing oxygen gas toward the outgoing steel flow when the molten steel is discharged from the converter to the ladle, and blowing oxygen gas into the molten steel in the ladle after the outgoing steel The method for melting ultra-low carbon steel according to claim 1, wherein measures are taken to adjust the dissolved oxygen concentration.
JP2005220250A 2005-07-29 2005-07-29 Method for manufacturing ultra-low carbon steel Pending JP2007031807A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114262766A (en) * 2021-11-30 2022-04-01 邯郸钢铁集团有限责任公司 Method for quickly decarbonizing RH refined ultra-low carbon steel

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JPH01246314A (en) * 1988-03-29 1989-10-02 Kawasaki Steel Corp Production of extremely low carbon steel by vacuum degassing treatment
JPH03153817A (en) * 1989-11-10 1991-07-01 Kawasaki Steel Corp Smelting method for dead soft steel
JPH10298629A (en) * 1997-04-23 1998-11-10 Sumitomo Metal Ind Ltd Method for melting extra-low carbon steel having high cleanliness
JP2000119732A (en) * 1998-10-07 2000-04-25 Nkk Corp Melting method for high cleanliness extra-low carbon steel

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Publication number Priority date Publication date Assignee Title
JPS5811721A (en) * 1981-07-16 1983-01-22 Kawasaki Steel Corp Vacuum refining method for molten steel
JPH01198419A (en) * 1988-02-03 1989-08-10 Sumitomo Metal Ind Ltd Method for melting low carbon steel
JPH01246314A (en) * 1988-03-29 1989-10-02 Kawasaki Steel Corp Production of extremely low carbon steel by vacuum degassing treatment
JPH03153817A (en) * 1989-11-10 1991-07-01 Kawasaki Steel Corp Smelting method for dead soft steel
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JP2000119732A (en) * 1998-10-07 2000-04-25 Nkk Corp Melting method for high cleanliness extra-low carbon steel

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114262766A (en) * 2021-11-30 2022-04-01 邯郸钢铁集团有限责任公司 Method for quickly decarbonizing RH refined ultra-low carbon steel

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