JP2017171994A - Secondary refining method of stainless steel molten metal - Google Patents
Secondary refining method of stainless steel molten metal Download PDFInfo
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本発明は、転炉または電気炉などで溶製され、粗脱炭されたステンレス鋼溶湯に対し、減圧下にて酸化性ガスを供給して、前記ステンレス鋼溶湯中の炭素を更に低下させるステンレス鋼溶湯の二次精錬方法に関する。 The present invention provides a stainless steel that further reduces the carbon in the molten stainless steel by supplying an oxidizing gas under reduced pressure to the molten stainless steel melted and roughly decarburized in a converter or electric furnace. The present invention relates to a secondary refining method for molten steel.
ステンレス鋼の精錬では、クロムを始めとしてニッケル、モリブデン、銅などの合金成分を添加する場合が多く、成分調整のために添加される大量の合金鉄や金属などの溶解のための熱補償が必要である。本明細書では、合金成分を添加するための合金鉄及び金属を「合金原料」と定義する。また、クロムを１０質量％以上含有するステンレス鋼では、クロムを含有しない炭素鋼と比較して、脱炭処理時の到達炭素濃度が高位となり、脱炭反応が停滞しやすいという特性がある。 In the refining of stainless steel, alloy components such as nickel, molybdenum, and copper are often added in addition to chromium, and heat compensation is required to dissolve a large amount of alloyed iron and metals added to adjust the components. It is. In this specification, alloy iron and metal for adding alloy components are defined as “alloy raw material”. In addition, stainless steel containing 10% by mass or more of chromium has a characteristic that the reached carbon concentration at the time of decarburization is higher than that of carbon steel not containing chromium, and the decarburization reaction is likely to be stagnant.
一般的に、溶湯（鋼浴）中の炭素を、酸素ガスを供給して酸化し、除去する工程において、溶湯中の炭素濃度が高位の場合、脱炭速度は炭素の濃度には依存せず、酸素の供給速度に依存する。この領域は、酸素の物質移動が脱炭反応の律速過程となっており、「脱炭最盛期」とも呼ばれる。一方、脱炭が進行して溶湯中の炭素濃度が希薄になると、炭素濃度の低下に伴って脱炭速度が低下する。この領域では、炭素の物質移動が脱炭反応の律速過程となっている。 Generally, in the process of oxidizing and removing carbon in molten metal (steel bath) by supplying oxygen gas, if the carbon concentration in the molten metal is high, the decarburization rate does not depend on the carbon concentration. Depends on the oxygen supply rate. In this region, the mass transfer of oxygen is the rate-determining process of the decarburization reaction, which is also called the “highest decarburization period”. On the other hand, when the decarburization progresses and the carbon concentration in the molten metal becomes dilute, the decarburization rate decreases as the carbon concentration decreases. In this region, carbon mass transfer is the rate-determining process of decarburization reaction.
大気圧よりも低圧の減圧雰囲気下で行われるステンレス鋼溶湯の真空脱炭処理では、溶湯中の炭素の酸化と溶湯中のクロムの酸化とが競合するために、酸素の物質移動が律速する領域においても、単純に酸素供給流量（「送酸速度」ともいう）を上昇するだけでは、脱炭速度を増大することが困難な場合がある。過剰に供給された酸素は溶湯中のクロムと反応してＣｒ２Ｏ３を生成するが、溶湯中のクロム濃度及びスラグ中のＣｒ２Ｏ３活量と平衡する溶湯中の溶存酸素濃度は、高温になるほど増大する。酸素の物質移動が脱炭反応を律速する領域では、脱炭反応速度は主に反応サイトの溶存酸素濃度に比例することから、したがって、高温になるほど高い脱炭速度が得られる傾向となる。 In the vacuum decarburization treatment of molten stainless steel performed under a reduced pressure atmosphere lower than atmospheric pressure, the region in which oxygen mass transfer is rate-determined because of the competition between carbon oxidation in the molten metal and chromium in the molten metal. However, it may be difficult to increase the decarburization rate simply by increasing the oxygen supply flow rate (also referred to as “acid feed rate”). The excessively supplied oxygen reacts with chromium in the molten metal to produce Cr 2 O 3 , but the dissolved oxygen concentration in the molten metal that balances with the chromium concentration in the molten metal and the Cr 2 O 3 activity in the slag is: Increasing at higher temperatures. In the region where the mass transfer of oxygen controls the decarburization reaction, the decarburization reaction rate is mainly proportional to the dissolved oxygen concentration at the reaction site. Therefore, the higher the temperature, the higher the decarburization rate tends to be obtained.
一方、炭素の物質移動が律速する領域では、溶湯の温度を上昇させると、気相のＣＯガスと平衡する溶湯中炭素濃度を低下させる効果が期待できる。真空脱炭処理の末期にＣＯガスの発生速度が低下して高真空度雰囲気となった条件では、平衡炭素濃度は溶湯中の炭素濃度に比べて十分に低いため、溶湯の温度上昇によって平衡炭素濃度を低下させることによる脱炭速度の増大効果は限定的と考えられるが、炭素の物質移動が律速する領域においても、定性的には溶湯が高温になるほど脱炭速度は増大する傾向となる。 On the other hand, in the region where the mass transfer of carbon is rate-limiting, if the temperature of the molten metal is increased, an effect of decreasing the carbon concentration in the molten metal that is in equilibrium with the gas phase CO gas can be expected. Under the condition that the generation rate of CO gas is reduced to a high vacuum atmosphere at the end of the vacuum decarburization treatment, the equilibrium carbon concentration is sufficiently lower than the carbon concentration in the molten metal. Although the effect of increasing the decarburization rate by reducing the concentration is considered to be limited, even in the region where the mass transfer of carbon is rate-limiting, the decarburization rate tends to increase as the temperature of the molten metal increases.
すなわち、ステンレス鋼溶湯の真空脱炭処理において、溶湯の温度を上昇させることで、炭素濃度をより短時間で目標とする炭素濃度まで低減することが可能となり、真空排気用の蒸気使用量の低減やクロムの酸化ロスの低減など製造コスト低減効果が期待できる。 That is, in the vacuum decarburization treatment of molten stainless steel, it is possible to reduce the carbon concentration to the target carbon concentration in a shorter time by increasing the temperature of the molten metal, and to reduce the amount of steam used for vacuum exhaust It can be expected to reduce production costs such as reducing oxidation loss of chromium and chromium.
しかしながら、溶湯温度を上昇させるために、金属アルミニウムなどの昇熱材を用いて溶湯の昇熱を行ったり、転炉やＡＯＤ（Argon Oxygen Decarburization）炉、電気炉などの前工程での終了時の溶湯温度を上昇させたりすることは、製造コスト低減のメリットを享受できなくなるばかりでなく、耐火物の損耗促進など、かえってデメリットが増加する。また、二次精錬後の溶湯は、次の連続鋳造などの工程に供するのに適正な成分及び温度に調整する必要があるので、必要以上に溶湯温度を上昇させると、冷却のために余計な冷材や時間が必要となり、製造コストや生産性の観点から好ましくない。 However, in order to raise the molten metal temperature, the molten metal is heated using a heating material such as metallic aluminum, or at the end of the previous process such as a converter, an AOD (Argon Oxygen Decarburization) furnace, or an electric furnace. Increasing the molten metal temperature not only makes it impossible to enjoy the merit of reducing the manufacturing cost, but also increases the demerit, such as promoting the wear of the refractory. In addition, since the molten metal after secondary refining needs to be adjusted to an appropriate component and temperature for use in the next process such as continuous casting, if the molten metal temperature is raised more than necessary, it is unnecessary for cooling. Cold material and time are required, which is not preferable from the viewpoint of manufacturing cost and productivity.
極低炭フェライト系ステンレス鋼を溶製する方法として、非特許文献１には、減圧下での上吹きランスからの酸素ガス吹錬による脱炭処理実施後に、上吹きランスからの酸素ガスの供給を停止して、溶湯収容容器の底部に配置されたポーラスプラグを介して溶湯中に大量のアルゴンガス（最大２５ＮＬ／(ｍｉｎ・溶鋼−ｔ)）を吹き込んで溶湯を強力に攪拌して脱炭する方法が提案されている。 As a method of melting ultra-low carbon ferritic stainless steel, Non-Patent Document 1 describes the supply of oxygen gas from the top blowing lance after performing decarburization processing by oxygen gas blowing from the top blowing lance under reduced pressure. Is stopped, and a large amount of argon gas (maximum 25 NL / (min · mol-mol-t)) is blown into the molten metal through a porous plug disposed at the bottom of the molten metal container, and the molten metal is vigorously stirred to decarburize. A method has been proposed.
尚、真空脱炭処理で所定の炭素濃度まで脱炭されたステンレス鋼溶湯には、金属アルミニウムやフェロシリコンなどの脱酸剤が添加され、溶湯中の酸素を除去するとともに、スラグ中の酸化クロムなどを還元するための脱酸処理が施される。脱酸処理では、ステンレス鋼溶湯上に存在するスラグの還元に伴って溶湯の脱硫が進行し、また、脱酸剤の添加後、鉄よりも酸素との親和性が高く、蒸気圧の比較的低いクロム、マンガン、バナジウム、ニオブ、チタンなどの各種合金成分の濃度調整が行われる。脱酸処理とは、脱酸剤の添加によって溶湯を脱酸した時点から、スラグの還元、更には溶湯中合金成分の調整終了までの期間を指す。 In addition, a deoxidizer such as metallic aluminum or ferrosilicon is added to the molten stainless steel decarburized by vacuum decarburization to remove oxygen in the molten metal, and chromium oxide in the slag. Deoxidation treatment is performed to reduce the above. In the deoxidation treatment, the desulfurization of the molten metal proceeds with the reduction of the slag present on the stainless steel molten metal, and after the addition of the deoxidizing agent, the affinity for oxygen is higher than that of iron, and the vapor pressure is relatively low. The concentration of various alloy components such as low chromium, manganese, vanadium, niobium and titanium is adjusted. The deoxidation treatment refers to a period from the time when the molten metal is deoxidized by addition of a deoxidizing agent to the end of the slag reduction and the adjustment of the alloy components in the molten metal.
一方、鉄よりも酸素との親和性が低いニッケル、モリブデン、銅、コバルトなどの合金成分（以下、「難酸化性元素」と称する）は、合金添加装置の容量が比較的小さく、且つ、添加する合金原料の種類の多い二次精錬設備での添加を避けて、転炉やＡＯＤ炉などによる一次精錬の段階、或いは、その出鋼時に添加され、成分調整されることが一般的である。また、高炭素フェロクロムや高炭素フェロマンガンなどの炭素を高濃度で含有する合金鉄を使用した方が大幅に安価である、クロムやマンガンの一次の成分調整も、転炉、ＡＯＤ炉などによる一次精錬の段階やその出鋼時に行われることが一般的である。 On the other hand, alloy components such as nickel, molybdenum, copper, and cobalt that have a lower affinity for oxygen than iron (hereinafter referred to as “non-oxidizable elements”) have a relatively small capacity of the alloy addition device and are added. In general, it is added at the stage of primary refining in a converter, AOD furnace or the like, or at the time of steel production, and the components are adjusted, avoiding the addition in secondary refining equipment where there are many types of alloy raw materials. In addition, it is much cheaper to use high-ferrous ferrochromium and high-carbon ferromanganese alloy iron containing high concentrations of carbon. The primary component adjustment of chromium and manganese is also performed by primary converters, AOD furnaces, etc. It is generally performed at the refining stage or at the time of steel production.
しかしながら、上記の非特許文献１のように、ガス流量を増加させてより強力に攪拌を行う方法では、真空脱炭処理容器となる溶湯収容容器（取鍋）容積に対して溶湯容量が多いと、溶湯のオーバーフローが発生する。溶湯のオーバーフローが生じると生産性を大きく阻害してしまうことから、取鍋内の溶湯量を制限する必要があり、効率的な真空脱炭処理ができない。また、非特許文献１は脱炭速度に及ぼす溶湯温度の影響は何ら考慮していない。 However, as in Non-Patent Document 1 described above, in a method in which stirring is performed more strongly by increasing the gas flow rate, the molten metal capacity is larger than the molten metal storage container (ladder) volume serving as a vacuum decarburization processing container. , Molten metal overflow occurs. If the molten metal overflows, the productivity is greatly hindered. Therefore, it is necessary to limit the amount of the molten metal in the ladle, and an efficient vacuum decarburization process cannot be performed. Non-Patent Document 1 does not consider the influence of the molten metal temperature on the decarburization rate.
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、転炉や電気炉などで溶製され、粗脱炭されたステンレス鋼溶湯に対して、減圧下で酸素を供給して真空脱炭処理を施し、その後、ステンレス鋼溶湯を攪拌しつつ、脱酸剤を添加し、その後、更に成分調整用の合金原料を添加してステンレス鋼溶湯を二次精錬するにあたり、攪拌用ガス流量を増大せずに一般的な範囲に抑え、且つ、ステンレス鋼溶湯の昇熱を実施することなく、真空脱炭処理時、特にステンレス溶湯中の炭素濃度が高位な領域で、ステンレス鋼溶湯の温度を高位に保持することができ、これによって脱炭速度を向上させ、真空処理時間を短縮することのできる、ステンレス鋼溶湯の二次精錬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 its object is to supply oxygen under reduced pressure to a stainless steel melt that has been melted and roughly decarburized in a converter or an electric furnace. Apply deoxidizer while stirring the molten stainless steel, and then add alloy raw materials for component adjustment to further refining the molten stainless steel. Suppress the gas flow to a general range without increasing the gas flow rate, and without raising the temperature of the molten stainless steel, vacuum decarburization treatment, especially in the region where the carbon concentration in the molten stainless steel is high, It is possible to provide a secondary refining method for molten stainless steel that can maintain the temperature of the steel at a high level, thereby improving the decarburization rate and shortening the vacuum treatment time.
上記課題を解決するための本発明の要旨は以下のとおりである。
［１］減圧下で、ステンレス鋼溶湯に酸素を供給して真空脱炭処理を施した後、前記ステンレス鋼溶湯を攪拌しつつ、脱酸剤を添加して前記溶湯を脱酸し、更に成分調整用の合金原料を添加して所定の成分のステンレス鋼溶湯を溶製する、ステンレス鋼溶湯の二次精錬方法であって、
前記ステンレス鋼溶湯に、銅、ニッケル、モリブデン、コバルトのうちの少なくともいずれか一種の難酸化性元素を添加するための合金原料を、前記真空脱炭処理中の前記ステンレス鋼溶湯に、当該ステンレス鋼溶湯中の炭素濃度が０．０２質量％以下となった段階で添加することを特徴とする、ステンレス鋼溶湯の二次精錬方法。
［２］前記真空脱炭処理中の排気ガスの成分濃度を、前記真空脱炭処理を実施するための二次精錬設備に備えられた分析装置を用いて分析し、前記排気ガス中の炭素含有ガスの濃度分析値に基づいて、前記ステンレス鋼溶湯中の炭素濃度が０．０２質量％以下となる時点を判定することを特徴とする、上記［１］に記載のステンレス鋼溶湯の二次精錬方法。
［３］前記難酸化性元素を添加するための合金原料を添加する直前の時点での前記ステンレス鋼溶湯の温度が１６５０℃以上１７００℃以下であることを特徴とする、上記［１］または上記［２］に記載のステンレス鋼溶湯の二次精錬方法。
The gist of the present invention for solving the above problems is as follows.
[1] Under reduced pressure, oxygen is supplied to the molten stainless steel to perform vacuum decarburization treatment, and then the molten stainless steel is stirred to add a deoxidizer to deoxidize the molten metal. A secondary refining method for molten stainless steel, comprising adding an alloy raw material for adjustment to melt a molten stainless steel of a predetermined component,
An alloy raw material for adding at least one kind of hardly oxidizable element of copper, nickel, molybdenum and cobalt to the molten stainless steel is used as the stainless steel molten metal during the vacuum decarburization treatment. A secondary refining method for molten stainless steel, characterized in that the addition is performed when the carbon concentration in the molten metal is 0.02% by mass or less.
[2] The component concentration of the exhaust gas during the vacuum decarburization treatment is analyzed using an analyzer provided in a secondary refining facility for performing the vacuum decarburization treatment, and the carbon content in the exhaust gas is obtained. The secondary refining of the molten stainless steel according to the above [1], wherein the time point at which the carbon concentration in the molten stainless steel is 0.02% by mass or less is determined based on a gas concentration analysis value. Method.
[3] The above [1] or the above, wherein the temperature of the molten stainless steel immediately before the addition of the alloy raw material for adding the hardly oxidizable element is 1650 ° C. or higher and 1700 ° C. or lower. The secondary refining method for molten stainless steel according to [2].
本発明によれば、特段の昇熱手段を講じることなく、酸素の物質移動が脱炭反応を律速する領域、つまり、脱炭最盛期の溶湯温度を従来よりも高位に維持することが可能となり、これにより、脱炭速度の向上及び真空脱炭処理時間の短縮が実現される。 According to the present invention, it is possible to maintain a region where oxygen mass transfer controls the decarburization reaction, that is, a molten metal temperature at the peak of decarburization higher than before without taking any special heat-up means. Thereby, the improvement of the decarburization speed and the shortening of the vacuum decarburization processing time are realized.
以下、本発明を具体的に説明する。 Hereinafter, the present invention will be specifically described.
極低炭素濃度（炭素濃度≦０．０１０質量％）のステンレス鋼を溶製するにあたっては、転炉やＡＯＤ炉、電気炉などで一次精錬工程の粗脱炭処理を行ったステンレス鋼溶湯に、更に二次精錬工程として減圧雰囲気下で酸素ガスを供給し、溶湯中の炭素濃度を更に低下させることが必要である。この減圧雰囲気下での酸素ガス供給によるステンレス鋼溶湯の脱炭処理（「真空脱炭処理」という）には、一般的に、二次精錬設備として、ＲＨ真空脱ガス設備やＶＯＤ（Vacuum Oxygen Decarburization）設備が使用されている。尚、一次精錬の施された溶湯に対して更に精錬を施す工程を二次精錬という。 When melting stainless steel with an extremely low carbon concentration (carbon concentration ≦ 0.010 mass%), the molten stainless steel subjected to the rough decarburization process in the primary refining process in a converter, AOD furnace, electric furnace, Further, as a secondary refining process, it is necessary to supply oxygen gas under a reduced pressure atmosphere to further reduce the carbon concentration in the molten metal. For decarburization treatment of molten stainless steel by oxygen gas supply under this reduced pressure atmosphere (referred to as “vacuum decarburization treatment”), RH vacuum degassing equipment and VOD (Vacuum Oxygen Decarburization) are generally used as secondary refining equipment. ) Equipment is in use. The process of further refining the molten metal that has undergone primary refining is called secondary refining.
ＶＯＤ設備を用いて真空脱炭処理を施す場合を例として説明すると、ＶＯＤ設備の減圧容器内に、一次精錬工程の粗脱炭処理の施されたステンレス鋼溶湯を収容する取鍋を装入し、減圧容器内を大気圧よりも減圧したのちに、上吹きランスから酸素ガスを取鍋内のステンレス鋼溶湯に向けて供給し、真空脱炭処理を実施する。この際、酸素ガスの供給速度は０．０７〜０．２０Ｎｍ３／(ｍｉｎ・溶鋼−ｔ)程度の範囲内とし、溶湯の炭素濃度の低下に伴ってクロムの酸化ロスが過大にならないように、酸素ガスの供給速度を次第に減少させるように調整することが好ましい。減圧下で酸素ガスを供給することで、溶湯中の炭素が、大気圧下で行われる一次精錬工程よりも更に除去される。この真空脱炭処理によって溶湯中の炭素濃度が製品規格の炭素濃度以下まで低下したなら、酸素ガスの供給を停止し、その後、取鍋の底部に設置した底吹き羽口またはポーラスプラグから２〜１０ＮＬ／(ｍｉｎ・溶鋼−ｔ)のアルゴンガスを溶湯中に吹き込んで、取鍋内の溶湯を攪拌しながら、金属アルミニウムなどの脱酸元素を添加し、溶湯中の酸素濃度の低下及び酸素ガス供給によって生じたスラグ中酸化クロムの還元を行い、更に、各種の成分濃度の調整を行った後、減圧容器を大気圧に戻して減圧下での精錬を終了する。尚、脱炭速度を促進させるために、真空脱炭処理中も、前記底吹き羽口またはポーラスプラグからアルゴンガスを溶湯中に吹き込んで溶湯を攪拌する。 The case where vacuum decarburization processing is performed using a VOD facility will be described as an example. A ladle containing a stainless steel melt that has undergone rough decarburization processing in the primary refining process is placed in a vacuum vessel of the VOD facility. After depressurizing the inside of the decompression vessel from atmospheric pressure, oxygen gas is supplied from the top blowing lance toward the molten stainless steel in the pan, and vacuum decarburization processing is performed. At this time, the oxygen gas supply rate is set within a range of about 0.07 to 0.20 Nm 3 / (min · molten steel-t), so that the oxidation loss of chromium does not become excessive as the carbon concentration of the molten metal decreases. The oxygen gas supply rate is preferably adjusted to gradually decrease. By supplying oxygen gas under reduced pressure, carbon in the molten metal is further removed than in the primary refining step performed under atmospheric pressure. If the carbon concentration in the molten metal is reduced to below the product standard carbon concentration by this vacuum decarburization treatment, the supply of oxygen gas is stopped, and then 2 to 2 from the bottom blowing tuyere or porous plug installed at the bottom of the ladle While blowing argon gas of 10 NL / (min · molten steel-t) into the molten metal and stirring the molten metal in the ladle, a deoxidizing element such as metallic aluminum is added to reduce the oxygen concentration in the molten metal and oxygen gas. After reducing the chromium oxide in the slag generated by the supply and adjusting various component concentrations, the vacuum vessel is returned to atmospheric pressure and the refining under reduced pressure is completed. In order to accelerate the decarburization speed, the molten metal is stirred by blowing argon gas into the molten metal from the bottom blowing tuyere or the porous plug even during the vacuum decarburizing process.
ステンレス鋼の精錬では、大量の合金成分を添加しており、合金成分を調整するための合金鉄及び金属の大量投入に伴う溶湯の温度降下が大きい。以下、合金成分を含有する合金鉄及び金属をまとめて「合金原料」と定義する。但し、従来、合金原料の多くは、転炉やＡＯＤ炉などの一次精錬中、或いは一次精錬後の出鋼時に溶湯に添加され、二次精錬工程において添加されるのは、金属アルミニウムやフェロシリコンなどの脱酸剤、脱酸後に添加する必要のあるチタン、ニオブ、バナジウムなどを含有する合金原料、及び、採取した溶湯サンプルの成分分析値を確認してから成分調整するための各成分の少量の調整分にとどまることが一般的であった。 In the refining of stainless steel, a large amount of alloy components are added, and the temperature drop of the molten metal accompanying large amounts of alloy iron and metal for adjusting the alloy components is large. Hereinafter, alloy iron and metal containing alloy components are collectively defined as “alloy raw material”. However, many of the alloy raw materials are conventionally added to the molten metal during primary refining, such as converters and AOD furnaces, or when steel is removed after primary refining, and in the secondary refining process, metal aluminum and ferrosilicon are added. A small amount of each component to adjust the component after confirming the component analysis value of the sample of the molten metal sample, and the alloy raw material containing titanium, niobium, vanadium, etc. that need to be added after deoxidation It was common to stay within the adjustment amount.
このような従来の合金原料の添加方法に比較して、真空脱炭処理前の合金原料の添加量を減少させ、その分だけ真空脱炭処理後の合金原料の添加量を増加させる合金原料の添加方法を採用することで、二次精錬後の溶湯温度を同一とする条件の下で、真空脱炭処理中の溶湯温度を無理なく上昇させることができる。すなわち、従来、真空脱炭処理前に添加していた合金原料を減少させることで、減少させた合金原料量による冷却分だけ、真空脱炭処理前の温度を無理なく上昇させることができ、その後、真空脱炭処理後の合金原料の添加量を、上記の減少させた合金原料量に相当する量だけ増大させ、増大させた合金原料量による冷却分だけ溶湯温度を低下させることで、二次精錬後の溶湯温度を無理なく従来と同じレベルとすることができる。 Compared with the conventional method of adding alloy raw materials, the amount of alloy raw materials before the vacuum decarburization treatment is reduced, and the amount of alloy raw materials after vacuum decarburization treatment is increased accordingly. By employ | adopting the addition method, the molten metal temperature in a vacuum decarburization process can be raised reasonably on the conditions which make the molten metal temperature after secondary refining the same. That is, by reducing the amount of alloy raw material that has been added before the vacuum decarburization treatment, the temperature before the vacuum decarburization treatment can be increased without difficulty by the amount of cooling due to the reduced amount of the alloy raw material. The amount of addition of the alloy raw material after the vacuum decarburization treatment is increased by an amount corresponding to the reduced amount of the alloy raw material, and the molten metal temperature is lowered by the amount of cooling due to the increased amount of the alloy raw material. The molten metal temperature after refining can be made to the same level as before without difficulty.
ステンレス鋼溶湯の真空脱炭処理の場合、前述したように、酸素の物質移動が脱炭反応を律速する領域であっても、また、炭素の物質移動が脱炭反応を律速する領域であっても、溶湯温度が高温になるほど高い脱炭速度が得られることから、真空脱炭処理中の溶湯温度を無理なく上昇させることにより、ステンレス鋼溶湯を高い脱炭速度で効率的に溶製可能となる。 In the case of the vacuum decarburization treatment of the molten stainless steel, as described above, even if the mass transfer of oxygen is a region where the decarburization reaction is rate-limiting, or the mass transfer of carbon is a region where the decarburization reaction is rate-limiting. However, since the higher the molten metal temperature, the higher the decarburization speed, it is possible to efficiently melt the molten stainless steel at a high decarburization speed by increasing the molten metal temperature during the vacuum decarburization process. Become.
しかしながら、真空脱炭処理後の脱酸処理では、金属アルミニウムやフェロシリコンなどの脱酸剤、及び、脱酸後に添加することが必要である、鉄よりも酸素との親和性の高いチタン、ニオブ、バナジウムなどの合金原料、更には、採取した溶湯サンプルの成分分析値を確認してから成分調整するための各成分の調整分の合金原料も含めて多種の合金原料を投入する必要がある。このため、これらに加えて新たに大量の合金原料を添加しようとすると、二次精錬設備の合金原料投入装置による合金原料の秤量、搬送及び添加のために大幅な時間の延長を招くことになる。尚、本明細書において、脱酸処理とは、脱酸剤の添加によってステンレス鋼溶湯を脱酸した時点から、ステンレス鋼溶湯上に存在するスラグの還元、更には溶湯中合金成分の成分調整終了までの期間を指す。 However, in the deoxidation treatment after vacuum decarburization treatment, it is necessary to add a deoxidizer such as metallic aluminum or ferrosilicon, and titanium, niobium having higher affinity with oxygen than iron, which must be added after deoxidation. In addition, it is necessary to input various alloy raw materials including alloy raw materials such as vanadium as well as alloy raw materials for adjusting each component for component adjustment after confirming the component analysis value of the collected molten metal sample. For this reason, if a large amount of alloy raw material is added in addition to these, it will cause a significant increase in time for weighing, transporting and adding the alloy raw material by the alloy raw material charging device of the secondary refining equipment. . In addition, in this specification, deoxidation treatment means the reduction of slag present on the stainless steel molten metal from the time when the molten stainless steel is deoxidized by addition of a deoxidizing agent, and the completion of the component adjustment of the alloy components in the molten metal. Refers to the period up to.
そこで、従来、真空脱炭処理前に添加されていた合金原料の添加タイミングを、真空脱炭処理後に行われる脱酸処理中に行わず、合金原料投入装置に余力のある、つまり、合金原料の添加の必要性の低い真空脱炭処理の末期に変更することにより、同様の効果を得ることができないかを検討した。 Therefore, conventionally, the addition timing of the alloy raw material that was added before the vacuum decarburization treatment is not performed during the deoxidation treatment that is performed after the vacuum decarburization treatment, and the alloy raw material charging device has a surplus, that is, the alloy raw material It was examined whether the same effect could be obtained by changing to the final stage of vacuum decarburization treatment with low need for addition.
その結果、真空脱炭処理中、ステンレス鋼溶湯中の炭素濃度が０．０２質量％以下となった段階、或いは、脱炭反応が炭素の物質移動律速となった段階で添加するのであれば、それ以降は従来の脱炭速度レベルに低下するだけであり、合金原料添加による溶湯温度の低下に起因する脱炭速度への影響は余り大きくなく、高炭素濃度の領域における脱炭速度の向上によって処理時間短縮のメリットを享受できることがわかった。尚、ステンレス鋼溶湯中の炭素濃度が０．０２質量％以下となった時点は、脱炭反応が炭素の物質移動律速となった領域に含まれる。 As a result, during vacuum decarburization treatment, if the carbon concentration in the molten stainless steel is 0.02 mass% or less, or if the decarburization reaction is added at the stage where the mass transfer rate of carbon is controlled, After that, it is only reduced to the conventional decarburization rate level, and the influence on the decarburization rate due to the decrease in the molten metal temperature due to the addition of the alloy raw material is not so great, and the improvement of the decarburization rate in the region of high carbon concentration It was found that the benefits of shortening the processing time can be enjoyed. In addition, when the carbon concentration in the molten stainless steel becomes 0.02% by mass or less, the decarburization reaction is included in a region where the mass transfer rate of carbon is controlled.
真空脱炭処理の末期に添加することが可能な合金原料の量に相当する分の添加量だけ、真空脱炭処理前に添加する合金原料の量を減少させることで、脱炭反応が酸素の物質移動律速となる高炭素濃度の領域における溶湯温度を可能な限り上昇させ、一方、脱炭速度が低下した、炭素の物質移動律速となる領域以降に、減少させた量に相当する量の合金原料を投入する。このようにすることで、溶湯温度を上昇させた高炭素濃度の領域における脱炭速度を増大させることができ、全体の処理時間の短縮が可能となる。 By reducing the amount of alloy raw material added before the vacuum decarburization process by an amount corresponding to the amount of alloy raw material that can be added at the end of the vacuum decarburization process, Increase the melt temperature in the high carbon concentration region where mass transfer is controlled, as much as possible, while the decarburization rate is reduced, and the amount of alloy corresponding to the decreased amount after the region where the mass transfer rate of carbon is controlled Input raw materials. By doing in this way, the decarburization speed | rate in the area | region of the high carbon concentration which raised molten metal temperature can be increased, and shortening of the whole process time is attained.
その際、真空脱炭処理の末期に添加する合金原料としては、以下の条件を満たすことが必要となる。まず、溶存酸素濃度が高い条件で添加されるので、鉄よりも酸素との親和性の高い元素を添加元素として含有する合金原料は、添加元素が鉄よりも優先して酸化されることから不適である。また、炭素を、例えば１質量％以上といった高濃度で含有している合金原料を添加することは、真空脱炭処理時間の延長を招くので好ましくない。 At that time, the alloy raw material added at the end of the vacuum decarburization process must satisfy the following conditions. First, since it is added under conditions where the dissolved oxygen concentration is high, an alloy material containing an element having an affinity for oxygen higher than that of iron as an additive element is not suitable because the additive element is oxidized in preference to iron. It is. In addition, it is not preferable to add an alloy raw material containing carbon at a high concentration of, for example, 1% by mass or more, because the vacuum decarburization treatment time is extended.
これらの条件を満足する合金原料としては、銅、ニッケル、モリブデン、コバルトを添加するための合金原料が該当する。つまり、真空脱炭処理の末期に添加する合金原料は、銅、ニッケル、モリブデン、コバルトのうちの少なくともいずれか一種を添加するための合金原料、つまり、難酸化性元素を含有する合金原料とする必要がある。これらの元素は、難酸化性元素であるので、溶存酸素濃度が高い条件でステンレス鋼溶湯中に添加されても酸化されず、また、難酸化性であることは、逆にいえば、易還元性であり、これらの元素は還元剤として炭素を使用しなくても安価に且つ容易に還元することができ、これらの元素を含有する合金原料は、合金鉄であっても、また、鉄合金以外の金属であっても、炭素含有量が低い、または、炭素を実質的に含有しない。 As an alloy material satisfying these conditions, an alloy material for adding copper, nickel, molybdenum, and cobalt is applicable. That is, the alloy raw material added at the end of the vacuum decarburization process is an alloy raw material for adding at least one of copper, nickel, molybdenum, and cobalt, that is, an alloy raw material containing a hardly oxidizable element. There is a need. Since these elements are hardly oxidizable elements, they are not oxidized even if added to the molten stainless steel under a condition where the dissolved oxygen concentration is high, and the fact that they are hardly oxidizable is easily reduced. These elements can be reduced easily and inexpensively without using carbon as a reducing agent. The alloy raw material containing these elements may be iron alloy or iron alloy. Even if it is other metals, carbon content is low or does not contain carbon substantially.
これらの難酸化性元素の合金原料は、何れも従来の一般的な合金原料の添加方法では、転炉などの一次精錬中、或いは一次精錬後の出鋼時において溶湯に添加されていたので、添加タイミングを真空脱炭処理の末期に変更することにより、真空脱炭処理中の溶湯温度が上昇し、脱炭速度を向上させることが可能となる。 These alloy materials of hardly oxidizable elements are all added to the molten metal during primary refining such as a converter or at the time of steel removal after primary refining in the conventional method of adding alloy raw materials, By changing the addition timing to the end of the vacuum decarburization process, the melt temperature during the vacuum decarburization process increases, and the decarburization rate can be improved.
真空脱炭処理の末期に添加する難酸化性元素の合金原料の添加量が多いほど、換言すれば、真空脱炭処理前に添加する難酸化性元素の合金原料投入量の減少量が多いほど、温度上昇による脱炭促進効果が大きくなるので好ましいが、ステンレス鋼の成分規格上から添加可能な量には自ずと制約があり、また、合金原料投入装置の設備能力の点からも、短時間の真空脱炭処理の末期に添加できる量には自ずと制約がある。したがって、これらの条件に応じて可能な範囲で真空脱炭処理の末期に添加する難酸化性元素の合金原料の添加量を増大させるように決定すればよい。脱炭反応促進の観点からは、真空脱炭処理の末期に添加する難酸化性元素の合金原料の添加量を５ｋｇ／溶鋼−ｔ以上、より望ましくは１０ｋｇ／溶鋼−ｔ以上とすることが好ましい。 The more the amount of the hardly oxidizable element alloy material added at the end of the vacuum decarburization process, the more the amount of decrease in the amount of the hardly oxidizable element alloy material added before the vacuum decarburization process increases. However, it is preferable because the effect of promoting decarburization due to temperature rise is increased. However, the amount that can be added due to the component specifications of stainless steel is naturally limited, and also from the viewpoint of the facility capacity of the alloy raw material charging device, it is a short time. The amount that can be added at the end of the vacuum decarburization process is naturally limited. Therefore, what is necessary is just to determine so that the addition amount of the alloy raw material of the hardly oxidizable element added in the last stage of a vacuum decarburization process may be increased to the extent possible according to these conditions. From the viewpoint of promoting the decarburization reaction, it is preferable that the amount of the alloy material of the hardly oxidizable element added at the end of the vacuum decarburization treatment is 5 kg / molten steel-t or more, more desirably 10 kg / molten steel-t or more. .
真空脱炭処理の末期に難酸化性元素の合金原料を添加する際の溶湯の炭素濃度が、上記のように０．０２質量％以下の領域であるので、真空脱炭処理開始時の例えば０．１５質量％といった炭素濃度から、真空脱炭処理の末期に難酸化性元素の合金原料が添加されるまでの広い炭素濃度範囲において、脱炭反応速度を向上させる効果が得られる。この脱炭反応の促進効果は、脱炭反応とクロムの酸化反応との競合が顕著となる、溶湯中炭素濃度が０．１質量％以下の領域で特に顕著である。 Since the carbon concentration of the molten metal when adding the alloy material of the hardly oxidizable element at the end of the vacuum decarburization treatment is in the region of 0.02% by mass or less as described above, for example, 0 at the start of the vacuum decarburization treatment. The effect of improving the decarburization reaction rate is obtained in a wide carbon concentration range from the carbon concentration of .15 mass% to the addition of the hardly oxidizable element alloy raw material at the end of the vacuum decarburization treatment. The effect of promoting the decarburization reaction is particularly remarkable in the region where the carbon concentration in the melt is 0.1% by mass or less, in which competition between the decarburization reaction and the chromium oxidation reaction becomes significant.
溶湯中炭素濃度が０．０２質量％以下の領域、つまり、炭素の物質移動が脱炭反応を律速する領域では、溶湯の温度上昇による脱炭反応への影響は相対的には小さいものの、高温ほど脱炭速度が大きい傾向は維持されるので、真空脱炭処理時間をより短縮するためには、難酸化性元素の合金原料を添加する際の溶湯中炭素濃度は低いほど好ましいといえる。しかし、溶湯中炭素濃度が、真空脱炭処理の目標炭素濃度近くまで低下してから難酸化性元素の合金原料を添加するのでは、炭素濃度が目標値に低下した時点までに脱酸剤の投入準備が整わずに、真空脱炭処理の延長を招くおそれがあるので、脱酸剤の添加タイミングの調整に影響を及ぼさない程度の時間の余裕を持って、難酸化性元素の合金原料を添加することが望ましい。 In the region where the carbon concentration in the molten metal is 0.02% by mass or less, that is, in the region where the mass transfer of carbon controls the decarburization reaction, although the influence on the decarburization reaction due to the temperature rise of the molten metal is relatively small, Since the tendency for the decarburization speed to increase is maintained, it can be said that the lower the carbon concentration in the melt when the alloy raw material of the hardly oxidizable element is added, the better. However, when adding the alloy raw material of the hardly oxidizable element after the carbon concentration in the molten metal has dropped to near the target carbon concentration of the vacuum decarburization treatment, the deoxidizer should be added by the time the carbon concentration drops to the target value. There is a risk that the vacuum decarburization process may be extended without preparation for charging, so that the alloy raw material of the hardly oxidizable element should be provided with a time margin that does not affect the adjustment of the deoxidizer addition timing. It is desirable to add.
逆に、溶湯中炭素濃度が０．０２質量％を超える領域で難酸化性元素の合金原料を添加すると、それ以降の脱炭速度は、温度が低下した分だけ、例えば従来並みの脱炭速度まで低下する。但し、難酸化性元素の合金原料を投入する時点までの脱炭速度は、上記と同様に向上するので、投入タイミングに応じた脱炭促進効果は得られる。したがって、炭素濃度が０．０２質量％以下の時点で難酸化性元素の合金原料を添加するとしても、真空脱炭処理の末期に投入する難酸化性元素の合金原料の全量を、溶湯中炭素濃度が０．０２質量％以下の期間に投入することが困難な場合には、溶湯中炭素濃度が０．０２質量％を超える時点で難酸化性元素の合金原料を部分的に添加することは排除しない。しかし、この場合でも難酸化性元素の合金原料を添加する時点の溶湯中の炭素濃度は、できるだけ低いことが望ましく、０．０５質量％以下とすることが好ましい。 On the other hand, when the alloy raw material of the hardly oxidizable element is added in the region where the carbon concentration in the molten metal exceeds 0.02 mass%, the subsequent decarburization rate is, for example, the same decarburization rate as the temperature is decreased. To fall. However, since the decarburization speed up to the time when the alloy raw material of the hardly oxidizable element is added is improved in the same manner as described above, the decarburization promoting effect according to the input timing can be obtained. Therefore, even if the alloy material of the hardly oxidizable element is added when the carbon concentration is 0.02% by mass or less, the total amount of the alloy material of the hardly oxidizable element to be introduced at the end of the vacuum decarburization treatment is reduced in the carbon in the melt. When it is difficult to input during a period when the concentration is 0.02% by mass or less, it is possible to partially add the alloy material of the hardly oxidizable element when the carbon concentration in the molten metal exceeds 0.02% by mass. Do not exclude. However, even in this case, the carbon concentration in the molten metal at the time of adding the alloy material of the hardly oxidizable element is desirably as low as possible, and is preferably 0.05% by mass or less.
合金原料の投入時期を溶湯中炭素濃度が０．０２質量％以下の期間に制御するためには、真空脱炭処理中の溶湯の炭素濃度を迅速に把握する必要がある。溶湯中成分の把握方法としては、溶湯から採取した溶湯サンプルの成分分析を実施するのが一般的であるが、分析結果が判明するまでに１０分間程度の時間を要することから、かえって真空脱炭処理時間を延長させてしまうおそれがある。そこで、溶湯サンプルを採取せずに、迅速に溶湯中炭素濃度を把握することを目的として、二次精錬設備に排ガス成分の分析装置を設置して排ガス中の炭素含有ガスの濃度を分析し、排気ガス中の炭素含有ガスの濃度に基づいてステンレス鋼溶湯中の炭素濃度が０．０２質量％以下となる時点を判定することを試みた。その結果、その有効性を確認することができた。 In order to control the charging time of the alloy raw material to a period in which the carbon concentration in the molten metal is 0.02% by mass or less, it is necessary to quickly grasp the carbon concentration of the molten metal during the vacuum decarburization treatment. As a method for grasping the components in the molten metal, it is common to analyze the components of the molten metal sample collected from the molten metal. However, since it takes about 10 minutes for the analysis result to become clear, vacuum decarburization is rather necessary. There is a risk of extending the processing time. Therefore, for the purpose of quickly grasping the carbon concentration in the molten metal without taking a molten metal sample, an exhaust gas component analyzer is installed in the secondary refining facility to analyze the concentration of the carbon-containing gas in the exhaust gas, Based on the concentration of the carbon-containing gas in the exhaust gas, an attempt was made to determine when the carbon concentration in the molten stainless steel was 0.02% by mass or less. As a result, the effectiveness was confirmed.
例えば、減圧容器からの真空排気ダクトの途中に、排ガス成分の分析装置として質量分析計を設置し、脱炭処理中の排ガス流量及び排ガス成分データをリアルタイムで測定し、採取した溶湯サンプルの炭素濃度分析値との相関を調査したところ、排ガス中のＣＯ２濃度と溶湯中炭素濃度とに強い相関があることがわかった。脱炭反応が炭素の物質移動に律速される領域においては、溶湯中炭素濃度の低下とともに脱炭反応速度が低下するので、溶湯中炭素濃度の低下とともに、排ガス中のＣＯ２濃度が低下し、排ガス中のＣＯ２濃度によって溶湯中炭素濃度の推定が可能となる。すなわち、質量分析計で分析した排ガス中のＣＯ２濃度を真空脱炭処理中にリアルタイムで表示し、所定の閾値に到達した時点で、溶湯中の炭素濃度が０．０２質量％以下になったものとして、上記の真空脱炭処理の末期に添加する難酸化性元素の合金原料の投入を行うことができる。 For example, in the middle of a vacuum exhaust duct from a decompression vessel, a mass spectrometer is installed as an exhaust gas component analyzer, and the exhaust gas flow rate and exhaust gas component data during decarburization treatment are measured in real time, and the carbon concentration of the collected molten metal sample When the correlation with the analytical value was investigated, it was found that there was a strong correlation between the CO 2 concentration in the exhaust gas and the carbon concentration in the molten metal. In the region where the decarburization reaction is rate-controlled by the mass transfer of carbon, the decarburization reaction rate decreases as the carbon concentration in the melt decreases, so the CO 2 concentration in the exhaust gas decreases as the carbon concentration in the melt decreases, The carbon concentration in the molten metal can be estimated from the CO 2 concentration in the exhaust gas. That is, the CO 2 concentration in the exhaust gas analyzed by the mass spectrometer is displayed in real time during the vacuum decarburization process, and when the predetermined threshold value is reached, the carbon concentration in the molten metal becomes 0.02% by mass or less. As a thing, the alloy raw material of the hardly oxidizable element added at the last stage of said vacuum decarburization process can be thrown in.
脱炭速度は、溶湯温度や溶湯中クロム濃度、溶湯量などの影響も受けるので、上記の閾値は、これらの操業条件に応じて、真空脱炭処理の末期に採取した溶湯サンプルの炭素濃度分析値と排ガス分析値との対応を調査した結果に基づいて決定することが望ましい。また、二次精錬設備の減圧容器や真空排気装置における漏れによる空気の吸引量が安定している場合は、上記のようにＣＯ２濃度のみを用いて判定できる場合もある。しかし、漏れによる空気の吸引量は設備条件によって一様でない場合もあり、上記のＣＯ２濃度の測定値に加えて、ＣＯ濃度や排ガス流量の測定も用いて溶湯の脱炭速度を判定した結果に基づいて難酸化性元素の合金原料の投入タイミングを決定することが、望ましい場合もある。 The decarburization rate is also affected by the molten metal temperature, the chromium concentration in the molten metal, the amount of molten metal, etc. Therefore, the above threshold value depends on these operating conditions, and the carbon concentration analysis of the molten metal sample collected at the end of the vacuum decarburization process It is desirable to make a determination based on the result of investigating the correspondence between the value and the exhaust gas analysis value. Moreover, when the air suction amount due to leakage in the decompression vessel or the vacuum exhaust device of the secondary refining equipment is stable, the determination may be made using only the CO 2 concentration as described above. However, the amount of air suction due to leakage may not be uniform depending on the equipment conditions, and the result of determining the decarburization speed of the molten metal using the measurement of the CO concentration and the exhaust gas flow rate in addition to the measurement value of the CO 2 concentration described above. In some cases, it may be desirable to determine the input timing of the hardly oxidizable element alloy raw material based on the above.
前述のとおり、溶湯中炭素濃度が０．０２質量％を超える高炭素濃度の領域において、溶湯温度を高位にすることで脱炭処理時間の短縮を図ることが可能である。この場合、溶湯温度は、脱炭反応を促進する観点から、難酸化性元素の合金原料を添加する直前の時点において、１６５０℃以上とすることが望ましい。但し、過剰に温度を上昇させすぎると、取鍋耐火物の損耗が増大する。取鍋耐火物の損耗を防止するために、難酸化性元素の合金原料を添加する直前の時点での溶湯温度は１７００℃を超えないようにすることが望ましい。 As described above, it is possible to shorten the decarburization processing time by increasing the melt temperature in a high carbon concentration region where the carbon concentration in the melt exceeds 0.02 mass%. In this case, from the viewpoint of promoting the decarburization reaction, the molten metal temperature is preferably set to 1650 ° C. or more immediately before the addition of the hardly oxidizable element alloy raw material. However, if the temperature is raised excessively, the ladle refractory wear increases. In order to prevent the ladle refractory from being worn, it is desirable that the molten metal temperature immediately before the addition of the hardly oxidizable element alloy raw material does not exceed 1700 ° C.
以上説明したように、本発明によれば、特段の昇熱手段を講じることなく、酸素の物質移動が脱炭反応を律速する領域、つまり、脱炭最盛期の溶湯温度を従来よりも高位に維持することが可能となり、これにより、脱炭速度の向上及び脱炭処理時間の短縮が実現される。 As described above, according to the present invention, without taking any special heating means, the region in which the mass transfer of oxygen controls the decarburization reaction, that is, the molten metal temperature at the maximum decarburization period is higher than before. As a result, the decarburization speed can be improved and the decarburization time can be shortened.
一次精錬用の転炉で炭素濃度を０．１５質量％、クロム濃度を１６．５質量％に調整したステンレス鋼溶湯をＶＯＤ設備で二次精錬して、ステンレス鋼溶湯を製造する６回の試験（試験番号１〜６）を行った。各試験における製造対象のステンレス鋼は、炭素濃度の上限値が０．０１０質量％、クロム濃度が１７．５質量％、銅濃度が１．５質量％である。試験番号１では、転炉からの出鋼時に合金原料の金属銅を取鍋内溶湯に添加し、試験番号２〜５では、ＶＯＤ設備での真空脱炭処理中に金属銅を取鍋内溶湯に添加し、試験番号６では、ＶＯＤ設備での真空脱炭処理が終了し、溶湯を金属アルミニウムで脱酸した後に金属銅を取鍋内溶湯に添加した。尚、試験番号１は従来の精錬方法である。 Six tests to produce molten stainless steel by secondary refining of molten stainless steel with a carbon concentration of 0.15 mass% and chromium concentration of 16.5 mass% in a converter for primary refining using VOD equipment (Test numbers 1 to 6) were performed. The stainless steel to be manufactured in each test has an upper limit of carbon concentration of 0.010 mass%, a chromium concentration of 17.5 mass%, and a copper concentration of 1.5 mass%. In test number 1, metal copper as an alloy material is added to the molten metal in the ladle when steel is discharged from the converter. In test numbers 2 to 5, the molten metal in the ladle is vacuum-decarburized in the VOD facility. In test number 6, the vacuum decarburization process in the VOD facility was completed, and after the molten metal was deoxidized with metallic aluminum, the metallic copper was added to the molten metal in the ladle. Test number 1 is a conventional refining method.
転炉から出鋼直後の取鍋内の溶湯温度は、転炉からの出鋼時に取鍋内に合金原料の金属銅を添加して銅濃度を１．５質量％に調整した従来方法の試験番号１の場合には１７０５℃であった。これに対して、転炉出鋼時に金属銅を添加せずに、二次精錬中に金属銅を添加した試験番号２〜６では、上記の試験番号１と転炉精錬時の終点溶湯温度を等しくしたところ、金属銅による吸熱が無くなった分だけ溶湯温度が上昇し、出鋼直後の取鍋中の溶湯温度は１７３０℃であった。 The temperature of the molten metal in the ladle immediately after the steel from the converter was tested in a conventional method in which the copper concentration was adjusted to 1.5 mass% by adding metallic copper as an alloy raw material into the ladle at the time of steel removal from the converter. In the case of No. 1, it was 1705 ° C. On the other hand, in test numbers 2 to 6 in which metallic copper was added during secondary refining without adding metallic copper during converter steelmaking, the above test number 1 and the end point molten metal temperature during converter refining were set as follows. As a result, the molten metal temperature increased by the amount of heat absorption by the metallic copper, and the molten metal temperature in the ladle immediately after the tapping was 1730 ° C.
各試験において、ＶＯＤ設備にて、取鍋底部に設置したポーラスプラグからアルゴンガスを底吹きしてステンレス鋼溶湯を攪拌しながら減圧雰囲気とした後、上吹きランスから酸素ガスの供給を開始して真空脱炭処理を行った。この真空脱炭処理中に、各試験において、クロム源として、クロム濃度１．０質量％相当分の高炭素フェロクロムを、上吹きランスからの送酸開始後直ちに取鍋内溶湯に投入した。 In each test, in the VOD facility, argon gas was blown from the porous plug installed at the bottom of the ladle to create a reduced-pressure atmosphere while stirring the molten stainless steel, and then oxygen gas supply was started from the top blowing lance. Vacuum decarburization treatment was performed. During this vacuum decarburization treatment, in each test, as a chromium source, high carbon ferrochrome corresponding to a chromium concentration of 1.0% by mass was introduced into the molten metal in the ladle immediately after the start of acid feeding from the top blowing lance.
また、試験番号２〜５では、溶湯中炭素濃度が０．０９０質量％となる時点（試験番号２）、溶湯中炭素濃度が０．０５０質量％となる時点（試験番号３）、溶湯中炭素濃度が０．０２０質量％となる時点（試験番号４）、溶湯中炭素濃度が０．０１０質量％となる時点（試験番号５）を目標時点として、銅濃度１．５質量％相当分の金属銅を取鍋内溶湯に投入した。金属銅を投入する直前のタイミングで溶湯温度を測定するとともに溶湯サンプルを採取し、金属銅を投入する直前の時点での溶湯中炭素濃度を分析した。 In Test Nos. 2 to 5, when the carbon concentration in the molten metal becomes 0.090% by mass (Test No. 2), when the carbon concentration in the molten metal becomes 0.050% by mass (Test No. 3), carbon in the molten metal A metal corresponding to a copper concentration of 1.5% by mass, with the time point (test number 4) when the concentration becomes 0.020% by mass and the time point (test number 5) when the carbon concentration in the molten metal becomes 0.010% by mass as the target time point. Copper was put into the molten metal in the pan. The molten metal temperature was measured at the timing immediately before the metallic copper was added, and a molten metal sample was taken, and the carbon concentration in the molten metal was analyzed immediately before the metallic copper was introduced.
金属銅を添加する際に、試験番号２、３では、過去の真空脱炭処理中の溶湯中炭素濃度推移の調査実績に基づいて、溶湯中炭素濃度が上記の目標時点（０．０９０質量％、０．０５０質量％）となる時点を推定して、金属銅の投入タイミングを決定した。一方、試験番号４、５では、減圧容器からの真空排気ダクトの途中に設置した質量分析計を用いて測定した排ガス中のＣＯ２濃度から、過去の調査実績に基づいて操業条件に応じて設定した閾値を用い、溶湯中炭素濃度が上記の目標時点（０．０２０質量％、０．０１０質量％）となる時点を判定して、金属銅の投入タイミングを決定した。 When adding metallic copper, in Test Nos. 2 and 3, the carbon concentration in the molten metal is the above target time point (0.090 mass%) based on the past investigation results of the carbon concentration in the molten metal during vacuum decarburization treatment. , 0.050 mass%) was estimated, and the timing of metal copper injection was determined. On the other hand, in test numbers 4 and 5, the CO 2 concentration in the exhaust gas measured using a mass spectrometer installed in the middle of the vacuum exhaust duct from the decompression vessel is set according to the operating conditions based on past survey results. The timing at which the carbon concentration in the molten metal reached the target time point (0.020 mass%, 0.010 mass%) was determined using the threshold value thus determined, and the timing of metal copper charging was determined.
その後、排ガス中のＣＯ２濃度測定値に基づいて推定した溶湯中の炭素濃度が０．００８０質量％となった段階で、上吹きランスからの酸素ガスの供給を停止し、脱酸剤として金属アルミニウムとフェロシリコンとを添加して真空脱炭処理を終了するとともに脱酸処理を開始した。 Thereafter, when the carbon concentration in the molten metal estimated based on the measured value of CO 2 concentration in the exhaust gas reached 0.0080% by mass, the supply of oxygen gas from the top blowing lance was stopped, and a metal was used as a deoxidizer. Aluminum and ferrosilicon were added to finish the vacuum decarburization process and start the deoxidation process.
試験番号１〜５では、脱酸剤を添加してから４分間底吹き攪拌してスラグを還元した後、各種の合金成分を添加し、更に４分間底吹き攪拌し、その後、溶湯成分を確認するための溶湯サンプルを採取して成分分析を実施した。試験番号６では、脱酸剤を添加してから４分間底吹き攪拌してスラグを還元した後、銅濃度１．５質量％相当分の金属銅を取鍋内溶湯に添加し、金属銅の添加終了後に各種の合金成分を添加し、更に４分間底吹き攪拌し、その後、溶湯成分を確認するための溶湯サンプルを採取して成分分析を実施した。 In Test Nos. 1 to 5, after adding a deoxidizer, bottom blowing and stirring for 4 minutes to reduce slag, various alloy components were added, and stirring was further performed for 4 minutes, and then the molten metal components were confirmed. A molten metal sample was collected for component analysis. In test number 6, after adding the deoxidizer, the bottom slag was stirred for 4 minutes to reduce the slag, and then copper metal equivalent to 1.5% by mass of copper was added to the molten metal in the ladle. After completion of the addition, various alloy components were added, and bottom blowing and stirring were further performed for 4 minutes. Thereafter, a molten metal sample for confirming the molten metal component was collected and component analysis was performed.
溶湯成分を確認するための溶湯サンプルを採取した後、約１０分間経過した時点で判明した各合金成分濃度の分析結果を確認し、この分析結果に基づいて各合金成分の濃度を微調整するための合金原料を添加し、この合金原料の添加後、更に４分間底吹き攪拌した。その後、最終的な溶湯サンプルを採取するとともに溶湯温度を確認して約２５分間の脱酸処理を終了し、減圧容器内を大気圧まで復圧してＶＯＤ設備での二次精錬を終了した。 In order to confirm the analysis result of each alloy component concentration found after about 10 minutes have elapsed after collecting a molten metal sample for confirming the melt component and finely adjust the concentration of each alloy component based on this analysis result The alloy raw material was added, and after the addition of the alloy raw material, bottom blowing stirring was further performed for 4 minutes. Thereafter, the final molten metal sample was collected and the molten metal temperature was confirmed, the deoxidation treatment for about 25 minutes was completed, the pressure inside the vacuum vessel was restored to atmospheric pressure, and the secondary refining in the VOD facility was completed.
試験番号６では、銅濃度１．５質量％相当分の金属銅を、真空脱炭処理中ではなく脱酸剤添加後に投入したことから、その影響により、各種の合金成分を添加、分析、再調整などの実施タイミングが遅れることになり、６分間の脱酸処理時間の延長を招いた。 In test No. 6, since copper equivalent to a copper concentration of 1.5% by mass was added after the deoxidizing agent was added, not during the vacuum decarburization treatment, various alloy components were added, analyzed, and reused due to the influence. The implementation timing such as adjustment was delayed, leading to an extension of the deoxidation treatment time of 6 minutes.
表１に、各試験の試験条件及び試験結果を示す。表１では、真空脱炭処理時間と脱酸処理時間との合計をＶＯＤ処理時間として示している。また、表１では、本発明の範囲内の試験条件で行った試験を本発明例と表示し、本発明の範囲外の試験条件で行った試験を比較例または従来例と表示している。 Table 1 shows the test conditions and test results of each test. In Table 1, the total of the vacuum decarburization treatment time and the deoxidation treatment time is shown as the VOD treatment time. In Table 1, tests conducted under test conditions within the scope of the present invention are indicated as examples of the present invention, and tests performed under test conditions outside the scope of the present invention are indicated as comparative examples or conventional examples.
表１に示した結果から、転炉出鋼時に金属銅を添加する従来の添加方法である試験番号１に対して、金属銅の添加タイミングを真空脱炭処理中に変更することによって真空脱炭処理時間の短縮が可能であり、特に、金属銅を添加する時点の溶湯中炭素濃度が０．０２質量％以下である試験番号４、５では、ＶＯＤ処理時間の短縮効果が大きいことがわかる。また、金属銅の添加タイミングを脱酸剤の添加後とした試験番号６では、真空脱炭処理時間は更に短縮されたものの、脱酸処理時間の延長を招いたことから、試験番号４、５に比べてＶＯＤ処理時間の短縮効果が小さかった。 From the results shown in Table 1, vacuum decarburization is performed by changing the addition timing of metal copper during the vacuum decarburization process with respect to test number 1, which is a conventional addition method of adding metal copper at the time of converter steelmaking. It can be seen that the treatment time can be shortened, and in particular, in test numbers 4 and 5 where the carbon concentration in the molten metal at the time of adding metallic copper is 0.02% by mass or less, the effect of shortening the VOD treatment time is great. Further, in test number 6 in which the addition timing of metallic copper was after the addition of the deoxidizer, the vacuum decarburization treatment time was further shortened, but the deoxidation treatment time was extended, so test numbers 4, 5 As compared with the above, the effect of shortening the VOD processing time was small.
上記実施例では、添加する難酸化性元素の合金原料が金属銅の場合について説明したが、ニッケル、モリブデンまたはコバルトを含有する極低炭素濃度のステンレス鋼についても、これらを添加するための金属ニッケル、フェロニッケル、フェロモリブデン、金属コバルトなどの合金原料の添加タイミングを、転炉出鋼時から真空脱炭処理中へと変更することによって、上記説明の金属銅の場合と同様に、真空脱炭処理中の溶湯温度を容易に上昇させることができ、それにより、脱炭反応が促進されて真空脱炭処理時間を短縮する効果が得られた。 In the above-described embodiment, the case where the alloy raw material of the hardly oxidizable element to be added is metallic copper, but the nickel metal for adding these also to the ultra-low carbon concentration stainless steel containing nickel, molybdenum or cobalt. By changing the timing of addition of alloy raw materials such as ferronickel, ferromolybdenum, and metallic cobalt from the time when the steel is discharged from the converter to the time during vacuum decarburization, vacuum decarburization is performed in the same manner as in the case of metallic copper described above. The temperature of the molten metal during the treatment can be easily increased, thereby promoting the decarburization reaction and obtaining the effect of shortening the vacuum decarburization treatment time.
Claims (3)
前記ステンレス鋼溶湯に、銅、ニッケル、モリブデン、コバルトのうちの少なくともいずれか一種の難酸化性元素を添加するための合金原料を、前記真空脱炭処理中の前記ステンレス鋼溶湯に、当該ステンレス鋼溶湯中の炭素濃度が０．０２質量％以下となった段階で添加することを特徴とする、ステンレス鋼溶湯の二次精錬方法。 Under reduced pressure, oxygen was supplied to the molten stainless steel and vacuum decarburization was performed. Then, while stirring the molten stainless steel, a deoxidizer was added to deoxidize the molten metal. A secondary refining method for molten stainless steel, in which an alloy raw material is added to melt a molten stainless steel of a predetermined component,
An alloy raw material for adding at least one kind of hardly oxidizable element of copper, nickel, molybdenum and cobalt to the molten stainless steel is used as the stainless steel molten metal during the vacuum decarburization treatment. A secondary refining method for molten stainless steel, characterized in that the addition is performed when the carbon concentration in the molten metal is 0.02% by mass or less.
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| JPH07157820A (en) * | 1993-12-07 | 1995-06-20 | Sumitomo Metal Ind Ltd | Method for promoting decarburization in molten steel |
| JP2002285222A (en) * | 2001-03-28 | 2002-10-03 | Kawasaki Steel Corp | Method for producing high chromium steel |
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