JP2009144244A - Refining method of high-chromium ferritic stainless steel for reducing carbon - Google Patents

Refining method of high-chromium ferritic stainless steel for reducing carbon Download PDF

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JP2009144244A
JP2009144244A JP2008315845A JP2008315845A JP2009144244A JP 2009144244 A JP2009144244 A JP 2009144244A JP 2008315845 A JP2008315845 A JP 2008315845A JP 2008315845 A JP2008315845 A JP 2008315845A JP 2009144244 A JP2009144244 A JP 2009144244A
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refining
vod
stainless steel
ferritic stainless
vibration sensor
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Sang Bum Lee
相 範 李
Min Oh Suk
▲眠▼ ▲肝▼ 石
Hee Ho Lee
喜 鎬 李
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Posco Holdings Inc
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Posco Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/005—Manufacture of stainless steel
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/068—Decarburising
    • C21C7/0685—Decarburising of stainless steel

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Waste-Gas Treatment And Other Accessory Devices For Furnaces (AREA)

Abstract

<P>PROBLEM TO BE SOLVED: To provide a refining method of a high-chromium ferritic stainless steel for reducing carbon. <P>SOLUTION: A method for refining a ferritic stainless steel comprising 5-30% Cr, ≤0.1% Ti and ≤0.02% C and manufactured through electric furnace (EAF) - refining furnace (AOD) - secondary refining (VOD) - composition adjustment (LT) - tundish - continuous casting steps comprises: a step of installing a vibration sensor on an outer wall of a VOD tank in a VOD facility in the secondary refining; a step of measuring a particular frequency among frequencies output by the vibration sensor; and a step of adjusting bottom-blowing agitation intensity of an oxygen-blowing decarburization apparatus and a vacuum decarburization apparatus during the secondary refining (VOD) step. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

本発明は、炭素を低減するための高クロムフェライト系ステンレス鋼の精錬方法に関し、特に、ＶＯＤ工程において取鍋底吹き撹拌強度を調整することにより、溶鋼中の炭素を最小化させる高クロムフェライト系ステンレス鋼の精錬方法に関する。   The present invention relates to a method for refining high chromium ferritic stainless steel for reducing carbon, and in particular, high chromium ferritic stainless steel that minimizes carbon in molten steel by adjusting the ladle bottom blowing agitation strength in the VOD process. The present invention relates to a steel refining method.

一般的に、フェライト系ステンレス鋼は、電気炉で溶解された原料を、アルゴン（Ａｒ）−酸素脱炭法（ＡＯＤ）により精錬した後、真空−酸素脱炭法（ＶＯＤ）により二次精錬を行う。この後、ＶＯＤタンク内に位置する取鍋で成分及び温度を調整した後、タンディッシュを経て連続鋳造を行う。この工程のうち、特に、ＶＯＤ工程において酸素吹錬脱炭機及びその後の真空脱炭機操業を行うとき、取鍋の下部からアルゴン（Ａｒ）のような不活性ガスを吹き込んで溶鋼を撹拌する作業を行うようになるが、これを「取鍋底吹き」と称する。本発明は、このような取鍋底吹き時に撹拌強度を調整することにより、溶鋼中の炭素を最小化させるための精錬方法に関し、高クロムフェライト系ステンレス製品の延伸率を増加させ、耐粒界腐食性を改善させるものである。   Generally, ferritic stainless steel is prepared by refining the raw material melted in an electric furnace by argon (Ar) -oxygen decarburization (AOD) and then by secondary refining by vacuum-oxygen decarburization (VOD). Do. Then, after adjusting a component and temperature with the ladle located in a VOD tank, continuous casting is performed through a tundish. Among these processes, in particular, when the oxygen blowing decarburization machine and the subsequent vacuum decarburization machine operation are performed in the VOD process, the molten steel is stirred by blowing an inert gas such as argon (Ar) from the bottom of the ladle. The work will be performed, and this is called “ladder bottom blowing”. The present invention relates to a refining method for minimizing carbon in molten steel by adjusting the stirring strength at the time of such ladle bottom blowing, increasing the stretch ratio of high chromium ferritic stainless steel products, and intergranular corrosion resistance It improves the sex.

通常のフェライト系ステンレス鋼は、オーステナイト系ステンレス鋼に比べて延伸率が低く、腐食性が低下するという問題があり、限られた用途でのみ使用されてきた。しかし、フェライト系ステンレス鋼は、ニッケル含有量が非常に低く、オーステナイト系ステンレス鋼に比べて価格が安いという長所がある。これにより、フェライト系ステンレス鋼の延伸率を高め、耐粒界腐食性を改善することにより、オーステナイト系ステンレス鋼を代替しようとする要求が多いのが現状である。   Ordinary ferritic stainless steel has a problem that it has a lower draw ratio and lower corrosivity than austenitic stainless steel, and has been used only for limited applications. However, ferritic stainless steel has the advantage that it has a very low nickel content and is cheaper than austenitic stainless steel. As a result, there are many demands to replace the austenitic stainless steel by increasing the stretch ratio of the ferritic stainless steel and improving the intergranular corrosion resistance.

一方、溶鋼中の炭素成分が低下するほど延伸率が増加し、耐粒界腐食性が改善されることは周知である。そして、ＶＯＤ工程により生産される高クロムフェライト系ステンレス鋼の場合、アルゴン（Ａｒ）−酸素脱炭法（ＡＯＤ）により粗脱炭を先に実施する。この後、真空−酸素脱炭法（ＶＯＤ）による二次精錬時には、酸素ガスを溶鋼中に吹き込むと同時に、下部のポーラスプラグからアルゴン（Ａｒ）ガスを吹き込むと、式（１）の反応により炭素が除去される。   On the other hand, it is well known that as the carbon component in molten steel decreases, the stretch ratio increases and the intergranular corrosion resistance is improved. And in the case of the high chromium ferritic stainless steel produced by a VOD process, rough decarburization is first implemented by the argon (Ar) -oxygen decarburization method (AOD). Thereafter, when secondary refining by vacuum-oxygen decarburization (VOD) is performed, oxygen gas is blown into the molten steel, and at the same time, argon (Ar) gas is blown from the lower porous plug. Is removed.

［Ｃ］＋１／２｛Ｏ｝＝｛ＣＯ｝−−−（１）   [C] +1/2 {O} = {CO} --- (1)

このとき、炭素が除去されると同時に、クロム酸化物が生成される。そして、酸素ガスにより除去可能な炭素濃度の限界に達すると、真空のレベルを５ｍｂａｒ以下にさらに低くし、下部のポーラスプラグからＡｒガスを吹き込みながら、これを用いて溶鋼を強く撹拌させる。このような撹拌過程で溶鋼中の炭素とクロム酸化物とが互いに反応して炭素を除去するが、これは、下記式（２）の反応により行われる。   At this time, chromium oxide is generated at the same time as carbon is removed. When the limit of the carbon concentration that can be removed by oxygen gas is reached, the vacuum level is further lowered to 5 mbar or lower, and the molten steel is vigorously stirred using Ar gas blown from the lower porous plug. In such a stirring process, carbon and chromium oxide in molten steel react with each other to remove carbon, which is performed by the reaction of the following formula (2).

３［Ｃ］＋（Ｃｒ２Ｏ３）＝２［Ｃｒ］＋３｛ＣＯ｝−−−（２） 3 [C] + (Cr 2 O 3 ) = 2 [Cr] +3 {CO} --- (2)

式（１）で表される酸素吹錬脱炭機と、式（２）で表される真空脱炭機中における底吹き作業は、取鍋の底部に設けられているポーラスプラグを用いる。このときのポーラスプラグは、耐火物で製作されたものであるため、使用回数が増えるにつれ、溶鋼による浸食及び摩耗が発生する。これにより、不活性ガスの全ての吹き込み量が溶鋼を撹拌させるために供給できずに、一部がポーラスプラグの浸食部位を介して外部に排出される。これにより、実際に溶鋼内に供給される底吹きガスの量は、流量計で指すガスの量とは差がある。   In the oxygen blowing smelting decarburizer represented by the formula (1) and the bottom blowing operation in the vacuum decarburizing machine represented by the formula (2), a porous plug provided at the bottom of the ladle is used. Since the porous plug at this time is made of a refractory material, as the number of uses increases, erosion and wear due to molten steel occur. As a result, all of the blowing amount of the inert gas cannot be supplied to stir the molten steel, and a part thereof is discharged to the outside through the erosion site of the porous plug. Thereby, the amount of the bottom blowing gas actually supplied into the molten steel is different from the amount of gas indicated by the flow meter.

このような撹拌強度の差は、操業方法のばらつきを引き起こし、最終的には、溶鋼中の炭素濃度のばらつきをもたらすようになる。一般的に、図１に示すように、真空脱炭時の脱炭速度は、底吹き撹拌流量に比例し、ポーラスプラグが正常な場合、底吹き撹拌流量は、撹拌強度に比例する。   Such a difference in the stirring intensity causes a variation in the operation method, and finally, a variation in the carbon concentration in the molten steel. In general, as shown in FIG. 1, the decarburization speed during vacuum decarburization is proportional to the bottom blowing stirring flow rate, and when the porous plug is normal, the bottom blowing stirring flow rate is proportional to the stirring strength.

反面、撹拌強度が大き過ぎた場合は、溶鋼が溢れ出る現象が発生し、ＶＯＤタンクの上部カバーに付着して地金を形成する。脱炭操業中に形成された地金の量が増加すると、その重さに耐えられず、上部カバーから脱落して溶鋼中に混入し、溶鋼中の炭素が再び増加する原因となる。   On the other hand, when the stirring strength is too large, a phenomenon that the molten steel overflows occurs and adheres to the upper cover of the VOD tank to form a bare metal. If the amount of bullion formed during the decarburization operation increases, it cannot withstand its weight, falls off the upper cover and enters the molten steel, and causes the carbon in the molten steel to increase again.

したがって、溶鋼中の炭素を最大限に除去するためには、底吹きによる撹拌強度を適正レベルに維持しなければならず、そのためには、ポーラスプラグに吹き込まれる流量を正確に測定できなければならない。これにより、ポーラスプラグに吹き込まれる流量を正確に測定するための様々な方法が提案されている。   Therefore, in order to remove the carbon in the molten steel to the maximum extent, the stirring strength by bottom blowing must be maintained at an appropriate level, and for that purpose, the flow rate blown into the porous plug must be accurately measured. . Accordingly, various methods have been proposed for accurately measuring the flow rate blown into the porous plug.

特に、大韓民国公開特許第２００２−００３２７１０号、アメリカ特許ＵＳ６，２６４，７１６などには、振動センサを取鍋の外面または取鍋を運搬する取鍋カーの側面に取り付け、センサから出力される振動指数を用いて取鍋内の撹拌強度を測定することを特徴とする。しかし、このような技術がステンレス鋼の生産に適用されたことはまだなく、特に、ＶＯＤタンクのような精錬容器の外壁に取り付け、振動指数を測定した例はない。これは、ＶＯＤタンクの外壁に取り付ける際には、取鍋または取鍋カーに取り付けるのに比べて、振動の強度が弱いため、取付位置のより精密な選定が必要になるからである。また、このように測定された撹拌強度を脱炭工程に適用した例もない。
大韓民国特許公開第２００２−００３２７１０号 米国特許ＵＳ６，２６４，７１６号 In particular, Korean Patent Laid-Open No. 2002-0032710, US Pat. No. 6,264,716, etc., attach a vibration sensor to the outer surface of the ladle or the side surface of the ladle car that carries the ladle, and the vibration index output from the sensor. The stirring strength in the ladle is measured using However, such a technique has not yet been applied to the production of stainless steel, and in particular, there is no example in which the vibration index is measured by attaching it to the outer wall of a refining vessel such as a VOD tank. This is because when attaching to the outer wall of the VOD tank, the strength of vibration is weaker than when attaching to a ladle or ladle car, so a more precise selection of the attachment position is required. Moreover, there is no example which applied the stirring intensity measured in this way to the decarburization process.
Korean Patent Publication No. 2002-0032710 US Patent US 6,264,716

そこで、本発明は、高クロムフェライト系ステンレス鋼の精錬方法において、電気炉からの出湯後、ＡＯＤ粗脱炭を経て、ＶＯＤでの脱炭過程において酸素吹錬脱炭機と真空脱炭機の取鍋下部のポーラスプラグによる底吹き撹拌制御を行うことにより、ステンレス鋼の炭素濃度を低減可能な技術を提供することを目的とする。特に、正確な撹拌強度を測定し、これを用いたＶＯＤ作業により、ステンレス鋼の延伸率を高め、耐粒界腐食性を改善する精錬方法を提供することをその目的とする。   Therefore, the present invention relates to a method for refining high chromium ferritic stainless steel, in which an oxygen blown decarburizer and a vacuum decarburizer are used in a decarburization process at VOD after AOD rough decarburization after tapping from an electric furnace. It aims at providing the technique which can reduce the carbon concentration of stainless steel by performing bottom blowing stirring control by the porous plug of the ladle lower part. In particular, an object of the present invention is to provide a refining method for measuring an accurate agitation strength and increasing the stretch ratio of stainless steel and improving the intergranular corrosion resistance by VOD work using this.

本発明は、高クロムフェライト系ステンレス鋼の精錬時における炭素の低減を目的として、ＶＯＤタンクの外壁に振動センサの取付位置を選定し、振動センサから出力された周波数の中から特定の周波数のみを測定するステップと、このように測定された特定の周波数値を用いて二次精錬過程のＶＯＤで底吹き撹拌強度を調整する、炭素を低減するための高クロムフェライト系ステンレス鋼の精錬方法を提供することを特徴とする。   In the present invention, for the purpose of reducing carbon during refining of high chromium ferritic stainless steel, the mounting position of the vibration sensor is selected on the outer wall of the VOD tank, and only a specific frequency is selected from the frequencies output from the vibration sensor. Provides a refining method of high chromium ferritic stainless steel to reduce carbon by adjusting the bottom blowing agitation strength with the VOD of the secondary refining process using the specific frequency value measured in this way and the step of measuring It is characterized by doing.

また、本発明では、ＶＯＤタンクの外壁に振動センサの取付位置を選定するとき、振動センサをＶＯＤタンク内の取鍋の取っ手に接する据置台と一直線上に置かれたタンクの外壁の位置から上下左右３０ｃｍ以内の位置でなければならず、振動センサから出力された特定の周波数は、１０〜４５Ｈｚの周波数領域帯で発生する振動指数のみを測定することが好ましい。また、ＶＯＤ操業時における底吹き撹拌強度の調整において、酸素吹錬脱炭機では振動センサから測定された底吹き撹拌強度を４００〜６００に制御し、真空脱炭機では振動センサから測定された振動指数から補正された底吹き撹拌強度を５５０〜７５０に制御することにより、溶鋼中の炭素濃度を最小化するための高クロムフェライト系ステンレス鋼の精錬方法を提供することを特徴とする。   Further, in the present invention, when selecting the mounting position of the vibration sensor on the outer wall of the VOD tank, the vibration sensor is moved up and down from the position of the outer wall of the tank placed in line with the cradle in contact with the handle of the ladle in the VOD tank. The position must be within 30 cm on the left and right, and the specific frequency output from the vibration sensor preferably measures only the vibration index generated in the frequency region band of 10 to 45 Hz. In addition, in the adjustment of the bottom blowing agitation strength during the VOD operation, the bottom blowing agitation intensity measured from the vibration sensor in the oxygen blowing smelting decarburizer was controlled to 400 to 600, and the bottom blowing agitation intensity was measured from the vibration sensor in the vacuum decarburizer. It is characterized by providing a refining method of high chromium ferritic stainless steel for minimizing the carbon concentration in molten steel by controlling the bottom blowing stirring intensity corrected from the vibration index to 550 to 750.

本発明によれば、１５〜３０％のクロムを含有し、チタン含有量が０．１％以下かつ炭素含有量が０．０２％以下の高クロムフェライト系ステンレス鋼をＶＯＤ設備で生産するとき、溶鋼の炭素濃度の低減のために、ＶＯＤ設備の外壁に取り付けられた振動センサを用いた取鍋底吹き撹拌制御を行うことにより、溶鋼中の炭素を除去し、ＶＯＤ設備の上部の地金による炭素濃度の増加を抑制することにより、最終的に６０ｐｐｍ以下の炭素濃度を得ることができ、これは、製品の延伸率を高め、耐粒界腐食性を改善するという効果がある。   According to the present invention, when producing a high chromium ferritic stainless steel containing 15-30% chromium, having a titanium content of 0.1% or less and a carbon content of 0.02% or less in a VOD facility, In order to reduce the carbon concentration of the molten steel, the carbon in the molten steel is removed by performing ladle bottom blowing stirring control using a vibration sensor attached to the outer wall of the VOD facility. By suppressing the increase in concentration, it is possible to finally obtain a carbon concentration of 60 ppm or less, which has the effect of increasing the stretch rate of the product and improving the intergranular corrosion resistance.

以下、本発明の好ましい実施例による取鍋底吹き撹拌制御による高クロムフェライト系ステンレス鋼の精錬方法を、添付図面を参照して詳細に説明する。   Hereinafter, a method for refining high chromium ferritic stainless steel by ladle bottom blowing stirring control according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

図２は、ＶＯＤタンクの外壁に振動センサが取り付けられた実際の位置を示しており、図３は、これを概略化して示している。本発明によれば、ＶＯＤ設備で炭素を除去する目的で行う底吹き作業により形成される溶鋼の撹拌強度を測定する方法において、前記ＶＯＤの外壁の特定位置には、底吹き撹拌による取鍋の振動に起因するＶＯＤの外壁の振動を測定するセンサが取り付けられている。そして、このセンサから出力された周波数の中から特定の周波数の振動指数を用いて底吹き撹拌の強度を測定することを特徴とする。   FIG. 2 shows an actual position where the vibration sensor is attached to the outer wall of the VOD tank, and FIG. 3 schematically shows this. According to the present invention, in the method of measuring the stirring strength of the molten steel formed by the bottom blowing operation for the purpose of removing carbon in the VOD facility, the specific position of the outer wall of the VOD is provided with a ladle by bottom blowing stirring. A sensor for measuring the vibration of the outer wall of the VOD caused by the vibration is attached. And the intensity | strength of bottom blowing stirring is measured using the vibration index of a specific frequency out of the frequency output from this sensor.

ここで、特定位置とは、ＶＯＤタンク内の取鍋の取っ手に接する据置台と一直線上に置かれたタンクの外壁の位置から上下左右３０ｃｍ以内の位置であることを意味し、特定の周波数の振動指数とは、１０〜４５Ｈｚの周波数領域帯で発生する振動指数のみを測定に用いることを意味する。   Here, the specific position means a position within 30 cm in the vertical and horizontal directions from the position of the outer wall of the tank placed in line with the cradle in contact with the handle of the ladle in the VOD tank. The vibration index means that only a vibration index generated in a frequency region band of 10 to 45 Hz is used for measurement.

特定位置を越えた所に振動センサを取り付けた場合は、振動指数が弱いため、精密な測定が不可能になる。また、特定の周波数領域帯以外の振動指数は、溶鋼の撹拌強度とは無関係なノイズであるため、精密な測定を妨げ、必ず除去されなければならない。   If a vibration sensor is attached beyond a specific position, the vibration index is weak, so precise measurement is impossible. In addition, vibration indices other than those in a specific frequency band are noises that are unrelated to the stirring strength of the molten steel, and thus prevent precise measurement and must be removed.

また、本発明によれば、ＶＯＤ設備で炭素を除去する目的で行う底吹き操業時に底吹き撹拌強度を調整して炭素を除去する方法において、前記振動センサから測定された振動指数は、正の整数値を有するようになり、ポーラスプラグが定常な状態のときにおける流量と比較して同じ値を有するように補正しなければならない。   According to the present invention, in the method of removing carbon by adjusting the bottom blowing agitation intensity during the bottom blowing operation performed for the purpose of removing carbon in the VOD facility, the vibration index measured from the vibration sensor is positive. It will have an integer value and must be corrected to have the same value compared to the flow rate when the porous plug is in a steady state.

補正により流量と同じ値を有する撹拌強度は、酸素吹錬脱炭機では４００〜６００を維持し、真空脱炭機では５５０〜７５０を維持するように底吹きガスの流量を制御することにより、溶鋼中の炭素濃度を最小化できることを特徴とする。   By controlling the flow rate of the bottom blowing gas so that the stirring intensity having the same value as the flow rate by correction is maintained at 400 to 600 in the oxygen blowing decarburizer and 550 to 750 in the vacuum decarburizer, It is characterized in that the carbon concentration in molten steel can be minimized.

以下、実施例とともに、撹拌強度を補正する方法及び炭素濃度を最小化できる方法を説明する。   A method for correcting the stirring intensity and a method capable of minimizing the carbon concentration will be described below together with examples.

本発明で明示した１５〜３０％のクロムを含有し、チタン含有量が０．１％以下かつ炭素含有量が０．０２％以下のフェライト系ステンレス鋼をＶＯＤ設備で生産するとき、上記図２及び図３で説明した位置に振動センサを取り付け、１０〜４５Ｈｚの周波数領域帯で発生する振動指数のみを測定すると、図４のような振動指数と底吹きガス流量との相関関係が生じる。   When producing ferritic stainless steel containing 15-30% chromium as specified in the present invention, having a titanium content of 0.1% or less and a carbon content of 0.02% or less in a VOD facility, FIG. When the vibration sensor is attached at the position described with reference to FIG. 3 and only the vibration index generated in the frequency region band of 10 to 45 Hz is measured, the correlation between the vibration index and the bottom blowing gas flow rate as shown in FIG. 4 occurs.

ここで、１点は、１回の操業を意味し、同じ流量から互いに異なる値の振動指数が出るのは、各々の操業により、使用される取鍋及び取鍋の使用回数が変化し、これにより、取鍋下部のポーラスプラグの状態が変化するからである。このとき、最も高い値の振動指数を有する底吹き流量の点が最も正常なポーラスプラグ状態であることが分かり、これを結ぶ直線が補正に用いられる。この直線上の振動指数値に適当な定数を乗算すると、図５のように、流量と同じ値を有する撹拌強度を得ることができる。   Here, one point means one operation, and the vibration index of different values from the same flow rate is different from each other, the ladle used and the number of use of the ladle change. This is because the state of the porous plug at the bottom of the ladle changes. At this time, it is found that the bottom blowing flow point having the highest vibration index is the most normal porous plug state, and a straight line connecting these points is used for correction. When the vibration index value on this straight line is multiplied by an appropriate constant, a stirring intensity having the same value as the flow rate can be obtained as shown in FIG.

図６は、本発明で提案した酸素吹錬脱炭機の撹拌強度と二次精錬（ＶＯＤ）操業後における溶鋼中の炭素濃度との関係を示しており、図７は、真空脱炭機の撹拌強度と二次精錬（ＶＯＤ）操業後における溶鋼中の炭素濃度との関係を示している。   FIG. 6 shows the relationship between the stirring strength of the oxygen blowing decarburizer proposed in the present invention and the carbon concentration in the molten steel after the secondary refining (VOD) operation, and FIG. The relationship between the stirring intensity and the carbon concentration in the molten steel after secondary refining (VOD) operation is shown.

これらの図から明らかなように、従来技術の場合、すなわち、底吹きガスの流量で制御する場合には、得られない撹拌強度と溶鋼の炭素濃度との関係を得ることができ、このとき、酸素吹錬脱炭機と真空脱炭機の撹拌強度値がそれぞれ４００〜６００、５５０〜７５０の範囲内に制御された場合、炭素濃度は６０ｐｐｍ以下となり、これを超えた場合、炭素濃度は増加することが分かった。   As is clear from these figures, in the case of the prior art, that is, when controlling by the flow rate of the bottom blowing gas, it is possible to obtain the relationship between the stirring strength that cannot be obtained and the carbon concentration of the molten steel, When the stirring strength values of the oxygen blowing decarburizer and the vacuum decarburizer are controlled within the range of 400 to 600 and 550 to 750, respectively, the carbon concentration is 60 ppm or less, and when exceeding this, the carbon concentration increases. I found out that

また、図８に示す撹拌強度とＶＯＤの上部カバーの地金付着量との関係により、図７において、撹拌強度値が８５０以上のときに炭素濃度が再び上昇したことは、ＶＯＤの上部カバーに付着していた地金によるもので、過度の撹拌は抑制されなければならないことが分かった。   In addition, due to the relationship between the stirring intensity shown in FIG. 8 and the amount of metal on the top cover of the VOD, in FIG. 7, the carbon concentration increased again when the stirring intensity value was 850 or more. It was found that excessive agitation had to be suppressed due to the bare metal that had adhered.

真空脱炭時における脱炭速度と底吹き撹拌流量との関係を示す図である。It is a figure which shows the relationship between the decarburization speed at the time of vacuum decarburization, and a bottom blowing stirring flow rate. 振動センサが実際に取り付けられた位置を示す写真である。It is a photograph which shows the position where the vibration sensor was actually attached. 振動センサの取付位置を概略的に示す図である。It is a figure which shows roughly the attachment position of a vibration sensor. 振動指数と底吹き流量との関係を示す図である。It is a figure which shows the relationship between a vibration index and a bottom blowing flow rate. 振動指数を撹拌強度で補正した後、撹拌強度と底吹き流量との関係を示す図である。It is a figure which shows the relationship between stirring intensity | strength and bottom blowing flow volume after correcting a vibration index with stirring intensity | strength. 本発明で提案した酸素吹錬脱炭機の撹拌強度と酸素吹錬脱炭機終点の炭素濃度との関係を示す図である。It is a figure which shows the relationship between the stirring intensity | strength of the oxygen blown decarburizer proposed by this invention, and the carbon concentration of an oxygen blown decarburizer end point. 本発明で提案した真空脱炭機の撹拌強度と真空脱炭機終点の炭素濃度との関係を示す図である。It is a figure which shows the relationship between the stirring intensity | strength of the vacuum decarburizer proposed by this invention, and the carbon concentration of a vacuum decarburizer end point. 本発明で提案した撹拌強度と地金付着量との関係を示す図である。It is a figure which shows the relationship between the stirring intensity | strength proposed by this invention, and the metal adhesion amount.

Claims (5)

電気炉（ＥＡＦ）−精錬炉（ＡＯＤ）−二次精錬（ＶＯＤ）−成分調整（ＬＴ）−タンディッシュ−連続鋳造工程を経て、Ｃｒ：５〜３０％、Ｔｉ：０．１％以下、Ｃ：０．０２％以下のフェライト系ステンレス鋼の精錬方法において、
前記二次精錬のＶＯＤ設備でＶＯＤタンクの外壁に振動センサを取り付けるステップと、前記振動センサから出力された周波数の中から特定の周波数のみを測定するステップと、前記二次精錬（ＶＯＤ）中に酸素吹錬脱炭機と真空脱炭機の底吹き撹拌強度を調整するステップとからなることを特徴とする、炭素を低減するための高クロムフェライト系ステンレス鋼の精錬方法。 Electric furnace (EAF)-refining furnace (AOD)-secondary refining (VOD)-component adjustment (LT)-tundish-through continuous casting process, Cr: 5-30%, Ti: 0.1% or less, C : In a refining method of ferritic stainless steel of 0.02% or less,
During the secondary refining (VOD), a step of attaching a vibration sensor to the outer wall of the VOD tank in the secondary refining VOD facility, a step of measuring only a specific frequency from the frequencies output from the vibration sensor, A method for refining high chromium ferritic stainless steel for reducing carbon, characterized by comprising a step of adjusting the bottom blowing stirring strength of an oxygen blowing decarburizer and a vacuum decarburizer. 前記ＶＯＤタンクの外壁への振動センサの取付位置は、ＶＯＤタンク内の取鍋の取っ手に接する据置台と一直線上に置かれたタンクの外壁の位置から上下左右３０ｃｍ以内であることを特徴とする、請求項１に記載の炭素を低減するための高クロムフェライト系ステンレス鋼の精錬方法。   The mounting position of the vibration sensor to the outer wall of the VOD tank is within 30 cm in the vertical and horizontal directions from the position of the outer wall of the tank placed in line with the cradle handle in contact with the ladle handle in the VOD tank. The method for refining high chromium ferritic stainless steel for reducing carbon according to claim 1. 前記特定の周波数は、１０〜４５Ｈｚの周波数領域帯であることを特徴とする、請求項１に記載の炭素を低減するための高クロムフェライト系ステンレス鋼の精錬方法。   The method for refining high chromium ferritic stainless steel for reducing carbon according to claim 1, wherein the specific frequency is a frequency region band of 10 to 45 Hz. 前記振動センサから測定された振動指数を底吹き流量で補正した酸素吹錬脱炭機の底吹き撹拌強度を４００〜６００に制御することにより、最終的に６０ｐｐｍ以下の炭素濃度を有するようにすることを特徴とする、請求項１に記載の炭素を低減するための高クロムフェライト系ステンレス鋼の精錬方法。   By controlling the bottom blowing agitation intensity of the oxygen blowing decarburization machine obtained by correcting the vibration index measured from the vibration sensor with the bottom blowing flow rate, the final carbon concentration is 60 ppm or less. The method for refining high chromium ferritic stainless steel for reducing carbon according to claim 1. 前記振動センサから測定された振動指数を底吹き流量で補正した真空脱炭機の底吹き撹拌強度を５５０〜７５０に制御することにより、最終的に６０ｐｐｍ以下の炭素濃度を有するようにすることを特徴とする、請求項１に記載の炭素を低減するための高クロムフェライト系ステンレス鋼の精錬方法。   By controlling the bottom blowing agitation intensity of the vacuum decarburizer that corrects the vibration index measured from the vibration sensor with the bottom blowing flow rate to 550 to 750, the final carbon concentration is 60 ppm or less. The method for refining high chromium ferritic stainless steel for reducing carbon according to claim 1, wherein
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