JP6410311B2 - Stainless steel refining method - Google Patents
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- JP6410311B2 JP6410311B2 JP2015020797A JP2015020797A JP6410311B2 JP 6410311 B2 JP6410311 B2 JP 6410311B2 JP 2015020797 A JP2015020797 A JP 2015020797A JP 2015020797 A JP2015020797 A JP 2015020797A JP 6410311 B2 JP6410311 B2 JP 6410311B2
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- 229910001220 stainless steel Inorganic materials 0.000 title claims description 61
- 239000010935 stainless steel Substances 0.000 title claims description 57
- 238000000034 method Methods 0.000 title claims description 28
- 238000007670 refining Methods 0.000 title claims description 27
- 239000002893 slag Substances 0.000 claims description 87
- 239000002994 raw material Substances 0.000 claims description 20
- 229910004298 SiO 2 Inorganic materials 0.000 claims description 17
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 17
- 239000001301 oxygen Substances 0.000 claims description 17
- 229910052760 oxygen Inorganic materials 0.000 claims description 17
- 238000007664 blowing Methods 0.000 claims description 14
- 238000002844 melting Methods 0.000 claims description 7
- 230000008018 melting Effects 0.000 claims description 7
- 238000011946 reduction process Methods 0.000 claims description 7
- 229910000831 Steel Inorganic materials 0.000 description 74
- 239000010959 steel Substances 0.000 description 74
- 229910005347 FeSi Inorganic materials 0.000 description 13
- 229910045601 alloy Inorganic materials 0.000 description 13
- 239000000956 alloy Substances 0.000 description 13
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 9
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 8
- 235000019738 Limestone Nutrition 0.000 description 8
- 238000005261 decarburization Methods 0.000 description 8
- 239000006028 limestone Substances 0.000 description 8
- 239000007789 gas Substances 0.000 description 5
- 229910052758 niobium Inorganic materials 0.000 description 5
- 229910000604 Ferrochrome Inorganic materials 0.000 description 4
- 229910000863 Ferronickel Inorganic materials 0.000 description 4
- 229910001030 Iron–nickel alloy Inorganic materials 0.000 description 4
- 230000007423 decrease Effects 0.000 description 4
- 229910052742 iron Inorganic materials 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 229910052759 nickel Inorganic materials 0.000 description 4
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 3
- WUKWITHWXAAZEY-UHFFFAOYSA-L calcium difluoride Chemical compound [F-].[F-].[Ca+2] WUKWITHWXAAZEY-UHFFFAOYSA-L 0.000 description 3
- 229910001882 dioxygen Inorganic materials 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 239000010436 fluorite Substances 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 238000003756 stirring Methods 0.000 description 3
- VVTSZOCINPYFDP-UHFFFAOYSA-N [O].[Ar] Chemical compound [O].[Ar] VVTSZOCINPYFDP-UHFFFAOYSA-N 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 238000009749 continuous casting Methods 0.000 description 2
- 238000006477 desulfuration reaction Methods 0.000 description 2
- 230000023556 desulfurization Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 1
- 229910017082 Fe-Si Inorganic materials 0.000 description 1
- 229910017133 Fe—Si Inorganic materials 0.000 description 1
- 229910001257 Nb alloy Inorganic materials 0.000 description 1
- 235000011941 Tilia x europaea Nutrition 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- -1 and specifically Substances 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- ODINCKMPIJJUCX-UHFFFAOYSA-N calcium oxide Inorganic materials [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 238000010409 ironing Methods 0.000 description 1
- 239000004571 lime Substances 0.000 description 1
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 239000002436 steel type Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Treatment Of Steel In Its Molten State (AREA)
Description
本発明は、ステンレス鋼の精錬方法に関し、具体的には、Ｎｂを含有する原料を用いて、アルゴン酸素脱炭装置（Argon Oxygen Decarburization、以降、単に「ＡＯＤ」という）でステンレス鋼を精錬するステンレス鋼の精錬方法に関するものである。 TECHNICAL FIELD The present invention relates to a method for refining stainless steel, and specifically, stainless steel for refining stainless steel using an argon oxygen decarburization apparatus (Argon Oxygen Decarburization, hereinafter simply referred to as “AOD”) using a raw material containing Nb. It relates to a steel refining method.
電気炉等でステンレス鋼の原料を溶解し、ステンレス鋼を製造する場合、原料として、ステンレス鋼の屑（スクラップ）を使用することができれば、原料コストを大幅に低減することが可能となる。そのため、ステンレス鋼の製造技術において、原料としてステンレス屑を多く使用できる技術は極めて重要である。 In the case of manufacturing stainless steel by melting a stainless steel raw material in an electric furnace or the like, the raw material cost can be greatly reduced if stainless steel scrap (scrap) can be used as the raw material. Therefore, in the stainless steel manufacturing technology, a technology that can use a large amount of stainless steel scrap as a raw material is extremely important.
ステンレス鋼は、いわゆる高合金鋼の一種であり、多くの合金元素が多量に配合されているが、その中には、特定の用途にのみ使用される元素がある。たとえば、Ｎｂは、その一つであり、耐粒界腐食性の向上や高温強度の向上などを目的とし、必要に応じで添加されている。 Stainless steel is a kind of so-called high-alloy steel, and many alloying elements are blended in a large amount, and some of them are used only for specific applications. For example, Nb is one of them, and is added as necessary for the purpose of improving intergranular corrosion resistance and improving high-temperature strength.
上記Ｎｂは、レアメタルの一種であり、埋蔵量も少なく、産出国も限られているため、高価な元素である。そこで、たとえば、ＳＵＳ３４７やＮＣＦ６２５等のＮｂ含有ステンレス鋼には、原料としてＮｂを含有したスクラップを使用し、スクラップ中のＮｂを有効活用することが望ましい。 Nb is an expensive element because it is a kind of rare metal, has a small reserve, and has a limited production country. Therefore, for example, for Nb-containing stainless steel such as SUS347 and NCF625, it is desirable to use scrap containing Nb as a raw material and to effectively use Nb in the scrap.
しかし、電気炉等でＮｂを含有したスクラップを溶解し、次工程のＡＯＤの脱炭工程で酸素吹精して脱炭した場合には、Ｎｂは酸化され、酸化物となってスラグ相へと移行してしまう。また、引き続き行われるＣｒ還元処理において、ＦｅＳｉ等の脱酸剤を添加しても、Ｎｂ酸化物がそのままスラグ中に留まり、Ｎｂロスが生ずることがある。斯かる場合には、Ｎｂロスを補うため、最終段階の取鍋精錬で、高価なＮｂ源、たとえば、Ｆｅ−Ｎｂ合金や純Ｎｂなどを添加する必要があり、原料コストの増大を引き起こす。そのため、Ｎｂ含有ステンレス鋼を製造する場合には、スクラップ中のＮｂをできる限り高い歩留りで溶鋼中に回収することが必要となる。 However, when scrap containing Nb is melted in an electric furnace or the like, and decarburized by blowing oxygen in the next AOD decarburization step, Nb is oxidized and converted into an oxide into a slag phase. Will migrate. Further, in the subsequent Cr reduction treatment, even if a deoxidizer such as FeSi is added, the Nb oxide may remain in the slag as it is, and Nb loss may occur. In such a case, in order to make up for the Nb loss, it is necessary to add an expensive Nb source, for example, an Fe—Nb alloy or pure Nb, in the final ladle refining, which causes an increase in raw material cost. Therefore, when manufacturing Nb containing stainless steel, it is necessary to collect | recover Nb in scrap in molten steel with the highest possible yield.
一方、一般的なステンレス鋼においては、Ｎｂは、溶接性を悪化したり、析出物を形成し、脆化を招いたりするため、不要な元素である。このような場合には、逆に、溶鋼中のＮｂ濃度が高くなるのを防止するため、スクラップ中のＮｂが、スラグ中に移行し、溶鋼中に残存しないようにする必要がある。しかし、スクラップを原料としてステンレス鋼を製造する場合には、スクラップ中のＮｂが不純物として残存することは不可避である。したがって、斯かる場合には、溶鋼中のＮｂ濃度をできる限り低減することが必要となる。 On the other hand, in general stainless steel, Nb is an unnecessary element because it deteriorates weldability, forms precipitates, and causes embrittlement. In such a case, conversely, in order to prevent the Nb concentration in the molten steel from becoming high, it is necessary to prevent Nb in the scrap from moving into the slag and not remaining in the molten steel. However, when stainless steel is manufactured using scrap as a raw material, it is inevitable that Nb in the scrap remains as an impurity. Therefore, in such a case, it is necessary to reduce the Nb concentration in the molten steel as much as possible.
ところで、ステンレス鋼中のＮｂ濃度を制御する技術としては、特許文献１の技術がある。この技術は、低Ｎｂ含有ステンレス鋼を、電気炉にてスクラップを用いて溶製するとき、溶落時の溶鋼中のＮｂ濃度と目標Ｎｂ濃度とからＮｂ残存率を求め、該Ｎｂ残存率に基いて出鋼時の目標Ｓｉ濃度を決定し、該目標Ｓｉ濃度になるように溶鋼中のＳｉ濃度を調節することで、ステンレス鋼の脱Ｎｂを図る技術である。 By the way, as a technique for controlling the Nb concentration in stainless steel, there is a technique of Patent Document 1. In this technology, when low-Nb-containing stainless steel is melted using scrap in an electric furnace, the Nb residual rate is obtained from the Nb concentration in the molten steel and the target Nb concentration at the time of melting, and the Nb residual rate is calculated. Based on this, the target Si concentration at the time of steel output is determined, and the Si concentration in the molten steel is adjusted so as to be the target Si concentration, thereby removing Nb from the stainless steel.
しかしながら、上記特許文献１に開示の技術は、電気炉で脱炭のための酸素吹精を行い、出鋼後、目標のＳｉ濃度になるよう、ＦｅＳｉ合金を投入し、Ｃｒ還元処理している。しかし、電気炉における酸素吹精は脱炭効率が悪く、Ｃｒが過剰に酸化ロスするため、その還元のためにＦｅＳｉ合金を多量に添加する必要がある。
また、低Ｎｂ濃度を達成するためには、出鋼後のＳｉ濃度を低く抑える必要があるが、Ｃ濃度が高い状態でＳｉ濃度を低くすると、酸素吹精によってＣＯガスが発生し、出鋼時にスラグが湧き上がり、操業に支障を来すという問題がある。
さらに、近年では、ステンレス鋼の精錬方法は、電気炉等で原料を溶解した後、ＡＯＤ等で脱炭し、Ｃｒ還元処理するのが一般的であり、Ｃｒ還元処理後の溶鋼中のＮｂ濃度が重要となる。しかし、上記特許文献１の技術は、電気炉溶解時のＮｂ濃度を制御する技術であり、ＡＯＤでのＣｒ還元処理後のＮｂ濃度制御にはそのまま適用できない。
However, the technique disclosed in Patent Document 1 performs oxygen blowing for decarburization in an electric furnace, and after ironing out, introduces a FeSi alloy so as to achieve a target Si concentration and performs Cr reduction treatment. . However, oxygen blowing in an electric furnace has poor decarburization efficiency and excessive oxidation loss of Cr. Therefore, it is necessary to add a large amount of FeSi alloy for the reduction.
Moreover, in order to achieve a low Nb concentration, it is necessary to keep the Si concentration after steel output low. However, if the Si concentration is low while the C concentration is high, CO gas is generated by oxygen blowing, and steel output There is a problem that slag sometimes springs up and hinders operation.
Furthermore, in recent years, the refining method of stainless steel is generally performed by melting raw materials in an electric furnace or the like, then decarburizing with AOD or the like, and performing Cr reduction treatment. Nb concentration in molten steel after Cr reduction treatment Is important. However, the technique of the above-mentioned Patent Document 1 is a technique for controlling the Nb concentration at the time of melting in an electric furnace, and cannot be applied as it is to the Nb concentration control after Cr reduction treatment with AOD.
本発明は、従来技術が抱える上記問題点に鑑みてなされたものであり、その目的は、Ｎｂを含有するスクラップ等を原料に用いてステンレス鋼を精錬する際、ＡＯＤでのＣｒ還元処理後の溶鋼中のＣｒ濃度を高い精度でかつ任意に調整することができるステンレス鋼の精錬方法を提案することにある。 The present invention has been made in view of the above-described problems of the prior art, and its purpose is to refining stainless steel using Nb-containing scrap or the like as a raw material after Cr reduction treatment with AOD. An object of the present invention is to propose a method for refining stainless steel capable of arbitrarily adjusting the Cr concentration in molten steel with high accuracy.
発明者らは、上記課題を解決するため、ＡＯＤにおけるＣｒ還元処理終了時点、即ち、Ｃｒ還元処理後の溶鋼中のＮｂ濃度、特に、Ｎｂ含有ステンレス鋼であるＳＵＳ３４７やＮＣＦ６２５、ＳＵＳ３０９のＣｒ還元処理後の溶鋼中のＮｂ濃度に及ぼす各種要因の影響を調査した。
その結果、Ｃｒ還元処理後における溶鋼中のＮｂの歩留り、すなわち、電気炉等で溶解し、出稿したときの溶鋼中のＮｂ濃度に対するＣｒ還元処理後のＮｂ濃度の比率（％）は、Ｃｒ還元処理終了時点のスラグ中のＣｒ酸化物濃度と極めてよい相関があり、スラグ中のＣｒ酸化物濃度を制御すれば、Ｎｂの歩留りを予測でき、ひいては、Ｃｒ還元処理後のＮｂ濃度を精度よく制御することができることを見出し、本発明を開発するに至った。
In order to solve the above-mentioned problems, the inventors have completed Cr reduction treatment at the end of Cr reduction treatment in AOD, that is, Nb concentration in molten steel after Cr reduction treatment, in particular, Cr reduction treatment of SUS347, NCF625, and SUS309, which are Nb-containing stainless steels. The influence of various factors on the Nb concentration in the later molten steel was investigated.
As a result, the yield of Nb in the molten steel after the Cr reduction treatment, that is, the ratio (%) of the Nb concentration after the Cr reduction treatment to the Nb concentration in the molten steel when melted in an electric furnace, etc. There is a very good correlation with the Cr oxide concentration in the slag at the end of the treatment, and if the Cr oxide concentration in the slag is controlled, the yield of Nb can be predicted, and consequently the Nb concentration after the Cr reduction treatment can be accurately controlled. As a result, the present invention has been developed.
すなわち、本発明は、Ｎｂを含有するステンレス鋼の原料を溶解した後、酸素吹精が可能な炉でステンレス溶鋼とスラグを共存させてＣｒ還元処理し、ステンレス鋼を精錬する方法において、上記溶解後のステンレス溶鋼中のＮｂ濃度と、予め求めておいたＣｒ還元処理後のスラグ中のＣｒ酸化物濃度とＮｂ歩留りとの関係式に基いて、上記スラグ中のＣｒ酸化物濃度を調整し、Ｃｒ還元処理後のステンレス溶鋼中のＮｂ濃度を制御することを特徴とするステンレス鋼の精錬方法を提案する。 That is, the present invention provides a method for refining stainless steel by dissolving Cr and reducing stainless steel in the presence of Nb-containing stainless steel in a furnace capable of oxygen blowing and coexisting with molten stainless steel and slag. Based on the relationship between the Nb concentration in the later stainless steel and the Cr oxide concentration in the slag after Cr reduction treatment and the Nb yield obtained in advance, the Cr oxide concentration in the slag is adjusted, We propose a method for refining stainless steel characterized by controlling the Nb concentration in the molten stainless steel after Cr reduction treatment.
本発明の上記ステンレス鋼の精錬方法は、上記Ｃｒ還元処理時のスラグをＣａＯ−ＳｉＯ２−Ｃｒ２Ｏ３系とすることを特徴とする。 The method for refining stainless steel according to the present invention is characterized in that the slag during the Cr reduction treatment is CaO—SiO 2 —Cr 2 O 3 .
また、本発明の上記ステンレス鋼の精錬方法は、上記酸素吹精が可能な炉としてＡＯＤを用いることを特徴とする。 The method for refining stainless steel according to the present invention is characterized in that AOD is used as a furnace capable of performing oxygen blowing.
また、本発明の上記ステンレス鋼の精錬方法は、上記Ｃｒ還元処理後のスラグ中のＣｒ酸化物濃度をｘ（ｍａｓｓ％）、Ｎｂ歩留りをｙ（％）としたとき、上記Ｃｒ還元処理後のスラグ中のＣｒ酸化物濃度ｘとＮｂ歩留りｙとの関係式として、下記（１）式；
ｙ＝ａｘ２＋ｂｘ＋ｃ ・・・（１）
ここで、上記ａ，ｂ，ｃは、定数である。
を用いることを特徴とする。
In the method for refining stainless steel according to the present invention, the Cr oxide concentration in the slag after the Cr reduction treatment is x (mass%) and the Nb yield is y (%). As a relational expression between the Cr oxide concentration x in the slag and the Nb yield y, the following formula (1):
y = ax 2 + bx + c (1)
Here, a, b, and c are constants.
It is characterized by using.
また、本発明の上記ステンレス鋼の精錬方法は、上記Ｃｒ還元処理後のスラグ中のＣｒ酸化物濃度ｘ（ｍａｓｓ％）とＮｂ歩留りｙ（％）との関係式として、下記（２）式；
ｙ＝２．３０ｘ２−２８．３２ｘ＋９７．４８ ・・・（２）
を用いることを特徴とする。
Further, in the method for refining stainless steel of the present invention, as a relational expression between Cr oxide concentration x (mass%) and Nb yield y (%) in the slag after the Cr reduction treatment, the following expression (2):
y = 2.30x 2 -28.32x + 97.48 (2)
It is characterized by using.
本発明によれば、ＡＯＤにおけるＣｒ還元処理後の溶鋼中のＮｂ濃度を高い精度でかつ任意に制御することが可能であるので、Ｎｂ含有ステンレス鋼を精錬するに当たっては、原料として用いるスクラップ中のＮｂのロスを抑えて、有効活用することが可能となり、また、Ｎｂレスのステンレス鋼を精錬するに当たっては、スクラップからＮｂの混入を抑止し、溶鋼中のＮｂ濃度を極微量まで低減することができる。したがって、本発明によれば、Ｎｂ含有量を気にすることなくスクラップをステンレス鋼の原料として使用できるので、原料コストを大幅に削減することができる。 According to the present invention, since it is possible to arbitrarily control the Nb concentration in the molten steel after Cr reduction treatment in AOD with high accuracy, in refining Nb-containing stainless steel, Nb loss can be suppressed and effectively utilized, and when refining Nb-less stainless steel, Nb contamination can be suppressed from scrap and the Nb concentration in molten steel can be reduced to a very small amount. it can. Therefore, according to the present invention, scrap can be used as a raw material for stainless steel without worrying about the Nb content, so that the raw material cost can be greatly reduced.
発明者らは、６０トン電気炉で、フェロニッケル、純ニッケル、フェロクロムの他、鉄屑やステンレス屑、Ｆｅ−Ｎｉ合金屑、Ｎｂ含有屑などのスクラップ等からなるＮｂを含有するステンレス原料を溶解し、出鋼した後、該溶鋼を、ＡＯＤにおいて、酸素吹精してＣを除去（脱炭）し、石灰石等を投入してスラグを生成させ、さらに、ＦｅＳｉ合金を投入してＣｒ還元処理した後、上記スラグを除去（脱滓）し、脱酸し、さらにＡｒガスで撹拌して脱硫処理を施した後、上記溶鋼を取鍋に出鋼し、最終の温度調整ならびに成分調整を行う取鍋精錬して、Ｎｂ含有ステンレス鋼であるＳＵＳ３４７やＮＣＦ６２５、ＳＵＳ３０９を合計１５チャージ溶製した後、連続鋳造してスラブとした。 The inventors melted a stainless steel raw material containing Nb made of ferronickel, pure nickel, ferrochrome, iron scrap, stainless steel scrap, Fe-Ni alloy scrap, scraps such as Nb-containing scrap, etc. in a 60-ton electric furnace. After the steel is discharged, the molten steel is blown with oxygen in AOD to remove C (decarburize), limestone or the like is added to generate slag, and further FeSi alloy is added to reduce Cr. Then, the slag is removed (desulfurized), deoxidized, and further desulfurized by stirring with Ar gas. Then, the molten steel is taken out into a ladle, and final temperature adjustment and component adjustment are performed. After ladle refining, SUS347, NCF625, and SUS309, which are Nb-containing stainless steels, were melted for a total of 15 charges, and then continuously cast into a slab.
その際、上記ＡＯＤでのＣｒ還元処理終了時点における溶鋼中のＮｂ濃度を調査した。その結果、Ｃｒ還元処理後の溶鋼中のＮｂ濃度に、大きなバラツキが認められた。この原因は、電気炉で溶解する原料、特に、ステンレス屑（スクラップ）中に含まれるＮｂの含有量がチャージごとに変化し、電気炉出鋼時のＮｂ濃度が変動したためであると考えられた。 At that time, the Nb concentration in the molten steel at the end of the Cr reduction treatment with the AOD was investigated. As a result, a large variation was observed in the Nb concentration in the molten steel after the Cr reduction treatment. This was thought to be because the Nb content contained in the raw material that melts in the electric furnace, in particular, the stainless steel scrap (scrap), varied with each charge, and the Nb concentration at the time of steel leaving the electric furnace fluctuated. .
そこで、電気炉出鋼時の溶鋼中のＮｂ濃度と、Ｃｒ還元処理後の溶鋼中のＮｂ濃度との関係を表す指標として、下記（１）式；
Ｎｂ歩留り（％）＝Ｃｒ還元処理後のＮｂ濃度／電気炉出鋼時のＮｂ濃度×１００
・・・（３）
で定義される「Ｎｂ歩留り」という概念を導入し、上記Ｎｂ歩留りに及ぼす各種要因の影響をさらに調査した。
Therefore, as an index representing the relationship between the Nb concentration in the molten steel at the time of steel discharge from the electric furnace and the Nb concentration in the molten steel after the Cr reduction treatment, the following equation (1):
Nb yield (%) = Nb concentration after Cr reduction treatment / Nb concentration at the time of steel leaving the electric furnace × 100
... (3)
The concept of “Nb yield” defined in (1) was introduced, and the influence of various factors on the Nb yield was further investigated.
その結果、Ｃｒ還元処理後のスラグ中のＣｒ酸化物濃度と、上記Ｎｂ歩留りとの間には、図１に示したように、極めてよい相関関係があり、Ｃｒ還元処理後のスラグ中のＣｒ酸化物濃度が低いほど、Ｎｂ歩留りが高くなる傾向があることがわかった。ここで、上記Ｃｒ酸化物濃度とは、スラグ中の全ＣｒをＣｒ２Ｏ３の濃度（ｍａｓｓ％）に換算した値のことをいう。
なお、Ｃｒ還元処理後の溶鋼中のＳｉ濃度と、Ｎｂ歩留りとの関係についても調べたが、図２に示したように、ばらつきが大きく、特許文献１のような相関関係は認められなかった。
As a result, as shown in FIG. 1, there is a very good correlation between the Cr oxide concentration in the slag after the Cr reduction treatment and the Nb yield, and the Cr in the slag after the Cr reduction treatment. It was found that the Nb yield tends to increase as the oxide concentration decreases. Here, the above-mentioned Cr oxide concentration refers to a value that the total Cr in terms of the concentration of Cr 2 O 3 (mass%) in the slag.
In addition, although the relationship between the Si concentration in the molten steel after the Cr reduction treatment and the Nb yield was also examined, as shown in FIG. 2, the variation was large and the correlation as in Patent Document 1 was not recognized. .
上記のように、Ｃｒ還元処理後のスラグ中のＣｒ酸化物濃度と、溶鋼中のＮｂ歩留りとの間によい相関関係ある理由について、発明者らは以下のように考えている。
ＡＯＤでＣを除去するために酸素吹精を行うと、溶鋼中のＣｒも酸化されると同時にＮｂも酸化され、酸化物となってスラグ中に移行する。しかし、その後、Ｆｅ−Ｓｉ合金等の脱酸剤を投入してＣｒ還元処理を行うと、Ｃｒ酸化物が還元されると共に、Ｎｂ酸化物も還元される。すなわち、Ｃｒ酸化物の還元処理により、スラグ中のＣｒ酸化物濃度が低下すると、スラグ中のＮｂ酸化物は還元され、その結果、溶鋼中のＮｂ濃度が高くなり、Ｎｂ歩留りが高くなる。
As described above, the inventors consider the reason why there is a good correlation between the Cr oxide concentration in the slag after the Cr reduction treatment and the Nb yield in the molten steel as follows.
When oxygen blowing is performed to remove C by AOD, Cr in the molten steel is also oxidized, and Nb is also oxidized, and becomes oxide and moves into the slag. However, if a deoxidizing agent such as an Fe—Si alloy is subsequently added to perform Cr reduction treatment, Cr oxide is reduced and Nb oxide is also reduced. That is, when the Cr oxide concentration in the slag decreases due to the reduction treatment of the Cr oxide, the Nb oxide in the slag is reduced. As a result, the Nb concentration in the molten steel increases and the Nb yield increases.
また、上記の結果から、Ｃｒ還元処理後の溶鋼中のＮｂ濃度は、下記（４）式；
２（Ｃｒ２Ｏ３）＋３Ｎｂ＝３（ＮｂＯ２）＋４Ｃｒ ・・・（４）
ここで、（４）式中の括弧はスラグ中の成分、下線は溶鋼中の成分を表す。
で示される反応によって支配されていることが推察された。
Moreover, from said result, Nb density | concentration in the molten steel after Cr reduction processing is following (4) Formula;
2 (Cr 2 O 3 ) +3 Nb = 3 (NbO 2 ) +4 Cr (4)
Here, the parentheses in the formula (4) represent components in the slag, and the underline represents components in the molten steel.
It was inferred that it was governed by the reaction shown in.
次いで、発明者らは、上記図１に示された１５チャージのデータを、Ｃｒ還元処理後のＮｂ歩留りをｙ（％）、スラグ中のＣｒ酸化物濃度をｘ（ｍａｓｓ％）として、下記（１）式；
ｙ＝ａｘ２＋ｂｘ＋ｃ ・・・（１）
の２次曲線で近似することを試みた。その結果、上記データは、下記（２）式；
ｙ＝２．３０ｘ２−２８．３２ｘ＋９７．４８ ・・・（２）
の回帰式で表され、その決定係数（寄与率）Ｒ２は０．９７であり、Ｃｒ還元処理後のスラグ中のＣｒ酸化物濃度とＮｂ歩留りとは極めて高い相関関係にあることがわかった。
Next, the inventors used the 15 charge data shown in FIG. 1 as follows, assuming that the Nb yield after Cr reduction treatment is y (%) and the Cr oxide concentration in the slag is x (mass%) ( 1) Formula;
y = ax 2 + bx + c (1)
An attempt was made to approximate with a quadratic curve. As a result, the above data is the following formula (2):
y = 2.30x 2 -28.32x + 97.48 (2)
The coefficient of determination (contribution rate) R 2 is 0.97, and it was found that the Cr oxide concentration in the slag after the Cr reduction treatment and the Nb yield have a very high correlation. .
上記のように、ＡＯＤでＣｒ還元処理してステンレス鋼を精錬するときに、Ｃｒ還元処理後のスラグ中のＣｒ酸化物濃度とＮｂ歩留りとの間に極めてよい相関関係あるということは、Ｃｒ還元処理終了時点におけるスラグ中のＣｒ酸化物濃度を調整すれば、Ｃｒ還元処理後の溶鋼中のＮｂ濃度を制御することができる、すなわち、電気炉出鋼時のＮｂ濃度と、ＡＯＤにおけるＣｒ還元処理後の目標Ｎｂ濃度から、目標とするＮｂ歩留りを設定し、該Ｎｂ歩留りを得るために必要なスラグ中のＣｒ酸化物濃度を、予め求めておいた上記（２）式から求め、そのＣｒ酸化物濃度となるようにＣｒ還元処理時のスラグ成分を調整すれば、Ｃｒ還元処理後の溶鋼中のＮｂ濃度を任意の値に制御することができることを示している。 As described above, when refining stainless steel by Cr reduction treatment with AOD, there is a very good correlation between the Cr oxide concentration in the slag after Cr reduction treatment and the Nb yield. If the Cr oxide concentration in the slag at the end of the treatment is adjusted, the Nb concentration in the molten steel after the Cr reduction treatment can be controlled, that is, the Nb concentration at the time of electric steel leaving and the Cr reduction treatment in the AOD. The target Nb yield is set from the target Nb concentration later, and the Cr oxide concentration in the slag necessary for obtaining the Nb yield is obtained from the above-described equation (2), and the Cr oxidation It is shown that the Nb concentration in the molten steel after the Cr reduction treatment can be controlled to an arbitrary value by adjusting the slag component during the Cr reduction treatment so as to be a product concentration.
ここで、上記（２）式は、前述したように、Ｎｂを含有するＳＵＳ３４７、ＮＣＦ６２５およびＳＵＳ３０９系のステンレス鋼のデータについての回帰式であることから、鋼種に依らず成り立つものと考えられる。
ただし、上記（２）式は、前述した（４）式のスラグ−メタル間の相平衡に基いたものであり、速度論的な因子を考慮していないことから、係数ａ、ｂ、ｃは、精錬設備によって微妙に異なる可能性がある。そこで、上記式を用いて本発明を実施し、Ｎｂ濃度を制御しようとする場合には、各精錬設備の実績データから回帰式を求め、係数の補正を適宜行っておくことが好ましい。なお、上記回帰式を求めるに当たっては、少なくとも１０チャージの実績データを用いることが好ましく、より高い精度を求める場合には、２０チャージ以上の実績データを用いるのが好ましい。
Here, since the above equation (2) is a regression equation for data of SUS347, NCF625, and SUS309 stainless steels containing Nb as described above, it is considered that the above equation (2) holds regardless of the steel type.
However, the above equation (2) is based on the slag-metal phase equilibrium of the above-described equation (4) and does not consider kinetic factors, so the coefficients a, b, and c are Depending on the refining equipment, it may be slightly different. Therefore, when the present invention is carried out using the above formula and the Nb concentration is to be controlled, it is preferable to obtain a regression formula from the actual data of each refining equipment and correct the coefficient appropriately. In obtaining the regression equation, it is preferable to use at least 10 charge result data, and to obtain higher accuracy, it is preferable to use result data of 20 charges or more.
次に、本発明のステンレス鋼の精錬方法について説明する。
本発明のステンレス鋼の精錬方法は、まず、電気炉等でＮｂを含有するステンレス原料を溶解し、Ｎｂを含有する溶鋼とする。ここで、Ｎｂを含有する溶鋼としたのは、Ｎｂを含有しない場合には、Ｎｂ濃度を制御する必要がなく、本発明を用いる必要がないからである。上記ステンレス原料としては、フェロニッケル、純ニッケル、フェロクロム等の他に、鉄屑やステンレス屑、Ｆｅ−Ｎｉ合金屑、Ｎｂ含有屑等のＮｂを含有するスクラップを用いる。ここで、上記スクラップとしては、ステンレス鋼を製造する観点から、Ｆｅ−Ｃｒ−Ｎｉ系のＮｂ含有合金屑、例えば、ＳＵＳ３４７屑、ＮＣＦ６２５屑や、Ｆｅ−３５％Ｎｉ−２５％Ｃｒ−１％Ｎｂ屑などを好ましく用いることができる。なお、本発明では、Ｎｂの濃度制御が可能であるので、Ｎｂを高濃度で含有する安価なものも用いることができることが特徴である。なお、上記説明では、ステンレス鋼原料の溶解に電気炉を用いているが、電気炉に限定されるものではなく、例えば、転炉や高周波誘導炉などを用いてもよい。
Next, the method for refining stainless steel according to the present invention will be described.
In the method for refining stainless steel of the present invention, first, a stainless steel raw material containing Nb is melted in an electric furnace or the like to obtain a molten steel containing Nb. Here, the reason why the molten steel containing Nb is used is that when Nb is not contained, it is not necessary to control the Nb concentration and it is not necessary to use the present invention. As the stainless material, scraps containing Nb such as iron scrap, stainless scrap, Fe-Ni alloy scrap, Nb-containing scrap, in addition to ferronickel, pure nickel, ferrochrome, and the like are used. Here, as the scrap, from the viewpoint of producing stainless steel, Fe—Cr—Ni-based Nb-containing alloy scraps such as SUS347 scrap, NCF625 scrap, Fe-35% Ni-25% Cr-1% Nb Waste and the like can be preferably used. In the present invention, since the Nb concentration can be controlled, an inexpensive one containing Nb at a high concentration can be used. In the above description, the electric furnace is used for melting the stainless steel raw material. However, the electric furnace is not limited to the electric furnace. For example, a converter or a high-frequency induction furnace may be used.
上記電気炉等で溶解し、出鋼した溶鋼は、その後、酸素ガスを吹精することが可能な炉で、酸素ガスを吹精して溶鋼中のＣを除去（脱炭）し、石灰石等を添加してスラグを生成させた後、ＦｅＳｉ等の脱酸剤を添加してＣｒ還元処理を施した後、上記スラグを除去（除滓）する。なお、上記脱酸剤としては、ＦｅＳｉの他に、Ａｌを用いてもよい。 The molten steel melted and produced in the above electric furnace or the like is then a furnace capable of blowing oxygen gas, blowing oxygen gas to remove (decarburize) C in the molten steel, limestone, etc. After adding slag to produce slag, a deoxidizer such as FeSi is added and Cr reduction treatment is performed, and then the slag is removed (removed). As the deoxidizer, Al may be used in addition to FeSi.
上記酸素ガスを吹精することが可能な炉としては、傾動してスラグを除滓することができる炉であることが好ましく、具体的には、ＡＯＤや転炉を挙げることができるが、以降の説明では、ＡＯＤを用いた例について説明する。 The furnace capable of blowing the oxygen gas is preferably a furnace that can be tilted to remove slag, and specifically includes an AOD and a converter. In the description, an example using AOD will be described.
ＡＯＤにおける上記脱炭工程においては、溶鋼中のＣがＣＯ２となって除去され、それと同時に、溶鋼中のＣｒやＮｂも酸化され、酸化物となってスラグ相に移行するが、その後のＣｒ還元処理工程では、スラグ中のＣｒ酸化物が還元されると同時に、Ｎｂ酸化物も還元されて溶鋼中に回収される。その後、上記スラグを除去するが、この除滓によって、スラグ中に残存するＮｂ酸化物は系外に排出される。 In the above decarburization step in AOD, C in the molten steel is removed as CO 2, and at the same time, Cr and Nb in the molten steel are also oxidized and converted into oxides and transferred to the slag phase. In the reduction treatment step, Cr oxide in the slag is reduced, and at the same time, Nb oxide is also reduced and recovered in the molten steel. Thereafter, the slag is removed. By this removal, the Nb oxide remaining in the slag is discharged out of the system.
したがって、上記Ｃｒ還元処理時に生成させるスラグの成分系は重要であり、本発明においては、ＣａＯ−ＳｉＯ２−Ｃｒ２Ｏ３系とするのが望ましい。というのは、Ｎｂを含有するステンレス鋼を製造する場合には、Ｃｒ還元処理時にスラグ中に存在するＮｂ酸化物をできるだけ還元し、Ｎｂを溶鋼中に回収する必要があるが、溶鋼中のＮｂ濃度は、前述したように、下記（４）式；
２（Ｃｒ２Ｏ３）＋３Ｎｂ＝３（ＮｂＯ２）＋４Ｃｒ ・・・（４）
に支配されているからである。
Therefore, the component system of slag generated during the Cr reduction treatment is important, and in the present invention, it is desirable to use a CaO—SiO 2 —Cr 2 O 3 system. This is because, when producing stainless steel containing Nb, it is necessary to reduce Nb oxide present in the slag as much as possible during Cr reduction treatment and recover Nb in the molten steel. As described above, the concentration is the following formula (4):
2 (Cr 2 O 3 ) +3 Nb = 3 (NbO 2 ) +4 Cr (4)
It is because it is dominated by.
また、Ｃｒ還元時のスラグをＣａＯ−ＳｉＯ２−Ｃｒ２Ｏ３系とする場合には、そのスラグの塩基度（ＣａＯ／ＳｉＯ２）は、０．９〜１．５の範囲とするのが好ましい。（ＣａＯ／ＳｉＯ２）が０．９未満では、スラグの粘度が高く流動性を確保できなくなり、一方、１．５を超えると、スラグを溶融状態に保持することができなくなるからである。より好ましくは、１．０〜１．３の範囲である。 Moreover, when the slag at the time of Cr reduction is a CaO—SiO 2 —Cr 2 O 3 system, the basicity of the slag (CaO / SiO 2 ) should be in the range of 0.9 to 1.5. preferable. This is because if (CaO / SiO 2 ) is less than 0.9, the viscosity of the slag is high and fluidity cannot be secured, while if it exceeds 1.5, the slag cannot be held in a molten state. More preferably, it is the range of 1.0-1.3.
また、上記ＣａＯ−ＳｉＯ２−Ｃｒ２Ｏ３系スラグ中のＣｒ２Ｏ３濃度は、０．１〜６ｍａｓｓ％の範囲とするのが好ましい。Ｃｒ２Ｏ３濃度を０．１ｍａｓｓ％未満とすると、高い歩留りでＮｂを回収できるという効果がある反面、ＦｅＳｉ合金を大量に添加する必要があるため、副原料コストの上昇を招くこと、および、平衡論的にも限界に近く、実施が困難だからである。一方、６ｍａｓｓ％を超えると、有価金属であるＣｒのロスが多くなり、原料コストが上昇するとともに、スラグを安定して溶融状態に保持できなくなるからである。より好ましくは、０．３〜５．５ｍａｓｓ％の範囲である。 Further, Cr 2 O 3 concentration of the CaO-SiO 2 -Cr 2 O 3 system in the slag is preferably in the range of 0.1~6mass%. When the Cr 2 O 3 concentration is less than 0.1 mass%, there is an effect that Nb can be recovered with a high yield, but on the other hand, it is necessary to add a large amount of FeSi alloy. This is because the balance is close to the limit and difficult to implement. On the other hand, if it exceeds 6 mass%, loss of Cr, which is a valuable metal, increases, the raw material cost increases, and the slag cannot be stably held in a molten state. More preferably, it is in the range of 0.3 to 5.5 mass%.
ここで、本発明の特徴である、Ｃｒ還元処理時における溶鋼中のＮｂ濃度制御方法について説明する。
先述したように、Ｃｒ還元処理後のスラグ中のＣｒ酸化物濃度とＮｂ歩留り（％）との間には極めて強い相関関係があり、スラグ中のＣｒ酸化物濃度（ｍａｓｓ％）をｘ、Ｎｂ歩留り（％）をｙとしたとき、下記（１）式のような２次式；
ｙ＝ａｘ２＋ｂｘ＋ｃ ・・・（１）
具体的には、下記（２）式；
ｙ＝２．３０ｘ２−２８．３２ｘ＋９７．４８ ・・・（２）
で高い寄与率を持って表すことができる。
Here, the Nb concentration control method in the molten steel at the time of Cr reduction process, which is a feature of the present invention, will be described.
As described above, there is a very strong correlation between the Cr oxide concentration in the slag after the Cr reduction treatment and the Nb yield (%), and the Cr oxide concentration (mass%) in the slag is expressed as x, Nb. When the yield (%) is y, a quadratic expression such as the following expression (1);
y = ax 2 + bx + c (1)
Specifically, the following formula (2):
y = 2.30x 2 -28.32x + 97.48 (2)
Can be expressed with a high contribution rate.
上記（２）式は、ＡＯＤでＣｒ還元処理を施してステンレス鋼を精錬するときのＣｒ還元処理後のスラグ中のＣｒ酸化物濃度とＮｂ歩留りとの間に相関関係にあることを示しているが、本発明は、上記（２）式を活用し、Ｃｒ還元処理後のスラグ中のＣｒ酸化物濃度を調整することで、Ｃｒ還元処理後のＮｂ歩留り、ひいては、Ｃｒ還元処理後の溶鋼中のＮｂ濃度を高い精度で制御する。 The above equation (2) indicates that there is a correlation between the Cr oxide concentration in the slag after Cr reduction treatment and the Nb yield when the stainless steel is refined by performing Cr reduction treatment with AOD. However, the present invention utilizes the above formula (2) and adjusts the Cr oxide concentration in the slag after the Cr reduction treatment, so that the Nb yield after the Cr reduction treatment, and thus in the molten steel after the Cr reduction treatment. The Nb concentration is controlled with high accuracy.
具体的には、電気炉から出鋼したときの溶鋼中のＮｂ濃度と、ＡＯＤでのＣｒ還元処理後の目標とするＮｂ濃度とから、目標Ｎｂ歩留りを求め、そのＮｂ歩留りと上記（２）式から、上記Ｃｒ還元処理後のＮｂ濃度を達成するために必要なスラグ中のＣｒ酸化物濃度を求め、上記Ｃｒ酸化物濃度になるよう、スラグの成分組成を調整することで、Ｃｒ還元処理後のＮｂ濃度を制御することができる。例えば、Ｃｒ歩留りを６０％以上としたい場合には、スラグ中のＣｒ酸化物濃度を１．５ｍａｓｓ％以下に低減すればよく、逆に、Ｃｒ歩留りを３０％以下としたい場合には、スラグ中のＣｒ酸化物濃度を３．２ｍａｓｓ％以上とすればよい。 Specifically, the target Nb yield is obtained from the Nb concentration in the molten steel when the steel is discharged from the electric furnace and the target Nb concentration after the Cr reduction treatment at the AOD, and the Nb yield and the above (2) From the formula, the Cr oxide concentration in the slag necessary for achieving the Nb concentration after the Cr reduction treatment is obtained, and the component composition of the slag is adjusted so as to be the Cr oxide concentration, thereby the Cr reduction treatment. The subsequent Nb concentration can be controlled. For example, when the Cr yield is desired to be 60% or more, the Cr oxide concentration in the slag may be reduced to 1.5 mass% or less. Conversely, when the Cr yield is desired to be 30% or less, The Cr oxide concentration may be 3.2 mass% or more.
ここで、上記スラグ中のＣｒ酸化物濃度の調整は、まず、ＡＯＤの脱炭工程における酸素吹精量および石灰の投入量から、スラグ中のＣｒ酸化物濃度を推定する。ここで、酸素吹精量のうち、炭素の除去に使われた酸素以外の酸素が溶鋼中のＣｒと反応してＣｒ酸化物を形成すると考え、Ｃｒ酸化物量を推定する。次いで、上記Ｃｒ酸化物量と目標とするＣｒ酸化物濃度から、必要とされるスラグ総量を算出し、そのスラグ総量となるよう石灰石を投入することで行うことができる。該推定濃度が目標のＣｒ酸化物濃度と異なる（高い）場合には、その差分に応じてＦｅＳｉの投入量を調整することにより行うことができる。なお、上記調整で、目標のＣｒ酸化物濃度とならなかった場合は、さらに、目標濃度となるよう、ＦｅＳｉ合金を投入すればよい。上記Ｃｒ酸化物濃度の調整にＦｅＳｉを添加する理由は、Ｓｉは、Ｃｒよりも酸化し易いからであり、ＦｅＳｉに代えて、Ａｌを添加してもよい。一方、Ｃｒ酸化物の濃度を増加させたい場合には、酸素吹錬をさらに継続すればよい。 Here, the adjustment of the Cr oxide concentration in the slag is performed by first estimating the Cr oxide concentration in the slag from the amount of oxygen blowing and the amount of lime input in the AOD decarburization step. Here, it is assumed that oxygen other than oxygen used for removing carbon reacts with Cr in molten steel to form Cr oxide, and the amount of Cr oxide is estimated. Next, the total amount of slag required can be calculated from the amount of Cr oxide and the target Cr oxide concentration, and limestone can be added so as to obtain the total amount of slag. When the estimated concentration is different (high) from the target Cr oxide concentration, it can be performed by adjusting the amount of FeSi input according to the difference. If the target Cr oxide concentration is not reached by the above adjustment, an FeSi alloy may be added so that the target concentration is further reached. The reason for adding FeSi for the adjustment of the Cr oxide concentration is that Si is more easily oxidized than Cr, and Al may be added instead of FeSi. On the other hand, when it is desired to increase the concentration of Cr oxide, oxygen blowing may be further continued.
次に、Ｃｒ還元処理が完了し、スラグを除去（除滓）した後の工程について説明する。
上記除滓後の工程は、通常公知の方法で行えばよく、本発明においては特に制限しないが、例えば、上記除滓後のＡＯＤ内に石灰石や蛍石等の造滓材を投入して新たなスラグを生成させ、Ａｒ撹拌して脱硫を促進した後、取鍋に出鋼し、該取鍋にて最終の温度調整および成分調整を施した後、連続鋳造法等で鋼素材（スラブ）とする。なお、上記撹拌に用いるガスは、Ａｒ以外の希ガスやＮ２ガスを用いてもよい。
Next, a process after the Cr reduction process is completed and slag is removed (removed) will be described.
The process after the above removal should be performed by a generally known method, and is not particularly limited in the present invention. For example, a new slagging material such as limestone or fluorite is introduced into the AOD after the above removal. Slag is generated, Ar is stirred and desulfurization is promoted, and then steel is taken out in a ladle. After final temperature adjustment and component adjustment in the ladle, a steel material (slab) is obtained by a continuous casting method or the like. And The gas used for the stirring may be a rare gas other than Ar or N 2 gas.
なお、上記新たに生成させるスラグは、ＣａＯ−ＳｉＯ２−ＭｇＯ系またはＣａＯ−ＳｉＯ２−ＭｇＯ−Ｆ系とするのが好ましい。その理由は、上記成分系に調整することにより、溶鋼中の酸素濃度が低下するので、脱硫を促進することができたり、酸素濃度の低下により、介在物の形態を制御することができたりするからである。 The newly generated slag is preferably CaO—SiO 2 —MgO or CaO—SiO 2 —MgO—F. The reason is that by adjusting to the above component system, the oxygen concentration in the molten steel decreases, so desulfurization can be promoted, or the form of inclusions can be controlled by the decrease in oxygen concentration. Because.
容量６０トンの電気炉で、フェロニッケル、純ニッケル、フェロクロム、鉄屑、ステンレス屑、Ｆｅ−Ｎｉ合金屑、Ｎｂ含有屑などのステンレス原料を溶解し、Ｎｂ濃度が０．０１６〜２．１７ｍａｓｓ％の範囲で変化した溶鋼とし、出鋼し、次いで、ＡＯＤで、上記溶鋼を酸素吹精して脱炭した後、石灰石を投入してＣａＯ−ＳｉＯ２−Ｃｒ２Ｏ３系スラグを生成させた後、ＦｅＳｉ合金を投入してＣｒ還元処理し、スラグを除滓した後、新たに石灰石および／または蛍石を投入してＣａＯ−ＳｉＯ２−ＭｇＯ系スラグまたはＣａＯ−ＳｉＯ２−ＭｇＯ−Ｆ系スラグを生成させ、Ａｒ撹拌して脱硫した後、取鍋に出鋼し、最終の温度調整ならびに成分調整を行う取鍋精錬することにより、各種成分組成のＮｂ含有ステンレス鋼を２０チャージ溶製した。 In an electric furnace with a capacity of 60 tons, stainless steel raw materials such as ferronickel, pure nickel, ferrochrome, iron scrap, stainless scrap, Fe-Ni alloy scrap, and Nb-containing scrap are melted, and the Nb concentration is 0.016 to 2.17 mass%. The molten steel was changed in the range, and the steel was discharged. Then, the molten steel was blown with oxygen and decarburized by AOD, and then limestone was added to generate CaO—SiO 2 —Cr 2 O 3 slag. Thereafter, FeSi alloy is added and Cr reduction treatment is performed, slag is removed, limestone and / or fluorite is newly added, and CaO—SiO 2 —MgO slag or CaO—SiO 2 —MgO—F system is added. After slag is generated and desulfurized by stirring with Ar, the steel is taken out into a ladle and refined in a ladle for final temperature adjustment and component adjustment, thereby producing Nb-containing stainless steels having various component compositions. Yaji was melted.
この際、ＡＯＤのＣｒ還元処理時に生成させるＣａＯ−ＳｉＯ２−Ｃｒ２Ｏ３系スラグ中のＣｒ酸化物濃度を０．４〜５．３ｍａｓｓ％の範囲で種々に変化させ、Ｃｒ還元処理終了時点の溶鋼中のＮｂ濃度を調査した。なお、上記スラグ中および溶鋼中の成分は、蛍光Ｘ線分析装置で定量分析した。 At this time, the Cr oxide concentration in the CaO—SiO 2 —Cr 2 O 3 slag generated during the AOD Cr reduction treatment is variously changed in the range of 0.4 to 5.3 mass%, and the Cr reduction treatment is completed. The Nb concentration in the molten steel was investigated. The components in the slag and molten steel were quantitatively analyzed with a fluorescent X-ray analyzer.
表１に、電気炉出鋼時の溶鋼中のＮｂ濃度、および、ＡＯＤにおけるＣｒ還元処理後のスラグおよび溶鋼の成分組成を示した。なお、表１に示したスラグ組成の合計が１００ｍａｓｓ％となっていないのは、スラグ中には、表１に示したＣａＯ，ＳｉＯ２，Ａｌ２Ｏ３，ＭｇＯ，Ｃｒ２Ｏ３，ＮｂＯの他に、ＦｅＯやＮｉＯ，Ｆなどが含まれているためである。
ここで、上記表１の結果を、Ｃｒ還元処理後のスラグ中のＣｒ酸化物濃度とＮｂ歩留りとの関係として示したのが図３である。図１と同様、Ｃｒ還元処理後のスラグ中のＣｒ酸化物濃度とＮｂ歩留りとの間には明確な相関関係が認められた。
また、図３中には、図１から得られた回帰式である下記（２）式；
ｙ＝２．３０ｘ２−２８．３２ｘ＋９７．４８ ・・・（２）
を重ねて記載したが、測定データと回帰式とのずれはほとんどない、即ち、Ｃｒ還元処理後のスラグ中のＣｒ酸化物濃度とＮｂ歩留りとの関係は、上記（２）式で精度よく表されることが確認された。
これに対して、上記表１の結果を、Ｃｒ還元処理後のＳｉ濃度とＮｂ歩留りとの関係として示したのが図４であり、図２と同様、Ｃｒ還元処理後の溶鋼中のＳｉ濃度とＮｂ歩留りとの間に相関関係は認められない。
Table 1 shows the Nb concentration in the molten steel at the time of steelmaking in the electric furnace, and the composition of the slag and molten steel after the Cr reduction treatment in the AOD. The total slag composition shown in Table 1 is not 100 mass% because the slag contains CaO, SiO 2 , Al 2 O 3 , MgO, Cr 2 O 3 and NbO shown in Table 1. This is because FeO, NiO, F and the like are included.
Here, FIG. 3 shows the results of Table 1 above as the relationship between the Cr oxide concentration in the slag after the Cr reduction treatment and the Nb yield. As in FIG. 1, a clear correlation was observed between the Cr oxide concentration in the slag after the Cr reduction treatment and the Nb yield.
Further, in FIG. 3, the following equation (2) which is a regression equation obtained from FIG. 1;
y = 2.30x 2 -28.32x + 97.48 (2)
However, there is almost no deviation between the measurement data and the regression equation, that is, the relationship between the Cr oxide concentration in the slag after the Cr reduction treatment and the Nb yield is expressed with the above equation (2) with high accuracy. It was confirmed that
On the other hand, FIG. 4 shows the results of Table 1 as the relationship between the Si concentration after the Cr reduction treatment and the Nb yield. Similar to FIG. 2, the Si concentration in the molten steel after the Cr reduction treatment. There is no correlation between Nb and Nb yield.
実施例１の結果、上記（２）式の有効性が確認できたので、上記式を活用し、Ｃｒ還元処理後の溶鋼中のＮｂ濃度を制御する実験を行った。
実験は、実施例１と同様、容量６０トンの電気炉で、フェロニッケル、純ニッケル、フェロクロム、鉄屑、ステンレス屑、Ｆｅ−Ｎｉ合金屑、Ｎｂ含有屑などのステンレス原料を溶解し、Ｎｂ濃度が０．５〜２ｍａｓｓ％の範囲で変化した溶鋼とした後、ＡＯＤで、上記溶鋼を酸素吹精して脱炭した後、石灰石を投入してＣａＯ−ＳｉＯ２−Ｃｒ２Ｏ３系スラグを生成させた後、ＦｅＳｉ合金を投入してＣｒ還元処理し、スラグを除滓した後、新たに石灰石および／または蛍石を投入してＣａＯ−ＳｉＯ２−ＭｇＯ系スラグまたはＣａＯ−ＳｉＯ２−ＭｇＯ−Ｆ系スラグを生成させ、Ａｒ撹拌して脱硫した後、取鍋に出鋼し、最終の温度調整ならびに成分調整を行う取鍋精錬することにより、Ｎｂ含有ステンレス鋼を３０チャージ溶製し、連続鋳造してスラブとした。
As a result of Example 1, the effectiveness of the above formula (2) was confirmed, so an experiment was conducted to control the Nb concentration in the molten steel after the Cr reduction treatment by utilizing the above formula.
In the experiment, in the same manner as in Example 1, in an electric furnace having a capacity of 60 tons, stainless steel raw materials such as ferronickel, pure nickel, ferrochrome, iron scrap, stainless steel scrap, Fe-Ni alloy scrap, and Nb-containing scrap were dissolved, and the Nb concentration after There was a molten steel was changed in the range of 0.5～2Mass%, in AOD, after decarburization by the molten steel and oxygen吹精, a CaO-SiO 2 -Cr 2 O 3 slag by introducing limestone After the formation, FeSi alloy is added and Cr reduction treatment is performed, slag is removed, limestone and / or fluorite is newly added, and CaO—SiO 2 —MgO-based slag or CaO—SiO 2 —MgO is added. -F-type slag is produced, Ar is stirred and desulfurized, then steel is taken out into a ladle, and the final temperature adjustment and component adjustment are performed to refine the ladle. , It was a slab continuous casting.
この際、上記３０チャージのうちの１０チャージについては、Ｃｒ還元処理後の溶鋼中のＮｂ濃度が０．３ｍａｓｓ％になるよう、また、１０チャージについては、Ｃｒ還元処理後の溶鋼中のＮｂ濃度が１.０ｍａｓｓ％になるよう、Ｃｒ還元処理時に生成させるスラグ中のＣｒ酸化物濃度を調整してＮｂ歩留りを制御し、得られたＣｒ還元処理後の溶鋼中のＮｂ濃度を測定した。また、残りの１０チャージについては、比較例として、Ｃｒ還元処理時に生成させるスラグ中のＣｒ酸化物濃度を調整することなくＣｒ還元処理し、得られたＣｒ還元処理後の溶鋼中のＮｂ濃度を測定した。 At this time, for 10 charges out of the 30 charges, the Nb concentration in the molten steel after Cr reduction treatment is 0.3 mass%, and for 10 charges, the Nb concentration in the molten steel after Cr reduction treatment The Nb yield was controlled by adjusting the Cr oxide concentration in the slag generated during the Cr reduction treatment so that the Nb concentration was 1.0 mass%, and the Nb concentration in the molten steel after the Cr reduction treatment was measured. For the remaining 10 charges, as a comparative example, the Cr reduction treatment was performed without adjusting the Cr oxide concentration in the slag generated during the Cr reduction treatment, and the Nb concentration in the molten steel after the Cr reduction treatment was obtained. It was measured.
上記の結果を表２に示した。この結果から、Ｃｒ還元処理時に生成させるスラグ中のＣｒ酸化物濃度を調整することなくＣｒ還元処理した場合には、Ｃｒ還元処理後の溶鋼中のＮｂ濃度が大きく変動しているのに対して、本発明を適用した場合には、目標Ｎｂ濃度の高低に拘わらず、高い精度でＣｒ還元処理後の溶鋼中のＮｂ濃度を制御することができることがわかる。 The results are shown in Table 2. From this result, when Cr reduction treatment is performed without adjusting the Cr oxide concentration in the slag generated during Cr reduction treatment, the Nb concentration in the molten steel after Cr reduction treatment varies greatly. When the present invention is applied, it can be seen that the Nb concentration in the molten steel after the Cr reduction treatment can be controlled with high accuracy regardless of the target Nb concentration.
Claims (5)
上記溶解後のステンレス溶鋼中のＮｂ濃度と、予め求めておいたＣｒ還元処理後のスラグ中のＣｒ酸化物濃度とＮｂ歩留りとの関係式に基いて、上記スラグ中のＣｒ酸化物濃度を調整し、Ｃｒ還元処理後のステンレス溶鋼中のＮｂ濃度を制御することを特徴とするステンレス鋼の精錬方法。 In a method of refining stainless steel, after melting a raw material of stainless steel containing Nb, coexisting stainless steel and slag in a furnace capable of oxygen blowing, Cr reduction treatment,
The Cr oxide concentration in the slag is adjusted based on the relational expression between the Nb concentration in the molten stainless steel after the melting and the Cr oxide concentration in the slag after Cr reduction treatment and the Nb yield obtained in advance. And controlling the Nb concentration in the molten stainless steel after the Cr reduction treatment.
記
ｙ＝ａｘ２＋ｂｘ＋ｃ ・・・（１）
ここで、上記ａ，ｂ，ｃは、定数である。 When the Cr oxide concentration in the slag after the Cr reduction treatment is x (mass%) and the Nb yield is y (%), the Cr oxide concentration x and the Nb yield y in the slag after the Cr reduction treatment are The method of refining stainless steel according to any one of claims 1 to 3, wherein the following formula (1) is used as a relational expression:
Y = ax 2 + bx + c (1)
Here, a, b, and c are constants.
記
ｙ＝２．３０ｘ２−２８．３２ｘ＋９７．４８ ・・・（２） The following formula (2) is used as a relational expression between the Cr oxide concentration x (mass%) in the slag after the Cr reduction treatment and the Nb yield y (%). The method for refining stainless steel according to claim 1.
Y = 2.30x 2 -28.32x + 97.48 (2)
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