JP2011214125A - Method for decarburizing chromium-containing steel by blowing oxygen - Google Patents
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本発明は、クロム含有鋼の吹酸脱炭方法に関するものである。 The present invention relates to a blown acid decarburization method for chromium-containing steel.
ステンレス鋼を代表とするクロム含有鋼を溶製する方法として、電気炉を用いる方法と転炉を用いる方法が採用されている。電気炉を用いる方法は鉄源として主にスクラップを用い、電気炉のみで仕上げ精錬を完了する普通法、炉外精錬にＶＯＤを用いる方法、ＡＯＤ炉を用いる方法が採用されている。転炉を用いる方法では、鉄源として主に高炉溶銑を用い、転炉内の溶銑にＦｅ−Ｃｒを添加して吹酸脱炭を行う。その後、炉外精錬としてＶＯＤ、ＡＯＤ、ＲＨ−ＯＢなどが組み合わされる（非特許文献１参照）。 As a method for melting chromium-containing steel typified by stainless steel, a method using an electric furnace and a method using a converter are employed. As a method using an electric furnace, scrap is mainly used as an iron source, and a normal method in which finishing refining is completed only by an electric furnace, a method using VOD for out-of-furnace refining, and a method using an AOD furnace are employed. In the method using a converter, blast furnace hot metal is mainly used as an iron source, and Fe-Cr is added to the hot metal in the converter to perform blown acid decarburization. Then, VOD, AOD, RH-OB, etc. are combined as outside refining (refer nonpatent literature 1).
クロム含有鋼の溶製において、鋼中のＣｒ源として主にＦｅ−Ｃｒが用いられる。Ｆｅ−Ｃｒには、Ｓ含有量が０．０３質量％以上である汎用Ｆｅ−Ｃｒと、Ｓ含有量が０．０２質量％以下である低硫黄Ｆｅ−Ｃｒとがある。低硫黄Ｆｅ−Ｃｒは汎用Ｆｅ−Ｃｒと比較して高価である。 In the melting of chromium-containing steel, Fe—Cr is mainly used as a Cr source in the steel. Fe-Cr includes general-purpose Fe-Cr having an S content of 0.03% by mass or more and low sulfur Fe-Cr having an S content of 0.02% by mass or less. Low sulfur Fe—Cr is more expensive than general purpose Fe—Cr.
鋼中に含有する硫黄は鋼品質に種々の悪影響を及ぼすため、クロム含有鋼においても鋼中の硫黄含有量を低減することが要求される。 Since sulfur contained in steel has various adverse effects on steel quality, it is required to reduce the sulfur content in steel even in chromium-containing steel.
しかし、高クロム溶鉄は脱硫が困難であることが知られており、クロム源としてＳ含有量が高い汎用Ｆｅ−Ｃｒを用いたのでは、クロム源添加後に溶湯脱硫を行ったとしても目標とするＳ含有量まで脱硫を進行させることが困難となる。 However, it is known that high chromium molten iron is difficult to desulfurize, and if general-purpose Fe-Cr having a high S content is used as the chromium source, even if the molten metal desulfurization is performed after adding the chromium source, it is a target. It becomes difficult to advance the desulfurization to the S content.
例えば上記した転炉を用いる方法では、溶銑予備処理にて脱硫した溶銑を転炉に供給し、転炉でＦｅ−Ｃｒを供給、溶解するが、吹酸脱炭の際にある程度は溶鋼の脱硫がなされるものの、その溶鋼中にクロムを含むため脱硫能力の限界がある。このため一般に、転炉で供給するＦｅ−Ｃｒは前記した低硫黄Ｆｅ−Ｃｒを使用する前提で、転炉に供給する溶銑は硫黄含有量を０．０１３質量％以下（吹酸脱炭開始時点での目標Ｓ含有量をＳ≦０．０１３質量％とすること）となるように溶銑予備処理することが求められていた。この転炉での処理の後、用途に応じて炉外精錬（二次精錬）で脱硫処理がなされるが、溶鋼にクロムを含み、炭素量も少ないため、その脱硫能力には限界があるため、転炉に供給する溶銑（吹酸脱炭開始時）はＳ含有量を０．０１３質量％以下とすることは重要である。 For example, in the method using the converter described above, the hot metal desulfurized in the hot metal pretreatment is supplied to the converter, and Fe-Cr is supplied and melted in the converter, but to some extent desulfurization of the molten steel during blown acid decarburization. However, there is a limit of desulfurization ability because the molten steel contains chromium. Therefore, in general, Fe-Cr supplied in the converter is based on the premise that the above-described low sulfur Fe-Cr is used, and the hot metal supplied to the converter has a sulfur content of 0.013 mass% or less (at the start of blowing acid decarburization). In this case, the hot metal preliminary treatment has been required so that the target S content in S is 0.01 ≦ 3% by mass). After treatment in this converter, desulfurization treatment is performed by out-of-furnace refining (secondary refining) depending on the application, but because the molten steel contains chromium and has a small amount of carbon, its desulfurization capacity is limited. It is important that the hot metal supplied to the converter (at the start of blowing acid decarburization) has an S content of 0.013% by mass or less.
なお本発明は、Ｆｅ−Ｃｒに含まれる硫黄と溶湯中のＳ量について取り扱うものであり、吹酸脱炭工程で添加する副原料（例えば炭材、Ｍｎ、Ｓｉ等を添加する合金鉄）中に含まれる硫黄は、前記した吹酸脱炭開始時のＳ含有量（０．０１３質量％以下）には含めない。 Note that the present invention deals with sulfur contained in Fe-Cr and the amount of S in the molten metal, and in the auxiliary materials added in the blowing acid decarburization step (for example, carbon steel, alloy iron to which Mn, Si, etc. are added). Is not included in the S content (0.013 mass% or less) at the start of the above-described blowing acid decarburization.
また上記した電炉を用いる方法でも、電炉でクロム含有粗溶鋼を溶製した後の脱硫能力には限界があり、低硫黄ステンレススクラップや低硫黄Ｆｅ−Ｃｒを使用する等の原料を選定し、溶製の前段階で硫黄の混入を防ぐ必要がある。 The method using the electric furnace also has a limit in the desulfurization capacity after the chrome-containing crude molten steel is melted in the electric furnace, so that raw materials such as low-sulfur stainless steel scrap and low-sulfur Fe-Cr are selected and melted. It is necessary to prevent sulfur contamination at the pre-production stage.
上記のように、高クロム溶鉄は脱硫が困難であることから、クロム源として高価な低硫黄Ｆｅ−Ｃｒが用いられていた。 As described above, since high chromium molten iron is difficult to desulfurize, expensive low sulfur Fe—Cr has been used as a chromium source.
特許文献１には、原料を電気炉に装入して含Ｃｒ溶銑を製造し、次いで転炉で吹酸脱炭し、脱ガス工程で真空脱炭及び脱酸を行い、その後に連続鋳造装置でスラブを製造する方法が記載されている。また特許文献２には、クロムを含んだ竪型炉溶湯と電気炉溶湯を合わせ湯した後に転炉で精錬する方法が記載されている。特許文献１、２に記載されたいずれの方法においても、クロム源を添加した後の溶湯について脱硫を行うため、脱硫精錬において高い脱硫効率を実現することが困難であり、クロム源としては高価な低硫黄Ｆｅ−Ｃｒを用いることとなる。
In
吹酸脱炭開始時点においてＳ≦０．０１３質量％程度が要求される低硫黄クロム含有鋼を溶製する場合においても、クロム源として、高価な低硫黄Ｆｅ−Ｃｒではなく安価な汎用Ｆｅ−Ｃｒを用いることができれば、鋼製造コストを低減することができる。そこで本発明は、吹酸脱炭開始時点においてＳ≦０．０１３質量％程度が要求される低硫黄クロム含有鋼を溶製する場合において、クロム源として安価な汎用Ｆｅ−Ｃｒを用いることを可能にするクロム含有鋼の吹酸脱炭方法を提供することを目的とする。 Even when melting low-sulfur chromium-containing steel that requires about S ≦ 0.013 mass% at the start of blowing acid decarburization, it is not an expensive low-sulfur Fe—Cr but an inexpensive general-purpose Fe— If Cr can be used, the steel manufacturing cost can be reduced. Therefore, the present invention can use inexpensive general-purpose Fe—Cr as a chromium source when melting low-sulfur chromium-containing steel that requires about S ≦ 0.013 mass% at the start of blowing acid decarburization. An object of the present invention is to provide a blown acid decarburization method for chromium-containing steel.
Ｃｒ含有量が１０％以上である高クロム溶湯であって、クロム源としてＳ含有量が高い汎用Ｆｅ−Ｃｒを用いた場合であっても、脱硫精錬後のＳ含有量を０．０１４〜０．０２０質量％程度まで低減するのであれば、通常の脱硫精錬で実現可能である。また、Ｃｒ含有量が４％以下の低クロム溶湯であれば、脱硫精錬でＳ含有量を０．０１０質量％以下まで低減することは容易である。そして、このように脱硫精錬を行った後の含クロム溶湯と低クロム溶湯とを混合し、この混合溶湯を精錬容器内で吹酸により脱炭することとすれば、クロム源としてＳ含有量が高い汎用Ｆｅ−Ｃｒを用いた場合であっても、吹酸脱炭開始時の溶湯中Ｓ含有量を０．０１３質量％以下とすることが可能となる。 Even if it is a high chromium molten metal having a Cr content of 10% or more and a general-purpose Fe—Cr having a high S content as a chromium source, the S content after desulfurization and refining is 0.014 to 0. If it is reduced to about .020 mass%, it can be realized by ordinary desulfurization refining. Moreover, if it is a low chromium molten metal whose Cr content is 4% or less, it is easy to reduce the S content to 0.010% by mass or less by desulfurization refining. And, if the chromium-containing molten metal after the desulfurization refining is mixed with the low chromium molten metal and the mixed molten metal is decarburized with blowing acid in the refining vessel, the S content as the chromium source is Even when high general-purpose Fe—Cr is used, the S content in the molten metal at the start of blowing acid decarburization can be made 0.013 mass% or less.
本発明は、上記知見に基づいてなされたものであり、その要旨は以下の通りである。
（１）電気炉にてＣ：２〜８質量％、Ｃｒ：１０質量％以上の含クロム溶湯を溶製し、Ｃｒ：４質量％以下の低クロム溶湯を準備し、前記含クロム溶湯Ｘ（トン）と低クロム溶湯とを混合してＣｒ：８〜２６質量％の混合溶湯Ｙ（トン）とし、０．５２≦Ｘ／Ｙ≦０．８０を満足し、前記混合溶湯を精錬容器内で吹酸により脱炭することを特徴とするクロム含有鋼の吹酸脱炭方法。
（２）前記含クロム溶湯のＣｒ源として、全Ｃｒ分のうち５０％相当分以上について、Ｓ含有量が０．０３質量％以上の汎用Ｆｅ−Ｃｒを用い、電気炉溶製後の含クロム溶湯のＳ含有量を０．０１４〜０．０２０質量％とし、前記低クロム溶湯のＳ含有量を０．０１０質量％以下とすることを特徴とする上記（１）に記載のクロム含有鋼の吹酸脱炭方法。
（３）前記混合溶湯の吹酸脱炭開始時点におけるＳ含有量を０．０１３質量％以下とすることを特徴とする上記（２）に記載のクロム含有鋼の吹酸脱炭方法。
（４）前記含クロム溶湯のＳｉ含有量を０．２〜１．０質量％とすることを特徴とする上記（１）〜（３）のいずれかに記載のクロム含有鋼の吹酸脱炭方法。
This invention is made | formed based on the said knowledge, The summary is as follows.
(1) A chromium-containing molten metal of C: 2 to 8% by mass and Cr: 10% by mass or more is melted in an electric furnace to prepare a low-chromium molten metal of Cr: 4% by mass or less. Ton) and a low chromium molten metal to obtain a mixed molten metal Y (ton) of Cr: 8 to 26% by mass, satisfying 0.52 ≦ X / Y ≦ 0.80. A method for blown acid decarburization of chromium-containing steel, characterized by decarburizing with blown acid.
(2) As a Cr source of the chrome-containing molten metal, a general-purpose Fe-Cr having an S content of 0.03% by mass or more is used for the equivalent of 50% or more of the total Cr content, and the chrome-containing after melting in an electric furnace. The S content of the molten metal is 0.014 to 0.020% by mass, and the S content of the low chromium molten metal is 0.010% by mass or less. Blow acid decarburization method.
(3) The method for blown acid decarburization of chromium-containing steel as described in (2) above, wherein the S content of the mixed molten metal at the start of blown acid decarburization is 0.013% by mass or less.
(4) The blown acid decarburization of the chromium-containing steel according to any one of the above (1) to (3), wherein the Si content of the chromium-containing molten metal is 0.2 to 1.0% by mass. Method.
本発明は、クロム含有鋼の吹酸脱炭方法において、Ｃｒ：１０質量％以上の含クロム溶湯とＣｒ：４質量％以下の低クロム溶湯を準備し、前記含クロム溶湯Ｘ（トン）と低クロム溶湯とを混合してＣｒ：８〜２６質量％の混合溶湯Ｙ（トン）とし、０．５２≦Ｘ／Ｙ≦０．８０を満足する比率とする。これにより、含クロム溶湯については電気炉溶製時にＳ含有量を０．０１４〜０．０２０質量％までの軽脱硫を行い、低クロム溶湯についてはＳ含有量を０．０１０質量％以下までの重脱硫を行い、両者を混合した場合、含クロム溶湯の原料としてＳ含有量が高い汎用Ｆｅ−Ｃｒを用いたとしても、混合溶湯の吹酸脱炭開始時点におけるＳ含有量を０．０１３質量％以下とすることができる。 The present invention provides a chromium-containing steel blown acid decarburization method in which Cr: 10% by mass or more of a chromium-containing molten metal and Cr: 4% by mass or less of a low-chromium molten metal are prepared. The mixture is mixed with the molten chromium to obtain a mixed molten metal Y (ton) of Cr: 8 to 26% by mass, and a ratio satisfying 0.52 ≦ X / Y ≦ 0.80. Thereby, about the chromium-containing molten metal, light desulfurization to S content 0.014-0.020 mass% is performed at the time of electric furnace melting, and about S chromium content to 0.010 mass% or less about low chromium molten metal When heavy desulfurization is performed and both are mixed, even if general-purpose Fe-Cr having a high S content is used as a raw material for the chromium-containing molten metal, the S content at the start of blowing acid decarburization of the mixed molten metal is 0.013 mass. % Or less.
本発明が対象とするクロム含有鋼は、低硫鋼を対象としており、転炉等の精錬容器における吹酸脱炭開始時点においてＳ含有量が０．０１３質量％以下、望ましくは０．０１１質量％以下である鋼を対象とする。 The chromium-containing steel targeted by the present invention is a low-sulfur steel, and the S content is 0.013 mass% or less, preferably 0.011 mass at the start of blowing acid decarburization in a refining vessel such as a converter. % Steel or less.
前述のとおり、高クロム溶鉄は脱硫精錬が困難であることが知られていた。その理由は以下のように説明できる。即ち、溶湯中に含まれるクロムは硫黄の活量を下げる。また、クロムは炭素の活量も下げるので、結果として溶湯中の酸素濃度が上昇することとなる。従って、下記式に示す脱硫反応は、溶湯中のＣｒ濃度が高くなるほど進行しづらくなる。図２は、溶鉄の脱硫精錬における溶鉄中クロム含有量と脱硫精錬後の溶鉄中硫黄濃度の関係を示したものである。脱硫精錬としては脱硫材にＣａＯを用い、通常の低硫溶鉄の製造を模した平衡実験の結果を示したものである。溶湯中のクロム濃度が高いほど、脱硫精錬後の硫黄濃度が高くなっていることがわかる。溶湯中クロム含有量が１０％以上となると、脱硫精錬を行ったとしても精錬終了時点での到達Ｓ含有量はたかだか０．０１４質量％が限界である。一方、溶湯中クロム含有量が４％以下であると、精錬終了時点で到達Ｓ含有量が０．００９質量％以下まで低減する。
ＣａＯ＋Ｓ＝ＣａＳ＋Ｏ
As described above, it has been known that high chromium molten iron is difficult to desulfurize and refine. The reason can be explained as follows. That is, chromium contained in the molten metal lowers the sulfur activity. Chromium also lowers the carbon activity, resulting in an increase in the oxygen concentration in the melt. Therefore, the desulfurization reaction shown in the following formula becomes difficult to proceed as the Cr concentration in the molten metal increases. FIG. 2 shows the relationship between the chromium content in molten iron and the sulfur concentration in molten iron after desulfurization refining in the desulfurization refining of molten iron. For desulfurization refining, CaO is used as a desulfurization material, and the results of an equilibrium experiment simulating the production of ordinary low-sulfur molten iron are shown. It can be seen that the higher the chromium concentration in the molten metal, the higher the sulfur concentration after desulfurization. When the chromium content in the molten metal is 10% or more, even if desulfurization refining is performed, the ultimate S content at the end of refining is at most 0.014% by mass. On the other hand, when the chromium content in the molten metal is 4% or less, the reached S content is reduced to 0.009% by mass or less at the end of refining.
CaO + S = CaS + O
含クロム鋼を溶製する際のクロム源として用いられるＦｅ−Ｃｒには、Ｓ含有量が０．０３質量％以上である汎用Ｆｅ−Ｃｒと、Ｓ含有量が０．０２質量％以下である低硫黄Ｆｅ−Ｃｒとがある。Ｃｒ含有量が８質量％以上であるクロム含有鋼を溶製する場合、クロム源としてＳ含有量が高い汎用Ｆｅ−Ｃｒを用いると、Ｆｅ−Ｃｒ添加後の溶湯中のＳ含有量がＣｒ源起因で０．００４質量％程度上昇する。Ｆｅ−Ｃｒ以外の主要な原料である鉄源、即ち高炉溶銑あるいは鉄スクラップからのＳ混入と合わせ、溶湯中のＳ含有量は０．０１４質量％まで上昇することになる。クロム源添加後の溶湯中のＳ含有量がここまで上昇すると、上記のようにクロムを含有する溶湯の脱硫は困難である。従って、吹酸脱炭開始時点においてＳ≦０．０１３質量％程度が要求される低硫黄クロム含有鋼を溶製する場合において、クロム源として高価な低硫黄Ｆｅ−Ｃｒが用いられていた。 Fe-Cr used as a chromium source for melting chromium-containing steel has a general-purpose Fe-Cr having an S content of 0.03% by mass or more and an S content of 0.02% by mass or less. There is low sulfur Fe-Cr. When melting a chromium-containing steel having a Cr content of 8% by mass or more, if general-purpose Fe-Cr having a high S content is used as the chromium source, the S content in the molten metal after the addition of Fe-Cr is the Cr source. It increases by about 0.004% by mass. Combined with the iron source, which is the main raw material other than Fe-Cr, that is, blast furnace hot metal or S contamination from iron scrap, the S content in the molten metal will rise to 0.014% by mass. If the S content in the molten metal after the addition of the chromium source is increased up to this point, it is difficult to desulfurize the molten metal containing chromium as described above. Therefore, in the case of melting low-sulfur chromium-containing steel that requires about S ≦ 0.013 mass% at the start of blowing acid decarburization, expensive low-sulfur Fe—Cr has been used as a chromium source.
Ｃｒ含有量が１０％以上である高クロム溶湯であって、クロム源としてＳ含有量が高い汎用Ｆｅ−Ｃｒを用いた場合であっても、脱硫精錬後のＳ含有量を０．０１４〜０．０２０質量％程度まで低減するのであれば、脱硫負荷が軽減されるため、電気炉を用いた通常の脱硫精錬で実現可能である。 Even if it is a high chromium molten metal having a Cr content of 10% or more and a general-purpose Fe—Cr having a high S content as a chromium source, the S content after desulfurization and refining is 0.014 to 0. If it is reduced to about .020 mass%, the desulfurization load is reduced, so that it can be realized by ordinary desulfurization refining using an electric furnace.
一方、Ｃｒ含有量が４％以下の低クロム溶湯であれば、図２から明らかなように、脱硫精錬でＳ含有量を０．０１０質量％以下まで低減することは容易である。例えば低クロム溶湯として高炉溶銑を用いる場合、精錬前のＳ含有量は０．０２０質量％程度であり、トーピードカー脱硫、ＫＲ脱硫などの炉外脱硫精錬によってＳ含有量を０．０１０質量％以下、０．００９質量％程度まで低減することができる。 On the other hand, if it is a low chromium molten metal having a Cr content of 4% or less, it is easy to reduce the S content to 0.010% by mass or less by desulfurization refining, as is apparent from FIG. For example, when blast furnace hot metal is used as the low chromium molten metal, the S content before refining is about 0.020 mass%, and the S content is 0.010 mass% or less by out-of-furnace desulfurization refining such as torpedo car desulfurization and KR desulfurization, It can be reduced to about 0.009% by mass.
そして図１に示すように、このように脱硫精錬を行った後の含クロム溶湯（Ｓ含有量：０．０１４質量％以上）と、同じく脱硫精錬を行った低クロム溶湯（Ｓ含有量：０．００９質量％程度）とを混合し、この混合溶湯を精錬容器内で吹酸により脱炭することとすれば、クロム源としてＳ含有量が高い汎用Ｆｅ−Ｃｒを用いた場合であっても、吹酸脱炭開始時の溶湯中Ｓ含有量を０．０１３質量％以下とすることが可能となる。 And as shown in FIG. 1, the chromium-containing molten metal (S content: 0.014 mass% or more) after performing desulfurization refining in this way, and the low chromium molten metal (S content: 0) which also performed desulfurization refining similarly About 0.09 mass%), and the mixed molten metal is decarburized with blowing acid in a refining vessel, even when general-purpose Fe-Cr having a high S content is used as a chromium source. The S content in the molten metal at the start of blowing acid decarburization can be made 0.013 mass% or less.
含クロム溶湯Ｘ（トン）と低クロム溶湯とを混合して、混合溶湯Ｙ（トン）を溶製する。Ｓ含有量について、含クロム溶湯は０．０１４質量％、低クロム溶湯は０．００９質量％、混合溶湯を０．０１３質量％以下とし、ＸとＹが満たすべき関係を計算すると、
０．０１４×Ｘ＋０．００９×（Ｙ−Ｘ）≦０．０１３×Ｙ
から、
Ｘ／Ｙ≦０．８０
が導かれる。
The mixed molten metal Y (ton) is made by mixing the chromium-containing molten metal X (ton) and the low chromium molten metal. Regarding the S content, the chromium-containing molten metal is 0.014% by mass, the low chromium molten metal is 0.009% by mass, the mixed molten metal is 0.013% by mass or less, and the relationship that X and Y should satisfy is calculated.
0.014 × X + 0.009 × (Y−X) ≦ 0.013 × Y
From
X / Y ≦ 0.80
Is guided.
電気炉でＣｒ含有量１０質量％以上の含クロム溶湯を溶製するに際し、溶湯とその上に形成される溶融スラグ成分との間には、クロム源溶解後の溶湯中Ｃｒ含有量が高くなるほどスラグ中Ｃｒ2Ｏ3濃度が高くなる関係がある。そして、電気炉にてＣｒ濃度５〜７０質量％の溶鉄を溶製したところ、溶鉄中のＣｒ濃度が５０質量％を超えると、固体のＣｒ2Ｏ3が生成しやすくなり、スラグラインに位置する炉壁耐火物が顕著に損耗されることがわかった。本発明において、含クロム溶湯と低クロム溶湯を混合してＣｒ含有量が最大２６質量％の混合溶湯を溶製しようとしている。そこで、炉壁耐火物を溶損しない条件として、低クロム溶湯中のＣｒ濃度をゼロと置き、
５０×Ｘ≧２６×Ｙ
から、
Ｘ／Ｙ≧２６／５０＝０．５２
が導かれる。
When melting a chromium-containing molten metal having a Cr content of 10% by mass or more in an electric furnace, the Cr content in the molten metal after melting the chromium source increases between the molten metal and the molten slag component formed thereon. There is a relationship in which the Cr 2 O 3 concentration in the slag increases. And when molten iron having a Cr concentration of 5 to 70% by mass was melted in an electric furnace, when the Cr concentration in the molten iron exceeds 50% by mass, solid Cr 2 O 3 is likely to be generated and is located in the slag line. It was found that the furnace wall refractory to be worn out significantly. In the present invention, an attempt is made to melt a mixed molten metal having a maximum Cr content of 26% by mass by mixing a chromium-containing molten metal and a low-chromium molten metal. Therefore, as a condition not to melt the furnace wall refractory, the Cr concentration in the low chromium molten metal is set to zero,
50 × X ≧ 26 × Y
From
X / Y ≧ 26/50 = 0.52
Is guided.
混合溶湯中のＣｒ含有量を定めたときに、含クロム溶湯中のＣｒ含有量とＸ／Ｙが満たすべき関係について示したのが図３である。図中実線は、混合溶湯のＣｒ含有量を本発明の下限である８質量％とする場合について示した。含クロム溶湯中のＣｒ含有量が１０質量％以上であれば、Ｘ／Ｙが０．８０以下において混合溶湯のＣｒ含有量を８質量％とすることができる点が明らかである。また図中の破線は、混合溶湯のＣｒ含有量を本発明の上限である２６質量％とする場合について示した。含クロム溶湯中のＣｒ含有量が５０質量％以下であれば、Ｘ／Ｙが０．５以上において混合溶湯のＣｒ含有量を２６質量％とすることができる点が明らかである。 FIG. 3 shows the relationship between the Cr content in the chromium-containing molten metal and X / Y when the Cr content in the mixed molten metal is determined. The solid line in the figure shows the case where the Cr content of the mixed molten metal is 8% by mass which is the lower limit of the present invention. If the Cr content in the chromium-containing molten metal is 10% by mass or more, it is clear that the Cr content of the mixed molten metal can be 8% by mass when X / Y is 0.80 or less. The broken line in the figure shows the case where the Cr content of the molten mixture is 26% by mass which is the upper limit of the present invention. If the Cr content in the chromium-containing molten metal is 50% by mass or less, it is clear that the Cr content of the mixed molten metal can be 26% by mass when X / Y is 0.5 or more.
クロム源溶解後の溶湯中クロム濃度とスラグ中Ｃｒ2Ｏ3濃度との関係については、当該含クロム溶湯中のＣ濃度が低くなるほどスラグ中Ｃｒ2Ｏ3濃度が高くなる傾向がある。溶湯中Ｃｒ濃度３０〜５０質量％、温度１６６０〜１７２０℃で電気炉にて含クロム溶湯を溶製する際、溶湯中Ｃ濃度とスラグ中Ｃｒ2Ｏ3濃度の関係を調査した結果を図４に示す。溶湯中Ｃ濃度を２質量％以上とすれば、スラグ中Ｃｒ2Ｏ3濃度が５質量％以下となり、炉壁耐火物の損耗を防止できる。溶湯中のＣ濃度が高くなるほどスラグ中Ｃｒ2Ｏ3濃度を低くすることができるが、上限については、含Ｃｒ溶鉄の飽和Ｃ濃度である８質量％とする。 Regarding the relationship between the chromium concentration in the molten metal after dissolution of the chromium source and the Cr 2 O 3 concentration in the slag, the Cr 2 O 3 concentration in the slag tends to increase as the C concentration in the chromium-containing molten metal decreases. FIG. 4 shows the results of investigating the relationship between the C concentration in the molten metal and the Cr 2 O 3 concentration in the slag when the chromium-containing molten metal is melted in an electric furnace at a Cr concentration of 30 to 50 mass% and a temperature of 1660 to 1720 ° C. Shown in If the C concentration in the molten metal is 2% by mass or more, the Cr 2 O 3 concentration in the slag becomes 5% by mass or less, and wear of the furnace wall refractory can be prevented. The higher the C concentration in the molten metal, the lower the Cr 2 O 3 concentration in the slag, but the upper limit is 8% by mass, which is the saturated C concentration of the Cr-containing molten iron.
含クロム溶湯を電気炉で溶製する際において、クロムの酸化を抑制する観点からも、上記配合比Ｘ／Ｙを０．５２≦Ｘ／Ｙ≦０．８０とすると好ましい。 When melting the chromium-containing molten metal in an electric furnace, the blending ratio X / Y is preferably 0.52 ≦ X / Y ≦ 0.80 from the viewpoint of suppressing the oxidation of chromium.
まず、Ｘ／Ｙ≧０．５２とすることで、混合溶湯のＣｒ含有量を最大の２６質量％とする場合において、含クロム溶湯中のＣｒ含有量を５０質量％以下に抑えることかできる。そして、電気炉精錬における溶湯中Ｃｒ濃度とスラグ中Ｃｒ2Ｏ3濃度の関係を調査した結果を図５に示す。精錬条件は図５中に記載したとおりである。溶湯中Ｃｒ濃度が５０質量％以下であればスラグ中Ｃｒ2Ｏ3濃度を低い範囲に抑えることができ、クロムの酸化ロスを低減できることがわかる。 First, by setting X / Y ≧ 0.52, the Cr content in the chromium-containing molten metal can be suppressed to 50% by mass or less when the Cr content of the mixed molten metal is set to the maximum of 26 mass%. Then, the results of investigating the relationship between the Cr concentration and the slag Cr 2 O 3 concentration in the molten metal in the electric furnace refining in FIG. The refining conditions are as described in FIG. It can be seen that if the Cr concentration in the molten metal is 50% by mass or less, the Cr 2 O 3 concentration in the slag can be suppressed to a low range, and the oxidation loss of chromium can be reduced.
また、図６に示すとおり、含クロム溶湯の電気炉溶製において、溶湯中のＣｒ濃度が１０％未満と低すぎるとかえって「スラグ中Ｃｒ2Ｏ3濃度／溶湯中Ｃｒ濃度」の比が上昇することがわかった。精錬条件は図６中に記載したとおりである。本発明においてはＸ／Ｙ≦０．８０としているので、混合溶湯中のＣｒ濃度が下限の８％であっても、含クロム溶湯中のＣｒ濃度を１０％以上とすることができ、「スラグ中Ｃｒ2Ｏ3濃度／溶湯中Ｃｒ濃度」が上昇しない良好範囲を維持できることがわかった。 In addition, as shown in FIG. 6, in the melting of the chromium-containing molten metal in the electric furnace, the ratio of “Cr 2 O 3 concentration in slag / Cr concentration in molten metal” increases rather than the Cr concentration in the molten metal is less than 10%. I found out that The refining conditions are as described in FIG. In the present invention, since X / Y ≦ 0.80, even if the Cr concentration in the mixed molten metal is 8%, which is the lower limit, the Cr concentration in the chromium-containing molten metal can be 10% or more. It was found that it was possible to maintain a favorable range in which “indium Cr 2 O 3 concentration / Cr concentration in molten metal” did not increase.
電気炉での含クロム溶湯の溶製において、含クロム溶湯中のＳｉ濃度が０．２質量％以上であれば、溶湯中Ｃｒの酸化を抑制し、クロムロスを低減できるので好ましい。含クロム溶湯中のＳｉ濃度の上限は１．０質量％とする。Ｓｉ濃度１．０質量％までは、Ｓｉ濃度が高いほどＣｒの酸化を抑えることができるが、Ｓｉ濃度が１．０質量％を超えてもクロム酸化抑制はほとんど改善しない。その上、Ｓｉ濃度が過剰であると、含クロム溶湯と低クロム溶湯を混合した後の吹酸脱炭精錬時に、溶湯中に含まれるシリコンが酸化してスラグ中ＳｉＯ2となり、スラグボリュームが増加し、結果的にクロムロスが増えるという悪影響がある。 In the melting of the chrome-containing molten metal in the electric furnace, it is preferable that the Si concentration in the chromized molten metal is 0.2% by mass or more because oxidation of Cr in the molten metal can be suppressed and chromium loss can be reduced. The upper limit of the Si concentration in the chromium-containing molten metal is 1.0% by mass. Up to a Si concentration of 1.0 mass%, the higher the Si concentration, the more the oxidation of Cr can be suppressed. However, even if the Si concentration exceeds 1.0 mass%, the suppression of chromium oxidation is hardly improved. In addition, if the Si concentration is excessive, the silicon contained in the molten metal is oxidized to SiO 2 in the slag at the time of blown acid decarburization and refining after mixing the chrome-containing molten metal and the low-chromium molten metal, increasing the slag volume. As a result, there is an adverse effect that chromium loss increases.
電気炉での含クロム溶湯の溶製に際しては、鉄源として主にスクラップ、クロム源としてＦｅ−Ｃｒが用いられる。Ｃｒ源としてのＦｅ−Ｃｒの全量を、Ｓ含有量が０．０３質量％以上の安価な汎用Ｆｅ−Ｃｒとすると好ましい。本発明においては、含クロム溶湯のＣｒ源として、全Ｃｒ分のうち５０％相当分以上について汎用Ｆｅ−Ｃｒを用いれば、コスト削減効果を享受することができる。 When melting a chromium-containing molten metal in an electric furnace, scrap is mainly used as an iron source, and Fe—Cr is used as a chromium source. It is preferable that the total amount of Fe—Cr as the Cr source is inexpensive general-purpose Fe—Cr having an S content of 0.03% by mass or more. In the present invention, if a general-purpose Fe—Cr is used for a Cr source of chromium-containing molten metal for a portion equivalent to 50% or more of the total Cr content, a cost reduction effect can be obtained.
含クロム溶湯のＣｒ源としてＳ含有量が高い汎用Ｆｅ−Ｃｒを用いるため、電気炉において脱硫精錬を行う。本発明においては、電気炉溶製後の含クロム溶湯のＳ含有量を低硫領域まで下げず、Ｓ含有量下限を０．０１４質量％とする。この程度のＳ含有量まで脱硫するのであれば、電気炉に溶湯トン当たり４０〜１００ｋｇのＣａＯ源を添加してスラグを形成することにより、脱硫精錬を行うことができる。含クロム溶湯のＳ含有量が高すぎると、Ｓ含有量が低い低クロム溶湯と混合しても混合後のＳ含有量を十分に下げることができない。含クロム溶湯のＳ含有量上限を０．２０質量％とすれば、本発明において混合後の混合溶湯のＳ含有量を目標レベルとすることが可能である。ただし、含クロム溶湯のＳ含有量が高くなるほど、Ｘ／Ｙを０．５２≦Ｘ／Ｙ≦０．８０の範囲内で低い値とすることが必要となる。 Since general-purpose Fe-Cr having a high S content is used as a Cr source for the chromium-containing molten metal, desulfurization refining is performed in an electric furnace. In the present invention, the S content of the chromium-containing molten metal after melting in the electric furnace is not lowered to the low sulfur region, and the lower limit of the S content is set to 0.014% by mass. If desulfurization is performed up to this level of S content, desulfurization refining can be performed by adding 40 to 100 kg of CaO source per ton of molten metal to the electric furnace to form slag. If the S content of the chromium-containing molten metal is too high, the S content after mixing cannot be lowered sufficiently even when mixed with a low chromium molten metal having a low S content. If the upper limit of the S content of the chromium-containing molten metal is 0.20% by mass, the S content of the mixed molten metal after mixing in the present invention can be set to the target level. However, as the S content of the molten chromium is increased, X / Y needs to be set to a lower value within the range of 0.52 ≦ X / Y ≦ 0.80.
低クロム溶湯としては、高炉溶銑を好ましく用いることができる。高炉溶銑であればＣｒ：４質量％以下とすることができる。また、Ｓ濃度が０．０１４〜０．０２０質量％の含クロム溶湯と混合してＳ濃度の低い混合溶湯とするため、低クロム溶湯はＳ濃度を低い濃度とする。本発明において、低クロム溶湯のＳ含有量を０．０１０質量％以下とすると好ましい。これにより、本発明において混合後の混合溶湯のＳ含有量を目標レベルとすることが可能である。ただし、低クロム溶湯のＳ含有量が高くなるほど、Ｘ／Ｙを０．５２≦Ｘ／Ｙ≦０．８０の範囲内で低い値とすることが必要となる。低クロム溶湯のＳ含有量を目標レベル以下まで低減するため、溶湯の脱硫処理を行う。高炉溶銑を用いる場合には、トーピード脱硫、ＫＲ脱硫などの通常用いられる脱硫手段により、容易に目標のＳ濃度まで脱硫を進行することができる。 As the low chromium molten metal, blast furnace hot metal can be preferably used. If it is a blast furnace hot metal, it can be made Cr: 4 mass% or less. Moreover, since it mixes with the chromium containing molten metal whose S density | concentration is 0.014-0.020 mass% and it is set as a mixed molten metal with a low S density | concentration, a low chromium molten metal makes S concentration low. In the present invention, the S content of the low chromium molten metal is preferably 0.010% by mass or less. Thereby, in this invention, it is possible to make S content of the mixed molten metal after mixing into a target level. However, the higher the S content of the low chromium molten metal, the lower the X / Y value must be within the range of 0.52 ≦ X / Y ≦ 0.80. In order to reduce the S content of the low chromium molten metal to below the target level, the molten metal is desulfurized. When blast furnace hot metal is used, desulfurization can easily proceed to a target S concentration by a commonly used desulfurization means such as torpedo desulfurization or KR desulfurization.
溶銑鍋中に含クロム溶湯と低クロム溶湯をそれぞれ装入することにより、溶銑鍋中で含クロム溶湯と低クロム溶湯を混合することができる。混合溶湯について続いて吹酸脱炭を行う。混合溶湯を例えば上底吹き転炉に装入し、吹酸脱炭精錬を行う。電気炉中で吹酸脱炭を行っても良い。ただし、常圧下で目標Ｃ濃度まで脱炭を行うとクロムの酸化ロスが大きくなるので、転炉では粗脱炭までを行い、続いてＶＯＤ法、ＲＨ法などの真空脱炭、あるいはＡＯＤ炉を用いた精錬を行い、クロムの酸化損失を抑えながら目標Ｃ濃度までの吹酸脱炭を行う。 By inserting the chrome-containing molten metal and the low-chromium molten metal into the hot metal ladle, respectively, the chrome-containing molten metal and the low-chromium molten metal can be mixed in the hot metal ladle. Subsequently, blown acid decarburization is performed on the molten metal. The mixed molten metal is charged into, for example, an upper bottom blowing converter, and blown acid decarburization refining is performed. Blow acid decarburization may be performed in an electric furnace. However, if decarburization is performed under normal pressure to the target C concentration, chromium oxidation loss increases. Therefore, rough decarburization is performed in the converter, followed by vacuum decarburization such as VOD method and RH method, or AOD furnace. Refining is performed and blown acid decarburization is performed up to the target C concentration while suppressing oxidation loss of chromium.
最大容量が１トンである試験電気炉を用いて含クロム溶湯を溶製し、低クロム溶湯として高炉溶銑を用い、両者を混合して混合溶湯とした。混合比Ｘ／Ｙ、含クロム溶湯、低クロム溶湯の各成分、その他の処理条件を表１に示す。混合溶湯のＹ＝１トンとなるように混合を行った。本発明範囲から外れる数値にアンダーラインを付している。 A chrome-containing molten metal was melted using a test electric furnace having a maximum capacity of 1 ton, a blast furnace molten iron was used as a low-chromium molten metal, and both were mixed to obtain a mixed molten metal. Table 1 shows the mixing ratio X / Y, each component of the chromium-containing molten metal, the low chromium molten metal, and other processing conditions. Mixing was performed so that the mixed molten metal Y = 1 ton. Numerical values that fall outside the scope of the present invention are underlined.
表１において、含クロム溶湯のＣｒ含有量については、低クロム溶湯（高炉溶銑）との混合割合に応じて、混合溶湯中のＣｒ含有量が表１に示す８．３〜２６．０質量％となるように調整した。 In Table 1, about Cr content of chromium-containing molten metal, according to the mixing ratio with low chromium molten metal (blast furnace molten iron), Cr content in mixed molten metal is 8.3-26.0 mass% which Table 1 shows. It adjusted so that it might become.
電気炉での溶融後の含クロム溶湯の成分が表１に示す成分値となるよう、スクラップ、Ｆｅ−Ｃｒ合金、Ｃｒ合金、炭材を黒鉛電極からのアーク加熱により溶解した。Ｆｅ−Ｃｒ合金として、Ｓ含有量が０．０３〜０．０５質量％である汎用Ｆｅ−Ｃｒ合金を用いた。Ｆｅ−Ｃｒ合金から混入したＳを低減するため、電気炉内にＣａＯ源を添加して塩基性スラグを形成し、脱硫を行った。ＣａＯ源として主に生石灰を用い、一部転炉スラグも用いた。添加するＣａＯ源は、ＣａＯ換算で溶湯１トンあたり４０〜１００ｋｇとした。これにより、表１に示すように含クロム溶湯のＳ含有量を０．０１４〜０．０１８質量％の範囲まで低減することができた。なお、混合前の含クロム溶湯の温度は１６３４〜１７１２℃であった。電気炉溶製終了時のスラグ中Ｃｒ2Ｏ3濃度、スラグ中Ｃｒ2Ｏ3濃度／溶湯中Ｃｒ濃度比を表１に示す。 Scrap, Fe—Cr alloy, Cr alloy, and carbonaceous material were melted by arc heating from a graphite electrode so that the components of the chromium-containing molten metal after melting in the electric furnace had the component values shown in Table 1. A general-purpose Fe—Cr alloy having an S content of 0.03 to 0.05 mass% was used as the Fe—Cr alloy. In order to reduce S mixed from the Fe—Cr alloy, a CaO source was added to the electric furnace to form a basic slag, and desulfurization was performed. Quick lime was mainly used as the CaO source, and some converter slag was also used. The CaO source to be added was 40 to 100 kg per ton of molten metal in terms of CaO. Thereby, as shown in Table 1, S content of the chromium-containing molten metal was able to be reduced to the range of 0.014-0.018 mass%. In addition, the temperature of the chromium-containing molten metal before mixing was 1634-1712 degreeC. Shown slag Cr 2 O 3 concentration at the time of electric furnace melting completion, the slag Cr 2 O 3 concentration / melt Cr concentration ratio in Table 1.
電気炉で含クロム溶湯を溶製するに際し、溶製後の電気炉の耐火物損耗状況を目視で評価し、スラグ接触面に凹みが確認された場合を「×」と評価し、凹みが確認される場合と確認されない場合が混在する水準については「△」と評価し、それ以外を「○」と評価した。結果を表１に示す。 When melting chrome-containing molten metal in an electric furnace, visually evaluate the refractory wear situation of the electric furnace after melting, and evaluate the case where a dent is confirmed on the slag contact surface as "x", confirming the dent The level where both the cases where it was confirmed and the case where it was not confirmed was evaluated as “△”, and the others were evaluated as “◯”. The results are shown in Table 1.
低クロム溶湯として高炉溶銑を用い、Ｓ含有量が表１に示すようにＳ≦０．００９質量％となるようにトーピードカーインジェクション法にて脱硫精錬を行った。高炉溶銑を用いているので、Ｃｒ含有量は０．０１質量％未満、Ｃ濃度：３．５〜４．５質量％、Ｓｉ濃度：０．１質量％未満であった。 Blast furnace hot metal was used as the low chromium molten metal, and desulfurization refining was performed by a torpedo car injection method so that the S content was S ≦ 0.009 mass% as shown in Table 1. Since blast furnace hot metal was used, the Cr content was less than 0.01% by mass, the C concentration was 3.5 to 4.5% by mass, and the Si concentration was less than 0.1% by mass.
まず低クロム溶湯を溶銑鍋中に装入し、次いでその上に含クロム溶湯を装入した。混合後の溶湯成分を表１に示す。 First, a low chromium molten metal was charged into a hot metal ladle, and then a molten chromium containing metal was charged thereon. The melt components after mixing are shown in Table 1.
本発明例である実施例１〜５においては、混合溶湯のＳ濃度がいずれも０．０１３質量％以下であった。特に含クロム溶湯の混合割合が低い実施例１〜３においては、Ｓ濃度が０．０１２質量％以下となっており、混合後の溶湯のＳ濃度を十分に低減できていることがわかる。実施例１〜５の含クロム溶湯における電気炉処理後スラグ中Ｃｒ2Ｏ3濃度は５質量％未満となっていた。また実施例１〜５では、電気炉耐火物損耗評価もいずれも○であった。 In Examples 1 to 5, which are examples of the present invention, the S concentration of the mixed molten metal was 0.013% by mass or less. In Examples 1 to 3 where the mixing ratio of the chromium-containing molten metal is particularly low, the S concentration is 0.012% by mass or less, and it can be seen that the S concentration of the molten metal after mixing can be sufficiently reduced. After the electric furnace process slag in chromium-containing molten Cr 2 O 3 concentration of Examples 1 to 5 had become less than 5 wt%. Moreover, in Examples 1-5, all of the electric furnace refractory wear evaluation were "good".
一方、比較例１では、混合比Ｘ／Ｙが本発明範囲よりも高く、混合溶湯のＳ濃度が０．０１３質量％を超えていた。また、比較例２では含クロム溶湯のＣｒ濃度が５０質量％を超えたために、電気炉耐火物損耗評価が×であった。またＣｒの酸化が進行してスラグ中Ｃｒ2Ｏ3が高く、クロムロスが大きかった。 On the other hand, in Comparative Example 1, the mixing ratio X / Y was higher than the range of the present invention, and the S concentration of the molten mixture exceeded 0.013 mass%. Further, in Comparative Example 2, the Cr concentration of the molten chrome-containing material exceeded 50% by mass, and therefore the evaluation of the electric furnace refractory wear was x. Further, the oxidation of Cr progressed, and Cr 2 O 3 in the slag was high, and the chromium loss was large.
比較例３では、含クロム溶湯のＣ濃度が低く、Ｃｒの酸化が進行してスラグ中Ｃｒ2Ｏ3が高く、クロムロスが大きかった。また、電気炉耐火物損耗評価が△であった。 In Comparative Example 3, the C concentration of the chromium-containing molten metal was low, the oxidation of Cr progressed, the Cr 2 O 3 in the slag was high, and the chromium loss was large. Moreover, the electric furnace refractory wear evaluation was Δ.
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