JP4742740B2 - Method for melting low-sulfur steel - Google Patents
Method for melting low-sulfur steel Download PDFInfo
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- JP4742740B2 JP4742740B2 JP2005238116A JP2005238116A JP4742740B2 JP 4742740 B2 JP4742740 B2 JP 4742740B2 JP 2005238116 A JP2005238116 A JP 2005238116A JP 2005238116 A JP2005238116 A JP 2005238116A JP 4742740 B2 JP4742740 B2 JP 4742740B2
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- 229910000831 Steel Inorganic materials 0.000 title claims description 119
- 239000010959 steel Substances 0.000 title claims description 119
- 238000000034 method Methods 0.000 title claims description 42
- 229910052717 sulfur Inorganic materials 0.000 title claims description 36
- 239000011593 sulfur Substances 0.000 title claims description 36
- 238000002844 melting Methods 0.000 title claims description 17
- 230000008018 melting Effects 0.000 title claims description 17
- 238000006477 desulfuration reaction Methods 0.000 claims description 51
- 230000023556 desulfurization Effects 0.000 claims description 51
- 239000002893 slag Substances 0.000 claims description 49
- 238000005261 decarburization Methods 0.000 claims description 46
- 238000007670 refining Methods 0.000 claims description 41
- 229910052751 metal Inorganic materials 0.000 claims description 32
- 239000002184 metal Substances 0.000 claims description 32
- 229910052748 manganese Inorganic materials 0.000 claims description 29
- 239000011572 manganese Substances 0.000 claims description 29
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 28
- 239000003795 chemical substances by application Substances 0.000 claims description 24
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims description 21
- 229910052698 phosphorus Inorganic materials 0.000 claims description 21
- 239000011574 phosphorus Substances 0.000 claims description 21
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 16
- 229910052799 carbon Inorganic materials 0.000 claims description 16
- 230000003009 desulfurizing effect Effects 0.000 claims description 15
- 235000008733 Citrus aurantifolia Nutrition 0.000 claims description 14
- 235000011941 Tilia x europaea Nutrition 0.000 claims description 14
- 239000004571 lime Substances 0.000 claims description 14
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 12
- 238000004519 manufacturing process Methods 0.000 claims description 8
- 238000003756 stirring Methods 0.000 claims description 7
- ODINCKMPIJJUCX-UHFFFAOYSA-N Calcium oxide Chemical compound [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 15
- 238000009849 vacuum degassing Methods 0.000 description 14
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 10
- 238000006243 chemical reaction Methods 0.000 description 8
- 235000012255 calcium oxide Nutrition 0.000 description 7
- 239000000292 calcium oxide Substances 0.000 description 7
- 239000011261 inert gas Substances 0.000 description 7
- 239000002904 solvent Substances 0.000 description 7
- 238000002347 injection Methods 0.000 description 6
- 239000007924 injection Substances 0.000 description 6
- 238000011084 recovery Methods 0.000 description 6
- 239000007789 gas Substances 0.000 description 5
- 229910052742 iron Inorganic materials 0.000 description 5
- 238000006722 reduction reaction Methods 0.000 description 4
- 229910000640 Fe alloy Inorganic materials 0.000 description 3
- 229910052782 aluminium Inorganic materials 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 238000007872 degassing Methods 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 238000007664 blowing Methods 0.000 description 2
- WUKWITHWXAAZEY-UHFFFAOYSA-L calcium difluoride Chemical compound [F-].[F-].[Ca+2] WUKWITHWXAAZEY-UHFFFAOYSA-L 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000010436 fluorite Substances 0.000 description 2
- 230000004907 flux Effects 0.000 description 2
- 230000012447 hatching Effects 0.000 description 2
- BHEPBYXIRTUNPN-UHFFFAOYSA-N hydridophosphorus(.) (triplet) Chemical compound [PH] BHEPBYXIRTUNPN-UHFFFAOYSA-N 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 230000000717 retained effect Effects 0.000 description 2
- 229910004261 CaF 2 Inorganic materials 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- 229910000616 Ferromanganese Inorganic materials 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000012159 carrier gas Substances 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 239000002826 coolant Substances 0.000 description 1
- 238000006356 dehydrogenation reaction Methods 0.000 description 1
- 230000000994 depressogenic effect Effects 0.000 description 1
- 229910001882 dioxygen Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- DALUDRGQOYMVLD-UHFFFAOYSA-N iron manganese Chemical compound [Mn].[Fe] DALUDRGQOYMVLD-UHFFFAOYSA-N 0.000 description 1
- 150000002696 manganese Chemical class 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 230000001172 regenerating effect Effects 0.000 description 1
- 238000010079 rubber tapping Methods 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
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- Treatment Of Steel In Its Molten State (AREA)
- Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
- Carbon Steel Or Casting Steel Manufacturing (AREA)
Description
本発明は、低硫鋼の溶製方法に関し、詳しくは、転炉からの出鋼時に溶鋼に混入して取鍋内に流出したスラグを取鍋から除去しないまま脱硫剤を装入し、脱硫剤と溶鋼とを強制的に攪拌して脱硫処理して低硫鋼を溶製する方法に関するものである。 The present invention relates to a method for melting low-sulfur steel, and more specifically, a desulfurization agent is charged without removing slag that has been mixed into molten steel and discharged into a ladle when steel is discharged from a converter, The present invention relates to a method for melting low-sulfur steel by forcibly stirring the agent and the molten steel to desulfurize the steel.
近年、従来にも増して不純物の少ない高級鋼製造に対する要請が増大しており、特に、鋼材の靭性を害する硫黄含有量の少ない低硫鋼が求められている。低硫鋼の製造においては、転炉での脱炭精錬工程の前に溶銑段階で脱硫処理を施すことが行われているが、硫黄濃度が０．００３質量％以下である所謂極低硫鋼では、更に転炉から出鋼後の溶鋼段階でも脱硫処理が行われている。溶鋼の脱硫剤としては、安価であることから、通常、主成分として石灰（ＣａＯ）を用い、これに融点降下剤としてのアルミナ（Ａｌ2 Ｏ3 ）、蛍石（ＣａＦ2 ）などを添加した脱硫剤が使用されている。 In recent years, there has been an increasing demand for the production of high-grade steels with less impurities than before, and in particular, low-sulfur steels with low sulfur content that impair the toughness of steel materials are required. In the production of low-sulfur steel, desulfurization treatment is performed in the hot metal stage before the decarburization refining process in the converter, but the so-called very low-sulfur steel having a sulfur concentration of 0.003% by mass or less. In addition, desulfurization treatment is also performed in the molten steel stage after steel output from the converter. As a desulfurizing agent for molten steel, lime (CaO) is usually used as a main component because it is inexpensive, and alumina (Al 2 O 3 ), fluorite (CaF 2 ), etc. as melting point depressants are added thereto. Desulfurizing agent is used.
この溶鋼の脱硫処理は、一般に、加熱手段や攪拌手段、更にはインジェクション手段を備えた、ＡＳＥＡ−ＳＫＦ法、ＶＡＤ法及びＬＦ法などと称される所謂「取鍋精錬法」によって行なわれている。これら取鍋精錬法の基本は、転炉で脱炭精錬された溶鋼を取鍋に受け、取鍋内の溶鋼上に上記脱硫剤を添加して溶鋼の攪拌を行ない、脱硫剤の滓化により形成されたスラグと溶鋼との間で所謂「スラグ−メタル反応」を行なって、溶鋼中の硫黄を除去するというものである。 This desulfurization treatment of molten steel is generally performed by a so-called “ladder refining method” called an ASEA-SKF method, a VAD method, an LF method, or the like equipped with a heating means, a stirring means, and further an injection means. . The basics of these ladle refining methods are to receive the molten steel decarburized and refined in the converter into the ladle, add the above desulfurizing agent to the molten steel in the ladle, stir the molten steel, and hatch the desulfurizing agent. A so-called “slag-metal reaction” is performed between the formed slag and the molten steel to remove sulfur in the molten steel.
ところで、脱硫反応は還元反応であるので、脱硫処理は強還元雰囲気下で行われる。一方、溶鋼の脱硫処理の前工程である転炉脱炭精錬は酸化精錬であり、この酸化精錬によって脱炭反応と同時に、酸化反応である脱燐反応が進行する。即ち、転炉での脱炭精錬時、溶銑に含有される燐は転炉内に形成されるスラグに移行して脱燐反応が進行する。転炉から取鍋への溶鋼の出鋼時、スラグカットボールなどによってスラグ流出対策が実施されるが、スラグの流出を完全には防止することができず、溶鋼に混じってスラグが取鍋内に流出する。 By the way, since the desulfurization reaction is a reduction reaction, the desulfurization treatment is performed in a strong reducing atmosphere. On the other hand, converter decarburization refining, which is a pre-process of the desulfurization treatment of molten steel, is oxidative refining, and by this oxidative refining, dephosphorization reaction that is oxidation reaction proceeds simultaneously with decarburization reaction. That is, at the time of decarburization and refining in the converter, phosphorus contained in the molten iron moves to slag formed in the converter and the dephosphorization reaction proceeds. When molten steel is discharged from the converter to the ladle, slag outflow countermeasures are implemented with slag cut balls, etc., but slag outflow cannot be completely prevented, and slag is mixed with molten steel in the ladle. To leak.
取鍋内に転炉スラグが存在した状態のまま脱硫処理を実施すると、スラグ中の燐は還元されて溶鋼に移行し、溶鋼中の燐含有量が増加する（これを「復燐」と呼ぶ）。従って、この復燐を防止するために、通常、脱硫処理の前には取鍋内に流出した転炉スラグは除去される。しかしながら、除滓するためには、除滓のための設備や要員が必要である上に、除滓による熱ロスが非常に大きく、また、除滓の際に溶鋼も流出して溶鋼歩留まりを低下させる。 When desulfurization treatment is performed with converter slag present in the ladle, phosphorus in the slag is reduced and transferred to molten steel, and the phosphorus content in the molten steel increases (this is called “rebound”). ). Therefore, in order to prevent this recovery, the converter slag that has flowed into the ladle is usually removed before the desulfurization treatment. However, in order to remove the steel, equipment and personnel are required for removal, and the heat loss due to the removal is very large, and the molten steel also flows out during removal to lower the molten steel yield. Let
特許文献１には、脱燐処理及び脱硫処理を施した溶銑を用いて転炉脱炭精錬を行い、脱炭精錬終了時の溶鋼中炭素含有量を０．１質量％以上に維持して出鋼した後、取鍋内のスラグに脱酸剤を添加し、取鍋内のスラグを除滓することなく真空脱ガス設備にて脱炭処理し、その後、脱酸処理及び脱硫処理を実施して極低硫鋼を溶製する方法が提案されている。
In
また、特許文献２には、転炉で脱炭精錬された溶鋼を収容する取鍋内に、石灰系物質とアルミナ源とが混合されたフラックスを添加して、転炉から流出したスラグとで脱硫能に優れた組成のスラグを形成し、次いで、スラグを除去しないまま溶鋼とスラグとを攪拌して脱硫処理する方法が提案されている。
しかしながら、これらの従来技術には以下の問題点がある。 However, these conventional techniques have the following problems.
即ち、特許文献１では、脱炭精錬終了時の溶鋼中炭素含有量を０．１質量％以上に維持していることから、その後に真空脱ガス設備における真空脱炭精錬が必須となり、処理工程を煩雑化させるのみならず、真空脱炭精錬の処理費用が必要であり、従来の除滓作業を実施した場合に比べて製造コストの削減効果は少ないと言わざるを得ない。また、特許文献２では、復燐防止の対策が講じられておらず、硫黄含有量は低くなるものの、燐含有量の低い溶鋼の溶製は困難であると言わざるを得ない。
That is, in
本発明は上記事情に鑑みてなされたもので、その目的とするところは、溶鋼に混入して転炉から取鍋に流出される転炉スラグを除去しないまま溶鋼を脱硫処理して低硫鋼を溶製するに当たり、処理工程を煩雑化することなく、復燐を抑えて脱硫処理することのできる、低硫鋼の溶製方法を提供することである。 The present invention has been made in view of the above circumstances, and its object is to desulfurize the molten steel without removing the converter slag mixed in the molten steel and flowing out from the converter to the ladle. It is an object to provide a method for melting low-sulfur steel, which can be desulfurized while suppressing dephosphorization without complicating the treatment process.
上記課題を解決するための第１の発明に係る低硫鋼の溶製方法は、溶銑段階で、脱硫処理及び燐濃度が０．０１０〜０．０３５質量％となるまでの脱燐処理の施された溶銑に対して、マンガン源としてマンガン鉱石を使用した転炉での脱炭精錬を行って炭素含有量が０．１質量％未満の溶鋼を溶製し、この溶鋼を取鍋に出鋼した後、取鍋内のスラグを除去することなく取鍋内に石灰系脱硫剤を添加し、次いで、溶鋼と石灰系脱硫剤とを攪拌して脱硫処理することを特徴とするものである。 The method for melting low-sulfur steel according to the first aspect of the present invention for solving the above-described problems is a desulfurization treatment until the desulfurization treatment and the phosphorous concentration become 0.010 to 0.035% by mass in the hot metal stage. against been hot metal, performing decarburization refining in a converter furnace using manganese ore carbon content was melted the molten steel is less than 0.1 wt% as a manganese source, tapping the molten steel into the ladle After that, the lime-based desulfurizing agent is added to the ladle without removing the slag in the ladle, and then the molten steel and the lime-based desulfurizing agent are stirred to perform the desulfurization treatment.
第２の発明に係る低硫鋼の溶製方法は、第１の発明において、前記脱炭精錬終了後の転炉内スラグは、燐含有量が３質量％以下であることを特徴とするものである。 The method for melting low-sulfur steel according to the second invention is characterized in that, in the first invention, the slag in the converter after the decarburization refining has a phosphorus content of 3% by mass or less. It is.
第３の発明に係る低硫鋼の溶製方法は、第１の発明において、前記脱炭精錬終了後の転炉内スラグは、燐含有量が２質量％以下であり、ＭｎＯ含有量が５質量％以上であることを特徴とするものである。 In the method for melting low-sulfur steel according to the third invention, in the first invention, the slag in the converter after completion of the decarburization refining has a phosphorus content of 2% by mass or less and an MnO content of 5 It is characterized by being at least mass%.
第４の発明に係る低硫鋼の溶製方法は、第１ないし第３の発明の何れかにおいて、前記低硫鋼は、硫黄含有量が０．００３質量％以下であり、マンガン含有量が０．６質量％以上であることを特徴とするものである。 According to a fourth aspect of the present invention, there is provided a method for melting low-sulfur steel according to any one of the first to third aspects, wherein the low-sulfur steel has a sulfur content of 0.003% by mass or less and a manganese content. It is characterized by being 0.6 mass% or more.
本発明によれば、脱燐処理及び脱硫処理の施された溶銑を使用して脱炭精錬を実施するので、転炉スラグの燐含有量は少なく、除滓せずに脱硫処理しても、復燐を抑制することができ、燐含有量の低い製品の溶製が可能である。また、転炉スラグは一旦溶融したものであり、仮に固化したとしても所謂プリメルト状態であり、石灰系脱硫剤の滓化を促進させて、効率的な脱硫を実施可能とする。更に、脱炭精錬では、０．１質量％未満まで溶鋼中炭素を低減するので、二次精錬では極低炭素鋼を除いて脱炭処理を実施する必要がない。また更に、転炉脱炭精錬でマンガン鉱石を使用した場合には、転炉内で溶鋼中にマンガンを歩留まらせることができるのみならず、取鍋内に流出したスラグ中のＭｎＯをも脱硫処理によって溶鋼中に還元することができる。このように、本発明によれば、低硫鋼の製造コストを大幅に削減することが可能となり、工業上有益な効果がもたらされる。 According to the present invention, since decarburization and refining is carried out using hot metal that has been subjected to dephosphorization and desulfurization treatment, the phosphorus content of the converter slag is low, and even if desulfurization treatment is performed without removing it, Recovery of phosphorus can be suppressed and a product having a low phosphorus content can be produced. Further, the converter slag is once melted and is in a so-called pre-melt state even if it is solidified, and promotes the hatching of the lime-based desulfurizing agent to enable efficient desulfurization. Furthermore, in the decarburization refining, the carbon in the molten steel is reduced to less than 0.1% by mass, so that in the secondary refining, it is not necessary to carry out the decarburization process except for the ultra-low carbon steel. Furthermore, when manganese ore is used in converter decarburization refining, not only can manganese be retained in molten steel in the converter, but also MnO in the slag flowing into the ladle is desulfurized. It can be reduced into molten steel by treatment. Thus, according to the present invention, the production cost of low-sulfur steel can be greatly reduced, and an industrially beneficial effect is brought about.
以下、本発明を具体的に説明する。 Hereinafter, the present invention will be specifically described.
高炉から出銑された溶銑を溶銑鍋やトーピードカーなどの溶銑保持・搬送用容器で受銑し、次工程の脱炭精錬を行なう転炉に搬送する。通常、この搬送途中で、溶銑に対して脱硫処理、脱燐処理及び脱珪処理などの溶銑予備処理が施されており、本発明においては、低硫鋼を溶製する方法であることから脱硫処理を実施し、また、溶製する鋼の成分規格上からは脱燐処理が必要でない場合でも、後工程の溶鋼段階での脱硫処理でスラグからの復燐を防止するために、脱燐処理を実施する。脱燐処理の前に脱珪処理を行ない、効率的な脱燐反応を阻害する珪素を予め除去しておくことが好ましい。 The hot metal discharged from the blast furnace is received in a hot metal holding / conveying vessel such as a hot metal ladle or torpedo car, and transferred to a converter for decarburization and refining in the next step. Usually, hot metal pretreatment such as desulfurization treatment, dephosphorization treatment and desiliconization treatment is performed on the hot metal during the conveyance, and in the present invention, desulfurization is performed because it is a method of producing low-sulfur steel. In order to prevent dephosphorization from the slag in the desulfurization process at the subsequent molten steel stage, even if no dephosphorization process is required due to the component specifications of the steel to be melted, the dephosphorization process To implement. It is preferable to carry out a desiliconization process before the dephosphorization process to remove in advance silicon that inhibits an efficient dephosphorization reaction.
また、脱燐処理を実施することで、安価なマンガン源としてマンガン鉱石を転炉内に添加し、このマンガン鉱石を高い歩留まりで溶鋼中に還元させることが可能となる。これは、溶銑段階で脱燐処理を施すことによって転炉精錬で必要とする媒溶剤を少なくすることができ、また、転炉内に装入する媒溶剤の量が少ないほどマンガン鉱石の還元が促進されるからである。転炉で使用する媒溶剤を最大限少なくするためには、溶銑の燐濃度を溶製する鋼の成分規格よりも低くなるまで脱燐処理することが好ましい。 Further, by carrying out the dephosphorization treatment, it becomes possible to add manganese ore as an inexpensive manganese source into the converter and reduce this manganese ore into molten steel with a high yield. This is because dephosphorization treatment is performed at the hot metal stage to reduce the amount of medium solvent required for converter refining, and the smaller the amount of medium solvent charged into the converter, the more the manganese ore is reduced. Because it is promoted. In order to minimize the amount of the solvent used in the converter, it is preferable to perform the dephosphorization process until the phosphorus concentration of the hot metal becomes lower than the component standard of the steel to be melted.
このようにして得た溶銑を一次精錬炉である転炉に装入して脱炭精錬を行なう。この転炉脱炭精錬では、マンガン源としてマンガン鉱石を添加しながら必要に応じて少量の生石灰などを媒溶剤として用い、酸素ガスを上吹き及び／または底吹きして溶銑の脱炭精錬を行なう。添加されたマンガン鉱石は送酸脱炭中に溶銑中の炭素によって還元され、還元されたマンガンは溶湯中に移行し、溶湯中のマンガン濃度が上昇する。転炉内に添加したマンガン鉱石のみでは、溶鋼のマンガン濃度が目的とする鋼の成分規格範囲に不足する場合には、転炉から取鍋などの溶鋼保持容器への溶鋼の出鋼時に高炭素フェロマンガンなどの合金鉄を所定量添加し、溶鋼のマンガン濃度を上昇させる。 The hot metal obtained in this way is charged into a converter, which is a primary refining furnace, and decarburized and refined. In this converter decarburization and refining, hot metal decarburization and refining is performed by adding a small amount of quick lime as a solvent and adding oxygen or as a bottom solvent as needed, while adding manganese ore as a manganese source. . The added manganese ore is reduced by carbon in the molten iron during the acid feeding decarburization, and the reduced manganese moves into the molten metal, and the manganese concentration in the molten metal increases. If only the manganese ore added to the converter has a manganese concentration in the molten steel that is not within the component specification range of the target steel, a high carbon content will be produced when the molten steel is discharged from the converter to a molten steel holding vessel such as a ladle. A predetermined amount of iron alloy such as ferromanganese is added to increase the manganese concentration of the molten steel.
マンガン鉱石を還元しながら溶銑の脱炭精錬を行ない、溶銑から溶鋼へと脱炭精錬された溶湯中の炭素濃度が０．１質量％未満の範囲まで脱炭精錬されたなら、転炉内への酸素ガスの供給を停止して脱炭精錬を終了する。このときの炭素濃度は、０．１質量％未満の範囲で、溶製する鋼の成分範囲に応じて決定する。炭素濃度の下限値は特に規定する必要はないが、０．０３質量％程度が好ましい。炭素濃度がこの範囲の場合が転炉脱炭精錬は最も効率的であるためである。即ち、炭素濃度が０．０３質量％未満では溶鋼が過酸化されて、鉄歩留まりが低下したり、脱酸剤原単位が上昇したりして、製造コストが上昇する。また、０．１質量％以上の場合には、脱炭反応による発熱量が少なく、鉄鉱石などの冷却材の使用量を少なくせざるを得ず、製造コストが上昇し、また、鋼製品の炭素含有量範囲は０．１質量％以下のものが大半であり、０．１質量％以上で脱炭精錬を終了すると、その後に、真空脱ガス設備を用いた脱炭精錬が必要になるからである。 If decarburization and refining of hot metal is performed while reducing manganese ore, and the carbon concentration in the molten metal decarburized and refined from hot metal to molten steel is reduced to a range of less than 0.1% by mass, it is transferred to the converter. The supply of oxygen gas is stopped and decarburization refining is completed. The carbon concentration at this time is determined in accordance with the component range of the steel to be melted within a range of less than 0.1% by mass. The lower limit of the carbon concentration is not particularly required, but is preferably about 0.03% by mass. This is because converter decarburization refining is most efficient when the carbon concentration is within this range. That is, when the carbon concentration is less than 0.03% by mass, the molten steel is peroxidized, the iron yield is reduced, the deoxidizer basic unit is increased, and the production cost is increased. In addition, when the content is 0.1% by mass or more, the amount of heat generated by the decarburization reaction is small, and the amount of coolant such as iron ore has to be reduced. Most of the carbon content range is 0.1% by mass or less, and when decarburization refining is completed at 0.1% by mass or more, decarburization refining using vacuum degassing equipment is required thereafter. It is.
また、後工程の溶鋼での脱硫処理における復燐を防止するために、転炉スラグの燐含有量が３質量％以下、望ましくは２質量％以下になるように、転炉脱炭精錬では、生石灰などの媒溶剤の使用量を調整することが好ましい。つまり、溶銑の燐含有量に応じて、転炉スラグの燐含有量が３質量％以下、望ましくは２質量％以下になるように、生石灰などの媒溶剤の使用量を調整することが好ましい。転炉スラグの燐含有量が３質量％以下になると、復燐を問題のないレベルまで抑えることができ、２質量％以下の場合には更に復燐が低減することを確認している。同様に、後工程の溶鋼の脱硫処理においてＭｎＯの還元を有効に活用するために、転炉スラグのＭｎＯ含有量が５質量％以上となるように、マンガン鉱石の添加量を調整することが好ましい。これは、経験的に得られるマンガン鉱石の還元量よりも過剰にマンガン鉱石を添加すればよい。 In the converter decarburization refining so that the phosphorus content in the converter slag is 3% by mass or less, preferably 2% by mass or less, in order to prevent dephosphorization in the desulfurization treatment in the molten steel in the subsequent process, It is preferable to adjust the amount of medium solvent such as quicklime. That is, it is preferable to adjust the usage amount of a medium solvent such as quicklime so that the phosphorus content of the converter slag is 3% by mass or less, preferably 2% by mass or less, depending on the phosphorus content of the hot metal. It has been confirmed that when the phosphorus content of the converter slag is 3% by mass or less, the recovery is suppressed to a level at which there is no problem, and when it is 2% by mass or less, the recovery is further reduced. Similarly, in order to effectively utilize the reduction of MnO in the desulfurization treatment of the molten steel in the subsequent step, it is preferable to adjust the amount of manganese ore added so that the MnO content of the converter slag becomes 5% by mass or more. . This may be achieved by adding manganese ore in excess of the reduced amount of manganese ore obtained empirically.
このようにして脱炭精錬して溶製した溶鋼を転炉から取鍋に出鋼する。出鋼の末期、溶鋼に混じって転炉スラグも取鍋に流出する。出鋼時、転炉スラグを積極的に取鍋に流出させる必要はなく、通常実施されるスラグ流出対策を実施する。出鋼後、溶鋼に混じって流出した転炉スラグを除去することなく、溶鋼を次工程の二次精錬炉に搬送する。石灰系脱硫剤は、脱硫処理を実施する後工程の例えばＬＦ炉（「取鍋精錬炉」ともいう）で添加してもよいが、石灰系脱硫剤の滓化を促進させて効率的な脱硫処理を実施するために、出鋼時或いは出鋼直後に取鍋内に添加することが好ましい。 The molten steel decarburized and refined in this way is discharged from the converter to the ladle. At the end of steelmaking, the converter slag also flows into the ladle mixed with molten steel. There is no need to actively flow converter slag into the ladle at the time of steel production. After the steel is discharged, the molten steel is transferred to the secondary refining furnace in the next step without removing the converter slag that has flowed out of the molten steel. The lime-based desulfurizing agent may be added, for example, in an LF furnace (also referred to as a “lader refining furnace”), which is a post-process for carrying out the desulfurization treatment. In order to carry out the treatment, it is preferable to add it to the ladle at the time of steel output or immediately after the steel output.
本発明の溶製対象である低硫鋼は高級鋼であることから、水素、窒素などの溶鋼中ガス成分も調整の対象になることが多く、従って、出鋼後に脱ガス処理と脱硫処理との双方を実施する場合が大半である。また、炭素濃度範囲が０．０３質量％以下の極低炭低硫鋼は脱炭処理も必要とし、この脱炭処理は脱ガス設備で実施する。脱ガス処理が必要でない場合には、脱硫処理のみを実施する。 Since the low-sulfur steel that is the object of melting of the present invention is a high-grade steel, gas components in the molten steel such as hydrogen and nitrogen are often subject to adjustment. In most cases, both are implemented. Moreover, the ultra-low-carbon low-sulfur steel with a carbon concentration range of 0.03% by mass or less also requires decarburization, and this decarburization is carried out in a degassing facility. If degassing is not necessary, only desulfurization is performed.
二次精錬炉として最も一般的なＲＨ真空脱ガス装置では、脱炭処理を含めた脱ガス処理と脱硫処理の双方を実施することは可能であるが、例えば脱炭処理は酸化反応であり、一方、脱硫処理は還元反応であることから、双方を同時に行なうことはできず、それぞれ個別に行なうためにＲＨ真空脱ガス装置における処理時間が延長し、生産性を阻害する。また、本来、ＲＨ真空脱ガス装置における脱硫効率よりも、ＬＦ炉など溶鋼と脱硫剤との攪拌が可能な二次精錬炉における脱硫効率の方が高いという基本的な利点もある。従って、本発明では、真空脱炭処理を含めた真空脱ガス処理をＲＨ真空脱ガス装置で行ない、脱硫処理をＡＳＥＡ−ＳＫＦ炉、ＶＡＤ炉、ＬＦ炉などで実施する。 In the most common RH vacuum degassing apparatus as a secondary refining furnace, it is possible to perform both degassing and desulfurization including decarburization. For example, decarburization is an oxidation reaction, On the other hand, since the desulfurization treatment is a reduction reaction, both cannot be carried out simultaneously, and the treatment time in the RH vacuum degassing apparatus is extended because they are carried out individually, thereby impeding productivity. In addition, there is a fundamental advantage that the desulfurization efficiency in the secondary refining furnace capable of stirring the molten steel and the desulfurizing agent such as an LF furnace is higher than the desulfurization efficiency in the RH vacuum degassing apparatus. Therefore, in the present invention, vacuum degassing processing including vacuum decarburization processing is performed with an RH vacuum degassing apparatus, and desulfurization processing is performed with an ASEA-SKF furnace, a VAD furnace, an LF furnace, or the like.
この場合、真空脱ガス処理と脱硫処理のどちらの処理を先に実施しても構わないが、真空脱ガス処理で、脱炭処理を必要とする場合には、真空脱ガス処理を先に実施することが好ましい。これは、脱炭処理は酸化反応であり、一方、脱硫処理は還元反応であり、また、転炉から出鋼された溶鋼は酸化された状態であることから、転炉から出鋼された溶鋼に脱酸処理を施さず、そのまま真空脱炭処理することが効率的であるからである。 In this case, either the vacuum degassing process or the desulfurization process may be performed first. However, when the decarburization process is required in the vacuum degassing process, the vacuum degassing process is performed first. It is preferable to do. This is because the decarburization treatment is an oxidation reaction, while the desulfurization treatment is a reduction reaction, and the molten steel removed from the converter is in an oxidized state. This is because it is efficient to perform a vacuum decarburization process without performing a deoxidation process.
ここでは、真空脱ガス処理を先に実施することで説明する。ＲＨ真空脱ガス装置では、真空脱炭処理が必要な場合には最初に真空脱炭処理を実施、真空脱炭処理後に、溶鋼を金属Ａｌなどで脱酸し、更に、処理を継続して脱水素処理、脱窒素処理、成分調整処理などを実施する。処理完了後は、溶鋼を次の脱硫処理工程に搬送する。 Here, a description will be given by performing the vacuum degassing process first. In the RH vacuum degassing device, when vacuum decarburization is required, first vacuum decarburization is performed. After the vacuum decarburization, the molten steel is deoxidized with metal Al, etc., and the treatment is continued to dehydrate. Elemental treatment, denitrification treatment, component adjustment treatment, etc. are performed. After the completion of the treatment, the molten steel is transported to the next desulfurization treatment step.
図１に、本発明で脱硫処理設備として用いたＬＦ炉の１例を示す。図１はＬＦ炉の概略縦断面図であり、図１において、１はＬＦ炉、２は取鍋、３は溶鋼、４はスラグ、５は昇降式の蓋、６はインジェクションランス、７は通電用の電極、８は蓋５と取鍋２とで形成する空間に不活性ガスを供給するためのガス導入管である。このＬＦ炉１においては、インジェクションランス６から、不活性ガスの他に不活性ガスを搬送用ガスとして粉体のフラックス及び金属を溶鋼中に吹き込むことができるようになっており、また、蓋５を貫通して合金鉄及び造滓剤を添加するための投入シュートが蓋５を貫通して設置されているが、図１ではこれらを省略している。
FIG. 1 shows an example of an LF furnace used as a desulfurization treatment facility in the present invention. FIG. 1 is a schematic longitudinal sectional view of an LF furnace. In FIG. 1, 1 is an LF furnace, 2 is a ladle, 3 is molten steel, 4 is a slag, 5 is a liftable lid, 6 is an injection lance, and 7 is energized. The electrode 8 is a gas introduction pipe for supplying an inert gas to the space formed by the lid 5 and the ladle 2. In the
ＬＦ炉１では、台車（図示せず）に積載されて搬送された取鍋２を台車に積載したまま所定の位置に固定し、上方から蓋５を取鍋２の上部に載せ、蓋５と取鍋２とで密閉された空間を形成する。出鋼時や出鋼直後に石灰系脱硫剤の添加が行われていない場合には、この時点で投入シュートを介して石灰系脱硫剤を添加する。また、溶鋼３が脱酸されていない場合には、この時点で金属Ａｌを添加して脱酸する。そして、この空間にガス導入管８を介してＡｒガスなどの不活性ガスを吹き込み、この空間を不活性ガス雰囲気に維持しながら、インジェクションランス６から不活性ガスを吹き込んで溶鋼３とスラグ４とを攪拌する。スラグ４には、石灰系脱硫剤が添加してあるので、溶鋼３はこの石灰系脱硫剤によって脱硫処理される。溶鋼３の硫黄濃度が０．００３質量％以下の所定の値になったなら、インジェクションランス６からの不活性ガス吹き込みを停止して脱硫処理を終了する。溶鋼３の温度が所望する温度よりも低い場合、或いは溶鋼３の成分濃度が所望する範囲にない場合には、電極７による溶鋼３の加熱或いは合金鉄の投入を実施する。このようにして硫黄濃度が０．００３質量％以下の低硫鋼の溶製を終了し、次の連続鋳造機などの鋳造工程に溶鋼３を搬送する。
In the
ここで、石灰系脱硫剤とは、ＣａＯを５０質量％以上含有するものであり、例えば、生石灰単独、或いは、生石灰に蛍石やアルミナなどの融点降下剤を添加した脱硫剤である。尚、スラグ４の酸素ポテンシャルを下げて脱硫反応を促進させるために、脱酸源をスラグ４に添加することが好ましい。脱酸源としては、金属アルミニウム、或いは、アルミニウムスクラップを溶解再生するときに発生するアルミドロス（金属Ａｌを３０〜５０質量％程度含有する）が適当である。
Here, the lime-based desulfurization agent contains CaO in an amount of 50% by mass or more, for example, quick lime alone or a desulfurization agent obtained by adding a melting point depressant such as fluorite or alumina to quick lime. In addition, it is preferable to add a deoxidation source to the
このように本発明では、脱燐処理及び脱硫処理の施された溶銑を使用して転炉で脱炭精錬を実施するので、取鍋２に混入する転炉スラグの燐含有量は少なく、除滓せずに脱硫処理しても、復燐を抑制することができ、燐含有量の低い製品の溶製が可能である。また、転炉スラグは一旦溶融したものであり、石灰系脱硫剤の滓化を促進させて、効率的な脱硫処理が実施可能となる。更に、転炉脱炭精錬でマンガン鉱石を使用した場合には、転炉内で溶鋼中にマンガンを歩留まらせることができるのみならず、取鍋内に流出したスラグ中のＭｎＯをも脱硫処理によって溶鋼中に還元することができ、低硫鋼の製造コストを大幅に削減することが可能となる。本発明は、特に、硫黄含有量が０．００３質量％以下であり、マンガン含有量が０．６質量％以上の低硫鋼を溶製する際に、上記効果を如何なく発揮する。 In this way, in the present invention, decarburization and refining is carried out in the converter using hot metal that has been subjected to dephosphorization and desulfurization treatment. Therefore, the phosphorus content of the converter slag mixed in the ladle 2 is small, Even if it is desulfurized without dripping, it is possible to suppress dephosphorization and to produce a product having a low phosphorus content. Further, the converter slag is once melted and promotes the hatching of the lime-based desulfurizing agent, so that efficient desulfurization treatment can be performed. Furthermore, when manganese ore is used in converter decarburization refining, not only can manganese be retained in molten steel in the converter, but also MnO in the slag that has flowed into the ladle is desulfurized. Can be reduced into molten steel, and the production cost of low-sulfur steel can be greatly reduced. In particular, the present invention exhibits the above-described effects when the low-sulfur steel having a sulfur content of 0.003% by mass or less and a manganese content of 0.6% by mass or more is melted.
高炉から出銑された溶銑に脱珪処理、脱硫処理及び脱燐処理を施し、燐濃度が０．０１０〜０．０３５質量％、硫黄濃度が０．００４〜０．００５質量％の溶銑を得た。この溶銑を転炉に装入して、脱炭精錬を実施した。この脱炭精錬では、酸素吹錬中にマンガン鉱石を溶鋼トン当たり３〜２０ｋｇ添加した。また、脱炭精錬終了後の転炉スラグの燐濃度が２質量％以下になるように、造滓剤として生石灰を投入した。このようにして転炉で溶製した溶鋼を取鍋に出鋼した。出鋼時の溶鋼中炭素濃度は０．０５〜０．０９質量％であり、出鋼時、転炉スラグが溶鋼に混入して取鍋に流出した。転炉スラグの燐濃度は１．５〜２．０質量％、ＭｎＯ濃度は６〜１０質量％であり、転炉スラグの取鍋への流出量はスラグ厚みから換算するとおよそ溶鋼トン当たり５〜１５ｋｇであった。このスラグを除去しないまま、先ず、ＲＨ真空脱ガス装置で脱水素処理を実施、次いで、図１に示すＬＦ炉で脱硫処理を実施した。脱硫剤としては８０質量％ＣａＯ−２０質量％Ａｌ2 Ｏ3 の石灰系脱硫剤を使用し、この脱硫剤をＬＦ炉で投入し、インジェクションランスから溶鋼トン当たり３〜１０ＮＬのＡｒガスを溶鋼中に吹き込んで攪拌した。脱硫処理終了後、黒鉛製の電極をスラグに浸漬させてアーク加熱し、処理中の温度補償を行った。 The hot metal discharged from the blast furnace is subjected to desiliconization treatment, desulfurization treatment and dephosphorization treatment to obtain hot metal having a phosphorus concentration of 0.010 to 0.035 mass% and a sulfur concentration of 0.004 to 0.005 mass%. It was. This hot metal was charged into a converter and decarburized and refined. In this decarburization refining, 3-20 kg of manganese ore was added per ton of molten steel during oxygen blowing. In addition, quick lime was added as a slagging agent so that the phosphorous concentration in the converter slag after decarburization and refining was 2% by mass or less. In this way, the molten steel melted in the converter was put into a ladle. The carbon concentration in the molten steel at the time of steel output was 0.05 to 0.09 mass%, and at the time of steel output, converter slag was mixed into the molten steel and flowed into the ladle. The phosphorus concentration of the converter slag is 1.5 to 2.0% by mass and the MnO concentration is 6 to 10% by mass. The amount of outflow of the converter slag to the ladle is approximately 5 ton per molten steel when converted from the slag thickness. It was 15 kg. Without removing this slag, first, dehydrogenation treatment was performed with an RH vacuum degassing apparatus, and then desulfurization treatment was performed with an LF furnace shown in FIG. As a desulfurization agent, a lime-based desulfurization agent of 80% by mass CaO-20% by mass Al 2 O 3 is used. And stirred. After completion of the desulfurization treatment, a graphite electrode was immersed in slag and arc-heated to compensate for the temperature during the treatment.
脱硫処理後の溶鋼中硫黄濃度は０．０００８質量％以下であった。また、溶鋼の復燐は０．００２〜０．００３質量％であり、問題のない範囲であった。溶鋼中マンガン濃度は脱硫処理中に０．１〜０．３質量％上昇した。また、除滓しないことにより、溶鋼温度の降下量を除滓した場合に比べて約５℃低減することができた。 The sulfur concentration in the molten steel after the desulfurization treatment was 0.0008% by mass or less. Moreover, the recovery of molten steel was 0.002 to 0.003% by mass, and there was no problem. The manganese concentration in the molten steel increased by 0.1 to 0.3% by mass during the desulfurization treatment. In addition, by not removing the steel, it was possible to reduce the molten steel temperature drop by about 5 ° C. as compared with the case where the temperature drop was removed.
１ ＬＦ炉
２ 取鍋
３ 溶鋼
４ スラグ
５ 蓋
６ インジェクションランス
７ 電極
８ ガス導入管
1 LF furnace 2 Ladle 3
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