JP5433941B2 - Melting method of high cleanliness bearing steel - Google Patents
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- JP5433941B2 JP5433941B2 JP2007302357A JP2007302357A JP5433941B2 JP 5433941 B2 JP5433941 B2 JP 5433941B2 JP 2007302357 A JP2007302357 A JP 2007302357A JP 2007302357 A JP2007302357 A JP 2007302357A JP 5433941 B2 JP5433941 B2 JP 5433941B2
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- 229910000831 Steel Inorganic materials 0.000 title claims description 128
- 239000010959 steel Substances 0.000 title claims description 128
- 238000000034 method Methods 0.000 title claims description 26
- 230000003749 cleanliness Effects 0.000 title claims description 14
- 238000002844 melting Methods 0.000 title claims description 11
- 230000008018 melting Effects 0.000 title claims description 11
- 229910052717 sulfur Inorganic materials 0.000 claims description 35
- 239000011593 sulfur Substances 0.000 claims description 35
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 34
- 229910052751 metal Inorganic materials 0.000 claims description 26
- 239000002184 metal Substances 0.000 claims description 26
- 239000002893 slag Substances 0.000 claims description 20
- 238000009849 vacuum degassing Methods 0.000 claims description 14
- 238000007670 refining Methods 0.000 claims description 13
- 239000003638 chemical reducing agent Substances 0.000 claims description 5
- 239000000203 mixture Substances 0.000 claims description 3
- 239000000126 substance Substances 0.000 claims description 3
- 238000003723 Smelting Methods 0.000 claims 1
- 238000006477 desulfuration reaction Methods 0.000 description 14
- 230000023556 desulfurization Effects 0.000 description 14
- ODINCKMPIJJUCX-UHFFFAOYSA-N Calcium oxide Chemical compound [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 12
- 238000004519 manufacturing process Methods 0.000 description 10
- 238000000926 separation method Methods 0.000 description 9
- 239000002245 particle Substances 0.000 description 8
- 235000012255 calcium oxide Nutrition 0.000 description 6
- 239000000292 calcium oxide Substances 0.000 description 6
- 239000007789 gas Substances 0.000 description 6
- 238000007667 floating Methods 0.000 description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 4
- 238000009826 distribution Methods 0.000 description 4
- 238000005188 flotation Methods 0.000 description 4
- 229910052760 oxygen Inorganic materials 0.000 description 4
- 239000001301 oxygen Substances 0.000 description 4
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 3
- 229910052782 aluminium Inorganic materials 0.000 description 3
- 239000003795 chemical substances by application Substances 0.000 description 3
- 229910052804 chromium Inorganic materials 0.000 description 3
- 239000011651 chromium Substances 0.000 description 3
- 238000009749 continuous casting Methods 0.000 description 3
- 238000005261 decarburization Methods 0.000 description 3
- 239000012467 final product Substances 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- 238000009628 steelmaking Methods 0.000 description 3
- 238000003756 stirring Methods 0.000 description 3
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 2
- 229910000796 S alloy Inorganic materials 0.000 description 2
- 230000001174 ascending effect Effects 0.000 description 2
- 238000007664 blowing Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000010894 electron beam technology Methods 0.000 description 2
- 238000010309 melting process Methods 0.000 description 2
- 229910052698 phosphorus Inorganic materials 0.000 description 2
- 239000011574 phosphorus Substances 0.000 description 2
- 238000010992 reflux Methods 0.000 description 2
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 1
- 229910017060 Fe Cr Inorganic materials 0.000 description 1
- 229910002544 Fe-Cr Inorganic materials 0.000 description 1
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- UPHIPHFJVNKLMR-UHFFFAOYSA-N chromium iron Chemical compound [Cr].[Fe] UPHIPHFJVNKLMR-UHFFFAOYSA-N 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000006837 decompression Effects 0.000 description 1
- 238000007872 degassing Methods 0.000 description 1
- 230000003009 desulfurizing effect Effects 0.000 description 1
- 229910001882 dioxygen Inorganic materials 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 125000004435 hydrogen atom Chemical class [H]* 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 238000005339 levitation Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
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Description
本発明は、自動車、建設機械及び産業機械などに使用される転動部品用の軸受鋼及びその溶製方法に関し、詳しくは、酸化物系非金属介在物が少なく、高性能で且つ高い信頼性を有する高清浄度軸受鋼及びその溶製方法に関するものである。 The present invention relates to a bearing steel for rolling parts used in automobiles, construction machinery, industrial machinery, and the like, and a method for melting the same. More specifically, the present invention relates to a high performance and high reliability with less oxide non-metallic inclusions. The present invention relates to a high cleanliness bearing steel having a melting point and a melting method thereof.
軸受鋼の疲労特性は、Ａｌ2Ｏ3などの酸化物系非金属介在物に影響することが知られており、疲労特性の改善を目的として、製鋼工程では酸化物系非金属介在物を低減するために種々の手法が採られている。 Fatigue properties of bearing steel are known to affect oxide-based nonmetallic inclusions such as Al 2 O 3, and oxide-based nonmetallic inclusions are reduced in the steelmaking process for the purpose of improving fatigue properties. Various techniques have been adopted to achieve this.
例えば、量産鋼においては、真空脱ガス処理によって酸化物系非金属介在物の浮上・分離を促進したり、取鍋内の溶鋼上に存在するスラグに金属Ａｌなどの脱酸剤を添加してスラグを還元し、スラグと溶鋼中のＡｌとの反応によるＡｌ2Ｏ3の生成を抑制したり、連続鋳造機の鋳型或いは鋳型直下に磁場発生装置を配置して鋳型内での酸化物系非金属介在物の浮上・分離を促進したりしている。 For example, in mass-produced steel, flotation / separation of oxide-based nonmetallic inclusions is promoted by vacuum degassing treatment, or a deoxidizer such as metal Al is added to slag present on molten steel in a ladle. Reduces slag, suppresses the formation of Al 2 O 3 due to the reaction of slag with Al in molten steel, or places a magnetic field generator directly under the mold of the continuous casting machine or the mold to prevent non-oxide It promotes the floating and separation of metal inclusions.
具体的に説明すると、特許文献１には、電気炉で酸素富化操業を行って溶鋼中の溶存酸素濃度を２５０ｐｐｍ以上の過酸化状態として原料中のＴｉなどを酸化してスラグ中に移行させ、このスラグを取鍋から排出した後にＳｉ脱酸、Ａｌ脱酸を順次実施して溶鋼及びスラグを脱酸し、その後、取鍋精錬炉、ＲＨ真空脱ガス装置で順次精錬することを特徴とする、高清浄度軸受鋼の製造方法が開示されている。特許文献１の製造方法を採用することにより、溶鋼中の溶存酸素濃度が９ｐｐｍ以下で、且つ酸化物系非金属介在物の円相当直径１０μｍ以上のものが断面３２０ｍｍ2あたり９個以内である清浄な軸受鋼が製造できるとしている。 Specifically, Patent Document 1 describes that oxygen enrichment operation is performed in an electric furnace, and the dissolved oxygen concentration in the molten steel is set to a peroxidized state of 250 ppm or more to oxidize Ti or the like in the raw material and transfer it to the slag. In addition, after discharging this slag from the ladle, Si deoxidation and Al deoxidation are sequentially performed to deoxidize the molten steel and slag, and then the slag is refined sequentially in a ladle refining furnace and RH vacuum degassing equipment. A method of manufacturing a high cleanliness bearing steel is disclosed. By adopting the production method of Patent Document 1, a clean oxygen concentration of dissolved steel is 9 ppm or less, and oxide-based nonmetallic inclusions having a circle equivalent diameter of 10 μm or more are within 9 per 320 mm 2 in cross section. It is said that it is possible to manufacture a simple bearing steel.
また、特許文献２には、製鋼工程の詳しい製造方法は開示していないものの、粒径が２５μｍ以上の塊状または粒状の酸化物系非金属介在物の個数が、検査対象である鋼３０００ｍｍ3あたりに１０個以下であれば、清浄な軸受鋼として使用可能であることが開示されている。 Patent Document 2 does not disclose a detailed manufacturing method of the steelmaking process, but the number of massive or granular oxide-based nonmetallic inclusions having a particle size of 25 μm or more per 3000 mm 3 of steel to be inspected. If it is 10 or less, it is disclosed that it can be used as a clean bearing steel.
また更に、より高い信頼性や性能の要求される軸受鋼を製造する方法として、特許文献３には、母材としてＭｎを０．２質量％を越えて含まない軸受鋼を用い、該母材を電子ビーム溶解法によって再溶解することを特徴とする、超清浄度軸受鋼の製造方法が開示されている。特許文献３によれば、酸化物系非金属介在物粒子の直径が１５μｍ以下である超清浄度軸受鋼が得られるとしている。
しかしながら、上記の従来技術には以下の問題点がある。 However, the above prior art has the following problems.
即ち、特許文献１に示される軸受鋼には粒径が１０μｍ以上の酸化物系非金属介在物が存在し、また、特許文献２に示される軸受鋼には粒径が２５μｍ以上の酸化物系非金属介在物が存在しており、特許文献１及び特許文献２ともに、これら酸化物系非金属介在物の上限値を規定していない。従って、例えば粒径が１００μｍの酸化物系非金属介在物であっても、存在個数が上記範囲を満足する限り、存在しても構わないことになる。粒径が１００μｍである大型の酸化物系非金属介在物が存在すると軸受鋼の特性は劣化することから、特許文献１及び特許文献２に提案される軸受鋼は、十分な疲労特性を有しているとはいいがたい。 That is, the bearing steel shown in Patent Document 1 has oxide-based nonmetallic inclusions with a particle size of 10 μm or more, and the bearing steel shown in Patent Document 2 has an oxide-based material with a particle size of 25 μm or more. Non-metallic inclusions exist, and neither Patent Document 1 nor Patent Document 2 define the upper limit of these oxide-based non-metallic inclusions. Therefore, for example, an oxide-based non-metallic inclusion having a particle size of 100 μm may be present as long as the number of existing particles satisfies the above range. The bearing steel proposed in Patent Document 1 and Patent Document 2 has sufficient fatigue characteristics because the characteristics of the bearing steel deteriorate when a large oxide-based nonmetallic inclusion having a particle size of 100 μm exists. I don't want to be.
特許文献３に示される軸受鋼は、酸化物系非金属介在物粒子の直径が１５μｍ以下であり、清浄性に優れており、十分な疲労特性が得られるものと想到される。しかしながら、電子ビーム溶解法によって再溶解しており、製造コストが余りにも高く、量産鋼には適用できない。 The bearing steel disclosed in Patent Document 3 has a diameter of oxide-based nonmetallic inclusion particles of 15 μm or less, is excellent in cleanliness, and is considered to have sufficient fatigue characteristics. However, it is remelted by the electron beam melting method, and the manufacturing cost is too high, and it cannot be applied to mass-produced steel.
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、製造コストが従来の量産鋼と同等で安価であるとともに、酸化物系非金属介在物が少なく、高性能で且つ高い信頼性を有する高清浄度軸受鋼並びにそ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 the object of the present invention is that the manufacturing cost is the same as that of conventional mass-produced steel and is inexpensive, and there are few oxide non-metallic inclusions, high performance and high performance. It is to provide a high cleanliness bearing steel having reliability and a method for melting the steel.
上記課題を解決するための第１の発明に係る高清浄度軸受鋼は、硫黄含有量が０．００２０質量％以上で且つ酸化物系非金属介在物の予測最大径が１５μｍ以下であることを特徴とするものである。 The high cleanliness bearing steel according to the first invention for solving the above problem is that the sulfur content is 0.0020 mass% or more and the predicted maximum diameter of the oxide-based nonmetallic inclusion is 15 μm or less. It is a feature.
また、第２の発明に係る高清浄度軸受鋼の溶製方法は、第１の発明に記載の高清浄度軸受鋼の溶製方法であって、予備脱硫処理された溶銑を転炉にて脱炭精錬し、得られた溶鋼を取鍋に出鋼し、出鋼された溶鋼をＲＨ真空脱ガス装置にて精錬することによって軸受鋼を溶製するにあたり、前記ＲＨ真空脱ガス装置にて精錬する前までに溶鋼中の硫黄濃度を０．００２０質量％以上に調整することを特徴するものである。 Further, the method for melting high cleanliness bearing steel according to the second invention is the method for melting high cleanliness bearing steel according to the first invention, wherein the hot metal subjected to preliminary desulfurization treatment is heated in a converter. Decarburizing and refining, removing the obtained molten steel into a ladle, and refining the molten steel with a RH vacuum degassing device to melt the bearing steel, with the RH vacuum degassing device Before the refining, the sulfur concentration in the molten steel is adjusted to 0.0020% by mass or more.
本発明によれば、軸受鋼の硫黄含有量を０．００２０質量％以上とするので、軸受鋼の溶製工程において、溶鋼上に存在するスラグと溶鋼との境界面と、溶鋼バルクと、の間の界面張力に大きな勾配が発生し、この界面張力の勾配によって溶鋼中に懸濁する酸化物はスラグ側に向って移動するので、溶鋼中に懸濁する酸化物の浮上・分離が促進され、その結果、酸化物系非金属介在物の予測最大径が１５μｍ以下である、酸化物系非金属介在物が少なく、高性能で且つ高い信頼性を有する高清浄度軸受鋼を、安価な製造コストで得ることができる。 According to the present invention, since the sulfur content of the bearing steel is 0.0020 mass% or more, in the melting process of the bearing steel, the boundary surface between the slag and the molten steel existing on the molten steel, and the molten steel bulk A large gradient occurs in the interfacial tension between them, and the oxide suspended in the molten steel moves toward the slag due to this gradient in interfacial tension, which promotes the floating and separation of the oxide suspended in the molten steel. As a result, the predicted maximum diameter of oxide-based non-metallic inclusions is 15 μm or less, and there are few oxide-based non-metallic inclusions. Can be obtained at a cost.
以下、本発明を具体的に説明する。 Hereinafter, the present invention will be specifically described.
本発明者等は、軸受鋼の清浄度を高めることを鋭意検討した。その結果、軸受鋼中の酸化物系非金属介在物は軸受鋼の硫黄含有量に影響することを見出した。これは、硫黄は溶鋼に対して表面活性元素であり、溶鋼中の硫黄濃度を増加させることにより、溶鋼の界面張力が増加し、これにより、溶鋼中に懸濁している酸化物の除去が促進され、軸受鋼中の酸化物系非金属介在物が少なくなるからである。 The present inventors diligently studied to increase the cleanliness of the bearing steel. As a result, it was found that oxide-based nonmetallic inclusions in the bearing steel affect the sulfur content of the bearing steel. This is because sulfur is a surface active element for molten steel, increasing the sulfur concentration in the molten steel increases the interfacial tension of the molten steel, which promotes the removal of oxides suspended in the molten steel. This is because there are fewer oxide-based non-metallic inclusions in the bearing steel.
つまり、溶鋼中の硫黄濃度を増加させることにより、溶鋼の界面張力が増加し、一方、スラグの界面張力は溶鋼中の硫黄濃度が変化しても変わらず、従って、スラグと溶鋼との境界面（以下、「スラグ−溶鋼境界面」と記す）と、溶鋼バルク（「バルク」とは周囲の影響を受けることのない内部のこと）とで界面張力の差が大きくなる。スラグ−溶鋼境界面と溶鋼バルクとで界面張力の差が大きくなると、必然的に、スラグ−溶鋼境界面と溶鋼バルクとの間の界面張力の勾配が大きくなる。 That is, by increasing the sulfur concentration in the molten steel, the interfacial tension of the molten steel increases, while the interfacial tension of the slag does not change even if the sulfur concentration in the molten steel changes, and therefore the interface between the slag and the molten steel. (Hereinafter referred to as “slag-molten steel interface”) and the molten steel bulk (“bulk” means the inside without being affected by the surroundings), the difference in interfacial tension becomes large. When the difference in interfacial tension between the slag-molten steel interface and the molten steel bulk increases, the gradient of the interfacial tension between the slag-molten steel interface and the molten steel inevitably increases.
溶鋼中に懸濁する酸化物には、溶鋼による界面張力により溶鋼から分離しようとする力が作用しているが、酸化物が、その前後左右から等しい界面張力を受けている場合には、界面張力によるそれぞれの力が打ち消し合い、界面張力が作用していない場合と同等になる。しかしながら、界面張力の勾配が存在する領域に酸化物が存在する場合には、界面張力が高い側の力の方が差分だけ強く、酸化物は界面張力の低い側の方向に移動することになる。 The oxide suspended in the molten steel is subjected to a force to be separated from the molten steel due to the interfacial tension caused by the molten steel. Each force due to tension cancels each other out, which is equivalent to the case where no interfacial tension acts. However, when oxide exists in the region where the gradient of interfacial tension exists, the force on the side with higher interfacial tension is stronger by the difference, and the oxide moves in the direction of the side with lower interfacial tension. .
即ち、溶鋼の硫黄濃度を或る程度確保し、スラグ−溶鋼境界面と溶鋼バルクとの間の界面張力の勾配を大きくすることで、溶鋼中に懸濁する酸化物の浮上・分離が促進されるとの知見が得られた。 That is, by ensuring a certain level of sulfur concentration in the molten steel and increasing the gradient of the interfacial tension between the slag-molten steel interface and the molten steel bulk, the floating and separation of oxides suspended in the molten steel are promoted. That knowledge was obtained.
そこで、或る特定の軸受鋼について硫黄の成分規格（Ｓ≦０．００４質量％）の範囲内で硫黄濃度を変化させて溶製し、連続鋳造により得られたブルーム鋳片を最終製品に圧延した後に最終製品から試料を切り出し、この試料の研磨面を顕微鏡観察して酸化物系非金属介在物の大きさを調査した。図１に調査結果を示す。尚、図１に示す縦軸の「予測最大径」とは、顕微鏡観察によって測定された酸化物系非金属介在物の大きさ別の分布図から、実際の分布図を予測し、予測した分布図における最大径である。これは、研磨面の顕微鏡観察によって観察される酸化物系非金属介在物は実際の大きさよりも小さく測定されるので、実際の大きさ及び分布を求めるために、顕微鏡による観察結果を統計学的に処理する手法であり、一般的に広く行われる手法である。当然のことながら、予測最大径は顕微鏡観察によって測定された最大径に比較して大きくなる。 Therefore, a certain bearing steel is melted by changing the sulfur concentration within the range of the sulfur component standard (S ≦ 0.004 mass%), and the bloom slab obtained by continuous casting is rolled into the final product. After that, a sample was cut out from the final product, and the polished surface of this sample was observed with a microscope to investigate the size of the oxide-based nonmetallic inclusions. The survey results are shown in FIG. Note that the “predicted maximum diameter” on the vertical axis shown in FIG. 1 is an estimated distribution by predicting an actual distribution map from the distribution map of oxide-based nonmetallic inclusions measured by microscopic observation. It is the maximum diameter in the figure. This is because the oxide-based non-metallic inclusions observed by microscopic observation of the polished surface are measured to be smaller than the actual size. Therefore, in order to obtain the actual size and distribution, the observation result by the microscope is statistically calculated. This is a technique that is generally performed widely. As a matter of course, the predicted maximum diameter is larger than the maximum diameter measured by microscopic observation.
図１に示すように、軸受鋼の硫黄濃度が高くなるほど、酸化物系非金属介在物の予測最大径は小さくなり、軸受鋼の硫黄濃度を０．００２０質量％以上確保することで、予測最大径は１５μｍ以下になることが確認できた。 As shown in FIG. 1, the higher the sulfur concentration of the bearing steel, the smaller the predicted maximum diameter of the oxide-based nonmetallic inclusions. By ensuring the sulfur concentration of the bearing steel of 0.0020% by mass or more, the predicted maximum It was confirmed that the diameter was 15 μm or less.
本発明に係る高清浄度軸受鋼は、これらの知見に基づいてなされたものであり、硫黄含有量が０．００２０質量％以上で且つ酸化物系非金属介在物の予測最大径が１５μｍ以下であることを特徴としている。 The high cleanliness bearing steel according to the present invention is made based on these findings, and the sulfur content is 0.0020% by mass or more and the predicted maximum diameter of the oxide-based nonmetallic inclusion is 15 μm or less. It is characterized by being.
硫黄含有量の上限は、その軸受鋼の成分規格の上限値とする。硫黄濃度が高いほど酸化物系非金属介在物は分離されやすいので、従って、目標とする硫黄濃度は、溶製対象の軸受鋼の成分規格上限値近傍とすることが好ましい。通常、軸受鋼の硫黄濃度規格には、下限値は設定されず、上限値は０．００５質量％程度であるので、０．００３〜０．００４質量を目標とすればよい。尚、軸受鋼には炭素鋼やクロムを含有する合金鋼など、種々存在するが、本発明は何れの鋼種の軸受鋼であっても適用することができる。 The upper limit of the sulfur content is the upper limit value of the component standard of the bearing steel. The higher the sulfur concentration, the easier the oxide-based non-metallic inclusions are separated. Therefore, the target sulfur concentration is preferably close to the component specification upper limit value of the bearing steel to be melted. Usually, the lower limit value is not set in the sulfur concentration standard of bearing steel, and the upper limit value is about 0.005% by mass, so 0.003 to 0.004 mass may be targeted. There are various types of bearing steel such as carbon steel and alloy steel containing chromium, but the present invention can be applied to any type of bearing steel.
次に、本発明に係る高清浄度軸受鋼の溶製方法について説明する。 Next, a method for melting high cleanliness bearing steel according to the present invention will be 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、この溶銑に対して脱硫処理を実施する。軸受鋼は低硫鋼であり、溶銑脱硫しないままでは溶製が困難であるからである。 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 desulfurization treatment is performed on this hot metal. This is because the bearing steel is a low-sulfur steel and is difficult to melt without hot metal desulfurization.
溶銑の脱硫方法としては、インペラーと呼ばれる攪拌子を溶銑に浸漬させ、回転するインペラーで溶銑を攪拌しながら溶銑上に添加したＣａＯ系脱硫剤を溶銑中に混合させて行う脱硫法や、ＣａＯ系脱硫剤やソーダ系脱硫剤をインジェクションランスを介して搬送用ガスとともに溶銑中に吹き込んで行う脱硫法、或いは、鉄被覆金属Ｍｇワイヤーを溶銑に高速度で供給して行う脱硫法など種々の脱硫方法が行われており、本発明においてはどの脱硫方法を用いても構わない。但し、次工程の転炉脱炭精錬工程を含め、その後の精錬工程での脱硫処理を避けるために、溶製対象の軸受鋼の硫黄成分規格値よりも低い値まで脱硫処理する。脱硫処理後、溶銑を次工程の転炉に搬送する。尚、溶銑段階において、製造コスト削減の観点から、脱燐処理や脱珪処理が広く行われているが、本発明においては、脱燐処理及び脱珪処理は実施しても実施しなくても、どちらでも構わない。 As a desulfurization method for hot metal, a desulfurization method in which a stirring bar called an impeller is immersed in hot metal, and a CaO-based desulfurizing agent added to the hot metal while stirring the hot metal with a rotating impeller is mixed into the hot metal, or a CaO type is used. Various desulfurization methods such as a desulfurization method in which a desulfurization agent or a soda-based desulfurization agent is blown into the hot metal together with a conveying gas through an injection lance, or a desulfurization method in which an iron-coated metal Mg wire is supplied to the hot metal at a high speed Any desulfurization method may be used in the present invention. However, in order to avoid the desulfurization process in the subsequent refining process including the converter decarburization refining process of the next process, the desulfurization process is performed to a value lower than the sulfur component standard value of the bearing steel to be melted. After desulfurization treatment, the hot metal is conveyed to the converter in the next process. In the hot metal stage, dephosphorization treatment and desiliconization treatment are widely performed from the viewpoint of manufacturing cost reduction. In the present invention, dephosphorization treatment and desiliconization treatment may or may not be performed. Either way.
脱硫した溶銑を転炉に装入して脱炭精錬を実施する。転炉精錬は生石灰などを媒溶剤として用いた通常の脱炭精錬を実施する。但し、この媒溶剤の添加量は、溶銑の予備脱燐処理に応じて設定する。つまり、予備脱燐処理により溶銑中燐濃度が最終製品レベル近傍まで低下している場合には生石灰の添加量を少なくし、溶銑中燐濃度が高い場合には大量の生石灰を添加する。そして、酸素ガスを上吹きまたは底吹きして溶銑の脱炭精錬を行う。溶製対象とする軸受鋼がクロムを含有する軸受鋼の場合には、転炉内にＦｅ−Ｃｒ合金などのクロム源を装入する。 The desulfurized hot metal is charged into the converter and decarburized. For converter refining, ordinary decarburization refining using quick lime as a solvent is carried out. However, the addition amount of this solvent is set according to the preliminary dephosphorization treatment of the hot metal. That is, the amount of quicklime added is reduced when the phosphorus concentration in the hot metal is lowered to near the final product level due to the preliminary dephosphorization treatment, and a large amount of quicklime is added when the phosphorus concentration in the hot metal is high. Then, degassing and refining of the hot metal is performed by blowing oxygen gas upward or bottom. When the bearing steel to be melted is a bearing steel containing chromium, a chromium source such as an Fe—Cr alloy is charged into the converter.
転炉にて脱炭精錬が終了したなら、得られた溶鋼を取鍋に出鋼する。出鋼時、転炉内から採取した溶鋼試料の硫黄分析値に照らし合わせ、溶鋼中の硫黄濃度が軸受鋼の硫黄濃度の規格上限値と離れていたならば、Ｆｅ−Ｓ合金を用いて硫黄分を増加させ、０．００２０質量％以上であって規格上限値近傍の値に調整する。Ｆｅ−Ｓ合金は必ずしも出鋼時に添加する必要はなく、次工程のＲＨ真空脱ガス装置の精錬前である限り、どの時点で添加しても構わないが、溶鋼中に懸濁した酸化物の浮上・分離を促進させるためには、酸化物の浮上時間を確保できることから、早い時期であるほど、つまり出鋼時または出鋼直後であることが好ましい。ＲＨ真空脱ガス装置の精錬前までに硫黄濃度の調整を完了する理由は、ＲＨ真空脱ガス装置における酸化物の浮上・分離効果を処理開始時から十分に得るためである。 When decarburization refining is completed in the converter, the obtained molten steel is taken out into a ladle. If the sulfur concentration in the molten steel deviates from the upper limit of the sulfur concentration of the bearing steel in light of the sulfur analysis value of the molten steel sample taken from the converter when the steel is produced, the sulfur can be reduced using the Fe-S alloy. The amount is increased to 0.0020% by mass or more and adjusted to a value near the upper limit of the standard. The Fe-S alloy does not necessarily need to be added at the time of steel production, and may be added at any time point as long as it is before refining of the RH vacuum degassing apparatus in the next step, but the oxide suspended in the molten steel In order to promote flotation / separation, it is possible to ensure the flotation time of the oxide, so that it is preferable that the earlier time, that is, the time at the time of steel extraction or immediately after the steel output. The reason for completing the adjustment of the sulfur concentration before the refining of the RH vacuum degassing apparatus is to sufficiently obtain the oxide flotation / separation effect in the RH vacuum degassing apparatus from the start of processing.
また、出鋼時、ＡｌやＳｉなどの強脱酸元素による溶鋼の脱酸処理を実施する。出鋼時に強脱酸元素を添加することで、脱酸により生成する酸化物の浮上・分離期間を長期間確保することができるので、溶鋼の清浄性を高めることが可能となる。 Moreover, deoxidation treatment of molten steel with strong deoxidation elements such as Al and Si is performed at the time of steel output. By adding a strong deoxidizing element at the time of steel output, it is possible to ensure a long period of floating and separation of oxides generated by deoxidation, so that the cleanliness of the molten steel can be improved.
出鋼時、溶鋼に巻き込まれて転炉内のスラグの一部が取鍋内に流出し、取鍋内の溶鋼上に滞留する。清浄鋼を得るにはこのスラグの酸素ポテンシャルを低くすることが望ましく、従って、出鋼時または出鋼直後に取鍋内にスラグ還元剤を添加し、スラグを還元することが好ましい。スラグ還元剤としては、Ａｌ、Ｓｉ、Ｃａ、Ｍｇの１種または２種以上の強還元剤を含有するものであれば、例えば金属Ａｌ単体であってもまた金属Ａｌと生石灰などの媒溶剤との混合体であっても構わない。特に好適なスラグ還元剤としては、安価であり経済性に優れることから金属Ａｌを５０質量％程度含有するアルミドロス（「Ａｌ灰」とも呼ぶ）を用いることが好ましい。 At the time of steel removal, a part of the slag in the converter is drawn into the ladle and flows out into the ladle and stays on the molten steel in the ladle. In order to obtain clean steel, it is desirable to reduce the oxygen potential of this slag. Therefore, it is preferable to reduce the slag by adding a slag reducing agent into the ladle at the time of or immediately after steelmaking. As a slag reducing agent, as long as it contains one or more strong reducing agents of Al, Si, Ca, and Mg, for example, even if it is a metallic Al alone, a metallic solvent such as metallic Al and quick lime, It may be a mixture of As a particularly suitable slag reducing agent, it is preferable to use aluminum dross (also referred to as “Al ash”) containing about 50% by mass of metal Al because it is inexpensive and excellent in economic efficiency.
その後、取鍋を次工程のＲＨ真空脱ガス装置に搬送する。ＲＨ真空脱ガス装置は、真空槽の下部に配置された上昇側浸漬管及び下降側浸漬管を取鍋内の溶鋼中に浸漬させ、真空槽内を減圧するとともに上昇側浸漬管にＡｒガスを還流用ガスとして吹き込み、環流用ガスによるガスリフトポンプ効果によって取鍋内の溶鋼を真空槽に導入し、真空槽内で溶鋼を減圧化に曝し、その後、下降側浸漬管を介して取鍋に溶鋼を戻すことで、溶鋼に真空脱ガス精錬を施す装置である。取鍋から真空槽内に流入し、真空槽内から取鍋に戻る溶鋼の流れを「環流」と呼んでいる。 Then, a ladle is conveyed to RH vacuum degassing apparatus of the next process. The RH vacuum degassing device immerses the ascending side dip tube and the descending side dip tube disposed in the lower part of the vacuum chamber in the molten steel in the pan, depressurizes the inside of the vacuum chamber, and supplies Ar gas to the ascending side dip tube. Blowing in as a reflux gas, the molten steel in the ladle is introduced into the vacuum tank by the gas lift pump effect of the reflux gas, and the molten steel is exposed to decompression in the vacuum tank, and then the molten steel is introduced into the ladle via the descending side dip tube. Is a device that applies vacuum degassing to the molten steel. The flow of molten steel that flows from the ladle into the vacuum chamber and returns to the ladle from inside the vacuum chamber is called “circular flow”.
このＲＨ真空脱ガス装置において、水素などのガス成分が除去されるに十分な時間以上、溶鋼を環流させたなら、必要に応じて化学成分の微調整を実施し、所定の化学成分組成の軸受鋼として仕上げる。ＲＨ真空脱ガス装置は、数ある真空脱ガス設備のなかでも特に溶鋼の攪拌力が強く、溶鋼中に懸濁した酸化物の浮上・分離が促進される。得られた溶鋼を、次工程の連続鋳造工程に搬送し、ブルームなどの鋳片に鋳造する。 In this RH vacuum degassing apparatus, if the molten steel is circulated for a time sufficient to remove a gas component such as hydrogen, fine adjustment of the chemical component is performed as necessary, and a bearing having a predetermined chemical component composition Finish as steel. Among the various vacuum degassing facilities, the RH vacuum degassing apparatus has particularly strong stirring power for molten steel, and promotes the floating and separation of oxides suspended in the molten steel. The obtained molten steel is transported to the next continuous casting step and cast into a slab such as bloom.
以上説明したように、本発明によれば、軸受鋼の硫黄含有量を０．００２０質量％以上とするので、軸受鋼の溶製工程において、スラグ−溶鋼境界面と溶鋼バルクとの間の界面張力に大きな勾配が発生し、この界面張力の勾配によって溶鋼中に懸濁する酸化物はスラグ側に移行しようとするので、溶鋼中に懸濁する酸化物の浮上・分離が促進され、その結果、酸化物系非金属介在物の予測最大径が１５μｍ以下である、酸化物系非金属介在物が少なく、高性能で且つ高い信頼性を有する高清浄度軸受鋼を得ることができる。 As described above, according to the present invention, the sulfur content of the bearing steel is set to 0.0020% by mass or more, so in the melting process of the bearing steel, the interface between the slag-molten steel interface and the molten steel bulk. A large gradient occurs in the tension, and the oxide suspended in the molten steel tends to move to the slag side due to the gradient in the interfacial tension, which promotes the levitation and separation of the oxide suspended in the molten steel. In addition, it is possible to obtain a high cleanliness bearing steel having high performance and high reliability with a small predicted oxide nonmetallic inclusion having a predicted maximum diameter of 15 μm or less, a small number of oxide nonmetallic inclusions.
Claims (1)
高炉から出銑された溶銑を溶製対象の軸受鋼の硫黄成分規格値よりも低い値まで予備脱硫処理し、予備脱硫処理された溶銑を転炉にて脱炭精錬して溶鋼とし、
該溶鋼の転炉から取鍋への出鋼時に、溶鋼にＡｌを添加して溶鋼の脱酸処理を行うとともに、溶鋼の硫黄濃度を０．００２０質量％以上であって前記硫黄成分規格値の上限値よりも０．００２質量％低い値から前記硫黄成分規格値の上限値までの値に調整し、
且つ、出鋼時または出鋼直後に取鍋内にスラグ還元剤を添加して取鍋内のスラグを還元し、
その後、溶鋼中の硫黄濃度が０．００２０質量％以上であって前記硫黄成分規格値の上限値よりも０．００２質量％低い値から前記硫黄成分規格値の上限値までの値に調整された溶鋼を、ＲＨ真空脱ガス装置にて精錬して所定の化学成分組成の軸受鋼に仕上げることを特徴とする、高清浄度軸受鋼の溶製方法。 A method for melting high cleanliness bearing steel having a sulfur content of 0.0020 mass% or more and a predicted maximum diameter of oxide-based nonmetallic inclusions of 15 μm or less,
The hot metal discharged from the blast furnace is predesulfurized to a value lower than the sulfur component standard value of the bearing steel to be melted, and the predesulfurized hot metal is decarburized and refined into a molten steel in a converter,
When the molten steel is discharged from the converter to the ladle, Al is added to the molten steel to deoxidize the molten steel, and the sulfur concentration of the molten steel is 0.0020% by mass or more, and the sulfur component standard value Adjust to a value from 0.002% by mass lower than the upper limit to the upper limit of the sulfur component standard value ,
In addition, the slag reducing agent is added to the ladle at the time of or immediately after the steel is extracted to reduce the slag in the ladle,
Thereafter, the sulfur concentration in the molten steel was 0.0020% by mass or more and was adjusted to a value from the value lower by 0.002% by mass than the upper limit value of the sulfur component standard value to the upper limit value of the sulfur component standard value . the molten steel, wherein the finish by refining in RH vacuum degassing apparatus to the bearing steel of a predetermined chemical composition, method smelting of highly clean bearing steel.
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