JP2010196114A - Method for producing bearing steel - Google Patents
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本発明は、清浄性が高く、転動疲労寿命特性に優れた軸受鋼の製造方法に関するものである。 The present invention relates to a method for producing a bearing steel having high cleanliness and excellent rolling fatigue life characteristics.
ベアリング、ローラなどの用途で使用される軸受鋼は、非常に厳しい転動疲労寿命特性が要求されており、そのためには、鋼中の非金属介在物を微細且つ少量に制御する技術が必須となっている。尚、現在、軸受鋼の製造プロセスとしては、転炉或いは電気炉で溶製した溶鋼を出鋼時にＡｌで脱酸し、先ず、アーク加熱機能を有するＬＦ炉（「取鍋精錬炉」ともいう）でフラックスと攪拌して非金属介在物の除去を図り、次いで、ＲＨ真空脱ガス炉でガス成分を除去するとともに更なる非金属介在物の除去を図り、その後、連続鋳造機で鋳造するという製造工程が一般的に行われている。 Bearing steels used in applications such as bearings and rollers are required to have extremely severe rolling fatigue life characteristics. To that end, technology to control non-metallic inclusions in steel to a minute and small amount is essential. It has become. Currently, as a bearing steel manufacturing process, molten steel melted in a converter or electric furnace is deoxidized with Al at the time of steel production, and first, an LF furnace having an arc heating function (also referred to as a “ladder refining furnace”). ) To stir with the flux to remove non-metallic inclusions, then remove the gas components in the RH vacuum degassing furnace and further remove non-metallic inclusions, and then cast with a continuous casting machine The manufacturing process is generally performed.
転動疲労寿命特性に影響する鋼中の非金属介在物としては、酸化物系非金属介在物（以下、単に「介在物」と記す）が大半を占めており、その起源は、脱酸剤として添加したＡｌと溶鋼中の溶存酸素とが反応して生成されるＡｌ2Ｏ3介在物であることが知られている。そのために、軸受鋼の転動疲労寿命特性を改善するべく、鋼中のＡｌ2Ｏ3介在物を低減する技術が多数提案されている。 Most non-metallic inclusions in steel that affect the rolling fatigue life characteristics are oxide-based non-metallic inclusions (hereinafter simply referred to as “inclusions”). It is known that Al 2 O 3 inclusions are produced by the reaction of Al added as dissolved with dissolved oxygen in molten steel. For this purpose, many techniques for reducing Al 2 O 3 inclusions in steel have been proposed in order to improve the rolling fatigue life characteristics of bearing steel.
例えば、特許文献１には、Ａｌ、Ａｌ合金及び／またはＳｉ合金を脱酸剤とする溶鋼の脱酸において、脱酸剤と同時にＣａＯ−ＳｉＯ2系フラックスを溶鋼に添加して脱酸する脱酸方法が提案されている。この技術は、脱酸剤と同時にＣａＯ−ＳｉＯ2系フラックスを溶鋼に添加すると、脱酸反応で生成するＡｌ2Ｏ3が迅速にＣａＯ−ＳｉＯ2系フラックスに吸収され、介在物がＣａＯ−ＳｉＯ2−Ａｌ2Ｏ3系の介在物に形態制御され、浮上・分離が促進されるという技術である。 For example, in Patent Document 1, in deoxidation of molten steel using Al, Al alloy and / or Si alloy as a deoxidizer, deoxidation is performed by adding a CaO—SiO 2 flux to the molten steel simultaneously with the deoxidizer. Acid methods have been proposed. In this technique, when a CaO—SiO 2 flux is added to a molten steel simultaneously with a deoxidizer, Al 2 O 3 produced by the deoxidation reaction is quickly absorbed by the CaO—SiO 2 flux, and inclusions are CaO—SiO 2. This is a technique in which the form is controlled by 2- Al 2 O 3 inclusions, and levitation and separation are promoted.
また、特許文献２には、転炉で溶製された溶鋼を取鍋に出鋼する際に、脱酸剤及び合金鉄、更に、質量比でＳｉＯ2：１０％以下、ＭｇＯ：６〜１５％未満、Ａｌ2Ｏ3：２５〜４５％、ＣａＯ：３５〜６０％を含有するスラグが取鍋内溶鋼上に形成されるようにフラックスを添加し、次いで、前記フラックスと溶鋼とを混合・撹拌し、しかる後、真空脱ガス処理による溶鋼撹拌処理を行うことを特徴とする清浄鋼の精錬方法が提案されている。この技術は、生石灰（ＣａＯ）をフラックスとして添加することにより生成されるＣａＯ−Ａｌ2Ｏ3系介在物は低融点化するものの粗大化し、却って転動疲労寿命特性を劣化させるので、全ての介在物をＡｌ2Ｏ3−ＭｇＯ系またはＡｌ2Ｏ3介在物として微細化させ、この介在物を、前記フラックスと溶鋼とを混合・撹拌することによってフラックスに吸収させるという技術である。 Further, Patent Document 2, when tapping the molten steel that is melted in a converter furnace ladle, a deoxidizer and ferroalloy, further, SiO 2 in a weight ratio: 10% or less, MgO: 6 to 15 %, Al 2 O 3 : 25 to 45%, CaO: 35 to 60%, a flux is added so that the slag is formed on the molten steel in the ladle, and then the flux and the molten steel are mixed. There has been proposed a method for refining clean steel characterized by stirring and then performing molten steel stirring by vacuum degassing. In this technique, CaO—Al 2 O 3 inclusions produced by adding quicklime (CaO) as a flux are coarsened although the melting point is lowered, and on the contrary, the rolling fatigue life characteristics are deteriorated. This is a technique in which a material is refined as an Al 2 O 3 —MgO-based or Al 2 O 3 inclusion, and the inclusion is absorbed into the flux by mixing and stirring the flux and molten steel.
また、特許文献３には、軸受鋼の成分組成からなる溶鋼を、塩基度が５以上のＣａＯ−Ａｌ2Ｏ3−ＭｇＯ系スラグを用いて精錬し、得られた溶鋼にＡｌを脱酸剤として添加することを特徴とする、転動疲労寿命特性に優れる軸受鋼の製造方法が提案されている。この技術は、介在物の形態をＡｌ2Ｏ3−ＭｇＯ系介在物とし、Ａｌ2Ｏ3−ＭｇＯ系介在物は溶鋼との界面エネルギーが小さく、クラスター化せず、介在物は、大きさが３μｍ以下の微細介在物となり、転動疲労寿命特性を劣化することがないとする技術である。 Patent Document 3 discloses that a molten steel having a component composition of bearing steel is refined using CaO—Al 2 O 3 —MgO-based slag having a basicity of 5 or more, and Al is added to the obtained molten steel as a deoxidizer. There has been proposed a method for producing a bearing steel excellent in rolling fatigue life characteristics, characterized by being added as In this technology, the inclusions are made of Al 2 O 3 —MgO-based inclusions, and the Al 2 O 3 —MgO-based inclusions have low interfacial energy with molten steel, do not cluster, and the inclusions have a size of This is a technique that does not deteriorate the rolling fatigue life characteristics because it becomes a fine inclusion of 3 μm or less.
上記に説明したように、軸受鋼の転動疲労寿命特性を向上させるための手段が多数提案されており、転動疲労寿命特性は改善されてきているが、未だ改善の余地はある。また、フラックスを添加し、このフラックス中に介在物を吸収させる技術では、例えば特許文献３に示すように、実操業においては、フラックスに、フラックスの滓化促進剤としてＣａＦ2（蛍石）などのフッ素源を添加する場合が多く、フッ素源を添加した場合には、取鍋耐火物の溶損が激しく、また、スラグからのフッ素（Ｆ）の溶出による環境への影響もあり、スラグのリサイクル利用が阻害されるという問題がある。 As described above, many means for improving the rolling fatigue life characteristics of bearing steel have been proposed and the rolling fatigue life characteristics have been improved, but there is still room for improvement. Further, in the technique of adding a flux and absorbing inclusions in the flux, as shown in, for example, Patent Document 3, in actual operation, as a flux hatching accelerator, CaF 2 (fluorite), etc. Fluorine source is often added, and when the fluorine source is added, the ladle refractory material is severely damaged, and there is also an environmental impact due to the elution of fluorine (F) from the slag. There is a problem that recycling is hindered.
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、ＣａＦ2などのフッ素源を含有しないフラックスを用いて、鋼中の介在物を微細化すると同時に介在物個数を低減し、清浄性が高く、転動疲労寿命特性に優れた軸受鋼を製造する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 thereof is to reduce the number of inclusions at the same time as the inclusions in the steel are refined by using a flux not containing a fluorine source such as CaF 2. Another object of the present invention is to provide a method for producing bearing steel having high cleanliness and excellent rolling fatigue life characteristics.
上記課題を解決するための本発明に係る軸受鋼の製造方法は、転炉または電気炉で溶製された溶鋼を収容する取鍋内に、フッ素源を実質的に含有しないＣａＯ−ＳｉＯ2系フラックスを添加し、次いで、大気下において、Ａｌにより脱酸された溶鋼と前記フラックスとを攪拌用ガスの溶鋼中への吹き込みによって攪拌し、該溶鋼のトータル酸素濃度が０．００３０質量％以下となった後に、下記の（１）で定義される［％Ｃａ］effが０．０００３質量％以上０．００１０質量％以下の範囲となるように溶鋼にＣａを添加し、その後、真空脱ガス装置において溶鋼を減圧下で精錬することを特徴とするものである。
[%Ca]eff=[質量%Ca]-(0.18+130×[質量%Ca])×[質量%T.O] …(1)
但し、（１）式において、［質量％Ｃａ］は溶鋼中のＣａ濃度（質量％）、［質量％Ｔ．Ｏ］は溶鋼中のトータル酸素濃度（質量％）である。
In order to solve the above problems, a bearing steel manufacturing method according to the present invention includes a CaO—SiO 2 system that does not substantially contain a fluorine source in a ladle that contains molten steel melted in a converter or an electric furnace. Flux is added, and then, in the atmosphere, the molten steel deoxidized by Al and the flux are stirred by blowing a stirring gas into the molten steel, and the total oxygen concentration of the molten steel is 0.0030% by mass or less. After that, Ca is added to the molten steel so that [% Ca] eff defined in the following (1) is in the range of 0.0003 mass% or more and 0.0010 mass% or less, and then a vacuum degassing apparatus. Is characterized by refining molten steel under reduced pressure.
[% Ca] eff = [mass% Ca]-(0.18 + 130 × [mass% Ca]) × [mass% TO] (1)
However, in the formula (1), [mass% Ca] is the Ca concentration (mass%) in the molten steel, and [mass% T.M. O] is the total oxygen concentration (mass%) in the molten steel.
本発明によれば、溶鋼のトータル酸素濃度に応じた所定量のＣａを添加して溶鋼中のＡｌ2Ｏ3介在物をＣａＯ−Ａｌ2Ｏ3系介在物に強制的に組成変更するので、Ａｌ2Ｏ3介在物に比べて溶鋼からの浮上・分離が促進され、ＣａＦ2などのフッ素源を含有しないＣａＯ−ＳｉＯ2系フラックスを用いても、フラックスによる鋼浴中のＣａＯ−Ａｌ2Ｏ3系介在物の吸収が促進されるとともに、残存するＣａＯ−Ａｌ2Ｏ3系介在物はＡｌ2Ｏ3介在物のようにクラスター化せず、小サイズのままであるので、清浄度の高い、転動疲労寿命特性に優れた軸受鋼が製造可能となる。また、フラックスはフッ素源を含有しないので、取鍋耐火物の溶損が抑制されるとともに、フラックが溶融して形成されるスラグからはフッ素が溶出せず、スラグのリサイクル利用を阻害する原因が解消され、スラグのリサイクル利用が促進される。 According to the present invention, a predetermined amount of Ca corresponding to the total oxygen concentration of the molten steel is added to forcibly change the composition of Al 2 O 3 inclusions in the molten steel into CaO—Al 2 O 3 inclusions. Floating / separation from molten steel is promoted compared to Al 2 O 3 inclusions, and even if a CaO—SiO 2 flux containing no fluorine source such as CaF 2 is used, CaO—Al 2 O in the steel bath by the flux is used. Absorption of 3 type inclusions is promoted, and the remaining CaO—Al 2 O 3 type inclusions are not clustered like Al 2 O 3 inclusions and remain in a small size, so the cleanliness is high. Thus, it becomes possible to produce a bearing steel having excellent rolling fatigue life characteristics. In addition, since the flux does not contain a fluorine source, melting of the ladle refractory is suppressed, and fluorine does not elute from the slag formed by melting the flack, which hinders recycling of slag. It will be eliminated and recycling of slag will be promoted.
以下、本発明を具体的に説明する。 The present invention will be specifically described below.
本発明が適用対象とする軸受鋼は、JIS G 4805で規定されるＳＵＪ１〜ＳＵＪ５などの高炭素クロム鋼軸受鋼、ＳＣＲ４２０、ＳＣＭ４２０などの浸炭軸受鋼、ＳＵＳ４４０Ｃなどの耐食・耐熱軸受鋼である。 Bearing steels to which the present invention is applied are high carbon chromium steel bearing steels such as SUJ1 to SUJ5 defined by JIS G 4805, carburized bearing steels such as SCR420 and SCM420, and corrosion-resistant and heat-resistant bearing steels such as SUS440C.
本発明においては、これらの軸受鋼を、転炉または電気炉で溶鋼を溶製し、この溶鋼を取鍋に出鋼し、取鍋内の溶鋼上にＣａＦ2などのフッ素源を含有しないＣａＯ−ＳｉＯ2系フラックスを添加し、このフラックスと、Ａｌで脱酸された溶鋼とを攪拌用ガスの吹き込みにより攪拌して、スラグ−メタル界面反応により鋼浴中の介在物を溶融したフラックス中に吸収させ、その後、該溶鋼のトータル酸素濃度が０．００３０質量％以下となった後に、溶鋼にＣａを添加してＡｌ2Ｏ3介在物をＣａＯ−Ａｌ2Ｏ3系介在物に強制的に改質し、その後、更に真空脱ガス装置における減圧化での精錬による攪拌で鋼浴中の介在物を凝集・合体させて除去する工程を経て製造する。 In the present invention, these bearing steels are produced by melting molten steel in a converter or electric furnace, taking out the molten steel into a ladle, and CaO not containing a fluorine source such as CaF 2 on the molten steel in the ladle. -A SiO 2 flux is added, and this flux and molten steel deoxidized with Al are stirred by blowing a stirring gas, and the inclusions in the steel bath are melted by the slag-metal interface reaction into the melted flux. Then, after the total oxygen concentration of the molten steel becomes 0.0030% by mass or less, Ca is added to the molten steel to force the Al 2 O 3 inclusions into CaO—Al 2 O 3 inclusions. Then, it is manufactured through a process of removing inclusions in the steel bath by agglomeration and coalescence by agitation by refining at reduced pressure in a vacuum degassing apparatus.
上記工程を経る本発明において、フラックスが溶融して形成されるスラグと溶鋼とのガス吹き込みによる攪拌、及び溶鋼へのＣａの添加は、アーク加熱機能を有するＬＦ炉や、アーク加熱機能は有さないものの、溶鋼に攪拌用ガスを吹き込んで溶鋼とスラグとを攪拌することのできるガスインジェクション装置を用いて実施する。また、溶鋼をＡｌで脱酸する時期は、転炉からの出鋼時や出鋼後のフッ素源を含有しないＣａＯ−ＳｉＯ2系フラックスを添加する以前であっても、また、フッ素源を含有しないＣａＯ−ＳｉＯ2系フラックスを添加した後のフラックスと溶鋼との攪拌処理中であっても、どちらでも構わない。また更に、溶鋼にＣａを添加する期間、或いは、溶鋼へのＣａ添加を完了した後も、ガス吹き込み攪拌によって前記スラグと溶鋼との攪拌を行っても構わない。尚、ＬＦ炉とは、取鍋内に昇降可能なアーク電極のみならず、原材料や造滓剤を添加する装置を有し、取鍋底部に設置されるポーラス煉瓦或いはインジェクションランスから攪拌用ガスを吹き込み、Ａｒガス雰囲気などの不活性雰囲気で原材料及び造滓剤などを添加し、溶鋼を精錬する設備である。また、ガスインジェクション装置とは、アーク加熱機能を有していないＬＦ炉相当の設備である。 In the present invention that has undergone the above-described steps, the slag formed by melting the flux and the stirring by blowing the molten steel and the addition of Ca to the molten steel have an LF furnace having an arc heating function and an arc heating function. Although there is not, it implements using the gas injection apparatus which can blow in the gas for stirring into molten steel, and can stir molten steel and slag. In addition, the time for deoxidizing the molten steel with Al is before the addition of the CaO-SiO 2 flux that does not contain the fluorine source at the time of steel output from the converter or after the steel output. even during the stirring process of the flux and molten steel after the addition of CaO-SiO 2-based flux that does not, does not matter either. Furthermore, the slag and molten steel may be stirred by gas blowing and stirring even after the Ca is added to the molten steel or after the Ca addition to the molten steel is completed. The LF furnace has not only an arc electrode that can be moved up and down in the ladle, but also a device for adding raw materials and a slagging agent. The stirring gas is supplied from porous brick or injection lance installed at the bottom of the ladle. It is a facility for refining molten steel by blowing and adding raw materials and a faux-forming agent in an inert atmosphere such as an Ar gas atmosphere. The gas injection device is equipment equivalent to an LF furnace that does not have an arc heating function.
溶鋼中の介在物をフラックスによって形態制御するとともに、このフラックスに介在物を吸収させる技術は、軸受鋼などの高清浄度鋼を製造する際の極めて有効な手段の１つである。但し、溶鋼とスラグとの界面反応を活性化するには、スラグに液相部を形成させることが不可欠であり、そのために、フラックスに滓化促進剤としてフッ素源を添加する、具体的には、５〜２５質量％のＣａＦ2を添加して、液相部を早期に且つ安定して形成させる技術は良く知られている（特許文献３を参照）。しかしながら、本発明では、ＣａＦ2などのフッ素源を実質的に含有しないＣａＯ−ＳｉＯ2系フラックスを用いており、フッ素源を含有しないフラックスであってもスラグ−メタル間反応を活性化させるために、溶鋼中にＣａを添加する。尚、フッ素源を実質的に含有しないＣａＯ−ＳｉＯ2系フラックスとは、不純物としてのフッ素（Ｆ）は含有することはあっても、意図的にＣａＦ2などのフッ素源が添加されていないフラックスという意味である。 A technique for controlling the form of inclusions in molten steel with a flux and absorbing the inclusions in the flux is one of extremely effective means for producing high cleanliness steel such as bearing steel. However, in order to activate the interfacial reaction between molten steel and slag, it is indispensable to form a liquid phase part in the slag, and for that purpose, a fluorine source is added to the flux as a hatching accelerator, specifically, A technique for adding 5 to 25% by mass of CaF 2 to form a liquid phase part early and stably is well known (see Patent Document 3). However, in the present invention, a CaO—SiO 2 flux that does not substantially contain a fluorine source such as CaF 2 is used. In order to activate the slag-metal reaction even if the flux does not contain a fluorine source. Then, Ca is added to the molten steel. The CaO—SiO 2 flux that does not substantially contain a fluorine source is a flux in which fluorine (F) as an impurity is contained but a fluorine source such as CaF 2 is not intentionally added. It means that.
Ａｌ脱酸直後の溶鋼は、溶鋼中の溶存酸素と、脱酸剤として添加されるＡｌとが反応して、鋼浴中に大量のＡｌ2Ｏ3介在物を含有する。本発明は、この溶鋼にＣａを添加することにより、Ａｌ2Ｏ3介在物をＣａＯ−Ａｌ2Ｏ3系介在物に強制的に形態変化させる。鋼浴中の介在物がＣａＯ−Ａｌ2Ｏ3系介在物に改質されることで、Ａｌ2Ｏ3介在物に比べて溶鋼からの浮上・分離が促進され、フラックスによる介在物の吸収が進行し、溶鋼の清浄度が高くなり、転動疲労寿命特性が向上する。 The molten steel immediately after Al deoxidation contains a large amount of Al 2 O 3 inclusions in the steel bath as a result of reaction between dissolved oxygen in the molten steel and Al added as a deoxidizer. In the present invention, by adding Ca to this molten steel, the Al 2 O 3 inclusions are forcibly changed into CaO—Al 2 O 3 inclusions. By improving the inclusions in the steel bath to CaO-Al 2 O 3 inclusions, the floatation / separation from the molten steel is promoted compared to the Al 2 O 3 inclusions, and the inclusions are absorbed by the flux. As it progresses, the cleanliness of the molten steel increases and the rolling fatigue life characteristics improve.
溶鋼にＣａを添加する方法は、Ｃａ−Ｓｉ合金粒或いはＣａ−Ｆｅ合金粒などの外周を薄鋼板で覆った鉄被覆Ｃａ合金ワイヤーを所定速度で溶鋼中に添加する方法や、粉体状のＣａ−Ｓｉ合金或いはＣａ−Ｆｅ合金を、不活性ガスとともに鉄浴中に吹き込む方法などが知られており、本発明においても、これらの方法を用いて添加する。 The method of adding Ca to the molten steel includes a method of adding an iron-coated Ca alloy wire whose outer periphery is covered with a thin steel plate, such as Ca—Si alloy grains or Ca—Fe alloy grains, into the molten steel at a predetermined rate, A method of blowing a Ca—Si alloy or a Ca—Fe alloy into an iron bath together with an inert gas is known. In the present invention, these methods are used for addition.
ところで、軸受鋼に対してＣａを添加する技術は、快削性を必要とする軸受鋼においては、ＣａＳ、ＭｎＳなどの硫化物を生成させる目的で、一般的に行われている。しかしながら、Ｃａを多量に添加するとＣａＯ−Ａｌ2Ｏ3系介在物の低融点化に伴う凝集・合体の進行により、１００μｍを超える巨大な介在物が溶鋼中に形成され、この巨大介在物が連続鋳造工程で鋳片の凝固シェルに捕捉されると、転動疲労寿命特性を大きく損なうことになる。 By the way, the technique which adds Ca with respect to bearing steel is generally performed in order to produce sulfides, such as CaS and MnS, in the bearing steel which requires free-cutting property. However, when a large amount of Ca is added, a large inclusion exceeding 100 μm is formed in the molten steel due to the progress of aggregation and coalescence accompanying the lower melting point of the CaO—Al 2 O 3 inclusion, and this huge inclusion is continuously formed. If caught in the solidified shell of the slab during the casting process, the rolling fatigue life characteristics will be greatly impaired.
このような理由から、転動疲労寿命特性を要求される軸受鋼では、Ｃａを添加しない製造方法が一般的である（特許文献２及び特許文献３を参照）。 For these reasons, in bearing steels that require rolling fatigue life characteristics, a manufacturing method in which Ca is not added is common (see Patent Document 2 and Patent Document 3).
本発明においては、上記のＣａＯ−Ａｌ2Ｏ3系介在物の低融点化に伴う凝集・合体に起因する問題を回避するために、溶鋼にＣａを添加する時期及び添加量を、下記に示すように適正な範囲に規定する。 In the present invention, in order to avoid problems caused by aggregation and coalescence associated with the lowering of the melting point of the CaO-Al 2 O 3 inclusions, the timing and amount of Ca added to the molten steel are shown below. It is specified in an appropriate range.
即ち、Ｃａの添加時期はＡｌによる脱酸後とし、しかも、添加時のＡｌ2Ｏ3介在物の総量を抑制する観点から、また更には、添加時のＣａの酸化度合を抑制する観点から、溶鋼中のトータル酸素濃度が０．００３０質量％以下となった後とする。ここで、溶鋼中のトータル酸素濃度とは、溶鋼中に介在物として含有される酸素と、溶鋼中に溶解して存在する溶存酸素との合計値である。但し、Ａｌは酸素との親和力が強く、Ａｌ脱酸後のトータル酸素はほとんどが介在物として含有される酸素である。 That is, Ca is added after deoxidation with Al, and from the viewpoint of suppressing the total amount of Al 2 O 3 inclusions at the time of addition, and further from the viewpoint of suppressing the degree of oxidation of Ca at the time of addition, After the total oxygen concentration in the molten steel becomes 0.0030 mass% or less. Here, the total oxygen concentration in the molten steel is a total value of oxygen contained as inclusions in the molten steel and dissolved oxygen existing by being dissolved in the molten steel. However, Al has a strong affinity for oxygen, and the total oxygen after Al deoxidation is mostly oxygen contained as inclusions.
また、Ｃａは以下の理由から多量に添加し過ぎないことが必要である。 Moreover, it is necessary not to add Ca too much for the following reasons.
本発明者らは、容量が３０ｋｇの溶解炉を用い、未脱酸の軸受鋼成分の溶鋼にフッ素源を含有しないＣａＯ−ＳｉＯ2系フラックスを上置きし、次いで、金属Ａｌを添加して脱酸した後、溶鋼中トータル酸素濃度が０．００３０質量％以下になった以降、溶鋼に、添加量を変えてＣａを添加し、その後、３０分の真空処理を施した際の溶鋼中介在物の組成及び介在物サイズの分布を調査する試験を実施した。 The inventors used a melting furnace with a capacity of 30 kg, placed a CaO—SiO 2 flux not containing a fluorine source on the molten steel of the non-deoxidized bearing steel component, and then added metal Al to remove it. After acidification, the total oxygen concentration in the molten steel becomes 0.0030% by mass or less, and then Ca is added to the molten steel while changing the addition amount, and then the inclusions in the molten steel when vacuum treatment is performed for 30 minutes. A study was conducted to investigate the composition and inclusion size distribution.
その結果、Ｃａ添加量が多い場合には、介在物組成はＣａＯ・Ａｌ2Ｏ3〜２ＣａＯ・Ａｌ2Ｏ3組成の融点の低い介在物となり、その最大径は５０μｍ以上であり、粗大な介在物が多く見られた。これに対して、Ｃａ添加量を適度に抑えた試験では、介在物組成はＣａＯ・６Ａｌ2Ｏ3〜ＣａＯ・２Ａｌ2Ｏ3組成となっており、その最大径は２０μｍ以下と小型であった。 As a result, when the amount of Ca added is large, the inclusion composition becomes inclusions with a low melting point of CaO · Al 2 O 3 to 2CaO · Al 2 O 3 composition, and the maximum diameter is 50 μm or more, which is coarse inclusions. Many things were seen. On the other hand, in the test in which the Ca addition amount was moderately suppressed, the inclusion composition was CaO · 6Al 2 O 3 to CaO · 2Al 2 O 3 , and the maximum diameter was as small as 20 μm or less. .
一方、Ｃａ添加量が少ない場合には、介在物組成は、一部にＣａＯ・６Ａｌ2Ｏ3組成が見られたものの、大半はＡｌ2Ｏ3のままであった。 On the other hand, if the Ca addition amount is small, inclusions composition, although CaO · 6Al 2 O 3 composition was observed to some, the majority remained Al 2 O 3.
本発明者らは、これらの結果をＣａ濃度及びトータル酸素濃度と関連付けして詳細調査し、その結果、介在物の微細化及び介在物の個数低下を達成する条件として、図１に示すＣａ添加量の適正範囲を得た。 The present inventors investigated these results in detail in association with the Ca concentration and the total oxygen concentration. As a result, as a condition for achieving the refinement of inclusions and the decrease in the number of inclusions, the Ca addition shown in FIG. A reasonable range of quantities was obtained.
つまり、Ｃａの添加時期を溶鋼のトータル酸素濃度が０．００３０質量％以下となった以降とするとともに、下記の（１）で定義される［％Ｃａ］effが０．０００３質量％以上０．００１０質量％以下の範囲となるようにＣａの添加量を調整することである。
[%Ca]eff=[質量%Ca]-(0.18+130×[質量%Ca])×[質量%T.O] …(1)
但し、（１）式において、［質量％Ｃａ］は溶鋼中のＣａ濃度（質量％）、［質量％Ｔ．Ｏ］は溶鋼中のトータル酸素濃度（質量％）である。
That is, the timing of Ca addition is after the total oxygen concentration of the molten steel becomes 0.0030 mass% or less, and [% Ca] eff defined by the following (1) is 0.0003 mass% or more and 0.0. It is to adjust the addition amount of Ca so that it may become the range of 0010 mass% or less.
[% Ca] eff = [mass% Ca]-(0.18 + 130 × [mass% Ca]) × [mass% TO] (1)
However, in the formula (1), [mass% Ca] is the Ca concentration (mass%) in the molten steel, and [mass% T.M. O] is the total oxygen concentration (mass%) in the molten steel.
上記に示す組成は、Ｃａ添加直後の組成であり、本発明においてはその後に真空脱ガス装置にて減圧下で精錬を行うので、この減圧下での精錬により蒸気圧の高いＣａはほとんどが溶鋼中から蒸発してしまうので、前述した低融点介在物の凝集・合体に起因する巨大介在物の生成も抑制することができる。つまり、介在物組成をＣａＯ・６Ａｌ2Ｏ3〜ＣａＯ・２Ａｌ2Ｏ3に維持することができる。 The composition shown above is a composition immediately after the addition of Ca. In the present invention, since refining is performed under reduced pressure in a vacuum degassing apparatus after that, most of the Ca having a high vapor pressure is obtained by refining under reduced pressure. Since it evaporates from the inside, it is possible to suppress the formation of giant inclusions resulting from the aggregation and coalescence of the low melting point inclusions described above. In other words, it is possible to maintain the composition of inclusions to CaO · 6Al 2 O 3 ~CaO · 2Al 2 O 3.
以上説明したように、本発明によれば、溶鋼のトータル酸素濃度に応じた所定量のＣａを添加して溶鋼中のＡｌ2Ｏ3介在物をＣａＯ−Ａｌ2Ｏ3系介在物に強制的に組成変更するので、Ａｌ2Ｏ3介在物に比べて溶鋼からの浮上・分離が促進され、ＣａＦ2などのフッ素源を含有しないＣａＯ−ＳｉＯ2系フラックスを用いても、フラックスによる鋼浴中のＣａＯ−Ａｌ2Ｏ3系介在物の吸収が促進されるとともに、残存するＣａＯ−Ａｌ2Ｏ3系介在物はＡｌ2Ｏ3介在物のようにクラスター化せず、小サイズのままであるので、清浄度の高い、転動疲労寿命特性に優れた軸受鋼が製造可能となる。また、フラックスはフッ素源を含有しないので、取鍋耐火物の溶損が抑制されるとともに、フラックが溶融して形成されるスラグの再利用が促進される。 As described above, according to the present invention, a predetermined amount of Ca corresponding to the total oxygen concentration of the molten steel is added to force the Al 2 O 3 inclusions in the molten steel to CaO—Al 2 O 3 inclusions. As the composition is changed, the floatation and separation from molten steel is promoted compared to Al 2 O 3 inclusions, and even in the case of using a CaO—SiO 2 flux that does not contain a fluorine source such as CaF 2 , The absorption of CaO—Al 2 O 3 inclusions is promoted, and the remaining CaO—Al 2 O 3 inclusions are not clustered like Al 2 O 3 inclusions and remain small in size. Therefore, it is possible to manufacture bearing steel with high cleanliness and excellent rolling fatigue life characteristics. Moreover, since the flux does not contain a fluorine source, the melting loss of the ladle refractory is suppressed, and the reuse of the slag formed by melting the flack is promoted.
１チャージの溶鋼量が２００トン規模の実機において、本発明を適用して軸受鋼を製造した（本発明例１〜３）。製造プロセスは、転炉−ＬＦ炉−ＲＨ真空脱ガス炉−連続鋳造機の工程である。 The bearing steel was manufactured by applying the present invention in an actual machine in which the amount of molten steel per charge was 200 tons (Invention Examples 1 to 3). A manufacturing process is a process of a converter-LF furnace-RH vacuum degassing furnace-continuous casting machine.
本発明例１〜３においては、転炉からの出鋼後、取鍋内に、フッ素源を実質的に含有しないＣａＯ−ＳｉＯ2系フラックスを添加し、この取鍋をＬＦ炉に搬送し、取鍋の底部に設置したガス吹き込み用のポーラス煉瓦からＡｒガスを攪拌用ガスとして吹き込んで、ＣａＯ−ＳｉＯ2系フラックスと溶鋼とを攪拌しながら、金属Ａｌを添加して溶鋼を脱酸し、Ａｌ脱酸後、溶鋼中のトータル酸素濃度が０．００３０質量％以下となった以降、鉄被覆Ｃａ−Ｓｉ合金ワイヤーを０．３ｋｇ／分・t-steelの添加速度で所定量添加した。その後、ＲＨ真空脱ガス炉で減圧下での精錬を４０分間実施した。 In the present invention Examples 1-3, after tapping from the converter, the ladle, the fluorine source was added containing substantially no CaO-SiO 2 based flux, conveying the ladle to the LF furnace, Ar gas was blown as a stirring gas from a porous brick for gas blowing installed at the bottom of the ladle, and while stirring the CaO-SiO 2 flux and molten steel, metal Al was added to deoxidize the molten steel, After Al deoxidation, after the total oxygen concentration in the molten steel became 0.0030% by mass or less, a predetermined amount of iron-coated Ca—Si alloy wire was added at an addition rate of 0.3 kg / min · t-steel. Then, refining under reduced pressure was carried out for 40 minutes in an RH vacuum degassing furnace.
また、比較のために、上記の本発明例１〜３と同一の工程を経るものの、Ｃａの添加量が本発明の範囲よりも少ない場合（比較例１）、及び、Ｃａの添加量が本発明の範囲よりも多い場合（比較例２及び比較例３）を実施した。更に、Ｃａを添加しないこと以外は本発明例１〜３と同一の工程で製造する場合（比較例４）、及び、本発明例１〜３で使用したフッ素源を含有しないＣａＯ−ＳｉＯ2系フラックスの代わりにＣａＦ2を含有するＣａＯ−ＳｉＯ2系フラックスを添加するとともにＣａを添加しないこと以外は、本発明例１〜３と同一の工程で製造する場合（比較例５）も実施した。尚、何れの場合も、スラグ組成中にＡｌ2Ｏ3成分を２０〜４０質量％程度含有させることを目的として、Ａｌ2Ｏ3成分を主成分とするフラックス（ボーキサイト）をＬＦ炉にて５ｋｇ／t-steel程度添加した。 For comparison, the same steps as those of Invention Examples 1 to 3 are performed, but the amount of Ca added is smaller than the range of the present invention (Comparative Example 1), and the amount of Ca added is Cases (Comparative Example 2 and Comparative Example 3) were carried out in excess of the scope of the invention. Further, in the case of producing in the same process as Invention Examples 1 to 3 except that Ca is not added (Comparative Example 4), and the CaO-SiO 2 system not containing the fluorine source used in Invention Examples 1 to 3 A case (Comparative Example 5) was also carried out in the same process as in Examples 1 to 3 of the present invention except that a CaO-SiO 2 flux containing CaF 2 was added instead of the flux and Ca was not added. In any case, 5 kg of flux (bauxite) containing the Al 2 O 3 component as a main component is contained in an LF furnace for the purpose of containing about 20 to 40 mass% of the Al 2 O 3 component in the slag composition. About / t-steel was added.
操業結果の評価方法としては、各プロセス段階で溶鋼試料を採取し、切断加工・研磨後の試料中の介在物を、光学顕微鏡及び走査型電子顕微鏡（ＳＥＭ）を用いて、介在物の個数、サイズ及び組成を調査した。介在物の個数及びサイズは、４００ｍｍ2視野の範囲の研磨面中に存在する介在物で評価した。 As a method for evaluating the operation results, a molten steel sample is collected at each process stage, and the inclusions in the sample after cutting and polishing are measured using an optical microscope and a scanning electron microscope (SEM). Size and composition were investigated. The number and size of inclusions were evaluated by inclusions present in the polished surface in the range of 400 mm 2 field of view.
図２に、比較例４及び比較例５における各プロセス段階でのＳＥＭによる介在物の組成変化を模式的に示し、また、図３に、本発明例１〜３における各プロセス段階でのＳＥＭによる介在物の組成変化を模式的に示す。 FIG. 2 schematically shows the composition change of inclusions by SEM in each process stage in Comparative Example 4 and Comparative Example 5, and FIG. 3 shows by SEM in each process stage in Invention Examples 1-3. The composition change of an inclusion is shown typically.
図２に示すように、フッ素源つまりＣａＦ2を含有するフラックスを使用した比較例５では、ＬＦ炉での処理中にＡｌ2Ｏ3介在物がＣａＯ−Ａｌ2Ｏ3系介在物に変化していることが分かる。一方、フッ素源を実質的に含有しないＣａＯ−ＳｉＯ2系フラックスを使用し且つＣａを添加しない比較例４では、Ａｌ2Ｏ3介在物の改質はほとんど起こらず、ＲＨ真空脱ガス精錬時にＡｌ2Ｏ3介在物の一部がＣａＯ−Ａｌ2Ｏ3系介在物に変化することが分かる。 As shown in FIG. 2, in Comparative Example 5 using a fluorine source, that is, a flux containing CaF 2 , the Al 2 O 3 inclusions changed to CaO—Al 2 O 3 inclusions during the treatment in the LF furnace. I understand that On the other hand, in Comparative Example 4 in which a CaO—SiO 2 flux that does not substantially contain a fluorine source is used and no Ca is added, Al 2 O 3 inclusions are hardly reformed, and Al is removed during RH vacuum degassing refining. it is understood that some of the 2 O 3 inclusions is changed to CaO-Al 2 O 3 inclusions.
これに対して、本発明例１〜３では、Ｃａを添加するまでは比較例４と同等であるが、Ｃａを添加することにより、Ａｌ2Ｏ3介在物がＣａＯ−Ａｌ2Ｏ3系介在物に変化しており、ＣａＦ2を含有するフラックスを使用した比較例５と大差ない挙動を示すことが分かった。 On the other hand, in Examples 1 to 3 of the present invention, the same as Comparative Example 4 until Ca is added, but by adding Ca, Al 2 O 3 inclusions are CaO—Al 2 O 3 -based inclusions. It turned out that it shows the behavior which is not different from Comparative Example 5 using the flux containing CaF 2 .
また、表１に、連続鋳造機のタンディッシュ内から採取した試料で調査した介在物最大径及び５μｍ以上の介在物の個数を示す。 Table 1 shows the maximum diameter of inclusions and the number of inclusions having a size of 5 μm or more investigated with samples collected from the tundish of a continuous casting machine.
表１に示すように、本発明例１〜３においては介在物の最大径及び個数ともに優れた結果であり、ＣａＦ2を含有するフラックスを使用した比較例５に勝るとも劣らない結果であった。これに対して、Ｃａの添加量が本発明の範囲よりも少ない比較例１では介在物の個数が多く、Ｃａの添加量が本発明の範囲よりも多い比較例２及び比較例３では介在物の最大径が大きく、本発明例１〜３よりも清浄性が劣ることが確認できた。 As shown in Table 1, in Inventive Examples 1 to 3, the maximum diameter and the number of inclusions were excellent, and the results were not inferior to Comparative Example 5 using a flux containing CaF 2 . . On the other hand, in Comparative Example 1 where the amount of Ca added is less than the range of the present invention, the number of inclusions is large, and in Comparative Examples 2 and 3 where the amount of Ca added is larger than the range of the present invention, inclusions are included. The maximum diameter was large, and it was confirmed that the cleanliness was inferior to Examples 1-3 of the present invention.
その後、圧延して製造された製品試料を用いて転動疲労寿命評価試験を実施した。その結果、本発明例１〜３及び比較例５では、１０7サイクル以上の転動疲労寿命特性を達成できることが確認できた。 Thereafter, a rolling fatigue life evaluation test was performed using a product sample produced by rolling. As a result, it was confirmed that in Examples 1 to 3 and Comparative Example 5 of the present invention, rolling fatigue life characteristics of 10 7 cycles or more could be achieved.
Claims (1)
[%Ca]eff=[質量%Ca]-(0.18+130×[質量%Ca])×[質量%T.O] …(1)
但し、（１）式において、［質量％Ｃａ］は溶鋼中のＣａ濃度（質量％）、［質量％Ｔ．Ｏ］は溶鋼中のトータル酸素濃度（質量％）である。 In a ladle containing molten steel melted in a converter or an electric furnace, a CaO—SiO 2 flux containing substantially no fluorine source is added, and then the molten steel deoxidized by Al in the atmosphere. And the flux are blown into the molten steel, and after the total oxygen concentration of the molten steel becomes 0.0030 mass% or less, [% Ca] eff defined by the following (1) Is produced by adding Ca to the molten steel so that is in the range of 0.0003 mass% or more and 0.0010 mass% or less, and then refining the molten steel under reduced pressure in a vacuum degassing apparatus. Method.
[% Ca] eff = [mass% Ca]-(0.18 + 130 × [mass% Ca]) × [mass% TO] (1)
However, in the formula (1), [mass% Ca] is the Ca concentration (mass%) in the molten steel, and [mass% T.M. O] is the total oxygen concentration (mass%) in the molten steel.
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| WO2019142947A1 (en) | 2018-01-22 | 2019-07-25 | 日本製鉄株式会社 | Carburized bearing steel component, and steel bar for carburized bearing steel component |
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| JPH05331523A (en) * | 1992-06-03 | 1993-12-14 | Kawasaki Steel Corp | Method for refining molten steel for bearing steel |
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| WO2019142947A1 (en) | 2018-01-22 | 2019-07-25 | 日本製鉄株式会社 | Carburized bearing steel component, and steel bar for carburized bearing steel component |
| KR20200102488A (en) | 2018-01-22 | 2020-08-31 | 닛폰세이테츠 가부시키가이샤 | Carburized bearing steel parts and rods for carburized bearing steel parts |
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