JP2010209372A - Method for producing clean steel having excellent sulfide corrosion crack resistance - Google Patents
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本発明は、湿潤硫化水素腐食環境下で使用される耐硫化物腐食割れ性に優れた清浄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 clean steel having excellent resistance to sulfide corrosion cracking used in a wet hydrogen sulfide corrosion environment.
一般に、湿潤硫化水素腐食環境下で使用される鋼材には、耐ＨＩＣ（水素誘起割れ）性能及び耐ＳＳＣ（硫化物応力腐食割れ）性能、つまり、優れた耐硫化物腐食割れ性が要求されている。鋼中に含有される硫黄（Ｓ）は、凝固過程でＭｎＳを生成し、しかも、凝固時の硫黄の偏析により、ＭｎＳの濃化した部位が鋳片に形成される。このＭｎＳは圧延時に圧延方向に長く伸び、水素の集積を促進させ、耐ＨＩＣ性能を低下させる。そこで、この水素誘起割れの発生を抑制する手段として、鋼成分の極低硫化とともに、カルシウム（Ｃａ）添加による硫化物の形態制御が一般的に行われている。ここで、硫化物の形態制御とは、Ｃａを添加することによって硫化物の形態をＭｎＳからＣａＳに改質することを差す。 In general, steel materials used in a wet hydrogen sulfide corrosion environment are required to have HIC (hydrogen induced cracking) resistance and SSC (sulfide stress corrosion cracking) resistance, that is, excellent sulfide corrosion cracking resistance. Yes. Sulfur (S) contained in the steel generates MnS during the solidification process, and a portion where MnS is concentrated is formed in the slab due to segregation of sulfur during solidification. This MnS extends long in the rolling direction during rolling, promotes hydrogen accumulation, and lowers the HIC resistance. Therefore, as a means for suppressing the occurrence of hydrogen-induced cracking, the form control of sulfides by adding calcium (Ca) is generally performed along with extremely low sulfurization of steel components. Here, the form control of sulfide refers to modifying the form of sulfide from MnS to CaS by adding Ca.
ところで、Ｃａは溶鋼温度域での蒸気圧が高く、溶鋼中への溶解度が低い。そのため、鋳造時の溶鋼中に所定量のＣａを残留させるために、Ｃａの添加は、取鍋精錬処理の最終段階或いは連続鋳造設備のタンディッシュ内で行われることが一般的であった。 By the way, Ca has a high vapor pressure in the molten steel temperature range and a low solubility in molten steel. Therefore, in order to leave a predetermined amount of Ca in the molten steel at the time of casting, the addition of Ca is generally performed in the final stage of the ladle refining process or in the tundish of the continuous casting equipment.
しかし、Ｃａは硫黄のみならず酸素との親和力も強く、溶鋼中に添加されたＣａは最初に酸素と反応し、ＣａＯ系酸化物としてＣａＯ−Ａｌ2Ｏ3の脱酸生成物を形成する。つまり、ＣａはＡｌで脱酸された溶鋼に添加されても、脱酸生成物であるＡｌ2Ｏ3をＣａＯ−Ａｌ2Ｏ3系介在物に改質する。その後、硫黄と反応してＣａＳを生成し、添加したＣａの一部が溶鋼中に溶解した形態で残留する。 However, Ca has a strong affinity not only for sulfur but also for oxygen, and Ca added to molten steel first reacts with oxygen to form a deoxidation product of CaO—Al 2 O 3 as a CaO-based oxide. That is, even if Ca is added to molten steel deoxidized with Al, it modifies Al 2 O 3 that is a deoxidation product into CaO—Al 2 O 3 inclusions. Then, it reacts with sulfur to produce CaS, and a part of the added Ca remains in a dissolved form in the molten steel.
従って、Ｃａの添加歩留まり（残留したＣａと添加したＣａとの比）は、溶鋼中の酸素濃度や硫黄濃度に左右され、Ｃａの添加量が同一であっても、溶鋼中に溶解して存在するＣａの濃度は変化し、前述した従来の添加方法では、溶鋼中の酸素量及び硫黄量によってＣａ歩留まりが左右され、耐ＨＩＣ性能の劣化を招くことがあった。 Therefore, the Ca addition yield (ratio of remaining Ca to added Ca) depends on the oxygen concentration and sulfur concentration in the molten steel, and is dissolved in the molten steel even if the amount of Ca is the same. The concentration of Ca to be changed varies, and in the conventional addition method described above, the Ca yield is affected by the amount of oxygen and sulfur in the molten steel, which may lead to deterioration of the HIC resistance.
また、溶鋼中のＣａＯ−Ａｌ2Ｏ3系介在物は、Ｃａ添加後の放置時間が長いほど、溶鋼中から浮上・分離しやすくなる。しかし、上述のように、Ｃａの特性上から、精錬工程の最終段階或いは連続鋳造設備のタンディッシュ内でのＣａ添加を余儀なくされ、十分な浮上・分離の時間を確保できず、Ａｌ2Ｏ3をＣａＯ−Ａｌ2Ｏ3系介在物に形態制御しても、溶鋼からの除去が進まず、溶鋼中に残留していた。尚、Ａｌ2Ｏ3はクラスター状となり、溶鋼からの浮上・分離性が悪いが、ＣａＯ−Ａｌ2Ｏ3系介在物は、低融点であり、一般的にはクラスターを形成せず、Ａｌ2Ｏ3に比較して浮上・分離性が良く、Ａｌ2Ｏ3をＣａＯ−Ａｌ2Ｏ3系介在物に形態制御することは、溶鋼の清浄度向上に寄与する。 Moreover, the CaO—Al 2 O 3 inclusions in the molten steel are more likely to float and separate from the molten steel as the standing time after Ca addition is longer. However, as described above, due to the characteristics of Ca, it is necessary to add Ca in the final stage of the refining process or in the tundish of the continuous casting equipment, and sufficient flotation and separation time cannot be secured, and Al 2 O 3 Even when the shape was controlled to CaO—Al 2 O 3 inclusions, the removal from the molten steel did not proceed, and it remained in the molten steel. Incidentally, Al 2 O 3 becomes clustered, but poor floating-isolation from the molten steel, CaO-Al 2 O 3 inclusions are low melting point, generally do not form clusters, Al 2 O 3 in good floating and separation resistance than the Al 2 O 3 to form control in CaO-Al 2 O 3 inclusions, which contribute to the cleanliness improvement of the molten steel.
生成したＣａＯ−Ａｌ2Ｏ3系介在物の浮上・分離を促進させるために、酸化物系介在物の形態制御のためのＣａ添加と、硫化物の形態制御のためのＣａ添加とを、２段階に分けて添加する方法が多数提案されている。 In order to promote the flotation and separation of the generated CaO—Al 2 O 3 inclusions, the addition of Ca for controlling the form of oxide inclusions and the addition of Ca for controlling the form of sulfides Many methods of adding in stages have been proposed.
例えば、特許文献１には、転炉から取鍋へ出鋼された溶鋼をＡｌで脱酸し、成分を調整した溶鋼にＣａ−Ｓｉ合金を添加してＣａＯ−Ａｌ2Ｏ3系介在物を生成させ、次いで、ＲＨ真空脱ガス装置にて精錬してＣａＯ−Ａｌ2Ｏ3系介在物を除去し、脱ガス精錬終了後に、取鍋内にＣａ−Ｓｉ合金を添加して硫化物の形態制御を行うことを特徴とする、清浄鋼の製造方法が提案されている。 For example, in Patent Document 1, the molten steel discharged from the converter to the ladle is deoxidized with Al, and a Ca—Si alloy is added to the molten steel whose components are adjusted to add a CaO—Al 2 O 3 inclusion. And then refining with an RH vacuum degassing device to remove CaO-Al 2 O 3 inclusions, and after degassing refining, a Ca-Si alloy is added to the ladle to form a sulfide. There has been proposed a method for producing clean steel characterized by performing control.
特許文献２には、転炉出鋼時若しくは出鋼後にＡｌなどの還元剤を所定量添加してキルド化した取鍋内溶鋼に、Ｃａ含有合金を添加し、且つ、このＣａ含有合金の添加の前または後に、該溶鋼を所定温度まで昇温しＣａＯを含有するフラックスを用いた脱硫処理を施し、次いで、真空脱ガス処理を施し、続いて該溶鋼をタンディッシュを経て連続鋳造する工程でのタンディッシュ内の溶鋼に、連続的若しくは間欠的にＣａ合金を添加することを特徴とする、Ｃａ添加鋼の製造方法が提案されている。 In Patent Document 2, a Ca-containing alloy is added to molten steel in a ladle that has been killed by adding a predetermined amount of a reducing agent such as Al at the time of or after the steel from the converter, and the addition of this Ca-containing alloy. Before or after the step, the molten steel is heated to a predetermined temperature and subjected to a desulfurization treatment using a flux containing CaO, followed by a vacuum degassing treatment, followed by continuous casting of the molten steel through a tundish. A method for producing Ca-added steel has been proposed, in which a Ca alloy is added continuously or intermittently to molten steel in the tundish.
また、特許文献３には、真空脱ガス設備において、真空槽を減圧するとともに取鍋底部に配置したインジェクションランスから、脱硫剤としてのＣａＯ−ＣａＦ2フラックスと、Ｃａ合金としてのＣａ−Ｓｉとの事前混合品を溶鋼中に吹き込んで脱硫処理及び脱水素処理を行い、その後、真空槽を大気圧に戻してから、前記ランスを介して溶鋼中にＣａ合金またはＣａ化合物を吹き込むことを特徴とする精錬方法が提案されている。 Patent Document 3 discloses that in a vacuum degassing facility, a vacuum tank is decompressed and an injection lance disposed at the bottom of a ladle is used to make CaO—CaF 2 flux as a desulfurizing agent and Ca—Si as a Ca alloy. The premixed product is blown into molten steel to perform desulfurization treatment and dehydrogenation treatment, and then the vacuum tank is returned to atmospheric pressure, and then Ca alloy or Ca compound is blown into the molten steel through the lance. A refining method has been proposed.
特許文献１〜３などに開示されるＣａの２段添加により、Ｃａの１段添加の場合に比較して溶鋼の清浄性は大幅に向上し、耐硫化物腐食割れ性に優れる鋼材の製造が格段に安定化した。しかしながら、上記従来技術には以下の問題点がある。 With the two-stage addition of Ca disclosed in Patent Documents 1 to 3 and the like, the cleanliness of the molten steel is greatly improved compared to the case of the first-stage addition of Ca, and the production of a steel material excellent in resistance to sulfide corrosion cracking can be achieved. Remarkably stabilized. However, the above prior art has the following problems.
即ち、特許文献１及び特許文献２では、転炉出鋼後の溶鋼に先ず脱硫処理を施し、その後、１段目のＣａ添加を実施するという点である。つまり、真空脱ガス設備における脱ガス精錬までに脱硫処理とＣａ添加との２回の処理が必要であり、生産性が低いのみならず、処理時間が長くなり溶鋼温度の降下量が大きくなるという問題点がある。特許文献２では、１段目のＣａ添加の後に脱硫処理を施すことも提案するが、この場合には、溶鋼の硫黄濃度が高い状態でＣａを添加することになり、Ｃａは脱硫剤としても機能するので、Ｃａの歩留まりが低下するという問題点も招く。 That is, in Patent Document 1 and Patent Document 2, the molten steel after the converter steel is first subjected to desulfurization treatment, and then the first-stage Ca addition is performed. In other words, two processes of desulfurization and Ca addition are required before degassing and refining in the vacuum degassing equipment, and not only the productivity is low, but the processing time is prolonged and the amount of decrease in molten steel temperature is increased. There is a problem. In Patent Document 2, it is also proposed to perform a desulfurization treatment after the first stage of Ca addition, but in this case, Ca is added in a state where the sulfur concentration of the molten steel is high, and Ca is also used as a desulfurization agent. Since it functions, the problem that the yield of Ca falls will also be caused.
また、特許文献２では、連続鋳造設備のタンディッシュで２段目のＣａ添加を実施しており、タンディッシュ内の溶鋼は連続的に入れ替わっており、溶鋼中のＣａ含有量が鋳造方向で変動するという問題点がある。また、タンディッシュ内での添加は添加深さが確保できないために、Ｃａ歩留りが悪く、またばらつきもも大きい。 Further, in Patent Document 2, the second stage of Ca addition is performed in the tundish of the continuous casting equipment, the molten steel in the tundish is continuously replaced, and the Ca content in the molten steel varies in the casting direction. There is a problem of doing. Moreover, since the addition depth in the tundish cannot secure the addition depth, the Ca yield is poor and the variation is large.
特許文献３では、真空脱ガス設備で１段目のＣａ添加及び脱硫処理を行っており、生産性は優れるが、１段目のＣａ添加により生成されるＣａＯ−Ａｌ2Ｏ3系介在物の浮上・分離の時間が短く、溶鋼中にＣａＯ−Ａｌ2Ｏ3系介在物が残留するという問題点がある。 In Patent Document 3, the first stage of Ca addition and desulfurization treatment is performed in a vacuum degassing facility, and although the productivity is excellent, the CaO—Al 2 O 3 inclusions generated by the first stage of Ca addition There is a problem that the floating and separation times are short, and CaO—Al 2 O 3 inclusions remain in the molten 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、高い生産性で効率良く、しかも、ＣａＯ−Ａｌ2Ｏ3系介在物の含有量が少なく、耐硫化物腐食割れ性に優れた清浄鋼を、２段階のＣａ添加によって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 its object is to achieve high productivity and efficiency, and a low content of CaO-Al 2 O 3 inclusions, and resistance to sulfide corrosion cracking. It is to provide a method for producing a clean steel excellent in quality by adding Ca in two stages.
本発明者らは、上記課題を解決するべく、試験・検討を行った。 The present inventors have conducted tests and studies to solve the above-described problems.
その結果、転炉からの出鋼後に取鍋内の溶鋼に対して行う脱硫処理において、１段目のＣａ添加を脱硫処理と同時に実施することで、工程が短縮されることによって生産性が向上するのみならず、脱硫処理後の溶鋼中硫黄濃度が従来に比較して低下するとの知見が得られた。これは、Ｃａは酸素との親和力が極めて強く、Ｃａを添加することにより、脱硫処理時の溶鋼の酸素ポテンシャルが低下し、還元反応である脱硫反応が促進されるためと考えられる。このＣａ添加を伴う脱硫処理後に、真空脱ガス処理、真空脱ガス処理後に更に２段目のＣａ添加を実施することで、硫黄濃度が極めて低く、且つ、酸化物系介在物及び硫化物系介在物が極めて少ない、耐硫化物腐食割れ性に優れた清浄鋼を高い生産性で製造できるとの知見を得た。 As a result, in the desulfurization process performed on the molten steel in the ladle after the steel from the converter, the first stage of Ca addition is performed simultaneously with the desulfurization process, thereby improving the productivity by shortening the process. In addition, the knowledge that the sulfur concentration in the molten steel after the desulfurization treatment is lower than the conventional one was obtained. This is presumably because Ca has an extremely strong affinity for oxygen, and the addition of Ca lowers the oxygen potential of the molten steel during the desulfurization treatment and promotes the desulfurization reaction, which is a reduction reaction. After this desulfurization treatment with Ca addition, vacuum degassing treatment, and further adding the second stage of Ca after vacuum degassing treatment, the sulfur concentration is extremely low, and oxide inclusions and sulfide inclusions We have learned that it is possible to produce clean steel with extremely few products and excellent resistance to sulfide corrosion cracking with high productivity.
本発明は、上記知見に基づいてなされたものであり、第１の発明に係る耐硫化物腐食割れ性に優れた清浄鋼の製造方法は、転炉から取鍋への出鋼時または出鋼後に溶鋼にＡｌを添加して溶鋼を脱酸し、先ず、この取鍋内の溶鋼にＣａＯを含有するフラックスを添加して脱硫処理を施すとともに、この脱硫処理時にＣａ含有金属を添加し、次いで、取鍋内の溶鋼に真空脱ガス処理を施し、更に、真空脱ガス処理後の取鍋内の溶鋼にＣａ含有金属を添加し、その後、該溶鋼を鋳造することを特徴とするものである。 The present invention has been made on the basis of the above knowledge, and the method for producing clean steel excellent in resistance to sulfide corrosion cracking according to the first invention can be obtained at the time of steel output from a converter to a ladle or steel output. Later, Al is added to the molten steel to deoxidize the molten steel. First, a flux containing CaO is added to the molten steel in the ladle to perform a desulfurization treatment, and a Ca-containing metal is added at the time of the desulfurization treatment. The molten steel in the ladle is subjected to vacuum degassing treatment, and further, a Ca-containing metal is added to the molten steel in the ladle after the vacuum degassing treatment, and then the molten steel is cast. .
第２の発明に係る耐硫化物腐食割れ性に優れた清浄鋼の製造方法は、第１の発明において、前記脱硫処理時におけるＣａ含有金属のＣａ純分の添加量を、Ｃａの添加歩留まりを１００％としたときに溶鋼中のＣａ濃度が下記の（１）式の範囲内となるように、溶鋼中のＡｌ濃度及びトータル酸素濃度に応じて調整することを特徴とするものである。
［％Ｃａ］≧0.01×［％Ａｌ］2/3＋0.9×［％Ｔ．Ｏ］…（１）
但し（１）式において、［％Ｃａ］は溶鋼中のＣａ濃度（質量％）、［％Ａｌ］は溶鋼中のＡｌ濃度（質量％）、［％Ｔ．Ｏ］は溶鋼中のトータル酸素濃度（質量％）である。
The method for producing clean steel excellent in resistance to sulfide corrosion cracking according to the second invention is the first invention, wherein the amount of pure Ca contained in the Ca-containing metal at the time of the desulfurization treatment is determined by the addition yield of Ca. It is characterized by adjusting according to the Al concentration and the total oxygen concentration in the molten steel so that the Ca concentration in the molten steel falls within the range of the following formula (1) when it is 100%.
[% Ca] ≧ 0.01 × [% Al] 2/3 + 0.9 × [% T. O] ... (1)
However, in the formula (1), [% Ca] is the Ca concentration (mass%) in the molten steel, [% Al] is the Al concentration (mass%) in the molten steel, and [% T.I. O] is the total oxygen concentration (mass%) in the molten steel.
本発明によれば、１段目のＣａ添加を脱硫処理と同時に実施するので、製造工程が短縮されることによって生産性が向上するのみならず、脱硫処理後の溶鋼中硫黄濃度が従来に比較して低下し、その結果、硫黄濃度が極めて低く、且つ、酸化物系介在物及び硫化物系介在物が極めて少ない、耐硫化物腐食割れ性に優れた清浄鋼を高い生産性で製造することが実現される。 According to the present invention, since the first stage of Ca addition is performed simultaneously with the desulfurization treatment, not only the productivity is improved by shortening the manufacturing process, but also the sulfur concentration in the molten steel after the desulfurization treatment is compared with the conventional one. As a result, it is possible to produce a clean steel with a high productivity, which has a very low sulfur concentration and a very small amount of oxide inclusions and sulfide inclusions and is excellent in resistance to sulfide corrosion cracking. Is realized.
以下、本発明を詳細に説明する。 Hereinafter, the present invention will be described in detail.
本発明に係る耐硫化物腐食割れ性に優れた清浄鋼の製造方法は、転炉から取鍋への出鋼時または出鋼後に溶鋼にＡｌを添加して溶鋼を脱酸し、先ず、この取鍋内の溶鋼にＣａＯを含有するフラックスを添加して脱硫処理を施すとともに、この脱硫処理時にＣａ含有金属を添加し、次いで、取鍋内の溶鋼に真空脱ガス処理を施し、更に、真空脱ガス処理後の取鍋内の溶鋼にＣａ含有金属を添加し、その後、該溶鋼を鋳造することを特徴とする。 The method for producing a clean steel excellent in resistance to sulfide corrosion cracking according to the present invention is to deoxidize the molten steel by adding Al to the molten steel at the time of or after the steel from the converter to the ladle. A flux containing CaO is added to the molten steel in the ladle and subjected to desulfurization treatment. At the time of this desulfurization treatment, a Ca-containing metal is added, and then the molten steel in the ladle is subjected to vacuum degassing treatment, and further, vacuum A Ca-containing metal is added to the molten steel in the ladle after the degassing treatment, and then the molten steel is cast.
耐ＨＩＣ鋼に必要な特性としては、（ａ）硫黄含有量が低いこと、（ｂ）酸化物系介在物が少ないこと、及び、（ｃ）ＣａＳが残留しないことが重要である。これらを全て兼ね備えるためには、（１）高効率な溶鋼の脱硫処理により極低硫化すること、（２）酸化物系介在物の組成を浮上・分離しやすい形態に制御して浮上・分離を促進すること、（３）最適なＣａ添加量によりＭｎＳの生成を防止するとともに、Ｃａの硫化物と酸化物との化合物（「オキシ−サルファイド系介在物」と称す）の生成を抑制することが重要である。 As characteristics required for the HIC-resistant steel, it is important that (a) the sulfur content is low, (b) there are few oxide inclusions, and (c) no CaS remains. In order to combine all of these, (1) ultra-low sulfidation by high-efficiency molten steel desulfurization, (2) control the composition of oxide inclusions to a form that is easy to float and separate, so (3) Preventing the formation of MnS by the optimum amount of Ca addition and suppressing the formation of a compound of Ca sulfide and oxide (referred to as “oxy-sulfide inclusions”). is important.
これらを満足するために、本発明においては、溶鋼に脱硫処理を施して極低硫化を図るとともに、Ｃａ添加を、１段目の酸化物系介在物の形態制御のための添加と、２段目の硫化物形態制御のための添加との２段に分けて添加し、且つ、１段目のＣａ添加の後に真空脱ガス精錬による強攪拌を溶鋼に施し、酸化物系介在物の浮上・分離を促進させる。また、２段目のＣａ添加は、溶鋼中のＣａ濃度を均一化させるためには、取鍋内溶鋼に添加する必要があり、また、凝固過程において溶鋼中にＣａを残留させるためには、２段目のＣａ添加は鋳造開始時期に近い段階が望ましく、従って、２段目のＣａ添加は真空脱ガス精錬終了後の取鍋内で行うこととした。尚、真空脱ガス精錬中つまり減圧下の溶鋼にＣａを添加しても、Ｃａは蒸気圧が高く、溶鋼中に留まるＣａは少量であり、効率的ではない。 In order to satisfy these requirements, in the present invention, the molten steel is subjected to desulfurization treatment to achieve extremely low sulfidation, and Ca addition is added for the purpose of controlling the form of oxide inclusions in the first stage and in two stages. Addition in two stages of addition for the sulfide form control of the eyes, and after the addition of Ca in the first stage, the molten steel is subjected to strong agitation by vacuum degassing refining to raise the oxide inclusions Promote separation. In addition, in order to make the Ca concentration in the molten steel uniform, the second stage Ca addition needs to be added to the molten steel in the ladle, and in order to leave Ca in the molten steel in the solidification process, The second stage of Ca addition is preferably at a stage close to the casting start time. Therefore, the second stage of Ca addition is performed in a ladle after completion of vacuum degassing refining. Even if Ca is added to the molten steel during vacuum degassing, that is, under reduced pressure, Ca has a high vapor pressure, and a small amount of Ca remains in the molten steel, which is not efficient.
溶鋼の脱硫処理は還元反応であるので、溶鋼の酸素ポテンシャルは低いほど望ましく、従って、本発明においては、転炉から取鍋への出鋼時または出鋼直後、溶鋼に金属Ａｌを添加して予め溶鋼を脱酸する。この脱酸処理により形成される脱酸生成物はＡｌ2Ｏ3（アルミナ）であり、溶鋼からの浮上・分離性は良くない。本発明ではこのＡｌ2Ｏ3の浮上・分離を促進させるために、出鋼時または出鋼直後にＡｌで脱酸し、１段目のＣａ添加までの時間、つまりＡｌ2Ｏ3の浮上・分離のための時間をできるだけ長く確保する。 Since the desulfurization treatment of the molten steel is a reduction reaction, it is desirable that the oxygen potential of the molten steel be as low as possible. Therefore, in the present invention, metal Al is added to the molten steel at the time of steel extraction from the converter to the ladle or immediately after the steel output. Deoxidize the molten steel in advance. The deoxidation product formed by this deoxidation treatment is Al 2 O 3 (alumina), and the floating and separation properties from the molten steel are not good. In the present invention, in order to promote the floating and separation of the Al 2 O 3, deoxidation by Al immediately after tapping or during tapping, time to Ca added in the first stage, ie floating of Al 2 O 3 · Ensure as long as possible the time for separation.
本発明における溶鋼の脱硫処理は、ＣａＯ系の安価な脱硫剤であっても極低硫鋼が得られることから、ＣａＯを含有するフラックスを脱硫剤として添加し、この脱硫剤と溶鋼とをインジェクションランスなどから吹き込む希ガスにより強攪拌して脱硫処理する。脱硫剤としてのＣａＯを含有するフラックスとしては、生石灰（ＣａＯ）単独、或いは、生石灰と、ＣａＯの滓化促進剤であるＡｌ2Ｏ3またはＳｉＯ2との混合物などを用いることができる。 Since the desulfurization treatment of the molten steel in the present invention can produce an extremely low sulfur steel even with a CaO-based inexpensive desulfurization agent, a flux containing CaO is added as a desulfurization agent, and the desulfurization agent and the molten steel are injected. Desulfurization is performed by vigorous stirring with a rare gas blown from a lance. As the flux containing CaO as a desulfurizing agent, quick lime (CaO) alone or a mixture of quick lime and Al 2 O 3 or SiO 2 which is a CaO hatching accelerator can be used.
溶鋼を効率的に脱硫するには、（１）溶鋼と脱硫剤との攪拌力を強めること、及び、（２）溶鋼の酸素ポテンシャルを低下させることが効果的である。本発明においては、脱硫処理時にＣａを添加するので、上記の両者を同時に満足させることができる。 In order to efficiently desulfurize molten steel, it is effective to (1) increase the stirring force between the molten steel and the desulfurizing agent and (2) reduce the oxygen potential of the molten steel. In the present invention, since Ca is added during the desulfurization treatment, both of the above can be satisfied at the same time.
即ち、本発明においては、溶鋼の脱硫処理はインジェクションランス或いは取鍋底部のポーラス煉瓦などからの攪拌用ガス（Ａｒガスなどの希ガス）の吹き込みによって脱硫剤と溶鋼とを強攪拌して行うが、インジェクションランスからの攪拌用ガスを搬送用ガスとして攪拌用ガスの吹き込みとともにＣａ合金の粉末を吹き込むか、或いは、その内部にＣａ合金を充填した鉄被覆ワイヤーを溶鋼中に添加することで、添加されるＣａが溶鋼中の酸素と反応して溶鋼が脱酸され、溶鋼の酸素ポテンシャルが低下すると同時、吹き込まれるＣａの一部は蒸気となり、これによって溶鋼の攪拌力が強化される。この２つの現象により、溶鋼の脱硫反応が促進される。また、Ｃａ添加により生成するＣａＯは、溶鋼中のＡｌ2Ｏ3と反応して、低融点のＣａＯ−Ａｌ2Ｏ3系介在物を形成する。 That is, in the present invention, the desulfurization treatment of the molten steel is performed by strongly stirring the desulfurizing agent and the molten steel by blowing a stirring gas (rare gas such as Ar gas) from an injection lance or a porous brick at the bottom of the ladle. , By adding the stirring gas from the injection lance as the carrier gas and blowing in the Ca alloy powder, or by adding an iron-coated wire filled with the Ca alloy into the molten steel When the molten Ca reacts with oxygen in the molten steel to deoxidize the molten steel and the oxygen potential of the molten steel decreases, a portion of the Ca that is blown becomes steam, thereby strengthening the stirring power of the molten steel. By these two phenomena, the desulfurization reaction of molten steel is accelerated. Further, CaO produced by addition of Ca reacts with Al 2 O 3 in the molten steel to form a CaO-Al 2 O 3 inclusions having a low melting point.
このＣａ添加を伴う溶鋼の脱硫処理後、取鍋に収容された溶鋼をＲＨ真空脱ガス装置などの真空脱ガス設備に搬送し、真空脱ガス設備で溶鋼に真空脱ガス精錬を施す。この真空脱ガス精錬による溶鋼の強攪拌によって、ＣａＯ−Ａｌ2Ｏ3系介在物の浮上分離が促進される。 After the desulfurization treatment of the molten steel accompanied by the addition of Ca, the molten steel accommodated in the ladle is transported to a vacuum degassing facility such as an RH vacuum degassing apparatus, and the molten steel is subjected to vacuum degassing refining in the vacuum degassing facility. Due to the strong stirring of the molten steel by this vacuum degassing refining, the floating separation of CaO—Al 2 O 3 inclusions is promoted.
つまり、このようにして溶鋼を処理することで、上記の耐ＨＩＣ鋼に必要な特性のうちの（ａ）の「硫黄含有量が低いこと」、及び（ｂ）の「酸化物系介在物の個数が少ないこと」の両者を満足することができる。尚、溶鋼に真空脱ガス精錬を施すことで、溶鋼中に溶解していたＣａの大部分は気化・蒸発してしまい、そのままでは硫化物の形態制御は期待できない。 That is, by treating the molten steel in this manner, among the characteristics required for the above-mentioned HIC steel, (a) “low sulfur content” and (b) “of oxide inclusions” Both “small number” can be satisfied. In addition, by performing vacuum degassing to the molten steel, most of Ca dissolved in the molten steel is vaporized and evaporated, and as it is, control of the form of sulfide cannot be expected.
ここで、１段目のＣａ添加は、溶鋼中のＡｌ2Ｏ3をＣａＯ−Ａｌ2Ｏ3系介在物に形態制御することを目的としており、従って、溶鋼中に懸濁しているＡｌ2Ｏ3の量に応じてＣａの添加量を決定することが好ましい。但し、溶鋼中に懸濁しているＡｌ2Ｏ3の量をリアルタイムで測定することは困難である。本発明者らは、溶鋼中に懸濁しているＡｌ2Ｏ3の量をリアルタイムで推定することのできる要素を検討した結果、溶鋼中に懸濁しているＡｌ2Ｏ3の量はトータル酸素濃度と強い相関があることを確認した。尚、トータル酸素濃度とは、溶鋼中に溶解している酸素と、酸化物として溶鋼中に存在する酸素との合計の酸素濃度である。 Here, the first stage of Ca addition aims at controlling the form of Al 2 O 3 in the molten steel into CaO—Al 2 O 3 inclusions, and therefore, Al 2 O suspended in the molten steel. It is preferable to determine the addition amount of Ca according to the amount of 3 . However, it is difficult to measure the amount of Al 2 O 3 suspended in the molten steel in real time. The present inventors have made study elements which can estimate the amount of Al 2 O 3 suspended in the molten steel in real time, the amount total oxygen concentration of Al 2 O 3 in suspension in the molten steel It was confirmed that there is a strong correlation. The total oxygen concentration is the total oxygen concentration of oxygen dissolved in the molten steel and oxygen present in the molten steel as an oxide.
即ち、溶鋼中のトータル酸素濃度からＣａの添加量を設定できることが分かった。また、溶鋼中に溶存するＣａの量は、溶鋼中のＡｌとの平衡によって定まる。これらから、１段目のＣａ添加量は、化学量論的な検討及び実際の反応効率を詳細に検討した結果、Ｃａの添加歩留まりを１００％としたときに溶鋼中のＣａ濃度が下記の（１）式の範囲内となるように、溶鋼中のＡｌ濃度及びトータル酸素濃度に応じて調整することが好ましいことが確認できた。
［％Ｃａ］≧0.01×［％Ａｌ］2/3＋0.9×［％Ｔ．Ｏ］…（１）
但し（１）式において、［％Ｃａ］は溶鋼中のＣａ濃度（質量％）、［％Ａｌ］は溶鋼中のＡｌ濃度（質量％）、［％Ｔ．Ｏ］は溶鋼中のトータル酸素濃度（質量％）である。
That is, it was found that the amount of Ca added can be set from the total oxygen concentration in the molten steel. The amount of Ca dissolved in the molten steel is determined by the equilibrium with Al in the molten steel. From these results, the Ca addition amount in the first stage was determined based on the stoichiometric and actual reaction efficiency. As a result, when the Ca addition yield was 100%, the Ca concentration in the molten steel was as follows ( It has been confirmed that it is preferable to adjust according to the Al concentration and the total oxygen concentration in the molten steel so as to be within the range of the formula 1).
[% Ca] ≧ 0.01 × [% Al] 2/3 + 0.9 × [% T. O] ... (1)
However, in the formula (1), [% Ca] is the Ca concentration (mass%) in the molten steel, [% Al] is the Al concentration (mass%) in the molten steel, and [% T.I. O] is the total oxygen concentration (mass%) in the molten steel.
また、溶鋼の脱硫処理と同時に１段目のＣａ添加を実施することで、上記のように効率的に溶鋼を脱硫処理することが可能になるとともに、従来のようにそれぞれを独立して実施していた場合に比較して、脱硫処理及び１段目のＣａ添加に費やす合計の処理時間を大幅に短縮することができ、高い生産性を確保することができる。 Also, by performing the first stage of Ca addition simultaneously with the desulfurization treatment of the molten steel, it becomes possible to efficiently desulfurize the molten steel as described above, and each is carried out independently as in the past. Compared with the case where it was, the total processing time spent for a desulfurization process and Ca addition of the 1st step | paragraph can be reduced significantly, and high productivity can be ensured.
２段目の硫化物の形態制御のためのＣａ添加は、真空脱ガス精錬後の取鍋内の溶鋼に対して実施する。２段目のＣａ添加は、インジェクションランスを介して搬送用ガスとともにＣａ合金の粉末を吹き込むか、或いは、その内部にＣａ合金を充填した鉄被覆ワイヤーを溶鋼中に添加して実施する。２段目のＣａ添加は、添加対象の溶鋼の硫黄濃度が低く且つ酸化物系介在物も少ないので、溶鋼中にＣａが０．００１０〜０．００３０質量％程度残留するように、Ｃａ純分の添加量を設定すればよい。これにより、耐ＨＩＣ鋼に必要な特性である（ｃ）の「ＣａＳが残留しないこと」が達成される。 The Ca addition for controlling the form of the second stage sulfide is performed on the molten steel in the ladle after vacuum degassing refining. The second stage of Ca addition is performed by blowing Ca alloy powder together with the carrier gas through the injection lance, or by adding an iron-coated wire filled with Ca alloy into the molten steel. Since the second stage of Ca addition has a low sulfur concentration in the molten steel to be added and a small amount of oxide inclusions, the pure Ca content is such that about 0.0010 to 0.0030 mass% of Ca remains in the molten steel. What is necessary is just to set the addition amount of. As a result, “CaS does not remain” of (c), which is a characteristic required for the HIC steel, is achieved.
以上説明したように、上記構成の本発明によれば、１段目のＣａ添加を脱硫処理と同時に実施するので、製造工程が短縮されることによって生産性が向上するのみならず、脱硫処理後の溶鋼中硫黄濃度が従来に比較して低下し、硫黄濃度が極めて低く、且つ、酸化物系介在物及び硫化物系介在物が極めて少ない、耐硫化物腐食割れ性に優れた清浄鋼を高い生産性で製造することが実現される。 As described above, according to the present invention having the above-described configuration, since the first stage of Ca addition is performed simultaneously with the desulfurization treatment, not only the productivity is improved by shortening the manufacturing process, but also after the desulfurization treatment. Highly clean steel with excellent resistance to sulfide corrosion cracking, with low sulfur concentration in molten steel compared to conventional steel, extremely low sulfur concentration, and extremely low oxide inclusions and sulfide inclusions Manufacturing with productivity is realized.
転炉から出鋼された、Ｃ：０．０２〜０．１質量％、Ｍｎ：０．５〜１．２質量％、Ｐ：０．０１質量％以下、Ｓ：０．００２５〜０．００５質量％、Ａｌ：０．０２〜０．０４質量％を含有する２００〜２６０トンの取鍋内溶鋼に対し、本発明による製造方法（本発明例）及び従来法による製造方法（比較例１〜４）を適用して耐ＨＩＣ鋼を製造した。 Steel is produced from the converter, C: 0.02 to 0.1 mass%, Mn: 0.5 to 1.2 mass%, P: 0.01 mass% or less, S: 0.0025 to 0.005 With respect to 200 to 260 tons of molten steel in a ladle containing mass% and Al: 0.02 to 0.04 mass%, the production method according to the present invention (example of the present invention) and the production method according to the conventional method (comparative examples 1 to 2) 4) was applied to produce HIC steel.
本発明例及び比較例１〜４の何れの場合も、転炉出鋼直後に金属Ａｌを添加して溶鋼を脱酸し、脱硫処理工程においては、ＣａＯ−Ａｌ2Ｏ3−ＳｉＯ2系のフラックスを脱硫剤として用い、黒鉛電極からのアーク加熱により溶鋼を昇温し、前記脱硫剤を滓化させ、溶鋼に浸漬させたインジェクションランスから１００〜１５０Ｎｍ3／ｈｒのＡｒガスを攪拌用ガスとして吹き込み、溶鋼及び脱硫剤を攪拌して脱硫した。この脱硫処理の後に、ＲＨ真空脱ガス装置を用いて、脱ガス処理、溶鋼成分の調整、攪拌による介在物の浮上・分離を行った。真空脱ガス精錬の処理時間は２０分間とし、何れの場合も同一とした。溶鋼へのＣａの添加方法はそれぞれ異なるので、以下に、本発明例及び比較例１〜４の各製造方法を説明する。 In any case of the present invention example and Comparative Examples 1 to 4, the molten steel is deoxidized by adding metal Al immediately after the converter steel, and in the desulfurization treatment step, the CaO—Al 2 O 3 —SiO 2 type is used. Using a flux as a desulfurizing agent, the molten steel is heated by arc heating from a graphite electrode, the desulfurizing agent is hatched, and Ar gas of 100 to 150 Nm 3 / hr is used as a stirring gas from an injection lance immersed in the molten steel. The molten steel and the desulfurizing agent were stirred and desulfurized. After this desulfurization treatment, degassing treatment, adjustment of molten steel components, and floating and separation of inclusions by stirring were performed using an RH vacuum degassing apparatus. The processing time for the vacuum degassing refining was 20 minutes and was the same in all cases. Since the method of adding Ca to the molten steel is different, each method of the present invention and Comparative Examples 1 to 4 will be described below.
本発明例では、脱硫処理時、インジェクションランスからのＡｒガスとともにＣａ−Ｓｉ合金粉末（Ｃａ：３０質量％、Ｓｉ：７０質量％）を１分間あたり２０〜３０ｋｇで吹き込み、その吹き込み量は１チャージあたり１５０〜２５０ｋｇとした。脱硫処理後、ＲＨ真空脱ガス装置で２０分間の脱ガス精錬を実施した後、取鍋をＲＨ真空脱ガス装置から払い出し、ワイヤーフィーダー装置を用い、Ｃａ−Ｓｉ合金（Ｃａ：３０質量％、Ｓｉ：７０質量％）を、その内部に充填した鉄被覆ワイヤーを１分間あたり２０〜３０ｋｇの添加速度で溶鋼の硫黄濃度に応じて１チャージあたり３０〜７０ｋｇ添加した。その後、この溶鋼を連続鋳造設備に搬送し、連続鋳造した。 In the present invention example, during the desulfurization treatment, Ca—Si alloy powder (Ca: 30% by mass, Si: 70% by mass) is injected at 20-30 kg per minute together with Ar gas from the injection lance, and the injection amount is 1 charge. 150 to 250 kg per unit. After desulfurization treatment, after performing degassing refining for 20 minutes with an RH vacuum degassing apparatus, the ladle is discharged from the RH vacuum degassing apparatus, and a Ca-Si alloy (Ca: 30% by mass, Si is used) using a wire feeder apparatus. : 70 mass%) of the iron-coated wire filled therein was added at 30 to 70 kg per charge at a rate of 20 to 30 kg per minute depending on the sulfur concentration of the molten steel. Thereafter, the molten steel was conveyed to a continuous casting facility and continuously cast.
比較例１では、真空脱ガス精錬後、取鍋をＲＨ真空脱ガス装置から払い出し、ワイヤーフィーダー装置を用い、前述の鉄被覆ワイヤーを１分間あたり２０〜３０ｋｇの添加速度で溶鋼の硫黄濃度に応じて１チャージあたり７０〜１１０ｋｇ添加した。その後、この溶鋼を連続鋳造設備に搬送し、連続鋳造した。 In Comparative Example 1, after the vacuum degassing refining, the ladle is discharged from the RH vacuum degassing apparatus, and the above iron-coated wire is used at a rate of addition of 20 to 30 kg per minute depending on the sulfur concentration of the molten steel using a wire feeder apparatus. 70 to 110 kg was added per charge. Thereafter, the molten steel was conveyed to a continuous casting facility and continuously cast.
比較例２では、脱硫処理終了後に、取鍋内溶鋼に浸漬させたインジェクションランスからＡｒガスを搬送用ガスとして前述のＣａ−Ｓｉ合金粉末を１分間あたり２０〜３０ｋｇで、１チャージあたり１５０〜２５０ｋｇ、溶鋼中へ吹き込んだ。その後、ＲＨ真空脱ガス装置で２０分間の脱ガス精錬を実施した後、取鍋を連続鋳造設備に搬送し、連続鋳造中、連続鋳造設備のタンディッシュ内の溶鋼に、ワイヤーフィーダー装置を用いて前述の鉄被覆ワイヤーを１分間あたり０．７〜１．０ｋｇの添加速度で溶鋼の硫黄濃度に応じて１チャージあたり７０〜１１０ｋｇ添加した。 In Comparative Example 2, after completion of the desulfurization treatment, the above-described Ca—Si alloy powder was used at 20 to 30 kg per minute from the injection lance soaked in the molten steel in the ladle as the carrier gas, and 150 to 250 kg per charge. And blown into the molten steel. Then, after carrying out degassing refining for 20 minutes with the RH vacuum degassing device, the ladle is transported to the continuous casting equipment, and during continuous casting, the molten steel in the tundish of the continuous casting equipment is used with a wire feeder device. The above iron-coated wire was added at 70 to 110 kg per charge at a rate of 0.7 to 1.0 kg per minute depending on the sulfur concentration of the molten steel.
比較例３では、真空脱ガス精錬後、取鍋内溶鋼に浸漬させたインジェクションランスからＡｒガスを搬送用ガスとして前述のＣａ−Ｓｉ合金粉末を１分間あたり２０〜３０ｋｇで、１チャージあたり１５０〜２５０ｋｇ、溶鋼中へ吹き込んだ。その後、取鍋を連続鋳造設備に搬送し、連続鋳造中、連続鋳造設備のタンディッシュ内の溶鋼に、ワイヤーフィーダー装置を用いて前述の鉄被覆ワイヤーを１分間あたり０．７〜１．０ｋｇの添加速度で溶鋼の硫黄濃度に応じて１チャージあたり７０〜１１０ｋｇ添加した。 In Comparative Example 3, after vacuum degassing and refining, 20 to 30 kg of the above-mentioned Ca—Si alloy powder was used per minute from an injection lance dipped in molten steel in the ladle, and Ar gas was used as a carrier gas. 250 kg was blown into the molten steel. Thereafter, the ladle is conveyed to a continuous casting facility. During continuous casting, the above iron-coated wire is 0.7 to 1.0 kg per minute using molten wire in the tundish of the continuous casting facility using a wire feeder device. Depending on the sulfur concentration of the molten steel at an addition rate, 70 to 110 kg was added per charge.
比較例４では、減圧下での真空脱ガス精錬時、取鍋内溶鋼に浸漬させたインジェクションランスからＡｒガスを搬送用ガスとして前述のＣａ−Ｓｉ合金粉末を１分間あたり２０〜３０ｋｇで、１チャージあたり１５０〜２５０ｋｇ、溶鋼中へ吹き込んだ。更に、ＲＨ真空脱ガス装置の真空槽を大気圧に戻した後、取鍋内溶鋼に浸漬させたインジェクションランスからＡｒガスを搬送用ガスとして前述のＣａ−Ｓｉ合金粉末を１分間あたり２０〜３０ｋｇで、１チャージあたり７０〜１１０ｋｇ、溶鋼中へ吹き込んだ。その後、この溶鋼を連続鋳造設備に搬送し、連続鋳造した。 In Comparative Example 4, at the time of vacuum degassing refining under reduced pressure, the aforementioned Ca—Si alloy powder was used at 20 to 30 kg per minute using Ar gas as a transfer gas from an injection lance immersed in molten steel in the ladle. 150-250 kg per charge was blown into the molten steel. Furthermore, after returning the vacuum tank of the RH vacuum degassing apparatus to atmospheric pressure, 20 to 30 kg of the above-mentioned Ca—Si alloy powder per minute is used with Ar gas as a carrier gas from an injection lance immersed in molten steel in the ladle. Then, 70 to 110 kg per charge was blown into the molten steel. Thereafter, the molten steel was conveyed to a continuous casting facility and continuously cast.
それぞれの製造方法において、各製造工程での溶鋼の成分を調査した。また、連続鋳造により得られた鋳片の幅中央で厚み方向１／４の位置から採取した試験片について、Ｓ及びＣａの含有量を調査するとともに、介在物の個数判定並びにＣａＯ−Ａｌ2Ｏ3系介在物におけるＣａＯ／Ａｌ2Ｏ3の質量比率を調査した。 In each manufacturing method, the component of the molten steel in each manufacturing process was investigated. In addition, for the test piece collected from the position in the thickness direction 1/4 at the center of the width of the slab obtained by continuous casting, the contents of S and Ca were investigated, the number of inclusions was determined, and CaO-Al 2 O The mass ratio of CaO / Al 2 O 3 in the 3 system inclusions was investigated.
それらの結果を表１に示す。表１では、脱硫処理工程の処理時間を併せて示している。尚、脱硫処理時間は、従来の脱硫処理方法である比較例１〜４の処理時間を１．０として指数化して表示し、また、鋳片の介在物個数は、Ｃａの１段添加である比較例１を基準として指数化して表示している。 The results are shown in Table 1. Table 1 also shows the treatment time of the desulfurization treatment process. Note that the desulfurization treatment time is expressed by indexing the treatment time of Comparative Examples 1 to 4 as a conventional desulfurization treatment method as 1.0, and the number of inclusions in the slab is one-stage addition of Ca. Indexed with the comparative example 1 as a reference.
表１から明らかなように、本発明例では、脱硫処理時間を２割程度短縮することができた。更に、脱硫処理後の溶鋼中硫黄濃度は比較例１〜４に比べて低く、極低硫鋼が得られることが分かった。また、鋳片のＣａ濃度を比較すると、一段のＣａ添加である比較例１では、１０〜３５ｐｐｍとばらつきが大きいのに対し、Ｃａを２段添加した比較例２〜４では、鋳片のＣａ濃度のばらつき幅は１５〜１９ｐｐｍと低下していた。なかでも、２段目のＣａを取鍋で添加した比較例４では、Ｃａ濃度のばらつき幅が小さくなっていた。 As is apparent from Table 1, in the present invention example, the desulfurization treatment time could be shortened by about 20%. Furthermore, it was found that the sulfur concentration in the molten steel after the desulfurization treatment was lower than those in Comparative Examples 1 to 4, and an extremely low sulfur steel was obtained. Further, when the Ca concentration of the slab is compared, in Comparative Example 1 in which Ca is added in one stage, the variation is large as 10 to 35 ppm, whereas in Comparative Examples 2 to 4 in which Ca is added in two stages, Ca in the slab is increased. The variation width of the concentration was reduced to 15 to 19 ppm. Especially, in the comparative example 4 which added the 2nd step | paragraph Ca with the ladle, the dispersion | variation width of Ca density | concentration was small.
本発明例では、鋳片のＣａ濃度のばらつき幅は１０ｐｐｍであり、比較例４よりも更に鋳片のＣａ濃度のばらつき幅が低下した。 In the example of the present invention, the variation width of the Ca concentration of the slab was 10 ppm, and the variation width of the Ca concentration of the slab was further reduced as compared with Comparative Example 4.
また、指数化した鋳片の介在物個数は、２段のＣａ添加である比較例２〜４では０．７５〜０．９８であるのに対し、本発明例では０．６６〜０．７２であり、同じ２段のＣａ添加でありながら、本発明例の優位性が確認できた。これは、本発明例においては介在物の浮上時間が長くなることに基づいている。 The number of inclusions in the slab indexed is 0.75 to 0.98 in Comparative Examples 2 to 4 in which Ca is added in two stages, while 0.66 to 0.72 in the present invention. Thus, the superiority of the present invention example could be confirmed while the same two-stage Ca addition. This is based on the fact that the floating time of inclusions becomes longer in the present invention example.
上記の調査結果に基づき、脱硫処理時間、低硫化度合い、工程数、酸化物系介在物組成制御の精度、酸化物系介在物浮上効率、酸化物系介在物浮上時間、Ｃａ歩留りの７つの項目について、本発明例及び比較例１〜４の各製造方法の優位性を比較・評価した結果を表２に示す。尚、表２の◎印は極めて良好、○は良好、△はやや不良、×は不良を表している。 Based on the above survey results, seven items of desulfurization treatment time, degree of low sulfidation, number of steps, oxide inclusion composition control accuracy, oxide inclusion flotation efficiency, oxide inclusion flotation time, and Ca yield Table 2 shows the results of comparing and evaluating the superiority of the production methods of the present invention and Comparative Examples 1 to 4. In Table 2, “◎” indicates extremely good, “◯” indicates good, “Δ” indicates slightly poor, and “×” indicates poor.
本発明例では、脱硫処理と同時にＣａを添加するので、それによる強攪拌及び脱酸効果により、脱硫処理時間及び低硫化度合いが比較例１〜４に比べて優れている。 In the example of the present invention, Ca is added at the same time as the desulfurization treatment, and therefore the desulfurization treatment time and the degree of low sulfidation are superior to those of Comparative Examples 1 to 4 due to the strong stirring and the deoxidation effect.
また、本発明例では、脱硫処理と同時に１段目のＣａ添加を実施するので、１段目のＣａ添加のための工程を必要とせず、１段添加の比較例１と同等の工程で処理することができる。これに対して、比較例２は、１段目のＣａ添加の工程が別途必要であり、更に、タンディッシュにおいてもＣａを添加する必要があり、比較例３は、タンディッシュにおいてもＣａを添加する必要がある。比較例４は、工程的には本発明例と同等である。 Further, in the present invention example, the first-stage Ca addition is performed simultaneously with the desulfurization treatment, so that the process for the first-stage Ca addition is not required, and the process is performed in the same process as the first-stage addition Comparative Example 1. can do. In contrast, Comparative Example 2 requires a separate step of adding Ca in the first stage, and further needs to add Ca in the tundish, and Comparative Example 3 adds Ca also in the tundish. There is a need to. Comparative Example 4 is equivalent in process to the inventive example.
また、Ｃａ添加が１段のみである比較例１に比べて、Ｃａ添加が２段である本発明例及び比較例２〜４では、酸化物系介在物組成の形態制御と、硫化物の形態制御のためのＣａを分割し、２段に分けて添加したことで、酸化物系介在物組成制御の精度が向上する。その中でも特に、本発明例では１段目のＣａ添加量を最適に制御できるので、溶鋼中のＡｌ2Ｏ3のほとんどを形態制御することが可能であり、酸化物系介在物組成制御の精度がより高い。 In addition, compared to Comparative Example 1 in which only one stage of Ca is added, in the present invention example and Comparative Examples 2 to 4 in which Ca is added in two stages, the form control of oxide inclusion composition and the form of sulfide By dividing Ca for control and adding it in two stages, the accuracy of the oxide inclusion composition control is improved. In particular, in the present invention example, since the amount of Ca added in the first stage can be optimally controlled, it is possible to control the form of almost all Al 2 O 3 in the molten steel, and the accuracy of the oxide inclusion composition control. Is higher.
また、各処理工程に要する時間及び処理間の所要時間を同じとした場合、酸化物系介在物の浮上時間を、酸化物系介在物形態制御のためのＣａ添加から鋳造までの時間と定義すると、本発明例が最も浮上時間が長く、これは、本発明例において酸化物系介在物が少ないことと一致する。 In addition, when the time required for each treatment step and the time required for the treatment are the same, the floating time of the oxide inclusions is defined as the time from Ca addition to casting for oxide inclusion form control. The example of the present invention has the longest rise time, which is consistent with the fact that there are few oxide inclusions in the example of the present invention.
また更に、鋳片のＣａ濃度のばらつき幅は、Ｃａを２段に分けて添加することで少なくなるが、特に、２段目のＣａを取鍋内の溶鋼に添加することで、Ｃａ濃度が均一化されることが分かる。 Furthermore, the variation width of the Ca concentration of the slab is reduced by adding Ca in two stages, and in particular, by adding the second stage Ca to the molten steel in the ladle, the Ca concentration is reduced. It turns out that it is equalized.
このように、本発明方法は、脱硫処理時間、低硫化度合い、工程数、酸化物系介在物組成制御の精度、酸化物系介在物浮上効率、酸化物系介在物浮上時間、Ｃａ歩留りの７つの全ての項目から見て、優れた製造方法であることが確認できた。 As described above, the method of the present invention has a desulfurization treatment time, a low degree of sulfidation, the number of steps, the accuracy of oxide inclusion composition control, the oxide inclusion flotation efficiency, the oxide inclusion flotation time, and the Ca yield. From all three items, it was confirmed that this was an excellent manufacturing method.
実施例１に記載した本発明例において、１段目のＣａ添加のＣａ−Ｓｉ合金の添加量を溶鋼中のＡｌ濃度及びトータル酸素濃度に対して変更し、鋳片の酸化物系介在物に及ぼす影響を調査した。鋳片の酸化物系介在物の調査方法は実施例１と同様の方法で実施した。 In the present invention example described in Example 1, the amount of Ca-Si alloy added in the first stage of Ca was changed with respect to the Al concentration and the total oxygen concentration in the molten steel, so that the oxide inclusions in the slab The effect was investigated. The method for investigating oxide inclusions in the slab was carried out in the same manner as in Example 1.
調査結果を表３に示す。尚、表３において、鋳片の酸化物系介在物の個数は、実施例１と同様に、Ｃａを１段で添加した、実施例１の比較例１を基準として、指数化して示している。 The survey results are shown in Table 3. In Table 3, the number of oxide inclusions in the slab is shown as an index on the basis of Comparative Example 1 of Example 1 in which Ca is added in one stage, as in Example 1. .
表３に示すように、（１）式で定まる範囲内のＣａを添加した試験１〜４は、Ｃａ添加量が（１）式で定まる範囲よりも少ない試験５〜８に比べて、鋳片のＣａ濃度が高く、且つ、鋳片の酸化物系介在物個数が少なくなっており、酸化物系介在物の低減効果が顕著であることが分かった。 As shown in Table 3, Tests 1 to 4 in which Ca within the range determined by Equation (1) was added, compared to Tests 5 to 8 where the amount of Ca addition is less than the range determined by Equation (1). It was found that the Ca concentration was high and the number of oxide inclusions in the slab was small, and the effect of reducing oxide inclusions was remarkable.
Claims (2)
［％Ｃａ］≧0.01×［％Ａｌ］2/3＋0.9×［％Ｔ．Ｏ］…（１）
但し（１）式において、［％Ｃａ］は溶鋼中のＣａ濃度（質量％）、［％Ａｌ］は溶鋼中のＡｌ濃度（質量％）、［％Ｔ．Ｏ］は溶鋼中のトータル酸素濃度（質量％）である。 In the molten steel, the Ca concentration in the molten steel is within the range of the following formula (1) when the addition amount of pure Ca of the Ca-containing metal during the desulfurization treatment is 100%. The method for producing clean steel excellent in resistance to sulfide corrosion cracking according to claim 1, wherein the adjustment is made in accordance with the Al concentration and the total oxygen concentration.
[% Ca] ≧ 0.01 × [% Al] 2/3 + 0.9 × [% T. O] ... (1)
However, in the formula (1), [% Ca] is the Ca concentration (mass%) in the molten steel, [% Al] is the Al concentration (mass%) in the molten steel, and [% T.I. O] is the total oxygen concentration (mass%) in the molten steel.
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| JP2018168454A (en) * | 2017-03-30 | 2018-11-01 | Ｊｆｅスチール株式会社 | Production method of high cleanliness steel |
| WO2019182056A1 (en) | 2018-03-23 | 2019-09-26 | Ｊｆｅスチール株式会社 | Method for manufacturing high-purity steel |
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