JP4879809B2 - Continuous casting method - Google Patents
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Description
本発明は、例えば自動車用薄鋼板等に用いられるＴｉを含有した低炭素もしくは極低炭素アルミキルド鋼の連続鋳造方法に関するものである。 The present invention relates to a continuous casting method of low carbon or extremely low carbon aluminum killed steel containing Ti used for, for example, thin steel sheets for automobiles.
低炭素もしくは極低炭素アルミキルド鋼は、ブリキや自動車用薄鋼板など高級な薄鋼板への使用が多い鋼種である。自動車用薄鋼板においては、近年品質の厳格化が急速に進んでおり、特に連続鋳造時に鋳片への介在物混入を防止する必要がある。介在物としては、脱酸生成物であるアルミナがクラスタリングしたアルミナクラスターと連続鋳造時に鋳型と鋳片の潤滑性を保持するために使用する酸化物を主成分とするパウダーの混入に大きく分けられる。 Low carbon or extremely low carbon aluminum killed steel is a steel type that is frequently used for high-grade thin steel sheets such as tinplate and automotive steel sheets. In automotive thin steel sheets, quality has become stricter in recent years, and it is particularly necessary to prevent inclusion inclusions in the slab during continuous casting. Inclusions can be broadly classified into alumina clusters in which alumina as a deoxidation product is clustered and powders mainly composed of oxide used to maintain the lubricity of the mold and slab during continuous casting.
大型のアルミナクラスターが鋳片表面に捕捉されると、圧延時に細長い筋状の欠陥となる。このような大型のアルミナクラスターの生成要因の一つとして、連続鋳造時に使用する浸漬ノズル内に付着したアルミナ粒子の凝集体の脱落が考えられる。また、浸漬ノズルへのアルミナ付着による詰まりが、ノズルから供給される溶鋼流れの偏りを誘因し、この溶鋼流れの偏りがパウダーの溶鋼中への巻き込みを助長することとなる。巻き込まれたパウダーは、プレス時の割れの起点となる。 When a large alumina cluster is captured on the surface of the slab, it becomes a strip-like defect during rolling. As one of the generation factors of such large-sized alumina clusters, it is conceivable that the aggregates of alumina particles adhering to the immersion nozzle used during continuous casting fall off. In addition, clogging due to alumina adhesion to the immersion nozzle induces a deviation of the molten steel flow supplied from the nozzle, and this deviation of the molten steel flow promotes the entrainment of powder into the molten steel. The entrained powder is the starting point for cracking during pressing.
浸漬ノズルのアルミナ付着による詰まりを抑制することが、鋳造の安定化及び欠陥発生の低減に繋がる。この浸漬ノズルのアルミナ付着による詰まり現象は、自動車用薄鋼板用の溶鋼で特に顕著であり、これまで種々の対策が講じられてきている。これまでの浸漬ノズル詰まり対策として、（１）浸漬ノズル内への不活性ガス吹き込み、（２）浸漬ノズル耐火物の改善、（３）脱酸生成物の組成制御などが挙げられる。（１）の浸漬ノズル内への不活性ガス吹き込みは最も一般的な方法であり、ノズル詰まり防止効果としては完全ではないものの、鋼種やその他の条件に関わらず効果がある。（２）の浸漬ノズルの耐火物では、耐火物中にＣａＯなどを混入させアルミナを耐火物に吸収させるもしくは低融点化させることで付着厚みを軽減するものである。この方法では、鋳造初期には効果を発揮するものの、耐火物へのアルミナ吸収能には限界があり完全な付着防止はできないこと、さらにＣａＯを含むため水分管理を厳重に行わないといけないなど作業性にも問題がある。（３）の脱酸生成物の制御の代表的な例としてＣａ添加が挙げられる。Ｃａ添加は、Ａｌ脱酸した後に、Ｃａを添加し酸化物の組成を低融点化し、ノズルへの付着を防止するものであり、低融点に完全に制御できれば詰まりを防止する最も効果的な方法である。しかしながら、Ｃａの添加歩留は非常に悪くコスト増大を招くこと、さらにスラグなどからの再酸化により酸化物の融点が高くなるとアルミナ以上にノズル詰まりを起こしやすいといった問題がある。これに対して、微量の希土類元素を用いる方法が開示されている（特許文献１）。これによれば、微量の希土類元素添加で浸漬ノズルの詰まりが防止でき、コスト的にも制御性も有利であるとされている。 Suppressing clogging due to alumina adhesion of the immersion nozzle leads to stabilization of casting and reduction of defects. The clogging phenomenon due to the alumina adhesion of the immersion nozzle is particularly remarkable in molten steel for automobile thin steel sheets, and various countermeasures have been taken so far. Examples of countermeasures against clogging of the immersion nozzle so far include (1) blowing an inert gas into the immersion nozzle, (2) improving the immersion nozzle refractory, and (3) controlling the composition of the deoxidized product. Inert gas blowing into the immersion nozzle (1) is the most common method, and although it is not perfect as a nozzle clogging prevention effect, it is effective regardless of the steel type and other conditions. In the refractory material of the immersion nozzle (2), the adhesion thickness is reduced by mixing CaO or the like into the refractory material to absorb alumina or lowering the melting point. Although this method is effective at the beginning of casting, there is a limit to the ability to absorb alumina to the refractory and it is impossible to prevent adhesion completely. Furthermore, since it contains CaO, moisture management must be strictly performed. There is also a problem with sex. As a typical example of the control of the deoxidation product of (3), Ca addition can be mentioned. Ca addition is a method for preventing clogging if it can be completely controlled to a low melting point by adding Ca to lower the melting point of the oxide composition after Al deoxidation and preventing the adhesion to the nozzle. It is. However, the Ca addition yield is very bad, leading to an increase in cost. Further, when the melting point of the oxide is increased by reoxidation from slag or the like, there is a problem that nozzle clogging is more likely to occur than alumina. On the other hand, a method using a trace amount of rare earth elements is disclosed (Patent Document 1). According to this, clogging of the immersion nozzle can be prevented by adding a small amount of rare earth elements, and controllability is also advantageous in terms of cost.
連続鋳造時の浸漬ノズル詰まりを安価かつ簡便な方法で防止するために特許文献１のように微量の希土類元素を添加する方法が開示されており、希土類元素の添加量や添加方法、脱酸生成物の組成の制御範囲などが規定されている。しかしながら、これらの特許において規定されている項目のみでは浸漬ノズル詰まり防止効果にはばらつきがあり、さらなる改善が望まれていた。浸漬ノズルの詰まり現象は、浸漬ノズルの耐火物組成や溶鋼組成によりその形態が異なるため、浸漬ノズルへの付着機構も異なることが考えられる。また、希土類元素を添加して酸化物組成を制御する場合、溶鋼中に含まれる酸素濃度だけではなく、希土類元素以外の脱酸元素（特にＡｌ）の濃度により変化する。このような観点での検討が不足していたため、上述したように希土類元素添加による浸漬ノズル詰まり抑制効果にばらつきが生じるものと推定される。 In order to prevent clogging of the immersion nozzle at the time of continuous casting by a cheap and simple method, a method of adding a trace amount of rare earth elements as disclosed in Patent Document 1 is disclosed. The control range of the composition of the product is defined. However, only the items specified in these patents have variations in the effect of preventing clogging of the immersion nozzle, and further improvement has been desired. Since the form of the clogging phenomenon of the immersion nozzle varies depending on the refractory composition and molten steel composition of the immersion nozzle, it is considered that the adhesion mechanism to the immersion nozzle is also different. In addition, when the oxide composition is controlled by adding a rare earth element, the oxide composition varies depending not only on the oxygen concentration contained in the molten steel but also on the concentration of deoxidizing elements (particularly Al) other than the rare earth element. Since the examination from such a viewpoint has been insufficient, it is presumed that the immersion nozzle clogging suppression effect due to the addition of the rare earth element varies as described above.
本発明の目的は、Ｔｉを含有する低炭素もしくは極低炭素アルミキルド鋼の連続鋳造時の浸漬ノズル詰まりを安価かつ制御が容易な方法でばらつきがなく安定的に防止することである。 An object of the present invention is to stably prevent immersion nozzle clogging in a low-cost and easy-to-control method during continuous casting of Ti-containing low carbon or extremely low carbon aluminum killed steel.
本発明者らは、上記課題を解決するために更なる考察を進め、以下に記載するように連続鋳造時の浸漬ノズルの詰まり問題を安価かつ容易に制御できる方法を考案した。 In order to solve the above-mentioned problems, the present inventors have made further considerations and devised a method that can control the clogging problem of the immersion nozzle during continuous casting at a low cost and easily as described below.
手段１は、Ｃ≦０．０２ｍａｓｓ％かつＴｉ≧０．０１ｍａｓｓ％を含むアルミキルド鋼をＡｌ2Ｏ3：４２〜５２ｍａｓｓ％、グラファイト：２０〜３０ｍａｓｓ％、ＳｉＯ2：１５〜２５ｍａｓｓ％、ＳｉＣ：５〜１０ｍａｓｓ％含む浸漬ノズルを用いて鋳型に溶鋼を供給する連続鋳造において、浸漬ノズル１本当り１０００ｔｏｎ以上を連続して鋳造する場合、鋳造開始前までに前記溶鋼中のＳ濃度を（１）式で示す範囲にすることを特徴とする連続鋳造方法である。
［％Ｓ］≦０．００４＋［％Ｔｉ］／１５ ・・・ （１）
ただし、［％Ｓ］、［％Ｔｉ］はそれぞれ溶鋼中のＳ、Ｔｉの含有量（ｍａｓｓ％）である。
Means 1 are aluminum killed steel containing C ≦ 0.02 mass% and Ti ≧ 0.01 mass%, Al 2 O 3 : 42 to 52 mass%, graphite: 20 to 30 mass%, SiO 2 : 15 to 25 mass%, SiC: 5 In continuous casting in which molten steel is supplied to a mold using an immersion nozzle containing 10 mass%, when continuously casting 1000 tons or more per immersion nozzle, the S concentration in the molten steel is expressed by equation (1) before the start of casting. It is the continuous casting method characterized by making it into the range shown by.
[% S] ≦ 0.004 + [% Ti] / 15 (1)
However, [% S] and [% Ti] are the contents (mass%) of S and Ti in the molten steel, respectively.
手段２は、Ｃ≦０．０２ｍａｓｓ％かつＴｉ≧０．０１ｍａｓｓ％を含むアルミキルド鋼をＡｌ2Ｏ3：４２〜５２ｍａｓｓ％、グラファイト：２０〜３０ｍａｓｓ％、ＳｉＯ2：１５〜２５ｍａｓｓ％、ＳｉＣ：５〜１０ｍａｓｓ％含む浸漬ノズルを用いて鋳型に溶鋼を供給する連続鋳造において、浸漬ノズル１本当り１０００ｔｏｎ以上を連続して鋳造する場合、鋳造開始前までに前記溶鋼中に希土類元素を（２）式で示す範囲になるように添加することを特徴とする連続鋳造方法である。
０．０８×［％Ａｌ］≦ＷREM≦０．２×［％Ａｌ］ ・・・ （２）
ただし、ＷREMは希土類元素の添加量（ｋｇ／ｔｏｎ）、［％Ａｌ］は溶鋼中のＡｌ含有量（ｍａｓｓ％）である。
0.08 × [% Al] ≦ W REM ≦ 0.2 × [% Al] (2)
However, W REM is the amount of rare earth element added (kg / ton), and [% Al] is the Al content (mass%) in the molten steel.
手段３は、Ｃ≦０．０２ｍａｓｓ％かつＴｉ≧０．０１ｍａｓｓ％を含むアルミキルド鋼をＡｌ2Ｏ3：４２〜５２ｍａｓｓ％、グラファイト：２０〜３０ｍａｓｓ％、ＳｉＯ2：１５〜２５ｍａｓｓ％、ＳｉＣ：５〜１０ｍａｓｓ％含む浸漬ノズルを用いて鋳型に溶鋼を供給する連続鋳造において、浸漬ノズル１本当り１０００ｔｏｎ以上を連続して鋳造する場合、鋳造開始前までに前記溶鋼中のＳ濃度を（１）式で示す範囲にし、前記溶鋼中に希土類元素を（２）式で示す範囲になるように添加することを特徴とする連続鋳造方法である。
［％Ｓ］≦０．００４＋［％Ｔｉ］／１５ ・・・ （１）
０．０８×［％Ａｌ］≦ＷREM≦０．２×［％Ａｌ］ ・・・ （２）
ただし、［％Ｓ］、［％Ｔｉ］、［％Ａｌ］はそれぞれ溶鋼中のＳ、Ｔｉ、Ａｌの含有量（ｍａｓｓ％）、ＷREMは希土類元素の添加量（ｋｇ／ｔｏｎ）である。
Means 3 are aluminum killed steel containing C ≦ 0.02 mass% and Ti ≧ 0.01 mass% in Al 2 O 3 : 42 to 52 mass%, graphite: 20 to 30 mass%, SiO 2 : 15 to 25 mass%, SiC: 5 In continuous casting in which molten steel is supplied to a mold using an immersion nozzle containing 10 mass%, when continuously casting 1000 tons or more per immersion nozzle, the S concentration in the molten steel is expressed by equation (1) before the start of casting. In the continuous casting method, the rare earth element is added to the molten steel so as to fall within the range represented by the formula (2).
[% S] ≦ 0.004 + [% Ti] / 15 (1)
0.08 × [% Al] ≦ W REM ≦ 0.2 × [% Al] (2)
However, [% S], [% Ti], and [% Al] are the contents (mass%) of S, Ti, and Al in the molten steel, respectively, and W REM is the amount of rare earth element added (kg / ton).
なお、希土類元素とは、元素の周期律表の中のＬａからＬｕまでの１５元素である。 The rare earth elements are 15 elements from La to Lu in the periodic table of elements.
本発明によれば、連続鋳造時の浸漬ノズルの詰まり問題を安価かつ容易に制御できる方法でばらつきなく安定的に改善でき、連続鋳造時の操業及び品質の安定化を達成することが可能である。 According to the present invention, the problem of clogging of the immersion nozzle during continuous casting can be stably improved without variation by a method that can be controlled inexpensively and easily, and it is possible to achieve stable operation and quality during continuous casting. .
本発明者らは、連続鋳造時の浸漬ノズルの付着物調査結果から推定した付着機構から、Ｔｉを含有する低炭素及び極低炭素アルミキルド鋼において、Ｔｉ濃度に応じたＳ濃度とすることにより浸漬ノズルの詰まりを抑制可能なことを見出した。さらに、微量な希土類元素の添加に関しては、脱酸平衡を支配しているＡｌ濃度レベルに応じて添加量を制御することにより、浸漬ノズル詰まり抑制効果を安定的に発揮させることができることを知見した。 From the adhesion mechanism estimated from the investigation results of the deposits of the immersion nozzle during continuous casting, the present inventors have immersed by setting the S concentration in accordance with the Ti concentration in the low carbon and ultra-low carbon aluminum killed steel containing Ti. We found that nozzle clogging can be suppressed. Furthermore, regarding the addition of a trace amount of rare earth elements, it was found that the effect of suppressing the clogging of the immersion nozzle can be stably exhibited by controlling the addition amount according to the Al concentration level governing the deoxidation equilibrium. .
以下に図表を参照しながら、本発明の好適な実施の形態について詳細に説明する。 Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
Ｔｉ≧０．０１ｍａｓｓ％を含有する自動車用薄鋼板用鋳片を連続鋳造する場合、Ｔｉを含有していない低炭素アルミキルド鋼よりも浸漬ノズルが詰まりやすい。このため、連続鋳造する際の浸漬ノズル詰まり現象に与えるＴｉ含有の有無の影響を調査した。Ａｌ2Ｏ3＝４７ｍａｓｓ％、グラファイト＝２６％、ＳｉＯ2＝１８ｍａｓｓ％、ＳｉＣ＝７ｍａｓｓ％及びその他の微量酸化物から成る浸漬ノズル（アルミナグラファイト質ノズルと呼ぶ）の付着物をＥＰＭＡ（Ｘ線マイクロアナライザー）により分析した結果、Ｔｉを含有する自動車用薄鋼板では地金と酸化物の混合状態であるに対して、Ｔｉを含有していない低炭素アルミキルド鋼は酸化物が主体の付着物である事が判明した。これは、付着物中に存在する地金が酸化物の付着力を増加させ脱落しにくくするために、詰まりが顕著であると推定される。また、Ｓ濃度が高くなると、地金と酸化物の混合層に加えて、酸化物のみの層が増加することがわかった。このようにＴｉとＳにより付着形態及び付着厚みが変化することを知見した。Ｔｉを含む極低炭素アルミキルド鋼に地金が付着しやすい原因として、アルミナグラファイト質の耐火物よりＳｉが溶鋼中に溶出してくるため、Ｔｉの活性度が高くなり浸漬ノズル壁近傍の溶鋼中にＴｉＮが析出し凝固しやすいと考えられる。このため、アルミナグラファイト質ノズルは熱間強度などの特性が優れるなどの理由で最も広く使用されている反面、Ｔｉを含有している極低炭素アルミキルド鋼の鋳造に対しては不利となる側面もある。さらに、Ｔｉが溶鋼に与える影響として、前述の析出物の影響以外にも（１）溶鋼の粘性を増加させる、（２）溶鋼の表面エネルギーを増加させることが挙げられ、Ｓが溶鋼に与える影響としては、（１）溶鋼の粘性を低下させる、（２）溶鋼の表面エネルギーを低下させることが挙げられる。上述のようにＴｉとＳは、正反対の作用を及ぼす元素であり、両者の濃度バランスに適正値があると推定し、検討を行った。なお、Ｃ≦０．０２ｍａｓｓ％の場合、転炉や二次精錬において酸素により脱炭するために溶鋼中の酸素濃度が増加し、Ａｌで脱酸する時に酸化物が多量に生成してしまう。このため、Ｃ≦０．０２ｍａｓｓ％のアルミキルド鋼は浸漬ノズル詰まりを生じやすい。また、Ｔｉは、自動車用薄鋼板において固溶ＣやＮなどを析出物として固定するために必要とされる元素であり、通常、０．０１ｍａｓｓ％以上添加される。 When continuously casting a slab for an automotive thin steel sheet containing Ti ≧ 0.01 mass%, the immersion nozzle is more easily clogged than a low carbon aluminum killed steel containing no Ti. For this reason, the influence of the presence or absence of Ti on the immersion nozzle clogging phenomenon during continuous casting was investigated. A deposit of an immersion nozzle (referred to as an alumina graphitic nozzle) composed of Al 2 O 3 = 47 mass%, graphite = 26%, SiO 2 = 18 mass%, SiC = 7 mass% and other trace oxides is used as EPMA (X-ray micro As a result of analysis by an analyzer), a thin steel plate for automobiles containing Ti is in a mixed state of metal and oxide, whereas low carbon aluminum killed steel not containing Ti is an oxide-based deposit. Things turned out. This is presumed that clogging is conspicuous because the bare metal present in the deposit increases the adhesion of the oxide and makes it difficult to fall off. It was also found that when the S concentration was increased, the oxide-only layer increased in addition to the mixed layer of metal and oxide. Thus, it was found that the adhesion form and the adhesion thickness are changed by Ti and S. The reason why metal is likely to adhere to ultra-low carbon aluminum killed steel containing Ti is that Si elutes from the refractory material of alumina graphite into the molten steel, so that the activity of Ti increases and the molten steel near the immersion nozzle wall It is thought that TiN precipitates and is easily solidified. For this reason, alumina graphite nozzles are most widely used for reasons such as excellent hot strength, but on the other hand, there are also disadvantageous aspects for casting ultra-low carbon aluminum killed steel containing Ti. is there. Furthermore, the influence of Ti on molten steel includes (1) increasing the viscosity of the molten steel, and (2) increasing the surface energy of the molten steel in addition to the effects of the precipitates described above, and the influence of S on the molten steel. (1) Decrease the viscosity of the molten steel, (2) Decrease the surface energy of the molten steel. As described above, Ti and S are elements having the opposite action, and it was estimated that there was an appropriate value in the concentration balance between the two. In addition, in the case of C ≦ 0.02 mass%, the oxygen concentration in the molten steel increases because of decarburization with oxygen in the converter and secondary refining, and a large amount of oxide is generated when deoxidizing with Al. For this reason, C ≦ 0.02 mass% aluminum killed steel is likely to clog the immersion nozzle. Ti is an element required for fixing solute C, N, and the like as precipitates in an automotive thin steel sheet, and is usually added in an amount of 0.01 mass% or more.
表１のＡに示す成分範囲（Ｔｉを含有する自動車用薄鋼板）において、Ｔｉ濃度とＳ濃度を適宜変化させて浸漬ノズルの詰まり状況を調査した。連続鋳造の形態を以下に記載する。まず、転炉で脱炭した溶鋼を取鍋に受けて、ＲＨ（真空脱ガス装置）を用いて脱炭処理を行う。脱炭後、Ａｌを添加し脱酸し、所定時間の攪拌を加えた後に、成分調整のための合金類を添加した。成分調整が終了した溶鋼は、取鍋から中間容器であるタンディッシュに耐火物製ノズルを介して供給し、タンディッシュから鋳型へＡｌ2Ｏ3＝４７ｍａｓｓ％、グラファイト＝２６％、ＳｉＯ2＝１８ｍａｓｓ％、ＳｉＣ＝７ｍａｓｓ％及びその他の微量酸化物から成る浸漬ノズルを用いて供給した。浸漬ノズルからの溶鋼供給速度は、浸漬ノズル直上に設置されたスライディングノズルにより制御される。浸漬ノズル内には、詰まり防止のために不活性ガスとしてＡｒを吹き込んでいる。浸漬ノズルには２つの孔があり、そこから鋳型へ溶鋼が供給される。ストランド当たり１６００ｔｏｎ連々鋳した後の浸漬ノズルの付着物の最大厚みにより評価した。鋳造条件は、鋳造幅１９００ｍｍ、鋳造厚２８０ｍｍ、鋳造速度１．３ｍ／ｍｉｎである。浸漬ノズルへのＡｒガス吹き込み速度は５（Ｎｌ／ｍｉｎ）である。Ｔｉ濃度及びＳ濃度は、各連々鋳ではその間のチャージは、できるだけ成分をそろえて実施した。図１からわかるように、（１）式に示したＴｉ濃度（ｍａｓｓ％）とＳ濃度（ｍａｓｓ％）の関係であれば、付着物の最大厚みが２５ｍｍ未満の良好な状態である。なお、図中のＴｉ濃度及びＳ濃度は、同一キャスト内の平均値としている。
［％Ｓ］≦０．００４＋［％Ｔｉ］／１５ ・・・ （１）
なお、Ｔｉ濃度は、自動車用薄鋼板（極低炭素アルミキルド鋼）で通常添加する濃度範囲としてＴｉ＝０．０１〜０．０５ｍａｓｓ％としている。
In the component range shown in A of Table 1 (Ti steel sheet for automobiles), the clogged state of the immersion nozzle was investigated by appropriately changing the Ti concentration and the S concentration. The form of continuous casting is described below. First, the molten steel decarburized in the converter is received in a ladle and decarburized using an RH (vacuum degasser). After decarburization, Al was added for deoxidation, and after stirring for a predetermined time, alloys for component adjustment were added. The molten steel whose components have been adjusted is supplied from the ladle to the tundish, which is an intermediate container, via a refractory nozzle, and Al 2 O 3 = 47 mass%, graphite = 26%, SiO 2 = 18 mass from the tundish to the mold. %, SiC = 7 mass%, and other submerged oxides. The molten steel supply speed from the immersion nozzle is controlled by a sliding nozzle installed immediately above the immersion nozzle. Ar is blown into the immersion nozzle as an inert gas to prevent clogging. The immersion nozzle has two holes from which molten steel is supplied to the mold. It evaluated by the maximum thickness of the deposit | attachment of the immersion nozzle after casting 1600ton per strand continuously. The casting conditions are a casting width of 1900 mm, a casting thickness of 280 mm, and a casting speed of 1.3 m / min. The Ar gas blowing speed into the immersion nozzle is 5 (Nl / min). Regarding the Ti concentration and S concentration, in each continuous casting, the charge between them was performed with as many components as possible. As can be seen from FIG. 1, if the relationship between the Ti concentration (mass%) and the S concentration (mass%) shown in the equation (1), the maximum thickness of the deposit is in a good state of less than 25 mm. In the figure, the Ti concentration and the S concentration are average values in the same cast.
[% S] ≦ 0.004 + [% Ti] / 15 (1)
In addition, Ti density | concentration is made into Ti = 0.01-0.05 mass% as a density | concentration range normally added with the thin steel plate for motor vehicles (very low carbon aluminum killed steel).
次に、表１のＢに示す成分範囲（Ｔｉを含有する自動車用薄鋼板）において、希土類元素の添加による浸漬ノズルの詰まり抑制について検討を行った。希土類元素を添加した場合の浸漬ノズルの付着物中の酸化物のほとんどは、アルミナに微量に希土類酸化物が含有されるものであった。それに対して、溶鋼をサンプリングして調査した酸化物は、希土類酸化物を含まないアルミナと希土類酸化物を含むアルミナが混在していた。従って、希土類元素を添加し浸漬ノズルの酸化物などの付着を抑制する効果は、少量の希土類酸化物を含むアルミナがノズルに優先的に付着し、大量に存在するアルミナの付着を防止することによるものと推定される。このことから、アルミナ中の希土類酸化物を含有する割合が重要であることがわかった。アルミナ中の希土類酸化物の濃度は、脱酸平衡を支配しているＡｌ濃度により変化することが推定される。従って、Ａｌ濃度に応じた最適な希土類元素の添加量が存在すると推定される。そのため、連続鋳造時の浸漬ノズル詰まり抑制に対するＡｌ濃度と希土類元素の添加量について検討を行った。希土類元素は、上述したプロセスの中で、ＲＨにおける成分調整のための合金添加の際に最後に添加している。希土類元素の添加には、Ｆｅ−Ｓｉ−３０％ＲＥＭ合金を用いた。希土類元素の添加量は、同一キャスト内（同一の連々鋳内）で同じとし、Ａｌ濃度についても同一キャスト内でできるだけ一定となるようにした。浸漬ノズル詰まりの評価に関しては、前述の方法と全く同様である。図２からわかるように、（２）式に示したＡｌ濃度（ｍａｓｓ％）と希土類元素の添加量の関係であれば、付着物の最大厚みが２５ｍｍ未満の良好な状態である。なお、図中のＡｌ濃度は、同一キャスト内の平均値としている。
０．０８×［％Ａｌ］≦ＷREM≦０．２×［％Ａｌ］ ・・・ （２）
ＷREM ： 希土類元素の添加量（ｋｇ／ｔｏｎ）
Next, in the component range shown in B of Table 1 (thin steel sheet for automobiles containing Ti), the suppression of clogging of the immersion nozzle by adding rare earth elements was examined. Most of the oxides in the deposits of the immersion nozzle when rare earth elements were added were those containing rare earth oxides in a small amount in alumina. On the other hand, the oxide investigated by sampling molten steel was a mixture of alumina containing no rare earth oxide and alumina containing rare earth oxide. Therefore, the effect of adding rare earth elements to suppress adhesion of oxides and the like of the immersion nozzle is due to the fact that alumina containing a small amount of rare earth oxide adheres preferentially to the nozzle and prevents adhesion of a large amount of alumina. Estimated. From this, it was found that the ratio of the rare earth oxide contained in alumina is important. It is presumed that the rare earth oxide concentration in alumina varies depending on the Al concentration governing the deoxidation equilibrium. Therefore, it is estimated that there is an optimum amount of rare earth element added according to the Al concentration. Therefore, the Al concentration and the addition amount of rare earth elements for the suppression of submerged nozzle clogging during continuous casting were examined. The rare earth element is added last in the above-described process when the alloy is added for adjusting the components in RH. An Fe-Si-30% REM alloy was used for addition of the rare earth element. The amount of rare earth element added was the same in the same cast (in the same continuous casting), and the Al concentration was made as constant as possible in the same cast. The evaluation of the immersion nozzle clogging is exactly the same as the method described above. As can be seen from FIG. 2, if the relationship between the Al concentration (mass%) and the addition amount of the rare earth element shown in the equation (2) is satisfied, the maximum thickness of the deposit is in a good state of less than 25 mm. The Al concentration in the figure is an average value in the same cast.
0.08 × [% Al] ≦ W REM ≦ 0.2 × [% Al] (2)
W REM : Amount of rare earth element added (kg / ton)
図中の上側に外れた領域では、過剰に希土類元素を添加したために溶鋼中の酸化物のほとんどが、希土類酸化物を含んだアルミナとなり詰まりを助長したものと推定される。一方、図中の下側に外れた領域では、希土類元素の添加量が少ないために、希土類酸化物を含んだアルミナはほとんどなく、浸漬ノズルの付着物も地金とアルミナであった。なお、今回添加した希土類元素濃度は、タンディッシュにおいて分析下限値（１ｐｐｍ）未満であり、表２中には添加元素として示していない。Ｔｉ濃度に関しては、前述したように自動車用薄鋼板（極低炭素アルミキルド鋼）で通常、添加される濃度範囲として、Ｔｉ＝０．０１〜０．０５ｍａｓｓ％としている。また、Ａｌ濃度に関しては、下限として脱酸に必要な濃度として０．０２ｍａｓｓ％以上とし、上限はコスト的な観点から０．０６ｍａｓｓ％としている。アルミナグラファイト質ノズルの成分は、熱間強度及び耐スポイル性などを考慮して、Ａｌ2Ｏ3：４２〜５２ｍａｓｓ％、グラファイト：２０〜３０ｍａｓｓ％、ＳｉＯ2：１５〜２５ｍａｓｓ％、ＳｉＣ：５〜１０ｍａｓｓ％となるような範囲である。 In the region deviated to the upper side in the figure, it is presumed that since rare earth elements were added excessively, most of the oxides in the molten steel became alumina containing rare earth oxides and promoted clogging. On the other hand, in the region deviated to the lower side in the figure, since the addition amount of rare earth elements was small, there was almost no alumina containing rare earth oxides, and the deposits on the immersion nozzle were bare metal and alumina. The rare earth element concentration added this time is less than the lower limit of analysis (1 ppm) in the tundish, and is not shown as an additive element in Table 2. Regarding the Ti concentration, Ti = 0.01 to 0.05 mass% is usually added as a concentration range in the thin steel sheet for automobiles (ultra-low carbon aluminum killed steel) as described above. Regarding the Al concentration, the lower limit is 0.02 mass% or more as the concentration necessary for deoxidation, and the upper limit is 0.06 mass% from the viewpoint of cost. The components of the alumina graphite nozzle are Al 2 O 3 : 42 to 52 mass%, graphite: 20 to 30 mass%, SiO 2 : 15 to 25 mass%, SiC: 5 to 5% in consideration of hot strength and spoil resistance. It is a range which becomes 10 mass%.
最後に、これまでの説明してきた効果について、浸漬ノズル詰まり時の付着物除去作業を行った割合として整理した。浸漬ノズルの詰まりが甚だしい場合、所定の溶鋼供給速度に追いつかない状況が発生する。この時に、浸漬ノズルの付着物を機械的に除去する作業を行う。このような作業を行った前後に鋳造している鋳片には介在物などが多く１級品から降格してしまい、１級品の歩留低下と生産性の低下（作業中に鋳造速度を低下させる場合が多い）を招く。連々鋳単位において、浸漬ノズル詰まり時の付着物除去作業を行った割合を図３に示す。例えば、１０回の連々鋳を行い、その内９回の連々鋳において浸漬ノズル詰まりの付着物除去作業を行った場合は、ノズル詰まり解消作業実施率が９０％となる。図３中の“通常操業”とはＴｉ及びＳ濃度の制御及び希土類元素も添加しない水準を示し、“希土類添加”とはＡｌ濃度に対する希土類元素の制御を行わない水準を示し、“Ｔｉ，Ｓ制御”とは［％Ｓ］≦０．００４＋［％Ｔｉ］／１５となるようにＳ濃度を制御した水準を示し、“適正希土類添加”とは０．０８×［％Ａｌ］≦ＷREM≦０．２×［％Ａｌ］となるように希土類元素を添加した水準を示し、“適正希土類添加＋Ｔｉ，Ｓ制御”とは前述の希土類添加とＳ濃度の制御を組み合わせた水準を示す。通常操業の場合、ほぼ全ての連々鋳単位で付着物除去作業を行っているのに対して、Ｔｉ及びＳ濃度の制御を行うことにより約１／３に低減する。また、希土類元素を添加すると付着物除去作業の頻度は約１／２に低減するものの、希土類元素を適正に添加した場合には約１／６に低減し大幅な浸漬ノズル詰まりの抑制が図られる。さらにＴｉ及びＳ濃度の制御と希土類元素を適正に添加することを組み合わせることにより１／１０以下に低減する。 Finally, the effects that have been described so far were organized as the ratio of the deposit removal work when the immersion nozzle was clogged. When the clogging of the immersion nozzle is severe, a situation occurs in which it cannot keep up with a predetermined molten steel supply speed. At this time, an operation of mechanically removing deposits from the immersion nozzle is performed. The slab cast before and after such work has many inclusions and is demoted from the first grade product, resulting in lower yield and lower productivity of the first grade product (the casting speed is reduced during the work). In many cases. FIG. 3 shows the rate at which the deposit removal operation was performed when the immersion nozzle was clogged. For example, in the case where ten consecutive castings are performed and the deposit removal work for submerged nozzle clogging is performed in nine consecutive castings, the nozzle clogging elimination work execution rate is 90%. In FIG. 3, “normal operation” indicates a level at which Ti and S concentrations are controlled and a rare earth element is not added, and “rare earth addition” indicates a level at which rare earth elements are not controlled with respect to Al concentration. “Control” indicates a level in which the S concentration is controlled to satisfy [% S] ≦ 0.004 + [% Ti] / 15. “Appropriate rare earth addition” is 0.08 × [% Al] ≦ W REM ≦ The level at which the rare earth element is added so as to be 0.2 × [% Al] is shown, and “appropriate rare earth addition + Ti, S control” indicates a level in which the above-described rare earth addition and S concentration control are combined. In the case of normal operation, the deposit removal operation is carried out in almost all casting units, whereas it is reduced to about 1/3 by controlling the Ti and S concentrations. In addition, when rare earth elements are added, the frequency of deposit removal is reduced to about 1/2, but when rare earth elements are properly added, the frequency is reduced to about 1/6, and drastic suppression of submerged nozzle clogging is achieved. . Furthermore, it reduces to 1/10 or less by combining the control of Ti and S concentrations and the appropriate addition of rare earth elements.
本発明に係る溶鋼成分について、以下、説明する。Ｃ、Ｔｉ、Ａｌについては前述した通りである。Ｓｉは、鉄鋼材料に不可避的に混入する元素であり、強度を確保するために添加する元素でもある。Ｓｉの範囲としては、０．００５〜０．０５ｍａｓｓ％である。Ｍｎも、Ｓｉと同様の元素であり、Ｍｎの範囲としては、０．０５〜１ｍａｓｓ％である。Ｐも、Ｓｉ、Ｍｎと同様の元素であるが、偏析などによる悪影響もあることから０．００５〜０．１％である。Ｓについては、０．００１〜０．０２ｍａｓｓ％である。Ｎｂについては、Ｔｉと同様に侵入型元素（ＣやＮ）を析出物として固定するために添加する。Ｎｂの範囲は、０．００１〜０．０４ｍａｓｓ％である。また、侵入型元素を析出物として固定するためにＢを添加する場合もあり、Ｂの範囲としては０．００１ｍａｓｓ％以下である。さらに、転炉において鉄スクラップを使用する際に混入する元素（Ｃｕ、Ｚｎ、Ｓｎ、Ｃｒ，Ｎｉなど）については、０．００１〜０．０４ｍａｓｓ％である。 The molten steel component according to the present invention will be described below. C, Ti, and Al are as described above. Si is an element that is inevitably mixed into the steel material, and is also an element that is added to ensure strength. The range of Si is 0.005 to 0.05 mass%. Mn is an element similar to Si, and the range of Mn is 0.05 to 1 mass%. P is an element similar to Si and Mn, but is 0.005 to 0.1% because there is an adverse effect due to segregation or the like. About S, it is 0.001-0.02 mass%. Nb is added to fix interstitial elements (C and N) as precipitates in the same manner as Ti. The range of Nb is 0.001 to 0.04 mass%. Further, B may be added to fix the interstitial element as a precipitate, and the range of B is 0.001 mass% or less. Furthermore, about elements (Cu, Zn, Sn, Cr, Ni, etc.) mixed when using iron scrap in a converter, it is 0.001-0.04 mass%.
また、前記浸漬ノズルの詰まり（酸化物などの付着）は鋳造を進めるにつれて増加していき、臨界の付着厚みを超えると溶鋼供給量（スループット量）に追従できなくなるため、連々鋳（取鍋を交換して複数のチャージを連続して連続鋳造すること）を増加させた場合の品質の不安定や浸漬ノズルの詰まり解消作業による降格などの問題となる。このような浸漬ノズル詰まりに起因する上記の問題が、浸漬ノズル1本当たりの鋳造量として１０００ｔｏｎから顕在化してくるため、これ以上とした。 In addition, clogging of the immersion nozzle (adhesion of oxides, etc.) increases as the casting progresses, and when the critical adhesion thickness is exceeded, it becomes impossible to follow the molten steel supply amount (throughput amount). This may cause problems such as instability in quality when the number of charges is continuously increased by exchanging and charging, and demotion due to work to eliminate clogging of the immersion nozzle. Since the above-mentioned problem due to such a clogging of the immersion nozzle becomes apparent from 1000 ton as a casting amount per immersion nozzle, it was set to be more than this.
以下、実施例および比較例を示しながら、本発明に係る連続鋳造方法について、詳細に説明する。 Hereinafter, the continuous casting method according to the present invention will be described in detail with reference to Examples and Comparative Examples.
以下の表２に示す条件で連続鋳造し、浸漬ノズル詰まり解消のための付着物除去作業の有無と鋳造後の浸漬ノズルの付着最大厚み及び製品での品質結果について比較した。連続鋳造の形態を以下に記載する。まず、転炉で脱炭した溶鋼を取鍋に受けて、ＲＨ（真空脱ガス装置）を用いて脱炭処理を行う。脱炭後、Ａｌを添加し脱酸し、所定時間の攪拌を加えた後に、成分調整のための合金類を添加した。成分調整が終了した溶鋼は、取鍋から中間容器であるタンディッシュに耐火物製ノズルを介して供給し、タンディッシュから鋳型へＡｌ2Ｏ3＝４７ｍａｓｓ％、グラファイト＝２６％、ＳｉＯ2＝１８ｍａｓｓ％、ＳｉＣ＝７ｍａｓｓ％及びその他の微量酸化物から成る浸漬ノズルを用いて供給した。浸漬ノズルからの溶鋼供給速度は、浸漬ノズル直上に設置されたスライディングノズルにより制御される。浸漬ノズル内には、詰まり防止のために不活性ガスとしてＡｒを吹き込んでいる。浸漬ノズルには２つの孔があり、そこから鋳型へ溶鋼が供給される。ストランド当たり１６００ｔｏｎの溶鋼を鋳造した。鋳造条件は、鋳造幅１９００ｍｍ、鋳造厚２８０ｍｍ、鋳造速度１．３ｍ／ｍｉｎである。浸漬ノズルへのＡｒガス吹き込み速度は５（Ｎｌ／ｍｉｎ）である。浸漬ノズル詰まり現象は、一つの連々鋳単位での評価となるため、Ｔｉ濃度、Ｓ濃度及びＡｌ濃度は、連々鋳の間、できるだけ成分をそろえて実施し、表２中に示した平均濃度は同一の連々鋳の全チャージの平均値を示している。また、希土類元素は、ＲＨにおいて成分調整のための合金類を添加した後に添加した。希土類元素は、Ｆｅ−Ｓｉ−３０％ＲＥＭ合金を用いて添加した。表２に示したＴｉ、Ｓ及びＡｌ以外の成分は、表３に示す。表３には、各々の連々鋳単位（８チャージ）における成分の範囲を示す。 表２中に示した総合評価の基準を、表４に示す。表２中の表面欠陥発生率は冷延コイル本数比率とした。表面欠陥の有無は、冷延後の通板ラインで目視確認した表面疵の有無により判断している。 Continuous casting was performed under the conditions shown in Table 2 below, and the presence / absence of a deposit removal operation for eliminating clogging of the immersion nozzle, the maximum thickness of the immersion nozzle after casting and the quality result of the product were compared. The form of continuous casting is described below. First, the molten steel decarburized in the converter is received in a ladle and decarburized using an RH (vacuum degasser). After decarburization, Al was added for deoxidation, and after stirring for a predetermined time, alloys for component adjustment were added. The molten steel whose components have been adjusted is supplied from the ladle to the tundish, which is an intermediate container, via a refractory nozzle, and Al 2 O 3 = 47 mass%, graphite = 26%, SiO 2 = 18 mass from the tundish to the mold %, SiC = 7 mass%, and other submerged oxides. The molten steel supply speed from the immersion nozzle is controlled by a sliding nozzle installed immediately above the immersion nozzle. Ar is blown into the immersion nozzle as an inert gas to prevent clogging. The immersion nozzle has two holes from which molten steel is supplied to the mold. 1600 tonnes of molten steel was cast per strand. The casting conditions are a casting width of 1900 mm, a casting thickness of 280 mm, and a casting speed of 1.3 m / min. The Ar gas blowing speed into the immersion nozzle is 5 (Nl / min). Since the immersion nozzle clogging phenomenon is evaluated in one continuous casting unit, the Ti concentration, S concentration and Al concentration were carried out by aligning the components as much as possible during continuous casting. The average concentration shown in Table 2 is The average value of all charges of the same continuous casting is shown. Further, the rare earth element was added after adding alloys for component adjustment in RH. The rare earth element was added using a Fe-Si-30% REM alloy. Components other than Ti, S and Al shown in Table 2 are shown in Table 3. Table 3 shows the range of components in each continuous casting unit (8 charges). Table 4 shows the criteria for comprehensive evaluation shown in Table 2. The surface defect occurrence rate in Table 2 was the cold rolled coil number ratio. The presence / absence of surface defects is determined by the presence / absence of surface defects visually confirmed by a sheet-passing line after cold rolling.
本発明例１、３，５では、希土類元素を添加していないが、［％Ｓ］≦０．００４＋［％Ｔｉ］／１５を満たしており、浸漬ノズル詰まり解消作業はなく、表面欠陥発生率も低位である。 In Invention Examples 1, 3, and 5, rare earth elements were not added, but [% S] ≦ 0.004 + [% Ti] / 15 was satisfied, and there was no work for eliminating the clogging of the immersion nozzle, and the surface defect occurrence rate Is also low.
本発明例６、８では、Ｓ濃度とＴｉ濃度の適正範囲からずれているが、希土類元素を適正添加量（０．００８×［％Ａｌ］≦ＷREM≦０．０２×［％Ａｌ］）となっているため、浸漬ノズル詰まり解消作業はなく、表面欠陥発生率も低位である。 In Inventive Examples 6 and 8, the S concentration and the Ti concentration deviate from the proper ranges, but the rare earth element was added in an appropriate amount (0.008 × [% Al] ≦ W REM ≦ 0.02 × [% Al]). Therefore, there is no work for eliminating the clogging of the immersion nozzle, and the surface defect occurrence rate is low.
本発明例２、４、７では、Ｓ濃度とＴｉ濃度の適正範囲及び希土類元素の適正添加量とも満たされており、浸漬ノズルの付着最大厚み、表面欠陥発生率とも非常に低く抑制できている。 In Invention Examples 2, 4, and 7, both the appropriate ranges of S concentration and Ti concentration and the appropriate addition amount of rare earth elements are satisfied, and the maximum adhesion thickness of the immersion nozzle and the surface defect occurrence rate can be suppressed very low. .
比較例１、４では、希土類元素を添加せず、Ｓ濃度とＴｉ濃度の適正範囲からもずれているため、浸漬ノズルの詰まり解消作業を実施している。また、表面欠陥発生率も非常に高い。 In Comparative Examples 1 and 4, the rare earth element is not added, and since the deviation from the appropriate ranges of the S concentration and the Ti concentration is performed, the clogging work of the immersion nozzle is performed. Also, the surface defect occurrence rate is very high.
比較例２、３、５、６では、Ｓ濃度とＴｉ濃度の適正範囲からずれ、希土類元素の適正添加量からも外れている。そのため、比較例２、３、６は浸漬ノズルの詰まり解消作業は行っていないものの、浸漬ノズルの付着物厚みが厚く、溶鋼の片流れが生じて表面欠陥発生率が高くなっていると考えられる。 In Comparative Examples 2, 3, 5, and 6, it deviates from the appropriate ranges of S concentration and Ti concentration, and deviates from the appropriate addition amount of rare earth elements. Therefore, in Comparative Examples 2, 3, and 6, although the clogging work of the immersion nozzle is not performed, the thickness of the deposit on the immersion nozzle is thick, and it is considered that the molten steel piece flows and the surface defect occurrence rate is high.
以上のように、本発明に係る連続鋳造方法によれば、操業性の低下やコストの増加を招くことなく、浸漬ノズルの詰まりを抑制し、操業及び品質の安定化を達成することが可能 As described above, according to the continuous casting method according to the present invention, it is possible to suppress clogging of the immersion nozzle and achieve stabilization of operation and quality without incurring a decrease in operability and an increase in cost.
Claims (3)
［％Ｓ］≦０．００４＋［％Ｔｉ］／１５ ・・・ （１）
ただし、［％Ｓ］、［％Ｔｉ］はそれぞれ溶鋼中のＳ、Ｔｉの含有量（ｍａｓｓ％）である。 Aluminum killed steel containing 0.001 mass% ≦ C ≦ 0.02 mass% and Ti ≧ 0.01 mass% is made of Al 2 O 3 : 42 to 52 mass%, graphite: 20 to 30 mass%, SiO 2 : 15 to 25 mass%, SiC: In continuous casting in which molten steel is supplied to a mold using an immersion nozzle containing 5 to 10 mass%, when continuously casting 1000 tons or more per immersion nozzle, the S concentration in the molten steel is set to (1) before the start of casting. A continuous casting method characterized in that the range is expressed by a formula.
[% S] ≦ 0.004 + [% Ti] / 15 (1)
However, [% S] and [% Ti] are the contents (mass%) of S and Ti in the molten steel, respectively.
０．０８×［％Ａｌ］≦ＷREM≦０．２×［％Ａｌ］ ・・・ （２）
ただし、ＷREMは希土類元素の添加量（ｋｇ／ｔｏｎ）、［％Ａｌ］は溶鋼中のＡｌ含有量（ｍａｓｓ％）である。 Aluminum killed steel containing 0.001 mass% ≦ C ≦ 0.02 mass% and Ti ≧ 0.01 mass% is made of Al 2 O 3 : 42 to 52 mass%, graphite: 20 to 30 mass%, SiO 2 : 15 to 25 mass%, SiC: In continuous casting in which molten steel is supplied to a mold using an immersion nozzle containing 5 to 10 mass%, when continuously casting 1000 tons or more per immersion nozzle, the rare earth element (2) is contained in the molten steel before the start of casting. It adds so that it may become the range shown by a type | formula, The continuous casting method characterized by the above-mentioned.
0.08 × [% Al] ≦ W REM ≦ 0.2 × [% Al] (2)
However, W REM is the amount of rare earth element added (kg / ton), and [% Al] is the Al content (mass%) in the molten steel.
［％Ｓ］≦０．００４＋［％Ｔｉ］／１５ ・・・ （１）
０．０８×［％Ａｌ］≦ＷREM≦０．２×［％Ａｌ］ ・・・ （２）
ただし、［％Ｓ］、［％Ｔｉ］、［％Ａｌ］はそれぞれ溶鋼中のＳ、Ｔｉ、Ａｌの含有量（ｍａｓｓ％）、ＷREMは希土類元素の添加量（ｋｇ／ｔｏｎ）である。 Aluminum killed steel containing 0.001 mass% ≦ C ≦ 0.02 mass% and Ti ≧ 0.01 mass% is made of Al 2 O 3 : 42 to 52 mass%, graphite: 20 to 30 mass%, SiO 2 : 15 to 25 mass%, SiC: In continuous casting in which molten steel is supplied to a mold using an immersion nozzle containing 5 to 10 mass%, when continuously casting 1000 tons or more per immersion nozzle, the S concentration in the molten steel is set to (1) before the start of casting. A continuous casting method characterized in that the rare earth element is added to the molten steel in a range indicated by the formula (2) within the range indicated by the formula.
[% S] ≦ 0.004 + [% Ti] / 15 (1)
0.08 × [% Al] ≦ W REM ≦ 0.2 × [% Al] (2)
However, [% S], [% Ti], and [% Al] are the contents (mass%) of S, Ti, and Al in the molten steel, respectively, and W REM is the amount of rare earth element added (kg / ton).
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