JP4811018B2 - Deoxidation method for molten steel - Google Patents
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本発明は、溶鋼の脱酸方法、特にTiによる脱酸を基本とした溶鋼の脱酸方法に関する。 The present invention relates to a method for deoxidizing molten steel, and more particularly to a method for deoxidizing molten steel based on deoxidation with Ti.
転炉あるいは電気炉で精錬された溶鋼は、脱酸元素により脱酸されてから鋳造に供されるのが一般的である。この脱酸元素として、Alは最も使用頻度が高いが、Alは脱酸によりAl2Ｏ3を生成し、それが介在物として溶鋼中に懸濁することになる。このAl2Ｏ3介在物は、その後の連続鋳造において連続鋳造用ノズルに付着し易いため、ノズルを閉塞する要因となり、著しく鋳造作業を阻害する。 In general, molten steel refined in a converter or electric furnace is subjected to casting after being deoxidized by a deoxidizing element. As this deoxidation element, Al is most frequently used, but Al produces Al 2 O 3 by deoxidation, which is suspended in the molten steel as inclusions. Since this Al 2 O 3 inclusion easily adheres to the nozzle for continuous casting in the subsequent continuous casting, it causes the nozzle to be clogged and remarkably hinders the casting operation.
また、Al2Ｏ3同士が凝集し、Al2Ｏ3クラスターとなり、鋼板での表面欠陥等の原因となる。さらに、CaおよびＳを添加してCaによるＳの形態を制御して被削性を向上した、いわゆる高Ｓ快削鋼では、溶鋼中のAl濃度が高くなると、CaによるＳの形態制御が阻害され、必要な快削性が得られない。 Further, Al 2 O 3 with each other are aggregated, become Al 2 O 3 clusters, causing surface defects such as a steel plate. Furthermore, in so-called high-S free-cutting steel in which machinability is improved by adding Ca and S to control the form of S by Ca, the control of the form of S by Ca is hindered when the Al concentration in the molten steel increases. As a result, the required free machinability cannot be obtained.
ここに、溶鋼中のAl濃度を低くし、Al2Ｏ3介在物の生成を抑制する手段として、Tiによって脱酸する方法が知られている。この方法は、生成するTi酸化物が微細なため、表面欠陥の要因になり難いという利点がある。しかし、溶鋼中の溶存酸素を全てTiで脱酸すると高コストになる問題があり、この点、特許文献１では、Ti添加前にAlを添加して溶存酸素の一部を脱酸してから、３分以上撹拌後にTiを添加する方法が提案されている。 Here, a method of deoxidizing with Ti is known as means for reducing the Al concentration in molten steel and suppressing the formation of Al 2 O 3 inclusions. This method has an advantage that it is difficult to cause surface defects because the Ti oxide produced is fine. However, if all dissolved oxygen in the molten steel is deoxidized with Ti, there is a problem that the cost becomes high. In this respect, Patent Document 1 adds Al before adding Ti and deoxidizes part of the dissolved oxygen. A method of adding Ti after stirring for 3 minutes or more has been proposed.
また、特許文献２には、Tiを添加する前にAl、SiおよびMgを添加するか、あるいは真空脱炭により予備脱酸を行い、溶存酸素を0.003〜0.015％に調整する方法が開示されている。同様に、具体的方法は記述されていないものの、特許文献３にはTi添加前の溶存酸素を60〜150ppmに、特許文献４には20〜200ppmにする方法が、それぞれ開示されている。
しかしながら、上記特許文献１の方法では、Alでの脱酸量の規定が無いため、Ti添加量にばらつきが出るので、コスト低減効果が十分ではない。また、Al2Ｏ3の除去には時間とともに撹拌力も必要であるが、それについての規定は無く、Al2Ｏ3除去が不十分になる場合がある。 However, in the method of Patent Document 1, since there is no regulation of the amount of deoxidation with Al, the amount of Ti added varies, so the cost reduction effect is not sufficient. Moreover, although stirring power is also required over time for the removal of Al 2 O 3 , there is no provision for this, and Al 2 O 3 removal may be insufficient.
また、上記特許文献２ないし４では、予備脱酸によるTi添加前の溶存酸素濃度を規定しているが、特に、酸素濃度の下限値がTi濃度と平衡する酸素濃度より低くなってしまうとTi酸化物が生成しない、すなわちTi脱酸にならない場合がある。 In Patent Documents 2 to 4, the dissolved oxygen concentration before Ti addition by preliminary deoxidation is specified. In particular, if the lower limit value of the oxygen concentration becomes lower than the oxygen concentration in equilibrium with the Ti concentration, Ti. Oxide may not be generated, that is, Ti deoxidation may not occur.
本発明は、かかる事情に鑑み、Alの予備脱酸後にTiにより脱酸を行うに際し、Alによる予備脱酸を最適化することによって、Al2Ｏ3介在物量の極めて少ない溶鋼を製造することを目的とするものである。 In view of such circumstances, the present invention aims to produce a molten steel with an extremely small amount of Al 2 O 3 inclusions by optimizing the preliminary deoxidation with Al when performing the deoxidation with Ti after the preliminary deoxidation of Al. It is the purpose.
さて、溶鋼にTiを添加してTi酸化物を生成させるためには、溶鋼中の溶存酸素がTiと平衡する酸素濃度以上である必要がある。すなわち、Alで予備脱酸をしてもTiと平衡する酸素濃度以上の酸素を溶鋼中に残す必要がある。しかし、良好な快削性を得るためのCaによる硫化物の形態制御を可能とするには、Al濃度に上限を設ける必要があり、このAl上限値と平衡する酸素濃度が、製品における設計Ti濃度であるTi目標値と平衡する酸素濃度超えの場合、Alでの予備脱酸後の溶存酸素濃度の下限値はAl上限値と平衡する酸素濃度超えとする必要がある。すなわち、Ti目標値と平衡する酸素量およびAl上限値と平衡する酸素量のいずれか大きい方超えの酸素量までの予備脱酸を行うことによって、常に微細なTi酸化物の生成が可能となる。 Now, in order to add Ti to molten steel to produce Ti oxide, it is necessary that the dissolved oxygen in the molten steel be equal to or higher than the oxygen concentration at which Ti is in equilibrium with Ti. That is, it is necessary to leave oxygen in the molten steel at an oxygen concentration equal to or higher than that of Ti even when pre-deoxidized with Al. However, in order to be able to control the form of sulfides with Ca to obtain good free-cutting properties, it is necessary to set an upper limit on the Al concentration, and the oxygen concentration that balances with this Al upper limit value is the design Ti in the product. When the oxygen concentration exceeds the Ti target value which is the concentration, the lower limit value of the dissolved oxygen concentration after preliminary deoxidation with Al needs to exceed the oxygen concentration which balances with the Al upper limit value. In other words, it is possible to always produce fine Ti oxides by performing pre-deoxidation up to the larger of the oxygen amount in equilibrium with the Ti target value and the oxygen amount in equilibrium with the Al upper limit value, whichever is greater. .
本発明は上記の知見に由来するものであり、その要旨は以下の通りである。
（Ａ） Ｓ：0.01〜0.2mass％およびCa：0.001〜0.01mass％を含有する溶鋼にAlを添加する予備脱酸を経てTi添加による脱酸を行うに当り、該予備脱酸では、要求される快削性能を得るために許容されるAl量（mass％）の上限値に対する平衡酸素濃度値と、製品における合金設計に従うTi含有量であるTi目標値に対する平衡酸素濃度値とのいずれか大きい値を超える溶鋼中溶存酸素濃度に調整することを特徴とする溶鋼の脱酸方法。
The present invention is derived from the above findings, and the gist thereof is as follows.
(A) When performing deoxidation by adding Ti through preliminary deoxidation in which Al is added to molten steel containing S: 0.01 to 0.2 mass% and Ca: 0.001 to 0.01 mass% , the preliminary deoxidation is required. Equilibrium oxygen concentration value relative to the upper limit value of Al amount (mass%) allowed for obtaining free-cutting performance and the equilibrium oxygen concentration value relative to the Ti target value that is the Ti content according to the alloy design in the product , whichever is greater A method for deoxidizing molten steel, comprising adjusting the dissolved oxygen concentration in the molten steel to exceed a value.
ここで、Al上限値とは、要求される快削性能を得るために許容されるAl量の上限を意味する。また、Ti目標値とは、製品における合金設計に従うTi含有量を意味する。 Here, the upper limit value of Al means the upper limit of the amount of Al allowed for obtaining the required free cutting performance. Moreover, Ti target value means Ti content according to the alloy design in a product.
（Ｂ）上記（Ａ）において、Alを添加した後、下記（１）式で表される時間ｔ（秒）にわたるガス撹拌処理を行い、その後Tiを添加することを特徴とする溶鋼の脱酸方法。
記
ｔ≧150×ε-0.5×１ｎ[（Ｏｏ−Ｏｅ）／Ｏ] ---（１）
ここで、Ｏｏ：Al添加前溶存酸素濃度
Ｏｅ：Al添加後溶存酸素濃度
Ｏ：Ti添加前目標介在物中酸素濃度
ε＝370.8GT／Ｗ×[１−298／Ｔ＋１ｎ（１＋0.677Ｈ／Ｐ）]
但し、Ｇ：撹拌ガス流量（Ｎm3／ｓ）
Ｔ：溶鋼温度（K）
Ｗ：溶鋼量（kg）
Ｈ：撹拌ガス吹き込み深さ（m）
Ｐ：雰囲気圧力（atm）
(B) Oite above (A), after the addition of Al, the following (1) performs a gas stirring treatment over time t (in seconds) of the formula, thereafter the molten steel, characterized in that the addition of Ti Deoxidation method.
T ≧ 150 × ε −0.5 × 1n [(Oo-Oe) / O] --- (1)
Here, Oo: dissolved oxygen concentration before Al addition Oe: dissolved oxygen concentration after Al addition O: oxygen concentration in target inclusion before Ti addition ε = 370.8 GT / W × [1-298 / T + 1n (1 + 0.677 H / P) ]
G: Stirring gas flow rate (Nm 3 / s)
T: Molten steel temperature (K)
W: Amount of molten steel (kg)
H: Stirring gas blowing depth (m)
P: Atmospheric pressure (atm)
本発明によれば、転炉あるいは電気炉で精錬された溶鋼に対して、溶鋼中溶存酸素をAlによって低減してからTiを添加して溶鋼を脱酸するため、Tiのみの脱酸に比較してTi添加量を少なくできる結果、コストの上昇は抑制される。また、Ti目標値およびAl上限値を基に適切な予備脱酸を実現するため、Ti脱酸に伴って微細なTi酸化物が生成する結果、製品の表面欠陥が抑制される。 According to the present invention, for molten steel refined in a converter or electric furnace, the dissolved oxygen in the molten steel is reduced by Al and then Ti is added to deoxidize the molten steel. Compared to Ti-only deoxidation. As a result, the amount of Ti added can be reduced, and as a result, an increase in cost is suppressed. Moreover, in order to implement | achieve suitable preliminary deoxidation based on Ti target value and Al upper limit, as a result of producing | generating a fine Ti oxide with Ti deoxidation, the surface defect of a product is suppressed.
さらに、Al添加後にAl2Ｏ3を除去する時間を適正に確保することによって、溶鋼中に懸濁するAl2Ｏ3量を最小限に抑えて、Ti脱酸による介在物の微細化をより促進できるため、連続鋳造用ノズルの閉塞、製品での表面疵を防止することが可能となり、工業上極めて有益である。 Furthermore, by ensuring adequate time to remove Al 2 O 3 after Al addition, the amount of Al 2 O 3 suspended in the molten steel is minimized, and inclusions are further refined by Ti deoxidation. Since it can be promoted, it becomes possible to prevent clogging of the nozzle for continuous casting and surface flaws in the product, which is extremely useful industrially.
以下、本発明を詳細に説明する。
本発明の方法は、転炉あるいは電気炉等の精錬炉から取鍋へ出鋼された溶鋼を、ＲＨ真空脱ガス装置等の取鍋精錬炉において、Alによって予備脱酸を行い、その後Tiにより脱酸を行うことが基本になる。
Hereinafter, the present invention will be described in detail.
In the method of the present invention, molten steel discharged from a refining furnace such as a converter or an electric furnace to a ladle is subjected to preliminary deoxidation with Al in a ladle refining furnace such as an RH vacuum degassing apparatus, and then with Ti. Deoxidation is fundamental.
ここに、上記Ti脱酸に際し、微細な介在物であるTi酸化物を生成させるためには、Ti添加時の溶存酸素をTi目標値と平衡する酸素濃度以上にする必要があり、そのために予備脱酸用のAl添加量を調整する必要がある。なお、Ti目標値と平衡する酸素濃度については、実際の溶鋼で予め実測した値を用いることが好ましいが、文献：「E.T.Turkdogen ： Physical Chemistry of High Temperature Technology，（1980），第５頁［Academic Press，New York］」に記載の式で計算される値を用いても構わない。 Here, in order to produce Ti oxides that are fine inclusions in the Ti deoxidation, it is necessary to make the dissolved oxygen at the time of Ti addition be equal to or higher than the oxygen concentration that is in equilibrium with the Ti target value. It is necessary to adjust the amount of Al added for deoxidation. In addition, about the oxygen concentration which equilibrates Ti target value, it is preferable to use the value measured beforehand with actual molten steel, but literature: “ETTurkdogen: Physical Chemistry of High Temperature Technology, (1980), page 5 [Academic Press, New York] ”may be used.
一方で、特にCaでの硫化物の形態制御による製品の快削性確保のためには、上述のとおりAl濃度に許容限界があり、そのAl上限値と平衡する溶存酸素濃度が、上記Ti目標値と平衡する値より大きい場合には、予備脱酸におけるAl添加量を、Al上限値を超えない範囲とすることも必要になる。このAl上限値と平衡する酸素濃度については、実際の溶鋼で予め実測した値を用いることが好ましいが、文献：「製鋼反応の推奨平衡値 日本学術振興会 製鋼第19委員会編（1984），第38２頁」に記載の式で計算される値を用いても構わない。 On the other hand, in order to secure the free-cutting property of the product, particularly by controlling the form of sulfide with Ca, the Al concentration has an allowable limit as described above, and the dissolved oxygen concentration that balances with the Al upper limit value is the Ti target. If the value is larger than the value that balances with the value, it is also necessary to set the Al addition amount in the preliminary deoxidation within a range not exceeding the Al upper limit value. As for the oxygen concentration in equilibrium with this Al upper limit, it is preferable to use the value measured in advance with actual molten steel, but the document: “Recommended equilibrium value of steelmaking reaction, Japan Society for the Promotion of Science, Steelmaking Committee 19 (1984), The value calculated by the formula described in “Page 382” may be used.
従って、以上の二点を考慮して、予備脱酸時のAl添加量は、添加後の溶存酸素濃度がTi目標値と平衡する酸素濃度およびAl上限値と平衡する酸素濃度のいずれか大きい値を超えるようにすることが肝要になる。 Therefore, considering the above two points, the amount of Al added during preliminary deoxidation is the larger of the oxygen concentration at which the dissolved oxygen concentration after addition is in equilibrium with the Ti target value and the oxygen concentration at which it is in equilibrium with the Al upper limit value. It is important to exceed this.
例えば、［Ti］目標値＝0.02mass％（平衡［０］＝18.1ppm）で［Al］上限値＝0.005mass％（平衡［０］＝4.5ppm）では、溶存酸素濃度が18.1ppm以上となるAl量を添加し、また、［Ti］目標値＝0.05mass％（平衡［０］＝9.8ppm）で［Al］上限値＝0.002mass％（平衡［０］＝17.7ppm）では、溶存酸素濃度が17.7ppm以上となるAl量を添加することになる。 For example, when [Ti] target value = 0.02 mass% (equilibrium [0] = 18.1 ppm) and [Al] upper limit = 0.005 mass% (equilibrium [0] = 4.5 ppm), the dissolved oxygen concentration is 18.1 ppm or more. Al is added, and [Ti] target value = 0.05 mass% (equilibrium [0] = 9.8 ppm) and [Al] upper limit = 0.002 mass% (equilibrium [0] = 17.7 ppm), dissolved oxygen concentration Therefore, an Al amount of 17.7 ppm or more is added.
Al添加後の溶存酸素の上限値は特に設ける必要はないが、上述の下限値に近いことが望ましい。なぜなら、溶存酸素が低ければ、その後のTi添加必要量が最小限でよく、生成Ti酸化物量も少なくなるので、より効果が大きくなるためである。ただし、溶鋼量、Al添加量の精度およびAl歩留りのばらつき等を予め把握しておき、溶存酵素濃度が上述の下限値を下回らないようにすることが大切である。 The upper limit value of dissolved oxygen after Al addition is not particularly required, but is preferably close to the lower limit value described above. This is because if the dissolved oxygen is low, the necessary amount of Ti added thereafter can be minimized, and the amount of generated Ti oxide is also reduced, so that the effect is further increased. However, it is important to know in advance the amount of molten steel, the accuracy of Al addition amount, the variation in Al yield, etc., so that the dissolved enzyme concentration does not fall below the above lower limit.
さらに、Al添加からTi添加までの間にガス攪拌処理を行うことが、Ti脱酸による介在物の微細化とAl2Ｏ3介在物量の低減とを促進するのに有効である。すなわち、ガス攪拌処理とは、RH真空脱ガス装置等の取鍋精錬炉において、溶鋼中へガスを吹き込み、溶鋼を撹拌することである。 Further, performing the gas stirring treatment between the addition of Al and the addition of Ti is effective in promoting the refinement of inclusions by Ti deoxidation and the reduction of the amount of Al 2 O 3 inclusions. That is, the gas agitation treatment is to blow gas into molten steel and stir the molten steel in a ladle refining furnace such as an RH vacuum degassing apparatus.
このガス攪拌処理の時間ｔについては、取鍋精錬炉でのガス撹拌、RH真空脱ガス装置やＶＯＤでの真空処理における、Al添加からの介在物酸素濃度の挙動から、下記の（１）式に従って求めることが好ましい。
記
ｔ≧150×ε−0.5×１ｎ{（Ｏｏ−Ｏｅ）／Ｏ} ---（１）
ここで、Ｏｏ：Al添加前溶存酸素濃度
Ｏｅ：Al添加後溶存酸素濃度
Ｏ：Ti添加前目標介在物中酸素濃度
ε＝370.8GT／Ｗ×{１−298／Ｔ＋１ｎ（１＋0.677Ｈ／Ｐ）}
但し、Ｇ：撹拌ガス流量（Ｎm3／ｓ）
Ｔ：溶鋼温度（K）
Ｗ：溶鋼量（kg）
Ｈ：撹拌ガス吹き込み深さ（m）
Ｐ：雰囲気圧力（atm）
なお、Ti添加前目標介在物中酸素濃度とは、懸濁Al2Ｏ3量の目標値と同義であり、具体的には鋼の清浄性に応じて決定することができる。また、εは溶鋼に与える撹拌力であり、上記に従って操業条件から算出する。
Regarding the time t of this gas stirring treatment, from the behavior of inclusion oxygen concentration from the addition of Al in the gas stirring in the ladle smelting furnace, the vacuum treatment in the RH vacuum degassing apparatus or VOD, the following equation (1) It is preferable to obtain according to
T ≧ 150 × ε− 0.5 × 1n {(Oo-Oe) / O} --- (1)
Here, dissolved oxygen concentration before addition of Oo: Al
Oe: dissolved oxygen concentration after Al addition
O: Oxygen concentration in target inclusion before Ti addition
ε = 370.8GT / W × {1-298 / T + 1n (1 + 0.677H / P)}
G: Stirring gas flow rate (Nm 3 / s)
T: Molten steel temperature (K)
W: Amount of molten steel (kg)
H: Stirring gas blowing depth (m)
P: Atmospheric pressure (atm)
The oxygen concentration in the target inclusion before Ti addition is synonymous with the target value of the suspended Al 2 O 3 amount, and can be specifically determined according to the cleanliness of the steel. Further, ε is a stirring force applied to the molten steel, and is calculated from the operating conditions according to the above.
上記の（１）式に従って算出された時間ｔのガス撹拌処理を行ってからTiを添加し、必要時間処理を行った後、取鍋あるいは鋳造設備でCa源を添加し、鋳片を製造する。Ca源については粉体やワイヤー等と形態は特に問う必要はなく、他の成分への影響が問題なければ、鉄−Ca合金やCa−Ｓ合金等、種類も特に問わない。 Ti is added after performing the gas agitation treatment for the time t calculated according to the above formula (1), and after the necessary time treatment, a Ca source is added with a ladle or casting equipment to produce a slab. . Regarding the Ca source, there is no particular need for the form such as powder or wire, and the type such as iron-Ca alloy or Ca-S alloy is not particularly limited as long as the influence on other components is not a problem.
以上のような処理により、Ti添加量が少なくできるため、コストを低く抑えることができ、また、Al添加後にAl2Ｏ3を除去するためのガス攪拌時間を確保することにとって、溶鋼中に懸濁するAl2Ｏ3量を最小限に抑え、かつTi脱酸により介在物の微細化も促進することが可能となる。 With the above treatment, the amount of Ti added can be reduced, so that the cost can be kept low, and in order to secure a gas agitation time for removing Al 2 O 3 after the addition of Al, it is suspended in the molten steel. It becomes possible to minimize the amount of turbid Al 2 O 3 and to promote the refinement of inclusions by Ti deoxidation.
転炉において、約200トンの溶鋼を酸素吹錬した後、該溶鋼を取鍋に出鋼した。出鋼の際に、一部鋼種はＳ，SiおよびMn合金等を添加し、成分調整を行った。出鋼終了後、取鍋をＲＨ真空脱ガス設備へ搬送し、減圧精錬を行った。減圧精錬は、一対の浸漬管を溶鋼中に浸漬し、その一方からArガスを0.033Ｎm3／ｓで吹込み、溶鋼を環流させた。なお、本鋼種はTi目標値：0.03mass％並びにAl上限値：0.005mass％のため、Al添加後の溶存酸素濃度がTiと平衡する13.8ppm以上となるAl添加予備脱酸を実施した。 In the converter, about 200 tons of molten steel was oxygen blown, and the molten steel was taken out into a ladle. At the time of steeling, some steel types added S, Si, Mn alloy, etc., and the component was adjusted. After the completion of steeling, the ladle was transported to the RH vacuum degassing facility and subjected to refining under reduced pressure. In the vacuum refining, a pair of dip tubes were immersed in molten steel, and Ar gas was blown from one of them at 0.033 Nm 3 / s to circulate the molten steel. In addition, since this steel type is Ti target value: 0.03 mass% and Al upper limit: 0.005 mass%, Al addition preliminary deoxidation was performed so that the dissolved oxygen concentration after addition of Al becomes 13.8 ppm or more in equilibrium with Ti.
すなわち、必要な成分調整を行った後、溶鋼中溶存酸素濃度を測定し、測定値に応じた量のAlを一括で添加した。その後、再び溶存酸素を測定し、一部の操業においてはTi添加前の介在物中酸素濃度の目標値を20ppmとして上記した（１）式から計算される時間のガス攪拌処理を実施後、Tiを0.03mass％になるように添加し、成分微調整後、脱酸処理を終了した。 That is, after making necessary component adjustments, the dissolved oxygen concentration in the molten steel was measured, and an amount of Al corresponding to the measured value was added all at once. Thereafter, the dissolved oxygen was measured again. In some operations, the target value of the oxygen concentration in the inclusions before addition of Ti was set to 20 ppm, and after the gas stirring treatment for the time calculated from the above equation (1), Ti Was added so that it might become 0.03 mass%, the deoxidation process was complete | finished after the component fine adjustment.
その後、取鍋へワイヤー状Fe−Ca合金を添加し、連続鋳造機にてスラブ鋳片に鋳造し、圧延を施して厚板製品とし、該製品における酸化物系介在物による表面欠陥の発生率を調査した。また、各条件で、連続で３チャージ精錬後、連々鋳を行った後、連続鋳造用ノズルを回収し、内部の付着物を調査した。 Then, wire-like Fe-Ca alloy is added to the ladle, cast into a slab slab with a continuous casting machine, rolled into a thick plate product, and the incidence of surface defects due to oxide inclusions in the product investigated. Moreover, after refining 3 charges continuously after each condition and performing casting continuously, the nozzle for continuous casting was collect | recovered and the deposit | attachment inside was investigated.
また、比較例として、Al予備脱酸を実施しなかった場合、溶存酸素がTiと平衡する値以下までAlを添加した場合、Al添加後、本発明以下の時間でTiを添加した場合についても、製品での酸化物系介在物による表面欠陥の発生率及び、連続鋳造用ノズル内部の付着物量を調査した。
表１に各操業における処理条件及び各調査結果を示す。なお、表面欠陥の発生率の調査結果は、溶存酸素がTiと平衡する値以下までAlを添加した場合の平均を1.0として、それとの比にて表示し、同様に、ノズル内部の付着物量の調査結果は、全調査対象のうち最も付着量の少なかった場合の付着物厚みを1.0とし、それに対する厚みの比にて表示した。
In addition, as a comparative example, when Al preliminary deoxidation was not performed, when Al was added to a value equal to or less than the value at which dissolved oxygen was equilibrated with Ti, and after addition of Al, when Ti was added at a time shorter than the present invention The incidence of surface defects due to oxide inclusions in the product and the amount of deposits inside the continuous casting nozzle were investigated.
Table 1 shows the processing conditions and the results of each survey in each operation. In addition, the investigation result of the incidence rate of surface defects is expressed as a ratio to the average when Al is added to a value equal to or less than the value at which dissolved oxygen equilibrates with Ti, and similarly, the amount of deposits inside the nozzle The results of the investigation were displayed as the ratio of the thickness to the thickness of the deposit when the amount of adhesion was the smallest among all survey targets, which was 1.0.
表１に示す結果から、本発明例で製造した厚板は比較例より表面欠陥も低減しており、予備脱酸時に生成したAl2Ｏ3の影響が小さく、Ti脱酸により介在物が微細化できており、しかもTi酸化物の量も少ないことがわかる。また、比較例１に比較して、Ti使用量も低減しており、コスト面でも有利なことが確認された。さらに、ガス攪拌を実施した場合は、特に連々鋳時の鋳造ノズル内付着物量が少なく、かつ表面欠陥のより抑制されている。 From the results shown in Table 1, the thick plate produced in the present invention example has reduced surface defects as compared with the comparative example, the influence of Al 2 O 3 produced during preliminary deoxidation is small, and the inclusions are fine due to Ti deoxidation. It can be seen that the amount of Ti oxide is small. Moreover, compared with the comparative example 1, the amount of Ti used was also reduced, and it was confirmed that it was advantageous also in terms of cost. Further, when gas agitation is performed, the amount of deposits in the casting nozzle during continuous casting is small, and surface defects are further suppressed.
Claims (2)
記
ｔ≧150×ε -0.5 ×１ｎ[（Ｏｏ−Ｏｅ）／Ｏ] ---（１）
ここで、Ｏｏ：Al添加前溶存酸素濃度
Ｏｅ：Al添加後溶存酸素濃度
Ｏ：Ti添加前目標介在物中酸素濃度
ε＝370.8GT／Ｗ×[１−298／Ｔ＋１ｎ（１＋0.677Ｈ／Ｐ）]
但し、Ｇ：撹拌ガス流量（Ｎm 3 ／ｓ）
Ｔ：溶鋼温度（K）
Ｗ：溶鋼量（kg）
Ｈ：撹拌ガス吹き込み深さ（m）
Ｐ：雰囲気圧力（atm） The method for deoxidizing molten steel according to claim 1, wherein after adding Al, gas stirring treatment is performed for a time t (second) represented by the following formula (1), and then Ti is added .
Record
t ≧ 150 × ε −0.5 × 1n [(Oo-Oe) / O] --- (1)
Here, dissolved oxygen concentration before addition of Oo: Al
Oe: dissolved oxygen concentration after Al addition
O: Oxygen concentration in target inclusion before Ti addition
ε = 370.8GT / W × [1-298 / T + 1n (1 + 0.677H / P)]
G: Stirring gas flow rate (Nm 3 / s)
T: Molten steel temperature (K)
W: Amount of molten steel (kg)
H: Stirring gas blowing depth (m)
P: Atmospheric pressure (atm)
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