JP2013167009A - Method for producing steel material having high cleanliness - Google Patents
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本発明は、鋼材の製造段階において、製品段階で製品性能を低下させる要因となり得る粗大な非金属介在物を低減させるとともに、製品性能を向上させることができる微細な非金属介在物を増加させることができる、清浄性の高い鋼材の製造方法に関する。 The present invention reduces the amount of coarse non-metallic inclusions that can cause the product performance to deteriorate at the product stage and increases the fine non-metallic inclusions that can improve the product performance in the production stage of the steel material. The present invention relates to a method for producing a highly clean steel material.
鋼材中の非金属介在物（以下、「介在物」という）は、製品段階で製品性能を低下させる要因となり得ることが知られている。特に、Ａｌキルド鋼中に存在するアルミナ系酸化物は硬質であり、クラスタを形成して粗大化することもある。例えば、最も清浄性を要求される軸受鋼といった清浄鋼では、鋼材中の酸化物が破壊の起点となり、転動疲労寿命を低下させることが知られている。また、大型構造物として用いられる厚板鋼においては、粗大酸化物が溶接時の靱性を低下させる場合がある。さらに、自動車用鋼板等に使用される薄板鋼では、粗大酸化物がスラブの表層欠陥であるふくれ疵の要因となり、鋼板表面の美麗さを損なう場合もある。上記に示した以外にも、加工性、強度、寿命といった製品性能が低下することから、溶鋼段階でこれら大型介在物を低減する対策が行われている。 It is known that non-metallic inclusions (hereinafter referred to as “inclusions”) in steel materials can cause product performance to deteriorate at the product stage. In particular, alumina-based oxides present in Al killed steel are hard and sometimes coarsen by forming clusters. For example, in clean steel such as bearing steel that requires the most cleanliness, it is known that oxides in the steel material serve as a starting point for fracture and reduce the rolling fatigue life. Moreover, in the thick steel plate used as a large structure, a coarse oxide may reduce the toughness at the time of welding. Further, in a thin steel plate used for an automotive steel plate or the like, a coarse oxide may cause blistering, which is a surface layer defect of a slab, and may impair the beauty of the steel plate surface. In addition to the above, since product performance such as workability, strength, and life deteriorates, measures are taken to reduce these large inclusions at the molten steel stage.
例えば、溶鋼中の酸化物を低減させるため、これまでに取鍋底部からの不活性ガス吹込みによる溶鋼撹拌、ＲＨ真空脱ガス装置における長時間環流処理といった技術が適用されている。 For example, in order to reduce oxides in molten steel, techniques such as molten steel agitation by blowing inert gas from the ladle bottom and long-time reflux treatment in an RH vacuum degassing apparatus have been applied.
その一例として、特許文献１には、「溶鋼撹拌のみからなる非金属介在物の浮上・分離工程」を「２０ｍｉｎ以上継続して行うこと」を特徴とする高清浄度鋼の溶製方法が開示されている。この手法は生成した非金属介在物を物理的に溶鋼から除去する技術に分類できる。この技術は、介在物を効率良く凝集させて見かけの介在物径を大きくして除去速度を増大させ、かつ、長時間処理することで鋼の清浄性を向上させるものである。 As an example, Patent Document 1 discloses a method for melting high cleanliness steel characterized by “continuing the flotation / separation step of non-metallic inclusions consisting only of molten steel stirring” for 20 minutes or longer ”. Has been. This method can be classified as a technique for physically removing the produced nonmetallic inclusions from the molten steel. This technique efficiently aggregates inclusions to increase the apparent inclusion diameter to increase the removal rate, and improves the cleanliness of steel by treating for a long time.
また、ＲＨ真空脱ガス装置を用いた処理において、その目的の多くは溶鋼からの脱ガスであるが、溶鋼を減圧処理することで脱炭反応、またそれに伴う脱酸反応を生じさせている。すなわち、未脱酸溶鋼を減圧処理することで脱炭脱酸反応を生じさせ、極低炭素鋼を溶製している。脱炭脱酸反応はＣＯガス発生を伴うため、溶鋼からは炭素と同時に酸素も除去されることになる。ただし、脱炭を目的とする場合、多くは反応速度を高めるために溶存酸素濃度が高い状態で減圧処理し、脱炭終了後にＡｌ等により残存する溶存酸素を低減する処理を行っている。 Further, in the treatment using the RH vacuum degassing apparatus, most of the purpose is degassing from molten steel, but decarburization reaction and accompanying deoxidation reaction are caused by depressurizing the molten steel. That is, decarburization deoxidation reaction is caused by subjecting non-deoxidized molten steel to a reduced pressure to produce ultra-low carbon steel. Since the decarburization and deoxidation reaction involves the generation of CO gas, oxygen is also removed from the molten steel as well as carbon. However, when decarburization is intended, in many cases, a reduced pressure treatment is performed in a state where the dissolved oxygen concentration is high in order to increase the reaction rate, and a treatment is performed to reduce the dissolved oxygen remaining by Al or the like after the completion of the decarburization.
このＲＨでの減圧処理に関して、例えば、特許文献２には、「転炉から溶鋼を末脱酸出鋼し」、「溶鋼中酸素濃度が１００ｐｐｍ以下になるまで炭素含有物を溶鋼に添加し、結果として溶鋼中酸素濃度を１００ｐｐｍ以下とした後にＡｌを添加する」ことを特徴とする高清浄鋼の溶製方法が開示されている。この手法は、炭素含有物を添加することで、溶鋼中の酸素をＣＯガスとして除去し、清浄性を高める技術である。しかしながら、この技術はＲＨでのＡｌ添加時のＡｌ２Ｏ３生成量を低減する技術であり、Ａｌ添加後に脱炭脱酸反応を活用する技術ではない。 Regarding the decompression treatment with RH, for example, Patent Document 2 discloses that “the molten steel is powdered and deoxidized from the converter”, “a carbon-containing material is added to the molten steel until the oxygen concentration in the molten steel becomes 100 ppm or less, As a result, a method for melting high-clean steel is disclosed, in which Al is added after the oxygen concentration in the molten steel is 100 ppm or less. This technique is a technique that removes oxygen in molten steel as CO gas by adding a carbon-containing material, thereby improving cleanliness. However, this technique is a technique for reducing the amount of Al 2 O 3 produced when Al is added in RH, and is not a technique for utilizing a decarburization deoxidation reaction after the addition of Al.
また、特許文献３には、「減圧処理により溶鋼を脱ガスする際、取鍋内の溶鋼にＭｇ系脱酸剤を添加し、脱酸生成物ＭｇＯを溶鋼とともに取鍋から真空容器に上昇させ、真空容器内で脱酸生成物ＭｇＯを鋼中炭素［Ｃ］と反応させ、反応生成物であるＣＯおよびＭｇガスを系外に気化分離する」ことを特徴とする技術が開示されている。この技術は、酸化物をＭｇＯ系に制御した上で、ＣＯとして脱酸して清浄性を向上させる技術である。しかしながら、この技術を用いて溶鋼を清浄化させるには大量のＭｇ系脱酸材が必要であることに加え、真空槽での処理条件が明確に示されていない。このため、たとえ脱酸生成物としてＭｇＯが生成したとしても、ＭｇＯが還元されずに溶鋼中に残存してしまう可能性がある。 Patent Document 3 states that “When degassing molten steel by decompression treatment, an Mg-based deoxidizer is added to the molten steel in the ladle, and the deoxidized product MgO is raised from the ladle to the vacuum vessel together with the molten steel. , A technique characterized by reacting the deoxidation product MgO with carbon in steel [C] in a vacuum vessel and evaporating and separating CO and Mg gas as reaction products out of the system. This technique is a technique for improving cleanliness by controlling the oxide to be MgO and deoxidizing it as CO. However, in order to clean molten steel using this technique, in addition to the need for a large amount of Mg-based deoxidizing material, the processing conditions in the vacuum chamber are not clearly shown. For this reason, even if MgO is generated as a deoxidation product, MgO may remain in the molten steel without being reduced.
一方、特許文献４には、「低炭素成分組成の溶鋼に、Ａｌ、ＲＥＭおよびＺｒを使用して複合脱酸処理を行うこと」を特徴とする、アルミナクラスターを低減した高清浄鋼の製造方法が開示されている。この手法は、生成した酸化物よりも強い脱酸元素を加えることで、生成した酸化物を還元、分解する技術に分類できる。この技術は介在物を物理的に除去する技術とは異なり、化学反応を介して介在物を低減する技術である。しかしながら、これらの強脱酸元素を添加する技術においては、クラスタを形成するアルミナ系酸化物は低減するものの、添加した強脱酸元素との酸化物に置き換わるため、強脱酸元素の添加に伴う酸化物低減効果は不十分であると考えられる。 On the other hand, Patent Document 4 discloses a method for producing high-clean steel with reduced alumina clusters, characterized in that “complex deoxidation treatment is performed on molten steel having a low carbon component composition using Al, REM, and Zr”. Is disclosed. This technique can be classified as a technique for reducing and decomposing the generated oxide by adding a deoxidizing element stronger than the generated oxide. This technique is different from the technique for physically removing inclusions, and is a technique for reducing inclusions through a chemical reaction. However, in the technique of adding these strong deoxidation elements, although the alumina-based oxides that form clusters are reduced, they are replaced by oxides with the added strong deoxidation elements. It is considered that the oxide reduction effect is insufficient.
また、粗大な酸化物は鋼材中で悪影響を及ぼす可能性がある一方、微細な酸化物を積極的に利用して鋼材の性能を向上させる技術も提案されている。
その一例として、特許文献５では、「溶鋼に脱酸剤を添加した後に、脱酸剤を添加した溶鋼よりも溶存酸素濃度が高い他の溶鋼を添加することを特徴とする溶鋼中の酸化物微細分散方法」が開示されている。この手法は、酸素供給速度を抑制しつつ、電圧印加や酸化性ガス吹込みに比べて多量の酸素を供給することにより、粗大な酸化物の生成を抑制しながら、酸化物を微細化する技術である。
Moreover, while a coarse oxide may have a bad influence in steel materials, the technique which improves the performance of steel materials actively using a fine oxide is also proposed.
As an example, Patent Document 5 states, “After adding a deoxidizer to molten steel, another molten steel having a higher dissolved oxygen concentration than the molten steel to which the deoxidizer is added is added. A "fine dispersion method" is disclosed. This technique is a technology that refines the oxide while suppressing the formation of coarse oxide by supplying a large amount of oxygen compared to voltage application and oxidizing gas blowing while suppressing the oxygen supply rate. It is.
しかしながら、上記特許文献１〜５に記載された発明に共通した技術的特性として、酸化物の分散量を増加させるために酸素濃度を増加させた場合、酸化物が粗大化してしまい、微細化効果が低下してしまうことがある。 However, as a technical characteristic common to the inventions described in Patent Documents 1 to 5, when the oxygen concentration is increased in order to increase the amount of oxide dispersion, the oxide becomes coarse, and the effect of miniaturization. May fall.
近年の製鋼技術の進歩に伴い、鋼材の清浄度は大幅に向上した。しかしながら、同時に製品性能の要求水準も高くなっていることから、更なる鋼材の清浄度向上が求められている。また、鋼材特性を向上させるための、酸化物微細化技術も求められている。近年、清浄鋼を溶製するにはＲＨに代表される環流型脱ガス装置を用いる場合が殆どである。これは、環流型脱ガス装置を用いることで、昇温、成分調整、介在物除去などの複数処理を同一装置で実現できるためと考えられる。しかしながら、環流型脱ガス装置を用いた溶鋼清浄化手法は既に数多く報告されており、環流処理の最適化といった従来技術の延長では大幅な清浄度向上は望めないのが現状である。 With recent advances in steelmaking technology, the cleanliness of steel has been greatly improved. However, since the required level of product performance is also increasing at the same time, further improvement in cleanliness of steel materials is required. There is also a need for oxide refinement technology for improving steel material characteristics. In recent years, in order to melt clean steel, a reflux type degassing apparatus represented by RH is almost always used. This is presumably because a plurality of processes such as temperature increase, component adjustment, inclusion removal, etc. can be realized with the same apparatus by using a reflux type degassing apparatus. However, many methods for cleaning molten steel using a recirculation type degassing apparatus have already been reported, and it is not possible to expect a significant improvement in cleanliness by extending the prior art such as optimization of recirculation treatment.
また、強脱酸元素を添加することで酸化物は微細分散できたとしても、製品性能を低下させる粗大介在物の低減との両立はできていない。強脱酸元素を利用した酸化物微細化技術に関しても、従来とは異なる切り口が必要である。 Moreover, even if the oxide can be finely dispersed by adding a strong deoxidizing element, it is not possible to achieve a reduction in coarse inclusions that reduce the product performance. Also regarding oxide refinement technology using a strong deoxidizing element, a different point from the conventional one is necessary.
本発明は、上記した課題に鑑みてなされたものであり、その目的は、環流型脱ガス装置を用いて、鋼材中の粗大酸化物を低減して清浄度を向上させるとともに、微細酸化物を確実に分散させる手法を提供することである。 The present invention has been made in view of the above-described problems, and its purpose is to reduce the coarse oxide in the steel material by using a reflux type degassing apparatus to improve the cleanliness, and to reduce the fine oxide. It is to provide a method to ensure dispersion.
本発明者らは、脱炭反応を積極的に活用することで、従来よりも清浄度の高い鋼が得られると考えた。すなわち、真空脱ガス装置を用いた減圧精錬において、真空槽内の溶鋼表面近傍では、下記（５）式で表される脱炭反応が生じている。自動車外装用の極低炭素鋼を溶製するにあたり、製鋼炉から未脱酸出鋼した溶鋼に対して真空脱ガス装置で減圧処理する際にこの反応を活用している。近年では、脱炭反応を活用することで、１０ｐｐｍを下回るような極低炭素鋼の溶製も可能となっている。しかしながら、炭素濃度が低下してくる脱炭末期では脱炭反応が停滞することに加え、脱炭終了後にＡｌを多量添加して脱酸した後の溶鋼では、脱炭反応が生じないことから、通常のＡｌキルドを対象に考えた場合、脱炭反応を活用することはできない。 The present inventors considered that a steel having a higher cleanliness than before can be obtained by actively utilizing the decarburization reaction. That is, in vacuum refining using a vacuum degassing device, a decarburization reaction represented by the following formula (5) occurs near the surface of the molten steel in the vacuum chamber. When melting ultra-low carbon steel for automobile exteriors, this reaction is utilized when the vacuum degassing equipment is used to depressurize the molten steel that has not been deoxidized from the steelmaking furnace. In recent years, by utilizing a decarburization reaction, it has become possible to produce ultra-low carbon steel that is less than 10 ppm. However, in addition to the fact that the decarburization reaction stagnate at the end of the decarburization when the carbon concentration decreases, the decarburization reaction does not occur in the molten steel after adding a large amount of Al after the decarburization and deoxidizing, When considering normal Al kills, decarburization reaction cannot be used.
Ｃ＋Ｏ＝ＣＯ（ｇ） ・・・（５）
しかしながら、本発明者らは、完全にＡｌで脱酸されていない溶鋼、あるいは、一度Ａｌを添加して溶鋼を昇熱させる操作を行った状況においても、送酸によりＡｌ濃度が低減し、酸素が溶存している溶鋼では、減圧下での脱炭反応を積極的に活用できることを着想した。
C + O = CO (g) (5)
However, the present inventors have also found that molten steel that has not been completely deoxidized with Al, or in a situation where Al has been added once to raise the temperature of the molten steel, the Al concentration is reduced by oxygen supply and oxygen is reduced. The idea is that the molten steel in which can be dissolved can actively utilize the decarburization reaction under reduced pressure.
すなわち、通常のＡｌキルド鋼では、減圧下であっても、溶鋼中のＡｌと溶存酸素が反応し、（６）式に示す反応式に従ってＡｌ２Ｏ３が生成される。Ａｌキルド鋼の平衡酸素濃度は、Ｃ脱酸における平衡酸素濃度と同水準であることから、Ａｌキルド鋼を減圧処理したとしても、Ａｌ２Ｏ３の生成が続き、鋼中にはＡｌ２Ｏ３が多量に生成していることになる。 That is, in a normal Al killed steel, Al in the molten steel reacts with dissolved oxygen even under a reduced pressure, and Al 2 O 3 is generated according to the reaction formula shown in Formula (6). Equilibrium oxygen concentration in the Al-killed steel, because it is the same level as the equilibrium oxygen concentration in the C deoxidation, even if vacuum treatment of Al-killed steel, generation of Al 2 O 3 is followed, during the steel Al 2 O 3 is produced in large quantities.
Ａｌ２Ｏ３（ｓ）＝２Ａｌ＋３Ｏ ・・・（６）
一方、低Ａｌ状態での減圧処理を考えた場合、低Ａｌ状態での平衡到達酸素濃度は、減圧処理時のＣ脱酸における平衡酸素濃度よりも高く、溶鋼中の酸素濃度はＣ脱酸平衡に従って低下する。脱炭反応下での平衡酸素濃度は非常に低位であり、真空槽内は強還元状態となることから、低Ａｌ状態で減圧処理を行っている間は、溶存酸素が溶鋼中炭素と反応することで減少し、一時的にＡｌ２Ｏ３の生成速度が極端に低い状態が作られることになる。さらに、溶鋼中酸素濃度が低位になってくると、酸化物として懸濁したＡｌ２Ｏ３の分解反応が生じるようになる。
Al 2 O 3 (s) = 2Al + 3O (6)
On the other hand, when considering decompression treatment in the low Al state, the equilibrium oxygen concentration in the low Al state is higher than the equilibrium oxygen concentration in C deoxidation during the decompression treatment, and the oxygen concentration in the molten steel is C deoxidation equilibrium. Decrease according to. Since the equilibrium oxygen concentration under the decarburization reaction is very low and the vacuum chamber is in a strongly reduced state, dissolved oxygen reacts with carbon in the molten steel during decompression treatment in a low Al state. Thus, a state in which the production rate of Al 2 O 3 is extremely low is temporarily created. Furthermore, when the oxygen concentration in the molten steel becomes low, a decomposition reaction of Al 2 O 3 suspended as an oxide occurs.
上述したように、通常のＡｌキルド鋼と脱炭反応を活用した低Ａｌ鋼を比較した場合、同じ酸素濃度の溶鋼を溶製するのであっても、溶存酸素の低減プロセスが異なり、Ａｌキルド鋼ではＡｌ２Ｏ３が生成されながら低減していくのに対し、低Ａｌ鋼ではＡｌ２Ｏ３が分解されながら低減してくことになる。このため、低Ａｌ鋼を減圧処理した場合、製品段階で同じ酸素濃度であっても、通常のＡｌキルド鋼よりも粗大な酸化物が極めて少ない、清浄度の高い鋼が得られることになる。この方法は、従来と同じ処理装置を使って溶製できることから、環流処理に伴う介在物の凝集、浮上除去といった溶鋼清浄化手法は、従来と何の変わりもなく活用できる。 As described above, when comparing ordinary Al killed steel and low Al steel utilizing decarburization reaction, even if molten steel with the same oxygen concentration is melted, the process of reducing dissolved oxygen is different, and Al killed steel Then, Al 2 O 3 is reduced while being generated, whereas in low Al steel, Al 2 O 3 is reduced while being decomposed. For this reason, when a low Al steel is subjected to a reduced pressure treatment, a steel having a high degree of cleanness can be obtained even with the same oxygen concentration at the product stage, with extremely less coarse oxide than ordinary Al killed steel. Since this method can be melted by using the same processing apparatus as in the prior art, molten steel cleaning methods such as agglomeration of inclusions and removal of levitating accompanying the reflux treatment can be used as before.
また、微細酸化物を確実に得るためには、凝固段階で生成する微細酸化物を活用する手法が最適である。凝固段階で溶存酸素が高い状況を作ることができれば、凝固過程ではより多くの微細酸化物を分散できる。この手法は、溶鋼段階で酸化物を微細化する手法よりも効果が大きく、安定している。このためには、凝固段階、すなわち、溶鋼段階末期で溶存酸素濃度が高い状態を作る必要がある。 In order to reliably obtain a fine oxide, a technique that utilizes the fine oxide generated in the solidification stage is optimal. If a situation in which dissolved oxygen is high in the solidification stage can be created, more fine oxides can be dispersed in the solidification process. This method is more effective and stable than the method of refining oxide at the molten steel stage. For this purpose, it is necessary to create a state in which the dissolved oxygen concentration is high at the solidification stage, that is, at the end of the molten steel stage.
脱炭反応を活用して脱酸した溶鋼の溶存酸素濃度は、減圧精錬時の真空度に依存することになる。このため、一度高真空精錬で溶存酸素濃度を低減した後に真空槽内圧力を高めて環流させると、溶存酸素濃度はその真空度に合わせて増加することになる。この時の酸素供給源は、取鍋スラグや耐火物内壁であり、過剰な酸素供給を回避できる。溶存酸素濃度のみを高くした状態で鋳込んだ場合、凝固過程で溶鋼中に溶け切れなくなった酸素が溶鋼成分と反応して生成する、いわゆる二次脱酸生成物が大量に生成することになる。仮に、同じ減圧操作を通常のＡｌキルド鋼に適用したとしても、溶存酸素濃度はＡｌ濃度によって決まっている。Ａｌキルド鋼において、同様に真空槽内圧力を高める操作を行い、酸素濃度が増加したとしても、増加した溶存酸素とＡｌが反応してＡｌ２Ｏ３を形成することから、それは溶存酸素濃度ではなく、酸化物が増大することを意味する。一方、減圧処理を経ずにＡｌで弱脱酸しただけでは、溶鋼中に粗大な酸化物が多数生成してしまうことになる。 The dissolved oxygen concentration of the molten steel deoxidized by utilizing the decarburization reaction depends on the degree of vacuum at the time of vacuum refining. For this reason, once the dissolved oxygen concentration is reduced by high vacuum refining and then refluxed by increasing the pressure in the vacuum chamber, the dissolved oxygen concentration increases in accordance with the degree of vacuum. The oxygen supply source at this time is a ladle slag or an inner wall of the refractory, and an excessive oxygen supply can be avoided. When casting with only the dissolved oxygen concentration raised, a large amount of so-called secondary deoxidation products will be produced, in which oxygen that is not completely melted in the molten steel reacts with the molten steel components during the solidification process. . Even if the same decompression operation is applied to normal Al killed steel, the dissolved oxygen concentration is determined by the Al concentration. In Al killed steel, the operation to increase the pressure in the vacuum chamber is similarly performed, and even if the oxygen concentration increases, the increased dissolved oxygen reacts with Al to form Al 2 O 3. It means that the oxide increases. On the other hand, if only weak deoxidation with Al without passing through the reduced pressure treatment, a large number of coarse oxides are generated in the molten steel.
このような状況を踏まえて本発明者らが検討した結果、減圧処理を行う際、その時点でのＡｌ濃度で決まる溶存酸素濃度よりも、炭素濃度と真空槽の圧力で決まる溶存酸素濃度が低くなる条件で減圧精錬を行うことで脱炭反応が生じ、粗大な酸化物を低減できることを知見した。さらに、この状態から真空槽内圧力を高くして環流させることで、溶存酸素濃度のみを増加できることを知見した。 As a result of the study by the present inventors based on such a situation, when performing the decompression process, the dissolved oxygen concentration determined by the carbon concentration and the pressure in the vacuum chamber is lower than the dissolved oxygen concentration determined by the Al concentration at that time. It has been found that decarburization reaction occurs by reducing pressure under the following conditions to reduce coarse oxides. Furthermore, it has been found that only the dissolved oxygen concentration can be increased by increasing the pressure in the vacuum chamber and refluxing from this state.
ＣとＡｌの酸化反応はそれぞれ（５）式、（６）式で表すことができ、それらを酸素濃度で整理すると（７）式、（８）式の形になる。（８）式で決まる酸素濃度が（７）式で決まる酸素濃度よりも低くなる条件は（９）式に示す形となる。 The oxidation reaction of C and Al can be represented by the formulas (5) and (6), respectively, and when they are arranged by the oxygen concentration, the forms of the formulas (7) and (8) are obtained. The condition that the oxygen concentration determined by equation (8) is lower than the oxygen concentration determined by equation (7) is as shown in equation (9).
％Ｏ_Ａｌ＝（Ｃ_７（定数）／％Ａｌ２）^1／3 ・・・（７）
％Ｏ_Ｃ＝Ｃ_８（定数）×Ｐ_ＣＯ／％Ｃ ・・・（８）
％Ａｌ＜Ｃ_９（定数）×（％Ｃ／Ｐ）^3／2 ・・・（９）
ここで、％Ｏ_Ａｌ：Ａｌの酸化反応から求まる溶鋼中Ｏ濃度、％Ｏ_Ｃ：Ｃの酸化反応から求まる溶鋼中Ｏ濃度、Ｃ_７：定数、％Ａｌ：Ｓｏｌ．Ａｌ濃度、Ｃ_８：定数、Ｐ_ＣＯ：ＣＯ分圧、％Ｃ：Ｃ濃度、Ｃ_９：定数、Ｐ：ＣＯ分圧と相関関係にある真空槽内の圧力である。
% O _Al = (C _7 (constant) /% Al 2) ^ 1/3 ··· (7)
% O_C = C_8 (constant) × P_CO /% C (8)
% Al < C_9 (constant) x (% C / P) ^ 3/2 (9)
Here,% O_Al : O concentration in molten steel obtained from oxidation reaction of Al,% O_C : O concentration in molten steel obtained from oxidation reaction of C, C_7 : constant,% Al: Sol. Al concentration, C _8: constant, P _CO: CO partial pressure,% C: C concentration, C _9: constant, P: is the pressure in the vacuum chamber which is correlated with the partial pressure of CO.
本発明者らは、上記検討を踏まえ、真空脱ガス装置で溶鋼を処理する際のＡｌ、Ｃ濃度および真空度、ならびに、その処理時間を明確化することで、本発明を完成するに至った。 Based on the above studies, the present inventors have clarified the Al, C concentration and degree of vacuum when processing molten steel with a vacuum degassing apparatus, and the processing time, thereby completing the present invention. .
本発明は、以下の通りである。
（１）製鋼炉から取鍋に出鋼した、質量％でＳｏｌ．Ａｌ：０．００５％以下、Ｓｉ：０．００５〜０．３％、Ｏ（全酸素濃度）：０．０２％以下を含有する溶鋼を、減圧清浄化処理として、環流型脱ガス装置において、（１）式を満たすＡｌ濃度、Ｃ濃度および真空槽内圧力で１０分間以上環流処理し、該還流処理中および処理後は、炭素以外の脱酸材を添加しないこと、すなわち、脱酸剤は炭素を含めて一切添加しないか、または、脱酸剤を添加するなら炭素に限ることを特徴とする、清浄性の高い鋼材の製造方法。
The present invention is as follows.
(1) The amount of Sol. In a reflux degassing apparatus, a molten steel containing Al: 0.005% or less, Si: 0.005-0.3%, O (total oxygen concentration): 0.02% or less is used as a vacuum cleaning treatment. A reflux treatment is performed for 10 minutes or more at an Al concentration, a C concentration and a vacuum tank pressure satisfying the formula (1), and no deoxidizer other than carbon is added during and after the reflux treatment. A method for producing a highly clean steel material, characterized in that carbon is not added at all or carbon is added if a deoxidizer is added.
Ａｌ＜０．０００８×（（１０１．３２５×Ｃ）／Ｐ０_former）1.5 ・・・（１）
Ａｌ：溶鋼中Ｓｏｌ．Ａｌ濃度（ｍａｓｓ％）
Ｃ：溶鋼中Ｃ濃度（ｍａｓｓ％）
Ｐ０_former：減圧清浄化処理時の真空槽内圧力（ｋＰａ）
（２）前記減圧清浄化処理を施した後、後環流処理として、質量％でＳｏｌ．Ａｌ：０．００５％以下、Ｓｉ：０．００５〜０．３％、Ｏ（全酸素濃度）：０．００５％以下を含有する溶鋼を、（４）式を満たす範囲の真空槽内圧力Ｐ０_latterで、３分間以上環流処理し、該環流処理中および処理後は炭素以外の脱酸剤を添加しないこと、すなわち、脱酸剤は炭素を含めて一切添加しないか、または、脱酸剤を添加するなら炭素に限ることを特徴とする、請求項１に記載した清浄性の高い鋼材の製造方法。
Al <0.0008 × ((101.325 × C) / P 0_former ) 1.5 (1)
Al: Sol. Al concentration (mass%)
C: C concentration in molten steel (mass%)
P 0_former : Pressure inside vacuum chamber (kPa) during vacuum cleaning process
(2) After the vacuum cleaning treatment, Sol. The pressure in the vacuum chamber P is within a range that satisfies the formula (4) for molten steel containing Al: 0.005% or less, Si: 0.005-0.3%, O (total oxygen concentration): 0.005% or less. Reflux treatment at 0_latter for 3 minutes or more, and no deoxidizer other than carbon is added during and after the reflux treatment, that is, the deoxidizer is not added at all including carbon, or the deoxidizer is not added. The method for producing a steel material with high cleanliness according to claim 1, wherein if added, the material is limited to carbon.
５＜Ｐ０_latter＜１５・・・・・（４）
Ｐ０_latter：後環流処理時の真空槽内圧力（ｋＰａ）
5 <P 0_latter <15 (4)
P 0_latter : Vacuum chamber pressure (kPa) during post- circulation
本発明によれば、環流型脱ガス装置を用いて、鋼材中の粗大酸化物を低減して粗大な酸化物量が極めて少なく清浄度が高い鋼材を効率良く製造できるとともに、従来よりも微細酸化物を確実に分散させ微細酸化物の分散量が大きい鋼材を効率良く製造できる。このよう鋼材を溶製することで、粗大酸化物による鋼材への悪影響を低減するとともに、鋼材に、高強度化、加工性向上といった新たな付加価値を付与することができる。これらは、既存の製鋼プロセスを大きく変更することなく溶製可能であることから、製造コストの増大を抑制可能であり、本発明の社会的貢献度は非常に大きい。 According to the present invention, a circulating degassing apparatus can be used to reduce the amount of coarse oxide in the steel material, thereby efficiently producing a steel material having a very small amount of coarse oxide and a high degree of cleanness. Can be reliably dispersed and a steel material having a large amount of fine oxide dispersed can be efficiently produced. By melting the steel material in this manner, it is possible to reduce the adverse effect of the coarse oxide on the steel material, and to add new added values such as higher strength and improved workability to the steel material. Since these can be melted without greatly changing the existing steelmaking process, the increase in production cost can be suppressed, and the social contribution of the present invention is very large.
１．本発明における用語の定義
「製鋼炉」とは、転炉または電気炉を指し、製鋼炉から出鋼された「溶鋼」とは、脱硫、脱りんもしくは脱炭といった一次精錬処理が実施された状態であるものとする。
1. Definition of Terms in the Present Invention “Steelmaking furnace” refers to a converter or electric furnace, and “molten steel” produced from the steelmaking furnace is a state in which primary refining treatment such as desulfurization, dephosphorization, or decarburization has been performed. Suppose that
「環流型脱ガス装置」とは、真空槽を要する溶鋼処理装置であって、代表的な装置としてＲＨがある。「環流処理」とは、環流型脱ガス装置を用いて、取鍋に溶鋼を受鋼している状態で、真空槽内圧力を低下させることで溶鋼を真空槽に吸い上げ、環流ガスを流すことで、溶鋼を取鍋と真空槽との間で環流させる操作を指す。環流中の溶鋼では、溶鋼が減圧雰囲気にさらされることから脱ガス反応が促進されるとともに、介在物の凝集、浮上除去が促進される。 The “circulating degassing device” is a molten steel processing device that requires a vacuum tank, and a representative device is RH. "Reflux treatment" means that the molten steel is sucked into the vacuum chamber by lowering the pressure in the vacuum chamber while the molten steel is received in the ladle using the recirculation type degassing device, and the reflux gas is allowed to flow. Then, it refers to the operation of circulating the molten steel between the ladle and the vacuum chamber. In the molten steel in the reflux, the molten steel is exposed to a reduced-pressure atmosphere, so that the degassing reaction is promoted and the inclusions are flocculated and lifted.
「脱炭脱酸反応」とは、（５）式で示されるように、炭素と酸素から一酸化炭素が生成する反応を示す。
「環流時間」とは、真空脱ガス装置で溶鋼を処理するに当たり、真空槽内が所定の圧力に到達した後、環流ガスを流して、溶鋼を、真空槽内と取鍋との間で循環させている間の時間を指す。
The “decarburization deoxidation reaction” refers to a reaction in which carbon monoxide is generated from carbon and oxygen as represented by the formula (5).
“Recirculation time” means that the molten steel is circulated between the vacuum chamber and the ladle by flowing the reflux gas after the vacuum tank reaches the specified pressure when processing the molten steel with the vacuum degassing device. Refers to the time during
「脱酸剤」とは、鉄以外の合金元素のうち、酸化物を形成する元素を含む金属単体もしくはその化合物を指し、Ｃ、Ａｌ、Ｓｉ、Ｍｎ、Ｔｉ、Ｍｇ、Ｃａが含まれる。
本発明において、環流脱ガス装置における精錬処理を、脱炭脱酸反応を生じさせて溶存酸素濃度を低減、並びに粗大酸化物を低減させることを目的とした「減圧清浄化処理」、溶存酸素濃度のみを増加させることを目的とした「後環流処理」と呼称する。また、減圧清浄化処理時の真空槽内圧力をＰ０_former、減圧清浄化処理後、すなわち、後環流処理時の真空槽内圧力をＰ０_latterと呼称する。
“Deoxidizer” refers to a simple metal or a compound containing an element that forms an oxide among alloy elements other than iron, and includes C, Al, Si, Mn, Ti, Mg, and Ca.
In the present invention, the refining process in the reflux degassing apparatus is to reduce the dissolved oxygen concentration by causing a decarburization deoxidation reaction, as well as the “reduced pressure reduction process” for the purpose of reducing coarse oxides, dissolved oxygen concentration This is referred to as “post-recirculation treatment” for the purpose of increasing only the amount. Further, vacuum cleaning process when the vacuum chamber pressure P 0_Former, after vacuum cleaning process, i.e., the vacuum chamber pressure during post-perfusion process is referred to as P 0_latter.
２．溶鋼組成
本発明を実施するに当たって、溶鋼段階の鋼に含まれる元素について説明する。以下、断りが無い限り全てｍａｓｓ％とする。
2. Molten steel composition In carrying out the present invention, elements contained in steel in the molten steel stage will be described. Hereinafter, unless otherwise noted, all are mass%.
［Ｓｏｌ．Ａｌ濃度：０．００５％以下］
本発明は、環流型脱ガス装置において、脱炭脱酸反応を活用して酸化物の分解反応を生じさせる。このため、減圧清浄化処理の前段階において、溶存酸素が完全に低減されていないことが必要である。このため、脱炭脱酸反応中は終始、溶鋼中のＳｏｌ．Ａｌ濃度は０．００５％以下である必要がある。この時、Ｓｏｌ．Ａｌ濃度は低位であるほうが脱炭脱酸反応を効率的に活用できる。
[Sol. Al concentration: 0.005% or less]
The present invention uses a decarburization deoxidation reaction in a reflux degassing apparatus to cause an oxide decomposition reaction. For this reason, it is necessary that the dissolved oxygen is not completely reduced in the previous stage of the vacuum cleaning treatment. For this reason, during decarburization deoxidation reaction, Sol. The Al concentration needs to be 0.005% or less. At this time, Sol. The lower the Al concentration, the more efficient the decarburization and deoxidation reaction can be made.
減圧清浄化処理を行う前段階として、Ａｌの酸化反応を利用した溶鋼昇熱処理を実施してもよい。昇温に必要な温度が高い場合、溶鋼中のＡｌ濃度は一時的に０．００５％を超える場合もあるが、昇熱操作に伴う酸素吹きによりＡｌ濃度を０．００５％以下に制御し、脱炭脱酸反応が生じるのに必要な酸素量を確保すればよい。Ｓｏｌ．Ａｌ濃度が低い場合、溶存酸素濃度は高くなり、脱炭脱酸反応を効率的に活用できる。一方で、Ａｌを完全に低減することは困難であることから、減圧清浄化処理中および後環流中の望ましいＳｏｌ．Ａｌ濃度は、０．０００５〜０．００２０％である。 As a stage before performing the vacuum cleaning treatment, a molten steel heat treatment using an oxidation reaction of Al may be performed. When the temperature required for the temperature increase is high, the Al concentration in the molten steel may temporarily exceed 0.005%, but the Al concentration is controlled to 0.005% or less by oxygen blowing accompanying the heating operation, What is necessary is just to ensure the amount of oxygen required for decarburization deoxidation reaction to occur. Sol. When the Al concentration is low, the dissolved oxygen concentration is high, and the decarburization and deoxidation reaction can be efficiently utilized. On the other hand, since it is difficult to completely reduce Al, desirable Sol. The Al concentration is 0.0005 to 0.0020%.
［Ｓｉ濃度：０．００５〜０．３％］
Ｓｉは、溶鋼中で脱酸元素として働き、鋼材中では焼き入れ性を高める。脱酸成分が低位過ぎると、溶鋼中酸素濃度が過度に高くなってしまう可能性があることから、Ｓｉは０．００５％以上含有されることが必要である。一方、Ｓｉが０．３％を超えて含有されると、溶存酸素濃度が低くなり過ぎ、脱炭脱酸反応が停滞する可能性がある。このことから、減圧清浄化処理中および後環流処理中は終始、Ｓｉ濃度は０．００５〜０．３％であることが必要である。
[Si concentration: 0.005 to 0.3%]
Si acts as a deoxidizing element in molten steel and enhances hardenability in steel. If the deoxidizing component is too low, the oxygen concentration in the molten steel may become excessively high, so Si needs to be contained in an amount of 0.005% or more. On the other hand, when Si exceeds 0.3%, the dissolved oxygen concentration becomes too low, and the decarburization and deoxidation reaction may stagnate. For this reason, the Si concentration needs to be 0.005 to 0.3% throughout the vacuum cleaning process and the post-circulation process.
［Ｏ濃度：０．０２％以下］
Ｏは、鋼材の製造過程において不可避的に含有される元素であり、溶存、もしくは酸化物として存在する。両者を明確に分離することは困難であり、かつ脱炭脱酸反応では溶存酸素とともに酸化物としての酸素も酸素源に成り得ると考えられることから、本発明でのＯ濃度は両者を合わせた全酸素濃度とする。本発明の対象鋼は清浄性の高い鋼であり、減圧清浄化処理後は脱酸材を新たに添加しなくても酸素濃度が低い状態にする必要がある。減圧清浄化処理する前の段階でＯ濃度が０．０２％を超えると、脱炭脱酸反応によって脱酸するのに長時間要し、生産性が低下することから、減圧清浄化処理する前の段階で、溶鋼中のＯ濃度は０．０２％以下であることが必要である。また、極端にＯ濃度が低い場合、脱炭脱酸反応を効率的に活用できないことから、減圧清浄化処理する前の段階ではＯ濃度が０．００３％以上であることが望ましい。
[O concentration: 0.02% or less]
O is an element inevitably contained in the manufacturing process of the steel material, and is present as dissolved or oxide. It is difficult to clearly separate the two, and in the decarburization and deoxidation reaction, it is considered that oxygen as an oxide as well as dissolved oxygen can be an oxygen source. Let it be the total oxygen concentration. The target steel of the present invention is a steel with high cleanliness, and after the vacuum cleaning treatment, it is necessary to make the oxygen concentration low even without newly adding a deoxidizer. If the O concentration exceeds 0.02% in the stage before the vacuum cleaning treatment, it takes a long time to deoxidize by the decarburization deoxidation reaction, and the productivity decreases. At this stage, the O concentration in the molten steel needs to be 0.02% or less. In addition, when the O concentration is extremely low, the decarburization and deoxidation reaction cannot be efficiently used. Therefore, it is desirable that the O concentration is 0.003% or more before the vacuum cleaning treatment.
減圧清浄化処理後は、酸化物としてのＯ濃度、および溶存酸素両者ともに低いことが望ましい。このため、減圧清浄化処理後のＯ濃度は０．００５％以下であることが望ましい。一方で、二次脱酸生成物を有効活用することを考えると、溶存酸素濃度が高いことが望ましい。しかしながら、過度にＯ濃度が高くなると、鋳造時に鋳型内で溶鋼が沸き、鋳込めなくなる可能性が高くなる。このことから、後還流処理後のＯ濃度は０．００８％以下であることが望ましい。 It is desirable that both the O concentration as the oxide and the dissolved oxygen are low after the vacuum cleaning treatment. For this reason, it is desirable that the O concentration after the vacuum cleaning treatment is 0.005% or less. On the other hand, considering effective utilization of the secondary deoxidation product, a high dissolved oxygen concentration is desirable. However, if the O concentration becomes excessively high, there is a high possibility that the molten steel will boil in the mold during casting and casting will not be possible. From this, it is desirable that the O concentration after the post-reflux treatment is 0.008% or less.
［Ｃ濃度：０．０３〜１．２％］
Ｃは、鋼材の製造過程において不可避的に含有される元素であり、脱炭脱酸反応を効率的に生じさせるためには、溶鋼中のＣ濃度が一定量以上含有されていることが望ましい。減圧清浄化処理する前の段階で０．０３％を下回ると、溶存酸素濃度が低い状況において脱炭脱酸反応が停滞することになる。脱炭脱酸反応を促進する点から、減圧清浄化処理する前の段階はＣ濃度が高いほうが望ましい。一方、製品性能の面からは、１．２％を超えてＣが含有されると過度に硬くなり過ぎることに加え、１．２％を超えてＣが含有されていても脱炭脱酸反応の効率は飽和している。このため、減圧清浄化処理する前の段階のＣ濃度は０．０３〜１．２％であることが望ましい。
[C concentration: 0.03-1.2%]
C is an element inevitably contained in the manufacturing process of the steel material, and it is desirable that the C concentration in the molten steel is contained in a certain amount or more in order to efficiently cause the decarburization deoxidation reaction. If it is less than 0.03% at the stage before the vacuum cleaning treatment, the decarburization deoxidation reaction will stagnate in a situation where the dissolved oxygen concentration is low. In terms of promoting the decarburization and deoxidation reaction, it is desirable that the C concentration is higher in the stage before the vacuum cleaning treatment. On the other hand, in terms of product performance, when C exceeds 1.2%, it becomes excessively hard, and even if it exceeds 1.2%, decarburization deoxidation reaction The efficiency of is saturated. For this reason, it is desirable that the C concentration in the stage before the vacuum cleaning treatment is 0.03 to 1.2%.
［Ｍｎ濃度：０．３〜２．５％］
Ｍｎは、鋼材の製造過程において不可避的に含有される元素であり、脱酸剤として有用であるとともに、鋼材中でＭｎＳを形成して赤熱脆性を防止する作用もある。左記の効果を得るにはＭｎが０．３％を超えて含有されることが望ましい。一方、Ｍｎが２．５％を超えて含有されても効果が飽和してしまうことから、減圧清浄化処理中および後環流処理中は終始Ｍｎ濃度は０．３〜２．５％であることが望ましい。
[Mn concentration: 0.3 to 2.5%]
Mn is an element that is inevitably contained in the manufacturing process of the steel material, and is useful as a deoxidizer, and also has an effect of preventing red hot brittleness by forming MnS in the steel material. In order to obtain the effects described on the left, it is desirable that Mn is contained in excess of 0.3%. On the other hand, even if Mn is contained in excess of 2.5%, the effect is saturated, so that the Mn concentration is 0.3 to 2.5% throughout the vacuum cleaning process and the post-circulation process. Is desirable.
本発明で溶製する清浄性の高い鋼には、上記したＡｌ、Ｃ、Ｓｉ、Ｍｎ、Ｏ以外に、Ｐ：０．１％以下、Ｓ：０．５５％以下を含有し、残部Ｆｅおよび不可避的不純物で構成される。また、上記以外に、製品に必要な機能を付加する目的で、Ｆｅの一部に換えて、さらに、Ｔｉ：０．００５％以下、Ｃｒ：２．０％以下、Ｎｂ：０．０５％以下、Ｍｏ：１．０％以下、Ｖ：０．３％以下、Ｂ：０．００４％以下、Ｃｕ：１．０％以下、Ｎｉ：３．０％以下、Ｓｎ：１．０％以下、Ｍｇ：０．００２％以下、Ｃａ：０．００２％以下、Ｎ：０．０２％以下を含有させても良い。 In addition to the above-mentioned Al, C, Si, Mn, and O, the highly clean steel melted in the present invention contains P: 0.1% or less, S: 0.55% or less, the balance Fe and Consists of inevitable impurities. In addition to the above, for the purpose of adding a necessary function to the product, Ti: 0.005% or less, Cr: 2.0% or less, Nb: 0.05% or less, instead of a part of Fe , Mo: 1.0% or less, V: 0.3% or less, B: 0.004% or less, Cu: 1.0% or less, Ni: 3.0% or less, Sn: 1.0% or less, Mg : 0.002% or less, Ca: 0.002% or less, N: 0.02% or less may be included.
３．溶製時の溶鋼成分測定方法
本発明において、脱炭脱酸反応を生じさせるには、脱炭脱酸反応を生じさせる前段階において、Ａｌ脱酸で決まる溶鋼中の酸素濃度よりも、溶鋼中の炭素濃度と真空槽内圧力から求まる酸素濃度が低い状態を構築する必要がある。
3. In the present invention, in order to cause decarburization and deoxidation reaction, in the stage before causing decarburization and deoxidation reaction, in the molten steel, the oxygen concentration in the molten steel determined by Al deoxidation is increased. It is necessary to construct a state in which the oxygen concentration obtained from the carbon concentration and the pressure in the vacuum chamber is low.
溶鋼中のＣ、Ｓｉ、Ａｌ濃度は、取鍋から採取したサンプルを分析することで測定できる。溶鋼中の全酸素濃度は特許第４８８８５１６号明細書（鉄鋼中酸素の分析方法）に基づき迅速分析できる。また、酸素濃淡電池を原理とする酸素濃度プローブで直接溶鋼の溶存酸素濃度を測定することができる。 C, Si, and Al concentration in the molten steel can be measured by analyzing a sample collected from the ladle. The total oxygen concentration in the molten steel can be quickly analyzed based on Japanese Patent No. 4888516 (method for analyzing oxygen in steel). Moreover, the dissolved oxygen concentration of molten steel can be directly measured with an oxygen concentration probe based on an oxygen concentration cell.
所定のｓｏｌ．Ａｌ、Ｓｉ濃度を満たすように溶鋼組成が調整されている場合、減圧清浄化処理前に全酸素濃度が０．０２％以下になっていることは容易に推定可能であることから、常に全酸素濃度を確認する必要はない。また、後環流処理前は、全酸素濃度に占める酸化物としての酸素量は僅かであることから、酸素濃度プローブの測定値が０．００５％以下であれば、常に全酸素濃度を確認する必要はない。 The predetermined sol. When the molten steel composition is adjusted to satisfy the Al and Si concentrations, it can be easily estimated that the total oxygen concentration is 0.02% or less before the vacuum cleaning treatment. There is no need to check the concentration. In addition, since the amount of oxygen as an oxide in the total oxygen concentration is small before the post-circulation treatment, it is necessary to always check the total oxygen concentration if the measured value of the oxygen concentration probe is 0.005% or less. There is no.
４．処理手順
本発明において、溶鋼は製鋼炉から取鍋に出鋼された後、環流型脱ガス装置にて減圧処理される。取鍋に出鋼された後、環流型脱ガス装置まで搬送される間に、合金等を添加して成分調整してもよい。
4). Treatment procedure In the present invention, the molten steel is discharged from a steelmaking furnace into a ladle and then subjected to a reduced pressure treatment by a circulating degassing apparatus. After the steel is taken out to the ladle, the composition may be adjusted by adding an alloy or the like while being transported to the reflux degasser.
環流型脱ガス装置にて、脱炭脱酸反応を生じさせる前段階で、Ａｌの酸化反応を利用した溶鋼昇熱処理を行ってもよい。その場合、一時的にＳｏｌ．Ａｌ濃度が０．００５％を超えてもよい。ただし、脱炭脱酸反応が生じる溶存酸素を確保し、反応中のＡｌ２Ｏ３生成を抑制するため、Ａｌ濃度が０．００５％以下になるまで送酸処理を行ってＡｌ濃度を低減させる必要がある。 In a reflux type degassing apparatus, molten steel heat treatment using an oxidation reaction of Al may be performed at a stage before the decarburization deoxidation reaction is caused. In that case, the Sol. The Al concentration may exceed 0.005%. However, in order to secure dissolved oxygen that causes decarburization and deoxidation reaction and to suppress the formation of Al 2 O 3 during the reaction, the acid concentration is reduced by reducing the Al concentration until the Al concentration becomes 0.005% or less. There is a need.
減圧清浄化処理を行うに当たり、真空槽内圧力を低下させ、溶鋼中の酸素濃度よりも、溶鋼中の炭素濃度と真空槽内圧力から求まる酸素濃度を低い状態にすることで脱炭脱酸反応を生じさせる。溶鋼中の炭素濃度と真空槽内圧力から求まる酸素濃度は、処理温度によっても変化するが、環流型脱ガス装置での処理中の溶鋼温度では、真空槽内圧力Ｐ０_formerを、（１）式を満たす範囲とすることで、確実に脱炭脱酸反応を生じさせることができる。脱炭脱酸反応は、溶鋼中酸素濃度と平衡酸素濃度の差異が大きいほど効果が大きいことから、真空槽内圧力はより低位であることが望ましい。 In performing vacuum cleaning treatment, decarburization and deoxidation reaction is achieved by lowering the pressure in the vacuum chamber and lowering the oxygen concentration obtained from the carbon concentration in the molten steel and the pressure in the vacuum chamber than the oxygen concentration in the molten steel. Give rise to Although the oxygen concentration obtained from the carbon concentration in the molten steel and the pressure in the vacuum chamber varies depending on the processing temperature, the pressure P 0_former in the vacuum chamber is expressed by the equation (1) at the molten steel temperature during the processing in the circulating degassing device. By making it the range which satisfy | fills, decarburization deoxidation reaction can be produced reliably. Since the decarburization deoxidation reaction is more effective as the difference between the oxygen concentration in the molten steel and the equilibrium oxygen concentration is larger, it is desirable that the pressure in the vacuum chamber is lower.
脱炭脱酸反応は、真空槽内の溶鋼面で生じる反応であるため、脱酸効果を得るためには、ある程度の反応時間が必要である。脱酸効果を確実に得るためには、減圧清浄化処理時の環流時間が１０分間以上であることが必要である。この環流時間が１０分間より短い場合、溶存酸素濃度を十分低下させることができない。一方、環流時間が２５分間を超えても脱酸効果は既に飽和しており、これ以上の処理時間増加は処理費用の増大を招くことになるため、環流時間は２５分間以内であることが望ましい。 Since the decarburization deoxidation reaction is a reaction that occurs on the molten steel surface in the vacuum chamber, a certain amount of reaction time is required to obtain the deoxidation effect. In order to ensure the deoxidation effect, it is necessary that the reflux time during the vacuum cleaning treatment is 10 minutes or more. When this reflux time is shorter than 10 minutes, the dissolved oxygen concentration cannot be lowered sufficiently. On the other hand, even if the reflux time exceeds 25 minutes, the deoxidation effect is already saturated, and further increase in treatment time will lead to an increase in treatment cost. Therefore, the reflux time is preferably within 25 minutes. .
上記減圧清浄化処理終了時点で、溶鋼は脱炭脱酸反応により溶存酸素が低下し、溶鋼中の酸化物は還元されて粒径が小さくなっている。さらに、従来の環流操作と同様に、介在物の凝集と浮上の効果も相まって、脱炭脱酸反応を活用していない状態と比較して、溶鋼中の酸化物は低減できており、清浄性の高い状態になっている。 At the end of the vacuum cleaning treatment, the molten steel has its dissolved oxygen lowered by the decarburization deoxidation reaction, and the oxide in the molten steel has been reduced to reduce the particle size. Furthermore, as in the case of the conventional reflux operation, combined with the agglomeration and floating effects of inclusions, the oxides in the molten steel can be reduced compared with the state where decarburization deoxidation reaction is not utilized, and the cleanliness It is in a high state.
このとき、溶存酸素と酸化物を形成するようなＡｌ、Ｓｉ、Ｍｎ、Ｔｉ、Ｍｇ、Ｃａといった脱酸材を添加してしまうと、僅かに残存している溶存酸素と反応して粗大な酸化物を形成してしまう可能性があるため、炭素以外の脱酸材は添加してはならない。但し、炭素は、炭素を添加した場合、溶鋼中に溶解するか、ＣＯガスとして気相に排出され、粗大な酸化物は形成されないため、減圧処理中もしくは処理後であっても添加してもよい。 At this time, if a deoxidizing material such as Al, Si, Mn, Ti, Mg, or Ca that forms oxides with dissolved oxygen is added, it reacts with the remaining dissolved oxygen to cause coarse oxidation. Deoxidizers other than carbon should not be added because they can form products. However, when carbon is added, carbon dissolves in the molten steel or is discharged into the gas phase as CO gas, and no coarse oxide is formed. Therefore, carbon may be added even during or after decompression. Good.
ここで、二次脱酸生成物を活用して鋼材の特性を向上させることを考えた場合、上記減圧清浄化処理の後、真空槽内圧力を意図的に増加させることで、溶存酸素濃度を高めることができる。 Here, when considering improving the properties of the steel material by utilizing the secondary deoxidation product, the dissolved oxygen concentration can be increased by intentionally increasing the pressure in the vacuum chamber after the vacuum cleaning treatment. Can be increased.
後環流処理を行うに当たり、溶鋼中Ａｌ濃度が低位である状態で、かつ、溶存酸素濃度よりも、溶鋼中の炭素濃度と真空槽内圧力から求まる酸素濃度の方が高い状態にして環流処理を行うことで、溶存酸素濃度のみを増加できる。溶鋼中の溶存酸素濃度は、処理前半の真空槽内圧力Ｐ０_formerと釣り合っていることから、真空槽内の圧力を高くしてＰ０_latterとした場合、Ｐ０_latterに見合った量の酸素が溶存酸素として溶鋼に入ることになる。この時、真空槽内圧力は（４）式を満たす範囲とすることで、確実に溶存酸素濃度を増加させることができる。 In the post-circulation treatment, the reflux treatment is performed in a state where the Al concentration in the molten steel is low and the oxygen concentration obtained from the carbon concentration in the molten steel and the pressure in the vacuum chamber is higher than the dissolved oxygen concentration. By doing so, only the dissolved oxygen concentration can be increased. Dissolved oxygen concentration in the molten steel, since it is balanced with the vacuum chamber pressure P 0_Former processing the first half, when the P 0_Latter by increasing the pressure in the vacuum chamber, the amount of oxygen dissolved oxygen commensurate with the P 0_Latter Will enter the molten steel. At this time, the dissolved oxygen concentration can be reliably increased by setting the pressure in the vacuum chamber to a range satisfying the equation (4).
上記した操作は、ＲＨ真空脱ガス装置を用いた溶鋼処理においては、脱ガス終了後の溶鋼成分調整時などに行われてきている。しかしながら、従来は溶鋼中に脱酸元素としてＡｌやＳｉが多量添加された溶鋼を処理していたため、真空槽内圧力を高くして環流させたとしても、酸素はＡｌやＳｉの酸化に消費されるため、本発明の効果として得られる、溶存酸素のみが増加することが知見されなかったと考えられる。 In the molten steel process using the RH vacuum degassing apparatus, the above operation has been performed at the time of adjusting the molten steel components after the degassing. However, in the past, molten steel with a large amount of Al or Si added as a deoxidizing element was treated in the molten steel, so oxygen was consumed for the oxidation of Al and Si even if the pressure in the vacuum chamber was increased and refluxed. Therefore, it is considered that it was not found that only dissolved oxygen obtained as an effect of the present invention increases.
溶存酸素濃度を増加させるには、（４）式に示すように、Ｐ０_latterを５ｋＰａよりも高く設定する必要がある。Ｐ０_latterが５ｋＰａよりも低い場合、溶存酸素濃度の上昇速度が遅く、生産性が低下してしまう。一方、真空槽内の圧力を高くして、Ｐ０_latterが１５ｋＰａを超える場合、浸漬管からの溶鋼吸い上げ高さが低位となり、環流操作に支障が現れ始めることから、Ｐ０_latterは１５ｋＰａ以下であることが必要である。 In order to increase the dissolved oxygen concentration, it is necessary to set P 0_latter higher than 5 kPa, as shown in the equation (4). When P 0_latter is lower than 5 kPa, the increasing rate of the dissolved oxygen concentration is slow, and the productivity is lowered. On the other hand, when the pressure in the vacuum chamber is increased and P 0_latter exceeds 15 kPa, the molten steel suction height from the dip tube becomes low, and troubles in the reflux operation begin to appear. Therefore, P 0_latter must be 15 kPa or less. is necessary.
溶存酸素濃度を増加させる効果を確実に得るには、後環流処理時の環流時間が３分間以上であることが必要である。環流時間が３分間より短い場合、溶存酸素濃度を増加させる効果は限定的である。一方、環流時間が１０分間を超えても、効果が既に飽和していることから、これ以上の処理時間増加は処理費用の増大を招くことになる。このため、溶存酸素濃度を増加させるための環流時間は３分間以上必要であり、１０分間以内であることが望ましい。 In order to reliably obtain the effect of increasing the dissolved oxygen concentration, it is necessary that the reflux time in the post-circulation treatment is 3 minutes or more. When the reflux time is shorter than 3 minutes, the effect of increasing the dissolved oxygen concentration is limited. On the other hand, even if the reflux time exceeds 10 minutes, since the effect is already saturated, further increase in the processing time will increase the processing cost. For this reason, the reflux time for increasing the dissolved oxygen concentration is required to be 3 minutes or longer, and is preferably within 10 minutes.
このとき、溶存酸素と酸化物を形成するようなＡｌ、Ｓｉ、Ｍｎ、Ｔｉ、Ｍｇ、Ｃａといった脱酸材を添加してしまうと、後還流処理によって増加させた溶存酸素と反応して粗大な酸化物を形成してしまう。このため、後還流処理中もしくは処理後は、炭素を除く脱酸材は添加してはならない。炭素を添加した場合、炭素は溶鋼中に溶解するか、ＣＯガスとして気相に排出され、粗大な酸化物は形成されないため、減圧処理中であっても添加してもよい。また、溶存酸素を効率的に増加させるため、真空槽内で送酸処理を行ってもよい。この時、送酸する時期は後環流処理開始直後が良く、送酸する時間は１分間以内であることが望ましい。 At this time, if a deoxidizing material such as Al, Si, Mn, Ti, Mg, and Ca that forms an oxide with dissolved oxygen is added, it reacts with the dissolved oxygen increased by the post-reflux treatment and is coarse. An oxide is formed. For this reason, deoxidizers other than carbon must not be added during or after the post-reflux treatment. When carbon is added, carbon dissolves in the molten steel or is discharged into the gas phase as CO gas, and a coarse oxide is not formed. Therefore, carbon may be added even during decompression. Moreover, in order to increase dissolved oxygen efficiently, you may perform an acid sending process within a vacuum chamber. At this time, it is preferable that the acid is fed immediately after the start of the post-circulation treatment, and the acid feeding time is preferably within 1 minute.
５．効果の確認方法
本発明の効果を確認するため、減圧清浄化処理前、減圧清浄化処理後、加えて、溶存酸素濃度を増加させる処理を行った場合、後環流処理後の溶存酸素濃度を測定した。
5. Method for confirming the effect In order to confirm the effect of the present invention, before the vacuum cleaning treatment, after the vacuum cleaning treatment, in addition, when the treatment for increasing the dissolved oxygen concentration is performed, the dissolved oxygen concentration after the post-perfusion treatment is measured. did.
また、減圧清浄化処理後および後環流処理後に採取した溶鋼のボンブサンプルの切断面を光学顕微鏡で観察し、測定視野面積２００ｍｍ２に存在する５．０μｍ以上２０μｍ以下の酸化物の個数を調査した。酸化物とは、ＥＤＳ付属の走査電子顕微鏡で測定した際、Ａｌ、Ｓｉ、Ｍｎ、Ｔｉ、Ｃａ、ＭｇおよびＯの占める割合が９０ａｔｍ％以上である介在物を指す。Ｓが１０ａｔｍ％以上含まれる介在物は、酸化物として計数しない。 Moreover, the cut surface of the bomb sample of the molten steel collected after the vacuum cleaning treatment and the post-circulation treatment was observed with an optical microscope, and the number of oxides of 5.0 μm or more and 20 μm or less existing in the measurement visual field area 200 mm 2 was investigated. . The oxide refers to an inclusion in which the proportion of Al, Si, Mn, Ti, Ca, Mg, and O is 90 atm% or more when measured with a scanning electron microscope attached to EDS. Inclusions containing 10 atm% or more of S are not counted as oxides.
表１に示す組成の鋼を溶製した。精錬段階において、高炉から出銑された溶銑を、溶銑予備処理で脱硫処理し、転炉型精錬容器（ＣＶ、Ｃｏｎｖｅｒｔｅｒ）にて脱Ｐおよび脱Ｃ処理した後、取鍋に受鋼した。出鋼の際、Ｓｉ、Ｍｎを含む合金元素を添加し、保温用のカバースラグを添加した。Ｈｅａｔ７，８，２１，２２の溶鋼量は８０ｔｏｎ規模であり、その他は２５０ｔｏｎ規模である。 Steels having the compositions shown in Table 1 were melted. In the refining stage, the hot metal discharged from the blast furnace was desulfurized by hot metal pretreatment, de-P and de-C treated in a converter-type refining vessel (CV, Converter), and then received in a ladle. When steeling, alloy elements including Si and Mn were added, and cover slag for heat insulation was added. The amount of molten steel of Heat 7, 8, 21, 22 is on the scale of 80 tons, and the others are on the scale of 250 tons.
取鍋内の溶鋼をＲＨ真空脱ガス装置にて、表２に示す条件で減圧清浄化処理を行った。Ｈｅａｔ１から６、Ｈｅａｔ１１から１５は、減圧清浄化処理後に、真空槽内圧力を高くした条件で後環流処理を行った。また、Ｈｅａｔ４，１６，１７では減圧清浄化処理末期に、Ｈｅａｔ４，５，１４，１５では後環流中に脱酸剤を添加した。この時、脱酸剤を添加してから環流時間を３分間以上確保した。さらに、Ｈｅａｔ１，３では後環流開始時に１分間以内で真空槽内で送酸処理を行った。 The molten steel in the ladle was subjected to a vacuum cleaning treatment under the conditions shown in Table 2 using an RH vacuum degasser. Heats 1 to 6 and Heats 11 to 15 were subjected to post-recirculation treatment under the condition that the pressure inside the vacuum chamber was increased after the vacuum cleaning treatment. Further, a deoxidizer was added at the end of the vacuum cleaning treatment for Heats 4, 16 and 17, and a deoxidizer was added during the rear reflux for Heats 4, 5, 14, and 15. At this time, after the deoxidizer was added, the reflux time was secured for 3 minutes or more. Further, in Heats 1 and 3, the acid sending treatment was performed in the vacuum chamber within 1 minute at the start of the rear reflux.
減圧清浄化処理前後、および、後環流処理後には酸素濃度プローブで溶鋼中酸素濃度を測定するとともに、溶鋼サンプルを採取し、迅速酸素濃度分析装置で全酸素濃度を得るとともに、化学分析に供して溶鋼成分を得た。さらに、減圧清浄化処理後に採取した溶鋼サンプルから検鏡用のミクロサンプルを切り出し、検鏡法にて５．０μｍ以上の酸化物個数を計数した。ＲＨ真空脱ガス装置における溶鋼温度は、Ｈｅａｔ７，８，２１，２２ではおよそ１５４０℃から１５５０℃で推移し、その他は１５５０℃から１５８０℃で推移したが、溶鋼昇熱処理直後は一時的に１６００℃を超える温度となった。ＲＨ真空脱ガス装置で処理した後は、連続鋳造法によって、スラブあるいはブルームといった半製品を得た。 Before and after the vacuum cleaning treatment and after the post-circulation treatment, the oxygen concentration in the molten steel is measured with an oxygen concentration probe, and a molten steel sample is taken, and the total oxygen concentration is obtained with a rapid oxygen concentration analyzer and used for chemical analysis. A molten steel component was obtained. Furthermore, a micro sample for speculum was cut out from the molten steel sample collected after the vacuum cleaning treatment, and the number of oxides of 5.0 μm or more was counted by a speculum method. The molten steel temperature in the RH vacuum degassing apparatus changed from about 1540 ° C. to 1550 ° C. in Heat 7, 8, 21 and 22, and the other changed from 1550 ° C. to 1580 ° C., but temporarily changed to 1600 ° C. immediately after the molten steel heat treatment. The temperature exceeded. After processing with the RH vacuum degassing apparatus, a semi-finished product such as slab or bloom was obtained by continuous casting.
減圧清浄化処理前後の本発明および比較鋼それぞれの酸素濃度および酸化物個数を表３に示す。また、図１にＣ、Ａｌ濃度および真空槽内圧力から求めた請求項１中のＡｌ濃度および（１）式が示す範囲をグラフで示す。図１のグラフの横軸は減圧清浄化処理前のＡｌ濃度、縦軸は（１）式によってＣ濃度とＰ０_formerから求まる値である。 Table 3 shows the oxygen concentration and the number of oxides of the present invention and the comparative steel before and after the vacuum cleaning treatment. FIG. 1 is a graph showing the Al concentration in claim 1 obtained from the C, Al concentration and the pressure in the vacuum chamber, and the range indicated by the expression (1). The horizontal axis of the graph in FIG. 1 is the Al concentration before the vacuum cleaning treatment, and the vertical axis is a value obtained from the C concentration and P 0_former by equation (1).
図１のグラフにおいて○印は減圧清浄化処理後の酸化物個数が１０個／２００ｍｍ２以下であったものであり、全て請求項１中のＡｌ濃度および（１）式が示す範囲内にある。図１のグラフにおいて×印で示すＡｌ濃度が０．００５％よりも高いＨｅａｔ１０，１１，１８，２１，２２では減圧清浄化処理後も酸化物個数が多く、減圧清浄化処理前Ａｌ濃度は０．００５０％以下であることが必要であることが分かる。また、同じく×印で示すＣ濃度とＰ０_formerから求まる値が減圧清浄化処理前Ａｌ濃度よりも低位であったＨｅａｔ９，１９では減圧清浄化処理後の酸化物個数が多く、Ｃ濃度とＰ０_formerから求まる値が減圧清浄化処理前Ａｌ濃度よりも高い条件で処理することが必要であることが分かる。
In the graph of FIG. 1, the ◯ marks indicate that the number of oxides after the vacuum cleaning treatment was 10/200 mm 2 or less, and all are within the range indicated by the Al concentration and the formula (1) in claim 1. . In the graph of FIG. 1, in
図１のグラフにおいて△印（Ｈｅａｔ１２，１３）のＡｌ、Ｃ、Ｐ０_formerは、請求項１中のＡｌ濃度および（１）式が示す範囲を満たすものの、環流時間が足りないため、減圧清浄化処理後の酸化物個数が多い。また、図１のグラフにおいて＊印（Ｈｅａｔ１６，１７）のＡｌ、Ｃ、Ｐ０_formerは請求項１中のＡｌ濃度および（１）式が示す範囲を満たすものの、減圧清浄化処理末期にに脱酸剤を添加したことによって酸化物個数が増加している。 In the graph of FIG. 1, Al, C, and P 0_former indicated by Δ (Heat12, 13) satisfy the Al concentration in claim 1 and the range indicated by the equation (1), but the reflux time is insufficient, so the pressure is reduced. Large number of oxides after treatment. In the graph of FIG. 1, Al, C, and P 0_former indicated by * (Heat 16, 17) satisfy the Al concentration in claim 1 and the range indicated by the formula (1), but are deoxidized at the end of the vacuum cleaning treatment. The number of oxides is increased by adding the agent.
さらに、図１のグラフにおいて＋印で示す減圧清浄化処理前のＳｉ濃度が本発明範囲を超える条件であったＨｅａｔ２０は、Ｓｉによって強脱酸されたことから脱炭脱酸反応が生じていないと考えられ、減圧清浄化処理後の酸化物個数が低減できていない。このため、減圧清浄化処理前Ｓｉ濃度は０．３％以下である必要がある。 Further, Heat 20 in which the Si concentration before the vacuum cleaning treatment indicated by + in the graph of FIG. 1 exceeded the range of the present invention was strongly deoxidized by Si, and thus no decarburization deoxidation reaction occurred. It is considered that the number of oxides after the vacuum cleaning treatment cannot be reduced. For this reason, the Si concentration before the vacuum cleaning treatment needs to be 0.3% or less.
表１に示したＨｅａｔ１から６およびＨｅａｔ１１から１５に対して、減圧清浄化処理後に溶存酸素濃度を増加させることを意図して後環流処理を行った。表４に後環流処理時の環流条件および処理後の酸素濃度をまとめて示す。 For the Heats 1 to 6 and Heats 11 to 15 shown in Table 1, post-circulation treatment was performed with the intention of increasing the dissolved oxygen concentration after the vacuum cleaning treatment. Table 4 summarizes the reflux conditions during post-circulation treatment and the oxygen concentration after treatment.
表４に示すように、真空槽内圧力を高くして環流することで、後環流処理後の溶存酸素濃度は、減圧清浄化処理後の溶存酸素よりも高くなっている。このため、真空槽内圧力を高くして後環流処理することで、溶存酸素濃度を高くできることが分かる。 As shown in Table 4, by circulating at a higher pressure in the vacuum chamber, the dissolved oxygen concentration after the post-circulation treatment is higher than the dissolved oxygen after the vacuum cleaning treatment. For this reason, it turns out that a dissolved oxygen concentration can be made high by raising the pressure in a vacuum chamber and carrying out a post-circulation process.
Claims (2)
Ａｌ＜０．０００８×（（１０１．３２５×Ｃ）／Ｐ０_former）1.5 ・・・（１）
Ａｌ：溶鋼中Ｓｏｌ．Ａｌ濃度（ｍａｓｓ％）
Ｃ：溶鋼中Ｃ濃度（ｍａｓｓ％）
Ｐ０_former：減圧清浄化処理時の真空槽内圧力（ｋＰａ） The amount of Sol. In a reflux degassing apparatus, a molten steel containing Al: 0.005% or less, Si: 0.005-0.3%, O (total oxygen concentration): 0.02% or less is used as a vacuum cleaning treatment. (1) A cleanliness, characterized in that the Al concentration, the C concentration and the vacuum chamber pressure satisfying the formula (1) are refluxed for 10 minutes or more, and no deoxidizer other than carbon is added during and after the refluxing treatment. High steel manufacturing method.
Al <0.0008 × ((101.325 × C) / P 0_former ) 1.5 (1)
Al: Sol. Al concentration (mass%)
C: C concentration in molten steel (mass%)
P 0_former : Pressure inside vacuum chamber (kPa) during vacuum cleaning process
５＜Ｐ０_latter＜１５・・・・・（４）
Ｐ０_latter：後環流処理時の真空槽内圧力（ｋＰａ） After the vacuum cleaning treatment, Sol. The pressure in the vacuum chamber P is within a range that satisfies the formula (4) for molten steel containing Al: 0.005% or less, Si: 0.005-0.3%, O (total oxygen concentration): 0.005% or less. The method for producing a steel material with high cleanliness according to claim 1, wherein a recirculation treatment is performed at 0_latter for 3 minutes or more, and a deoxidizer other than carbon is not added during and after the recirculation treatment.
5 <P 0_latter <15 (4)
P 0_latter : Vacuum chamber pressure (kPa) during post- circulation
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| JP2015161022A (en) * | 2014-02-28 | 2015-09-07 | 新日鐵住金株式会社 | Method for smelting highly clean steel |
| JP2015183259A (en) * | 2014-03-25 | 2015-10-22 | 新日鐵住金株式会社 | Method for melting high cleanliness steel |
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