TWI485257B - Method of producing steel - Google Patents
Method of producing steel Download PDFInfo
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- TWI485257B TWI485257B TW101126007A TW101126007A TWI485257B TW I485257 B TWI485257 B TW I485257B TW 101126007 A TW101126007 A TW 101126007A TW 101126007 A TW101126007 A TW 101126007A TW I485257 B TWI485257 B TW I485257B
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/06—Deoxidising, e.g. killing
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/10—Supplying or treating molten metal
- B22D11/108—Feeding additives, powders, or the like
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/10—Handling in a vacuum
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Mechanical Engineering (AREA)
- Treatment Of Steel In Its Molten State (AREA)
- Continuous Casting (AREA)
Description
本發明係關於氧化物系非金屬夾雜物較少的高潔淨度鋼之製造方法。The present invention relates to a method for producing high-purity steel having less oxide-based non-metallic inclusions.
Al全靜鋼(Al killed steel)係在從轉爐中出鋼時或出鋼後，添加作為脫氧劑的金屬Al，除去轉爐中由於氧化精煉(脫碳精煉)而上升的熔鋼中之氧後，利用連續鑄造機鑄造成作為軋延用素材的鑄片。藉由該金屬Al的添加，熔鋼中會生成Al2 O3 作為脫氧生成物，若該Al2 O3 無法從熔鋼中上浮/分離而殘留於鑄片中，則在鋼製品中會產生因Al2 O3 所引起的龜裂、表面瑕疵。Al killed steel is a metal Al added as a deoxidizing agent after tapping from a converter or after tapping, and removing oxygen in the molten steel which is raised by oxidative refining (decarburization refining) in the converter. A cast piece as a material for rolling is cast by a continuous casting machine. By the addition of the metal Al, Al 2 O 3 is formed as a deoxidation product in the molten steel, and if the Al 2 O 3 cannot be floated/separated from the molten steel and remains in the cast piece, it is generated in the steel product. Cracks and surface defects caused by Al 2 O 3 .
所以，在減少鋼中所殘留的Al2 O3 之目的下，自過去以來已採用在收容經出鋼之熔鋼的盛鋼桶內添加金屬Al、Al浮渣(Al dross)，將存在於熔鋼湯面上之熔渣的低級氧化物(easily-reductive oxide)(FeO、MnO)予以還原，降低熔渣中的低級氧化物之後，再施行Al脫氧的方法(例如參照專利文獻1)。又，所謂「Al浮渣」，係指將使用為飲料用罐、建築材料、汽車用鋁輪圈等的鋁金屬在待回收再生而施行再溶解的階段所生成之含有30~40質量%左右金屬Al的鋁之氧化物、氮化物的混合物。Therefore, in the purpose of reducing the amount of Al 2 O 3 remaining in the steel, it has been used in the past to add metal Al and Al dross to the ladle containing the molten steel of the tapped steel, which will exist in After reduction of the lower-reductive oxide (FeO, MnO) of the slag on the molten steel noodle, the lower oxide in the slag is lowered, and then Al deoxidation is performed (for example, refer to Patent Document 1). In addition, the term "Al scum" refers to a product containing 30 to 40% by mass of aluminum metal used for beverage cans, building materials, aluminum rims for automobiles, etc., which is re-dissolved during regeneration and regeneration. A mixture of aluminum oxide and nitride of metal Al.
再者，為降低脫氧生成物，亦提案有限制脫氧劑種類與添 加順序的技術。例如，專利文獻2提案有依照脫氧力由弱至強的順序添加脫氧劑的方法，具體而言，依照Mn→Si→Al的順序進行添加之方法。根據專利文獻2，藉由依照脫氧力由弱至強的順序添加脫氧劑，而進行脫氧生成物的凝聚，形成由複數化合物所構成的脫氧生成物，促進從熔鋼中的上浮/分離。然而，該手法會有形成大量MnO，導致熔渣中之MnO濃度上升的問題。MnO係屬於低級氧化物，會與隨後所添加之脫氧力較強的熔鋼中之Al進行反應，導致Al2 O3 會在熔鋼中持續形成，不易獲得潔淨度高的鋼。Further, in order to reduce the deoxidation product, a technique for limiting the type and addition order of the deoxidizer has also been proposed. For example, Patent Document 2 proposes a method of adding a deoxidizing agent in order from weak to strong in deoxidizing power, and specifically, a method of adding in the order of Mn→Si→Al. According to Patent Document 2, by adding a deoxidizing agent in order from weak to strong in deoxidizing power, aggregation of a deoxidizing product is carried out to form a deoxidizing product composed of a plurality of compounds, thereby promoting floating/separation from the molten steel. However, this method has a problem that a large amount of MnO is formed, resulting in an increase in the concentration of MnO in the slag. MnO is a lower-grade oxide, which reacts with Al in a molten steel which is subsequently added with a strong deoxidizing power, so that Al 2 O 3 is continuously formed in the molten steel, and it is difficult to obtain a steel having high cleanliness.
相對於此，專利文獻3提案有最初經由依殘留溶存氧的方式調整添加量而添加Al浮渣，接著再依照Mn、Si的順序添加，最後添加金屬Al而施行脫氧的方法。該脫氧方法雖可減少MnO的生成量，但針對在利用Al進行脫氧前添加Mn之方面而言，係與專利文獻2相同，會有無法完全抑制MnO生成的問題。On the other hand, Patent Document 3 proposes a method in which Al scum is added by adjusting the amount of addition in the form of residual dissolved oxygen, followed by addition in the order of Mn and Si, and finally metal Al is added to perform deoxidation. In the deoxidation method, the amount of MnO produced can be reduced. However, in the case where Mn is added before deoxidation by Al, as in Patent Document 2, there is a problem that MnO formation cannot be completely suppressed.
再者，亦提案有主要的脫氧劑並非使用金屬Al，而是使用Ti、Ca的技術(例如參照專利文獻4)，此係以含Ti鋼為對象的技術，Ti相較於Al而言係屬高價位，無法應用於普通的鋼種。Further, it has been proposed that a main deoxidizing agent is not a metal Al but a technique using Ti or Ca (for example, refer to Patent Document 4), which is a technique involving Ti steel, and Ti is higher than Al. It is of high price and cannot be applied to ordinary steel grades.
另一方面，作為用以使脫氧生成物無害化的技術，專利文獻5與專利文獻6提案有於熔鋼浴面上的熔渣中添加MgO源的技術。根據專利文獻5與專利文獻6，在添加MgO源 之後，若將熔渣與熔鋼進行攪拌，脫氧生成物Al2 O3 便會與MgO源進行反應而形成MgO-Al2 O3 尖晶石，MgO-Al2 O3 尖晶石係凝聚/合體性較小，能夠使脫氧生成物保持微細，從而可無害化。On the other hand, as a technique for detoxifying a deoxidation product, Patent Document 5 and Patent Document 6 propose a technique of adding a MgO source to molten slag on a molten steel bath surface. According to Patent Document 5 and Patent Document 6, after the MgO source is added, if the slag and the molten steel are stirred, the deoxidation product Al 2 O 3 reacts with the MgO source to form MgO-Al 2 O 3 spinel. The MgO-Al 2 O 3 spinel is small in agglomeration/combination property, and the deoxidation product can be kept fine and can be made harmless.
再者，作為在熔渣或熔鋼中添加MgO源的技術，專利文獻7提案有於RH真空脫氣裝置中開始進行精煉之後，立刻將MgO源添加至真空槽內的熔鋼中，並使盛鋼桶內的熔鋼與熔渣之間形成富MgO層，利用該富MgO層抑制熔鋼與熔渣間之反應的技術。又，專利文獻8揭示有在盛鋼桶內添加熔渣改質劑而對盛鋼桶內熔渣進行改質，然後在盛鋼桶內的熔渣中添加MgO源，使盛鋼桶內的熔渣固化，俾抑制盛鋼桶內熔渣從盛鋼桶流出至餵槽的技術。Further, as a technique for adding a MgO source to molten slag or molten steel, Patent Document 7 proposes to immediately add a MgO source to the molten steel in the vacuum tank after starting the refining in the RH vacuum degassing apparatus, and A MgO-rich layer is formed between the molten steel and the molten slag in the ladle, and the MgO-rich layer is used to suppress the reaction between the molten steel and the molten slag. Further, Patent Document 8 discloses that a slag modifier is added to a steel ladle to modify the slag in the ladle, and then a MgO source is added to the slag in the ladle to make the inside of the ladle The slag is solidified, and the technique of suppressing the slag flowing from the ladle to the feeding tank is suppressed.
[專利文獻1]日本專利特開平5-230516號公報[Patent Document 1] Japanese Patent Laid-Open No. Hei 5-230516
[專利文獻2]日本專利特開昭54-94422號公報[Patent Document 2] Japanese Patent Laid-Open No. 54-94422
[專利文獻3]日本專利特開2009-120930號公報[Patent Document 3] Japanese Patent Laid-Open Publication No. 2009-120930
[專利文獻4]日本專利特開2000-144330號公報[Patent Document 4] Japanese Patent Laid-Open Publication No. 2000-144330
[專利文獻5]日本專利特開2004-169147號公報[Patent Document 5] Japanese Patent Laid-Open Publication No. 2004-169147
[專利文獻6]日本專利特開2003-171714號公報[Patent Document 6] Japanese Patent Laid-Open Publication No. 2003-171714
[專利文獻7]日本專利特開平6-116623號公報[Patent Document 7] Japanese Patent Laid-Open No. Hei 6-161623
[專利文獻8]日本專利特開2008-240136號公報[Patent Document 8] Japanese Patent Laid-Open Publication No. 2008-240136
近年從生產性提升的觀點而言，連續鑄造機的鑄造速度已高速化，即便習知僅應用專利文獻1所提案的熔渣改質方法而獲得充分高潔淨性之鋼製品，仍會產生因氧化物系非金屬夾雜物(以下簡記為「夾雜物」)而造成的缺陷。特別係相當於多加熱連續鑄造(稱為「序列連續鑄造(sequentially continuous casting)」)的盛鋼桶更換時之鑄片，會出現因夾雜物引發的缺陷。In recent years, from the viewpoint of productivity improvement, the casting speed of the continuous casting machine has been increasing, and even if it is known that only the slag upgrading method proposed in Patent Document 1 is used to obtain a sufficiently high-cleanness steel product, there is still a cause. Defects caused by oxide-based non-metallic inclusions (hereinafter abbreviated as "inclusions"). In particular, the cast piece, which is equivalent to the multi-heated continuous casting (referred to as "sequentially continuous casting"), has a defect due to inclusions.
此現象係由於在鑄造速度呈高速化的操作中，盛鋼桶內的熔渣、及存在於該熔渣附近之熔鋼中的夾雜物(由脫氧生成物、與轉爐熔渣中的CaO、或作為造渣劑而添加至盛鋼桶中的生石灰中之CaO凝聚而形成)在熔鋼從盛鋼桶注入至餵槽的末期被捲入於盛鋼桶內所形成的渦流中並流出至餵槽的頻度提高，又，在餵槽中熔鋼滯留時間亦相對縮短，因而導致在未上浮分離之情況下便直接被注入至鑄模內的頻度提高所致。又，若從盛鋼桶朝餵槽的熔鋼注入量(每單位時間)變多，在盛鋼桶內的渦流產生時期便提早。即，從盛鋼桶內的殘留熔鋼量較多的時點便產生渦流。This phenomenon is due to the slag in the ladle and the inclusions in the molten steel existing in the vicinity of the slag during the operation of increasing the casting speed (from the deoxidation product, CaO in the converter slag, Or CaO coagulation added to the quicklime in the ladle as a slagging agent) is entangled in the vortex formed in the ladle at the end of the molten steel from the ladle to the feed tank and flows out to The frequency of the feeding tank is increased, and the residence time of the molten steel in the feeding tank is also relatively shortened, thereby causing an increase in the frequency of being directly injected into the mold without being floated and separated. Moreover, if the amount of molten steel injected from the ladle to the feed tank (per unit time) is increased, the period of vortex generation in the ladle is early. That is, eddy current is generated from the time when the amount of residual molten steel in the ladle is large.
為提升熔鋼的潔淨性，減少熔渣中的低級氧化物係屬有效，但專利文獻2與專利文獻3會生成MnO，如前述難謂充足。In order to improve the cleanliness of the molten steel, it is effective to reduce the lower oxides in the slag, but Patent Document 2 and Patent Document 3 generate MnO, which is difficult to say as described above.
再者，為使盛鋼桶內的熔渣不會被捲入渦流中，使盛鋼桶內熔渣固化係屬有效，雖然專利文獻5~8所提案之將MgO源添加至熔渣係屬有效，但若過剩添加，則熔渣雖會固化，但會損及熔渣的脫氧生成物吸收能力，反而會發生潔淨性惡化的情況。又，為使熔渣固化，必須使所添加MgO源與熔渣進行反應，引用文獻5~8中，MgO源係使用MgO灰渣(clinker)，需要將所添加的MgO灰渣與熔渣進行攪拌等處理。但是，在熔鋼未脫氧的情況，若如通常所施行般在熔鋼中吹入氣體而攪拌熔渣，為接近與熔鋼中氧濃度間之平衡關係，熔渣中的FeO、MnO等低級氧化物濃度上升，因而會有脫氧後的熔鋼因熔渣而被再氧化，導致潔淨度降低的問題。又，吹入熔鋼中的氣體之上浮區域係屬局部性，因而若氣體吹入速度不足，便無法均質地攪拌熔渣，亦會有殘留有低級氧化物的還原及熔渣固化不足之區域的問題。Furthermore, in order to prevent the slag in the ladle from being caught in the vortex, it is effective to solidify the slag in the ladle, although the addition of the MgO source to the slag is proposed in Patent Documents 5-8. It is effective, but if it is added excessively, the slag will solidify, but it will damage the absorption capacity of the slag deoxidation product, and the cleanliness will worsen. Further, in order to solidify the slag, it is necessary to react the added MgO source with the slag. In References 5 to 8, the MgO source uses MgO ash (clinker), and it is necessary to carry out the added MgO ash and slag. Stir and other treatments. However, in the case where the molten steel is not deoxidized, if the gas is blown into the molten steel and the slag is stirred as usual, the equilibrium relationship between the oxygen concentration in the molten steel is approached, and the FeO, MnO, etc. in the slag are low-grade. When the concentration of the oxide increases, there is a problem that the molten steel after deoxidation is reoxidized by the slag, resulting in a decrease in cleanliness. Moreover, the floating area of the gas blown into the molten steel is local, so if the gas blowing speed is insufficient, the slag cannot be uniformly stirred, and there is a region where the reduction of the lower oxide remains and the slag solidification remains. The problem.
本發明係有鑒於此種實情而完成，其目的係在於提供：即便未施行攪拌等，仍可使盛鋼桶內熔渣充分固化，俾不致被捲入從盛鋼桶注入至餵槽末期所形成之渦流中，且熔鋼潔淨性相較於習知技術而言更加提升，即便在高速鑄造下仍可獲得夾雜物較少之潔淨性優異的鑄片的高潔淨度鋼之製造方法。The present invention has been made in view of such a fact, and the object thereof is to provide that the slag in the ladle can be sufficiently solidified even if stirring or the like is not performed, and is not involved in being injected from the ladle to the end of the feeding tank. In the eddy current formed, the cleanliness of the molten steel is improved as compared with the prior art, and a high-purity steel manufacturing method of a cast piece excellent in cleanness with less inclusions can be obtained even under high-speed casting.
為解決上述問題，本發明主旨係如下。In order to solve the above problems, the gist of the present invention is as follows.
[1]一種鋼之製造方法，係包括有：從轉爐中將對熔鐵施行脫碳精煉而獲得的熔鋼，依未脫氧狀態出鋼至盛鋼桶中的步驟；出鋼後，對存在於盛鋼桶內的熔鋼上之熔渣添加金屬Al或Al浮渣之後，添加MgO源，而將熔渣中的低級氧化物予以還原，並且將熔渣中MgO濃度調節為6~15質量%的步驟；其次，在真空脫氣裝置中，使熔鋼中的碳與熔鋼中的溶存氧在減壓下進行反應，而將溶存氧濃度降低至0.050質量%以下，熔鋼中的溶存氧濃度成為0.050質量%以下之後，於減壓下的熔鋼中添加金屬Al而對熔鋼施行脫氧的步驟；然後，將熔鋼利用連續鑄造機鑄造成鋼胚鑄片的步驟，前述MgO源係含有氫氧化物與碳氧化物，將該MgO源加熱至1000℃而經由熱分解生成的氣體係每1kg前述MgO源為5mol以上，從轉爐中出鋼以後，直到利用真空脫氣裝置將金屬Al添加至熔鋼中為止，均未實施Mn的添加，當必須調整熔鋼的Mn濃度時，係在利用金屬Al對熔鋼施行脫氧後，於減壓下的熔鋼中添加含Mn之金屬而進行Mn濃度調整。[1] A method for producing steel, comprising: a step of extruding a molten steel obtained by decarburization and refining from a converter, and discharging the steel into a steel ladle according to an undeoxidized state; After adding metal Al or Al scum to the slag on the molten steel in the ladle, the MgO source is added, and the lower oxide in the slag is reduced, and the MgO concentration in the slag is adjusted to 6-15 mass. % step; secondly, in the vacuum degassing device, the carbon in the molten steel is reacted with the dissolved oxygen in the molten steel under reduced pressure, and the dissolved oxygen concentration is lowered to 0.050% by mass or less, and the dissolved in the molten steel After the oxygen concentration is 0.050 mass% or less, a step of deoxidizing the molten steel by adding metal Al to the molten steel under reduced pressure; and then casting the molten steel into a steel slab by a continuous casting machine, the aforementioned MgO source Containing hydroxide and carbon oxide, the gas system generated by thermal decomposition by heating the MgO source to 1000 ° C is 5 mol or more per 1 kg of the aforementioned MgO source, after tapping from the converter, until the metal is removed by using a vacuum degassing device No addition of Mn was added until Al was added to the molten steel. After, the Mn concentration must be adjusted when the molten steel, the use of metal based on Al deoxidation purposes of molten steel, the Mn-containing additive metal in the molten steel is carried out under reduced pressure in adjusting the Mn concentration.
[2]如上述[1]所記載的鋼之製造方法，其中，在使熔鋼中的碳與熔鋼中的溶存氧在減壓下進行反應之階段的初期，於熔鋼中添加碳材。[2] The method for producing steel according to the above [1], wherein the carbon material is added to the molten steel at the initial stage of the reaction between the carbon in the molten steel and the dissolved oxygen in the molten steel under reduced pressure. .
[3]如上述[1]或上述[2]所記載的鋼之製造方法，其中，連續鑄造機之穩定鑄造區域中之每股(strand)的熔鋼鑄造量係 4.5噸/分鐘以上。[3] The method for producing steel according to the above [1], wherein the strand casting amount in the stable casting region of the continuous casting machine is 4.5 tons / minute or more.
[4]如上述[1]至上述[3]中任一項所記載的鋼之製造方法，其中，將從轉爐中出鋼時之熔鋼中的溶存氧濃度控制為0.075質量%以下。[4] The method for producing steel according to any one of the above [1], wherein the dissolved oxygen concentration in the molten steel when the steel is tapped from the converter is controlled to be 0.075 mass% or less.
根據本發明，對存在於從轉爐出鋼的熔鋼浴面上之熔渣添加金屬Al或Al浮渣之後，將含有氫氧化物與碳氧化物的MgO源添加至盛鋼桶內的熔渣中，而將熔渣中的鐵氧化物及錳氧化物等低級氧化物予以還原，並且使熔渣的熔點上升，至少使熔渣的其中一部分固化，因而使盛鋼桶內的熔渣之低級氧化物含量降低，且，藉由含有氫氧化物與碳氧化物的MgO源的添加導致之熔渣熔點上升所伴隨的固化，而減少從盛鋼桶朝餵槽的熔渣流出量。又，利用由添加至熔渣之含有氫氧化物與碳氧化物的MgO源經由熱分解反應所生成的H2 O氣體及CO2 氣體，使熔渣被攪拌，因而即便未施行強制性攪拌，仍可實現效率良好地進行先前投入的金屬Al或Al浮渣與熔渣間之反應，且亦可促進MgO源中的MgO於熔渣中的分散及溶解。此時，H2 O氣體係在被加熱至400℃左右的較低溫度階段產生，CO2 氣體係在被加熱至700℃左右的較高溫度階段產生，因而利用從投入初期開始即持續產生的氣體，便可有效率地攪拌熔渣。又，使用塊狀MgO源的情況，特別係所投入的MgO源會輕易地侵入至熔渣層中 並分散。藉由該等作用，即便在投入物分佈有出現若干不均的情況，仍可進行安定的熔渣組成控制。According to the present invention, after adding metal Al or Al scum to the slag present on the molten steel bath surface of the tapping of the converter, the MgO source containing the hydroxide and the carbon oxide is added to the slag in the ladle Medium, and lowering the lower oxide such as iron oxide and manganese oxide in the slag, and raising the melting point of the slag to at least partially cure the slag, thereby lowering the slag in the ladle The oxide content is lowered, and the slag outflow from the ladle to the feed tank is reduced by the solidification of the melting point of the slag caused by the addition of the MgO source containing the hydroxide and the carbon oxide. Further, the slag is stirred by the H 2 O gas and the CO 2 gas generated by the thermal decomposition reaction of the MgO source containing the hydroxide and the carbon oxide added to the slag, so that even if the forced stirring is not performed, It is still possible to efficiently carry out the reaction between the previously charged metal Al or Al scum and the slag, and also to promote the dispersion and dissolution of MgO in the slag in the MgO source. At this time, the H 2 O gas system is generated at a relatively low temperature stage heated to about 400 ° C, and the CO 2 gas system is generated at a relatively high temperature stage heated to about 700 ° C, and thus is continuously generated from the initial stage of the input. The gas can efficiently stir the slag. Further, in the case of using a bulk MgO source, in particular, the MgO source to be introduced easily intrudes into the slag layer and is dispersed. By these effects, stable slag composition control can be performed even when there is some unevenness in the distribution of the input material.
再者，真空脫氣裝置係使熔鋼中的碳與溶存氧在減壓下進行反應，而使溶存氧濃度降低至0.050質量%以下，然後，添加金屬Al而對熔鋼施行脫氧，因而可抑制脫氧生成物的生成量，再者，未將Mn添加至未脫氧熔鋼中，當必須調整熔鋼的Mn濃度時，係在利用金屬Al對熔鋼施行脫氧後，將含Mn之金屬添加至熔鋼中而進行Mn濃度調整，因而Mn添加時的溶存氧濃度充分低，不會產生因Mn添加而造成的MnO生成，俾可防止熔渣的MnO濃度上升。Further, the vacuum degassing device causes the carbon in the molten steel to react with the dissolved oxygen under reduced pressure to lower the dissolved oxygen concentration to 0.050% by mass or less, and then adds the metal Al to deoxidize the molten steel, thereby The generation amount of the deoxidation product is suppressed, and further, Mn is not added to the undeoxidized molten steel. When the Mn concentration of the molten steel must be adjusted, the metal containing Mn is added after the molten steel is deoxidized by the metal Al. Since the Mn concentration is adjusted to the molten steel, the dissolved oxygen concentration at the time of Mn addition is sufficiently low, and MnO generation due to the addition of Mn does not occur, and the MnO concentration of the slag can be prevented from increasing.
即，本發明係協同組合基於減少熔渣中的低級氧化物而達成的潔淨性提升效果、基於降低熔渣從盛鋼桶的流出量而達成的潔淨性提升效果、以及基於減少脫氧生成物之生成量而達成的潔淨性提升效果，而可製造夾雜物極少的高潔淨度鋼。That is, the present invention synergistically combines the cleansing effect achieved by reducing the lower oxide in the slag, the cleansing effect by reducing the outflow of the slag from the ladle, and the reduction of the deoxidation product. A cleansing effect achieved by the amount of production, and a high-purity steel with few inclusions can be produced.
以下，針對本發明進行具體說明，惟並不僅侷限於此。Hereinafter, the present invention will be specifically described, but it is not limited thereto.
將熔鐵裝入轉爐中，從上吹吹管或底吹風口將氧氣供應至熔鐵而對熔鐵施行脫碳精煉，將熔鋼進行熔製。該轉爐脫碳精煉中，為將爐內所生成的熔渣鹼度(質量%CaO/質量%SiO2 )調整於3~5之範圍內，係添加生石灰，且為防止轉爐爐體的耐火物遭熔損，係視需要添加白雲石。又，亦可進一步將錳 礦石添加至爐內作為熔鋼成分調整用Mn源。簡言之，只要採行通常所施行的轉爐脫碳精煉手法對熔鐵施行脫碳精煉即可。The molten iron is charged into the converter, oxygen is supplied to the molten iron from the upper blow pipe or the bottom blow port, and the molten iron is subjected to decarburization refining to melt the molten steel. In the converter decarburization refining, in order to adjust the slag basicity (mass% CaO/mass% SiO 2 ) generated in the furnace to a range of 3 to 5, quicklime is added, and refractory for preventing the converter furnace body is added. Melted, add dolomite as needed. Further, manganese ore may be further added to the furnace as a source of Mn for adjusting the composition of the molten steel. In short, as long as the decarburization refining method commonly used in the converter is carried out, the molten iron can be decarburized and refined.
但，本發明係以製造夾雜物較少的潔淨鋼為目的，由於脫氧生成物的生成量越少則越有利於潔淨化，因而較佳係將脫碳精煉結束時的熔鋼中之溶存氧濃度控制為0.075質量%以下。此處，所謂「溶存氧」，並非指依氧化物形態懸浮於熔鋼中的氧，而是指溶解於熔鋼中而存在的氧。However, the present invention is aimed at producing clean steel having less inclusions, and the smaller the amount of deoxidation product produced, the more advantageous it is for cleaning, and therefore it is preferable to dissolve oxygen in the molten steel at the end of decarburization refining. The concentration is controlled to be 0.075 mass% or less. Here, the term "dissolved oxygen" does not mean oxygen suspended in a molten steel in the form of an oxide, but refers to oxygen which is dissolved in a molten steel.
脫碳精煉結束時的溶存氧濃度係與熔鋼中的碳濃度成反比，因而只要在碳濃度為0.035質量%以上、較佳係0.040質量%以上的狀態下結束脫碳精煉，便可將溶存氧濃度控制為0.075質量%以下。另一方面，本發明係以低碳鋼(碳濃度：0.02~0.07質量%左右)及極低碳鋼(碳濃度：0.0030質量%以下)為對象，若脫碳精煉結束時的熔鋼中碳濃度超過0.10質量%，則在下一步驟的真空脫氣裝置中，於減壓下進行的脫碳精煉會延長，導致生產性降低，因而脫碳精煉結束時的熔鋼中碳濃度較佳係設為0.10質量%以下。The dissolved oxygen concentration at the end of the decarburization refining is inversely proportional to the carbon concentration in the molten steel. Therefore, if the carbon concentration is 0.035 mass% or more, preferably 0.040 mass% or more, the decarburization refining is completed, and the solution can be dissolved. The oxygen concentration is controlled to be 0.075 mass% or less. On the other hand, the present invention is directed to low carbon steel (carbon concentration: about 0.02 to 0.07 mass%) and extremely low carbon steel (carbon concentration: 0.0030 mass% or less), and carbon in the molten steel at the end of decarburization refining. When the concentration exceeds 0.10% by mass, in the vacuum degassing apparatus of the next step, the decarburization refining under reduced pressure is prolonged, resulting in a decrease in productivity, and thus the carbon concentration in the molten steel at the end of decarburization refining is preferably set. It is 0.10% by mass or less.
在Si、Al、Ti、Ca等任一脫氧劑均未添加至盛鋼桶內的情況下，將所獲得之熔鋼依未脫氧狀態從轉爐出鋼至盛鋼桶中。從轉爐出鋼至盛鋼桶中的末期，即轉爐內的熔鋼量減少之時點，會在爐內的熔鋼中形成渦流，導致轉爐內的熔渣被捲入於渦流中，並隨熔鋼一起流出至盛鋼桶內，滯留於盛鋼 桶內的熔鋼上。如前述，在出鋼時不可添加脫氧劑，但可添加生石灰(CaO純份95質量%左右)。利用該生石灰的添加，流出至盛鋼桶中的熔渣會被稀釋，便可降低熔渣中的鐵氧化物及錳氧化物等低級氧化物之濃度。In the case where any deoxidizer such as Si, Al, Ti, Ca, etc. is not added to the ladle, the obtained molten steel is tapped from the converter into the ladle according to the undeoxidized state. From the tapping of the converter to the end of the ladle, that is, when the amount of molten steel in the converter is reduced, eddy currents are formed in the molten steel in the furnace, causing the slag in the converter to be entangled in the vortex and with melting The steel flows out together into the steel drum and stays in Shenggang On the molten steel inside the barrel. As described above, the deoxidizing agent may not be added during tapping, but quicklime (about 95% by mass of CaO pure fraction) may be added. With the addition of the quicklime, the slag flowing out into the ladle can be diluted to lower the concentration of lower oxides such as iron oxides and manganese oxides in the slag.
在該盛鋼桶內的熔渣中，首先添加用以將熔渣中的鐵氧化物及錳氧化物等低級氧化物予以還原的金屬Al或Al浮渣。金屬Al或Al浮渣的添加量係確保能利用Al將熔渣中的鐵氧化物及錳氧化物全部還原、或將其中一部分還原至無害化程度的充分量。具體而言，從轉爐吹煉結束時的熔鋼中溶存氧量或出鋼後的熔鋼中碳濃度，推估熔渣中的鐵氧化物及錳氧化物之量，再決定金屬Al或Al浮渣的添加量。一般而言，在熔鋼中溶存氧量較少(出鋼後的熔鋼中碳濃度較高)的情況，熔渣中的低級氧化物之量會有變少的傾向，另一方面，在熔鋼中溶存氧量較多(出鋼後的熔鋼中碳濃度較低)的情況，熔渣中的低級氧化物之量會有變多的傾向。但，熔渣中的低級氧化物濃度會受操作形態的影響而變化，因而較佳係藉由定期執行盛鋼桶內的熔渣分析而確保精度。In the slag in the ladle, first, a metal Al or Al scum for reducing a lower oxide such as iron oxide or manganese oxide in the slag is added. The addition amount of the metal Al or Al scum ensures a sufficient amount to reduce all of the iron oxide and the manganese oxide in the slag by using Al or to reduce a part thereof to a degree of detoxification. Specifically, the amount of dissolved iron in the molten steel at the end of the converter blowing or the concentration of carbon in the molten steel after tapping is used to estimate the amount of iron oxide and manganese oxide in the slag, and then the metal Al or Al is determined. The amount of scum added. In general, when the amount of dissolved oxygen in the molten steel is small (the carbon concentration in the molten steel after tapping is high), the amount of lower oxides in the slag tends to decrease, and on the other hand, When the amount of dissolved oxygen in the molten steel is large (the carbon concentration in the molten steel after tapping is low), the amount of the lower oxide in the slag tends to increase. However, the concentration of the lower oxide in the slag is affected by the operation mode, and therefore it is preferable to ensure the accuracy by periodically performing slag analysis in the ladle.
若已添加金屬Al或Al浮渣，便立刻將含有氫氧化物與碳氧化物的MgO源添加至盛鋼桶內的熔渣中。藉由該含有氫氧化物與碳氧化物的MgO源之添加，而使熔渣的MgO濃度提升至6~15質量%之範圍。若熔渣的MgO濃度未滿6質量%，則盛鋼桶內熔渣的固化不足，無法抑制熔鋼中的夾雜 物缺陷之增加。又，若熔渣的MgO濃度超過15質量%，則熔渣雖會固化，但會損及熔渣的脫氧生成物吸收能力，反而會導致潔淨性惡化。此處所示之「熔渣的MgO濃度」係指使所添加MgO源中的MgO均勻溶解於盛鋼桶內的熔渣中所計算而得的值，即便部分性存有未溶解的MgO、或局部性MgO濃度超過此值以上，均設為涵蓋在此範圍內。含有氫氧化物與碳氧化物的MgO源之具體添加量指標，在經驗上係確認依MgO純份計為0.15~0.4kg/熔鋼-噸左右，但由於會依照熔渣對盛鋼桶的流出量及生石灰對盛鋼桶內的添加量而有所改變，因而必須配合該等的量而增減。If metal Al or Al scum has been added, the MgO source containing hydroxide and carbon oxide is immediately added to the slag in the ladle. The MgO concentration of the slag is increased to a range of 6 to 15% by mass by the addition of the MgO source containing the hydroxide and the carbon oxide. If the MgO concentration of the slag is less than 6% by mass, the solidification of the slag in the ladle is insufficient, and the inclusion in the molten steel cannot be suppressed. The increase in physical defects. In addition, when the MgO concentration of the slag exceeds 15% by mass, the slag is solidified, but the absorbing property of the slag is deteriorated, and the cleanliness is deteriorated. The "MgO concentration of the slag" as used herein refers to a value calculated by uniformly dissolving MgO in the added MgO source in the slag in the ladle, even if partially undissolved MgO, or If the localized MgO concentration exceeds this value, it is set to be included in this range. The specific addition amount index of the MgO source containing hydroxide and carbon oxide is empirically confirmed to be about 0.15 to 0.4 kg/melt-ton depending on the pure fraction of MgO, but since it will be in accordance with the slag to the ladle The amount of outflow and quicklime vary with the amount added in the ladle and must be increased or decreased in conjunction with these amounts.
經添加金屬Al或Al浮渣後的盛鋼桶內之熔渣組成，係CaO-Al2 O3 系或CaO-Al2 O3 -SiO2 系，因從MgO源所夾帶入的MgO，會導致熔渣的熔點上升。由於熔渣的熔點上升，熔渣便開始固化，導致熔融狀態的區域減少。又，含有氫氧化物與碳氧化物的MgO源在經由熱分解產生氣體時會被奪取大量的熱，因而藉由MgO源產生的冷卻效果，熔渣的平均溫度相較於使用MgO灰渣的情況而言更快降低，受此影響而使盛鋼桶內熔渣進行固化。The composition of the slag in the ladle after adding the metal Al or Al scum is CaO-Al 2 O 3 or CaO-Al 2 O 3 -SiO 2 , due to the MgO entrained from the MgO source. This causes the melting point of the slag to rise. As the melting point of the slag rises, the slag begins to solidify, resulting in a decrease in the molten state. Further, the MgO source containing the hydroxide and the carbon oxide is subjected to a large amount of heat when the gas is generated by thermal decomposition, so that the average temperature of the slag is higher than that of the MgO ash by the cooling effect by the MgO source. In the case of a faster reduction, the slag in the ladle is solidified by this effect.
再者，投入至盛鋼桶內之含有氫氧化物與碳氧化物的MgO源，會從熔渣接收熱並生成H2 O氣體與CO2 氣體。利用經由該分解反應所生成的H2 O氣體及CO2 氣體，盛鋼桶內的熔渣受到攪拌，因而即便熔鋼或熔渣未施行強制性攪 拌，仍可實現效率良好地進行先前投入的金屬Al或Al浮渣與熔渣間的反應。為能有效地攪拌熔渣，較佳係使用經由加熱至1000℃的熱分解所生成之氣體係每1kg前述MgO源為5mol以上的MgO源。此處，1000℃的試驗溫度係參照並採用一般灼燒減量(ignition loss、ig.loss)測定的條件。前述經由熱分解所生成的氣體並無必要特別設定上限，在必須抑制熔渣泡沫化(foaming)的情況等，亦可設定適當上限(例如，每1kg前述MgO源為40mol以下等)。Further, the MgO source containing hydroxide and carbon oxide charged into the ladle receives heat from the slag and generates H 2 O gas and CO 2 gas. By using the H 2 O gas and the CO 2 gas generated by the decomposition reaction, the slag in the ladle is stirred, so that even if the molten steel or the slag is not subjected to forced stirring, the previously input can be efficiently performed. The reaction between metal Al or Al scum and slag. In order to effectively stir the slag, it is preferred to use a gas system formed by thermal decomposition heated to 1000 ° C for 5 kg or more of MgO source per kg of the aforementioned MgO source. Here, the test temperature of 1000 ° C is referred to and measured by a general ignition loss (ig. loss). The gas generated by the thermal decomposition does not need to have an upper limit, and an appropriate upper limit (for example, 40 mol or less per 1 kg of the MgO source) may be set in the case where it is necessary to suppress slag foaming.
再者，較佳係使用氫氧化物經熱分解而生成的H2 O係每1kg MgO源為3mol以上，且所含有的碳氧化物經熱分解而生成的CO2 係每1kg MgO源為2mol以上的MgO源。此時，H2 O氣體係在被加熱至400℃左右的較低溫度階段產生，CO2 氣體係在被加熱至700℃左右的較高溫度階段產生，因而利用從投入初期開始即持續產生的氣體，便可有效率地攪拌熔渣。在使用不含氫氧化物的MgO源的情況，由於在投入至熔渣上之後直到氣體產生呈活性化為止較耗時，因而會導致熔渣依MgO源上浮於熔渣上的狀態凝固，會有無法有效地進行攪拌的情況。Further, it is preferable that the H 2 O system formed by thermal decomposition of the hydroxide is 3 mol or more per 1 kg of the MgO source, and the CO 2 produced by thermal decomposition of the contained carbon oxide is 2 mol per 1 kg of the MgO source. The above MgO source. At this time, the H 2 O gas system is generated at a relatively low temperature stage heated to about 400 ° C, and the CO 2 gas system is generated at a relatively high temperature stage heated to about 700 ° C, and thus is continuously generated from the initial stage of the input. The gas can efficiently stir the slag. In the case of using a MgO source containing no hydroxide, since it is time consuming until the gas generation is activated after being introduced onto the slag, the slag is solidified in a state in which the MgO source floats on the slag. There is a case where stirring cannot be performed efficiently.
再者，使用塊狀MgO源的情況，特別係所投入的MgO源容易侵入至熔渣層中並分散。Further, in the case of using a bulk MgO source, in particular, the MgO source to be charged is easily intruded into the slag layer and dispersed.
藉由該等作用，即便在投入物的分佈出現若干不均的情況，仍可進行安定的熔渣組成控制。By these effects, even if there is a slight unevenness in the distribution of the input material, stable slag composition control can be performed.
塊狀的尺寸係在能迅速進行侵入至熔渣層的前提下，其餘並無限制，較佳係中間(median)粒徑為2cm左右以上。從促進MgO源溶解的觀點而言，上限較佳係5cm左右。The size of the block is not limited as long as it can rapidly invade the slag layer, and it is preferable that the median particle diameter is about 2 cm or more. From the viewpoint of promoting dissolution of the MgO source, the upper limit is preferably about 5 cm.
所使用的MgO源較佳係規定為經1000℃的灼燒減量後，MgO源中的MgO濃度為50質量%以上的MgO源。其理由係CaO、Al2 O3 、SiO2 等含量較多的物質對熔點提升的效果較少，為提高熔點必須增多MgO源的添加量。The MgO source to be used is preferably a MgO source having a MgO concentration of 50% by mass or more in the MgO source after a reduction in ignition at 1000 °C. The reason is that substances having a large content such as CaO, Al 2 O 3 , and SiO 2 have little effect on the melting point, and it is necessary to increase the amount of the MgO source to increase the melting point.
作為含有氫氧化物與碳氧化物的塊狀MgO源，係可使用塊狀組成物(composition of matter)，例如使用在鎂鹽的水溶液中添加碳酸鈉而析出的碳酸鎂與氫氧化鎂之複合化合物的粉體，經成形為壓塊(briquet)狀者等。若採用依此將鎂化合物的微小初級粒子使用水泥等黏合劑成形為塊狀者，相較於使用氧化鎂灰渣之類較大粒徑燒結粒子的情況，由於比表面積較大、初級粒子間的結合力亦會在溫度上升過程中消失，因而促進於熔渣中的溶解及分散，俾可更均質地進行熔渣的固化。又，MgO源中所含的氫氧化物或碳氧化物未必一定是鎂化合物，只要是從Mg、Ca、Al中選擇之1種以上氫氧化物或碳氧化物，同樣地會產生氣體並可利用於攪拌熔渣，因而亦可將該等與氧化鎂粉末進行混合並結塊化(agglomeration)而使用為MgO源。As a bulk MgO source containing a hydroxide and a carbon oxide, a composition of matter can be used, for example, a composite of magnesium carbonate and magnesium hydroxide precipitated by adding sodium carbonate to an aqueous solution of a magnesium salt. The powder of the compound is formed into a briquet shape or the like. If the fine primary particles of the magnesium compound are formed into a block using a binder such as cement, the larger specific surface area and the primary particles are used as compared with the case of using a larger particle size sintered particle such as magnesia ash. The bonding force also disappears during the temperature rise, thereby promoting dissolution and dispersion in the slag, and the slag can be solidified more homogeneously. Further, the hydroxide or carbon oxide contained in the MgO source is not necessarily a magnesium compound, and as long as it is one or more kinds of hydroxides or carbon oxides selected from the group consisting of Mg, Ca, and Al, gas is generated in the same manner. By stirring the slag, it is also possible to mix and agglomerate the magnesium oxide powder and use it as a source of MgO.
若將含有氫氧化物與碳氧化物的MgO源添加至盛鋼桶內的熔渣中，便將收容有熔鋼的盛鋼桶搬送至RH真空脫氣裝 置、DH真空脫氣裝置等真空脫氣裝置中。If a MgO source containing hydroxide and carbon oxide is added to the slag in the ladle, the ladle containing the molten steel is transferred to the RH vacuum degassing device. In a vacuum degassing device such as a DH vacuum degassing device.
真空脫氣裝置中，至少熔鋼的其中一部分係暴露於減壓下的環境。本發明中，熔鋼係呈未脫氧狀態，藉由將熔鋼暴露於減壓下的環境，由於減壓下的環境之CO氣體分壓較低，因而熔鋼中的碳與熔鋼中的溶存氧會產生反應，引發生成CO氣體的反應(C+O→CO)。藉由該反應(稱為「未靜反應(rimming reaction)」)，熔鋼中的碳濃度及溶存氧濃度會減少，熔鋼便呈被脫碳及脫氧的狀態。本發明中，未靜反應係持續至熔鋼中的溶存氧濃度成為0.050質量%以下為止、較佳係持續至成為0.030質量%以下為止。碳與氧係與各自原子量呈比例地減少。In the vacuum degasser, at least a portion of the molten steel is exposed to an environment under reduced pressure. In the present invention, the molten steel is in an undeoxidized state, and by exposing the molten steel to an environment under reduced pressure, the carbon partial pressure in the molten steel is lower due to the lower partial pressure of CO gas in the environment under reduced pressure. Dissolved oxygen generates a reaction that initiates a reaction to generate CO gas (C+O→CO). By this reaction (referred to as "rimming reaction"), the carbon concentration and the dissolved oxygen concentration in the molten steel are reduced, and the molten steel is in a state of being decarburized and deoxidized. In the present invention, the unreacted reaction system continues until the dissolved oxygen concentration in the molten steel is 0.050% by mass or less, and preferably continues to be 0.030% by mass or less. The carbon and oxygen systems decrease in proportion to the respective atomic weights.
若因未靜反應而使熔鋼中的碳濃度降低，便不易引發未靜反應，因而較佳係在引發未靜反應的階段初期時點，便在減壓下的熔鋼中添加碳材(焦炭、石墨等)，使熔鋼中的碳濃度上升，俾促進未靜反應。但，若碳材添加量過多，較高於目標熔鋼成分的碳濃度，便需要進行伴隨對熔鋼供給氧源的脫碳處理，導致成為使熔鋼中的夾雜物增加之原因，因而在未靜反應的時點所添加的碳材添加量必須設定於未靜反應後的熔鋼中碳濃度不會超過目標熔鋼成分的碳濃度之範圍內。If the carbon concentration in the molten steel is lowered due to the unreacted reaction, it is less likely to cause an unstatic reaction. Therefore, it is preferable to add a carbon material (coke) to the molten steel under reduced pressure at the initial stage of the stage in which the static reaction is not initiated. , graphite, etc.), so that the carbon concentration in the molten steel rises, and promotes the unstatic reaction. However, if the amount of carbon material added is too high and the carbon concentration of the target molten steel component is higher than that of the target molten steel component, it is necessary to carry out decarburization treatment with the molten steel supply oxygen source, which causes an increase in inclusions in the molten steel. The amount of carbon material added at the time of no static reaction must be set within a range in which the carbon concentration in the molten steel after the static reaction does not exceed the carbon concentration of the target molten steel component.
依此持續進行未靜反應，在熔鋼中的溶存氧濃度為0.050質量%以下、且熔鋼中的碳濃度成為目標鋼種成分範圍內的任意時點，便於減壓下的熔鋼中添加金屬Al而對熔鋼施行 脫氧。溶存氧濃度係例如可利用以氧濃淡電池作為感測器的測定裝置進行測定。藉由金屬Al的添加，引發所添加Al與溶存氧的反應(2Al+3O→Al2 O3 )，使溶存氧一口氣減少至數ppm左右的濃度，停止未靜反應。在添加金屬Al的時點的溶存氧濃度為0.050質量%以下之前提下，其餘則無需特別限定，但由於溶存氧濃度越低，則脫氧生成物的生成量變得越少，因而較佳係盡可能降低溶存氧濃度。金屬Al的添加量係設定成在去除溶存氧之後，熔鋼中溶解有0.01~0.07質量%的Al。According to this, the static reaction is continued, the dissolved oxygen concentration in the molten steel is 0.050% by mass or less, and the carbon concentration in the molten steel becomes any point within the range of the target steel species, and the metal Al is easily added to the molten steel under reduced pressure. The molten steel is deoxidized. The dissolved oxygen concentration can be measured, for example, by a measuring device using an oxygen-dense battery as a sensor. By the addition of the metal Al, the reaction between the added Al and the dissolved oxygen (2Al+3O→Al 2 O 3 ) is initiated, and the dissolved oxygen gas is reduced to a concentration of about several ppm to stop the unstatic reaction. When the dissolved oxygen concentration at the time of adding the metal Al is 0.050% by mass or less, the rest is not particularly limited, but the lower the dissolved oxygen concentration, the smaller the amount of the deoxidized product is formed, so it is preferable to Reduce the dissolved oxygen concentration. The amount of addition of the metal Al is set so that 0.01 to 0.07 mass% of Al is dissolved in the molten steel after the dissolved oxygen is removed.
從轉爐中出鋼以後直到在真空脫氣裝置中於熔鋼中添加金屬Al為止，均未實施Mn的添加。較佳係直到利用金屬Al進行脫氧為止，與Mn同樣地亦未添加Si。The addition of Mn was not carried out until the metal Al was added to the molten steel after the tapping in the converter until the vacuum degassing device. It is preferable that Si is not added in the same manner as Mn until deoxidation is performed by metal Al.
但，當必須根據所熔製之熔鋼的鋼種成分規格進行Mn或Si的調整時，係在利用金屬Al進行脫氧處理後，便將Mn源或Si源添加至熔鋼中而實施成分調整。此情況，Mn源係使用高碳錳鐵(FMnH)或金屬錳等含Mn之金屬進行調整，而含Mn之金屬中最廉價的高碳錳鐵係含有7質量%左右的碳，藉由添加高碳錳鐵，便會導致熔鋼中的碳濃度提高。所以，考慮因高碳錳鐵等含Mn之金屬的添加所造成之碳濃度提高份，而調整未靜反應結束時的熔鋼中碳濃度。由於金屬錳並未含有碳，因而當Mn源係使用金屬錳的情況，便無需考慮碳濃度的提高份。又，在必須調整Nb、V、B、Ca、Ti 等微量添加元素的情況，亦是在利用金屬Al進行脫氧處理後實施。However, when it is necessary to adjust Mn or Si according to the steel component specification of the molten steel to be melted, after the deoxidation treatment is performed by the metal Al, the Mn source or the Si source is added to the molten steel to carry out component adjustment. In this case, the Mn source is adjusted using a metal containing Mn such as high carbon manganese iron (FMnH) or manganese metal, and the most expensive high carbon manganese iron in the Mn containing metal contains about 7 mass% of carbon by adding High carbon ferromanganese will cause an increase in the carbon concentration in the molten steel. Therefore, the carbon concentration in the molten steel at the end of the non-static reaction is adjusted in consideration of the carbon concentration increase portion due to the addition of the Mn-containing metal such as high carbon ferromanganese. Since manganese metal does not contain carbon, when manganese metal is used as the source of manganese, it is not necessary to consider an increase in carbon concentration. Also, it is necessary to adjust Nb, V, B, Ca, Ti The case where an element is added in a small amount is also carried out after deoxidation treatment using metal Al.
依此，即便在調整熔鋼的Mn濃度之情況，含Mn之金屬的添加時期亦是經Al脫氧後的溶存氧濃度極低之時點，因而含Mn之金屬中的Mn與溶存氧不會產生反應，俾防止在含Mn之金屬添加時生成屬於低級氧化物的MnO。Accordingly, even when the Mn concentration of the molten steel is adjusted, the addition period of the metal containing Mn is a point at which the dissolved oxygen concentration after deoxidation of Al is extremely low, so that Mn and dissolved oxygen in the metal containing Mn are not generated. The reaction, 俾 prevents the formation of MnO belonging to the lower oxide when the metal containing Mn is added.
若真空脫氣裝置中的脫氣精煉已結束，便將收容有熔鋼的盛鋼桶搬送至鋼胚連續鑄造機中，並利用連續鑄造機進行鑄造而製得鋼胚鑄片。在連續鑄造機中，從提升生產性的觀點而言，較佳係依穩定鑄造區域中之每股的熔鋼鑄造量為4.5噸/分鐘以上之高速鑄造進行鑄造。If the degassing refining in the vacuum degassing device is completed, the steel ladle containing the molten steel is transferred to a steel continuous casting machine, and cast by a continuous casting machine to obtain a steel blank cast piece. In the continuous casting machine, from the viewpoint of improving productivity, casting is preferably carried out by high-speed casting in which the amount of molten steel per casting in the stable casting zone is 4.5 tons/min or more.
隨著連續鑄造機中的鑄造經過，盛鋼桶內的熔鋼減少，在即將進行序列連續鑄造的盛鋼桶交換前，盛鋼桶內的熔鋼高度變得極低，在從盛鋼桶朝餵槽的熔鋼流出孔(盛鋼桶噴嘴)附近之盛鋼桶內熔鋼會形成渦流。在該渦流中會捲入盛鋼桶內的熔渣、及存在於該熔渣附近之熔鋼中的夾雜物，並流出至餵槽，且在流出至餵槽的其中一部分無法上浮的情況下流出至鑄模內，成為鑄片的夾雜物。高速鑄造時，由於從盛鋼桶朝餵槽的熔鋼注入流量較多，因而從盛鋼桶內的殘留熔鋼較多的時點開始便在盛鋼桶內形成渦流，導致盛鋼桶內的熔渣及存在於該熔渣附近之熔鋼中夾雜物被捲入於渦流中的頻度提高。As the casting in the continuous casting machine passes, the molten steel in the ladle is reduced, and the molten steel in the ladle becomes extremely low before the exchange of the steel ladle to be serially cast, in the steel drum. The molten steel in the ladle near the molten steel outflow hole (the ladle nozzle) of the feed tank forms a vortex. In the eddy current, the slag contained in the ladle and the inclusions in the molten steel existing in the slag are taken up and flowed out to the feed tank, and in a case where a part of the feed tank is not floatable. It flows out into the mold and becomes an inclusion of the cast piece. In high-speed casting, since the flow rate of the molten steel from the ladle to the feeding tank is large, eddy current is formed in the ladle from the time when the residual molten steel in the ladle is large, resulting in the inside of the ladle The frequency with which the slag and the molten steel existing in the vicinity of the slag are caught in the eddy current is increased.
然而，本發明係藉由添加含有氫氧化物與碳氧化物的MgO源，而使盛鋼桶內熔渣固化，因而盛鋼桶內的熔渣不易被捲入於渦流中，尚且，添加金屬Al或Al浮渣而將熔渣中的低級氧化物予以還原，並且在Al脫氧後進行熔鋼成分的Mn調整，因而可防止新生成MnO，降低熔渣的氧勢，使存在於熔渣附近之熔鋼中夾雜物減少，再者，在溶存氧濃度為0.050質量%以下之時點進行Al脫氧，因而使脫氧生成物的生成量本身減少，藉由該等效果的協同組合，便可確保熔鋼的潔淨性，結果可實現即便在每股的熔鋼鑄造量為4.5噸/分鐘以上之高速鑄造下，仍可製造夾雜物較少之潔淨性優異的鋼胚鑄片。However, in the present invention, by adding a MgO source containing a hydroxide and a carbon oxide, the molten slag in the ladle is solidified, so that the slag in the ladle is not easily caught in the eddy current, and metal is added. Al or Al scum reduces the lower oxide in the slag, and after the deoxidation of Al, the Mn adjustment of the molten steel component is performed, thereby preventing the newly formed MnO and reducing the oxygen potential of the slag, so that it exists in the vicinity of the slag. In the molten steel, the amount of inclusions is reduced. Further, when the dissolved oxygen concentration is 0.050% by mass or less, Al deoxidation is performed, so that the amount of deoxidation product produced is itself reduced, and the synergistic combination of these effects ensures the melting. As a result of the cleanliness of the steel, even in the case of high-speed casting in which the amount of molten steel per casting is 4.5 tons/min or more, it is possible to produce a steel slab having excellent cleanliness with less inclusions.
根據實施例，對本發明進行更詳細說明。將本發明應用於下述步驟：將利用爐容量300噸的上底吹轉爐所熔製之熔鋼，利用RH真空脫氣裝置進行精煉，然後使用用以鑄造厚235mm、寬1100mm鋼胚鑄片的二股型鋼胚連續鑄造機(two-strand-type slab continuous casting machine)，製造薄鋼板用鋼胚鑄片。又，作為比較，亦施行本發明範圍外的操作。將4加熱當作一個單位並依同一條件進行熔製，在連續鑄造時實施該等4加熱的序列連續鑄造，並將4加熱當作1個單位進行試驗。The invention is illustrated in more detail in accordance with embodiments. The invention is applied to the following steps: a molten steel melted by an upper bottom blowing converter having a furnace capacity of 300 tons is used for refining by means of an RH vacuum degassing device, and then used for casting a steel slab having a thickness of 235 mm and a width of 1100 mm. A two-strand-type slab continuous casting machine for producing steel slabs for thin steel sheets. Further, as a comparison, operations outside the scope of the present invention are also performed. The heating of 4 was regarded as one unit and was melted under the same conditions, and the sequential heating of the four heating sequences was carried out during continuous casting, and the heating was performed as one unit.
在未對所製造鑄片施行表面清理的情況下施行熱軋而形 成薄鋼板，所獲得薄鋼板經酸洗處理後施行冷軋，並對經冷軋後的鋼板施行鍍錫，調查該經鍍錫的鋼板中因氧化物系夾雜物所造成的表面缺陷。Hot rolling is performed without surface cleaning of the produced cast piece The steel sheet was formed into a thin steel sheet, and the obtained steel sheet was subjected to pickling treatment, followed by cold rolling, and the cold-rolled steel sheet was subjected to tin plating to investigate surface defects caused by oxide-based inclusions in the tin-plated steel sheet.
表1係顯示本發明例及比較例的操作條件、及薄鋼板中因氧化物系夾雜物所造成的表面缺陷指數。此處，表1所示之表面缺陷指數，係將未添加含有氫氧化物與碳氧化物的塊狀組成物之MgO源的比較例1中因缺陷所造成的衰退率(degradation rate)設為基準(1.00)，經指數化而表示者。作為含有氫氧化物與碳氧化物的塊狀組成物之MgO源而使用的MgO球，係將含有氫氧化鎂、碳酸鎂及氧化鎂，且Mg(OH)2 含量約20質量%以上、MgCO3 含量約20質量%以上、灼燒減量(1000℃處理)約20質量%、灼燒減量後的殘留物中之MgO濃度80質量%以上的粉狀組成物成形為粒徑約30mm之壓塊的塊狀助熔劑。若將其加熱至1000℃，則經由熱分解所生成的H2 O係每1kg MgO源為3.4mol以上，經由熱分解所生成的CO2 係每1kg MgO源為2.4mol以上。Table 1 shows the operating conditions of the examples and comparative examples of the present invention, and the surface defect index due to oxide-based inclusions in the steel sheet. Here, the surface defect index shown in Table 1 is a deterioration rate due to a defect in Comparative Example 1 in which MgO source containing no bulk composition of hydroxide and carbon oxide is added. Benchmark (1.00), expressed by indexation. The MgO ball used as a MgO source containing a bulk composition of a hydroxide and a carbon oxide contains magnesium hydroxide, magnesium carbonate, and magnesium oxide, and has a Mg(OH) 2 content of about 20% by mass or more and MgCO. 3, the content of about 20% by mass or more, the ignition loss (1000 ° C treatment) of about 20% by mass, and the powdery composition having a MgO concentration of 80% by mass or more in the residue after the ignition reduction is formed into a compact having a particle diameter of about 30 mm. Blocky flux. When it is heated to 1000 ° C, the H 2 O produced by thermal decomposition is 3.4 mol or more per 1 kg of the MgO source, and the CO 2 produced by thermal decomposition is 2.4 mol or more per 1 kg of the MgO source.
所有的實施例及比較例中，將未脫氧的熔鋼出鋼至盛鋼桶中之後，於盛鋼桶內的熔渣上添加Al浮渣，所有的實施例及部分比較例再進一步添加MgO球，而施行熔渣控制。又，比較例8係在盛鋼桶內的熔渣上投入Al浮渣與MgO灰渣之後，將被覆耐火物之吹管浸漬於熔鋼中2m左右，依約1Nm3 /min的吹入速度吹入Ar氣體3分鐘而進行攪拌。比較 例8所使用的MgO灰渣係將從海水所取出的氫氧化鎂施行煅燒而成者，含有90質量%以上之MgO，並含有SiO2 、CaO、Al2 O3 、Fe2 O3 等少量氧化物作為不純物。In all the examples and comparative examples, after the undeoxidized molten steel is tapped into the ladle, Al scum is added to the slag in the ladle, and all the examples and some comparative examples are further added with MgO. Ball, and slag control is applied. Further, in Comparative Example 8, after the Al scum and the MgO ash were put into the slag in the ladle, the refractory-coated blow pipe was immersed in the molten steel for about 2 m, and was blown at a blowing speed of about 1 Nm 3 /min. Ar gas was introduced for 3 minutes and stirred. The MgO ash used in Comparative Example 8 is obtained by calcining magnesium hydroxide taken out from seawater, containing 90% by mass or more of MgO, and containing SiO 2 , CaO, Al 2 O 3 , Fe 2 O 3 , or the like. A small amount of oxide is used as an impurity.
相較於比較例1而言，本發明例1~5可將夾雜物減低至1/3以下。相對於此，經添加含有氫氧化物與碳氧化物之MgO球者的添加量較多、熔渣中的MgO含量超過本發明範圍的比較例2，及MgO球添加量較少、熔渣中的MgO含量未達本發明範圍的比較例4，係無法獲得充分的夾雜物減低效果。又，在RH真空脫氣的未靜反應中雖未添加Mn源、但未添加MgO球的比較例3，係無法獲得充分的夾雜物減低效果。比較例6雖使用MgO球進行熔渣組成的控制，但Al添加前的溶存氧濃度高於0.050質量%，因而無法獲得充分的夾雜物減低效果。又，比較例7雖使用MgO球進行熔渣組成的控制，但在未靜反應中有添加Mn源，因而熔渣中的MnO濃度上升，無法獲得充分的夾雜物減低效果。又，取代MgO球的添加，改為添加MgO灰渣並施行發泡攪拌而進行熔渣控制的比較例8，亦無法獲得充分的夾雜物減低效果。In comparison with Comparative Example 1, the inventive examples 1 to 5 can reduce the inclusions to 1/3 or less. On the other hand, in the case of adding MgO balls containing hydroxides and carbon oxides, the addition amount was large, the MgO content in the slag was more than the range of the present invention, and the amount of MgO balls added was small, and the slag was In Comparative Example 4 in which the MgO content did not reach the range of the present invention, a sufficient inclusion reducing effect could not be obtained. Further, in Comparative Example 3 in which no Mn source was added but no MgO ball was added in the static reaction of RH vacuum degassing, a sufficient inclusion reduction effect could not be obtained. In Comparative Example 6, although the control of the slag composition was performed using MgO balls, the dissolved oxygen concentration before the addition of Al was higher than 0.050% by mass, and thus a sufficient inclusion reducing effect could not be obtained. Further, in Comparative Example 7, although MgO balls were used to control the slag composition, the Mn source was added during the non-static reaction, so that the MnO concentration in the slag increased, and a sufficient inclusion reduction effect could not be obtained. Further, in place of the addition of the MgO balls, in Comparative Example 8 in which MgO ash was added and foaming and stirring were carried out to carry out slag control, a sufficient inclusion reduction effect could not be obtained.
依此，藉由應用本發明，可確認即便在每股的熔鋼鑄造量為4.5噸/分鐘以上之高速鑄造下，仍可製造夾雜物較少之潔淨性優異的鋼。According to the present invention, it has been confirmed that even in the case of high-speed casting in which the amount of molten steel per strand is 4.5 tons/min or more, it is possible to produce steel having excellent cleanliness with less inclusions.
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