JP2017083400A - Evaluation method for refractory material - Google Patents
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本発明は鋼の鋳造に使用する耐火物，特に溶鋼の流量を制御するスライディングノズル（以下「ＳＮ」という。）装置に使用されるプレートに代表される，使用時に摺動部となる部分を含む炭素含有耐火物の評価方法に関する。 The present invention includes a refractory material used for steel casting, particularly a sliding nozzle (hereinafter referred to as “SN”) device for controlling the flow rate of molten steel, and a portion that becomes a sliding portion during use. The present invention relates to a method for evaluating carbon-containing refractories.
ＳＮプレートの主要な損耗形態である摺動面の面荒れは，鋳造中に稼動面である摺動面が脱炭され，脆弱化し，組織が，脱落，剥離などの現象を生じる現象である。この面荒れは化学的要因や物理的要因などいくつかの要素が組み合わさり生じると考えられている。多くの場合，酸化に起因して生じると考えられているが，一般的な電気炉を用いた酸化試験等ではこのＳＮプレートの酸化，面荒れを再現，評価することができない。これは鋳造中，摺動面は溶鋼と長時間接することから，溶鋼や溶鋼中成分との反応に起因した酸化，脱炭がＳＮプレートの酸化，面荒れの主要因であると考えられるからである。 The rough surface of the sliding surface, which is the main form of wear of the SN plate, is a phenomenon in which the sliding surface, which is the working surface, is decarburized and weakened during casting, and the structure undergoes phenomena such as dropping and peeling. This rough surface is considered to be caused by a combination of several factors such as chemical factors and physical factors. In many cases, it is thought to be caused by oxidation, but the oxidation and surface roughness of this SN plate cannot be reproduced and evaluated by an oxidation test using a general electric furnace. This is because the sliding surface is in contact with the molten steel for a long time during casting, so it is thought that oxidation and decarburization due to the reaction with the molten steel and the components in the molten steel are the main causes of SN plate oxidation and surface roughness. is there.
このため例えば特許文献１では，高周波誘導炉を用いて１５５０℃〜１７００℃，酸素濃度を１０〜５００ｐｐｍに調整した溶鋼とＳＮプレートれんがを反応させて，ＳＮプレートれんがの鋼浴部に脱炭層を形成させ，この脱炭層の厚みを評価する方法が提案されている。 For this reason, for example, in Patent Document 1, by using a high-frequency induction furnace, a molten steel adjusted to 1550 ° C. to 1700 ° C. and an oxygen concentration of 10 to 500 ppm is reacted with an SN plate brick, and a decarburized layer is formed on the steel bath portion of the SN plate brick. A method for forming and evaluating the thickness of the decarburized layer has been proposed.
さらに特許文献２には，酸素濃度が３０〜１２０ｐｐｍで１５５０℃〜１６５０℃の範囲に調整された溶鋼と３００分間反応させたときの稼動面の脱炭層の厚みが１５００μｍ以下である窒化アルミニウムの含有量が１．５質量％以上７．０質量％以下のＳＮプレートれんがが示されている。この特許文献２の評価方法は溶鋼中の酸素によってＳＮプレートれんがの炭素が酸化，脱炭される現象を評価することから，実機で使用後に生じる酸化に起因した面荒れ現象を再現性良く評価することが可能であるとされている。 Further, Patent Document 2 contains aluminum nitride in which the thickness of the decarburized layer on the working surface is 1500 μm or less when reacted for 300 minutes with molten steel adjusted to a range of 1550 ° C. to 1650 ° C. with an oxygen concentration of 30 to 120 ppm. An SN plate brick with an amount of 1.5 mass% to 7.0 mass% is shown. Since the evaluation method of this patent document 2 evaluates the phenomenon that the carbon of SN plate brick is oxidized and decarburized by oxygen in molten steel, it evaluates the rough surface phenomenon caused by oxidation after use in the actual machine with good reproducibility. It is said that it is possible.
一方，非特許文献１では，金属Ａｌの含有量が異なるＳＮプレート材質を作製し，高周波誘導炉を用いて，１６００℃の温度条件で３時間，ＳＳ４００とこれらのＳＮプレート用耐火物材質との反応試験を行い，稼動面の組織を評価している。この非特許文献１では金属Ａｌを６％以上添加したＳＮプレート材質では表層にＡｌ２Ｏ３を主成分とした緻密層を形成することが確認されており，実鋳造の結果と良く一致しており，酸素濃度が高い鋼種条件で使用されたＳＮプレートの摺動面の組織を良く再現できている。 On the other hand, in Non-Patent Document 1, SN plate materials with different contents of metal Al are produced, and using a high frequency induction furnace, the temperature of 1600 ° C. for 3 hours, SS400 and these SN plate refractory materials A reaction test is conducted to evaluate the working structure. In this Non-Patent Document 1, it is confirmed that the SN plate material to which 6% or more of metallic Al is added forms a dense layer mainly composed of Al 2 O 3 on the surface layer, which is in good agreement with the result of actual casting. Therefore, the structure of the sliding surface of the SN plate used under steel grade conditions with a high oxygen concentration can be reproduced well.
また，非特許文献２には溶存酸素濃度が低いと推測される極低炭素鋼で使用されたＳＮプレートの調査結果が報告されている。非特許文献２でも稼動面の酸化層では微粒部が消失し，空隙を形成していることが報告されている。しかしながら，その現象の全てを説明するメカニズム等についての考察はなされておらず，耐火物中の炭素がどのような反応により酸化され一酸化炭素を生成したかについては触れられていない。 In addition, Non-Patent Document 2 reports the results of a survey of SN plates used in ultra-low carbon steel that is estimated to have a low dissolved oxygen concentration. Non-Patent Document 2 also reports that fine particles disappear and voids are formed in the oxide layer on the working surface. However, no consideration has been given to the mechanism that explains all of the phenomena, and no mention is made of the reaction by which the carbon in the refractory is oxidized to produce carbon monoxide.
さらに，非特許文献３では，縦型管状炉を用いた室内実験ではあるが，同じくＳＮプレートの摺動面の損耗，面荒れを評価することを目的として，極低炭Ａｌ−Ｋ鋼（Ｃ；２０ｐｐｍ），低炭Ａｌ−Ｋ鋼（Ｃ；４１０ｐｐｍ），極低炭Ｓｉ−Ｋ鋼（Ｃ；２０ｐｐｍ）の３種類の鋼種を炉に入れ，真空置換を行ったＡｒ雰囲気下，１５６０℃の温度条件で，アルミナ微粉と炭素から構成される単純系試料と反応させる試験を行い，界面の組織の評価と考察を行っている。極低炭Ａｌ−Ｋ鋼（Ｃ；２０ｐｐｍ）との反応試験結果として，試料の稼動面で２００μｍ程度の脆化層を形成し，炭素とＡｌ２Ｏ３粒の消失が確認されており，低炭Ａｌ−Ｋ鋼（Ｃ；４１０ｐｐｍ）でも同様に，１００μｍ程度の炭素とＡｌ２Ｏ３粒が消失した脆化層の形成が確認されている。 Furthermore, in Non-Patent Document 3, although it is a laboratory experiment using a vertical tubular furnace, for the purpose of evaluating wear and surface roughness of the sliding surface of the SN plate, an extremely low carbon Al-K steel (C 20ppm), low-carbon Al-K steel (C; 410ppm), ultra-low-carbon Si-K steel (C; 20ppm), and put it in a furnace. Tests are conducted to react with a simple sample composed of alumina fine powder and carbon under temperature conditions, and the interface structure is evaluated and discussed. As a result of the reaction test with ultra-low-carbon Al-K steel (C; 20 ppm), an embrittled layer of about 200 μm was formed on the working surface of the sample, and the disappearance of carbon and Al 2 O 3 grains was confirmed. Similarly, the formation of an embrittled layer in which about 100 μm of carbon and Al 2 O 3 grains have disappeared has been confirmed even in the case of carbon Al—K steel (C; 410 ppm).
本発明が解決しようとする課題は，例えば高炉一貫製鉄所等で一般に生産されるＡｌ−Ｋ鋼や低炭Ａｌ−Ｋ鋼など，溶存酸素濃度が低いと考えられる鋼種の鋳造に長時間使用されるＳＮプレートの摺動面の面荒れ現象を試験室レベルで再現することにある。言い換えれば本発明は，その面荒れ現象に関し，実操業の条件に応じて高い精度で再現することができる評価方法を提供することを目的とする。なお，溶存酸素濃度とは，酸化物等の鋼中介在物として含まれる酸素を除いたものをいう。以下，同じ。 The problem to be solved by the present invention is, for example, used for a long time in casting of steel types considered to have a low dissolved oxygen concentration, such as Al-K steel and low-carbon Al-K steel, which are generally produced in blast furnace integrated steelworks. The surface roughness phenomenon of the sliding surface of the SN plate is reproduced at the laboratory level. In other words, an object of the present invention is to provide an evaluation method that can reproduce the surface roughness phenomenon with high accuracy according to the conditions of actual operation. The dissolved oxygen concentration refers to the concentration excluding oxygen contained as inclusions in steel such as oxides. same as below.
電気炉による製造を主とする製鉄所で生産される比較的溶存酸素濃度が高い鋼種を鋳造するＳＮプレートと同様，高炉一貫製鉄所等で一般に生産されるＡｌ−Ｋ鋼や低炭Ａｌ−Ｋ鋼など溶存酸素濃度が低いと考えられる鋼種の鋳造におけるＳＮプレートの摺動面の面荒れ現象の主たる原因，メカニズムは，ＳＮプレートを構成する耐火物の脱炭，脱炭による剥離，脱落などの組織劣化，組織劣化部分のＳＮプレートの摺動に伴う機械的摩耗又は溶鋼流による摩耗，化学的侵食等である。このような原因のうち，特に損傷の契機すなわち最初の原因である脱炭に関し，使用条件に合致するように試験条件を最適化することが必要である。 Al-K steel and low-carbon Al-K generally produced in blast furnace integrated steelworks, etc., as well as SN plates for casting steel types with relatively high dissolved oxygen concentration produced at steelworks mainly manufactured by electric furnaces The main cause and mechanism of the surface roughness phenomenon of the sliding surface of the SN plate in the casting of steel grades that are considered to have low dissolved oxygen concentration such as steel are the decarburization of the refractory that constitutes the SN plate, delamination by decarburization, dropping off, etc. Examples of such deterioration include mechanical wear due to sliding of the SN plate in the degraded portion of the tissue, wear due to molten steel flow, and chemical erosion. Among these causes, especially with regard to the trigger of damage, that is, decarburization, which is the first cause, it is necessary to optimize the test conditions so as to meet the use conditions.
電気炉による製造を主とする製鉄所で生産される比較的溶存酸素濃度が高い鋼種を鋳造するＳＮプレートの摺動面は，鋼中の溶存酸素により酸化，脱炭を受けると考えられるが，溶存酸素濃度が低いと考えられるＡｌ−Ｋ鋼や低炭Ａｌ−Ｋ鋼等の鋼種を鋳造する場合は，異なったメカニズムで酸化，脱炭すると考えられる。本発明は特にこの観点により，ＳＮプレートの面荒れを高い再現性で評価する方法を見いだした。 Although the sliding surface of the SN plate that casts steel with a relatively high dissolved oxygen concentration produced at steelworks, mainly manufactured by electric furnaces, is thought to be oxidized and decarburized by dissolved oxygen in the steel. When casting steel grades such as Al-K steel and low-carbon Al-K steel, which are considered to have low dissolved oxygen concentration, it is thought that oxidation and decarburization are performed by different mechanisms. In particular, the present invention has found a method for evaluating the surface roughness of the SN plate with high reproducibility from this viewpoint.
すなわち，本発明は次の１から４に記載の耐火物の評価方法である。
１． 鋼の連続鋳造用の摺動部に使用される炭素含有耐火物について，試料に溶融鉄を接触させる耐火物の評価方法において，前記溶融鉄の溶存酸素濃度が１０ｐｐｍ未満であることを特徴とする耐火物の評価方法。（請求項１）
２． 前記溶融鉄の鉄源が，高炭素鋼，銑鉄又は鋳鉄から選択する１又は複数である，前記１に記載の耐火物の評価方法。（請求項２）
３． 前記溶融鉄の炭素含有量が２．１４質量％以上５．５質量％以下である，前記１又は前記２に記載の耐火物の評価方法。（請求項３）
４． 前記溶融鉄と前記試料とを接触させる際の雰囲気が大気雰囲気である，前記１から前記３のいずれかに記載の耐火物の評価方法。（請求項４）
That is, the present invention is a refractory evaluation method described in the following 1 to 4.
1. About the carbon-containing refractory used for the sliding part for continuous casting of steel, the dissolved oxygen concentration of the molten iron is less than 10 ppm in the refractory evaluation method in which molten iron is brought into contact with a sample. Refractory evaluation method. (Claim 1)
2. 2. The refractory evaluation method according to 1, wherein the iron source of the molten iron is one or more selected from high carbon steel, pig iron or cast iron. (Claim 2)
3. 3. The refractory evaluation method according to 1 or 2 above, wherein the molten iron has a carbon content of 2.14% by mass or more and 5.5% by mass or less. (Claim 3)
4). 4. The method for evaluating a refractory according to any one of 1 to 3, wherein the atmosphere when the molten iron and the sample are brought into contact with each other is an air atmosphere. (Claim 4)
溶存酸素濃度が低い鋼を使用する従来技術の試験室での評価を行っても，実操業の再現性が低いケースが多かった。この原因は明確にされていないが，実操業と試験室での評価との違いが生じるのは，鋼中の溶存酸素濃度以外にも鋼中の炭素含有量，供給熱量，雰囲気等の影響があると考えられる。従来技術では溶存酸素濃度が低い鋼種に供する炭素含有耐火物の試験室での評価においても，実操業における鋼成分に近い，すなわち炭素含有量等も低い「鋼」を使用することが必要との技術思想が支配的であった。しかし，従来の鋼を使用した試験室での評価方法では溶存酸素濃度を１０ｐｐｍ未満に維持することは実質的に困難であり，仮に非酸化雰囲気の環境を整備することで酸素濃度を維持しようとしても，大規模な設備が必要，試験自体も高いコストになる等により，現実的ではない。本発明は「鋼」にはない高い炭素含有量の溶融鉄を使用することで，大気雰囲気でも溶融鉄内の溶存酸素濃度を極めて低く維持することができ，しかも，耐火物試料中からの炭素成分の鋼中への移動を抑制して，実操業では試験室での評価時よりも生じ易いと考えられる耐火物内での炭素によるＡｌ２Ｏ３等の還元反応等の再現性も高めることが可能になる。これらにより，単に溶存酸素濃度が低い「鋼」を使用する従来技術には得られない再現性の高い試験室での評価が可能となる。 In many cases, the reproducibility of the actual operation was low even when evaluation was performed in a prior art laboratory using steel with low dissolved oxygen concentration. The reason for this is not clarified, but the difference between actual operation and laboratory evaluation is due to the effects of carbon content, supply heat, atmosphere, etc., in addition to the dissolved oxygen concentration in steel. It is believed that there is. In the prior art, even in the laboratory evaluation of carbon-containing refractories used for steel grades with low dissolved oxygen concentration, it is necessary to use “steel” that is close to the steel components in actual operation, that is, low in carbon content, etc. Technical thought was dominant. However, it is practically difficult to maintain the dissolved oxygen concentration below 10 ppm by the conventional evaluation method in the laboratory using steel, and it is attempted to maintain the oxygen concentration by preparing a non-oxidizing atmosphere environment. However, this is not realistic because large-scale equipment is required and the test itself is expensive. In the present invention, by using molten iron having a high carbon content not found in “steel”, the dissolved oxygen concentration in the molten iron can be kept extremely low even in an atmospheric environment, and carbon from the refractory sample can be maintained. Suppress the movement of components into steel, and increase the reproducibility of reduction reactions such as Al 2 O 3 by carbon in refractories, which are considered to be more likely to occur in actual operations than during evaluation in the laboratory. Is possible. As a result, it is possible to perform evaluation in a highly reproducible laboratory that cannot be obtained by the conventional technology using only “steel” having a low dissolved oxygen concentration.
すなわち本発明により，鋼の連続鋳造に長時間使用されるＳＮプレートの摺動面の面荒れ現象を試験室レベルで，実操業の特に鋼種条件に応じて的確に再現することができる。ひいては効率的に，摺動面の損傷を軽減したＳＮプレート用耐火物を開発することが可能となる。なお，本発明は，鋼の連続鋳造において上ノズル，下部ノズル等の，他の部位に使用する耐火物の評価にも適用することできる。 That is, according to the present invention, the surface roughness phenomenon of the sliding surface of the SN plate that is used for continuous casting of steel for a long time can be accurately reproduced at the laboratory level according to the steel type conditions of actual operation. As a result, it is possible to efficiently develop a refractory for an SN plate that reduces damage to the sliding surface. In addition, this invention is applicable also to evaluation of the refractory material used for other parts, such as an upper nozzle and a lower nozzle, in the continuous casting of steel.
以下に本発明の実施の形態を述べる。 Embodiments of the present invention will be described below.
本発明の評価方法を実施するための評価装置は，例えば図５に示すように高周波誘導炉内面側に内張りした評価対象とする耐火物試料，その高周波誘導炉内に任意の成分に調整された鉄源（さまざまな成分の鉄）を高周波により溶融した溶融鉄，前記溶融鉄の溶存酸素濃度を測定する酸素センサー，前記溶融鉄の温度を測定する温度センサーを基本的な構成とする。なお，評価対象とする耐火物試料は高周波誘導炉の壁又は底に内張り材として構成することができるほか，内張り材は評価対象とする耐火物試料以外の構造物として，評価対象とする耐火物試料を溶融鉄浴内に浸漬する方法も採ることができる。 The evaluation apparatus for carrying out the evaluation method of the present invention is adjusted to an arbitrary component in the high-frequency induction furnace, for example, as shown in FIG. The basic configuration includes a molten iron obtained by melting an iron source (iron of various components) at a high frequency, an oxygen sensor that measures the dissolved oxygen concentration of the molten iron, and a temperature sensor that measures the temperature of the molten iron. The refractory sample to be evaluated can be configured as a lining material on the wall or bottom of the induction furnace, and the lining material is a refractory to be evaluated as a structure other than the refractory sample to be evaluated. A method of immersing the sample in the molten iron bath can also be employed.
溶融鉄は，銑鉄，鋳鉄，高炭素鋼，溶鋼等を鉄源としつつ，目的に応じて溶存酸素濃度を調整すればよい。前記酸素センサーや温度センサーで溶存酸素濃度や温度をモニターし，鉄源の供給調整や電圧調整等により試験条件の管理・制御を行う。 For molten iron, pig iron, cast iron, high carbon steel, molten steel, etc. may be used as the iron source, and the dissolved oxygen concentration may be adjusted according to the purpose. The dissolved oxygen concentration and temperature are monitored by the oxygen sensor and temperature sensor, and the test conditions are managed and controlled by adjusting the supply of iron sources and adjusting the voltage.
前記の耐火物試料の内面を溶融鉄と接触させ，所定の条件で所定時間維持する。耐火物試料の材質としては，一般に広く用いられる焼成タイプのアルミナ−炭素系材質や，Ａｌ等の低融点の金属を添加し，これらの金属の少なくとも一定量以上を残存させた不焼成もしくは低温焼成タイプの材質など，アルミナ，マグネシア，スピネル等の耐火性骨材に加え，主に炭素を含有するＳＮプレート用耐火物の材質，その他目的に応じて成分や構造を任意に調整した材質を用いることができる。 The inner surface of the refractory sample is brought into contact with molten iron and maintained under predetermined conditions for a predetermined time. As materials for refractory samples, generally used firing-type alumina-carbon materials and low melting point metals such as Al are added, and at least a certain amount of these metals are left unfired or low-temperature fired. In addition to refractory aggregates such as alumina, magnesia, spinel, etc., use materials of refractories for SN plates that mainly contain carbon, and other materials whose structures and structures are arbitrarily adjusted according to the purpose. Can do.
溶融鉄の温度としては，ＳＮプレート用耐火物が使用される実鋳造における温度と同条件とすることが望ましく，概ね１５００〜１７００℃の範囲で，個別の条件に応じた温度に設定することができる。溶融鉄の温度は，酸素センサーを溶融鉄の上表面から５０ｍｍ以上深い位置に挿入し，測定することが望ましい。また，溶融鉄の温度は，試験時，少なくとも３０分毎に測定を行い，設定温度よりも±２０℃以内の温度範囲に制御することが望ましい。 The temperature of the molten iron is preferably set to the same conditions as those in actual casting in which SN plate refractories are used, and the temperature may be set within a range of about 1500 to 1700 ° C. according to individual conditions. it can. It is desirable to measure the temperature of the molten iron by inserting an oxygen sensor at a position deeper than 50 mm from the upper surface of the molten iron. In addition, the temperature of the molten iron is preferably measured at least every 30 minutes during the test and controlled within a temperature range within ± 20 ° C of the set temperature.
溶融鉄の溶存酸素濃度は，少なくとも試験開始時と試験終了時に測定を行い，試験が溶存酸素濃度１０ｐｐｍ未満の条件で実施されたか確認することが必要である。溶存酸素濃度１０ｐｐｍ以上の条件では，溶融鉄中の酸素の影響が強くなって耐火物試料中の炭素が酸化され，さらに溶存酸素濃度が高くなると酸化鉄を生成し，酸化鉄が耐火物試料中の構成物と反応して耐火物試料の溶損を過度に促進することから，本来の目的である低酸素濃度の溶鋼に対する耐火物試料稼動面の脆化等の評価を適切に行うことができなくなる。 It is necessary to measure the dissolved oxygen concentration of the molten iron at least at the start and end of the test, and to confirm whether the test was conducted under a condition where the dissolved oxygen concentration is less than 10 ppm. Under the condition where the dissolved oxygen concentration is 10 ppm or more, the influence of oxygen in the molten iron becomes strong and the carbon in the refractory sample is oxidized, and when the dissolved oxygen concentration becomes higher, iron oxide is generated, and the iron oxide is in the refractory sample. Because it reacts with the components of the refractory material and excessively promotes the refractory sample melting damage, it is possible to appropriately evaluate the embrittlement of the refractory sample working surface for the low oxygen concentration molten steel, which is the original purpose. Disappear.
また，金属Ａｌや金属Ｍｇ，又はこれらの合金等の，低融点金属を含む耐火物試料については，溶存酸素濃度が１０ｐｐｍ以上の条件では，稼動面でＡｌ２Ｏ３やスピネルを主成分とする緻密層を形成し，耐火物内部でＡｌ２Ｏ３と炭素の反応により生じたＣＯ（ｇ）やＡｌ（ｇ），ＡｌＯ（ｇ）成分が，溶融鉄中へ溶出することを防ぐことから，組織が劣化せず，本来の目的である稼動面の脆化等の評価を適切に行うことができなくなる。 In addition, for refractory samples containing low melting point metals such as metal Al, metal Mg, or alloys thereof, Al 2 O 3 or spinel is the main component in terms of operation when the dissolved oxygen concentration is 10 ppm or more. A dense layer is formed, and CO (g), Al (g), and AlO (g) components generated by the reaction of Al 2 O 3 and carbon inside the refractory are prevented from eluting into the molten iron. The structure does not deteriorate, and the original purpose, such as the embrittlement of the operating surface, cannot be properly evaluated.
溶存酸素濃度が特に低い溶鋼の鋳造を再現する場合や溶存酸素濃度が低い場合の現象を強調して確認したい場合には，溶融鉄中の溶存酸素濃度は５ｐｐｍ以下にすることが望ましい。 When reproducing the casting of molten steel with a particularly low dissolved oxygen concentration or when it is desired to emphasize and confirm the phenomenon when the dissolved oxygen concentration is low, the dissolved oxygen concentration in the molten iron is preferably 5 ppm or less.
溶融鉄と耐火物試料を接触，反応させる時間は，実鋳造の条件に応じて設定すればよいが，一般的に６０分以上３００分以下であることが望ましい。これは，実鋳造の取鍋用のＳＮプレートの使用条件を考慮した場合，通常１回の鋳造時間が３０分〜９０分程度であり，多くの場合５〜１０回程度受鋼するので，その１回の鋳造での状況を再現するためには少なくとも６０分以上反応させることが望ましいからである。６０分未満では稼動面に評価可能な脆化層を形成することが困難である。この評価時間が長時間であるほど脆化層の形成が大きくなるが，３００分以下で概ね適切に評価することが可能である。３００分を超える長時間では，高周波誘導炉の消費電力が大きくなり，エネルギーコストが大きくなって，無駄である。 The time for contacting and reacting the molten iron and the refractory sample may be set according to the actual casting conditions, but it is generally desirable that the time is 60 minutes or more and 300 minutes or less. This is because, considering the use conditions of the SN plate for actual casting ladle, the casting time for one time is usually about 30 minutes to 90 minutes, and in many cases the steel is received about 5 to 10 times. This is because it is desirable to react for at least 60 minutes in order to reproduce the situation in one casting. If it is less than 60 minutes, it is difficult to form an embrittlement layer that can be evaluated on the operating surface. The longer the evaluation time is, the larger the embrittlement layer is formed. However, the evaluation can be made appropriately in about 300 minutes or less. If the time is longer than 300 minutes, the power consumption of the high frequency induction furnace increases, resulting in a wasteful energy cost.
接触試験が終了すると，耐火物試料を内張りした誘導炉を傾転するなどして溶融鉄を排出し，内張りした耐火物試料を冷却する。なお，耐火物試料を溶融鉄浴内に浸漬する場合は，溶融試験終了後に浸漬した耐火物試料を溶融鉄から引き上げ，耐火物試料を冷却する。 When the contact test is completed, the molten iron is discharged by tilting the induction furnace lined with the refractory sample, and the lined refractory sample is cooled. When the refractory sample is immersed in the molten iron bath, the immersed refractory sample is lifted from the molten iron and the refractory sample is cooled.
冷却した耐火物試料は，稼動面からほぼ垂直方向の断面を表出させるように切断し，溶融鉄と接していた稼動面側の脱炭層，脆化層の厚みを測定し，外観及び顕微鏡観察，ＥＰＭＡその他の組織・成分等の調査手段にて評価をすることができる。 The cooled refractory sample is cut so that a substantially vertical cross section is exposed from the working surface, the thickness of the decarburized layer and the embrittled layer on the working surface side in contact with the molten iron is measured, and the appearance and microscopic observation , EPMA and other means such as tissues and components can be used for evaluation.
溶融鉄中の溶存酸素濃度が少ない鋼種を鋳造する条件を再現すための本発明で用いる低酸素濃度の鉄源は，高炭素鋼，銑鉄又は鋳鉄から選択する１又は複数とすることができる。高炭素鋼は，その定義上，概ねその炭素含有量が１．０質量％以上２．１４質量％以下，銑鉄又は鋳鉄の炭素含有量は概ね２．１４質量％以上５．５質量％以下であって溶存酸素濃度は１０ｐｐｍ未満になると推測される。 The low oxygen concentration iron source used in the present invention for reproducing the conditions for casting a steel type having a low dissolved oxygen concentration in the molten iron may be one or more selected from high carbon steel, pig iron or cast iron. High carbon steel, by definition, has a carbon content of 1.0% to 2.14% by mass, and the carbon content of pig iron or cast iron is generally 2.14% to 5.5% by mass. Therefore, the dissolved oxygen concentration is estimated to be less than 10 ppm.
炭素を多く含有する鋼（高炭素鋼）を鉄源として用いると，その溶融鉄中の溶存酸素濃度が低くなるので，高周波誘導炉の内部を大気雰囲気下で実施することも可能である。すなわち，高炭素鋼に含有される炭素は，高炭素鋼が高周波誘導加熱により大気雰囲気下で溶融する過程や，その溶融鉄が大気雰囲気と接する界面での酸化をある程度抑制する補償効果を発揮する。炭素含有量が１．０質量％以下では酸化抑制効果が低く，大気雰囲気での評価中に溶存酸素濃度が１０ｐｐｍ以上となりやすい。 If steel containing a large amount of carbon (high carbon steel) is used as the iron source, the dissolved oxygen concentration in the molten iron will be low, so the inside of the high-frequency induction furnace can also be carried out in an air atmosphere. In other words, the carbon contained in high-carbon steel exhibits a compensation effect that suppresses oxidation to some extent in the process in which high-carbon steel melts in the atmosphere by high-frequency induction heating and the interface where the molten iron contacts the atmosphere. . When the carbon content is 1.0% by mass or less, the effect of suppressing oxidation is low, and the dissolved oxygen concentration tends to be 10 ppm or more during the evaluation in the air atmosphere.
このように本発明の評価方法で用いる鉄源は，炭素を多く含有するほど好ましい。この点、高炭素鋼の最大炭素含有量は約２．１４質量％なので，より炭素を多く含有する銑鉄又は鋳鉄を用いることがより望ましい。銑鉄又は鋳鉄の炭素含有量は，その定義上，その下限は２．１４質量％である。ただし，鉄源の炭素含有量が溶融鉄における炭素の飽和溶解度に近づくと，耐火物試料の稼動面近傍の炭素が溶融鉄中へ溶出しにくくなることから，ＳＮプレートの稼動面の脱炭現象を実鋳造に近い条件で再現することが困難となる。また，図６に示すように炭素含有量が１５００℃以上の温度条件，かつ炭素含有量が５質量％を超える場合，黒鉛結晶が析出する。析出した黒鉛結晶が大気雰囲気と接して燃焼する等の問題が生じる可能性があり，安定した評価を実施することが困難となる。よって，鉄源の炭素含有量は，５．５質量％以下であることがより望ましい。 Thus, the iron source used in the evaluation method of the present invention is more preferable as it contains more carbon. In this regard, since the maximum carbon content of high carbon steel is about 2.14% by mass, it is more desirable to use pig iron or cast iron containing more carbon. By definition, the lower limit of the carbon content of pig iron or cast iron is 2.14% by mass. However, if the carbon content of the iron source approaches the saturation solubility of carbon in the molten iron, the carbon near the working surface of the refractory sample will not easily elute into the molten iron, so the decarburization phenomenon on the working surface of the SN plate. Is difficult to reproduce under conditions close to actual casting. In addition, as shown in FIG. 6, when the carbon content is 1500 ° C. or more and the carbon content exceeds 5 mass%, graphite crystals are precipitated. There is a possibility that the precipitated graphite crystals may burn in contact with the air atmosphere, making it difficult to perform stable evaluation. Therefore, it is more desirable that the carbon content of the iron source is 5.5% by mass or less.
耐火物試料と溶融鉄との接触面積は大きいことが好ましい。よって，溶融鉄浴の深さはできるだけ深く，例えば耐火物試料の高さの少なくとも約１／２以上であることが望ましい。約１／２未満であると，評価するために十分な耐火物試料との接触面の面積を確保することが困難であることに加えて，溶融鉄と大気との接触面からの酸化の影響を受ける部分の割合が大きくなり，目的とする評価を適正に行うことができる領域が狭くなる。 The contact area between the refractory sample and the molten iron is preferably large. Therefore, it is desirable that the depth of the molten iron bath be as deep as possible, for example, at least about 1/2 or more of the height of the refractory sample. If it is less than about 1/2, it is difficult to ensure a sufficient contact area with the refractory sample to be evaluated, and the influence of oxidation from the contact surface between the molten iron and the atmosphere. The ratio of the parts that receive is increased, and the area where the target evaluation can be properly performed is narrowed.
本発明での高周波誘導炉内（溶融鉄浴上部）の雰囲気は，厳密な評価を行うことを目的として誘導炉内を密閉し，その内部雰囲気をＡｒやＮ２に置換して酸素の影響を極力除外した条件にして試験を行うことも可能であるが，大気雰囲気で実施することができる。これは，本発明の評価方法で用いる溶融鉄が高濃度の炭素を含有することからその溶存酸素濃度が著しく低いだけでなく，大気雰囲気下での試験中であっても含有炭素が優先的に酸化されることで，長時間，安定して低い溶存酸素濃度を維持することが可能であるからである。大気雰囲気での評価が可能になることで，大がかりな評価設備が不要となり，また高価なＡｒやＮ２を使用する必要もない。 The atmosphere in the high frequency induction furnace (the upper part of the molten iron bath) in the present invention is sealed for the purpose of strict evaluation, and the inside atmosphere is replaced with Ar or N 2 to influence the influence of oxygen. Although it is possible to conduct the test under conditions excluded as much as possible, it can be performed in an atmospheric environment. This is because the molten iron used in the evaluation method of the present invention contains a high concentration of carbon, so that not only the dissolved oxygen concentration is remarkably low, but also the contained carbon is given priority even during the test in the air atmosphere. This is because, by being oxidized, it is possible to stably maintain a low dissolved oxygen concentration for a long time. Since the evaluation in the air atmosphere is possible, a large-scale evaluation facility is not required, and it is not necessary to use expensive Ar or N 2 .
なお，溶存酸素濃度は，溶融鉄の表面から５０ｍｍ以上深い位置にて酸素センサー等を用いて測定することが望ましい。これは，本発明の評価方法では溶融鉄の炭素含有量が多いので，また高周波誘導炉による溶融鉄浴内では対流ないしは撹拌現象が生じるので，溶融鉄中の溶存酸素濃度は概ね均一となり，しかも溶融鉄内の炭素含有量が多いので大気中の酸素によって溶融鉄内の酸素濃度が高くなることは殆ど無いが，溶融鉄浴の大気と接するごく表層においては溶存酸素濃度が高くなる可能性があるからである。 The dissolved oxygen concentration is preferably measured using an oxygen sensor or the like at a position deeper than 50 mm from the surface of the molten iron. This is because the carbon content of the molten iron is high in the evaluation method of the present invention, and convection or stirring phenomenon occurs in the molten iron bath by the high-frequency induction furnace, so that the dissolved oxygen concentration in the molten iron is almost uniform, Since the carbon content in the molten iron is high, the oxygen concentration in the molten iron is hardly increased by oxygen in the atmosphere, but the dissolved oxygen concentration may increase in the very surface layer in contact with the atmosphere in the molten iron bath. Because there is.
本発明の評価方法では，溶融鉄を排出して任意の温度まで耐火物試料を冷却し，継続して鉄源を投入して溶融し任意の時間維持する，又は溶融鉄浴内に浸漬する場合は，溶融試験終了後に浸漬した耐火物試料を溶融鉄から引き上げ，耐火物試料を冷却した後に，溶融鉄浴内に浸漬する，という工程を複数回行うこともできる。このような繰り返しにより，冷却を含み複数回の鋳造に供される条件，例えば溶鋼鍋用のＳＮプレートについて，耐熱衝撃性等をも評価する，より実鋳造の条件に近付けた評価を行うことが可能となる。 In the evaluation method of the present invention, when the molten iron is discharged and the refractory sample is cooled to an arbitrary temperature, the iron source is continuously charged and melted and maintained for an arbitrary time, or immersed in a molten iron bath The refractory sample immersed after completion of the melting test can be lifted from the molten iron, the refractory sample cooled, and then immersed in the molten iron bath a plurality of times. By repeating such a process, it is possible to evaluate conditions closer to the conditions of actual casting by evaluating the thermal shock resistance etc. of the conditions for cooling and including multiple castings, such as the SN plate for molten steel pans. It becomes possible.
また，繰り返し試験を行う場合は，２回目以降の試験条件として，例えば溶融鉄内に酸化鉄を加えて溶存酸素濃度を１０ｐｐｍ以上の条件に変更する，或いはＳＳ４００等を溶融して溶存酸素濃度を１０ｐｐｍ以上の条件に変更するなど，溶存酸素濃度が異なる鋼種を受鋼する鋳造条件を想定した試験を行うこともできる。さらに，２回目以降の試験条件として，溶融鉄に例えばＣａＯ−Ａｌ２Ｏ３系の合成スラグなどを添加することで，１回目の試験で形成されたＳＮプレート摺動面の脆化層へのスラグ成分の浸潤等，鋼種成分が異なる鋼種を鋳造する条件を想定した評価を行うことが可能となる。 Also, when performing a repeated test, the test conditions for the second and subsequent times, for example, by adding iron oxide in the molten iron and changing the dissolved oxygen concentration to a condition of 10 ppm or more, or by melting SS400 etc. to reduce the dissolved oxygen concentration. It is also possible to perform a test assuming casting conditions for receiving steel types having different dissolved oxygen concentrations, such as changing to a condition of 10 ppm or more. Furthermore, as test conditions for the second and subsequent times, for example, by adding a synthetic slag of CaO—Al 2 O 3 system to molten iron, the SN plate sliding surface formed in the first test can be applied to the brittle layer. It is possible to perform evaluation assuming conditions for casting steel types with different steel type components such as infiltration of slag components.
また，耐火物試料を溶融鉄に曝す時間の一部又は全部において溶融鉄を機械的に撹拌するか，又は浸漬した耐火物試料を回転させることもできる。すなわち，耐火物試料に対する溶融鉄の接触・流動速度を高めることで，耐火物試料に接触する部分の溶融鉄内の炭素含有量や溶存酸素濃度の分布をより均一にすることが可能となると共に，鋳造における溶鋼流速の要素を加えた評価をも行うことができる。 It is also possible to mechanically agitate the molten iron or rotate the immersed refractory sample during part or all of the time of exposing the refractory sample to the molten iron. In other words, by increasing the contact and flow rate of molten iron to the refractory sample, it becomes possible to make the distribution of the carbon content and dissolved oxygen concentration in the molten iron in the part in contact with the refractory sample more uniform. Therefore, it is possible to perform an evaluation by adding an element of the molten steel flow velocity in casting.
［実鋳造での使用結果と損傷メカニズム等の推測］
まず，溶存酸素濃度が異なる複数の鋼の実鋳造に使用された複数のＳＮプレートの使用後品の摺動面の組織を調査し，面荒れ等損傷のメカニズムを推測した。
[Estimation of actual casting results and damage mechanism]
First, the structure of the sliding surface of the used product of multiple SN plates used for actual casting of multiple steels with different dissolved oxygen concentrations was investigated, and the mechanism of damage such as surface roughness was estimated.
表１に示す３種の組成が異なる耐火物（材質Ａ，Ｂ，Ｃ）につき，溶存酸素濃度が異なる複数の鋼の実鋳造に使用された複数のＳＮプレートの使用後品の摺動面の組織を調査して面荒れのメカニズムを推測すると共に，本発明の評価方法及び従来（比較例）の評価方法を行って，比較した。 For the refractory materials (materials A, B, C) with three different compositions shown in Table 1, the sliding surfaces of the used products of the plurality of SN plates used for actual casting of a plurality of steels having different dissolved oxygen concentrations The structure was investigated and the roughening mechanism was estimated, and the evaluation method of the present invention and the conventional (comparative example) evaluation method were performed for comparison.
材質Ａは，化学成分としてＡｌ２Ｏ３を７６質量％，ＺｒＯ２を９質量％，ＳｉＯ２を７質量％，Ｃを５．５質量％含有し，金属Ａｌは含まない。なお，材質Ａは１０００℃以上の非酸化雰囲気で焼成したものである。
材質Ｂは，化学成分としてＡｌ２Ｏ３を７９質量％，ＺｒＯ２を９．５質量％，ＳｉＯ２を４．０質量％であり，Ｃを４．５質量％含有し，金属Ａｌは含まない。この材質Ｂは，材質Ａの損耗改善を目的として，Ａｌ２Ｏ３粒子を還元するＣ成分を減量すると共に，組織の緻密化を行い，耐火物組織中の酸化，還元反応により生じるＡｌガスやＡｌ２Ｏガス，ＣＯガスの移動を抑制することで，脆化層形成の軽減を図った材質である。
材質Ｃは，化学成分としてＡｌ２Ｏ３を９２質量％，ＳｉＯ２を２質量％，金属Ａｌを５質量％，Ｃを３．５質量％含有している。この材質Ｃは，材質Ａの損耗改善を目的として，Ａｌ２Ｏ３粒子を還元するＣ成分を減量すると共に，熱間での組織の緻密化を狙って金属Ａｌを含有させた材質，すなわち炭素成分の減量及び熱間での組織の緻密化により，脆化層形成の軽減を図った材質である。なお，材質Ｃは１０００℃未満の非酸化雰囲気で焼成したものである。
これら材質Ａ，Ｂ，Ｃの耐火物の詳細は表１に示すとおりで、以下、その評価結果を説明する。
Material A is, Al 2 O 3 of 76 wt% as chemical components, the ZrO 2 9 wt%, a SiO 2 7 mass%, C and containing 5.5% by weight, metal Al is not included. The material A was fired in a non-oxidizing atmosphere at 1000 ° C. or higher.
Material B is a for Al 2 O 3 Chemical composition 79 wt%, a ZrO 2 9.5% by mass, a the SiO 2 4.0 wt%, containing C 4.5 mass%, metal Al is included Absent. For the purpose of improving the wear of the material A, this material B reduces the C component that reduces Al 2 O 3 particles, densifies the structure, and produces Al gas generated by oxidation and reduction reactions in the refractory structure. It is a material that reduces embrittlement layer formation by suppressing the movement of Al 2 O gas and CO gas.
The material C contains 92% by mass of Al 2 O 3 , 2 % by mass of SiO 2 , 5% by mass of metal Al, and 3.5% by mass of C as chemical components. For the purpose of improving the wear of the material A, this material C reduces the C component that reduces the Al 2 O 3 particles, and is a material containing metallic Al for the purpose of densifying the structure in the hot state, ie, carbon. It is a material that reduces the formation of embrittlement layers by reducing the amount of components and densifying the structure during hot processing. The material C was fired in a non-oxidizing atmosphere of less than 1000 ° C.
Details of the refractories of these materials A, B, and C are as shown in Table 1, and the evaluation results will be described below.
まず，これら材質からなるＳＮプレートを実鋳造に供した結果を調査した。
＜材質Ａの実鋳造での使用結果の例＞
某製鉄所タンディッシュ用のＳＮプレートとして，鋼中の溶存酸素濃度が１０ｐｐｍ未満と推測されるＡｌ−Ｋ鋼を主に鋳造した後の組織を調査した。
First, the results of subjecting SN plates made of these materials to actual casting were investigated.
<Example of results of actual casting of material A>
As an SN plate for Sakai Works tundish, the structure after casting mainly Al-K steel whose dissolved oxygen concentration in steel was estimated to be less than 10 ppm was investigated.
この外観写真を図１に，その面荒れ部のミクロ組織を図２に示す。これらから，内孔付近のエッジ部の摺動面たる稼働面では組織が白く酸化し，組織が脆弱化している（この稼働面では組織が白く酸化し，組織が脆弱化している部分を本発明では「面荒れ部」という。）。 その稼動面では表面から約５００μｍの地金の付着，浸潤層があり，さらにその内部では深さ約１０００μｍを超える脆化層が観られる。その脆化層では，炭素の消失の他にマトリックスのＡｌ２Ｏ３微粒子が消失しており，空隙が多く観られる。 The appearance photograph is shown in FIG. 1, and the microstructure of the rough surface is shown in FIG. From these, on the working surface which is the sliding surface of the edge portion near the inner hole, the structure is oxidized white and the structure is weakened (in this working surface, the structure is oxidized white and the structure is weakened). Then, it is called “Rough surface”.) On the working surface, there is an infiltrated / infiltrated layer of about 500 μm from the surface, and an embrittled layer exceeding a depth of about 1000 μm is observed inside. In the embrittlement layer, in addition to the disappearance of carbon, the Al 2 O 3 fine particles of the matrix disappear, and many voids are observed.
＜材質Ｃの実鋳造での使用結果の例＞
鋼中の溶存酸素濃度が１０ｐｐｍ未満と推測されるＡｌ−Ｓｉ−Ｋ鋼を主に鋳造した後の組織を調査した。図３に摺動面のミクロ組織を示す。
<Example of results of actual casting of material C>
The structure after the main casting of Al-Si-K steel in which the dissolved oxygen concentration in the steel was estimated to be less than 10 ppm was investigated. FIG. 3 shows the microstructure of the sliding surface.
稼動面では約４００μｍ以下程度の厚い地金の付着が認められ，その内部では約５００μｍ以下程度の深さの脆化層が観察される。脆化層では炭素の消失だけでなく，Ａｌ２Ｏ３微粒子が消失しており，マトリックスでは空隙が多く目立つ。なお，鋼種は異なるものの溶存酸素濃度が１０ｐｐｍ未満と同程度の場合，稼動面では同様のマトリックスの脆弱化組織等が観られる。 Adhesion of thick metal of about 400 μm or less is recognized on the operation surface, and an embrittled layer having a depth of about 500 μm or less is observed inside. In the embrittlement layer, not only the disappearance of carbon but also Al 2 O 3 fine particles have disappeared, and many voids are conspicuous in the matrix. When the dissolved oxygen concentration is almost the same as less than 10 ppm, although the steel types are different, the same matrix weakening structure is observed in terms of operation.
次に，材質Ｃを鋼中の溶存酸素濃度が２０ｐｐｍ以上と推測されるＳｉ−Ｋ鋼を主に鋳造した後の組織を調査した。図４に摺動面である稼働面のミクロ組織を示す。 Next, the structure of the material C after the main casting of Si-K steel in which the dissolved oxygen concentration in the steel is estimated to be 20 ppm or more was investigated. FIG. 4 shows the microstructure of the working surface that is the sliding surface.
稼動面では厚さ約１００〜２００μｍ程度の変質層が観察される。この変質層には少量の粒状のＦｅが存在するが，Ａｌ２Ｏ３を主成分とした緻密な組織を形成している。この変質層内部の組織には，地金やスラグの浸潤は観察されず，緻密で健全な状態を保持していることから，この変質層が保護層として機能していると考えられる。 A deteriorated layer having a thickness of about 100 to 200 μm is observed on the operating surface. This altered layer contains a small amount of granular Fe, but forms a dense structure mainly composed of Al 2 O 3 . In the structure inside this altered layer, infiltration of metal and slag is not observed, and it maintains a dense and healthy state. Therefore, this altered layer is considered to function as a protective layer.
このように，低炭Ａｌ−Ｋ鋼やＡｌ−Ｋ鋼，炭素鋼などの鋼中の溶存酸素濃度が１０ｐｐｍ未満と考えられる条件で長時間鋳造されたＳＮプレートの稼動面は，地金付着や地金およびスラグ成分の浸潤の他，金属Ａｌを含まない材質／多量に含む材質とも共通して稼動面内部で炭素とＡｌ２Ｏ３微粒が消失した脆化層を形成していることを本発明者らは知見した。 Thus, the working surface of the SN plate cast for a long time under the condition that the dissolved oxygen concentration in steels such as low-carbon Al-K steel, Al-K steel, and carbon steel is considered to be less than 10 ppm is In addition to the infiltration of metal and slag components, it is common for materials that do not contain metallic Al / materials that contain a large amount to form a brittle layer in which carbon and Al 2 O 3 fine particles have disappeared inside the working surface. The inventors have found out.
低い溶存酸素濃度の鋼種を長時間受鋼するＳＮプレート用耐火物の稼動面付近は，高温条件で還元雰囲気に曝されていると考えられる。この組織ではＡｌ２Ｏ３微粒が消失していることから，Ａｌ２Ｏ３が還元されＡｌ（ｇ）やＡｌＯ（ｇ）等の気相として消失していると推測される。未使用の状態ではマトリックス中にはＡｌ２Ｏ３微粒と炭素が共存していることから，Ａｌ２Ｏ３微粒が耐火物中の炭素により還元され，炭素ととともに消失していることが推測される。Ａｌ２Ｏ３粒の消失は，比表面積が大きい微粒で多く，比較的比表面積が小さい中間域の粒度のものは残存している。このことから，Ａｌ２Ｏ３粒は炭素や還元性の雰囲気と接する比表面積の大きい微粒部から還元され，気相として消失したと考えられる。 It is considered that the vicinity of the working surface of the SN plate refractory that receives steel for a low dissolved oxygen concentration for a long time is exposed to a reducing atmosphere under high temperature conditions. Since Al 2 O 3 fine particles disappear in this structure, it is presumed that Al 2 O 3 is reduced and disappears as a gas phase such as Al (g) or AlO (g). In the unused state, Al 2 O 3 fine particles and carbon coexist in the matrix, so it is estimated that Al 2 O 3 fine particles are reduced by carbon in the refractory and disappear together with carbon. The The disappearance of Al 2 O 3 grains is mostly in the form of fine grains having a large specific surface area, and those having a particle size in the intermediate range having a relatively small specific surface area remain. From this, it is considered that the Al 2 O 3 grains were reduced from the fine particles having a large specific surface area in contact with the carbon or reducing atmosphere and disappeared as a gas phase.
これに対し，金属Ａｌを含有するＳＮプレート用の材質でもＳｉ−Ｋ鋼等の溶存酸素濃度が高い鋼の鋳造に使用されたＳＮプレートの稼動面では，緻密なＡｌ２Ｏ３層を形成しており，脆化層はなく，緻密層内部も健全な組織を保持している。これはＳＮプレート内部から耐火物稼動面に移動したＡｌと溶鋼中の酸素が反応し，界面付近でＡｌ２Ｏ３層を形成するためと推測される。 On the other hand, a dense Al 2 O 3 layer is formed on the working surface of the SN plate used for casting of steel with high dissolved oxygen concentration, such as Si-K steel, even for SN plate material containing metal Al. There is no embrittlement layer and the inside of the dense layer maintains a healthy structure. This is presumably because Al moved from the SN plate to the refractory working surface reacts with oxygen in the molten steel to form an Al 2 O 3 layer near the interface.
前述の非特許文献２は，溶存酸素濃度が低い（鋼中の溶存酸素濃度が数ｐｐｍ程度）と推測される極低炭素鋼で使用されたＳＮプレートを調査した報告であって，稼動面の酸化層では微粒部が消失し，空隙を形成していることが報告されている。 The non-patent document 2 described above is a report investigating an SN plate used in an extremely low carbon steel that is estimated to have a low dissolved oxygen concentration (the dissolved oxygen concentration in the steel is about several ppm). It has been reported that fine particles disappear and voids are formed in the oxide layer.
一方，前述の非特許文献３では，極低炭Ａｌ−Ｋ鋼（Ｃ；２０ｐｐｍ）及び低炭Ａｌ−Ｋ鋼（Ｃ；４１０ｐｐｍ）との反応試験の後に試料の稼動面で観察された脆化層は，試料中のＡｌ２Ｏ３粒が試料中の炭素により還元され，Ａｌ２Ｏ３が炭素とともに気相の形で溶鋼中へ溶出したものと考察されている。 On the other hand, in the above-mentioned Non-Patent Document 3, embrittlement observed on the working surface of the sample after a reaction test with extremely low-carbon Al-K steel (C; 20 ppm) and low-carbon Al-K steel (C; 410 ppm). The layer is considered that Al 2 O 3 grains in the sample are reduced by carbon in the sample, and Al 2 O 3 is eluted into the molten steel together with carbon in a gas phase.
また，極低炭Ｓｉ−Ｋ鋼と反応試験を行った試料の脆化層は５０μｍ程度と薄く，また界面で連続した緻密なＡｌ２Ｏ３層を形成している。これは，試験に用いた極低炭Ｓｉ−Ｋ鋼中の酸素濃度が数十ｐｐｍ程度と高く，試料内部で還元され気相となり界面で溶鋼中に溶出したＡｌが溶鋼中の酸素により酸化され，表層で連続したＡｌ２Ｏ３緻密層を形成するものと考察されている。 In addition, the embrittlement layer of the sample subjected to the reaction test with the ultra low carbon Si—K steel is as thin as about 50 μm, and a dense Al 2 O 3 layer continuous at the interface is formed. This is because the oxygen concentration in the ultra-low-carbon Si-K steel used for the test is as high as several tens of ppm, and Al that is reduced inside the sample and becomes a gas phase and elutes into the molten steel at the interface is oxidized by the oxygen in the molten steel. , It is considered to form a continuous Al 2 O 3 dense layer in the surface layer.
非特許文献３で用いた試料は，アルミナと炭素から構成されており金属Ａｌを含まないことから，実際にこの材質系を実鋳造での極低炭Ｓｉ−Ｋ鋼に供しても，摺動面ではＡｌ２Ｏ３緻密層を形成せず，むしろ溶存酸素濃度が低いＡｌ−Ｋや炭素鋼と比較して，摺動面は酸化に起因した損耗，面荒れが大きくなると推察される。 Since the sample used in Non-Patent Document 3 is composed of alumina and carbon and does not contain metal Al, even if this material system is actually used for ultra-low-carbon Si-K steel in actual casting, it will slide. It is presumed that the Al 2 O 3 dense layer is not formed on the surface, but rather the wear and surface roughness due to oxidation are increased on the sliding surface as compared with Al-K and carbon steel having a low dissolved oxygen concentration.
この非特許文献３の実験結果と実鋳造との違いは，非特許文献３の実験が縦型管状炉で，３００ｇと少量の鋼と，６ｍｍ×６ｍｍ×６０ｍｍと小形状の試料とで実施されており，小型の閉鎖系かつ静的な条件で実施されていることから，耐火物中のＡｌ２Ｏ３微粒が還元され生成した極微量のＡｌであっても，界面で溶鋼流により移動することなく，界面に留まり溶鋼中の酸素と反応しＡｌ２Ｏ３層を形成し易い条件であるために生じたものと推測される。 The difference between the experimental results of Non-Patent Document 3 and actual casting is that the experiment of Non-Patent Document 3 is carried out in a vertical tubular furnace with 300 g and a small amount of steel, and a small sample of 6 mm × 6 mm × 60 mm. Because it is carried out under a small closed system and static conditions, even a very small amount of Al produced by reduction of Al 2 O 3 particles in the refractory is moved by the molten steel flow at the interface. It is presumed that this occurred because the conditions remained at the interface and easily reacted with oxygen in the molten steel to form an Al 2 O 3 layer.
これに対して，前述の非特許文献１では溶鋼量も数〜数十ｋｇ程度あり，誘導加熱により生じる溶鋼の対流も実鋳造を評価するに十分な流動速度を有していると考えられることから，より実鋳造に近い条件といえる。 On the other hand, in the above-mentioned Non-Patent Document 1, the amount of molten steel is about several to several tens of kg, and it is considered that the convection of the molten steel caused by induction heating has a flow rate sufficient to evaluate actual casting. Therefore, it can be said that the conditions are closer to actual casting.
このような条件で耐火物の稼動面表層で緻密なＡｌ２Ｏ３層を形成するには，耐火物中から多量のＡｌの気相が発生し，稼動面に供給される必要がある。このため非特許文献１で報告されている試料は，金属Ａｌ無添加及び３％添加では稼動面にＡｌ２Ｏ３緻密層を形成しておらず，Ａｌ２Ｏ３緻密層を形成するには，金属Ａｌの添加量が６質量％以上と多量に金属Ａｌが必要であることが示されている。これらは，経験的に実鋳造でＳＮプレートの稼動面表層に緻密層を形成する金属Ａｌ量とよく一致している。 In order to form a dense Al 2 O 3 layer on the surface of the working surface of the refractory under such conditions, a large amount of Al gas phase must be generated from the refractory and supplied to the working surface. Therefore samples reported in Non-Patent Document 1 does not form a Al 2 O 3 dense layer in the operation surface in the metal Al no additives and 3% added to an Al 2 O 3 dense layer Therefore, it is shown that a large amount of metal Al is necessary with the addition amount of metal Al being 6 mass% or more. These empirically match well with the amount of metal Al that forms a dense layer on the working surface of the SN plate by actual casting.
以上から，Ａｌ−Ｋや炭素鋼等，鋼中の溶存酸素濃度が低い鋼種を長時間受鋼する場合，ＳＮプレートの摺動面では，ＳＮプレート用耐火物中の炭素の溶鋼への溶出は生じるが，鋼中の溶存酸素濃度が数ｐｐｍ程度と極微量であることから，鋼中の溶存酸素による酸化の影響は小さいと判断される。よって，稼動面付近のＳＮプレート用耐火物内部では，炭素を含むことから高温下では還元雰囲気となり，炭素がＡｌ２Ｏ３により酸化されＣＯ（ｇ）となり，一方のＡｌ２Ｏ３は炭素により還元され，Ａｌ（ｇ），ＡｌＯ（ｇ）となり，ＣＯ（ｇ）やＡｌ（ｇ），ＡｌＯ（ｇ）が溶鋼と接する界面へ移動し，溶鋼中に溶出することで，摺動面のマトリックス中の炭素やＡｌ２Ｏ３微粒が消失し，空隙を生じることで組織が脆化し，さらに地金やスラグが付着することで摺動面の損傷，面荒れが進行すると考えられる。 From the above, when steel grades with low dissolved oxygen concentration in steel such as Al-K and carbon steel are received for a long time, the elution of carbon in the refractory for SN plate to the molten steel will occur on the sliding surface of SN plate. However, since the dissolved oxygen concentration in the steel is very small, about several ppm, it is judged that the effect of oxidation by the dissolved oxygen in the steel is small. Therefore, inside the SN plate refractory near the working surface, since it contains carbon, it becomes a reducing atmosphere at a high temperature, and the carbon is oxidized by Al 2 O 3 to CO (g), while one Al 2 O 3 is made by carbon. Reduced to Al (g), AlO (g), and CO (g), Al (g), AlO (g) move to the interface in contact with the molten steel and elute into the molten steel. It is considered that the carbon and Al 2 O 3 fine particles in the inside disappear, the voids are formed, the structure becomes brittle, and the metal and slag adhere to the sliding surface and the surface becomes rough.
特許文献１で示された評価条件は，鋼中の溶存酸素濃度を１０〜５００ｐｐｍに調整されており，鋼中の溶存酸素による耐火物中の炭素等の成分の酸化の影響を評価することには適しているが，Ａｌ−Ｋや炭素鋼等，鋼中の溶存酸素濃度が低い鋼種を鋳造することで生じる耐火物組織の脆化を評価することには，必ずしも適切ではない。 The evaluation condition shown in Patent Document 1 is that the dissolved oxygen concentration in the steel is adjusted to 10 to 500 ppm, and the effect of oxidation of components such as carbon in the refractory by the dissolved oxygen in the steel is evaluated. Is suitable, but is not necessarily suitable for evaluating embrittlement of a refractory structure caused by casting a steel type having a low dissolved oxygen concentration in the steel, such as Al-K or carbon steel.
これらのことから本発明者らは，Ａｌ−Ｋや炭素鋼等，鋼中の溶存酸素濃度が低い鋼種を受鋼する場合のＳＮプレート用耐火物の摺動面たる稼働面の組織脆化を評価するには，鋼中の溶存酸素の影響を受けない条件で試験をする，すなわち酸素を殆ど含まない溶鋼や溶銑を試験に用いることが必要であると考えた。 From these facts, the present inventors have made the structure embrittlement of the working surface, which is the sliding surface of the refractory for SN plate, when receiving a steel type having a low dissolved oxygen concentration in the steel, such as Al-K and carbon steel. For the evaluation, it was considered necessary to test under conditions that are not affected by dissolved oxygen in the steel, that is, to use molten steel or hot metal containing almost no oxygen.
［本発明の評価方法の例］
材質Ａの本発明の評価方法，及び特許文献１に示された従来の評価方法による試験後の脆化層の厚みを各々１００とする指数で，材質Ｂ，材質Ｃの比較を行った
[Example of evaluation method of the present invention]
The materials B and C were compared with an index with the thickness of the embrittled layer after the test according to the evaluation method of the present invention of the material A and the conventional evaluation method shown in Patent Document 1 as 100 respectively.
各耐火物試料は，表１の化学成分となるように所定の原料を混合し，混練，成形後に所定の温度で焼成し，これらの成形・焼成後の試料から高周波誘導炉内張り用の試料形状（高さ約６５ｍｍ×壁肉厚相当長さ約４０ｍｍ×幅約５０ｍｍ）に切り出して得た。 Each refractory sample is mixed with the specified raw materials so as to have the chemical components shown in Table 1, kneaded and fired at a predetermined temperature after molding. From these molded and fired samples, a sample shape for high-frequency induction furnace lining is obtained. It was obtained by cutting into a height of about 65 mm × a wall thickness equivalent length of about 40 mm × a width of about 50 mm.
本発明の評価方法では，高周波誘導炉内側に前記の耐火物試料を設置し，その内部空間に銑鉄を入れ，高周波により直接，銑鉄を加熱溶融し，耐火物試料と溶銑を接触させて試験を行った。溶存酸素濃度は１時間毎に測定し，試験中の溶存酸素濃度が１０ｐｐｍ未満であることを確認した。 In the evaluation method of the present invention, the above-mentioned refractory sample is placed inside the high-frequency induction furnace, pig iron is placed in the internal space, the pig iron is heated and melted directly by high frequency, and the test is conducted by bringing the refractory sample and hot metal into contact with each other. went. The dissolved oxygen concentration was measured every hour to confirm that the dissolved oxygen concentration during the test was less than 10 ppm.
比較例の評価方法は，従来の評価方法の一例である特許文献１に示された評価方法とした。この比較例の方法では，高周波誘導炉内に耐火物試料を設置し，内部の空間に鉄源を入れ，高周波により直接鉄を加熱溶融し，耐火物試料と溶鉄を接触させて試験を行った。３０分毎に溶存酸素濃度を測定し，炭素源（黒鉛）を添加しながら溶存酸素濃度が２０〜３０ｐｐｍの範囲になるように調整した。 The evaluation method of the comparative example was the evaluation method shown in Patent Document 1 which is an example of a conventional evaluation method. In the method of this comparative example, a refractory sample was installed in a high-frequency induction furnace, an iron source was placed in the internal space, iron was heated and melted directly by high frequency, and the test was conducted by bringing the refractory sample and molten iron into contact with each other. . The dissolved oxygen concentration was measured every 30 minutes, and the dissolved oxygen concentration was adjusted to a range of 20 to 30 ppm while adding a carbon source (graphite).
本発明の評価方法，比較例の評価方法共に試験は大気雰囲気下で行い，溶鉄の温度条件を１６００℃±２０℃の範囲に調整し，３時間連続して試験を行った。試験終了後は，高周波誘導炉を傾転させて溶銑を排出し，炉内を冷却した後，内張りした耐火物試料を解体した。解体後の耐火物試料は，適宜評価用の試料形状に切り出し，その断面のミクロ組織観察を行い，溶銑と接する稼動面の脆化層の厚さ等を測定し，評価した。 Both the evaluation method of the present invention and the evaluation method of the comparative example were performed in an air atmosphere, and the temperature condition of the molten iron was adjusted to a range of 1600 ° C. ± 20 ° C., and the test was continuously performed for 3 hours. After the test was completed, the induction furnace was tilted to discharge the hot metal, the furnace was cooled, and then the refractory sample lined was disassembled. After dismantling, the refractory samples were appropriately cut into sample shapes for evaluation, the microstructure of the cross section was observed, and the thickness of the brittle layer on the working surface in contact with the hot metal was measured and evaluated.
＜材質Ａについて＞
材質Ａの，本発明の評価方法によるミクロ組織を図７の上段に，その稼働面の拡大を図７の下段に示す。
<About material A>
The microstructure of the material A according to the evaluation method of the present invention is shown in the upper part of FIG. 7, and the enlarged operation surface is shown in the lower part of FIG.
本発明の評価方法及び従来の評価方法共に，稼動面ではＡｌ２Ｏ３粒子とＣが消失し，空隙が目立つ脆化層を形成し，実操業での使用後品とよく類似した組織となっている。これは，同じメカニズムで稼動面の脆化層を形成したことを示している。 In both the evaluation method of the present invention and the conventional evaluation method, Al 2 O 3 particles and C disappear on the operation surface, and an embrittlement layer with conspicuous voids is formed, resulting in a structure that is very similar to the product after use in actual operation. ing. This indicates that a brittle layer on the working surface was formed by the same mechanism.
＜材質Ｂについて＞
本発明による評価の結果，材質Ａを１００とする指数に対し材質Ｂは６０となって，脆化層の厚みが大幅に軽減された。これに対し比較例の評価方法では材質Ａを１００とする指数に対し材質Ｂは８０となって，やや変質層が軽減される程度の，本発明の評価方法での結果よりも軽微な改善を示した。
<About material B>
As a result of the evaluation according to the present invention, the material B was 60 with respect to the index where the material A was 100, and the thickness of the brittle layer was greatly reduced. On the other hand, in the evaluation method of the comparative example, the material B is 80 with respect to the index where the material A is 100, and the slightly deteriorated layer is slightly reduced compared to the result of the evaluation method of the present invention. Indicated.
材質Ｂを某製鉄所での溶存酸素濃度が１０ｐｐｍ未満と推測される極低炭素鋼の実鋳造操業に供したところ，材質Ｂは材質Ａと比較して摺動面の損傷が大幅に改善され，良好な耐用性を得ることができた。 When material B was subjected to an actual casting operation of ultra-low carbon steel, which is estimated to have a dissolved oxygen concentration of less than 10 ppm at Sakai Steel Works, the damage of sliding surface of material B is significantly improved compared to material A. , Good durability was obtained.
＜材質Ｃについて＞
本発明による評価の結果，材質Ａを１００とする指数に対し材質Ｃは８０となって，２割程度の脆化層の厚みがわずかに軽減する結果となった。熱間での組織を緻密化するには金属Ａｌの含有量が相対的に少なかったためと推測される。これに対し比較例の評価方法では材質Ａを１００とする指数に対し材質Ｃは１０となって，変質層が大幅に軽減された。
<About material C>
As a result of the evaluation according to the present invention, the material C was 80 with respect to the index where the material A was 100, and the thickness of the embrittled layer of about 20% was slightly reduced. It is presumed that the metal Al content was relatively small for densifying the hot structure. On the other hand, in the evaluation method of the comparative example, the material C was 10 with respect to the index where the material A was 100, and the deteriorated layer was greatly reduced.
材質Ｃを某製鉄所での溶存酸素濃度が１０ｐｐｍ未満と推測される極低炭素鋼の実鋳造操業に供したところ，材質Ｃは材質Ａとほぼ同等であり，摺動面の損傷を改善することができなかった。すなわち，比較例の評価方法では良好な結果を得たにもかかわらず実鋳造の使用においては改善することができなかった。本発明の評価方法が実鋳造の使用結果をより高精度で再現していることがわかる。 When material C was subjected to the actual casting operation of ultra-low carbon steel, which is estimated to have a dissolved oxygen concentration of less than 10 ppm at Sakai Steel Works, material C is almost the same as material A and improves sliding surface damage. I couldn't. In other words, the evaluation method of the comparative example could not be improved in the use of actual casting, although good results were obtained. It can be seen that the evaluation method of the present invention reproduces the actual casting use result with higher accuracy.
Claims (4)
前記溶融鉄の溶存酸素濃度が１０ｐｐｍ未満であることを特徴とする耐火物の評価方法。 Regarding the refractory containing carbon used in the sliding part for continuous casting of steel,
The method for evaluating a refractory, wherein the dissolved iron has a dissolved oxygen concentration of less than 10 ppm.
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| CN110726662A (en) * | 2019-10-22 | 2020-01-24 | 方大炭素新材料科技股份有限公司 | Experimental device for evaluating molten slag iron and erosion resistance of refractory material |
| CN112611667A (en) * | 2020-11-03 | 2021-04-06 | 北京科技大学 | Physical simulation test device for steel ladle slag line resistant material erosion corrosion and use method |
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| CN112611667A (en) * | 2020-11-03 | 2021-04-06 | 北京科技大学 | Physical simulation test device for steel ladle slag line resistant material erosion corrosion and use method |
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