JP2012020316A - Continuous casting method of wear resisting steel and wear resisting steel - Google Patents
Continuous casting method of wear resisting steel and wear resisting steel Download PDFInfo
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本発明は、産業機械や運搬機器などに使用される耐摩耗鋼の連続鋳造方法及びこの連続鋳造方法によって鋳造された鋳片から製造される耐摩耗鋼に関する。 The present invention relates to a continuous casting method of wear-resistant steel used for industrial machines, transportation equipment, and the like, and to a wear-resistant steel manufactured from a slab cast by this continuous casting method.
土、砂などによる摩耗を受ける部材には、長寿命化を目的として耐摩耗性に優れる鋼材つまり耐摩耗鋼が使用される。鋼材の耐摩耗性は、鋼材を高硬度化することによって向上することが知られており、優れた耐摩耗性を要求される耐摩耗鋼としては、Ｃｒ、Ｍｏなどの合金元素を大量に添加した鋼材に焼入れなどの熱処理を施し、高硬度化した鋼材が使用されてきた。 For a member subjected to wear due to soil, sand, or the like, a steel material having excellent wear resistance, that is, wear-resistant steel is used for the purpose of extending the life. It is known that the wear resistance of steel materials is improved by increasing the hardness of the steel materials. For wear-resistant steels that require excellent wear resistance, alloy elements such as Cr and Mo are added in large quantities. Steel materials that have been hardened by heat treatment such as quenching have been used.
例えば、特許文献１には、Ｃ：０．１０〜０．１９質量％を含有し、Ｓｉ、Ｍｎを適正量含有し、残部をＦｅ及び不可避的不純物とし、Ｃeqを０．３５〜０．４４とする鋼を熱間圧延後、直接焼入れし、または９００〜９５０℃に再加熱した後に焼入れし、引き続いて３００〜５００℃で焼戻しを行い、表面硬さを３００ＨＶ（ビッカース硬さ）以上とする耐摩耗鋼の製造方法が提案されている。 For example, Patent Document 1 contains C: 0.10 to 0.19 mass%, contains appropriate amounts of Si and Mn, the balance is Fe and inevitable impurities, and Ceq is 0.35 to 0.44. The steel to be subjected to hot rolling is directly quenched or reheated to 900 to 950 ° C. and then quenched, and subsequently tempered at 300 to 500 ° C. to obtain a surface hardness of 300 HV (Vickers hardness) or higher. A method for producing wear-resistant steel has been proposed.
特許文献２には、Ｃ：０．１０〜０．２０質量％を含有し、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ｎ、Ａｌ、Ｏを適正量に調整し、残部をＦｅ及び不可避的不純物とし、或いは更にＣｕ、Ｎｉ、Ｃｒ、Ｍｏ、Ｂのうちの１種以上を含有する鋼を熱間圧延後、直接焼入れし、または放冷した後に再加熱して焼入れし、３４０ＨＢ（ブリネル硬さ）以上の硬さを有する耐摩耗鋼の製造方法が提案されている。 Patent Document 2 contains C: 0.10 to 0.20 mass%, Si, Mn, P, S, N, Al, O are adjusted to appropriate amounts, and the balance is Fe and inevitable impurities, Alternatively, steel containing one or more of Cu, Ni, Cr, Mo, B is hot-rolled, directly quenched, or allowed to cool and then reheated and quenched, and 340HB (Brinell hardness) or more A method for producing a wear-resistant steel having a hardness of 10 mm has been proposed.
特許文献３には、Ｃ：０．０７〜０．１７質量％を含有し、Ｓｉ、Ｍｎ、Ｖ、Ｂ、Ａｌを適正量に調整し、残部をＦｅ及び不可避的不純物とし、或いは更にＣｕ、Ｎｉ、Ｃｒ、Ｍｏのうちの１種以上を含有する鋼を熱間圧延後、直接焼入れし、または一旦空冷した後に再加熱して焼入れし、表面硬さが３２１ＨＢ（ブリネル硬さ）以上で且つ曲げ加工性に優れた耐摩耗鋼の製造方法が提案されている。 Patent Document 3 contains C: 0.07 to 0.17% by mass, Si, Mn, V, B, and Al are adjusted to appropriate amounts, and the balance is Fe and inevitable impurities, or further Cu, A steel containing one or more of Ni, Cr and Mo is hot-rolled, directly quenched, or once air-cooled and then reheated and quenched, and the surface hardness is 321 HB (Brinell hardness) or more A method for producing a wear-resistant steel having excellent bending workability has been proposed.
特許文献１〜３に記載される技術は、合金元素を多量に添加し、固溶硬化、変態硬化、析出硬化などを活用して高硬度化することで、耐摩耗特性を向上させている。しかしながら、合金元素を多量に添加し、固溶硬化、変態硬化、析出硬化などを活用して鋼のマトリックスを高硬度化した場合には、溶接性及び加工性が著しく低下する。 The techniques described in Patent Documents 1 to 3 improve wear resistance characteristics by adding a large amount of alloy elements and increasing the hardness by utilizing solid solution hardening, transformation hardening, precipitation hardening, and the like. However, when a large amount of alloy elements are added and the steel matrix is hardened by utilizing solid solution hardening, transformation hardening, precipitation hardening, etc., the weldability and workability are significantly reduced.
これに対して、特許文献４には、Ｃ：０．１０〜０．４５質量％、Ｔｉ：０．１０〜１．０質量％を含有し、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ｎ、Ａｌを適正量に調整し、残部をＦｅ及び不可避的不純物とし、或いは更にＣｕ、Ｎｉ、Ｃｒ、Ｍｏ、Ｂのうちの１種以上を含有し、０．５μｍ以上の大きさを有するＴｉＣを主体とする析出物を１ｍｍ2あたり４００個以上含み、連続鋳造で鋳造された耐摩耗鋼が提案されている。 On the other hand, Patent Document 4 contains C: 0.10 to 0.45 mass%, Ti: 0.10 to 1.0 mass%, Si, Mn, P, S, N, and Al. It is adjusted to an appropriate amount, and the balance is Fe and inevitable impurities, or further contains at least one of Cu, Ni, Cr, Mo, B, and mainly contains TiC having a size of 0.5 μm or more. A wear-resistant steel that contains 400 or more precipitates per mm 2 and is cast by continuous casting has been proposed.
特許文献４においては、高い硬度を有するＴｉＣを主体とする粗大な析出物を凝固時に生成させ、この析出物によって耐摩耗性を向上させるので、鋼のマトリックス自体は高硬度化させる必要はなく、曲げ加工性及び溶接性に優れた耐摩耗鋼を製造することが可能となる。 In Patent Document 4, a coarse precipitate mainly composed of TiC having a high hardness is generated at the time of solidification, and the wear resistance is improved by this precipitate. Therefore, it is not necessary to increase the hardness of the steel matrix itself, It becomes possible to produce a wear-resistant steel excellent in bending workability and weldability.
ところで、高濃度のＴｉを含有する鋼の連続鋳造では、炭素鋼に比較して縦割れ、ノロカミなどの鋳片表面欠陥が発生しやすいことが知られている。そこで、このようなＴｉ含有鋼の表面欠陥を低減するべく、特許文献５には、０．０５〜１．５質量％のＴｉを含有する溶鋼を連続鋳造するにあたり、鋳型振動ストロークＳを２〜５ｍｍ、鋳型振動数ｆを１２０サイクル／ｍｉｎ以上とし、且つ、ｆ×Ｓ≦６００を満たす条件で、０．８〜１．２ｍ／ｍｉｎの鋳造速度の範囲で鋳造する技術が提案されている。 By the way, it is known that continuous casting of steel containing a high concentration of Ti tends to cause slab surface defects such as vertical cracks and blades as compared with carbon steel. Therefore, in order to reduce the surface defects of such Ti-containing steel, Patent Document 5 discloses that the mold vibration stroke S is 2 to 2 when continuously casting a molten steel containing 0.05 to 1.5 mass% Ti. A technique has been proposed in which casting is performed within a casting speed range of 0.8 to 1.2 m / min under the conditions of 5 mm, a mold frequency f of 120 cycles / min or more, and satisfying f × S ≦ 600.
特許文献５によれば、鋳型振動条件を低ストローク且つ高振動数とするので、炭素鋼の鋳造に一般的に使用されるモールドパウダーを使用しても、オシレーションマークを浅くすると同時に、ノロカミなどの表面欠陥を防止することができるとしている。 According to Patent Document 5, since the mold vibration condition is a low stroke and a high frequency, even if a mold powder generally used for casting of carbon steel is used, the oscillation mark is made shallow and at the same time, It is said that surface defects can be prevented.
また、特許文献６には、Ｔｉ含有鋼を対象としていないが、Ｔｉ含有鋼と同様に表面欠陥の発生しやすいステンレス鋼の連続鋳造において、高粘性のモールドパウダーを使用することによる、鋳型と凝固シェルとの潤滑不良を防止するために、高粘性のモールドパウダーを鋳型内に添加すると同時に、鋳型の溶鋼湯面下における鋳型と凝固シェルとの間に、植物油、脂肪酸エステル類、鉱物油、これらの混合物などの液体潤滑剤を流入させて鋳造する技術が提案されている。 In addition, Patent Document 6 does not target Ti-containing steels, but, as with Ti-containing steels, in continuous casting of stainless steel, where surface defects are likely to occur, by using a highly viscous mold powder, the mold and solidification can be achieved. In order to prevent poor lubrication with the shell, high-viscosity mold powder is added into the mold, and at the same time, vegetable oil, fatty acid esters, mineral oil, etc., between the mold and the solidified shell under the molten steel surface of the mold. A technique for casting by injecting a liquid lubricant such as a mixture of these has been proposed.
高濃度のＴｉを含有する鋼の連続鋳造では、溶鋼中のＴｉがモールドパウダー中のＳｉＯ2を還元してＴｉＯ2が形成され、モールドパウダーの特性が変わってしまい、安定した鋳造を維持することが困難になる。特に、モールドパウダー中のＳｉＯ2が減少すると、溶融状態でのモールドパウダーの粘度が上昇して、モールドパウダーの消費量が低下し、つまり、鋳型と凝固シェルとの間隙への溶融したモールドパウダーの流れ込み量が低下し、鋳片表面に縦割れが発生したり、鋳型と凝固シェルとの焼き付きによる拘束性ブレークアウトが発生したりする。また、モールドパウダーの特性が変わってしまうことで、凝固シェルと溶融したモールドパウダーとの界面張力、濡れ角などの物性値が変化し、ノロカミが発生しやすくなる。 In continuous casting of steel containing a high concentration of Ti, Ti in the molten steel reduces SiO 2 in the mold powder to form TiO 2, which changes the characteristics of the mold powder and maintains stable casting. Becomes difficult. In particular, when SiO 2 in the mold powder decreases, the viscosity of the mold powder in the molten state increases and the consumption of the mold powder decreases, that is, the molten mold powder in the gap between the mold and the solidified shell. The flow-in amount decreases, vertical cracks occur on the surface of the slab, and constraining breakout occurs due to seizure between the mold and the solidified shell. In addition, since the properties of the mold powder are changed, physical properties such as the interfacial tension and the wetting angle between the solidified shell and the molten mold powder are changed, and it becomes easy to generate a scab.
更に、モールドパウダーの消費量が低下することで、鋳型内溶鋼湯面上の溶融したモールドパウダー層（モールドパウダー溶融層という）の厚みが厚くなり、モールドパウダー溶融層の厚みが厚くなると、モールドパウダー溶融層の上部は冷却されやすくなり、鋳型内溶鋼湯面の変動などに起因してモールドパウダーと溶鋼とが混在して凝固する所謂「ディッケル」が発生しやすくなる。このディッケルの発生は、溶鋼の流動によって凝固シェルに付着（ノロカミとなる）したり、モールドパウダーの流れ込みを阻害したりする。 Furthermore, when the consumption of mold powder decreases, the thickness of the molten mold powder layer (called mold powder melt layer) on the molten steel surface in the mold increases, and the mold powder melt layer increases in thickness. The upper part of the molten layer is easily cooled, and so-called “dickel” is easily generated due to a mixture of mold powder and molten steel due to fluctuations in the molten steel surface in the mold. The generation of the Dickel adheres to the solidified shell due to the flow of molten steel (becomes a scab) or inhibits the flow of mold powder.
また更に、モールドパウダーの粘度が上昇することにより、ノズル閉塞防止のために浸漬ノズル内孔に吹き込んだＡｒガスなどの不活性ガスのモールドパウダー溶融層への離脱が妨げられ、凝固シェルに捕捉される不活性ガス気泡が増加する。 Furthermore, the increase in the viscosity of the mold powder prevents the inert gas such as Ar gas blown into the immersion nozzle inner hole from being released from the mold powder melt layer to prevent the nozzle clogging, and is trapped by the solidified shell. Increased inert gas bubbles.
特許文献５及び特許文献６について、このようなＴｉ含有鋼の連続鋳造時の問題点を解消可能か否かを検証すれば、特許文献５は、鋳型振動条件を低ストローク且つ高振動数に制御するだけであり、溶鋼中のＴｉがモールドパウダー中のＳｉＯ2を還元してモールドパウダー中のＳｉＯ2が減少し、モールドパウダーの特性が変化することに起因する問題点を解消するには十分とはいえない。即ち、Ｔｉ含有鋼に最適なモールドパウダーが必要である。また、特許文献５は、低ストローク且つ高振動数とするので、モールドパウダー消費量が基本的に少なく、鋳型と凝固シェルとの焼き付きによる拘束性ブレークアウトに対しては不利である。 If it is verified whether Patent Document 5 and Patent Document 6 can solve such problems at the time of continuous casting of Ti-containing steel, Patent Document 5 controls mold vibration conditions at a low stroke and a high frequency. It is just enough to eliminate the problems caused by Ti in the molten steel reducing SiO 2 in the mold powder and reducing SiO 2 in the mold powder and changing the properties of the mold powder. I can't say that. That is, an optimum mold powder for Ti-containing steel is required. Further, since Patent Document 5 has a low stroke and a high frequency, the amount of mold powder consumption is basically small, which is disadvantageous for a restrictive breakout due to seizure between the mold and the solidified shell.
特許文献６は、液体潤滑剤による鋳型と凝固シェルとの潤滑改善効果が期待できるが、液体潤滑剤を鋳型内の溶鋼湯面下で供給しており、従来の菜種油を潤滑剤として鋳型内溶鋼湯面上方から供給した設備に比較して、鋳型の構造が複雑になり、設備コストが高くなるという問題点がある。また、鋳型の壁面に液体潤滑剤供給口が開口しており、鋳造開始時にこの液体潤滑剤供給口に溶鋼が差し込んで、液体潤滑剤が閉塞する、或いは、凝固シェルの引き抜き抵抗となってブレークアウトが発生するなどのトラブルの発生する恐れがある。 Patent document 6 can be expected to improve the lubrication between the mold and the solidified shell by the liquid lubricant. However, the liquid lubricant is supplied under the surface of the molten steel in the mold, and the molten steel in the mold using conventional rapeseed oil as the lubricant. Compared with the equipment supplied from above the hot water surface, there is a problem that the structure of the mold becomes complicated and the equipment cost increases. In addition, a liquid lubricant supply port is opened on the wall of the mold, and molten steel is inserted into the liquid lubricant supply port at the start of casting, so that the liquid lubricant is blocked or a solidified shell is pulled out and breaks. There is a risk of troubles such as out.
本発明はこのような事情に鑑みてなされたもので、その目的とするところは、Ｔｉを含有する耐摩耗鋼を連続鋳造するにあたり、溶鋼中のＴｉがモールドパウダー中のＳｉＯ2を還元してモールドパウダー中のＳｉＯ2が減少しても、モールドパウダーの粘度の上昇を抑えることができ、それにより、モールドパウダーの消費量が確保され、鋳片表層部の縦割れ、ノロカミ、捕捉ガス気泡の少ない、表面性状の良好な鋳片を鋳造することのできる、耐摩耗鋼の連続鋳造方法を提供するとともに、この連続鋳造方法によって製造される耐摩耗鋼を提供することである。 The present invention has been made in view of such circumstances. The purpose of the present invention is to reduce the SiO 2 in the mold powder by reducing Ti in the molten steel when continuously casting the wear-resistant steel containing Ti. Even if the SiO 2 in the mold powder decreases, the increase in the viscosity of the mold powder can be suppressed, thereby ensuring the consumption of the mold powder, the vertical cracking of the slab surface layer, the slosh, the trapped gas bubbles An object of the present invention is to provide a continuous casting method of wear-resistant steel capable of casting a slab having a good surface property, and to provide a wear-resistant steel produced by this continuous casting method.
上記課題を解決するための本発明に係る耐摩耗鋼の連続鋳造方法は、Ｃ：０．０５〜０．３５質量％、Ｓｉ：０．０５〜１．０質量％、Ｍｎ：０．１〜２．０質量％、Ｂ：０．０００３〜０．００３０質量％、Ａｌ：０．００２〜０．１質量％、Ｔｉ：０．１〜１．０質量％、Ｃｒ：０．１〜１．０質量％、Ｍｏ：０．０５〜１．０質量％を含有し、残部がＦｅ及び不可避的不純物からなる溶鋼を連続鋳造機で鋳造するにあたり、連続鋳造用鋳型の振動条件を、振幅：３．０〜９．０ｍｍ、振動数：６０ｃｐｍ以上１２０ｃｐｍ未満とし、０．１〜５．０質量％の脂肪酸を配合したモールドパウダーを使用して、０．６〜１．０ｍ／ｍｉｎの鋳造速度で鋳造することを特徴とする。 The continuous casting method of wear-resistant steel according to the present invention for solving the above problems is as follows: C: 0.05 to 0.35% by mass, Si: 0.05 to 1.0% by mass, Mn: 0.1 to 0.1%. 2.0 mass%, B: 0.0003-0.0030 mass%, Al: 0.002-0.1 mass%, Ti: 0.1-1.0 mass%, Cr: 0.1-1. When casting a molten steel containing 0% by mass, Mo: 0.05 to 1.0% by mass, the balance being Fe and inevitable impurities with a continuous casting machine, the vibration conditions of the continuous casting mold are set to amplitude: 3 0.0 to 9.0 mm, frequency: 60 cpm or more and less than 120 cpm, and using a mold powder containing 0.1 to 5.0 mass% fatty acid at a casting speed of 0.6 to 1.0 m / min. It is characterized by casting.
また、本発明に係る耐摩耗鋼は、第１の発明に記載の耐摩耗鋼の連続鋳造方法によって鋳片に鋳造され、その後、該鋳片の熱間圧延によって製造されたものであることを特徴とする。 In addition, the wear-resistant steel according to the present invention is manufactured by casting the slab by the continuous casting method of the wear-resistant steel described in the first invention, and then hot rolling the slab. Features.
本発明によれば、連続鋳造用鋳型の振動条件を、振幅：３．０〜９．０ｍｍ、振動数：６０ｃｐｍ以上１２０ｃｐｍ未満とし、０．１〜５．０質量％の脂肪酸を配合したモールドパウダーを使用して、０．６〜１．０ｍ／ｍｉｎの鋳造速度でＴｉ含有耐摩耗鋼を連続鋳造するので、モールドパウダーに配合された脂肪酸の燃焼熱により、溶融したモールドパウダーと溶鋼との界面の温度が上昇して、該界面でのモールドパウダーの粘度の上昇が抑制され、その結果、モールドパウダーの消費量が確保され、鋳片表層部の縦割れ、ノロカミ、捕捉ガス気泡の少ない、表面性状の良好な耐摩耗鋼用鋳片を鋳造することが実現される。 According to the present invention, a mold powder in which vibration conditions of a continuous casting mold are set to amplitude: 3.0 to 9.0 mm, vibration frequency: 60 cpm or more and less than 120 cpm, and 0.1 to 5.0% by mass of a fatty acid is blended. Is used to continuously cast Ti-containing wear-resistant steel at a casting speed of 0.6 to 1.0 m / min, so that the interface between the molten mold powder and molten steel due to the heat of combustion of fatty acids mixed in the mold powder. As a result, the increase in the viscosity of the mold powder at the interface is suppressed. As a result, the consumption of the mold powder is ensured, and the surface of the slab surface layer is vertically cracked, sloppy, less trapped gas bubbles, and the surface. It is possible to cast a slab for wear-resistant steel having good properties.
以下、本発明を詳細に説明する。 Hereinafter, the present invention will be described in detail.
本発明で対象とする耐摩耗鋼は、特許文献４に提案される耐摩耗鋼と同様に、曲げ加工性及び溶接性に優れる耐摩耗鋼であり、高い硬度を有するＴｉ炭化物（ＴｉＣ）を主体とする粗大な析出物（０．５μｍ以上）を連続鋳造工程の凝固時に生成させ、この析出物を後工程の熱間圧延工程において可能な限り固溶させずに残留させ、鋼の耐摩耗性を向上させるというものである。ここで、Ｔｉ炭化物を主体とする析出物とは、ＴｉＣ単体、或いはＴｉＣとＴｉＮ、ＴｉＳとの複合析出物などである。 The wear resistant steel targeted by the present invention is a wear resistant steel excellent in bending workability and weldability, similar to the wear resistant steel proposed in Patent Document 4, and is mainly composed of Ti carbide (TiC) having high hardness. A coarse precipitate (0.5 μm or more) is generated during solidification in the continuous casting process, and this precipitate is left as solid solution as possible in the subsequent hot rolling process, so that the wear resistance of the steel Is to improve. Here, the precipitate mainly composed of Ti carbide is TiC alone or a composite precipitate of TiC, TiN, and TiS.
このようにして耐摩耗性を発現する、本発明の対象とする耐摩耗鋼は、Ｃ：０．０５〜０．３５質量％、Ｓｉ：０．０５〜１．０質量％、Ｍｎ：０．１〜２．０質量％、Ｂ：０．０００３〜０．００３０質量％、Ａｌ：０．００２〜０．１質量％、Ｔｉ：０．１〜１．０質量％、Ｃｒ：０．１〜１．０質量％、Ｍｏ：０．０５〜１．０質量％を含有し、残部をＦｅ及び不可避的不純物とする。以下に、本発明の対象とする耐摩耗鋼の成分組成を上記範囲に限定した理由を説明する。 In this way, the wear-resistant steel that is the subject of the present invention and exhibits wear resistance is C: 0.05 to 0.35 mass%, Si: 0.05 to 1.0 mass%, Mn: 0.00. 1 to 2.0 mass%, B: 0.0003 to 0.0030 mass%, Al: 0.002 to 0.1 mass%, Ti: 0.1 to 1.0 mass%, Cr: 0.1 to 0.1 mass% 1.0 mass%, Mo: 0.05-1.0 mass% is contained, and the remainder is made into Fe and an unavoidable impurity. Hereinafter, the reason why the component composition of the wear-resistant steel as the object of the present invention is limited to the above range will be described.
Ｃ：０．０５〜０．３５質量％
Ｃは、金属組織においてマトリックス硬度を向上させて耐摩耗性を向上させるとともに、硬質な第二相（以下、硬質相ともいう）としてのＴｉ炭化物を形成し、耐摩耗性の向上に有効な元素であり、このような効果を得るためには、０．０５質量％以上の含有量を必要とする。一方、含有量が０．３５質量％を超える場合は、硬質相としてのＴｉ炭化物が粗大になり、曲げ加工時にＴｉ炭化物を起点として割れが発生する。従って、Ｃ含有量を０．０５〜０．３５質量％の範囲に限定した。尚、好ましくは０．１５〜０．３０質量％の範囲である。
C: 0.05-0.35 mass%
C is an element effective in improving wear resistance by improving matrix hardness in a metal structure to improve wear resistance and forming Ti carbide as a hard second phase (hereinafter also referred to as hard phase). In order to obtain such an effect, a content of 0.05% by mass or more is required. On the other hand, when the content exceeds 0.35% by mass, the Ti carbide as the hard phase becomes coarse, and cracks occur starting from the Ti carbide during bending. Therefore, the C content is limited to a range of 0.05 to 0.35% by mass. In addition, Preferably it is the range of 0.15-0.30 mass%.
Ｓｉ：０．０５〜１．０質量％
Ｓｉは、脱酸元素として有効な元素であり、その効果を得るためには０．０５質量％以上を含有する必要がある。また、Ｓｉは鋼に固溶して固溶強化により高硬度化に寄与する有効な元素であるが、１．０質量％を超えて含有させると、延性、靭性が低下し、更に、介在物が増加するなどの問題を生じる。従って、Ｓｉ含有量を０．０５〜１．０質量％の範囲に限定した。尚、好ましくは０．０５〜０．４０質量％の範囲である。
Si: 0.05-1.0 mass%
Si is an effective element as a deoxidizing element, and in order to obtain the effect, it is necessary to contain 0.05% by mass or more. Si is an effective element that contributes to high hardness by solid solution strengthening by solid solution in steel. However, when it exceeds 1.0% by mass, ductility and toughness are reduced, and inclusions are further added. Cause problems such as increase. Therefore, Si content was limited to the range of 0.05-1.0 mass%. In addition, Preferably it is the range of 0.05-0.40 mass%.
Ｍｎ：０．１〜２．０質量％
Ｍｎは、固溶強化により高硬度化に寄与する有効な元素であり、その効果を得るためには０．１質量％以上を含有する必要がある。一方、２．０質量％を超えて含有させた場合には溶接性が劣化する。従って、Ｍｎ含有量を０．１〜２．０質量％の範囲に限定した。尚、好ましくは０．１〜１．６０質量％の範囲である。
Mn: 0.1 to 2.0% by mass
Mn is an effective element that contributes to increasing the hardness by solid solution strengthening, and in order to obtain the effect, it is necessary to contain 0.1% by mass or more. On the other hand, when the content exceeds 2.0% by mass, the weldability deteriorates. Therefore, the Mn content is limited to a range of 0.1 to 2.0% by mass. In addition, Preferably it is the range of 0.1-1.60 mass%.
Ｂ：０．０００３〜０．００３０質量％
Ｂは、粒界に偏析し、粒界を強化して靭性向上に有効に寄与する元素であり、この効果を得るためには０．０００３質量％以上を含有させる必要がある。一方、０．００３０質量％を超えて含有させた場合には溶接性が低下する。従って、Ｂ含有量を０．０００３〜０．００３０質量％の範囲に限定した。尚、好ましくは０．０００３〜０．００１５質量％の範囲である。
B: 0.0003 to 0.0030 mass%
B is an element that segregates at the grain boundary and strengthens the grain boundary to effectively contribute to the improvement of toughness. In order to obtain this effect, it is necessary to contain 0.0003% by mass or more. On the other hand, when it contains exceeding 0.0030 mass%, weldability will fall. Therefore, the B content is limited to a range of 0.0003 to 0.0030% by mass. In addition, Preferably it is the range of 0.0003-0.0015 mass%.
Ａｌ：０．００２〜０．１質量％
Ａｌは、脱酸剤として作用し、この効果を得るためには０．００２質量％以上を含有させる必要がある。一方、０．１質量％を超えて含有させた場合には鋼の清浄性を低下させる。従って、Ａｌ含有量を０．００２〜０．１質量％の範囲に限定した。
Al: 0.002 to 0.1% by mass
Al acts as a deoxidizing agent, and in order to obtain this effect, it is necessary to contain 0.002% by mass or more. On the other hand, when the content exceeds 0.1% by mass, the cleanliness of the steel is lowered. Therefore, Al content was limited to the range of 0.002-0.1 mass%.
Ｔｉ：０．１〜１．０質量％
Ｔｉは、硬質な第二相としてのＴｉ炭化物を形成し、耐摩耗性の向上に有効な元素であり、このような効果を得るためには、０．１質量％以上の含有量を必要とする。一方、含有量が１．０質量％を超える場合は、硬質相としてのＴｉ炭化物が粗大になり、曲げ加工時にＴｉ炭化物を起点として割れが発生する。更には、Ｔｉ合金添加量の増加によるコスト上昇やモールドパウダーの変質の影響度が大きくなる。従って、Ｔｉ含有量を０．１〜１．０質量％の範囲に限定した。尚、好ましくは０．１〜０．５質量％の範囲である。
Ti: 0.1 to 1.0% by mass
Ti is an element that forms Ti carbide as a hard second phase and is effective in improving wear resistance. To obtain such an effect, a content of 0.1% by mass or more is required. To do. On the other hand, when the content exceeds 1.0% by mass, the Ti carbide as the hard phase becomes coarse, and cracks are generated starting from the Ti carbide during bending. Furthermore, the increase in cost due to an increase in the amount of Ti alloy added and the degree of influence of mold powder alteration increase. Therefore, the Ti content is limited to a range of 0.1 to 1.0% by mass. In addition, Preferably it is the range of 0.1-0.5 mass%.
Ｃｒ：０．１〜１．０質量％
Ｃｒは、焼入性を向上させる効果を有し、この効果を得るためには０．１質量％以上を含有させる必要がある。一方、１．０質量％を超えて含有させた場合には溶接性が低下する。従って、Ｃｒ含有量を０．１〜１．０質量％の範囲に限定した。尚、好ましくは０．１〜０．４０質量％の範囲である。
Cr: 0.1 to 1.0% by mass
Cr has an effect of improving hardenability, and in order to obtain this effect, it is necessary to contain 0.1% by mass or more. On the other hand, when the content exceeds 1.0% by mass, the weldability decreases. Therefore, the Cr content is limited to a range of 0.1 to 1.0% by mass. In addition, Preferably it is the range of 0.1-0.40 mass%.
Ｍｏ：０．０５〜１．０質量％
Ｍｏは、焼入性を向上させる効果を有し、この効果を得るためには０．０５質量％以上を含有させる必要がある。一方、１．０質量％を超えて含有させた場合には溶接性が低下する。従って、Ｍｏ含有量を０．０５〜１．０質量％の範囲に限定した。尚、好ましくは０．０５〜０．４０質量％の範囲である。
Mo: 0.05-1.0 mass%
Mo has an effect of improving hardenability, and in order to obtain this effect, it is necessary to contain 0.05% by mass or more. On the other hand, when the content exceeds 1.0% by mass, the weldability decreases. Therefore, the Mo content is limited to a range of 0.05 to 1.0% by mass. In addition, Preferably it is the range of 0.05-0.40 mass%.
このようにして、本発明の対象とする耐摩耗鋼は、その成分組成が限定されている。転炉及びＲＨ真空脱ガス装置などを用いて上記の成分範囲に調製した耐摩耗鋼用の溶鋼を、スラブ連続鋳造機やブルーム連続鋳造機で連続鋳造する。この連続鋳造にあたり、連続鋳造用鋳型の振動条件を、振幅：３．０〜９．０ｍｍ、振動数：６０ｃｐｍ以上１２０ｃｐｍ未満とし、０．１〜５．０質量％の脂肪酸（脂肪族モノカルボン酸）を配合したモールドパウダーを使用して、０．６〜１．０ｍ／ｍｉｎの鋳造速度で鋳造する。 In this way, the component composition of the wear resistant steel targeted by the present invention is limited. Molten steel for wear-resistant steel prepared in the above component range using a converter, an RH vacuum degassing apparatus, or the like is continuously cast by a slab continuous casting machine or a bloom continuous casting machine. In this continuous casting, the vibration conditions of the casting mold for continuous casting are as follows: amplitude: 3.0 to 9.0 mm, frequency: 60 cpm or more and less than 120 cpm, 0.1 to 5.0 mass% fatty acid (aliphatic monocarboxylic acid) ) Is used to cast at a casting speed of 0.6 to 1.0 m / min.
使用するモールドパウダーは、鋼の連続鋳造において一般的に使用されているモールドパウダーに、所定量の脂肪酸を添加し、混合することで、作製することができる。即ち、ＣａＯ、ＳｉＯ2、Ａｌ2Ｏ3、Ｆｅ2Ｏ3、ＭｇＯ、ＭｎＯ、ＢａＯ、Ｂ2Ｏ3などの酸化物を基材とし、これら基材に、Ｎａ2Ｏ、Ｋ2Ｏ、Ｌｉ2Ｏなどのアルカリ金属の酸化物、ＮａＦ、ＫＦ、ＬｉＦ、ＣａＦ2、ＭｇＦ2、ＡｌＦ3、Ｎａ3ＡｌＦ3などのフッ化物、及びこれら金属の炭酸化物や硝酸化物などの、基材の物性を調整するための物性調整材と、カーボンブラックや人造黒鉛などのモールドパウダーの溶融速度を調整するための溶融速度調整材と、更に、必要に応じて、基材の主成分であるＣａＯやＳｉＯ2などの成分調整材と、が添加されて構成された一般的なモールドパウダーに、所定量の脂肪酸を添加して混合することで、作製することができる。脂肪酸としては、ステアリン酸（融点６９〜７０℃）、パルミチン酸（融点６３〜６４℃）などを用いることができる。 The mold powder to be used can be prepared by adding and mixing a predetermined amount of fatty acid to mold powder generally used in continuous casting of steel. That is, oxides such as CaO, SiO 2 , Al 2 O 3 , Fe 2 O 3 , MgO, MnO, BaO, and B 2 O 3 are used as base materials, and Na 2 O, K 2 O, Li, and the like are used as the base materials. Properties of base materials such as oxides of alkali metals such as 2 O, fluorides such as NaF, KF, LiF, CaF 2 , MgF 2 , AlF 3 , Na 3 AlF 3 , and carbonates and nitrates of these metals For adjusting the physical properties, a melting rate adjusting material for adjusting the melting rate of mold powder such as carbon black and artificial graphite, and, if necessary, CaO and SiO which are the main components of the base material It can be produced by adding and mixing a predetermined amount of fatty acid to a general mold powder constituted by adding a component adjusting material such as 2 . As the fatty acid, stearic acid (melting point: 69 to 70 ° C.), palmitic acid (melting point: 63 to 64 ° C.), or the like can be used.
ステアリン酸などの脂肪酸を配合したモールドパウダーを鋳型内の溶鋼湯面に添加すると、溶鋼からの熱付与によってモールドパウダーが溶融する際に、配合した脂肪酸が燃焼して発熱する。この発熱により、溶鋼と溶融したモールドパウダーとの界面の温度が上昇する。本発明においても、溶融したモールドパウダー中のＳｉＯ2は溶鋼中のＴｉによって還元され、溶融状態のモールドパウダー中のＳｉＯ2は初期濃度よりも減少し、溶融したモールドパウダーの粘度は上昇する傾向にあるが、物質の粘度は温度上昇によって低下することから、溶鋼と溶融したモールドパウダーとの界面の温度が脂肪酸の燃焼熱によって上昇し、溶融したモールドパウダーの粘度の上昇が抑制される。 When mold powder blended with fatty acid such as stearic acid is added to the molten steel surface in the mold, the blended fatty acid burns and generates heat when the mold powder melts by applying heat from the molten steel. Due to this heat generation, the temperature of the interface between the molten steel and the molten mold powder rises. In the present invention, SiO 2 in the mold powder melted is reduced by Ti in the molten steel, SiO 2 in the mold powder in a molten state is decreased from the initial concentration, the trend viscosity of the molten mold powder to rise However, since the viscosity of the substance decreases with an increase in temperature, the temperature at the interface between the molten steel and the molten mold powder increases due to the combustion heat of the fatty acid, and the increase in the viscosity of the molten mold powder is suppressed.
これにより、Ｔｉを高濃度に含有した溶鋼の連続鋳造においても、モールドパウダーの消費量が確保され、鋳片表層部の縦割れ、ノロカミ、捕捉ガス気泡の少ない、表面性状の良好な耐摩耗鋼用鋳片を鋳造することが可能となる。また、凝固シェルと鋳型との潤滑が確保され、拘束性ブレークアウトを発生することなく、安定した操業が達成される。尚、スラブ連続鋳造機においては、凝固シェルと鋳型との焼き付きを防止し、拘束性ブレークアウトを防止するためには、モールドパウダーの消費量を、鋳片の単位表面積あたり０．２０ｋｇ／ｍ2以上、望ましくは０．２５ｋｇ／ｍ2以上確保する必要のあることが知られている。 As a result, even in continuous casting of molten steel containing Ti at a high concentration, the consumption of mold powder is ensured, and the wear-resistant steel with good surface properties, with less vertical cracks in the surface of the slab, no stagnation, and trapped gas bubbles. It becomes possible to cast a casting slab. Further, lubrication between the solidified shell and the mold is ensured, and stable operation is achieved without causing a restrictive breakout. In a slab continuous casting machine, in order to prevent seizure between the solidified shell and the mold and to prevent a restrictive breakout, the consumption of mold powder is 0.20 kg / m 2 per unit surface area of the slab. As described above, it is known that it is necessary to secure 0.25 kg / m 2 or more.
モールドパウダー中の脂肪酸の配合量が０．１質量％未満では、脂肪酸の燃焼による発熱効果を十分に得ることができない。一方、脂肪酸の配合量が５．０質量％を超えるとモールドパウダーが溶解しにくくなり、好ましくない。 When the blending amount of the fatty acid in the mold powder is less than 0.1% by mass, the heat generation effect due to the burning of the fatty acid cannot be sufficiently obtained. On the other hand, when the amount of the fatty acid exceeds 5.0% by mass, the mold powder becomes difficult to dissolve, which is not preferable.
本発明では、鋳造対象の耐摩耗鋼が高合金鋼であることから、高温での鋳片の脆化を考慮して、定常鋳造域の鋳造速度を、近年の連続鋳造操業では比較的遅い鋳造速度である０．６〜１．０ｍ／ｍｉｎの範囲内で設定する。１．０ｍ／ｍｉｎを超える鋳造速度では、鋳片に横割れ、横ヒビ割れ、巨大縦割れなどの欠陥の発生する恐れがあり、一方、０．６ｍ／ｍｉｎ未満では、生産性が低下する。 In the present invention, since the wear-resistant steel to be cast is a high alloy steel, considering the brittleness of the slab at high temperature, the casting speed in the steady casting area is relatively slow in recent continuous casting operations. The speed is set within a range of 0.6 to 1.0 m / min. If the casting speed exceeds 1.0 m / min, defects such as lateral cracks, lateral cracks, and giant vertical cracks may occur in the slab, whereas if it is less than 0.6 m / min, productivity is reduced.
そして、この鋳造速度の範囲で、連続鋳造用鋳型の振動条件を、振動波形を正弦波或いは偏移正弦波とし、振幅：３．０〜９．０ｍｍ、振動数：６０ｃｐｍ以上１２０ｃｐｍ未満に設定する。つまり、特許文献５に提案される、「低ストローク且つ高振動数」に制御するのではなく、特許文献５よりも振動数を下げ、炭素鋼の連続鋳造で一般的に行われている範囲を含む鋳型振動条件に設定する。尚、この振動条件は、「低ストローク且つ高振動数」に比較して、モールドパウダーの消費量が増大するという作用・効果がある。ここで、鋳型の振幅とは、鋳型振動の変位の上限位置から下限位置までの距離、つまり鋳型の振動ストロークの１／２の値である。 In this casting speed range, the vibration conditions of the continuous casting mold are set such that the vibration waveform is a sine wave or a shifted sine wave, the amplitude is 3.0 to 9.0 mm, and the vibration frequency is 60 cpm or more and less than 120 cpm. . In other words, instead of controlling to “low stroke and high frequency” proposed in Patent Document 5, the frequency is lower than that of Patent Document 5, and the range generally performed in continuous casting of carbon steel is used. Set to include mold vibration conditions. In addition, this vibration condition has the effect | action and effect that the consumption of mold powder increases compared with "low stroke and high frequency." Here, the amplitude of the mold is a distance from the upper limit position to the lower limit position of the displacement of the mold vibration, that is, a value that is ½ of the vibration stroke of the mold.
鋳造された鋳片は、必要に応じて表面手入れが施された後、次工程の熱間圧延工程に搬送されて熱間圧延され、厚鋼板、薄鋼板、形鋼などの製品となる。 The cast slab is subjected to surface care as necessary, and then transferred to the next hot rolling step and hot rolled to become a product such as a thick steel plate, a thin steel plate, or a shaped steel.
以上説明したように、本発明によれば、モールドパウダーに配合された脂肪酸の燃焼熱によって、溶融したモールドパウダーと溶鋼との界面の温度が上昇し、該界面でのモールドパウダーの粘度の上昇が抑制され、その結果、モールドパウダーの消費量が確保され、鋳片表層部の縦割れ、ノロカミ、捕捉ガス気泡の少ない、表面性状の良好な耐摩耗鋼用鋳片を鋳造することが実現される。 As described above, according to the present invention, the temperature of the interface between the molten mold powder and the molten steel rises due to the combustion heat of the fatty acid blended in the mold powder, and the viscosity of the mold powder at the interface increases. As a result, the consumption of mold powder is ensured, and it is possible to cast a cast slab for wear-resistant steel with a good surface property that has few vertical cracks, scents and trapped gas bubbles in the slab surface layer. .
連続鋳造機長さ２６ｍ、スラブ厚み２５０ｍｍ、スラブ幅１５００〜１９００ｍｍの垂直曲げ型スラブ連続鋳造機を用い、Ｔｉ含有鋼の試験鋳造を行った。鋳造速度は０．６〜１．０ｍ／ｍｉｎとし、モールドパウダーは、脂肪酸としてステアリン酸を０．８〜４．５質量％の範囲で含有する脂肪酸含有モールドパウダーと、脂肪酸を含有しない通常のモールドパウダーとを使用し、鋳型振動条件を種々変更した。表１に試験鋳造の試験条件及び試験結果を示す。尚、鋳型の振動数が６０ｃｐｍ未満の試験は行っていないが、これは、振動数を６０ｃｐｍ未満とすると、モールドパウダーの消費量が低下してブレークアウトの発生する頻度が高いことによる。また、比較例６では、鋳型振動数を１８０ｃｐｍとしたが、鋳造中に連続鋳造機全体が異常な振動を起こし、鋳造の継続が不可能となったため、試験を中止した。 Test casting of Ti-containing steel was performed using a vertical bending slab continuous casting machine having a continuous casting machine length of 26 m, a slab thickness of 250 mm, and a slab width of 1500 to 1900 mm. The casting speed is 0.6 to 1.0 m / min, and the mold powder includes a fatty acid-containing mold powder containing stearic acid in a range of 0.8 to 4.5 mass% as a fatty acid, and a normal mold not containing a fatty acid. Various mold vibration conditions were changed using powder. Table 1 shows test conditions and test results of the test casting. In addition, although the test that the vibration frequency of the mold is less than 60 cpm is not performed, this is because if the vibration frequency is less than 60 cpm, the consumption of mold powder is reduced and the frequency of occurrence of breakout is high. In Comparative Example 6, the mold frequency was set to 180 cpm, but the entire continuous casting machine vibrated abnormally during casting, and the casting could not be continued, so the test was stopped.
鋳造終了後、スラブの長辺面及び短辺面の計４面の全ての面を表面手入れすることなく、直径が０．５ｍｍ以上の気泡を顕微鏡により測定した。測定対称スラブは、鋳造速度、二次冷却条件などの鋳造条件が安定した状態下で鋳造されたスラブとし、測定面積を１．９５ｍ2とした。この測定値をその鋳造条件での代表値とした。そして、観察された気泡の密度が２００個／ｍ2未満の場合を「○」、２００個／ｍ2以上の場合を「×」と評価して、表１の「鋳片での気泡欠陥評価」の欄に記載した。気泡の密度が２００個／ｍ2以上の場合は圧延後の製品の表面性状が大幅に悪化することから、評価の閾値とした。 After completion of casting, bubbles having a diameter of 0.5 mm or more were measured with a microscope without taking care of all four surfaces of the long side surface and the short side surface of the slab. The measurement symmetrical slab was a slab cast under conditions where casting conditions such as casting speed and secondary cooling conditions were stable, and the measurement area was 1.95 m 2 . This measured value was a representative value under the casting conditions. Then, the when the density of the observed bubble is less than 200 / m 2 "○", 200 / m 2 or more when evaluated as "×" bubble defect evaluation of the "slab Table 1 "In the column. When the bubble density was 200 / m 2 or more, the surface property of the product after rolling was greatly deteriorated, and therefore, it was set as a threshold for evaluation.
スラブに表面手入れを施すことなく、スラブを厚鋼板に熱間圧延し、厚鋼板において、深さが０．２ｍｍ以上の欠陥の面積を目視により測定し、この面積が２５ｃｍ2／ｍ2未満の場合を「○」、この面積が２５ｃｍ2／ｍ2以上の場合を「×」と評価して、表１の「圧延後の製品評価」の欄に記載した。 The surface of the slab is hot-rolled into a thick steel plate without performing surface maintenance, and the area of the defect having a depth of 0.2 mm or more is visually measured in the thick steel plate, and this area is less than 25 cm 2 / m 2 . The case was evaluated as “◯”, and the case where the area was 25 cm 2 / m 2 or more was evaluated as “x” and described in the column of “Product evaluation after rolling” in Table 1.
また、パワーショベル、ブルドーザー、ホッパー、バケットなどの産業機械や運搬機器などに必要な耐摩耗性の評価結果を、「材料特性」として評価した。耐摩耗性はＡＳＴＭ Ｇ−６５に準拠した摩耗試験によって行い、ＳＳ４００（軟鋼）の耐摩耗性を１．０として耐摩耗比で評価した。耐摩耗比が大きいほど耐摩耗性に優れていることを意味する。尚、摩耗砂としては、１００質量％ＳｉＯ2砂を使用した。表１では、ＳＳ４００との耐摩耗比で５．０を超えるものを「○」、５．０未満のものを「×」として表示した。 In addition, the evaluation results of wear resistance required for industrial machines such as excavators, bulldozers, hoppers, buckets, and transportation equipment were evaluated as “material properties”. Abrasion resistance was evaluated by an abrasion test according to ASTM G-65, and SS400 (mild steel) was evaluated as a wear resistance ratio with an abrasion resistance of 1.0 as 1.0. A larger wear resistance ratio means better wear resistance. As the wear sand was used 100 wt% SiO 2 sand. In Table 1, the wear resistance ratio with SS400 exceeding 5.0 was displayed as “◯”, and those less than 5.0 as “x”.
表１からも明らかなように、本発明例においては、「鋳片での気泡欠陥評価」、「圧延後の製品評価」及び「材料特性」の全てが良好であり、表面性状の良好な耐摩耗鋼を製造できることが確認された。 As is clear from Table 1, in the present invention example, “evaluation of bubble defects in slab”, “evaluation of product after rolling”, and “material properties” are all good, and the surface property is good. It was confirmed that wear steel could be produced.
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