JP4419605B2 - Steel sheet for double-wound pipe and manufacturing method thereof - Google Patents
Steel sheet for double-wound pipe and manufacturing method thereof Download PDFInfo
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本発明は、表面に銅などの自己ろう付け性を有する金属をめっきし、管状に成形した後、めっきした金属の融点以上に短時間加熱して製造される２重巻きパイプに用いて好適な鋼板およびその製造方法に関するものである。 INDUSTRIAL APPLICABILITY The present invention is suitable for use in a double-wound pipe manufactured by plating a metal having self-brazing properties such as copper on the surface, forming it into a tubular shape, and then heating it for a short time to the melting point or more of the plated metal. The present invention relates to a steel plate and a manufacturing method thereof.
各種コンプレッサーとアクチュエータの接続パイプや自動車のブレーキチューブ、オイルチューブ等の分野では、銅パイプと同様な外観と優れた熱的特性、美観性を有し、かつ、鉄の高強度と強靭性とを具えたいわゆる２重巻きパイプが使用されている。この２重巻きパイプについては、例えば、「鉄と鋼」第66年(1980)第１号ｐ130〜137に詳細な説明があり、一般的な製造方法は次のとおりに行われる。２重巻きパイプの素材には、板厚約0.3mm程度の冷延鋼板が用いられており、まず、この素材鋼板の表裏面に銅の電気めっきを施してからスリットしてフープとする。このフープを、造管用ロールで、鋼板の圧延方向がパイプの軸方向となるように、かつ、パイプの壁が２重となるように鋼板を２周分丸める加工を行い、その後、銅の融点(1083℃)以上に加熱して銅を溶融させることにより、板間の隙間を埋めて鋼板どうしを互いに接合する、いわゆる「自己ろう付け処理(セルフ・ブレージング処理)」を施す。ろう付け後のパイプは、その後、冷間で形状矯正、寸法精整等を施して製品とする。このようにして製造された２重巻きパイプには、上述した用途から、気密性や成形性などにおいて高い信頼性が要求される。 In the fields of connecting pipes for various compressors and actuators, automobile brake tubes, oil tubes, etc., it has the same appearance as copper pipes, excellent thermal characteristics, aesthetics, and high strength and toughness of iron. A so-called double-winding pipe is used. About this double winding pipe, for example, "Iron and steel" 66th year (1980) 1st issue p130-137 is explained in detail, and a general manufacturing method is performed as follows. A cold-rolled steel sheet having a thickness of about 0.3 mm is used as the material for the double-pipe pipe. First, copper electroplating is applied to the front and back surfaces of the material steel sheet, and then slitted into a hoop. This hoop is rolled with a pipe making roll so that the steel sheet is rolled twice so that the rolling direction of the steel sheet is the axial direction of the pipe and the wall of the pipe is doubled, and then the melting point of copper A so-called “self-brazing process (self-brazing process)” in which the steel sheets are joined to each other by filling the gap between the plates by heating to (1083 ° C.) or higher to melt the copper is performed. The pipe after brazing is then subjected to shape correction, dimensional adjustment, etc. in a cold state to obtain a product. The double-wound pipe manufactured in this way is required to have high reliability in terms of airtightness and formability from the above-described uses.
さて、２重巻きパイプに用いられる素材鋼板は、その基本特性として、パイプ成形用金型や治具、工具等の消耗を軽減するため、また、造管(管巻き)工程における形状凍結性を向上するために、ある程度の強度を確保しながらも、軟質で成形性に優れることが必要である。そこで、このような特性を満たすものとして、２重巻きパイプ用鋼板には従来から、低炭素鋼を素材とし、箱焼鈍で製造した板厚が0.35mm以下の冷延鋼板が用いられている。しかし、この箱焼鈍材は、材質的には軟質で良好な成形性を有するため、２重巻きパイプ用素材として好適である反面、焼鈍工程に数日間を要するため生産効率が悪く、またコイルの長手方向、幅方向における材質の均一性に劣るという問題点がある。また、従来から用いられている箱焼鈍材は、素材鋼板の結晶粒が大きく、二重巻きパイプに成形後のろう付け処理で結晶粒がさらに粗大化したり、あるいは、異常粗大粒が発生したりし、パイプとしての成形性や強度、靭性の低下を招くという問題があった。さらに、造管後のろう付け処理においては、めっきした銅が溶融した際、素材鋼板の結晶粒界中へ浸透し、脆化を引き起こすという問題もあった。 The basic properties of the steel sheet used for double-wound pipes are to reduce the wear of pipe-forming dies, jigs, tools, etc., and to form freezing in the pipe making process. In order to improve, it is necessary to be soft and excellent in moldability while securing a certain degree of strength. In order to satisfy these characteristics, cold rolled steel sheets having a thickness of 0.35 mm or less made of box annealing are conventionally used as steel sheets for double-pipe pipes. However, this box annealed material is soft and has good moldability, so it is suitable as a material for double-wound pipes. On the other hand, it takes several days for the annealing process, and the production efficiency is poor. There is a problem that the uniformity of the material in the longitudinal direction and the width direction is inferior. Also, conventionally used box annealed materials have large crystal grains in the steel sheet, and the grains are further coarsened by the brazing process after forming into a double-wound pipe, or abnormal coarse grains are generated. However, there is a problem that the formability, strength, and toughness of the pipe are reduced. Furthermore, in the brazing process after pipe forming, when the plated copper is melted, it penetrates into the crystal grain boundary of the material steel plate and causes embrittlement.
このような問題に対する技術として、例えば、特許文献１には、冷延鋼板を、Ｈ2を２vol％以上含むＮ2−Ｈ2混合ガス中で再結晶温度〜850℃の温度で焼鈍処理することにより、素地鋼板の表層部に層厚50〜100μmの微細なAlＮの析出物層を設けた耐銅浸透性等に優れる２重巻きパイプ用銅めっき鋼板が開示されている。また、特許文献２には、Ｃ：0.0005〜0.020wt％と、Nb：0.003〜0.040wt％、Ti：0.005〜0.060wt％の１種または２種とを含有する鋼素材を、圧延終了温度1000〜850℃で熱間仕上圧延し、750℃以下で巻き取り、次いで、冷間圧延し、650〜850℃×20秒以下で連続焼鈍し、圧下率20％以下の２次冷間圧延を行うことにより、優れた成形性を有しかつ造管−熱処理後においてもフェライト粒径の粗大化が抑制され、優れた強度、靭性を有する２重巻きパイプ用鋼板が開示されている。
しかしながら、特許文献１の２重巻きパイプ用鋼板は、焼鈍する際の窒化反応を利用して、素材鋼板に、微細なAlＮ析出物が緻密に分散した厚さ50〜100μmの表層部を形成する必要があるため、基本的に窒化時間を十分に確保できる箱焼鈍法で製造する必要がある。そのため、先述した箱焼鈍法に起因する生産効率が低く、材質の均一性に劣るという問題は未解決のままである。
また、特許文献２の鋼板は、その素材として極低炭素鋼を使用するため、いわゆる脱ガス設備が必要となり、また、仕上圧延終了温度が1000〜850℃と高いため熱間圧延が難しく、均一な材質を得にくいという問題がある。
However, the double-pipe steel plate disclosed in Patent Document 1 uses a nitriding reaction during annealing to form a surface layer portion having a thickness of 50 to 100 μm in which fine AlN precipitates are densely dispersed in the raw steel plate. Since it is necessary, basically, it is necessary to manufacture by a box annealing method capable of ensuring a sufficient nitriding time. Therefore, the problem that the production efficiency resulting from the above-described box annealing method is low and the uniformity of the material is poor remains unsolved.
Moreover, since the steel sheet of Patent Document 2 uses ultra-low carbon steel as a raw material, so-called degassing equipment is required, and since the finish rolling finish temperature is as high as 1000 to 850 ° C., hot rolling is difficult and uniform. There is a problem that it is difficult to obtain a new material.
また、上述したように、２重巻きパイプ用鋼板の製造には、生産効率に優れた連続焼鈍法を採用することが有利である。しかし、この焼鈍法は、冷却速度が大きく、焼鈍温度で固溶したＣが冷却中に析出するのに十分な時間がないため、固溶Ｃを多量に含んだ状態で製品となる。そのため、鋼板強度が増加したり、あるいは、時効により降伏応力が増加したりして、２重巻き管の製造工程で成形不良を生ずる虞がある。 In addition, as described above, it is advantageous to employ a continuous annealing method with excellent production efficiency for the production of a steel sheet for a double-pipe pipe. However, this annealing method has a high cooling rate, and there is not enough time for C dissolved in the annealing temperature to precipitate during cooling, so that the product contains a large amount of solid solution C. For this reason, there is a possibility that the steel sheet strength increases or the yield stress increases due to aging, resulting in a forming defect in the manufacturing process of the double-rolled tube.
本発明の目的は、従来技術が抱えていた上記問題点を解決し、材質が軟質かつ均一で造管性に優れる他、造管したパイプの成形性に優れ、造管後のろう付け等の熱処理においても異常粗大粒や溶融銅の浸入のない２重巻きパイプ用鋼板を提供すると共に、その鋼板の連続焼鈍による有利な製造方法を提案することにある。 The object of the present invention is to solve the above-mentioned problems of the prior art, the material is soft and uniform and excellent in pipe forming property, excellent in moldability of the pipe formed, brazing after pipe forming, etc. An object of the present invention is to provide a steel sheet for a double-wound pipe that is free of abnormal coarse grains and molten copper intrusion in heat treatment, and to propose an advantageous manufacturing method by continuous annealing of the steel sheet.
発明者らは、上記課題を解決するために研究を重ねた結果、鋼成分としてのＣやその他の添加元素を適正な範囲に制御した上で、熱間圧延における仕上圧延終了温度を従来よりも低温側に変更し、最終製品(冷延焼鈍板)段階で結晶粒径を大きくすることによって、２重巻きパイプ用素材として最適な冷延鋼板を製造し得ることを知見し、本発明を完成させた As a result of repeated researches to solve the above-mentioned problems, the inventors controlled the finish rolling end temperature in hot rolling as compared with the conventional one after controlling C and other additive elements as steel components to an appropriate range. We found that the best cold-rolled steel sheet can be manufactured as a material for double-wound pipes by changing to the low temperature side and increasing the crystal grain size in the final product (cold-rolled annealed sheet) stage, and completed the present invention. Let
すなわち、本発明は、Ｃ：０．０２〜０．０８ｍａｓｓ％、Ｍｎ：０．１５〜０．５０ｍａｓｓ％、Ａｌ：０．１０ｍａｓｓ％以下を含み、残部がFeおよび不可避的不純物からなり、フェライト組織の平均結晶粒径が１０〜３０μｍでかつ板厚方向の平均粒径（ｄ Ｔ ）と圧延方向の平均粒径（ｄ Ｌ ）の比（ｄ Ｌ ／ｄ Ｔ ）が１．４以下の等軸粒であることを特徴とする２重巻きパイプ用鋼板である。 That is, the present invention includes C: 0.02 to 0.08 mass%, Mn: 0.15 to 0.50 mass%, Al: 0.10 mass% or less, with the balance being Fe and inevitable impurities, An equiaxed axis having an average crystal grain size of 10 to 30 μm and a ratio (d L / d T ) of the average grain size (d T ) in the thickness direction to the average grain size (d L ) in the rolling direction of 1.4 or less It is a steel plate for double winding pipes characterized by being a grain .
本発明の鋼板は、上記成分組成に加えてさらに、Ｂ：0.0005〜0.0020mass％、Ti：0.002〜0.020mass％のうちの１種または２種、および／または、Cu：0.5mass％以下、Ni：0.5mass％以下のうちの１種または２種を含有することが好ましい。 In addition to the above component composition, the steel plate of the present invention may further include one or two of B: 0.0005 to 0.0020 mass%, Ti: 0.002 to 0.020 mass%, and / or Cu: 0.5 mass% or less, Ni : It is preferable to contain 1 type or 2 types of 0.5 mass% or less.
また、本発明は、Ｃ：０．０２〜０．０８ｍａｓｓ％、Ｍｎ：０．１５〜０．５０ｍａｓｓ％、Ａｌ：０．１０ｍａｓｓ％以下を含有し、残部がＦｅおよび不可避的不純物からなる鋼素材を、仕上圧延終了温度：７７０〜８４０℃で熱間圧延し、巻取温度：６５０〜７５０℃で巻き取り、次いで冷間圧延し、焼鈍温度：６５０〜８００℃で連続焼鈍することを特徴とする２重巻きパイプ用鋼板の製造方法を提案する。 The present invention also includes a steel material containing C: 0.02 to 0.08 mass%, Mn: 0.15 to 0.50 mass%, Al: 0.10 mass% or less, with the balance being Fe and inevitable impurities. , Hot rolling at a finish rolling finish temperature: 770-840 ° C., coiling temperature: 650-750 ° C., then cold rolling, and annealing temperature: 650-800 ° C. A method of manufacturing a steel sheet for a double-wound pipe is proposed.
本発明の製造方法は、上記成分組成に加えてさらに、Ｂ：0.0005〜0.0020mass％、Ti：0.002〜0.020mass％のうちの１種または２種、および／または、Cu：0.5mass％以下、Ni：0.5mass％以下のうちの１種または２種を含有する鋼素材を用いることが好ましい。 In addition to the above component composition, the production method of the present invention further includes one or two of B: 0.0005 to 0.0020 mass%, Ti: 0.002 to 0.020 mass%, and / or Cu: 0.5 mass% or less, It is preferable to use a steel material containing one or two of Ni: 0.5 mass% or less.
本発明の製造方法は、連続焼鈍法を採用しているので、高い生産効率で、軟質かつ均一な材質の２重巻きパイプ用鋼板を製造することができる。また、本発明の２重巻きパイプ用鋼板は、材質が軟質かつ均一であるので、材料に起因するトラブルがなく高い歩留まりで安定した造管ができる他、造管用の金型や治具、工具の摩耗を低減し、その寿命の延長を図ることができる。さらに、本発明の鋼板を用いた２重巻きパイプは、造管後のろう付け処理で異常な粗大粒や溶融銅の侵入を起こさないので、従来と同等以上の品質を経済的に得ることができる。 Since the manufacturing method of the present invention employs a continuous annealing method, a steel plate for a double-wound pipe made of a soft and uniform material can be manufactured with high production efficiency. In addition, since the steel sheet for double-pipe pipes of the present invention is soft and uniform, it can be stably tube-formed with a high yield without any trouble caused by the material, and a mold, jig, or tool for tube-making It is possible to reduce the wear and extend the service life. Further, the double-pipe pipe using the steel plate of the present invention does not cause abnormal coarse grains or molten copper intrusion in the brazing process after the pipe making, so that it is possible to economically obtain a quality equal to or higher than the conventional one. it can.
本発明において、鋼素材の成分組成を上記範囲に制限する理由について説明する。
Ｃ：0.02〜0.08mass％
Ｃは、鋼板の強度を高める元素であり、低減することにより軟質化し、変形応力の低減、形状凍結性の改善を通して造管時の成形性の向上を図ることができる。しかし、0.02mass％未満になると自己ろう付け工程における結晶粒の粗大化が顕著になり、必要とする強度および靭性の確保が困難となるほか、いわゆるオレンジピール現象に似た肌荒れを発生する可能性が増大する。一方、0.08mass％を超えると、ろう付けの冷却工程で多くの低温変態相が生成するため、パイプが硬質化して、成形性が低下する。また、溶接性も低下する傾向にある。したがって、Ｃは0.02〜0.08mass％の範囲とする。なお、より安定した材質と優れた延性を必要とする場合は、0.025〜0.06mass％の範囲とするのが好ましい。
In the present invention, the reason for limiting the component composition of the steel material to the above range will be described.
C: 0.02-0.08 mass%
C is an element that enhances the strength of the steel sheet, and can be softened by reducing it, and can improve the formability during pipe making through reducing deformation stress and improving shape freezing property. However, if it becomes less than 0.02 mass%, the coarsening of crystal grains in the self-brazing process becomes remarkable, making it difficult to secure the required strength and toughness, and the possibility of causing rough skin similar to the so-called orange peel phenomenon. Will increase. On the other hand, if it exceeds 0.08 mass%, many low-temperature transformation phases are generated in the brazing cooling step, so that the pipe becomes hard and the moldability is lowered. Also, the weldability tends to decrease. Therefore, C is in the range of 0.02 to 0.08 mass%. In addition, when a more stable material and excellent ductility are required, the range is preferably 0.025 to 0.06 mass%.
Mn：0.15〜0.50mass％
Mnは、Ｓに起因する熱間割れを防止するのに有効な元素であり、含有するＳ量に応じて添加する必要がある。また、Mnは、結晶粒の微細化効果、特に、高温における結晶粒の粗大化を抑制する効果を有する。これらの効果を発現するためには、0.15mass％以上の含有が必要である。しかし、過度に含有すると、耐食性を劣化したり、鋼板を硬質化して冷間圧延性が悪くなるので、その上限を0.50mass％とする。なお、より良好な耐蝕性と成形性が必要な場合には、0.40mass％以下とするのが好ましい。
Mn: 0.15-0.50mass%
Mn is an element effective for preventing hot cracking due to S, and needs to be added according to the amount of S contained. In addition, Mn has an effect of suppressing crystal grain refinement, particularly an effect of suppressing crystal grain coarsening at high temperatures. In order to express these effects, it is necessary to contain 0.15 mass% or more. However, if contained excessively, the corrosion resistance deteriorates or the steel sheet is hardened to deteriorate the cold rolling property, so the upper limit is made 0.50 mass%. In addition, when better corrosion resistance and moldability are required, it is preferable to set it as 0.40 mass% or less.
Al：0.10mass％以下
Alは、鋼の脱酸に必要な元素であり、鋼の清浄度を向上させるためには0.01mass％以上の含有量が望ましい。しかし、含有量が多過ぎると、表面性状の劣化を招くので、その上限を0.10mass％とする。なお、材質の安定性という観点からは0.02〜0.06mass％の範囲で含有するのが望ましい。
Al: 0.10 mass% or less
Al is an element necessary for deoxidation of steel, and in order to improve the cleanliness of steel, a content of 0.01 mass% or more is desirable. However, if the content is too large, the surface properties are deteriorated, so the upper limit is made 0.10 mass%. In addition, it is desirable to contain in the range of 0.02-0.06 mass% from a viewpoint of material stability.
本発明の鋼板は、上記必須成分以外に、Ｂ，Tiのうちの１種または２種、および／または、Cu，Niのうちの１種または２種を下記の範囲で含有することができる。
Ｂ：0.0005〜0.0020mass％、Ti：0.002〜0.020mass％
Ｂ，Tiは、造管後の組織を微細化して強度を確保すると共に、Ｎを迅速に固定して自己ろう付け後の時効劣化を抑制する効果を有するため、造管性の改善に寄与する元素である。このような効果は、Ｂ：0.0005mass％以上、Ti：0.002mass％以上の含有量で発揮される。しかし、Ｂ：0.0020mass％超え、Ti：0.020mass％超え含有すると、熱間加工性が劣化して、熱延鋼板の耳割れ等の不具合を発生するので好ましくない。よって、Ｂ，Tiは、Ｂ：0.0005〜0.0020mass％および／またはTi：0.002〜0.020mass％の範囲で含有することができる。より好ましくは、Ｂ：0.0005〜0.0015mass％および／またはTi：0.005〜0.015mass％の範囲である。
In addition to the above essential components, the steel sheet of the present invention may contain one or two of B and Ti and / or one or two of Cu and Ni in the following ranges.
B: 0.0005 to 0.0020 mass%, Ti: 0.002 to 0.020 mass%
B and Ti have the effect of reducing the aging deterioration after self-brazing by minimizing the structure after pipe making and securing the strength, and contribute to the improvement of pipe making. It is an element. Such an effect is exhibited at a content of B: 0.0005 mass% or more and Ti: 0.002 mass% or more. However, if B: more than 0.0020 mass% and Ti: more than 0.020 mass%, the hot workability deteriorates and problems such as ear cracks of the hot-rolled steel sheet occur, which is not preferable. Therefore, B and Ti can be contained in the range of B: 0.0005 to 0.0020 mass% and / or Ti: 0.002 to 0.020 mass%. More preferably, it is the range of B: 0.0005-0.0015mass% and / or Ti: 0.005-0.015mass%.
Cu：0.5mass％以下、Ni：0.5mass％以下
Cu，Niは、２重巻きパイプに特有なCuの電気めっき工程およびそれを造管した後の自己ろう付け工程において、めっきの密着性を向上させ、濡れ性を改善する効果があるので、鋼管の信頼性を増すためには含有することが好ましい元素である。この効果を得るためには、Cu：0.05mass％以上、Ni：0.05mass％以上を含有することが好ましい。しかし、添加量がそれぞれ0.5mass％を超える場合には、鋼板の変形抵抗が増加し、冷間圧延性の低下を招く。また、冷間圧延性の観点から、Cu，Niの合計量は0.7mass％以下とすることが好ましい。よって、Cu，Niを含有する場合には、Cu：0.5mass％以下、Ni：0.5mass％以下のうちの１種または２種を含有することが好ましく、Cu，Niの合計量は0.7mass％以下とすることがさらに好ましい。
Cu: 0.5 mass% or less, Ni: 0.5 mass% or less
Cu and Ni have the effect of improving the adhesion of the plating and improving the wettability in the electroplating process of Cu, which is unique to double-rolled pipes, and in the self-brazing process after it is piped. In order to increase the reliability, it is an element that is preferably contained. In order to acquire this effect, it is preferred to contain Cu: 0.05 mass% or more and Ni: 0.05 mass% or more. However, when the addition amount exceeds 0.5 mass%, the deformation resistance of the steel sheet increases and the cold rolling property is lowered. From the viewpoint of cold rollability, the total amount of Cu and Ni is preferably 0.7 mass% or less. Therefore, when Cu and Ni are contained, it is preferable to contain one or two of Cu: 0.5 mass% or less and Ni: 0.5 mass% or less, and the total amount of Cu and Ni is 0.7 mass%. More preferably, it is as follows.
本発明の鋼板において、上記以外の成分は、Feおよび不可避的不純物である。
ただし、不可避的不純物として含有されるSi，Ｐ，Ｓ，Ｎは下記の範囲に制限することが好ましい。
Si：0.05mass％以下
Siは、多量に含有すると、めっきの密着性の低下や耐食性の低下を引き起こすほか、固溶強化により鋼を硬質化して成形時の変形抵抗の増加を招くので、0.05mass％以下とするのが好ましい。特に優れた耐食性が必要な場合には、0.02mass％以下に制限するのがより好ましい。
In the steel sheet of the present invention, components other than those described above are Fe and inevitable impurities.
However, Si, P, S, and N contained as inevitable impurities are preferably limited to the following ranges.
Si: 0.05 mass% or less
When Si is contained in a large amount, it causes a decrease in plating adhesion and corrosion resistance, and also hardens the steel by solid solution strengthening and causes an increase in deformation resistance during molding. preferable. In particular, when excellent corrosion resistance is required, it is more preferable to limit to 0.02 mass% or less.
Ｐ：0.02mass％以下
Ｐは、鋼を硬質化させるほか、フランジ加工性(パイプ成形後の拡管加工性)や形状凍結性、耐食性を悪化させる有害な元素であるため、極力低減し0.02mass％以下とするのが好ましい。これらの特性が特に重要視される場合には、0.01mass％以下とするのがより好ましい。
P: 0.02 mass% or less P is a harmful element that hardens steel and also deteriorates flange formability (pipe-forming workability after pipe forming), shape freezing property, and corrosion resistance. The following is preferable. When these characteristics are regarded as particularly important, the content is more preferably 0.01 mass% or less.
Ｓ：0.02mass％以下
Ｓは、鋼中に硫化物系介在物として存在し、鋼板の延性を減少し、耐食性の劣化をもたらす元素であるので、その上限を0.02mass％とするのが好ましい。特に良好な加工性が要求される用途においては、0.01mass％以下とすることが望ましい。
S: 0.02 mass% or less S is an element that exists as sulfide inclusions in steel, reduces the ductility of the steel sheet, and causes deterioration of corrosion resistance. Therefore, the upper limit is preferably set to 0.02 mass%. In applications that require particularly good workability, it is desirable that the content be 0.01 mass% or less.
Ｎ：0.0050mass％以下
Ｎは、含有量が増加すると、素材鋼板中の固溶Ｎが増加して、耐時効性を悪化させる可能性がある。このような悪影響を回避するためには、Ｎは0.0050mass％以下とすることが好ましい。なお、材質の安定性、製品歩留まりの向上の観点からは、0.0030mass％以下とするのがより好ましい。
N: 0.0050 mass% or less When the content of N increases, solid solution N in the raw steel plate increases, which may deteriorate aging resistance. In order to avoid such adverse effects, N is preferably 0.0050 mass% or less. In addition, from the viewpoint of improving the stability of the material and the product yield, it is more preferable to set it to 0.0030 mass% or less.
次に、本発明の鋼板について説明する。
本発明の鋼板は、基本的にフェライト組織からなり、フェライトの他は、Feの炭化物等が含まれる。そのフェライト組織の平均結晶粒径は、10〜30μmであることが必要である。平均結晶粒径が10μm未満では、鋼が硬質化し、造管時の形状凍結性が悪化し製品不良の発生や金型や工具等の磨耗の増加を招く。一方、平均結晶粒径が30μmを超えると、軟質化し過ぎて造管性が不安定となるほか、造管−熱処理後の組織を均一微細に保つことが困難となり、パイプとして必要な強度および靭性が得られなくなる。したがって、素材鋼板でのフェライト組織の平均結晶粒径は10〜30μmの範囲に規制する必要がある。
Next, the steel plate of the present invention will be described.
The steel sheet of the present invention is basically composed of a ferrite structure, and includes Fe carbide and the like in addition to ferrite. The average crystal grain size of the ferrite structure needs to be 10 to 30 μm. If the average crystal grain size is less than 10 μm, the steel becomes hard and the shape freezing property at the time of pipe making deteriorates, resulting in the occurrence of product defects and increased wear of molds and tools. On the other hand, if the average crystal grain size exceeds 30 μm, it becomes too soft and the tube forming property becomes unstable, and it becomes difficult to keep the structure after tube forming and heat treatment uniform and fine, and the strength and toughness required as a pipe Cannot be obtained. Therefore, it is necessary to regulate the average crystal grain size of the ferrite structure in the raw steel plate within a range of 10 to 30 μm.
なお、連続焼鈍法により製造する本発明鋼板のフェライト粒は等軸粒であり、従来のアルミキルド鋼の箱焼鈍材特有の展伸粒とは形態が異なる。その結果、あるいは焼鈍法の違いに起因する粒界構造、粒界偏析等の違いにより、従来の箱焼鈍材において問題となっていた、自己ろう付け処理を行った際に溶融した銅が結晶粒界への侵入し脆性を引き起こすという問題点が解消される、即ち、溶融銅の粒界への侵入が抑制されて耐銅浸透性が改善されるという効果が得られることも新たに判明した。ここで、等軸粒とは、圧延方向と平行な板厚断面で観察したときに、板厚方向の平均粒径(ｄT)と圧延方向の平均粒径(ｄL)の比(ｄL/ｄT)が1.4以下であることを意味する。また、箱焼鈍材に見られる粗大な表層のフェライト粒は本発明鋼にはなく、これも、耐銅浸透性の点では有利である。 In addition, the ferrite grains of the steel sheet of the present invention manufactured by the continuous annealing method are equiaxed grains, and the form is different from the expanded grains peculiar to the box annealed material of the conventional aluminum killed steel. As a result, or due to differences in grain boundary structure, grain boundary segregation, etc. due to differences in annealing methods, copper that has melted during the self-brazing process, which has been a problem in conventional box annealing materials, is crystal grains. It has also been newly found that the problem of intrusion into the boundary and causing brittleness is solved, that is, the penetration of molten copper into the grain boundary is suppressed and copper permeation resistance is improved. Here, the equiaxed grain is the ratio (d L ) of the average grain size (d T ) in the thickness direction to the average grain size (d L ) in the rolling direction when observed in the thickness cross section parallel to the rolling direction. / d T ) is 1.4 or less. Moreover, the coarse surface layer ferrite grains found in the box annealed material are not present in the steel of the present invention, and this is also advantageous in terms of resistance to copper penetration.
なお、本発明の２重巻きパイプ用鋼板に求められる機械的特性は、造管性およびパイプ製品での機械的特性を考慮した場合には、軟質過ぎても、硬質過ぎても好ましくない。なぜならば、軟質過ぎると、造管後のパイプ強度が低くなり過ぎる等の問題があり、一方、硬質過ぎると、造管時の形状凍結性が劣化して造管性が悪化したり、造管後のパイプの加工性が低下したり、造管用の金型や治具等の磨耗を速める等の問題があるからである。したがって、良好な造管性およびパイプ品質を確保するためには、素材鋼板の降伏応力(ＹＳ)は、215〜300MPa程度であることが好ましい。より、好ましくは、220〜280MPaである。 Note that the mechanical properties required for the double-pipe steel sheet of the present invention are not preferable whether they are too soft or too hard in view of pipe forming properties and mechanical properties of pipe products. This is because, if it is too soft, there is a problem that the pipe strength after pipe making becomes too low. On the other hand, if it is too hard, the shape freezing property at the time of pipe making deteriorates and the pipe forming property deteriorates. This is because there is a problem that the workability of the later pipe is deteriorated and the wear of the mold or jig for pipe making is accelerated. Therefore, in order to ensure good tubeability and pipe quality, the yield stress (YS) of the material steel plate is preferably about 215 to 300 MPa. More preferably, it is 220 to 280 MPa.
ちなみに、造管後のパイプに求められる機械的特性は、７mmφ程度の径のパイプの場合、降伏応力(ＹＳ)：210〜280MPa、引張強度：290〜350MPa、伸び(Ｅｌ)：40％以上である。また、180°曲げを行った際に、ろう付け時の銅浸透などに起因する表面割れを生じないこと、異常粗大粒の存在に起因する表面の肌荒れ等の発生がないことも重要な要求特性である。 Incidentally, the mechanical properties required for pipes after pipe making are as follows: Yield stress (YS): 210-280 MPa, Tensile strength: 290-350 MPa, Elongation (El): 40% or more is there. In addition, when bending 180 °, it is important that there are no surface cracks due to copper penetration during brazing, and that there is no surface roughness due to the presence of abnormally large grains. It is.
次に、本発明の２重巻きパイプ用鋼板の製造方法について説明する。
本発明の鋼板は、上記好適な成分組成に調整した鋼を転炉、電気炉等で溶製し、鋳造して鋼スラブとし、この鋼スラブを熱間圧延し、酸洗し、冷間圧延し、その後、連続焼鈍して製造することが好ましい。鋼スラブの製造方法としては、造塊−分塊法あるいは連続鋳造法のいずれでもよいが、スラブ品質、特に成分のマクロ偏析を防止するためには連続鋳造法で製造するのが好ましい。また、鋼スラブを熱間圧延するに際しては、いったん室温まで冷却してから加熱炉で再加熱するのが一般的であり、この時のスラブ加熱温度(ＳＲＴ)は、後述する熱間圧延仕上終了温度を確保するためには1000〜1250℃とすることが好ましい。なお、仕上圧延終了温度が確保できるならば、上記再加熱法に代えて、室温まで冷却することなく加熱炉に装入する温片装入や鋳造スラブをそのまま圧延する直接圧延などの省エネルギープロセスを採用してもよい。
Next, the manufacturing method of the steel plate for double winding pipes of this invention is demonstrated.
The steel sheet of the present invention is a steel slab prepared by melting a steel adjusted to the above-mentioned preferred component composition in a converter, electric furnace, etc., and hot rolling, pickling, and cold rolling the steel slab. Then, it is preferable to manufacture by continuous annealing. The method for producing the steel slab may be either the ingot-making method or the continuous casting method, but it is preferably produced by the continuous casting method in order to prevent slab quality, particularly macro segregation of components. Also, when hot rolling a steel slab, it is generally cooled to room temperature and then reheated in a heating furnace. The slab heating temperature (SRT) at this time is the hot rolling finish described later In order to ensure temperature, it is preferable to set it as 1000-1250 degreeC. If the finish rolling finish temperature can be secured, instead of the above reheating method, an energy saving process such as hot strip charging into the heating furnace without cooling to room temperature or direct rolling for rolling the cast slab as it is can be performed. It may be adopted.
熱間圧延終了温度（ＦＤＴ）
熱間圧延の仕上圧延終了温度は、770〜840℃の範囲であることが必要である。仕上圧延終了温度が840℃を上回ると、冷延、焼鈍後の鋼板組織が過度に微細化して造管性が低下する。一方、770℃を下回るとスケールに起因する表面の庇の発生が顕在化することに加えて、母板となる熱延コイルの幅方向の微視組織の均一性が低下し、素材鋼板の形状不良を招くため、造管性の低下を引き起こす。したがって、仕上圧延終了温度は770〜840℃の範囲とする。好ましくは、780〜830℃の範囲である。
Hot rolling finish temperature (FDT)
The finish rolling finishing temperature of the hot rolling needs to be in the range of 770 to 840 ° C. When the finish rolling finish temperature exceeds 840 ° C., the steel sheet structure after cold rolling and annealing is excessively refined, and the pipe forming property is lowered. On the other hand, when the temperature is below 770 ° C, the generation of surface wrinkles due to scale becomes obvious, and the uniformity of the microstructure in the width direction of the hot-rolled coil that becomes the base plate decreases, resulting in the shape of the steel plate It causes defects and causes a drop in tubeability. Accordingly, the finish rolling finish temperature is set to a range of 770 to 840 ° C. Preferably, it is the range of 780-830 degreeC.
巻取温度（ＣＴ）
熱間圧延された鋼板は、必要に応じて水冷等により強制冷却し、コイルに巻き取る。この時の巻取温度は、650〜750℃の範囲とする必要がある。巻取温度が750℃を超えると、結晶組織が粗大化し、これが冷延、焼鈍後にも継承されて、冷延鋼板の材質の不均一を招き、造管性の低下を招く。また、コイルの内巻部、中央部、外巻部ならびにコイルの幅端部と幅中央部の熱履歴の差が大きいために、コイルの長手方向、幅方向の材質のばらつきが大きくなり、これも造管性には好ましくない。一方、巻取温度が650℃未満となると、冷延焼鈍後の組織がフェライト粒径で10μmを下回り、過度に細粒となって硬質化するため好ましくない。即ち、前述のように熱間圧延終了温度を調整すると共に巻取温度を650〜750℃の範囲に制御することで、熱延鋼板を比較的粗大でかつ均一な組織とすることができ、ひいては、冷延・焼鈍後においても軟質で均一な鋼板を得ることができる。
Winding temperature (CT)
The hot-rolled steel sheet is forcibly cooled by water cooling or the like as necessary, and is wound on a coil. The coiling temperature at this time needs to be in the range of 650 to 750 ° C. When the coiling temperature exceeds 750 ° C., the crystal structure becomes coarse, which is inherited even after cold rolling and annealing, causing unevenness of the material of the cold rolled steel sheet and reducing the pipe forming property. In addition, because of the large difference in the thermal history between the coil inner winding, center, outer winding and coil width end and width center, there is a large variation in the length and width of the coil. However, this is not preferable for tube forming. On the other hand, if the coiling temperature is less than 650 ° C., the structure after cold rolling annealing is less than 10 μm in ferrite grain size, and is excessively fine and hardened, which is not preferable. That is, by adjusting the hot rolling end temperature as described above and controlling the coiling temperature in the range of 650 to 750 ° C., the hot-rolled steel sheet can have a relatively coarse and uniform structure, and thus Even after cold rolling and annealing, a soft and uniform steel sheet can be obtained.
なお、上記熱延終了後に強制冷却を行う場合には、鋼板組織の再結晶を促し、材質の均一化を促進するために、仕上圧延終了後から強制冷却開始までに少なくとも１秒以上の放冷時間を設けることが好ましい。また、コイルの先端、後端における通板を安定させ、鋼帯の全長に亘って安定して熱間圧延することを容易とし、均一な材質を得るために、粗圧延を終えたシートバーを仕上圧延機入側で接合し、連続的に仕上圧延(エンドレス圧延)を行うことが好ましい。さらに、コイル幅方向の温度ムラを防止するために、シートバーのエッジヒーターを適用することが好ましい。
熱延したコイルは、その後、常法に従い、酸洗、冷間圧延する。この冷間圧延における圧下率は、冷延焼鈍後に均一な組織を得るため70〜90％の範囲とすることが好ましい。
When forced cooling is performed after the hot rolling is completed, the steel sheet structure is recrystallized, and in order to promote homogenization of the material, it is allowed to cool for at least 1 second from the end of finish rolling to the start of forced cooling. It is preferable to provide time. In addition, in order to stabilize the passage plate at the front and rear ends of the coil, to facilitate stable hot rolling over the entire length of the steel strip, and to obtain a uniform material, It is preferable to join at the entrance of the finishing mill and continuously perform finish rolling (endless rolling). Furthermore, it is preferable to apply an edge heater for the seat bar in order to prevent temperature unevenness in the coil width direction.
The hot-rolled coil is then pickled and cold-rolled in accordance with conventional methods. The rolling reduction in this cold rolling is preferably in the range of 70 to 90% in order to obtain a uniform structure after cold rolling annealing.
連続焼鈍
本発明においては、冷間圧延した鋼板は、生産効率の向上、材質の均一化を目的として連続焼鈍法を採用する。この時の焼鈍温度は、650〜800℃で行う必要がある。焼鈍温度が650℃を下回ると、組織の大半が未再結晶組織となり、実質的に造管することが不可能となるからである。再結晶組織とし十分な軟質化を図るためには、焼鈍温度は650℃以上とする必要がある。しかし、極低炭素鋼の加工用冷延鋼板で行われているように、800℃を超える高温で焼鈍した場合には、鋼組織の粗大化、不均一化が進むために、造管−熱処理後の組織の均一化、微細化が達成できなくなる。よって、連続焼鈍における焼鈍温度は650〜800℃の範囲とする。材質の安定性の点からは700〜800℃の範囲が好ましい。なお、焼鈍温度での保持時間(均熱時間)は、10〜120秒の範囲であることが好ましい。10秒未満では、再結晶が不十分となり、安定した再結晶組織を得られない場合がある。一方、120秒を超えると、生産性を阻害する。また、焼鈍後の冷却は、冷却速度30〜150℃/secで行い、その後、350〜450℃の温度範囲で20〜120秒程度の過時効処理を行ってもよい。
Continuous annealing In the present invention, a cold-rolled steel sheet employs a continuous annealing method for the purpose of improving production efficiency and homogenizing the material. The annealing temperature at this time needs to be 650-800 degreeC. This is because when the annealing temperature is below 650 ° C., most of the structure becomes a non-recrystallized structure, and it becomes impossible to form a tube substantially. In order to obtain a recrystallized structure and sufficient softening, the annealing temperature needs to be 650 ° C. or higher. However, as is done with cold-rolled steel sheets for processing of ultra-low carbon steel, when annealing at a high temperature exceeding 800 ° C, the steel structure becomes coarser and non-uniform, so pipe-forming and heat treatment Later homogenization and refinement of the structure cannot be achieved. Therefore, the annealing temperature in the continuous annealing is set to a range of 650 to 800 ° C. The range of 700-800 degreeC is preferable from the point of stability of a material. The holding time (soaking time) at the annealing temperature is preferably in the range of 10 to 120 seconds. If it is less than 10 seconds, recrystallization becomes insufficient and a stable recrystallized structure may not be obtained. On the other hand, if it exceeds 120 seconds, productivity will be inhibited. Moreover, cooling after annealing may be performed at a cooling rate of 30 to 150 ° C./sec, and then an overaging treatment may be performed for about 20 to 120 seconds in a temperature range of 350 to 450 ° C.
スキンパス圧延（調質圧延）
連続焼鈍を行った鋼板は、表面粗度の調整、形状矯正、機械的特性改善(降伏点伸びの抑制)のほか、必要に応じて板厚低減を目的としたスキンパス圧延を行ってもよい。スキンパスの圧下率（伸び率）は、２％以下であることが好ましいが、１％程度でも上記効果を十分に得ることができる。なお、このスキンパス圧延は、必要ない場合は省いてもよい。
Skin pass rolling (temper rolling)
The steel sheet that has been subjected to continuous annealing may be subjected to skin pass rolling for the purpose of reducing the sheet thickness, if necessary, in addition to adjusting the surface roughness, correcting the shape, and improving the mechanical properties (suppressing the yield point elongation). The skin pass reduction rate (elongation rate) is preferably 2% or less, but the effect can be sufficiently obtained even at about 1%. This skin pass rolling may be omitted if not necessary.
表面処理
上述した工程により製造された本発明の鋼板は、その後、Cu等の自己ろう付け作用を有する金属を電気めっきしてから、スリットしてフープとし、２重巻きパイプに造管し、ろう付け処理を施し、製品とする。上記ろう付け性を向上するために、連続焼鈍ラインの出側あるいは別ラインにおいて、NiめっきやZnめっき等を行い、その後、Cu等の自己ろう付け作用を有する金属の電気めっきを行ってもよい。ろう付け後のパイプは、Cu等の金属により表面が被覆されているため、基本的にはさらなる表面処理は不要であるが、上記金属めっきの作用を補うような、Znめっきやターンめっき、化学的あるいは電気化学的処理、塗装などを造管後、必要に応じて行ってもよい。
Surface treatment The steel sheet of the present invention manufactured by the above-described process is then electroplated with a metal having a self-brazing action such as Cu, and then slits into a hoop, which is then piped into a double-rolled pipe. The product is processed by attaching. In order to improve the brazing property, Ni plating or Zn plating may be performed on the exit side of the continuous annealing line or in another line, and thereafter, electroplating of a metal having a self-brazing function such as Cu may be performed. . Since the surface of the pipe after brazing is covered with a metal such as Cu, basically no further surface treatment is required, but Zn plating, turn plating, chemicals, etc., that supplement the above-mentioned metal plating function. It may be carried out as necessary after the pipes are made, for example, by manual or electrochemical treatment or painting.
表１に示す成分組成を有し、残部が実質的にFeからなる鋼を転炉で溶製し、連続鋳造により260mm厚の鋼スラブとし、この鋼スラブを５パスの粗圧延により30mm厚のシートバーとし、７スタンドのタンデム圧延機で、表１中に併記した温度条件で仕上圧延する熱間圧延を行い、板厚2.6mmあるいは2.9mmの熱延鋼板とした。この熱延鋼板を、塩酸酸洗ラインで酸洗し、タンデム圧延機で0.34〜0.37mmの板厚に冷間圧延し、その後、同じく表１に併記した温度で連続焼鈍し、さらにその一部は、焼鈍後、スキンパス圧延を行い、２重巻きパイプ用鋼板とした。このようにして得た２重巻きパイプ用鋼板について、下記の要領で平均結晶粒径および引張特性を測定した。
(1) 平均結晶粒径；２重巻きパイプの素材に用いた鋼板から試験片を採取し、圧延方向と平行な方向の断面組織を、光学顕微鏡を用いて100倍で観察し、フェライト組織の平均結晶粒径を、JIS G 0552に規定された切断法に準拠して求めた。なお、フェライトの平均結晶粒径を求めるに際しては、板厚方向と圧延方法の各々の方向に線分を引き、これらの線分と交差する結晶粒数から求められる平均粒径を各々ｄT，ｄLとした時に、これらｄLとｄTの平均をフェライト組織の平均粒径とした。
(2) 引張特性；上記鋼板の圧延方向からJIS ５号引張試験片を採取し、JIS Z 2241 に準拠して引張試験を行い、降伏応力(ＹＳ)、引張強度(ＴＳ)および伸び(Ｅｌ)を測定した。
A steel having the composition shown in Table 1 and the balance substantially consisting of Fe is melted in a converter and made into a steel slab of 260 mm thickness by continuous casting. This steel slab is made 30 mm thick by rough rolling of 5 passes. Using a 7-stand tandem rolling mill as a sheet bar, hot rolling was performed by finish rolling under the temperature conditions listed in Table 1 to obtain a hot-rolled steel sheet having a thickness of 2.6 mm or 2.9 mm. This hot-rolled steel sheet is pickled with a hydrochloric acid pickling line, cold-rolled to a thickness of 0.34 to 0.37 mm with a tandem rolling mill, and then continuously annealed at the same temperature as shown in Table 1, and a part thereof. Was subjected to skin pass rolling after annealing to obtain a steel sheet for a double-pipe pipe. About the steel plate for double winding pipes obtained in this way, the average crystal grain size and tensile properties were measured in the following manner.
(1) Average crystal grain size: Test specimens were taken from the steel sheet used for the material of the double-pipe pipe, and the cross-sectional structure in the direction parallel to the rolling direction was observed at 100 times using an optical microscope. The average crystal grain size was determined according to the cutting method defined in JIS G 0552. In determining the average crystal grain size of ferrite, line segments are drawn in the plate thickness direction and the rolling method, and the average particle diameters determined from the number of crystal grains intersecting these line segments are d T , When d L was taken, the average of these d L and d T was taken as the average grain size of the ferrite structure.
(2) Tensile properties: JIS No. 5 tensile test specimens were taken from the rolling direction of the steel sheet and subjected to a tensile test according to JIS Z 2241. Yield stress (YS), tensile strength (TS) and elongation (El) Was measured.
さらに、上記２重巻きパイプ用鋼板に厚さ10μmの電気銅めっきを施し、外径6.4mmφの２重巻きパイプに成形加工し、５％の引抜加工を行った後、1120℃×20secの熱処理を施すことにより銅めっき層を溶融させて自己ろう付け処理を行った。この際、造管性について造管時の製品歩留り、トラブル発生頻度、引抜加工治具の寿命を下記の要領で評価した。また、上記のようにして製造したろう付け後の２重巻きパイプについて引張特性、曲げ試験、熱処理による異常粗大粒の発生の有無および溶融銅の浸透深さを調査した。
(1) 製品歩留り；非定常部その他の素材要因以外の不良部を除いた製品歩留まり（＝製品重量／素材重量×100(％)）で評価した。
(2) 加工治具の寿命(工具寿命指数)；従来の箱焼鈍材における引抜加工用治具の磨耗による取換え頻度（＝取換え回数／素材重量(回/ｔ)）に対する、本発明の鋼板を用いたときの取換え頻度の比で評価した。
(3) 引張特性；ろう付け後のパイプを長さ300mmに切り出し、引張試験を行い、降伏応力(ＹＳ)、引張強度(ＴＳ)、伸び(Ｅｌ)を測定した。なお、引張試験における標点距離は、50mmとした。
(4) 異常粗大粒の有無；ろう付け後のパイプの横断面組織を５％ナイタール液で腐食した後、光学顕微鏡を用いて100倍で観察し、異常粗大粒の発生有無を調査した。ここで、異常粗大粒とは、最長径が50μmを超える大きさの粗大粒を意味し、横断面を４箇所測定し、そのうちの１箇所でも異常粗大粒が認められた場合には、異常粗大粒有りと評価した。
(5)曲げ性；ろう付け後のパイプを180°曲げし、割れの発生有無、表面の肌荒れを目視観察し、いずれも無い物を良と評価した。
(6)銅浸透深さ；異常粗大粒の有無を調査した試料について、ＸＭＡ(Ｘ線マイクロアナリシス)分析装置を用いて、ろう付け部のCu特性Ｘ線像を、前述した４箇所について撮影し、Cuの侵入深さ(μm)を測定した。
Furthermore, the steel sheet for double-pipe pipes is plated with 10μm thick copper, formed into a double-pipe pipe with an outer diameter of 6.4mmφ, 5% drawn, and then heat treated at 1120 ℃ × 20sec. The copper plating layer was melted by performing a self-brazing process. At this time, the product yield at the time of pipe making, the frequency of trouble occurrence, and the life of the drawing jig were evaluated in the following manner for pipe forming. In addition, the double-rolled pipe after brazing manufactured as described above was examined for tensile characteristics, bending test, occurrence of abnormally large grains by heat treatment, and penetration depth of molten copper.
(1) Product yield: Evaluated by product yield (= product weight / material weight × 100 (%)) excluding defective parts other than unsteady parts and other material factors.
(2) Life of the processing jig (tool life index): The frequency of replacement of the conventional box annealed material due to wear of the drawing jig (= number of replacements / material weight (times / t)). Evaluation was based on the ratio of replacement frequency when using steel plates.
(3) Tensile properties: The brazed pipe was cut into a length of 300 mm, subjected to a tensile test, and measured for yield stress (YS), tensile strength (TS), and elongation (El). The gauge distance in the tensile test was 50 mm.
(4) Presence or absence of abnormal coarse particles: After corroding the cross-sectional structure of the pipe after brazing with 5% nital solution, it was observed with an optical microscope at a magnification of 100 to investigate the presence or absence of abnormal coarse particles. Here, the abnormal coarse particles mean coarse particles having a maximum diameter exceeding 50 μm, and when the cross-section is measured at four points, and abnormal coarse particles are observed at one of them, the abnormal coarse particles are observed. Evaluated as having grains.
(5) Bendability: The brazed pipe was bent 180 °, and the presence or absence of cracks and the surface roughness of the surface were visually observed, and none was evaluated as good.
(6) Copper penetration depth: Using the XMA (X-ray microanalysis) analyzer, Cu characteristic X-ray images of the brazed part were taken at the above-mentioned four locations for the samples investigated for the presence of abnormally large grains. , Cu penetration depth (μm) was measured.
上記測定の結果を表２にまとめて示した。この結果から、素材の成分組成が適正範囲にありかつ適正な条件で製造された本発明の鋼板は、造管時の製品歩留まりが高く、造管性は良好であることがわかる。これらの事実は、素材鋼板のコイル内の長手方向、幅方向の変動が小さいために、造管加工性が安定して行えたことによるものである。また、本発明の鋼板を造管した場合には、従来の箱焼鈍材と比較して、造管治具の寿命が、約15％向上することが確認された。この原因は、詳細は不明であるが、表面の元素濃化の有無によるものと思われる。治具・工具寿命の延長は、副材料のコスト低減の観点からは大きなメリットである。また、本発明の鋼板を用いて製造された２重巻きパイプは、異常粗大粒の発生もなく、また、銅の浸透深さも浅く、引張特性、曲げ性にも優れている。一方、本発明の成分組成を外れる比較例の鋼板を用いて２重巻きパイプを製造した場合には、造管性が従来の箱焼鈍材と比較して悪く、治具の寿命の延長も得られなかった。また、得られたパイプの特性も引張特性、曲げ性、異常粗大粒の発生有無のうちのいずれか１つ以上が劣っていた。 The results of the above measurements are summarized in Table 2. From this result, it can be seen that the steel sheet of the present invention having the component composition of the material in the proper range and manufactured under the proper conditions has a high product yield at the time of pipe making and good pipe forming property. These facts are due to the fact that the tube forming workability can be stably performed because the fluctuation in the longitudinal direction and the width direction in the coil of the material steel plate is small. Moreover, when the steel plate of this invention was pipe-formed, it was confirmed that the lifetime of a pipe making jig | tool improves about 15% compared with the conventional box annealing material. The reason for this is unknown, but it seems to be due to the presence or absence of surface element concentration. Extending the life of jigs and tools is a great advantage from the viewpoint of cost reduction of secondary materials. Moreover, the double-wound pipe manufactured using the steel plate of the present invention has no abnormally large grains, has a shallow copper penetration depth, and is excellent in tensile properties and bendability. On the other hand, when a double-pipe pipe is manufactured using a steel plate of a comparative example that deviates from the component composition of the present invention, the pipe forming property is worse than that of a conventional box annealing material, and the life of the jig is also extended. I couldn't. In addition, the obtained pipe was inferior in any one or more of tensile properties, bendability, and presence / absence of abnormal coarse grains.
表１のNo.１の成分組成を有する鋼スラブを、表３に示す条件で熱間圧延し、冷間圧延し、その後、連続焼鈍し、さらにその一部については連続焼鈍後、スキンパス圧延し、板厚0.34〜0.35mmの２重巻きパイプ用鋼板を製造した。また、比較例として、従来鋼である低炭素アルミキルド鋼を箱焼鈍し、同一板厚の２重巻きパイプ用鋼板を製造した。これらのパイプ用素材鋼板について、実施例１と同様にして特性を評価した。また、これらの素材鋼板の表面に、実施例１と同様の銅めっき(厚み10μm)を行い、6.4mmφの２重巻きパイプを製造し、やはり、実施例１と同様の要領で、２重巻きパイプとしての特性を評価した。 A steel slab having the composition of No. 1 in Table 1 is hot-rolled under the conditions shown in Table 3, cold-rolled, then continuously annealed, and a part thereof is subjected to skin-pass rolling after continuous annealing. A steel sheet for a double-wound pipe having a thickness of 0.34 to 0.35 mm was manufactured. As a comparative example, a low-carbon aluminum killed steel, which is a conventional steel, was box-annealed to produce a double-pipe steel plate having the same thickness. About these raw material steel plates for pipes, the characteristic was evaluated like Example 1. FIG. Moreover, the same copper plating (thickness 10 μm) as in Example 1 is applied to the surface of these material steel plates to produce a 6.4 mmφ double-winding pipe. Again, in the same manner as in Example 1, double-winding The characteristics as a pipe were evaluated.
得られた試験結果を表４に示した。この表４からわかるように、本発明の鋼板は、素材段階では、軟質で適当な強度を有しており、しかも、素材の長手方向、幅方向の均一性に優れているために造管性に優れ、さらには造管治具の寿命が15〜20％程度向上している。また、造管後のパイプも、適正な強度、延性および曲げ性を示しており、また、異常粗大粒の発生も認められない。また、銅浸透深さも従来の箱焼鈍材と比較して小さい。一方、本発明を外れる条件で製造した素材鋼板は、材質均一性に劣ったり、あるいは、硬質過ぎたりして造管性に劣ると共に、造管後のパイプも引張特性、曲げ性、異常粗大粒の有無のいずれか１つ以上で、従来の箱焼鈍材よりも劣るという結果が得られた。 The test results obtained are shown in Table 4. As can be seen from Table 4, the steel sheet of the present invention is soft and has an appropriate strength at the material stage, and is excellent in uniformity in the longitudinal direction and the width direction of the material, so that its pipe forming property. In addition, the life of the pipe making jig is improved by about 15 to 20%. Moreover, the pipe after pipe formation also shows appropriate strength, ductility, and bendability, and generation of abnormally coarse grains is not observed. Also, the copper penetration depth is small compared to conventional box annealed materials. On the other hand, the material steel plate manufactured under conditions that deviate from the present invention is inferior in material uniformity or too hard and inferior in pipe forming property, and the pipe after pipe forming also has tensile properties, bendability, and abnormally coarse grains. The result that it was inferior to the conventional box annealing material by any one or more of presence or absence of was obtained.
本発明の２重巻きパイプ用鋼板は、各種コンプレッサーとアクチュエータの接続パイプや自動車のブレーキチューブ、オイルチューブ等の分野のほか、気密性とろう付け性が要求される各種の用途に用いることができる。
The steel sheet for double-wound pipes according to the present invention can be used for various applications that require airtightness and brazing, in addition to fields such as connecting pipes for various compressors and actuators, automobile brake tubes, and oil tubes. .
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