JP7312583B2 - Cast iron pipe and its manufacturing method - Google Patents
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Description
本発明は、鋳鉄管およびその製造方法に関し、とりわけ、製造が容易でコストのかからない耐食性に優れた耐食層を有する鋳鉄管およびその製造方法に関する。 TECHNICAL FIELD The present invention relates to a cast iron pipe and its manufacturing method, and more particularly to a cast iron pipe having a corrosion-resistant layer which is easy to manufacture at low cost and has excellent corrosion resistance, and its manufacturing method.
従来から上下水道管などに用いられる鋳鉄管は、一般的には、金型遠心鋳造などの方法で鋳造され、その後、組織改善のために約８００～１０００℃の焼鈍炉に入れられて１～２時間程度焼鈍処理が施される。焼鈍処理は酸素雰囲気下で行われるため、外周面が酸化されて空隙を有する厚い酸化皮膜（酸化スケールとも呼ばれる）が生成される。その後、生成した酸化鉄皮膜をショットブラスト処理などによりすべて除去し、耐食用のジンクリッチペイントや耐食用の塗装等が施されている。 Cast iron pipes conventionally used for water and sewage pipes are generally cast by a method such as mold centrifugal casting, and then placed in an annealing furnace at about 800 to 1000 ° C. for 1 to 2 hours in order to improve the structure. Since the annealing treatment is performed in an oxygen atmosphere, the outer peripheral surface is oxidized to form a thick oxide film (also called oxide scale) having voids. After that, the generated iron oxide film is completely removed by shot blasting or the like, and zinc-rich paint for corrosion resistance or coating for corrosion resistance is applied.
一方、ショットブラスト処理に関連した手間と時間を削減するため、酸化鉄皮膜の発生を防止する目的で、焼鈍処理前に鋳鉄管の外周面にアルミニウムまたはアルミニウム合金皮膜を被着させ、焼鈍熱処理を行うことにより、外周面に酸化アルミニウム皮膜を形成する方法も開示されている（特許文献１）。 On the other hand, in order to reduce the labor and time associated with shot blasting, and for the purpose of preventing the generation of an iron oxide film, a method of forming an aluminum oxide film on the outer peripheral surface by applying an aluminum or aluminum alloy film to the outer peripheral surface of a cast iron pipe before annealing treatment and performing annealing heat treatment is also disclosed (Patent Document 1).
また、鋳物砂や酸化スケールなど、鋳鉄管の表面に付着している異物を除去するためにショットブラスト処理を行い、その後、亜鉛系金属を溶融して鋳鉄管の表面に吹き付け、続いて、ジンクリッチペイントを上塗りして鋳鉄管の表面に亜鉛系の防食層を形成する鋳鉄管の防食方法も開示されている（特許文献２）。 In addition, a method for preventing corrosion of cast iron pipes is also disclosed, in which shot blasting is performed to remove foreign substances adhering to the surface of cast iron pipes, such as foundry sand and oxide scale, after which a zinc-based metal is melted and sprayed onto the surface of the cast iron pipes, and zinc-rich paint is then topcoated to form a zinc-based anti-corrosion layer on the surface of the cast iron pipes (Patent Document 2).
しかしながら、特許文献２の方法では、酸化皮膜を除去するには手間と時間がかかり、さらに酸化皮膜を除去することにより、さらなる防食層が必要となりコスト高となるためさらに改善の余地がある。 However, the method of Patent Document 2 requires time and effort to remove the oxide film, and removing the oxide film requires an additional anti-corrosion layer, which increases the cost. Therefore, there is still room for improvement.
また、特許文献１の方法では、得られる防食皮膜の膜厚が薄く耐食性が十分とは言えない。 In addition, in the method of Patent Document 1, the film thickness of the anticorrosion film obtained is thin and the corrosion resistance is not sufficient.
そこで、本発明は、生産性の向上された耐食性に優れた耐食層を外面に有する鋳鉄管を提供することを課題とする。 SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a cast iron pipe having a corrosion-resistant layer on the outer surface thereof with improved productivity and excellent corrosion resistance.
本発明者らは、焼鈍処理により得られる酸化皮膜を耐食層の一部として利用し、亜鉛系溶射皮膜と組み合わせることにより、ショットブラスト処理時間の短縮、溶射量および溶射時間の短縮が可能となり、生産性の向上された耐食性に優れた耐食層を有する鋳鉄管が得られることを見出し、本発明を完成した。 The inventors of the present invention have found that by using an oxide film obtained by annealing as part of the corrosion-resistant layer and combining it with a zinc-based thermal spray coating, it is possible to shorten the shot blasting time, the amount of thermal spraying, and the thermal spraying time, and that a cast iron pipe having a corrosion-resistant layer with improved productivity and excellent corrosion resistance can be obtained, and completed the present invention.
すなわち、本発明は、
［１］焼鈍により生成される酸化皮膜層およびその外面の亜鉛系溶射皮膜層からなる耐食層を外面に有する鋳鉄管、
［２］前記酸化皮膜層が、少なくとも鋳鉄表面のケイ素を含む緻密な層を含む上記［１］記載の鋳鉄管、
［３］酸化皮膜層およびその外面の亜鉛系溶射皮膜層からなる耐食層を外面に有する鋳鉄管の製造方法であって、
鋳造した鋳鉄管を焼鈍し、表面に酸化皮膜の層を生成する工程、および
前記酸化皮膜層の外面に亜鉛系溶射を行い亜鉛系溶射皮膜層を形成する工程
を含む鋳鉄管の製造方法、ならびに
［４］亜鉛系溶射皮膜層を形成する工程の前に、得られた酸化皮膜層の空隙率の高い表層部分を除去する工程を含む上記［３］記載の製造方法
に関する。
That is, the present invention
[1] A cast iron pipe having on its outer surface a corrosion-resistant layer consisting of an oxide film layer produced by annealing and a zinc-based thermal spray coating layer on its outer surface,
[2] The cast iron pipe according to [1] above, wherein the oxide film layer comprises at least a dense layer containing silicon on the surface of the cast iron,
[3] A method for manufacturing a cast iron pipe having, on its outer surface, a corrosion-resistant layer comprising an oxide film layer and a zinc-based thermal spray coating layer on its outer surface,
The present invention relates to a cast iron pipe manufacturing method comprising the steps of annealing a cast iron pipe to form an oxide film layer on the surface thereof, and the step of forming a zinc-based thermal spray coating layer by performing zinc-based thermal spraying on the outer surface of the oxide coating layer, and [4] to the manufacturing method described in the above [3], which includes a step of removing a surface layer portion of the obtained oxide coating layer having a high porosity before the step of forming the zinc-based thermal spray coating layer.
本発明は、焼鈍処理により得られる酸化皮膜を耐食層の一部として利用し、亜鉛系溶射皮膜と組み合わせることにより、ショットブラスト処理時間の短縮と溶射量および溶射時間の短縮が可能となり、生産性の向上された耐食性に優れた耐食層を外面に有する鋳鉄管を得ることができる。 The present invention utilizes an oxide film obtained by annealing as part of the corrosion-resistant layer and combines it with a zinc-based thermal sprayed coating, thereby shortening the shot blasting time, the amount of thermal spraying, and the thermal spraying time. It is possible to obtain a cast iron pipe having a corrosion-resistant layer on the outer surface with improved productivity and excellent corrosion resistance.
＜鋳鉄管＞
本発明の一つの実施態様としては、焼鈍により生成される酸化皮膜層およびその外面の亜鉛系溶射皮膜層からなる耐食層を外面に有することを特徴とする鋳鉄管が提供される。
<Cast iron pipe>
One embodiment of the present invention provides a cast iron pipe characterized by having, on its outer surface, a corrosion-resistant layer comprising an oxide film layer formed by annealing and a zinc-based thermally sprayed coating layer on its outer surface.
（焼鈍により生成される酸化皮膜層）
焼鈍により生成される酸化皮膜層は、酸化鉄およびケイ酸化鉄を主成分とし、鋳造した鋳鉄管の組織改善のために焼鈍処理として約８００～１２００℃で数分から数十分加熱することにより、空気中の酸素により鋳鉄管表面に形成される皮膜によるものである。焼鈍は鋳鉄管の組織改善のために行われる処理であり、セメンタイトの分解およびマトリックスのフェライト化を目的とする。ダクタイル鋳鉄管の焼鈍の場合は、一般的には連続焼鈍炉で行われ、８７０℃以上の温度でセメンタイトを完全に分解し、基地組織のオーステナイト化を行う。セメンタイトの分解は、処理時間と処理温度に依存し、処理温度が高いほど処理時間を短くすることができる一方で、処理温度が低いほど長い処理時間を必要とする。
(Oxide film layer generated by annealing)
The oxide film layer formed by annealing is mainly composed of iron oxide and iron silicate, and is a film formed on the surface of the cast iron pipe by oxygen in the air by heating at about 800 to 1200 ° C. for several minutes to several tens of minutes as an annealing treatment to improve the structure of the cast iron pipe. Annealing is a process performed to improve the structure of cast iron pipes, and aims to decompose cementite and convert the matrix to ferrite. Annealing of ductile cast iron pipes is generally carried out in a continuous annealing furnace, and the cementite is completely decomposed at a temperature of 870° C. or higher to austenitize the matrix structure. The decomposition of cementite depends on the treatment time and the treatment temperature. The higher the treatment temperature, the shorter the treatment time, while the lower the treatment temperature, the longer the treatment time required.
酸化皮膜層は、焼鈍の条件によっては、鋳鉄管表面近傍では緻密な酸化皮膜となるが、鋳鉄管表面から離れるにしたがって空隙率が高くなる傾向がある。緻密な酸化皮膜と空隙率の高い酸化皮膜との割合は、焼鈍の条件により変動する。焼鈍により生成される酸化皮膜はそのまま使用することができるが、鋳鉄管素地への密着性の観点から、鋳鉄表面近傍の緻密な酸化皮膜層を耐食層に用いることがより好ましい。ここで、図３のＥＰＭＡの組成像（ＣＯＭＰＯ）により酸化皮膜の構成を説明すると、酸化皮膜層２は、大きく分けて、鋳管部１により近い緻密な酸化皮膜層２ａと、表層の空隙率の高い酸化皮膜層２ｂとの二層構造を有する。また図３のＥＰＭＡの元素マッピングの各元素の画像より、鉄管部１により近い緻密な酸化皮膜層２ａがケイ酸化鉄（Ｆｅ2ＳｉＯ4など）を主成分とするケイ素を含む層であり、表層の空隙率の高い酸化皮膜層２ｂが酸化鉄（Ｆｅ3Ｏ4、Ｆｅ2Ｏ3など）を主成分とする層であることがわかる。このため、酸化皮膜のうち空隙率が高すぎる鋳鉄管素地表面からより離れた表層部分は、ショットブラスト、サンドブラスト、高圧水などの高圧流体（エアーを含む）の吹き付け、電気化学的処理、酸などによる化学的処理などにより除去し、酸化皮膜層全体としての空隙率を低下させることができる。 Depending on the annealing conditions, the oxide film layer becomes a dense oxide film in the vicinity of the cast iron pipe surface, but the porosity tends to increase as the distance from the cast iron pipe surface increases. The ratio of the dense oxide film and the highly porous oxide film varies depending on the annealing conditions. Although the oxide film formed by annealing can be used as it is, it is more preferable to use a dense oxide film layer in the vicinity of the cast iron surface as the corrosion-resistant layer from the viewpoint of adhesion to the cast iron pipe base. Here, the structure of the oxide film will be described with reference to the composition image (COMPO) of EPMA in FIG. Further, from the image of each element of the EPMA element mapping in FIG. 3, the dense oxide film layer 2a closer to the iron pipe portion 1 is a layer containing silicon whose main component is iron silicate oxide (Fe 2 SiO 4 etc.), and the oxide film layer 2b with a high surface porosity is a layer whose main component is iron oxide (Fe 3 O 4 , Fe 2 O 3 etc.). For this reason, the surface layer portion of the oxide film that is farther away from the cast iron pipe base surface where the porosity is too high can be removed by shot blasting, sand blasting, spraying high-pressure fluid (including air) such as high-pressure water (including air), electrochemical treatment, chemical treatment with acid, etc., and the porosity of the oxide film layer as a whole can be reduced.
焼鈍処理の方法は、特に限定されるものではないが、電気炉、ガスバーナー炉および連続焼鈍炉などにより熱処理して行われる。通常連続焼鈍炉の場合、焼鈍処理の条件は、８００～１２００℃で５～３０分行われる。 The annealing treatment method is not particularly limited, but heat treatment is performed using an electric furnace, a gas burner furnace, a continuous annealing furnace, or the like. In the case of a continuous annealing furnace, the annealing treatment is usually performed at 800 to 1200° C. for 5 to 30 minutes.
（亜鉛系溶射皮膜層）
亜鉛系溶射皮膜層は、鋳鉄管の外面の焼鈍により生成される酸化皮膜の外面に亜鉛系金属を溶射することにより形成される。亜鉛系溶射皮膜としては、亜鉛溶射皮膜、亜鉛－アルミ合金溶射皮膜、亜鉛－アルミ擬合金溶射皮膜、亜鉛－ケイ素含有アルミ擬合金溶射皮膜、亜鉛－ケイ素マンガン含有アルミ擬合金溶射皮膜、亜鉛－スズ合金溶射皮膜などが挙げられる。なお、亜鉛－アルミニウム擬合金とは、溶射された亜鉛とアルミニウムとが不規則に重なり合い、外見的に亜鉛－アルミニウム合金を形成しているものをいう。
(Zinc-based thermal spray coating layer)
The zinc-based thermal spray coating layer is formed by thermally spraying a zinc-based metal onto the outer surface of the oxide coating formed by annealing the outer surface of the cast iron pipe. The zinc-based thermal spray coating includes zinc thermal spray coating, zinc-aluminum alloy thermal spray coating, zinc-aluminum pseudo alloy thermal spray coating, zinc-silicon-containing aluminum pseudo alloy thermal spray coating, zinc-silicon manganese-containing aluminum pseudo alloy thermal spray coating, zinc-tin alloy thermal spray coating, and the like. Incidentally, the zinc-aluminum pseudo-alloy means that thermally sprayed zinc and aluminum are irregularly overlapped to form a zinc-aluminum alloy in appearance.
溶射皮膜の膜厚は、溶射材料の種類、得られる鋳鉄管の用途によって適宜設定することができるが、水道管用の鋳鉄管の場合、例えば、亜鉛溶射皮膜では、日本ダクタイル鉄管協会規格のＪＤＰＡ Ｚ ２０１０－２００９「ダクタイル鋳鉄管合成樹脂塗装」に規定されている、１３０ｇ／ｍ2以上の溶射量で十分な効果を得ることができる。また、溶射皮膜の鉄地との密着性を考慮すれば、溶射量の上限は３００ｇ／ｍ2が好ましく、２６０ｇ／ｍ2がより好ましい。本発明においては、酸化皮膜層を耐食層に利用することにより、１００ｇ／ｍ2以上の溶射量で十分な耐食効果を得ることができる。もちろん他の溶射材を用いた場合には、その防食性の観点から溶射量の好ましい値は変動するものである。 The thickness of the thermal spray coating can be appropriately set depending on the type of thermal spray material and the application of the cast iron pipe to be obtained, but in the case of cast iron pipes for water pipes, for example, in the case of zinc thermal spray coating, a sufficient effect can be obtained with a thermal spray amount of 130 g / m 2 or more, which is specified in the Japan Ductile Iron Pipe Association standard JDPA Z 2010-2009 “Ductile cast iron pipe synthetic resin coating”. Further, considering the adhesion of the thermal spray coating to the steel substrate, the upper limit of the thermal spraying amount is preferably 300 g/m 2 , more preferably 260 g/m 2 . In the present invention, by using the oxide film layer as the corrosion-resistant layer, a sufficient corrosion-resistant effect can be obtained with a thermal spray amount of 100 g/m 2 or more. Of course, when other thermal spraying materials are used, the preferred amount of thermal spraying varies from the viewpoint of anti-corrosion properties.
溶射方法は特に限定されるものではないが、たとえばガス溶射法やアーク溶射法、プラズマ溶射法があげられる。より具体的には、回転しながら管軸方向に移送される鋳鉄管に、固定した溶射ガンにより亜鉛、亜鉛－アルミニウム擬合金または亜鉛－アルミニウム合金、亜鉛－ケイ素マンガン含有アルミ擬合金を溶射する方法、回転させた鋳鉄管に、溶射ガンを移動させながら亜鉛を溶射する方法があげられる。 The thermal spraying method is not particularly limited, and examples thereof include gas spraying, arc spraying, and plasma spraying. More specifically, there is a method of thermally spraying zinc, a zinc-aluminum quasi-alloy, a zinc-aluminum alloy, or a zinc-silicon-manganese-containing aluminum quasi-alloy with a fixed thermal spray gun onto a cast-iron pipe that is transported in the axial direction while rotating, and a method of thermally spraying zinc onto a rotated cast-iron pipe while moving the thermal spray gun.
＜鋳鉄管の製造方法＞
本発明の別の一実施態様としては、酸化皮膜層およびその外面の亜鉛系溶射皮膜層からなる耐食層を外面に有する鋳鉄管の製造方法であって、
鋳造した鋳鉄管を焼鈍し、表面に酸化皮膜の層を生成する工程、および
前記酸化皮膜層の外面に亜鉛系溶射を行い亜鉛系溶射皮膜層を形成する工程
を含む鋳鉄管の製造方法が提供される。
<Manufacturing method of cast iron pipe>
Another embodiment of the present invention is a method for manufacturing a cast iron pipe having, on its outer surface, a corrosion-resistant layer comprising an oxide film layer and a zinc-based thermal spray coating layer on its outer surface,
Provided is a method for manufacturing a cast iron pipe, comprising the steps of: annealing a cast iron pipe to form an oxide film layer on the surface;
（焼鈍）
酸化皮膜の層を形成するための焼鈍については、上述の鋳鉄管について説明した内容が適用される。
(annealing)
As for the annealing for forming the oxide film layer, the content described above for the cast iron pipe is applied.
（酸化皮膜層）
焼鈍により生成される酸化皮膜の層については、上述の鋳鉄管について説明した内容が適用される。
(Oxide layer)
As for the layer of oxide film produced by annealing, the content described above for the cast iron pipe is applied.
（亜鉛系溶射皮膜層）
亜鉛系溶射皮膜層については、その形成とともに、上述の鋳鉄管について説明した内容が適用される。
(Zinc-based thermal spray coating layer)
As for the zinc-based thermal spray coating layer, the content described above for the cast iron pipe is applied along with its formation.
また、一実施形態の鋳鉄管の製造方法においては、鋳鉄表面のケイ素を含む緻密な酸化皮膜層を耐食層に使用するために、酸化皮膜のうち空隙率が高すぎる鋳鉄管素地表面からより離れた表層部分を、ショットブラスト、サンドブラスト、高圧流体（エアーを含む）の吹き付け、電気化学的処理、酸などによる化学的処理などにより除去する工程を亜鉛系溶射皮膜を形成する工程の前に含めることが好ましい。これにより耐食性に優れた鋳鉄管を得ることができる。 In the method for manufacturing a cast-iron pipe according to one embodiment, in order to use the dense oxide film layer containing silicon on the surface of the cast iron as the corrosion-resistant layer, it is preferable to include a step of removing the surface layer portion of the oxide film farther from the base surface of the cast-iron pipe having too high a porosity by shot blasting, sand blasting, spraying with a high-pressure fluid (including air), electrochemical treatment, chemical treatment with acid or the like, before the step of forming the zinc-based thermal spray coating. As a result, a cast iron pipe having excellent corrosion resistance can be obtained.
以下、実施例により本発明を詳しく説明するが、本発明はこれらの実施例に限定されるものではない。 EXAMPLES The present invention will be described in detail below with reference to Examples, but the present invention is not limited to these Examples.
実施例１および２
鋳造後の呼び径１００のダクタイル鋳鉄管を、９０ｍｍ×１３０ｍｍ（長径が管軸と平行）の試験片に裁断し、得られた試験片を電気炉（マッフル炉）において１０００℃で１５分加熱処理（焼鈍）した。その後、炉内で室温まで冷却し（８℃／分）、管外面に相当する面に亜鉛溶射を表１に示す溶射量で溶射し、耐食層を形成させ、試験片を得た。
Examples 1 and 2
A ductile cast iron pipe with a nominal diameter of 100 after casting was cut into test pieces of 90 mm × 130 mm (long diameter parallel to the pipe axis), and the obtained test pieces were heat-treated (annealed) at 1000 ° C. for 15 minutes in an electric furnace (muffle furnace). After that, it was cooled to room temperature in a furnace (8° C./min), and the surface corresponding to the outer surface of the pipe was thermally sprayed with zinc at the amount shown in Table 1 to form a corrosion-resistant layer and obtain a test piece.
比較例１
亜鉛溶射を行わなかった以外は実施例１と同様にして試験片を得た。
Comparative example 1
A test piece was obtained in the same manner as in Example 1, except that zinc thermal spraying was not performed.
比較例２
加熱処理（焼鈍）後に形成された酸化皮膜を、管外面に鋼製のショット球を高速で投射することにより（ショットブラスト処理）すべて除去してから亜鉛溶射を行った以外は実施例１と同様にして試験片を得た。
Comparative example 2
A test piece was obtained in the same manner as in Example 1, except that the oxide film formed after the heat treatment (annealing) was completely removed by blasting steel shot balls onto the outer surface of the tube at high speed (shot blasting) and then zinc spraying was performed.
比較例３
鋳造後の呼び径１００のダクタイル鋳鉄管を、ガスバーナー炉において９００～１１００℃で５～２５分間加熱処理（焼鈍）した。その後、１～８℃／分で６５０℃まで冷却し、加熱処理（焼鈍）後に形成された皮膜を、管外面に鋼製のショット球を高速で投射することにより（ショットブラスト処理）すべて除去した。管外面に亜鉛溶射を表１に示す溶射量で溶射し、耐食層を形成させた。その後、鋳鉄管を９０ｍｍ×１３０ｍｍ（長径が管軸と平行）の試験片に裁断し、試験片を得た。
Comparative example 3
A ductile cast iron pipe having a nominal diameter of 100 after casting was heat-treated (annealed) at 900 to 1100° C. for 5 to 25 minutes in a gas burner furnace. After that, the pipe was cooled to 650°C at a rate of 1 to 8°C/min, and the film formed after the heat treatment (annealing) was completely removed by projecting steel shot balls onto the outer surface of the pipe at high speed (shot blasting). Zinc was thermally sprayed onto the outer surface of the pipe at the amount shown in Table 1 to form a corrosion-resistant layer. After that, the cast iron pipe was cut into test pieces of 90 mm×130 mm (long diameter parallel to the pipe axis) to obtain test pieces.
評価試験
各実施例および比較例において得られた耐食層を有する試験片について下記（１）～（４）の評価を行った。結果を表１に示す。
Evaluation Test The following (1) to (4) evaluations were performed on the test pieces having a corrosion-resistant layer obtained in each example and comparative example. Table 1 shows the results.
（１）付着性（クロスカット法）
実施例および比較例で得られた試験片の溶射皮膜の付着性について、ＪＩＳ Ｋ ５６００－５－６（塗料一般試験方法－第５部：塗膜の機械的性質－第６節：付着性（クロスカット法））に準拠して付着性評価を行った。具体的には、塗装面にカッターにより２ｍｍ幅で碁盤目の切り込みを入れて２５個のマスをつくり、セロハンテープを用いて剥離試験を行い、残存した碁盤目の状態で次に示す分類に分けた。
＜試験結果の分類＞
分類０：カットの縁が完全に滑らかで、どの格子の目にもはがれがない。
分類１：カットの交差点における塗膜の小さなはがれ。クロスカット部分で影響を受けるのは、明確に５％を上回ることはない。
分類２：塗膜がカットの縁に沿って、および／または交差点においてはがれている。クロスカット部分で影響を受けるのは、明確に５％を超えるが１５％を上回ることはない。
分類３：塗膜がカットの縁に沿って、部分的または全面的に大はがれを生じており、および／または目のいろいろな部分が、部分的または全面的にはがれている。クロスカット部分で影響を受けるのは、明確に１５％を超えるが３５％を上回ることはない。
分類４：塗膜がカットの縁に沿って、部分的または全面的に大はがれを生じており、および／または数か所の目が、部分的または全面的にはがれている。クロスカット部分で影響を受けるのは、明確に３５％を超えるが６５％を上回ることはない。
分類５：はがれの程度が分類４を超える場合。
(1) Adhesion (cross-cut method)
The adhesion of the thermal spray coating of the test pieces obtained in Examples and Comparative Examples was evaluated according to JIS K 5600-5-6 (General test method for paint-Part 5: Mechanical properties of coating film-Section 6: Adhesion (cross-cut method)). Specifically, a cutter was used to make 2 mm-wide grid cuts on the coated surface to form 25 squares, which were subjected to a peeling test using cellophane tape.
<Classification of test results>
Class 0: The edges of the cut are completely smooth, and there is no detachment on any grid mesh.
Category 1: Small delamination of the coating at the intersection of cuts. No more than 5% is clearly affected in the crosscut portion.
Category 2: The coating is peeling off along the edges of the cuts and/or at the intersections. The crosscut portion is affected by clearly more than 5%, but not more than 15%.
Class 3: The coating has partially or totally peeled off along the edges of the cuts and/or has partially or totally peeled off in various parts of the eye. The crosscut portion is affected by clearly more than 15% but not more than 35%.
Class 4: The paint film is partially or totally peeled off along the edge of the cut and/or partially or totally peeled off in several spots. The crosscut portion is affected clearly above 35% but not above 65%.
Category 5: When the degree of peeling exceeds Category 4.
（２）付着性（プルオフ試験）
実施例および比較例で得られた試験片の溶射皮膜と酸化皮膜との付着強度について、ＪＩＳ Ｋ ５６００－５－７（塗料一般試験方法－第５部：塗膜の機械的性質－第７節：付着性（プルオフ法））に準拠して試験を行った。
(2) Adhesion (pull-off test)
The adhesion strength between the thermal spray coating and the oxide coating of the test pieces obtained in Examples and Comparative Examples was tested according to JIS K 5600-5-7 (General test method for paint-Part 5: Mechanical properties of coating film-Section 7: Adhesion (pull-off method)).
（３）耐食性（耐中性塩水噴霧性）
耐食層の長期耐久性を確認すべく、ＪＩＳ Ｋ ５６００－７－１（塗料一般試験方法－第７部：塗膜の長期耐久性－第１節：耐中性塩水噴霧性）に準拠して試験を行った。
(3) Corrosion resistance (neutral salt spray resistance)
In order to confirm the long-term durability of the corrosion-resistant layer, a test was conducted in accordance with JIS K 5600-7-1 (General test methods for paints-Part 7: Long-term durability of coating film-Section 1: Neutral salt spray resistance).
実施例および比較例の各試験片に、カッターナイフで素地に達するスクラッチを施し、塩化ナトリウム水溶液（５％）を噴霧して、外観を観察した。赤錆が観察されるまでの日数の平均を比較例１を対照として指数化した。なお、クロスカットの両側それぞれ２ｍｍ以内は観察の対象としなかった。 Each test piece of Examples and Comparative Examples was scratched with a cutter knife to reach the substrate, sprayed with an aqueous sodium chloride solution (5%), and observed for appearance. The average number of days until red rust was observed was indexed using Comparative Example 1 as a control. The area within 2 mm on each side of the cross-cut was not observed.
（４）ＳＥＭ画像
実施例および比較例の各試験片を切断し、断面をＳＥＭで確認した（図１Ａおよび図１Ｂ、３００倍）。このＳＥＭ画像から焼鈍により生成した皮膜層および亜鉛溶射皮膜層の膜厚を測定した。
(4) SEM image Each test piece of Examples and Comparative Examples was cut, and the cross section was confirmed by SEM (Figs. 1A and 1B, 300x magnification). From this SEM image, the film thickness of the coating layer produced by annealing and the zinc thermal spray coating layer were measured.
表１の評価から明らかなように、実施例１および２の焼鈍により生じた酸化皮膜層および亜鉛溶射皮膜層からなる耐食層は、亜鉛溶射皮膜層のない比較例１と比べて非常に高い耐食性を有し、焼鈍により生じた酸化皮膜層をショットブラスト処理により除去した比較例２および３と比較しても同程度以上の耐食性を示すことがわかる。 As is clear from the evaluation in Table 1, the corrosion-resistant layers composed of the oxide film layer formed by annealing and the zinc sprayed film layer in Examples 1 and 2 have very high corrosion resistance compared to Comparative Example 1, which does not have a zinc sprayed film layer, and even when compared to Comparative Examples 2 and 3 in which the oxide film layer produced by annealing is removed by shot blasting, the corrosion resistance is at least comparable.
実施例３
鋳造後の呼び径１００のダクタイル鋳鉄管を、１３０ｍｍの長さに切断して試験片とし、得られた試験片を電気炉（マッフル炉）において１０００℃で１５分加熱処理（焼鈍）した。その後、炉内で室温まで冷却し（８℃／分）、管外面に相当する面に亜鉛溶射を溶射量１３０ｇ／ｍ2で溶射し、耐食層を形成させ、試験片を得た。その後、試験片を切断し、断面をＥＰＭＡにかけ、元素マッピングを行った（図２）。
Example 3
A cast ductile cast iron pipe with a nominal diameter of 100 was cut into a length of 130 mm to obtain a test piece, and the obtained test piece was heat-treated (annealed) at 1000° C. for 15 minutes in an electric furnace (muffle furnace). After that, the tube was cooled to room temperature (8° C./min) in a furnace, and the surface corresponding to the outer surface of the pipe was thermally sprayed with zinc at a rate of 130 g/m 2 to form a corrosion-resistant layer to obtain a test piece. After that, the specimen was cut, and the cross section was subjected to EPMA for elemental mapping (Fig. 2).
実施例４
鋳造後の呼び径１００のダクタイル鋳鉄管を、ガスバーナー炉において９００～１１００℃で５～２５分間加熱処理（焼鈍）した。その後、１～８℃／分で６５０℃まで冷却し、加熱処理（焼鈍）後に形成された皮膜層の管外面側に亜鉛溶射を溶射量１３０ｇ／ｍ2で溶射し、耐食層を形成させた。その後、鋳鉄管を切断し、断面をＥＰＭＡにかけ、元素マッピングを行った（図３）。
Example 4
A ductile cast iron pipe having a nominal diameter of 100 after casting was heat-treated (annealed) at 900 to 1100° C. for 5 to 25 minutes in a gas burner furnace. After that, the pipe was cooled to 650°C at a rate of 1 to 8°C/min, and the outer surface of the coating layer formed after the heat treatment (annealing) was sprayed with zinc at a spraying rate of 130 g/m 2 to form a corrosion-resistant layer. After that, the cast iron pipe was cut, the cross section was subjected to EPMA, and elemental mapping was performed (Fig. 3).
図２では図３と比較して酸化皮膜層が薄く、緻密であることが分かる。図３では、酸化皮膜層２が厚く、ケイ素を多く含む緻密な層２ａと、空隙率の高い層２ｂとの二層に分かれていることが分かる。 In FIG. 2, it can be seen that the oxide film layer is thinner and denser than in FIG. In FIG. 3, it can be seen that the oxide film layer 2 is thick and divided into two layers: a dense layer 2a containing a large amount of silicon and a layer 2b having a high porosity.
１ 鉄管部
２ 焼鈍により生成される酸化皮膜層
２ａ ケイ素を含む緻密な酸化皮膜層
２ｂ 表層の空隙率の高い酸化皮膜層
３ 亜鉛溶射皮膜層
REFERENCE SIGNS LIST 1 Iron pipe 2 Oxide film layer produced by annealing 2a Dense oxide film layer containing silicon 2b Oxide film layer with high surface porosity 3 Zinc sprayed film layer
Claims (3)
前記酸化皮膜層が、前記鋳鉄管素地側に生成されるケイ素を含むケイ酸化鉄を主成分とする緻密な層と、前記亜鉛系溶射皮膜層側に生成される酸化鉄を主成分とする層とを含む、鋳鉄管。 A cast iron pipe having on its outer surface a corrosion-resistant layer consisting of an oxide film layer formed on the cast iron pipe base material by annealing and a zinc-based thermal spray coating layer on its outer surface ,
A cast iron pipe, wherein the oxide coating layer includes a dense layer composed mainly of iron silicate containing silicon generated on the cast iron pipe base side, and a layer composed mainly of iron oxide generated on the zinc-based thermal spray coating layer side.
鋳造した鋳鉄管を焼鈍し、鋳鉄管素地の上に酸化皮膜の層を生成する工程であって、前記酸化皮膜層が、前記鋳鉄管素地側に生成されるケイ素を含むケイ酸化鉄を主成分とする緻密な層と、前記亜鉛系溶射皮膜層側に生成される酸化鉄を主成分とする層とを含む、工程、および
前記酸化皮膜層の外面に亜鉛系溶射を行い亜鉛系溶射皮膜層を形成する工程
を含む鋳鉄管の製造方法。 A method for manufacturing a cast iron pipe having on its outer surface a corrosion-resistant layer comprising an oxide film layer and a zinc-based thermal spray coating layer on its outer surface,
A cast iron pipe is annealed to form an oxide film layer on the cast iron pipe base, wherein the oxide film layer includes a dense layer mainly composed of iron silicate containing silicon formed on the cast iron pipe base side and a layer mainly composed of iron oxide formed on the zinc-based sprayed coating layer side, and a step of forming a zinc-based sprayed coating layer by performing zinc-based thermal spraying on the outer surface of the oxide film layer.
鋳造した鋳鉄管を焼鈍し、鋳鉄管素地の上に酸化皮膜の層を生成する工程、および
前記酸化皮膜層の外面に亜鉛系溶射を行い亜鉛系溶射皮膜層を形成する工程
を含み、
前記亜鉛系溶射皮膜層を形成する工程の前に、得られた酸化皮膜層の空隙率の高い表層部分を除去する工程を含む、製造方法。 A method for manufacturing a cast iron pipe having on its outer surface a corrosion-resistant layer comprising an oxide film layer and a zinc-based thermal spray coating layer on its outer surface,
annealing the cast iron pipe to form a layer of oxide film on the cast iron pipe substrate; and
a step of forming a zinc-based thermal spray coating layer by performing zinc-based thermal spraying on the outer surface of the oxide coating layer;
including
A manufacturing method , comprising a step of removing a surface layer portion having a high porosity of the obtained oxide coating layer before the step of forming the zinc-based thermal spray coating layer.
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| JP2003096541A (en) | 2001-09-21 | 2003-04-03 | Kawasaki Steel Corp | High tensile hot dip galvanizing steel sheet and high tensile galvannealed steel sheet having excellent balance in strength and ductility, plating adhesion, and corrosion resistance |
| JP2006233311A (en) | 2005-02-28 | 2006-09-07 | Jfe Steel Kk | Method for producing spray-coated steel sheet having excellent corrosion resistance and equipment line for steel sheet |
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| FR2593831B1 (en) * | 1986-02-06 | 1994-01-21 | Irsid | PROCESS FOR THE PROTECTIVE COATING OF AN IRON OR STEEL PRODUCT AND COATED PRODUCT |
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