JP2018178217A - Galvanized steel pipe - Google Patents
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Abstract
Description
本発明は、比較的厚みのある溶融亜鉛めっきを施した鋼管に関し、特に、曲げ加工やフレア成形（管端拡大加工）等の後加工が施される溶融亜鉛めっき鋼管等に有用な鋼管に関するものである。 The present invention relates to a relatively thick hot-dip galvanized steel pipe, and more particularly to a steel pipe useful for hot-dip galvanized steel pipe or the like to which post-processing such as bending or flare forming (pipe end enlargement processing) is performed. It is.
土中等に埋設されるガス管等には、長期間埋設されたままであっても、腐食等による破損が生じないように、例えば、片面当り５５０ｇ／ｍ2以上の溶融亜鉛めっきが施された鋼管が使用される。 For example, a steel pipe that is subjected to hot-dip galvanization of 550 g / m 2 or more per side so that damage due to corrosion or the like does not occur in a gas pipe etc. buried in soil etc. even if it is buried for a long time Is used.
しかし、溶融亜鉛めっき層の厚さを増すと、曲げ加工や、管端部に接続等のためのフレア加工（鍔出し加工）等を施した場合に、該めっき層が剥離現象を生起し易くなり、めっき層厚さを増大させても、期待する耐腐食性を発揮できない欠点があった。 However, when the thickness of the hot-dip galvanized layer is increased, the plated layer is likely to cause a peeling phenomenon when bending, flare processing (connection processing) or the like for connection to the tube end, etc. is performed. Even if the plating layer thickness is increased, there is a drawback that the expected corrosion resistance can not be exhibited.
さらに、近年においては、ＥＵ連合で規定されたＲｏＨＳ指令に準拠して、合金中のＰｂ、Ｃｄ規制がなされ、Ｐｂを１．３質量％以下程度含む蒸留亜鉛インゴットに代えて、低Ｐｂ・低Ｃｄ含有量の電解亜鉛を溶融めっき亜鉛に供することが増えているが、低Ｐｂの溶融亜鉛浴では、いわゆるめっき飛びと称する、部分的にめっき皮膜が形成されない欠陥が生じやすい欠点も生じている。 Furthermore, in recent years, in accordance with the RoHS Directive specified by the EU Union, Pb and Cd in alloys are restricted, and instead of a distilled zinc ingot containing 1.3% or less by mass of Pb, low Pb · low Increasing use of Cd content electrolytic zinc for hot-dip galvanizing zinc is increasing, but in low Pb hot-dip zinc baths, there is also a defect called so-called plating jump, which tends to cause defects such as partial plating film not formed .
本発明は、該埋設管のような腐食環境下において使用される、比較的厚みのある溶融亜鉛めっきを施された鋼管に後加工を施した場合であっても、めっき層の剥離現象を生じることのない、加工性に優れた溶融亜鉛めっき鋼管を提供することを目的とする。 The present invention causes peeling of the plating layer even when post-processing is performed on a relatively thick hot-dip galvanized steel pipe used in a corrosive environment such as the buried pipe. It is an object of the present invention to provide a hot-dip galvanized steel pipe excellent in workability, which never occurs.
特許文献１〜３には、ＲｏＨＳ指令に従って、Ｐｂ含有量を０．１質量％以下、Ｃｄ含有量を０．０１質量％以下に低減した溶融亜鉛浴を用いた場合であっても、不めっき発生の少ない溶融亜鉛めっき材の製造方法が記載されている。これらの技術においては、溶融亜鉛浴中にＳｎ、Ｓｂ、Ｂｉ、又はＩｎ等の金属を微量に添加している。 In the patent documents 1 to 3, even in the case of using a molten zinc bath in which the Pb content is reduced to 0.1 mass% or less and the Cd content to 0.01 mass% or less according to the RoHS directive, no plating A method of producing a hot-dip galvanized material with low occurrence is described. In these techniques, a small amount of metal such as Sn, Sb, Bi or In is added to the molten zinc bath.
引用文献４には、溶融亜鉛めっき鋼管の曲げ加工性等を向上させるために、質量％で、Ｃ：０．００１〜０．０２％、Ｓｉ：０．０５％以下、Ｍｎ：０．０５〜０．３％、Ｎｂ；０．０３％以下、Ｔｉ：０．０３％以下とした鋼管に溶融亜鉛めっきを施す技術が、引用文献５には、鋼材の表面に溶融亜鉛めっきを施した後、溶融Ｚｎ−Ａｌ−Ｍｇ合金めっきを行う技術が、各々記載されている。 In the cited reference 4, C: 0.001 to 0.02%, Si: 0.05% or less, Mn: 0.05 to 0.05% by mass in order to improve the bending workability and the like of the hot-dip galvanized steel pipe. The technology of applying hot dip galvanizing to a steel pipe with 0.3%, Nb: 0.03% or less, Ti: 0.03% or less, according to cited reference 5, after applying hot dip galvanization to the surface of a steel material, Techniques for performing hot-dip Zn-Al-Mg alloy plating are each described.
引用文献１〜３に開示の技術では、微量添加成分の含有量調整が面倒であり、また、加工時のめっき層の剥離についての考察はなされていない。 In the techniques disclosed in the cited references 1 to 3, the adjustment of the content of the trace additive component is troublesome, and no consideration is given to the peeling of the plating layer at the time of processing.
特許文献４に開示の技術では、Ｃ含有量を０．０２％以下、Ｓｉ含有量を０．０５％以下に抑制して、素材鋼管の強度が過大となって、曲げ加工性等が劣化することを防止しつつ、Ｎｂ添加による細粒強化及び析出強化を狙ったものであるが、ある程度の曲げ加工性は維持できても、鋼管強度面で十分とはいえず、また、４００ｇ／ｍ2までのめっき付着量について記載されるのみで、それ以上、例えば、片面当り５５０ｇ／ｍ2を超える厚さの溶融めっき鋼管について記載するところがなく、耐腐食性の面でも十分なものということはできない。 In the technology disclosed in Patent Document 4, the C content is suppressed to 0.02% or less, the Si content to 0.05% or less, the strength of the material steel pipe becomes excessive, and bending workability and the like deteriorate. It aims at fine grain strengthening and precipitation strengthening by Nb addition while preventing corrosion, but even if it can maintain a certain degree of bending workability, it can not be said that it is sufficient in terms of steel pipe strength, and 400 g / m 2 There is no description about hot-dip galvanized steel pipe having a thickness of more than 550 g / m 2 per side, for example, even if the plating adhesion amount up to is described, and it can not be said that it is sufficient in terms of corrosion resistance. .
また、特許文献５に開示の技術では、溶融亜鉛めっきの後、溶融Ｚｎ−Ａｌ−Ｍｇ合金めっきを行うことから、通常の溶融亜鉛めっき設備とは別に、溶融Ｚｎ−Ａｌ−Ｍｇ合金めっき設備を用意する必要があり、また、その溶融合金浴についても、Ａｌ：４〜２０％、Ｍｇ：０．１〜５％に維持する必要があり、鋼板とは異なり、溶融亜鉛合金めっき浴表面の大気からの隔離が難しい鋼管の溶融めっき設備においては、表面に酸化物等が生じ易く、操業を困難にする欠点があった。 Further, in the technology disclosed in Patent Document 5, since hot-dip galvanizing is followed by hot-dip Zn-Al-Mg alloy plating, hot-dip Zn-Al-Mg alloy plating facilities are separated from ordinary hot-dip galvanizing facilities. It is necessary to prepare, and the molten alloy bath also needs to maintain Al: 4 to 20%, Mg: 0.1 to 5%, and unlike the steel plate, the atmosphere of the surface of the hot-dip zinc alloy plating bath In the hot-dip plating equipment of a steel pipe which is difficult to separate from the above, oxides and the like are easily generated on the surface, which has a drawback of making operation difficult.
本発明は、このような実情に鑑み、比較的厚みのある電解亜鉛を素材とする溶融亜鉛めっきを施した鋼管で、フレア加工や曲げ加工を行ってもめっき層の剥離を生ぜず、耐腐食性に富んだ溶融亜鉛めっき鋼管を提供することを課題とする。 In view of such circumstances, the present invention is a galvanized steel pipe made of electrolytic zinc having a relatively large thickness, and does not cause peeling of the plating layer even if flare processing or bending processing is performed, and corrosion resistance It is an object of the present invention to provide a hot-dip galvanized steel pipe rich in properties.
本発明者らは、まず、溶融亜鉛めっき付着量を片面当り５５０ｇ／ｍ2以上とした亜鉛を素材とする溶融亜鉛めっき鋼管の断面について、観察を行った。
その結果、めっき層は、最表層側から、η層、ζ層、及びδ１層の順に積層構造となっていることが判明した。
以下、各層について述べる。
The present inventors firstly observed the cross section of a hot-dip galvanized steel pipe made of zinc and having a hot-dip galvanization adhesion amount of 550 g / m 2 or more per one surface.
As a result, it was found that the plating layer had a laminated structure in the order of the η layer, the weir layer, and the δ1 layer from the outermost layer side.
Each layer will be described below.
＜η層＞
めっき層の最表面に形成される、ほぼ純Ｚｎからなるη相単相からなる層であり、耐腐食性の主体となる層である。
めっき鋼管の表面全体を、このη層で被覆することにより、高い耐腐食性が得られる。
<Η layer>
It is a layer consisting of an η-phase single phase consisting of substantially pure Zn, which is formed on the outermost surface of the plating layer, and is a layer mainly serving as corrosion resistance.
By coating the entire surface of the plated steel pipe with this η layer, high corrosion resistance can be obtained.
＜ζ層＞
ζ層は、後述するδ１層の表面から、柱状に伸長するめっき層の主体となる組織であり、δ１層に隣接する部分（下部ζ層）は、ζ相の密な柱状組織からなるが、めっき表面側の前述したη層に隣接する上部ζ層においては、凝固時に、粗大な柱状晶間にη相が混入した混層を形成している。ζ相は、δ１相に次ぐ硬さを有しているので、ζ相単独部分においては、δ１相と同様に、層内剥離（き裂）を生じる虞がある。
<Ζ layer>
The weir layer is the main structure of the plating layer extending in a columnar shape from the surface of the δ1 layer described later, and the portion (lower weir layer) adjacent to the δ1 layer is a dense columnar structure of weir phase, In the upper weir layer adjacent to the above-described η layer on the plating surface side, a mixed layer in which the η phase is mixed between coarse columnar crystals is formed at the time of solidification. Since the ζ phase has a hardness next to the 1 1 phase, in the ζ phase alone part, there is a possibility that intralayer separation (crack) may occur as in the 1 1 phase.
＜δ１層＞
δ１層は、最も素材鋼管側に形成される柵状の組織であって、他層に比較して、鋼材から溶出したＦｅ分を多く含むため、高硬度の層として、比較的薄く均一に層状に形成される傾向がある。
本発明が対象とするめっき鋼管と比較して、極めて薄いめっき層が形成されるめっき鋼板においては、δ１層も極めて薄い層状の形態となることで、めっき層と鋼板表層との剥離を抑制する効果を奏するものであるが、片面当り５５０ｇ／ｍ2以上もの厚さを有する厚めっき鋼管においては、このδ１層も、めっき鋼板のδ１相に比較して厚く柵状に形成され、その硬度が高いことにより、曲げ加工やフレア加工時に、δ１層内において層内剥離を生ずることが判明した。
<Δ1 layer>
The δ1 layer is a fence-like structure formed most on the side of the material steel pipe, and contains a large amount of Fe eluted from the steel as compared to the other layers, so it is relatively thin and uniformly layered as a high hardness layer. It tends to be formed.
In the plated steel plate in which the extremely thin plated layer is formed compared to the plated steel pipe targeted by the present invention, the δ1 layer is also in the form of an extremely thin layer, thereby suppressing the peeling between the plated layer and the steel plate surface Although the effect is exhibited, in the case of a thick plated steel pipe having a thickness of 550 g / m 2 or more per side, this δ1 layer is also formed in a fence shape thicker than the δ1 phase of the plated steel plate, and its hardness is It was found that due to the high level, intralayer delamination occurs in the δ1 layer during bending and flare processing.
前述した通り、ζ相は柱状組織、δ１相は柵状組織となるが、めっき組織を断面で観察したとき、最表層から（１）η層；η相が主体の層、（２）ζ層；ζ相が主体ではあるが、上部にη相が混入した層、（３）δ１層；δ１相が主体の層と区別できる。これらの各層の境界を以下に示す手順により定義する（図１の下部に示す参考写真を参照）。 As described above, the gauze phase has a columnar structure and the δ1 phase has a fence-like structure, but when the plating structure is observed in cross section, from the outermost layer, (1) η layer; layer mainly composed of 相 phase, (2) ζ layer A layer in which the ζ phase is mixed at the top, (3) δ1 layer; and a layer in which the δ1 phase is mainly. The boundaries of these layers are defined by the following procedure (see the reference picture shown at the bottom of FIG. 1).
＜η層とζ層（η相とζ相の混相からなるζ層（上部）の境界＞
めっき層の断面観察において、光学顕微鏡であればエッチング(例えば２５℃の０．０３％ナイタール（エタノール＋０．０３％硝酸）に２０秒浸漬)、走査型電子顕微鏡であれば反射電子像あるいはエッチング後の二次電子像により、η相とζ相は判別可能である。めっき層の断面写真を撮影し、η層とζ層が含まれるように写真画像をトリミングし、２階調（二値化）処理によりη相とζ相を明確にする。η相とζ相の境界は入り組んでいるが、ここでは断面写真のη相とζ相の境界に任意の線分を引いた時、前記線分を境に互いの領域にはみ出たη相とζ相各々の面積が等しくなる、即ちη相の面積：ζ相の面積＝１：１となる線分Ａを探しだし、この線分Ａが含まれる直線をη層とζ層（η相とζ相の混相）の境界と決定した。
<The boundary between the η layer and the cocoon layer (the cocoon layer (upper part) consisting of mixed η phase and ζ phase)>
In the cross-sectional observation of the plating layer, etching (for example, immersion in a 0.03% nital (ethanol + 0.03% nitric acid) at 25 ° C for 20 seconds) for an optical microscope, reflected electron image or after etching for a scanning electron microscope The η phase and the ζ phase can be distinguished by the secondary electron image of The cross-sectional photograph of the plating layer is taken, the photographic image is trimmed so that the ζ layer and the ζ layer are included, and the η phase and the ζ phase are clarified by two gradation (binarization) processing. The boundary between the 相 phase and the zeta phase is intricate, but here, when an arbitrary line segment is drawn to the ζ phase and the zeta phase boundary of the cross-sectional photograph, the η phase that protrudes into each other bordering on the line segment Search for a line segment A in which the area of each ζ phase is equal, that is, the area of η phase: area of = phase = 1: 1, and straight lines including this line A are η layer and ζ layer (η phase It was decided that the boundary of mixed phase
＜ζ層（下部）とδ１層の境界＞
同様に、めっき層の断面観察において、光学顕微鏡であればナイタールエッチング、走査型電子顕微鏡であれば反射電子像あるいはエッチング後の二次電子像により、ζ相とδ１相は判別可能である。めっき層の断面写真を撮影し、ζ層とδ１層が含まれるように写真画像をトリミングし、２階調（二値化）処理によりζ相とδ１相を明確にする。ζ相とδ１相の境界は入り組んでいる場合もあるが、ここでは断面写真のζ相とδ１相の境界に任意の線分を引いた時、前記線分を境に互いの領域にはみ出たζ相とδ１相各々の面積が等しくなる、即ちζ：δ１＝１：１となる線分Ｂを探しだし、この線分Ｂが含まれる直線をζ層とδ１層との境界と決定した。
<Boundary layer (lower part) and boundary of δ1 layer>
Similarly, in cross-sectional observation of the plating layer, it is possible to distinguish between the ζ phase and the δ1 phase by nital etching in the case of an optical microscope and by a backscattered electron image or a secondary electron image after etching in the case of a scanning electron microscope. A cross-sectional photograph of the plating layer is taken, the photographic image is trimmed so as to include the cocoon layer and the δ1 layer, and the cocoon phase and the δ1 phase are clarified by a two gradation (binarization) process. The boundary between the glaze phase and the δ1 phase may be intricate, but here, when an arbitrary line segment is drawn at the boundary between the glaze phase and the δ1 phase in the cross-sectional photograph, they protrude into each other from the line segment A line segment B in which the area of each of the haze phase and the δ1 phase is equal, ie, ζ: δ1 = 1: 1, was found, and the straight line including the line segment B was determined as the boundary between the wing layer and the δ1 layer.
上記の手順で決定した境界により、「最表層」から「η層とζ層（η相とζ相の混層からなる上部ζ層）の境界；即ち線分Ａ」までの厚みを「η層平均厚み」、「η層とζ層（η相とζ相の混層からなる上部ζ層）の境界；即ち線分Ａ」から「ζ層（下部ζ層）とδ１層の境界；即ち線分Ｂ」までの厚みを「ζ層平均厚み」、「ζ層とδ１層の境界；即ち線分Ｂ」と「δ１層と素材鋼管の界面；即ち母材表面」までの厚みを「δ１層平均厚み」とした。
図１下部の参考写真における線分Ｃは線分Ａと線分Ｂとの中央に引いた線分であり、線分ＡＣは、線分Ａと線分Ｃとの中央に引いた線分、線分ＢＣは、線分Ｃと線分Ｂとの中央に引いた線分であるので、線分ＡＣと線分ＢＣで挟まれる面積は、全ζ層の５０％となる。
According to the boundary determined by the above procedure, the thickness from "the outermost layer" to "the boundary between the 層 layer and the ζ layer (the upper ζ layer consisting of a mixture of η phase and ζ phase); Thickness, the boundary between η layer and ζ layer (upper weir layer consisting of mixed layers of ζ phase and; phase); from line segment A to the boundary between weir layer (lower weir layer) and δ1 layer; The average thickness of the layer to the “base layer thickness” is “the boundary between the base layer and the δ1 layer; ie, the line segment B” and “the interface between the δ1 layer and the steel pipe; ".
Line segment C in the reference photograph in the lower part of FIG. 1 is a line segment drawn at the center of line segment A and line segment B, and line segment AC is a line segment drawn at the center of line segment A and line segment C. Since the line segment BC is a line segment drawn at the center of the line segment C and the line segment B, the area sandwiched by the line segment AC and the line segment BC is 50% of the entire heel layer.
本発明者らは、曲げ加工やフレア加工時に発生し易いδ１層や、ζ層の層内剥離を抑制できるめっき層の形態を種々検討した結果、以下の４点がめっきの層内剥離の抑制に効果的であることが判明し、本発明を成すに至ったものである。
（１）ζ層とη層とが境界部分で適度に混合しており、軟質なη相がζ相に入り込むことで、ζ層内の剥離や亀裂の伝播を防止する。この効果を発揮するためには、前記境界を越えて、お互いの領域に入り込む相の個数が合計で１０個以上あることが望ましい。これ未満の混合状態ではき裂の伝播防止効果が十分に発揮できない場合がある。
（２）δ１層の厚みを適度に変動させて、δ１層内における剥離や亀裂の伝播を防止する。この効果を発揮するためには、境界を越えて、お互いの領域に入り込む相の個数が合計で２個以上あり、δ１層の最大厚さがδ１層の平均厚さの１．５倍以上であるようにδ１相の厚みを変動させることが望ましい。これら未満では亀裂の伝播防止効果が十分に発揮できない場合がある。
（３）ζ層厚さ／δ１層厚さを所定値以上として、最も硬いδ１層内の剥離・亀裂の伝播を防止する。この効果を発揮するためには、厚さ比で（ζ層）／（δ１層）が２．０以上、更には５．０以上であることが望ましい。これら未満では亀裂の伝播防止効果を十分に発揮できない場合がある。
（４）めっき層の断面においてζ層の厚さの中心線を中央として、該中心線の両側各ζ層の厚さの２５％の範囲におけるη相の混入割合が１〜１０面積％であれば、フレア加工等を施してもめっき層の剥離現象を生じ難い溶融亜鉛めっき鋼管とすることができる。
As a result of examining various forms of the δ1 layer which is easily generated at the time of bending and flare processing and the form of the plating layer capable of suppressing the intralayer peeling of the weir layer, the following four points suppress the intralayer peeling of plating. It has been found that the present invention is effective.
(1) The cocoon layer and the η layer are appropriately mixed at the boundary portion, and the soft 相 phase enters the cocoon phase to prevent the propagation of separation and cracks in the cocoon layer. In order to exert this effect, it is desirable that the total number of phases entering into each other region is 10 or more beyond the boundary. In the mixed state below this, the crack propagation preventing effect may not be sufficiently exhibited.
(2) The thickness of the δ1 layer is appropriately varied to prevent the propagation of separation and cracks in the δ1 layer. In order to exert this effect, the number of phases entering into each other beyond the boundary is 2 or more in total, and the maximum thickness of the δ1 layer is 1.5 or more times the average thickness of the δ1 layer It is desirable to vary the thickness of the δ1 phase as it is. If it is less than these, the crack propagation preventing effect may not be sufficiently exhibited.
(3) By setting the weir layer thickness / δ1 layer thickness to a predetermined value or more, the propagation of separation / cracks in the hardest δ1 layer is prevented. In order to exert this effect, it is desirable that (thickness) / (. Delta.1 layer) is 2.0 or more, and more preferably 5.0 or more. If it is less than these, the crack propagation preventing effect may not be sufficiently exhibited.
(4) The mixed ratio of め っ き phase in the range of 25% of the thickness of each wedge layer on both sides of the centerline of the thickness of the wedge layer is 1 to 10% area For example, it is possible to provide a hot-dip galvanized steel pipe which hardly causes the peeling phenomenon of the plating layer even when subjected to flare processing or the like.
本発明の要旨は、以下のとおりである。
（１）鋼管の表面に溶融亜鉛めっき層が形成された溶融亜鉛めっき鋼管であって、
溶融亜鉛めっき層が表面側からη相が主体のη層、ζ相にη相が混入したζ層、及びδ１相が主体のδ１層からなり、
前記η層とζ層の境界は、互いの領域にはみ出したη相とζ相の面積が等しくなる線分であり、
前記めっき層断面におけるζ層の中心線の上下各ζ相層の全厚に対して２５％の範囲、即ちζ相層の全厚さの中央５０％の範囲におけるη相の面積比が１〜１０面積％であることを特徴とする溶融亜鉛めっき鋼管。
The gist of the present invention is as follows.
(1) A hot-dip galvanized steel pipe in which a hot-dip galvanized layer is formed on the surface of the steel pipe,
The hot-dip galvanized layer is composed of an η layer mainly composed of η phase from the surface side, a ζ layer composed of η phase mixed with ζ phase, and a δ1 layer mainly composed of δ1 phase,
The boundary between the η layer and the cocoon layer is a line segment in which the areas of the ζ phase and the cocoon phase which are projected into each other are equal
The area ratio of η phase in the range of 25% with respect to the total thickness of the respective upper and lower phase layers of the center line of the soot layer in the cross section of the plated layer Hot-dip galvanized steel pipe characterized in having 10% by area.
（２）前記η層とζ層の境界で互いにはみ出す部分が境界長さ１００μｍあたり合計で１０個以上であることを特徴とする前記（１）記載の溶融亜鉛めっき鋼管。 (2) The hot-dip galvanized steel pipe according to the above (1), wherein the portions which stick out each other at the boundary between the η layer and the weir layer are 10 or more in total per 100 μm of boundary length.
（３）前記溶融亜鉛めっき層における、
前記ζ層とδ１層の境界は、互いの領域にはみ出したζ相とδ１相の面積が等しくなる線分であり、
前記境界で互いにはみ出す部分が境界１００μｍあたり２個以上であり、
δ１層の最大厚さがδ１層の平均厚さの１．５倍以上であることを特徴とする前記（１）又は（２）のいずれかに記載の溶融亜鉛めっき鋼管。
(3) In the hot-dip galvanized layer
The boundary between the cocoon layer and the δ1 layer is a line segment in which the area of the cocoon phase and the δ1 phase that has been projected into each other is equal,
Two or more out of each other at the boundary are per 100 μm of the boundary,
The hot-dip galvanized steel pipe according to any one of the above (1) or (2), wherein the maximum thickness of the δ1 layer is 1.5 times or more the average thickness of the δ1 layer.
（４）前記溶融亜鉛めっき層のうち、前記鋼管表面との界面に形成されるδ１層と、前記ζ層の厚さの比率：（ζ層）／（δ１層）が２．０以上であることを特徴とする前記（１）乃至（３）のいずれかに記載の溶融亜鉛めっき鋼管。 (4) Of the hot-dip galvanized layers, the ratio of the thickness of the δ1 layer formed at the interface with the steel pipe surface and the thickness of the weir layer: (weather layer) / (δ1 layer) is 2.0 or more The hot dip galvanized steel pipe according to any one of the above (1) to (3), characterized in that
（５）前記厚さの比率：（ζ層）／（δ１層）が５．０以上であることを特徴とする前記（４）に記載の溶融亜鉛めっき鋼管。 (5) The hot-dip galvanized steel pipe according to the above (4), wherein the ratio of the thickness: (basket layer) / (δ1 layer) is 5.0 or more.
（６）前記溶融亜鉛めっき層におけるめっき付着量が片面当り５５０ｇ／ｍ2以上であることを特徴とする前記（１）乃至（５）のいずれかに記載の溶融亜鉛めっき鋼管。 (6) The hot-dip galvanized steel pipe according to any one of (1) to (5), wherein the amount of plating adhesion on the hot-dip galvanized layer is 550 g / m 2 or more per one side.
（７）前記溶融亜鉛めっき鋼管の組成が、質量％で、Ｃ：０．００５以上０．１５％以下、Ｓｉ：０．１５％以上０．２５％以下、Ｍｎ：０．２０％以上１．６０％以下、Ｐ：０．０４％以下、Ｓ：０．０４％以下であって、残部がＦｅ及び不可避不純物であることを特徴とする前記（１）乃至（６）のいずれかに記載の溶融亜鉛めっき鋼管。 (7) The composition of the hot-dip galvanized steel pipe is, in mass%, C: 0.005 or more and 0.15% or less, Si: 0.15% or more and 0.25% or less, Mn: 0.20% or more. 60% or less, P: 0.04% or less, S: 0.04% or less, and the balance is Fe and an unavoidable impurity according to any one of the above (1) to (6) Galvanized steel pipe.
本発明のめっき鋼管によれば、曲げ加工やフレア加工を行っても、厚く形成されためっき層の剥離を生じることなく、耐腐食性に優れためっき鋼管を、生産性良く得ることができる。 According to the plated steel pipe of the present invention, it is possible to obtain a plated steel pipe excellent in corrosion resistance with good productivity without causing peeling of the thickly formed plating layer even if bending or flare processing is performed.
図１の模式図に図示した様に、溶融亜鉛めっき浴に浸漬して、所定時間経過後に引き上げると、鋼材表面にＦｅ含有量が高く、融点の高いδ１相が柵状に形成され、その表面からζ相が柱状に発達していく。δ１相に近いζ相は相対的に緻密に形成されるが、上部においては、やや粗な柱状晶を形成し、隣接する柱状晶の間には、純Ｚｎに近いη相が、粗な柱状晶間に入り込んで形成された本発明で定義する混相状のζ層が形成される。 As illustrated in the schematic view of FIG. 1, when immersed in a hot-dip galvanizing bath and pulled up after a predetermined time, a high Fe content and a high melting point δ1 phase are formed in a fence shape on the steel surface. Ζ Phases develop into columnar shape. The ζ phase close to the δ1 phase is formed relatively densely, but at the upper part, somewhat coarse columnar crystals are formed, and between adjacent columnar crystals, the η phase close to pure Zn is coarse columnar A mixed phase soot layer as defined in the present invention formed between the crystals is formed.
δ１相とζ相は、共にＺｎとＦｅとの金属間化合物であり、鋼管素材との界面に形成されるδ１相の方が、Ｆｅ含有割合が高く、硬さも大きい。
η相は、ほぼ純粋のＺｎから構成された単相であり、めっき層成分の中では柔らかい相であって、溶融亜鉛めっき浴から引き上げられた時点では、未だ溶融状態を維持していると考えられる。
The δ1 phase and the zeta phase are both intermetallic compounds of Zn and Fe, and the δ1 phase formed at the interface with the steel pipe material has a higher Fe content and a larger hardness.
The η phase is a single phase composed of substantially pure Zn, and is considered to be a soft phase among the components of the plating layer, and still maintain a molten state when pulled out from the hot dip galvanizing bath Be
このような層構造のめっき層を有する鋼管に対して、フレア加工などを行った場合、めっき層の剥離は、最も硬いδ１相が主体であるδ１層や、これに次ぐ硬さのζ相主体のζ層の層内で生じていることが判明した。 When flare processing is performed on a steel pipe having a plating layer having such a layered structure, peeling of the plating layer is mainly caused by the δ1 layer mainly composed of the hardest δ1 phase, and the copper phase mainly having a hardness second to this. It has been found that it occurs in the layer of the coral layer.
本発明は、以上のような検討過程を経て上記（１）〜（７）に記載の発明に至ったものであり、以下、順次説明する。 The present invention has reached the inventions described in the above (1) to (7) through the above-described examination process, and will be sequentially described below.
本発明の鋼板の成分組成及びその限定理由について説明する。 The component composition of the steel plate of the present invention and the reason for limitation will be described.
（Ｃ：０．００５〜０．１５％）
Ｃは、強度を確保するために有効な元素であり、含有量が少ないと、その効果が発揮されないので、０．００５％以上が望ましい。さらに望ましくは、０．０１％以上である。しかし、Ｃを過剰に添加すると、強度が高くなりすぎて、伸びが低下し、曲げ加工性が劣化するため、０．１５％以下が望ましい。
(C: 0.005 to 0.15%)
C is an element effective for securing strength, and if its content is small, its effect can not be exhibited, so 0.005% or more is desirable. More preferably, it is 0.01% or more. However, if C is added excessively, the strength is too high, the elongation is reduced, and the bending workability is deteriorated. Therefore, 0.15% or less is desirable.
（Ｓｉ：０．１５〜０．２５％）
Ｓｉは、本発明では重要な元素である。溶融亜鉛めっき性の観点からは、Ｆｅ−Ｚｎ合金層が発達する「ヤケ」防止成分として、０．１５％以上、０．２５％以下の含有量範囲が良好である。また、Ｓｉ含有量が低いと、素材鋼管表面に形成されるめっき層の厚みが、全体として薄くなる傾向があるため、厚みのあるめっき層を形成するためには、０．１５％以上の含有量が必要である。
一方、過大な含有量は、素材鋼管の硬度を上昇させるため、加工性確保の観点から上限は０．２５％に設定した。
(Si: 0.15 to 0.25%)
Si is an important element in the present invention. From the viewpoint of hot-dip galvanizing properties, the content range of 0.15% or more and 0.25% or less is good as the “burn” preventing component in which the Fe—Zn alloy layer develops. In addition, when the Si content is low, the thickness of the plating layer formed on the surface of the material steel pipe tends to be thin as a whole, so in order to form a thick plating layer, the content of 0.15% or more The amount is necessary.
On the other hand, the upper limit of the excessive content is set to 0.25% from the viewpoint of securing the formability in order to increase the hardness of the material steel pipe.
（Ｍｎ：０．２０〜１．６％）
Ｍｎは、強度を得るのに有効な元素である。Ｓｉを０．１５〜０．２５％の範囲に限定したため、添加量が少ないとＭｎ／Ｓｉ質量比が低くなり、溶接時の溶接欠陥が発生し易くなるので、０．２０％以上、更には、０．４０％以上の含有量が望ましい。反対に過剰に添加すると、強度が高くなりすぎて、伸びが低下し、曲げ加工性が劣化するため、１．６％以下とすることが望ましい。
(Mn: 0.20 to 1.6%)
Mn is an element effective to obtain strength. Since Si is limited to the range of 0.15 to 0.25%, the Mn / Si mass ratio is low when the addition amount is small, and welding defects at the time of welding are easily generated. Therefore, 0.20% or more, further, A content of 0.40% or more is desirable. On the other hand, if it is added excessively, the strength is too high, the elongation is reduced, and the bending workability is deteriorated.
（Ｐ：０．０４％以下）
Ｐ：Ｐは不純物として鋼中に存在するが、その量が０．０４％を超えると、中心偏析が増加し、成形加工時に介在物を起点として、割れが進展し易くなるため、０．０４％以下とすることが望ましい。さらに望ましくは、０．０２％以下である。
(P: 0.04% or less)
P: P is present as an impurity in the steel, but if its amount exceeds 0.04%, central segregation will increase and cracks will easily develop from inclusions during forming, so 0.04 It is desirable to make it% or less. More preferably, it is 0.02% or less.
（Ｓ：０．０４％以下）
Ｓも不純物として鋼中に存在するが、その量が０．０４％を超えると、割れの原因となるため、０．０４％以下とすることが望ましい。さらに、望ましくは、０．０１％以下である。
(S: 0.04% or less)
S is also present in the steel as an impurity, but if it exceeds 0.04%, it causes cracking, so it is desirable to make it 0.04% or less. Furthermore, desirably, it is 0.01% or less.
次に、本発明に係る溶融亜鉛めっき鋼管の製造方法について、説明する。
本発明に係るめっき鋼管においては、溶融亜鉛めっき層と素材鋼管表面との界面反応の不均一化を増大させることが、製法上のポイントである。
即ち、前記界面に形成されるδ１層や、該δ１層上に形成されるζ層が過度に均一で、平坦であると、それらの層内に、フレア加工等を行った際にき裂が発生し易く、かつ、この亀裂が長大化する傾向があるので、適度に不均一化した方が、き裂が発生し難くなり、また、発生した場合においても、途中で境界層に当接して、き裂の伝播を食い止めることが可能となると思われる。
Next, a method of manufacturing a galvanized steel pipe according to the present invention will be described.
In the plated steel pipe according to the present invention, it is a point of the manufacturing method to increase the nonuniformity of the interfacial reaction between the hot-dip galvanized layer and the surface of the material steel pipe.
That is, if the δ1 layer formed at the interface or the weir layer formed on the δ1 layer is excessively uniform and flat, a crack may occur when flare processing is performed in those layers. Since this crack tends to grow and this crack tends to lengthen, it is difficult for the crack to be generated if it is made uneven appropriately, and even if it occurs, it abuts on the boundary layer in the middle. It seems possible to stop the propagation of the crack.
具体的には、溶融亜鉛めっき鋼管表面は、耐腐食性を確保する観点から、η相単相で形成される必要があるが、η層とζ層の境界においては、両者が適度に嵌入して、混相を形成する必要がある。これを実現するためには、例えば、ＺｎＣｌ2−ＮＨ4Ｃｌ系フラックスを使用してフラックス浴温４０〜９０℃で浸漬し、その後、該フラックス浴温±１０℃、即ち、３０〜１００℃程度で乾燥する方法が考えられる。乾燥時間は鋼管の肉厚と乾燥温度に依存するために一概には決められないが、５〜３０分の範囲から適宜選ぶことができる。 Specifically, the surface of the hot-dip galvanized steel pipe needs to be formed of η-phase single phase from the viewpoint of securing corrosion resistance, but at the boundary between η layer and ζ layer, both fit properly. It is necessary to form a mixed phase. In order to realize this, for example, immersion is performed at a flux bath temperature of 40 to 90 ° C. using a ZnCl 2 -NH 4 Cl based flux, and then the flux bath temperature ± 10 ° C., that is, about 30 to 100 ° C. The method of drying with can be considered. The drying time is not determined in general because it depends on the thickness of the steel pipe and the drying temperature, but can be appropriately selected from the range of 5 to 30 minutes.
フラックス乾燥温度を１００℃以下とすることにより、局所的にフラックスの濃淡が発生した状態で、鋼管が溶融亜鉛浴中に浸漬されることで、めっき反応点が分散し、前述したような、
（１）ζ層とη層とが境界部分で適度に混合しており、軟質なη相がζ相に入り込み、
（２）ζ層の厚さの中心線を中央として、該中心線の両側各２５％の範囲におけるη相の混入割合が１〜１０面積％であり、
更には、
（３）η層とζ層の境界で互いにはみ出す部分が境界長さ１００μｍあたり合計で１０個以上であり、
（４）δ１層の厚みが適度に変動し、δ１層とζ層の境界で互いにはみ出す部分が境界長さ１００μｍあたり合計で２個以上で、δ１層の最大厚さがδ１層の平均厚さの１．５倍以上であり、
（５）ζ層厚さ／δ１層厚さの比が２．０以上、或いは５．０以上となる、
という特徴を有するめっき層を実現することができる。
By setting the flux drying temperature to 100 ° C. or lower, the steel pipe is immersed in the molten zinc bath in a state where flux concentration is locally generated, and the plating reaction point is dispersed, as described above,
(1) The cocoon layer and the 適度 layer are mixed appropriately at the boundary, and the soft η phase enters the cocoon phase,
(2) The mixing ratio of η phase in the range of 25% on both sides of the center line with the center line of the thickness of the cocoon layer as the center is 1 to 10 area%,
Furthermore,
(3) There are a total of 10 or more in total per 100 μm of boundary length, portions protruding over each other at the boundary of η layer and ζ layer,
(4) The thickness of the δ1 layer fluctuates moderately, and the portions sticking out each other at the boundary between the δ1 layer and the weir layer are 2 or more in total per 100 μm of boundary length, and the maximum thickness of the δ1 layer is the average thickness of the δ1 layer More than 1.5 times of
(5) The ratio of wedge layer thickness / δ1 layer thickness is 2.0 or more, or 5.0 or more,
A plated layer having the following features can be realized.
また、めっき工程に先立つ酸洗工程において、過酸洗とする手法も有効である。
例えば、３〜２０％Ｈ2ＳＯ4で、４０〜８０℃、浸漬時間３０分以上（上限は特に設けないが、生産性の観点から６０分以下が望ましい）あるいは３〜１５％ＨＣｌで、４０〜８０℃、浸漬時間１０分以上（上限は特に設けないが、生産性の観点から３０分以下が望ましい）の条件で過酸洗とすることができる。酸洗後、水洗といった比較的長時間の酸洗を行って、素材鋼管表面を適度に粗面化することによっても、めっき反応点の分散化が進行し、δ１層に厚み変動が生じると共に、該δ１層がうねり、き裂の伝播が抑制される効果や、ζ層／δ１層の厚さ比を増大することができる。
In addition, in the pickling step prior to the plating step, a method of peracid pickling is also effective.
For example, 3 to 20% H 2 SO 4 at 40 to 80 ° C., immersion time 30 minutes or more (upper limit is not particularly provided, but 60 minutes or less is desirable from the viewpoint of productivity) or 3 to 15% HCl 40 Peracid washing can be performed under the conditions of -80 ° C., immersion time of 10 minutes or more (the upper limit is not particularly provided, but 30 minutes or less is desirable from the viewpoint of productivity). Even after acid pickling, acid pickling for a relatively long time such as washing with water is carried out to roughen the surface of the material steel pipe appropriately, dispersion of the plating reaction points proceeds and thickness variation occurs in the δ1 layer, The δ1 layer swells, the effect of suppressing the propagation of a crack, and the thickness ratio of the wedge layer / δ1 layer can be increased.
上述したフラックス乾燥温度の低温化と、過酸洗は、一方のみを実施してもよいし、両者を組み合わせて実施することも可能である。 Only one of the above-described lowering of the flux drying temperature and the peracid washing may be performed, or both may be performed in combination.
以下、実施例について説明する。
＜供試材＞
めっき用素管は、低炭素熱延板を電縫製管した１００Ａ（外径１１４．３ｍｍΦ×肉厚４．５ｍｍｔ）鋼管を用いた。鋼材成分は質量％でＣ：０．０６％、Ｓｉ：０．２１％、Ｍｎ：０．２４％、Ｐ：０．００７％、Ｓ：０．００２％であった。
Examples will be described below.
<Test material>
As a raw pipe for plating, a 100 A (outer diameter 114.3 mm ×× thickness 4.5 mm t) steel pipe in which a low carbon hot-rolled sheet is used as an electric sewing pipe is used. The steel components were C: 0.06%, Si: 0.21%, Mn: 0.24%, P: 0.007%, S: 0.002% by mass.
＜脱脂・酸洗工程＞
脱脂及び酸洗は、５％ＫＯＨで６０℃×１５ｍｉｎ．で脱脂した後、水洗し、表１に記載の各種酸洗条件にて酸洗後、水洗した。
<Degreasing and pickling process>
Degreasing and pickling were carried out with 5% KOH at 60 ° C. × 15 min. After degreasing, water was washed, and after pickling under various pickling conditions shown in Table 1, it was washed with water.
＜フラックス処理工程＞
ＺｎＣｌ2−３ＮＨ4Ｃｌ（３号フラックス）３５％濃度のフラックスにより、表１に記載のフラックス浸漬条件、乾燥条件によりフラックス処理を行った。
<Flux treatment process>
The flux treatment was performed under the flux immersion conditions and the drying conditions described in Table 1 with a flux of 35% concentration of ZnCl 2 -3NH 4 Cl (No. 3 flux).
＜めっき工程＞
めっき浴は、電解亜鉛溶融めっき浴を使用し、４７０℃、浴面フラックスなしで、浸漬時間は１２０ｓｅｃ．を基準として変化させ、めっき付着量を変化させた。めっき浴から引き上げ後、１０ｓｅｃ．放置、のち水冷を行った。
<Plating process>
The plating bath is an electrolytic zinc hot-dip plating bath, 470 ° C., no bath surface flux, and an immersion time of 120 sec. The plating adhesion amount was changed as a standard. After pulling up from the plating bath, 10 sec. It was left to stand and then water cooled.
＜めっき層断面観察＞
フレア未加工部からサンプルを切り出し、埋め込み研磨した。めっき層のη、ζ、δ１の各相が明確に判別できるように、エタノール＋０．０３％硝酸溶液に２０ｓｅｃ浸漬し、エッチングした。
<Cross-section observation of plating layer>
A sample was cut out from the flared raw part and embedded and polished. In order to be able to clearly distinguish each phase of η, ζ, δ1 of the plating layer, it was immersed for 20 seconds in an ethanol + 0.03% nitric acid solution and etched.
めっき層の断面写真を撮影し、２階調（二値化）処理により各相を更に明確にした。面積比でη相：ζ相＝１：１となる線分を探しだし、この線分が含まれる直線をη層とζ層（η相とζ相の混相からなるζ層上部）の境界と決定した。なお、η層とζ層に互いにはみ出す部分は境界長さ１００μｍあたりの合計を算出した。はみ出す個数が１０個以上の場合は○、１０個未満の場合は×と評価した。
同様に面積比でζ相：δ１相＝１：１となる線分を探しだし、この線分が含まれる直線をζ層（ζ層下部）とδ１層との境界と決定した。なお、ζ層とδ１層に互いにはみ出す部分は境界長さ１００μｍあたり合計で２個以上であった。
これらの手順で決定した境界により、「η層厚み」、「ζ層厚み」、「δ１層厚み」を測定した。
A cross-sectional photograph of the plating layer was taken, and each phase was further clarified by two gradation (binarization) processing. Search for a line segment with 比 phase: ζ phase = 1: 1 in area ratio, and the straight line containing this line segment with the boundary of η layer and ζ layer (upper part of ζ phase and mixed phase of ζ phase and ζ phase) Were determined. In addition, the part which overflowed mutually to eta layer and a wedge layer calculated the total per 100 micrometers of boundary length. In the case where the number of overhangs was 10 or more, it was evaluated as ○, and in the case of less than 10, it was evaluated as x.
Similarly, a line segment having a phase ratio of δ1 phase = 1: 1 in terms of area ratio was searched, and a straight line including this line segment was determined as the boundary between the moss layer (lower layer of moss layer) and the δ1 layer. In addition, the part which mutually overflowed in the cocoon layer and the (delta) 1 layer was 2 or more in total per 100 micrometers of boundary length.
Based on the boundaries determined by these procedures, "η layer thickness", "ζ layer thickness", and "δ1 layer thickness" were measured.
またζ層内のη相面積比率も断面写真から画像解析により測定した。
測定の結果、ζ層の層内剥離が生じにくいめっき層においては、ζ層を画定する上下の境界線（η層及びδ１層との境界線）の中央線の両側各２５％の範囲、即ち、ζ層の全厚さの中央５０％の領域において、η相が１〜１０面積％含まれていることが判明した。
また、はみ出し個数は１０個以上であれば、き裂伝播を安定して抑制することができる。
Moreover, the η phase area ratio in the cocoon layer was also measured by image analysis from the cross-sectional photograph.
As a result of the measurement, in the plating layer in which delamination in the weir layer is difficult to occur, the range of 25% on both sides of the center line of the upper and lower boundaries (the boundaries between η layer and δ1 layer) defining the weir layer, ie It was found that in the central 50% region of the total thickness of the weir layer, 1 to 10 area% of η phase was contained.
In addition, if the number of protrusions is 10 or more, crack propagation can be stably suppressed.
＜めっき付着量測定＞
フレア未加工部からサンプルを３０ｍｍ×３０ｍｍ切り出し、重量を測定した。重量測定後、剥離液（１０％ＨＣｌ＋イビット７００ＢＫ）にてめっき層を剥離した。めっき層剥離後、重量を再度測定し、減量からめっき付着量を算出した。
<Measurement of plating adhesion amount>
A sample was cut out of 30 mm × 30 mm from the flared unprocessed part and the weight was measured. After the weight measurement, the plating layer was peeled off with a peeling solution (10% HCl + Ibit 700 BK). After peeling of the plating layer, the weight was measured again, and the plating adhesion amount was calculated from the weight loss.
図２は、表１に示す酸洗を施した後、フラックス処理を行って、電解亜鉛溶融めっき浴により、めっき層を形成した試験片の断面図を示す。 FIG. 2 shows a cross-sectional view of a test piece on which a plating layer is formed by the electrolytic zinc hot-dip plating bath after performing the pickling shown in Table 1 and then performing the flux treatment.
＜めっき密着性評価＞
フレア加工機（日商テクノ製）により溶融亜鉛めっき鋼管の管端部を１５ｍｍフレア加工（鍔出し加工）した。フレア加工部の管外面側のめっき層剥離状態を目視、あるいはテーピング（ＪＩＳＺ１５２２に規定された粘着テープを使用し、テープを貼りつけない部分を３０ｍｍ以上残して、フレア加工部に貼りつけ、めっき面に垂直になるように強く引っ張り、テープを瞬間的に引き剥がす）により確認し、以下に示す評点をつけた。○と△を合格とした。
○：めっき密着性良好（テーピングによってもめっきが剥離しない）
△：めっき密着性やや良（テーピングによって僅かに粉状めっき付着が認められる）
×：めっき密着不良（テーピングによりテープ側にめっきが付着する）
××：めっき剥離（目視でフレア加工部にめっき剥離が認められる）
<Plating adhesion evaluation>
The end of the hot-dip galvanized steel pipe was flared 15 mm by a flare processing machine (manufactured by Nissho Techno Co., Ltd.). The peeling state of the plating layer on the tube outer surface side of the flared part is observed visually or taping (use an adhesive tape defined in JIS Z 1522 and affix the taped part to the flared part leaving 30 mm or more with no tape attached And the tape was instantaneously pulled off), and the score shown below was given. ○ and を were accepted.
:: Good plating adhesion (the plating does not peel even by taping)
Δ: Plating adhesion somewhat good (Slight powder plating adhesion is observed by taping)
X: Poor adhesion to plating (plating adheres to the tape side by taping)
× ×: Plating peeling (Plating peeling is observed in the flared portion visually)
本発明例ではめっき密着性がいずれも良好であった。一方、比較例においては、目視あるいはテーピングによってめっき剥離が認められ、埋設用途などの長期間にわたる耐腐食性は期待できない。 In the examples of the present invention, the plating adhesion was all good. On the other hand, in the comparative example, plating peeling is recognized by visual inspection or taping, and corrosion resistance over a long period such as embedding use can not be expected.
本発明によれば、埋設管等の耐腐食性を要求される厚肉溶融亜鉛めっき鋼管であって、曲げ加工やフレア加工を施しても、めっき層の剥離を生じない使い勝手の良い溶融亜鉛めっき鋼管が得られ、その製造に於いても、微量添加元素の管理等の必要がなく、産業上の利点は大きい。 According to the present invention, a thick-walled galvanized steel pipe requiring corrosion resistance such as a buried pipe, etc., which is easy to use, does not cause peeling of the plating layer even when bending or flare processing is performed. A steel pipe can be obtained, and there is no need to manage trace additive elements in its production, and the industrial advantage is great.
Claims (7)
溶融亜鉛めっき層が表面側からη相が主体のη層、ζ相にη相が混入したζ層、及びδ１相が主体のδ１層からなり、
前記η層とζ層の境界は、互いの領域にはみ出したη相とζ相の面積が等しくなる線分であり、
前記めっき層断面におけるζ層の中心線の上下各ζ相層の全厚に対して２５％の範囲、即ちζ相層の全厚さの中央５０％の範囲におけるη相の面積比が１〜１０面積％であることを特徴とする溶融亜鉛めっき鋼管。 A hot-dip galvanized steel pipe in which a hot-dip galvanized layer is formed on the surface of the steel pipe,
The hot-dip galvanized layer is composed of an η layer mainly composed of η phase from the surface side, a ζ layer composed of η phase mixed with ζ phase, and a δ1 layer mainly composed of δ1 phase,
The boundary between the η layer and the cocoon layer is a line segment in which the areas of the ζ phase and the cocoon phase which are projected into each other are equal
The area ratio of η phase in the range of 25% with respect to the total thickness of the respective upper and lower phase layers of the center line of the soot layer in the cross section of the plated layer Hot-dip galvanized steel pipe characterized in having 10% by area.
前記ζ層とδ１層の境界は、互いの領域にはみ出したζ相とδ１相の面積が等しくなる線分であり、
前記境界で互いにはみ出す部分が境界長さ１００μｍあたり合計で２個以上であり、
δ１層の最大厚さがδ１層の平均厚さの１．５倍以上であることを特徴とする請求項１又は２のいずれかに記載の溶融亜鉛めっき鋼管。 In the hot dip galvanized layer,
The boundary between the cocoon layer and the δ1 layer is a line segment in which the area of the cocoon phase and the δ1 phase that has been projected into each other is equal,
The portions that protrude from each other at the boundary are two or more in total per 100 μm of boundary length,
The hot-dip galvanized steel pipe according to any one of claims 1 and 2, wherein the maximum thickness of the δ1 layer is 1.5 or more times the average thickness of the δ1 layer.
Ｃ：０．００５以上０．１５％以下、
Ｓｉ：０．１５％以上０．２５％以下、
Ｍｎ：０．２０％以上１．６０％以下、
Ｐ ：０．０４％以下、
Ｓ ：０．０４％以下であって、
残部がＦｅ及び不可避不純物であることを特徴とする請求項１乃至６のいずれか１項に記載の溶融亜鉛めっき鋼管。 The composition of the hot-dip galvanized steel pipe is, by mass%,
C: 0.005 or more and 0.15% or less,
Si: 0.15% or more and 0.25% or less,
Mn: 0.20% to 1.60%,
P: 0.04% or less,
S: 0.04% or less,
The hot dip galvanized steel pipe according to any one of claims 1 to 6, wherein the balance is Fe and an unavoidable impurity.
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| CN112322968A (en) * | 2020-09-28 | 2021-02-05 | 日照钢铁控股集团有限公司 | Thermal-base non-flower high-strength galvanized plate for photovoltaic support and preparation process thereof |
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