JP5799874B2 - Method for producing hot-dip galvanized steel pipe - Google Patents
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Description
本発明は、溶融亜鉛めっき鋼管の製造方法に関し、特に、めっきを施す対象の鋼管として、熱間での電気抵抗溶接によって継目部が接合されてなる電縫鋼管（以下、単に「電縫鋼管」という）を採用した溶融亜鉛めっき鋼管の製造方法に関する。 The present invention relates to a method for manufacturing a hot dip galvanized steel pipe, and in particular, as a steel pipe to be plated, an electric-welded steel pipe (hereinafter simply referred to as “electric-welded steel pipe”) in which a seam portion is joined by hot electric resistance welding. The present invention relates to a method for manufacturing a hot dip galvanized steel pipe.
通常、電縫鋼管は、以下のようにして造管される。素材である帯鋼を加熱炉で９００〜９６０℃に加熱し、加熱された帯鋼を一群の成形ロールによって円筒状に連続成形し、その継目部をそのまま熱間で電気抵抗溶接することにより接合し、続いて絞り圧延を行って所定の外径および肉厚の電縫鋼管に仕上げる。絞り圧延後、電縫鋼管を所定の長さに切断し、さらに曲がりを矯正する。 Usually, an electric resistance steel pipe is manufactured as follows. The steel strip, which is the raw material, is heated to 900-960 ° C. in a heating furnace, the heated steel strip is continuously formed into a cylindrical shape by a group of forming rolls, and the joint is joined by hot electrical resistance welding as it is. Subsequently, drawing rolling is performed to finish the ERW steel pipe with a predetermined outer diameter and wall thickness. After drawing and rolling, the electric resistance welded steel pipe is cut into a predetermined length, and the bending is further corrected.
このようにして造管された電縫鋼管は、溶融亜鉛めっきを施すに際し、表面に付着しているスケールを酸洗によって除去され、フラックス処理が施される。スケールを除去された電縫鋼管は、約４６０℃の溶融亜鉛めっき浴に浸漬し所定時間経過後に引き上げられ、外面および内面の順で余剰の溶融亜鉛をエアーワイピングなどで除去した後、冷却される。こうして、電縫鋼管の表面に亜鉛めっき皮膜が形成された溶融亜鉛めっき鋼管が製造される。 When the hot-dip galvanized steel pipe is formed in this manner, the scale adhering to the surface is removed by pickling and flux treatment is performed. The ERW steel pipe from which the scale has been removed is immersed in a hot dip galvanizing bath at about 460 ° C., pulled up after a lapse of a predetermined time, and is cooled after removing excess molten zinc in the order of the outer surface and the inner surface by air wiping or the like. . In this way, a hot-dip galvanized steel pipe having a galvanized film formed on the surface of the electric resistance steel pipe is manufactured.
溶融亜鉛めっき鋼管は、ＪＩＳ Ｇ ３４４２で規定される水配管用亜鉛めっき鋼管や、ＪＩＳ Ｇ ３４５２で規定される配管用炭素鋼鋼管の白管として使用される。従来、溶融亜鉛めっき鋼管を配管として成り立たせるため、管端同士を溶接接合したり、管端部にねじ切り加工を施して管端部同士をねじ接合したりして接続するのが主流であった。しかし、近年では、鋼管を接続する際の施工効率の要請から、管端部を鍔状に広げるフレア加工を施し、その鍔状の管端部同士をフランジおよびボルトを用いて接続するジョイント工法が一般化している。 The hot dip galvanized steel pipe is used as a white pipe of a galvanized steel pipe for water piping specified by JIS G 3442 or a carbon steel pipe for piping specified by JIS G 3542. Conventionally, in order to establish a hot-dip galvanized steel pipe as a pipe, it has been the mainstream to connect the pipe ends by welding them together or by threading the pipe ends and screwing the pipe ends together. . However, in recent years, due to the demand for construction efficiency when connecting steel pipes, there is a joint construction method in which flare processing is performed to expand the pipe ends into a bowl shape, and the flange-like pipe ends are connected to each other using flanges and bolts. It is generalized.
図１は、フレア加工された溶融亜鉛めっき鋼管をジョイント工法で接続した状態を示す断面図である。同図に示すように、溶融亜鉛めっき鋼管１は、フレア加工により、管端部１ａが概ね９０°に広がる鍔状に形成される。そして、ジョイント工法では、溶融亜鉛めっき鋼管１の鍔状管端部１ａ同士を間にガスケット４を挟んで突き合わせ、突き合わせた鍔状管端部１ａを一対のフランジ２によって挟み込み、フランジ２同士をボルト３で締結する。
FIG. 1 is a cross-sectional view showing a state in which flared galvanized steel pipes are connected by a joint method. As shown in the figure, the hot dip galvanized steel pipe 1 is formed in a bowl shape in which the pipe end portion 1a extends approximately 90 ° by flare processing. In the joint method, the flanged pipe ends 1a of the hot-dip galvanized steel pipe 1 are butted together with the gasket 4 interposed therebetween, the butted flanged pipe ends 1a are sandwiched between the pair of
このように、ジョイント工法においては、溶融亜鉛めっき鋼管に予めフレア加工を施すことが不可欠である。 Thus, in the joint method, it is indispensable to pre-flare the hot dip galvanized steel pipe.
しかし、フレア加工は、溶融亜鉛めっき鋼管に著しい塑性変形を与える加工である。このため、特許文献１に記載されるように、フレア加工時に溶融亜鉛めっき鋼管のめっき皮膜が剥離することがある。めっき皮膜が鋼管母材表面から剥離し、脱落した場合（いわゆる、皮膜の剥がれが発生した場合）、その溶融亜鉛めっき鋼管は製品として出荷することができない。めっき皮膜が脱落するまでに至らなくとも膨れた状態で鋼管母材表面に残っている場合（いわゆる、皮膜の膨れが発生した場合）には、めっき皮膜の膨れが例えば２箇所以上発生していると、その溶融亜鉛めっき鋼管は製品として出荷することができない。 However, the flaring process is a process that gives significant plastic deformation to the hot-dip galvanized steel pipe. For this reason, as described in Patent Document 1, the plating film of the hot-dip galvanized steel pipe may be peeled off during flare processing. When the plating film peels off from the surface of the steel pipe base material and falls off (so-called film peeling occurs), the hot dip galvanized steel pipe cannot be shipped as a product. If the plating film remains on the surface of the steel pipe base material even if the plating film does not fall off (so-called film swelling occurs), swelling of the plating film occurs, for example, at two or more locations. And the hot dip galvanized steel pipe cannot be shipped as a product.
ここで、前記特許文献１に記載されるように、２００６年に、欧州連合により、電子・電気機器における特定有害物質の使用を制限するＲｏＨＳ（Restriction of Hazardous Substances）指令が施行され、このＲｏＨＳ指令では、対象製品中のＰｂ（鉛）の含有率が０．１質量％以下、Ｃｄ（カドミウム）の含有率が０．０１質量％以下に制限されている。通常、電縫鋼管の溶融亜鉛めっきに用いる亜鉛には蒸留亜鉛が使用されており、溶融亜鉛めっき鋼管は、ＲｏＨＳ指令で規定される基準値を超えて、Ｐｂを０．３〜１．３質量％程度、Ｃｄを０．０３〜０．１質量％程度含有する溶融亜鉛めっき浴から製造される。これに対し、溶融亜鉛めっきの亜鉛として最純亜鉛を使用すれば、溶融亜鉛めっき鋼管は、Ｐｂを０．１質量％以下、Ｃｄを０．０１質量％以下で含有する溶融亜鉛めっき浴から製造され、ＲｏＨＳ指令の規制に対応することができる。 Here, as described in Patent Document 1, in 2006, the European Union enforced the RoHS (Restriction of Hazardous Substances) directive restricting the use of specific hazardous substances in electronic and electrical equipment. Then, the content rate of Pb (lead) in the target product is limited to 0.1% by mass or less, and the content rate of Cd (cadmium) is limited to 0.01% by mass or less. Normally, distilled zinc is used as the zinc used for hot dip galvanization of ERW steel pipes, and hot dip galvanized steel pipes exceed the standard values specified by the RoHS directive, and Pb is 0.3 to 1.3 masses. %, Manufactured from a hot dip galvanizing bath containing about 0.03 to 0.1% by mass of Cd. On the other hand, if the purest zinc is used as the zinc for hot dip galvanizing, the hot dip galvanized steel pipe is manufactured from a hot dip galvanizing bath containing Pb at 0.1% by mass or less and Cd at 0.01% by mass or less. And comply with the regulations of the RoHS directive.
上記したフレア加工時のめっき皮膜の剥離は、蒸留亜鉛を使用した溶融亜鉛めっき浴から製造された溶融亜鉛めっき鋼管であっても、最純亜鉛を使用した溶融亜鉛めっき浴から製造され、ＲｏＨＳ指令の規制に対応した溶融亜鉛めっき鋼管であっても、発生し得る。 Peeling of the plating film at the time of flare processing is manufactured from a hot dip galvanizing bath using the purest zinc, even if it is a hot dip galvanized steel pipe manufactured from a hot dip galvanizing bath using distilled zinc. Even hot-dip galvanized steel pipes that comply with these regulations may occur.
本発明の目的は、次の特性を有する溶融亜鉛めっき鋼管の製造方法を提供することである：
（１）熱間での電気抵抗溶接によって継目部が接合されてなる電縫鋼管に溶融亜鉛めっきを施す場合に、フレア加工時のめっき皮膜の剥離を防止できること；
（２）ＲｏＨＳ指令の規制にも対応した溶融亜鉛めっき鋼管を製造できること。
The object of the present invention is to provide a method for producing a hot-dip galvanized steel pipe having the following properties:
(1) When hot-dip galvanizing is applied to an electric resistance steel pipe in which a seam is joined by electrical resistance welding in the hot state, the peeling of the plating film during flare processing can be prevented;
(2) A hot-dip galvanized steel pipe compatible with the regulations of the RoHS directive can be manufactured.
本発明の要旨は、次の通りである。 The gist of the present invention is as follows.
帯鋼を加熱し、加熱された帯鋼を一群のロールによって円筒状に成形し、その継目部を熱間で電気抵抗溶接することにより接合し、続いて絞り圧延を行って電縫鋼管を造管する造管工程と、
造管工程の後に電縫鋼管を酸洗しスケールを除去する酸洗工程と、
スケールを除去された電縫鋼管に溶融亜鉛めっきを施すめっき工程と、を含む溶融亜鉛めっき鋼管の製造方法であって、
当該溶融亜鉛めっき鋼管の製造方法は、
造管工程にて帯鋼を１０００℃±２０℃に加熱して電縫鋼管を造管し、
酸洗工程で酸洗を行う前の電縫鋼管の表面粗度を中心線平均粗さで２．０μｍ以上とし、酸洗を行った後の電縫鋼管の表面粗度を中心線平均粗さで４．０μｍ以上とすること、
を特徴とする溶融亜鉛めっき鋼管の製造方法。
The steel strip is heated, the heated steel strip is formed into a cylindrical shape by a group of rolls, and the joints are joined by hot electrical resistance welding, followed by drawing and forming an ERW steel pipe. Pipe making process,
Pickling process to remove scale by pickling ERW steel pipe after pipe making process;
A method for producing a hot-dip galvanized steel pipe, comprising a plating step of hot-dip galvanizing the scaled ERW steel pipe,
The manufacturing method of the hot dip galvanized steel pipe is as follows:
In the pipe making process, the steel strip is heated to 1000 ° C. ± 20 ° C. to make an ERW steel pipe,
The surface roughness of the ERW steel pipe before pickling in the pickling process is set to 2.0 μm or more in the centerline average roughness, and the surface roughness of the ERW steel pipe after pickling is set to the centerline average roughness. To be 4.0 μm or more,
A method for producing a hot dip galvanized steel pipe.
この溶融亜鉛めっき鋼管の製造方法は、めっき工程において、Ｐｂ：０．１質量％以下およびＣｄ：０．０１質量％以下を含有する溶融亜鉛めっき浴を用いて電縫鋼管に溶融亜鉛めっきを施すことが好ましい。 In the method of manufacturing the hot dip galvanized steel pipe, the hot dip galvanizing is performed on the ERW steel pipe using a hot dip galvanizing bath containing Pb: 0.1% by mass or less and Cd: 0.01% by mass or less in the plating step. It is preferable.
本発明の溶融亜鉛めっき鋼管の製造方法は、下記の顕著な効果を有する：
（１）熱間での電気抵抗溶接によって継目部が接合されてなる電縫鋼管に溶融亜鉛めっきを施す場合に、フレア加工時のめっき皮膜の剥離を防止できること；
（２）ＲｏＨＳ指令の規制にも対応した溶融亜鉛めっき鋼管を製造できること。
The method for producing a hot-dip galvanized steel pipe of the present invention has the following remarkable effects:
(1) When hot-dip galvanizing is applied to an electric resistance steel pipe in which a seam is joined by electrical resistance welding in the hot state, the peeling of the plating film during flare processing can be prevented;
(2) A hot-dip galvanized steel pipe compatible with the regulations of the RoHS directive can be manufactured.
本発明者は、上記目的を達成するため、熱間での電気抵抗溶接によって継目部が接合されてなる電縫鋼管に溶融亜鉛めっきを施すことを前提とし、鋭意検討を重ねた。その結果、以下の知見を得た。 In order to achieve the above-mentioned object, the present inventor has made extensive studies on the assumption that hot-dip galvanizing is applied to an electric-welded steel pipe in which a seam portion is joined by hot electric resistance welding. As a result, the following knowledge was obtained.
（ａ）溶融亜鉛めっきを施すに際し、スケールを除去された電縫鋼管の母材表面が、平滑な状態ではなく、むしろ適度な凹凸で肌荒れしている状態であると、鋼管母材表面に形成された亜鉛めっき皮膜の剥離を防止することができる。これは、鋼管母材表面の適度な凹凸により、亜鉛めっき皮膜を構成するζ（ツェータ）相の結合が強固になり、めっき皮膜と鋼管母材表面との密着性が向上することによる。 (A) When hot-dip galvanizing is performed, the base material surface of the ERW steel pipe from which the scale has been removed is not a smooth state, but rather a rough surface with moderate irregularities. The peeling of the applied galvanized film can be prevented. This is because the bond between the ζ (zeta) phases constituting the galvanized film is strengthened by the appropriate irregularities on the surface of the steel pipe base material, and the adhesion between the plated film and the surface of the steel pipe base material is improved.
（ｂ）電縫鋼管の母材表面に適度な凹凸を生じさせるには、電縫鋼管を造管する際に、素材である帯鋼の加熱温度を高めるのが有効である。帯鋼の加熱温度を高めると、造管中にスケールの生成が促進するため、このスケールを最終的に酸洗によって除去すれば、電縫鋼管の母材表面に適度な凹凸が現れるからである。 (B) In order to cause moderate unevenness on the surface of the base material of the electric resistance welded steel pipe, it is effective to increase the heating temperature of the steel strip as the material when the electric resistance welded steel pipe is formed. When the heating temperature of the steel strip is increased, scale formation is promoted during pipe making. If this scale is finally removed by pickling, appropriate irregularities appear on the surface of the base material of the ERW steel pipe. .
（ｃ）ただし、帯鋼の加熱温度を高め過ぎると、スケールの生成が過度になることから、得られる電縫鋼管の肉厚が減少し、要求される肉厚寸法を満たさなくなる。このため、帯鋼の加熱温度は、高めるにしても制限がある。 (C) However, if the heating temperature of the steel strip is increased too much, the scale is excessively generated, so that the thickness of the obtained electric resistance welded steel pipe is reduced and the required thickness dimension is not satisfied. For this reason, even if it raises the heating temperature of strip steel, there is a restriction.
本発明は、上記（ａ）〜（ｃ）の知見に基づき完成させたものである。すなわち、本発明の溶融亜鉛めっき鋼管の製造方法は、
帯鋼を加熱し、加熱された帯鋼を一群のロールによって円筒状に成形し、その継目部を熱間で電気抵抗溶接することにより接合し、続いて絞り圧延を行って電縫鋼管を造管する造管工程と、
造管工程の後に電縫鋼管を酸洗しスケールを除去する酸洗工程と、
スケールを除去された電縫鋼管に溶融亜鉛めっきを施すめっき工程と、を含み、
造管工程にて帯鋼を１０００℃±２０℃に加熱して電縫鋼管を造管し、
酸洗工程で酸洗を行う前の電縫鋼管の表面粗度を中心線平均粗さで２．０μｍ以上とし、酸洗を行った後の電縫鋼管の表面粗度を中心線平均粗さで４．０μｍ以上とすること、を特徴とする。
The present invention has been completed based on the above findings (a) to (c). That is, the manufacturing method of the hot dip galvanized steel pipe of the present invention is:
The steel strip is heated, the heated steel strip is formed into a cylindrical shape by a group of rolls, and the joints are joined by hot electrical resistance welding, followed by drawing and forming an ERW steel pipe. Pipe making process,
Pickling process to remove scale by pickling ERW steel pipe after pipe making process;
A plating process for hot-dip galvanizing the scaled ERW steel pipe,
In the pipe making process, the steel strip is heated to 1000 ° C. ± 20 ° C. to make an ERW steel pipe,
The surface roughness of the ERW steel pipe before pickling in the pickling process is set to 2.0 μm or more in the centerline average roughness, and the surface roughness of the ERW steel pipe after pickling is set to the centerline average roughness. It is characterized by being 4.0 μm or more.
以下に、本発明の溶融亜鉛めっき鋼管の製造方法を上記のように規定した理由および好ましい態様について説明する。 Below, the reason and preferable aspect which prescribed | regulated the manufacturing method of the hot-dip galvanized steel pipe of this invention as mentioned above are demonstrated.
本発明では、電縫鋼管を造管する際に、帯鋼を１０００℃±２０℃に加熱する。帯鋼の加熱温度をこのような範囲に規定する理由は、次のとおりである。 In the present invention, the strip steel is heated to 1000 ° C. ± 20 ° C. when the ERW steel pipe is formed. The reason why the heating temperature of the steel strip is specified in such a range is as follows.
帯鋼の加熱温度が９８０℃以上である場合、造管時にスケールの生成が促進するため、造管された電縫鋼管を酸洗しスケールを除去すると、電縫鋼管の母材表面に適度な凹凸が現れる。具体的には、酸洗を行う前にあっては、スケールが付着した状態の電縫鋼管の表面粗度を中心線平均粗さ（Ｒａ）で２．０μｍ以上とすることができ、さらに酸洗を行ってスケールを除去した後にあっては、電縫鋼管の表面粗度を中心線平均粗さ（Ｒａ）で４．０μｍ以上とすることができる。酸洗によるスケール除去後に、電縫鋼管の母材表面が中心線平均粗さ（Ｒａ）４．０μｍ以上の表面粗度の凹凸であれば、溶融亜鉛めっき後に、めっき皮膜と鋼管母材表面との密着性が向上し、フレア加工時のめっき皮膜の剥離を防止することができる。 When the heating temperature of the steel strip is 980 ° C. or higher, scale formation is promoted during pipe making. Therefore, if the scale is removed by pickling the piped electric resistance welded steel pipe, the surface of the base metal of the electric resistance welded steel pipe is moderate. Unevenness appears. Specifically, before pickling, the surface roughness of the ERW steel pipe with the scale attached can be set to 2.0 μm or more in terms of centerline average roughness (Ra). After washing and removing the scale, the surface roughness of the electric resistance welded steel pipe can be set to 4.0 μm or more in terms of the centerline average roughness (Ra). After removing the scale by pickling, if the surface of the base material of the ERW steel pipe has irregularities with a surface roughness of centerline average roughness (Ra) of 4.0 μm or more, after the hot dip galvanization, the plating film and the surface of the steel pipe base material It is possible to prevent the peeling of the plating film during flare processing.
ただし、帯鋼の加熱温度が１０２０℃を超えた場合、造管時にスケールの生成が過度になり、これに伴って、得られる電縫鋼管の肉厚が過剰に減少するため、要求される肉厚寸法を満たさなくなるおそれがある。このとき、電縫鋼管の表面粗度は、酸洗を行う前のスケールが付着した状態では、中心線平均粗さ（Ｒａ）で４．５μｍを超え、さらに酸洗を行ってスケールを除去した状態では、中心線平均粗さ（Ｒａ）で８．０μｍを超える。 However, if the heating temperature of the steel strip exceeds 1020 ° C., the scale is excessively generated during pipe making, and the thickness of the resulting ERW steel pipe is excessively reduced. The thickness dimension may not be satisfied. At this time, the surface roughness of the ERW steel pipe exceeded 4.5 μm in the center line average roughness (Ra) in the state where the scale before the pickling was attached, and the pickling was further performed to remove the scale. In the state, the center line average roughness (Ra) exceeds 8.0 μm.
したがって、フレア加工時のめっき皮膜の剥離を防止すると同時に、電縫鋼管の肉厚を要求される寸法内に確保するため、帯鋼の加熱温度は１０００℃±２０℃とする。 Therefore, in order to prevent peeling of the plating film during flare processing and to ensure the thickness of the ERW pipe within the required dimensions, the heating temperature of the steel strip is set to 1000 ° C. ± 20 ° C.
本発明において、酸洗は、電縫鋼管に付着したスケールを完全に除去し、鋼管母材表面の面粗度を中心線平均粗さ（Ｒａ）で４．０μｍ以上とすることができる限り、その条件に特に限定はなく、慣用される方法を適用できる。例えば、酸洗浴として、硫酸を１５〜１７質量％程度、Ｆｅ（鉄）を１．８〜４．３質量％程度含み、温度が７０〜８５℃程度の硫酸浴を用い、この酸洗浴に、造管された電縫鋼管を２０〜３０分間浸漬する。浸漬中、電縫鋼管を遥動させてもよいし、酸洗浴を撹拌してもよい。 In the present invention, pickling removes the scale attached to the ERW steel pipe completely, and the surface roughness of the steel pipe base material surface can be 4.0 μm or more in terms of the center line average roughness (Ra). The conditions are not particularly limited, and a commonly used method can be applied. For example, as a pickling bath, a sulfuric acid bath containing about 15 to 17% by mass of sulfuric acid and about 1.8 to 4.3% by mass of Fe (iron) and having a temperature of about 70 to 85 ° C. is used. The formed ERW steel pipe is immersed for 20 to 30 minutes. During immersion, the ERW steel pipe may be swung or the pickling bath may be stirred.
また、本発明において、溶融亜鉛めっきは、スケールを除去された電縫鋼管の母材表面に所望の目付け量で亜鉛めっき皮膜を形成することができる限り、その条件に特に限定はなく、慣用される方法を適用できる。例えば、温度が４６０〜４７０℃程度の溶融亜鉛めっき浴を用い、このめっき浴に、スケールを除去された電縫鋼管を浸漬する。浸漬時間は３０〜２２５秒程度である。このときのめっき浴は、蒸留亜鉛を使用し、Ｐｂを０．３〜１．３質量％程度、Ｃｄを０．０３〜０．１質量％程度含有するものであってもよいし、最純亜鉛を使用し、Ｐｂを０．１質量％以下、Ｃｄを０．０１質量％以下で含有するものであってもよい。後者のように最純亜鉛を使用した溶融亜鉛めっき浴の場合、ＲｏＨＳ指令の規制に対応した溶融亜鉛めっき鋼管を製造できる点で有用である。 Further, in the present invention, hot dip galvanization is not particularly limited and is commonly used as long as a galvanized film can be formed with a desired basis weight on the surface of the base material of the ERW steel pipe from which scale has been removed. Can be applied. For example, a hot dip galvanizing bath having a temperature of about 460 to 470 ° C. is used, and the ERW steel pipe from which the scale has been removed is immersed in this plating bath. The immersion time is about 30 to 225 seconds. The plating bath at this time may use distilled zinc and may contain about 0.3 to 1.3% by mass of Pb and about 0.03 to 0.1% by mass of Cd. Zinc may be used, and Pb may be 0.1% by mass or less and Cd may be 0.01% by mass or less. In the case of the hot dip galvanizing bath using the purest zinc like the latter, it is useful in that a hot dip galvanized steel pipe corresponding to the regulations of the RoHS directive can be manufactured.
さらに、溶融亜鉛めっきの際、めっき浴から鋼管を引き上げ、内外面の余剰の溶融亜鉛を除去した後の冷却は、６０〜８５℃程度の温水に浸漬して行うのが好ましい。温水による緩冷却により、亜鉛めっき皮膜の硬さが低下し、これに伴ってめっき皮膜中の残留応力やひずみが低減するため、フレア加工時のめっき皮膜の剥離が生じ難くなるからである。 Furthermore, at the time of hot dip galvanization, it is preferable that the steel pipe is lifted from the plating bath, and the cooling after removing excess hot dip zinc on the inner and outer surfaces is immersed in warm water of about 60 to 85 ° C. This is because the hardness of the galvanized film is lowered by the slow cooling with warm water, and the residual stress and strain in the plated film are reduced accordingly, so that the plating film is hardly peeled off during the flare processing.
帯鋼の加熱温度を種々変更して電縫鋼管を造管し、溶融亜鉛めっき鋼管を製造する試験を実施した。この試験では、下記の表１に示すとおり、帯鋼の加熱温度ごとに試験Ｎｏ．１〜９に区分し、試験Ｎｏ．１〜９それぞれで２０本ずつ電縫鋼管を造管し、溶融亜鉛めっき鋼管を製造した。 Various tests were carried out to produce hot-dip galvanized steel pipes by changing the heating temperature of the steel strip and making ERW steel pipes. In this test, as shown in Table 1 below, Test No. 1 to 9, and the test No. 20 ERW steel pipes were made for each of 1 to 9 to produce hot dip galvanized steel pipes.
［試験条件］
（１）帯鋼の加熱温度
上記の表１に示すとおり、９００℃から１０５０℃の範囲内で変更した。
[Test conditions]
(1) Heating temperature of steel strip As shown in Table 1 above, the temperature was changed within the range of 900 ° C to 1050 ° C.
（２）電縫鋼管の仕様
・材質：低炭素鋼（Ｃ：０．０５〜０．１０質量％、Ｍｎ：０．２０〜０．６０質量％、Ｓｉ：０．１８〜０．２３質量％、Ｐ≦０．３５質量％、Ｓ≦０．００５質量％、その他：Ｆｅおよび不純物）
・寸法：外径１１４．３ｍｍ、肉厚４．５ｍｍ、長さ３００ｍｍ
(2) Specifications of ERW steel pipe ・ Material: Low carbon steel (C: 0.05 to 0.10 mass%, Mn: 0.20 to 0.60 mass%, Si: 0.18 to 0.23 mass%) P ≦ 0.35 mass%, S ≦ 0.005 mass%, other: Fe and impurities)
・ Dimensions: outer diameter 114.3mm, wall thickness 4.5mm, length 300mm
（３）酸洗条件
・酸洗浴：硫酸を１５〜１７質量％、Ｆｅを１．８〜４．３質量％含む硫酸浴
・酸洗浴の温度：７０〜８５℃
・酸洗浴への浸漬時間：２０〜３０分
・酸洗後のフラックス処理：ＺｎＣｌ2−ＮＨ4Ｃｌ浴に０．１〜５分間浸漬
(3) Pickling conditions ・ Pickling bath: sulfuric acid bath containing 15 to 17% by mass of sulfuric acid and 1.8 to 4.3% by mass of Fe ・ Temperature of the pickling bath: 70 to 85 ° C.
・ Immersion time in pickling bath: 20 to 30 minutes ・ Flux treatment after pickling: immersion in ZnCl 2 —NH 4 Cl bath for 0.1 to 5 minutes
（４）溶融亜鉛めっき条件
・めっき浴：Ｐｂを０．００２質量％、Ｃｄを０質量％、Ｆｅを０．０２６質量％で含有する溶融亜鉛めっき浴
・めっき浴の温度：４６０〜４７０℃
・めっき浴への浸漬時間：３０〜６０秒
・めっき後の管外面の余剰溶融亜鉛の除去：１．２〜２．２ｋｇｆ／ｃｍ2の常温の圧縮空気を噴射
・めっき後の管内面の余剰溶融亜鉛の除去：１２０〜１８０℃の蒸気を０．５〜２秒間、６〜１１ｋｇｆ／ｃｍ2の圧力で吹付け
・めっき皮膜の目標目付け量：４００ｇ／ｍ2
・余剰溶融亜鉛除去後の冷却：６０〜８５℃の温水に０．５分間浸漬
(4) Hot dip galvanizing conditions-Plating bath: Hot dip galvanizing bath containing 0.002% by mass of Pb, 0% by mass of Cd and 0.026% by mass of Fe-Temperature of plating bath: 460-470 ° C
・ Immersion time in plating bath: 30 to 60 seconds ・ Removal of excess molten zinc on the outer surface of the pipe after plating: Injecting compressed air at room temperature of 1.2 to 2.2 kgf / cm 2・ Excess of the inner surface of the pipe after plating Removal of molten zinc: Spraying steam at 120 to 180 ° C. for 0.5 to 2 seconds at a pressure of 6 to 11 kgf / cm 2. Target amount of plating film: 400 g / m 2
・ Cooling after removal of excess molten zinc: Immersion in hot water at 60 to 85 ° C. for 0.5 minutes
［評価方法］
（１）電縫鋼管の表面粗度
酸洗を行う前と行った後で電縫鋼管の表面粗度を調査した。その際、試験Ｎｏ．１〜９それぞれの２０本全ての電縫鋼管について、各々の外面（ただし、継目部を除く部分）で長手方向に沿った表面変位を計測し、中心線平均粗さ（Ｒａ）を算出した。そして、各試験Ｎｏ．１〜９では、得られた２０本の中心線平均粗さ（Ｒａ）の平均値を表面粗度として算出した。上記の表１に、その結果を示す。
[Evaluation method]
(1) Surface roughness of ERW steel pipe The surface roughness of ERW steel pipe was investigated before and after pickling. At that time, Test No. With respect to all 20 ERW steel pipes 1 to 9, the surface displacement along the longitudinal direction was measured on each outer surface (excluding the seam portion), and the center line average roughness (Ra) was calculated. And each test No. In 1 to 9, the average value of the 20 centerline average roughnesses (Ra) obtained was calculated as the surface roughness. The results are shown in Table 1 above.
（２）電縫鋼管の肉厚
スケールを除去した電縫鋼管の肉厚を調査した。その際、試験Ｎｏ．１〜９それぞれの２０本全ての溶融亜鉛めっき鋼管について、継目部分を除き周方向全域にわたって肉厚を計測し、所望の肉厚寸法を満たしているか否かを評価した。なお、肉厚計測には、マイクロメータを用いた。
(2) ERW steel pipe wall thickness The thickness of the ERW steel pipe from which the scale was removed was investigated. At that time, Test No. For all 20 hot dip galvanized steel pipes 1 to 9, the thickness was measured over the entire circumferential direction except for the joint portion, and it was evaluated whether or not the desired thickness dimension was satisfied. A micrometer was used for measuring the wall thickness.
上記の表１中で、「肉厚」の欄の記号の意味は、次の通りである。
○：良。２０本の全てで、所望の肉厚寸法を満足したことを示す。
×：不可。所望の肉厚寸法を満足しないものが、２０本のうちで１本でも認められたことを示す。
In Table 1 above, the meanings of the symbols in the “wall thickness” column are as follows.
○: Good. It shows that all 20 pieces satisfied the desired thickness dimension.
×: Impossible. This indicates that even one of the 20 pieces that did not satisfy the desired thickness dimension was recognized.
（３）溶融亜鉛めっき鋼管のめっき皮膜の耐剥離性
スケールを除去した電縫鋼管に溶融亜鉛めっきを施し、溶融亜鉛めっき鋼管のめっき皮膜の耐剥離性を調査した。その際、試験Ｎｏ．１〜９それぞれの２０本全ての溶融亜鉛めっき鋼管について、フレア加工を行い、めっき皮膜の剥がれおよび膨れの発生状況を評価した。上記の表１に、その評価結果を示す。
(3) Peeling resistance of plating film of hot-dip galvanized steel pipe Hot-dip galvanizing was applied to the ERW steel pipe from which the scale had been removed, and the peeling resistance of the plating film of the hot-dip galvanized steel pipe was investigated. At that time, Test No. Flare processing was performed on all 20 hot dip galvanized steel pipes 1 to 9, and the occurrence of peeling and swelling of the plating film was evaluated. Table 1 shows the evaluation results.
上記の表１中で、「めっき皮膜の耐剥離性」の欄の記号の意味は、次の通りである。
○：良。２０本の全てで、剥がれおよび膨れのいずれも認められなかったことを示す。
△：可。剥がれは認められないが、膨れが１箇所以内で認められたものが、２０本のうちで１本でもあったことを示す。
×：不可。剥がれが１箇所以上で認められるか、膨れが２箇所以上で認められたものが、２０本のうちで１本でもあったことを示す。
In Table 1 above, the meanings of the symbols in the column of “Peeling resistance of plating film” are as follows.
○: Good. It shows that neither peeling nor blistering was observed in all 20 pieces.
Δ: Yes. Although peeling is not recognized, it is shown that the number of blisters observed within one place was at least one out of 20.
×: Impossible. It is shown that at least one of the 20 pieces was peeled off at one or more places, or the swelling was found at two or more places.
［評価結果］
表１に示すように、帯鋼の加熱温度が本発明の規定範囲（１０００℃±２０℃）を満足する試験Ｎｏ．３、６、７および８では、酸洗前後の電縫鋼管の表面粗度が本発明の規定範囲内となり、溶融亜鉛めっき鋼管におけるめっき皮膜の耐剥離性が良好であった。これと同時に、鋼管の肉厚も良好であった。
[Evaluation results]
As shown in Table 1, test No. 1 in which the heating temperature of the steel strip satisfies the specified range of the present invention (1000 ° C. ± 20 ° C.). In 3, 6, 7 and 8, the surface roughness of the ERW steel pipe before and after pickling was within the specified range of the present invention, and the peel resistance of the plating film in the hot dip galvanized steel pipe was good. At the same time, the thickness of the steel pipe was good.
帯鋼の加熱温度が本発明の規定範囲の下限（９８０℃）を下回る試験Ｎｏ．１、２、４および５では、酸洗前後の電縫鋼管の表面粗度が本発明の範囲に到達せず、鋼管の肉厚が良好であったものの、溶融亜鉛めっき鋼管におけるめっき皮膜の耐剥離性が不芳であった。 Test No. in which the heating temperature of the steel strip is lower than the lower limit (980 ° C.) of the specified range of the present invention. In 1, 2, 4 and 5, the surface roughness of the ERW steel pipe before and after pickling did not reach the range of the present invention, and the thickness of the steel pipe was good. The peelability was poor.
帯鋼の加熱温度が本発明の規定範囲の上限（１０２０℃）を上回る試験Ｎｏ．９では、酸洗前後の電縫鋼管の表面粗度が本発明の規定範囲内となり、溶融亜鉛めっき鋼管におけるめっき皮膜の耐剥離性が良好であったものの、鋼管の肉厚が不芳であった。 Test No. in which the heating temperature of the steel strip exceeds the upper limit (1020 ° C.) of the specified range of the present invention. In No. 9, the surface roughness of the ERW steel pipe before and after pickling was within the specified range of the present invention, and the peel resistance of the plating film on the hot dip galvanized steel pipe was good, but the thickness of the steel pipe was poor. It was.
なお、試験Ｎｏ．１〜９のいずれでも、溶融亜鉛めっき鋼管におけるめっき皮膜は、所望の目付け量を満たし、良好に形成できた。 In addition, Test No. In any of 1 to 9, the plating film on the hot-dip galvanized steel pipe satisfied the desired basis weight and could be formed satisfactorily.
本発明は、フレア加工を実施する溶融亜鉛めっき鋼管の製造に有効に利用できる。 INDUSTRIAL APPLICATION This invention can be utilized effectively for manufacture of the hot dip galvanized steel pipe which performs flare processing.
１：溶融亜鉛めっき鋼管、 １ａ：鍔状管端部、
２：フランジ、 ３：ボルト、 ４：ガスケット
1: hot dip galvanized steel pipe, 1a: end of hooked pipe,
2: flange, 3: bolt, 4: gasket
Claims (2)
造管工程の後に電縫鋼管を酸洗しスケールを除去する酸洗工程と、
スケールを除去された電縫鋼管に溶融亜鉛めっきを施すめっき工程と、を含む溶融亜鉛めっき鋼管の製造方法であって、
当該溶融亜鉛めっき鋼管の製造方法は、
造管工程にて帯鋼を９８０〜１０２０℃に加熱して電縫鋼管を造管し、
酸洗工程で酸洗を行う前の電縫鋼管の表面粗度を中心線平均粗さで２．０μｍ以上とし、酸洗を行った後の電縫鋼管の表面粗度を中心線平均粗さで４．０μｍ以上とすること、
を特徴とする溶融亜鉛めっき鋼管の製造方法。 The steel strip is heated, the heated steel strip is formed into a cylindrical shape by a group of rolls, and the joints are joined by hot electrical resistance welding, followed by drawing and forming an ERW steel pipe. Pipe making process,
Pickling process to remove scale by pickling ERW steel pipe after pipe making process;
A method for producing a hot-dip galvanized steel pipe, comprising a plating step of hot-dip galvanizing the scaled ERW steel pipe,
The manufacturing method of the hot dip galvanized steel pipe is as follows:
In the pipe making process, the steel strip is heated to 980 to 1020 ° C. to make an electric resistance steel pipe,
The surface roughness of the ERW steel pipe before pickling in the pickling process is set to 2.0 μm or more in the centerline average roughness, and the surface roughness of the ERW steel pipe after pickling is set to the centerline average roughness. To be 4.0 μm or more,
A method for producing a hot dip galvanized steel pipe.
を特徴とする請求項１に記載の溶融亜鉛めっき鋼管の製造方法。 In the plating step, hot-dip galvanizing is performed on the ERW steel pipe using a hot-dip galvanizing bath containing Pb: 0.1% by mass or less and Cd: 0.01% by mass or less,
The manufacturing method of the hot dip galvanized steel pipe of Claim 1 characterized by these.
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| JPS5367638A (en) * | 1976-11-30 | 1978-06-16 | Nippon Kokan Kk | Method of preventing zinc plating seizure of electroounite portion of electroounite tube |
| JPS63199886A (en) * | 1987-02-16 | 1988-08-18 | Sumitomo Metal Ind Ltd | Production of steel pipe having superior surface cleanness |
| JPH04131324A (en) * | 1990-09-21 | 1992-05-06 | Kawasaki Steel Corp | Method for preventing surface roughening of heat treated steel pipe |
| JP3938052B2 (en) * | 2003-01-14 | 2007-06-27 | 住友金属工業株式会社 | ERW steel pipe with excellent plating adhesion and workability and its manufacturing method |
| JP5559479B2 (en) * | 2008-01-22 | 2014-07-23 | Ｊｆｅスチール株式会社 | Hot-dip galvanized steel pipe and method for producing hot-dip galvanized steel pipe |
| JP5476651B2 (en) * | 2009-07-21 | 2014-04-23 | Ｊｆｅスチール株式会社 | Hot-dip galvanized steel pipe and method for producing hot-dip galvanized material |
| JP5482091B2 (en) * | 2009-10-22 | 2014-04-23 | 新日鐵住金株式会社 | Method for producing hot-dip galvanized steel pipe |
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