JPS60224794A - Corrosion-resistant double-plated steel pipe - Google Patents

Abstract

PURPOSE:To obtain the titled steel pipe having improved corrosion resistance in spite of its thin plating with increased productivity by electroplating the surface diffusion layer of a steel pipe with a Zn-Ni or Zn-Co alloy, galvanizing the resulting alloy layer, and forming a chromate layer as required. CONSTITUTION:The surface diffusion layer of a steel pipe rich with nickel or the like is electroplated with the Zn-Ni or Zn-Co alloy, and the resulting alloy layer is galvanized to form a Zn layer. Though the total thickness of the layers is 1/2-1/3 of the thickness of a conventional single Zn layer, the corrosion resistance of the pipe is remarkably improved and the productivity is increased by 2-3 times. The surface protecting chromate layer can be formed well because the top layer is made of Zn.

Description

[Detailed Description of the Invention] Industrial Application Fields This invention is applicable to automobile brake systems or fuel,
This invention relates to relatively small-diameter corrosion-resistant polymer-plated steel pipes used as piping for lubricating oil, etc.

<Prior art> Conventionally, pipes, fuel, and water C' were mainly used for braking of automobiles.
For bone oil etc. 1! ii! The tube has a Z on the outer surface for anti-corrosion protection.
A Zn-plated steel pipe is used which has a n electroplating layer formed thereon, and further has a hechromate coating layer formed thereon with the u ln electroplating layer.

However, in recent years in cold regions, as a measure to prevent road surfaces from freezing, it has become more common to spray chlorides such as calcium chloride onto the road surface. Therefore, it has become necessary for the above-mentioned piping material to exhibit a high degree of 1m1 edibility in the cold and harsh F-lagoon eclipse.

In response to such a request, increasing the thickness of the Zr + eye layer mentioned above cannot be considered, but increasing the thickness of the Zn plating layer is not desirable as it will greatly reduce productivity and increase the cost to 41M. . Formation of a 2n-Ni alloy plating layer instead of the above Zn plating layer (-J, since pinholes etc. are likely to occur in the case of a thin film, a hechromate film layer is formed on the Zn-Ni alloy plating layer) Since it is extremely difficult to achieve sufficient corrosion resistance, there will be a drawback if sufficient corrosion resistance cannot be achieved.Although formation of a synthetic resin film layer on the Zn metal or Zn-Ni alloy plating layer cannot be considered, it is difficult to achieve sufficient adhesion. Purpose of the Invention In view of the above, the present invention aims to provide a low-cost corrosion-resistant polymer-plated steel pipe that exhibits sufficient anti-corrosion properties in cold and severely corrosive environments. do.

<Summary of the Invention> The gist of this first invention is to form a ZnN+i or Zn-Co base metal electroplating layer on the nickel diffusion layer in a steel pipe in which a diffusion layer of nickel or the like is generated in the outer surface N base iron. Then, on the ZnN+i or Zn-Co alloy electroplating layer, (1) a corrosion-resistant polymer plated steel pipe with a Zn electroplating layer formed thereon, and (2) a Zn electroplating layer are formed, and the Zn Corrosion-resistant polymer-plated steel pipe with a chromate film layer formed on the electroplating layer, even if the polymer plating layer thickness is 1/2 to 1/3 that of conventional Zn-plated steel pipe, the corrosion resistance is significantly improved and @Efficiency is the traditional Z
2 to 3 times higher than that of n-plated and chromate-treated steel pipes.
Can be stratified with twice as many Nupid tree.

The reason why the corrosion-resistant polymer-plated steel pipe according to the present invention is limited as described above will be explained below.

B) Layer thickness of nickel diffusion layer Generally, nickel-containing steel has better strength and corrosion resistance than carbon steel, but carbon steel has better formability during cold pipe manufacturing. Taking this point into consideration, a nickel plating layer is formed on the surface of the pipe-making material using a soft element steel plate, a diffusion layer is formed by heating the plating metal alloy into the base steel, and then a diffusion layer is formed on the diffusion layer. Ni diffusion/Zn forming Zn electroplated layer
The electroplated steel pipe and the conventional Zn electroplated steel pipe were subjected to a salt spray test to evaluate their corrosion resistance. As a result, Ni diffusion and
Zn i [The corrosion resistance of pneumatic-plated steel pipe is the same as that of conventional Zn'! It was found that this was improved over plating steel pipes.

However, if the diffusion layer of nickel or the like is shallow, the effect of improving corrosion resistance will be weak, so the layer thickness was limited to 50 μm or more.

a) Composition and layer thickness of Zn-Ni f(J) Zn-Co alloy electroplated layer Conventional Zn t[air-plated steel pipe, Zn-Ni alloy electroplated steel pipe and Zn-Co alloy electroplated steel pipe] A salt spray test was conducted on each sample in which the plating layer thickness was kept almost constant to evaluate the corrosion resistance. As a result, it was found that the corrosion resistance S of the 7.0-Ni and Z n Co alloy electroplated steel pipes was superior to that of the Zn electroplated steel pipes. The composition of this Zn-Ni & Zn-Co alloy electroplating layer is mainly dependent on the composition of nickel sulfate # and cobalt sulfate in the electroplating bath, as it contains CO. If Ni and Co are less than 5%, the effect of improving corrosion resistance is weak, and if it is more than 20%, the effect of improving corrosion resistance is small despite the increase in content. Therefore, a range of 5 to 20% is an appropriate amount. The composition of the Zn-N plated alloy electroplated layer is ZnO-5% and Ni 3-20%, and the composition of the Zn-Go alloy electroplated layer is ZngO-5% and Ni 3-20%.
-woS%, cos-so%.

7. Since the corrosion resistance of the n-Ni and Zn-Co alloy electroplated layers is superior to that of the Zn electroplated layer as described below (see Table 1), the layer thickness can be reduced, and the ffcZn The layer thickness of the electroplated layer can also be reduced. As a result of basic experiments on this layer, the layer thickness rJ of the ZnN+ and Zn-Co alloy electroplating layer is /~10 μm, the layer thickness of the Zn electroplating layer is λ~/Q77 m, and The thickness of the polymerized plating layer is suitably in the range of 3 to 20 μm, thereby improving the plating efficiency.

Example of implementation A) Base material (steel pipe) Material: 5PCC1 Outer diameter: 447 Otsu11, Wall thickness: 07 mm, Shape: UOO type ERW steel pipe.

1) Nickel electroplating bath liquid: Watt bath, liquid temperature: 50°C1 current density: /□ A
/ d m2, energizing time: 95 seconds, plating layer thickness: 3μ
mo 11) Heating diffusion atmosphere: Li' (J decomposition gas, temperature change: RisooC
% retention time: 5 minutes, layer thickness of Ni diffusion layer:
n-Ni alloy electroplating bath solution: zinc sulfate/nickel sulfate IV/sulfuric acid) IJum, l1fUA: sooC, current density: Otsu Q A/d
nt2, energization time 30 seconds, composition: Zn 9 Q%
, N170%.

Plating thickness: Otsuμ771゜2) Zr + electroplating process bath liquid, zinc sulfate/aluminum sulfate, /ammonium chloride/boric acid, liquid temperature: SO'C5 Current density: qQ A /
dn? , Current application time: 30 seconds, Plating layer thickness: 17 μm
0 e) Chromate treatment process Bath liquid: Sodium dichromate/sulfuric acid, immersion time near seconds.

f) One base material shown in A), C) and II).
A sample material (long) was prepared from the matte steel pipe (A) produced by the method and the base material shown in a), c), 2) and e) from the matte steel pipe (B) produced through the treatment steps. 300 questions) were collected.
Corrosion resistance was evaluated by a salt spray test based on the provisions of JIS standard Z-237/. Also, as a comparison material, conventional Zn
An electrically welded (layer thickness: 2 s μm) and chromate-treated steel pipe was used. The results are shown in Table 1.

The test material (B) of the corrosion-resistant polymer-plated steel pipe according to the present invention (see Figure 1) has significantly higher corrosion resistance than the comparative material (see Figure 2), despite having a thinner coating layer. was found to be excellent.

In addition, instead of the above Zn-Ni alloy electroplating, Zr+-
The corrosion resistance of the Co alloy electroplated test material is
It has been confirmed that it is almost equivalent to the alloy electroplated test material.

<Effects of the Invention> As described above, the corrosion-resistant polymer-plated steel pipe according to the present invention has an FQ-Ni diffusion layer 4=k, which has excellent corrosion resistance, and Z
In other words, since the Zn-Ni or 2n-Co alloy electroplating layer is formed by selecting Ni and Co as coarse metals that are corroded by chlorides, Conventional Z +1
Despite having a thinner plating layer than electroplated steel pipes, it exhibits excellent corrosion resistance and improves the durability of automobiles even under the harsh corrosive environment of driving on frozen roads sprayed with chloride and on P8 roads near the sea. It has the effect of bringing about.

[Brief explanation of drawings]

FIG. 1 is a microscopic photograph of a corrosion-resistant polymer-plated steel pipe according to this development 1u11, and FIG. 2 is a microscopic photograph of a conventional steel pipe with a Zn-metssa/chromate coating layer. 1... Outer surface layer base iron, 2... Diffusion layer, 5... Zn-
N1 alloy electroplating layer, 4...Zn electroplating layer, 3
-... Chromate film layer, 6... Cu plating layer. Conqueror [i story: 3z Nital (X420) #lIt→
[: 3ze9-ru (X420)4/

Claims (1)

[Claims] (1) In a steel pipe in which a nickel-rich diffusion layer with a layer thickness of 0 μm or more is formed in the outer surface layer of the steel, a Zn-Ni or Zn-Co fluoroelectroplated layer is applied onto the nickel diffusion layer. A monocorrosive polymer-plated steel sheet comprising: a Zn electroplating layer formed on the Zn-Ni or Zn-Co alloy coating layer. (2J outer surface tvim subterranean layer jOμn) or more of nickel-rich diffusion layer has been formed, a Zn-Ni or Zn-C0 alloy electroplating layer is applied to the 2-layer diffusion layer. A corrosion-resistant polymer plated steel pipe characterized in that a Zn electroplating layer is formed on the M6 Zn-Ni i or Zn-C0 alloy electroplating layer, and a chromate film layer is formed on the Zn electroplating layer. .