JPH0215627B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method of manufacturing a fuel pipe for an automobile. <Prior art> Conventional fuel pipes for automobiles are made by, for example, forming a copper plating layer on one or both sides of a strip made of mild steel, and joining the strips so that the copper plating layer is formed on the inner peripheral surface. It was manufactured as ERW steel pipe. <Problems to be solved by the invention> The fuel pipe manufactured in this way can be put to practical use when the fuel oil is gasoline, but as of late, the use of gasohol (alcohol-containing gasoline) has been increasing. However, it was difficult to obtain sufficient corrosion resistance.
The reason for this is that even with Cu plating, pinholes often occur in the welded parts when forming ERW steel pipes.
This is because electric contact occurs due to the presence of moisture. Furthermore, the elution of copper ions into gasohol is caused by rubber parts in fuel piping (hose, diaphragm, etc.)
There was a risk of accelerating deterioration. Therefore, it is possible to use stainless steel pipes with good corrosion resistance as fuel pipes, but fuel pipes require plastic processing such as bending, flaring, and drawing.
Stainless steel pipes that are difficult to plastically work are unsuitable and expensive. <Object of the Invention> In view of the above, an object of the present invention is to provide a fuel pipe for an automobile that has sufficient corrosion resistance against gasohol, has excellent plastic workability, and is inexpensive to manufacture. <Means for Solving the Problems> The method for manufacturing an automobile fuel pipe of the present invention involves forming a Ni plating layer of 0.5 to 9 μm on one or both sides of a mild steel strip, and then applying the Ni plating layer to the strip. is joined to form an ERW steel pipe on the inner peripheral surface, and this ERW steel pipe is further heat-treated at 800 to 1100°C for 5 minutes or more in a reducing gas or inert gas atmosphere. Has characteristics. <Example> Hereinafter, an example of the method for manufacturing a fuel pipe for an automobile according to the present invention will be described in detail with reference to the drawings. (1) Form a Ni plating layer 2 on both sides or one side of a strip plate 1 made of mild steel by electroplating or the like (Fig. 1). At this time, the thickness of the Ni plating layer is 0.5
~9 μm, preferably 1 to 5 μm. If it is less than 0.5 μm, a sufficiently deep Ni diffusion layer cannot be obtained,
Moreover, if the thickness exceeds 9 μm, the amount of Ni used increases and the formation time becomes longer, so that there is no cost advantage. (2) After edge-scarfing both sides of the strip plate 1 on which the Ni plating layer 2 is formed, welding is performed by high-frequency induction welding or low-frequency resistance welding through a forming process to form Ni plating at least on the inner circumferential side. The electric resistance welded steel pipe 3 has layers (Fig. 2). Note that in the illustrated example, the dotted line region is the welding region A. (3) The above-mentioned ERW steel pipe 3 is introduced into an annealing furnace and heat-treated in a reducing gas or inert gas atmosphere at 800 to 1100°C for 5 minutes or more to form a Ni diffusion layer 5 on the surface of the steel pipe base material 1. 3 and 4). Here, even if there is a pinhole 7, due to the diffusion of the Ni plating layer 2 into the base material 1,
The state changes from A to B in FIG. 5, and the exposure of the base material 1 at the pinhole portion disappears. Note that the two-dot chain line B in Figures 4 and 5 indicates the steel pipe base material 1.
The boundary of Ni plating layer 2 is shown. At this time, if the heating temperature (steel pipe surface temperature) is less than 800°C (the normal annealing temperature for ERW steel pipes), it will take time for diffusion to occur, making it impractical; if it exceeds 1100°C, the steel pipe base material may deteriorate. Furthermore, heating equipment is also expensive. The heating time is as described above, but is usually set so that the depth of the Ni diffusion layer 5 is 5 μm or more. Examples of the reducing gas include LPG decomposition gas and NH ₃ decomposition gas, and examples of the inert gas include N ₂ and Ar. <Effects of the Invention> The automobile fuel pipe manufactured as described above has a solid solution of Ni in Fe on the surface of the steel pipe base material, and a diffusion layer that gradually becomes integrated with the Ni-rich base material toward the surface. death,
It produces the following effects. (a) The surface side is Ni-rich and has excellent corrosion resistance.
Has wear resistance. In other words, Ni is a more penetrating metal than Fe, so sacrificial corrosion does not occur, and even if there is a peehole in the general part of the Ni plating layer before welding to form a steel pipe or in the welded part (bead part), the Ni plating will not occur. Most of it disappears due to layer diffusion, and corrosion resistance (gasohol resistance) is significantly improved. (b) The Ni diffusion layer is only present on the surface of the steel pipe and is integrated with the base material with an unclear boundary between the steel pipe and the base material, so even if strength processing such as flaring or drawing is performed, the Cracks do not occur as with plating layers, and the workability is as good as the mild steel pipe before surface treatment. (c) The method for manufacturing fuel pipes for automobiles according to the present invention requires only adding a Ni plating layer forming process, for example, an electroplating process, to the conventional electric resistance welded steel pipe manufacturing line (the diffusion process can be replaced by the conventional annealing process). (However, the processing temperature conditions are higher than conventional methods), and the corrosion resistance of automotive fuel pipes can be greatly improved at extremely low cost. (d) Furthermore, since the Ni plating layer only needs to be very thin,
Coupled with the small diameter of automobile fuel pipes (usually 20 mm or less), there is little increase in weight or flow resistance of the fuel pipes. In addition, JP-A-52-115747, JP-A-53-
Publication No. 5037 discloses that the corrosion resistance is improved by forming a Ni layer on the surface of a steel pipe and subjecting it to heat treatment, but the method of the present invention is different from the method of the present invention in the formation means of the Ni layer and its thickness. do.
That is, in the present invention, the Ni layer is formed by plating.
In contrast to the conventional technology described above,
Ni layer 0.1-1mm or 10μm by thermal spraying or coating
~1 mm). In the case of thermal spraying or coating, if it is difficult to form a thin layer of less than 10 μm as in the case of plating, and if it is formed to a thickness of less than 10 μm, heat treatment in the temperature range (800 to 1100°C) as in the present invention is required. It was recognized that even if this was done, the pinholes would not disappear and corrosion resistance would not improve. Next, Table 1 shows the results of a corrosion resistance test conducted to confirm the effects of the present invention. (Test method) After forming a 2 μm thick Ni plating layer on both sides of a 0.7 mm thick mild steel plate (SPCC) by electroplating, an electric resistance welded steel pipe (φ8, wall thickness 0.65 mm, length 1200 mm) was formed using conventional methods.
After manufacturing and diffusing Ni by heat treatment in a reducing atmosphere at 900°C for 10 minutes, we cut it in half and separated it into a beaded part (welded part) and a non-beaded part (general part) on the inner peripheral surface.
This was evaluated using a salt spray test (J15Z2371).
For comparison, a similar salt spray test was also conducted on a sample on which a Ni layer was formed but no heat treatment was performed. 【table】

[Brief explanation of drawings]

The illustrated examples illustrate this invention, and FIG. 1 is a cross-sectional view of a steel strip with a Ni layer formed thereon, FIG. 2 is a cross-sectional view of an electric resistance welded steel pipe formed by welding the steel strip of FIG. 1, and FIG. Fig. 2 is a sectional view showing the state of the ERW steel pipe after heat treatment; Fig. 4 is an enlarged sectional view of Fig. 3;
The figure shows the principle of pinhole disappearance due to diffusion of the Ni plating layer. 1... Steel strip plate (steel pipe base material), 2... Ni plating layer, 3... Steel pipe, 5... Ni diffusion layer.

Claims (1)

[Scope of Claims] 1. A method of manufacturing a fuel pipe for an automobile, characterized by comprising the following manufacturing steps. (1) 0.5 to 9 μm on one or both sides of a mild steel strip
The process of forming a Ni plating layer. (2) A step of joining the strip plates on which the Ni plating layer has been formed so as to have the Ni plating layer on the inner circumferential side to form an electric resistance welded steel pipe. (3) A step of diffusing the Ni layer by subjecting the electric resistance welded steel pipe to heat treatment in a reducing gas or inert gas atmosphere at 800 to 1100° C. for 5 minutes or more.