JPS6261667B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a relatively thin steel pipe with a pipe diameter of approximately 20 m/m or less, which is widely used for supplying gas and liquid to automobiles and various other machines and equipment, and which has a corrosion-resistant alloy coating on its inner circumferential wall. This paper relates to improvements in steel pipes and methods for manufacturing them. Conventional small-diameter steel pipes and their manufacturing methods in which this type of Sn-based Zn fused coating is formed on the inner circumferential surface of the pipes can contain the maximum amount of
An alloy wire containing about 20% by weight or less of Zn was inserted into the inside of a tube member, and then heated and fused to form an alloy coating. However, with regard to these alloy wire rods, the Zn content must be naturally limited due to the malleability during wire drawing, and furthermore, there are problems related to corrosion resistance or coating uniformity. Even if one wanted to increase the Zn content, it was impossible to produce a wire with a Zn content of more than about 20% by weight, so the objective could not be fully achieved. Therefore, further improvement was desired. The present invention has extremely effectively solved these conventional problems by using a Sn wire material whose peripheral surface is electroplated with Zn to a desired thickness. will be explained in detail. That is, an electrolytic coating of Zn of a desired thickness is applied to the circumferential surface of the Sn wire so that the Zn content exceeds approximately 20% by weight, and the inner circumferential surface has been previously subjected to cleaning treatments such as degreasing and derusting. The wire rod is inserted into a tube member with or without a Cu electroplating layer so as to overlap approximately the entire length of the tube member, and then placed in an atmospheric gas furnace at a temperature higher than the melting temperature of the wire rod. When heated to 920℃ ~
At around 930℃ (under atmospheric pressure), Zn reaches its boiling point and vaporizes, and at the same time, taking advantage of the properties of Zn that promotes wettability, as the amount of Zn relative to Sn is increased, the vapor pressure and wettability associated with heating increase. By further increasing the diffusion rate, the creeping up (diffusion) on the inner circumferential surface is significantly promoted, and a uniform fused coating consisting of Sn base and Zn is formed on the inner circumferential wall surface.
Furthermore, if necessary, chromate treatment is applied to the coating film. In this way, the present invention provides a fused coating of an alloy with a desired Zn content on the inner circumferential surface of a tube member by using a Sn wire rod whose circumferential surface is coated with Zn. It will be done. Furthermore, in conjunction with the improvement in productivity due to the simple processing method, the uniformity of the coating film can be promoted in conjunction with the vapor pressure accompanying the increase in Zn, and the corrosion resistance can be improved. Next, an example will be shown. Example 1 Pipe member: Material SPPC, pipe diameter 6.35m/m, inner diameter
4.93m/m, length 1000m/m

【table】

[Table] Heating conditions: Continuous passage through the furnace by using a horizontal continuous atmosphere furnace (atmosphere gas composition: CO20%, H ₂ 20%, remaining N) Temperature: 1120°C, time: 7 minutes, fused film thickness: 13.5
μ Chromate treatment: Immersed in a solution with the product name Dipsol Z-493 for 20 seconds at room temperature, then washed with hot water and dried Example 2 Pipe member: Material SPPC, pipe diameter 10.0 m/m, inner diameter
8.0m/m, pipe length 1500m/m

[Table] Heating conditions: Same as Example 1, but fusion coating thickness 6.5
The results of a corrosion resistance comparison test (according to JISZ-2371) between Examples 1 and 2 of each of the above and a conventional alloy wire (82% by weight of Sn-18% by weight of Zn) are shown below.

[Table] However, R means red rust spots, and RR means flowing red rust.

Claims (1)

[Claims] 1 Sn containing 21% by weight or more of Zn on the inner peripheral surface of the pipe member
A small-diameter steel pipe having a corrosion-resistant alloy coating on its inner circumferential wall, which is characterized by forming a fusion coating consisting of Zn. 2 Inside a pipe member that has been previously subjected to cleaning treatment such as degreasing and derusting, there is a
A Sn wire coated with a Zn electroplating layer is inserted, and then heated in an atmosphere gas furnace to a temperature higher than the melting temperature of the wire to form a fused coating consisting of Sn base and Zn on the inner peripheral wall surface. A method for producing a small diameter steel pipe having a corrosion-resistant alloy coating on the inner circumferential wall, characterized by: