JPH02129367A - Surface treated steel pipe excellent in corrosion resistance and its production - Google Patents

Abstract

PURPOSE:To inexpensively provide a ceramic-coated steel pipe excellent in adhesive strength at high temp. and corrosion resistance by applying a chromium carbide layer on the surface of a steel pipe composed of carbon steel in which carbon concentration in the steel is limited and further forming a ceramic coating layer on the above layer. CONSTITUTION:A steel pipe composed of steel and low-alloy steel containing 0.08-0.8% carbon is prepared. Chromizing treatment is applied to the internal surface or the internal and external surface of the above steel pipe to form a chromium carbide layer. Subsequently, corrosion resisting ceramic coating is applied to the above.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to surface-treated steel pipes used for chemical plant piping, seawater cooling pipes, superheaters and reheaters of thermal power plants, etc., particularly for corrosion resistance and high temperature adhesion. The present invention relates to a steel pipe having an excellent ceramic coating layer and a method for manufacturing the same.

Conventional technology For steel pipes that require high corrosion resistance, such as pipes for chemical blunts and seawater cooling pipes, ceramics (SL3 N 4 ) with excellent corrosion resistance are used on the inner or outer surfaces of the pipe.

μm N, TLc, TiN,
SLC, Si2 03. HaI2O3 etc.)
Surface-treated steel pipes coated with

As a method for coating the ceramics, chemical vapor deposition (CVD), physical vapor deposition (PVD), or plasma vapor deposition (plasma CVD) is used.

When using these methods, conventionally, ceramics are coated directly onto the substrate, or other ceramics are coated by CVD, PVD, or plasma carbon to reduce the required thermal expansion difference between the ceramic and the substrate.
A method of applying surface treatment using VD is used.

However, with either coating method, the adhesion between the steel tube required as a substrate and the ceramic coating film is weak, and in an environment with rapid temperature changes, thermal expansion between the ceramic and the base material (steel tube) There is a problem that peeling of ceramics occurs due to the difference.

In addition, the method of coating other ceramics as a base layer in order to alleviate the difference in thermal expansion between the ceramic and the substrate not only increases processing costs, but also increases the There is a problem in that components in the lower layer coating are mixed into the coating as impurities, significantly deteriorating the corrosion resistance of the upper layer coating.

Problems to be Solved by the Invention In view of the above-mentioned circumstances, the present invention has been developed to provide a material with excellent high-temperature adhesion without coating a ceramic base layer to alleviate the difference in thermal expansion between the base material and the ceramic coating layer. The purpose of this paper is to propose a surface-treated steel pipe with excellent corrosion resistance and a method for manufacturing the same.

Means for Solving the Problems As a result of various studies on ceramic coating methods for the inner surface or both the inner and outer surfaces of steel pipes, the inventor has determined that chroma coating is applied to the inner or outer surfaces of steel pipes in advance for the purpose of surface modification of the steel pipes. They discovered that a ceramic coating layer with excellent high-temperature adhesion could be improved by forming a chromium carbide layer through Ising treatment, and completed the invention.

The gist of this invention is that the carbon concentration in steel is 0.05 to 18%
A surface-treated steel pipe comprising a chromium carbide layer on the inner or outer surfaces of the steel pipe made of carbon steel and low alloy steel, and a ceramic coating layer on the chromium carbide layer, and a method for producing the same. This method is characterized by forming a chromium carbide layer on the inner or outer surfaces of the steel pipe by chromizing treatment, and then coating it with ceramics having excellent corrosion resistance.

Here, ceramics with excellent corrosion resistance include Si3
N4. /V N, TjC, Tj N, 5LO
2, SjC.

M2O3 etc. are used.

Further, as a coating method for the ceramic coating layer, the above-mentioned CVD, PVD, and plasma CVD are used.

Function In this invention, the target steel has a carbon concentration in the steel of 0.05 to 0.05.
The reason why we limited it to 0.8% carbon steel and low alloy steel is because if the carbon concentration in the steel is less than 0.05%, a chromium carbide layer will not be formed on the surface even if the steel pipe surface is subjected to chromizing treatment.
On the other hand, if the carbon concentration in the steel exceeds 0.8%, the chromium carbide layer formed by the chromizing treatment becomes porous and the adhesion strength decreases.

The chromizing treatment methods for forming a chromium carbide layer on the inner or outer surfaces of a steel pipe include: ■ Filling the steel pipe with a penetrant and applying the chromizing treatment to the inner surface while the pipe remains stationary; ■ Filling the entire steel pipe with a penetrant. It is possible to use a method of embedding the material in water and applying chromization treatment to both the inner and outer surfaces.

In these methods, a mixture of metallic chromium powder and alumina powder is used as a penetrant, and a small amount of halide is added to the powder, which is then heat treated at high temperatures in hydrogen or inert gas. be.

The thickness of the chromium carbide layer formed on the surface of the steel pipe is 2.
~50 proof is suitable. The reason for this is that it is practically difficult to form a chromium carbide layer with a uniform thickness of less than 2 mm on the surface of the steel pipe, and in addition, 2 layers or more are required to absorb the difference in thermal expansion; This is because, if it exceeds this, the ceramic coating becomes porous and the ceramic coating formed thereon grows starting from the pores, making it difficult to obtain a smooth ceramic coating.

When a chromium carbide layer is formed on the surface of a steel pipe by chromizing, the surface of the steel pipe is modified, and as a result, impurities may be mixed into the ceramic coating layer applied on the chromium carbide layer. There is no corrosion at all, and the corrosion resistance of the ceramic coating layer is maintained.

Furthermore, since the chromium carbide layer has excellent high-temperature adhesion, there is no possibility that the ceramic coating will peel off due to the difference in thermal expansion between the ceramic and the base material.

Examples Example 1 Test tubes of the steel types shown in Table 1 (30 mφ x 6 mt x 2
00ml) is buried in a penetrating agent consisting of metallic chromium, ammonium chloride and alumina, and subjected to chromizing treatment at a temperature of 900'C or higher in an Ar atmosphere, and then PV
The outer surface of the tube was coated with Si2N4 by D treatment.

After holding this treated steel pipe at a temperature of 400°C for 1 hour,
The specimen was immediately placed in water at 20'C and the cracking and peeling of the coating film was examined. The results are also shown in Table 1 in comparison with the case without chromizing treatment.

From the results in Table 1, it can be seen that those that were subjected to chromizing treatment in advance exhibited good adhesion.

In addition, as ceramics, M N, Tic, Tj
N.

5L02. When each of SjC and /V2O3 was coated in the same manner as above, Si2N
Similar results were obtained when coating No. 4.

Below is a blank space Example 2 Steel test tube (50g x 10m) having the components shown in Table 2
After applying the same chromizing treatment as in Example 1 to the 100s (t
and M2O3 were coated.

Table 3 shows the results of 100 repeated tests in which the steel pipe to be treated was heated to a temperature of 400'C for 1 hour and then cooled in the air for 1 hour, and cracks and peeling of the coating film were investigated.

Table 3 shows that for steel pipes whose carbon concentration in the steel deviates from the component values of the present invention, cracking and peeling occurred in any of the ceramic coating layers after 20 repeated tests, and the ceramic coating layer did not peel after 40 tests. In contrast, in the case of the steel of the present invention, no abnormalities were observed in the ceramic coating layer even after 100 tests, indicating good adhesion.

As described in detail below, the ceramic-coated steel pipe according to the present invention has excellent corrosion resistance and high temperature adhesion, and has excellent corrosion resistance even when used under harsh conditions such as chemical plant piping and seawater cooling pipes. It is something that can be demonstrated.

In addition, since the method of this invention forms a ceramic coating layer on the chromium carbide layer formed by chromizing treatment, an undercoating of thermal expansion relaxation ceramics is not required, and ceramic-coated steel pipes with excellent corrosion resistance and high temperature adhesion can be produced. This has the great effect of being able to provide it at a low cost.

Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Yoshihisa Oshida”ff Voluntary Procedure Amendment 1, Case Description 1988 Patent Application No. 281030 2, Title of Invention Surface-treated steel pipe with excellent corrosion resistance and its manufacturing method 3 , Relationship to the case of the person making the amendment Applicant Address 4-5-33 Kitahama, Chuo-ku, Osaka (Administrative district changed on February 13, 1999) Name (211) Sumitomo Metal Industries Co., Ltd. 4, Agent Address: Ginza Building (56), 3-3-12 Ginza, Chuo-ku, Tokyo
1-0274) Column 6 of detailed explanation of the invention in the specification, contents of amendment

Claims (1)

[Scope of Claims] 1 A steel pipe made of carbon steel and low alloy steel with a carbon concentration of 0.05 to 0.8% has a chromium carbide layer on the inner or outer surfaces, and a ceramic layer is formed on the chromium carbide layer. A surface-treated steel pipe with excellent corrosion resistance characterized by having a coating layer. 2. A chromium carbide layer is formed on the inner or outer surfaces of a steel pipe made of carbon steel and low alloy steel with a carbon concentration of 0.05 to 0.8% by chromizing treatment, and then coated with corrosion-resistant ceramics. A method for manufacturing surface-treated steel pipes with excellent corrosion resistance.