JPH04165087A - Surface coated metallic product and production thereof - Google Patents

Abstract

PURPOSE:To produce the surface coated metallic product having excellent corrosion resistance in severe environment by coating the surface of a metallic base material with ceramic layers, such as silicon nitride layer, and further, providing a glassy coating layer thereon. CONSTITUTION:At least >=1 layers of the ceramic layers selected from the silicon nitride layer, silicon carbide layer and silicon carbonitride are applied on the surface of the metallic base material (steel for structural purposes, spring steel, etc.). The surface coated metallic base material is then brought into contact with a compd. (chloride, sulfate, etc.) contg. >=1 kinds of Li, Na, K, Rb, etc., and is then heat treated at >=500 deg.C to form the coating layer consisting of the glass layer further on the ceramic layers. The pinholes of the ceramic layers are embedded by the film of the glass layer in this way and the ceramic layers are shut off from the atmosphere where the product is used. The surface coated metallic product which can be used in the severe oxidative atmosphere is easily obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface-coated metal product and a method for manufacturing the same.

[Prior art and problems] General metal materials soften at temperatures above about 1000°C,
In addition, oxidation from the surface progresses from 600° C. or higher in the atmosphere. In order to improve the deterioration of such metal materials at high temperatures, various heat-resistant alloys such as Inconel, Monel, Nimonic, Zircaloy, and Hastelloy have been developed. However, even in the heat-resistant alloy, there is a problem in that the oxidation corrosion limit temperature is lowered in the presence of corrosion products containing chlorine, sulfur, etc., and the corrosion reaction is significantly accelerated.

For this reason, in order to improve the corrosion resistance of metal materials at high temperatures, attempts have been made to form highly corrosion-resistant coatings on the surfaces of heat-resistant steel and other metal base materials. The coating substance formed on the surface of the metal material includes alumina,
Ceramic materials such as silicon carbide and silicon nitride are known. As a technique for forming such a film, PVD method or CV
Although there are methods such as D method, the CVD method, which has a high film formation rate, is used.

However, there are minute pinholes etc. in the ceramic coating coated on the metal base material, and corrosion progresses through the pinholes in a high temperature environment.
Furthermore, since coatings made of non-oxide ceramics such as silicon carbide and silicon nitride are oxidized at high temperatures, there is a problem in that they transform into porous oxides.

The present invention was made to solve the above-mentioned conventional problems, and provides a surface-coated metal product that has excellent corrosion resistance in harsh environments, and a method for easily manufacturing such surface-coated metal products. This is what I am trying to do.

[Means for Solving the Problems] The surface-coated metal base material according to the present invention coats the surface of the metal base material with at least one ceramic layer selected from a silicon nitride layer, a silicon carbide layer, and a silicon carbonitride layer. Furthermore, a coating layer made of glass is provided on the ceramic layer.

Examples of the metal base material include steel materials such as structural steel, spring steel, bearing steel, and tool steel, stainless steel, heat-resistant alloys such as Inconel, Monel, Nimonic, Zircaloy, Nosteroy, and pure metals. I can do it.

In order to improve the adhesion between the metal base material and at least one ceramic layer selected from a silicon nitride layer, a silicon carbide layer, and a silicon carbonitride layer, TiN, Ti, etc. are added to the interface thereof.
Other coatings such as c may also be formed.

Further, the method for producing a surface-coated metal product according to the present invention includes the steps of coating the surface of a metal base material with at least one ceramic layer selected from a silicon nitride layer, a silicon carbide layer, and a silicon carbonitride layer; The coated metal base material is Li, Na
5K, Rb, CS % M g % Ca s S r
SB a SS c s Y SL a sTh,Z
n, Cd, Hg% 8% AI, Ga, In% Ge
, Sn and Pb, and then heat-treated at 500° C. or higher to form a glassy coating layer on the ceramic layer of the metal base material. It is characterized by the following:

A known thin film forming technique may be employed as a means for coating at least one ceramic layer selected from the silicon nitride layer, silicon carbide layer, and silicon carbonitride layer. For example, in the CVD method, 810g4 of silicon is used as the raw material gas.
, SiH4, NH3 as nitrogen source, CH4 as carbon source
under a gas atmosphere mixed with hydrogen or inert gas, using
The ceramic layer is formed on the metal base material by heating at about 1000°C.

Examples of the metal compounds include chlorides, sulfates, nitrates, and oxides.

As a method for bringing the coated metal base material into contact with the compound, for example, a method of immersing the coated metal base material in an aqueous solution, a non-aqueous solution of the compound, or a molten salt of the compound can be adopted. The immersion time is not particularly limited, but the object of the present invention can be achieved by immersion for a few seconds to several hours, usually 1 minute to 1 hour. After the immersion step, a step of drying the solvent may be performed, but since the solvent is also removed in the heat treatment step, the drying step may be omitted.

The reason why the temperature in the heat treatment step is limited is that if the temperature is less than 500° C., a good glassy film cannot be formed on the ceramic layer. The upper limit temperature of the heat treatment may be lower than or equal to the deformation temperature of the metal base material used. Further, the heat treatment step is performed in the air or in an inert gas atmosphere containing an oxidizing gas such as oxygen. The heat treatment time may be about 10 minutes to 10 hours.

[Function] According to the present invention, by providing a coating layer made of vitreous material on the ceramic layer on the surface of the metal base material, the peeholes in the ceramic layer can be filled with the vitreous coating, and Since the inner coating of the ceramic layer can be shielded from the use atmosphere by the coating, the progress of oxidation can be significantly suppressed. Therefore, a surface-coated metal product having excellent corrosion resistance under harsh environments can be obtained.

Further, according to the method of the present invention, a surface-coated metal base material covered with at least one ceramic layer selected from a silicon nitride layer, a silicon carbide layer, and a silicon carbonitride layer is L I SN.
a SK −, Rb SCs SM g s Ca %
5rSBa%5cSYSLaSTh, ZnSCd.

Hg5B, AI, Gas I n5Ge%Sn and P
A uniform glassy coating can be formed on the ceramic layer by contacting it with a compound containing at least one metal selected from b and then heat-treating it at 500° C. or higher. The reason why a uniform glassy film is formed by such heat treatment is that when the portion near the surface of the ceramic layer is oxidized by heat treatment, the metal element in the compound that is in contact with the surface and can become a glass component is incorporated. ,
This is thought to be due to the formation of a glass phase with a lower melting temperature. Once a glassy film is formed on the surface-coated metal base material, the internal ceramic layer is shielded from the operating atmosphere and oxidation reactions are significantly suppressed. surface-coated metal products with excellent corrosion resistance can be produced.

[Example code] Examples of the present invention will be described in detail below.

Example First, a 10 μm thick TiN film was formed on a 5t JS43Q stainless steel test piece (dimensions 25×25×2 mm) by CVD, and then a 20 μm thick silicon nitride (Si3N4) film was formed by the same CVD method.

Subsequently, the silicon nitride film-coated test piece was immersed in a 20°C saturated salt (NaCl) aqueous solution and dried.
Heat treatment was carried out at a temperature of 800° C. for 3 hours in a vertical annular furnace.

After cooling the vertical annular furnace, the test piece taken out from the furnace had a glass-like gloss on its surface. Furthermore, when the test piece was cut and the cross section was observed with an optical microscope, the photograph shown in Figure 1 was obtained, and it was confirmed that a glassy film of about 10 μm was formed on the surface of the silicon nitride layer. Ta.

In addition, the surface of the 5US430 test piece had a thickness of 2
A test piece coated with a 0 μm TiN film (Comparative Example 1), an uncoated 5US480 test piece (Comparative Example 2), an uncoated 5TLS310 test piece made of heat-resistant steel (Comparative Example 3)
), the NCP800 test piece (Comparative Example 4) and the vitrified test piece of the above example were heated in an electric furnace at 800°C for 30 minutes, and then cooled in air for 10 minutes, one cycle, and every 50 cycles. A repeated oxidation test was conducted by applying saturated saline. Figure 2 shows the measurement results of the corrosion penetration depth by observing the cross section of the test piece after 150 cycles.

As is clear from Fig. 2, Comparative Examples 1 to 4 (B in Fig. 2)
-E) It can be seen that significant corrosion progressed inside the base metal in all of the test pieces.

On the other hand, in the vitrified test piece of Example (A in FIG. 2), there was no crack in the glassy coating, and no progress of corrosion into the inside of the base material was observed.

[Effects of the Invention] As detailed above, according to the present invention, the high temperature corrosion resistance of the metal base material is improved, the heat resistance is high, there is no corrosion at high temperatures, and it can be used in harsh oxidizing atmospheres. heat-resistant structural materials,
It is possible to provide surface-coated metal products useful for high-temperature corrosion-resistant structural materials and the like, as well as a method for easily producing such surface-coated metal products.

[Brief explanation of the drawing]

Figure 1 is a photograph taken with a cross-sectional optical microscope showing the layered structure of the vitrified sample in the example of the present invention, and Figure 2 is the penetration depth of corrosion after the high-temperature corrosion test of the test pieces of the example and comparative example. FIG. Applicant's representative Patent attorney Takehiko Suzue q -Ti N layer Figure 1 Figure 2t Manufacturing method 3, relationship with the case of the person making the amendment Patent applicant Lime Co., Ltd. 4, agent 3-7-2-7 Kasumigaseki, Chiyoda-ku, Tokyo, detailed description of the amendment, box 10, pages 9-11 In the line ``Figure 1...
``Photograph'' should be corrected to ``Figure 1 is a photograph of the crystal structure of a vitrified sample in an example of the present invention taken with a cross-sectional optical microscope.''

Claims (2)

[Claims] (1) The surface of the metal base material is coated with at least one ceramic layer selected from a silicon nitride layer, a silicon carbide layer, and a silicon carbonitride layer, and a coating layer made of glass is further provided on the ceramic layer. surface-coated metal products. (2) coating the surface of the metal base material with at least one ceramic layer selected from a silicon nitride layer, a silicon carbide layer, and a silicon carbonitride layer; Rb, Cs,
Mg, Ca, Sr, Ba, Sc, Y, La, Th, Zn
, Cd, Hg, B, Al, Ga, In, Ge, Sn, and Pb, and then heat-treated at 500° C. or higher to form the ceramic layer of the metal base material. 1. A method for manufacturing a surface-coated metal product, comprising the step of forming a coating layer made of glass thereon.