JPH06272013A - Aluminum alloy coated chrome material - Google Patents

Abstract

PURPOSE:To obtain an Al alloy coated chromium material excellent in high temp. oxidation resistance, nitriding resistance and molten salt resistance and having a uniform thickness and excellent adhesion by coating a metallic chro mium matrix having high density and high purity with an Al-Cr alloy having a specified thickness. CONSTITUTION:A metallic chromium matrix having >=95% relative density and >=99.9% purity is coated with an Al-Cr alloy having 60 to 120mum thickness. The metallic chromium matrix can be obtd. by subjecting metallic Cr having high purity to molding or forming by a powder metallurgical method, drawing method, melting method or the like, and preferably, after the molding or forming, it is annealed at about 1000 to 1500 deg.C for about 3hr in an H2 gas to uniformize the structure and to remove stress. Furthermore, at the time of coating and forming the Al Cr alloy, the metallic chromium matrix formed by a hot-dip Al plating method, flame spraying method, calorizing method or the like is coated with a prescribed amt. of Al, which is thereafter subjected to heat treatment at about 400 to 600 deg.C to execute thermal diffusing treatment of the Cr material into the Al coating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a high temperature oxidation resistance and a high temperature oxidation resistance which are useful for a heating furnace used in a high temperature corrosive environment, various incinerators, main bodies such as reactors, various detector protection tubes and parts. The present invention relates to an aluminum alloy-coated chromium material having excellent nitriding properties and molten salt resistance, a uniform thickness, and excellent adhesion.

[0002]

2. Description of the Related Art Conventionally, iron-based materials have been used as materials used in high-temperature equipment such as heating furnaces, incinerators, main bodies of high-temperature reactors, piping, various detector protection tubes, and supply nozzles for each combustion gas and air. Alloys, nickel-based alloys, chrome-nickel alloys, chrome-nickel-cobalt alloys, chrome-cobalt-iron alloys and the like are industrially used.

[0003]

However, the temperature is about 1000 ° C.
There is almost no metal material that can maintain stable oxidation resistance, nitriding resistance, and molten salt resistance in the above-mentioned high temperature range, and it is inevitable to replace it in a short period of time. In addition, the corrosion mode of these heat-resistant materials rarely exhibits general corrosion, and defects or peeling of the protective oxide film or the corroded part of the film itself may be caused by sulfur,
Corrosion factors such as chlorine, vanadium salts, and sulfates often enter the base material and form corrosion forms such as pitting corrosion, intergranular corrosion, and metal dust formation. Further, in the present situation, more severe corrosion damage is caused in the case of material deterioration such as high temperature creep strength and brittleness.

Recently developed pure chrome processed materials (for example, JP-A-1-316435, JP-A-2-88758, etc.) are materials exhibiting unprecedented high temperature corrosion resistance, but under a high temperature exposure for a long time. The protective oxide film formed on the surface of the steel partly peels off, and a material deterioration phenomenon such as carburization and nitriding occurs through the site, resulting in severe damage.

Further, as a means for extending the life of the pure chromium processed material, the surface of the base material is coated with various heat resistance and corrosion resistance. For example, it is often the case that aluminum-based or silicon-based material is subjected to thermal spraying, plating by coating, refractory lining, or the like. Although high temperature corrosion resistance is improved by these coating layers, in the conventional coating layer, the difference in the coefficient of thermal expansion between the base material and the coating layer, the generation of brittle intermetallic compounds, and the external stress and thermal strain due to growth Problems such as cracking and peeling occur, and a coated chrome material having sufficient durability for a long time has not yet been found. In addition, in terms of nitriding resistance, it is necessary to have a coating layer thickness that allows the coating material to function as a nitrogen absorption / removal material (getter function) to some extent, but if these coating layers are thickened, the coating layer becomes coarse and the strength deteriorates. At present, there are problems such as easy peeling.

[0006]

Means for Solving the Problems The inventors of the present invention have made diligent studies to solve the above-mentioned problems, and as a result, a material composed of high relative density and high-purity metallic chromium was coated with aluminum to provide excellent adhesion. The present invention has been completed by finding that a heat-resistant chromium material excellent in high temperature oxidation resistance, nitriding resistance, and molten salt resistance can be obtained by forming a uniform chromium-aluminum alloy layer.

That is, according to the present invention, a metallic chromium base material having a relative density of 95% or more and a purity of 99.9% or more has a thickness of 60 to 60%.
The present invention relates to an aluminum alloy-coated chrome material coated with an aluminum-chromium alloy having a thickness of 120 μm.

The present invention will be described in detail below.

The relative density of the metallic chromium base material that constitutes the chromium material of the present invention must be 95% or more.
When the relative density is less than 95%, thermal cracks and external stress cause microcracks between the coating layer and the chromium base material,
High-temperature corrosion occurs violently due to the penetration of corrosion factors in the atmosphere. Further, the purity of the chromium base material is required to be 99.9% or more, and when impurities, especially carbon, nitrogen and oxygen are large, when exposed to a high temperature for a long time, the aluminum alloy coating layer and the chromium base material are not exposed. Voids and cracks caused by these impurities tend to form between the material and the material, and the high temperature corrosion resistance effect cannot be expected. The molding method is not particularly limited,
For example, a powder metallurgy method, a drawing method, a melting method and the like can be exemplified.

In the powder metallurgy method, the purity is 99.9% or more and the powder size is 10 to 10 in a sealed container made of stainless steel or steel.
Chromium powder of 40 μm is enclosed and 10 ⁻⁴ to 10 ⁻⁵ m
Evacuate to about mHg and flush the adsorbed gas that causes brittleness of metallic chromium. Next, the container filled with this chromium powder was heated to 1000 to 1350 ° C. under a hot isostatic pressing machine (HIP) at a pressure of 500 to 1000 kg.
It is consolidated at f / mm ² for 0.5 hours or more. Then, the consolidated body is hot-rolled to obtain a rolled body. Hot rolling is, for example,
Although a general-purpose hot roll is often used, it is desirable to carry out two-step rolling to prevent cracking of the rolled body. As the rolling conditions, the heating temperature is 600 to 1000 ° C. and the rolling rate is less than 50% / roll, so that a rolled body having no cracks, fine crystal grains and a relative density of 95% or more can be obtained.

In the drawing method, drawn seamless tubes and various protective tubes can be manufactured at 600 ° C. or higher.

The melting method includes, for example, an argon gas arc melting method, a high frequency induction melting method, and the like, and there is a method of pouring into a mold having a predetermined shape immediately after melting or a method of continuously manufacturing a molten chromium ingot.

After the above-mentioned forming, 1000 to 1000 in hydrogen gas for the purpose of homogenizing the structure of the chromium material and removing stress.
It is preferable to anneal for about 3 hours under the condition of 1500 ° C.

Next, the method of coating the chromium material with aluminum will be described. As the aluminum coating method, for example, a molten aluminum plating method, a flame spraying method, a calorizing method, or the like can be applied. In applying these methods, first, a chromium material processed into a predetermined shape is degreased and washed with water.

Next, in the hot dip aluminum plating method, the aluminum plate is dipped in a zinc chloride flux or a zinc chloride-lithium chloride flux at 300 to 330 ° C. for an antioxidant treatment, and then dipped in an aluminum bath at 650 to 750 ° C. In the flame spraying method, the surface of the chromium material is roughened by grit blasting, and then aluminum powder or a wire material is flame sprayed on the surface to form a sprayed layer of 500 to 600 μm. The Calorize method is a method of diffusing aluminum on the surface of a chrome material at a high temperature. An alloy powder catalyst containing aluminum-iron as a main component, ammonium chloride and a chrome material are placed in a closed container, and the container is heated to a temperature of 1000 to 1
Hold in a furnace maintained at 100 ° C. for about 1 hour and gradually cool. Excessive aluminum content in the aluminum layer formed by the above method is removed by a centrifugal separator, mechanical cutting, or the like.

Subsequently, a heat diffusion treatment of the chromium material on the aluminum coating is performed. The condition is 400 ~
The heat treatment may be performed in a temperature range of 600 ° C. in an oxidizing atmosphere such as oxygen, and by such treatment, the aluminum coating layer has a uniform thickness with respect to the shape of the chromium base material. The diffusion of the chromium material is preferably performed over the entire thickness of the coated aluminum.

If the thermal diffusion temperature is less than 400 ° C., the diffusion of aluminum into the chromium material is insufficient and the thickness of the aluminum alloy coating layer may not reach 60 μm. Further, when the thermal diffusion and infiltration treatment is performed at a temperature over 600 ° C., thermal strain occurs due to the difference in thermal expansion coefficient between the chromium base material and the aluminum coating layer in the initial process, and the aluminum coating layer is cracked or peeled. And so on. Therefore, it is not possible to obtain an aluminum-coated chrome material having sufficient durability and corrosion resistance for a long time,
Further, mechanical properties such as tensile strength of the chromium base material itself may be significantly deteriorated due to the progress of internal oxidation.

The thickness of the aluminum-chromium alloy layer is 60.
If the thickness is less than μm, the corrosion factor reacts with the alloy layer, and the entire alloy layer becomes a corrosion product, or if the thickness of the alloy layer exceeds 120 μm, the alloy layer undergoes crack peeling, etc. This is not preferable because the chrome material and the corrosion factor directly react with each other. The thickness of the alloy layer may be determined by measuring aluminum and chromium by energy dispersive X-ray (EDX) analysis or the like.

[0019]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Examples 1 to 4 have the purity and relative density shown in Table 1 and a particle size of 50 to 100 μm.
m metal chrome powder to PVA (polyvinyl alcohol)
2% was added, and after mixing, the chromium powder was added to a length of 125 m.
It was sealed in a stainless steel closed container having a width of m, a width of 33 mm, and a height of 10 mm, and after substituting with argon gas for about 15 minutes, it was evacuated to a vacuum degree of 10 ⁻⁵ mmHg and vacuum sealed.

This closed metal container was heated at 1000 ° C. and 500 kgf / mm ² by a hot isostatic pressing machine (HIP).
And consolidated for 30 minutes. Furthermore, roll diameter 200mm
Hot rolling at 750 ° C. with a hot rolling device of φ and a rotation speed of 27 rpm, 15% per rolling, and a final rolling ratio of 7%.
After rolling to 0%, it was slowly cooled and the metal container was removed to obtain a chromium material. Then, the obtained chromium material was annealed in hydrogen at 1400 ° C. for 3 hours to obtain a chromium material.

This chromium material was immersed in a 15% hydrochloric acid aqueous solution at 60 ° C. for degreasing, washed with water and dried. Then 320
It was immersed in a zinc chloride-lithium chloride mixed flux bath at 20 ° C. for 20 seconds and then in a molten aluminum bath at 650 ° C. for 5 minutes. After that, heat diffusion treatment was performed by heating at 400 ° C. to 550 ° C. for 50 minutes with oxygen gas. Table 1 shows each physical property value of the obtained aluminum alloy-coated chromium material.
According to EDX analysis, the thickness of the aluminum alloy coating layer is 60.
It can be seen that the thickness is uniform up to 120 μm and that there is dimensional accuracy. The mechanical properties were not significantly deteriorated, and no microcracks were observed at the interface between the aluminum alloy coating layer and the chromium material.

Next, a high temperature gas corrosion test was performed on the aluminum alloy-coated chromium material. The test method is as follows. Various materials are suspended on a thermobalance, and the temperature is raised to 1000 ° C. while flowing argon gas. The test starts when the argon gas is switched to air and the gas flow rate becomes constant. The weight change due to corrosion (weight increase here) is measured over time.

The results are shown in FIG. It can be seen that in Examples 1 to 4, the weight increase is small, and the curves of weight change and time follow the parabolic law and are excellent in high temperature corrosion resistance. Further, no abnormality was found in the aluminum alloy coating layer after the test. FIG. 2 shows the EDX line component analysis (chromium, aluminum, oxygen, nitrogen) results of the cross section of the aluminum alloy-coated chromium material after the high temperature gas corrosion test.

The horizontal axis of the figure indicates the distance scanned from the surface,
The vertical axis represents the qualitative strength of the element. In the aluminum alloy layer, the distance from the surface to the line inflection points of chromium and aluminum is the alloy layer thickness. From FIG. 2, it was found that the alloy layer had a thickness of 80 μm and nitrogen element was not present in the alloy layer. Therefore, it is understood that the aluminum alloy layer is homogeneous, the presence of nitrogen from the air is not recognized, and the aluminum alloy-coated chromium material also has excellent nitriding resistance especially at high temperatures.

FIG. 3 shows the state of the metal structure at the EDX analysis location (near the surface of the aluminum alloy-coated chromium material).

Further, Table 1 also shows the mechanical strength of the aluminum alloy-coated chromium material after the high temperature gas corrosion test. The aluminum alloy coating layer was sound, there was no internal oxidation, and no significant decrease in mechanical strength was observed.

Comparative Examples 1 to 7 Comparative Example 1 is a chromium base material prepared in the same manner as in Example 1, and is not coated with aluminum. Comparative Examples 2 to 5 are aluminum alloy-coated chromium materials obtained by the same manufacturing method as in the example, but the purity, relative density, and aluminum alloy layer thickness of the chromium material are changed. In Comparative Examples 6 to 7, alumina or zirconia powder was plasma sprayed to a thickness of 100 μm on a chromium base material prepared by the same method as in Example 1. Comparative Example 1
Table 1 shows the respective physical property values of ~ 7. It can be seen that the thickness of the aluminum alloy coating layer deviates from 60 to 120 μm, the interface between the aluminum alloy coating layer and the chromium base material is non-uniform, and the dimensional accuracy is poor. Microcracks were also observed at the interface between the aluminum alloy coating layer and the chromium material. Further, the mechanical strength is also lowered, and it is considered that this is because the oxidizing environmental factor penetrates inside through the cracks and defects generated in the aluminum coating, causing internal oxidation and the like, thus lowering the tensile strength.

Next, FIG. 1 shows the results of a high temperature gas corrosion test performed on each material of Comparative Examples 1 to 7 by the same method as in the example. Comparative Example 1 is a pure chrome material, the weight increase is significant, and a chromium oxide film is formed on the surface, but partial peeling was observed. It can be seen that swelling on the surface of the aluminum alloy coating layers of Comparative Examples 2 to 5 and peeling of the ends of the test piece were observed, and the weight increase was large. The rapid change in the weight increase curve of Comparative Example 5 after 6 hours was due to the fact that the chromium-aluminum alloy layer was too thick and the alloy layer cracked, and the underlying chromium material directly reacted with air. . In Comparative Examples 6 to 7, the initial weight increase was small, but the weight increased gradually. When the test piece after the test was observed, the interface between the sprayed layer and the chromium base material was peeled off, and that portion was locally subjected to high temperature oxidation and nitriding. Also, FIG.
Section ED of Comparative Example 1 (pure chrome material) after high temperature corrosion test
The results of X-ray component analysis (chromium, aluminum, oxygen, nitrogen) are shown. The presence of oxygen and nitrogen in the air is recognized on the surface of the chromium material, which indicates that oxidation and nitriding have occurred. FIG. 5 is a diagram showing the state of the metal structure at the EDX analysis place. Further, Table 1 shows the mechanical strength of each material after the high temperature gas corrosion test. The aluminum alloy coating layer peeled off, and a nitriding layer and an oxide layer were observed on the chromium base material, so that the mechanical strength of the chromium base material itself was significantly reduced.

[0030]

As is apparent from the above description, according to the present invention, the purity and relative density of the chromium base material is limited, and the aluminum alloy coating layer having a uniform and proper thickness is formed on the chromium base material. (1) It is possible to obtain a chromium material which has oxidation resistance, nitriding resistance, and molten salt resistance at high temperatures and can be stably used at high temperatures. (2) The base material strength is hardly changed by the aluminum alloy coating treatment. (3) High dimensional accuracy can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing the results of a high temperature gas corrosion test of each material of Examples 1 to 4 and Comparative Examples 1 to 7.

FIG. 2 is a diagram showing EDX analysis results near the surface of the aluminum alloy-coated chromium material of Example 1.

FIG. 3 is a diagram showing a metallographic structure of a portion of an aluminum alloy-coated chromium material of Example 1 which was subjected to EDX analysis near the surface thereof.

FIG. 4 ED in the vicinity of the surface of the chromium material of Comparative Example 1
It is a figure which shows a X analysis result.

FIG. 5: ED near the surface of the chromium material of Comparative Example 1
It is a figure which shows the metallographic structure of the part which performed X analysis.

[Table 1]

Claims (1)

[Claims] 1. A relative density of 95% or more and a purity of 99.9%.
An aluminum alloy-coated chromium material obtained by coating the above metal chromium base material with an aluminum-chromium alloy having a thickness of 60 to 120 μm.