JPH09209118A - Heat resistant coated stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a heat resistant coated stainless steel increased in heat resistance and durability by forming a firm intermediate layer on the space between an aluminum coating layer on the surface and a base material. SOLUTION: A primary layer 3a composed of an aluminum alloy of aluminum and iron is formed on the topmost surface layer of a base material 8 composed of a stainless steel as a heat resistant coated stainless steel, a secondary layer 3b in which aluminum-iron compounds and aluminum-nickel compounds are dispersed into a ferritic stainless essentially consisting of iron and chromium is formed on the intermediate part, and the center part 8 is composed of an austenitic stainless.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel having a heat resistant coating, and more particularly to a heat resistant coated stainless steel used for a heating wire of a preheating plug for a diesel engine.

[0002]

2. Description of the Related Art Conventionally, heat-resistant coated stainless steel coated with aluminum by hot dip plating has been put into practical use. However, stainless steel thin wires and stainless steel thin plates coated with aluminum by hot dipping are
The aluminum alloy layer obtained by hot dip plating is brittle,
At high temperatures, the base material, stainless steel, also becomes brittle. Similarly, the aluminum alloy layer obtained by the diffusion treatment is also brittle, and the alloy layer peels off from the stainless steel that is the base material at high temperature, and the base material also becomes brittle.

[0003]

SUMMARY OF THE INVENTION In view of the above problems, the object of the present invention is to provide a heat-resistant coated stainless steel having improved heat resistance and durability by forming a strong intermediate layer between the aluminum coating layer and the base material. To provide steel.

[0004]

In order to solve the above-mentioned problems, the structure of the present invention is such that a first layer made of aluminum and iron / aluminum alloy is formed on the outermost surface, and iron / chromium is the main component in the intermediate layer. The second layer in which the aluminum / iron compound and the aluminum / nickel compound are dispersed is formed in the ferritic stainless steel, and the austenitic stainless steel is present in the central portion.

Further, in the constitution of the present invention, the thickness of the first layer is 10 μm or less, and the average crystal grain size of the second layer is 10 μm or less.
３０30 μm.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In order to improve heat resistance and durability of stainless steel, an alloy powder of chromium and aluminum is bonded to the surface of stainless steel as a base material using an adhesive and the temperature is set to 1100 ° C. Heat treatment is performed in a vacuum of about 2 hours. As a result, a first layer of aluminum and an iron / aluminum alloy having a thickness of 10 μm or less is formed on the surface of the base material, and an aluminum / iron compound and A second layer having a thickness of 20 μm or more in which a nickel compound is dispersed is formed, and austenitic stainless steel is formed at the center.

[0007]

EXAMPLE A synthetic rubber adhesive composed of acrylic rubber, an organic solvent, isohexane gas, etc. was applied onto the surface of an austenitic stainless steel wire (SUS304) 8 having a wire diameter of 0.25 mm by spraying. On the surface of synthetic rubber adhesive,
An alloy powder consisting of 50% by weight of chromium and 50% by weight of aluminum was adhered and heat treated in a vacuum at a temperature of 1100 ° C. for about 2 hours.

As a result of analyzing the cross section of the heat resistant coated stainless steel wire 2 according to the present invention thus obtained, as shown in FIG. 1, the surface of the stainless steel wire 8 has a fine dispersed phase having a thickness of 10 to 50 μm. The Fe-Cr-Ni-Al alloy layer 3 was formed. The alloy layer 3 on the surface of the stainless steel wire 8 is not a single layer, but an alloy layer having a thickness of 10 μm or less made of aluminum and an aluminum-iron alloy on the outermost surface, that is, the first layer 3
a having a thickness of 20 μm or more in which the aluminum / iron compound and the aluminum / nickel compound are dispersed inside the ferrite matrix of the crystal grains 4a having the grain size of 10 to 30 μm and forming the ferrite phase 4 inside the first layer 3a. It has been found that there is an alloy layer or second layer 3b. The average crystal grain size of the aluminum / iron compound and the aluminum / nickel compound was 1 μm or less. In the central portion 8 of the cross section of the heat resistant coated stainless steel wire 2, that is, the stainless steel wire as the base material,
There is austenitic stainless steel having an average crystal grain size of 20 to 50 μm. The second layer 3b of the ferrite base is
It is softer than the iron-aluminum alloy of the first layer 3a.

As a result of measuring the tensile strength of the heat resistant coated stainless steel wire 2 obtained according to the present invention and the comparative product, as shown in FIG. 2, the heat resistant coated stainless steel wire 2 according to the present invention has a tensile strength of 800 MPa. It was As a comparative product, the strength of the stainless steel wire (corresponding to the base material 8 in the invention) heat-treated without coating the alloy powder was 455 MPa. The heat-resistant coated stainless steel wire 2 according to the present invention is due to the difference in the coefficient of thermal expansion between the second layer 3b formed on the surface of the base material (stainless steel wire) 8 made of the alloy layer of the ferrite base and the austenitic stainless steel of the base material 8. The generated thermal stress or the residual stress generated between the polycrystalline alloy layers causes the base material 8
It is thought that it worked on the surface of the and improved the strength.

Heat-resistant coated stainless steel wire 2 according to the present invention
And a stainless steel wire made of SUS304 as a comparison product,
As a result of a heat resistance test in which a stainless steel wire made of FCH2 (Fe-Cr-Al alloy) was heated in the atmosphere at a temperature of 1100 ° C for about 25 hours, the stainless steel wire made of SUS304 was not measured after heating for about 1 hour. FCH2 (Fe-Cr
-Al) stainless steel wire has a tensile strength of 417 MPa
On the other hand, the heat resistant coated stainless steel wire 2 according to the present invention had a tensile strength of 670 MPa even after heating for 25 hours.

FIG. 3 shows changes (decrease) in exposure time and tensile strength of the heat resistant coated stainless steel wire 2 according to the present invention and a stainless steel wire made of FCH2 (Fe-Cr-Al) as a comparative product. . Heat resistant coated stainless steel wire 2 according to the present invention
Shows that the degree of strength reduction is significantly smaller than that of the comparative stainless steel wire made of FCH2 (Fe-Cr-Al).

Heat-resistant coated stainless steel wire 2 according to the present invention
And a stainless steel wire made of FCH2 (Fe-Cr-Al) as a comparative product were subjected to the above-mentioned heat resistance test by changing the wire diameter of the base material 8 variously. Heat resistant coated stainless steel wire 2 according to the present invention
The tensile strength of is up to 0.5 mm as a comparative product.
It is smaller than that of stainless steel wire made of FCH2 (Fe-Cr-Al). Further, the heat resistant coated stainless steel plate 2 according to the present invention
Then, with respect to a stainless steel plate made of FCH2 (Fe-Cr-Al) as a comparative product, the above-mentioned heat resistance test was conducted by changing the plate thickness of the substrate 8. The tensile strength of the heat-resistant coated stainless steel sheet 2 according to the present invention is FCH2 (F
It is smaller than that of stainless steel sheet made of e-Cr-Al).
As a comparative product, a stainless steel wire made of FCH2 (Fe-Cr-Al) is very difficult to perform plastic working (drawing, bending, etc.) when the wire diameter is 0.2 mm or less. FCH2 (F
The thickness of the stainless steel plate made of e-Cr-Al) is 0.2 mm.
Below, plastic working (drawing, bending, etc.) is very difficult. On the other hand, both the heat-resistant coated stainless steel wire 2 and the heat-resistant coated stainless steel sheet 2 according to the present invention use the base material 8 having relatively good workability so that the plastic working can be performed even if the wire diameter and the plate thickness are further reduced. There are no problems (drawing, bending, etc.).

FIG. 4 shows the relationship between the grain size of the ferrite phase in the second layer 3b of the heat resistant coated stainless steel 2 according to the present invention and the elongation at break. The crystal grain size of the second layer 3b is 10
It can be seen that the elongation at break increases when the thickness is more than μm. The crystal grain size of the ferrite phase of the second layer 3b is preferably 10 μm or more.

FIG. 5 shows the relationship between the crystal grain size and the tensile strength of the aluminum / iron compound and the aluminum / nickel compound dispersed in the second layer 3b. It can be seen that the tensile strength is remarkably improved when the crystal grain size of the compound dispersed in the second layer 3b is 1 μm or less.

From the above, in the heat-resistant coated stainless steel 2 according to the present invention, if the heat treatment time is too long, the austenite phase crystals in the central portion 8 grow and the ferrite phase of the second layer 3b disappears. A processing time of about 2 hours is suitable. Since the first layer 3a is brittle, it is preferable that it is thin. The alumina of the first layer 3a has high heat resistance, and the second layer 3b
To prevent the oxidation of.

Next, the heat treatment time for obtaining the heat resistant coated stainless steel wire 2 according to the present invention described above is changed variously,
A plurality of samples having different thicknesses of the first layer 3a made of a composite phase of aluminum and an aluminum-iron alloy were prepared. After conducting a winding test on the obtained heat-resistant coated stainless steel wire 2, the surface of each heat-resistant coated stainless steel wire 2 was observed, and as shown in FIG. 6, the thickness of the first layer 3a was 10
It was found that when the thickness exceeds μm, cracks are generated in the first layer 3a. From this point as well, it is not preferable to prolong the heat treatment time for obtaining the heat resistant coated stainless steel wire 2 according to the present invention.

As the base material 8 used in the present invention,
It is desirable to use austenitic stainless steel that is less likely to form carbides and martensite during heat treatment. In particular, austenitic stainless steel having a chemical composition of 0.15 wt% carbon or less, 15 to 26 wt% chromium, and 3.5 to 28 wt% nickel is suitable. When the composition ratio of carbon is increased, carbides of the second layer 3b are precipitated at the grain boundaries, which promotes brittleness.

[0018]

As described above, according to the present invention, the first layer made of aluminum and iron / aluminum alloy is formed on the outermost surface, and the aluminum / iron compound is contained in the intermediate layer of ferritic stainless steel containing iron / chromium as a main component. Since the second layer in which the aluminum-nickel compound is dispersed is formed and the austenitic stainless steel is present in the central portion, the following effects can be obtained.

A heat-resistant coated stainless steel having excellent heat resistance and tensile strength, which has a ferrite Fe-Cr-Ni-Al alloy layer on the surface by depositing chromium / aluminum particles on the surface of austenitic stainless steel and heat-treating it. Is obtained.

In the case of stainless steel composed of FCH2 (Fe-Cr-Al), it is very difficult to plastically work a stainless steel wire having a wire diameter of 0.2 mm or less or a stainless steel plate having a plate thickness of 0.2 mm or less. However, the heat-resistant coated stainless steel according to the present invention uses a base material having relatively good workability,
There is no problem in plastic working even if the wire diameter or plate thickness is smaller.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a thin wire using a heat resistant coated stainless steel according to the present invention.

FIG. 2 is a diagram showing the heat resistance strength of the heat resistant coated stainless steel according to the present invention and a conventional product.

FIG. 3 is a diagram showing the heat resistance strength of the heat resistant coated stainless steel according to the present invention and a conventional product.

FIG. 4 is a diagram showing the relationship between the average grain size of the ferrite phase of the second layer and the elongation at break in the heat resistant coated stainless steel according to the present invention.

FIG. 5 is a diagram showing the relationship between the average grain size of the second layer and the tensile strength of the heat resistant coated stainless steel according to the present invention.

FIG. 6 is a diagram showing the relationship between the thickness of the first layer and the crack occurrence rate in the heat resistant coated stainless steel according to the present invention.

[Explanation of symbols]

2: Heat resistant coated stainless steel wire 3: Alloy layer 3a: First
Layer 3b: Second layer 8: Center part (base material)

Claims (7)

[Claims] 1. A first layer made of aluminum and an iron / aluminum alloy is formed on the outermost surface, and an aluminum / iron compound and an aluminum / nickel compound are dispersed in a ferritic stainless steel containing iron / chromium as a main component in an intermediate layer. A heat-resistant coated stainless steel, characterized in that a second layer is formed and austenitic stainless steel is present in the center. 2. The thickness of the first layer is 10 μm or less,
The heat-resistant coated stainless steel according to claim 1. 3. The average crystal grain size of the second layer is 10 to 30 μm.
The heat-resistant coated stainless steel according to claim 1, which is m. 4. The crystal grain size of the aluminum / iron compound and the aluminum / nickel compound dispersed in the second layer is 1 μm.
The heat-resistant coated stainless steel according to claim 1, which is m or less. 5. The composition of austenitic stainless steel in the central portion is such that carbon is 0.15 wt% or less and chromium is 15 to 26 wt.
%, Nickel 3.5-28 wt%, heat resistant coated stainless steel according to claim 1. 6. The heat resistant coated stainless steel thin wire according to claim 1, wherein the wire diameter is 0.5 mm or less. 7. The heat-resistant coated stainless steel thin plate according to claim 1, which has a plate thickness of 0.5 mm or less.