JP2912761B2 - Manufacturing method of ferritic stainless steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is excellent in heat resistance and corrosion resistance, has high hardness, and can form a film containing alumina as a main component on the surface by heat treatment in an oxidizing gas atmosphere. The present invention relates to a method for producing ferritic stainless steel (ferritic stainless alloy) suitable for parts such as chucks, gears, and shafts of cutting tools and power tools.

[0002]

2. Description of the Related Art Conventionally, Ni-containing ferritic stainless steel has been manufactured by so-called melting casting or powder metallurgy. In the former case, a raw material mother alloy is blended so as to have a desired composition, and an ingot of Ni-containing ferritic stainless steel is formed by melting and casting, and a predetermined ingot is formed by plastic working such as rolling or machining such as cutting. Finish in shape.
However, in this case, the Ni-containing ferritic stainless steel has poor workability, and there is a problem that plastic working such as rolling is particularly difficult.

[0003] In the latter case, a raw material mother alloy is blended so as to have a desired composition, and an ingot is formed and pulverized.
The powder obtained by the atomizing method or the like and an organic binder are mixed and finished to a predetermined shape by direct pressure molding or injection molding, and then the binder is blown off by heat treatment or the like, and then sintered. However, in this case, there is a problem that it is difficult to accurately obtain a predetermined shape by shrinkage or the like, and it is difficult to manufacture a thin or large one.

[0004]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a Ni-containing ferritic stainless steel which not only can be accurately formed into a predetermined shape but also can easily form an alumina film on the surface. It is an object to provide a method that can be obtained.

[0005]

In order to solve the above-mentioned problems, in the method for producing a ferritic stainless steel according to the present invention, Ni is adhered to the surface of an Fe-Cr-Al-based alloy, and the Ni-based alloy is heated in a non-oxidizing atmosphere. By performing heat treatment, the F
Ni is diffused into an e-Cr-Al alloy to obtain a ferrite-based stainless steel alloy having a Ni content of 2 to 25% by weight.
-To obtain a Cr-Ni-Al alloy.

[0006] Ni adhered to the surface of the Fe-Cr-Al-based alloy diffuses into the Fe-Cr-Al-based alloy by heat treatment to increase the hardness. When the content exceeds 25% by weight, the formation of a necessary ferrite phase is hindered, the austenite phase increases, and the hardness is rather lowered. In the case of the present invention, as a method of adhering Ni to the surface of the Fe-Cr-Al-based alloy, a method of applying Ni plating to the Fe-Cr-Al-based alloy or a method of pressing a Ni material to the Fe-Cr-Al-based alloy by pressure welding. Method and the like.

A ferrite-based Fe-Cr-Ni-Al-based alloy (hereinafter referred to as "Fe-Cr-Ni-Al-based alloy") obtained by Ni diffusion and having a stainless steel composition has a C content.
r: 20 to 40% by weight, Ni: 2 to 25% by weight, Al:
2 to 8% by weight, Ti: 0 to 0.5% by weight, Zr, Y, H
Any one or more of f, Ce, La, Nd and Gd: 0.05 to 1.0% by weight, the balance: a composition substantially composed of Fe (hereinafter, appropriately referred to as “appropriate composition”) ) Is preferable. To obtain the proper composition,
The thickness and composition of the e-Cr-Al-based alloy and the amount of adhered Ni are preferably set. With this composition, the obtained Fe-Cr-Ni-
The Al-based alloy has a hardness of Hv = 300 or more, and is subjected to a heat treatment in an oxidizing gas atmosphere so that a film having an alumina component as a main component can be deposited on the surface with high adhesion force in a dense and sufficient thickness. And a hardness of Hv = 500 or more can be obtained.

Of course, in the case of the present invention, the present invention is not limited to this. For example, Ni may be produced by closely contacting a commercially available Fe-Cr-Al-based steel sheet with Ni having a weight of 2 to 33% of the weight of the sheet as described above. You may make it. Hereinafter, the present invention will be described more specifically. First, the raw material metal and the mother alloy are weighed at a compounding ratio at which the composition after the diffusion of Ni becomes the above-mentioned appropriate composition, and among them, those other than Ni are melt-cast, and Fe-Cr
-To obtain an ingot of an Al-based alloy. Then, after subjecting the ingot to desired plastic working as necessary, Ni in an amount of 2 to 33% by weight with respect to the total weight (100% by weight) of the processed product is obtained.
Is brought into close contact by pressing a pure Ni plate or by applying Ni plating. It goes without saying that the amount of Ni to be adhered is adjusted according to the composition after Ni diffusion.

[0009] Following the adhesion of Ni, plastic working is performed as necessary, and then, under a condition (non-oxidizing atmosphere) where oxidation does not occur at the interface between Ni and the Fe-Cr-Al alloy.
00 to 1400 ° C (preferably 1200 to 1300 ° C)
Heat treatment for diffusing Ni. By this heat treatment, Ni diffuses into the alloy without melting, and a ferritic stainless steel having a target composition is obtained.

[0010] The heat treatment is carried out under such a condition that it does not oxidize at the interface between Ni and the Fe-Cr-Al alloy. If an oxide is formed at the interface, the diffusion of Ni is hindered, and the resulting ferritic stainless steel is obtained. Is not uniform. Further, Fe-Cr-
If the thickness of the Al-based alloy is too large, a high-temperature and long-time heat treatment is required. Therefore, it is generally preferable that the thickness of the Fe-Cr-Al-based alloy be about 1 mm or less. Also, pure Ni
When using an Fe-Cr-Al-based alloy which is inferior in workability as compared with Ni, it is better to avoid applying excessively large composition processing after bringing Ni into close contact with the Fe-Cr-Al-based alloy.

Further, the ferritic stainless steel thus obtained is subjected to machining if necessary,
In an atmosphere or an oxidizing gas atmosphere such as an oxygen gas, for example, heat treatment is performed at a temperature exceeding 1000 ° C. to deposit an alumina (aluminum oxide) component on the surface.
By this heat treatment, a layer mainly composed of alumina (alumina coating) is formed on the surface of the alloy. The Al element in the alloy is oxidized by heat treatment in an oxidizing gas atmosphere, and is formed on the surface of the alloy as a ceramic made of alumina having high hardness. By doing so, a Fe-Cr-Ni-Al-based alloy with an alumina film accurately finished in a predetermined shape is completed. This is suitable for blades and mechanical parts that require wear resistance.

An alloy (part) with an alumina coating has a surface layer containing alumina as a main component, and therefore has a high surface hardness, and has excellent toughness because the base material is an alloy. In addition, when a ceramic film is formed on a metal surface by a sputtering method, a CVD method, or the like, a boundary surface is formed between the film and the metal base material, so that the adhesion strength between the film and the base material is small, While sufficient abrasion resistance cannot be obtained because the thickness of the layer is limited, the surface layer mainly composed of alumina according to the present invention has a shape in which alumina roots are formed in the base material. Therefore, the adhesive strength with the base material is large, and the thickness of this surface layer can be increased to 10 to 50 μm.

In the present invention, at the stage of good workability, such as a Fe-Cr-Al-based alloy before Ni diffusion or a clad material in which Ni having good workability adheres to the surface,
Processing required for forming a predetermined shape such as plastic working can be performed. Whatever the shape, for example, Ni plating
e-Cr-Al-based alloy,
This is because i-diffusion can be performed without any trouble. Fe with poor workability
-It becomes possible to work very easily and accurately as compared with the case of performing post-processing on a Cr-Ni-Al-based alloy. In this case, it can be said that economic efficiency and mass production effect required for industrial production are remarkable. In other words, it is suitable for mass production.

[0014]

In the ferritic stainless steel obtained by the production method of the present invention, 2 to 25% by weight of Ni diffused in the Fe-Cr-Al alloy acts to increase the hardness. In the case of the present invention, Ni diffusion can be performed without any trouble even if processing into a predetermined shape is performed at a favorable stage of workability before Ni diffusion processing, and the powder metallurgy method is not accompanied by a large dimensional change. , Can be accurately and easily finished to a predetermined shape.

[0015] The obtained ferritic stainless steel is C
r: 20 to 40% by weight, Ni: 2 to 25% by weight, Al:
2 to 8% by weight, Ti: 0 to 0.5% by weight, Zr, Y, H
Any one or more of f, Ce, La, Nd and Gd: 0.05 to 1.0% by weight, the balance: If the alloy is substantially composed of Fe, the hardness, Excellent heat and corrosion resistance and heat treatment
There is an advantage that a rooted alumina film is formed in the alloy, the surface hardness and abrasion resistance are good, and the base material hardness can be very high.

[0016]

Embodiments of the present invention will be described below. The present invention is not limited to the following embodiments. Example 1 Cr: 23% by weight, Al: 3.5% by weight, Zr: 0.1
Weight%, balance: Rolled ingot made of Fe, ground the surface to a thickness of 0.05 mm, washed, pretreated, and immersed in an electroless Ni plating solution at 65 ° C. for about 1 hour. An Ni layer having a thickness of about 2.5 μm was formed on the surface by electroless plating, and Ni was adhered thereto. The Ni-coated Fe-Cr-Al-based alloy plate thus obtained was placed in an Ar gas atmosphere for 12 hours.
Hold at 00 ° C. for 15 hours, and replace Ni on the surface with Fe-Cr-A
A uniform Ni-containing ferritic stainless steel sheet was obtained by diffusing into an l-based alloy.

The composition of the obtained steel sheet is Cr: 2
0.5% by weight, Al: 3.1% by weight, Ni: 10.9% by weight, Zr: 0.1% by weight, balance: Fe. Also, with respect to hardness, Hv = approximately 350, which is a considerable improvement. -Example 2-Cr: 42.50% by weight, Al: 8.8% by weight, Zr:
0.3% by weight, balance: Ingot made of Fe was rolled to a plate thickness of 2 mm, and its surface was ground and washed to obtain a plate thickness of 1.6.
Thus, a rolled plate of an Fe-Cr-Al-based alloy having a thickness of 1 mm was obtained. Then, this rolled plate is sandwiched between Ni rolled plates having a thickness of 0.2 mm by separately grinding and washing the surface, and the entire plate is 1 m thick.
m, and Ni was adhered to the surface of the Fe-Cr-Al-based alloy.

Then, at 1300 ° C. in an Ar gas atmosphere,
Holding for 12 hours, Ni was diffused into the Fe-Cr-Al alloy to obtain a Ni-containing ferritic stainless steel sheet. The composition of the obtained steel sheet was as follows: Cr: 32.0% by weight, Al: 6.6% by weight, Ni: 24.5% by weight, Z:
r: 0.2% by weight, balance: Fe. Also, with respect to the hardness, Hv = approximately 400, which is a considerable improvement.

Further, the obtained steel sheet is placed in the air at 120
When kept at 0 ° C. for 2 hours and cooled rapidly by air cooling, an oxide layer mainly composed of alumina (alumina coating) was deposited on the surface. At this time, the base material hardness is Hv = about 550.
Met. Example 3 Cr: 40.0% by weight, Al: 8.5% by weight, Zr:
0.3 wt%, balance: Ingot made of Fe was rolled to a plate thickness of 0.7 mm, and its surface was ground and washed to obtain a rolled plate of an Fe-Cr-Al-based alloy having a plate thickness of 0.5 mm. Was. Then, this rolled plate is separately sandwiched between Ni rolled plates having a surface thickness of 0.2 mm by grinding and washing the surface, and the whole is rolled until the plate thickness becomes 0.8 mm, and an Fe-Cr-Al alloy is formed. Ni was adhered to the surface.

Then, at 1250 ° C. in an Ar gas atmosphere,
After holding for 20 hours, Ni was diffused into the Fe-Cr-Al alloy to obtain a Ni-containing ferritic stainless steel sheet. The composition of the obtained steel sheet was as follows: Cr: 31.5% by weight, Al: 6.7% by weight, Ni: 21.4% by weight, Z:
r: 0.2% by weight, balance: Fe. Also, with respect to the hardness, Hv = approximately 400, which is a considerable improvement.

Further, the obtained steel sheet was placed in the air at 115
When kept at 0 ° C. for 20 hours and cooled rapidly by air cooling, an oxide layer mainly composed of alumina (alumina film) was deposited on the surface. At this time, the base material hardness is Hv = about 500
Met. -Comparative Example 1-Cr: 23.0% by weight, Al: 3.5% by weight, Zr:
It is a rolled plate of 0.2% by weight, the balance being Fe and having a thickness of 0.1 mm. The hardness was Hv = about 200.

In the case of the example, the hardness was much higher than Hv = about 200 in the case of the comparative example due to the diffusion of Ni.
In addition, since plastic working such as rolling was performed before the diffusion of Ni, it could be performed smoothly without any trouble. FIGS. 1 and 2 are scanning electron micrographs (magnification: about 1300 times) showing the metal structure of the cross section of the Ni-containing ferritic stainless steel sheet obtained in Example 1. FIG. 2 shows a Ni structure portion in the structure of FIG. 1, and the whiter portion indicates that the Ni concentration is higher. FIG. 3 is a graph showing a line analysis result of Ni concentration by EPMA at a position where a white line is drawn in FIG. FIG. 3 shows that the Ni concentration is higher as the analysis line A is higher. From FIGS. 1-3, Ni
Is found to be uniformly diffused in the alloy.

The Ni-containing ferritic stainless steel sheet obtained according to the present invention was examined for deformation resistance, and was found to be about twice as large as the Fe-Cr-Al alloy.

[0024]

The ferritic stainless steel obtained by the production method of the present invention has a high hardness because 2 to 25% by weight of Ni is diffused in the Fe-Cr-Al-based alloy. Since the mechanical processing can be performed without any trouble before the diffusion, it can be accurately and easily finished to a predetermined shape, and is very useful because of its suitability for mass production.

The obtained ferritic stainless steel contains 20 to 40% by weight of Cr, 2 to 25% by weight of Ni,
Al: 2 to 8% by weight, Ti: 0 to 0.5% by weight, Zr,
Any one or more of Y, Hf, Ce, La, Nd, and Gd: 0.05 to 1.0% by weight, and the remainder: if substantially composed of Fe, ,
In addition to being surely excellent in terms of hardness, heat resistance and corrosion resistance, heat treatment in an oxidizing atmosphere can produce a rooted alumina film in the alloy, good surface hardness and abrasion resistance, An additional advantage is that a material having a very high base metal hardness can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph (magnification: about 1) showing a metal structure of a cross section of a ferritic stainless steel sheet of Example 1.
300 times).

FIG. 2 is a scanning electron micrograph (approximately 1 magnification) showing a metal structure of a cross section of the ferritic stainless steel sheet of Example 1.
300 times).

FIG. 3 is a graph showing a line analysis result of Ni concentration by EPMA at a position where a white line is drawn in FIG. 1;

[Explanation of symbols]

 A Analysis line

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-52252 (JP, A) JP-A-3-150347 (JP, A) JP-A-62-161950 (JP, A) (58) Investigation Field (Int.Cl. ⁶ , DB name) C23C 10 / 28,8 / 18,12 / 00 C22C 38/00 302

Claims (5)

(57) [Claims] 1. A keep in close contact with Ni on the surface of the Fe-Cr-Al alloy in a non-oxidizing atmosphere 1200-1300
Ni is diffused into the Fe-Cr-Al-based alloy by performing a heat treatment at a temperature of 200 ° C, and the ferrite-based stainless steel composition Fe-Cr-Ni-Al having a Ni content of 2 to 25% by weight is used.
A method for producing a ferritic stainless steel to obtain a base alloy. 2. The method according to claim 1, wherein the Ni is plated on the surface of the Fe-Cr-Al alloy by subjecting the Fe-Cr-Al alloy to Ni plating.
The method for producing a ferritic stainless steel according to claim 1, wherein 3. A Ni material is pressed into contact with the Fe—Cr—Al alloy to form Ni on the surface of the Fe—Cr—Al alloy.
The method for producing a ferritic stainless steel according to claim 1, wherein 4. The method according to claim 1, wherein the Fe—Cr—Ni—Al alloy is C
r: 20 to 40% by weight, Ni: 2 to 25% by weight, Al:
2 to 8% by weight, Ti: 0 to 0.5% by weight, Zr, Y, H
4. The composition according to claim 1, wherein at least one of f, Ce, La, Nd and Gd has a composition of 0.05 to 1.0% by weight, and the balance substantially consists of Fe. A method for producing a ferritic stainless steel according to the above item. 5. The ferritic stainless steel according to claim 1, wherein an alumina component is precipitated on the surface by subjecting the Fe—Cr—Ni—Al alloy to a heat treatment in an oxidizing gas atmosphere. Steel production method.