Iron oxide film, alloy steel, and method for forming iron oxide film

Abstract

To provide an iron oxide film including a resistance function to electrolytic corrosion with an adjacent metal product, and to provide an alloy steel for forming the iron oxide film and a method for forming an iron oxide film.SOLUTION: An iron oxide film contains an iron sesquioxide (Fe2O3) and a triiron tetraoxide (Fe3O4). The iron oxide film is formed of a dual-layer film including an upper layer film containing an iron sesquioxide and an underlayer film containing a triiron tetraoxide. In this case, the upper layer film has a thickness that can be thinner than a thickness of the underlayer film. The underlayer film may further contain an oxide of at least one element selected from Cr or Mn.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an iron oxide film containing iron(III) oxide and iron(II,III) oxide, an alloy steel for forming the iron oxide film, and a method for forming the iron oxide film.

Background Art

[0002] Conventionally, in order to manufacture parts that require insulation using steel materials, measures have been taken to impart insulation by replacing part of the parts with ceramics such as alumina having insulation properties, or covering the surface of the parts with a resin such as PPS (see Patent Document 1).

[0003] Alternatively, among steel materials manufactured with predetermined components, there are cases where insulation is provided to the parts by forming an insulating oxide layer on the surface of the parts by high-temperature heating (see Patent Documents 2 and 3).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when a part of the parts disclosed in Patent Document 1 is replaced and added with a resin, there is a problem that the wear resistance and strength are insufficient compared with the steel material. In addition, in the case of ceramics, the toughness is insufficient compared with the steel material, and there are also problems in workability. In addition, all of these materials have a higher material cost than steel materials, and the cost of the entire part increases.

[0006] On the other hand, as disclosed in Patent Document 2, when the surface of a steel material is oxidized to impart insulating properties to the parts, this is advantageous in terms of cost, but the hardness of conventional alloy steel is below 50HRC (HRC: Rockwell hardness C scale), and it is difficult to use such steel for long periods of time as parts in high-load environments that require wear resistance, fatigue strength, and the like.

[0007] This is because the carbon content, which contributes greatly to the hardness of alloy steel, is extremely low. In addition, the temperature required to form the oxide layer is in the high range of about 980 to 1220°C, so even if the material had high hardness before treatment, it may soften.

[0008] Even if high hardness could be achieved by heating to about 1200°C for both quenching and oxidation, the dimensions would vary greatly before and after the treatment. Therefore, in order to manufacture high-precision parts, grinding or other processes would be required after oxidation, and the oxide layer that had been so carefully formed would be ground away.

[0009] Furthermore, the material disclosed in Patent Document 3 also describes a method of oxidizing the surface of the steel material to give the part insulation, but does not disclose any information on the hardness or strength of the material, nor does it state any particular consideration. In addition, the method of forming the oxide layer involves immersion in an acid solution, which poses problems such as a decrease in material strength due to hydrogen embrittlement and a burden on the natural environment.

[0010] Therefore, an object of the present invention is to provide an iron oxide film that has resistance to electrolytic corrosion with adjacent metal products, an alloy steel for forming said iron oxide film, and a method for forming an iron oxide film that can be produced at low cost. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, the iron oxide film of the present invention is Fe 2 O 3 (iron trioxide) and Fe 3 O 4 (iron tetroxide), containing at least Fe 2 O3 An upper layer film containing 3 O 4 and a lower layer film containing FeO are formed. Further, the lower layer film can further contain an oxide of at least one element selected from Cr and Mn.

[0012] In the invention of the alloy steel for forming the oxide film described above, by weight, C: 0.01% or more and less than 1.0%, Si: 0.01% or more and less than 1.0%, Mn: 0.01 - 2.0%, Cr: 1.0 - 9.0%, Mo: 1.5 - 6.0%, Al: 0.01 - 5.0%, V: 0.01 - 1.2% are contained, and the balance is an alloy steel composed of Fe and inevitable impurities. Further, by weight, W: 0.01 - 2.0% can also be contained.

[0013] Also, in the invention of the method for forming the iron oxide film described above, an iron oxide film is formed on the surface of the alloy steel in the temperature range of 500°C or more and 600°C or less. In this case, the iron oxide film can also be formed on the surface of the alloy steel in an atmosphere containing at least one of oxygen or water vapor.

Advantages of the Invention

[0014] The iron oxide film of the present invention has an upper layer film containing Fe 2 O 3 (iron sesquioxide) on the outermost surface, and the lower layer film directly below contains Fe 3 O 4 (magnetite). Therefore, it can be coated on the surface of steel products that require corrosion resistance functions such as corrosion prevention parts.

[0015] Also, by using an alloy steel having a predetermined chemical composition and forming an iron oxide film on the surface of the alloy steel in the temperature range of 500°C or more and 600°C or less and in an atmosphere containing oxygen or water vapor, the alloy steel can be maintained at a hardness exceeding 58 HRC (Rockwell hardness C scale), and at the same time, an iron oxide film having insulating properties (corrosion resistance function) can be formed on the surface of the alloy steel at low production costs.

Brief Description of the Drawings

[0016]

Figure 1

Embodiment for Carrying Out the Invention

[0017] Details of the iron oxide film, which is one embodiment of the present invention, will be described with reference to the drawings. A microstructure photograph (magnification: 1000 times) of the iron oxide film of the present invention formed on the surface of alloy steel is shown in FIG. 1. As shown in FIG. 1, the iron oxide film of the present invention is formed on alloy steel (0.84 wt% C, 0.18 wt% Si, 0.27 wt% Mn, 4.07 wt% Cr, 4.24 wt% Mo, 0.95 wt% V, 0.08 wt% W, 0.019 wt% Al) and has a two-layer structure of an upper layer film and a lower layer film.

[0018] The upper layer film is a film laminated above the lower layer film described later, and iron(III) oxide (Fe 2 O 3 ) is contained therein. Therefore, the upper layer film has insulating properties. The lower layer film is a film laminated below the aforementioned upper layer film, and iron(II,III) oxide (Fe 3 O 4 ) is contained therein. Further, depending on the chemical composition of the alloy steel as the base material, an oxide of at least one element selected from Cr and Mn can be further contained in the lower layer film.

[0019] Next, regarding the alloy steel for forming the iron oxide film, which is one embodiment of the present invention, the content of each element contained in the alloy steel will be described below. Regarding the chemical composition of the alloy steel for forming the iron oxide film of the present invention, it is assumed that (1) it is within a component range in which an iron oxide film having insulating properties can be formed on the surface, (2) it is within a component range in which precipitated particles (carbides, etc.) having conductivity of a size that penetrates the iron oxide film are not formed, and (3) it is within a component range in which it is not easily softened even when an oxidation treatment is performed after quenching and tempering, and a hardness exceeding 58 HRC can be obtained.

[0020] C (carbon) was set in the range of 0.01% or more and less than 1.0% by weight. If the amount of C exceeds this range, the toughness of the alloy steel may decrease, and the carbides in the matrix may coarsen in some cases. Also, the hot workability of the alloy steel may deteriorate. On the other hand, if it is less than this range, the surface hardness of the alloy steel will be less than 58 HRC.

[0021] Si (silicon) was set in the range of 0.01% or more and less than 1.0% by weight. If the amount of Si exceeds this range, the toughness of the alloy steel may decrease, or the hot workability may deteriorate. On the other hand, if it is below this range, the insulation of the oxide layer formed on the surface may decrease, or the machinability may deteriorate.

[0022] For Mn (manganese), it was set in the range of 0.01 - 2.0% by weight. If it exceeds this range, the workability may deteriorate. On the other hand, if it is below this range, it is necessary to strictly select the raw materials, which will rather increase the material cost.

[0023] Cr (chromium) was set in the range of 1.0 - 9.0% by weight. If it exceeds this range, the oxide layer of the alloy steel will become thinner and the insulation of the oxide layer will decrease. If it is below this range, the insulation of the oxide layer of the alloy steel will decrease

[0024] Mo (molybdenum) was set in the range of 1.5 - 6.0% by weight. If it exceeds this range, the carbides may coarsen, or the toughness of the alloy steel may decrease. On the other hand, if it is below this range, after the oxidation treatment, the surface hardness of the alloy steel may be less than 58 HRC.

[0025] Al (aluminum) was set in the range of 0.01 - 5.0% by weight. If it exceeds this range, after the oxidation treatment, the surface hardness of the alloy steel may be less than 58 HRC, or the non - metallic inclusions may increase and the fatigue strength may decrease. On the other hand, if it is below this range, the insulation of the oxide layer will decrease.

[0026] V (vanadium) can also be contained in the range of 0.01 to 1.2% by weight. If it exceeds this range, there is a risk that the carbides will coarsen or the toughness of the alloy steel will decrease. In addition, W (tungsten) may be further contained in the range of 0.01 to 2.0% by weight.

[0027] Next, the method for forming the iron oxide film, which is an embodiment of the present invention, will be described. The alloy steel for forming the iron oxide film that has been subjected to the prior quenching and tempering treatment is subjected to oxidation heat treatment in a temperature range of 500°C or higher and 600°C or lower. Even when the oxidation heat treatment is performed in the temperature range of 500°C or higher and 600°C or lower, the alloy steel has sufficient tempering softening resistance characteristics, and a hardness (hardness of the alloy steel) exceeding 58 HRC can be sufficiently ensured.

[0028] In addition, during the above-described oxidation heat treatment step, an iron oxide film can be surely formed on the surface of the alloy steel by performing the oxidation heat treatment of the alloy steel in an atmosphere containing either oxygen or water vapor, or in an atmosphere containing both oxygen and water vapor.

Claims

1. Fe ２ O ３ and Fe ３ O ４ An iron oxide film containing ２ O ３ The iron oxide film is characterized in that it is formed from an upper layer film containing ３ O ４ and a lower layer film containing

2. The iron oxide film according to claim 1, wherein the lower layer film further contains an oxide of at least one element selected from Cr and Mn.

3. An alloy steel for forming the iron oxide film according to claim 1 or 2, wherein the alloy steel contains, by weight%, C: 0.01% or more and less than 1.0%, Si: 0.01% or more and less than 1.0%, Mn: 0.01 to 2.0%, Cr: 1.0 to 9.0%, Mo: 1.5 to 6.0%, Al: 0.01 to 5.0%, V: 0.01 to 1.2%, and the balance consists of Fe and unavoidable impurities.

4. The alloy steel according to claim 3, further containing, by weight%, W: 0.01 to 2.0%.

5. A method for forming the iron oxide film according to claim 1 or 2, characterized in that the iron oxide film is formed on the surface of the alloy steel in a temperature range of 500°C or more and 600°C or less.

6. The method for forming an iron oxide film according to claim 5, characterized in that the iron oxide film is formed on the surface of the alloy steel in an atmosphere containing at least one of oxygen or water vapor.

Images