Iron oxide film, iron oxide film-coated member, alloy steel for iron oxide film-coated member, and method for manufacturing iron oxide film-coated member

Abstract

To provide an iron oxide film equipped with electrolytic corrosion resistance function to an adjacent metal product, a member on a surface of which the iron oxide film is coated, an alloy steel for the iron oxide film-coated member, and a method for manufacturing an iron oxide film-coated member in which the member can be manufactured at a low cost.SOLUTION: An iron oxide film contains diiron trioxide (Fe2O3) and triiron tetraoxide (Fe3O4), where the iron oxide film is formed of two layer films of an upper layer film containing diiron trioxide and a lower layer film containing triiron tetraoxide. In this case, both the upper layer film and the lower layer film are allowed to contain each element of Cr and Mn.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an iron oxide film containing each iron oxide of iron(III) oxide (Fe2O3) and iron(II,III) oxide (Fe3O4), an iron oxide film-coated member coated with the iron oxide film, alloy steel used for the iron oxide film-coated member, and a method for manufacturing the iron oxide film-coated member.

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 some of the parts disclosed in Patent Document 1 were replaced with resin and added, there were problems with the wear resistance and strength being insufficient compared to steel. Also, ceramics lacked toughness compared to steel, and there were problems with workability. In addition, the material costs of all of these materials were higher than steel, which increased the cost of the entire part.

[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 having an anticorrosion function with an adjacent metal product, a member having the iron oxide film coated on the surface (iron oxide film-coated member), alloy steel for use of the iron oxide film-coated member, and a method for manufacturing the iron oxide film-coated member that can be manufactured at low cost.

Means for Solving the Problems

[0011] In order to solve the above problems, the invention of the iron oxide film is formed from an upper layer film containing iron(III) oxide (Fe2O3) and a lower layer film containing iron(II,III) oxide (Fe3O4). Further, each of the upper layer film and the lower layer film contains elements of Cr and Mn.

[0012] Regarding the invention of the iron oxide film-coated member, the above-described iron oxide film is coated on the surface of a base material made of alloy steel to form an oxide layer containing Fe3O4 and Si on the surface layer of the base material. In this case, the amount of Si contained in the oxide layer can be made larger than the amount of Si in the base material. Further, the amounts of Cr and Mn contained in the oxide layer may be made larger than the amounts of Cr and Mn in the lower layer film.

[0013] In the invention of the alloy steel for forming these iron oxide films, in terms of 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% are contained, and the balance is alloy steel composed of Fe and inevitable impurities. Further, in terms of weight%, W: 0.01 to 2.0% can also be contained.

[0014] Further, in the invention of the method for forming the above-described iron oxide film (manufacturing the iron oxide film-coated member), an iron oxide film is formed on the surface of the above-described alloy steel in a temperature range of 500°C or more and 600°C or less. In this case, the iron oxide film can be formed on the surface of the alloy steel in an atmosphere containing at least one of oxygen or water vapor.

Effects of the Invention

[0015] The iron oxide film of the present invention has an upper layer film containing iron(III) oxide (Fe2O3) on its outermost surface, and the underlying layer film directly below contains iron(II,III) oxide (Fe3O4). In addition, both the upper layer film and the underlying layer film contain Cr and Mn. Therefore, it can be coated on the surface of steel products that require an anti-corrosion function while maintaining a certain level of durability, such as anti-corrosion components.

[0016] Also, by forming an iron oxide film on the surface of alloy steel using alloy steel having a predetermined chemical composition in a temperature range of 500°C or higher and 600°C or lower 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), ensuring durability. At the same time, an iron oxide film having insulation (anti-corrosion function) can be coated on the surface of the alloy steel at a low manufacturing cost.

Brief Description of the Drawings

[0017]

Figure 1

Embodiments for Carrying Out the Invention

[0018] Details of the iron oxide film-coated member, which is one embodiment of the present invention, will be described with reference to the drawings. A microstructural photograph (magnification: 1000 times) of the iron oxide film-coated member, which is one embodiment of the present invention, is shown in FIG. 1. The iron oxide film-coated member of this embodiment is formed from a base material (alloy steel) and an iron oxide film coated on the base material as shown in FIG. 1. Further, the iron oxide film has a two-layer structure of an upper layer film located on the outermost surface and a lower layer film located on the base material side.

[0019] The upper layer film is a film laminated above the lower layer film located on the base material side, and the film contains iron(III) oxide (Fe2O3). Therefore, the upper layer film has insulation. The lower layer film is a film laminated below the above-described upper layer film, and the film contains iron(II,III) oxide (Fe3O4).

[0020] In addition, both the upper layer film and the lower layer film contain Cr and Mn. As a result of analyzing the cross-sections of the upper layer film and the lower layer film of the iron oxide film shown in Fig. 1 by EPMA, it was confirmed that both the upper layer film and the lower layer film contain both Cr and Mn in an amount of 0.2 to 0.4 mass%.

[0021] On the surface layer of the base material, that is, the surface of the base material existing immediately below the lower layer film, an oxide layer containing Fe3O4 and Si is formed. The amount of Si contained in the oxide layer is larger than the amount of Si contained in the base material. Also, the amounts of Cr and Mn contained in the oxide layer are larger than the amounts of Cr and Mn contained in the lower layer film.

[0022] Next, regarding the alloy steel which is the base material of the iron oxide film-coated member which is one embodiment of the present invention, the range of the content of each element contained in the alloy steel will be described below. The chemical composition of the alloy steel for the iron oxide film-coated member of the present invention is (1) within the component range in which an iron oxide film having insulation on the surface can be formed, (2) within the component range in which precipitated particles (carbides, etc.) having conductivity of a size that penetrates the iron oxide film are not formed, and (3) on the premise that it satisfies each condition of not being easily softened even when an oxidation treatment is performed after quenching and tempering and having a hardness exceeding 58 HRC.

[0023] C (carbon) was 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 base structure may coarsen. 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.

[0024] Si (silicon) is 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 will decrease, or the machinability will deteriorate.

[0025] For Mn (manganese), the range is 0.01 to 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 instead increase the material cost.

[0026] For Cr (chromium), the range is 1.0 to 9.0% by weight. If it exceeds this range, the oxide layer of the alloy steel becomes thinner and the insulation of the oxide layer decreases. If it is below this range, the insulation of the oxide layer of the alloy steel decreases.

[0027] For Mo (molybdenum), the range is 1.5 to 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, the surface hardness of the alloy steel may be less than 58 HRC after the oxidation treatment.

[0028] For Al (aluminum), the range is 0.01 to 5.0% by weight. If it exceeds this range, the surface hardness of the alloy steel may be less than 58 HRC after the oxidation treatment, or there may be more non-metallic inclusions and the fatigue strength may decrease. On the other hand, if it is below this range, the insulation of the oxide layer decreases.

[0029] V (vanadium) can also be contained in the range of 0.01 to 1.2% by weight. If it exceeds this range, the carbides may coarsen or the toughness of the alloy steel may decrease. In addition, W (tungsten) may be further contained in the range of 0.01 to 2.0% by weight.

[0030] Next, the manufacturing method of the iron oxide film-coated member, which is one embodiment of the present invention, will be described. After installing the pre-hardened and tempered alloy steel in a heat treatment furnace, the temperature in the heat treatment furnace is raised from the furnace temperature (room temperature) to the target temperature, that is, a temperature range of 500°C or more and 600°C or less.

[0031] After the furnace reaches the target temperature, it is held for a predetermined time in the range of about 1 to 24 hours according to the size of the alloy steel to perform oxidation heat treatment. After the predetermined holding time has elapsed, the temperature in the heat treatment furnace is lowered to room temperature (cooled down), and the alloy steel is taken out of the furnace.

[0032] In the oxidation heat treatment, either a gas of oxygen (O2) or water vapor (H2O), or a mixed gas containing oxygen and water vapor is supplied into the heat treatment furnace. The timing of supplying these gases into the heat treatment furnace can be appropriately adjusted when the temperature in the heat treatment furnace is rising to the target temperature (during temperature rise) or when the target temperature is reached. Note that a part of the gas supplied into the heat treatment furnace may be mixed with air (or nitrogen).

[0033] The supply of either a gas of oxygen (O2) or water vapor (H2O), or a mixed gas containing both oxygen and water vapor into the heat treatment furnace is stopped at either the time when the holding time at the target temperature ends or during the temperature drop to room temperature. As described above, by performing oxidation heat treatment on the alloy steel in an atmosphere containing at least either oxygen (O2) or water vapor (H2O) in the heat treatment furnace, an iron oxide film is formed on the surface of the alloy steel.

[0034] The iron oxide film-coated member shown in FIG. 1 is obtained by coating an iron oxide film on a base material made of alloy steel by the manufacturing method described above. Specifically, after installing alloy steel (by weight%, C: 0.84%, Si: 0.18%, Mn: 0.27%, Cr: 4.07%, Mo: 4.24%, Al: 0.019%, V: 0.95%, W: 0.08%) in the heat treatment furnace, when the temperature in the furnace reached the range of 200 to 300 °C during the process of raising the temperature in the furnace to 550 °C, the temperature was raised while introducing water vapor into the furnace.

[0035] After that, after the temperature in the furnace reached 550 °C, it was maintained at a furnace temperature of 550 °C for 24 hours, and then the temperature in the furnace was cooled to room temperature to cool the alloy steel. During this period, water vapor was continuously introduced into the furnace. Then, after confirming that the temperature in the furnace dropped to the temperature range of 200 to 300 °C, the supply of water vapor into the furnace was stopped. By the above manufacturing method, the surface of the alloy steel was coated with an iron oxide film having a two-layer structure of an upper layer film and a lower layer film as shown in FIG. 1.

Claims

1. An iron oxide film formed on the surface of a substrate made of alloy steel, wherein the iron oxide film has an upper layer film containing Fe ２ O ３ and a lower layer film containing Fe ３ O ４ , and both the upper layer film and the lower layer film contain Cr and Mn. An iron oxide film characterized by this.

2. An iron oxide film-coated member, wherein the iron oxide film according to Claim 1 is coated on the surface of the alloy steel substrate.

3. On the surface layer of the base material, Fe ３ O ４ and an oxide layer containing Si are formed, and the iron oxide film-coated member according to claim 2 is characterized in that.

4. The iron oxide film-coated member according to Claim 3, wherein the amount of Si contained in the oxide layer is greater than the amount of Si in the substrate.

5. The iron oxide film-coated member according to Claim 4, wherein the amounts of Cr and Mn contained in the oxide layer are greater than the amounts of Cr and Mn in the underlying film.

6. An alloy steel used for the iron oxide film-coated member according to any one of Claims 2 to 5, 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.

7. The alloy steel for the iron oxide film-coated member according to Claim 6, further containing, by weight%, W: 0.01 to 2.0%.

8. A method for manufacturing the iron oxide film-coated member according to any one of Claims 2 to 5, wherein the iron oxide film is coated on the surface of the alloy steel substrate in a temperature range of 500°C or more and 600°C or less.

9. The method for manufacturing the iron oxide film-coated member according to Claim 8, wherein the iron oxide film is coated on the surface of the alloy steel substrate in an atmosphere containing at least one of oxygen or water vapor.

10. A method for manufacturing the iron oxide film-coated member according to Claim 8, 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.

11. The method for manufacturing the iron oxide film-coated member according to Claim 10, wherein the alloy steel further contains, by weight%, W: 0.01 to 2.0%.

12. The method for manufacturing the iron oxide film-coated member according to claim 10, characterized by coating the surface of the substrate made of the alloy steel with the iron oxide film in an atmosphere containing at least one of oxygen or water vapor.

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