Alloy steel for forming oxide film, galvanic corrosion prevention component, and method for producing the same

Abstract

To provide an alloy steel for forming an oxide film which is capable of maintaining its original hardness while exhibiting resistance to galvanic corrosion against adjacent metal products, as well as a galvanic corrosion prevention component using the alloy steel and a method for producing the same.SOLUTION: In an alloy steel for forming an oxide film which contains, in wt.%, C: 0.01-1.0%, Si: 0.01-1.0%, Mn: 0.01-2.0%, Cr: 1.0-9.0%, Mo: 1.5-6.0%, Al: 0.01-5.0%, and V: 0.01-1.2%, with the balance being Fe and inevitable impurities, an oxide film is formed on the surface of the alloy steel. This makes it possible to maintain the original hardness while exhibiting resistance to galvanic corrosion against adjacent metal products.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an alloy steel containing chromium, molybdenum, etc. for forming an oxide film, an electrolytic corrosion prevention part using the same, and a method for producing the same. [Background technology]

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

[0003] Alternatively, some steel materials manufactured with a specified composition can be heated at high temperatures to form an insulating oxide layer on the surface of the part, thereby giving the part insulating properties (see Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-236259 A [Patent Document 2] JP 2013-199674 A [Patent Document 3] JP 2004-84767 A Summary of the Invention [Problem 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, the objective of the present invention is to provide an alloy steel for forming an oxide film that can maintain high strength (or hardness) while having electrical insulation between adjacent metal products, an electrolytic corrosion prevention part using the same, and a method for manufacturing the electrolytic corrosion prevention part. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, the present invention relates to an alloy steel for forming an oxide film, which contains, by weight, 0.01-1.0% C, 0.01-1.0% Si, 0.01-2.0% Mn, 1.0-9.0% Cr, 1.5-6.0% Mo, 0.01-5.0% Al, 0.01-1.2% V, with the balance being Fe and unavoidable impurities.

[0012] Alternatively, the alloy steel may be an oxide film forming alloy steel containing, by weight, 0.01-1.0% C, 0.01-0.5% Si, 0.01-1.0% Mn, 1.0-9.0% Cr, 1.5-6.0% Mo, 0.01-5.0% Al, 0.01-1.2% V, 0.01-0.5% W, with the balance being Fe and unavoidable impurities.

[0013] Next, the invention of the electrolytic corrosion prevention part is made by coating the surface of the oxide film-forming alloy steel with an oxide film using the above-mentioned invention of the oxide film-forming alloy steel. The surface hardness of this alloy steel for forming an oxide film can be 58HRC or more on the Rockwell C scale.

[0014] In the method for producing an electrolytic corrosion prevention part, an oxide film is formed on the surface of the above-mentioned alloy steel for oxide film formation at a temperature range of 500° C. to 600° C. In this case, the oxide film may be formed on the surface of the alloy steel for oxide film formation in an atmosphere containing at least either oxygen or water vapor. Effect of the Invention

[0015] The alloy steel for forming an oxide film of the present invention has a predetermined composition and can form an insulating oxide layer (oxide film) on the surface of the steel material while maintaining a hardness exceeding 58HRC (Rockwell hardness C scale). In addition, the electrolytic corrosion prevention part of the present invention can achieve a hardness exceeding 58HRC by subjecting the alloy steel for forming an oxide film to a heat treatment of quenching and tempering, and then, by performing a finish processing to ensure the dimensional accuracy of the part and then performing an oxidation heat treatment, even if an insulating oxide film is formed, the dimensional change of the part due to the oxidation treatment can be kept relatively small. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The content of each element contained in the oxide film-forming alloy steel according to one embodiment of the present invention will be described. The chemical composition of the oxide film-forming alloy steel of the present invention satisfies the following conditions: (1) the composition range allows an insulating oxide layer to be formed on the surface, (2) the composition range does not allow conductive precipitate particles (such as carbides) of a size large enough to penetrate the oxide layer to be formed, and (3) the composition range allows the alloy steel to be resistant to softening even when subjected to oxidation treatment after quenching and tempering, and allows the alloy steel to have a hardness exceeding 58HRC.

[0017] The range of C (carbon) is set to 0.01 to 1.0% by weight. If the C content exceeds this range, the toughness of the alloy steel may decrease, and the carbides in the matrix structure may become coarse. In addition, the hot workability of the alloy steel for forming an oxide film may deteriorate. On the other hand, if the C content is less than this range, the surface hardness of the alloy steel for forming an oxide film becomes less than 58HRC.

[0018] The content of silicon (Si) is set to 0.01 to 1.0% by weight. If the amount of silicon exceeds this range, the toughness of the alloy steel for forming an oxide film may decrease, or the hot workability may deteriorate. On the other hand, if the amount of silicon is below this range, the insulating property of the oxide layer formed on the surface may decrease, or the machinability may deteriorate.

[0019] The Mn (manganese) content is set to the range of 0.01 to 2.0% by weight. If the content exceeds this range, the workability may deteriorate. On the other hand, if the content is below this range, the raw materials must be carefully selected, which may result in higher material costs.

[0020] Cr (chromium) is in the range of 1.0 to 9.0% by weight. If it exceeds this range, the oxide layer of the alloy steel for forming an oxide film becomes thin and the insulating properties of the oxide layer decrease. If it falls below this range, the insulating properties of the oxide layer of the alloy steel for forming an oxide film decrease.

[0021] Mo (molybdenum) is set to the range of 1.5 to 6.0% by weight. If it exceeds this range, the carbides may become coarse or the toughness of the alloy steel for forming an oxide film may decrease. On the other hand, if it is below this range, the surface hardness of the alloy steel for forming an oxide film may become less than 58HRC after oxidation treatment.

[0022] The content of aluminum (Al) is set to the range of 0.01 to 5.0% by weight. If the content exceeds this range, the surface hardness of the alloy steel for forming the oxide film after oxidation treatment may become less than 58HRC, or nonmetallic inclusions may increase, causing a decrease in fatigue strength. On the other hand, if the content is below this range, the insulating properties of the oxide layer may decrease.

[0023] V (vanadium) can be contained in the range of 0.01 to 1.2% by weight. If the amount exceeds this range, the carbides may become coarse or the toughness of the alloy steel for forming an oxide film may decrease. W (tungsten) may be further contained in the range of 0.01 to 0.5% by weight.

[0024] Next, an electrolytic corrosion prevention part using an oxide film-forming alloy steel and a manufacturing method thereof according to one embodiment of the present invention will be described. In the invention of the electrolytic corrosion prevention part using an oxide film-forming alloy steel of the present invention, an oxide film is formed on the surface of the oxide film-forming alloy steel, which is the base material. In this case, the surface hardness of the oxide film-forming alloy steel, which is the base material, is preferably 58HRC or more on the Rockwell C scale.

[0025] Furthermore, even if the alloy steel for forming oxide films, which has been previously quenched and tempered, is again heat-treated at a temperature range of 500°C or higher and 600°C or lower, the alloy steel for forming oxide films has sufficient temper softening resistance characteristics and can fully ensure a hardness (hardness of alloy steel) exceeding 58HRC.

[0026] In addition, in the above-mentioned oxidation heat treatment process, the alloy steel for forming an oxide film is heat-treated in an atmosphere containing either oxygen or water vapor, or in an atmosphere containing both oxygen and water vapor, thereby forming an oxide film on the surface of the alloy steel for forming an oxide film.

[0027] In this case, it is desirable to carry out the treatment after the final processing such as molding or cutting of the electrolytic corrosion prevention part. This is because even if heat treatment is carried out in an oxygen atmosphere after the final processing, the heating temperature is relatively low at 500 to 600°C, and the dimensional change of the electrolytic corrosion prevention part is very small.

Claims

1. An alloy steel for forming an oxide film, comprising, by weight, 0.01-1.0% C, 0.01-1.0% Si, 0.01-2.0% Mn, 1.0-9.0% Cr, 1.5-6.0% Mo, 0.01-5.0% Al, 0.01-1.2% V, with the balance being Fe and unavoidable impurities.

2. 2. The alloy steel for forming an oxide film according to claim 1, characterized in that it contains, by weight, 0.01-1.0% C, 0.01-0.5% Si, 0.01-1.0% Mn, 1.0-9.0% Cr, 1.5-6.0% Mo, 0.01-5.0% Al, 0.01-1.2% V, 0.01-0.5% W, and the balance being Fe and unavoidable impurities.

3. 3. An electrolytic corrosion prevention part using the alloy steel for forming an oxide film according to claim 1 or 2, characterized in that the surface of the alloy steel for forming an oxide film is coated with an oxide film.

4. 4. The electrolytic corrosion prevention part according to claim 3, wherein the surface hardness of the alloy steel for forming the oxide film is 58 HRC or more on the Rockwell C scale.

5. 4. The method for producing an electrolytic corrosion prevention part according to claim 3, wherein the oxide film is formed on the alloy steel for forming an oxide film in a temperature range of 500° C. to 600° C.

6. 5. The method for producing an electrolytic corrosion prevention part according to claim 4, wherein the oxide film is formed on the alloy steel for forming an oxide film in a temperature range of 500° C. to 600° C.

7. 6. The method for producing an electrolytic corrosion-preventing part according to claim 5, wherein the oxide film is formed on the surface of the alloy steel for forming an oxide film in an atmosphere containing at least either oxygen or water vapor.

8. 7. The method for producing an electrolytic corrosion-preventing part according to claim 6, wherein the oxide film is formed on the surface of the alloy steel for forming an oxide film in an atmosphere containing at least either oxygen or water vapor.