JPH04193965A - Method for composite surface treatment of cast iron material - Google Patents

Abstract

PURPOSE:To form a film excellent in rust proofing effect and having metallic luster on the surface of cast iron parts with tight adhesion by removing molding sand on the surface and graphite in cast iron parts, thereafter forming an Fe3O4 film, furthermore applying multiple layered electroless plating of Ni to its surface and executing heat treatment. CONSTITUTION:A casting by various cast iron contg. graphite in the structure and stuck with molding sand on the surface is subjected to electrolytic treatment in a molten salt bath constituted of NaOH and neutral salt to remove the molding sand on the surface and the graphite. Next, for giving rust proofing effect, oxidizing treatment is executed in a steam atmosphere to form an Fe3O4, layer on the surface, and, for providing metallic luster, to which multiple layered plating is applied so that the total thickness of electroless Ni plating with at least >=1mum thickness in each layer shall be regulated to >=5mum. Then, for improving the adhesion of the Ni plating layers, heating treatment is executed in the air at a temp. of <=40O deg.C at which metallic luster is held for time in accordance with the thickness of the casting.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for preventing the formation of red rust on the surface of cast iron castings in which graphite is coated in the matrix.

[Conventional technology] Cast iron containing graphite in the matrix, such as cored malleable cast iron, spheroidal graphite cast iron, vermicular cast iron, and gray cast iron, is heated in cold water.
When applied to hot water supply and drainage parts, it is necessary to prevent the formation of red rust on the cast iron surface in order to prevent the formation of red water. Currently, stainless steel pipe fittings are used as rust-free pipe fittings, but they are expensive and difficult to use as general-purpose pipe fittings. It is desired to develop a surface treatment method that is inexpensive and exhibits rust prevention performance and metallic luster comparable to that of stainless steel.

Today, surface treatment methods that exhibit corrosion and wear resistance on film surfaces include hot-dip aluminum plating, nitriding, and electroless N1
Plating etc. are known.

In Japanese Patent Publication No. 58-25745, F e3 was applied to the surface of cast iron.
A method of improving corrosion resistance and wear resistance by forming a 04 film is described in JP-A-58-71377, a method of obtaining corrosion-resistant cast iron by forming a stable iron oxide (CFe30a, etc.) on the surface of cast iron. is disclosed.

Further, US Patent No. 71-748668/47 discloses a descaling and degraphitizing method called molten salt electrolytic treatment.

[Problems to be Solved by the Invention] The antirust effect on the cast iron surface by coating graphite on the surface is to prevent the occurrence of rust by forming a film on the metal surface that is free of cracks and pinholes. If foundry sand or graphite exists on the cast iron surface, the surface treatment film will not be completely formed on the cast iron surface due to interference from the graphite, and a local battery will be formed between it and the locally exposed base, resulting in red rust. The present inventor has clarified that. Therefore, individual treatments such as hot-dip aluminum plating, nitriding treatment, and electroless Ni plating are not recommended as surface treatment methods for the purpose of rust prevention for cast iron with graphite in the base or castings with molding sand adhering to them. It's not perfect.

Also, JP 58-25745 and JP 58-7137
7 is a treatment for cast iron surfaces, but it does not take into account the removal of graphite from the treated surface, and it is difficult to completely prevent red rust that forms between incomplete films that are interfered with by graphite. It is. Moreover, no metallic luster is observed on the surface after treatment.

U.S. Patent No. 71-746663/47 is known as a method for degraphitizing the surface of cast iron, and this is used as a pretreatment method to improve the brittleness of cast iron during brazing. Therefore, no study has been conducted as a pretreatment to improve the rust prevention effect.

Furthermore, with the various conventional surface treatment methods mentioned above, even if an anti-rust effect is achieved, the color of the treated surface is black or gray. is unreasonable to apply.

An object of the present invention is to provide a surface treatment method that has an anticorrosion effect and imparts metallic luster.

[Means for Solving the Problems] In order to solve the above problems, the present invention first uses a molten salt electrolytic treatment method to expose the surface of cast iron to a depth of about 50 μm, which interferes with the formation of a surface treatment film. After removing the molding sand and graphite, Fe
A film of zoa of about 1 to 30 μm is formed on the cast iron surface. That is, by removing the graphite on the surface of the cast iron that obstructs the formation of a rust preventive film through molten salt electrolytic treatment, it is possible to form a uniform and complete rust preventive film over the entire surface of the cast iron. Next, the treated surface is coated with at least one electroless Ni plating film having a thickness of about 5 μm to 30 μm for the purpose of imparting a silvery white metallic luster. Further, for the purpose of improving the adhesion of the Ni plating film, heat treatment is performed in the atmosphere at a temperature of 400° C. or lower at which the metallic luster of the plating film is maintained. In addition, heat treatment at temperatures above 300°C in the air will oxidize the plating film, causing loss of metallic luster and color spots. Do it inside.

[Independent surface treatment of the cast iron surface that retains graphite in the active core did not show a complete rust prevention effect, but it removed foundry sand and graphite on the cast iron surface that interfered with the formation of the surface treatment film. Later, Fe30z was added to the surface by oxidation treatment in a steam atmosphere.
To form a film of 100% and achieve a complete rust prevention effect, at least 100% of the treated film is added to make the surface beautiful.
By applying the composite surface treatment of the present invention, which is characterized by a thin layer or more of electroless Ni plating film, it exhibits an excellent rust prevention effect and maintains a silvery-white metallic luster γk comparable to that of stainless steel. It's an excellent thing to do. In addition, when the thickness of the electroless Ni plating film is 5 μm or less, no metallic luster is exhibited and the base color appears through the plating film.

Example] An example of the surface treatment method of the present invention will be described according to the following example.

The method of this example consists of the following steps: (a) degraphitization treatment, (b) surface oxidation treatment, (c) electroless Ni plating treatment, and (d) film stabilization heat treatment. Each step will be explained in detail below.

(B) Degraphitization process by molten salt electrolysis treatment. As a pretreatment, hydroxide is used for the purpose of removing graphite on the surface of the cored malleable cast iron sample.) A bath consisting of IJium and neutral salts at a temperature of 4.
The sample is immersed in an alkaline redox bath at 60°C, and the sample surface is cleaned by electrolytic treatment. The electrolysis procedure is (1
) The sample is held at the cathode and sand and oxide film on the sample surface are removed by reducing action. (2) The sample is held at the anode and the graphite on the surface of the sample is removed by reaction with a salt bath agent by oxidation. (3) The oxide film formed on the surface of the sample in step (2) is removed by reduction by holding the sample again at the cathode.

After that, after cooling to room temperature by air cooling and water cooling,
Wash with 0°C hot water.

(b) Surface oxidation treatment step After the treatment step in (a) above is completed, the sample is left in a steam atmosphere at about 400°C for about 1 to 60 minutes to form a FezOa layer of about 1 μm to 30 μm on the sample surface. .

(c) Electroless Ni plating treatment process In order to impart a silvery white metallic luster to the sample surface, the above (
The surface of the sample on which step (b) has been completed is subjected to hydrogen reduction treatment or shot peening treatment at least once to clean and activate the surface, and then electroless Ni plating treatment is applied to the sample surface to a thickness of about 5 μm to 30 μm. Apply with a film thickness of

In addition, in the electroless Ni plating process, the first plating layer is a Ni-P plating layer with a phosphorus content of 9%, and the second layer is a N1-P plating layer with a phosphorus content of 1%. It may also be composed of a plating layer.

If the film thickness is less than 5 μm, the color of the base will show through, making it impossible to obtain metallic luster, and if it is more than 30 μm, the total film thickness will become too thick to be used.

(d) Film stabilization heat treatment process In order to improve the adhesion between the Ni plating film on the surface of the sample and the base, after the step (c) above is completed, approximately 200°
Heat treatment is performed at a temperature of C for about 1 hour in an air atmosphere.

By performing the above composite surface treatment, it is possible to form a surface treatment film on the cast iron surface with a total thickness of approximately 50 μm or less, which has rust prevention properties and develops a silvery white metallic luster. .

In this way, by keeping the total thickness of the surface treatment film that has a rust-preventing effect to 50 μm or less, preferably 3゜μm or less, it can be applied to areas where the accuracy of combination with threaded parts is a problem. Application becomes possible.

Figure 1 shows the state of the surface treatment film of the sample treated according to the above example, or the surface treatment film has invaded the holes where graphite that was exposed on the cast iron surface was removed. It shows the situation. Furthermore, the film itself maintains continuity.

FIG. 2 shows the surface treatment film of a sample in which the degraphitizing step (a) in the above example was omitted.

Figure 3 shows the average occurrence of red rust on the surfaces of 10 samples when immersed in tap water at a temperature of 125°C for one week. In sample A, which was subjected to electroless Ni plating treatment, rust formed on the sample surface although the metallic luster was maintained.
In sample B, which was subjected to degraphitization treatment and nitridation treatment, the occurrence of rust was significantly reduced, but the metallic luster disappeared. on the other hand,
In sample C of the present invention, almost no rust was observed even after being immersed for one week, and the metallic luster on the surface remained as it was at the beginning of the test.

[Effects of the Invention] As is clear from the above explanation, the composite surface treatment method of the present invention can be applied to cast iron castings, which are cheaper than stainless steel, to prevent the occurrence of red rust on the surface, and to prevent the occurrence of red rust on the surface. +s4 is now used as a rust-free pipe fitting, as it maintains the same metallic luster as white stainless steel.
[ff] It can be applied as a substitute for stainless steel pipe joints, and to parts for water supply and drainage for cold water and hot water, where the generation of red water is a problem.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the state of the surface treatment film of a sample in which cored malleable cast iron was subjected to degraphitization treatment, followed by surface oxidation treatment and electroless Ni plating treatment. FIG. 2 is a diagram showing the relationship between the surface treatment film and graphite of a sample subjected to surface oxidation treatment and electroless N1 plating treatment when core malleable cast iron is subjected to degraphitization treatment. FIG. 3 is a diagram showing the average occurrence of red rust and metallic luster on the surface of a sample when immersed in tap water at a water temperature of 25° C. for one week. 1: Ni plating layer 2: Fe30n layer 3: Graphite 4: Fe base 5: Traces of graphite falling off 6: Discontinuity of plating film Figure 1 Figure 2 Figure 3 BC Sample

Claims (4)

[Claims] 1. (b) A process of removing casting sand and/or graphitization from the surface of a cast iron material having graphite in the matrix by molten salt electrolysis treatment, (b) Providing anti-corrosion properties on the surface of the rough material by oxidation treatment. Step of forming a film of Fe_3O_4, (c)
At least one layer of electroless Ni plating film is formed on the treated surface of the cast iron material, each layer having a thickness of 1 μm or more, and each layer having a total thickness of 5 μm.
A method for composite surface treatment of cast iron materials, characterized by comprising a step of coating with a film thickness of at least 100%. 2. 2. The composite surface treatment method for cast iron materials according to claim 1, further comprising adding a decarburization treatment step by heat treatment before the step (a). 3. The surface treatment film formed in the step (c) above is heat-treated in an atmospheric atmosphere at a sample surface temperature of 400 ° C. or less for a time depending on the thickness of the sample, and then in the steps (a) to (c) above. A composite surface treatment method for cast iron materials, characterized by comprising the steps of: 4. Heat-treating the surface treatment film formed in steps (a) to (c) above at a sample surface temperature of 300°C or higher for a period of time depending on the thickness of the sample in an inert gas atmosphere substituted with oxygen. A composite surface treatment method for cast iron materials, characterized by: