JP2000119838A - Coating type carburizing composition, and carburizing method using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carburizing composition capable of selectively performing carbonization at a specified part and being applied to the inner surface of a formed article and a structure having a sealed space or a semi-sealed structure to perform the carburization, and to provide a carburizing method using the composition. SOLUTION: A carburizing agent and a carburization accelerator inactive to a water paint as necessary are mixed in the water paint. The composition is coated on a part to be carburized of an object to be treated after the surface of the object to be treated to form a carburized layer is purified, dried to form a film, and the object to be treated on which a film is formed is then heated for a sufficient time at a temperature enough to form the carburized layer to form the carburized layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating type carburizing composition for steel and a carburizing method using the same. More specifically, the present invention relates to a coating type carburizing composition in which a carburizing agent and, if necessary, a carburizing accelerator are blended in an aqueous paint, and a carburizing method using the same.

[0002]

2. Description of the Related Art Carburizing treatment for diffusing and infiltrating carbon into the surface of steel is the most widely used method for hardening steel. Generally, the carburizing method includes a solid carburizing method,
There are a liquid carburizing method and a gas carburizing method, both of which are performed using a carburizing agent.

[0003] That is, in the solid carburizing method, a part to be carburized is put in a carburizing box, a solid carburizing agent is filled around the carburizing box and the carburizing agent is heated to 860 ° C or more. At this time, oxygen in the carburizing box reacts with the carburizing agent to generate carbon monoxide and carbon dioxide. In the presence of the carburizing agent (C), the following equation is maintained between carbon monoxide and carbon dioxide.

[0004]

Embedded image

[0005] The carburizing reaction is based on the 2CO =
The nascent C generated by CO ₂ + C is deposited on the surface of the steel material, and the deposited C gradually diffuses toward the inside of the steel material.

In the liquid carburizing method, a method of immersing a part to be carburized in a salt bath containing a carburizing agent is common. In the gas carburizing method, a part to be carburized is put into a carburizing box, and a carburizing gas such as methane, propane, or butane is introduced into the carburizing box, and carburizing is performed by bringing the part into contact with the gas.

[0007] The carburizing method according to these prior arts mainly targets small members and small parts, and is basically based on carburizing the whole members and parts. The applicable range is limited, and only specific parts are selectively carburized. Carburizing was not possible. For example, in an intermediate structure or the like, the hardness of a specific portion is increased, and the wear resistance of the specific portion is imparted. On the other hand, the remaining portion is formed from the viewpoint of workability and cutability for assembling and processing into a final structure. It is often desirable not to impart these properties. In such a case, refractory clay is applied to a portion not requiring carburizing treatment, or SiO ₂ ,
In some cases, carburizing treatment is performed by applying Cu powder using Al ₂ O ₃ or Na ₂ O as an adhesive, but the carburizing prevention effect cannot be said to be sufficient, and there is a disadvantage that it takes time and effort. Was. Further, carburizing may be considered by applying Cu plating to a portion where carburizing is not desired, but has the drawback that it is troublesome and extremely expensive.

In the conventional carburizing method, as described above, parts to be carburized are buried in a carburizing agent, or are treated by contacting with a carburizing gas. Therefore, in these methods, a steel material having a closed space or a semi-closed structure is used. It is extremely difficult to carburize the inner surface of a molded article or structure made of steel. Further, when carburizing is performed on the inner surface of such a molded article or structure, there is a problem that oxidative combustion of the carburizing agent does not sufficiently proceed.
As a field in which it is desired to perform carburizing treatment on the inner surface of a molded article or a structure having such a closed space or semi-closed structure, attention has recently been paid to a technique of transporting powder using a liquid or gas as a carrier. Is illustrated. In slurry transportation, the amount of powder transported can be increased by increasing the solid / liquid ratio and flow rate. In such a case, it is strongly desired to improve the abrasion resistance on the inner surface and the curved portion of the transport steel pipe for transporting the slurry.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to selectively carburize a specific portion which has been impossible with the conventional carburizing method, and to provide a closed space or semi-closed structure. An object of the present invention is to provide a carburizing composition which can be applied to the inner surface of a molded article, a structure, or the like, and which can be carburized, and a carburizing method using the above composition.

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, the use of a composition in which a carburizing agent and, if necessary, a carburizing accelerator are blended in a water-based paint achieves the above object. We have found that we can achieve this and have created the present invention.

That is, the first aspect of the present invention relates to a coating type carburizing composition comprising a carburizing agent and, if necessary, a carburizing accelerator inert to the above-mentioned water-based paint. In the coating type carburizing composition, the aqueous coating is an aqueous coating obtained by dispersing an olefin polymer resin in an aqueous medium, and 10 to 100 parts by weight of charcoal powder per 100 parts by weight of the resin as a carburizing agent. It is preferable to blend 5-80 parts by weight of sodium carbonate per 100 parts by weight of the resin as a carburizing accelerator.

In a second aspect of the present invention, the above-mentioned coating type carburizing composition is applied to a portion of the object to be carburized, dried to form a film, and the object having the film formed thereon is treated. The present invention relates to a carburizing method including a step of forming a carburized layer by heating at a temperature sufficient for forming a carburized layer for a sufficient time.

[0013] The coating type carburizing composition is an aqueous coating obtained by dispersing an olefin polymer resin in an aqueous medium, and is used as a carburizing agent. When 100 to 100 parts by weight and as a carburizing accelerator, 5-80 parts by weight of sodium carbonate per 100 parts by weight of the resin are blended, the coating type carburizing composition is dried at a coating amount of 10 to 100 g /.
As will be m ² was applied to the site to carburizing of the workpiece,
The composition is heated to a temperature sufficient to form a film by drying the composition to form a film, and the object on which the film is formed is heated at 900 to 1200 ° C. for a time sufficient to form a carburized layer. Is preferred.

[0014]

The embodiments of the present invention will be described below. (Water-based paint) The water-based paint used in the coating type carburizing composition according to the present invention is a base which forms a film after drying on the surface of the object to be carburized to form a carburized layer,
The water-based paint is not particularly limited as long as it can form a film on the surface of the object to be treated and does not release harmful substances when the carburized layer is formed by heating. Examples of such a water-based paint include an inorganic water-based paint containing water glass or the like as a main component and an organic water-based paint in which a thermoplastic resin is dispersed in an aqueous medium. In addition, various additives known in the technical field related to water-based paints may be added to these water-based paints as a base, as long as the objects and effects of the present invention are not impaired.

A film can be easily formed in a short time by heating at a relatively low temperature, and the formed film is excellent in adhesion and workability with a steel material to be treated. It is preferable to use an aqueous coating material in which an olefin-based polymer resin is dispersed in an aqueous medium, from the viewpoint that no harmful substance is released even when heated during the formation of the resin. Examples of such an olefin polymer resin include a resin composed of an olefin polymer such as polyethylene and polypropylene;
Resins composed of olefin-based copolymers such as propylene copolymers and blended polymers of these can be mentioned, and these can be used alone or as a mixture of two or more. In addition, these resins have properties as a water-based paint,
It is preferable to use a powder having an average particle size of about 0.1 to 3 μm in consideration of the formation of a film on the workpiece and the workability. In addition, these resins are used in an amount of 10 wt.
It is preferred to mix in an amount of about 40 parts by weight. Further, a small amount of an organic solvent, an antifoaming agent or the like for improving wettability may be added.

(Carburizing agent) In the coating type carburizing composition of the present invention, a carburizing agent is blended with the above-mentioned aqueous paint.
Examples of the carburizing agent used at that time include graphite powder, carbon black powder, and charcoal powder, and these can be used alone or as a mixture of two or more kinds.
The present inventors have conducted a thermal analysis of these carburizing agents in the atmosphere. As a result, graphite powder rapidly oxidized and burned at around 750 ° C., but a portion did not burn even after the temperature was raised to 1000 ° C. or more. It remained. In contrast, carbon black rapidly oxidized and burned at 650 ° C, and charcoal powder rapidly oxidized and burned at around 500 ° C. Further, with carbon black and charcoal powder, no residual weight was observed after the temperature was raised to 1000 ° C. or higher. From these experimental results, as a carburizing agent for forming a uniform carburized layer by a short heat treatment, carbon black and charcoal powder, which can rapidly oxidize and burn at low temperatures and increase the carburizing gas pressure, are more preferable. Is charcoal powder.

(Carburizing Accelerator) In the coating type carburizing composition of the present invention, when heating to form a carburized layer, CO _{2 is used.}
It is preferable to add a carburizing accelerator for the purpose of increasing the pressure and promoting carburization. In particular, when performing a carburizing heat treatment on a molded product or a structure having a structure such as a closed space, a semi-closed space,
That is, the carburizing accelerator plays an important role under conditions where the oxygen for oxidizing and burning the carburizing agent is lean, so that it is necessary to mix the carburizing accelerator with the coating type carburizing composition of the present invention. Such carburization promoter, when added to an aqueous coating composition comprising a base, at the time of heating for forming the storage time and film coating type carburizing composition generates no gas, such as CO _2, the carburization temperature There is no particular limitation as long as a gas is generated for the first time when heated. These carburizing accelerators are determined depending on the type of the aqueous medium used and the method of forming the film, but sodium carbonate and its equivalents are preferred. For example, in the case where the base coating is an aqueous coating obtained by dispersing an olefin-based polymer resin in an aqueous medium, barium carbonate (BaCO ₃ ) is used as a base coating to reduce CO ₂ during dispersion blending. It is not preferable to use potassium permanganate (K ₂ MnO ₄ ) because O ₂ is generated at the time of dispersion blending.

(Blending) In the coating type carburizing composition according to the present invention, a carburizing agent and, if necessary, a carburizing accelerator inert to the above-mentioned water-based paint are blended in the water-based paint. It is appropriately selected in consideration of the physical properties of the film to be formed, the viscosity of the paint, the generation time of the carburizing gas, and the like.

A specific example of a composition using an aqueous paint prepared by dispersing an olefin polymer in an aqueous medium as an aqueous paint, and using charcoal powder as a carburizing agent and sodium carbonate as a carburizing accelerator will be described below. I do.
The hardness of the carburized layer to be formed is set to 600 or more in Vickers hardness, the thickness of the carburized layer is set to 1 to 500 μm, and the applicability of the composition, the pot life of the composition, the carburizing property of the composition, etc. are examined and an appropriate composition is determined. decide.

The amount of charcoal powder added as a carburizing agent is as follows.
The amount is preferably from 10 to 100 parts by weight, particularly preferably from 30 to 80 parts by weight, per 100 parts by weight.
If the compounding amount of the charcoal powder exceeds 100 parts by weight, the resin content is insufficient, the adhesion and workability of the formed film to the object to be treated are reduced, and the viscosity of the coating when applied is significantly increased, It is not preferable because it becomes difficult to apply by dipping, brush coating, roll coating or the like. Conversely, if the compounding amount is less than 10 parts by weight, it takes a long time to generate carburizing gas, and a long time is required for the carburizing heat treatment, which is not preferable.

The addition amount of sodium carbonate as a carburizing accelerator is preferably from 5 to 80 parts by weight, particularly preferably from 15 to 50 parts by weight, per 100 parts by weight of the resin.
If the compounding amount of the carburizing accelerator is less than 5 parts by weight based on 100 parts by weight of the resin, the effect as the carburizing accelerator is undesirably reduced. Conversely, when the amount exceeds 80 parts by weight, the liquid properties of the composition are reduced, and the pot life is undesirably shortened.

(Carburizing Method) A method of performing a carburizing process using the coating type carburizing composition according to the present invention thus formulated will be described below. The object to be carburized using the composition of the present invention is not particularly limited as long as it is a steel material that has been conventionally carburized. In particular, it is notable that a specific portion of a steel material can be selectively carburized, and a molded product or structure having a closed space or a semi-closed structure can be subjected to carburization. .

In the carburizing method according to the second aspect of the present invention, it is preferable that the part to be carburized as a pretreatment is first cleaned by alkali degreasing, washing with an organic solvent or the like. This cleaning method is not particularly limited as long as an appropriate film is formed after the coating type carburizing composition according to the present invention is applied and dried, and then a uniform carburized layer is formed when carburizing treatment is performed.

The coating type carburizing composition according to the present invention is applied to the surface of the object to be treated thus cleaned, and the application method at this time takes into consideration the part of the object to be carburized which requires carburizing. Is appropriately selected from coating methods used in the field of aqueous paints. Examples of such coating methods include brush coating, roll coating, spray coating, blade coating,
Knife coating, immersion, and the like. The coating amount of the coating type carburizing composition at this time is appropriately selected in consideration of the material of the object to be treated, the thickness of the carburized layer, and the like.
It is preferable to apply the coating so as to be 0 g / m ² . If the amount of the dried film exceeds 100 g / m ² , the adhesion and workability of the film deteriorate, which is not preferable. Conversely, the dry film amount is 10
If it is less than g / m ² , the carburizing source becomes insufficient and a long heating time is required to obtain a desired carburized layer, which is not preferable.

The coating-type carburizing composition according to the present invention coated in this manner is dried to form a film. The drying method depends on the water-based coating component used as the base of the coating-type carburizing composition to be used. That is, when using an inorganic water-based paint such as water glass, it is dried by natural drying or the like, and when a dispersion liquid obtained by dispersing a thermoplastic resin such as an olefin polymer resin in an aqueous medium is used as a base of the water-based paint. Is heated to a temperature above the boiling point of water and above the melting point of the resin used. For example, when an olefin polymer resin is used, 10
A film is formed by heating to 0 to 150 ° C.

After a film is formed on a desired portion of the object to be treated in this manner, heating is performed at a carburizing heat treatment temperature. The heating temperature at this time is appropriately selected depending on the type of the carburizing agent to be used, the application amount, and the like. You. For example, when using charcoal powder as a carburizing agent, a temperature range of 900 to 1200 ° C. is preferable from the viewpoint that a carburized layer can be formed by a short heat treatment. The carburizing heat treatment is performed by a method known in the art, such as heating in a furnace, high-frequency heat treatment, and the like. It is also possible to perform a metal surface treatment such as quenching subsequent to the carburizing treatment.

[0027]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples. (Workpiece) In the examples of the present invention, a low alloy steel having the following composition was used as a workpiece.

Steel component weight% C 0.234 Mn 0.440 Cr 0.300 Si 0.227 Ni 0.030 Al 0.030 Ti 0.016 P 0.008 S 0.002 B 0.0040 N 0040 Fe balance

(Coating type carburizing composition) As the coating type carburizing composition of the present invention, paint 1 or paint 2 having the following composition was used. Ingredients Paint 1 Paint 2 Polyethylene resin 100 parts by weight 100 parts by weight Charcoal powder 50 parts by weight 50 parts by weight 40 parts by weight of sodium carbonate 50 parts by weight

[Example 1] A steel plate (1.6 mm thick, 80 mm wide, 150 mm long) composed of the above components was degreased and then coated on one side with paint 1 so as to have a dry film amount of 50 g / m ^2. Then, the film was heated at 120 ° C. for 1 minute to form a film. The steel sheet having a film formed on one side in this manner is shown in FIG.
As shown in the figure, and inserted into a stainless steel foil bag. After tightly bending the open part of this stainless steel foil bag and enclosing the steel plate,
This was inserted into a muffle furnace heated to 1100 ° C. to perform a carburizing heat treatment. Eight minutes later, the stainless steel foil bag enclosing the steel sheet was taken out, and the carburizing heat treatment was completed. At this time, the steel sheet required 3 minutes to rise to 1100 ° C.
For 5 minutes. The hardness of the steel sheet after the carburizing treatment was measured. Table 1 shows the results. Further, the cross-sectional structure was separately observed to evaluate the formed carburized layer.

[0031]

[Table 1]

As shown in Table 1, on the surface to which the coating-type carburizing composition was applied (coating surface coated with paint 1), the Vickers hardness was 211 to 182 at a depth of about 150 μm from the surface layer. (A part of about 0.8 mm from the Vickers hardness 172). Further, as a result of observation of the cross-sectional structure, it was confirmed that a carburized layer had been formed. On the other hand, on the surface where the coating-type carburizing composition was not applied (the surface on which the coating 1 was not applied), the surface hardness showed a measured value almost equal to the hardness at the center of the plate thickness as is clear from Table 1. As a result of observation of the cross-sectional structure, it was confirmed that a carburized layer was not formed. From these results, it can be seen that carburization is selectively performed only on the surface to which the coating-type carburizing composition according to the present invention has been applied.

(Example 2) A steel pipe made of the above high-tensile steel material (sheet thickness 4.0 mm, pipe outer diameter 26.5 mm, pipe length 150 m)
m), paint 2 was injected into the inner surface, and the amount of adhesion was controlled by a method of dripping the surplus.
/ M ^2, and dried at 120 ° C. for 90 seconds to form a film on the inner surface of the steel pipe. This steel pipe was moved vertically in the high-frequency heating coil shown in FIG. 2 and heated (moved from the pipe end to the pipe end in 30 seconds). Heating temperature is about 1
100 ℃, the steel pipe passes through the high-frequency heating coil, about 1
After 0 seconds, water quenching was performed to complete the carburizing and quenching treatment.

Table 2 shows the measurement results of the hardness of the carburized and hardened steel pipe. Further, the cross-sectional structure was separately observed to evaluate the formed carburized layer.

[0035]

[Table 2]

From the result of observation of the cross-sectional structure, it was found that a carburized layer was formed at a depth of about 75 μm on the inner surface of the steel pipe. Also, from Table 2, the hardness of the formed carburized layer was 946 to 639 in Vickers hardness, which was higher than the Vickers hardness 478 at the center of the plate thickness (at a position about 2 mm from the surface).

As is clear from the above results, the coating type carburizing composition according to the present invention containing a carburizing agent and a carburizing accelerator was applied only to the inner surface of a steel pipe, and dried to form a film. It was found that a sufficient carburized layer was formed even on the inner surface of a small-diameter steel pipe where oxidation combustion of the steel did not proceed sufficiently.

[0038]

As described above, according to the present invention, a coating type carburizing composition comprising a water-based coating material and a carburizing agent is applied only to a portion requiring carburizing and dried to form a film. By performing carburizing heat treatment using this film as a carbon source, a carburized layer can be selectively formed efficiently in a short time.

Further, in the conventional method, the carburizing agent and the above-mentioned aqueous solution are contained in the aqueous coating on the inner surface of a molded article or a structure having a closed space or semi-enclosed space structure in which the oxidizing combustion of the carburizing agent does not sufficiently proceed. A coating type carburizing composition comprising an inert carburizing accelerator mixed with a paint is applied and dried to form a film, and the film is subjected to a carburizing heat treatment using the film as a carbon source, so that such a portion is formed. It is also possible to efficiently form the carburized layer in a short time.

[0040]

[Brief description of the drawings]

FIG. 1 is a perspective view showing a state in which a coating-type carburizing composition according to the present invention is applied to one side and a steel sheet formed into a film is inserted into a stainless steel foil bag.

FIG. 2 is a cross-sectional view showing an outline of performing a carburizing heat treatment on a steel pipe by high-frequency heating.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bag made of stainless steel 2 Steel plate 3 Steel pipe 4 High frequency heating coil 5 Tube end sealing core 6 Water cooling device

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masahiro Murakami 7-7 Takatani Shinmachi, Ichikawa City, Chiba Prefecture Nisshin Steel Research Institute (72) Inventor Kenji Okishi 7th Takatani Shinmachi, Ichikawa City, Chiba Prefecture 1 Nisshin Steel Corporation Technical Research Institute (72) Inventor Kenichi Shinoda 34 Hamacho, Gamagori-shi, Aichi Prefecture In-house (72) Inventor Toshifumi Kamachi 34-Hamacho, Gamagori-shi, Aichi In-house

Claims (5)

[Claims] 1. A coating type carburizing composition comprising a water-based paint and a carburizing agent. 2. The coating type carburizing composition according to claim 1, further comprising an inert carburizing accelerator for the water-based paint. 3. The water-based paint is an aqueous paint obtained by dispersing an olefin polymer resin in an aqueous medium, and 10 to 100 parts by weight of charcoal powder per 100 parts by weight of the resin as a carburizing agent, and a carburizing accelerator. The above resin 10
The coating type carburizing composition according to claim 2, wherein 5-80 parts by weight of sodium carbonate is blended per 0 parts by weight. 4. The coating-type carburizing composition according to any one of claims 1 to 3, which is applied to a portion of the object to be carburized and dried to form a film, and the film is formed. A carburizing method, comprising a step of heating an object to be treated at a temperature sufficient for forming a carburized layer for a sufficient time to form a carburized layer. 5. An aqueous coating composition obtained by dispersing an olefin polymer resin in an aqueous medium, 10 to 100 parts by weight of charcoal powder per 100 parts by weight of the resin as a carburizing agent and 100 parts by weight of the resin as a carburizing accelerator. A coating type carburizing composition containing 5 to 80 parts by weight of sodium carbonate per part is applied to a part to be carburized of the object to be treated so as to have a dry film amount of 10 to 100 g / m ^2, and the composition is dried. Heating the film to a temperature sufficient to form a film to form a film, and heating the formed film at 900-1200 ° C. for a time sufficient to form a carburized layer, thereby forming a carburized layer. , Carburizing method.