JP3242060B2 - Room temperature carburizing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a treated product made of a steel material of a special steel such as carbon steel or alloy steel, tool steel, special purpose steel or a mixture thereof, and a product made of a non-ferrous metal material such as aluminum. Regarding the metal surface treatment method as a carburizing treatment performed for the purpose of improving the wear resistance etc. of the treated product, especially the treated product composed of low carbon steel or low carbon content special steel, the surface of the treated product is treated with carbide powder. The present invention relates to a normal temperature carburizing method capable of injecting a body and diffusing a carbon element in the carbide powder to a surface of a product to be treated to obtain a deeper carburizing layer.

[0002]

2. Description of the Related Art Conventionally, for example, methods for improving the wear resistance of steel include quenching, nitriding, various plating methods, and carburizing.

[0003] Quenching is a process in which steel is heated to an austenitic structure and then quenched in a coolant to generate a martensite structure and increase the hardness.

[0004] Nitriding includes gas nitriding and liquid nitriding. For example, in gas nitriding, an alloy steel such as aluminum or chromium is kept at a high temperature in ammonia gas to diffuse nitrogen into the surface layer of the steel to form a hard nitride. This is a process for forming a layer.

[0005] In various plating methods, hot-dip plating,
Diffusion infiltration plating, electroplating, etc., for example, hot-dip plating is a plating method performed by immersing a product to be treated in a molten metal bath and pulling it out of the metal bath after a predetermined time elapses. There are zinc plating and hot-dip tin plating.

[0006] Carburizing treatment is generally a treatment in which low-carbon steel or low-carbon special steel is heated in a carburizing atmosphere to increase the carbon content of the surface layer of the steel.
Solid carburizing method, gas carburizing method, and liquid carburizing method,
Among them, the gas carburizing method has advantages in that the surface carbon concentration can be adjusted and mass production is possible, and the gas carburizing method is mainly used. After this carburizing treatment, the surface is hardened by quenching.

[0007]

The conventional method for hardening steel has the following problems.

(1) In quenching, for example, when quenched into high carbon steel, there is a problem that the whole hardens and becomes brittle, and the fatigue strength decreases.

[0009] In addition, the product to be processed is deformed due to thermal strain, transformation strain, and strain due to a shift in transformation time caused by the quenching operation due to quenching, and the effect of the deformation is a serious problem particularly in pressed parts. There is a problem that the equipment cost of the quenching process is high.

(2) In the nitriding treatment, the deformation is smaller than that of quenching, but there is a problem that the cost of chemicals used is high and the equipment cost is high.

(3) In various plating methods, for example, in a hot-dip plating method, a molten liquid metal for immersing a solid metal product is required, and therefore, a heating facility for constantly maintaining the liquid metal in a molten state. There are problems such as high cost and pollution problems such as environmental pollution due to harmful vapor generated during processing using harmful chemicals.

(4) In the case of carburizing, in addition to the high possibility of occurrence of an abnormal carburizing layer serving as a decarburized layer and high equipment costs, special knowledge is required for the processing operation, and explosion occurs. There was a danger.

The present invention has been developed in order to solve the problems in the course of the process. The carbon element is diffused to the surface of the article to be treated by relatively inexpensive equipment and at ordinary temperature, and the resistance of the article to be treated is improved. It is an object of the present invention to provide a room temperature carburizing method capable of improving abrasion and fatigue strength.

[0014]

In order to achieve the above object, the cold carburizing method of the present invention is applied to a surface of a product to be treated made of, for example, carbon steel or special steel or a mixture thereof.
Preferably, higher hardness and higher melting point than the article to be treated,
The method is characterized in that a carbide powder is sprayed to diffuse a carbon element in the carbide powder to a surface of a product to be treated.

Preferably, the carbide powder is injected at an injection speed of 80 m / sec or more or an injection pressure of 0.3 MPa or more.

The article to be treated is widely used as a metal material,
Including low-carbon steel with a carbon content of about 0.15% or less or special steel with a low carbon content, including those made of non-ferrous metal materials such as steel and aluminum, the effect of improving the wear resistance of the product to be treated can be improved. Will be noticeable. Further, carburizing can be performed on a decarburized layer of an abnormal carburized layer by a known carburizing process.

The carbon steel exemplified here is an alloy of iron and carbon and usually has a carbon content of 0.02% to about 2%, and a small amount of silicon, manganese, phosphorus, sulfur, etc. The special steel is a steel in which a special element is inserted into carbon steel to exhibit special properties, and includes alloy steel, tool steel, special use steel, and the like.

The carbide powder is, for example, B ₄ C, Si
C, preferably, a powder of a carbide such as SiC (α), TiC, or VC, having an average particle size of 80 μm to an average particle size of 300 μm
Powder, depending on the implementation, preferably the average particle size is 80μ
Use fine powder of m or less.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION When a carbide powder is jetted at a high speed onto the surface of a processed product made of a metal material, the law of energy invariance is obtained by a change in the speed of the powder before and after collision with the surface of the processed product. When considered, heat energy is generated. Since this energy conversion is performed only at the deformed portion where the carbide powder collides, a local temperature rise occurs near the surfaces of the carbide powder and the article to be treated.

Since the temperature rise is proportional to the speed of the carbide powder before collision, increasing the speed of the carbide powder can increase the temperature of the surfaces of the carbide powder and the article to be treated. . At this time, it is considered that the carbide powder is heated on the surface of the article to be treated and further thermally decomposed, and the carbon element in the carbide forming the carbide powder is activated and adsorbed on the surface of the article to be treated and diffuses and penetrates. Can be

Therefore, the cold carburizing method of the present invention is different from the carburizing treatment in the conventional surface hardening treatment,
When the carbide powder collides with the steel product to be processed by blasting, the carbon powder in the carbon powder generated by the thermal decomposition and the decomposition of the carbon powder generated by the temperature rise is applied to the surface of the product to be processed. Carburizing is performed by diffusion infiltration.

When the carbide powder collides with the article to be treated, the temperature of the carbide powder and the article to be treated partially rises. However, since the treatment is actually carried out at normal temperature, the carburizing treatment of the present invention is carried out in the present invention. In the specification, it is referred to as “normal temperature carburizing treatment”.

To explain in more detail, taking as an example the gas carburizing process generally performed, the carburizing atmosphere gas is methane (CH ₄ ), propane (C ₃ H ₈ ) or butane (C ₄
A hydrocarbon-based gas H _10), a mixture of air at a constant rate used as a raw material. When this mixed gas is heated, carbon monoxide (CO), hydrogen (H ₂ ), and nitrogen (N ₂ ) are generated by an endothermic reaction. Carburization mainly involves thermal dissociation of this CO gas represented by the following formula. The activated carbon produced is reacted with Fe in the steel.

2CO = C + CO ₂ That is, if the CO gas is merely physically attached to the surface of the steel so that the CO gas can be easily removed by an external force, heating or other physical method, the Fe and CO gas in the steel will not be obtained. Cannot cause a reaction, but when heat or other energy is given for a certain amount or more, CO gas is activated and adsorbed on the surface of Fe.
It is considered that the activated adsorbed CO gas thermally dissociates into carbon dioxide and carbon, and activated carbon generated by this reaction diffuses into the lattice of Fe to cause carburization.

Here, a problem in the gas carburizing process is that, in order to control the amount of carbon to be diffused to a target concentration, in addition to the main reaction, the equilibrium state of H ₂ , CO gas, H ₂ O, etc. This requires specialized knowledge, such as deepening the understanding of the side reaction, which indicates, and understanding the relationship between the components and concentrations of the carburizing atmosphere gas.

In consideration of the above-described phenomenon in the conventional gas carburizing treatment, it is considered that the following carbon diffusion phenomenon occurs in the normal temperature carburizing treatment of the present invention.

For example, when carbide powder is sprayed on the surface of a product to be treated made of carbon steel and collides with the surface of the product to be treated, the powder rebounds, but after the collision, the speed is reduced. The ratio of the speed before and after the collision, that is, the coefficient of restitution is the material of the product to be treated,
Depending on the hardness, the lost kinetic energy is largely converted to thermal energy other than sound from the law of energy invariance. Thermal energy is considered to be internal friction due to deformation of the collision part of the product to be processed at the time of collision, but heat is exchanged only at the deformed part where the injected carbide powder collided, so the temperature becomes partially high . At this time, it is considered that the carbide powder is thermally decomposed because it is heated on the surface of the article to be treated, and activated carbon in the carbide powder is activatedly adsorbed and diffused into the article to be treated.

In the present invention, the surface of the article to be treated is not heat-treated by heating, but rather, the injected carbide powder is heated to cause a thermal decomposition reaction, and the generated carbon element is removed from the surface of the article to be treated. Therefore, the carbide powder needs to have a higher hardness and a higher melting point than the product to be treated. Conversely, when heat-treating the surface of the article to be treated, it is necessary to use a powder having a higher hardness and a higher melting point than the article to be treated.For example, when using a carbide powder as the powder, It is considered that the carbide powder does not thermally decompose, but penetrates and disperses inside the surface of the article to be treated.

As described above, the carbide powder used in the present invention is composed of carbide, which is generally lower in density than metal (eg, SiC: 3.2 g / cm ³ , B ₄ C: 2.5 g / cm ³⁾ . ³ ) Deformation at the time of collision is small even if it is injected at high speed to the product to be treated. Therefore, in the present invention, compared to the conventional gas carburizing method that requires heating the whole product to be processed to a high temperature, etc. Deformation of the product to be treated is small and carburizing is possible.

[Blasting Apparatus] The blasting apparatus may be a direct pressure type, a suction type gravity type, or another blasting apparatus as long as it is an air type. Here, the direct pressure type blasting apparatus will be described.

In FIG. 1 and FIG. 2, reference numeral 51 denotes a cabinet of a blasting device 50, which is provided with a charging port 53 for charging a product to be processed, and an injection nozzle 52 for spraying an abrasive onto the product to be processed supplied from the charging port 53. Are provided in the cabinet 51.

A hopper 58 is provided at a lower portion of the cabinet 51, and a lowermost end of the hopper 58 communicates with an upper portion of a collection tank 40 for collecting abrasives provided near the cabinet 51 via a conduit 55. .

The recovery tank 40 is a so-called cyclone.
As shown in FIG. 1, a tank for separating dust from an abrasive material, comprising a cylindrical portion 41 having a cylindrical shape at an upper portion, and a conical portion 42 having a conical shape gradually narrowing downward at a lower portion. Then, an inlet 43 is provided on the upper side wall of the cylindrical portion 41 of the recovery tank 40, and a conduit 55 is connected to the inlet 43 via a communication pipe 45. The axial direction of the communication pipe 45 is tangential to the inner wall surface of the cylindrical portion 41 having a circular cross section.
The airflow that has flowed into the space 0 descends while rotating along the inner wall of the cylindrical portion 41.

The lower end of the conical portion 42 of the collection tank 40 is connected to a tank 4 for pumping the abrasive through a dump valve 46.
The tank 47 is provided at its lower end with an abrasive adjuster 48 at the lower end of the tank 47 for adjusting the amount of abrasive abrasive injected from the injection nozzle 52. And is in communication with the injection nozzle 52.

The feature of the direct pressure type blasting apparatus is that when compressed air is fed into the tank 47, the abrasive is sent together with the compressed air by the compressed air from the abrasive adjuster 48 at the lower part of the tank 47, and the inside of the pipe 54 is fed. The abrasive is fed toward the injection nozzle 52, and the abrasive is injected from the injection nozzle 52 together with the compressed air to the product to be processed in the cabinet 51.

The dump valve 46 is configured to move up and down by the operation of an electromagnetic valve linked to a foot switch or micro switch (not shown), and to open and close the collection tank 40 and the tank 47 by the up and down movement of the dump valve 46. ing. When the foot switch or the micro switch is actuated, the dump valve 46 is raised to shut off the space between the collection tank 40 and the tank 47, and at the same time, the compressed air is filled in the tank 47, and the abrasive in the tank 47 is pressed by the compressed air. The compressed air and the abrasive are mixed appropriately in the abrasive controller 48 through the abrasive controller 48, and the spray nozzle 5 is passed through a pipe (not shown) through an abrasive supply port 49.
Injected from 2.

Next, when the switch is returned to its original position, the dump valve 46 is lowered to open the space between the collection tank 40 and the tank 47, and the compressed air in the tank 47 escapes into the collection tank 40, and the pressure in the tank 47 becomes atmospheric pressure. become. Immediately before the pressure in the tank 47 becomes the atmospheric pressure, when the dump valve 46 is lowered, the injection of the abrasive is stopped from the injection nozzle 52 immediately, and at the same time, the abrasive accumulated at the bottom of the collection tank 40 falls into the tank 47 at a stretch. .

On the other hand, a connecting pipe 44 is provided substantially at the center of the upper end wall of the recovery tank 40, and this connecting pipe 44
7, and communicates with the dust collector 56.

The dust collector 56 rotates the exhaust fan 59 to discharge the air in the dust collector 56 to the outside air. The air blower 59 causes the cabinet 5 of the blast device 50
1, the inside of the conduit 55 and the collection tank 40 become negative pressure, and the compressed air supplied from the compressor (not shown) is jetted from the jet nozzle 52 together with the abrasive. 40, an air current flows to the dust collector 56.

[Example 1] Using the above-mentioned blasting device 50, SPCC, which is a low-carbon steel having a carbon content of 0.12% or less as a product to be treated, is charged from a charging port 53 into a barrel 64 in the cabinet 51. Then, blasting was performed by spraying the abrasive onto the surface of the workpiece using a spray nozzle 52 under the processing conditions shown in Table 1, using a carbide powder made of SiC, which is a carbide, as an abrasive.

[0041]

[Table 1]

As Comparative Example 1 of Example 1 above, SPCC was blast-processed as a product to be treated under the processing conditions shown in Table 2 by using the above-mentioned “metal surface treatment and heat treatment method” by the present applicant. .

[0043]

[Table 2]

Further, after the processing of the above-mentioned Example 1, the processing steps of the comparative example 1 were further performed to obtain a comparative example 2.

Table 3 shows the results of the measurement of the surface hardness of the articles treated according to Example 1, Comparative Example 2 and Comparative Example 2.
Shown in

[0046]

[Table 3]

From the results shown in Table 3, it can be seen that in Example 1, which was treated by the normal temperature carburizing method of the present invention, carbon diffused and carburized on the surface of the product to be treated, and the surface hardness increased. Therefore, it is considered that the abrasion resistance and the fatigue strength of the processed product itself are increased.

Example 2 Next, blasting was performed under the processing conditions shown in Table 4 using SPHE which is a low-carbon steel having a carbon content of 0.10% or less as a product to be treated.

[0049]

[Table 4]

Further, as Comparative Example 3 of Example 2 above, SPHE was blasted under the processing conditions shown in Table 5 by the “metal surface heat treatment method” in the same manner as in Comparative Example 2.

[0051]

[Table 5]

Table 6 shows the results of the measurement of the hardness and the carbon content of the surface of the product to be treated in Example 2 and Comparative Example 3 described above.

[0053]

[Table 6]

From the results shown in Table 6, although the surface hardness was increased in both Example 2 and Comparative Example 3, in Example 2 by the cold carburizing method of the present invention, carbon in SiC diffused to the surface of SPHE, It can be seen that the carbon content is increased due to the carburizing treatment, and the hardness is increased accordingly.

[0055]

(1) Carburizing treatment can be performed in a short time by blast processing which is relatively inexpensive and has a low possibility of generating pollution, thereby increasing the wear resistance and fatigue strength of a steel product.

(2) It is not necessary to heat the whole product to be processed, and it can be processed at normal temperature. Also, since the carbide powder to be used is a relatively low-density carbide, the product to be processed is less deformed and the defect rate is lower. Deterioration and quality improved.

(3) Further effects can be further enhanced by performing a conventional heat treatment as the secondary treatment.

[Brief description of the drawings]

FIG. 1 is a front view showing a blast device used in an embodiment of the present invention.

FIG. 2 is a plan view showing a blast device used in an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 40 Collection tank 41 Cylindrical part 42 Conical part 43 Inflow port 44 Connecting pipe 45 Communication pipe 46 Dump valve 47 Tank 48 Abrasive conditioner 50 Blasting device 51 Cabinet 52 Injection nozzle 53 Inlet 54 Pipe 55 Pipe 55 Duct 56 Dust collector 57 Discharge pipe 58 Hopper 59 exhaust fan

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 24/00 C23C 26/00

Claims (4)

(57) [Claims] 1. A cold carburizing method comprising: spraying a carbide powder on a surface of an article to be treated made of a metal material; and diffusing a carbon element in the carbide powder to the surface of the article to be treated. 2. The injection of said carbide powder is performed at an injection speed of 80 m /
The room-temperature carburizing method according to claim 1, wherein the method is performed at a pressure of at least sec or a pressure of at least 0.3 MPa. 3. The method according to claim 1, wherein the material to be treated has a carbon content of about 0.1.
The room temperature carburizing method according to claim 1 or 2, wherein the carbon powder is made of a low carbon steel or a special steel having a low carbon content of 5% or less and has a higher hardness and a higher melting point than the target product. 4. The method according to claim 1, wherein the carbide powder is SiC, preferably SiC (α).
The normal temperature carburizing method according to any one of claims 1 to 3.