JP2664276B2 - Metal surface hardening method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for hardening a metal surface, and more particularly to a method for hardening a metal surface using heat of chemical reaction.

2. Description of the Related Art When metal is used as a material for machine parts, industrial equipment, equipment, etc., it is necessary to avoid scratches, cracks, cracks, etc. on the surface, or wear on the surface due to friction. The metal surface hardening treatment performed to prevent the surface damage and wear is an industrially very important technique. In the old days, quenching of steel with water or oil started, and recently, the development of surface hardening methods using advanced technologies such as laser, plasma or electron beam has been widely performed.

Since the surface hardening of the metal is literally for hardening only the surface of the metal, the energy to be applied is preferably essentially concentrated only on the metal surface. However, in the heating by the usual means, the temperature of the processed material becomes uniform to the inside. For this reason, for example, in order to harden the surface of a steel material, it is necessary to go through steps of carburizing, quenching and tempering. Such a process is very complicated and the production efficiency is not good. In addition, the surface hardening of Ti is often due to nitrogen diffusion, but the processing temperature is limited to prevent deformation of the base material,
The processing time extends for several tens of hours. On the other hand, a method of performing surface hardening by concentrating energy on the surface using a laser, plasma, an electron beam, or the like as described above has been implemented. However, these advanced technologies
Inevitably resulted in high costs.

Further, among the metals, the elements of the groups IVa and Va of the periodic table, ie, Ti, V, Zr, Nb, Hf and Ta, have excellent corrosion resistance and are industrially important metals. In particular, Ti is lighter than iron-based metals and has excellent strength and corrosion resistance, so that it is widely used as a material for aircraft and chemical plants. However, since Ti has insufficient wear resistance, a surface hardening treatment is indispensable when it is used as a component such as a sliding portion.

As the surface hardening method of Ti, for example, a plating method, a cyan bath method, a borate bath method, a gas nitriding method, a thermal spraying method or a surface melting method using a high energy beam, etc. have been conventionally proposed. Has disadvantages.

In the plating method, the pretreatment process is complicated, and there is a risk that the Ti product absorbs hydrogen during the plating process and causes hydrogen embrittlement. In the cyan bath method and the borate method, since highly toxic waste liquid is generated, it is difficult to treat the waste liquid. In the gas nitriding method, the metal to be treated is exposed to very high temperatures. For this reason, there is a risk of causing deformation and deterioration of mechanical characteristics, and a processing time of several hours to several tens of hours is required.
Even if processing is performed using plasma, this risk and processing time are not significantly improved. In these plating methods, cyan bath method, borate bath method and gas nitriding method, the entire surface is usually hardened, and it is difficult to heat only a necessary portion of the metal to be processed. In the thermal spraying method, the adhesion between the hardened layer and the base material decreases,
In addition, post-processing is often required. Further, when a method of irradiating the surface with a high energy beam using a laser, plasma, an electron beam, or the like to melt the surface or attach a hard substance is used, the obtained cured layer exhibits excellent characteristics. However, as mentioned above, these advanced technologies inevitably lead to high costs.

[Problems to be Solved by the Invention] The present invention has been made in view of the above circumstances. In order to harden a metal surface, a simple apparatus configuration is used, and in a very short time, good wear resistance is obtained. It is an object of the present invention to provide a method for hardening a metal surface, which makes it possible to obtain a hardened layer.

[Means for Solving the Problems] The present inventors have considered using heat of chemical reaction as a means for intensively heating the surface of a metal to be treated.
For example, the elements of the periodic table IVa group and Va group, namely Ti,
It is known that an aggregate of elemental powders such as V, Zr, Nb, Hf, and Ta causes a chain nitriding reaction in a nitrogen atmosphere.
In most cases, the heat generated by the nitridation reaction causes these powders to instantaneously reach a high temperature of 2000 ° C. or higher. Therefore, the nitridation reaction of these metals is considered to be suitable as a high energy source. However, these reactions are generally difficult to control.

Therefore, the present inventors, as a result of earnest research, by applying a composition containing a powder capable of causing an exothermic reaction with nitrogen to the metal surface, causing an exothermic reaction and performing a heat treatment,
It has been found that the metal surface can be cured while controlling the reaction.

That is, the metal surface hardening method of the present invention is a step of forming a heat generating layer by applying a composition containing a powder capable of causing an exothermic reaction with nitrogen to a metal surface, and forming a heat generating layer on the metal on which the heat generating layer is formed. The method is characterized by including a step of introducing a gas containing nitrogen and a step of heating at least a part of the heat generating layer to start an exothermic reaction, and performing a heat treatment on the metal surface by the exothermic reaction.

The composition containing the powder capable of causing an exothermic reaction with nitrogen contains a binder and a solvent, and the bond and the solvent are preferably decomposed and eliminated in the heat treatment step.

As the metal, a group IVa metal, a group Va metal, or at least two alloys selected from these metals can be used. An alloy containing at least one selected from these metals in an amount of 50 mol% or more can be used.

The gas containing nitrogen preferably consists essentially of nitrogen, ammonia, or a mixture of at least 50 mol% of any of these and an inert gas.

Further, in the method of the present invention, the thickness of the cured layer formed on the metal surface can be adjusted by adjusting the application amount of the composition. Further, by adding a substance not participating in the exothermic reaction to the composition or by interposing a substance not participating in the exothermic reaction between the composition and the metal, the thickness of the cured layer formed on the metal surface is reduced. Can be adjusted.

The heating can be performed by, for example, electric heating or arc heating. Further, as a method of applying the composition, for example, a dipping method or a brush coating method can be used.

[Function] According to the surface hardening method of the present invention, once the exothermic reaction is started by heating a part of the heat generating layer, a reaction occurs in a chain without any need for further heating, electric power and the like, Its linear velocity reaches 1 to 10 cm / sec. Therefore,
The exothermic reaction ends in a very short time. That is, the metal surface can be concentrated and rapidly heated in a short time by an exothermic reaction of the composition applied to the surface without using an expensive device such as a laser. On the other hand, when the exothermic reaction is completed, only the metal surface is heated and the uncured portion, that is, the base material is not heated, so that the metal surface is rapidly cooled.

According to the present invention, when a composition containing a powder capable of causing an exothermic reaction with nitrogen on a metal surface is applied, and the exothermic reaction is performed in an atmosphere containing nitrogen, with simple equipment, in a very short time,
The metal surface can be nitrided without adversely affecting the base material.

Further, according to the present invention, a binder can be mixed into a composition containing a powder capable of causing an exothermic reaction with nitrogen, and can be applied in the form of a paste to a metal surface, regardless of the shape of the metal to be treated. The surface hardening treatment can be performed effectively without any problem. Local nitriding is also possible.

Further, according to the present invention, since the amount of heat generation can be controlled by changing the amount of application of the composition containing the powder capable of generating heat with nitrogen, the curing depth from the surface due to nitriding can be reduced. It can be changed arbitrarily. In addition, the calorific value can be controlled by adding an exothermic reaction product or an additive that does not participate in the exothermic reaction to a composition containing a powder capable of causing an exothermic reaction with nitrogen.

In this way, according to the present invention, only the metal surface can be heated and cooled in a very short time, so that a nitriding treatment with solid solution atoms becomes possible.

EXAMPLES Hereinafter, the present invention will be described specifically with reference to the drawings.

FIG. 1 is a cross-sectional view illustrating a metal sample on which a heating layer is formed. As shown in FIG. 1, according to the present invention, a heat generating layer 2 containing a powder capable of causing an exothermic reaction with nitrogen is formed on a metal sample 1. Metal sample 1 having this heat generating layer 2
Is subjected to an exothermic reaction, for example, in a reactor shown in FIG. The reaction apparatus 12 has a sealable chamber 13 provided with a carbon heater 1 in the apparatus.
A metal sample 1 having a heating layer 2 therein is disposed such that one end of the heating layer 2 is in contact with the carbon heater 11. apparatus
12 is filled with nitrogen.

Hereinafter, various embodiments of the present invention in which the surface of a metal sample is hardened by using such an apparatus will be described.

Example 1 A Ti powder was prepared as a powder capable of causing an exothermic reaction with nitrogen, and a 4% aqueous polyvinyl alcohol solution was added to the Ti powder.
A composition containing a powder capable of causing an exothermic reaction with nitrogen was prepared by adding 0.5% by weight and kneading. Using this composition, while increasing or decreasing the number of coatings,
Change as shown in the table, 10mm using the dipping method
It was applied to five types of industrial pure Ti samples having dimensions of 20 mm x 1 mm and dried to obtain a heat generating layer. The exothermic reaction was started by placing the industrial pure Ti sample on which the heat generating layer was formed in a reactor having a nitrogen atmosphere of 10 atm and bringing a carbon heater into contact with one end of the heat generating layer to energize. The reaction was completed in 2 seconds. After the reaction was completed, the treated Ti sample was immediately taken out of the reactor, and the exothermic layer after the reaction was peeled off. The exothermic reaction converted the exothermic layer to TiN. This TiN was easily peelable. Table 1 shows the curing depth and Hv (Vickers hardness) of the obtained Ti sample. Further, the polyvinyl alcohol used as the binder was decomposed and released by the high heat during the reaction, and did not affect the obtained Ti sample. There was no unevenness on the surface of the cured Ti sample, and no exothermic reaction powder was attached.

Comparative Example 1 Two industrial pure Ti samples similar to those in Example 1 were prepared, and each was subjected to nitriding at 800 ° C. for 20 hours and 40 hours in a nitrogen atmosphere. Hardening depth and Hv (Vickers hardness) of the treated Ti sample were measured. Table 1 shows the results.

As is clear from Table 1, the curing depth can be adjusted by changing the application amount. Also,
According to the present invention, it can be understood that the same curing treatment can be performed in an extremely short time as compared with the conventional case.

Example 2 A composition containing a powder capable of causing an exothermic reaction with nitrogen was applied in the same manner as in Example 1 using a Zr plate having a size of 10 mm × 20 mm × 1 mm. After drying, the weight of the obtained heat generating layer was 2.1 g. Thereafter, an exothermic reaction was performed in the same manner. This reaction was completed in 3.5 seconds. After the reaction was completed, the treated Zr sample was immediately taken out of the reactor, and the reacted exothermic layer was peeled off. The reacted heat generating layer was easily peelable. The obtained Zr sample was cured to a depth of 130 μm from the surface, and its hardness was Hv1100.

Example 3 A mixture was prepared by adding 20 mol% of TaN to Ta, and to the resulting mixture was added 0.5 parts by weight of a 6% by weight ethyl cellulose alcohol solution to prepare a composition containing a powder capable of causing an exothermic reaction with nitrogen. Prepared. This TaN is added to prevent the Ta powder from fusing to the Ta plate during the exothermic reaction. This composition is 10 mm × 20 using the dipping method.
It was applied to a Ta plate with dimensions of mm × 0.5 mm and dried. After drying, the weight of the resulting heat generating layer was 1.8 g. The obtained Ta sample was placed in an atmosphere of 10 atm of nitrogen, a carbon heater was brought into contact with one end of the heat generating layer, and an exothermic reaction was started by energizing. The reaction was completed in 2 seconds. After the reaction was completed, the treated Ta sample was immediately taken out of the reactor, and the exothermic layer after the reaction was peeled off. This heat generating layer was easily peelable. The obtained Ta sample was hardened to a depth of 60 μm from the surface, and the hardness was Hv1800. No unevenness was observed on the Ta surface, and no adhesion of the residual heat generating layer was observed. Ethyl cellulose used as a binder is one that is decomposed and released by high heat during the reaction,
It did not affect the obtained Ta sample.

Example 4 A composition similar to that of Example 1 was applied and dried using a Ti-6Al-4V alloy having a size of 10 mm × 20 mm × 1 mm. The obtained heat generating layer weighed 2.1 g. Further, an exothermic reaction was started in the same manner as in Example 1 using this alloy sample. The reaction is 2.
Finished in 5 seconds. After the reaction was completed, the treated alloy sample was immediately taken out of the reactor, and the exothermic layer after the reaction was peeled off. The resulting cure depth was 150 μm and Hv 1100.

Example 5 A mixture in which TiN was added to Ti in the ratio shown in Table 2 was prepared, and a powder capable of causing an exothermic reaction with nitrogen by adding 0.5 parts by weight of a 6% by weight ethyl cellulose alcohol solution to the obtained mixture. Was prepared. This composition was applied to an industrial pure Ti sample having a size of 10 mm × 20 mm × 1 mm using a dipping method and dried. After drying, the weight of the resulting heat generating layer is shown in Table 2. The resulting Ti sample was placed in an atmosphere of 10 atm of nitrogen, a carbon heater was brought into contact with one end of the heat generating layer, and an exothermic reaction was started by energizing.
The reaction was completed in 2 seconds. After the reaction was completed, the treated Ti sample was immediately taken out of the reactor, and the exothermic layer after the reaction was peeled off. This heat generating layer was easily peelable.
Table 2 shows the curing depth of the obtained Ti sample and its Vickers hardness. No irregularities were observed on the Ti surface, and no heat generation was observed. Ethyl cellulose used as a binder was decomposed and released by high heat during the reaction, and did not affect the obtained Ti sample.

As is clear from Table 2, according to the present invention, an exothermic reaction product or an additive that does not participate in the exothermic reaction is added to a composition containing a metal powder capable of causing an exothermic reaction with nitrogen, and the amount thereof is reduced. By changing it, the curing depth can be adjusted.

In the above example, a substance that does not participate in the exothermic reaction was added to the composition.However, the present invention is not limited to this. The amount can be limited to control the thickness of the cured layer.

In the above embodiment, the nitriding was performed in a nitrogen atmosphere. However, the present invention is not limited to this. In an ammonia atmosphere, an atmosphere substantially consisting of a mixture of 50 mol% or more of nitrogen and an inert gas or Nitriding can be performed in an atmosphere consisting essentially of a mixture of 50 mol% or more of ammonia and an inert gas.

[Effects of the Invention] As described above, when the surface hardening method of the present invention is used, the metal surface is hardened by concentrating and heating the metal surface in a very short time with a simple apparatus configuration, A hardened wear-resistant layer with good quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a metal on which a heat generating layer is formed, and FIG. 2 is a view showing an example of a reaction apparatus used in the present invention. 1 ... metal, 2 ... heating layer, 11 ... heater, 12 ... reactor, 13 ... chamber

Claims (6)

(57) [Claims] 1. A step of forming a heat generating layer by applying a composition containing a powder capable of causing an exothermic reaction with nitrogen to a metal surface, and introducing a gas containing nitrogen onto the metal on which the heat generating layer is formed. A method for hardening a metal surface, comprising the steps of: starting an exothermic reaction by heating at least a part of the heat generating layer; and heating the metal surface by the exothermic reaction. 2. The method according to claim 1, wherein the composition contains a binder and a solvent, and the binder and the solvent are decomposed and eliminated in a heat treatment step. 3. The metal surface according to claim 1, wherein the nitrogen-containing gas has a concentration of nitrogen and / or ammonia of 50 mol% or more based on the entire mixture of nitrogen and / or ammonia and an inert gas. Curing method. 4. The powder which causes the exothermic reaction is made of a powder having a periodic table IV.
The method according to claim 1, wherein the powder is a powder of at least one metal selected from the group consisting of a group a metal, a group Va metal, Al, Si and B. 5. The method for hardening a metal surface according to claim 1, wherein the thickness of the hardened layer formed on the metal surface is adjusted by adjusting the application amount of the composition. 6. A cured layer formed on a metal surface by adding a substance not involved in an exothermic reaction to the composition or by interposing a substance not involved in an exothermic reaction between the composition and a metal. The metal surface hardening method according to claim 1, wherein the thickness is adjusted.