KR20060114368A - Method for activating surface of metal member - Google Patents

Abstract

A method for activating the surface of a metal member, that is, activating a passivated coating film present in the surface of a high alloy steel member, which makes it difficult to effect a diffusion penetration treatment such as a gas nitriding method or a gas carburizing method for forming a nitrided layer, a carburized layer or a carburized and nitrided layer on the surface of a metal member, which method comprises using a gas generally used in a gas heat treatment, forming an HCN gas in a furnace through the utilization of a catalytic action of the surface of a metal to be treated and/or a material of the furnace, to thereby activate the passivated surface of the high alloy steel member. The above method is free from disadvantages such as the formation of deposits in a furnace, the wear of the wall surface in a furnace, and the necessity of the treatment for converting an exhaust gas to a harmless material, which have been problems in the case of a conventional activation treatment using a halogen compound, and thus can be advantageously used as a method for activating the surface of a metal member which is useful as a pretreatment for a diffusion penetration treatment.

Description

METHOD FOR ACTIVATING SURFACE OF METAL MEMBER}

The present invention relates to a metal member pretreatment method for activating a metal member surface prior to performing diffusion penetration treatment such as nitriding or carburization.

For the purpose of improving mechanical properties such as wear resistance and fatigue strength, gas nitriding or gas carburizing, in which a nitride layer or a carburized layer is formed on the surface of a metal member, is mainly widely applied to a member made of an iron-based material.

When such a treatment is performed on a member surface made of alloy steel, particularly high alloy steel, the passivation coating (oxide, etc.) present on the member surface can prevent nitrogen or carbon from invading and diffusing into the metal member surface. It is a problem to generate the processing defect or the processing unevenness of the member. For this reason, the activation process of the surface of a metal member is performed before this diffusion penetration process. As the surface activation treatment, the most widely adopted method is to use a chloride compound represented by malcomizing treatment. As the chloride, vinyl chloride resin, ammonium chloride, methylene chloride and the like are used.

The said chloride is put together with a metal member in a process furnace, and is heated. The chloride decomposes by heating, and HCl is produced, and the generated HCl breaks down (denatures) the passivation film on the surface of the metal member to activate the surface, thereby ensuring diffusion penetration treatment such as nitriding or carburizing in the next step. I'm letting you.

However, as described above, surface activation of the metal member by chloride not only damages the wall surface of the furnace in which the HCl generated by decomposition is made of brick or metal, but also gas nitriding or gas softnitriding. In the present invention, ammonium chloride is produced by reacting with ammonia, which is an atmospheric gas, and the ammonium chloride accumulates in the furnace and the exhaust system to cause an obstacle, as well as remaining on the surface of the metal member (work) to prevent corrosion and fatigue of the member. It is causing a decrease in strength.

In recent years, as an alternative to the method of using a chloride, a fluoride compound which belongs to the same halogen group (NF ₃₎ activation of the surface of the metal member by the method is put into practical use (for example, Patent Document 1). The NF ₃ is decomposed by heating to generate fluorine, thereby activating the metal member surface by converting the passivation film on the surface of the metal member into a fluoride film. However, in the method of activating the surface of the metal member by the fluorine compound (NF ₃ ), a high degree of treatment is required for the detoxification of NF ₃ and HF contained in the exhaust gas, which hinders the spread of the method.

The method of activating the surface of the metal member using the halide has problems such as problems of deposits in the furnace, damage to the walls of the furnace, and the need for a detoxification treatment facility of the exhaust gas. Against this background, the development of a method of activating the surface of a metal member without using a halide is in progress.

The ammonia gas nitriding method of patent document 2 is a method of reducing activation of the passivation film on the surface of an alloy steel member by producing | generating the reducing radical and CO which are produced | generated by pyrolysis of acetone on the surface of the high chromium alloy copper member which is a workpiece | work. According to this method, acetone thermally decomposes on the surface of the heated high chromium alloy steel member according to the following formula (1), and reducing radicals and CO are produced on the surface of the high chromium alloy member.

2 (CH ₃ ) CO → 2CH _3. + CO... (One)

The oxide film MO on the surface of the metal member is reduced by the following formula (2).

5MO + 2CH _3. → 5M + 2CO + 3H ₂ O... (2)

Since the main component of the surface oxide film of the high chrome alloy steel member is Cr ₂ O ₃

5Cr ₂ O ₃ + 6CH _3. → 10Cr + 6CO + 9H ₂ O... (3)

CO generated according to the above formulas (1) to (3) reacts with ammonia which is an atmosphere gas to generate HCN according to the following formula (4).

CO + NH ₃ → HCN + H ₂ O... (4)

HCN produced by the above formula (4) reduces the passivation film on the surface of the high chromium alloy member by the following reaction.

Cr ₂ O ₃ + 6HCN → 2Cr (CN ₃ ) + 3H ₂ O... (5)

C and N of the resulting Cr (CN) ₃ diffuse into the surface of the high chromium alloy member, contributing to carburization and nitriding, and no residue is formed on the surface of the member.

On the other hand, the activation reaction of the surface of the high chromium alloy steel member by the said chloride is represented by following formula (6).

Cr ₂ O ₃ + 6HCl → 2CrCl ₃ + 3H ₂ O... (6)

The chromium chloride remains on the surface of the member, causing the member to corrode.

Patent Document 1: Japanese Patent Publication No. Pyeongseong 3-44457

Patent Document 2: Japanese Patent Application Publication Pyeongseong 9-38341

As mentioned above, the method of patent document 2 is excellent in the point which solved the problem of the activation method of the surface of the metal member by the chloride of patent document 1 in principle. However, since the method described in Patent Document 2 uses acetone of liquid at normal temperature and normal pressure, an apparatus for introducing acetone vapor is required, and since the flow rate control of acetone is not easy, a metal member having a uniform active surface is used. There is a drawback that it is difficult to obtain.

MEANS TO SOLVE THE PROBLEM In order to solve the said subject, the present inventors focused on the development of the method of using the compound which is gas at normal temperature and normal pressure instead of the acetone which has a problem in handling, and completed this invention.

That is, the structure of this invention is as follows.

1. A mixed gas containing a carbon supply compound, which is a gas at room temperature, and ammonia as an essential component, is heated to 300 ° C. or higher in a heating furnace to catalyze the action of a metal member, a metal furnace wall, or a metal jig in the heated mixed gas. By generating HCN, and causing the generated HCN to act on the surface of the metal member.

2. The method for activating the surface of a metal member according to 1 above, wherein the carbon supply compound is at least one compound selected from acetylene, ethylene, propane, butane and carbon monoxide.

3. The method of activating the surface of a metal member according to 1 above, wherein the metal furnace inner wall or the metal jig contains at least one metal selected from Fe, Ni, CO, Cu, Cr, Mo, Nb, V, Ti, and Zr.

4. The method of activating the surface of the metal member according to 1 above, wherein the HCN concentration generated in the furnace is 100 mg / m 3 or more, and the dew point of the atmosphere gas in the furnace is 5 ° C. or less.

[Effects of the Invention]

According to the present invention, a surface passivating film of a high alloy steel member which makes it difficult to diffuse infiltration treatment such as a gas nitriding method or a gas carburizing method for forming a nitride layer, a carburized layer or a carburized nitride layer on the surface of a metal member, The surface of the high-alloyed steel member which is produced by passivating HCN gas in the furnace by catalyzing the surface of the metal to be processed and / or the metal furnace material using the gas streams normally handled in heat treatment. By activating the surface of the metal member, which is useful as a pre-stage treatment of diffusion penetration treatment, which does not involve harmful effects such as internal deposits of the furnace, damage to the walls of the furnace, or detoxification of the exhaust gas, which have been a problem in the activation process by halides. Activation treatments can be provided.

Next, the present invention will be described in more detail with reference to the best mode for carrying out the invention.

According to the patent document 2, CH ₃ · (methyl radicals) generated by thermal decomposition of the acetone in the formula (1) is reduction of the oxide film on the surface of the metal member. The CO produced by the above formulas (1) and (2) reacts with ammonia in the atmospheric gas on the metal surface to generate HCN. HCN acts on the metal oxide film by the formula (5).

The inventors of the present invention suggest that CH ₃ and HCN (reaction products of CO, which is another pyrolysis product, and ammonia of an atmospheric gas,) produced by pyrolysis of acetone are added to the passivation film from the comparison of equations (2) and (5). It is assumed that the presence of both CH ₃ and HCN is a sufficient condition for activation of the surface of the high chromium alloy steel member, but it is not necessarily a requirement. The development and the confirmation of the activation effect of the surface of the metal member by HCN.

A gas selected from a nitriding atmosphere gas (NH ₃ : N ₂ = molar ratio 1: 1) and various carbon-containing compounds which are gas at room temperature and normal pressure is introduced into a muffle furnace made of SUS310S, and heated to 550 ° C. The production of HCN was investigated. As a result, it was confirmed that carbon monoxide, carbon dioxide, acetylene, ethylene, propane and butane each produced HCN clearly in combination with ammonia.

On the other hand, except that the inner wall of the muffle furnace was replaced with a brick furnace, HCN was not detected in all cases as a result of analyzing the amount of HCN produced by the above experiment. From this, it became clear that the catalysis of the metal surface is an essential condition for the HCN formation reaction by ammonia and these gases.

HCN production reaction by ammonia and the carbon-containing compound can be represented by the following formula, respectively.

NH ₃ + CO → HCN + H ₂ O... (7)

2NH ₃ + 2CO ₂ → 2HCN + H ₂ O + O ₂ … (8)

2NH ₃ + C ₂ H ₂ → 2HCN + 3H ₂ . (9)

2 NH ₃ + C ₂ H ₄ → 2HCN + 4H ₂ . 10

3NH ₃ + C ₃ H ₈ → 3HCN + 7H ₂ … (11)

4NH ₃ + C ₄ H ₁₀ → 4HCN + 9H ₂ … (12)

The comparison of the amount of HCN produced by the reaction between the nitriding atmosphere gas (NH ₃ : N ₂ = molar ratio 1: 1) and the gas selected from various carbon-containing compounds is performed by the nitriding atmosphere gas (NH ₃ : N ₂ = molar ratio 1: 1). Each carbon-containing compound was contained in an equivalent ratio of 1%, and the inner wall was introduced into a muffle made of SUS310S, heated at 550 ° C. for 30 minutes to carry out the reactions of formulas (7) to (12). As a result, the amount of HCN produced by each carbon-containing compound was in the following order.

C ₂ H ₂ >CO> C ₂ H ₄ > C ₄ H ₁₀ > C ₃ H ₈ > CO ₂

For those carbon-containing compounds that were found to produce HCN in reaction with a nitriding atmosphere gas, each of these compounds was introduced into the furnace at the initial stage of nitriding treatment to evaluate whether or not there was an activating action using SUS304 plate. It was. As a result, C ₂ H ₂ , CO, C ₂ H ₄ , C ₄ H ₁₀ and C ₃ H ₈ are characterized in that the uniformity of nitriding and nitridation of the SUS304 sheet is compared with the controlled nitriding treatment without introducing a carbon-containing compound. Obvious effects were found in weight gain by nitrogen infiltration. On the other hand, in the case of using CO ₂ , there was no difference from the controlled nitriding treatment in any of the uniform nitriding property and the weight increase of the test piece, and no activation activity was observed on the surface of the SUS304 sheet for CO ₂ .

Despite the fact that HCN is generated by the introduction of CO _{2 in} the furnace, it is not possible to obtain an activation action on the surface of the SUS304 sheet, which is O ₂ and H ₂ which are by-products of the HCN formation reaction of the formula (8). It is assumed that this is due to the reoxidation of the surface of the SUS304 sheet material by the oxidation action of O. As for CO, HCN is produced as described above, but this contradicts the phenomenon that stainless steel is not uniformly nitrided in a gas soft-nitriding atmosphere in which RX gas containing ammonia and CO is present, but the above contradiction is caused by the following reasons. I can think of it. Here, RX gas is a mixture of hydrocarbon gas (e.g., propane gas, butane gas, natural gas) and air in almost chemical equivalent weight, decomposed in a catalyst layer maintained at 1000 ° C, and CO, H ₂ (N ₂ ) as a main component. and the gas is widely used as a small amount of the carburizing gas and a gas containing CO ₂ and H ₂ O.

CO contained in NH ₃ : R x gas = molar ratio 1: 1, which is a typical composition of gas soft nitriding, is about 10% in capacity ratio. Therefore, it is assumed that HCN necessary for the activation of the surface of the metal member is sufficiently present in the gas soft nitriding furnace. However, RX gas having no dew point control has a considerable amount of H ₂ O (around 2% by volume) and a CO _{2 of} about 0.5% by volume. Since it exists, the surface of the said SUS304 board | plate material activated by these oxidation reactions is reoxidized, and it is judged that the invasion of nitrogen in the said board | plate material surface is interrupted.

Therefore, when CO gas is selected as the carbon supply compound for activation of the surface of the metal member, it is preferable to use a single CO gas instead of RX gas. However, since the required injection amount of CO gas in the present invention is about 1/10 (capacity) of the gas soft-nitriding atmosphere, the influence of H ₂ O and CO _{2 in} the RX gas is reduced, so that RX gas is It may be used as a case.

Judging from the equation on the right side of the reaction formulas (7) to (12) above, among these compounds having cyanogenic function, the oxidation of by-products in the case of CO ₂ is the highest, and then CO, and all hydrocarbon compounds are reducing hydrogen. Create Therefore, in order to prevent reoxidation, it is preferable to select a hydrocarbon compound as a carbon supply compound.

The activation action of the surface of the alloy steel member according to the present invention is due to HCN. The activation effect depends on the HCN concentration in the furnace atmosphere. The appropriate concentration of HCN to obtain a satisfactory activation action is in the range of 100 to 30,000 mg / m 3. If the concentration of HCN is less than 100 mg / m 3, the above activation cannot be expected. On the other hand, when the concentration of HCN is more than 30,000 mg / m 3, the activating effect is saturated, which is not only economically disadvantageous, but also sooting due to thermal decomposition of the carbon feed compound, which is not preferable.

Moreover, it is preferable that the dew point of in-furnace atmospheric gas is 5 degrees C or less. If the dew point is higher than 5 DEG C, the metal surface activated by HCN gas is reoxidized by H ₂ O in the atmosphere and passivated again.

In the method of the present invention, an advantage in terms of environment is that HCN, which contributes to the activation of the metal member surface, is put into the member surface and contributes to nitriding and carburizing of the member, as described in the reaction formula (5). In addition to leaving no residue, HCN, which does not contribute to the reaction and is discharged as exhaust gas, can easily be burned and harmless by the ammonia combustion device attached to the nitriding device, and no new additional equipment is necessary.

A new advantage of the present invention is the shortening of the nitriding treatment time by the smooth process progression in the nitriding treatment process. Gas nitriding of a metal member is normally performed on the following schedule.

The metal member is placed in the furnace, and the atmosphere in the furnace is vacuum purged or replaced with nitrogen gas, followed by introducing a nitrogen atmosphere gas (NH ₃ + N ₂ ) 1 to 10 times the volume of the furnace, thereby raising the temperature to the nitriding treatment temperature of the metal member. Maintain constant temperature after The furnace pressure during the process is maintained by the pressure valve at about +0.5 kPa at atmospheric pressure, and the extruded exhaust gas is burned and decomposed by the exhaust gas combustion device.

In the method with the fluorine-type gas shown by the said patent document 1, as described in the Example of Unexamined-Japanese-Patent No. 2501925, after carrying out the activation process of a member by introducing a fluorine-type gas, it nitrates after exhausting a fluoride-type gas. It is necessary to introduce atmospheric gas into the furnace.

In the present invention, on the other hand, in the step of raising the temperature of the metal member to the nitriding treatment temperature, the carbon supply compound is introduced into the nitriding atmosphere gas, HCN is generated to activate the surface of the metal member, and then the introduction of the carbon supply compound is stopped. The process can be carried out as it is. As a result, the treatment time of the nitriding process can be significantly shortened, and the reoxidation phenomenon of the surface of the metal member, which has been a problem in the conventional treatment when transitioning from the activation to the nitriding process, can be solved fundamentally.

The technical features and effects of the present invention are as described above. EMBODIMENT OF THE INVENTION Below, preferable embodiment of this invention is described. As the treatment used in the present invention, it is preferable that the inner wall is made of metal, but even if the inner wall is not made of metal, the metal member to be treated may be a catalyst of HCN, and the jig for holding the metal member in the furnace may be made of metal. As a metal which comprises the said metal inner wall, a metal member, and a jig | tool, it is preferable to contain at least 1 metal chosen from Fe, Ni, CO, Cu, Cr, Mo, Nb, V, Ti, and Zr, for example.

Examples of the metal member to be surface activated in the method of the present invention include cold die steel, hot die steel, plastic die steel, high speed tool steel, powder high speed tool steel, chromium molybdenum steel, maraging steel, austenitic stainless steel, and ferritic stainless steel. And martensitic stainless steels, martensitic heat resistant steels, austenitic heat resistant steels, and nickel based alloys. These metal members are placed in accordance with a conventional method by an appropriate jig in the treatment furnace and subjected to surface activation.

The surface treatment gas supplied into the furnace is a carbon supply compound and ammonia, which are gases at normal temperature and pressure, and are supplied into the furnace from a dedicated bomb. The gas is placed in a furnace, and the atmosphere in the furnace is replaced with a vacuum purge or nitrogen gas, followed by introduction of a nitriding atmosphere gas (ammonia alone or ammonia + nitrogen gas or ammonia + nitrogen gas + hydrogen gas) into the furnace. After establishing a reducing atmosphere, the temperature is started to introduce the carbon feed compound of the present invention. The ammonia gas and the carbon supply compound, when heated to 300 ° C. or higher in the furnace, form HCN by catalysis of the metal surface. The flow rate ratio of ammonia, which is a nitriding atmosphere gas, and the flow rate of the carbon feed compound to be introduced should be within the range of 1: 0.0001 to 1: 0.1. If the flow rate ratio of the carbon supply compound is lower than 1: 0.0001, the activating effect cannot be obtained because the amount of HCN is low. If the flow rate ratio of the carbon feed compound is greater than 1: 0.1, the activation effect is saturated, which is economically disadvantageous.

The carbon supply compound is one or more gaseous compounds selected from acetylene, ethylene, propane, butane and carbon monoxide as described above, and may be supplied into the treatment furnace simultaneously with the ammonia-containing gas as described above. Initiating the introduction of the carbon supply compound when the furnace temperature of the ammonia-containing gas reaches about 300 ° C. is preferable for the efficient use of the carbon supply compound. However, the concentration of the carbon supply compound in the furnace atmosphere is increased early to shorten the treatment time. In order to achieve the HCN production from the initial stage, it is preferable to introduce a carbon supply compound at the same time as the temperature rise starts.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows the structure of the process furnace used by this invention.

2 is a micrograph of a cut surface of a test piece of Example 1. FIG.

3 is a micrograph of a cut surface of a test piece of Comparative Example 1. FIG.

[Description of the code]

1: muffle furnace 2: outer case

3: heater 4: internal container (retort)

5 gas introduction pipe 6 exhaust pipe

7: motor 8: fan

9: metal jig 10: gas guide tube

11 inverted funnel 12 vacuum pump

13 exhaust gas combustion device 14 carbon supply compound gas cylinder

15: ammonia gas cylinder 16: nitrogen gas cylinder

17: hydrogen gas cylinder 18: flow meter

19 gas control valve

Hereinafter, an Example and a comparative example are given and this invention is demonstrated further more concretely. In addition, the following Example and the comparative example were implemented using the processing furnace of the structure shown in FIG. In Fig. 1, 1 is a muffle, 2 is an outer case, 3 is a heater, 4 is an inner container, 5 is a gas introduction pipe, 6 is an exhaust pipe, 7 is a motor, 8 is a fan, 9 is a metal jig, 10 is gas guide, 11 is inverted funnel, 12 is vacuum pump, 13 is exhaust gas combustor, 14 is carbon gas compound gas cylinder, 15 is ammonia gas cylinder, 16 is nitrogen gas cylinder, 17 is hydrogen A gas cylinder, 18 is a flow meter and 19 is a gas control valve.

Example 1

To Figure internal volume 100L N ₂ gas and NH ₃ gas was set to a SUS304 plate by using the SUS310S Muffle in the furnace shown in Figure 1, to send a flow rate of 200L / H, and the temperature was raised to 550 ℃ 75 minutes from room temperature. The injection of 2 L / H of acetylene gas was started when the atmospheric temperature became 100 degreeC (18 minutes after the start of temperature rising). After raising the temperature to 550 ° C., the temperature of the atmosphere was maintained for 2 hours. At this point, the injection of acetylene gas was stopped, while the NH ₃ gas and the N ₂ gas were further flowed at 550 ° C. for 4 hours, and then the heating was stopped. Only the N ₂ gas was kept flowing, and the furnace was cooled, and the test piece in the furnace was taken out when the ambient temperature became 100 ° C or lower.

In addition, the exhaust gas from the furnace was branched, and a part of the exhaust gas was absorbed into a 2 mass% caustic soda solution to conduct HCN analysis. From the analysis results of the HCN absorbent liquid, the average HCN concentration in the furnace atmosphere during the acetylene gas injection period was 8,000 mg / m 3. The weight gain before and after nitriding treatment of the SUS304 test piece was measured to be 20 g / m 2. The SUS304 test piece was cut and polished, etched with a Marble's solution, and the cut surface was observed with an optical microscope. A nitride layer having a uniform thickness of 50 μm was formed (FIG. 2 shows a microscope photograph with a magnification of 500 times. ). When 5 points of surface hardness of the said test piece were measured with the Vickers hardness tester, the value was distributed between Hv = 1200-1250.

Example 2

Example Set the SUS304 plate in a muffle furnace used in the first and sent to the flow rate of the NH ₃ gas and N ₂ gas respectively, 200L / H, and the mixture was heated 75 minutes from room temperature to 550 ℃. The injection of propane gas 5L / H was started when the atmospheric temperature became 100 degreeC (18 minutes after the start of temperature rise) on the way. After raising the temperature to 550 ° C., the temperature of the atmosphere was maintained for 2 hours. At this point, the propane gas was stopped, while the NH ₃ gas and the N ₂ gas were further flowed at 550 ° C. for 4 hours, and then the heating was stopped. and flow continues only N ₂ gas to the furnace cooling to ambient temperature the specimen was taken out of the furnace of greater than 100 ℃ point.

In addition, the exhaust gas from the furnace was branched, and a part of the exhaust gas was absorbed into a 2% by mass aqueous solution of caustic soda for HCN analysis. From the analysis results of the HCN absorption liquid, the average HCN concentration in the furnace atmosphere during propane gas injection period was 400 mg / m 3. The weight increase before and after nitriding treatment of the SUS304 test piece was measured to be 18 g / m 2. The SUS304 test piece was cut and polished, etched with a marble solution, and the cut surface was observed with an optical microscope. A nitride layer having a uniform thickness of 45 µm was formed. When 5 points | pieces of the surface hardness of the said test piece were measured with the Vickers hardness meter, any value was distributed between Hv = 1200-1250.

Example 3

Example 1 sets a SUS304 plate in a muffle furnace used in and sent to the flow rate of the NH ₃ gas and N ₂ gas respectively, 200L / H, and the mixture was heated 75 minutes from room temperature to 550 ℃. The injection of CO gas 5L / H was started in the middle (at 18 minutes after the start of temperature rising) when the atmospheric temperature became 100 degreeC. After raising the temperature to 550 ° C., the temperature of the atmosphere was maintained for 2 hours. At this point, the injection of CO gas was stopped, and the nitriding was continued by flowing NH ₃ gas and N ₂ gas at 550 ° C. for 4 hours, and then the heating was stopped. and flow continues only N ₂ gas to the furnace cooling to ambient temperature the specimen was taken out of the furnace of greater than 100 ℃ point.

In addition, the exhaust gas from the furnace was branched, and a part of the exhaust gas was absorbed into a 2% by mass aqueous solution of caustic soda for HCN analysis. From the analysis results of the HCN absorbent liquid, the average HCN concentration in the furnace atmosphere during the CO gas injection period reached 1,000 mg / m 3. It was 18 g / m <2> when the weight increase before and after nitriding treatment of the SUS304 test piece was measured. The SUS304 test piece was cut and polished, etched with a marble liquid, and the cut surface was observed with an optical microscope. A nitride layer having a uniform thickness of 45 µm was formed. When 5 points | pieces of the surface hardness of the said test piece were measured with the Vickers hardness meter, any value was distributed between Hv = 1200-1250.

Example 4

Example 1 sets a SUS304 plate in a muffle furnace used in and sent to the flow rate of the NH ₃ gas and N ₂ gas respectively, 200L / H, and the mixture was heated 75 minutes from room temperature to 550 ℃. During the ambient temperature with a 100 ℃ time (after 18 minutes from the start of the temperature elevation) it was added to initiate the injection of C ₂ H ₄ gas 5L / H in. After raising the temperature to 550 ° C., the temperature of the atmosphere was maintained for 2 hours, and the injection of C ₂ H ₄ gas was stopped at this point, while the NH ₃ gas and N ₂ gas were further flowed at 550 ° C. for 4 hours to further carry out nitriding. The heating was stopped and only the N ₂ gas was continued to flow, and the test piece in the furnace was taken out at the point where the furnace was cooled and the ambient temperature became 100 ° C or lower.

In addition, the exhaust gas from the furnace was branched, and a part of the exhaust gas was absorbed into a 2 mass% aqueous solution of caustic soda for HCN analysis. From the analysis results of the HCN absorbent liquid, the average HCN concentration in the furnace atmosphere during the C ₂ H ₄ gas injection period reached 1,200 mg / m 3. It was 18 g / m <2> when the weight increase before and after nitriding treatment of the SUS304 test piece was measured. The SUS304 test piece was cut and polished, etched with a marble liquid, and the cut surface was observed with an optical microscope. A nitride layer having a uniform thickness of 45 µm was formed. When 5 points | pieces of the surface hardness of the said test piece were measured with the Vickers hardness meter, any value was distributed between Hv = 1200-1250.

Example 5

Example 1 sets a SUS304 plate in a muffle furnace used in and sent to the flow rate of the NH ₃ gas and N ₂ gas respectively, 200L / H, and the mixture was heated 75 minutes from room temperature to 550 ℃. The atmosphere during the temperature is 100 ℃ time (after 18 minutes from the start of the temperature elevation) was added to initiate the injection of C ₄ H ₁₀ gas 5L / H in. After raising the temperature to 550 ° C., the temperature was maintained for 2 hours, and the injection of the C ₄ H ₁₀ gas was stopped at this point, while the NH ₃ gas and the N ₂ gas were further flowed at 550 ° C. for 4 hours, and then nitriding was carried out. The heating was stopped and only the N ₂ gas was continued to flow, and the test piece in the furnace was taken out at the point where the furnace was cooled and the ambient temperature became 100 ° C or lower.

In addition, the exhaust gas from the furnace was branched, and a part of the exhaust gas was absorbed into a 2 mass% aqueous solution of caustic soda for HCN analysis. From the analysis results of the HCN absorbent liquid, the average HCN concentration in the furnace atmosphere during the C ₄ H ₁₀ gas injection period reached 600 mg / m 3. It was 18 g / m <2> when the weight increase before and after nitriding treatment of the SUS304 test piece was measured. The SUS304 test piece was cut and polished, etched with a marble liquid, and the cut surface was observed with an optical microscope. A nitride layer having a uniform thickness of 45 µm was formed. When 5 points | pieces of the surface hardness of the said test piece were measured with the Vickers hardness meter, any value was distributed between Hv = 1200-1250.

Comparative Example 1

Example 1 sets a SUS304 plate in a muffle furnace used in and sent to the flow rate of the NH ₃ gas and N ₂ gas respectively, 200L / H, and the mixture was heated 75 minutes from room temperature to 550 ℃. After raising the temperature to 550 ° C., the temperature was maintained for 6 hours, and the NH ₃ gas and the N ₂ gas were continuously flowed to proceed with nitriding. Then, the heating was stopped and only the N ₂ gas was continued to be cooled, and the atmosphere temperature was 100 ° C. or lower. At that point, the test piece in the furnace was taken out.

The exhaust gas from the furnace was branched, and a part of the exhaust gas was absorbed into a 2% by mass aqueous solution of caustic soda for HCN analysis. As a result of analyzing the HCK absorbent liquid, HCN was not detected at all and it was confirmed that HCN was not present at all in the furnace atmosphere. It was 10 g / m <2> when the weight increase before and after nitriding treatment of the SUS304 test piece was measured. The SUS304 test piece was cut and polished, etched and cut with a marble solution, and the cut surface was observed by an optical microscope. A nitride layer having a non-uniform thickness of 8 to 18 µm was formed (shown in FIG. ). When five points of surface hardness of the test piece were measured by a Vickers hardness tester, the surface value of the test piece was greatly changed from Hv = 500 to 1100, and the absolute value thereof was lower than that of the example.

According to the present invention, a surface passivating film of a high alloy steel member which makes it difficult to diffuse infiltration treatment such as a gas nitriding method or a gas carburizing method for forming a nitride layer, a carburized layer or a carburized nitride layer on the surface of a metal member, By using a gas flow which is usually treated by heat treatment, catalyzing the surface of the metal and / or metal furnace material to generate HCN gas in the furnace to activate the surface of the passivating high alloy steel member. Thus, the method of activation of the surface of a metal member, which is useful as a pre-stage treatment of diffusion penetration treatment, which does not involve detriment such as in-house sediment, abrasion of the inner wall surface, or detoxification of exhaust gas, which has conventionally been a problem in the activation treatment by halides. Can be provided.

Claims (4)

At a normal temperature and pressure, a mixed gas containing a carbon supply compound and ammonia as an essential component is heated to 300 ° C. or higher in a heating furnace, and the catalytic action of a metal member, a metal furnace inner wall, or a metal jig in the heated mixed gas is performed. By generating HCN, and causing the generated HCN to act on the surface of the metal member. The method of claim 1, wherein the carbon supply compound is at least one compound selected from acetylene, ethylene, propane, butane and carbon monoxide. The method of activating a metal member surface according to claim 1, wherein the metal furnace inner wall or the metal jig contains at least one metal selected from Fe, Ni, CO, Cu, Cr, Mo, Nb, V, Ti, and Zr. The method of activating a surface of a metal member according to claim 1, wherein the HCN concentration generated in the furnace is 100 mg / m 3 or more, and the dew point of the atmosphere gas in the furnace is 5 ° C. or less.

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