WO2005068679A1

WO2005068679A1 - Method for activating surface of metal member

Info

Publication number: WO2005068679A1
Application number: PCT/JP2005/000607
Authority: WO
Inventors: Kaoru Hoshino; Makoto Miyashita; Takashi Kawamura; Toshiko Totsuka; Hiroshi Eiraku; Kuniji Yashiro; Takumi Kurosawa
Original assignee: Parker Netsushori Kogyo K.K.
Priority date: 2004-01-20
Filing date: 2005-01-19
Publication date: 2005-07-28
Also published as: CN1910303A; KR20060114368A; EP1707646A4; DE602005015934D1; US20070204934A1; KR100858598B1; JPWO2005068679A1; JP4861703B2; CN1910303B; EP1707646B1; EP1707646A1

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

Specification

Activation method of metal member surface

Technical field

The present invention relates to a metal member pretreatment method for activating a metal member surface prior to subjecting the metal member to a diffusion and infiltration treatment such as nitriding and carburizing.

Background art

[0002] In order to improve mechanical properties such as wear resistance and fatigue strength, a gas nitriding method or a gas carburizing method in which a nitrided or carburized layer is formed on the surface of a metal member is performed by using a component made of an iron-based material. It is mainly widely implemented.

[0003] When these treatments are performed on the surface of a member made of an alloy steel, particularly a high alloy steel, the passivation film (oxide, etc.) present on the surface of the member causes nitrogen or carbon to enter the metal member surface. This is a problem in that the penetration and diffusion of the components are hindered, and processing defects and processing unevenness of the above members occur. Therefore, prior to these diffusion and infiltration treatments, activation treatment of the surface of the metal member is performed. The most widely used surface activation treatment is a method using a chloride compound represented by a marcoizing treatment. As the chloride, a butyl chloride resin, a salted ammonium salt, methylene chloride, or the like is used.

[0004] The chloride is placed in a processing furnace together with a metal member and heated. By the heating, these chlorides are decomposed to generate HC1, and the generated HC1 destroys (modifies) the passivation film on the surface of the metal member and activates the surface. Make sure that the diffusion and infiltration treatment is assured.

[0005] However, the surface activation of the metal member by the above-mentioned salt ridden is performed by gas nitriding / gas nitrocarburizing in which the decomposition-generated H C1 only wears the furnace inner wall made of brick / metal. Reacts with ammonia, which is an atmospheric gas, to produce ammonium chloride, which remains on the surface of a metal member (work) that is not only a cause of trouble due to deposition of the salt in the furnace or the exhaust system. This leads to a reduction in the corrosion resistance and fatigue strength of the member.

[0006] In recent years, as an alternative to the above-described method using a chloride, fluorine belonging to the same halogen group has been used. A method of activating the surface of a metal member with a nitrogen compound (NF) has been put into practical use (for example,

Three

Permission 1). The above NF is decomposed by heating to generate fluorine, and the generated fluorine is a metal

Three

The passivation film on the member surface is changed to a fluoride film to activate the metal member surface. However, in the method of activating the metal member surface with a fluorine compound (NF),

Three

Advanced treatment is required to detoxify the contained NF and HF, which hinders the spread of the method.

Three

It has become.

[0007] The method of activating a metal member surface using the halogen compound has problems such as a problem of deposits in a furnace, wear of a furnace inner wall, and a need for a detoxification facility for exhaust gas. Against this background, development of a method for activating a metal member surface without using a halide has been promoted.

[0008] The ammonia gas nitriding method described in Patent Document 2 generates a reducing radical generated by thermal decomposition of acetone and CO on the surface of a high chromium alloy steel member, which is a work, thereby reducing the surface of the alloy steel member. This is a method of activating the passivation film by reduction. According to this method, acetone is thermally decomposed according to the following equation (1) on the surface of the heated high chromium alloy steel member, and reducing radicals and CO are generated on the surface of the high chromium alloy member.

2 (CH) CO → 2CH-+ CO (1)

3 3

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

5MO + 2CH-→ 5M + 2CO + 3H O (2)

3 2

Since the main component of the surface oxide film of high chromium alloy steel members is Cr 2 O

twenty three

5Cr〇 + 6CH-→ 10Cr + 6CO + 9H O (3)

2 3 3 2

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

CO + NH → HCN + H O… (4)

3 2

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

Cr O + 6HCN → 2Cr (CN) + 3H O

2 3 3 2

The C and N of the generated Cr (CN) diffuse into the surface of high chromium alloy members and contribute to carburizing and nitriding.

Three

As a result, no residue is generated 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 chloride is expressed by the following equation (6).

Cr O + 6HCl → 2CrCl + 3H O (6)

2 3 3 2

The above-mentioned chrome salt residue remains on the surface of the member and becomes a substance causing corrosion of the member. Patent Document 1: JP-A-3-44457

Patent Document 2: Japanese Patent Application No. 9-38341

Disclosure of the invention

Problems to be solved by the invention

[0010] As described above, the method described in Patent Document 2 is excellent in that the problem of the method for activating the surface of a metal member with chlorides described in Patent Document 1 is solved in principle. However, since the method described in Patent Document 2 uses acetone which is liquid at normal temperature and normal pressure, it requires an apparatus for introducing acetone vapor, and since it is not easy to control the flow rate of acetone, it has a uniform active surface. There is a disadvantage that it is difficult to obtain a metal member.

Means for solving the problem

[0011] In order to solve the above problems, the present inventors have developed a method using a compound that is a gas at normal temperature and normal pressure in place of acetone, which has a problem in handling, and completed the present invention. That is, the configuration of the present invention is as follows.

1. A mixed gas containing a carbon supply compound and ammonia, which are gaseous at normal temperature and normal pressure, is heated to 300 ° C or more in a heating furnace, and the metal member and the inner wall of the metal furnace are heated in the heated mixed gas. Alternatively, a method for activating the surface of a metal member, wherein HCN is generated by a catalytic action of a metal jig, and the generated HCN is caused to act on the surface of the metal member.

[0012] 2. The method for activating the surface of a metal member according to the above 1, wherein the carbon supply compound is at least one compound selected from acetylene, ethylene, propane, butane and carbon monoxide.

[0013] 3. The metal furnace inner wall or the metal jig contains one or more metals selected from the group consisting of Fe, Ni, Co, Cu, Cr, Mo, Nb, V, Ti and Zr. The method for activating the surface of a metal member according to claim 1.

[0014] 4. The concentration of HCN generated in the furnace is 100 mg / m ³ or more, 2. The method for activating a metal member surface according to the above 1, wherein the dew point of the metal is 5 ° C. or less.

The invention's effect

[0015] According to the present invention, a high-alloy steel part which is difficult to perform a diffusion and infiltration treatment such as a gas nitriding method or a gas carburizing method in which a nitrided layer, a carburized layer or a carbonitrided layer is formed on the surface of a metal member. The surface passivation film is formed by using gases normally used in gas heat treatment and generating HCN gas in the furnace by utilizing the catalytic action of the surface of the metal and / or metal furnace material to be treated. By activating the surface of the passivated high-alloy steel member, the detrimental treatment of the furnace deposits and the inner wall of the furnace, which had been a problem with the activation treatment with halogens, and the detoxification of exhaust gas Thus, it is possible to provide a method for activating the surface of a metal member, which is useful as a pre-treatment of the diffusion and infiltration treatment without adverse effects.

BEST MODE FOR CARRYING OUT THE INVENTION

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

According to Patent Document 2, CH · (methyl) formed by thermal decomposition of acetone of the above formula (1) is used.

3 radicals) reduce the oxide film on the surface of the metal member. The CO generated by the above equations (1) and (2) reacts with ammonia in the atmospheric gas on the metal surface to generate HCN. HCN acts on the metal oxide film according to the above formula (5).

[0017] The present inventors have found that CH 'and HCN (another pyrolysis product)

Three

The reaction product of CO and ammonia in the atmospheric gas is similar in terms of the effect on the passivation film by comparing the above equations (2) and (5), and the presence of both CH 'and HCN Is

Three

A force that is a sufficient condition for activation of the surface of a high chromium alloy steel member is not necessarily a necessary condition, and it is assumed that it is not a necessary condition. We worked on confirming the revitalization effect.

[0018] Nitrogen atmosphere gas (NH: N = molar ratio 1: 1) and various types of carbon containing gas at normal temperature and normal pressure

3 2

The gas selected from the compounds was introduced into a matsufur furnace made of SUS310S and heated to 550 ° C to investigate the formation of HCN. As a result, it was confirmed that carbon monoxide, carbon dioxide, acetylene, ethylene, propane, and butane each clearly generate HCN in combination with ammonia.

[0019] On the other hand, the same experiment as above was performed except that the inner wall of the Matsufuru furnace was replaced with a brick furnace. As a result, HCN was not detected in all cases. This indicates that the catalytic action of the metal surface is an essential condition for the HCN generation reaction between ammonia and these gases.

[0020] The HCN generation reaction by ammonia and the carbon-containing compound can be represented by the following equations, respectively.

NH + CO → HCN + H O… (7)

3 2

2NH + 2CO → 2HCN + H O + O

3 2 2 2

2NH + CH → 2HCN + 3H… (9)

3 2 2 2

2NH + CH → 2HCN + 4H… (10)

3 2 4 2

3NH + CH → 3HCN + 7H (11)

3 3 8 2

4NH + CH → 4HCN + 9H… (12)

3 4 10 2

[0021] A gas selected from a nitriding atmosphere gas (NH: N = molar ratio 1: 1) and various carbon-containing compounds.

3 2

The comparison of the amount of HCN generated by the reaction with nitric acid is based on the nitriding atmosphere gas (NH: N molar ratio 1: 1).

3 2

), Each carbon-containing compound is contained in an equivalent ratio of 1%, and the inner wall is introduced into a SUS310S Matsufuru furnace, heated to 550 ° C for 30 minutes, and the reaction of the above formulas (7)-(12) is carried out. I did it. As a result, the amount of HCN produced by each carbon-containing compound was in the following order.

CH> CO> CH> CH> CH> CO

2 2 2 4 4 10 3 8 2

[0022] For these carbon-containing compounds that have been confirmed to generate HCN by reaction with a nitriding atmosphere gas, each of these compounds is introduced into a heating furnace at the initial stage of the nitriding treatment to have an activating effect. Whether or not it was evaluated using a SUS304 plate material. As a result, C

2

H, CO, CH, CH and CH are control

2 2 4 4 10 3 8

Compared with the nitriding treatment, a clear effect was observed in the above SUS304 plate material in terms of uniformity of nitriding and weight increase due to nitrogen intrusion. In contrast, when CO is used, the average

2

-There is no difference between the nitriding property and the weight increase of the test piece compared with the control nitriding treatment.There is no activation effect on CO on the surface of the above SUS304 plate.

2

won.

[0023] Despite the generation of HCN due to the introduction of CO in the furnace, The lack of activation on the surface of the material is presumed to be due to the re-oxidation of the surface of the SUS304 sheet by the oxidizing effect of O and HO, which are by-products of the HCN formation reaction in equation (8). Is done. As for C〇, the ability to generate HCN as described above contradicts the phenomenon that stainless steel is not uniformly nitrided in a gas nitrocarburizing atmosphere in which ammonia and RX gas containing CO are present. Is considered as follows. Here, RX gas is a mixture of hydrocarbon gas (for example, propane gas, butane gas, natural gas) and air at almost chemical equivalents, and decomposes in a catalyst layer maintained at 1000 ° C to produce C〇 and H (N). A gas containing a small amount of CO and H〇 as its main component and is widely used as a carburizing gas.

[0024] The typical composition of gas nitrocarburizing is NH: RX gas = molar ratio of 1: 1 and the CO contained in the composition is about 10% by volume. Therefore, it is presumed that the HCN necessary for activating the surface of metal members is sufficiently present in the gas nitrocarburizing furnace, but the RX gas whose dew point is not controlled has a considerable amount of H〇 (around 2% by volume) and 0%. Since about 5% by volume of CO is present, the surface of the SUS304 plate activated by these oxidation is re-oxidized, preventing the infiltration of nitrogen into the plate surface. Is determined.

Therefore, when selecting CO gas as a carbon supply compound for activating the metal member surface, it is desirable 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 nitrocarburizing atmosphere, the influence of HO and C In some cases, it can be used as a C〇 source.

[0026] Judging from the formulas on the right side of the above reaction formulas (7) to (12), among these compounds having a cyanogenic effect, the oxidizing effect of by-products in the case of CO is the highest, followed by CO In addition, all hydrocarbon compounds generate reducing hydrogen. Therefore, in order to prevent reoxidation, it is desirable to select a hydrocarbon compound as the carbon feed compound.

[0027] The activation effect of the alloy steel member surface according to the present invention is due to HCN. The above activation effect depends on the HCN concentration in the furnace atmosphere. Proper concentration of HCN to obtain activating effect satisfying ranges from 100- 30, 000mg / m ^3. If the concentration of HCN is less than 100 mg / m ³ , the above activating effect cannot be expected. On the other hand, HCN concentration 30, the activating effect is saturated at OOOmgZm ³ exceeds, not only economically disadvantageous, is not preferred in the sooting by thermal decomposition of a carbon feed I匕合product (carbon produced in the furnace) occurs .

The dew point of the furnace atmosphere gas is preferably 5 ° C or less. If the above dew point is higher than 5 ° C, the metal surface activated by HCN gas is re-oxidized by H〇 in the atmosphere.

2

Passivate again.

[0028] The environmental advantage of the method of the present invention is that, as explained in the above reaction formula (5), HCN that has contributed to activation of the surface of a metal member is taken into the surface of the member and nitrogen of the member is reduced. HCN, which contributes to carving and carburization, does not leave residue on the surface of the member, and is discharged as exhaust gas without contributing to the reaction, can be easily detoxified by the ammonia combustion device attached to the nitriding device. And no new equipment is required.

[0029] A further advantage of the present invention is that the nitridation processing time is reduced by the smooth progress of the nitridation process. Gas nitriding of metal members is usually performed according to the following schedule.

After the metal member was set in the furnace and the atmosphere in the furnace was vacuum-purged or replaced with nitrogen gas, the nitriding atmosphere gas (NH + N) was reduced to 1% of the furnace volume per hour.

3 2 While introducing the 10-fold amount, raise the temperature to the nitriding temperature of the metal parts and maintain it at a constant temperature. The furnace pressure during processing is atmospheric pressure

The pressure is maintained at +0.5 kPa by a pressure valve, and the extruded exhaust gas is burned and decomposed by an exhaust gas combustion device.

[0031] In the method using a fluorine-based gas described in Patent Document 1, as described in the example of Japanese Patent No. 2501925, a fluorine-based gas is introduced to activate the members. After implementation, it is necessary to exhaust the fluorinated gas and then introduce the nitriding atmosphere gas into the furnace.

On the other hand, in the present invention, in the step of raising the temperature of the metal member to the nitriding temperature, a carbon supply compound is introduced into the nitriding atmosphere gas to generate HCN to activate the metal member surface, and thereafter, the carbon supply compound By stopping the introduction, the process can be shifted to the nitriding step. This greatly reduces the time required for the nitridation process, and the reoxidation phenomenon on the metal member surface, which has been a problem with the conventional process when transitioning from activation to nitridation. Can be solved in principle.

[0033] The technical features and effects of the present invention are as described above. Hereinafter, preferred embodiments of the present invention will be described. It is preferable that the inner wall of the processing furnace used in the present invention is made of metal.However, even if the inner wall is not made of metal, the metal member to be treated serves as a catalyst for HCN, and the metal member is used as a furnace. The jig to be held inside may be made of metal. The metal constituting the metal inner wall, the metal member, and the jig includes, for example, one or more metals selected from Fe, Ni, Co, Cu, Cr, Mo, Nb, V, Ti, and Zr. Is preferred.

[0034] Metal members subjected to the surface activation treatment by the method of the present invention include steel for cold mold, steel for hot mold, steel for plastic mold, high speed tool steel, powder high speed tool steel, These include chromium molybdenum steel, maraging steel, austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, martensitic heat-resistant steel, austenitic heat-resistant steel, and nickel-based superalloys. The metal member is placed in the processing furnace by an appropriate jig according to a conventional method and subjected to a surface activation treatment.

[0035] The surface treatment gases supplied into the furnace are a carbon supply compound and ammonia, which are gases at normal temperature and normal pressure, and are supplied into the furnace from dedicated cylinders. For these gases, the metal members are set in the furnace, the atmosphere in the furnace is vacuum purged or replaced with nitrogen gas, and then the nitriding atmosphere gas (ammonia alone or ammonia + nitrogen gas or ammonia + nitrogen gas + After introducing a hydrogen gas) and establishing a reducing atmosphere, the temperature is raised and the carbon supply compound of the present invention is introduced. When the ammonia gas and the carbon supply mixture are heated in a furnace at 300 ° C or higher, HCN is generated by the catalytic action of the metal surface. The ratio of the flow rate of the nitriding atmosphere gas, ammonia, to the flow rate of the carbon feed conjugate to be introduced should be in the range of 1: 0.000001 to 1: 0.1. If the flow rate ratio of the carbon-supplying compound is lower than 1: 0.000001, the activation effect cannot be obtained because the amount of generated HCN is low. If the flow rate ratio of the carbon-supplying compound is more than 1: 0.1, the activation effect is saturated and economically disadvantageous.

[0036] The carbon supply compound is one or more gaseous compounds selected from acetylene, ethylene, propane, butane and carbon monoxide as described above, and is supplied into the processing furnace simultaneously with the ammonia-containing gas as described above. You can also. When the temperature of the ammonia-containing gas in the furnace reaches about 300 ° C., the introduction of the carbon supply compound is started. Although it is preferable in terms of efficient use of the material, in order to increase the concentration of the carbon supply compound in the furnace atmosphere at an early stage and to shorten the processing time, the carbon supply compound is introduced at the same time as the temperature rise, and It is desirable to generate HCN.

Example

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. The following examples and comparative examples were performed using a processing furnace having the structure shown in FIG. In Figure 1, 1 is a Matsufur furnace, 2 is its outer shell, 3 is a heater, 4 is an inner vessel (retort), 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 a gas guide cylinder, 11 is a umbrella, 12 is a vacuum pump, 13 is an exhaust gas combustion device, 14 is a carbon supply compound gas cylinder, 15 is an ammonia gas cylinder, 16 is a nitrogen gas cylinder, and 17 is a hydrogen gas cylinder. , 18 is a flow meter and 19 is a gas control valve.

[Example 1]

Fig. 1 (Use a SUS310S Matsufune furnace with an inner volume of 100L shown here. Inside the furnace, set the SUS304 plate and feed NH gas and N gas at a flow rate of 200 L / H, respectively, from room temperature to 55

The temperature was raised to 0 ° C in 75 minutes. When the ambient temperature reached 100 ° C. (18 minutes after the start of heating), the injection of acetylene gas 2LZH was started. After the temperature was raised to 550 ° C, the ambient temperature was maintained for 2 hours.At this point, while the injection of acetylene gas was stopped, NH gas and N gas were allowed to flow at 550 ° C for another 4 hours to advance nitriding. Then, the heating was stopped, the furnace was cooled by continuing to flow only N gas, and the test piece in the furnace was taken out when the ambient temperature became 100 ° C or less.

[0039] 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 to perform HCN analysis. From the analysis results of the HCN absorbing solution, the average HCN concentration in the furnace atmosphere during the acetylene gas injection period was 8,000 mg / m ³ . The weight increase of the SUS304 test piece before and after the nitriding treatment was measured and found to be 20 g / m ² . When the SUS304 test piece was cut and polished, etched with a marble solution, and the cut surface was observed with an optical microscope, a nitrided layer with a uniform thickness of 50 / im was formed (Fig. Photo is shown). When the surface hardness of the test piece was measured at 5 points using a Vickers hardness tester, all the values were found to have a distribution of Hv = 1200 to 1250.

[Example 2] A SUS304 plate was set in the Matsufuru furnace used in Example 1, and NH gas and N gas were fed at a flow rate of 200 LZH, respectively, and the temperature was raised from room temperature to 550 ° C in 75 minutes. The injection of 5LZH propane gas was started when the ambient temperature reached 100 ° C (18 minutes after the start of heating). After raising the temperature to 550 ° C, the atmosphere temperature was maintained for 2 hours.At this point, while propane gas injection was stopped, NH gas and N gas were further flowed at 550 ° C for 4 hours to allow nitriding to proceed. The heating was stopped, only N gas was kept flowing, and the furnace was cooled. When the temperature of the furnace reached 100 ° C or less, the test piece in the furnace was taken out.

Further, 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, and HCN analysis was performed. From the analysis results of the HCN absorption solution, the average HCN concentration in the furnace atmosphere during the propane gas injection period was 400 mg / m ³ . The weight increase of the SUS304 test piece before and after the nitriding treatment was measured and found to be 18 g / m ² . The SUS304 specimen was cut and polished, etched with a marble solution, and the cut surface was observed with an optical microscope. As a result, a nitride layer having a uniform thickness of 45 μm was formed. When the surface hardness of the test specimen was measured at five points using a Vickers hardness tester, the values of V and deviation were distributed between Hv = 1200-1250.

Example 3

The SUS304 plate was set in the Matsufurn furnace used in Example 1, and ΝΗ gas and Ν gas were fed at a flow rate of 200 LZH each, and the temperature was raised from room temperature to 550 ° C in 75 minutes. When the temperature of the atmosphere reached 100 ° C (18 minutes after the start of heating), injection of 5 L / H of C〇 gas was started. After the temperature was raised to 550 ° C, the ambient temperature was maintained for 2 hours.At this time, while the injection of C〇 gas was stopped, NH gas and N gas were further flowed at 550 ° C for 4 hours to advance nitriding. Then, the heating was stopped, only the N gas was kept flowing, the furnace was cooled, and the test piece in the furnace was taken out when the ambient temperature became 100 ° C or less.

Further, 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, and HCN analysis was performed. From the analysis results of the HCN absorption solution, the average HCN concentration in the furnace atmosphere during the CO gas injection period reached 1,000 mg / m ³ . The weight increase of the SUS304 test piece before and after the nitriding treatment was measured and found to be 18 gZm ² . SUS304 specimen was cut and polished, etched with marble solution, and the cut surface was observed with an optical microscope. After all, a nitride layer having a uniform thickness of 45 zm was formed. When the surface hardness of the test piece was measured at five points using a Vickers hardness tester, all values were distributed between Hv = 1200-1250.

Example 4

The SUS304 plate was set in the Matsufurn furnace used in Example 1 and ΝΗ gas and Ν gas were

3 2 Each was fed at a flow rate of 200 LZH, and the temperature was raised from room temperature to 550 ° C in 75 minutes. When the temperature of the atmosphere reached 100 ° C (18 minutes after the start of heating), injection of CH gas 5LZH was started.

twenty four

Started. After raising the temperature to 550 ° C, maintain the ambient temperature for 2 hours.At this point, inject CH gas.

twenty four

While stopping, nitriding was performed by flowing NH gas and N gas at 550 ° C for another 4 hours.

3 2

After that, the heating was stopped and only the N gas was kept flowing, the furnace was cooled and the ambient temperature dropped to 100 ° C or less.

2

By the way, the test piece in the furnace was taken out.

[0045] Further, 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, and HCN analysis was performed. From the analysis results of the HCN absorbing solution, the CH gas injection period

twenty four

The average HCN concentration in the furnace atmosphere reached 1,200 mg / m ³ . The weight increase of the SUS304 test piece before and after the nitriding treatment was measured and found to be 18 g / m ² . The SUS304 specimen was cut and polished, etched with a marble solution, and the cut surface was observed with an optical microscope. As a result, a nitride layer having a uniform thickness of 45 μΐη was formed. The surface hardness of the test piece was measured at five points using a Vickers hardness tester, and all values were distributed between Ην = 1200-1250.

Example 5

3 2 Each was fed at a flow rate of 200 LZH, and the temperature was raised from room temperature to 550 ° C in 75 minutes. When the temperature of the atmosphere reached 100 ° C (18 minutes after the start of heating), the injection of CH gas 5 L / H was started.

4 10

Started. After raising the temperature to 550 ° C, maintain the ambient temperature for 2 hours.At this point, inject C H gas.

4 10

3 2

2

By the way, the test piece in the furnace was taken out.

[0047] Exhaust gas from the furnace is branched, and a part of the exhaust gas is absorbed into a 2% by mass aqueous solution of caustic soda. HCN analysis was performed. From the analysis results of the HCN absorbing solution, the CH gas injection period

4 10

The average HCN concentration in the furnace atmosphere reached 600 mg / m ³ . The weight increase of the SUS304 test piece before and after the nitriding treatment was measured and found to be 18 gZm ² . When 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 zm was formed. When the surface hardness of the test piece was measured at five points using a Vickers hardness tester, all values were distributed between Hv = 1200-1250.

[Comparative Example 1]

32 Each was fed at a flow rate of 200 L / H, and the temperature was raised from room temperature to 550 ° C in 75 minutes. After raising the temperature to 550 ° C, the ambient temperature was maintained for 6 hours, and nitriding was allowed to proceed by flowing NH gas and N gas

3 2

2

By the way, the test piece in the furnace was taken out.

[0049] 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 to perform HCN analysis. As a result of analyzing the HCN absorbent, it was confirmed that no HCN was detected at all and no HCN was present in the furnace atmosphere. The weight の of the SUS304 test piece before and after the nitriding treatment was measured and found to be 10 g / m ² . The SUS304 specimen was cut and polished, etched with a marble solution, and the cut surface was observed with an optical microscope. As a result, a nitrided layer with a nonuniform thickness of 8 to 18 μm was formed (Fig. Magnification micrograph is shown). When the surface hardness of the test piece was measured at five points using a Vickers hardness tester, Hv = 500-1100 was obtained, and the absolute value was lower than that of the example.

Industrial applicability

[0050] According to the present invention, a high-alloy steel part which is difficult to perform a diffusion and infiltration treatment such as a gas nitriding method or a gas carburizing method in which a nitrided layer, a carburized layer or a carbonitrided layer is formed on the surface of a metal member. The surface passivation film is formed by using gases normally used in gas heat treatment and generating HCN gas in the furnace by utilizing the catalytic action of the surface of the metal and / or metal furnace material to be treated. By activating the surface of a high-alloyed steel member that has been passivated, it has been difficult to activate the surface with the Halogen compound, and the sediment in the furnace and the inner wall of the furnace have been damaged. Further, it is possible to provide a method for activating the surface of a metal member which is useful as a pre-stage treatment of the diffusion and infiltration treatment without causing any adverse effects such as a detoxification treatment of exhaust gas.

Brief Description of Drawings

FIG. 1 is a diagram showing the structure of a processing furnace used in the present invention.

[FIG. 2] A micrograph of a cut surface of the test piece of Example 1

[FIG. 3] A micrograph of a cut surface of the test piece of Comparative Example 1.

Explanation of symbols

[0052] 1: Matsufuru furnace

2: outer shell

3: heater

4: Inner container (retort)

5: Gas inlet pipe

6: Exhaust pipe

7: Motor

8: Fan

9: metal jig

10: Gas guide cylinder

11: umbrella

12: vacuum pump

13: Exhaust gas combustion device

14: Gas cylinder for carbon supply compound

15: Ammonia gas cylinder

16: Nitrogen gas cylinder

17: Hydrogen gas cylinder

18: Flow meter

19: Gas control valve

Claims

The scope of the claims

[1] A mixed gas containing a carbon feed mixture and ammonia as essential components at normal temperature and normal pressure is heated to 300 ° C or more in a heating furnace, and a metal member or a metal material is heated in the heated mixed gas. A method for activating the surface of a metal member, wherein HCN is generated by a catalytic action of a furnace inner wall or a metal jig, and the generated HCN is caused to act on the surface of the metal member.

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

[3] The metal furnace inner wall or the metal jig contains one or more metals selected from Fe, Ni, Co, Cu, Cr, Mo, Nb, V, Ti and Zr according to claim 1. The method for activating the surface of a metal member according to the above.

[4] The concentration of HCN generated in the furnace is 100 mg / m ³ or more, and the dew point force of the atmosphere gas in the furnace. 2. The method for activating the surface of a metal member according to claim 1, wherein the temperature is C or less.