KR100247657B1 - Method for nitriding nickel alloy - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitriding method for forming a nitride layer on the surface of a nickel alloy to improve surface hardness and the like. It is composed of forming a nitride layer on the surface of the nickel alloy by forming a deep and uniform nitride layer on the surface of the nickel alloy to increase the surface hardness of the nickel alloy.

Description

Nitriding Method of Nickel Alloy

1 is a furnace configuration diagram used for the nitriding treatment of the present invention,

2 is another furnace configuration diagram,

3 is an enlarged cross-sectional view of a nickel alloy plate (Inconel 600) made of a nitride treatment,

4 is an enlarged cross-sectional view of a nickel alloy plate (Inconel 751) made of nitriding treatment;

5 is an enlarged cross-sectional view of a nickel alloy plate (Hastelloy C) made of nitriding.

<Description of the symbols for the main parts of the drawings>

1: Muffler 2: Outskirts

3: heater 4: container

5: gas introduction pipe 6: exhaust pipe

7: motor 8: fan

11: metal mesh basket 13: vacuum pump

14: gas discharge treatment apparatus 15, 16: bombe

17: flow meter 18: valve

The present invention relates to a nitriding method for forming a nitride layer on the surface of a nickel alloy to improve surface hardness and the like.

High nickel-containing alloys such as Inconel (Ni-Cr), Hastelloy (Ni-Cr-Mo), and Incoroy have been widely used as alloys excellent in heat resistance and corrosion resistance.

In recent years, there has been a high demand for improving the characteristics such as wear resistance of nickel-containing alloys and extending their use range.

However, a method of increasing the surface hardness of nickel alloys such as Inconel has not been established at present.

The research on the method of improving the strength of the base material by fire and extrusion hardening and the study of the superplastic material using the powder material has been made.

However, according to the method of improving the base material strength by extrusion hardening, the workability of the alloy is deteriorated because the rigidity of the whole alloy is increased.

In addition, a superplastic material using a powder material is very expensive, there is a problem in practical use.

On the other hand, in the general surface hardening method made of metal, ① plating method, ② coating method such as PVD, and ③ diffusion penetration method such as nitriding and boride are mainstream.

However, for nickel alloys, some coating methods such as hard chromium plating and alumina coating have been practically used as described above.

These methods have drawbacks such as limitations in application range and processing cost due to difficulty in quality control and thin film thickness that are unique to the coating method.

In addition, as for the surface hardening method as the diffusion penetration method, plasma ion nitriding using a blower discharge has been tested in part for Inconel and Hastelloy alloys.

However, almost no nitride hardened layer is formed even when such plasma ionization is performed on the nickel alloy.

If formed, only a few microns of ultra-thin layer are partially formed.

Therefore, in the present state, nitriding of the nickel alloy is almost abandoned and is far from practical use.

This invention is made | formed in view of such a situation, Comprising: It aims at providing the nickel alloy nitriding method which makes the surface hardness of a nickel alloy high by forming the nitride layer of uniform thickness on the surface of a nickel alloy.

In order to achieve the above object, the nickel alloy nitriding method of the present invention maintains a nickel alloy in a heated state in a fluorine-based gas atmosphere, and then maintains it in a heated state under a nitride atmosphere to form a surface layer of the nickel alloy as a nitride layer. Take the configuration.

Next, this invention is demonstrated in detail.

In the present invention, nickel alloys are subjected to fluorination treatment in a fluorine-based gas atmosphere, followed by nitriding in a nitride atmosphere.

In the said nickel alloy used as the object of this invention, nickel alloy whose nickel content is 25 weight% or more (it abbreviates as "%" hereafter) is mainly used.

For example, Ni-Cr, Ni-Cr-Mo, Ni-Cr-Fe can be mentioned.

Specific examples thereof include high nickel-containing alloys such as Inconel-based, Hastelloy-based, and Incoroy-based.

In the present invention, the nickel alloy is nickel content of 25% or more.

In addition, the shape of the nickel alloy and the like is also not questioned.

In addition, the degree of processing does not matter, too.

All of the material which consists of nickel alloys, the intermediate | middle product which consists of nickel alloys, and the finished product which consists of nickel alloys falls in the range of the nickel alloy of this invention.

Examples of the fluorine-based gas used in the fluorine-based gas atmosphere in which the nickel alloy is contained therein include a fluorine compound gas composed of NF ₃ , BF ₃ , CF ₄ , HF, SF ₆ , WF ₆ , CHF ₃ , and SiF ₄ . May be used alone or in combination.

In addition to these, other fluorine compound gas containing F in the molecule can also be used as the fluorine-based gas.

In addition, a F ₂ gas and a pre-made F ₂ gas generated by pyrolyzing such a fluorine compound gas in a pyrolysis device can also be used as the fluorine-based gas.

In some cases, such as the fluorine compound gas, F ₂ gas mixture is used.

The fluorine-based gas such as fluorine compound gas and F ₂ gas can be used alone, but is usually diluted and used in an inert gas such as N ₂ gas.

For such diluted gases the concentration of the fluorine-based gas itself is, for example, 10,000-100,000 ppm, preferably 20,000-70,000 ppm, more preferably 30,000-50,000 ppm.

In the present invention, the nickel alloy is placed under such a fluorine-based gas atmosphere to be maintained in a heated state and treated with fluorination.

This is the greatest feature of this invention.

In this case, the heat preservation is carried out by heating and maintaining the nickel alloy at a temperature of, for example, 550-600 ° C.

The nickel alloy holding time in the fluorine-based gas atmosphere may be appropriately selected depending on the type of alloy, the shape size of the alloy, the heating temperature, and the like, and is usually set to several tens to several tens of minutes.

The nickel alloy is treated in such a fluorine gas atmosphere so that "N" atoms, which could not penetrate the nickel alloy metal in the past, can penetrate.

The reason for this is not clear at this stage, but it can be thought of as follows.

That is, an oxide film of NiO is formed on the surface of the nickel alloy to inhibit the penetration of "N" atoms which act as a nitride.

When the nickel alloy on which the oxide film is formed is kept under a fluorine-based gas atmosphere as described above, penetration of "N" atoms having a nitriding effect is facilitated as compared with the oxide film of NiO. Thus, the surface of the nickel alloy is fluorinated. By processing, it forms in the surface state easy to penetrate the "N" atom.

Therefore, if the nickel alloy which is in the surface state which is easy to penetrate such an "N" atom is kept in a heating state under a nitriding atmosphere as shown below, the "N" atom in the nitride gas has a constant thickness to the nickel alloy metal. It is conceivable that a deep and uniform nitride layer is formed because it penetrates uniformly.

As described above, the nickel alloy in which the "N" atom is easily penetrated by the fluorine treatment is then maintained in a heated state under nitriding atmosphere and subjected to nitriding treatment.

In this case, as the nitriding gas nitriding atmosphere to create a group consisting of only NH ₃ gas is used again, it is also used a mixed gas of a gas (e.g. RX gas) with NH ₃ and a carbon source.

Mixed use of both is also widely used.

Typically uses a mixture of an inert gas such as N ₂ gas to the group, the gas mixture.

In some cases, a mixture of these gases with H ₂ gas is also widely used.

Under such a nitriding atmosphere, the nickel alloy formed in the fluorination treatment is maintained in a heated state.

In this case, holding | maintenance in a heating state is normally set to 500-700 degreeC, and a processing time is set to 3-6 hours.

By this nitriding treatment, the surface layer of the nickel alloy is formed into a densely uniform nitride layer (the whole becomes one layer).

As a result, the surface hardness reaches Hv = 800-1100 while the hardness of the base metal of the nickel alloy is Hv = 280-380.

Although the thickness of the cured layer formed at this time is basically dependent on the nitriding temperature and the nitriding treatment time, it is difficult to form the nitride layer below 500 ° C, and above 650 ° C, the fluoride film is destroyed and Ni is easily oxidized to form the nitride layer. You can see the tendency to be uneven.

On the other hand, when the fluorination temperature is usually 400 ° C. or less, sufficient fluoride layer is not formed, and when the fluorination temperature is 600 ° C. or more, the fluorination reaction is so severe that the consumption of the muffle furnace furnace is increased, which is not suitable as an industrial process.

In the nitride layer formation, the difference between the fluoride temperature and the nitride temperature is preferably as small as possible.

For example, a sufficient nitride layer will not be formed even if it cools once after fluorination and it continues to nitrate.

Such fluorination treatment and nitriding treatment are carried out, for example, in a metal muffle shown in FIG.

That is, in this muffle, fluorination is first performed, followed by nitriding.

In Fig. 1, reference numeral 1 denotes a muffle, 2 denotes an outer perimeter, 3 denotes a heater, 4 denotes an inner container, 5 denotes a gas introduction pipe, 6 denotes an exhaust pipe, and 7 denotes a motor. , 8 is a fan, 11 is a metal basket, 13 is a vacuum pump, 14 is a gas exhaust treatment system, 15 and 16 are cylinders, 17 is a flow meter, and 18 is a flowmeter. Valve.

The nickel alloy 10 is put into a furnace as described above, and fluorine treatment is carried out while introducing a fluorine-based gas such as NF ₃ or the like into the muffle furnace 1, and then the gas is discharged from the exhaust pipe 6 by the vacuum pump 13. It is taken out by the action of and detoxified in the gas discharge treatment apparatus 14 and discharged to the outside.

Next, the cylinder 15 is connected to the flow path to introduce nitriding gas into the muffle furnace 1 for nitriding, and thereafter, the gas is discharged to the outside via the exhaust pipe 6 and the gas exhaust treatment device 14. .

In this series of operations, fluorination and nitriding are performed.

It is also possible to use the apparatus of FIG. 2 instead of the apparatus of FIG.

In the apparatus, the left side of the drawing is a fluorination chamber and the right side is a nitriding chamber.

In the figure, 2 'is a metal basket, 3' is a heater, 5 'is a gas exhaust pipe, 6' and 7 'are opening and closing lids, and 11' is a foundation, and ) Is a furnace body having a heat insulation wall, and 22 is a partition wall that moves up and down, and is divided into two chambers 23 and 24 on the left and right sides in the furnace body 21 by this partition wall 22.

(23) is formed in the fluorination chamber and (24) is formed in the nitriding chamber.

25 is a stand made up of two rails, and a metal basket 2 'containing nickel alloy is burned, and the basket 2' is allowed to slide on the rails to travel between the threads 23 and 24. It is supposed to be.

10 'is a leg of the mount 25. FIG.

Denoted at 26 is a gas inlet pipe for introducing a fluorine-based gas into the fluorine treatment chamber, at 27 a temperature sensor, and at 28 a nitride gas inlet pipe.

Moreover, the material of the said muffle furnace 1 of metal is not stainless steel, but a high-nickel heat-resistant alloy is preferable.

This apparatus is a continuous apparatus and the temperature is raised in the inactivation chamber 23 by heating when nitriding is performed in the nitriding treatment chamber 24. In this state, a nickel alloy is introduced into the fluorination treatment chamber 23, and fluorination is performed. After the gas in the processing chamber 23 is exhausted, the partition wall 22 is raised to put the nickel alloy together with the metal basket 2 'into the nitriding chamber 24 to lower the partition wall 22.

Subsequently, the fluorination treatment and the nitriding treatment are performed continuously rather than the nitriding treatment in that state.

In particular, in performing the fluorination treatment, NF ₃ may be used as the fluorine-based gas.

In other words, NF ₃ is not reactive at room temperature and is easy to handle in the form of gas, which facilitates work and makes detoxification of the exhaust gas simple.

Next, an Example is described.

Inconel 600 (Ni: 76, Cr: 16, Fe: 8) and Inconel 751 (Ni: 73, Cr: 16, Ti: 2.5) and Hastelloy C (Ni: 56, Cr: 16, Mo: 7) Three kinds of nickel alloy sheet materials were prepared, and the mixture was put in a furnace shown in FIG. 1, and the furnace was sufficiently purged with vacuum, and the temperature was increased to 550 ° C.

Then, fluorine-based gas (NF ₃ 10Vol% + N ₂ 90Vol%) was added in the state, and the furnace was brought to atmospheric pressure and held for 30 minutes in that state.

Next, after discharging the fluorine-based gas from the furnace, a nitrogen gas (NH ₃ 50Vol% + N ₂ 25Vol% + H ₂ 25Vol%) was introduced to raise the furnace to 570 ° C, and maintained for 3 hours in that state. Nitrided.

In this manner, the nitrided Inconel 600, Inconel 751, and Hasterloy C plated surfaces of the three kinds of nickel alloy plates were 15 mu m, 12 mu m, and 10 mu m, respectively, as shown in FIGS. The surface hardening layer B which consists of a nitride layer of micrometers is formed.

A is a base material of a nickel alloy.

The surface hardness of these surface hardened layers B was both Hv = 800-1000.

Inconel 600, Inconel 751 and Hasterloy C were made of three kinds of nickel alloy plates, and fluorination treatment was performed in the same manner as in Example 1.

Next, nitriding treatment was performed at a temperature of 620 ° C. for 3 hours, using a mixed gas of NH ₃ 50 Vol% + N ₂ 25 Vol% as the nitriding gas.

After the nitriding treatment, the nitriding treatment was performed at 620 占 폚 for 3 hours using the same fluorine-based gas as in Example 1, and further nitriding treatment at 620 占 폚 for 3 hours using the above-mentioned nitriding gas.

Thus, the thickness of the hardened layer which consists of the nitride layers formed in the surface about three types of nickel alloys which performed the fluorination process and the nitriding process twice continuously was measured.

As a result, the thicknesses of the hardened layers of three kinds of nickel alloy sheet materials of Inconel 600, Inconel 751 and Hasterloy C were 25 µm, 20 µm and 18 µm, respectively, and the surface hardness was the same as that of Example 1.

As the fluorine-based gas, a mixed gas of F ₂ 10 Vol% + N ₂ 90 Vol% was used.

Other than that, the fluorination treatment and the nitriding treatment were performed with respect to the three kinds of nickel alloy sheet materials as in Example 1.

As a result, the same nitride hardened layer was formed in the surface of three types of board | plate materials after a process, and the surface hardness was the same as that of Example 1.

As described above, the nitriding method of the nickel alloy of the present invention removes organic and inorganic foreign matter adhering to the nickel alloy by maintaining the nickel alloy in a heated state in a fluorine-based gas atmosphere and simultaneously removes an oxide film on the surface of the nickel alloy. It is converted to a fluoride film and then nitrided.

By converting the oxide film on the nickel alloy surface into a fluoride film in this manner, the nickel alloy surface is protected by the action of the fluoride film.

That is, the surface of the nickel alloy is protected by the presence of the fluoride film even if time passes between the fluorination treatment and the nitriding treatment.

Therefore, the oxide film does not occur again on the surface of the nickel alloy.

And since such a fluoride film can permeate "N" atom, "N" atom penetrates into the surface layer of nickel alloy by predetermined thickness and uniformity at the time of nitriding process.

As a result, without increasing the rigidity of the base material of the nickel alloy, only the surface layer can be formed with a dense and homogeneous nitride layer at a predetermined depth, and the surface hardness can be greatly improved.

Claims (4)

A nickel alloy containing 25% or more of nickel in a fluorine-based gas atmosphere is maintained in a heated state at 550-600 ° C., and then maintained in a heated state under a nitriding atmosphere to form a surface layer of the nickel alloy as a nitride layer. Nitriding Method of Nickel Alloy. The nickel alloy nitriding method according to claim 1, wherein the gas for producing a fluorine-based gas atmosphere is composed of one or more of the following (a), (b) and (c) and an inert gas which dilutes it. (a) at least one fluorine compound gas selected from the group consisting of NF ₃ , BF ₃ , CF ₄ , HF, SF ₆ , WF ₆ , CHF ₃ and SiF ₄ , (b) a F ₂ gas produced by pyrolysing the fluorine compound gas of (a), and (c) premade F ₂ gas The method of claim 1, wherein the group gas is gas to create a nitriding atmosphere consisting of only NH _3, mixed gas of NH ₃ and RX gas, or the groups gas, an inert gas is mixed with an inert gas any one of mixed gas mixed gas, or A method of nitriding a nickel alloy, wherein the mixed gas is a mixture of H ₂ gas and inert gas mixed gas. The nickel alloy nitriding method according to claim 1, wherein the nickel alloy is kept in a heated state under a nitriding atmosphere, and the nickel alloy is heated within a range of 500 to 700 ° C.