JP2014504329A - Surface treatment of metal objects - Google Patents

Abstract

The specification discloses a method of forming a diffusion surface layer extending from the outer surface to the inside of a metal substrate or member to be treated.
In the first activation stage, the method includes an activation processing furnace containing an inert fine particle heat-resistant material for forming the diffusion surface layer and a metal-based material including a metal and a metal halide. The activation process furnace in the activation process furnace for a first period of time to activate at least an external surface region of the metal-based material to form an activated metal-based material. An inert gas flow and a hydrogen halide gas flow introduced into the inert particulate refractory material and the metal-based material, and providing a diffusion treatment furnace in the next diffusion stage, wherein the metal substrate is placed in the diffusion treatment furnace The metal substrate has been pretreated to form a diffusion region that extends from the outer surface of the metal substrate to the inside without forming an oxide layer on the outer surface of the metal substrate. ,internal Diffusion treatment furnace sealed to prevent nitrogen from diffusing to form the white layer formed at least partially by the diffusion region and the outer compound or iron nitride, iron carbide or iron carbonitride compound The diffusion surface layer is formed on the metal substrate in an inert gas atmosphere in the absence of hydrogen halide gas for at least the second period and in the presence of the activated metal base substrate. The metal substrate is treated to form.
[Selection] Figure 1

Description

  The present invention relates to a method and apparatus for treating a metal substrate to obtain a diffusing surface layer on the substrate.

  Traditionally, in metal surface treatment, after formation of a nitrided surface on a substrate, physical vapor deposition is performed on the surface as a deposited coating such as titanium, chromium nitride, carbon carbonitriding.

  Several treatments are also performed where the surface material is diffused into the surface region of the substrate while nitrogen diffuses to the surface forming a chromium or titanium nitride or carbon nitride layer on the surface.

  European Patent Nos. 0471276, 0252480, 0303191 and the published patent specifications of International Publication No. WO / 47794 disclose such processing methods.

EP 0471276 European Patent No. 0252480 EP 0303191 International Publication WO / 47794

  Such a method can provide a surface treatment with better performance. This is because the surface layer here is a diffusion layer and not just a coating layer attached to the substrate. However, actual control of materials and parameters to obtain the desired results has proven to be extremely difficult.

  The use of a halide gas such as HCI mixed with a reactive gas such as hydrogen and / or ammonia or a flammable gas causes problems in the manufacture of mixed gas panels.

  In addition, HCl and other halide gases are relatively expensive, and extensive use of such gases can make the processing steps of the desired product relatively expensive.

  Halide gas also instantly at low temperatures with ammonia and ammonium chloride can cause clogging of gas pipes and backflow to gas supply device solenoid valves and flow meters that can cause clogging and potential damage to equipment. Can react.

  International Patent Application No. PCT / AU2006 / 001031 discloses a processing method and processing apparatus that allows a desired diffusion layer to be formed on a metal substrate product. The disclosed method supplies a halide gas over the treatment period. And while the method is functioning without problems, the processing costs are very high due to the volume of halide gas used.

  Accordingly, it is an object of the present invention to provide a method for forming a diffusion surface layer on a metal substrate by a more economical technique than prior art processes while maintaining the reliability and safety of processing of the metal substrate. There is.

Accordingly, a first aspect of the invention provides a method for forming a diffusing surface layer that extends into the interior of the outer surface of a metal substrate. The method includes:
(I) providing an activation treatment furnace containing an inert particulate heat-resistant material and a metal-based material for forming the diffusion surface layer in the activation stage, wherein the activation treatment furnace is activated; In order to form an activated metal base material having a surface region, inert particulates in an activation treatment furnace only for a first period to treat the outer surface region of the metal base material in an atmosphere of hydrogen halide gas Having an inert gas stream introduced into the refractory material and the metal-based material;
(Ii) providing a diffusion treatment furnace in the diffusion step, introducing the metal substrate into the diffusion treatment furnace, and forming the diffusion region extending from the outer surface to the inside of the metal substrate; Pre-treated, where at least partly formed by internal diffusion region and external compound or iron nitride, iron carbide or iron carbonitride compound without forming an oxide layer on the outer surface of the metal substrate Nitrogen is diffused to form a white layer, and in an atmosphere of inert gas in a diffusion processing furnace sealed so that the atmosphere does not enter, in the absence of hydrogen halide gas, for at least a second period and In the presence of an activated metal base substrate, the metal substrate is treated to form the diffusion surface layer on the metal substrate.

Conveniently, the method described above can further include:
(I) In the pretreatment step, the diffusion region extending from the surface of the metal substrate to the inside is formed, where nitrogen forms an internal diffusion region and a white layer of an external compound or iron nitride, iron carbide or iron carbonitride compound. Diffused to form,
(Ii) prior to the metal diffusion step, to prevent the formation of surface oxidation on the surface or to remove the surface oxidation formed on the surface, the metal substrate formed in the pretreatment step To process.

  In a preferred configuration, the method described above can be implemented in a single processing furnace that is a diffusion processing furnace that also operates as an activation processing furnace.

  Preferably, the inert gas stream in the activation stage is nitrogen and / or argon. Conveniently, the inert particulate refractory material used in the processing furnace or multiple processing paths may be aluminum oxide or silicon carbide.

  Conveniently, when the diffusion furnace contains an inert refractory particulate material, it is fluidized by the flow of inert gas during the metal diffusion stage. Alternatively, such inert heat resistant particulate material is fluidized or at least partially fluidized by vibration means. During the metal diffusion stage, ammonia is preferably not supplied to the diffusion furnace.

  In a particularly preferred embodiment, the second period is longer than the first period. Thus, the relatively expensive hydrogen halide gas is used for a much shorter period of time to obtain the desired diffusion layer on the metal substrate. During the diffusion phase, no hydrogen halide gas will be used, but a small amount of hydrogen halide gas may be used for a short period of time for reactivation of the metal base material, if desired. Normally, as needed, the hydrogen halide gas is supplied in pulses during a period when no hydrogen halide gas is supplied into the vessel and at least one period during which the hydrogen halide gas is supplied during the diffusion stage. The

  Conveniently, an inert gas stream may be supplied to the diffusion furnace during the second period, the inert gas stream changing from zero flow rate to a flow rate above the minimum flow rate for the diffusion furnace. To do.

  Conveniently, the treatment temperature in the first and second periods in the treatment furnace or treatment furnaces between the activation stage and the diffusion stage is between 500 ° C. and 750 ° C. is there.

  Preferably, in one embodiment, the hydrogen halide gas stream may be continuously supplied to the activation processing furnace only during the first period.

  As another method that can be adopted, the hydrogen halide gas may be supplied in a pulsed manner during the first period by a supply period and a non-supply period. Conveniently, the hydrogen halide gas used may be selected from among hydrogen chloride gas, hydrogen bromide gas, hydrogen fluoride gas or hydrogen iodide gas.

  The hydrogen halide gas supplied to the activation treatment furnace or the diffusion treatment furnace is mixed with an inert carrier gas (for example, nitrogen and / or argon gas) outside the treatment furnace or the plurality of treatment furnaces. It is preferable. Conveniently, when supplied, the hydrogen halide gas and the inert carrier gas enter the lower region of the processing furnace or processing furnaces.

  In a further embodiment, the hydrogen gas may be generated in the processing furnace or multiple processing furnaces by supply of ammonium chloride (NH 4 Cl). Ammonium chloride may be supplied in solid or pellet form through a transfer tube or pipe so that it separates into hydrogen gas and hydrogen chloride (HCl) gas in the transfer pipe or tube. Heated.

  An inert gas, such as nitrogen or argon, is also fed through the transfer tube so that the hydrogen chloride gas is at least partially mixed with the inert gas by the time it enters the furnace. Can also be done. Such a transport system may be utilized either in the activation stage or, if necessary, in the diffusion stage. If this transfer system is utilized, the processing temperature of the furnace may be close to 700 ° C. or higher.

The metal-based material for forming the diffusion surface layer can be selected from at least one of the following.
(I) a solid metal or metal alloy (ii) a metal or metal alloy coated on a substrate carrier (iii) a particulate or powdered metal or metal alloy (iv) a metal coated on an inert heat resistant particulate material or Metal alloy (v) Metal halide particles or powder (anhydrous or hydrated)
(Vi) Inert heat resistant particulate material or metal halide material coated on substrate carrier (anhydrous or hydrated)

  The metal-based material is chromium, titanium, vanadium, niobium, tantalum, tungsten, molybdenum, manganese, and alloys thereof, iron-based alloys or metal halides having the metal elements described above, and chromium, bromine, It may be selected from those containing a halide selected from iodine and fluorine.

  The metal substrate is conveniently an iron-based metal or an iron-based metal alloy.

  Conveniently, nitrogen as an inert gas is introduced into the diffusion furnace during the second period.

"Metal substrate" shall include metal parts suitable for heat treatment made from iron-based metals or iron-based metal alloys.
In accordance with the method of the present invention, when hydrogen chloride is the halide gas utilized and chromium metal particles are used to form the diffusion surface layer, on the chromium metal particles in the fluidized bed furnace during the activation stage; Similarly, it is believed that hydrogen chloride forms an activated chromium chloride layer on the surface of aluminum oxide.

  During the metal diffusion stage of the process, a solid phase interaction between the activated chromium chloride and the nitrogen-rich iron surface of the metal substrate to form the diffusion surface layer on the substrate. Happens.

This also occurs when the treatment furnace, usually a fluidized bed furnace, is not substantially flowed by an inert gas stream and when the bed is flowed. Bed flow can be generated either by a suitable gas flow or by vibration means as known in the art.
The process has a notable economic advantage when the hydrogen halide gas, typically hydrogen chloride, is expensive and minimizes its use.

  In general, it is desirable that substantially no holes exist in the outer portion of the diffusion region (the white layer). The white layer is usually iron nitride, iron carbide and / or iron carbonitride and is usually either epsilon and / or gamma foam.

  According to the present invention, it is possible to provide a method for forming a diffusion surface layer on a metal substrate by a method more economical than the prior art process while maintaining the reliability and safety of the treatment of the metal substrate. it can.

It is a schematic sectional drawing of the fluidized bed furnace which can be utilized in the process of this invention. FIG. 2 is a detailed cross-sectional view of a seal arrangement that can be used with the fluidized bed furnace shown in FIG. 1. FIG. 2 is a detailed cross-sectional view of a seal arrangement that can be used with the fluidized bed furnace shown in FIG. 1. It is a graph which shows the weight% density | concentration of nitrogen (N), chromium (Cr), and iron (Fe) with respect to the depth in the processed sample of Example 1 manufactured by this invention. 2 is a graph showing the weight percent of nitrogen (N), chromium (Cr), iron (Fe) and copper (Cu) with respect to depth in the copper carrier substrate of Example 1 coated with activated chromium. 2 is a graph showing the critical percentage concentrations of nitrogen (N), chromium (Cr) and iron (Fe) versus depth in a treated metal sample of Example 1 not manufactured according to the present invention. 2 is a graph showing the weight percent of nitrogen (N), chromium (Cr), iron (Fe), and copper (Cu) versus depth in the copper carrier substrate of Example 1 coated with unactivated chromium. 2 is a graph showing the weight percent of chromium (Cr), iron (Fe) and nitrogen (N) with respect to depth in a treated metal sample of Example 2 made according to the present invention. Weight of chromium (Cr), iron (Fe) and nitrogen (N) with respect to depth in the treated activated chromium sample utilized in Example 2 obtained by carrying out the process of the present invention It is a graph which shows%. % By weight of iron (Fe), nitrogen (N) and chromium (Cr) relative to depth in the metal sample when not treated with a pre-activated chromium sample as described in Example 2 It is a graph to show. Iron (Fe), chromium (Cr), nitrogen (N), carbon (C) and depth to depth in metal samples treated according to the present invention utilizing activated chromium particles as described in Example 3 Figure 2 is a quantitative depth profile showing the weight percent of oxygen (O). 12 shows the microstructure of the treated metal sample shown in FIG. 11 (Example 3). It is an X-ray diffraction analysis which shows that the diffused layer in the processed metal sample (Example 3) was mainly chromium nitride. Quantitative depth showing weight percent of chromium (Cr), iron (Fe), nitrogen (N), carbon (C) and oxygen (O) relative to depth in a metal sample treated as described in Example 4. It is a profile. Quantitative depth showing weight percent of chromium (Cr), iron (Fe), nitrogen (N), carbon (C) and oxygen (O) relative to depth in a metal sample treated as described in Example 4. It is a profile. Figure 5 shows the microstructure of the treated metal sample shown in Example 4;

  Referring to the drawings schematically showing the main part of a fluidized bed treatment apparatus according to a preferred embodiment of the present invention, at least the pretreatment stage in the heat treatment step may not be completed in a fluidized bed heat treatment apparatus, and other known techniques It can be seen from the above description that a heat treatment apparatus can be used at this stage. Furthermore, it is desirable that the activation stage and the diffusion stage be performed in the same fluidized bed heat treatment furnace, but it is equally possible that multiple isolated fluidized bed heat treatment furnaces are used for the activation stage and the diffusion stage. Is possible.

  As shown in FIG. 1, the apparatus includes a fluidized bed furnace 10 having an inner vessel 11 for containing inert heat-resistant fine particles 12 such as aluminum oxide (Al 2 O 3), but other inert heat-resistant materials can be adopted. .

  The furnace includes a heating zone 14 that will be heated in a conventional manner by burning the outer insulating layer 13 and fuel gas, by electrical resistance heating, or by other suitable means.

  In the figure, the heating region 14 is heated by a burner 16 to which fuel gas is supplied.

  An inert gas main supply line 17 for allowing the heat-resistant material 12 to flow as necessary is provided at the bottom of the container 11.

  The gas supply line 17 prevents the flow of gas flow in an airtight container and includes a main distributor 18 and a second distributor 19 that are generally made of a porous material structure for fluidization and heat treatment. Is connected to

  A further gas transport line 20 is provided so that the halogenated gas and inert carrier gas can be led to the bottom of the vessel via a distributor 21 separated from the distributor 18/19.

A carrier inert gas line (e.g., nitrogen and / or argon) is fed via line 70 to a hydrogen halide gas supplied via line 71 and mixed at valve 72 before being conveyed via line 20. Can be supplied.
The amount of inert gas conveyed via lines 70 and 17 and the amount of hydrogen halide gas conveyed via line 71 are metered so that the amount of gas conveyed to the furnace 10 is known. May be.

  The distributor 21 may be disposed in the rough heat-resistant material region 80 in the lower part of the sealed container 11.

  As an alternative, the conveying line 20 may enter through the bottom of the sealed container or any place that is the target of the distributor 21 arranged in the lower region of the sealed container, as indicated by the broken line. .

In this arrangement, the transfer line 20 may pass upward as indicated by 20 ′ before the halogenated and inactivated carrier gas returns to the distributor 21 in the lower region of the sealed container 11. In addition, one or more heating coils 81 may be provided.
The heating coil 81 is preferably just in or just above the rough refractory material region 80.

It is preferable that the halogenated gas and the inert carrier gas are sufficiently mixed outside the sealed container, and heated before the mixed gas enters the sealed container.
Preferably, heat is generated by heat exchange with the fluidized bed processing furnace region.

  With the arrangement illustrated by the solid lines, heating of the gas mixed externally occurs as the line 20 passes downward through the heated refractory material in the sealed container. Other arrangements can be employed as well.

  For example, one or more transfer pipe coils may be arranged in a line 20 in the closed vessel.

  In addition, the conveyance line 20 may pass through the heating region 14 together with one or more coils disposed in the region 14.

  In yet another possible arrangement, the pre-mixed inert carrier gas and hydrogen halide gas are directly fed into the furnace so that they are discharged via the distributor 21 without being pre-heated. You may enter.

  Metering and mixing equipment (not shown in detail) is used to ensure the proper ratio of halogenated gas to inert carrier / fluid gas used in the activation stage of the process. .

  The discharge channel 22 extends from the upper region of the closed vessel 11 for safety purposes, and the exhaust gas leaks in a controlled manner and can be processed downstream (not shown).

  Some of the refractory materials can leak along this path, and this material is generally collected in a dust collection box or container 23.

  From time to time, some reaction products may solidify in the passage 22 leading to a dead end passage.

  The scraper mechanism 24 may be provided for scraping such material, and may preferably be retracted into the collection box 23. Other approaches are not limited to the physical scraper shown.

  For example, the inert gas supplied in a pulsed form is sometimes used to crush or move the material in the discharge path 22 and return it to the sealed container 11.

  Conveniently, particulate metal or metal alloy (when utilized in the processing step) can be introduced via the discharge passage 22.

  Such a storage area 25 for particulate metal is provided with a metering valve or the like to convey a desired amount of metal particles or metal coated particulate material into the passage 22.

  When used, the scraper mechanism 24 or extruder may be used to push the metal into the sealed container 11 as needed. This is preferably performed when the bed is sinking (ie, not being processed) such that there is no gas flow or there is a minimum gas flow outward along the passage 22.

  As shown in FIG. 1, the first sealing means 27 used for the cover member 29 is provided around the upper access opening 28 communicating with the internal space of the sealed container 11.

The first sealing means 27 seals the sealed container 11 against the intrusion of air during the processing step. The features of the first sealing means 27 are easier to see in FIGS. 2 and 3, here for convenience shown with a cover member 29 for the upper access opening 28.
The first sealing means 27 is disposed between two annular flanges 33 and 34 which are on a member 35 supported by the hermetic container 11 and surround the opening 28 and which have a radial gap. A first external seal portion 30 formed by an annular flange 31 on the cover member 29 that meshes with the seal material 32 is provided.

  The first sealing means 27 is disposed between the outer flange 31 supported on the member 35 and the outer flange 31 on the cover member 29 and the annular flange 39 disposed on the inner side and supported by the cover member 29. And a second inner seal portion 36 formed by an annular flange 37 that meshes with the sealing material 38 to be formed.

  The sealant 32 or 38 may be any compressible sealant that functions at an appropriate processing temperature in the furnace, but may include ceramic fibers or VITON® rubber material.

  As shown in FIG. 2 a, when the first sealing means 27 is operatively engaged, a sealing area 40 is established between the flanges 31 and 37.

  A gas distribution tube 41 is disposed in this region 40 for conveying nitrogen, argon or other inert gas to the region 40 with such pressure that the gas leaks toward the opening 28 of the sealed container. , Supplied externally through a pipe schematically indicated by reference numeral 42. When leakage can occur, intrusion of oxygen in the atmosphere into the sealed container 11 is prevented.

  The sealing means 27 further includes a third seal portion 43 formed by an inner annular flange 39 that engages within a region 44 that normally contains the same kind of inert heat resistant particulate material 45 as that contained in the sealed container 11. Have.

  The particulate material 45 is supplied to the distributor 47 via the line 46 to assist at least the entry of the flange 39 into the particulate material 45 as the cover member 29 moves to the closed position shown in the figure. It may be made to flow by supplying active gas.

  The cover member 29 is removed to allow access to the sealed container 11. For example, this operation occurs when a processing member (for example, a metal substrate) is introduced into or removed from the sealed container.

  In the arrangement of the seal shown in FIG. 3, two annular flanges 82 and 83 rising from the member 35 are provided, which form a seal space 84 around or between the surrounding sealed portions.

  The flanges 82 and 83 are fixed to the welded or sealed portion 35 and have different heights in order to obtain the seal space 84. The upper edges 85 and 86 of the flange 82 are pushed into the appropriate sealing material 87 in an annular recess 88 in the cover member or lid 29 for sealing. Preferably, the upper edge 85 of the flange 82 is slightly lower than the upper edge 86 of the flange 83, so that if a gas leak from the seal space 84 occurs, it will be less than the outside of the sealed container. Leaks inward.

  The sealing material 87 may be the same type of material as described above for the sealing materials 32 and 38 of FIG. 2a.

  The inert gas transfer tube 42 is provided to transfer an inert gas (for example, nitrogen) to the distribution ring 41 in the seal space 84. When the furnace 10 is used, the cover member 29 is closed, and the seal space 84 is pressurized with an inert gas at a pressure higher than that in the sealed container and higher than atmospheric pressure.

  Gas leaks from the seal space 84 may occur in the direction passing through both the upper flange edges 85 and 86, but if a leak occurs, it will preferentially pass the edge 85 and the Return to sealed space.

  Thus, the required atmosphere is maintained in the sealed container without allowing unnecessary oxygen to enter the sealed container from outside air. Inside the sealing space 84, a further annular flange 89 is provided with a heat insulating material 87 between them. The heat insulating material 87 can be the same material as the heat insulating material 87 described above.

As shown in FIG. 3, the heat-resistant particle material 91 is deposited, but in the slope portion where the material is about 60 degrees with respect to the horizontal direction, further such material passes through the flange edge 85 to the inside. Returned to the sealed container 11 by gravity, helped by the inert gas leaking into the container.
In this way, leakage of refractory material from the sealed container is prevented or maintained at a very low level.

  Conveniently, the volume of the sealing space 84 is minimized to minimize the use of inert gas.

  The lid or cover member 29 supports a processing basket (or similar) support device 92, and the cover member 29 preferably has thermal insulation to avoid at least heat loss.

  In some applications, particularly when performing batch processing, it may also include a cooling coil or tube within the lid or cover member 29 to cool the furnace 10 when required at the end of the processing step. desirable.

  The lid or cover member 29 may also optionally support plugs 93 to minimize space on the processing floor.

In the following, the process of the invention according to some preferred embodiments will be described.
In the pretreatment stage, the metal part (or substrate) to be treated is subjected to a known surface treatment such as nitriding or carbonitriding. This can be obtained in a variety of different equipment including salt baths, gas heat treatment equipment, vacuum plasma equipment and fluidized bed furnaces. However, it is desirable that the so-called white layer formed through this first stage has substantially no significant pores.

  Other desirable factors are also related to the white layer microstructure, including concentration, depth, and the absence of pores therein.

  When creating a nitriding or carbonitriding structure, two regions are created.

  The first inner region is a diffusion region in which nitrogen diffuses from the substrate surface through the diffusion region into the substrate, and the hardness of the substrate is increased. The second outer region is, for example, an international A white layer that can be composed of either epsilon and / or gamma layers as illustrated in patent application number PCT / AU2006 / 001031.

  When the pretreatment stage of this process is carried out in a fluidized bed heat treatment furnace, its control includes, for carbonitriding, ammonia / nitrogen (for nitriding) and carbon containing gas (eg natural gas and / or Carbon dioxide) to the bed.

  During the carbonitriding process, it is important that some oxygen is included in the process that is contributed by hydrocarbon gas, carbon dioxide and / or oxygen.

  Once the pretreatment step is successfully completed, the part or substrate to be treated needs to be treated so that no surface oxides are present on the surface of the metal to be diffusion treated.

In order to obtain (or maintain) a suitable surface finish, one of the following options may be employed:
(I) The surface of the part or substrate may be mechanically treated like re-polishing and may be maintained in an inert atmosphere before the procedure according to the second stage.
(Ii) The surface of the part or substrate can be treated in a completely inert gas atmosphere or during evacuation between the pretreatment stage and the metal diffusion stage until activation. .
(Iii) Some surface oxides on the surface of the component or the substrate can be removed in the activation step using a combination of halogenated gas and hydrogen.
(Iv) The surface of the part may be the subject of a wet polishing process, where the grain, air and water pressure may be altered to blast the surface. This process selectively removes the cover layer while maintaining the desired white layer.

  In the activation stage of the process, the metal or metal base material whose surface is to be diffusion treated is placed and held in a fluidized bed furnace operating at a temperature lower than 750 ° C, preferably higher than 700 ° C. May be.

  Conveniently, the temperature is in the range of 500 ° C to 700 ° C, usually about 575 ° C. The floor itself includes an inert heat resistant particulate material, such as Al2O3, along with the desired metal that is to be diffused to the particulate or powdered surface in the floor or coated with the inert heat resistant particulate. May be.

  Such metals preferably comprise 5 to 30 percent by weight of flooring material, i.e. balanced to become an inert heat resistant particulate material. The bed is then fluidized by a flow of a halogenated gas (eg, hydrogen chloride) and an inert gas without a metal substrate to be treated during the first period.

  Said inert gas is argon and / or nitrogen in the presence of a halogenated gas (eg HCl) premixed in a separately introduced inert carrier gas stream (eg nitrogen and / or argon). May be. Preferably, the metal powder introduced into the floor should be of high purity and preferably free of surface oxides.

  Thus, measurements need to be taken before the powder enters the floor and while they remain on the floor itself to prevent contact with the atmosphere. The gas used must also be highly pure. The shared inert gases that can be used in the process are high purity nitrogen (oxygen below 10 ppm), high purity argon (oxygen below 5 ppm), and the first pretreatment stage process includes This is further dried by passing industrial ammonia with less than 500 ppm water vapor and, for example, a solid desiccant before use. The hydrogen halide gas used may suitably be industrial HCl, but other hydrogen halide gases may be used. Said hydrogen halide gas preferably constitutes 0.2 to 3% of the total gas stream flowing to the fluidized heat treatment bed furnace.

  The hydrogen halide gas stream needs to be well mixed with the inert carrier gas and rigorously adjusted before entering the bed. This is important in avoiding unevenness in the floor. The hydrogen halide gas may be preheated before it enters the bed so that it is most reactive when it enters the bed.

  The residual heat of the halogenated gas and the inert carrier gas is effective in further reducing the amount of hydrogen halide gas required.

  The first period may suitably be 45 to 120 minutes, preferably from 60 to produce an activated layer on the diffusion metal and on the inert fluid medium (aluminum oxide) in the bed. It may be between 90 minutes. When chromium is used and the hydrogen halide gas is hydrogen chloride, the activated layer is chromium chloride.

  At the end of this initial activation period, the pretreated metal substrate (pretreated as described above) is immediately introduced into the hearth or the hearth containing the activated metal base material and halogenated. The gas flow is stopped.

  During the next metal diffusion stage, the metal substrate on which a diffusion layer is to be formed is a second period (preferably 1 to 8 hours, preferably in the pre-activated floor. For 4 to 8 hours) under an inert gas atmosphere.

  The bed is conveniently kept at a temperature below 750 ° C, preferably in the range of 500 ° C to 700 ° C, and preferably about 575 ° C. The fluidized bed in the metal diffusion stage may have a minimum inert gas flow that is substantially reduced to a high inert gas flow that is highly fluidized.

  The inert gas may be nitrogen. In some cases, if the bed is deemed to require some reactivation, it is desirable to have a halide gas stream supplied in pulses during the second stage.

  During the treatment process, it is generally desirable to maintain a relatively uniform temperature level within the floor, i.e., between various heights within the floor. This may be realized by providing a temperature monitoring means and changing the flow of the inert gas to the floor according to the detected temperature.

  The metal or metal base material used to supply the metal to be diffused into the diffusion surface layer of the metal substrate to be treated is in the form of particulates or one or more solid block members, substrate carrier May be selected from at least one of a solid metal or metal alloy that is either a metal or an alloy coated on the substrate, wherein the substrate carrier is particulate or one or more solid block members; The substrate carrier is coated on the substrate metal or metal alloy or the metal substrate to be treated, metal halide particles or powder (anhydrous or hydrated), and the substrate carrier within processing conditions. Does not react with the formed metal halide material (anhydrous or hydrated), wherein the substrate carrier is When a particle-like or one or more solid block members, wherein the substrate carrier is in the range of processing conditions, does not react with the metal substrate to be said coating metal or metal alloy or process.

  Preferably, the metals of the metal base material used to provide the metal to be diffusion treated include those containing chromium, titanium, vanadium, niobium, tantalum, tungsten, molybdenum, manganese, and iron based alloys. It is possible to select from these alloys.

  Conveniently, the metal halide described above may comprise a metal selected as described above and a halide selected from chlorine, bromine, iodine, fluorine. For example, CrCl2 and CrCl3 can be dissolved in water or ethanol to form a suspension, which can be applied onto a suitable carrier substrate or carrier group to form a suitable coating. The material can be immersed in the suspension.

  Some examples of preferred embodiments of the process of the present invention are described below.

Example 1

Hardened and tempered 38mm diameter and 5mm thick sample (autenitised at 1020 ° C, air cooled, tempered twice at 575 ° C) AISI H13 hot work tool steel, 35% ammonia, 5% carbon dioxide, nitrogen Carbonitriding was performed at 575 ° C for 3.5 hours under 60% atmosphere.
Prior to carbonitriding, the surface of this sample was pretreated with # 1200 SiC abrasive to ensure a good surface finish.

  This created a surface structure consisting of a 1 micron layer rich in oxygen just above a 10 micron compound layer of epsilon iron carbonitride and finally an internal diffusion region of 70-90 microns.

  The surface of the carbonitrided sample is subjected to wet abrasive spraying while holding the compound layer and diffusion layer in order to remove the oxide layer. The chromium composition in the compound layer is defined to be about 4 wt%.

  A sample of pure copper having a diameter of 38 mm and a thickness of 5 mm is polished by a commercial component manufacturer to have a No. 1200 SiC finish prior to electrohard chromium plating. A 2 micron pure chromium layer is produced by this method.

  Copper is selected as the substrate carrier, as Cr and Cu are essentially insoluble, so the chromium layer does not corrode by diffusion into the copper sample during heating. This chrome-plated sample is immersed in a fluidized bed heat treatment reactor having a diameter of 90 mm and a depth of 250 mm containing 3 kg of alumina oxide powder having an average particle size of 125 microns and a purity of 99.99%.

  The fluidized bed is heated to 575 ° C. under a nitrogen atmosphere, at which temperature hydrogen chloride gas is added to the feed gas stream to a concentration of 1% of the total gas stream. This “activation” phase lasted for 1 hour. After this activation stage, the chrome plated copper sample was cooled to room temperature in a stream of nitrogen.

  Immediately after removal from the fluid bed reactor to the atmospheric environment, the chromium plated copper sample activated by hydrogen chloride was bonded to the physically carbonitrided sample and subjected to clamping pressure. This bond was obtained in a fluidized bed furnace, heated to 575 ° C. under a stream of nitrogen, held at this temperature for 4 hours, and cooled to room temperature under a stream of nitrogen.

  This experiment was repeated, where the bond consists of chromium-plated copper that has not been treated with hydrogen chloride as described above and a carbonitrided sample.

  In releasing the bond, the chemical composition of the two bonded surfaces was analyzed using Glow Discharge Optical Emission Spectroscopy (GDOES). When the surface of a chromium plated copper sample was activated with hydrogen chloride, it was found that this surface reacted with the carbonitrided sample. Chromium moves from the activated chrome-plated sample to the carbonitrided sample (FIG. 4), and there is a reduction of chromium on the chrome-plated copper sample (FIG. 5). Nitrogen diffuses into the surface to increase the amount of chromium on the carbonitrided surface to a maximum amount consistent with the maximum amount of chromium (FIG. 4). Iron moved from the carbonitrided sample to the chromium plated sample (FIG. 5). In response, the iron concentration decreased on the carbonitrided sample (FIG. 4). On the other hand, no reaction occurred between the non-activated chromium plated copper and the carbonitrided surface.

  There was no increase in chromium on the carbonitrided surface (FIG. 6) or a decrease in chromium from the chromium plated copper sample (FIG. 7). This example illustrates the importance of activation of the chromium surface with hydrogen chloride in transferring chromium metal from the chromium surface to a surface region rich in nitrogen.

Example 2
Hardened and tempered 38mm diameter and 5mm thick sample (autenitised at 1020 ° C, air cooled, tempered twice at 575 ° C) AISI H13 hot work tool steel, 35% ammonia, 5% carbon dioxide, nitrogen Carbonitriding was performed at 575 ° C for 3.5 hours under 60% atmosphere.

  Prior to carbonitriding, the surface of this sample was pretreated with a # 1200 SiC abrasive to provide a good surface finish. This created a surface structure consisting of a 1 micron layer rich in oxygen just above a 10 micron compound layer of epsilon iron carbonitride and finally an internal diffusion region of 70-90 microns.

  The surface of the carbonitrided sample is subjected to wet abrasive spraying while holding the compound layer and diffusion layer in order to remove the oxide layer. The chromium composition in the compound layer is defined to be about 4 wt%.

  Chromium with a diameter of 38 mm and a thickness of 5 mm and a purity of 99.99% is polished to a No. 1200 SiC finish and contains 3 kg of alumina powder with an average particle size of 125 microns and a purity of 99.99%. A fluidized bed with a diameter of 90 mm and a depth of 250 mm It is immersed in a heat treatment reactor. The fluidized bed was heated to 575 ° C. under a nitrogen atmosphere, at which temperature hydrogen chloride gas was added to the feed gas stream until a concentration of 1% of the stream was reached. This “activation” phase lasted for 1 hour. After this activation step, the chromium sample was cooled to room temperature in a nitrogen stream.

  Immediately after removal from the fluidized bed reactor to the atmospheric environment, the chromium sample activated by hydrogen chloride was bonded to the physically carbonitrided sample and subjected to clamping pressure. This bond was obtained in a fluidized bed furnace, heated to 575 ° C. under a stream of nitrogen, held at this temperature for 4 hours, and cooled to room temperature under a stream of nitrogen. This experiment was repeated, where the bond consists of chromium that has not been treated with hydrogen chloride as described above and a carbonitrided sample. When the bond was released, the chemical composition of the two bonded surfaces was analyzed using Glow Discharge Optical Emission Spectroscopy (GDOES).

  For Example 1, this surface reacted with the carbonitrided sample by activating the chromium surface with hydrogen chloride gas.

  Nitrogen is diffusing to the surface in order to move chromium from the activated chromium sample to the carbonitrided sample to a maximum amount consistent with the maximum amount of chromium (FIG. 8).

Iron migrated from the carbonitrided sample to the chromium plated sample (Figure 9).
In response, the iron concentration decreased on the carbonitrided sample (FIG. 8). On the other hand, no reaction occurred between the previously unactivated chromium and the carbonitrided surface. There was no increase in chromium on the carbonitrided surface (FIG. 10).

Example 3

Two hardened and tempered specimens with a diameter of 38 mm and a thickness of 5 mm (autenitised at 1020 ° C, air cooled, tempered twice at 575 ° C) AISI H13 hot work tool steel, 35% ammonia, 5% carbon dioxide Carbonitriding was performed at 575 ° C for 3.5 hours in an atmosphere of 60% nitrogen.
Prior to carbonitriding, the surface of each sample was pretreated with # 1200 SiC abrasive to ensure a good surface finish.

  This created a surface structure consisting of a 1 micron layer rich in oxygen just above a 10 micron compound layer of epsilon iron carbonitride and finally an internal diffusion region of 70-90 microns.

  The surface of the carbonitrided sample is subjected to wet abrasive spraying while holding the compound layer and diffusion layer in order to remove the oxide layer. The chromium composition in the compound layer is defined to be about 4 wt%. In a fluidized bed heat treatment reactor having a diameter of 90 mm and a depth of 250 mm, 380 g of chromium powder having an average particle size of 80 microns and a purity of 99.99% was mixed with 3.4 kg of alumina powder having an average particle size of 125 microns and a purity of 99.99%.

  This fluidized bed is heated to 575 ° C. in a high purity nitrogen atmosphere with sufficient flow for fluidization, and at this temperature the carbonitrided sample AISH13 described above is heated and flowing powder. Soaked for 4 hours. The sample was cooled to 350 ° C. under a stream of nitrogen in the fluidized bed and cooled in the atmosphere. As a result of this process, there was no increase in chromium on the carbonitrided surface.

  In a fluidized bed heat treatment reactor having a diameter of 90 mm and a depth of 250 mm, 380 g of chromium powder having an average particle size of 80 microns and a purity of 99.99% was mixed with 3.4 kg of alumina powder having an average particle size of 125 microns and a purity of 99.99%.

  This fluidized bed is heated to 575 ° C. under a high purity nitrogen atmosphere with sufficient flow for fluidization, at which temperature hydrogen chloride gas is fed into the feed gas stream until a concentration of 1% of the stream is reached. Added.

  This “activation” phase lasted for 1 hour. After activation, a sample of carbonitrided AISH13 prepared as described above was immersed in a heated flowing powder with the hydrogen chloride gas flow stopped. The heat treatment here is 575 ° C. for 4 hours.

The sample was cooled to 350 ° C. under a stream of nitrogen in the fluidized bed and cooled in the atmosphere.
In this test, a significant chromium increase on the carbonitrided surface (about 70 wt%, see quantitative depth profile in FIG. 12) is identifiable, uniform and continuous 2.5 micron. It was confirmed that a layer having a thickness (FIG. 12) was formed. X-ray diffraction analysis showed that the layer was mainly CrN (FIG. 13).

Example 4

  Two steel grades with higher tempering resistance than AISI H13 hot tool steel were selected to evaluate the possibility of increasing the processing temperature above 575 ° C.

  Hardened and tempered 38 mm diameter and 5 mm thick sample (autenitised at 1050 ° C., oil cooled, tempered twice at 575 ° C.) powder metallurgy tool steel Crucible CPM 1V® and conventional ingot metallurgy Bohler -Uddeholm QRO® 90 was carbonitrided at 575 ° C for 3.5 hours in an atmosphere of 35% ammonia, 5% carbon dioxide, 60% nitrogen.

  Prior to carbonitriding, the surface of each sample was pretreated with # 1200 SiC abrasive to ensure a good surface finish.

  This created a surface structure consisting of a 1 micron layer rich in oxygen just above a 10 micron compound layer of epsilon iron carbonitride and finally an internal diffusion region of 70-90 microns.

  The surface of the carbonitrided sample is subjected to wet abrasive spraying while holding the compound layer and diffusion layer in order to remove the oxide layer. The chromium composition in the compound layer is defined to be about 4 wt%.

  In a fluidized bed heat treatment reactor having a diameter of 90 mm and a depth of 250 mm, 380 g of chromium powder having an average particle size of 80 microns and a purity of 99.99% is mixed with 3.4 kg of alumina oxide powder having an average particle size of 125 microns and a purity of 99.99%. It was.

  The fluidized bed is heated to 625 ° C. under a high purity nitrogen atmosphere with sufficient flow for fluidization, at which temperature hydrogen chloride gas is fed into the feed gas stream to a concentration of 1% of the stream. Added. This “activation” phase lasted for 1 hour.

  After activation, each grade of carbonitrided sample prepared as described above was immersed in a heated flowing powder under a high purity nitrogen atmosphere for 4 hours.

  The sample was cooled to 350 ° C. under a stream of nitrogen in the fluidized bed and removed from the fluidized bed reactor and cooled in the atmosphere.

In this test, a significant chromium increase on the carbonitrided surface (about 70 wt%, see quantitative depth profile in FIGS. 14 and 15) was confirmed along with the corresponding nitrogen peak value.
Compared to treatment at 575 ° C., performing the chromium deposition step at 625 ° C. resulted in an increase of about 4-6 microns in layer thickness (FIG. 15).

  Under the CrN layer, the diffusion region and core hardness were substantially maintained.

DESCRIPTION OF SYMBOLS 11 Inner container 10 Fluidized bed furnace 13 External insulation layer 14 Heating area 16 Burner 12 Heat resistant material 17 Gas supply line 20 Gas conveyance line 71 Line 72 Valve 70 Line 21 Distributor 80 Heat resistant material area

Claims (25)

A method of forming a diffusing surface layer that extends into the interior of an outer surface of a metal substrate, the method comprising:
(I) providing an activation treatment furnace containing an inert particulate heat-resistant material and a metal-based material for forming the diffusion surface layer in the activation stage, wherein the activation treatment furnace is activated; In order to form an activated metal base material having a surface region, inert particulates in an activation treatment furnace only for a first period to treat the outer surface region of the metal base material in an atmosphere of hydrogen halide gas Having a flow of inert gas introduced into the refractory material and the metal-based material;
(Ii) providing a diffusion treatment furnace in the diffusion step, introducing the metal substrate into the diffusion treatment furnace, and forming the diffusion region extending from the outer surface to the inside of the metal substrate; Pre-treated, where at least partly formed by internal diffusion region and external compound or iron nitride, iron carbide or iron carbonitride compound without forming an oxide layer on the outer surface of the metal substrate Nitrogen is diffused to form a white layer, and in an atmosphere of inert gas in a diffusion processing furnace sealed so that the atmosphere does not enter, in the absence of hydrogen halide gas, for at least a second period and In the presence of an activated metal base substrate, the metal substrate is treated to form the diffusion surface layer on the metal substrate.   The method according to claim 1, wherein the activation processing furnace is the same as the diffusion processing furnace.   The method according to claim 1, wherein the diffusion processing furnace is different from the activation processing furnace. The method according to claim 1, further comprising:
(I) In the pretreatment step, the diffusion region extending from the surface of the metal substrate to the inside is formed, where nitrogen forms an internal diffusion region and a white layer of an external compound or iron nitride, iron carbide or iron carbonitride compound. Diffused to form,
(Ii) Prior to the metal diffusion step, the metal substrate formed in the pretreatment step to prevent the formation of surface oxidation on the surface or to remove the surface oxidation formed on the surface Process.   5. The method according to claim 1, wherein the inert gas stream in the activation stage is nitrogen and / or argon.   6. The method according to claim 1, wherein the inert particulate heat-resistant material is aluminum oxide or silicon carbide.   7. The method according to claim 1, wherein the diffusion furnace contains an inert heat-resistant particulate material that is fluidized by an inert gas flow during the metal diffusion stage.   7. The method according to claim 1, wherein the diffusion furnace contains an inert heat-resistant particulate material that is at least partially fluidized by vibration means during the metal diffusion stage.   9. The method according to claim 1, wherein no ammonia is supplied to the diffusion processing furnace during the metal diffusion stage.   10. The method according to claim 1, wherein the second period is longer than the first period.   11. The method according to claim 1, wherein during the second period, the hydrogen halide gas is at least one of a period in which there is no hydrogen halide gas flow and a period in which the hydrogen halide gas flow flows. During the period, the diffusion treatment furnace is supplied in pulses.   12. The method according to any one of claims 1 to 11, wherein the diffusion treatment furnace contains an inert heat resistant particulate material, and an inert gas stream is supplied to the diffusion treatment furnace for a second period of time. The active gas flow changes from zero flow rate to a flow rate above the minimum flow rate for the diffusion furnace.   13. The method according to claim 1, wherein a temperature of 500 to 750 ° C. is maintained in the activation processing furnace during the first predetermined period.   14. The method according to claim 1, wherein a temperature of 500 to 750 ° C. is maintained in the diffusion processing furnace during the second predetermined period.   15. The method according to claim 1, wherein the hydrogen halide gas is continuously supplied to the activation processing furnace during the first predetermined period.   15. The method according to claim 1, wherein the hydrogen halide gas is pulsed to the activation treatment furnace during a supply period divided by a non-supply period during the first predetermined period. Supplied.   17. The method according to any one of claims 1 to 16, wherein the hydrogen halide gas is selected from hydrogen chloride gas, hydrogen bromide gas, hydrogen fluoride gas, or hydrogen iodide gas.   15. The method according to claim 1, wherein the hydrogen halide gas is mixed with the inert gas prior to entering the activation treatment furnace.   15. The method according to claim 1, wherein the hydrogen halide gas is mixed with the inert gas prior to entering the diffusion treatment furnace.   The method of claim 1, wherein ammonium chloride is supplied to the activation furnace during the activation stage, and the ammonium chloride is supplied with hydrogen gas and hydrogen chloride for activation of the metal base material. Heated while being introduced to separate into (HCl) gas.   21. The method according to claim 18, 19 or 20, wherein a mixture of the hydrogen halide gas and the inert carrier gas enters a lower region of the activation processing furnace or diffusion processing furnace. 22. The method according to any one of claims 1 to 21, wherein the metal-based material for forming the diffusion surface layer is selected from at least one of the following.
(I) a solid metal or metal alloy (ii) a metal or metal alloy coated on a substrate carrier (iii) a particulate or powdered metal or metal alloy (iv) a metal coated on an inert heat resistant particulate material or Metal alloy (v) Metal halide particles or powder (anhydrous or hydrated)
(Vi) Inert heat resistant particulate material or metal halide material coated on substrate carrier (anhydrous or hydrated)   23. A method according to any one of claims 1 to 22, wherein the metal-based material is chromium, titanium, vanadium, niobium, tantalum, tungsten, molybdenum, manganese, and alloys thereof, an iron-based alloy or the above-mentioned Selected from metal halides having selected metal elements and those containing halides selected from chromium, bromine, iodine and fluorine.   24. The method according to any of claims 1 to 23, wherein the metal substrate is an iron-based metal or an iron-based metal alloy.   25. The method according to claim 1, wherein the inert gas introduced into the diffusion processing furnace during the second predetermined period is nitrogen.