Gas oxynitriding method

Abstract

The present invention discloses a gas oxynitriding method comprising the steps of: removing foreign substances from the surface of an object; introducing the object into a chamber of a nitriding furnace; injecting nitrogen into the chamber and raising the temperature within the chamber; injecting ammonia and carbon dioxide into the chamber and exposing the object while maintaining the pressure and temperature within the chamber; cooling the temperature within the chamber; maintaining the pressure and temperature within the chamber and then injecting steam into the chamber to oxynitrid the object and form an oxide film (Fe3O4) layer; and cooling the temperature within the chamber and then removing the object from the chamber. According to the present invention, nitrogen, ammonia, and water vapor are used, and the reaction time of oxynitriding can be reduced through pressure control.

Description

Technology Field

[0001] The present invention relates to a gas oxynitridation method, and more specifically, to a gas oxynitridation method for piping components such as valves and manifolds. Background Technology

[0002] The contents presented in this section are intended merely to provide background information for the present invention and do not constitute prior art.

[0003] Piping components and fittings, such as various plug valves, choke valves, tees, crosses, and elbows, that constitute manifold modules used in oil and shale gas field development often require both impact strength and high surface hardness.

[0004] In such cases, a method of applying a special treatment to the surface of a part to improve properties such as surface hardness, wear resistance, and heat resistance, while providing the interior with appropriate strength to significantly increase resistance to impact, is called surface hardening.

[0005] As one of the surface hardening methods, nitriding involves heating steel for nitriding in an ammonia stream or salt bath to diffuse and penetrate nitrogen, thereby forming an iron nitride (FeN) layer on the surface of the steel in the nitriding furnace.

[0006] These nitriding methods include gas nitriding, liquid nitriding (or salt bath nitriding), soft nitriding, and ion nitriding.

[0007] Gas nitriding is a method of obtaining a nitrided layer with high hardness on a metal surface by reacting activated nitrogen, produced by heating and decomposing ammonia gas, with the metal surface, and requires a process time of about 50 to 100 hours.

[0008] Unlike other surface hardening treatments, nitriding is performed at significantly lower temperatures below the transformation point. Since it is processed at temperatures of 500 to 600°C, it is widely used as a surface hardening treatment with minimal deformation. However, to obtain high hardness, steel grades containing nitride-forming elements such as chromium and molybdenum are essential, which imposes many restrictions on the steels that can be treated. Prior art literature

[0009] Republic of Korea Registered Patent No. 10-2196477 (Published Dec. 30, 2020) The problem to be solved

[0010] The problem that the present invention aims to solve is to provide a gas oxynitriding method capable of improving the corrosion resistance, wear resistance, moisture resistance, and surface hardness of an object through oxynitriding.

[0011] The problem that the present invention aims to solve is not limited to the problems mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0012] To achieve the above objectives, according to one embodiment based on the technical concept of the present invention, the method comprises: a step of removing foreign substances from the surface of an object; a step of introducing the object from which foreign substances have been removed into the chamber of a nitriding furnace; a step of injecting nitrogen (N2) into the chamber at a constant pressure and raising the temperature so that the temperature inside the chamber becomes 540 to 560°C; a step of injecting ammonia (NH3) and carbon dioxide (CO2) into the chamber and exposing the object while maintaining the pressure inside the chamber at 200 mmAq and the temperature in the range of 540 to 560°C for 480 minutes; a step of cooling the temperature inside the chamber to 510 to 530°C; a step of maintaining the pressure inside the chamber at 0.4 to 0.6 MPa and the temperature at 510 to 530°C for 300 minutes, then injecting steam into the chamber and oxynitriding the object while maintaining the temperature at 510 to 530°C for 20 minutes to form an oxide film (Fe3O4) layer; A gas nitriding method is disclosed, configured to include the step of cooling the temperature inside the chamber to 130°C or lower and then removing the object from the chamber.

[0013] In addition, the gas oxynitriding method is characterized by the heating step being carried out gradually over 240 minutes.

[0014] In addition, the gas nitriding method is characterized in that the step of cooling the temperature inside the chamber to 510 to 530°C occurs while the pressure inside the chamber is maintained at 50 to 200 mmAq.

[0015] In addition, the gas oxynitriding method is characterized in that the step of forming an oxide film layer involves injecting steam of 0.4 to 0.6 MPa into a chamber at a temperature of 510 to 530°C for 30 minutes to oxynitrid the object and form an oxide film (Fe3O4) layer.

[0016] In addition, the gas nitriding method is characterized in that the step of cooling the temperature inside the chamber to 130°C or lower is performed by slowly cooling for 120 minutes while maintaining the pressure inside the chamber at 50 to 200 mmAq.

[0017] Specific details of other embodiments are included in "Specific details for implementing the invention" and the attached "drawings".

[0018] The advantages and / or features of the present invention and the methods for achieving them will become clear by referring to the various embodiments described below in detail together with the accompanying drawings.

[0019] However, it should be understood that the present invention is not limited to the configurations of each embodiment disclosed below, but may be implemented in various different forms, and that each embodiment disclosed in this specification is provided merely to make the disclosure of the present invention complete and to fully inform those skilled in the art of the scope of the present invention, and that the present invention is defined only by the scope of each claim of the claims. Effects of the invention

[0020] According to the present invention, the corrosion resistance, wear resistance, moisture resistance, and surface hardness of an object can be improved through oxynitridation compared to conventional technology.

[0021] The effects obtainable by the gas nitriding method according to the technical concept of the present invention are not limited to the effects mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art to which the present invention belongs from the description below. Brief explanation of the drawing

[0022] FIG. 1 is a flowchart of a gas nitriding method according to one embodiment of the present invention. Figure 2 is a graph of a gas nitriding method according to one embodiment of the present invention. Figure 3 is a schematic diagram of a hardened layer formed on an object. Specific details for implementing the invention

[0023] Before describing the present invention in detail, it should be understood that the terms and words used in this specification should not be interpreted as being limited to their ordinary or dictionary meanings, and that the inventor of the present invention may appropriately define and use the concepts of various terms to best describe their invention, and furthermore, that these terms and words should be interpreted in a meaning and concept consistent with the technical spirit of the present invention.

[0024] In other words, it should be understood that the terms used in this specification are used merely to describe preferred embodiments of the present invention and are not intended to specifically limit the content of the present invention, and that these terms are defined in consideration of various possibilities of the present invention.

[0025] In addition, it should be noted that in this specification, singular expressions may include plural expressions unless the context clearly indicates a different meaning, and that even if they are expressed in a similarly plural form, they may include the meaning of the singular.

[0026] Throughout this specification, where it is stated that a component "includes" another component, unless specifically stated otherwise, this may mean that it does not exclude any other component but may include any other component.

[0027] Furthermore, it should be noted that in cases where it is stated that a component "exists inside or is installed in connection with" another component, this component may be installed in direct connection or contact with the other component, or it may be installed at a certain distance apart, and in the case where it is installed at a certain distance apart, there may be a third component or means for fixing or connecting the component to the other component, and a description of this third component or means may be omitted.

[0028] On the other hand, if it is stated that one component is "directly connected" or "directly connected" to another component, it should be understood that there is no third component or means.

[0029] Likewise, other expressions describing the relationship between each component, such as “between” and “right between”, or “adjacent to” and “directly adjacent to”, should be interpreted as having the same intent.

[0030] In addition, it should be understood that in this specification, terms such as “one side,” “other side,” “one side,” “other side,” “first,” “second,” etc., are used to clearly distinguish one component from another component, and that the meaning of the component is not restricted by such terms.

[0031] In addition, position-related terms such as "up," "down," "left," and "right" used in this specification should be understood as indicating the relative position of the corresponding component in the drawing, and unless an absolute position is specified, these position-related terms should not be understood as referring to an absolute position.

[0032] Furthermore, in specifying the reference numerals for each component of each drawing in this specification, the same component has the same reference numeral even if it is shown in different drawings; that is, the same reference numeral throughout the specification indicates the same component.

[0033] In the drawings attached to this specification, the size, position, connection relationships, etc., of each component constituting the present invention may be described in a partially exaggerated, reduced, or omitted manner for the convenience of explanation or to sufficiently clearly convey the concept of the present invention, and therefore, the proportions or scale may not be strictly accurate.

[0034] In addition, in the following description of the present invention, detailed descriptions of components that are deemed to unnecessarily obscure the essence of the present invention, such as known technologies including prior art, may be omitted.

[0035] Hereinafter, embodiments of the present invention will be described in detail with reference to the relevant drawings.

[0036] FIG. 1 is a flowchart of a gas nitriding method according to one embodiment of the present invention.

[0037] Referring to FIG. 1, a gas nitriding method (S100) according to one embodiment of the present invention may be configured to include removing foreign substances from the surface of an object (S110), introducing an object into a chamber of a nitriding furnace (S120), injecting nitrogen into the chamber and raising the temperature (S130), injecting ammonia and carbon dioxide into the chamber (S140), cooling (S150), injecting steam and forming an oxide film layer (S160), and cooling and discharge (S170).

[0038] Figure 2 is a graph of a gas nitriding method according to one embodiment of the present invention.

[0039] Referring to FIGS. 1 and 2, foreign substances on the surface of the object can be removed (S110). For example, the surface of the object can be cleaned first using alcohol and then cleaned second using methylene chloride (MC). Before removing the foreign substances, the appearance, material, and quantity of the object can be visually checked.

[0040] Next, the object from which the material has been removed can be introduced into the chamber of the nitriding furnace (S120). The object, for example, piping components and pipe fittings such as various plug valves, choke valves, Tees, Crosses, and Elbows that constitute a manifold module used in oil field and shale gas field development, can be laid out in a basket and taken out. Care must be taken to maintain the spacing between the parts and to prevent the parts from colliding with each other.

[0041] Next, nitrogen (N2) is injected into a chamber with constant pressure, and the pressure inside the chamber is maintained at 50 mmAq to 200 mmAq, and the temperature can be raised to 540°C to 560°C (S130).

[0042] Here, the heating step (S130) is characterized by being carried out gradually over 240 minutes.

[0043] Next, ammonia (NH3) gas and carbon dioxide (CO2) are injected into the chamber in a ratio of 4:1, and the object can be exposed for 480 minutes while maintaining the pressure inside the chamber at 200 mmAq and the temperature in the range of 550 ± 10℃, i.e., 540 to 560℃ (S140).

[0044] Next, the temperature inside the chamber can be cooled to a range of 520±10℃, i.e., 510℃ to 530℃ (S150).

[0045] Here, the step (S150) of cooling the temperature inside the chamber to 510°C to 530°C is characterized by taking place for about 30 minutes while the pressure inside the chamber is maintained at 50 mmAq to 200 mmAq.

[0046] Next, the pressure inside the chamber is maintained at 50 mmAq to 200 mmAq for 300 minutes, and the temperature is maintained in the range of 520 ± 10℃, i.e., 510℃ to 530℃. Then, steam is injected into the chamber to maintain the temperature at 510℃ to 530℃ for 30 minutes, thereby oxynitrating the object to form an oxide film (Fe3O4) layer (S160).

[0047] The step of forming an oxide film layer is characterized by injecting steam of 0.4 MPa to 0.6 MPa into a chamber at a temperature of 510°C to 530°C for 30 minutes to oxynitrate the object and form an oxide film (Fe3O4) layer.

[0048] Finally, the temperature inside the chamber is cooled to 130°C or lower, and then the object can be removed from the chamber (S170).

[0049] Here, the step of cooling the temperature inside the chamber to 130°C or lower is characterized by slowly cooling for 120 minutes while maintaining the pressure inside the chamber at 50 mmAq to 200 mmAq.

[0050] Figure 2 is a graph of a gas nitriding method according to one embodiment of the present invention.

[0051] Referring to FIG. 2, the present invention may be configured to include a step of removing foreign substances from the surface of an object (S110), loading an object to be nitrided into the chamber of a nitriding furnace (S120), a step of raising the temperature to 550±10℃ by introducing nitrogen (N2) gas (S130), a step of nitriding by introducing ammonia (NH3) gas (S140), a step of lowering the temperature inside the chamber under a constant pressure (S150), a step of oxynitriding the object under a constant pressure to form an oxide film layer (S160), and a step of cooling under a constant pressure (S170).

[0052] Referring to FIGS. 1 and 2, the nitriding method of the present invention consists of a series of continuous steps in the order of a heating step (S130) → nitriding step (S140) → isothermal cooling step (S150) → oxynitriding step (S160) → cooling step (S170) after loading a material to be nitrided into the chamber of a nitriding furnace, and each step is examined in detail as follows.

[0053] First, regarding the heating step (S110), the heating step (S110), which is performed after loading the object into the chamber of the nitriding furnace, is a process of vacuuming the inside of the nitriding furnace to 0.05 mbar or less, then introducing nitrogen (N2) gas into the chamber so that the internal pressure of the nitriding furnace becomes 200 mmAq and heating to 540°C to 560°C.

[0054] Secondly, regarding the nitriding step (S140), the internal pressure of the chamber is set to 200 mmAq, and a thin nitriding film is formed on the surface of the object by introducing ammonia (NH3) gas and an oxidizing gas, such as carbon dioxide (CO2), at a temperature of 540°C to 560°C, and is maintained for 8 hours, and the time can be increased or decreased depending on the amount of charge.

[0055] The nitriding step (S140) can be performed repeatedly several times as needed, and the number of processes and time performed can be increased or decreased depending on the thickness of the compound layer and the depth of the hardened layer.

[0056] The formation of a hardened layer imparts corrosion resistance and wear resistance to the object, and in some cases, by controlling the nitrogen potential in the chamber, the nitrogen compound layer, which is the second hardened layer (20, see FIG. 3), may not be formed, and only the first hardened layer (10) and the third hardened layer (30) may be formed.

[0057] Fifth, the oxidation step (S160) is a process that imparts corrosion resistance to iron-based metal parts by performing oxidation treatment for 30 minutes at a temperature of 520±10℃, i.e., 510℃ to 530℃.

[0058] Oxide film formation is a process designed to achieve uniform nitriding and improve the nitriding rate; it involves oxidizing passivation films that can act as barriers to the nitriding reaction on the surface of the workpiece, or nanometer-sized impurity films that may remain.

[0059] As a final step, the cooling step (S170) is a process of cooling to a temperature of 130°C, which is relatively higher than room temperature, while maintaining the pressure inside the chamber at 50 mmAq to 200 mmAq. Steam may be injected into the chamber during the cooling step. Steam with a pressure of 0.4 MPa to 0.6 MPa may be used.

[0060] Figure 3 is a schematic diagram of a hardened layer formed on an object.

[0061] Referring to FIG. 3, a first hardened layer (10) is formed on the surface of the object, and as it goes further inward, a second hardened layer (20), a third hardened layer (30), and a base layer (40) of the object are located.

[0062] The first hardened layer (10) is an oxide layer formed as a result of the oxidation step (S160) according to the oxidation process and is composed of a magnetite film, which is an iron oxide layer mainly composed of Fe3O4.

[0063] Additionally, the second hardening layer (20) is a compound layer of nitrogen and iron, mainly composed of iron nitride such as Fe2N, Fe3N, Fe4N, which is generated in the nitriding step (S140), and the third hardening layer (30) is a diffusion layer in which nitrogen atoms are diffused into the iron-based metal.

[0064] As such, according to one embodiment of the present invention, the corrosion resistance, wear resistance, moisture resistance, and surface hardness of an object can be improved through oxynitridation compared to conventional technology.

[0065] Although various preferred embodiments of the present invention have been described above with some examples, the descriptions of various embodiments described in the "Specific details for carrying out the invention" section are merely illustrative, and those skilled in the art to which the present invention pertains will understand that the present invention can be modified in various ways or equivalent embodiments can be carried out based on the above description.

[0066] In addition, since the present invention can be implemented in various other forms, the present invention is not limited by the description above. The above description is provided merely to make the disclosure of the present invention complete and to fully inform those skilled in the art of the scope of the present invention, and it should be understood that the present invention is defined only by each claim of the claims. Explanation of the symbols

[0067] 10: 1st hardened layer, 20: 2nd hardened layer, 30: 3rd hardened layer, 40: Base layer

Claims

Claim 1 A step of removing foreign substances from the surface of an object; a step of introducing the object from which foreign substances have been removed into the chamber of a nitriding furnace; a heating step of vacuuming the inside of the chamber to a constant pressure, then injecting nitrogen (N2) to maintain the pressure inside the chamber at 50 to 200 mmAq and gradually raising the temperature inside the chamber to 540°C to 560°C; a step of injecting ammonia (NH3) and carbon dioxide (CO2) into the chamber, and exposing the object for 480 minutes while maintaining the pressure inside the chamber at 200 mmAq and the temperature in the range of 540°C to 560°C; a step of cooling the temperature inside the chamber to 510°C to 530°C; a step of maintaining the pressure inside the chamber at 0.4 MPa to 0.6 MPa and the temperature at 510°C to 530°C for 300 minutes, then injecting steam into the chamber and oxynitriding the object for 20 minutes while maintaining the temperature at 510°C to 530°C to form an oxide film (Fe3O4) layer A gas nitriding method configured to include the steps of: forming; and cooling the temperature inside the chamber to 130°C or lower, and then removing the object from the chamber. Claim 2 A gas nitriding method according to claim 1, wherein the heating step is characterized by vacuuming the inside of the chamber to 0.05 mbar or less and gradually heating over 240 minutes. Claim 3 A gas nitriding method according to claim 1, wherein the step of cooling the temperature inside the chamber to 510°C to 530°C occurs while the pressure inside the chamber is maintained at 50 mmAq to 200 mmAq. Claim 4 A gas oxynitriding method according to claim 1, wherein the step of forming the oxide film layer is characterized by injecting steam of 0.4 MPa to 0.6 MPa into a chamber at a temperature of 510°C to 530°C for 30 minutes to oxynitrid the object and form an oxide film (Fe3O4) layer. Claim 5 A gas nitriding method according to claim 1, wherein the step of cooling the temperature inside the chamber to 130°C or lower is characterized by slowly cooling for 120 minutes while maintaining the pressure inside the chamber at 50 mmAq to 200 mmAq.

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