Two-stage gas nitriding method for improving wear and corrosion resistance

Abstract

A method for strengthening the surface of a metal part comprises: nitriding the metal part, machining the metal part to a smoothness value less than 1.0 micron, nitriding the metal part a second time, and polishing the metal part to a smoothness value less than about 0.8 micron.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 62 / 967,895, filed on January 30, 2020, entitled “Two-Stage Gas Nitriding Process for Improving Wear and Corrosion Resistance,” the entire disclosure of which is expressly incorporated herein by reference. Technical Field

[0003] The present invention relates to a gas nitriding method for use with a fluid injector assembly and, more particularly, to a two-stage gas nitriding method configured to improve the wear and corrosion resistance of metal parts. Background Art

[0004] Existing fluid injectors or other metal components often begin to fail after a period of use because the surface of the injector's valve seat begins to wear and deform or corrode after being subjected to multiple impact loads from the injector's check ball. The wear and deformation of the valve seat often results in a high injector discharge flow rate and may ultimately lead to failure of the injector. Therefore, there is a need for an injector having a valve seat that has increased resistance to wear, cavitation, deformation, and / or corrosion caused by the impact load of the check ball. Summary of the invention

[0005] In one embodiment of the present invention, a method for strengthening the surface of a metal component is provided, the method comprising: nitriding the metal component; machining the metal component to a first smoothness value of less than 1.0 micrometer; nitriding the metal component for a second time; and polishing the metal component to a second smoothness value of less than about 0.8 micrometer.

[0006] In another embodiment of the present invention, a metal component is provided, which includes a diffusion zone composed of α-phase iron nitride and a compound layer located on the diffusion zone, the compound layer including ε-phase iron nitride and γ'-phase iron nitride, wherein the compound layer forms an upper surface of the metal component.

[0007] In another embodiment of the present invention, a fluid injector is provided. The fluid injector includes a pilot valve seat and a check ball, the check ball is configured to move in the fluid injector to allow fluid injection when the check ball is spaced apart from the pilot valve seat, and to prevent fluid injection when the check ball is in contact with the pilot valve seat, the pilot valve seat includes a diffusion zone composed of α-phase iron nitride, and a compound layer located on the diffusion zone, the compound layer including ε-phase iron nitride and γ'-phase iron nitride, wherein the compound layer forms an upper surface of the pilot valve seat. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Advantages and features of embodiments of the present disclosure will become more apparent from the following detailed description of exemplary embodiments when viewed in conjunction with the accompanying drawings, in which:

[0009] Figure 1 shows a cross-sectional view of a fluid injector that has been subjected to the two-stage nitriding process of the present disclosure;

[0010] Figure 2 is a flow chart of the two-stage nitriding process of the present invention; and

[0011] Figure 3 Shows Figure 1 Diagram of the layers of the surface of the injector valve seat.

[0012] In the several figures, corresponding reference numerals indicate corresponding parts. Although the drawings represent embodiments of the present disclosure, the drawings are not necessarily to scale, and certain features may be enlarged to better illustrate and explain the present disclosure. The examples set forth herein illustrate embodiments of the present disclosure in one form, and such examples should not be construed as limiting the scope of the present disclosure in any way. DETAILED DESCRIPTION

[0013] Reference Figure 1 , a cross-sectional view of a portion of a fluid injector 10 is shown. The injector 10 generally includes a pilot valve seat 12 and a check ball 14. The check ball 14 is configured to move within the injector 10 to allow fluid injection when the check ball 14 is spaced apart from the pilot valve seat 12, and to prevent fluid injection when the check ball 14 is in contact with the pilot valve seat 12. However, as the check ball 14 transitions from being spaced apart from the pilot valve seat 12 to being in contact with the pilot valve seat 12, there are various contact or impact zones 16 where the check ball 14 impacts or contacts the pilot valve seat 12. Without the compound layer 18 provided by the two-step nitriding nitriding process 100 described further below, these impact zones 16 have previously been the site of various wear and deformation in the valve seat 12 after being subjected to multiple impact loads during operation of the injector 10. Such wear and deformation of the valve seat 12 may corrode or otherwise change the shape of the valve seat 12 such that the check ball 14 and valve seat 12 no longer fully seal against each other, thereby causing high injector discharge flow and ultimately failure of the injector 10 .

[0014] refer to Figure 2The two-step nitriding process 100 produces a compound layer 18 on the upper surface of the valve seat 12, which increases its ability to withstand impact loads from the check ball 14, and thus withstands wear, cavitation and deformation of the valve seat 12 caused by the check ball 14. Therefore, the valve seat 12 that has been subjected to the process 100 is able to withstand wear and deformation of longer-term use / operation of the injector 10, and thus reduce the likelihood and / or amount of injector discharge flow over time. The process 100 can also be applied to other metal components to provide similar improvements in strength and wear resistance and deformation resistance.

[0015] The two-step nitriding process 100 generally includes a first step 102 of providing a soft seat for the valve seat 12, a second step 104 of nitriding the seat 12, a third step 106 of machining the seat 12, a fourth step 108 of nitriding the seat 12 again or for a second time, and a fifth step 110 of polishing the seat 12. The nitriding steps 104 and 108 can generally be performed in various ways, for example, the nitriding can be performed by physical vapor deposition, chromium nitriding, titanium nitriding, plasma (ion) nitriding, and / or other various nitriding methods. In addition, the nitriding steps 104 and 108 can be performed using the same method or different methods. The machining step 106 is configured to machine the seat 12 to a smoothness value (Rz), or the average distance between peaks and valleys in the surface, of less than 1 micron, and can include grinding the seat 12 and / or polishing the seat 12. The polishing step 110 is configured to polish the pad 12 to remove the spalling layer generated during the nitriding step 108 and provide a smoothness value (Rz) of less than about 0.8 microns, or more specifically about 0.5 microns.

[0016] refer to Figure 3 The two-step nitridation process 100 produces multiple layers in the valve seat 12. Specifically, the process 100 results in the valve seat 12 having a core 20 ( Figure 1 ), a diffusion zone 22 located on or outside the core 20, and a compound layer 18 located on or outside the diffusion zone 22. In other words, the core 20 is located inside both the compound layer 18 and the diffusion zone 22. The compound layer 18 is generally composed of ε-phase iron nitride (Fe 2-3N) and γ' phase iron nitride (Fe4N), and is generally 3 to 15 microns thick, more specifically 10 to 15 microns thick. In various embodiments, γ' phase iron nitride and ε phase iron nitride are present in the compound layer 18 at a ratio of 1:19 to 3:1. The diffusion zone 22 is generally formed by α phase iron or ferrite (iron in a body-centered cubic (BCC) structure) formed by diffusion into the core 20 through the compound layer 18, and generally has a thickness of 100 to 200 microns. The core 20 is generally formed of tool steel, particularly H13 tool steel, and forms the remainder of the valve seat 12. In various embodiments, the compound layer 18 has a hardness value greater than 67HRC, the diffusion layer 22 has a hardness value less than 67HRC, and the core 20 has a hardness value of 55 to 59HRC.

[0017] Although various embodiments of the present disclosure have been shown and described, it should be understood that these embodiments are not limited thereto. Those skilled in the art may change, modify and further apply these embodiments. Therefore, these embodiments are not limited to the details previously shown and described, but also include all such changes and modifications.

[0018] In addition, the connecting lines shown in the various figures included herein are intended to represent exemplary functional relationships and / or physical couplings between various elements. It should be noted that many alternative or additional functional relationships or physical connections may exist in actual systems. However, benefits, advantages, solutions to problems, and any elements that may cause any benefits, advantages, or solutions to occur or become more significant should not be interpreted as key, necessary, or essential features or elements. Therefore, the scope of the present invention is limited only by the appended claims, wherein unless explicitly stated, the reference to an element in the singular does not mean "one and only one", but "more than one". In addition, in the case of using a phrase similar to "at least one of A, B, or C" in the claims, it is intended that the phrase be interpreted as meaning that A alone may exist in an embodiment, B alone may exist in an embodiment, C alone may exist in an embodiment, or any combination of elements A, B, or C may exist in a single embodiment; for example, A and B, A and C, B and C, or A and B and C.

[0019] In the detailed description herein, reference to "one embodiment," "an embodiment," "an exemplary embodiment," etc. indicates that the described embodiment may include a particular feature, structure, or characteristic, but each embodiment may not necessarily include the particular feature, structure, or characteristic. Furthermore, these phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in conjunction with an embodiment, it is considered to be within the knowledge of those skilled in the art who have the benefit of this disclosure to affect such feature, structure, or characteristic in conjunction with other embodiments (whether or not explicitly described). After reading the description, a person skilled in the relevant art will understand how to implement the invention in alternative embodiments.

[0020] Furthermore, no element, component, or method step in this disclosure is intended to be dedicated to the public, regardless of whether the element, component, or method step is explicitly stated in the claims. Claim elements herein are not to be interpreted under 35 U.S.C. §112(f) unless the element is explicitly stated using the phrase "means for..." As used herein, the terms "comprise," "comprising," or any other variation thereof, are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements, but may also include other elements not explicitly listed or other elements inherent to those processes, methods, articles, or apparatus.

Claims

1. A method for strengthening the surface of a metal part, comprising: nitriding the metal component; machining the metal component to a first smoothness value of less than 1.0 micrometer after nitriding the metal component; nitriding the metal component a second time after machining the metal component to the first smoothness value; and After the metal component is nitrided for the second time, the metal component is polished to a second smoothness value below 0.8 micrometers, thereby forming a compound layer on the diffusion region of the metal component.

2. The method of claim 1, wherein: The step of machining the metal part includes at least one of grinding the metal part and polishing the metal part.

3. The method of claim 1, wherein: The metal component is a valve seat of a fluid injector.

4. A metal component, comprising: a diffusion zone consisting of α-phase iron nitride; as well as a compound layer on the diffusion zone, the compound layer comprising ε-phase iron nitride and γ'-phase iron nitride, wherein the compound layer forms the upper surface of the metal component, the diffusion zone being formed by diffusion of the compound layer into a nitrided and machined tool steel core, The compound layer has a smoothness value of less than 0.8 micrometers, or the diffusion zone has a thickness of 100 to 200 micrometers.

5. The metal component according to claim 4, wherein: The ratio of the γ′-phase iron nitride to the ε-phase iron nitride in the compound layer is 1:19 to 3:

1.

6. The metal component of claim 4 further comprising a tool steel core located within both the diffusion zone and the compound layer.

7. A fluid ejector, comprising: Pilot valve seat; as well as a check ball configured to move within the fluid injector to allow fluid injection when the check ball is spaced apart from the pilot valve seat and to prevent fluid injection when the check ball is in contact with the pilot valve seat, the pilot valve seat including a diffusion zone comprised of alpha-phase iron nitride, and A compound layer is located on the diffusion zone, the compound layer includes ε-phase iron nitride and γ'-phase iron nitride, wherein the diffusion zone is formed by diffusing the compound layer into the nitrided and machined pilot valve seat, and the compound layer forms the upper surface of the pilot valve seat.

8. The fluid ejector of claim 7, wherein: The compound layer has a smoothness value of 0.8 micrometers or less.

9. The fluid ejector of claim 7, wherein: The thickness of the diffusion zone is 100 to 200 microns.

10. The fluid ejector of claim 7, wherein: The ratio of γ′-phase iron nitride to ε-phase iron nitride in the compound layer is 1:19 to 3:

1.

11. The fluid ejector of claim 7, wherein: The pilot valve seat also includes a tool steel core located inside both the diffusion zone and the compound layer.

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