WO2021154360A1

WO2021154360A1 - Two-stage gas nitriding process for improved wear and erosion resistance

Info

Publication number: WO2021154360A1
Application number: PCT/US2020/058519
Authority: WO
Inventors: Romaine O. Edwards; Kurt W. Schoenegge; Manoj M. THETE; Darin BARTHOLOMEW
Original assignee: Cummins Inc
Current assignee: Cummins Inc
Priority date: 2020-01-30
Filing date: 2020-11-02
Publication date: 2021-08-05
Anticipated expiration: 2022-07-30
Also published as: CN115210401A; CN115210401B

Abstract

A method of strengthening a surface of a metallic member comprising nitriding the metallic member, machining the metallic member to a smoothness value of less than 1.0 micron, nitriding the metallic member a second time, and polishing the metallic member to a smoothness value of approximately 0.8 micron or less.

Description

TWO-STAGE GAS NITRIDING PROCESS FOR IMPROVED WEAR AND EROSION

RESISTANCE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. Provisional Patent Application

Serial No. 62/967,895, filed on January 30, 2020, and entitled “TWO-STAGE GAS NITRIDING PROCESS FOR IMPROVED WEAR AND EROSION RESISTANCE,” the complete disclosure of which is expressly incorporated by reference herein.

TECHNICAL FIELD OF THE DISCLOSURE

[0002] The present disclosure relates to a gas nitriding process for use with fluid injector components, and more particularly to a two-stage gas nitriding process configured to improve wear and erosion resistance of metallic components.

BACKGROUND OF THE DISCLOSURE

[0003] Present fluid injectors or other metallic components often begin to fail after a length of use due to a surface of a valve seat of the injector beginning to wear and deform or erode after withstanding the load of impact of a check ball of the injector multiple times. The wear and deformation of the valve seat often leads to high injector drain flow, and ultimately, could lead to failure of the injector. Thus, a need exists for an injector with a valve seat with increased resistance to wear, cavitation, deformation, and/or erosion caused by the impact load of the check ball.

SUMMARY OF THE DISCLOSURE

[0004] In one embodiment of the present disclosure, a method of strengthening a surface of a metallic member is provided. The method includes nitriding the metallic member, machining the metallic member to a first smoothness value of less than 1.0 micron, nitriding the metallic member a second time, and polishing the metallic member to a second smoothness value of approximately 0.8 micron or less.

[0005] In another embodiment of the present disclosure, a metallic member is provided.

The metallic member includes a diffusion zone comprised of alpha phase iron nitride, and a compound layer positioned over the diffusion zone, the compound layer comprising epsilon phase iron nitride and gamma prime phase iron nitride, wherein the compound layer forms an upper surface of the metallic member.

[0006] In a further embodiment of the present disclosure, a fluid injector is provided. The fluid injector includes a pilot valve seat, and a check ball, the check ball being configured to move within the fluid injector to allow fluid to be injected when the check ball is spaced apart from the pilot valve seat and to prevent fluid from being injected when the check ball is in contact with the pilot valve seat, the pilot valve seat comprising a diffusion zone comprised of alpha phase iron nitride, and a compound layer positioned over the diffusion zone, the compound layer comprising epsilon phase iron nitride and gamma prime phase iron nitride, wherein the compound layer forms an upper surface of the pilot valve seat..

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Advantages and features of the embodiments of this disclosure will become more apparent from the following detailed description of exemplary embodiments when viewed in conjunction with the accompanying drawings, wherein:

[0008] FIG. 1 shows a cross-sectional view of a fluid injector having been subjected to a two-stage nitriding process of the present disclosure;

[0009] FIG. 2 a flow chart of the two-stage nitriding process of the present disclosure; and

[0010] FIG. 3 shows a diagram of layers of a surface of a valve seat of the injector of

FIG. 1.

[0011] Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments of the present disclosure, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the present disclosure. The exemplifications set out herein illustrate embodiments of the disclosure, in one form, and such exemplifications are not to be construed as limiting the scope of the disclosure in any manner. DETAILED DESCRIPTION OF THE DRAWINGS [0012] Referring to FIG. 1, a cross-sectional view of a portion of a fluid injector 10 is shown. Injector 10 generally includes a pilot valve seat 12 and a check ball 14. Check ball 14 is configured to move within injector 10 to allow fluid to be injected when check ball 14 is spaced apart from pilot valve seat 12 and to prevent fluid from being injected when check ball 14 is in contact with pilot valve seat 12. However, when check ball 14 transitions from being spaced apart from pilot valve seat 12 to being in contact with pilot valve seat 12, there are various contact or impact zones 16 where check ball 14 impacts or contacts pilot valve seat 12. Absent a compound layer 18 provided via a two-step nitriding process 100, described further below, these impact zones 16 have previously been the site of various wear and deformation in valve seat 12 after withstanding the load of impact multiple times during operation of injector 10. This wear and deformation of valve seat 12 can erode or otherwise change the shape of valve seat 12 such that check ball 14 and valve seat 12 no longer fully seal against each other and, therefore, can lead to high injector drain flow, and ultimately, may lead to failure of injector 10.

[0013] With reference to FIG. 2, two-step nitriding process 100 creates compound layer

18 on an upper surface of valve seat 12 which increases its ability to withstand the load of impact from check ball 14 and therefore withstand the wear, cavitation, and deformation to valve seat 12 caused by check ball 14. As such, valve seat 12, having been subjected to process 100, is capable of withstanding wear and deformation for longer periods of use/operation of injector 10 and, therefore, decreases the likelihood and/or quantity of injector drain flow over time. Process 100 may also be applied to other metallic components to provide similar improvements in strength and resistance to wear and deformation.

[0014] Two-step nitriding process 100 generally comprises a first step 102 of providing a soft machine seat for valve seat 12, a second step 104 of nitriding seat 12, a third step 106 of machining seat 12, a fourth step 108 of nitriding seat 12 again or a second time, and a fifth step 110 of polishing seat 12. Nitriding steps 104 and 108 can generally be carried out in various ways, for example, the nitriding may be done by way of physical vapor deposition, chromium nitriding, titanium nitriding, plasma (ion) nitriding, and/or other various methods of nitriding. Furthermore, nitriding steps 104 and 108 may be carried out using the same method or different methods. Machining step 106 is configured to machine seat 12 down to a smoothness value (R_z), or average distance between peaks and valleys in the surface, of less than 1 micron, and may include grinding seat 12 and/or polishing seat 12. Polishing step 110 is configured to polish seat 12 to remove a flaking layer produced during the nitriding step 108, and provide a smoothness value (R_z) of approximately 0.8 micron or less, or more specifically about 0.5 micron.

[0015] With reference to FIG. 3, two-step nitriding process 100 creates a plurality of layers in valve seat 12. Specifically, process 100 results in valve seat 12 having a core 20 (FIG. 1), a diffusion zone 22 positioned over or external of core 20, and compound layer 18 positioned over or external of diffusion zone 22. In other words, core 20 is positioned internal to both compound layer 18 and diffusion zone 22. Compound layer 18 is generally formed of combination of epsilon phase iron nitride (Fe2-3N) and gamma prime phase iron nitride (Fe4N), and generally has a thickness between 3 - 15 microns, and more specifically between 10-15 microns. In various embodiments, gamma prime phase iron nitride and epsilon phase iron nitride are present in compound layer 18 in a ratio of 1:19 to 3:1. Diffusion zone 22 is typically formed of alpha phase iron or ferrite (iron in the body-centered cubic (BCC) structure) formed through diffusion of compound layer 18 into core 20 and generally has a thickness between 100 and 200 microns. Core 20 is typically formed of tool steel, specifically HI 3 tool steel, and forms the remainder of valve seat 12. In various embodiments, compound layer 18 has a hardness value of more than 67 HRC, diffusion layer 22 has a hardness value of less than 67 HRC, and core 20 has a hardness value between 55 to 59 HRC.

[0016] While various embodiments of the disclosure have been shown and described, it is understood that these embodiments are not limited thereto. The embodiments may be changed, modified and further applied by those skilled in the art. Therefore, these embodiments are not limited to the detail shown and described previously, but also include all such changes and modifications.

[0017] Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical system. However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements. The scope is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Moreover, where a phrase similar to “at least one of A, B, or C” is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B or C may be present in a single embodiment; for example, A and B, A and C,

B and C, or A and B and C.

[0018] In the detailed description herein, references to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art with the benefit of the present disclosure to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments.

[0019] Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. § 112(f), unless the element is expressly recited using the phrase “means for.” As used herein, the terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

Claims

WHAT IS CLAIMED IS:

1. A method of strengthening a surface of a metallic member comprising: nitriding the metallic member; machining the metallic member to a first smoothness value of less than 1.0 micron; nitriding the metallic member a second time; and polishing the metallic member to a second smoothness value of approximately 0.8 micron or less.

2. The method of claim 1, wherein the step of machining the metallic member includes at least one of grinding the metallic member and polishing the metallic member.

3. The method of claim 1, wherein the metallic member is a valve seat of a fluid injector.

4. A metallic member comprising: a diffusion zone comprised of alpha phase iron nitride; and a compound layer positioned over the diffusion zone, the compound layer comprising epsilon phase iron nitride and gamma prime phase iron nitride, wherein the compound layer forms an upper surface of the metallic member.

5. The metallic member of claim 4, wherein a ratio of the gamma prime phase iron nitride to the epsilon phase iron nitride in the compound layer is between 1:19 and 3:1.

6. The metallic member of claim 4, wherein the compound layer has a smoothness valve of approximately 0.8 micron or less.

7. The metallic member of claim 4, wherein a thickness of the diffusion zone is between approximately 100-200 micron.

8. The metallic member of claim 4, further comprising a tool steel core positioned internal to both the diffusion zone and the compound layer.

9. A fluid injector comprising: a pilot valve seat; and a check ball, the check ball being configured to move within the fluid injector to allow fluid to be injected when the check ball is spaced apart from the pilot valve seat and to prevent fluid from being injected when the check ball is in contact with the pilot valve seat, the pilot valve seat comprising a diffusion zone comprised of alpha phase iron nitride, and a compound layer positioned over the diffusion zone, the compound layer comprising epsilon phase iron nitride and gamma prime phase iron nitride, wherein the compound layer forms an upper surface of the pilot valve seat.

10. The fluid injector of claim 9, wherein the compound layer has a smoothness value of approximately 0.8 micron or less.

11. The fluid injector of claim 9, wherein a thickness of the diffusion zone is between approximately 100-200 micron.

12. The fluid injector of claim 9, wherein a ratio of the gamma prime phase iron nitride to the epsilon phase iron nitride in the compound layer is between 1:19 and 3:1.

13. The metallic member of claim 4, wherein the pilot valve seat further comprises a tool steel core positioned internal to both the diffusion zone and the compound layer.