A method of nitriding a high-strength alloy steel

Abstract

This invention discloses a nitriding process for high-strength alloy steel, comprising the following steps: 1) semi-finish turning; 2) turning of the nitrided surface; 3) applying an anti-nitriding protective paint; 4) nitriding treatment; 5) removal of excess material; and 6) finishing of the nitrided surface. The processing method of this invention allows for a machining allowance on the non-nitrided surface of the workpiece that is greater than the depth of the nitrided layer, greatly increasing the tolerance for errors in subsequent operations, ensuring the processing quality of the workpiece, and improving the yield.

Description

Technical Field

[0001] This invention relates to the field of nitriding technology for parts, and more particularly to a nitriding method for high-strength alloy steel. Background Technology

[0002] High-strength alloy steel is widely used in aerospace, precision machinery, and other fields, requiring extremely high surface hardness, wear resistance, and fatigue strength, especially in engine gas turbines and bearing housings. Nitriding is a key heat treatment method for strengthening the surface of such steels. However, nitriding involves high temperatures and long holding times, inevitably causing dimensional changes and shape distortions in the workpiece.

[0003] The current conventional process flow is typically as follows: rough machining → tempering → semi-finishing → finishing of the non-nitrided surface to design dimensions → leaving grinding allowance on the nitrided surface → copper plating or applying anti-nitriding paint to the non-nitrided surface (requiring extreme precision) → nitriding → removing the protective layer → grinding the nitrided surface to design dimensions. The core of the existing technology lies in "ensuring dimensions first, then providing protection." To prevent the non-nitrided surface from hardening during nitriding, strict surface protection (such as copper plating) must be performed before nitriding. This not only increases the production cycle and environmental pressure, but also has irreversible consequences if the protection fails. Disadvantages of the existing technology:

[0004] (1) Extremely low process tolerance: Existing anti-seepage protection (especially copper plating) requires zero defects. If local leakage occurs on the non-nitrided surface, since the surface is already at the final size, the hardened layer cannot be removed by processing, directly leading to the scrapping of the part. Using anti-seepage coatings, it is impossible to apply them evenly on complex parts, and it is impossible to ensure that they will not fall off during processing and transportation. Furthermore, it is impossible to guarantee a stable coating and good adhesion to the workpiece surface at high temperatures, and there is no dripping.

[0005] (2) Deformation cannot be corrected: The non-nitrided surface has been machined before nitriding. The slight deformation (such as ellipticity and curvature) after long-term nitriding at high temperature cannot be eliminated by subsequent cutting, which affects the assembly accuracy. Summary of the Invention

[0006] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a nitriding process for high-strength alloy steel, which leaves a machining allowance on the non-nitrided surface that is greater than the depth of the nitrided layer, greatly increasing the tolerance for subsequent operations, ensuring the machining quality of the workpiece, and improving the yield.

[0007] The present invention provides a nitriding process for high-strength alloy steel, comprising the following steps:

[0008] 1) Semi-finish turning;

[0009] The workpiece is semi-finished, and a machining allowance greater than the depth of the nitrided layer is reserved on both the nitrided and non-nitrided surfaces.

[0010] 2) Nitriding surface machining;

[0011] The nitrided surface of the workpiece is machined by turning, leaving only the grinding allowance on the nitrided surface;

[0012] 3) Apply a waterproof protective coating;

[0013] Apply a waterproof protective coating to the non-nitrided surfaces of the workpiece using a large-area brushing or dip coating method;

[0014] 4) Nitriding treatment;

[0015] The painted workpiece is then placed in a furnace for nitriding treatment.

[0016] 5) Remove excess material;

[0017] After nitriding, the non-nitrided surfaces of the workpiece are precision turned or ground to remove the reserved machining allowance until the dimensions and geometric tolerances required by the design are met; this removes any possible leakage hardened layer and eliminates the thermal deformation caused by nitriding.

[0018] 6) Nitriding surface finishing;

[0019] The nitrided surface of the workpiece is ground to achieve the required dimensions and geometric tolerances as specified in the design.

[0020] Furthermore, in step 1), the reserved machining allowance is no less than 1 mm on each side.

[0021] Furthermore, in step 2), the grinding allowance of the nitrided surface is 0.1-0.2 mm.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] (1) The processing method of the present invention breaks the traditional thinking that "the non-nitrided surface must be processed in place before nitriding". It leaves a processing allowance greater than the depth of the nitrided layer on the non-nitrided surface of the workpiece, which completely solves the problem of workpiece scrapping due to inadequate anti-seepage protection (leakage). Even if the protective paint is not applied well, the mistakenly hardened part can be removed in the subsequent machining process without affecting the quality of the finished product. It has a high fault tolerance rate and greatly improves the yield.

[0024] (2) In the processing method of the present invention, since a margin is reserved on the non-nitrided surface, the precision requirements for the anti-seepage protective paint coating are reduced, the process difficulty is reduced, and the efficiency is improved;

[0025] (3) The processing method of the present invention retains the processing allowance of the non-nitrided surface, and corrects the dimensional changes and shape distortions caused by nitriding through the finishing process after nitriding, thereby fundamentally ensuring the coaxiality, cylindricity and other form and position tolerances of the workpiece, and avoiding the assembly problems caused by nitriding deformation.

[0026] It should be understood that the description in the Summary of the Invention is not intended to limit the key or essential features of the embodiments of the present invention, nor is it intended to restrict the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0027] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0028] Figure 1 This is a flowchart of the nitriding process for high-strength alloy steel. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0030] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0031] Please refer to Figure 1 The present invention provides a nitriding process for high-strength alloy steel, comprising the following steps:

[0032] 1) Semi-finish turning;

[0033] The workpiece is semi-finished, with a machining allowance greater than the depth of the nitrided layer reserved on both the nitrided and non-nitrided surfaces; the reserved machining allowance is not less than 1 mm on each side, and at this time, none of the surfaces of the workpiece have reached the final size.

[0034] 2) Nitriding surface machining;

[0035] The nitrided surface of the workpiece is machined by turning, leaving only the grinding allowance of the nitrided surface; the grinding allowance of the nitrided surface is 0.1-0.2mm, so that the nitrided surface can complete the nitriding treatment normally, while leaving the allowance for grinding correction after deformation.

[0036] 3) Apply a waterproof protective coating;

[0037] A protective coating is applied to the non-nitrided surface of the workpiece using a large-area brushing or dipping method. Since the non-nitrided surface will be processed to remove excess material later, the coating here does not need to be as precise as the micron-level boundary as in traditional processes, thus reducing the difficulty of the process.

[0038] 4) Nitriding treatment;

[0039] After the paint is applied, the workpiece is put into the furnace for nitriding treatment. At this time, the nitrided surface obtains high hardness, and the non-nitrided surface is protected. Even if there is a local failure, it will be removed in subsequent processing.

[0040] 5) Remove excess material;

[0041] After nitriding, the non-nitrided surfaces of the workpiece are precision turned or ground to remove the reserved machining allowance until the dimensions and geometric tolerances required by the design are met. This machining removes any possible leakage hardening layer and eliminates the thermal deformation caused by nitriding. A machining allowance of more than 1 mm on one side is sufficient to cover the conventional nitriding layer depth and nitriding deformation, ensuring that the leakage hardening layer is completely removed during machining.

[0042] 6) Nitriding surface finishing;

[0043] The nitrided surface of the workpiece is ground to achieve the required dimensions and geometric tolerances as specified in the design.

[0044] In this embodiment, the processing method of this application breaks away from the traditional thinking that "the non-nitrided surface must be properly machined before nitriding." A machining allowance greater than the depth of the nitrided layer is reserved on the non-nitrided surface of the workpiece. Even if individual pinholes, bubbles, or incomplete protection (leaking) occur during the painting process, causing nitrogen atoms to penetrate the surface and form a hardened layer, this hardened layer will be directly turned / ground off during subsequent allowance removal processing, without affecting the final surface material properties. This completely solves the problem of workpiece scrap due to inadequate anti-seepage protection (leaking), resulting in a high fault tolerance rate and greatly improving the yield. Simultaneously, it corrects dimensional changes and shape distortions caused by nitriding treatment, fundamentally ensuring the coaxiality, cylindricity, and other geometric tolerances of the workpiece, avoiding assembly difficulties caused by nitriding deformation, ensuring product quality, suitable for mass production, and with high promotional value.

[0045] In the description of this specification, the terms "one embodiment," "some embodiments," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0046] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A nitriding process for high-strength alloy steel, characterized in that, Includes the following steps: 1) Semi-finish turning; The workpiece is semi-finished, and a machining allowance greater than the depth of the nitrided layer is reserved on both the nitrided and non-nitrided surfaces. 2) Nitriding surface machining; The nitrided surface of the workpiece is machined by turning, leaving only the grinding allowance on the nitrided surface; 3) Apply a waterproof protective coating; Apply a waterproof protective coating to the non-nitrided surfaces of the workpiece using a large-area brushing or dip coating method; 4) Nitriding treatment; The painted workpiece is then placed in a furnace for nitriding treatment. 5) Remove excess material; After nitriding, the non-nitrided surfaces of the workpiece are precision turned or ground to remove the reserved machining allowance until the dimensions and geometric tolerances required by the design are met; this removes any possible leakage hardened layer and eliminates the thermal deformation caused by nitriding. 6) Nitriding surface finishing; The nitrided surface of the workpiece is ground to achieve the required dimensions and geometric tolerances as specified in the design.

2. The nitriding process for high-strength alloy steel according to claim 1, characterized in that, In step 1), the machining allowance is no less than 1 mm on each side.

3. The nitriding process for high-strength alloy steel according to claim 1, characterized in that, In step 2), the grinding allowance of the nitrided surface is 0.1-0.2 mm.

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