A method for reinforcing a cylinder head seat bore

Abstract

The application provides a cylinder cover seat hole strengthening method, comprising the following steps: high-frequency quenching the cylinder cover seat hole by using a high-frequency quenching device; tempering the quenched cylinder cover; and performing nitriding and oxidizing treatment on the tempered cylinder cover seat hole, so that a composite strengthening layer with a depth of 100-150 microns is formed on the surface layer of the quenched zone after the treatment. The cylinder cover seat hole strengthening method effectively solves the problem of easy wear of the cylinder cover seat hole, ensures and improves the wear resistance of the cylinder cover, improves the product quality, and improves the reliability of the product. Meanwhile, the method solves the problem that a compact structure type part cannot be strengthened by inlaying, has high processing efficiency, and achieves good results.

Description

Technical Field

[0001] This invention belongs to the field of engine processing technology, and in particular relates to a method for strengthening cylinder head seat holes. Background Technology

[0002] Engines require lightweight design, but power systems typically exhibit high power and high burst pressure. To meet these requirements, high standards are set for cylinder head seat bore material selection, overall heat treatment strength, strength consistency, surface hardening layer depth / hardness, and wear resistance of the hardened layer. Due to the compact design of the cylinder head, the valve seat rings are no longer integrally formed with the cylinder head using an inlay process; instead, local hardening of the cylinder head valve seat bores replaces the inlay method. The weakness of existing lightweight cast iron cylinder head valve seat bore heat treatment manufacturing technology limits the improvement of overall engine performance and lags significantly behind advanced heat treatment manufacturing technologies for similar parts. Current cylinder head seat bore strengthening commonly uses induction hardening, but the hardened seat bores are prone to wear during the break-in period with the valves, failing to meet engine design requirements. Summary of the Invention

[0003] In view of this, the present invention aims to propose a method for strengthening the valve seat bore of a cylinder head, so as to solve the problem that the heat treatment effect of the valve seat bore of the existing lightweight new cast iron cylinder head is not good, which affects the service life of the cylinder head.

[0004] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0005] A method for strengthening cylinder head seat bores includes:

[0006] High-frequency quenching equipment is used to quench the cylinder head seat bore;

[0007] The quenched cylinder head is then tempered.

[0008] The tempered cylinder head seat bore is subjected to oxynitriding treatment to form a composite reinforcement layer with a depth of 100-150 μm on the surface of the quenched zone. This composite reinforcement layer comprises an oxynitriding high-hardness compound layer and a high-frequency tempering layer. The oxynitriding high-hardness compound layer needs to have a thickness of 17-18 μm and a surface hardness of 650 HV. 0.025 -700HV 0.025 .

[0009] Furthermore, the high-frequency quenching of the cylinder head seat bore using a high-frequency quenching equipment includes:

[0010] The cylinder head is preheated for 2 seconds using a high-frequency quenching device;

[0011] After preheating, let the cylinder head stand still for 2 seconds;

[0012] The cylinder head is heated using a high-frequency quenching device to achieve high-frequency quenching of the cylinder head seat bore.

[0013] Furthermore, the tempering of the quenched cylinder head includes:

[0014] The cylinder head is tempered at a temperature of 400℃ for 2 hours.

[0015] Furthermore, the tempered cylinder head seat bore undergoes oxynitriding treatment to form a composite reinforcement layer with a depth of 100-150 μm on the surface of the quenched zone, including:

[0016] The cylinder head seat bore is subjected to oxygen-nitriding treatment at a temperature of 540℃ for 4 hours, with a medium concentration of 35%-38%.

[0017] Compared with the prior art, the cylinder head seat hole strengthening method of the present invention has the following advantages:

[0018] The cylinder head seat hole strengthening method described in this invention effectively solves the problem of easy wear of cylinder head seat holes, ensuring and improving the wear resistance of the cylinder head, improving product quality, and enhancing product reliability. It also solves the problem of not being able to increase the strength of a type of compact part using inlay, achieving high processing efficiency and good results. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0020] Figure 1 This is a flowchart of a cylinder head seat hole strengthening method according to an embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of the metallographic structure of the cylinder head cross-section after treatment by the cylinder head seat hole strengthening method described in an embodiment of the present invention. Detailed Implementation

[0022] 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, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0023] Figure 1 This is a flowchart of a cylinder head seat bore strengthening method according to an embodiment of the present invention. See also... Figure 1 This method specifically includes the following steps:

[0024] Step 101: Use a high-frequency quenching device to perform high-frequency quenching on the cylinder head seat hole.

[0025] Specifically, the above-mentioned high-frequency quenching of the cylinder head seat bore using high-frequency quenching equipment includes the following steps:

[0026] Step 1011: Preheat the cylinder head for 2 seconds using a high-frequency quenching device.

[0027] Step 1012: After preheating, let the cylinder head stand still for 2 seconds.

[0028] Step 1013: Use high-frequency quenching equipment to heat the cylinder head to achieve high-frequency quenching of the cylinder head seat hole.

[0029] In practical applications, the cylinder head valve seat ring holes must first undergo high-frequency quenching. Existing CNC high-frequency quenching machine tools can be used. The quenching process of these machine tools is automatically controlled, and adjustable parameters include: output power, preheating time, pause time, heating time, and inductor lifting gap. In practical use, those skilled in the art can adjust the hardened layer depth and hardness of the parts by setting the preheating time, pause time, and inductor lifting gap to fixed values, and only adjusting the output power and heating time, according to actual processing needs.

[0030] For example, if the highest power of the high-frequency quenching equipment used is 100 kilowatts, then when the output power of the high-frequency quenching equipment is set to 17%, the preheating time is set to 2 seconds, the pause time to 2 seconds, the heating time to 6 seconds, and the inductor lifting gap to 2 mm. Those skilled in the art can also adjust the output power and heating time of the high-frequency quenching equipment according to actual needs to achieve high-frequency quenching of the cylinder head seat bore, so that a high-frequency hardened layer of a certain thickness is formed at the cylinder head seat bore for subsequent further strengthening treatment.

[0031] Step 102: Temper the quenched cylinder head.

[0032] Specifically, the above-mentioned tempering of the quenched cylinder head includes:

[0033] The cylinder head is tempered at a temperature of 400℃ for 2 hours.

[0034] Step 103: Perform oxynitriding treatment on the tempered cylinder head seat bore to form a composite reinforcement layer with a depth of 100-150 μm on the surface of the quenched zone after treatment; wherein, the composite reinforcement layer includes an oxynitriding high-hardness compound layer and a high-frequency fire-strengthened layer, the thickness of the oxynitriding high-hardness compound layer needs to reach 17-18 μm, and the surface hardness needs to reach 650 HV. 0.025-700HV 0.025 .

[0035] For example, if the thickness of the oxynitride high-hardness compound layer needs to reach 17.5 μm, then the thickness of the composite reinforcement layer is 82.5-132.5 μm.

[0036] By studying the temperature, time, and medium concentration of oxynitriding treatment and achieving optimal matching with the high-frequency induction hardening strengthening zone, a high-hardness Fe-N compound layer and a high-hardness diffusion layer with high strength, toughness, and good high-temperature stability were obtained. This resulted in a composite strengthening layer with a surface roughness ≤ Ra0.8μm, a surface hardness of 550HV-700HV, and no decrease in the performance of the cylinder head substrate after overall strengthening treatment, thus achieving the goal of wear resistance for the cylinder seat ring. Furthermore, oxynitriding treatment can further improve the hardness of the high-frequency induction hardening layer, achieving a surface hardness of 650HV. 0.025 -700HV 0.025 This helps to extend the service life of the valve seat.

[0037] Specifically, the above-mentioned oxygen-nitriding treatment of the cylinder head seat bore after tempering, so that a composite reinforcement layer with a depth of 100-150μm is formed on the surface of the quenched zone after treatment, includes: oxygen-nitriding treatment of the cylinder head seat bore at a temperature of 540℃ for 4 hours, with a medium concentration of 35%-38%.

[0038] In practical applications, since the oxynitriding treatment temperature is 540℃-580℃, which is lower than the phase transformation temperature of cast iron, no structural transformation occurs during the treatment, thus no structural stress is generated. Furthermore, the oxynitriding treatment includes an oxidation process at 350℃, which slows down the cooling rate of the high-temperature workpiece and reduces the generation of thermal stress. Therefore, oxynitriding treatment is a micro-deformation strengthening technology with minimal impact on the tensile strength, yield strength, and elongation at break of the base material. In this embodiment, a temperature of 540℃, a treatment time of 4 hours, and a medium concentration of 35%-38% are selected to effectively form an oxynitrided high-hardness compound layer. For example, the medium can be an aqueous solution of formamide or urea, and the medium concentration is the corresponding concentration of formamide or urea in the aqueous solution.

[0039] Furthermore, due to the potential presence of a 0.01-0.02mm coating on the surface after oxynitriding, the positional coordinates, diameter, and thickness of machined valve guide holes, locating pin holes, mating surfaces, etc., may change, resulting in dimensional deviations. To address this, the original CNC machining process needs to be evaluated and the machining steps adjusted accordingly. Simultaneously, physical protection such as graphite fillers should be applied to the machined areas to ensure the machining accuracy of the finished cylinder head. Those skilled in the art can choose to make adjustments based on actual needs, which will not be elaborated upon here.

[0040] Analysis of cylinder head seat bore condition after oxynitriding treatment:

[0041] The cylinder head underwent oxynitriding treatment according to the set process parameters. The results included hardness analysis, metallographic analysis, and changes in the diameter of machined holes after treatment of the dissected cylinder head sample. The results are as follows:

[0042] The surface hardness test results are shown in Table 1. As can be seen from Table 1, after oxynitriding, the surface hardness of the main wear area, the seat ring cone surface, increased from 500-550 HV0.2 to 637-771 HV0.2, showing a certain improvement; while the surface of the heat-treated area and other non-frequency quenched parts increased from 240-260 HV0.2 to 625-676 HV0.2, showing a significant improvement in surface hardness.

[0043] Table 1. Surface hardness test results (HV0.2)

[0044] Before oxynitrification 500-550 240-260 After oxynitriding 637-771 625-676

[0045] Cross-section metallography Figure 2 As shown, the metallographic structure is dense and without abnormalities. Figure 2 (a) is the cross-sectional metallographic structure of the fire surface (i.e. cylinder head body) after oxynitriding. It can be seen that the metallographic structure is pearlite + ferrite. The compound layer formed after oxynitriding is uniform and complete, and no obvious diffusion layer can be observed in the metallographic structure. Figure 2 (b) is the cross-sectional metallographic structure of the seat ring cone surface after high-frequency quenching and oxynitriding. It can be seen that the metallographic structure is still the martensitic structure formed after high-frequency induction quenching. The compound layer formed after oxynitriding is uniform and complete, while the diffusion layer is not obvious.

[0046] After the cylinder head underwent overall oxynitriding, the microstructure showed no abnormalities, and the surface and cross-sectional hardness were improved to varying degrees. Furthermore, a compound layer with high hardness, good wear resistance, and red hardness was formed on the surface, which helps improve the high-temperature wear resistance of the cylinder head cone bearing. After component testing, it was found that the worn parts were the valves (as shown in Table 2 below), while the bearing bores showed virtually no wear, meeting the bearing bore wear resistance standards.

[0047] Table 2. Break-in status of the valve seat and valve fit.

[0048]

[0049] The changes in the cylinder head guide tube, locating pin hole, cylinder head thickness, etc. after the cylinder head oxynitriding treatment are shown in Table 3 below. The order of processing steps basically does not affect the assembly and use of the cylinder head. Some pin holes can be appropriately enlarged by 0.005 during CNC machining to ensure the final size requirements of the cylinder head. For example, as shown in Table 3 below.

[0050] Table 3

[0051]

[0052]

[0053] As can be seen from Table 3 above, after high-frequency quenching and tempering, the cylinder head seat bore is subjected to overall oxygen-nitriding treatment, and the performance of both the seat bore and the cylinder head body can meet the requirements of this engine model.

[0054] The cylinder head seat hole strengthening method described in this embodiment effectively solves the problem of easy wear of cylinder head seat holes, ensuring and improving the wear resistance of the cylinder head, improving product quality, and enhancing the reliability of the product. It also solves the problem of not being able to increase the strength of a type of compact part using inlay, achieving high processing efficiency and good results.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for strengthening cylinder head seat bores, characterized in that, include: High-frequency quenching equipment is used to quench the cylinder head seat bore; The quenched cylinder head is then tempered. The tempered cylinder head seat bore is subjected to oxynitriding treatment to form a composite reinforcement layer with a depth of 100-150 μm on the surface of the quenched zone. This composite reinforcement layer comprises an oxynitriding high-hardness compound layer and a high-frequency quenching reinforcement layer. The oxynitriding high-hardness compound layer needs to have a thickness of 17-18 μm and a surface hardness of 650 HV. 0.025 -700HV 0.025 ; The high-frequency quenching of the cylinder head seat bore using a high-frequency quenching equipment includes: The cylinder head is preheated for 2 seconds using a high-frequency quenching device; After preheating, let the cylinder head stand still for 2 seconds; The cylinder head is heated using a high-frequency quenching device to achieve high-frequency quenching of the cylinder head seat bore. The step of tempering the quenched cylinder head includes: The cylinder head is tempered at a temperature of 400℃ for 2 hours. The process of performing oxynitriding on the tempered cylinder head seat bore to form a composite reinforcement layer with a depth of 100-150 μm on the surface of the quenched zone includes: The cylinder head seat bore is subjected to oxygen-nitriding treatment at a temperature of 540℃ for 4 hours, with a medium concentration of 35%-38%.

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