Method for improving the contact fatigue resistance of the seat surface of a needle valve

Abstract

The present disclosure provides a method for improving the contact fatigue resistance of the seat surface of a needle valve body, comprising the following steps: S1, using the conical surface of a target needle to perform rotary extrusion processing on the conical seat surface in the deep part of the blind hole of the needle valve body blank which has been processed with a center hole, a seat surface and a ball socket; S2, performing carburizing, quenching and tempering treatment on the needle valve body after step S1; S3, performing abrasive flow lapping and extrusion processing on the seat surface of the needle valve body after step S2. The present disclosure sequentially performs cold rotary extrusion, carburizing, quenching and tempering, and abrasive flow lapping and extrusion treatment on the needle valve body blank, realizes the synergistic improvement of high-precision processing, mechanical property strengthening and stress state optimization of the conical seat surface in the deep part of the blind hole of the needle valve body, makes the seat surface obtain an ideal residual compressive stress state, and thus significantly improves the contact fatigue resistance and service life of the seat surface of the needle valve body under high-pressure injection working conditions.

Description

Technical Field

[0001] This disclosure relates to the field of needle valve body manufacturing and processing technology, and in particular to a method for improving the contact fatigue resistance of the needle valve body seat surface. Background Technology

[0002] The needle valve body is a core component of the fuel injection system, and its seat surface repeatedly contacts and seals with the needle valve during injection. As fuel injection pressure gradually increases from 50-200 MPa to over 300 MPa, the high injection pressure exacerbates contact fatigue wear on the needle valve body seat surface, causing uneven fuel injection, unstable atomization, and affecting combustion efficiency and emissions. In severe cases, contact fatigue can induce cracks on the seat surface, leading to needle valve body failure. Therefore, improving the contact fatigue resistance of the needle valve body seat surface is crucial for enhancing the lifespan and reliability of fuel engines.

[0003] Based on this, the inventors of this disclosure propose a method to improve the contact fatigue resistance of the needle valve body seat surface, in order to solve one or more of the above-mentioned technical problems. Summary of the Invention

[0004] This disclosure solves the above-mentioned technical problems through the following technical solution: The purpose of this disclosure is to provide a method for improving the contact fatigue resistance of the needle valve body seat surface.

[0005] The method for improving the contact fatigue resistance of the needle valve body seat surface according to the first aspect of this disclosure includes the following steps: S1. For the needle valve body blank that has completed the machining of the central hole, seat surface and ball socket, the conical surface of the target ejector pin is used to spin-extrude the conical seat surface deep in the blind hole of the needle valve body. S2. Carburizing, quenching and tempering are performed on the needle valve body after step S1. S3. Perform abrasive flow extrusion processing on the needle valve body seat surface after step S2.

[0006] This disclosure sequentially performs cold spinning extrusion, carburizing, quenching and tempering, and abrasive flow extrusion on the needle valve body blank, achieving high-precision machining of the deep conical seat surface of the blind hole in the needle valve body, synergistic improvement of mechanical properties and stress state optimization, so that the seat surface obtains an ideal residual compressive stress state, thereby significantly improving the contact fatigue resistance and service life of the needle valve body seat surface under high-pressure jetting conditions.

[0007] In one or more embodiments, in step S1, the spin extrusion is a cold spin extrusion, and the spin extrusion feed is 0.05~0.50mm.

[0008] In one or more embodiments, in step S1, after the spin extrusion process, the dislocation density in the surface layer of the seat increases to 10. 9 ~10¹0 roots / cm²; Some of the mechanical energy from the rotary extrusion process is stored as internal energy in the surface layer of the seat.

[0009] In one or more embodiments, in step S1, the target ejector pin includes an ejector pin body and a rotary extrusion cone surface disposed at the front end of the ejector pin body, wherein the taper of the rotary extrusion cone surface is adapted to the taper of the needle valve body seat surface. The target ejector pin is screwed into the inner wall of the needle valve body blank and applies a spinning force to the seat surface of the needle valve body through the spinning cone.

[0010] In one or more embodiments, in step S2, a vacuum pulse carburizing process or an external gas internal solid carburizing process is used for carburizing treatment, the carburizing temperature is 880~950℃, the carburizing time is 3~6h, the strong carburizing potential is 0.9~1.1%, and the diffusion carburizing potential is 0.7~0.9%.

[0011] In one or more embodiments, in step S2, after carburizing, quenching and tempering, the hardness of the carburized layer on the needle valve body seat surface is 650~850HV, the depth of the carburized layer is 0.4~1.4mm, the length of the strip-shaped carbide does not exceed 5μm, and the size of the particulate carbide does not exceed 1.8μm.

[0012] In one or more embodiments, in step S3, the abrasive flow is driven by a pressure of 3~30MPa through the channel between the hole wall of the needle valve body and the tube wall of the abrasive flow guide tube.

[0013] In one or more embodiments, in step S3, an abrasive flow guide tube is provided in the hole of the needle valve body, and a channel for the abrasive flow is formed between the outer wall of the guide tube and the hole wall of the needle valve body. The guide tube has an outer conical surface that is opposite to the seat surface of the needle valve body. After the abrasive particles flow through the channel and are processed by the seat surface, they enter the guide tube and are discharged through the connecting hole opened at the head of the guide tube under the action of the pressure difference inside and outside the guide tube.

[0014] In one or more embodiments, in step S3, after abrasive flow extrusion, the residual compressive stress on the needle valve body seat surface reaches 500~1000MPa.

[0015] In one or more embodiments, the needle valve body blank is made of 18CrNi8 low-carbon low-alloy steel. Attached Figure Description

[0016] The above and other features, properties and advantages of this disclosure will become more apparent from the following description taken in conjunction with the accompanying drawings and embodiments, wherein: Figure 1This is a flowchart of a method for improving the contact fatigue resistance of the needle valve body seat surface; Figure 2 This is a schematic diagram of the cold turning process of the needle valve body seat surface in step 1 of this disclosure; Figure 3 This is a schematic diagram of the abrasive flow extrusion process performed on the needle valve body seat surface in step 3 of this disclosure; Figure 4 for Figure 3 Enlarged structural diagram at point A; Figure 5 This is a schematic diagram showing the change in the residual stress state of the seat surface before and after abrasive flow machining according to this disclosure.

[0017] 1. Needle valve body; 2. Inner hole wall; 3. Seat surface; 5. Target ejector pin; 51. Ejector pin body; 52. Rotary extrusion cone surface; 6. Drainage pipe; 61. Connecting hole. Detailed Implementation

[0018] The present disclosure will be further described below with reference to specific embodiments and accompanying drawings. More details are set forth in the following description in order to provide a full understanding of the present disclosure. However, the present disclosure can obviously be implemented in many other ways different from those described herein. Those skilled in the art can make similar extensions and derivations based on actual application situations without departing from the spirit of the present disclosure. Therefore, the scope of protection of the present disclosure should not be limited by the content of this specific embodiment.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure; the terms “comprising” and “having”, and any variations thereof, in the specification, claims and foregoing description of the drawings of this disclosure are intended to cover non-exclusive inclusion.

[0020] It should be noted that, in the following content, the needle valve body 1 referred to in this disclosure is a valve body component that cooperates with the needle valve to form a sealing pair in the fuel injection system. It has a central hole and a conical seat surface 3 located near the closed end of the central hole. The seat surface 3 contacts and seals with the conical surface of the needle valve during the injection process.

[0021] The aforementioned central hole is a blind hole. Due to the narrow space at the depth of the blind hole, the accessibility of ordinary machining tools is severely limited, so the machining quality of the seat surface can never meet the requirements.

[0022] Based on this, this disclosure proposes a method to improve the contact fatigue resistance of the needle valve body seat surface, which specifically includes the following steps: Step S1: For the needle valve body blank that has completed the machining of the central hole, seat surface and ball socket, use the conical surface of the target ejector pin to spin-extrude the conical seat surface deep in the blind hole of the needle valve body.

[0023] Optionally, the needle valve body blank mentioned above can be made of low-carbon low-alloy steel, specifically 18CrNi8 low-carbon low-alloy steel, but this is not limited.

[0024] Figure 2 A schematic diagram of cold spin extrusion processing of the needle valve body seat surface is shown. The aforementioned spin extrusion processing refers to a processing method in which a tool with a conical surface is used to apply a rotational feed force to the conical surface of a part at room temperature, causing plastic deformation of the surface layer. This differs from simple axial pressing or elastic burnishing. Room temperature spin extrusion is equivalent to cold spin extrusion, referring to spin extrusion performed at room temperature without additional heating of the workpiece.

[0025] Specifically, the cold spin extrusion in step S1 introduces a high dislocation density on the seat surface of the needle valve body blank, increasing its internal energy. These changes in microstructure and energy promote carbon diffusion during the carburizing process in step S2 (see below), resulting in a more dispersed distribution of carbides. This improvement effectively reduces the interfacial stress between carbide particles and the matrix when the seat surface is subjected to impact during the needle valve body's service life, thereby inhibiting the initiation of microcracks and improving contact fatigue resistance.

[0026] like Figure 2 As shown, after the conventional machining of the central hole, seat surface 3 and ball socket is completed, the seat surface 3 of the low-carbon low-alloy steel needle valve body 1 blank is subjected to room temperature spin extrusion machining using the target ejector pin 5.

[0027] Please continue to refer to Figure 2 The target ejector pin 5 includes an ejector pin body 51 and a spin extrusion cone surface 52 located at the front end of the ejector pin body 51. The taper of the spin extrusion cone surface 52 is adapted to the taper of the seat surface 3 of the needle valve body 1 to ensure uniform contact between the spin extrusion cone surface 52 and the seat surface 3 during spin extrusion processing.

[0028] The needle valve body blank is based on the machined end face and guided by the machined inner hole wall 2. The target ejector pin 5 is screwed in along the inner hole wall 2 and applies a spun force to the seat surface 3 through the spun cone surface 52.

[0029] Specifically, the spin feed of the target ejector pin 5 is controlled within the range of 0.05~0.50mm, but the specific value is not limited here and can be adjusted according to the material of the needle valve body 1, the size of the seat surface 3 and the accuracy requirements.

[0030] Through spin extrusion, the dislocation density within the surface layer of seat 3 was reduced from 10. 7 ~10 8 The number of roots per cm² can be increased to 10.9 ~10¹ 0 The deformation energy stored in the surface layer of the seat surface 3 is measured in roots per cm². Furthermore, a portion of the mechanical energy from the rotary extrusion is stored as internal energy in the surface layer of the seat surface 3, while the remaining portion is carried away by the lubricating fluid through the surface temperature rise of the seat surface 3. Thus, the deformation internal energy stored in the surface layer of the seat surface 3 provides additional driving force for the diffusion of carbon atoms during the subsequent carburizing process.

[0031] It should be noted that the structural form of the target pin 5 is based on... Figure 2 This example is provided for illustration, but it is not a limitation. Other tools that can apply rotational extrusion force to the deep conical seat surface of a blind hole at room temperature can also be used.

[0032] Step S2: Carburize, quench, and temper the needle valve body after step S1.

[0033] The carburizing process can be performed using either vacuum pulse carburizing or external gas-internal solid carburizing. External gas-internal solid carburizing refers to a process that uses a controlled atmosphere for carburizing and inserts a solid carbon rod into the central hole of the needle valve body 1.

[0034] In the aforementioned carburizing treatment, the carburizing temperature is 880~950℃, and the carburizing time is 3~6h. By adjusting the carburizing process parameters, the strong carburizing potential is controlled to be 0.9~1.1%, and the diffusion carburizing potential is controlled to be 0.7~0.9%. After carburizing, quenching and tempering treatments are performed to achieve the strengthening and toughening of the needle valve body 1.

[0035] It should be noted that the high internal energy generated in the deformed layer of the seat surface 3 during spin extrusion can promote carbon diffusion during the carburizing process. That is, the deformation internal energy stored in the spin extrusion deformed layer of the seat surface 3 in step S1 can promote the diffusion of carbon atoms during the carburizing process, effectively suppressing the precipitation of network carbides and large particle carbides in the carburized layer of the seat surface 3, thereby obtaining an ideal high-strength and high-toughness carburized layer structure.

[0036] This is a key synergistic effect that distinguishes it from conventional carburizing processes. In conventional carburizing processes, the surface layer of the seat 3 does not possess additional deformation internal energy, and carbon atom diffusion relies solely on carburizing temperature and carbon potential gradient. However, in this disclosure, the high dislocation density and high internal energy in the spin-extruded layer provide more diffusion channels and driving forces for carbon atoms, enabling a more uniform carburized layer structure and suppressing the precipitation of harmful carbides under the same carburizing temperature and time conditions.

[0037] Specifically, in step S2 of this disclosure, after the needle valve body 1 undergoes carburizing, quenching and tempering treatment, the carburized layer on the seat surface 3 of the needle valve body 1 has the following characteristics: the hardness of the carburized layer is 650~850HV, the depth of the carburized layer is 0.4~1.4mm, there are no obvious network carbides, the length of the strip carbides does not exceed 5μm, and the size of the large particle carbides does not exceed 1.8μm.

[0038] The specific microstructure parameters of the carburized layer depend on the comprehensive control of the steel composition of the needle valve body 1 and the carburizing process parameters. The carburizing temperature range and holding time can be selected based on the characteristics of the steel composition of the needle valve body 1.

[0039] Specifically, for low-carbon, low-alloy steel with a low carbon content, carburizing within the range of 880~950℃ can ensure sufficient austenitization without excessive grain growth. The high carbon potential in the strong carburizing stage ensures the surface carbon concentration, while the lower carbon potential in the diffusion stage smooths out the carbon concentration gradient. Combined with the energy storage and carburizing effect of the deformation layer in step S1, this can effectively suppress the precipitation of network carbides and large-particle carbides.

[0040] Step S3: Perform abrasive flow extrusion processing on the needle valve body seat surface after step S2.

[0041] Figure 3 A schematic diagram of the abrasive flow extrusion process for the needle valve body seat surface is shown. (Example) Figure 3 and Figure 4 As shown, this step involves abrasive flow extrusion processing of the central hole of the needle valve body 1 after step S2.

[0042] Specifically, abrasive flow refers to a fluid medium composed of a viscous carrier and abrasive particles, which performs micro-cutting and extrusion on the surface of a part when it flows under pressure.

[0043] This disclosure provides a guide tube 6 within the central hole of the needle valve body 1. The outer wall of the guide tube 6 and the inner wall 2 of the needle valve body 1 form a channel for the abrasive flow. The guide tube 6 has an outer conical surface opposite to the seat surface 3 of the needle valve body 1. After the abrasive flow passes through the channel and is processed by the seat surface 3, it enters the guide tube 6 through a connecting hole 61 at the head of the guide tube 6 and is discharged under the pressure difference between the inside and outside of the guide tube 6.

[0044] Specifically, this disclosure uses a pressure of 3~30MPa to drive an abrasive flow, which performs precision machining on the seat surface 3 as it flows through. By optimizing the driving force and the cross-sectional differences of the abrasive flow, the grinding, polishing and extrusion effects of the abrasive flow on the seat surface 3 are enhanced, thereby improving the surface finish of the seat surface 3 and improving the residual stress state of the carburized surface layer of the seat surface 3.

[0045] It should be noted that due to the difference in phase transformation temperature and phase transformation volume effect between the carburized layer and the substrate, a residual compressive stress layer will be obtained on the surface of the seat surface 3 of the needle valve body 1 after carburizing heat treatment. However, since there is no constraint on the outer side of the seat surface 3, the residual compressive stress near the surface of the seat surface 3 will decrease. This phenomenon can be called the near-surface reduction phenomenon of residual compressive stress (hereinafter referred to as the stress head phenomenon).

[0046] Please refer to Figure 5 , Figure 5The left and right sides show the distribution of residual compressive stress formed on the surface layer of the front and rear seats of the abrasive flow extrusion. For example... Figure 5 As shown in the figure on the left, the residual compressive stress in the near-surface region is significantly reduced, corresponding to the stress dip phenomenon mentioned above. Figure 5 The diagram on the right represents the distribution state after abrasive flow extrusion processing. Through the grinding, polishing and extrusion action of the abrasive flow on the seat surface 3, a small plastic deformation of the high-strength carburized surface layer is caused, eliminating the above-mentioned stress depression phenomenon. After the reduction of near-surface residual compressive stress is eliminated, the residual compressive stress on the surface of seat surface 3 reaches 500~1000MPa.

[0047] This disclosure utilizes the intense grinding and extrusion action of abrasive flow on the seat surface 3 to induce minute plastic deformation of the high-strength carburized surface layer of the seat surface 3, thereby eliminating the aforementioned stress depression phenomenon and improving the residual stress state of the carburized surface layer of the seat surface 3. Figure 5 The residual stress state of the surface layer of seat surface 3 after abrasive flow extrusion is also shown. It can be seen that the phenomenon of reduction of near-surface residual compressive stress is eliminated, and the residual compressive stress on the surface of seat surface 3 reaches 500~1000MPa.

[0048] In other words, this disclosure utilizes abrasive flow as a fluid medium, which can be uniformly flowed across the conical surface of the seat surface 3 through the guide tube 6, achieving full coverage grinding of the deep seat surface 3 of the blind hole. In addition, the depth and intensity of the abrasive flow grinding can be precisely controlled by pressure and abrasive parameters to avoid over-processing and damage to the carburized layer.

[0049] Example 1

[0050] Taking the 18CrNi8 low-carbon low-alloy steel needle valve body 1 as an example, the specific implementation of the method disclosed herein is explained.

[0051] Step S1: As Figure 2 As shown, after the 18CrNi8 needle valve body 1 blank is machined with the central hole, seat surface 3, and ball socket, the seat surface 3 of the needle valve body 1 is spun at room temperature using the target ejector pin 5, and the spun feed is 0.25mm.

[0052] Step S2: Using a vacuum pulse carburizing process, the 18CrNi8 needle valve body 1 is heated to 900℃ in a vacuum carburizing furnace and carburized for 4 hours, with a strong carburizing-diffusion time ratio of 1:10. The strong carburizing potential is 0.95%, and the diffusion carburizing potential is 0.75%. After carburizing, high-pressure gas quenching and tempering at 170℃ are performed. The microstructure and properties of the carburized layer on the seat surface 3 of the needle valve body 1 after heat treatment are as follows: the hardness of the carburized layer reaches 780HV, the depth of the carburized layer is 0.7mm, the length of the strip-shaped carbides does not exceed 3μm, and the size of the granular large carbides does not exceed 1μm.

[0053] Step S3: Perform abrasive flow machining on the central hole of the needle valve body 1 after step S2. For example... Figure 3 As shown, an abrasive flow is driven by a pressure of 20 MPa, and the pressurized abrasive flow precisely processes the seat surface 3. The ratio of the cross-sectional area between the inner wall 2 of the needle valve body 1 and the outer wall of the guide tube 6, the cross-sectional area between the upper end of the seat surface 3 of the needle valve body 1 and the upper end of the outer conical surface of the guide tube 6, the cross-sectional area between the lower end of the seat surface 3 of the needle valve body 1 and the lower end of the outer conical surface of the guide tube 6, the total area of ​​the connecting hole 61 of the guide tube 6, and the cross-sectional area of ​​the inner hole of the guide tube 6 is 2:2:1:1.1:2.5. After abrasive flow extrusion processing, the residual compressive stress on the surface of the seat surface 3 of the 18CrNi8 needle valve body 1 can reach 550~700 MPa.

[0054] It should be noted that other low-carbon, low-alloy steels, such as 20CrMo, may also be used as the material for the needle valve body 1 in this disclosure, and no limitation is made here.

[0055] The foregoing description has already given numerous features and advantages, including various alternative implementations, as well as details of the structure and function of the apparatus and method. The intent of this document is exemplary and not exhaustive or limiting. It will be apparent to those skilled in the art that various modifications can be made within the full scope indicated by the broad superordinate meaning of the terms expressed in the appended claims, particularly in terms of structure, materials, elements, components, shapes, dimensions, and arrangement of components, including combinations of these aspects within the scope of the principles described herein. Such various modifications are intended to be included herein without departing from the spirit and scope of the appended claims.

[0056] In the description of the embodiments of this disclosure, unless otherwise expressly specified and limited, the technical terms such as "installation", "connection", "joining", and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can also refer to a mechanical connection. For those skilled in the art, the specific meaning of the above terms in the embodiments of this disclosure can be understood according to the specific circumstances.

[0057] This disclosure uses specific terms to describe embodiments of the present disclosure. Terms such as "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic associated with at least one embodiment of the present disclosure. Therefore, it should be emphasized and noted that references to "an embodiment," "one embodiment," or "an alternative embodiment" in different locations throughout this specification do not necessarily refer to the same embodiment. Furthermore, certain features, structures, or characteristics in one or more embodiments of the present disclosure can be appropriately combined.

[0058] While this disclosure has described above with reference to preferred embodiments, it is not intended to limit the scope of this disclosure. Any changes and modifications can be made by those skilled in the art without departing from the spirit and scope of this disclosure. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this disclosure, without departing from the content of the technical solution, fall within the protection scope defined by the claims of this disclosure.

Claims

1. A method for improving the contact fatigue resistance of a needle valve body seat surface, characterized in that, Includes the following steps: S1. For the needle valve body blank that has completed the machining of the central hole, seat surface and ball socket, the conical surface of the target ejector pin is used to spin-extrude the conical seat surface deep in the blind hole of the needle valve body. S2. Carburizing, quenching and tempering are performed on the needle valve body after step S1. S3. Perform abrasive flow extrusion processing on the needle valve body seat surface after step S2.

2. The method for improving the contact fatigue resistance of the needle valve body seat surface according to claim 1, characterized in that, In step S1, the spin extrusion process is a cold spin extrusion process, and the spin extrusion feed rate is 0.05~0.50mm.

3. The method for improving the contact fatigue resistance of the needle valve body seat surface according to claim 2, characterized in that, In step S1, after the spin extrusion process, the dislocation density in the surface layer of the seat increases to 10. 9 ~10¹ 0 roots / cm²; Some of the mechanical energy from the rotary extrusion process is stored as internal energy in the surface layer of the seat.

4. The method for improving the contact fatigue resistance of the needle valve body seat surface according to claim 1, characterized in that, In step S1, the target ejector pin includes an ejector pin body and a rotary extrusion cone surface disposed at the front end of the ejector pin body, wherein the taper of the rotary extrusion cone surface is adapted to the taper of the needle valve body seat surface. The target ejector pin is screwed into the inner wall of the needle valve body blank and applies a spinning force to the seat surface of the needle valve body through the spinning cone.

5. The method for improving the contact fatigue resistance of the needle valve body seat surface according to claim 1, characterized in that, In step S2, a vacuum pulse carburizing process or an external gas internal solid carburizing process is used for carburizing treatment. The carburizing temperature is 880~950℃, the carburizing time is 3~6h, the strong carburizing potential is 0.9~1.1%, and the diffusion carburizing potential is 0.7~0.9%.

6. The method for improving the contact fatigue resistance of the needle valve body seat surface according to claim 5, characterized in that, In step S2, after carburizing, quenching and tempering, the hardness of the carburized layer on the needle valve body seat surface is 650~850HV, the depth of the carburized layer is 0.4~1.4mm, the length of the strip-shaped carbide does not exceed 5μm, and the size of the particulate carbide does not exceed 1.8μm.

7. The method for improving the contact fatigue resistance of the needle valve body seat surface according to claim 1, characterized in that, In step S3, the abrasive flow is driven by a pressure of 3~30MPa through the channel between the hole wall of the needle valve body and the tube wall of the abrasive flow guide tube.

8. The method for improving the contact fatigue resistance of the needle valve body seat surface according to claim 7, characterized in that, In step S3, an abrasive flow guide tube is provided in the central hole of the needle valve body, and a channel for the abrasive flow is formed between the outer wall of the guide tube and the hole wall of the central hole of the needle valve body. The guide tube has an outer conical surface that is opposite to the seat surface of the needle valve body. After the abrasive particles flow through the channel and are processed by the seat surface, they enter the guide tube and are discharged through the connecting hole opened at the head of the guide tube under the action of the pressure difference inside and outside the guide tube.

9. The method for improving the contact fatigue resistance of the needle valve body seat surface according to claim 8, characterized in that, In step S3, after abrasive flow extrusion processing, the residual compressive stress on the needle valve body seat surface reaches 500~1000MPa.

10. The method for improving the contact fatigue resistance of the needle valve body seat surface according to claim 1, characterized in that, The needle valve body blank is made of 18CrNi8 low-carbon low-alloy steel.

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