A diesel engine valve and hardening treatment method thereof

Abstract

The present invention relates to a marine diesel engine, and more particularly to a diesel engine valve and a hardening treatment method thereof. The method comprises: heating a valve blank to a set temperature, then placing it in a valve-shaped inner cavity of a preset mold, wherein the inner side of the valve-shaped inner cavity is designed to be contoured to the outer surface of the valve blank, and providing a plurality of raised rings at positions corresponding to the valve sealing surface of the valve blank. Pressure is applied to the valve blank, causing the raised rings to act on the valve sealing surface of the valve blank to cause deformation hardening. The valve blank is then removed, water-cooled, and subjected to stress relief treatment. The process is simple, efficient, and can increase the depth of the hardened layer, stabilize the quality of the deformation hardening, and ensure the safety, reliability, and service life of the diesel engine.

Description

Technical Field

[0001] The invention relates to a marine diesel engine, in particular to a diesel engine air valve and a hardening treatment method thereof. Background Art

[0002] Nickel-based alloy valve is one of the key moving parts of the heart of high-power diesel engine, and it is also its basic parts and vulnerable parts. Figure 1 As shown, the valve body 1 of a nickel-based alloy gas valve comprises a valve stem 11, a valve disc 12, and a tapered valve sealing surface 13 connecting the outer sides of the valve stem 11 and the valve disc 12. As the "heart" of a diesel engine, it is a key component that determines its performance and reliability. As a fundamental component, it plays a crucial role in the engine's maintenance cycle and service life. If the valve fails during its service life, it can directly cause serious consequences such as deformation or even damage to components such as the cylinder, piston, and supercharger, resulting in significant financial losses for the user.

[0003] Since the air valve is a consumable part and is located at the "heart", the diesel engine needs to be disassembled when replacing it, which is labor-intensive and time-consuming. If the air valve fails during use, it will inevitably cause a shutdown accident, especially for marine diesel engines, where the loss caused by air valve failure will be even greater.

[0004] Many high-power diesel engine models in my country use nickel-based alloys to manufacture their valves. To reduce the friction and wear caused by the high-frequency, rapid impact contact between the valve disc cone (i.e., the valve sealing surface) and the valve seat cone during operation and extend the valve's service life, it is necessary to improve the hardness and wear resistance of this area. According to design requirements, the hardened layer depth of some valve disc cones should be ≥3.5mm and the hardness of the hardened layer should be ≥450HV. Currently, two methods for hardening the cone surface of high-power diesel engine valve discs made of nickel-based alloys are cold rolling and hot rolling.

[0005] During cold rolling, excessive deformation creates the risk of cracking. Consequently, the hardened layer depth achieved with cold rolling can only reach 0.5-0.7mm, which falls short of design requirements. While hot rolling is less prone to cracking, it involves more steps, is complex to operate, requires more equipment, and results in low production efficiency. The temperature fluctuations in the hardened area are wide, and the hardening quality is inconsistent. While the hardened layer depth can be increased to 2.9-3.3mm, it still falls short of the design requirement of a 3.5mm or greater hardened layer depth on the conical surface of the valve disc. This results in less-than-ideal safety, reliability, and service life for the valve. Summary of the Invention

[0006] The purpose of the present invention is to provide a diesel engine valve and a hardening treatment method thereof, which has a simple process and high production efficiency, and can increase the depth of the hardened layer, stabilize the deformation hardening quality, and ensure the safety, reliability and service life of the diesel engine operation.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention provides a method for hardening a diesel engine valve, the method comprising: heating a valve blank to a set temperature, and then placing the valve blank in a valve-profiling inner cavity of a preset mold, wherein the inner surface of the valve-profiling inner cavity is designed to be contoured to the outer surface of the valve blank, and a plurality of raised rings are provided at positions corresponding to the valve sealing surface of the valve blank. Pressure is applied to the valve blank so that the raised rings act on the valve sealing surface of the valve blank to cause deformation hardening, and then the valve blank is taken out, water-cooled, and subjected to stress relief treatment.

[0009] By adopting the above technical solution, while ensuring that the mechanical properties of the nickel-based alloy valve substrate after solid solution and aging are not degraded, the heating temperature of the hardened area is increased, that is, the valve blank is heated to a set temperature, reducing its deformation resistance. Under the same pressure, the deformation amount and deformation depth are increased. The multiple raised rings provided within the valve contour cavity of the preset mold increase the deformation amount and deformation depth of the valve sealing surface of the valve blank. Correspondingly, the deformation and even fracture of the austenite grains become more severe. While the dislocation density increases significantly, the grain boundary area increases significantly, significantly enhancing the deformation hardening effect. Post-deformation water cooling, i.e., rapid cooling, reduces the softening effect caused by recovery and retains more crystal defects in the hardened area. Subsequent stress relief treatment helps to eliminate some internal stresses and causes some carbides and intermetallic compounds to precipitate in a granular and highly dispersed manner at dislocations, grain boundaries, twin boundaries, and subgrain boundaries, thereby ensuring a better deformation hardening effect.

[0010] Furthermore, the valve blank is heated in a heat treatment furnace, the heating temperature is set at 650-740°C, and the holding time is 1.5-3h.

[0011] Furthermore, the cross-section of the raised ring is conical, the height protruding from the inner surface of the preset mold is 1.8~2.4mm, the width of the raised ring close to the preset mold is 3.5~4.3mm, and the spacing between the bottoms of adjacent raised rings is 1.4~1.8mm.

[0012] Furthermore, a hydraulic press is used to apply pressure to the valve blank, and the pressure of the hydraulic press is set to 1700~3600 tons.

[0013] Furthermore, the stress relief treatment is specifically as follows: placing the water-cooled valve blank into a heat treatment furnace for stress relief, setting the heating temperature to 540-630°C, holding time to 3.5-5.5h, and air cooling.

[0014] In a second aspect, the present invention provides a diesel engine valve, comprising a valve body, wherein the valve sealing surface of the valve body is treated by the above-mentioned diesel engine valve hardening treatment method.

[0015] The present invention achieves a hardened layer depth on the conical surface of nickel-based alloy high-power diesel engine valves that is more than six times deeper than that achieved by cold rolling at the same pressure, without the risk of cracking. It is also approximately 1mm deeper than that achieved by hot rolling at the same pressure, fully meeting the design requirement of a hardened layer depth of ≥3.5mm. Furthermore, compared to other hardening methods, the present invention offers simpler operation, higher production efficiency, more stable valve quality, and improved valve reliability, fatigue strength, and service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the structure of the gas valve before hardening treatment;

[0017] Figure 2 Schematic diagram of the process of the hardening treatment method of the diesel engine valve according to the present invention;

[0018] Figure 3 Schematic diagram of the structure of the preset mold in an embodiment of the present invention;

[0019] Figure 4 This is a schematic diagram of the structure of the gas valve after hardening treatment.

[0020] In the figure, 1 is the valve body, 11 is the valve stem, 12 is the valve disc, 13 is the valve sealing surface, 14 is the groove, 2 is the preset mold, 21 is the inner cavity, and 22 is the raised ring. DETAILED DESCRIPTION

[0021] The following describes the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art will readily appreciate the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the various details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are intended only to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0022] It should be noted that the illustrations provided in the following embodiments are merely schematic illustrations of the basic concept of the present invention. The illustrations only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed arbitrarily, and the component layout may also be more complex.

[0023] Example 1, see Figure 2As shown, a method for hardening a diesel engine valve comprises the following steps:

[0024] S1. Heating: Heat the nickel-based alloy valve blank in a heat treatment furnace at 710°C for 2 hours. While ensuring that the mechanical properties of the nickel-based alloy valve substrate, which has undergone solid solution and aging, are not reduced, increase the heating temperature of the hardened area, i.e., heat the valve blank to the set temperature, to reduce its deformation resistance. Under the same pressure, the deformation amount and deformation depth will increase.

[0025] S2, placing the heated and insulated nickel-based alloy valve blank in the valve-shaped inner cavity of the preset mold, see Figure 3 As shown, the inner surface of the valve-profiling inner cavity 21 of the pre-set mold 2 is designed to conform to the outer surface of the valve blank. Three raised rings 22 are provided at locations corresponding to the valve sealing surface 13 of the nickel-based alloy valve blank. These raised rings have a conical cross-section and protrude 1.8 mm from the inner surface of the pre-set mold. The width of the raised rings near the pre-set mold, i.e., the width of the bottom of the raised rings, is 3.5 mm. The spacing between the bottoms of adjacent raised rings is 1.4 mm. The axis of each raised ring 22 is perpendicular to the conical surface of the pre-set mold 2 for strain hardening. The protruding portion of the raised ring is symmetrical with its axis, and the top of the raised ring has a circular arc transition.

[0026] Due to the multiple raised rings 22 set in the valve profiling inner cavity 21 of the preset mold 2, the deformation amount and deformation depth of the valve sealing surface 13 of the nickel-based alloy valve blank are increased. Accordingly, the deformation and even breakage of the austenite grains become more serious. While the dislocation density is significantly increased, the grain boundary area is greatly increased, and the deformation hardening effect is significantly improved.

[0027] S3, deformation hardening: A hydraulic press is used to apply pressure to the nickel-based alloy valve blank. The pressure is set at 1900 tons until the larger end face of the valve disc 12 of the valve body 1 is flush with the upper end face of the mold. This causes the raised ring to act on the valve sealing surface of the valve blank, causing deformation hardening. The valve blank is then immediately removed and water-cooled. Water cooling after deformation is a rapid cooling process, which reduces the softening effect caused by recovery and retains more crystal defects in the hardened area.

[0028] S4, stress relief treatment: Place the water-cooled nickel-based alloy valve blank in a heat treatment furnace for stress relief. The heating temperature is set at 570°C, the holding time is 4 hours, and the valve is air-cooled. Stress relief treatment helps to eliminate some internal stress and causes some carbides and intermetallic compounds to precipitate in granular and highly dispersed locations such as dislocations, grain boundaries, twin boundaries, and subgrain boundaries, thereby ensuring a better deformation hardening effect.

[0029] See also Figure 4As shown, three annular grooves 14 are formed on the valve sealing surface 13 of the nickel-based alloy valve after hardening treatment.

[0030] After the hardened surface of the valve disc was dissected along the diameter direction, the hardness and depth of the hardened layer on the valve sealing surface 13 and the bottom of the groove 14 were measured using a Vickers hardness tester. The interval between each measuring point was 0.1mm. The hardness of the hardened layer on the valve sealing surface 13 and the bottom of the groove 14 was 472~513HV, the depth of the hardened layer on the valve sealing surface 13 was 5.6mm, and the depth of the hardened layer at the bottom of the groove 14 was 3.9mm. No cracks were found after color flaw detection.

[0031] Embodiment 2, a method for hardening a diesel engine valve, comprising the following steps:

[0032] S1, heating, using a heat treatment furnace to heat the nickel-based alloy valve blank, the heating temperature is set to 740 ° C, and the holding time is 3 hours.

[0033] S2, placing the heated and insulated nickel-based alloy valve blank in a pre-set mold, placing it within the valve-shaped inner cavity of the pre-set mold. The inner surface of the valve-shaped inner cavity of the pre-set mold is designed to be contoured to the outer surface of the valve blank. Four raised rings are provided at positions corresponding to the valve-shaped inner cavity and the valve sealing surface of the nickel-based alloy valve blank. The raised rings have a conical cross-section and protrude 2.3mm above the inner surface of the pre-set mold. The width of the raised ring near the pre-set mold, i.e., the bottom width of the raised ring, is 4.1mm. The spacing between the bottoms of adjacent raised rings is 1.8mm. The axis of each raised ring is perpendicular to the conical surface of the pre-set mold for deformation hardening, and the protruding portion of the raised ring is symmetrical with its axis. The top of the raised ring has an arc transition.

[0034] S3, deformation hardening, use a hydraulic press to apply pressure to the nickel-based alloy valve blank. The hydraulic press pressure is set to 3550 tons until the large end face of the valve disc of the valve body and the upper end face of the mold are in the same plane, so that the raised ring acts on the valve sealing surface of the valve blank to produce deformation hardening. The valve blank is immediately removed and water-cooled.

[0035] S4, stress relief treatment, the water-cooled nickel-based alloy valve blank is placed in a heat treatment furnace for stress relief, the heating temperature is set to 620℃, the holding time is 5h, and air cooling is performed.

[0036] After the hardened surface of the valve disc was cut open along the diameter direction, the hardness and depth of the hardened layer on the valve sealing surface 13 and the bottom of the groove 14 were measured using a Vickers hardness tester. The interval between each measuring point was 0.1 mm. The hardness of the hardened layer on the valve sealing surface 13 and the bottom of the groove 14 was 467~518 HV, the depth of the hardened layer on the valve sealing surface 13 was 6.2 mm, and the depth of the hardened layer at the bottom of the groove 14 was 4.1 mm. No cracks were found after color flaw detection.

[0037] Embodiment 3, a method for hardening a diesel engine valve, comprising the following steps:

[0038] S1, heating, using a heat treatment furnace to heat the nickel-based alloy valve blank, the heating temperature is set to 650 ° C, and the holding time is 2 hours.

[0039] S2, placing the heated and insulated nickel-based alloy valve blank in a pre-set mold, placing it in the valve-shaped inner cavity of the pre-set mold. The inner surface of the valve-shaped inner cavity of the pre-set mold is designed to be contoured to the outer surface of the valve blank. Three raised rings are provided at positions corresponding to the valve-shaped inner cavity and the valve sealing surface of the nickel-based alloy valve blank. The raised rings have a conical cross-section and protrude 2.1mm above the inner surface of the pre-set mold. The width of the raised ring near the pre-set mold, i.e., the bottom width of the raised ring, is 3.8mm. The spacing between the bottoms of adjacent raised rings is 1.6mm. The axis of each raised ring is perpendicular to the conical surface of the pre-set mold for deformation hardening, and the protruding portion of the raised ring is symmetrical with its axis. The top of the raised ring has an arc transition.

[0040] S3, deformation hardening, use a hydraulic press to apply pressure to the nickel-based alloy valve blank. The hydraulic press pressure is set to 2800 tons until the large end face of the valve disc of the valve body and the upper end face of the mold are in the same plane, so that the raised ring acts on the valve sealing surface of the valve blank to produce deformation hardening. The valve blank is immediately removed and water-cooled.

[0041] S4, stress relief treatment, the water-cooled nickel-based alloy valve blank is placed in a heat treatment furnace for stress relief, the heating temperature is set to 540℃, the holding time is 4h, and air cooling is performed.

[0042] After the hardened surface of the valve disc was cut open along the diameter direction, the hardness and depth of the hardened layer on the valve sealing surface 13 and the bottom of the groove 14 were measured using a Vickers hardness tester. The interval between each measuring point was 0.1 mm. The hardness of the hardened layer on the valve sealing surface 13 and the bottom of the groove 14 was 463~504 HV, the depth of the hardened layer on the valve sealing surface 13 was 5.9 mm, and the depth of the hardened layer at the bottom of the groove 14 was 3.8 mm. No cracks were found after color flaw detection.

[0043] Embodiment 4, a method for hardening a diesel engine valve, comprising the following steps:

[0044] S1, heating, using a heat treatment furnace to heat the nickel-based alloy valve blank, the heating temperature is set to 680 ° C, and the holding time is 1.5 hours.

[0045] S2, placing the heated and insulated nickel-based alloy valve blank in a pre-set mold, placing it in the valve-shaped inner cavity of the pre-set mold. The inner surface of the valve-shaped inner cavity of the pre-set mold is designed to be contoured to the outer surface of the valve blank. Four raised rings are provided at positions corresponding to the valve-shaped inner cavity and the valve sealing surface of the nickel-based alloy valve blank. The raised rings have a conical cross-section and protrude 2.4mm above the inner surface of the pre-set mold. The width of the raised ring near the pre-set mold, i.e., the bottom width of the raised ring, is 4.3mm. The spacing between the bottoms of adjacent raised rings is 1.5mm. The axis of each raised ring is perpendicular to the conical surface of the pre-set mold for deformation hardening, and the protruding portion of the raised ring is symmetrical with its axis. The top of the raised ring has an arc transition.

[0046] S3, deformation hardening, use a hydraulic press to apply pressure to the nickel-based alloy valve blank. The hydraulic press pressure is set to 1700 tons until the large end face of the valve disc of the valve body and the upper end face of the mold are in the same plane, so that the raised ring acts on the valve sealing surface of the valve blank to produce deformation hardening. The valve blank is immediately removed and water-cooled.

[0047] S4, stress relief treatment, the water-cooled nickel-based alloy valve blank is placed in a heat treatment furnace for stress relief, the heating temperature is set to 630℃, the holding time is 3.5h, and air cooling is performed.

[0048] After the hardened surface of the valve disc was cut open along the diameter direction, the hardness and depth of the hardened layer on the valve sealing surface 13 and the bottom of the groove 14 were measured using a Vickers hardness tester. The interval between each measuring point was 0.1 mm. The hardness of the hardened layer on the valve sealing surface 13 and the bottom of the groove 14 was 469~521 HV, the depth of the hardened layer on the valve sealing surface 13 was 6.4 mm, and the depth of the hardened layer at the bottom of the groove 14 was 4.1 mm. No cracks were found after color flaw detection.

[0049] The above embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent substitution or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention.

Claims

1. A method for hardening a diesel engine valve, characterized in that: The method comprises: heating a valve blank in a heat treatment furnace, setting the heating temperature to 650-740°C and holding the temperature for 1.5-3 hours, then placing the blank in a valve-shaped inner cavity of a preset mold, wherein the inner side surface of the valve-shaped inner cavity is designed to be contoured to the outer surface of the valve blank, and providing a plurality of raised rings at positions corresponding to the valve sealing surface of the valve blank in the valve-shaped inner cavity, applying pressure to the valve blank so that the raised rings act on the valve sealing surface of the valve blank to cause deformation and hardening, and then removing the valve blank, water cooling it, and performing stress relief treatment. The cross section of the raised ring is conical, and the height protruding from the inner surface of the preset mold is 1.8~2.4mm. The width of the raised ring close to the preset mold is 3.5~4.3mm, and the spacing between the bottoms of adjacent raised rings is 1.4~1.8mm.

2. The method for hardening a diesel engine valve according to claim 1, wherein: A hydraulic press is used to apply pressure to the valve blank, and the pressure of the hydraulic press is set to 1700~3600 tons.

3. The hardening treatment method for a diesel engine valve according to claim 1 or 2, characterized in that: The stress relief treatment is as follows: the water-cooled valve blank is placed in a heat treatment furnace for stress relief, the heating temperature is set at 540~630℃, the holding time is 3.5~5.5h, and air cooling is performed.

4. A diesel engine valve, comprising a valve body, characterized in that: The valve sealing surface of the valve body is treated by the hardening treatment method for a diesel engine valve according to any one of claims 1 to 3.

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