A heat treatment processing method for eliminating magnetic marks of a camshaft of a high-power diesel engine

Abstract

The patent relates to the technical field of processing technology, in particular to a heat treatment processing method for eliminating magnetic marks of camshafts of high-power diesel engines, which comprises the following steps: S1: after heat treatment by a traditional process, when flaw detection is performed, the cam profile where the magnetic marks are visible to the naked eye are in a stack, induction heating is performed on a medium-frequency device, temperature is measured by an infrared temperature measuring instrument, and high-temperature normalizing is completed; S2: the inductor and the medium-frequency device in step S1 are used for induction heating, temperature is measured by an infrared temperature measuring instrument, and conventional normalizing is completed; S3: medium-frequency induction heating quenching and low-temperature tempering are performed according to the traditional process; and S4: magnetic particle flaw detection is performed according to the traditional process. By adopting the scheme, the qualified product rate is significantly improved, and the waste product rate is significantly reduced. In addition, compared with other process methods for reducing banded structures, the present application reduces power consumption, significantly reduces oxidation and decarburization of workpieces, saves a large amount of raw materials, and solves the problems of high energy consumption, serious oxidation and decarburization of workpieces, and large loss of raw materials.

Description

Technical Field

[0001] This invention relates to the field of processing technology, specifically a heat treatment method for eliminating magnetic traces on a high-power diesel engine camshaft. Background Technology

[0002] Camshafts made of 50CrMo4H material are one of the key moving parts of a high-power diesel engine, and also its fundamental components. As the "heart" moving part, it is crucial in determining the performance and reliability of the diesel engine. As a basic component, it plays a vital role in the reliability and service life of the diesel engine. If the camshaft fails during use, it will directly cause the diesel engine to shut down and damage related parts, resulting in huge economic losses for the user.

[0003] In my country, various models of high-power diesel engines use camshafts made of 50CrMo4H material. To ensure the service life of the camshafts, the drawings require that each cam profile undergo heat treatment followed by quenching to a hardness of 60-64 HRC, a hardened layer depth of 5-8 mm, and a martensite grade of 4-7. Magnetic particle testing should show no visible magnetic traces. The traditional heat treatment and flaw detection method for high-power diesel engine camshafts made of 50CrMo4H material is: forging normalizing - rough machining followed by quenching and tempering - semi-finishing followed by medium-frequency induction heating quenching, low-temperature tempering - magnetic particle testing.

[0004] Due to the large size of high-power diesel engine camshafts, the degree of segregation varies in different parts of the raw steel bars. After the steel bars are forged into camshaft blanks, areas with more severe segregation will still be retained to varying degrees in the blanks. This results in significant inhomogeneity in the metallographic structure of these areas after quenching and low-temperature tempering using traditional processes. During magnetic particle inspection, the uneven quenching structure will lead to visible magnetic trace accumulation, failing to meet the product drawing requirements. Based on actual production testing, due to differences in the degree of segregation between different batches of raw materials, it is common for camshafts treated with the same process to exhibit visible magnetic trace accumulation on the cam profile surface as high as 18-37% during magnetic particle inspection, resulting in substantial scrap losses.

[0005] Once the supply status of raw material steel bars is determined, there are two traditional methods to reduce camshaft composition segregation: increasing the forging ratio of the blank or performing diffusion annealing on the blank. However, both methods suffer from problems such as high energy consumption, severe oxidation and decarburization of the workpiece, large raw material loss, and high production costs, which cannot meet the needs of large-scale, low-cost production. Summary of the Invention

[0006] The present invention aims to provide a heat treatment method for eliminating magnetic traces on the camshaft of a high-power diesel engine, in order to solve the problems of high energy consumption, severe oxidation and decarburization of the workpiece, and large loss of raw materials.

[0007] To achieve the above objectives, the basic solution of the present invention is as follows: a heat treatment method for eliminating magnetic tracks on a high-power diesel engine camshaft, comprising the following steps: S1: After traditional heat treatment, at the cam-shaped surface where magnetic traces are visible to the naked eye during flaw detection, a special inductor for heating and quenching is used to perform induction heating on a medium-frequency device. The temperature is measured with an infrared thermometer. The temperature is heated from room temperature to above 980℃ for 28-34 seconds. After heating, the temperature is air-cooled to below 500℃ to complete the high-temperature normalizing. S2: Use the sensor and intermediate frequency equipment from step S1 for induction heating, measure the temperature with an infrared thermometer, heat to 930-970℃, heating time is 17-23 seconds, after heating is completed, air cool to below 400℃ to complete the normal heating. S3: Perform medium-frequency induction heating quenching and low-temperature tempering according to traditional processes; S4: Perform magnetic particle testing according to traditional processes.

[0008] Furthermore, the intermediate frequency device is selected as a 350kW intermediate frequency device.

[0009] Furthermore, in step S1, the high-temperature normalizing heating temperature is 1050℃, the heating time is 33s, and after heating, it is air-cooled to below 400℃.

[0010] Furthermore, in step S2, the conventional normalizing heating temperature is 934°C, the heating time is 17 seconds, and after heating, the temperature is air-cooled to below 400°C.

[0011] Furthermore, in step S1, the high-temperature normalizing heating temperature is 1094℃ and the heating time is 30s; in step S2, the conventional normalizing heating temperature is 967℃ and the heating time is 23s.

[0012] The working principle of this solution is as follows: At the cam profile surface where visible magnetic traces accumulate, an additional medium-frequency induction heating high-temperature normalizing process is added to allow the segregating atoms to diffuse rapidly and appropriately at high temperatures, thereby reducing the banded structure and preventing visible magnetic trace accumulation after induction heating quenching and low-temperature tempering. Adding a medium-frequency induction heating conventional normalizing process refines the coarse grains formed during high-temperature induction heating, preparing the microstructure for final surface quenching. Following traditional medium-frequency quenching and low-temperature tempering, magnetic particle testing is performed to ensure the camshaft achieves the induction heating quenching quality required by the drawings.

[0013] The beneficial effects of this solution are as follows: The 50CrMo4H camshaft profile treated using this invention exhibits a hardness of 60-63.5 HRC using a Leeb hardness tester, a surface hardening layer depth of 5.4-7.8 mm at eight locations on the same profile using a Vickers hardness tester, and a martensite grade of 4-6 at eight locations on the same profile using a metallographic microscope. Magnetic particle inspection reveals no visible magnetic trace accumulation, resulting in a significantly improved yield and a significantly reduced scrap rate. Furthermore, compared to other processes for reducing banded structures, this invention reduces energy consumption and significantly decreases workpiece oxidation and decarburization, saving considerable raw materials. Detailed Implementation

[0014] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0015] A heat treatment method for eliminating magnetic tracks on a high-power diesel engine camshaft includes the following steps: S1: After traditional heat treatment, at the cam-shaped surface where magnetic traces are visible to the naked eye during flaw detection, a special inductor for heating and quenching is used to perform induction heating on a 350Kw medium frequency device. The temperature is measured with an infrared thermometer. The temperature is heated from room temperature to above 980℃ for 28-34 seconds. After heating, the temperature is air-cooled to below 500℃ to complete the high-temperature normalizing. S2: Use the sensor and intermediate frequency equipment from step S1 for induction heating, measure the temperature with an infrared thermometer, heat to 930-970℃, heating time is 17-23 seconds, after heating is completed, air cool to below 400℃ to complete the normal heating. S3: Perform medium-frequency induction heating quenching and low-temperature tempering according to traditional processes; S4: Perform magnetic particle testing according to traditional processes.

[0016] Traditional processes include the following steps: 1. Cutting: Cut 50CrMo4H hot-rolled steel bars to a fixed length, remove material ends, surface oxide scale, cracks and other appearance defects, and prepare forging billets; 2. Forging: Heat to 1180~1220℃ and forge into a camshaft blank. The final forging temperature shall not be lower than 850℃, and air cool after forging. 3. Forging billet normalizing: Heat to 870-910℃, hold for 40-60 minutes for every 25mm of effective thickness of the billet, remove from the furnace and air cool to eliminate forging stress and homogenize the basic structure; 4. Rough machining: Turn the outer diameter, end face, and journal; rough mill the cam profile, leaving allowance for finishing; remove surface oxide scale and forging flash to complete the initial shape machining of the part; 5. Overall tempering: After oil quenching at 840-870℃, the matrix is ​​tempered at 580-640℃ to obtain tempered sorbite, ensuring strength and toughness. 6. Semi-finishing: finish turning each journal and end face, semi-finish milling the cam profile, strictly controlling dimensional tolerances, and reserving machining allowance for the hardened layer in the final surface hardening; 7. Induction hardening and low-temperature tempering of cam profile: The cam working surface is induction heated at 880-920℃ and rapidly cooled by spraying quenching liquid. The cam profile is rapidly cooled to form a martensitic structure, and then tempered at 160-200℃ to achieve a surface hardness of 60-64HRC and a hardened layer depth of 5-8mm. 8. Magnetic particle inspection: Non-destructive testing of the entire part, requiring no visible magnetic traces on the cam surface.

[0017] The camshaft processed using this embodiment has a hardness of 60-62 HRC as measured by a Leeb hardness tester, a hardened layer depth of 5.5-7.4 mm at 8 locations on the same surface as measured by a Vickers hardness tester, a martensite grade of 5-6 at 8 locations on the same surface as measured by a metallographic microscope, and no magnetic trace accumulation visible to the naked eye after magnetic particle inspection. Example 2

[0018] A heat treatment method for eliminating magnetic tracks on a high-power diesel engine camshaft includes the following steps: S1: After traditional heat treatment, at the cam-shaped surface where magnetic traces are visible to the naked eye during flaw detection, a special inductor for heating and quenching is used to perform induction heating on a 350Kw medium frequency device. The temperature is measured with an infrared thermometer. The temperature is heated from room temperature to 1050℃ for 33 seconds. After heating, the temperature is air-cooled to below 400℃ to complete the high-temperature normalizing. S2: Use the sensor and intermediate frequency equipment from step S1 for induction heating, measure the temperature with an infrared thermometer, heat to 934°C, heating time is 17 seconds, after heating is completed, air cool to below 400°C to complete the normal heating. S3: Perform medium-frequency induction heating quenching and low-temperature tempering according to traditional processes; S4: Perform magnetic particle testing according to traditional processes.

[0019] The camshaft processed using this embodiment has a hardness of 60.5-62.5 HRC as measured by a Leeb hardness tester, a hardened layer depth of 5.4-6.9 mm at 8 locations on the same surface as measured by a Vickers hardness tester, a martensite grade of 4-5 at 8 locations on the same surface as measured by a metallographic microscope, and no magnetic trace accumulation visible to the naked eye after magnetic particle inspection. Example 3

[0020] A heat treatment method for eliminating magnetic tracks on a high-power diesel engine camshaft includes the following steps: S1: After traditional heat treatment, at the cam-shaped surface where magnetic traces are visible to the naked eye during flaw detection, a special inductor for heating and quenching is used to perform induction heating on a 350Kw medium frequency device. The temperature is measured with an infrared thermometer. The temperature is heated from room temperature to 1050℃ for 28 seconds. After heating, the temperature is air-cooled to below 400℃ to complete the high-temperature normalizing. S2: Use the sensor and intermediate frequency equipment from step S1 for induction heating, measure the temperature with an infrared thermometer, heat to 942℃, heating time is 19 seconds, after heating is completed, air cool to below 400℃ to complete the normal heating. S3: Perform medium-frequency induction heating quenching and low-temperature tempering according to traditional processes; S4: Perform magnetic particle testing according to traditional processes.

[0021] The camshaft processed using this embodiment has a hardness of 60.5-62 HRC as measured by a Leeb hardness tester, a hardened layer depth of 5.9-7.8 mm at 8 locations on the same surface as measured by a Vickers hardness tester, a martensite grade of 4-5 at 8 locations on the same surface as measured by a metallographic microscope, and no magnetic trace accumulation visible to the naked eye after magnetic particle inspection. Example 4

[0022] A heat treatment method for eliminating magnetic tracks on a high-power diesel engine camshaft includes the following steps: S1: After traditional heat treatment, at the cam-shaped surface where magnetic traces are visible to the naked eye during flaw detection, a special inductor for heating and quenching is used to perform induction heating on a 350Kw medium frequency device. The temperature is measured with an infrared thermometer. The temperature is heated from room temperature to 1094℃ for 30 seconds. After heating, the temperature is air-cooled to below 400℃ to complete the high-temperature normalizing. S2: Use the sensor and intermediate frequency equipment from step S1 for induction heating, measure the temperature with an infrared thermometer, heat to 967°C, and heat for 23 seconds. After heating, air cool to below 400°C to complete the normal heating. S3: Perform medium-frequency induction heating quenching and low-temperature tempering according to traditional processes; S4: Perform magnetic particle testing according to traditional processes.

[0023] The camshaft processed using this embodiment has a hardness of 61-63.5 HRC as measured by a Leeb hardness tester, a hardened layer depth of 5.8-7.6 mm at 8 locations on the same surface as measured by a Vickers hardness tester, a martensite grade of 5-6 at 8 locations on the same surface as measured by a metallographic microscope, and no magnetic trace accumulation visible to the naked eye after magnetic particle inspection.

[0024] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0025] The above descriptions are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A heat treatment method for eliminating magnetic traces on a high-power diesel engine camshaft, characterized in that: Includes the following steps: S1: After traditional heat treatment, at the cam-shaped surface where magnetic traces are visible to the naked eye during flaw detection, a special inductor for heating and quenching is used to perform induction heating on a medium-frequency device. The temperature is measured with an infrared thermometer. The temperature is heated from room temperature to above 980℃ for 28-34 seconds. After heating, the temperature is air-cooled to below 500℃ to complete the high-temperature normalizing. S2: Use the sensor and intermediate frequency equipment from step S1 for induction heating, measure the temperature with an infrared thermometer, heat to 930-970℃, heating time is 17-23 seconds, after heating is completed, air cool to below 400℃ to complete the normal heating. S3: Perform medium-frequency induction heating quenching and low-temperature tempering according to traditional processes; S4: Perform magnetic particle testing according to traditional processes.

2. The heat treatment method for eliminating magnetic tracks on a high-power diesel engine camshaft according to claim 1, characterized in that: The intermediate frequency equipment selected is a 350kW intermediate frequency equipment.

3. The heat treatment method for eliminating magnetic tracks on a high-power diesel engine camshaft according to claim 1, characterized in that: In step S1, the high-temperature normalizing heating temperature is 1050℃, the heating time is 33s, and after heating, the temperature is air-cooled to below 400℃.

4. The heat treatment method for eliminating magnetic tracks on a high-power diesel engine camshaft according to claim 1, characterized in that: In step S2, the normalizing heating temperature is 934℃, the heating time is 17s, and after heating, the temperature is air-cooled to below 400℃.

5. The heat treatment method for eliminating magnetic tracks on a high-power diesel engine camshaft according to claim 1, characterized in that: In step S1, the high-temperature normalizing heating temperature is 1094℃ and the heating time is 30s; in step S2, the conventional normalizing heating temperature is 967℃ and the heating time is 23s.