Alloy steel camshaft heat treatment deformation control method

Abstract

The invention provides a heat treatment deformation control method for an alloy steel camshaft, which comprises the following steps: in a pre-heating preparation stage, carrying out an outer circle rough grinding process so as to control the jerk value before heat treatment to be within 0.05 mm, and naturally and vertically placing and charging; after the surface hardening treatment, cooling to 820-850 DEG C in the furnace, keeping the temperature for 2-4 hours, and then slowly cooling; the elongation of the alloy steel part after heat treatment is reserved to be 0.2-0.3 mm before quenching; and in the quenching treatment stage, the temperature is kept at 820 + / -25 DEG C for 90 + / -30 min, and an oil-based quenching medium is used for quenching The problems that in the prior art, alloy steel is prone to large deformation after heat treatment, the product percent of pass is low, and the quality stability is poor can be effectively solved, the percent of pass of the cam shaft is improved, and the quality stability of the cam shaft product is greatly guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of surface heat treatment, in particular to a heat treatment deformation control method for alloy steel camshafts. BACKGROUND

[0002] In the related technical field, especially for the heat treatment method of camshafts made of 18CrNiMo7-6 alloy steel (a high-strength carburizing chromium-nickel-molybdenum structural steel), the traditional heat treatment process often uses carburizing and quenching heat treatment methods. While improving the surface hardness, wear resistance and corrosion resistance of the parts, significant post-heat treatment deformation often occurs, mainly manifested as bending deformation and total length shrinkage deformation. This deformation phenomenon has an adverse effect on the geometric precision and performance of the product, thereby reducing the yield and stability of product quality.

[0003] For the pre-heat preparation stage, the traditional process usually only focuses on the basic size and appearance inspection of the parts, and lacks effective control measures for the runout amount. Especially for complex camshafts, the cumulative deformation during machining cannot be fully eliminated, which directly leads to the aggravation of deformation in the subsequent heat treatment process.

[0004] In the carburizing stage, the existing technology often ignores the influence of the cooling method after carburizing heat preservation on the deformation of the parts. The traditional cooling method often causes the parts to cool rapidly at high temperature, inducing rapid phase transformation of the internal organization of the material, and then causing irreversible deformation, especially rapid cooling in the high temperature zone, which is one of the main reasons for the post-heat treatment deformation of alloy steel parts.

[0005] As for the size control during the quenching process, the traditional process usually corrects the size of the parts after heat treatment, but this method cannot prevent or reduce the deformation during quenching, often leading to the size of the parts exceeding the allowed tolerance range. In addition, during the quenching process, the selection of quenching temperature, holding time and quenching medium is not accurate, which also easily causes additional deformation of the parts, especially the control of cooling speed, which is crucial for inhibiting post-heat treatment deformation.

[0006] Finally, in terms of deformation detection, although vernier calipers are commonly used to measure length and dial indicators are used to measure runout in the industry, there is a lack of a standardized detection process to ensure that the deformation of the parts after heat treatment meets the strict process requirements. This inaccurate detection method and process often leads to poor consistency of product quality, making it difficult to meet the high precision requirements of camshafts in modern industrial production.

[0007] In summary, the existing 18CrNiMo7-6 alloy steel camshaft heat treatment method has deficiencies in many aspects such as pre-heat preparation, carburizing, quenching and deformation detection, which leads to frequent deformation problems of the final product after heat treatment, directly affecting the performance and service life of the camshaft, especially in application occasions with strict requirements on size accuracy and runout. Therefore, an effective method for controlling the heat treatment deformation of 18CrNiMo7-6 alloy steel camshaft is needed to improve product quality and yield. SUMMARY

[0008] The purpose of the present application is to provide an alloy steel camshaft heat treatment deformation control method, especially for 18CrNiMo7-6 alloy steel, which minimizes the deformation after heat treatment by optimizing each processing step, thereby solving the above-mentioned technical problems, improving the deformation quality of the camshaft after heat treatment, ensuring that the deformation of the part meets the process requirements, and thereby improving the stability of the quality of the camshaft.

[0009] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: An alloy steel camshaft heat treatment deformation control method for 18CrNiMo7-6 alloy steel, comprising the following steps: (1) In the pre-heat preparation stage, the alloy steel camshaft is rough ground on the outer circle, and the runout of the alloy steel camshaft before heat treatment is controlled to be within 0.05 mm.

[0010] By strengthening the control of the runout of the camshaft before heat treatment in the pre-heat preparation stage, an additional rough grinding process on the outer circle is added, and the runout of the part is controlled to be within 0.05 mm, thereby reducing the influence of machining deformation factors and greatly eliminating the cumulative deformation of the part; (2) In the carburizing stage, on the one hand, the furnace loading method is natural vertical placement. On the other hand, after the carburizing and heat preservation of the alloy steel camshaft are completed, the alloy steel camshaft is cooled to the high temperature section in the furnace, the temperature of the high temperature section is 820-850℃, and the alloy steel camshaft is kept at the high temperature section for 2-4h, and then taken out for slow cooling.

[0011] By designing the furnace loading method to be natural vertical placement in the carburizing stage, the influence of external force on deformation during heat treatment is avoided, and the influence of external factors is reduced. By adding a section of furnace cooling, after the carburizing and heat preservation of the part are completed, the part is first cooled in the furnace to 820-850℃ for 2-4h, and then taken out for slow cooling, so that the part will not be rapidly cooled after carburizing, thereby reducing the deformation caused by rapid phase change of the part organization.

[0012] (3) Before quenching, the size of the alloy steel camshaft is estimated and controlled, and the elongation of the alloy steel camshaft after heat treatment is reserved, and the elongation is 0.2-0.3mm.

[0013] By controlling the size of the part before quenching, collecting the quenching elongation size through the quenching test, reserving the deformation size before quenching, controlling the size of the part before quenching, reserving the heat treatment elongation size of 0.2-0.3 mm, and ensuring that the size of the part after quenching meets the process requirements.

[0014] (4) In the quenching treatment stage, the alloy steel camshaft is placed at a quenching temperature of 820±25℃ for 90±30min, and oil-based quenching medium is used for quenching to control the deformation after heat treatment.

[0015] This step optimizes the quenching temperature, holding time, quenching medium and cooling speed of the part under the premise of ensuring that other indicators of the part are qualified, so as to reduce the deformation amount of the part.

[0016] Preferably, the grinding wheel used in the outer circle rough grinding process is selected from one or more of alumina, silicon carbide, diamond or cubic boron nitride, to ensure the surface finish and dimensional accuracy of the part.

[0017] Preferably, after the surface hardening treatment stage of the alloy steel part is completed, the cooling temperature of the high temperature section is 830℃, and the holding time is 3 hours, further optimizing the microstructure stability and size control after heat treatment.

[0018] Preferably, the elongation allowance of the alloy steel part after heat treatment is 0.25mm, which is obtained based on the comprehensive analysis of the thermal expansion coefficient of the material and the processing technology, to realize the minimum heat treatment deformation.

[0019] Preferably, the holding time at the quenching temperature is selected from 60min, 90min or 120min, which is suitable for alloy steel parts of different sizes and shapes, and ensures the quenching effect and dimensional stability.

[0020] Preferably, the oil-based quenching medium is K oil, and the specific components include a combination of base oil, additives and antioxidants, which provides the best quenching cooling characteristics.

[0021] Preferably, during the quenching process of the alloy steel part, the stirring mode of K oil is 100% stirring, which ensures the uniform temperature of the quenching medium and reduces the deformation of the part during heat treatment.

[0022] Preferably, during the deformation detection stage of the alloy steel part after heat treatment, the precision is 0.02mm when measuring the length using a vernier caliper, and the precision is 0.01mm when using a dial gauge to detect the runout amount with two center clamping, which ensures the accurate control of the size and geometric accuracy of the part.

[0023] The beneficial effects of the present application are: The machining method for controlling camshaft heat treatment deformation of the application can effectively control the deformation of the camshaft, maximally reduce the deformation of the part, significantly improve the dimensional stability of the alloy steel after heat treatment, thereby improving the machining precision and product quality of the heat treated part, effectively prolonging the service life of the part and reducing the subsequent processing cost.

[0024] The method of the application controls the deformation after heat treatment. Through testing, it is found that the deformation of the camshaft after quenching is controlled within ≤0.4mm, and the surface hardness is 58-62HRC, which fully meets the process requirements of the camshaft, thereby widening the application of the camshaft and having popularization and application value in some application fields requiring high dimensional precision and high wear resistance. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a schematic view of a camshaft deformation position. DETAILED DESCRIPTION

[0026] The preferred embodiments will be described below to illustrate the embodiments of the application, and those skilled in the art can easily understand other advantages and effects of the application from the contents disclosed in the specification. The application can also be implemented or applied by different specific embodiments, and various modifications or changes can be made to the details in the specification based on different views and applications without departing from the spirit of the application. It should be understood that the preferred embodiments are only for illustrating the application, and are not intended to limit the protection scope of the application.

[0027] As Figure 1 shown, for the camshaft of 18CrNiMo7-6 alloy steel, the part will change in structure during heat treatment, thereby causing deformation of the part after heat treatment, mainly including bending deformation and total length shrinkage deformation, and the elongation after quenching reaches 0.27-0.65mm. The arrow direction in the figure is the direction of deformation, and the deformation amount is 0.1-1.1mm. The inventors have found through long-term research and analysis that the main factors affecting the bending deformation of the camshaft during heat treatment are: 1) pre-heat machining deformation: about 0.15mm of bending deformation of the part before heat treatment is found in the early stage of the test, which seriously affects the subsequent heat treatment deformation; 2) carburizing deformation: the main factors causing carburizing deformation are clamping methods and deformation caused by rapid cooling; 3) quenching deformation: the main factors affecting quenching deformation are quenching temperature, holding time and quenching medium, and the quenching deformation not only has bending deformation, but also has elongation deformation of the part. Only by maximally eliminating the deformation of each process, can the final heat treatment deformation of the part be better controlled. Therefore, selecting appropriate process methods, clamping methods and cooling methods is the key technology for controlling the deformation of the camshaft.

[0028] Based on the above analysis, the inventors conducted relevant tests, by controlling the deformation of the parts before heat treatment, the cooling method of the parts during carburizing, the clamping method of the parts during carburizing and quenching, the quenching temperature, the quenching time and the quenching medium to control the deformation of the camshaft, thereby solving the deformation problem of the camshaft, controlling the elongation deformation of the parts within 0.2mm, and controlling the bending deformation of the parts within 0.4mm, thereby solving the problem of excessive deformation of the camshaft.

[0029] The following is a preferred embodiment of the present application, a processing method for controlling the heat treatment deformation of an alloy steel camshaft is implemented from the following aspects: Firstly, the deformation of the camshaft before quenching is controlled, the machining process of the camshaft is optimized, and a cam profile grinding process is added, the profile grinding process adopts concentric grinding of the camshaft, and the runout of the parts before quenching is controlled within 0.05mm.

[0030] Through tests, it is proved that the addition of this cam profile grinding process significantly improves the runout of the camshaft, and the detection shows that the maximum runout is improved from 0.15mm to 0.05mm, and the runout of the parts is greatly improved.

[0031] Then, during the carburizing stage, on the one hand, the clamping method of the parts is optimized, the parts are vertically clamped on the tool naturally, and the deformation caused by external factors is reduced. On the other hand, the cooling method of the carbon completion is improved, which is changed from slow cooling to furnace cooling to 820-850℃ before slow cooling, specifically, after the carburizing and heat preservation of the alloy steel camshaft is completed, the alloy steel camshaft is cooled to a high temperature section in the furnace, the temperature of the high temperature section is 820-850℃, and the alloy steel camshaft is kept in the high temperature section for 2-4h, and then taken out for slow cooling, which can greatly improve the cooling deformation of the parts.

[0032] Preferably, the temperature of the high temperature section is 830℃, and the holding time is 3 hours, which can make the process of austenite to martensite transformation in the parts more stable, reduce the microstructure unevenness and deformation caused by rapid cooling, and further optimize the organizational stability and size control after heat treatment.

[0033] Through tests, it is proved that after the parts are carburized, the runout of the parts is detected, and the runout of the parts is ≤0.2mm, and there is no large deformation out of tolerance.

[0034] Further, the pre-quenching machining size of the parts is also controlled, a large number of tests show that the total length of the camshaft after quenching increases to different degrees, and the increase range is generally between 0.05-0.3mm, in order to ensure that the total length of the parts after quenching is within the technical requirements, the pre-quenching deformation tolerance of the parts is reserved, and it is ensured that the total length of the parts after quenching meets the process requirements.

[0035] Experiments show that, by this pre-treatment before quenching, the total length of the part is well controlled, and the elongation deformation after quenching is 100% qualified.

[0036] In addition, the quenching process needs to be optimized, and a specific quenching medium needs to be selected, under the premise of ensuring other quenching indicators qualified, the lowest quenching temperature is selected to reduce the phase change degree of the part during the heating process and the quenching process, thereby reducing the quenching deformation. The process parameters for processing the part in this embodiment are: quenching temperature 820±25℃, holding time 90±30min. In order to adapt to alloy steel parts of different sizes and shapes, the holding time at the quenching temperature can be selected from 60min, 90min or 120min.

[0037] After holding, oil cooling is used. The preferred oil-based quenching medium is K oil, which has specific components including a combination of base oil, additives and antioxidants, providing optimal quenching cooling characteristics. The base oil in K oil provides good cooling performance, while the additives and antioxidants enhance the lubricity and oxidation resistance of the quenching medium, reducing the wear and oxidation of the part during the quenching process, thereby reducing the risk of deformation.

[0038] Experiments show that, by this quenching process optimization, the deformation of the part is reduced to the maximum extent, and the final heat treatment deformation of the part after quenching is 0.4mm, meeting the process requirements.

[0039] Further, during the quenching process of the alloy steel part, the stirring mode of K oil is 100% stirring, which can ensure uniform temperature distribution of the quenching medium during the quenching process, avoiding part deformation caused by local supercooling or overheating, and significantly improving the dimensional stability and microstructure consistency of the alloy steel part after quenching, thereby improving the mechanical properties and service life of the part.

[0040] In further embodiments, during the deformation detection stage after heat treatment of the alloy steel part, the length of the part is detected using a vernier caliper, and the size of the part should meet the process requirements; the runout amount is detected using two center drills for clamping and a dial gauge, and the runout amount of the part should be ≤0.4mm. When measuring the length using a vernier caliper, the accuracy is 0.02mm, and when detecting the runout amount using two center drills for clamping and a dial gauge, the accuracy is 0.01mm. Here, the vernier caliper and dial gauge are used to accurately measure the length and runout amount of the part, and the two center drills for clamping ensure the positioning accuracy during measurement, avoiding inaccurate evaluation of the size of the part due to measurement errors. This embodiment can accurately control the size and geometric accuracy of the alloy steel part after heat treatment, avoiding part scrap due to excessive deformation, and improving production efficiency and economic benefits.

[0041] By implementing the above technical solutions, the dimensional accuracy and mechanical properties of alloy steel parts after heat treatment can be significantly improved, thereby indirectly affecting the performance and service life of the parts in actual operation. In practical applications, these technical solutions can ensure that parts maintain good dimensional stability and mechanical strength when subjected to harsh conditions such as high temperature, high pressure, or high-speed movement, thus improving the operational reliability and working efficiency of the equipment.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlling deformation during heat treatment of alloy steel camshafts, specifically for camshafts made of 18CrNiMo7-6 alloy steel, characterized in that... include: (1) In the preheating preparation stage, the outer diameter of the alloy steel camshaft is rough ground to control the runout before heat treatment to within 0.05 mm. Then, the furnace is loaded using a natural vertical placement method. (2) During the carburizing stage, after the carburizing and heat preservation of the alloy steel camshaft is completed, the alloy steel camshaft is cooled to the high temperature section in the furnace. The temperature of the high temperature section is 820-850℃, and it is kept in the high temperature section for 2-4 hours. After that, it is taken out of the furnace and slowly cooled. (3) Before quenching, the dimensions of the alloy steel camshaft are estimated and controlled, and the elongation of the alloy steel camshaft after heat treatment is reserved, wherein the elongation is 0.2-0.3 mm; (4) During the quenching stage, the alloy steel camshaft is placed at a quenching temperature of 820±25℃ and held for 90±30 min. It is then quenched using an oil-based quenching medium to control the deformation after heat treatment.

2. The method for controlling deformation during heat treatment of alloy steel camshafts according to claim 1, characterized in that, After the carburizing and heat preservation process, the alloy steel camshaft is cooled to a high-temperature zone temperature of 830°C and the heat preservation time is 3 hours.

3. The method for controlling deformation during heat treatment of alloy steel camshafts according to claim 1 or 2, characterized in that, The allowable elongation of the alloy steel camshaft after heat treatment is 0.25 mm.

4. The method for controlling deformation during heat treatment of alloy steel camshafts according to claim 1 or 2, characterized in that, The holding time at the quenching temperature is selected from 60 min, 90 min, or 120 min to accommodate alloy steel parts of different sizes and shapes.

5. The method for controlling deformation during heat treatment of alloy steel camshafts according to claim 1 or 2, characterized in that, The oil-based quenching medium is K oil, and its specific components include, but are not limited to, a combination of base oil, additives, and antioxidants.

6. The method for controlling deformation during heat treatment of alloy steel camshafts according to claim 5, characterized in that, During the quenching process of the alloy steel camshaft, the K oil is stirred 100% to ensure uniform temperature of the quenching medium and reduce deformation of parts during heat treatment.

7. The method for controlling deformation during heat treatment of alloy steel camshafts according to claim 1 or 2, characterized in that, The grinding wheel used in the outer diameter rough grinding process is selected from one or more of alumina, silicon carbide, diamond, or cubic boron nitride grinding wheels to ensure surface finish and dimensional accuracy of the parts.

8. The method for controlling deformation during heat treatment of alloy steel camshafts according to claim 1 or 2, characterized in that, It also includes S5 deformation detection: using vernier calipers to measure length with an accuracy of 0.02mm, and using two centers clamped together with a dial indicator to detect runout with an accuracy of 0.01mm, ensuring precise control of part dimensions and geometric accuracy.

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