Composite heat treatment process suitable for working in environment of 300 DEG C

Abstract

The invention belongs to the field of material science and engineering, and relates to a composite heat treatment process suitable for working in an environment of 300 DEG C. According to the composite heat treatment process, a workpiece is tempered at the use temperature of 380 DEG C after high-frequency quenching through a method combining sulfur carbonitriding and high-frequency quenching, the surface hardness of the outer circle phi 34 is 54-56 HRC, and the technical requirement for the use temperature of 300 DEG C is met. A method of combining sulfur-carbonitriding and high-frequency quenching is adopted, and a compound layer of sulfur, carbon and nitrogen is formed on the surface of a workpiece, so that the hardening layer depth of the workpiece is increased, the alternating load resistance of the workpiece is enhanced, the surface friction coefficient is reduced, the surface hardness is improved, the toughness of the center of the workpiece is kept, the risk of brittle fracture is reduced, and the wear resistance of the workpiece is improved; and the process repeatability is good, and stable product quality can be ensured.

Description

Technical Field

[0001] The invention belongs to the field of material science and engineering, and relates to a composite heat treatment process suitable for working in a 300°C environment. Background Art

[0002] Sulfur-carbonitriding, as a chemical heat treatment process widely recognized by the industry, has the core advantage of accurately forming a layer of compounds rich in sulfur, carbon and nitrogen on the surface of the material. This special structure greatly enhances the surface hardness of the material and significantly improves the wear resistance and abrasion resistance. The extremely low friction coefficient of the sulfide layer greatly reduces the wear between moving parts, thereby improving mechanical efficiency, effectively preventing seizure, and significantly enhancing the durability of the workpiece under alternating loads, thereby extending the service life.

[0003] However, despite the many advantages of the sulfur-carbonitriding process, its complex process flow and high production cost are always its disadvantages that cannot be ignored. In addition, the depth of the hardened layer of this process is relatively limited. For high-end workpieces with strict requirements on the depth of the hardened layer, sulfur-carbonitriding alone is difficult to meet the requirements. Therefore, in practical applications, it is often necessary to combine other surface heat treatment technologies, such as induction quenching, to further increase the depth of the hardened layer, but this also increases the complexity and cost of the process accordingly.

[0004] In terms of workpiece surface hardness improvement technology, induction heating (covering various types such as high frequency, industrial frequency, medium frequency, etc.) has always occupied an important position. In addition, various means such as flame heating, laser heating, electron beam heating, electrolyte heating and bath heating also have their own advantages. These surface heat treatment technologies all have the ability to accurately control the heating area and temperature, so that a modified layer with excellent performance can be formed while meeting the design requirements. However, induction heating technology has a significant limitation: its tempering temperature is usually limited to between 150-200°C. When the workpiece needs to work in a high temperature environment such as 300°C, the surface hardness of the product treated with induction heating may drop significantly, which greatly affects the wear resistance.

[0005] In summary, although existing technologies such as sulfur-carbonitriding and induction heating have performed well in improving the surface hardness of workpieces, they still have many shortcomings and limitations, especially when processing workpieces in high temperature environments. Therefore, we urgently need a new type of heat treatment process to overcome the defects of existing technologies and meet the stringent requirements of workpieces on hardness and wear resistance in high temperature environments. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a composite heat treatment process suitable for working in an environment of 300°C, which ensures the hardness of the outer surface of the product and the depth of the hardened layer by combining sulfur-carbonitriding + high-frequency quenching. The process has good repeatability and stable workpiece quality.

[0007] To achieve the above object, the present invention provides the following technical solution: a composite heat treatment process suitable for working in a 300°C environment, comprising the following steps:

[0008] S1, pre-heat treatment of 35CrMoVA material, quenching and tempering to hardness of 311-375HBW;

[0009] S2, after the quenching and tempering is completed, the workpiece is fine turned and milled, and then the whole is sulfur-carbonitrided to form a 0.3-0.5mm carburized layer with a hardness of 545-615HV10. The specific process is as follows:

[0010] S21, wash the product and place it vertically on the work clothes;

[0011] S22, exhaust air into the furnace, nitrogen flow rate is 1.0m 3 / h, close the exhaust valve after 40 minutes, heat up with the furnace to 300℃, 400℃, 480℃, keep warm for 1 hour each, then heat up to nitriding temperature 570±5℃, keep warm for 5-6 hours, at this time the ammonia flow rate is 1.6-1.8m 3 / h, and drip ethanol + thiourea 100-140 drops / min, then raise the temperature to 595±5℃, keep warm for 3h, and the nitrogen flow rate is 1.0m 3 / h;

[0012] S23, cooling with nitrogen to below 150°C and then air cooling out of the furnace;

[0013] S3, polish the workpiece after sulfur-carbonitriding, and then perform high-frequency quenching on the outer φ34×24 area to ensure that the hardness reaches 52-56HRC and the hardened layer depth is 2-3mm. The high-frequency quenching process is as follows:

[0014] S31, placing the workpiece in a special fixture, calling the workpiece processing program from the program and confirming it, and running the program for preheating, heating and cooling;

[0015] S32, coolant quenching liquid is circulated during the heating process, the quenching liquid pressure meets the process requirements, and tempering is performed after high-frequency quenching.

[0016] Optionally, the high-frequency quenching process parameters are: AC voltage 380±2V, AC current 50~60A, frequency 50±0.2KHZ, moving frequency 4HZ, preheating time 2S, heating time 10S, cooling time 5S, quenching liquid concentration 3~5%, quenching liquid temperature 25~35℃, tempering temperature is 380±10℃, and tempering holding time is 2~2.5h.

[0017] Optionally, during the sulfur-carbonitriding treatment, the heating and insulation steps are strictly performed according to the temperature and time parameters to ensure the uniformity and hardness requirements of the carburized layer.

[0018] Optionally, in step S31, after the workpiece is placed in the fixture, the angle of the workpiece is adjusted, the inductor is moved to the heating position, and the relative position and gap between the workpiece and the inductor are adjusted to ensure heating uniformity and quenching effect.

[0019] Optionally, the tempering step is performed immediately after high-frequency quenching to avoid deformation and cracking of the workpiece caused by quenching stress while ensuring the toughness of the core of the workpiece.

[0020] The beneficial effect of the present invention is that the product of the present invention uses a method combining sulfur carbonitriding and high-frequency quenching to make the workpiece tempered at a use temperature of 380°C after high-frequency quenching, and the surface hardness of the outer circle Φ34 is 54-56HRC, which meets the technical requirement of a use temperature of 300°C. The method combining sulfur carbonitriding and high-frequency quenching is adopted to form a sulfur, carbon, and nitrogen compound layer on the surface of the workpiece, increase the depth of the hardened layer of the workpiece, enhance the ability of the workpiece to resist alternating loads, reduce the surface friction coefficient, increase the surface hardness, maintain the toughness of the core of the workpiece, reduce the risk of brittle fracture, improve the wear resistance of the workpiece, and have good process repeatability, which can ensure stable product quality.

[0021] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0023] Figure 1 It is a schematic diagram of the product structure of the present invention;

[0024] Figure 2 It is the overall sulfur-carbonitriding process curve diagram of the present invention. DETAILED DESCRIPTION

[0025] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0026] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0027] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0028] See also Figure 1-2 , which is a composite heat treatment process suitable for working in an environment of 300°C, for material 35CrMoVA, including the following steps:

[0029] 1. According to the technical requirements of the workpiece, select appropriate process parameters for preliminary heat treatment - quenching and tempering treatment 311-375HBW;

[0030] 2. After the quenching and tempering is completed, the workpiece is processed by fine turning and milling, and the overall sulfur-carbonitriding is 0.3-0.5mm, and the hardness is 545-615HV10; its process flow: after the product is cleaned, it is placed vertically on the tooling; the air is discharged into the furnace, and the nitrogen flow rate is 1.0m 3 / h, close the exhaust valve after 40min, raise the temperature to 300℃, 400℃, 480℃ and keep it for 1h respectively, then raise the temperature to nitriding temperature of 570±5℃, keep it for 5~6h (ammonia decomposition rate 55-60%), at this time the ammonia flow rate is 1.6~1.8m 3 / h, and drip ethanol + thiourea 100-140 drops / min at the same time, raise the temperature to 595±5℃ with the furnace, keep warm for 3h, and the nitrogen flow rate is 1.0m 3 / h; cool down with nitrogen to below 150℃ and then air cool out of the furnace. The product structure diagram is as follows Figure 1 As shown, the overall sulfur-carbonitriding heat treatment process curve is as follows Figure 2 shown.

[0031] 3. After the overall sulfur-carbonitriding and polishing treatment, the outer circle Φ34×24 area is subjected to high-frequency quenching to ensure the hardness of 52-56HRC and the hardened layer depth of 2-3mm. The process flow is as follows: place the workpiece in a special fixture and adjust the angle of the workpiece; move the sensor to the heating position, adjust the relative position and gap between the workpiece and the sensor; call out the processing program of the workpiece from the program, confirm the program, press the "heating cut" button, and run it automatically once. After normal operation, open the coolant quenching liquid circulation system, adjust the pressure of the quenching liquid, ensure that the pressure value meets the process requirements, start high-frequency quenching of the workpiece, and temper it immediately after high-frequency quenching. High-frequency quenching process parameters: AC voltage 380±2V, AC current 50~60A, frequency 50±0.2KHZ, moving frequency 4HZ, preheating time 2S, heating time 10S, cooling time 5S, quenching liquid concentration 3~5%, quenching liquid temperature 25~35℃, tempering temperature 380±10℃, tempering holding time 2~2.5h.

[0032] The heat treatment process of the present invention combines sulfur carbonitriding and high-frequency quenching to achieve an optimized balance between surface performance and internal performance, improve the overall durability and economy of the workpiece, and is suitable for a working environment with a use temperature of 300°C, and improves wear resistance and fatigue resistance. The surface hardened layer formed by sulfur carbonitriding of the workpiece has good wear resistance and seizure resistance, while high-frequency quenching can accurately control the depth of the hardened layer. The combination of the two can obtain an excellent hardness gradient in a specific area, which not only ensures high hardness and wear resistance of the surface, but also maintains good toughness of the core.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A composite heat treatment process suitable for working in an environment of 300°C, characterized in that: The following steps are involved: S1, pre-heat treatment of 35CrMoVA material, quenching and tempering to hardness of 311-375HBW; S2, after the quenching and tempering is completed, the workpiece is fine turned and milled, and then the whole is sulfur-carbonitrided to form a 0.3-0.5mm carburized layer with a hardness of 545-615HV10. The specific process is as follows: S21, wash the product and place it vertically on the work clothes; S22, exhaust air into the furnace, nitrogen flow rate is 1.0m 3 / h, close the exhaust valve after 40 minutes, heat up with the furnace to 300℃, 400℃, 480℃, keep warm for 1 hour each, then heat up to nitriding temperature 570±5℃, keep warm for 5-6 hours, at this time the ammonia flow rate is 1.6-1.8m 3 / h, and drip ethanol + thiourea 100-140 drops / min, then raise the temperature to 595±5℃, keep warm for 3h, and the nitrogen flow rate is 1.0m 3 / h; S23, cooling with nitrogen to below 150°C and then air cooling out of the furnace; S3, polish the workpiece after sulfur-carbonitriding, and then perform high-frequency quenching on the outer φ34×24 area to ensure that the hardness reaches 52-56HRC and the hardened layer depth is 2-3mm. The high-frequency quenching process is as follows: S31, placing the workpiece in a special fixture, calling the workpiece processing program from the program and confirming it, and running the program for preheating, heating and cooling; S32, coolant quenching liquid is circulated during the heating process, the quenching liquid pressure meets the process requirements, and tempering is performed after high-frequency quenching.

2. A composite heat treatment process suitable for working in a 300°C environment according to claim 1, characterized in that: The high-frequency quenching process parameters are: AC voltage 380±2V, AC current 50~60A, frequency 50±0.2KHZ, moving frequency 4HZ, preheating time 2S, heating time 10S, cooling time 5S, quenching liquid concentration 3~5%, quenching liquid temperature 25~35℃, tempering temperature is 380±10℃, and tempering holding time is 2~2.5h.

3. A composite heat treatment process suitable for working at 300°C according to claim 1, characterized in that: During the sulfur-carbonitriding treatment process, the heating and insulation steps are strictly carried out in accordance with the temperature and time parameters to ensure the uniformity and hardness requirements of the carburized layer.

4. A composite heat treatment process suitable for working at 300°C according to claim 1, characterized in that: In step S31, after the workpiece is placed in the fixture, the angle of the workpiece is adjusted, the inductor is moved to the heating position, and the relative position and gap between the workpiece and the inductor are adjusted to ensure heating uniformity and quenching effect.

5. The composite heat treatment process suitable for working in a 300°C environment according to claim 1, characterized in that: The tempering step is carried out immediately after high-frequency quenching to avoid deformation and cracking of the workpiece caused by quenching stress, while ensuring the toughness of the core of the workpiece.

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