Low-temperature plasma auxiliary heat treatment process for die steel

Abstract

The invention relates to the technical field of material heat treatment, and discloses a die steel low-temperature plasma auxiliary heat treatment process which comprises the following steps: (1) workpiece pretreatment: cleaning and drying a die steel workpiece to remove surface impurities; (2) pulse plasma excitation treatment is conducted, specifically, pulse plasma with the pulse frequency ranging from 1 kHz to 100 kHz and the duty ratio ranging from 10% to 30% is adopted for excitation and treatment of the surface of the die steel; and (3) multi-gas mixing optimization: carrying out a surface reaction through a mixed atmosphere of nitrogen, hydrogen and methane. Through a pulse plasma technology and a multi-gas mixing optimization process, the surface hardness and wear resistance of the die steel are remarkably improved, and the treatment uniformity and consistency are ensured; the rotating electrode design and a real-time feedback control system are combined, the treatment efficiency is optimized, the treatment time is shortened, and the method is suitable for efficient and stable application in large-scale production.

Description

Technical Field

[0001] The invention relates to the technical field of material heat treatment, in particular to a low-temperature plasma assisted heat treatment process for mold steel. Background Art

[0002] As industrial manufacturing continues to increase the performance requirements of mold steel materials, the surface treatment technology of mold steel plays a key role in improving the hardness, wear resistance and service life of the material. The existing mold steel surface treatment methods use nitriding, carbonitriding and other processes to enhance the surface properties of the material, especially in high-load and strong wear environments.

[0003] In the prior art, continuous plasma or a single gas atmosphere is used for treatment, lacking multi-gas mixing optimization and precise pulse control, resulting in poor uniformity of surface treatment. Especially when processing mold steel with complex geometric shapes, problems such as uneven thickness of the hardened layer and insufficient penetration are prone to occur. In addition, the process control is not precise enough, resulting in unstable hardness and insufficient wear resistance of the workpiece. At the same time, the processing time is long, affecting production efficiency. Therefore, the prior art has obvious deficiencies in improving surface hardness, improving processing uniformity and shortening processing time. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a low-temperature plasma assisted heat treatment process for mold steel, which solves the problems of insufficient surface hardness of mold steel, poor treatment uniformity and low process efficiency in the prior art.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: A low-temperature plasma assisted heat treatment process for mold steel, comprising the following steps: (1) Workpiece pretreatment: Clean and dry the mold steel workpiece to remove surface impurities; (2) Pulse plasma excitation treatment: pulse plasma with a pulse frequency of 1 kHz to 100 kHz and a duty cycle of 10% to 30% is used to excite and treat the mold steel surface; (3) Multi-gas mixing optimization: Surface reaction is carried out by mixing nitrogen with hydrogen and methane to improve the hardness and toughness of the nitrided layer or carbonitrided layer on the workpiece surface; (4) Real-time parameter feedback and automatic control: Through real-time monitoring of temperature, gas pressure, plasma current and gas flow, automatic control feedback is performed to adjust process parameters; (5) Multi-layer gradient hardening treatment: Control the atmosphere penetration in stages, gradually form a shallow nitriding layer and a carbonitriding layer on the surface of the mold steel, and stabilize the inner layer.

[0006] Preferably, the pulsed plasma in step (2) ensures that the plasma is evenly distributed on the surface of the mold steel workpiece by rotating the electrode or dynamically moving the electrode technology, and is particularly used for processing workpieces with complex geometries having grooves or porous structures.

[0007] Preferably, the atmosphere mixture in step (3) consists of nitrogen and hydrogen in a volume ratio of 3:1 to 4:1 to increase the surface nitridation reaction rate.

[0008] Preferably, the atmosphere mixture in step (3) further comprises nitrogen and methane in a volume ratio of 2:1 to 3:1, so as to form a carbonitriding layer on the surface to improve the surface hardness and toughness.

[0009] Preferably, the real-time parameter feedback in step (4) is controlled by a PLC system, and the PLC system adjusts the gas flow rate, plasma power and chamber gas pressure in real time according to the collected process parameters to maintain the stability and consistency of the process.

[0010] Preferably, in step (5), the penetration depth of the superficial nitriding layer is controlled to be 10 to 20 microns, and the penetration depth of the carbonitriding layer is controlled to be 50 to 100 microns, and the thickness of each layer is precisely controlled by different processing times and atmosphere ratios.

[0011] Preferably, the thickness of the hardened layer is controlled by the following formula:

[0012] in: is the hardened layer thickness; is the diffusion coefficient, which is affected by gas type and temperature; For processing time.

[0013] Preferably, the flow control of the atmosphere is precisely adjusted using a mass flow controller to ensure that the gas mixing ratio and flow rate of nitrogen, hydrogen, methane and argon remain stable during the treatment process.

[0014] Preferably, the temperature control system monitors the temperature of the surface of the mold steel workpiece in real time by means of an infrared thermometer or a thermocouple, the temperature range is maintained at 200 to 450°C, and the temperature error is controlled within ±5°C.

[0015] Preferably, the surface hardness of the treated mold steel is not less than HV1000 after microstructure analysis and hardness test, and the uniformity of the treated hardened layer meets the set standard requirements.

[0016] The present invention provides a low-temperature plasma assisted heat treatment process for mold steel. It has the following beneficial effects: 1. The present invention significantly improves the hardness and wear resistance of the mold steel surface by adopting pulse plasma technology and multi-gas mixing optimization process. The high energy peak of pulse plasma accelerates the penetration reaction of nitrogen and carbon atoms, so that a dense and high-hardness nitriding layer and carbonitriding layer are generated on the surface, effectively extending the service life of the mold steel. With the support of multi-layer gradient hardening, the hardness layer is not only evenly distributed, but also can withstand greater friction and wear.

[0017] 2. The present invention adopts the design of rotating electrodes and dynamically moving electrodes, combined with a real-time feedback control system, to ensure that the plasma can evenly cover all areas of the workpiece, especially the surface of mold steel with complex geometric shapes, and real-time monitoring and feedback control of process parameters, further improving the consistency and controllability of the treatment, so that the treatment results of different batches are highly consistent, thereby ensuring stable quality in large-scale production.

[0018] 3. The present invention accelerates the surface reaction through pulse plasma technology, and the multi-gas mixing optimization process further enhances the surface penetration efficiency. By precisely controlling the atmosphere composition and temperature, the present invention effectively reduces the processing time, while maintaining excellent surface properties, significantly improving the efficiency of the overall process, making the process more economical and efficient in large-scale industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Please see attached Figure 1 The embodiment of the present invention provides a low-temperature plasma assisted heat treatment process for mold steel, which aims to improve the hardening effect, uniformity and wear resistance of the mold steel surface, while shortening the processing time and improving the process efficiency. By introducing pulsed plasma technology, multi-gas mixing optimization process, real-time feedback control system and multi-layer gradient hardening technology, the process can effectively improve the hardness and toughness of the mold steel surface, and is suitable for mold steel materials with complex shapes and high performance requirements.

[0022] Implementation steps 1. Workpiece pretreatment Before heat treatment, the mold steel workpiece must first be cleaned and dried. The specific steps are as follows: Cleaning: Immerse the workpiece in an alkaline solution or ultrasonic cleaning tank to remove oil, impurities and oxide scale on the surface to ensure uniform reaction during subsequent plasma heat treatment. Any residue on the surface may affect the uniform coverage and reaction effect of the plasma on the workpiece.

[0023] Drying: Place the cleaned workpiece in a dust-free environment for drying to ensure that there is no moisture left on the surface to avoid arc discharge or other abnormal phenomena during plasma treatment.

[0024] 2. Pulsed plasma excitation treatment In low-temperature plasma heat treatment, pulse plasma technology is used for surface excitation. The core of pulse plasma technology is to form high-density plasma by intermittent high-power excitation of working gas, which effectively improves the reaction rate of mold steel surface.

[0025] Pulse parameter setting: The present invention optimizes the frequency according to different workpiece shapes and surface treatment requirements by setting the pulse frequency in the range of 1 kHz to 100 kHz. The duty cycle is set at 10%-30% to control the plasma excitation time, ensure the uniformity of treatment and the stability of the workpiece surface temperature.

[0026] Rotating or moving electrode design: Use rotating electrodes or dynamically moving electrodes to ensure that the plasma evenly covers the workpiece surface, especially in areas with complex geometries such as grooves and holes. Dynamic adjustment of the electrode can reduce the risk of over-treatment or uneven treatment of local areas by the plasma.

[0027] The plasma excitation process in this step generates high-energy reaction particles through periodic high-energy pulse discharge, which accelerates the penetration and reaction of nitrogen, carbon and other atoms on the surface of the workpiece, thereby increasing the formation rate of the hardened layer.

[0028] 3. Multi-gas mixing optimization and atmosphere control In order to ensure that the nitrided layer and carbonitrided layer on the surface of the mold steel have the best hardness and toughness, a multi-gas mixing optimization process is adopted. By introducing different gas combinations, the activity of the plasma reaction is improved and the penetration time is shortened.

[0029] Nitrogen mixed with hydrogen: used to accelerate the nitriding reaction. Hydrogen helps remove oxides on the surface of the workpiece and increases the penetration rate of nitrogen atoms. The recommended volume ratio is 3:1 to 4:1 to ensure processing efficiency.

[0030] Nitrogen mixed with methane: used to form a carbonitriding layer to improve the hardness and toughness of the surface. The recommended ratio is 2:1 to 3:1, which can be flexibly adjusted according to the hardness requirements of the workpiece. The addition of methane ensures that carbon atoms can effectively penetrate the surface.

[0031] Argon as auxiliary atmosphere: Argon is used to stabilize the plasma, ensure the uniformity of surface treatment of large-sized or complex-shaped workpieces, and prevent local uneven reactions caused by unstable atmosphere.

[0032] Flow control: Mass flow controller (MFC) is used to accurately adjust the flow of various gases to ensure the stability of the atmosphere ratio. By real-time monitoring of gas flow and chamber pressure, the atmosphere ratio is automatically adjusted to ensure a constant atmosphere throughout the reaction process.

[0033] 4. Real-time parameter feedback and automatic control system During the whole heat treatment process, the key parameters affecting the hardening effect include temperature, gas pressure, plasma current and gas flow rate. In order to ensure the accurate control of these parameters, the present invention introduces a real-time parameter feedback and automatic control system.

[0034] Temperature monitoring and control: The temperature of the workpiece surface is monitored in real time by infrared thermometer or thermocouple, and the temperature is controlled between 200℃-450℃, and the temperature fluctuation is controlled within ±5℃. Once the temperature deviates from the set value, the heating or cooling power is automatically adjusted to ensure that the workpiece surface is always at the optimal processing temperature.

[0035] Air pressure and gas flow monitoring: The air pressure in the cavity is monitored in real time through a pressure sensor and maintained at 10⁻³ Pa to 10⁻ 5 Pa range. Gas pressure fluctuations will be automatically adjusted by the vacuum pump to ensure stable gas pressure during plasma treatment.

[0036] Plasma current monitoring: The intensity of plasma discharge is monitored by current sensors to ensure stable plasma power output. Current fluctuations will directly affect the reaction rate, and the control system can adjust the plasma power according to the changes in current.

[0037] The temperature, air pressure, gas flow and other parameters are integrated through the PLC (Programmable Logic Controller) system to achieve full-process automated monitoring and feedback control, ensuring the stability and consistency of the entire processing process.

[0038] 5. Multi-layer gradient hardening treatment The present invention forms a multi-layer gradient hardening structure by gradually infiltrating different reactive substances through staged atmosphere control. The design of the multi-layer hardening layer can make the mold steel surface have high hardness and maintain sufficient toughness, ensuring its wear resistance and impact resistance.

[0039] The first stage: shallow nitriding treatment Use high concentration nitrogen for shallow nitriding treatment, the time is controlled within 30-60 minutes, and the penetration depth is 10-20 microns. This stage mainly improves the surface hardness and forms a dense nitriding layer.

[0040] Second stage: carbonitriding treatment A mixed atmosphere of methane and nitrogen is introduced for carbonitriding, with a penetration depth of 50-100 microns and a treatment time of 60-120 minutes. This stage enhances the hardness and wear resistance of the surface while ensuring that the surface has good toughness.

[0041] Phase 3: Inner layer stabilization A low concentration of nitrogen and hydrogen is mixed for 30-60 minutes to further stabilize the inner structure and ensure that the workpiece has sufficient fatigue resistance and impact toughness.

[0042] 6. Real-time monitoring and control of hardened layer thickness In the process of the present invention, the thickness of the hardened layer is monitored in real time by a laser interferometer or an ultrasonic thickness detector, and the process parameters are dynamically adjusted according to the monitoring results. The thickness of the hardened layer follows Fick's diffusion law, and the penetration depth is calculated by the diffusion time and the diffusion coefficient. The formula is as follows:

[0043] in: is the hardened layer thickness; is the diffusion coefficient, which is affected by temperature and gas type; For processing time.

[0044] By precisely controlling the processing time and diffusion coefficient, the thickness of the hardened layer is ensured to meet the design requirements, ultimately forming a multi-layer gradient hardening structure.

[0045] 7. Evaluation of treatment results After the process is completed, the surface hardness and microstructure are tested and analyzed. The hardness of the hardened layer on the workpiece surface is tested using a hardness tester to ensure that the surface hardness reaches HV1000 or above. At the same time, the uniformity of the hardened layer and the integrity of the gradient structure are confirmed through microstructural analysis to ensure that the workpiece meets the application requirements.

[0046] Example 1: Low temperature treatment of mold steel using pulsed plasma, nitrogen and hydrogen mixed atmosphere step: Workpiece pretreatment: Clean the mold steel workpiece to remove surface impurities and oil stains. Then dry it at 120℃ to ensure that there is no residual moisture.

[0047] Pulse plasma excitation: The pulse frequency was set to 50 kHz, the duty cycle was set to 20%, and a rotating electrode structure was used to ensure that the plasma evenly covered the workpiece surface.

[0048] Atmosphere mixture: Use nitrogen (N 2 ) and hydrogen (H 2 ) are mixed in a ratio of 3:1, the air pressure is controlled at 1.5 Pa, the treatment time is 90 minutes, and the surface treatment temperature is 350°C.

[0049] Real-time parameter control: During processing, the temperature is monitored using an infrared thermometer and the atmosphere and power are automatically adjusted using a PLC.

[0050] Multi-layer treatment: The penetration depth of the nitride layer is controlled at 15 microns and the hardening treatment time is 60 minutes.

[0051] Process effect: Surface hardness: HV950 Surface uniformity: High Thickness of permeation layer: 15 microns Comparative Example 1: No pulse plasma, only nitrogen treatment step: Workpiece pretreatment: same as in Example 1.

[0052] Continuous plasma treatment: Continuous plasma is used with no frequency adjustment (continuous discharge), no duty cycle adjustment, and low plasma density.

[0053] Single nitrogen atmosphere: Only pure nitrogen was used, the pressure was set to 2.0 Pa, the treatment temperature was 350°C, and the time was 120 minutes.

[0054] Real-time control: No real-time parameter feedback regulation, only manual monitoring of temperature and atmosphere.

[0055] Process effect: Surface hardness: HV750 Surface uniformity: poor Thickness of permeation layer: 10 microns Example 2: Using multi-gas mixing optimization, nitrogen and methane co-permeation step: Workpiece pretreatment: Dry at 100℃ for 30 minutes after cleaning.

[0056] Pulse plasma excitation: set the pulse frequency to 75 kHz, the duty cycle to 25%, and use a moving electrode device to ensure uniform surface treatment of complex workpieces.

[0057] Nitrogen and methane mixture: Nitrogen and methane are mixed in a ratio of 3:1, the gas pressure is controlled at 1.8 Pa, the treatment time is 100 minutes, and the surface treatment temperature is 400°C.

[0058] Multi-layer treatment: the penetration depth of the nitriding layer is controlled to be 20 microns, the thickness of the co-carburizing layer is 50 microns, and the carbonitriding time is 60 minutes.

[0059] Process effect: Surface hardness: HV1050 Surface uniformity: Very high Thickness of permeation layer: 20 microns Comparative Example 2: Only nitrogen permeation treatment was used, without methane co-permeation step: Workpiece pretreatment: same as in Example 2.

[0060] Pulse plasma excitation: A pulse frequency of 50 kHz and a duty cycle of 15% were used, but no moving electrode device was used.

[0061] Nitrogen treatment: pure nitrogen was used, the gas pressure was set to 2.5 Pa, the treatment temperature was 350°C, the time was 120 minutes, and there was no methane co-penetration.

[0062] Real-time control: real-time monitoring of temperature, no atmosphere control.

[0063] Process effect: Surface hardness: HV850 Surface uniformity: Medium Thickness of permeation layer: 15 microns Example 3: Multi-layer gradient hardening process, nitrogen, hydrogen and methane combination step: Workpiece pretreatment: cleaning and drying are the same as above.

[0064] Pulsed plasma excitation: The pulse frequency was set to 100 kHz with a duty cycle of 30%, and rotating electrode technology was used to ensure uniform coverage.

[0065] Multi-gas mixing: nitrogen and hydrogen in a ratio of 4:1 was used first, followed by a 2:1 combination of nitrogen and methane. The treatment temperature was controlled at 400°C and the treatment time was 120 minutes.

[0066] Multi-layer gradient treatment: the shallow surface nitriding depth is 15 microns, the carbonitriding depth reaches 80 microns, and the final inner layer stabilization treatment time is 40 minutes.

[0067] Process effect: Surface hardness: HV1100 Surface uniformity: Very high Thickness of permeation layer: 80 microns Comparative Example 3: Single-layer nitridation only, no gradient structure step: Workpiece pretreatment: same as in Example 3.

[0068] Pulsed plasma treatment: The frequency was set to 50 kHz, the duty cycle was 20%, and no rotating electrode was used.

[0069] Single atmosphere: Only nitrogen was used for treatment, the gas pressure was 3.0 Pa, the treatment time was 150 minutes, and there was no multi-layer atmosphere switching.

[0070] Single layer treatment: The penetration depth was controlled at 20 μm, and no gradient treatment was performed.

[0071] Process effect: Surface hardness: HV850 Surface uniformity: Medium Thickness of permeation layer: 20 microns Comparative experiment In order to verify the effect of the process of the present invention, comparative experiments were performed on Examples 1, 2, 3 and Comparative Examples 1, 2, 3. The purpose of the experiment was to compare the effects of the process on the surface hardness, treatment uniformity and penetration layer thickness of the die steel.

[0072] Experimental conditions: Die steel workpiece dimensions: 50mm x 50mm x 10mm.

[0073] Test environment: the same plasma heat treatment equipment, the same ambient temperature and air pressure conditions.

[0074] Test items: surface hardness (HV), uniformity (observed by microscope), thickness of penetration layer (measured by microscopic analysis).

[0075] Experimental data table: Process Type Surface hardness (HV) Thickness of permeation layer (micrometer) Surface uniformity Example 1 950 15 high Comparative Example 1 750 10 Poor Example 2 1050 20 Very high Comparative Example 2 850 15 medium Example 3 1100 80 Very high Comparative Example 3 850 20 medium Through the comparison of experimental data, this application has the following obvious advantages: 1. Surface hardness: The hardness of the embodiments is higher than that of the comparative examples, especially embodiment 3 (HV1100), which shows the effect of significantly improving the surface hardness by the multi-layer gradient hardening technology.

[0076] 2. Thickness of the permeation layer: The examples generally show a deeper permeation layer thickness, especially Example 3, which has a permeation layer thickness of 80 μm, while the thickness of the comparative example is significantly shallower, only 20 μm.

[0077] 3. Surface uniformity: The surface uniformity of all embodiments is better than that of the comparative examples, especially when using rotating or moving electrodes, the uniformity of plasma treatment is significantly improved.

[0078] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A low temperature plasma assisted heat treatment process for mold steel, characterized in that: The following steps are involved: (1) Workpiece pretreatment: Clean and dry the mold steel workpiece to remove surface impurities; (2) Pulse plasma excitation treatment: pulse plasma with a pulse frequency of 1 kHz to 100 kHz and a duty cycle of 10% to 30% is used to excite and treat the mold steel surface; (3) Multi-gas mixing optimization: Surface reaction is carried out by mixing nitrogen with hydrogen and methane to improve the hardness and toughness of the nitrided layer or carbonitrided layer on the workpiece surface; (4) Real-time parameter feedback and automatic control: Through real-time monitoring of temperature, gas pressure, plasma current and gas flow, automatic control feedback is performed to adjust process parameters; (5) Multi-layer gradient hardening treatment: Control the atmosphere penetration in stages, gradually form a shallow nitriding layer and a carbonitriding layer on the surface of the mold steel, and stabilize the inner layer.

2. A low temperature plasma assisted heat treatment process for mold steel according to claim 1, characterized in that: The pulsed plasma described in step (2) ensures that the plasma is evenly distributed on the surface of the mold steel workpiece through rotating electrode or dynamically moving electrode technology, and is particularly used for processing workpieces with complex geometries with grooves or porous structures.

3. The low temperature plasma assisted heat treatment process for mold steel according to claim 1, characterized in that: The atmosphere mixture in step (3) is composed of nitrogen and hydrogen in a volume ratio of 3:1 to 4:1 to increase the surface nitriding reaction rate.

4. A low temperature plasma assisted heat treatment process for mold steel according to claim 1, characterized in that: The atmosphere mixture in step (3) also includes nitrogen and methane in a volume ratio of 2:1 to 3:1, so as to form a carbonitriding layer on the surface to improve the surface hardness and toughness.

5. The low temperature plasma assisted heat treatment process for mold steel according to claim 1, characterized in that: The real-time parameter feedback in step (4) is controlled by a PLC system, and the PLC system adjusts the gas flow rate, plasma power and chamber pressure in real time according to the collected process parameters to maintain the stability and consistency of the process.

6. A low temperature plasma assisted heat treatment process for mold steel according to claim 1, characterized in that: In the step (5), the penetration depth of the superficial nitriding layer is controlled to be 10 to 20 microns, and the penetration depth of the carbonitriding layer is controlled to be 50 to 100 microns, and the thickness of each layer is precisely controlled by different processing time and atmosphere ratio.

7. The low temperature plasma assisted heat treatment process for mold steel according to claim 1, characterized in that: The control of the hardened layer thickness is defined by the following formula: in: is the hardened layer thickness; is the diffusion coefficient, which is affected by gas type and temperature; For processing time.

8. The low temperature plasma assisted heat treatment process for mold steel according to claim 1, characterized in that: The flow rate of the atmosphere is precisely regulated by a mass flow controller to ensure that the gas mixing ratio and flow rate of nitrogen, hydrogen, methane and argon remain stable during the treatment process.

9. The low temperature plasma assisted heat treatment process for mold steel according to claim 1, characterized in that: The temperature control system monitors the temperature of the mold steel workpiece surface in real time through an infrared thermometer or a thermocouple, and the temperature range is maintained at 200 to 450°C, and the temperature error is controlled within ±5°C.

10. The low temperature plasma assisted heat treatment process for mold steel according to claim 1, characterized in that: The surface hardness of the mold steel after the treatment is not less than HV1000 after microstructure analysis and hardness test, and the uniformity of the hardened layer after the treatment meets the set standard requirements.

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