A method for carburizing metal and alloy workpieces based on flash joule heat

Abstract

This invention discloses a method for carburizing metals and alloys based on flash Joule heating technology, belonging to the field of surface strengthening technology for metal materials. The method involves pre-treating the workpiece by impurity removal, grinding, and drying, then placing it within the heating zone of a flash Joule heating carburizing reaction chamber. Under inert gas purging conditions, gaseous, liquid, and / or solid carbon sources are introduced to form a carburizing system. By applying an instantaneous pulse voltage, a Joule heating effect is generated, rapidly heating the workpiece surface to 800-1050°C within milliseconds. This induces the carbon source to decompose, generating active carbon atoms that diffuse into the workpiece to form a carburized layer. The workpiece is then rapidly cooled and tempered to eliminate residual stress. This invention utilizes the instantaneous high-temperature characteristics of flash Joule heating to achieve rapid and efficient carburizing, significantly reducing energy consumption compared to traditional carburizing processes. It allows for precise control of the carburized layer depth and hardness, maintaining good core toughness while ensuring surface hardness and wear resistance. It is suitable for surface strengthening treatment of various metals and alloys.

Description

Technical Field

[0001] This invention relates to the field of surface strengthening treatment technology for metallic materials, specifically to a method for carburizing low-carbon alloys based on flash Joule heating technology. Background Technology

[0002] Metal or alloy workpieces are widely used in key fields such as automobile manufacturing, construction machinery, aerospace, and rail transportation, and are crucial materials for manufacturing wear-resistant components such as chains, gears, bearings, crankshafts, and drive shafts. However, some metals or alloys have inherent defects such as low surface hardness and poor wear resistance, which severely restrict their service life and reliability under high load and high wear conditions. Carburizing treatment, which involves infiltrating carbon atoms into the surface layer of a metal or alloy under specific media and temperatures, forms a surface layer with high hardness and high wear resistance, thereby significantly improving the service life of components. It has become a core method for upgrading the performance of metals and alloys and is an important technological requirement for ensuring the quality of high-end equipment manufacturing and promoting the green and low-carbon development of the equipment manufacturing industry.

[0003] Traditional carburizing methods require the entire process of carbon atom adsorption, decomposition, and diffusion from the medium to the surface of the metal or alloy, and the treatment effect directly determines the service performance of the parts. However, existing carburizing methods generally have significant drawbacks: ① Extremely high energy consumption, requiring the entire furnace and workpiece to be heated to high temperatures and held at those temperatures for several to tens of hours, with a slow heating rate (usually <10℃ / min), resulting in low production efficiency and poor economic performance; ② Poor uniformity of the carburized layer, with uneven distribution of temperature and carbon potential fields within the furnace, easily leading to significant differences in the depth and hardness of the carburized layer in different parts of the workpiece, especially in areas such as corners and holes of complex-shaped parts, where over-carburization or under-carburization is likely to occur; ③ High risk of workpiece performance damage, with prolonged high-temperature holding easily leading to coarse alloy grains and decreased core toughness, and residual stress easily generated during cooling, increasing the cost of subsequent tempering and other processes.

[0004] In recent years, flash Joule heating technology, which has emerged in the fields of materials science and thermal processing, has provided a new approach to overcoming the technical bottlenecks in carburizing processes. This technology generates a Joule heating effect by directly or indirectly applying high-current pulses on the target material at the millisecond to second level, achieving instantaneous heating of the material with peak temperatures reaching several degrees Celsius, while also possessing an extremely rapid heating rate (10⁻⁶). 4 ~10 6 It boasts significant advantages such as lower temperature / s, lower energy consumption (40%–60% energy saving compared to traditional heat treatment methods), and extremely short processing time (milliseconds). Currently, flash Joule heating technology has been successfully applied in fields such as rapid sintering of metallic materials and preparation of nanomaterials, demonstrating its enormous potential for efficient, low-carbon, and precise control in the field of materials thermal processing.

[0005] For the processing needs of metals or alloys, flash Joule heating technology has unique application feasibility: low-carbon alloys themselves have good electrical conductivity, and an effective current path can be formed without the addition of an additional conductive medium. By precisely controlling the current parameters, directional instantaneous heating of the workpiece surface can be achieved; the extremely high heating rate of this technology can quickly overcome the diffusion limitations of carbon atoms in the alloy, significantly improving the migration ability and penetration efficiency of carbon atoms, completing the carburizing process in a very short time, avoiding the problems of grain coarsening and performance degradation caused by prolonged high temperatures in traditional methods; at the same time, by adjusting the pulse voltage, current density, and discharge time, the carburizing temperature, carburizing time, and carbon potential can be precisely controlled, achieving precise control of the carburized layer depth and hardness, and improving the uniformity of the carburized layer; in addition, flash Joule heating technology can be carried out in a vacuum or inert atmosphere, effectively suppressing oxidation and decarburization on the workpiece surface, reducing harmful gas emissions, and conforming to the trend of green manufacturing development.

[0006] Currently, in the field of metal and alloy carburizing, no publicly available literature systematically proposes a method for achieving efficient, low-carbon, and precise carburizing using flash Joule heating technology. Existing methods generally suffer from high energy consumption, low efficiency, unstable carburized layer quality, and significant environmental impact, which falls far short of the demands of high-end equipment manufacturing for high-performance, low-energy-consumption, and green production of components. Therefore, developing a metal or alloy carburizing method based on flash Joule heating technology to overcome the technical bottlenecks of traditional carburizing methods and achieve efficient, precise, and green carburizing modification of low-metal or alloy components is an urgent need for the transformation and upgrading of the equipment manufacturing industry, and has significant engineering application value and economic and social benefits. Summary of the Invention

[0007] The purpose of this invention is to provide a carburizing method for low-carbon alloys based on flash Joule heating technology. This method overcomes the technical bottleneck of traditional carburizing methods, which rely on slow heating followed by prolonged holding. By utilizing the instantaneous high-energy heating characteristics of flash Joule heating, it achieves rapid adsorption, decomposition, and diffusion of carbon atoms on the surface of low-carbon alloy parts. This significantly shortens carburizing time and reduces energy consumption while ensuring the uniformity and stability of the carburized layer, thus improving the efficiency and quality of the carburizing process. This meets the demands of high-end equipment manufacturing for high-performance, low-carbon components.

[0008] The implementation steps of this invention are as follows:

[0009] 1) Select the metal or alloy workpiece to be carburized and pre-treat it: remove oil, dust and other impurities from the workpiece surface to make the surface free of oil film and reflective; then grind the workpiece surface to remove the oxide scale and rust layer; finally place the pre-treated workpiece in a 120℃ constant temperature drying oven for 2-3 hours to remove the surface adsorbed moisture and avoid moisture affecting the subsequent conductivity and carburizing effect, and obtain the workpiece to be processed.

[0010] 2) Place the pretreated workpiece obtained in step (1) into the heating area of ​​the flash Joule thermal carburizing reaction chamber, and cover or clamp it with a conductive or semi-conductive medium so that the workpiece is in an environment of pulse electric field and current coupling. The conductive or semi-conductive medium is preferably graphite felt, graphite sheet, conductive carbon fiber or its composite material, which is used to form a stable current path and realize the rapid Joule heating of the workpiece during the pulse discharge process.

[0011] 3) After sealing the cavity, start the atmosphere control system. First, purge the reaction cavity with inert gas to remove air. The inert gas is nitrogen or argon, with a flow rate of 5-15 L / min and a purging time of 5-10 minutes to prevent oxidation or decarburization of the workpiece during high-temperature treatment. Subsequently, according to the carburizing process requirements, introduce gaseous carbon sources, liquid carbon sources, and / or solid carbon sources to construct a single or mixed carbon source carburizing system, and perform flash Joule heating carburizing treatment under inert gas protection or a mixed atmosphere. Specifically, this includes: a) When using a gaseous carbon source, introduce a mixture of inert gas and gaseous carbon source medium into the cavity and maintain a stable carburizing atmosphere. The gaseous carbon source is a gas that can decompose or react at high temperatures to generate active carbon atoms, preferably including one or more of carbon monoxide, methane, propane, and acetylene, and carbon dioxide can be further introduced as a further agent. a) To control the carbon potential of the carbon layer by using a carbon potential regulating gas; b) When using a liquid carbon source and / or a solid carbon source, before or during clamping, ensure that the surface of the workpiece to be processed is in full contact with or coated with the liquid carbon source and / or the solid carbon source, and then perform flash evaporation Joule heating treatment under an inert gas protective atmosphere, so that the liquid carbon source or solid carbon source is pyrolyzed at high temperature to generate active carbon atoms and diffuse into the workpiece surface; wherein, the liquid carbon source includes methanol, ethanol or other carbon-containing organic liquids, and the solid carbon source includes activated carbon, carbon black, graphite powder or their composites.

[0012] 4) Under the stable carburizing atmosphere described in step (3), start the large capacitor pulse discharge system and apply instantaneous pulse voltage to the electrodes at both ends of the reaction chamber. The Joule heating effect is generated through the resistance of the workpiece itself, so as to achieve rapid heating of the workpiece. Typical pulse parameters are: voltage 50~150V, current density 100~800 A / cm², single pulse duration 5~1000 ms, total discharge heating time 5~5000 ms. By adjusting the pulse parameters, the surface of the workpiece can be rapidly heated to the target carburizing temperature range of 800~1050℃ in milliseconds to seconds. This induces the carburizing medium in the carburizing atmosphere to decompose rapidly on the surface of the workpiece to generate active carbon atoms. The active carbon atoms are adsorbed on the surface of the workpiece and rapidly diffuse into the interior to form a uniform carburized layer.

[0013] 5) After pulse heating carburizing is completed, immediately stop applying the pulse current, maintain the carburizing atmosphere flow, and at the same time start the rapid cooling system. By introducing high-flow-rate cooling gas (nitrogen or argon) into the cavity, the workpiece temperature is rapidly reduced to below 200°C within 1 to 5 minutes. This prevents the workpiece from being in a high-temperature state for a long time, which would lead to coarse grains and reduced core toughness. At the same time, it inhibits excessive diffusion of carbon atoms in the carburized layer and ensures the stability of the carburized layer depth and hardness.

[0014] 6) Take the low-carbon alloy workpiece processed in step (5) out of the reaction chamber and perform post-processing on the workpiece: first, use sandpaper to polish and remove the slight oxide layer or fixture contact marks that may be generated on the surface of the workpiece, then place the workpiece in a tempering furnace at 200~250 ℃ and keep it at 1~2 hours to eliminate the residual stress generated during the carburizing process. Finally, perform quality assessments such as carburizing depth detection, surface hardness detection, and microstructure observation on the workpiece to ensure that the carburizing depth, hardness and uniformity meet the preset technical requirements.

[0015] Furthermore, the pretreatment method described in step (1) is a key prerequisite for ensuring the quality of carburizing: oil stains and oxide scale will hinder the contact between the carburizing medium and the workpiece surface, resulting in the inability of activated carbon atoms to be effectively adsorbed and diffused, thus causing defects such as uneven carburizing layer and undercarburization; surface moisture will evaporate instantaneously under the action of pulsed current, triggering local arc discharge, which not only increases energy consumption, but may also damage the surface finish of the workpiece. Therefore, thoroughly removing impurities, oxide scale and moisture from the workpiece surface is an important foundation for ensuring the stability of the flash Joule thermal carburizing process and the qualified quality of the carburized layer.

[0016] Furthermore, the clamping structure described in step (2) adopts an adjustable combination support and covering fixing method to adapt to metal or alloy workpieces of different sizes and geometric shapes, including but not limited to wires, plates, block parts, and irregularly shaped structural parts; the workpiece is partially covered, clamped, or surrounded by a conductive or semi-conductive medium, so that it is stably placed within the pulse heating area of ​​the flash Joule heating reaction chamber, while constructing a continuous and uniform current conduction path; the effective contact area between the conductive or semi-conductive medium and the workpiece is preferably controlled within the range of 10% to 30% of the workpiece surface area. While ensuring stable pulse current transmission and rapid Joule heating, it avoids the excessively large coating area from obstructing the contact between the carburizing atmosphere or carbon source and the workpiece surface, thereby improving the uniformity of the carburized layer formation. For slender shafts, thin-walled or easily deformable workpieces, flexible support and buffer positioning structures are used during clamping to reduce the stress concentration effect of mechanical constraints on the workpiece. The temperature distribution and current coupling state of the workpiece are monitored in real time during pulse heating, and the coating state or clamping position is dynamically adjusted according to the monitoring results to ensure the stability and consistency of the carburizing process.

[0017] Furthermore, the synergistic regulation of the carbon source type and its introduction method described in step (3) has a significant impact on the formation rate, thickness, and microstructure of the carburized layer. When a gaseous carbon source is used, carburizing media such as methane, propane, acetylene, and carbon monoxide can undergo thermal decomposition or gas-phase reaction at high temperatures of 800~1050℃, continuously generating highly active carbon atoms or carbon-based intermediates, providing sufficient and controllable carbon supply to the metal surface. The introduction of inert gas as a carrier gas and dilution gas can effectively regulate the partial pressure of active carbon components in the carburizing atmosphere, inhibit the excessive cracking reaction of the carburizing medium, reduce the deposition of carbon on the workpiece surface, and isolate external air from entering the reaction chamber, thereby preventing oxidation or decarburization of the workpiece surface under high temperature conditions. When a liquid carbon source and / or a solid carbon source is used, it undergoes thermal decomposition reaction under the rapid heating effect of flash Joule heating, similarly generating active carbon atoms and diffusing them into the metal matrix, achieving a carburizing effect comparable to or complementary to that of a gaseous carbon source.

[0018] Furthermore, the pulse heating described in step (4) is the core step in achieving efficient carburizing in this invention: the instantaneous high temperature characteristics of flash Joule heating allow the carburizing medium to decompose rapidly on the workpiece surface and generate active carbon atoms, while significantly increasing the diffusion rate of carbon atoms in the metal or alloy lattice. Compared with the traditional continuous heating carburizing process, the diffusion efficiency is increased by about 5 to 10 times, thereby completing the formation of the carburized layer in a very short time and greatly shortening the processing cycle. By precisely controlling parameters such as pulse voltage, current density, and pulse duration, the depth of the carburized layer can be controlled and adjusted. The depth of the carburized layer is preferably controlled within the range of 0.1 to 1.5 mm. During the pulse heating process, the surface layer of the workpiece rapidly heats up to the carburizing reaction temperature range, while the core temperature is relatively low, forming a significant radial temperature gradient. This ensures sufficient carburizing strengthening of the surface layer while effectively inhibiting grain growth in the core and maintaining good overall strength and toughness performance of the core. If the pulse energy input is too high, it may cause the workpiece surface to overheat, the grains to become coarse, or even local melting. If the energy input is insufficient, the carburizing medium will not decompose sufficiently and the carbon atoms will not diffuse enough, resulting in undercarburization. Therefore, it is necessary to optimize the pulse parameter combination according to the workpiece material, size and target carburization layer requirements.

[0019] Furthermore, the key to the rapid cooling method described in step (5) is controlling the cooling rate. An excessively fast cooling rate may cause cracks or deformation defects in the workpiece, while an excessively slow cooling rate cannot effectively suppress grain coarsening and excessive carbon atom diffusion. This invention controls the cooling rate to 50~200℃ / min by adjusting the cooling gas flow rate, achieving rapid cooling of the workpiece while avoiding crack formation. Simultaneously, it ensures the uniform distribution of carbon atoms in the diffusion layer, improving the matching of hardness and toughness of the diffusion layer.

[0020] Furthermore, the tempering treatment described in step (6) is a necessary step to eliminate residual stress: during the carburizing process, there is a significant temperature gradient and carbon concentration distribution difference between the surface layer and the core of the workpiece, which will generate residual stress. If tempering treatment is not performed, the workpiece may deform or crack during subsequent service. Low-temperature tempering at 200~250℃ can effectively release residual stress without affecting the hardness and wear resistance of the carburized layer, ensuring the dimensional stability and reliability of the workpiece.

[0021] The beneficial effects of this invention are as follows:

[0022] 1. This invention applies flash Joule heating technology to the carburizing process of low-carbon alloys, utilizing the Joule heating effect generated by millisecond-level instantaneous pulse current to cause the workpiece surface to heat at 10°C. 3 ~10 5 The heating rate of ℃ / s quickly reaches the carburizing temperature range, which significantly shortens the processing time compared with the traditional continuous heating (usually <10℃ / min) carburizing process. The overall energy consumption is reduced by 40% to 65% compared with the traditional carburizing method, which greatly improves production efficiency, reduces production costs, and meets the needs of green and low-carbon manufacturing development.

[0023] 2. This invention achieves controllable adjustment of carburized layer depth and surface properties through coordinated control of pulse parameters and carburizing atmosphere. The carburized layer is uniformly distributed, effectively improving the over-carburizing or under-carburizing problems caused by uneven temperature field and carbon potential field in traditional carburizing process, improving the quality of carburizing treatment, and meeting the application requirements of surface strengthening for high-performance parts.

[0024] 3. This invention adopts an instantaneous pulse heating mode, which enables the surface of the workpiece to quickly reach the carburizing temperature while the core temperature is maintained at a low level. This effectively avoids problems such as coarse alloy grains and decreased core toughness caused by long-term high-temperature heat preservation in traditional methods. After treatment, the surface of the workpiece has high hardness and high wear resistance, while the core retains its original strength and toughness. The excellent strength and toughness matching significantly improves the service life and reliability of the parts.

[0025] 4. The method of the present invention does not require the addition of chemical reagents such as carburizing catalysts, thus avoiding the damage to workpiece performance and environmental hazards caused by chemical reagent residues in traditional liquid carburizing and gas carburizing. The method is clean and green, and the subsequent tempering treatment is simple, which greatly simplifies the production process and reduces subsequent processing costs.

[0026] 5. The method of the present invention is applicable to carburizing treatment of various metals and alloys. It has strong adaptability to workpiece size and shape. Whether it is a small precision part or a large complex structural part, it can achieve efficient and uniform carburizing. It has broad prospects for industrial promotion and can promote the high-end upgrading of equipment manufacturing parts.

[0027] 6. The overall process flow of this invention is simple and can be integrated with an automated control system to realize continuous operation of clamping, atmosphere control, pulse heating and cooling treatment, which is conducive to large-scale production and improves production stability and economic benefits. Detailed Implementation

[0028] The present invention will be further described below with reference to the embodiments, but it is not intended to limit the present invention in any way. All modifications, equivalent substitutions, etc. made under the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0029] Example 1

[0030] A carburizing treatment for 20Mn2 wire (Φ10mm) based on flash Joule heating technology, the specific steps are as follows:

[0031] 1) Pretreatment of workpiece: Immerse the wire workpiece to be treated in an alkaline degreasing solution of sodium hydroxide to remove surface oil and impurities, then rinse with clean water and dry to obtain pretreated workpiece.

[0032] 2) Clamping and sealing: The pretreated workpiece is placed in the pulse heating area of ​​the flash Joule hot carburizing reaction chamber, and then covered and fixed with graphite felt to place it in an environment of pulse electric field and current coupling. The reaction chamber is then sealed.

[0033] 3) Atmosphere control: High-purity nitrogen gas is introduced into the reaction chamber for purging at a flow rate of 10 L / min for 8 minutes to remove air; after purging, the atmosphere is switched to carburizing atmosphere, which is a mixture of nitrogen and methane in a volume ratio of 2:1, and the chamber pressure is maintained at approximately 0.12 MPa.

[0034] 4) Pulse heating carburizing: Start the pulse discharge system, apply an instantaneous pulse voltage, set the voltage to 100 V and the current density to 400 A / cm². 2 The duration of a single pulse is 5 ms, which rapidly heats the surface of the workpiece to about 950 ℃ and completes the carburizing process. Methane decomposes under high temperature to produce active carbon atoms and diffuse into the interior of the workpiece to form a carburized layer.

[0035] 5) Rapid cooling: Stop pulse heating, maintain inert gas flow and introduce high-flow-rate nitrogen for cooling, so that the workpiece temperature drops below 200 ℃ within a few minutes.

[0036] 6) Post-treatment: After the workpiece has cooled, it is taken out and the surface is cleaned. Then it is tempered at about 220 °C for 1.5 hours.

[0037] Upon inspection, the workpiece was found to have formed a uniform carburized layer with a depth of approximately 0.7 mm, significantly improved surface hardness, and no obvious oxidation or decarburization was observed.

[0038] Example 2

[0039] A carburizing treatment for 20Mn2 wire (Φ10mm) based on flash Joule heating technology, the specific steps are as follows:

[0040] 1) Pretreatment of workpiece: Immerse the wire workpiece to be treated in an alkaline degreasing solution of sodium hydroxide to remove surface oil and impurities, then rinse with clean water and dry to obtain pretreated workpiece.

[0041] 2) Clamping and sealing: The pretreated workpiece is placed in the pulse heating area of ​​the flash Joule hot carburizing reaction chamber, and then covered and fixed with graphite felt to place it in an environment of pulse electric field and current coupling. The reaction chamber is then sealed.

[0042] 3) Atmosphere control: High-purity nitrogen gas is introduced into the reaction chamber for purging at a flow rate of 10 L / min for 8 minutes to remove air; after purging, the atmosphere is switched to carburizing atmosphere, which is a mixture of nitrogen and methane in a volume ratio of 2:1, and the chamber pressure is maintained at approximately 0.12 MPa.

[0043] 4) Pulse heating carburizing: Start the pulse discharge system, apply an instantaneous pulse voltage, set the voltage to 80 V and the current density to 300 A / cm². 2 The duration of a single pulse is 10 ms, which rapidly heats the surface of the workpiece to about 900 ℃ and completes the carburizing process. Methane decomposes under high temperature to produce active carbon atoms and diffuse into the interior of the workpiece to form a carburized layer.

[0044] 5) Rapid cooling: Stop pulse heating, maintain inert gas flow and introduce high-flow-rate nitrogen for cooling, so that the workpiece temperature drops below 200 ℃ within a few minutes.

[0045] 6) Post-treatment: After the workpiece has cooled, it is taken out and the surface is cleaned. Then it is tempered at about 220 °C for 1.5 hours.

[0046] Upon inspection, the workpiece was found to have formed a uniform carburized layer with a depth of approximately 0.5 mm, significantly improved surface hardness, and no obvious oxidation or decarburization was observed.

[0047] Example 3

[0048] A carburizing treatment for 20Mn2 wire (Φ10mm) based on flash Joule heating technology, the specific steps are as follows:

[0049] 1) Pretreatment of workpiece: Immerse the wire workpiece to be treated in an alkaline degreasing solution of sodium hydroxide to remove surface oil and impurities, then rinse with clean water and dry to obtain pretreated workpiece.

[0050] 2) Clamping and sealing: The pretreated workpiece is placed in the pulse heating area of ​​the flash Joule hot carburizing reaction chamber, and then covered and fixed with graphite felt to place it in an environment of pulse electric field and current coupling. The reaction chamber is then sealed.

[0051] 3) Introduction of liquid carbon source: A liquid carburizing medium, selected from methanol, ethanol, acetone, or mixtures thereof, is injected into the reaction chamber as a carbon source. It is uniformly distributed on the workpiece surface via atomized spraying, and a small amount of nitrogen is simultaneously introduced as a carrier gas to maintain an inert environment and media transport stability within the chamber. Under the instantaneous high temperature of flash Joule heating, the liquid carbon source undergoes rapid thermal decomposition and partial reforming reactions, generating a gaseous intermediate rich in active carbon atoms, effectively improving the carbon atom supply rate and carburizing efficiency.

[0052] 4) Pulse heating carburizing: Start the pulse discharge system, apply an instantaneous pulse voltage, set the voltage to 80 V and the current density to 300 A / cm². 2 The duration of a single pulse is 10 ms, which rapidly heats the surface of the workpiece to about 900 ℃ and completes the carburizing process. Methane decomposes under high temperature to produce active carbon atoms and diffuse into the interior of the workpiece to form a carburized layer.

[0053] 5) Rapid cooling: Stop pulse heating, maintain inert gas flow and introduce high-flow-rate nitrogen for cooling, so that the workpiece temperature drops below 200 ℃ within a few minutes.

[0054] 6) Post-treatment: After the workpiece has cooled, it is taken out and the surface is cleaned. Then it is tempered at about 220 °C for 1.5 hours.

[0055] Testing revealed that the workpiece formed a uniform carburized layer with a depth of 0.1-1.5 mm, significantly improved surface hardness, and showed no obvious oxidation or decarburization.

[0056] Example 4

[0057] A carburizing treatment for 20Mn2 wire (Φ10mm) based on flash Joule heating technology, the specific steps are as follows:

[0058] 1) Pretreatment of workpiece: Immerse the wire workpiece to be treated in an alkaline degreasing solution of sodium hydroxide to remove surface oil and impurities, then rinse with clean water and dry to obtain pretreated workpiece.

[0059] 2) Clamping and sealing: The pretreated workpiece is placed in the pulse heating area of ​​the flash Joule hot carburizing reaction chamber, and then covered and fixed with graphite felt to place it in an environment of pulse electric field and current coupling. The reaction chamber is then sealed.

[0060] 3) Introduction of solid carbon source: A solid carburizing medium is arranged on or around the surface of the workpiece, so that the workpiece is in direct contact with or closely surrounded by the solid carbon source. The solid carburizing medium is selected from activated carbon, carbon black, graphite powder, or a composite thereof. At the same time, nitrogen gas is introduced into the reaction chamber to form an inert protective atmosphere to prevent the workpiece from oxidizing under high temperature conditions. Under the instantaneous high temperature of flash Joule heating, the solid carbon source releases active carbon species, which migrate and diffuse to the surface of the workpiece, continuously providing a carbon source for the carburizing process.

[0061] 4) Pulse heating carburizing: Start the pulse discharge system, apply an instantaneous pulse voltage, set the voltage to 80 V and the current density to 300 A / cm². 2 The duration of a single pulse is 10 ms, which rapidly heats the surface of the workpiece to about 900 ℃ and completes the carburizing process. Methane decomposes under high temperature to produce active carbon atoms and diffuse into the interior of the workpiece to form a carburized layer.

[0062] 5) Rapid cooling: Stop pulse heating, maintain inert gas flow and introduce high-flow-rate nitrogen for cooling, so that the workpiece temperature drops below 200 ℃ within a few minutes.

[0063] 6) Post-treatment: After the workpiece has cooled, it is taken out and the surface is cleaned. Then it is tempered at about 220 °C for 1.5 hours.

[0064] Testing revealed that the workpiece formed a uniform carburized layer with a depth of 0.1-1.5 mm, significantly improved surface hardness, and showed no obvious oxidation or decarburization.

[0065] Example 5

[0066] A carburizing treatment for Q345 wire (Φ8mm) based on flash Joule heating technology, the specific steps are as follows:

[0067] 1) Pretreatment of workpiece: Immerse the wire workpiece to be treated in an alkaline degreasing solution of sodium hydroxide to remove surface oil and impurities, then rinse with clean water and dry to obtain pretreated workpiece.

[0068] 2) Clamping and sealing: The pretreated workpiece is placed in the pulse heating area of ​​the flash Joule hot carburizing reaction chamber, and then covered and fixed with graphite felt to place it in an environment of pulse electric field and current coupling. The reaction chamber is then sealed.

[0069] 3) Introduction of liquid carbon source: A liquid carburizing medium, selected from methanol, ethanol, acetone, or mixtures thereof, is injected into the reaction chamber as a carbon source. It is uniformly distributed on the workpiece surface via atomized spraying, and a small amount of nitrogen is simultaneously introduced as a carrier gas to maintain an inert environment and media transport stability within the chamber. Under the instantaneous high temperature of flash Joule heating, the liquid carbon source undergoes rapid thermal decomposition and partial reforming reactions, generating a gaseous intermediate rich in active carbon atoms, effectively improving the carbon atom supply rate and carburizing efficiency.

[0070] 4) Pulse heating carburizing: Start the pulse discharge system, apply an instantaneous pulse voltage, set the voltage to 80 V and the current density to 300 A / cm². 2 The duration of a single pulse is 5 ms, which rapidly heats the surface of the workpiece to about 900 ℃ and completes the carburizing process. Methane decomposes under high temperature to produce active carbon atoms and diffuse into the interior of the workpiece to form a carburized layer.

[0071] 5) Rapid cooling: Stop pulse heating, maintain inert gas flow and introduce high-flow-rate nitrogen for cooling, so that the workpiece temperature drops below 200 ℃ within a few minutes.

[0072] 6) Post-treatment: After the workpiece has cooled, it is taken out and the surface is cleaned. Then it is tempered at about 220 °C for 1.5 hours.

[0073] Tests showed that the workpiece formed a uniform carburized layer with a depth of 0.1-0.8 mm, significantly improved surface hardness, and no obvious oxidation or decarburization was observed.

Claims

1. A carburizing treatment method for metals or alloys based on flash Joule heating technology, characterized in that, Includes the following steps: 1) Workpiece pretreatment: Remove oil and dust from the workpiece surface, and grind the workpiece surface to remove oxide scale and rust layer to obtain the workpiece to be processed; 2) Clamping and sealing: The workpiece to be processed is loaded into the flash Joule hot carburizing reaction chamber, so that it is in the pulse heating area of ​​the reaction chamber, and then the chamber is sealed. 3) Atmosphere Control and Carbon Source Introduction: An inert gas, such as nitrogen or argon, is introduced into the sealed cavity to remove air. During the carburizing process, gaseous, liquid, and / or solid carbon sources are introduced to form a single or mixed carbon source carburizing system. When a gaseous carbon source is introduced, an inert gas is introduced into the cavity to form a mixed atmosphere with the gaseous carbon source medium. The gaseous carbon source includes gases that can decompose or react at high temperatures to generate active carbon atoms, preferably one or more of carbon monoxide, methane, propane, and acetylene. Carbon dioxide can be further introduced as a carbon potential control gas. When a liquid and / or solid carbon source is introduced, the surface of the workpiece to be processed is brought into contact with the liquid and / or solid carbon source, and heated carburizing is performed under an inert gas protective atmosphere. The liquid carbon source includes methanol, ethanol, or other carbon-containing organic liquids, and the solid carbon source includes activated carbon, carbon black, graphite powder, or their composites. 4) Pulse heating carburizing: Start the pulse discharge system and apply an instantaneous pulse voltage to the reaction chamber to generate flash Joule heat in the conductive or semi-conductive medium. The surface of the workpiece is rapidly heated to 800-1050 ℃ through heat conduction and heat radiation to complete the carburizing process. The total pulse heating time is 5-10000 ms. 5) Rapid cooling: After stopping pulse heating, cooling gas is introduced to cool the workpiece to below 200 ℃ within 1 to 5 minutes; 6) Post-treatment: After removing the workpiece and cleaning its surface, temper it at 200-250 ℃ for 1-2 hours to complete the carburizing process.

2. The method according to claim 1, characterized in that, The metal or alloy mentioned in step 1) is low-carbon steel, alloy structural steel, stainless steel, tool steel or its composite material; preferably, the metal or alloy includes one or more of 20Mn2, Q345, 20Cr, 40Cr, 15CrMn, 20CrMnTi, 12CrMo, 42CrMo, 35CrMo, GCr15, 304 stainless steel and 316 stainless steel.

3. The method according to claim 1, characterized in that, In step 2), an adjustable support and covering structure is used to fix the workpiece within the pulse heating area of ​​the reaction chamber. The workpiece is partially covered, clamped, or surrounded by a conductive or semi-conductive medium to form a stable current conduction path and achieve flash Joule heating. The effective contact area between the conductive or semi-conductive medium and the workpiece accounts for 10% to 30% of the workpiece surface area. In the case of workpieces that are prone to deformation or are sensitive to stress, a flexible support positioning method is used, and the workpiece temperature and heating status during the heating process are monitored and controlled.

4. The method according to claim 1, characterized in that, The pulse parameters mentioned in step 4) are: voltage 50~150V, current density 100~800A / cm. 2 The duration of a single pulse is 5~1000ms; the surface heating rate of the workpiece is 10. 3 ~10 5 ℃ / s, the depth of the carburized layer is controlled to be 0.1~1.5mm.

5. The method according to claim 1, characterized in that, The pulse application method in step 4) is either single pulse or multi-pulse mode. In multi-pulse mode, the interval between single pulses is 0.5 to 10 seconds.

6. The method according to claim 1, characterized in that, The cooling gas mentioned in step 5) is nitrogen or argon, and the cooling rate is controlled by adjusting the flow rate of the cooling gas.