A heat treatment method for improving the service life of a copper extrusion die

Abstract

This invention provides a heat treatment method for improving the lifespan of copper extrusion dies, relating to the field of metal material heat treatment technology. The method comprises six core steps: die pretreatment, segmented preheating, gradient quenching, cryogenic stabilization, multi-stage tempering, and aging strengthening. Through multi-stage gradient heating, dynamic cooling rate control, low-temperature stabilization, and precise hardness control, combined with multiple mathematical models to quantify process parameters, the method achieves homogenization and refinement of the die's internal structure. This application reduces thermal stress through segmented preheating, avoids structural transformation cracks through gradient quenching, reduces retained austenite through cryogenic treatment, and promotes carbide dispersion and precipitation through multi-stage tempering and aging strengthening. Ultimately, the die achieves a hardness uniformity of ≤±1HRC, increases toughness by 25-30, increases fatigue strength by 30-40, and extends service life to over 3000 cycles, significantly outperforming existing technologies. It is applicable to the production and processing of dies for extrusion molding of copper profiles, copper tubes, and copper rods.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology for metallic materials, and specifically to a heat treatment method for improving the lifespan of copper extrusion dies. Background Technology

[0002] Copper and copper alloys possess excellent electrical and thermal conductivity and corrosion resistance, making them widely used in aerospace, electronics, and building materials industries. Their forming and processing largely relies on extrusion processes. Copper extrusion dies, as the core component of extrusion molding, must withstand high temperatures (300-500°C) during operation. High pressure (100-300MPa) and severe friction and wear, along with repeated thermal cycling impacts, make molds prone to failure modes such as wear, deformation, and cracks, which seriously affect production efficiency and product quality.

[0003] In existing technologies, copper extrusion dies are mostly made of H13 hot work die steel, and their heat treatment process typically includes single-stage preheating, isothermal quenching, and single or double tempering. However, traditional processes have the following key drawbacks:

[0004] If the temperature rises too quickly during the preheating stage, a large temperature gradient will form inside the mold, generating significant thermal stress, which will create hidden dangers for subsequent quenching cracks.

[0005] The quenching process uses a single cooling medium (such as pure oil or pure water) with a fixed cooling rate, which cannot match the dynamic requirements of martensitic transformation, resulting in uneven microstructure transformation and excessively high retained austenite content (typically...). ), poor mold dimensional stability;

[0006] The tempering process design is simple, focusing only on hardness adjustment, without fully eliminating quenching stress or achieving dispersed precipitation of carbides, resulting in insufficient mold toughness (impact toughness). ), poor fatigue resistance;

[0007] Lacking cryogenic stabilization treatment and vacuum aging strengthening, the internal structure of the mold has defects, insufficient wear resistance and high temperature stability, and the service life is usually only 500-800 extrusion cycles, which is difficult to meet the needs of large-scale industrial production.

[0008] Therefore, developing a heat treatment process that can synergistically optimize the uniformity, hardness, toughness and wear resistance of the die structure, and significantly improve the life of copper extrusion dies, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0009] The purpose of this invention is to provide a heat treatment method to improve the life of copper extrusion dies. Through multi-stage collaborative process design and quantitative parameter control, it solves the problems of uneven die hardness, insufficient toughness, poor fatigue resistance and short service life in the prior art.

[0010] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0011] In a first aspect, the present invention provides a heat treatment method for improving the life of copper extrusion dies, comprising the following steps:

[0012] S1: Mold pretreatment;

[0013] S2: Segmented preheating treatment, carried out in a multi-stage gradient heating mode, with the heating rate and holding time of each stage controlled by a quantitative formula;

[0014] S3: Gradient quenching treatment, using a composite cooling medium system, dynamically adjusting the cooling rate according to the real-time temperature of the mold;

[0015] S4: Cryogenic stabilization treatment, which involves heat preservation in an ultra-low temperature environment and precise control of heating and cooling rates;

[0016] S5: Multi-stage tempering treatment, tempering is carried out in multiple different temperature ranges, and the final hardness is controlled by a hardness prediction model.

[0017] S6: Aging enhancement treatment, the aging process is completed in a vacuum environment to promote the dispersion and precipitation of carbides.

[0018] As a further improvement to the technical solution of the present invention, in step S1, the mold pretreatment includes sequential degreasing and stress-relief annealing: using an alkaline cleaning agent (sodium hydroxide mass fraction 5-8%). Sodium carbonate mass fraction 3-5 Surfactant mass fraction 1-2 ) in 60-80 Ultrasonic cleaning for 15-20 minutes; stress-relief annealing temperature: 550-600°C Heating rate 5-10 After holding at the temperature for 2-4 hours, cool it to room temperature with the furnace.

[0019] As a further improvement to the technical solution of the present invention, in step S2, the segmented preheating treatment is divided into three stages, and the parameters of each stage satisfy the following relationship:

[0020] Phase 1: Preheating Temperature = heating rate Insulation time ,in, , This represents the maximum thickness of the mold (mm). ;

[0021] Second stage: Preheating temperature heating rate Insulation time ,in, , ;

[0022] Third stage: Preheating temperature =950-980℃, heating rate Insulation time ,in, .

[0023] As a further improvement to the technical solution of the present invention, in step S3, during the gradient quenching process, the composite cooling medium has a mass fraction of 20-30%. The composition of the polyethylene glycol aqueous solution and the dynamic cooling rate satisfy the formula:

[0024] ;

[0025] in, (Base cooling rate) (Temperature coefficient) (Initial quenching temperature), T is the real-time temperature of the mold ( ), (Medium ratio coefficient); When the mold temperature drops to point( When the cooling rate is adjusted to until the mold temperature reaches 100°C. Then remove it.

[0026] As a further improvement to the technical solution of the present invention, in step S4, the cryogenic stabilization treatment uses liquid nitrogen as the cooling medium: after the mold is quenched, it is placed at room temperature for 30-60 minutes, and then placed in a cryogenic chamber at 10-15 degrees Celsius. When the temperature drops to -120℃, the holding time must meet the following formula:

[0027] ;

[0028] in, , This represents the maximum thickness of the mold (mm). (Initial temperature before cryogenic treatment). (Target temperature for cryogenic treatment); after the insulation period ends, the temperature will naturally rise to room temperature.

[0029] As a further improvement to the technical solution of the present invention, in step S5, the multi-stage tempering process is divided into three consecutive tempering processes:

[0030] Phase 1: Tempering Temperature heating rate Keep warm for 2-3 hours;

[0031] Second stage: Tempering temperature heating rate Keep warm for 3-4 hours;

[0032] Third stage: Tempering temperature heating rate Hold at the heat for 4-5 hours; after each tempering, air cool to room temperature. During the tempering process, the mold hardness meets the prediction formula:

[0033] ;

[0034] in, (Initial hardness after quenching) (Tempering time coefficient) (Time Index) The time for a single tempering cycle is (h). (Tempering temperature coefficient) The temperature at which a single tempering is performed (K).

[0035] As a further improvement to the technical solution of the present invention, in step S6, the aging strengthening treatment is carried out in a vacuum aging furnace: vacuum degree ,by Heat up to Keep warm for 6-8 hours, then... Cool to room temperature; the amount of carbide precipitation during aging process satisfies the formula:

[0036] ;

[0037] in, (Maximum carbide precipitation). (Precipitation rate constant) The effective time is in hours (h). (Activation energy for carbide precipitation). (Gas constant) The aging temperature (K) is used.

[0038] As a further improvement to the technical solution of the present invention, the copper extrusion die is made of H13 hot work die steel, and its chemical composition by mass fraction is: C 0.32-0.45. Si 0.80-1.20 Mn 0.20-0.50 Cr 4.75-5.50 Mo 1.10-1.75 V 0.80-1.20 P , The balance is Fe.

[0039] Secondly, the present invention also provides a copper extrusion die, which is treated using the aforementioned heat treatment method for improving the life of copper extrusion dies. The die has a hardness of 50-55 HRC and an impact toughness of [missing information]. The carbide particle size is Service life 3000 extrusion cycles.

[0040] Thirdly, the present invention also provides an application of the heat treatment method for improving the life of copper extrusion dies as described above, which is applied in the production of dies for extrusion molding of copper profiles, copper tubes or copper rods.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] This invention overcomes the limitations of traditional heat treatment methods, which involve a synergistic process encompassing pre-treatment of the mold, segmented preheating, gradient quenching, cryogenic stabilization, multi-stage tempering, and aging strengthening. It achieves a comprehensive optimization of the mold's internal temperature gradient through segmented preheating, gradient heating, gradient quenching, dynamic cooling rate control during gradient quenching to prevent structural transformation cracks, and cryogenic stabilization to reduce residual austenite content. Multi-stage tempering and aging strengthening further promote the dispersion and precipitation of carbides. This process optimizes the mold's thermal stress, microstructure uniformity, and mechanical properties, significantly improving hardness uniformity, toughness, and fatigue resistance. It also effectively refines carbide particles to enhance wear resistance, ultimately extending the mold's service life. Furthermore, the process parameters can be precisely controlled using quantitative formulas to adapt to the production needs of copper extrusion dies of different sizes and specifications, demonstrating strong industrial applicability and promotional value. Attached Figure Description

[0043] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0044] Figure 1 This is a schematic diagram of the process flow of a heat treatment method for improving the life of copper extrusion dies according to an embodiment of the present invention. Detailed Implementation

[0045] The present invention will be described in detail below with reference to specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0046] Reference Figure 1 In a first aspect, the present invention provides a heat treatment method for improving the life of copper extrusion dies, comprising the following steps:

[0047] S1: Mold pretreatment;

[0048] S2: Segmented preheating treatment, carried out in a multi-stage gradient heating mode, with the heating rate and holding time of each stage controlled by a quantitative formula;

[0049] S3: Gradient quenching treatment, using a composite cooling medium system, dynamically adjusting the cooling rate according to the real-time temperature of the mold;

[0050] S4: Cryogenic stabilization treatment, which involves heat preservation in an ultra-low temperature environment and precise control of heating and cooling rates;

[0051] S5: Multi-stage tempering treatment, tempering is carried out in multiple different temperature ranges, and the final hardness is controlled by a hardness prediction model.

[0052] S6: Aging enhancement treatment, the aging process is completed in a vacuum environment to promote the dispersion and precipitation of carbides.

[0053] In practice, a collaborative optimization system is constructed through a complete process involving mold pretreatment, segmented preheating, gradient quenching, cryogenic stabilization, multi-stage tempering, and aging strengthening. First, pretreatment removes impurities and residual stress from the mold surface. Then, segmented preheating is performed using a multi-stage gradient heating mode, with precise control of the heating rate and holding time using quantitative formulas to ensure uniform temperature inside the mold. Next, a composite cooling medium system is used, and the cooling rate is dynamically adjusted based on the real-time mold temperature to complete gradient quenching. Then, cryogenic stabilization is performed under precise control of the heating and cooling rates in an ultra-low temperature environment. Next, tempering is performed multiple times at different temperature ranges, with the final hardness controlled using a hardness prediction model. Finally, aging strengthening is completed in a vacuum environment to promote carbide dispersion and precipitation, forming a complete performance optimization closed loop.

[0054] The method of this invention breaks through the limitations of traditional heat treatment with single-stage operation and coarse parameters. Through the synergistic effect of each process step, it achieves simultaneous optimization of mold thermal stress, microstructure uniformity and mechanical properties. It can not only significantly improve the mold hardness uniformity, toughness and fatigue strength, but also effectively refine carbide particles to improve wear resistance, and ultimately greatly extend the service life of the mold. Moreover, the process parameters can be precisely controlled by quantitative formulas to adapt to the production needs of copper extrusion dies of different sizes and specifications, and has strong industrial applicability and promotion value.

[0055] In some embodiments, step S1, the mold pretreatment includes sequential degreasing and stress-relieving annealing: using an alkaline cleaning agent (sodium hydroxide mass fraction 5-8%). Sodium carbonate mass fraction 3-5 Surfactant mass fraction 1-2 ) in 60-80 Ultrasonic cleaning for 15-20 minutes; stress-relief annealing temperature: 550-600°C Heating rate 5-10 After holding at the temperature for 2-4 hours, cool it to room temperature with the furnace.

[0056] It should be noted that the mold pretreatment in step S1 is carried out in the order of degreasing, rust removal, and stress-relieving annealing. A specific ratio of alkaline cleaning agent is used, and the temperature is maintained at 60-80°C. The mold is then ultrasonically cleaned for 15-20 minutes to remove surface oil and oxide scale using the cavitation effect of ultrasound; finally, the mold is placed at 550-600 degrees Celsius. In the environment, with After heating and holding at that temperature for 2-4 hours, the furnace is cooled to eliminate residual stress from machining through atomic diffusion.

[0057] This invention can thoroughly remove impurities from the mold surface that affect the heat treatment effect through targeted degreasing, avoiding structural defects caused by impurities; the subsequent stress-relief annealing can effectively eliminate residual stress generated during machining, prevent cracks caused by stress superposition during heat treatment, lay a good foundation for the smooth implementation of subsequent heat treatment processes, and ensure the stability of the overall performance of the mold.

[0058] In some embodiments, step S2, the segmented preheating process is divided into three stages, and the parameters of each stage satisfy the following relationship:

[0059] Phase 1: Preheating Temperature = heating rate Insulation time ,in, , This represents the maximum thickness of the mold (mm). ;

[0060] Second stage: Preheating temperature heating rate Insulation time ,in, , ;

[0061] Third stage: Preheating temperature =950-980℃, heating rate Insulation time ,in, .

[0062] It should be noted that the segmented preheating process in step S2 is divided into three consecutive stages, and the parameters of each stage are quantified and correlated through a specific formula. The first stage uses 8-12... Increase the temperature to 300-400 The heat preservation time is determined by the formula. Calculation, where The preheating coefficient is... For the maximum thickness of the mold, The thermal conductivity within this temperature range is primarily used to eliminate the initial temperature difference; the second stage uses... Increase the temperature to 600-700 Insulation time according to The third stage involves determining and promoting the initial dissolution of carbides; Heat to 850-900 Insulation time is determined by Calculations are performed to ensure that the overall temperature of the mold is consistent.

[0063] The three-stage gradient heating mode, combined with a quantified holding time formula, can precisely control the heating process of the mold, significantly reduce the internal temperature gradient, and reduce the generation of thermal stress. The temperature and speed matching design of each stage can not only avoid the uneven structure caused by excessive heating, but also promote the dissolution of carbides and temperature equilibrium through gradual heating, which provides a guarantee for the uniform transformation of martensite in the subsequent quenching process, and further improves the stability of mold structure and performance consistency.

[0064] In some embodiments, in step S3, during the gradient quenching process, the composite cooling medium has a mass fraction of 20-30%. The composition of the polyethylene glycol aqueous solution and the dynamic cooling rate satisfy the formula:

[0065] ;

[0066] in, (Base cooling rate) (Temperature coefficient) (Initial quenching temperature), T is the real-time temperature of the mold ( ), (Medium ratio coefficient); When the mold temperature drops to point( When the cooling rate is adjusted to until the mold temperature reaches 100°C. Then remove it.

[0067] It should be noted that the composite cooling medium ratio design takes into account both cooling efficiency and gentleness, avoiding austenite decomposition caused by slow cooling of pure oil or quenching cracks caused by excessively fast cooling of pure water; the dynamic cooling rate formula can precisely adjust the cooling intensity according to the real-time temperature of the mold, and switch the cooling rate at the Ms point, which can ensure sufficient martensite transformation, reduce the volume expansion stress during the martensite transformation process, reduce the crack incidence, and improve the uniformity of mold structure and hardness stability.

[0068] In some embodiments, in step S4, the cryogenic stabilization treatment uses liquid nitrogen as the cooling medium: after the mold is quenched, it is placed at room temperature for 30-60 minutes, and then placed in a cryogenic chamber at 10-15 degrees Celsius. When the temperature drops to -120℃, the holding time must meet the following formula:

[0069] ;

[0070] in, , This represents the maximum thickness of the mold (mm). (Initial temperature before cryogenic treatment). =-120℃ (cryogenic target temperature); after the insulation is completed, The heating rate returned to room temperature.

[0071] It should be noted that the cryogenic stabilization treatment in step S4 uses liquid nitrogen as the cooling medium. After the mold is quenched, it is placed at room temperature for 30-60 minutes to equilibrate the temperature, and then... Cooling to -120℃, the holding time is determined by the formula. Calculation, where This is the cryogenic coefficient. For the maximum thickness of the mold, This is the initial temperature before cryogenic treatment. The target temperature for cryogenic treatment; after the insulation is completed, the temperature will be as follows: Heat to room temperature.

[0072] The room temperature placement before cryogenic treatment avoids stress impact caused by excessive temperature difference. The ultra-low temperature environment can reduce the thermodynamic stability of the retained austenite, forcing it to transform into martensite, while promoting the precipitation of fine carbides. The quantified holding time formula and precise control of heating and cooling rates can ensure the full transformation of the retained austenite and avoid structural cracking during cryogenic treatment, effectively improving the dimensional stability and hardness of the mold and reducing the risk of deformation during use.

[0073] In some embodiments, step S5, the multi-stage tempering process is divided into three consecutive tempering processes:

[0074] Phase 1: Tempering Temperature heating rate Keep warm for 2-3 hours;

[0075] Second stage: Tempering temperature heating rate Keep warm for 3-4 hours;

[0076] Third stage: Tempering temperature heating rate Hold at the heat for 4-5 hours; after each tempering, air cool to room temperature. During the tempering process, the mold hardness meets the prediction formula:

[0077] ;

[0078] in, (Initial hardness after quenching) (Tempering time coefficient) (Time Index) The time for a single tempering cycle is (h). (Tempering temperature coefficient) The temperature at which a single tempering is performed (K).

[0079] It should be noted that the three tempering designs at different temperature ranges each have their own focus: low-temperature tempering eliminates quenching stress and reduces brittleness, medium-temperature tempering promotes carbide precipitation and improves toughness, and high-temperature tempering achieves the best match between hardness and toughness. The hardness prediction formula can adjust the tempering parameters in reverse according to the target hardness to ensure that the mold hardness uniformity is ≤±1HRC, while completely eliminating quenching stress, dispersing and precipitating fine carbides, significantly improving the toughness and fatigue resistance of the mold, and avoiding failure caused by residual stress or insufficient toughness during use.

[0080] In some embodiments, in step S6, the aging strengthening treatment is performed in a vacuum aging furnace: vacuum degree ,by Heat up to Keep warm for 6-8 hours, then... Cool to room temperature; the amount of carbide precipitation during aging process satisfies the formula:

[0081] ;

[0082] in, (Maximum carbide precipitation). (Precipitation rate constant) The effective time is in hours (h). (Activation energy for carbide precipitation). (Gas constant) The aging temperature (K) is used.

[0083] It should be noted that the aging strengthening treatment in step S6 is performed under vacuum conditions. The aging process is carried out in a vacuum aging furnace, with Heat up to After keeping warm for 6-8 hours, Cool to room temperature; the amount of carbide precipitation during aging is determined by the formula:

[0084] Control, among which, To achieve the maximum carbide precipitation, The precipitation rate constant is For time limit, The activation energy for carbide precipitation. The gas constant is This refers to the aging temperature. A vacuum environment prevents oxidation of the mold surface, ensuring that the mold's appearance and internal performance remain unaffected. Precise control of heating and cooling rates and holding time, combined with a carbide precipitation formula, allows for the refinement of carbide particle size to a specific value. This significantly improves the dispersion and stability of carbides, thereby enhancing the wear resistance and high-temperature stability of the mold and extending its service life under high temperature, high pressure and high friction conditions.

[0085] In some embodiments, the copper extrusion die is made of H13 hot work die steel, with a chemical composition of C 0.32-0.45 by mass fraction. Si 0.80-1.20 Mn 0.20-0.50 Cr 4.75-5.50 Mo 1.10-1.75 V 0.80-1.20 P , The balance is Fe. The specific chemical composition design of H13 hot work die steel can fully utilize the performance optimization effect of the heat treatment process of this application. Among them, elements such as Cr, Mo, and V can promote the precipitation and refinement of carbides, C element ensures the hardness of the die, Si and Mn elements improve the toughness and hardenability of the steel, and low P and S content reduces impurities and defects. The synergistic effect of material and process can maximize the improvement of the comprehensive mechanical properties of the die and provide material guarantee for extending the service life of the die.

[0086] Secondly, the present invention also provides a copper extrusion die, which is treated using the aforementioned heat treatment method for improving the life of copper extrusion dies. The die has a hardness of 50-55 HRC and an impact toughness of [missing information]. Residual austenite content The carbide particle size is Service life 3000 extrusion cycles. The core performance indicators of the mold after heat treatment by the method of this invention, the reasonable matching of hardness and toughness, ensures the load-bearing capacity and impact resistance of the mold under high pressure extrusion conditions. The low residual austenite content and refined carbide particles improve the dimensional stability and wear resistance of the mold. The service life of ≥3000 cycles is 2-3 times longer than that of traditional processes, which can significantly reduce the frequency of mold replacement and production costs in the production process, and meet the needs of large-scale industrial production.

[0087] Thirdly, this invention also provides an application of the heat treatment method described above for improving the lifespan of copper extrusion dies, specifically in the production of dies for extruding copper profiles, tubes, or rods. By applying the aforementioned heat treatment method to the production process of dies for extruding copper profiles, tubes, or rods, process parameters can be flexibly adjusted according to the size, shape, and working conditions of different types of copper extrusion dies, achieving targeted performance optimization for various types of copper extrusion dies. This expands the application scope of the heat treatment method of this invention, adapting to the die production needs of different copper extrusion products such as copper profiles, tubes, and rods. It is particularly suitable for large, complex-shaped copper extrusion dies, solving common problems such as easy wear, cracking, and short service life of various copper extrusion dies under high temperature, high pressure, and high friction conditions. It provides an efficient and reliable die treatment solution for the copper extrusion molding industry and has broad industrial application value.

[0088] To provide a clearer understanding of the invention, the invention is further described below:

[0089] Reference Figure 1 This invention provides a heat treatment method for improving the life of copper extrusion dies, comprising the following steps:

[0090] S1: Mold Pre-treatment

[0091] The core purpose of pretreatment is to remove impurities from the mold surface and eliminate residual stress from machining, laying the foundation for subsequent heat treatment. The specific steps are as follows:

[0092] Degreasing treatment: Use an alkaline cleaning agent (sodium hydroxide mass fraction 5-8%). Sodium carbonate mass fraction 3-5 Fatty alcohol polyoxyethylene ether surfactants, mass fraction 1-2 ), in 60-80 Ultrasonic cleaning for 15-20 minutes is performed to remove cutting oil, rust-preventive oil, and other oil stains from the mold surface using the cavitation effect of ultrasound.

[0093] Stress-relief annealing: Place the mold in a box-type resistance furnace, and... The heating rate increases to 550-600 The furnace is kept at a constant temperature for 2-4 hours to eliminate residual stress generated during machining through atomic diffusion. Then, it is cooled to room temperature with the furnace to avoid secondary stress generation.

[0094] S2: Segmented preheating treatment

[0095] A three-stage gradient heating mode is adopted, and the parameters of each stage are precisely controlled through quantitative formulas to ensure uniform temperature inside the mold and reduce thermal stress. The parameters of each stage are as follows:

[0096] First stage preheating: temperature heating rate The heat preservation time is determined by the formula. Calculate, where, (The preheating coefficient is determined by the thermal conductivity of the mold material.) This represents the maximum thickness of the mold (mm). (Thermal conductivity of H13 steel in this temperature range); This stage mainly eliminates the initial temperature difference between the mold surface and the interior;

[0097] Second stage preheating: temperature heating rate Insulation time , , This stage promotes the initial dissolution of carbides inside the mold, creating conditions for the uniformity of the quenched structure.

[0098] Third stage preheating: temperature =950-980℃, heating rate Insulation time , This stage ensures that the overall temperature of the mold is uniform, avoiding structural stress caused by uneven temperature during quenching.

[0099] S3: Gradient quenching treatment

[0100] A combination of composite cooling medium and dynamic cooling rate control is used to ensure sufficient martensitic transformation while preventing crack formation. The specific process is as follows:

[0101] Cooling medium configuration: 20-30% by mass Aqueous solutions of polyethylene glycol with 70-80 The mineral oil is mixed and stirred evenly to serve as a composite cooling medium; the addition of polyethylene glycol can adjust the cooling rate, avoid the austenite decomposition caused by the slow cooling of pure oil, and at the same time alleviate the quenching cracks caused by the excessively rapid cooling of pure water.

[0102] Dynamic cooling control: preheat to The mold is rapidly immersed in the composite cooling medium, and the cooling rate satisfies the formula ,in (Base cooling rate) (Temperature coefficient, reflecting the rate of change of cooling rate as temperature decreases), T0 = 1030℃ - 1050℃ (initial quenching temperature), T is the real-time temperature of the mold (monitored by an infrared thermometer). (The medium ratio coefficient is finely adjusted based on the mixing ratio of polyethylene glycol and mineral oil.)

[0103] Stage cooling switching: When the mold temperature drops to the martensitic transformation initiation temperature ( When this occurs, the cooling rate is adjusted to [a certain value] via an automatic temperature control system. until the mold temperature reaches 100°C. Then remove it; this stage can reduce the volume expansion stress during the martensitic transformation process and reduce the crack incidence.

[0104] S4: Cryogenic Stabilization Treatment

[0105] Cryogenic treatment promotes the transformation of retained austenite to martensite, improving the dimensional stability of the mold. The specific steps are as follows:

[0106] Intermediate placement: After quenching, the mold is placed at room temperature for 30-60 minutes to allow the surface and internal temperatures of the mold to reach equilibrium, avoiding excessive temperature stress caused by direct deep cooling;

[0107] Cryogenic treatment: The mold is placed in a liquid nitrogen cryogenic chamber to... The cooling rate drops to -120℃, and the holding time is calculated according to the formula. calculate, , (Initial temperature before cryogenic treatment). =-120℃ (cryogenic target temperature); Under ultra-low temperature conditions, the thermodynamic stability of the retained austenite decreases, forcibly transforming it into martensite, while fine carbides precipitate.

[0108] Temperature recovery: After the insulation period ends, The heating rate is controlled to bring the mold back to room temperature, avoiding structural cracking caused by excessively rapid heating.

[0109] S5: Multi-stage tempering process

[0110] The process involves tempering at three different temperature ranges, using a hardness prediction model to precisely control the final properties, eliminate quenching stress, and promote the dispersed precipitation of carbides. The specific process is as follows:

[0111] First stage tempering (low-temperature tempering): Temperature heating rate Keep warm for 2-3 hours; the main purpose is to eliminate residual stress generated during quenching, reduce the brittleness of martensite, and maintain high hardness.

[0112] Second stage tempering (medium-temperature tempering): Temperature heating rate Keep warm for 3-4 hours; during this stage, martensite begins to decompose, precipitating fine carbides. The mold toughness is significantly improved;

[0113] Third-stage tempering (high-temperature tempering): Temperature heating rate Keep warm for 4-5 hours; promote the aggregation and spheroidization of carbides, further eliminate residual stress, and achieve the best match between hardness and toughness.

[0114] Hardness control: The mold hardness meets the prediction formula after each tempering. ,in (Initial hardness after quenching) (Tempering time coefficient) (Time Index) The time for a single tempering cycle is (h). (Tempering temperature coefficient) The single tempering temperature (K) can be used to adjust the tempering parameters in reverse according to the target hardness, ensuring that the mold hardness uniformity is ≤±1HRC.

[0115] S6: Time-Effective Processing

[0116] Aging treatment is performed in a vacuum environment to further refine carbide particles and improve the wear resistance and high-temperature stability of the mold. Specific parameters are as follows:

[0117] Vacuum conditions: Place the tempered mold into a vacuum aging furnace and evacuate it to a vacuum level. To avoid oxidation of the mold surface;

[0118] Aging process: The heating rate increased to Keep warm for 6-8 hours, then... The cooling rate is reduced to room temperature;

[0119] Carbide precipitation control: The amount of carbide precipitation during aging process satisfies the formula:

[0120] ,in (Maximum carbide precipitation). (Precipitation rate constant) The effective time is in hours (h). (Activation energy for carbide precipitation in H13 steel). (Gas constant) The aging temperature (K) is used; this formula allows for precise control of carbide precipitation and particle size, refining the carbide particle size to a minimum. This significantly improves the wear resistance of the mold.

[0121] Furthermore, this application also provides a copper extrusion die, which, after being treated by the above-mentioned heat treatment method, has a hardness of 50-55 HRC and an impact toughness of [missing information]. The carbide particle size is With a service life of ≥3000 extrusion cycles, it is 2-3 times better than existing technologies.

[0122] Furthermore, the heat treatment method of this application can be widely used in the production of molds for extrusion molding of copper profiles, copper tubes or copper rods, and is especially suitable for large and complex-shaped copper extrusion molds, with good prospects for industrial application.

[0123] To more clearly illustrate the technical solution of this application, the following detailed description is provided in conjunction with specific embodiments:

[0124] Example 1

[0125] This embodiment is for the maximum thickness. The H13 steel copper profile extrusion die uses the heat treatment method of this application, and the specific steps are as follows:

[0126] S1: Mold Pre-treatment

[0127] Degreasing: Alkaline cleaning agent (NaOH) , surfactants ), ultrasonic cleaning at 70℃ for 18 minutes;

[0128] Stress-relief annealing: heating rate Keep warm for 3 hours, then cool to room temperature with the furnace.

[0129] S2: Segmented preheating treatment

[0130] Phase 1: , , ;

[0131] Phase Two: , , ;

[0132] Phase Three:

[0133] =980℃, , .

[0134] S3: Gradient quenching treatment

[0135] Composite cooling medium: 25 polyethylene glycol aqueous solution

[0136] Cooling rate formula: v_c = 18 × (1 + 1.0 × (1050 - T) / 1050) × 1.0;

[0137] when ( When (point), the cooling rate is adjusted to Cool to take out.

[0138] S4: Cryogenic Stabilization Treatment

[0139] Leave at room temperature for 45 minutes;

[0140] cooling rate To -120℃, insulation time:

[0141] ;

[0142] heating rate It will rise back to room temperature.

[0143] S5: Multi-stage tempering process

[0144] Phase 1: heating rate n, keep warm for 2.5 hours,

[0145] ;

[0146] Phase Two: heating rate Keep warm for 3.5 hours.

[0147] ;

[0148] Phase Three: heating rate Keep warm for 4.5 hours.

[0149] .

[0150] S6: Time-Effective Processing

[0151] vacuum degree ;

[0152] heating rate , Keep warm for 7 hours;

[0153] Carbide precipitation:

[0154] ;

[0155] cooling rate Cool to room temperature.

[0156] Performance testing

[0157] After the above processing, the mold performance test results are as follows:

[0158] Hardness: 51-53 HRC (uniformity) 1HRC);

[0159] Impact toughness: ;

[0160] Residual austenite content: ;

[0161] Carbide particle size: ;

[0162] Actual extrusion service life: 3186 cycles (the service life of traditional process dies under the same working conditions is 720 cycles).

[0163] Example 2

[0164] This embodiment is for the maximum thickness. The specific steps for using the H13 steel copper tube extrusion die are as follows:

[0165] S1: Mold Pre-treatment

[0166] Degreasing: NaOH , surfactants , Ultrasonic cleaning for 20 minutes;

[0167] Rust removal: 15 Pickle with hydrochloric acid solution at room temperature for 10 minutes, then rinse with water.

[0168] Stress-relief annealing: heating rate Keep warm for 4 hours, then cool with the furnace.

[0169] S2: Segmented preheating treatment

[0170] Phase 1: , , ;

[0171] Phase Two: , , ;

[0172] Phase Three: , , .

[0173] S3: Gradient quenching treatment

[0174] Composite cooling medium: 28 Aqueous solutions of polyethylene glycol;

[0175] Cooling rate formula: v_c = 18 × (1 + 1.0 × (1050 - T) / 1050) × 1.0;

[0176] Adjust the cooling rate as needed Cool to take out.

[0177] S4: Cryogenic Stabilization Treatment

[0178] Let it sit at room temperature for 60 minutes;

[0179] cooling rate -120℃, insulation time:

[0180] ;

[0181] heating rate It will rise back to room temperature.

[0182] S5: Multi-stage tempering process

[0183] Phase 1: heating rate Keep warm for 3 hours. ;

[0184] Phase Two: heating rate Keep warm for 4 hours. ;

[0185] Phase Three: heating rate Keep warm for 5 hours. .

[0186] S6: Time-Effective Processing

[0187] vacuum degree ;

[0188] After 8 hours of heat preservation, the amount of carbide precipitation was... ;

[0189] cooling rate Cool to room temperature.

[0190] Performance testing

[0191] Hardness: 50-52 HRC (uniformity) );

[0192] Impact toughness: ;

[0193] Residual austenite content: ;

[0194] Carbide particle size: ;

[0195] Actual extrusion lifespan: 3162 cycles (the lifespan of traditional process dies is 650 cycles).

[0196] As can be seen from the above embodiments, the heat treatment method of this application significantly improves the comprehensive mechanical properties and service life of copper extrusion dies through multi-stage collaborative processes and quantitative parameter control, and has important industrial application value.

[0197] The heat treatment method of the present invention for improving the life of copper extrusion dies has the following significant advantages:

[0198] Thermal stress is significantly reduced: Through three-stage segmented preheating and a quantified heat preservation time formula, the internal temperature gradient of the mold is reduced by 40-50%. This effectively avoids hot cracks generated during preheating and quenching;

[0199] Microstructure uniformity optimization: dynamic cooling rate control during gradient quenching ensures uniform martensite transformation, and cryogenic treatment reduces the retained austenite content to 5%. The following improvements result in a 30-40% increase in mold dimensional stability. ;

[0200] Synergistic improvement in mechanical properties: The combination of multi-stage tempering and aging strengthening processes ensures that the mold hardness uniformity is ≤±1HRC and the impact toughness is increased by 25-30%. Fatigue resistance increases by 30-40%. This achieves the best balance between hardness, toughness, and wear resistance.

[0201] Service life significantly extended: carbide particles refined to... The wear resistance of the mold is improved by 50-60%. The service life is extended from 500-800 times in the existing technology to more than 3,000 times, significantly reducing production costs;

[0202] Highly operable process: All key parameters are quantified through mathematical models, facilitating precise control in industrial production and applicable to copper extrusion dies of different sizes and shapes.

[0203] The technical solutions provided by the embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the embodiments of the present invention. The descriptions of the embodiments above are only for helping to understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the embodiments of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A heat treatment method for improving the service life of copper extrusion dies, characterized in that, Includes the following steps: S1: Mold pretreatment; S2: Segmented preheating treatment, carried out in a multi-stage gradient heating mode, with the heating rate and holding time of each stage controlled by a quantitative formula; S3: Gradient quenching treatment, using a composite cooling medium system, dynamically adjusting the cooling rate according to the real-time temperature of the mold; S4: Cryogenic stabilization treatment, which involves heat preservation in an ultra-low temperature environment and precise control of heating and cooling rates; S5: Multi-stage tempering treatment, tempering is carried out in multiple different temperature ranges, and the final hardness is controlled by a hardness prediction model. S6: Aging enhancement treatment, the aging process is completed in a vacuum environment to promote the dispersion and precipitation of carbides.

2. The heat treatment method for improving the life of copper extrusion dies according to claim 1, characterized in that: In step S1, the mold pretreatment includes sequential degreasing and stress-relieving annealing: using an alkaline cleaning agent at 60-80°C. Ultrasonic cleaning for 15-20 minutes; stress-relief annealing temperature: 550-600°C Heating rate 5-10 After holding at the temperature for 2-4 hours, cool it to room temperature with the furnace.

3. The heat treatment method for improving the life of copper extrusion dies according to claim 1, characterized in that: In step S2, the segmented preheating process is divided into three stages, and the parameters of each stage satisfy the following relationship: Phase 1: Preheating Temperature = heating rate Insulation time ,in, , For the maximum thickness of the mold, ; Second stage: Preheating temperature heating rate Insulation time ,in, , ; Phase 3: Preheating Temperature =950-980℃, heating rate Insulation time ,in, .

4. The heat treatment method for improving the life of copper extrusion dies according to claim 1, characterized in that: In step S3, during the gradient quenching process, the composite cooling medium comprises 20-30% by mass. The cooling rate of the polyethylene glycol aqueous solution dynamically satisfies the formula: ； in, Based on cooling rate, For temperature coefficient, T represents the initial quenching temperature, and T represents the real-time temperature of the mold. This is the medium ratio coefficient; when the mold temperature drops to... At point, the cooling rate is adjusted to until the mold temperature reaches 100°C. Then remove it.

5. The heat treatment method for improving the life of copper extrusion dies according to claim 1, characterized in that: In step S4, the cryogenic stabilization treatment uses liquid nitrogen as the cooling medium: after quenching, the mold is placed at room temperature for 30-60 minutes, and then placed in a cryogenic chamber at 10-15 degrees Celsius. The holding time for cooling to -120℃ meets the formula: ； in, , For the maximum thickness of the mold, This is the initial temperature before cryogenic treatment. The target temperature is for cryogenic treatment; after the insulation period ends, the temperature will naturally rise back to room temperature.

6. The heat treatment method for improving the life of copper extrusion dies according to claim 1, characterized in that: In step S5, the multi-stage tempering process is divided into three consecutive tempering processes: Phase 1: Tempering Temperature heating rate Keep warm for 2-3 hours; Second stage: Tempering temperature heating rate Keep warm for 3-4 hours; Third stage: Tempering temperature heating rate Hold at the heat for 4-5 hours; after each tempering, air cool to room temperature. During the tempering process, the mold hardness meets the prediction formula: ； in, This represents the initial hardness after quenching. This is the tempering time coefficient. For time index, This refers to the time for a single tempering cycle. This is the tempering temperature coefficient. This refers to the temperature at which a single tempering is performed.

7. The heat treatment method for improving the life of copper extrusion dies according to claim 1, characterized in that: In step S6, the aging strengthening treatment is carried out in a vacuum aging furnace: vacuum degree ,by Heat up to Keep warm for 6-8 hours, then... Cool to room temperature; the amount of carbide precipitation during aging process satisfies the formula: ； in, To achieve the maximum carbide precipitation, The precipitation rate constant is For time limit, The activation energy for carbide precipitation. The gas constant is... This refers to the aging temperature.

8. The heat treatment method for improving the life of copper extrusion dies according to claim 1, characterized in that: The copper extrusion die is made of H13 hot work die steel, and its chemical composition by mass fraction is: C 0.32-0.

45. Si 0.80-1.20 Mn 0.20-0.50 Cr 4.75-5.50 Mo 1.10-1.75 V 0.80-1.20 P , The balance is Fe.

9. A copper extrusion die, characterized in that: The copper extrusion die is treated using the heat treatment method for improving its lifespan according to any one of claims 1-8, wherein the die has a hardness of 50-55 HRC and an impact toughness of [missing information]. The carbide particle size is Service life 3000 extrusion cycles.

10. An application of a heat treatment method for improving the life of copper extrusion dies as described in any one of claims 1-8, characterized in that: The heat treatment method for improving the life of copper extrusion dies is applied in the production of dies for extrusion molding of copper profiles, copper tubes or copper rods.

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