Regulation and control method for nitridation permeable layer of die-casting die

Abstract

The invention relates to a regulation and control method for a nitridation permeable layer of a die-casting die. The regulation and control method comprises the following steps that the die-casting die is pretreated and partitioned; the pretreated mold is placed in nitriding equipment, nitrogen and hydrogen are introduced into the nitriding equipment, the volume ratio of the nitrogen to the hydrogen is (4-5): 1, and heat preservation is conducted after the temperature in the nitriding equipment is increased to a first temperature interval; the nitriding reaction rate in the nitriding equipment is monitored and calculated in real time, and according to the subareas of the die-casting die, a subarea heating program is started, and different areas of the die-casting die are subjected to subarea heating; adjusting the volume ratio of the nitrogen to the hydrogen to be 1: 1, maintaining the temperature of each zone set by the zone heating program, and maintaining the process parameters of the stage until the thickness and hardness of the nitride layer reach target values; and after the nitriding treatment is finished, the mold is cooled to the tapping temperature under the protective atmosphere. The hardness distribution uniformity, the thermal fatigue resistance, the wear resistance and the overall service life of the die-casting die can be improved.

Description

Technical Field

[0001] This invention relates to the field of surface treatment technology for die casting molds, and in particular to a method for controlling the nitriding penetration layer of die casting molds. Background Technology

[0002] Die casting molds are key equipment in die casting production. They must withstand repeated impacts from high-temperature molten metal and rapid heating and cooling, placing extremely high demands on the mold surface's resistance to thermal fatigue, wear, and corrosion. Gas nitriding, as a mature surface strengthening technology, is widely used in the surface treatment of die casting molds. By forming a high-hardness nitrided layer on the mold surface, its service life can be significantly improved.

[0003] Traditional gas nitriding processes typically employ a fixed ammonia decomposition rate or a fixed ratio of nitrogen-hydrogen mixtures and a constant processing temperature. This static process can be effective for molds with simple structures and uniform wall thickness. However, with the development of manufacturing, die-cast parts are becoming increasingly complex in shape, and correspondingly, molds are exhibiting irregular shapes, containing different structural regions with vastly different heat capacities and heat dissipation conditions, such as deep cavities, thin walls, sharp corners, and thick mold frames. When using traditional static nitriding processes to treat such irregularly shaped molds, the window for achieving optimal nitriding kinetics varies across different parts of the mold under fixed temperature and gas phase composition. Thin-walled and sharp-cornered areas, due to rapid heating and strong nitrogen atom adsorption capacity, are prone to over-nitriding, forming an excessively thick, brittle, bright white layer, or even peeling. Conversely, thick areas, due to high thermal inertia and slow heating, result in insufficient nitriding, a shallow penetration layer, and inadequate hardness and wear resistance. This unevenness in nitriding layer depth and hardness directly leads to performance imbalances in various parts of the mold during service, making it highly susceptible to thermal fatigue cracking in weak areas.

[0004] Therefore, existing gas nitriding methods cannot solve the core technical problem of achieving uniform and controllable control over the depth, hardness, and microstructure of the nitriding gradient penetration layer for die-casting molds with complex geometries within a single nitriding cycle. This severely restricts further improvements in the performance and lifespan of high-end die-casting molds. Summary of the Invention

[0005] Therefore, it is necessary to provide a method for controlling the nitriding penetration layer of die-casting molds, which can effectively improve the nitriding uniformity of die-casting molds with complex geometric features and enhance the performance and service life of die-casting molds.

[0006] The technical solution is as follows: A method for controlling the nitriding penetration layer of a die-casting mold, the method comprising the following steps:

[0007] Pre-treat and partition the die-casting mold;

[0008] The pretreated mold is placed in a nitriding device, and nitrogen and hydrogen are introduced into the nitriding device. The volume ratio of nitrogen to hydrogen is 4~5:1. The temperature inside the nitriding device is raised to the first temperature range and then kept at that temperature.

[0009] The nitriding reaction rate inside the nitriding equipment is monitored and calculated in real time. When the reaction rate reaches the first preset threshold, the volume ratio of nitrogen to hydrogen is adjusted to 2.5~3.5:1, and the zone heating program is started according to the zone of the die-casting mold to implement zone heating for different areas of the die-casting mold.

[0010] The volume ratio of nitrogen to hydrogen is adjusted to 1:1, and the temperature of each zone is maintained as set in the partitioned heating program. The process parameters at this stage are maintained until the nitrided layer thickness and hardness reach the target values.

[0011] After the nitriding process is completed, the mold is cooled to the oven temperature under a protective atmosphere.

[0012] In one embodiment, real-time monitoring and calculation of the nitridation reaction rate includes:

[0013] Monitor the pressure change rate ΔP / Δt inside the nitriding equipment and / or the ammonia decomposition rate α in the furnace gas;

[0014] Based on the pressure change rate and / or ammonia decomposition rate, the reaction rate R is calculated using a pre-established reaction kinetic model, where R = k1*(ΔP / Δt) / P0 + k2*α, the pressure change rate ΔP / Δt is in Pa / s, P0 is the reference pressure in Pa, and k1 and k2 are weighting coefficients that satisfy k1 + k2 = 1. The above calculation is performed using dimensionless processing.

[0015] In one embodiment, the step of pre-treating the die-casting mold specifically includes:

[0016] The die-casting mold is cleaned by ultrasonic cleaning followed by wiping with anhydrous ethanol.

[0017] After cleaning, the die-casting mold is subjected to stress-relieving annealing at a temperature of 600℃~650℃, held for 0.5~1.5 hours, and then cooled to room temperature.

[0018] In one embodiment, the die-casting mold is divided into a complex cavity area, a deep hole area, a corner stress concentration area, and a planar area. In the partition heating program, the partition heating temperature is set as follows: complex cavity area: 490~500℃; deep hole area: 430~460℃; corner stress concentration area: 480~490℃; planar area: 500~510℃.

[0019] In one embodiment, the steps are as follows: the pretreated mold is placed in a nitriding device, nitrogen and hydrogen are introduced into the nitriding device, the volume ratio of nitrogen to hydrogen is 4~5:1, and the temperature inside the nitriding device is raised to a first temperature range and then kept at that temperature, the first temperature range is 340~360°C, and the holding time is 1.5~2h, and the furnace pressure is maintained at 0.12~0.15MPa.

[0020] In one embodiment, the steps include: adjusting the volume ratio of nitrogen to hydrogen to 1:1, maintaining the temperature of each zone as set in the zone heating program, and maintaining the process parameters at this stage until the nitrided layer thickness and hardness reach the target values. Specifically, this includes:

[0021] Adjust the volume ratio of nitrogen to hydrogen to 1:1 and maintain the temperature of each zone as set in the partition heating program.

[0022] Receive feedback signals from the online hardness monitoring system, and reduce the nitrogen flow rate proportionally when the monitored surface hardness value exceeds the second preset threshold.

[0023] Once the thickness and hardness of the nitrided layer reach the target values, the nitriding process is completed.

[0024] In one embodiment, the steps are: receiving a feedback signal from an online hardness monitoring system; when the monitored surface hardness value exceeds a second preset threshold, reducing the nitrogen flow rate proportionally; hardness detection is multi-point detection with at least 3 detection points per area; the second preset threshold is 650~680HV; when the hardness is too high, reducing the nitrogen ratio by 5%~10%.

[0025] In one embodiment, the protective atmosphere is a hydrogen or nitrogen atmosphere.

[0026] In one embodiment, the steps are as follows: The pretreated mold is placed in a nitriding device; nitrogen and hydrogen are introduced into the nitriding device, with a nitrogen to hydrogen volume ratio of 4-5:1; the furnace body of the nitriding device is heated to a first temperature range and then kept at that temperature; the nitrogen purity is ≥99.99%, the hydrogen purity is ≥99.95%, and the total flow rate of the nitrogen-hydrogen mixed gas is 0.8-1.2 m³ / h. 3 / h.

[0027] In one embodiment, the step is as follows: After the nitriding treatment is completed, the mold is cooled to the oven exit temperature under a protective atmosphere. The cooling method is as follows:

[0028] The temperature was lowered to 250℃ at a rate of 4~6℃ / min and held for 1 hour; then lowered to below 100℃ at a rate of 8~10℃ / min, maintaining a protective atmosphere with a nitrogen-hydrogen volume ratio of 1:1 throughout the process.

[0029] The beneficial effects of this technical solution are as follows:

[0030] The above-mentioned method for controlling the nitriding penetration layer of die-casting molds, in the process of processing, combines the dynamically adjusted nitrogen-hydrogen gas ratio with a zoned heating program based on the mold structure, and precisely controls the process transition point according to the real-time monitored nitriding reaction rate. This can effectively solve the problems of uneven nitriding layer depth and unsatisfactory hardness caused by differences in heat capacity and heat dissipation conditions in different parts of irregular die-casting molds in traditional nitriding. As a result, a high-quality nitriding layer with uniform thickness and dense structure can be obtained simultaneously on the entire mold surface, which is beneficial to improving the uniformity of hardness distribution, thermal fatigue resistance, wear resistance and overall service life of die-casting molds. Attached Figure Description

[0031] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a flowchart illustrating the process of controlling the nitriding penetration layer of a die-casting mold as described in one embodiment. Detailed Implementation

[0034] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0035] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0036] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0037] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0038] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0039] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0040] See Figure 1 , Figure 1 This diagram illustrates a flowchart of a method for controlling the nitriding penetration layer of a die-casting mold according to an embodiment of the present invention. The method for controlling the nitriding penetration layer of a die-casting mold includes the following steps:

[0041] S10: Pre-treat and partition the die-casting mold;

[0042] S20: Place the pretreated mold in the nitriding equipment, introduce nitrogen and hydrogen into the nitriding equipment, with a nitrogen to hydrogen volume ratio of 4~5:1, and heat the nitriding equipment to the first temperature range and then keep it at that temperature.

[0043] S30: Real-time monitoring and calculation of the nitriding reaction rate in the nitriding equipment. When the reaction rate reaches the first preset threshold, the volume ratio of nitrogen to hydrogen is adjusted to 2.5~3.5:1, and the zone heating program is started according to the zone of the die-casting mold to implement zone heating for different areas of the die-casting mold.

[0044] S40: Adjust the volume ratio of nitrogen to hydrogen to 1:1 and maintain the temperature of each zone set in the zone heating program. Maintain the process parameters at this stage until the nitriding layer thickness and hardness reach the target values.

[0045] S50: After nitriding, the mold is cooled to the oven temperature under a protective atmosphere.

[0046] The above-mentioned method for controlling the nitriding penetration layer of die-casting molds, in the process of processing, combines the dynamically adjusted nitrogen-hydrogen gas ratio with a zoned heating program based on the mold structure, and precisely controls the process transition point according to the real-time monitored nitriding reaction rate. This can effectively solve the problems of uneven nitriding layer depth and unsatisfactory hardness caused by differences in heat capacity and heat dissipation conditions in different parts of irregular die-casting molds in traditional nitriding. As a result, a high-quality nitriding layer with uniform thickness and dense structure can be obtained simultaneously on the entire mold surface, which is beneficial to improving the uniformity of hardness distribution, thermal fatigue resistance, wear resistance and overall service life of die-casting molds.

[0047] Optionally, depending on the die-casting mold, in step S20, the ratio of nitrogen to hydrogen can be 4:1, 4.2:1, 4.5:1, 4.8:1, 5:1, or any ratio within this range. In step S30, the volume ratio of nitrogen to hydrogen can be 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, or any ratio within this range.

[0048] In one embodiment, real-time monitoring and calculation of the nitriding reaction rate includes: monitoring the pressure change rate ΔP / Δt within the nitriding equipment and / or the ammonia decomposition rate α in the furnace gas; and calculating the reaction rate R based on the pressure change rate and / or the ammonia decomposition rate using a pre-established reaction kinetic model, where R = k1*(ΔP / Δt) / P0 + k2*α, the pressure change rate ΔP / Δt is in Pa / s, P0 is the reference pressure in Pa, and k1 and k2 are weighting coefficients, satisfying k1 + k2 = 1. The above calculation is dimensionless. The pressure change rate directly reflects the volume change of the gaseous substances generated by ammonia decomposition, while the ammonia decomposition rate characterizes the nitrogen potential. Integrating these two parameters through weighting coefficients allows for a more comprehensive assessment of the reaction kinetic state. This implementation method allows process stage transitions to be dynamically triggered based on the actual reaction progress, rather than relying on fixed time parameters. This allows for accurate capture of the critical time points when the surface compound layer is fully formed and nitrogen atom diffusion becomes the control step, providing precise timing control for subsequent adjustments to the gas ratio and the initiation of zone heating. This avoids the problem of an excessively shallow nitriding layer caused by inaccurate judgment of the transition period.

[0049] Specifically, the reference pressure P0 is set to 0.1 MPa, matching the initial pressure of conventional nitriding. Weighting coefficients are adjusted according to the mold material: for example, when the mold is H13 steel, k1=0.6 and k2=0.4, thus the impact of pressure changes on the reaction rate is more significant. When the die-casting mold is made of 3Cr2W8V steel, k1=0.4 and k2=0.6, the ammonia decomposition rate has a greater impact on nitrogen penetration. The monitoring frequency is every 10 seconds, collecting pressure and ammonia decomposition rate data, which are automatically substituted into the formula by the PLC system to calculate the reaction rate R.

[0050] Furthermore, the first preset value is 0.8~0.9. For example, when R≥0.8, subsequent process adjustments are triggered.

[0051] It should be noted that the first preset threshold R is used to determine whether the nitriding reaction has moved from the surface-active adsorption stage to the nitrogen atom diffusion control stage, thereby deciding whether to adjust the gas ratio and initiate the zone heating program. Its setting is mainly based on the following factors: Material characteristics: Different mold steels (such as H13 and 3Cr2W8V) have different adsorption and diffusion capabilities for nitrogen, requiring corresponding threshold adjustments. Process objectives: Target nitriding layer depth, hardness, and microstructure uniformity. Experimental data: Through preliminary process experiments, the optimal reaction rate at which process conversion can achieve the best nitriding effect is determined.

[0052] For example, for H13 steel, which has a strong nitrogen adsorption capacity, the diffusion stage needs to be entered promptly after the surface reaction is basically complete to avoid over-nitriding. Therefore, the R value is set to 0.85. For 3Cr2W8V steel, nitrogen diffusion is slower, requiring a longer surface activation stage to ensure sufficient nitrogen atom penetration. Therefore, the R value is set to 0.9 to improve wear resistance. For P20 steel, a thin and hard nitrided layer is required, necessitating early entry into the diffusion control stage to avoid excessive nitriding. Therefore, the R value is set to 0.8 to prevent film adhesion. For high-alloy mold steel, with its high alloying element content and challenging nitriding process, the diffusion stage needs to be entered after sufficient surface reaction to avoid excessive brittle phases on the surface. Therefore, the R value is set to 0.88 to achieve uniform depth and prevent embrittlement.

[0053] In one embodiment, step S10: pre-treating the die-casting mold, specifically including:

[0054] S11: Clean the surface of the die-casting mold by ultrasonic cleaning followed by wiping with anhydrous ethanol.

[0055] S12: After cleaning, the die-casting mold is subjected to stress-relieving annealing at a temperature of 600℃~650℃, held for 0.5~1.5h and then cooled to room temperature.

[0056] Specifically, ultrasonic cleaning utilizes the cavitation effect to thoroughly remove oil and particulate matter from the mold and cavity surfaces, while anhydrous ethanol wiping further removes residual polar contaminants and allows them to evaporate quickly, ensuring surface cleanliness. Stress-relief annealing releases residual stress generated during machining by heating the mold to below its recrystallization temperature and holding it there. This absolute surface cleanliness ensures uniform adsorption of active nitrogen atoms during the initial nitriding stage, preventing uneven diffusion caused by contamination. Furthermore, it helps eliminate internal stress, thereby reducing the risk of mold deformation and dimensional deviations during the nitriding heat treatment process.

[0057] Furthermore, the ultrasonic cleaning parameters are as follows: power 200~300W, cleaning medium is alkaline cleaning agent, pH=10~11, cleaning time 15~20min, and rinsing 3 times with deionized water after cleaning. Anhydrous ethanol is applied using a lint-free cloth and wiped in the same direction to avoid secondary contamination. Stress-relief annealing is performed in a box-type resistance furnace with a heating rate of 10℃ / min. After holding at this temperature, the furnace is cooled to room temperature at a cooling rate ≤5℃ / min to avoid rapid cooling and the re-induction of stress.

[0058] In one embodiment, the die-casting mold is divided into zones: a complex cavity zone, a deep hole zone, a corner stress concentration zone, and a planar zone. In the zone heating process, the zone temperatures are set as follows: complex cavity zone: 490~500℃; deep hole zone: 430~460℃; corner stress concentration zone: 480~490℃; planar zone: 500~510℃. This zoned approach is based on a compensation mechanism of heat conduction and nitrogen atom diffusion kinetics. A relatively lower temperature is used for corner areas with good heat dissipation and low heat capacity to suppress over-nitriding; a higher temperature is used for deep hole areas with slow heat dissipation and high heat capacity to promote nitrogen atom diffusion inwards. This differentiated temperature field implementation can offset thermal differences caused by the mold geometry. Through precise temperature compensation, all parts of the mold achieve similar nitriding kinetic conditions, which is beneficial for achieving uniformity in the overall nitriding layer depth of complex-shaped molds, while avoiding brittle spalling at sharp corners due to over-nitriding.

[0059] Specifically, the zoning is based on thermal simulation analysis using a 3D model of the mold. Areas with a heat capacity ≥ 500 J / (kg・℃) are designated as complex cavity areas, areas with a depth-to-diameter ratio ≥ 5 are designated as deep hole areas, areas with a corner radius ≤ 3 mm are designated as corner stress concentration areas, and the remainder are designated as planar areas. The heating equipment employs a multi-zone temperature-controlled nitriding furnace, with each zone equipped with an independent thermocouple and heating tube. The temperature control accuracy is ±5℃. During zone heating startup, the temperature is increased to the set temperature at a rate of 5℃ / min to avoid sudden temperature rises and thermal stress.

[0060] In one embodiment, step S20 involves placing the pretreated mold in a nitriding apparatus, introducing nitrogen and hydrogen gas into the apparatus at a volume ratio of 4-5:1, and then heating the apparatus to a first temperature range of 340-360°C for 1.5-2 hours, maintaining the furnace pressure at 0.12-0.15 MPa. This temperature range constitutes the pre-nitriding stage, ensuring sufficient atomic activity for surface reaction while preventing premature and rapid nitride growth due to excessively high temperatures. The appropriate holding time ensures temperature equilibrium and complete surface activation of the mold. Controlling the furnace pressure within this range helps maintain stable gas flow and ensures atmosphere uniformity. Furthermore, the optimized combination of temperature, time, and pressure parameters facilitates uniform activation of the mold surface, forming the active surface layer necessary for high-quality nitriding, thereby further enhancing the subsequent nitriding effect.

[0061] Furthermore, the temperature was increased from room temperature to 340-360°C at a rate of 12°C / min, with a nitrogen-hydrogen mixture continuously introduced during the heating process to remove air from the furnace. During the holding phase, the furnace pressure was controlled by the combined action of the inlet flow rate and the exhaust valve, with pressure fluctuations kept within ±0.01 MPa. The ammonia decomposition rate in the furnace was recorded 10 minutes before the end of the holding phase.

[0062] In one embodiment, step S40: adjusting the volume ratio of nitrogen to hydrogen to 1:1 and maintaining the temperature of each zone as set in the zone heating program, maintaining the process parameters at this stage until the nitrided layer thickness and hardness reach the target values, specifically includes:

[0063] S41: Adjust the volume ratio of nitrogen to hydrogen to 1:1 and maintain the temperature of each zone set in the zone heating program.

[0064] S42: Receive feedback signals from the online hardness monitoring system, and reduce nitrogen flow rate proportionally when the monitored surface hardness value exceeds the second preset threshold.

[0065] S43: Once the thickness and hardness of the nitrided layer reach the target values, the nitriding process ends.

[0066] When the nitrogen-hydrogen ratio is adjusted to 1:1, the penetration and diffusion rates of nitrogen atoms reach an optimal balance, ensuring both the increase in nitrided layer thickness and preventing excessive precipitation of nitrides such as Fe2N, which could lead to increased brittleness. The online hardness system monitors surface hardness changes in real time. When the hardness exceeds a threshold, the nitrogen flow rate is reduced. Excessive nitrogen content can cause nitrogen atoms to penetrate too quickly, forming supersaturated nitrides, resulting in high hardness and decreased toughness. Adjusting the ratio allows for precise control of nitride precipitation. This precise control over the hardness and microstructure of the final nitrided layer prevents brittle layers caused by over-nitriding and ensures consistency across different batches. It is particularly suitable for surface treatment of precision die-casting molds with stringent performance requirements.

[0067] Further, in step S41: the nitrogen-hydrogen ratio switching is achieved through a mass flow controller, and the switching process lasts for 5 minutes to avoid fluctuations in the furnace atmosphere caused by sudden changes in flow rate. In step S42: the online hardness monitoring system uses a portable ultrasonic hardness tester, collecting data every 30 seconds. When the hardness value exceeds 650~680HV, the flow rate adjustment program is activated. In step S43: the target thickness is set to 0.15~0.25mm, and the target hardness is 600~650HV. When the monitoring data reaches the target value three times consecutively, nitriding is considered complete.

[0068] In one embodiment, step S42 involves receiving a feedback signal from an online hardness monitoring system. When the monitored surface hardness value exceeds a second preset threshold, the nitrogen flow rate is reduced proportionally. Hardness detection is performed using multi-point detection with at least three detection points per area. The second preset threshold is 650~680 HV. When the hardness is too high, the nitrogen ratio is reduced by 5%~10%. Multi-point detection with at least three detection points per area avoids the randomness of single-point detection and ensures the overall uniformity of regional hardness, especially for areas prone to hardness fluctuations, such as complex cavity areas. The second preset threshold of 650~680 HV is determined based on the usage requirements of the die-casting mold. Hardness above this threshold will lead to increased brittleness of the nitrided layer, making it prone to cracking during thermal fatigue cycles. The 5%~10% reduction in nitrogen flow rate has been verified through process testing and can effectively reduce hardness without affecting the continuity and density of the nitrided layer. This method can avoid premature mold failure caused by excessive local hardness, improve the consistency of hardness in all areas, ensure that the mold is subjected to uniform stress when subjected to impact loads, extend its service life, and ensure the accuracy of process adjustment by proportional control of flow rate adjustment, avoiding excessive adjustment range that leads to low hardness.

[0069] It should be noted that the second preset threshold is used to determine whether the surface hardness of the nitrided layer is too high, thereby deciding whether to reduce the nitrogen flow rate to adjust the nitriding rate. Its setting is mainly based on the following factors: Performance requirements: Die-casting molds typically require a surface hardness between 600-650 HV; excessive hardness increases brittleness and easily leads to cracking. Material brittleness limit: Different steels have different brittle transition hardnesses, and this limit must be avoided. Structural risk: Edges, thin-walled areas are prone to embrittlement due to excessive nitriding, requiring the setting of a safety threshold.

[0070] For example, in complex cavity areas, where the cavity structure is complex and stress concentration is easy, the hardness should not be too high to avoid cracking during service. Therefore, the second preset threshold is set to 650~660HV. In deep hole areas, heat dissipation is slow and nitriding is prone to be too deep. The hardness threshold should be appropriately increased to compensate for insufficient diffusion. Therefore, the second preset threshold is set to 660~670HV. In corner stress concentration areas, nitriding is prone to be over-concentrated. A lower threshold is set to suppress the formation of brittle layers. Therefore, the second preset threshold is set to 640~650HV. In planar areas, heat dissipation is uniform, and the hardness target can be appropriately increased to improve wear resistance. Therefore, the preset threshold is set to 670~680HV.

[0071] Furthermore, the online hardness testing method is as follows: In complex cavity areas, five testing points are evenly distributed along the cavity contour, including the bottom, sidewalls, and corners. In deep hole areas, one testing point is set at the hole opening, halfway down the hole, and the bottom. In corner stress concentration areas and planar areas, three evenly distributed testing points are set each. During testing, the sensor probe is perpendicular to the mold surface, with a contact pressure of 0.5N. Outliers are removed from the test data, and the average value is taken. Flow rate adjustment is automatically executed by the PLC system, reducing the nitrogen flow rate while simultaneously fine-tuning the hydrogen flow rate to maintain the total flow rate between 0.8 and 1.2 m³. 3 / h.

[0072] In one embodiment, the protective atmosphere is either hydrogen or nitrogen. After nitriding, the mold surface temperature is high, making it prone to oxidation with oxygen in the air, generating oxides such as Fe3O4 and Fe2O3, which damage the nitrided layer structure. Hydrogen, as a reducing atmosphere, can react with the oxide film on the mold surface, preventing oxidation while also promoting the conversion of residual unstable nitrides in the nitrided layer. Nitrogen, as an inert atmosphere, isolates the mold from air, preventing oxygen from contacting the mold surface, thus providing simple protection. This helps prevent oxidation failure of the nitrided layer during cooling, ensuring the integrity and density of the nitrided layer, while protecting the surface finish of the mold, reducing subsequent grinding processes, and lowering production costs.

[0073] Specifically, if the mold material contains alloying elements such as chromium and molybdenum, a hydrogen atmosphere should be preferred, ensuring that the oxygen content in the furnace is ≤0.1% and that an explosion-proof device is installed. When using a nitrogen atmosphere, the atmosphere should be introduced immediately after the nitriding treatment is completed, switching to a protective atmosphere until the mold cools to the furnace exit temperature, which helps reduce production costs.

[0074] In one embodiment, step S20 involves placing the pretreated mold in a nitriding device, introducing nitrogen and hydrogen gas into the nitriding device at a volume ratio of 4-5:1, and then heating the furnace body of the nitriding device to a first temperature range and maintaining that temperature. The nitrogen purity is ≥99.99%, the hydrogen purity is ≥99.95%, and the total flow rate of the nitrogen-hydrogen mixed gas is 0.8-1.2 m³ / h. 3 / h.

[0075] High-purity nitrogen and hydrogen prevent impurities such as gas, moisture, and carbon dioxide from entering the furnace. Oxygen reacts with the mold surface to form an oxide film, hindering nitrogen atom penetration. Moisture can cause pinholes and porosity in the nitrided layer. Carbon dioxide reacts with hydrogen to form carbon monoxide, affecting the stability of the reaction atmosphere. Total flow rate: 0.8~1.2 m³ / h 3The design of the flow rate ( / h) ensures sufficient gas circulation within the furnace, promptly removing reaction byproducts such as excess hydrogen produced by ammonia decomposition, while maintaining stable furnace pressure to prevent energy waste or pressure runaway due to excessive flow. This improves the purity and efficiency of the nitriding reaction, reduces defects such as oxidation points and loose nitriding layers caused by impurities, and enhances the density of the nitriding layer. The stable gas flow rate also ensures precise control of process parameters, reducing the risk of process failure due to gas fluctuations.

[0076] Furthermore, the protective gases are supplied as follows: nitrogen is treated by a molecular sieve dryer to achieve a moisture content ≤10ppm; hydrogen is treated by a deoxygenation device to achieve an oxygen content ≤5ppm. A mass flow controller is used to regulate the nitrogen and hydrogen gas flow rates, and the total flow rate is displayed in real time via a flow meter. Data is recorded hourly to ensure the flow rate is maintained between 0.8 and 1.2 m³ / h. 3 / h, fluctuation not exceeding ±0.05m 3 / h.

[0077] In one embodiment, step S50: After the nitriding treatment is completed, the mold is cooled to the oven exit temperature under a protective atmosphere. The cooling method is as follows:

[0078] The temperature was lowered to 250℃ at a rate of 4~6℃ / min and held for 1 hour; then lowered to below 100℃ at a rate of 8~10℃ / min, maintaining a protective atmosphere with a nitrogen-hydrogen volume ratio of 1:1 throughout the process.

[0079] Staged cooling avoids thermal stress in the mold caused by excessively rapid cooling. The first stage cools to 250℃ at a rate of 4-6℃ / min. This rate promotes further diffusion of nitrogen atoms in the nitrided layer, resulting in a more uniform microstructure, while avoiding stress concentration caused by excessive temperature differences. Holding at 250℃ for 1 hour eliminates residual stress generated during cooling and stabilizes the nitrided layer microstructure. The second stage cools to below 100℃ at a rate of 8-10℃ / min. At this temperature, the mold is relatively low, and rapid cooling does not generate significant stress. Furthermore, removing the mold from the oven below 100℃ prevents moisture from condensing on the mold surface at room temperature. Maintaining a 1:1 nitrogen-hydrogen ratio throughout the process continuously protects the mold surface and prevents oxidation during cooling. This minimizes mold deformation and residual stress during cooling, reducing deformation and preventing assembly difficulties or dimensional inaccuracies caused by deformation. Simultaneously, it protects the integrity of the nitrided layer, ensuring that the hardness and thickness of the nitrided layer meet target requirements after cooling.

[0080] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0081] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for controlling the nitrided penetration layer of a die casting mold, characterized by, The method for regulating the nitriding permeation layer of the die-casting mold comprises the following steps: The die-casting mold is pretreated and partitioned; The pretreated mold is placed in a nitriding device, nitrogen and hydrogen are introduced into the nitriding device, the volume ratio of the nitrogen to the hydrogen is 4-5:1, the nitriding device is heated to a first temperature interval and then is kept warm; The nitriding reaction rate in the nitriding device is monitored and calculated in real time, wherein, when the reaction rate reaches a first preset threshold, the volume ratio of the nitrogen to the hydrogen is adjusted to 2.5-3.5:1, a partitioned temperature rising program is started according to the partition of the die-casting mold, and the different areas of the die-casting mold are subjected to partitioned temperature rising; The volume ratio of the nitrogen to the hydrogen is adjusted to 1:1, and the temperature of each area set in the partitioned temperature rising program is maintained, and the process parameters in this stage are maintained until the thickness and hardness of the nitriding layer reach target values; After the nitriding treatment is completed, the mold is cooled to a furnace discharge temperature under a protective atmosphere.

2. The method of claim 1, wherein the method is characterized by: The real-time monitoring and calculation of the nitriding reaction rate comprises: The pressure change rate ΔP / Δt in the nitriding device and / or the ammonia decomposition rate α in the furnace gas are monitored; Based on the pressure change rate and / or the ammonia decomposition rate, the reaction rate R is calculated through a pre-established reaction kinetics model, wherein R=k1*(ΔP / Δt) / P0+k2*α, the pressure change rate ΔP / Δt is in Pa / s, P0 is a reference pressure in Pa, k1 and k2 are weight coefficients, and k1+k2=1, and the above calculation adopts dimensionless processing.

3. The method of claim 1, wherein the method is characterized by: The step of pretreating the die-casting mold specifically comprises: The die-casting mold is surface cleaned, and is wiped with anhydrous ethanol after ultrasonic cleaning; After cleaning, the die-casting mold is subjected to stress relief annealing treatment, the annealing temperature is 600-650°C, and the mold is cooled to room temperature after being kept warm for 0.5-1.5 h.

4. The method of claim 1, wherein the method is characterized by: The partition of the die-casting mold comprises a complex cavity area, a deep hole area, an edge and corner stress concentration area, and a plane area, and in the partitioned temperature rising program, the temperature setting for partitioned temperature rising is as follows: the complex cavity area: 490-500°C; the deep hole area: 430-460°C; the edge and corner stress concentration area: 480-490°C; and the plane area: 500-510°C.

5. The method of claim 1, wherein the method is characterized by: In the step of placing the pretreated mold in the nitriding device, introducing nitrogen and hydrogen into the nitriding device, and heating the nitriding device to a first temperature interval and then keeping warm, the first temperature interval is 340-360°C, the maintaining time is 1.5-2 h, and the furnace chamber pressure is maintained at 0.12-0.15 MPa.

6. The method of claim 1, wherein the method is characterized by: In the step of adjusting the volume ratio of the nitrogen to the hydrogen to 1:1, maintaining the temperature of each area set in the partitioned temperature rising program, and maintaining the process parameters in this stage until the thickness and hardness of the nitriding layer reach target values, specifically comprising: The volume ratio of the nitrogen to the hydrogen is adjusted to 1:1, and the temperature of each area set in the partitioned temperature rising program is maintained; A feedback signal from an online hardness monitoring system is received, and when the monitored surface hardness value exceeds a second preset threshold, the nitrogen flow is reduced in proportion; After the thickness and hardness of the nitriding layer reach target values, the nitriding treatment is completed.

7. The method of claim 6, wherein the method is characterized by: Step: receiving feedback signals from the online hardness monitoring system, and proportionally reducing the nitrogen flow rate when the monitored surface hardness value exceeds a second preset threshold value, the hardness detection being multi-point detection of at least 3 detection points per region, the second preset threshold value being 650-680 HV, and the nitrogen proportion being reduced by 5%-10% when the hardness is too high.

8. The method of claim 1, wherein the method is characterized by: The protective atmosphere is a hydrogen or nitrogen atmosphere.

9. The method of claim 1, wherein the method is characterized by: Step: Put the pre-processed mold into the nitriding equipment, pass nitrogen and hydrogen into the nitriding equipment, the volume ratio of the nitrogen and the hydrogen is 4-5:1, and heat the furnace body of the nitriding equipment to the first temperature interval and then keep warm, the purity of the nitrogen is ≥99.99%, the purity of the hydrogen is ≥99.95%, the total flow of the nitrogen-hydrogen mixed gas is 0.8-1.2 m 3 / h. Step: After the first temperature interval is reached, the furnace body of the nitriding equipment is heated to the second temperature interval, and then kept warm, the total flow of the nitrogen-hydrogen mixed gas is 0.8-1.2 m 3 / h. Step: After the second temperature interval is reached, the furnace body of the nitriding equipment is heated to the third temperature interval, and then kept warm, the total flow of the nitrogen-hydrogen mixed gas is 0.8-1.2 m 3 / h. Step: After the third temperature interval is reached, the furnace body of the nitriding equipment is heated 10. The method for controlling the nitriding penetration layer of a die-casting mold according to claim 1, characterized in that, Step: after the nitriding treatment is completed, the mold is cooled to the furnace discharge temperature under a protective atmosphere, and the cooling mode is: decreased to 250 DEG C at a rate of 4-6 DEG C / min, and held for 1 h; decreased to below 100 DEG C at a rate of 8-10 DEG C / min, and a protective atmosphere of a nitrogen-hydrogen volume ratio of 1:1 is maintained throughout the process.

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