Multi-zone precise temperature control heat treatment equipment and heat treatment method

Abstract

The heat treatment equipment comprises an inner furnace body, an outer furnace body, a vacuumizing component, a heating temperature control component, a cooling temperature control component, a heat exchange component, a fan component and a spray cooling component, all the parts are specifically arranged, particularly, the heating parts which are arranged in the heating stage and the heat preservation stage and are arranged for the shaft elements, independent control over all the areas and independent control over all the areas of the spray nozzle are adopted, and the specific arrangement mode in the heat treatment process is combined; particularly, high-pressure inert gas quenching and atomized cooling liquid composite cooling are combined, and independent control of a spray nozzle is matched, so that more uniform and reliable heating, heat preservation and quenching of the shaft element are realized, and the fatigue life and the dimensional stability of the shaft element are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment of metallic materials, and particularly relates to a heat treatment device and method with multi-zone precise temperature control. Background Technology

[0002] In the processing of metallic materials, heat treatment is an important process used to improve the microstructure and properties of metallic materials, such as increasing strength, hardness, toughness, and wear resistance. Traditional heat treatment methods have drawbacks, including high energy consumption leading to increased production costs; difficulty in achieving uniform heat treatment for complex or large-sized metal workpieces, thus affecting product quality consistency; and difficulty in precisely controlling heating and cooling rates, failing to meet the stringent requirements of some special metallic materials for heat treatment processes.

[0003] In numerous industrial fields such as machinery manufacturing, aerospace, and rail transportation, shaft components are core parts for transmitting motion and power. Their performance largely determines the operational accuracy, reliability, and service life of the entire mechanical equipment. Shaft components generally refer to components whose length is much larger than their circumferential dimension. Shaft components typically have large dimensions and long lengths, and extremely stringent requirements are placed on their mechanical properties. They generally require heat treatment such as quenching and tempering to improve their internal structure and regulate their mechanical properties. The precision of the heat treatment, especially the temperature control accuracy during the heating, holding, and cooling stages, directly affects the final quality and safety of the shaft component. However, due to the size and shape of shaft components, current heat treatment methods generally employ trolley-type resistance furnaces or gas-fired furnaces. Because of the large size, long length, and complex shape of shaft components, the temperature field distribution within the furnace is easily affected by factors such as the layout of heating elements, furnace cavity structure, and workpiece placement, resulting in significant differences in the heating rate of different regions of the component (such as the end and middle, surface and core). During the heating process, the surface layer of shaft-like components often reaches the target temperature first, while the core temperature lags significantly. This temperature gradient generates substantial thermal stress within the workpiece. Furthermore, some heating equipment lacks segmented temperature control mechanisms for long shaft-like components, failing to adjust heating power based on the thermal conductivity characteristics of different parts of the component, further exacerbating temperature control deviations during the heating phase. During the holding phase, due to the long length but relatively small circumference of shaft-like components, achieving a homogeneous transformation of their internal structure requires extremely high temperature stability. However, existing heat treatment equipment does not provide segmented, precise control during the holding process, easily leading to uneven temperature fluctuations at the ends and in the middle. For long shaft-like components exceeding 3 meters in length, existing temperature measurement methods (such as single-point thermocouple measurement) can only reflect localized temperatures and cannot monitor the temperature distribution across the entire length of the component in real time. This makes it difficult to accurately determine whether the entire workpiece has reached a uniform holding state, thus affecting the quality of the microstructure transformation and causing uneven mechanical properties of the component. During the cooling stage, existing technologies for cooling shaft components mainly include oil cooling, water cooling, air cooling, and isothermal cooling. However, existing cooling equipment generally suffers from low temperature control accuracy and poor cooling uniformity. This can easily lead to significant differences in cooling rates between the two ends and the middle of the shaft component, as well as between the surface and the core, resulting in large internal stresses and causing technical problems such as workpiece bending and warping.

[0004] The book "Vacuum Heat Treatment Technology" (written by Wang Zhongcheng, Chemical Industry Press, October 2015) discloses a vacuum quenching furnace in Chapter 3, Section 3.3 of Vacuum Heat Treatment Equipment. However, it only generally discloses that heating, heat preservation and quenching can be carried out through a vacuum heating furnace, but does not provide specific implementation details.

[0005] Chinese invention patent publication CN114657362A discloses a vacuum local heat treatment device and method for shaft-type workpieces, which achieves local heating and cooling operations on shaft-type components by setting up local heating and cooling components; however, this technical solution cannot perform specific and precise temperature control heating and efficient quenching of the entire shaft-type component.

[0006] In summary, current metal heat treatment technologies for shaft components suffer from problems such as insufficient temperature control accuracy, poor uniformity, and weak adaptability in the three core stages of heating, holding, and cooling. These issues make it difficult to meet the production demands of modern industry for high-precision, high-performance shaft components. Therefore, developing a metal heat treatment technology solution that can achieve precise temperature control for heating, holding, and cooling of shaft components has become an urgent technical problem to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a highly efficient heat treatment method and equipment for metal materials, which can reduce energy consumption, achieve uniform heat treatment of metal workpieces, accurately control heating and cooling rates, and improve the performance and product quality of metal materials.

[0008] Specifically, this is achieved through the following equipment setup and process flow: A heat treatment device with multi-zone precise temperature control; including an inner furnace body, an outer furnace body, a vacuum pumping component, a heating temperature control component, a cooling temperature control component, a heat exchange component, a fan component, and a spray cooling component.

[0009] The inner furnace body is integrally disposed inside the outer furnace body. The inner furnace body is used to bear, heat, keep warm and cool the heat-treated workpieces, and includes the inner furnace shell and the inner furnace door.

[0010] The outer furnace body is used to support the inner furnace body, heat exchange components and fan components, and includes an outer furnace shell and an outer furnace door, with the inner furnace door and the outer furnace door facing each other and matched in position.

[0011] The vacuuming component is used to perform vacuuming operations on the inner furnace body, and includes a vacuum tube and a vacuum pump. The port of the vacuum tube is located on the inner furnace shell.

[0012] The heating and temperature control components include a radiant heating component, a temperature monitoring component, and a temperature control component. Both the radiant heating component and the temperature monitoring component are located inside the inner furnace shell. The radiant heating component is used to radiate heat onto the workpiece inside the inner furnace shell. The temperature monitoring component is used to detect the temperature of the workpiece in real time and transmit the temperature result to the temperature control component. The temperature control component is used to control the radiant heating component to achieve the specific heating temperature of the workpiece. Three sets of radiant heating components are provided, respectively located in the front, middle, and rear sections of the inner furnace shell. The temperature control component independently controls the temperature of each of the three sets of radiant heating components. Three sets of temperature monitoring components are also provided, respectively located in the front, middle, and rear sections of the inner furnace shell.

[0013] The cooling and temperature control component includes a gas injection pipe; the injection port of the gas injection pipe is located on the outer furnace shell.

[0014] The fan components include a cooling fan.

[0015] The heat exchange component includes a water inlet, a water outlet, and a heat exchange tube. The water inlet is located at the bottom of the outer furnace shell, the water outlet is located at the top of the outer furnace shell, and the heat exchange tube is located between the water inlet and the water outlet inside the outer furnace shell. The heat exchange tube is located between the cooling fan and the inner furnace body, and is located on the outside of the inner furnace body on the side away from the inner furnace door.

[0016] The spray cooling component includes a spray nozzle, which is disposed on the inner periphery of the inner furnace shell. Multiple sets of spray nozzles are disposed in the front, middle and rear sections of the inner furnace shell.

[0017] Preferably, the cooling and temperature control component further includes a high-pressure gas storage tank and a gas flow control valve. The high-pressure gas storage tank is used to store high-pressure inert gas, the gas flow control valve is used to regulate the flow and pressure of the inert gas, and the gas injection pipe is used to introduce the high-pressure gas in the high-pressure gas storage tank into the outer furnace body. The high-pressure gas storage tank and the gas flow control valve are located outside the outer furnace shell. One end of the gas injection pipe is connected to the high-pressure gas storage tank, and the other end is connected to the inside of the outer furnace shell through an injection port. The gas flow control valve is installed on the gas injection pipe.

[0018] Preferably, the spray cooling component further includes a coolant storage tank, a coolant delivery pipe, and a spray pump. The coolant storage tank is used to store coolant, the coolant delivery pipe connects the coolant storage tank and the spray nozzle, and a spray pump is installed on the coolant delivery pipe to apply pressure to the coolant in the coolant delivery pipe. The spray nozzle is used to atomize the delivered coolant and spray it toward the workpiece to achieve spray cooling.

[0019] Preferably, the temperature monitoring component is a thermocouple.

[0020] Preferably, the spray nozzles are provided in three sets.

[0021] Preferably, the radiant heating component is a graphite heating tube.

[0022] Preferably, the heat treatment equipment also includes a control device, which is electrically connected to the vacuum pumping unit, heating temperature control unit, cooling temperature control unit, heat exchange unit, fan unit, and spray cooling unit, and is used to control the entire heat treatment process. The control device can automatically adjust the operating status of each component based on the set heat treatment process parameters and data transmitted from various sensors, achieving precise control of parameters such as heating rate, holding time, and cooling rate, and monitoring and displaying various parameters during the heat treatment process in real time.

[0023] Preferably, the heating and temperature control component further includes a transformer and a power regulator, which are connected to the radiant heating component to provide the electrical energy required for radiant heating. The power of the transformer can be adjusted via the control device and the power regulator, thereby regulating the current flowing into the radiant heating component and achieving precise control of the heating rate.

[0024] A heat treatment method for precise temperature control in multiple zones for shaft-type workpieces includes the following steps: (1) Pretreatment: The shaft workpiece is cleaned and degreased to remove surface oil and impurities to ensure the heat treatment effect.

[0025] (2) Zoned heating: The pre-treated shaft workpiece is placed horizontally into the inner furnace of the heat treatment equipment, the inner furnace is sealed, and a vacuum is drawn into the inner furnace. After the vacuum degree in the inner furnace reaches 0.5~2Pa, current is simultaneously supplied to the three sets of radiant heating components set in the front, middle and rear sections of the inner furnace shell. The front, middle and rear sections of the shaft workpiece are vacuum radiantly heated by the heat radiation of the radiant heating components. The heating rate is controlled by controlling the current to ≤10℃ / min. During the heating process, the front, middle and rear sections of the shaft workpiece are monitored in real time by the temperature monitoring component. When it is found that the heating rate of any section is greater than or less than the set heating rate, the current of that section is adjusted by the temperature control component to adjust the heating heat so that the heating rate of that section meets the set heating rate. The heating is stopped when the temperature of the shaft workpiece rises to 1025~1035℃.

[0026] (3) Heat preservation: heat preservation at 1025~1035℃ for 55~65min; real-time temperature monitoring of the front, middle and rear sections of the shaft workpiece is performed by the temperature monitoring component. When the temperature of any section is found to be lower than the lower limit threshold, the current supplied to the radiation heating component set in that section is increased by the temperature control component to reheat the shaft workpiece in that section. When the temperature monitoring component detects that the temperature of any end is higher than the upper limit threshold, the high-frequency alternating current supplied to the induction heating coil of that section is reduced to keep the heat preservation temperature between the upper and lower limit thresholds. After heat preservation, the vacuum is broken. The lower limit threshold is 3℃ lower than the heat preservation temperature, and the upper limit threshold is 3℃ higher than the heat preservation temperature.

[0027] (4) Quenching: First, the shaft workpiece is quenched by circulating high-pressure inert gas. The rapid flow of high-pressure inert gas removes the heat from the surface of the workpiece. When the temperature monitoring component detects that any section of the front, middle and rear of the shaft workpiece is below 580~620℃, the spray nozzle of that section is turned on. Coolant is sprayed onto that section of the shaft workpiece through the spray nozzle for spray cooling. When the temperature of any section of the shaft workpiece drops to 100~130℃, the spray cooling of that section is stopped. All spray nozzles are stopped when the temperature of all sections drops to 100~130℃.

[0028] (5) Take out the shaft workpiece after the quenching treatment in step (4) to obtain the shaft workpiece after quenching heat treatment.

[0029] Preferably, the heat treatment method is performed using the aforementioned heat treatment equipment.

[0030] Preferably, the following steps are included after step (5): (6) Tempering treatment: The shaft workpieces taken out in step (5) are placed into the tempering furnace, heated to 175~185℃, and held for 160~195min. Then the tempering furnace is stopped, and the shaft workpieces are taken out of the furnace and air-cooled to room temperature to obtain the heat-treated shaft workpieces.

[0031] Preferably, in step (2), the heating power is set to 140~160W (e.g., the power of a transformer) (frequency controlled by PID) to precisely control the heating speed.

[0032] Preferably, the heating rate in step (2) is 3~10℃ / min.

[0033] Preferably, in step (4), the pressure of the high-pressure inert gas is 1~3 bar, and the inert gas flow rate is 0.1~0.5 m / s. 3 / min.

[0034] By controlling the pressure and flow rate of the high-pressure gas, as well as the spray volume and spray time of the spray coolant, the cooling rate can be precisely controlled, preventing cracks or deformation of metal workpieces during the cooling process.

[0035] Preferably, in step (4), the injection velocity of the coolant is 0.05~0.15m. 3 / min, spraying time is 6~12min.

[0036] Preferably, in step (4), the atomization pressure of the coolant sprayed by the spray nozzle in the front and rear sections of the inner furnace shell is 0.5~0.8MPa; and the atomization pressure in the middle section of the inner furnace shell is 0.3~0.6MPa.

[0037] Preferably, the length of the front section of the inner furnace body is L1, the length of the middle section is L2, and the length of the rear section is L3, satisfying L1:L2:L3=(0.9~1.1):(1.2~1.8):(0.9~1.1).

[0038] Preferably, the shaft workpiece is made of 4Cr13 steel, 3Cr13 steel, 40Cr13 steel, 9Cr18 steel, 60CrMo3-1 or 2Cr13 steel.

[0039] The shaft-type workpieces described in this invention are not limited to straight shaft-type workpieces, but refer to workpieces whose length dimension is significantly larger than their circumferential dimension.

[0040] The technical advantages of this invention are as follows: 1. This invention achieves efficient radiant heating through graphite heating tubes during the heating stage by combining radiant heating technology with a vacuum heating environment (achieving pollution-free heating by eliminating oxidizing gases and avoiding oxidation and decarburization of metal workpieces during heating). More importantly, it incorporates segmented and zoned temperature control technology (independently configuring graphite heating tubes and closed-loop temperature control systems for the front, middle, and rear sections of shaft components). This allows for rapid surface heating of shaft components, increasing heating efficiency by more than 40% compared to traditional methods. Crucially, it implements zoned temperature control tailored to the characteristics of shaft components. If a section deviates from the heating rate, the temperature of that section can be adjusted individually. The temperature of each section is adjusted individually based on the current, ensuring stable heating for all sections. Furthermore, since the middle section of shaft components is prone to heat accumulation due to its location, a slightly larger area is set for this section, while smaller areas are set for the ends to achieve focused heating. Gradient power compensation is implemented at the connection points between the middle section and the ends, ensuring uniform temperature throughout the entire length with a temperature difference ≤5℃, thus avoiding thermal stress deformation. Simultaneously, during the heat preservation stage, the vacuum environment effectively suppresses heat radiation loss. Individual heating is achieved by independently adjusting the current of the graphite heating tubes in each zone based on real-time temperature measurements, ensuring that the overall workpiece temperature fluctuation during the heat preservation stage is controlled within ±2℃.

[0041] 2. This invention achieves precise cooling control during the heat treatment of shaft components through the synergistic effect of high-pressure inert gas quenching and spray-dried coolant composite cooling technology, combined with a segmented and zoned spray cooling strategy. In the high-pressure inert gas quenching stage, high-pressure inert gas is circulated as the cooling medium. With the placement of water-cooled heat exchange tubes and the cooling fan, the high-pressure inert gas, after its previous heat exchange with the shaft component, is recirculated back to the shaft component through contact with the heat exchange tubes. This forms a high-speed airflow layer based on gas dynamics principles, creating a uniform cooling boundary layer on the workpiece surface. The first stage utilizes the low thermal conductivity of gas in the high-temperature zone to achieve relatively slow initial cooling (cooling rate controlled at around 12~18℃ / min), effectively suppressing the temperature difference between the workpiece surface and core, and avoiding internal stress concentration caused by excessive rapid cooling. When the workpiece temperature drops to the medium-temperature zone (e.g., around 600℃), the atomization cooling system is activated for the spray-cooling stage. High-pressure nozzles atomize the coolant into micro-droplets with a particle size ≤50μm. Rapid cooling is achieved by utilizing the evaporative heat absorption effect of these droplets on the workpiece surface (cooling rate increased to 45~55℃ / min). In this stage, by adjusting the atomization pressure (0.3~0.8MPa) and the spray nozzles set in three zones around the workpiece, the uniformity of coolant coverage in the front, middle, and rear sections of the shaft component is ensured. Simultaneously, to address the axial heat capacity differences of the shaft component, a three-zone independent cooling strategy is adopted. This achieves high-frequency focused spraying in the front and rear sections (journal area) of the shaft component. By setting smaller areas at both ends and relatively concentrated spraying, the atomization pressure (0.5~0.8MPa) is adjusted to achieve localized rapid cooling, compensating for uneven heat dissipation caused by the complex structure in these areas. Meanwhile, in the middle section (shaft body),... The cooling system employs uniform spraying (in a relatively large area), controlling the atomization pressure (0.3~0.6MPa) through a ring-shaped nozzle array to ensure full circumferential coverage of the coolant and maintain the stability of the cooling rate (fluctuation ≤±10%). This ensures that the temperature difference along the entire length of the workpiece during quenching is ≤5℃, preventing deformation caused by uneven cooling. Simultaneously, the segmented synergistic effect of high-pressure gas and spraying controls the temperature difference between the workpiece surface and core to ≤50℃, effectively suppressing crack initiation. Furthermore, precise control of the cooling rate ensures uniform hardness distribution of the workpiece (HV fluctuation ≤±15), significantly improving fatigue life and dimensional stability.

[0042] 3. This invention achieves temperature compensation and control by incorporating a temperature monitoring component. Based on the real-time workpiece temperature transmitted from the component, the induction heating coils during the heating and holding stages are controlled. During the quenching stage, the nozzle atomization pressure can be precisely adjusted according to the real-time workpiece temperature, improving production efficiency and product quality stability. Furthermore, this invention integrates heating, holding, and quenching into a single device, resulting in a compact structure, small footprint, and ease of installation and maintenance. It is suitable for heat treatment of similar metal materials, including shaft components, and has broad application prospects. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the internal structure of a multi-zone precision temperature control heat treatment device according to one embodiment of the present invention.

[0044] Figure 2 This is a side view schematic diagram of the distribution structure of the heating components and spray nozzles inside the furnace body according to one embodiment of the present invention.

[0045] Figure 3 This is a schematic diagram of hardness testing and hardness results according to one embodiment of the present invention.

[0046] Figure 4 This is a schematic diagram showing the hardness test and hardness results of the comparative implementation method.

[0047] Figure 5 This is a microscopic metallographic image of different parts of an embodiment of the present invention.

[0048] Figure 6 Microscopic metallographic images of different parts of the implementation method are shown for comparison.

[0049] Wherein: 101-Inner furnace shell; 111-Graphite furnace bed; 102-Inner furnace door; 103-Radiant heating components and spray cooling components; 131-Graphite heating tube; 132-Spray nozzle; 133-Ceramic pad; 201-Outer furnace shell; 202-Outer furnace door; 203-Gas injection pipe; 301-Cooling fan; 401-Water inlet; 402-Heat exchange tube; 403-Water outlet; 501-Vacuum tube; A - The cooling water discharged; Figure 1 The direction of the middle arrow indicates the flow direction of the high-pressure inert gas. Detailed Implementation

[0050] The technical solution of the present invention will be further described in conjunction with the embodiments: The device used in this embodiment is specifically as follows: like Figure 1 and Figure 2The heat treatment equipment shown is a multi-zone precise temperature control device according to a specific embodiment, including an inner furnace body, an outer furnace body, a vacuum pumping component, a heating temperature control component, a cooling temperature control component, a heat exchange component, a fan component, and a spray cooling component.

[0051] like Figure 1 As shown, the inner furnace body is integrally disposed inside the outer furnace body. The inner furnace body is used to bear, heat, keep warm and cool the heat-treated workpiece, and includes an inner furnace shell and an inner furnace door.

[0052] The outer furnace body is used to support the inner furnace body, heat exchange components and fan components, and includes an outer furnace shell and an outer furnace door, with the inner furnace door and the outer furnace door facing each other and matched in position.

[0053] The vacuuming component is used to perform vacuuming operations on the inner furnace body, and includes a vacuum tube and a vacuum pump. The port of the vacuum tube is located on the inner furnace shell.

[0054] like Figure 2 As shown, the heating and temperature control component includes a graphite heating tube, a temperature monitoring component, and a temperature control component. Both the graphite heating tube and the temperature monitoring component (thermocouple) are located inside the inner furnace shell. The graphite heating tube is used to radiate heat to the workpiece inside the inner furnace. The thermocouple is used to detect the temperature of the workpiece in real time and transmit the temperature result to the temperature control component. The temperature control component is used to control the graphite heating tube to achieve heating of the workpiece at a specific temperature. Figure 1 As shown, the graphite heating tubes are arranged in three sets, respectively located in the front, middle and rear sections of the inner furnace shell. The temperature control components independently control the temperature of the graphite heating tubes. The temperature monitoring components are also arranged in three sets, respectively located in the front, middle and rear sections of the inner furnace shell.

[0055] like Figure 1 As shown, the cooling and temperature control component includes a gas injection pipe; the injection port of the gas injection pipe is located on the outer furnace shell.

[0056] like Figure 1 As shown, the fan component includes a cooling fan.

[0057] like Figure 1 As shown, the heat exchange component includes a water inlet, a water outlet, and a heat exchange tube. The water inlet is located at the bottom of the outer furnace shell, the water outlet is located at the top of the outer furnace shell, and the heat exchange tube is located between the water inlet and the water outlet inside the outer furnace shell, and is also located between the cooling fan and the inner furnace body. Figure 1 As shown, this positioning allows for the formation of a shape similar to the one shown after the high-pressure inert gas is injected. Figure 1 The circulation shown is such that the airflow is combined with the blowing of the cooling fan at the heat exchange tubes to flow upwards and downwards to the outside, thus forming a circulation, and at this point, the heat exchange tubes can be fully exchanged and cooled.

[0058] like Figure 2 As shown, the spray cooling component includes a spray nozzle, which is disposed on the inner periphery of the inner furnace shell and combined with... Figure 1 The spray nozzles shown are arranged in three sets, located in the front, middle and rear sections of the inner furnace shell.

[0059] In this embodiment, the cooling and temperature control component further includes a high-pressure gas storage tank and a gas flow control valve. The high-pressure gas storage tank is used to store high-pressure inert gas, and the gas flow control valve is used to regulate the flow and pressure of the inert gas. The gas injection pipe is used to introduce the high-pressure gas in the high-pressure gas storage tank into the outer furnace body. The high-pressure gas storage tank and the gas flow control valve are located outside the outer furnace shell. One end of the gas injection pipe is connected to the high-pressure gas storage tank, and the other end is connected to the inside of the outer furnace shell through an injection port. The gas flow control valve is installed on the gas injection pipe.

[0060] In this embodiment, the spray cooling component further includes a coolant storage tank, a coolant delivery pipe, and a spray pump. The coolant storage tank is used to store coolant. The coolant delivery pipe connects the coolant storage tank and the spray nozzle. A spray pump is installed on the coolant delivery pipe to apply pressure to the coolant in the coolant delivery pipe. The spray nozzle (atomizing nozzle) is used to atomize the delivered coolant and spray it toward the workpiece to achieve spray cooling.

[0061] In this embodiment, the heat treatment equipment also includes a control device. The control device is electrically connected to the vacuum pumping component, heating temperature control component, cooling temperature control component, heat exchange component, fan component, and spray cooling component, and is used to control the entire heat treatment process. The control device can automatically adjust the operating status of each component based on the set heat treatment process parameters and data transmitted from various sensors, achieving precise control of parameters such as heating rate, holding time, and cooling rate, and monitoring and displaying various parameters during the heat treatment process in real time.

[0062] In this embodiment, the heating and temperature control component further includes a transformer and a power regulator, which are connected to the radiant heating component to provide the electrical energy required for radiant heating. The power of the transformer can be adjusted via the control device and the power regulator, thereby regulating the current flowing into the radiant heating component and achieving precise control of the heating rate.

[0063] Example 1 A heat treatment method for shaft-type workpieces with multi-zone precise temperature control, implemented in a heat treatment workshop using the above-mentioned apparatus, wherein the shaft-type workpieces in this embodiment are made of 4Cr13 martensitic stainless steel; includes the following steps: (1) Pretreatment: The shaft workpiece is cleaned and degreased to remove surface oil and impurities to ensure the heat treatment effect. Then the shaft workpiece is placed on a graphite furnace bed and ceramic pad.

[0064] (2) Zoned heating: The pre-treated shaft workpiece is placed horizontally into the inner furnace of the heat treatment equipment, the inner furnace is sealed, and the inner furnace is evacuated. The evacuation is stopped when the vacuum degree in the inner furnace reaches 1 Pa. At the same time, high-frequency alternating current is passed into the three sets of induction heating coils set in the front, middle and rear sections of the inner furnace cavity. The length of the front section L1 in the inner furnace cavity is 1 m, the length of the middle section L2 is 1.25 m, and the length of the rear section L3 is 0.95 m, which meets the requirement of L1:L2:L3=(0.9~1.1):(1.2~1.8):(0.9~1.1). The induction heating power supply is set to 150W, and the heating rate is precisely controlled. Vacuum induction heating is applied to the front, middle, and rear sections of the shaft-like workpiece, with a heating rate of 8℃ / min for each section. During heating, temperature monitoring components monitor the front, middle, and rear sections of the shaft-like workpiece in real time. If the heating rate of any section is found to be greater than or less than the set heating rate (the threshold is the standard heating rate ±1℃, i.e., if it is lower than 7℃ / min or higher than 9℃ / min, the current is adjusted), the current of that section is adjusted via the temperature control component to regulate the heating heat, ensuring that the heating rate of that section meets the set heating rate. Heating is stopped once the temperature of the shaft-like workpiece reaches 1030℃. During heating, the current is adjusted by regulating the power, precisely controlling the heating rate so that the metal workpiece reaches the predetermined temperature in a short time, reducing energy consumption.

[0065] (3) Heat preservation: The temperature of the front, middle and rear sections of the shaft workpiece is monitored in real time by temperature monitoring components. When the temperature of any section is found to be lower than the lower limit threshold (1027℃), the current flowing into the graphite heating tube in that section is increased by adjusting the power regulator to reheat that section of the shaft workpiece. The power is set to 150W. After the upper limit threshold (1033℃) is reached, the current flowing into the graphite heating tube in that section is reduced. The current is adjusted in real time to ensure that the heat preservation temperature is around 1030℃. This operation is continued for 60 minutes to complete the heat preservation operation. This ensures that the internal structure of the metal is fully homogenized. Then the vacuum is broken.

[0066] (4) Quenching: First, the shaft workpiece is quenched by circulating high-pressure inert gas, and the cooling fan is turned on simultaneously. The specific circulation direction is as follows: Figure 1As shown, after high-pressure inert gas is introduced through the gas injection pipe, the high-pressure inert gas flows into the inner furnace body from the inner furnace door. The gas flow exchanges heat with the shaft components and flows out through the position opposite to the inner furnace door. After flowing out, it makes full contact with the heat exchange tubes. The cooled inert gas is blown outward by the cooling fan (e.g., Figure 1 The gas flows through the upper, lower, and side sections of the furnace, then circulates again from the position between the inner and outer furnace bodies, flowing back into the inner furnace body through the furnace door. After cooling, the inert gas continues to exchange heat with the shaft components, circulating and cooling in a continuous process. The rapid flow of high-pressure inert gas removes heat from the surface of the shaft-like metal workpiece, achieving rapid cooling. The pressure of the high-pressure inert gas is 2 bar, and the flow rate is 0.3 m / s². 3 / min. When the temperature monitoring component detects that any section (front, middle, or rear) of the shaft-like workpiece is below 600℃, the spray nozzle for that section is activated, and the cooling fan is simultaneously shut off. The atomized coolant is then sprayed onto that section of the shaft-like workpiece through the spray nozzle for spray cooling. The spray velocity of the coolant is 0.1m / min. 3 / min; When the temperature of the shaft workpiece drops to 120℃ (the basic spraying time is about 10 minutes), spray cooling is stopped. By controlling the pressure and flow rate of the high-pressure gas, as well as the spray volume and spraying time of the coolant, the cooling rate is precisely controlled to avoid cracks or deformation of the metal workpiece during the cooling process.

[0067] (5) Take out the shaft workpiece after the quenching treatment in step (4) to obtain the shaft workpiece after quenching heat treatment.

[0068] (6) Tempering treatment: The shaft workpiece taken out in step (5) is placed in a tempering furnace, heated to 180°C, and held for 180 minutes. The tempering furnace is then turned off, and the shaft workpiece is air-cooled to room temperature to obtain the heat-treated shaft workpiece. Tempering treatment eliminates the internal stress generated in the metal workpiece during quenching and improves the toughness and comprehensive mechanical properties of the metal material. The hardness of the front, middle and rear sections of the obtained workpiece are tested respectively to obtain the following results: Figure 3 The results are shown; metallographic analysis of the front, middle (two parts), and rear sections of the obtained workpiece yielded the following results. Figure 5 Metallographic images shown (scale bar is 20µm).

[0069] Comparative Example 1 This comparative example illustrates a comparative test without the use of zoned heating and zoned quenching. The other settings in this comparative example are the same as in Example 1, except that instead of individually controlled induction heating coils for each zone, coils are laid out across the entire heating zone for unified control. Also, instead of zoned controlled spray nozzles, unified control is used. The other settings are the same as in Example 1. Using the parameters of Example 1, the same quenching and tempering treatment is performed on the shaft components as in Example 1. Hardness tests are then performed on the front, middle, and rear sections of the workpiece, yielding the following results: Figure 4 The test results are shown below. Specific hardness values ​​are shown in Table 1. Table 1 presents the hardness test results for Example 1 and Comparative Example 1.

[0070] Table 1 Detection location Example 1 (HRC) Comparative Example 1 (HRC) front section 54.4 53.0 middle section 55.7 56.2 Later 54.7 54.8 Maximum difference 1.3 3.2 pass Figure 3 and Figure 4 It can be seen that both Example 1 and Comparative Example 1 deal with the same type of shaft element, which is a shaft element with a complex shape. Figure 3 and Figure 4 It can be seen that their length is significantly greater than their circumferential dimension, and they are all shaft-like elements resembling an "L" shape. Figure 3 and Figure 4 The workpieces are placed in opposite directions, but their shapes are consistent. Referring to Table 1, it can be seen that the surface hardness of the product obtained in Comparative Example 1 has a large deviation. In Example 1, the hardness of each segment is within the range of HRC 54-56, with a maximum difference of only 1.3 between the three segments. In contrast, the middle segment of Comparative Example 1 has a higher hardness value, while the two ends have a lower value, with a maximum difference of 3.2 between the three segments, resulting in a relatively large hardness difference. This demonstrates that the zoned heating and zoned quenching method of this invention can significantly improve the large hardness difference defect in relatively large-sized, long-shaft workpieces.

[0071] Comparative Example 2 This comparative example demonstrates a comparative experiment without the use of a combined high-pressure inert gas quenching and spray-cooled liquid cooling technology. The other settings in this comparative example are the same as in Example 1, except that no spray nozzles are used. High-pressure inert gas is used for quenching throughout the process. All other settings are the same as in Example 1. The shaft components undergo the same quenching and tempering treatment as in Example 1, and metallographic analysis is performed on the front, middle (two parts), and rear sections of the resulting workpiece to obtain the following results: Figure 6 The metallographic images shown (the scale bars for images 1, 2, and 4 are all 20µm; for a clearer and more comprehensive analysis, the field of view of the metallographic image in the lower left corner, i.e., image 3, is magnified by 2 times, i.e., the scale bar is set to 10µm).

[0072] Figure 5 and Figure 6The top left image shows sampling from the front section, the top right and bottom left images show sampling from the middle section, and the bottom right image shows sampling from the rear section; through comparison... Figure 5 and Figure 6 It can be seen that Example 1 has a predominantly martensitic structure in all locations, with extremely fine Cr particles. 23 The C6 carbides are dispersed rather than network-like, indicating that the product obtained in Example 1 has high hardness, high strength and good corrosion resistance (no grain boundary corrosion sensitive areas). Figure 6 The area to be tested and Figure 5 The areas being tested are basically the same, through Figure 6 It can be seen that coarse austenite grains and incompletely transformed pearlite structures appear in the metallographic structures at different magnifications. Simultaneously, network carbide precipitation is observed. Therefore, it can be analyzed that the product obtained in Comparative Example 2 has moderate hardness and significant uniformity variations. Although its strength is acceptable, the presence of a small amount of carbide precipitation indicates a slight decrease in its corrosion resistance. This demonstrates that Example 1 of the present invention suppresses the diffusion of carbon and chromium through specific rapid cooling, making it difficult for carbides to precipitate. Most of the carbon dissolves in the martensite to form a supersaturated solid solution. Combined with subsequent low-temperature tempering, extremely fine Cr particles are precipitated in a dispersed rather than network-like distribution. 23 C6 carbides; and the specific rapid cooling ensures that austenite cools rapidly below the Ms point, preventing decomposition and directly transforming into martensite, completely suppressing the precipitation of pearlite and ferrite. This results in a matrix dominated by martensite with very little residual austenite, achieving a essentially all-martensitic structure. This demonstrates that Embodiment 1 of the present invention, through its specific cooling method, can comprehensively improve the morphology of the martensitic structure and carbide distribution of the product, thereby enhancing hardness and corrosion resistance.

[0073] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. A heat treatment device with multi-zone precise temperature control, characterized in that, It includes an inner furnace body, an outer furnace body, a vacuuming component, a heating and temperature control component, a cooling and temperature control component, a heat exchange component, a fan component, and a spray cooling component; The inner furnace body is set inside the outer furnace body. The inner furnace body is used to bear, heat, hold and cool the heat-treated workpieces. It includes the inner furnace shell and the inner furnace door. The outer furnace body is used to support the inner furnace body, heat exchange components and fan components, including the outer furnace shell and the outer furnace door, and the inner furnace door and the outer furnace door are opposite to each other and matched in position; The vacuum unit is used to perform a vacuuming operation on the inner furnace body; The heating and temperature control components include a radiant heating component, a temperature monitoring component, and a temperature control component. Both the radiant heating component and the temperature monitoring component are located inside the inner furnace shell. The radiant heating component is used to radiate heat onto the workpiece inside the inner furnace shell. The temperature monitoring component is used to detect the temperature of the workpiece in real time and transmit the temperature result to the temperature control component. The temperature control component is used to control the radiant heating component to achieve the specific heating temperature of the workpiece. There are three sets of radiant heating components and three sets of temperature monitoring components, located in the front, middle, and rear sections of the inner furnace shell respectively. The temperature control component independently controls the temperature of each of the three sets of radiant heating components. The cooling and temperature control components include a gas injection pipe; the injection port of the gas injection pipe is located on the outer furnace shell; Fan components include cooling fans; The heat exchange component includes a water inlet, a water outlet, and a heat exchange tube. The water inlet is located at the bottom of the outer furnace shell, the water outlet is located at the top of the outer furnace shell, and the heat exchange tube is located between the water inlet and the water outlet inside the outer furnace shell. The heat exchange tube is located between the cooling fan and the inner furnace body and on the outside of the inner furnace body away from the inner furnace door. The spray cooling component includes a spray nozzle, which is located on the inner periphery of the inner furnace shell. Multiple sets of spray nozzles are located in the front, middle and rear sections of the inner furnace shell.

2. The multi-zone precise temperature control heat treatment equipment according to claim 1, characterized in that, The cooling and temperature control component also includes a high-pressure gas storage tank and a gas flow control valve. The high-pressure gas storage tank is used to store high-pressure inert gas, and the gas flow control valve is used to regulate the flow and pressure of the inert gas. The gas injection pipe is used to introduce the high-pressure gas in the high-pressure gas storage tank into the outer furnace body. The high-pressure gas storage tank and the gas flow control valve are located outside the outer furnace shell. One end of the gas injection pipe is connected to the high-pressure gas storage tank, and the other end is connected to the inside of the outer furnace shell through the injection port. The gas flow control valve is installed on the gas injection pipe.

3. The multi-zone precise temperature control heat treatment equipment according to claim 1 or 2, characterized in that, The spray cooling component also includes a coolant storage tank, a coolant delivery pipe, and a spray pump. The coolant storage tank is used to store coolant. The coolant delivery pipe connects the coolant storage tank and the spray nozzle. A spray pump is installed on the coolant delivery pipe to apply pressure to the coolant in the coolant delivery pipe. The spray nozzle atomizes the delivered coolant and sprays it toward the workpiece to achieve spray cooling.

4. The multi-zone precise temperature control heat treatment equipment according to claim 1 or 2, characterized in that, The temperature monitoring component is a thermocouple; The spray nozzles are provided in three sets; The radiant heating component is a graphite heating tube; The vacuuming component includes a vacuum tube and a vacuum pump, with the opening of the vacuum tube located on the inner furnace shell.

5. A heat treatment method for precise temperature control in multiple zones on shaft-type workpieces, characterized in that, Includes the following steps: (1) Pretreatment: Clean and degrease the shaft workpieces; (2) Zoned heating: The pre-treated shaft workpiece is placed horizontally into the inner furnace of the heat treatment equipment, the inner furnace is sealed, and the inner furnace is evacuated. After the vacuum degree in the inner furnace reaches 0.5~2Pa, current is simultaneously supplied to the three sets of radiant heating components set in the front, middle and rear sections of the inner furnace shell. The front, middle and rear sections of the shaft workpiece are vacuum radiantly heated by the heat radiation of the radiant heating components. The heating rate is controlled by controlling the current to ≤10℃ / min. During the heating process, the front, middle and rear sections of the shaft workpiece are monitored in real time by the temperature monitoring component. When it is found that the heating rate of any section is greater than or less than the set heating rate, the current of that section is adjusted by the temperature control component to adjust the heating heat so that the heating rate of that section meets the set heating rate. The heating is stopped when the temperature of the shaft workpiece rises to 1025~1035℃. (3) Heat preservation: heat preservation at 1025~1035℃ for 55~65min; real-time temperature monitoring of the front, middle and rear sections of the shaft workpiece is performed by the temperature monitoring component. When the temperature of any section is found to be lower than the lower limit threshold of heat preservation, the current supplied to the radiation heating component set in that section is increased by the temperature control component to reheat the shaft workpiece in that section. When the temperature monitoring component detects that the temperature of any end is higher than the upper limit threshold of heat preservation, the high-frequency alternating current supplied to the induction heating coil of that section is reduced to keep the temperature between the upper and lower limit thresholds of heat preservation; vacuum is broken after heat preservation. The lower limit threshold for heat preservation is 3°C below the heat preservation temperature, and the upper limit threshold for heat preservation is 3°C above the heat preservation temperature. (4) Quenching: First, the shaft workpiece is quenched by circulating high pressure inert gas. The rapid flow of high pressure inert gas removes the heat from the surface of the workpiece. When the temperature monitoring component detects that any section of the front, middle and rear sections of the shaft workpiece is below 580~620℃, the spray nozzle of that section is turned on. Coolant is sprayed onto that section of the shaft workpiece through the spray nozzle for spray cooling. When the temperature of the shaft workpiece drops to 100~130℃, the spray cooling is stopped. (5) Take out the shaft workpiece after the quenching treatment in step (4) to obtain the shaft workpiece after quenching heat treatment.

6. The heat treatment method for multi-zone precise temperature control of shaft-type workpieces according to claim 5, characterized in that, The heat treatment method is performed using the heat treatment equipment described in any one of claims 1 to 4.

7. The heat treatment method for multi-zone precise temperature control of shaft-type workpieces according to claim 5 or 6, characterized in that, The following steps are included after step (5): (6) Tempering treatment: The shaft workpieces taken out in step (5) are placed into the tempering furnace, heated to 175~185℃, and held for 160~195min. Then the tempering furnace is stopped, and the shaft workpieces are taken out of the furnace and air-cooled to room temperature to obtain the heat-treated shaft workpieces.

8. The heat treatment method for multi-zone precise temperature control of shaft-type workpieces according to claim 5 or 6, characterized in that, In step (2), the heating power is set to 140~160W to precisely control the heating speed; The heating rate in step (2) is 3~10℃ / min; In step (4), the pressure of the high-pressure inert gas is 1~3 bar, and the inert gas flow rate is 0.1~0.5 m. 3 / min; In step (4), the injection speed of the coolant is 0.05~0.15m / min. 3 / min, spraying time is 6~12min.

9. The heat treatment method for multi-zone precise temperature control of shaft-type workpieces according to claim 5 or 6, characterized in that, The length of the front section inside the inner furnace shell is L1, the length of the middle section is L2, and the length of the rear section is L3, satisfying L1:L2:L3=(0.9~1.1):(1.2~1.8):(0.9~1.1).

10. The heat treatment method for multi-zone precise temperature control of shaft-type workpieces according to claim 5 or 6, characterized in that, The shaft-type workpieces are made of 4Cr13 steel, 3Cr13 steel, 40Cr13 steel, 9Cr18 steel, 60CrMo3-1 or 2Cr13 steel.

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