Energy-saving spheroidizing annealing process for high-carbon steel wire rod

Abstract

The invention discloses an energy-saving spheroidizing annealing process for a high-carbon steel wire rod, and relates to the technical field of material heat treatment, and the energy-saving spheroidizing annealing process for the high-carbon steel wire rod comprises the following steps: putting the high-carbon steel wire rod into an annealing furnace, heating to a critical temperature, synchronously introducing a carbon-rich atmosphere, and carrying out spheroidizing annealing on the high-carbon steel wire rod within a preset fluctuation range of the critical temperature, periodically fluctuating the temperature of the high-carbon steel wire rod based on the fluctuation period, maintaining the austenitizing time, controlling the temperature to be the heat preservation temperature, maintaining the heat preservation time, and periodically cooling the high-carbon steel wire rod to room temperature based on the cooling stage. According to the method, through periodic fluctuation of the temperature, local carbon balance of the high-carbon steel wire rod is damaged, austenitizing of the high-carbon steel wire rod is accelerated, the carbon-rich atmosphere is introduced to enable spheroidizing annealing to be carried out at the critical temperature lower than the austenitizing temperature, the needed heating temperature is reduced, and therefore the phenomenon that in the spheroidizing annealing process, the spheroidizing time is shortened is reduced. The heating temperature and the heating time required by austenitizing the high-carbon steel wire rod are reduced, and the energy consumption of spheroidizing annealing is reduced.

Description

Technical Field

[0001] This application relates to the field of materials heat treatment technology, and in particular to an energy-saving spheroidizing annealing process for high-carbon steel wire. Background Technology

[0002] Spheroidizing annealing of high-carbon steel wire is a heat treatment process specifically designed to improve the microstructure and properties of high-carbon steel. Its core objective is to transform lamellar or network cementite into spheroidal cementite, thereby significantly improving the material's plasticity, machinability, and cold heading ability, while providing a good microstructure basis for subsequent heat treatment.

[0003] Currently, when spheroidizing annealing high-carbon steel, the heating, holding, and cooling of high-carbon steel are often carried out by fixed processing time and temperature. Even when the high-carbon steel wire has reached the requirements of each stage of spheroidizing annealing, energy is still consumed for processing, resulting in high energy consumption for spheroidizing annealing of high-carbon steel wire. Summary of the Invention

[0004] The main purpose of this application is to provide an energy-saving spheroidizing annealing process for high-carbon steel wire, aiming to solve the technical problem of high energy consumption in spheroidizing annealing of high-carbon steel wire.

[0005] To achieve the above objectives, this application proposes an energy-saving spheroidizing annealing process for high-carbon steel wire, the process comprising: High-carbon steel wire is placed in an annealing furnace and heated to a preset critical temperature. A preset carbon-rich atmosphere is introduced, wherein the critical temperature is lower than the austenitizing temperature. Within a preset fluctuation range of the critical temperature, the temperature of the high-carbon steel wire is periodically fluctuated based on a preset fluctuation period, while maintaining a preset austenitizing time. The temperature is controlled to a preset heat preservation temperature and maintained for a preset heat preservation time; Based on a preset cooling stage, the high-carbon steel wire is cooled to room temperature in stages to complete the spheroidizing annealing of the high-carbon steel wire.

[0006] In one embodiment, the step of placing the high-carbon steel wire into an annealing furnace, heating it to a preset critical temperature, and simultaneously introducing a preset carbon-rich atmosphere includes: The high-carbon steel wire is heated to the critical temperature at a rate of 200~300℃ / h, wherein the critical temperature is 20℃ lower than the austenitizing temperature. After reaching the critical temperature, the carbon-rich atmosphere is introduced and maintained for 15 to 25 minutes. In one embodiment, the step of introducing the carbon-rich atmosphere and maintaining it for 15-25 minutes after reaching the critical temperature includes: After reaching the critical temperature, the carbon-rich atmosphere is introduced to make the carbon activity of the high-carbon steel material 0.02 wt%C higher than the average carbon activity of the high-carbon steel material at the critical temperature, and this is maintained for 15 to 25 minutes.

[0007] In one embodiment, the carbon-rich atmosphere consists of 99.5% N2 and 0.05% CH4.

[0008] In one embodiment, the step of periodically fluctuating the temperature of the high-carbon steel wire within a preset fluctuation range of the critical temperature based on a preset fluctuation period, while maintaining a preset austenitizing time, includes: The critical temperature is subjected to a sinusoidal or square wave periodic change with a temperature variation range of ±15℃, and maintained for 40~60 minutes.

[0009] In one embodiment, the annealing furnace includes a central heating component and an edge heating component. The central heating component heats the space within a preset range of the geometric center point of the annealing furnace, and the edge heating component heats the space outside the preset range of the geometric center point.

[0010] In one embodiment, before the step of controlling the temperature to a preset heat preservation temperature and maintaining it for a preset heat preservation time, the method further includes: The central heating component is stopped, and convection is carried out inside the annealing furnace to reduce the temperature to the holding temperature, wherein the convection wind speed is 0.8~1.2 m / s.

[0011] In one embodiment, the step of controlling the temperature to a preset heat preservation temperature and maintaining it for a preset heat preservation time includes: When the temperature drops to 690°C, it is heated by the edge heating component to maintain the temperature between 685°C and 695°C for 30 to 40 minutes.

[0012] In one embodiment, the step of gradually cooling the high-carbon steel wire to room temperature based on a preset cooling stage includes: The temperature is lowered to 580°C at a rate of 1.5°C / min; When the temperature reaches 580°C, the temperature is reduced to 500°C at a rate of 0.8°C / min. When the temperature reaches 500°C, the high-carbon steel wire is allowed to cool naturally to room temperature.

[0013] In one embodiment, the high-carbon steel wire is a wire with a carbon content higher than 0.6%.

[0014] One or more technical solutions proposed in this application have at least the following technical effects: High-carbon steel wire is placed in an annealing furnace and heated to a preset critical temperature. A preset carbon-rich atmosphere is introduced, wherein the critical temperature is lower than the austenitizing temperature. Within a preset fluctuation range of the critical temperature, the temperature of the high-carbon steel wire is periodically fluctuated based on a preset fluctuation period, and a preset austenitizing time is maintained. The temperature is controlled to a preset holding temperature and maintained for a preset holding time. Based on a preset cooling stage, the high-carbon steel wire is cooled to room temperature in stages to complete the spheroidizing annealing of the high-carbon steel wire.

[0015] Currently, the spheroidizing annealing of high-carbon steel wire rods often involves fixed processing times and temperatures for heating, holding, and cooling. Even after the high-carbon steel wire rods have reached the required spheroidizing annealing stages, energy consumption remains high due to ongoing processing. This application addresses this issue by improving the high-carbon steel spheroidizing annealing process to reduce energy consumption. Specifically, instead of directly initiating austenitization by setting the temperature above the austenitization threshold, this application heats the wire rod to a value below the austenitization threshold. Periodic temperature fluctuations disrupt the local carbon balance of the high-carbon steel wire rod, accelerating austenitization. Furthermore, introducing a pre-set carbon-rich atmosphere ensures that the spheroidizing annealing occurs around the austenitization threshold, reducing the required heating temperature. Therefore, this application can reduce the heating temperature and the time required to maintain the heating temperature during the spheroidizing annealing process to austenitize high-carbon steel wire, thereby reducing the energy consumption of spheroidizing annealing. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating the energy-saving spheroidizing annealing process for high-carbon steel wire in this application. Figure 2 This is a schematic flowchart of Example 2 of the energy-saving spheroidizing annealing process for high-carbon steel wire in this application; Figure 3 This is a schematic flowchart of Example 3 of the energy-saving spheroidizing annealing process for high-carbon steel wire in this application.

[0019] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] It should be understood that the specific embodiments described herein are merely illustrative of the technical solutions of this application and are not intended to limit this application.

[0021] To better understand the technical solution of this application, a detailed description will be provided below in conjunction with the accompanying drawings and specific implementation methods.

[0022] Spheroidizing annealing of high-carbon steel wire is a heat treatment process specifically designed to improve the microstructure and properties of high-carbon steel. Its core objective is to transform lamellar or network cementite into spheroidal cementite, thereby significantly improving the material's plasticity, machinability, and cold heading ability, while providing a good microstructure basis for subsequent heat treatment.

[0023] Currently, when spheroidizing annealing high-carbon steel, the heating, holding, and cooling of high-carbon steel are often carried out by fixed processing time and temperature. Even when the high-carbon steel wire has reached the requirements of each stage of spheroidizing annealing, energy is still consumed for processing, resulting in high energy consumption for spheroidizing annealing of high-carbon steel wire.

[0024] Based on this, embodiments of this application provide an energy-saving spheroidizing annealing process for high-carbon steel wire, referring to... Figure 1 , Figure 1 This is a schematic flowchart of the first embodiment of the energy-saving spheroidizing annealing process for high-carbon steel wire in this application.

[0025] In this embodiment, the energy-saving spheroidizing annealing process for high-carbon steel wire includes steps S10 to S40: Step S10: Place the high-carbon steel wire into an annealing furnace, heat it to a preset critical temperature, and introduce a preset carbon-rich atmosphere, wherein the critical temperature is lower than the austenitizing temperature. It should be noted that high-carbon steel wire refers to wire-shaped materials drawn from carbon steel with a carbon content typically between 0.60% and 1.00%. An annealing furnace is an industrial heating device used for annealing heat treatment of metallic materials. It can precisely control the temperature and atmosphere inside the furnace to improve the material's microstructure and properties. In this embodiment, the critical temperature refers to a set temperature point near the starting temperature of the pearlite-to-austenite transformation in high-carbon steel. The austenitizing temperature refers to the temperature required for high-carbon steel to completely transform into an austenitic microstructure, which is usually significantly higher than the Ac1 (Austenite Critical Temperature 1) temperature. Holding at temperatures above this level will lead to grain coarsening and increased energy consumption. Carbon-rich atmosphere: refers to the protective gas with a high carbon potential introduced into the annealing furnace, used to prevent decarburization of the wire surface and to control the surface carbon content.

[0026] It is understood that the critical temperature in this embodiment is set below the austenitizing temperature. At this temperature, the high-carbon steel wire undergoes only partial phase transformation or is in the two-phase region of pearlite and austenite, avoiding the risk of grain growth and high energy consumption caused by complete austenitization. At the same time, the introduction of a carbon-rich atmosphere can effectively suppress the decarburization phenomenon on the surface of the wire caused by high temperature and maintain the carbon chemical potential gradient required for carbide spheroidization. Thus, while ensuring the quality of spheroidizing annealing, the energy required for heating is reduced and the heating time is shortened, while avoiding the deterioration of material properties caused by surface decarburization.

[0027] Step S20: Within a preset fluctuation range of the critical temperature, the temperature of the high-carbon steel wire is periodically fluctuated based on a preset fluctuation period, while maintaining a preset austenitizing time. It should be noted that the preset fluctuation range refers to a temperature interval set around the critical temperature, used to implement small-scale temperature fluctuation control during the annealing process. The fluctuation period refers to the length of time it takes for the temperature to go from a high point to a low point and back to a high point, serving as a time reference parameter for periodic temperature control operations. The austenitizing time refers to the effective heat treatment time, equivalent to the traditional holding stage, set near the critical temperature to promote carbide spheroidization; this time is "maintained" as a preset value in this patent as a process control benchmark.

[0028] Understandably, by periodically fluctuating the temperature within a preset range near the critical temperature, the carbon concentration field and phase interface energy inside the high-carbon steel wire remain in a non-steady state, enhancing the driving force for carbon atom migration. Furthermore, this fluctuation is confined to a range below the austenitizing temperature, avoiding grain coarsening and excessive energy consumption. The periodic temperature changes can repeatedly activate carbide nucleation and growth processes, promoting the formation of fine, dispersed spherical carbides. Therefore, this embodiment can improve spheroidization efficiency and microstructure uniformity without extending or even shortening the effective heat treatment time.

[0029] Step S30: Control the temperature to a preset heat preservation temperature and maintain it for a preset heat preservation time; It should be noted that the holding temperature refers to a constant target temperature set during the spheroidizing annealing process to ensure complete spheroidization of carbides. The holding time refers to the duration of time the temperature is maintained constant at the holding temperature, used to ensure the spheroidization transformation of the internal structure of the high-carbon steel wire. Understandably, in this embodiment, after completing the periodic temperature fluctuations, the temperature is precisely controlled at a preset holding temperature and maintained for a preset holding time. This allows the high-carbon steel wire, having already activated carbon diffusion through the fluctuation stage, to enter a steady-state spheroidization stage, which is beneficial for the growth and rounding of spherical carbides. Simultaneously, this holding temperature remains below the austenitizing temperature, avoiding excessive grain growth and unnecessary energy consumption. The steady-state holding provides sufficient and controllable ripening conditions for the carbides, preventing microstructure inhomogeneity caused by continuous temperature fluctuations. Thus, while ensuring spheroidization quality, it improves microstructure uniformity and process controllability.

[0030] Step S40: Based on a preset cooling stage, the high-carbon steel wire is cooled to room temperature in stages to complete the spheroidizing annealing of the high-carbon steel wire.

[0031] It should be noted that the cooling stage refers to the complete heat treatment process in spheroidizing annealing, from the end of the holding period to the material cooling to room temperature. Staged cooling refers to dividing the entire cooling process into two or more temperature segments, each using a different cooling method or cooling rate.

[0032] It is understood that the cooling process in this embodiment adopts a preset staged cooling strategy, rather than the traditional fixed-rate slow cooling throughout the process. This allows the cooling rate of high carbon steel wire to be precisely controlled in the critical temperature range to maintain the stability of the spheroidized structure, while the cooling can be accelerated in the lower temperature range to shorten the cycle.

[0033] In one feasible implementation, the specific embodiment of periodically fluctuating the temperature of the high-carbon steel wire within a preset fluctuation range of the critical temperature based on a preset fluctuation period, while maintaining a preset austenitizing time, may also be: The critical temperature is subjected to a sinusoidal or square wave periodic change with a temperature variation range of ±15℃, and maintained for 40~60 minutes.

[0034] It should be noted that the temperature change amplitude refers to the maximum deviation of the temperature fluctuation from the center temperature, which in this embodiment is ±15℃, indicating that the temperature fluctuates within a range of 15℃ above and below the critical temperature. Sinusoidal periodic change refers to the temperature continuously and smoothly rising and falling within a set amplitude according to a sine function over time, forming a periodic temperature waveform. Square wave periodic change refers to the temperature rapidly switching between the upper and lower limits of the set amplitude in a step-like manner, with the high and low temperature plateaus lasting for equal durations or distributed according to a set ratio, forming a temperature sequence similar to a square wave.

[0035] Understandably, this embodiment uses a temperature variation range of ±15℃ to periodically control the critical temperature using a sinusoidal or square wave pattern, limiting the process to a time window of 40–60 minutes. This allows the high-carbon steel wire to undergo repeated micro-regional phase transformations and carbon concentration redistribution within the pearlite-austenite two-phase region. The sinusoidal wave provides a continuous gradient driving force, while the square wave enhances the dissolution-precipitation cycle through alternating high and low temperature platforms. Both effectively disrupt the local diffusion equilibrium. The temperature variation in this embodiment is sufficient to stimulate changes in the carbide interfacial energy to drive spheroidization, but not enough to induce overall austenite grain coarsening, thereby significantly improving spheroidization efficiency and carbide roundness in a relatively short time.

[0036] In summary, this embodiment involves placing high-carbon steel wire into an annealing furnace and heating it to a preset critical temperature. A preset carbon-rich atmosphere is then introduced, wherein the critical temperature is lower than the austenitizing temperature. Within a preset fluctuation range of the critical temperature, the temperature of the high-carbon steel wire is periodically fluctuated based on a preset fluctuation period, while maintaining a preset austenitizing time. The temperature is controlled to a preset holding temperature and maintained for a preset holding time. Based on a preset cooling stage, the high-carbon steel wire is gradually cooled to room temperature to complete the spheroidizing annealing of the high-carbon steel wire.

[0037] Currently, the spheroidizing annealing of high-carbon steel often involves fixed processing times and temperatures for heating, holding, and cooling. Even when the high-carbon steel wire reaches the required spheroidizing annealing stage, energy consumption remains high due to ongoing processing. This embodiment addresses this issue by improving the high-carbon steel spheroidizing annealing process to reduce energy consumption. Specifically, instead of directly initiating austenitization by setting the temperature above the austenitization threshold, this embodiment heats the high-carbon steel wire to a value below the austenitization threshold. Periodic temperature fluctuations disrupt the local carbon balance of the high-carbon steel wire, accelerating austenitization. Furthermore, introducing a pre-set carbon-rich atmosphere ensures that the spheroidizing annealing occurs around the austenitization threshold, reducing the required heating temperature. Therefore, this embodiment can reduce the heating temperature and the time required to maintain the heating temperature during the spheroidizing annealing process to austenitize the high-carbon steel wire, thereby reducing the energy consumption of spheroidizing annealing.

[0038] Based on the first embodiment of this application, in the second embodiment of this application, the content that is the same as or similar to that in Embodiment 1 above can be referred to the above description, and will not be repeated hereafter. Based on this, please refer to... Figure 2 Step S20, the energy-saving spheroidizing annealing process for high-carbon steel wire further includes steps S21~S22: Step S21: The high carbon steel wire is heated to the critical temperature at a rate of 200~300℃ / h, wherein the critical temperature is 20℃ lower than the austenitizing temperature. It should be noted that the heating rate refers to the magnitude of temperature increase per unit time, and in this step, it specifically refers to the heating speed used to heat the high-carbon steel wire from the initial temperature to the critical temperature.

[0039] Understandably, this embodiment employs a relatively rapid heating rate of 200–300 °C / h to heat the high-carbon steel wire to a critical temperature 20 °C below the austenitizing temperature. This avoids both the temperature range for complete austenite formation and the prolonged high-power heating required by traditional slow heating methods. The higher heating rate reduces accumulated heat loss from the furnace and ineffective heating time, while the 20 °C safety margin effectively prevents grain coarsening or localized overheating. Therefore, this embodiment significantly shortens the heating cycle and reduces energy consumption while ensuring the safety of the material microstructure.

[0040] Step S22: After reaching the critical temperature, the carbon-rich atmosphere is introduced and maintained for 15-25 minutes.

[0041] It should be noted that the duration of maintenance refers to the length of time a stable state is maintained under specific process conditions.

[0042] In one feasible implementation, the specific embodiment of introducing the carbon-rich atmosphere after reaching the critical temperature and maintaining it for 15-25 minutes can also be: After reaching the critical temperature, the carbon-rich atmosphere is introduced to make the carbon activity of the high-carbon steel material 0.02 wt%C higher than the average carbon activity of the high-carbon steel material at the critical temperature, and this is maintained for 15 to 25 minutes. The carbon-rich atmosphere consists of 99.5% N2 and 0.05% CH4.

[0043] It should be noted that carbon activity refers to the effective carbon chemical potential exhibited by a material under specific temperature and atmosphere, usually expressed as equivalent carbon mass fraction (wt%C). It is used to measure the tendency of the atmosphere to increase or decrease the carbon content of the steel surface. The higher the carbon activity, the more beneficial it is to suppress decarburization or achieve slight carburization. In this embodiment, the average carbon activity is the reference carbon activity value corresponding to the bulk microstructure of the high-carbon steel material when it is in thermodynamic equilibrium at the critical temperature. The carbon-rich atmosphere is a protective atmosphere composed of 99.5% nitrogen and 0.05% methane by volume. Trace amounts of CH4 in the atmosphere decompose at high temperatures to produce active carbon atoms, thereby increasing the carbon potential in the furnace.

[0044] It is understood that in this embodiment, a carbon-rich atmosphere consisting of 99.5% N2 and 0.05% CH4 is introduced at the critical temperature, so that the carbon activity in the furnace is precisely 0.02 wt%C higher than the average carbon activity of high-carbon steel material, and this is maintained for 15 to 25 minutes. This slight positive carbon potential difference is sufficient to counteract the tendency of carbon elements to diffuse from the surface to the atmosphere at high temperature, but it is not enough to cause obvious carburization or carbon black precipitation, thereby ensuring that there are no decarburization defects on the surface while avoiding the risk of excessive carbonization.

[0045] In one feasible implementation, the specific implementation method of introducing the carbon-rich atmosphere after reaching the critical temperature and maintaining it for 15-25 minutes can also be: The furnace temperature is increased from the critical temperature to a target temperature 8°C higher than the critical temperature at a rate of 0.5°C / min. After reaching the target temperature, the heating is paused for 1 minute every 5 minutes, and the process is repeated 4 times.

[0046] It should be noted that the target temperature refers to an intermediate temperature point that is slightly higher than the critical temperature, but still significantly lower than the austenitizing temperature. It is used to enhance the spheroidization driving force of carbides without initiating complete austenitization.

[0047] Understandably, in this embodiment, under the premise that the carbon-rich atmosphere has been fully established and the risk of surface decarburization has been suppressed, the temperature is only slightly increased by 8°C, and through a cycle of 5 minutes of heating and 1 minute of heat interruption, the carbon concentration field inside the high-carbon steel wire is enhanced to diffuse under the drive of micro-heating. The small temperature fluctuation caused by the short-term heat interruption can break the local equilibrium, induce fluctuations in the carbide interface energy, and promote the formation of fine spherical cores. Without increasing the risk of grain growth, the uniformity of spheroidization and the roundness of carbides are significantly improved, and the subsequent main heat preservation time is shortened.

[0048] In one feasible implementation, during each 1-minute pause in heating during the pulsed heat preservation process, the convection fan inside the annealing furnace is simultaneously activated to provide unidirectional circulating airflow at a wind speed of 0.6 m / s, with the direction parallel to the axial direction of the high-carbon steel wire coil; when heating resumes, the fan is immediately shut off, and the furnace temperature is maintained solely by natural convection.

[0049] It should be noted that unidirectional circulating air supply refers to the convection fan driving the atmosphere inside the furnace in a fixed direction to form a unidirectional circulating airflow along the axial direction of the annealing furnace, avoiding eddies or local dead zones. Axial parallel means that the airflow direction is consistent with the central axis of the high-carbon steel wire coil, ensuring that the airflow penetrates the gaps between the coil layers and enhances internal heat transfer.

[0050] It is understood that in this embodiment, axial unidirectional circulation is initiated only within a 1-minute window during which heating is paused, and the wind speed is strictly limited to 0.6 m / s. This effectively breaks the thermal stagnation caused by the accumulation between layers of high-carbon steel wire coils, thereby significantly improving the spheroidization uniformity of the coil core and surface without increasing the total energy consumption.

[0051] In one feasible implementation, during unidirectional circulating air supply, the CH4 flow rate of the carbon-rich atmosphere is synchronously adjusted so that it is increased to 120% of the original flow rate within 10 seconds after the start of air supply and returned to the original set value 15 seconds before the end of air supply, in order to compensate for the instantaneous dilution of local carbon potential caused by airflow disturbance.

[0052] It should be noted that instantaneous carbon potential dilution refers to the phenomenon that the concentration of activated carbon components in a local area temporarily decreases at the moment of forced convection start-up due to the rapid flow of fresh protective gas, which may induce micro-area decarbonization tendency.

[0053] It is understood that this embodiment eliminates the risk of micro-decarburization caused by forced convection by simultaneously adjusting the CH4 flow rate of the carbon-rich atmosphere during unidirectional circulating air supply, thereby improving the surface consistency of the spheroidized structure without changing the overall atmosphere composition and main process temperature.

[0054] In summary, in this embodiment, the temperature is raised to the critical temperature at a rate of 200-300℃ / h. Once the temperature is reached, a carbon-rich atmosphere consisting of 99.5% N2 and 0.05% CH4 is immediately introduced, so that the carbon activity in the furnace is 0.02 wt%C higher than the average carbon activity of the high-carbon steel material at the critical temperature. This state is maintained for 15-25 minutes, followed by subsequent periodic temperature fluctuations, heat preservation, and staged cooling.

[0055] By increasing the heating rate to 200–300 °C / h and controlling the target temperature to 20 °C below the austenitizing temperature, the heating time was shortened and grain coarsening was avoided. Introducing a carbon-rich atmosphere of a specific composition at the critical temperature, ensuring the carbon activity is precisely 0.02 wt%C higher than the material's average carbon activity and maintaining this level for 15–25 minutes, effectively suppressed surface decarburization and prevented excessive carburization. This significantly improved process efficiency and reduced energy consumption without sacrificing the quality of the material's surface and core microstructure.

[0056] Based on the first and second embodiments of this application, in the third embodiment of this application, the content that is the same as or similar to that in embodiments one and two above can be referred to the above description, and will not be repeated hereafter. Based on this, please refer to... Figure 3Step S40: The annealing furnace includes a central heating component and an edge heating component. The central heating component heats the space within a preset range of the geometric center point of the annealing furnace, and the edge heating component heats the space outside the preset range of the geometric center point. The energy-saving spheroidizing annealing process for high-carbon steel wire also includes steps S41-S45: Step S41: Stop the central heating component and perform convection in the annealing furnace to reduce the temperature to the holding temperature, wherein the convection wind speed is 0.8~1.2 m / s.

[0057] It should be noted that the central heating element refers to the heating device in the annealing furnace specifically designed to heat the space within a preset range of the geometric center point of the furnace chamber. The edge heating element refers to the heating device in the annealing furnace used to heat areas outside the preset range of the geometric center point (i.e., the surrounding area of ​​the furnace chamber), and its temperature is independently controlled from that of the central heating element. Convection refers to the operation of promoting heat transfer and temperature uniformity within the annealing furnace through forced airflow.

[0058] It is understood that in this embodiment, the central heating component is stopped while the edge heating component is retained. Combined with a convective wind speed of 0.8 to 1.2 m / s, the heat in the high-temperature zone at the center of the furnace is quickly carried to the edge and dissipated evenly. This wind speed range is sufficient to enhance the heat exchange efficiency, and will not cause uneven structure due to excessively high wind speed causing the surface of the high-carbon steel wire to cool too quickly. Thus, before entering the subsequent cooling stage, the temperature is efficiently and smoothly brought back to the holding temperature.

[0059] Step S42: When the temperature drops to 690°C, the edge heating component is used to heat the temperature to maintain it between 685°C and 695°C for 30 to 40 minutes.

[0060] It is understandable that in this embodiment, when the temperature drops to 690°C, only the edge heating components are used to compensate for the heating of the furnace periphery, so that the overall temperature is stabilized in a narrow range of 685°C to 695°C and maintained for 30 to 40 minutes. This temperature is still in the two-phase region near Ac1 of high carbon steel, which is conducive to short-range diffusion of carbon atoms. In addition, the use of only the edge heating components avoids overheating in the central region. Combined with convective cooling, the radial temperature gradient can be reduced, thereby effectively enhancing the spheroidization effect and improving the uniformity of the microstructure during the cooling stage.

[0061] Step S43: The temperature is reduced to 580°C at a rate of 1.5°C / min; Understandably, this embodiment uses a cooling rate of 1.5℃ / min to cool the high-carbon steel wire from approximately 690℃ to 580℃. This rate is slow enough to suppress the non-equilibrium precipitation of proeutectoid cementite or lamellar pearlite, ensuring the stability of the formed spheroidized carbide structure. Furthermore, compared to traditional furnace cooling, this embodiment significantly accelerates the cooling process within the safe cooling window that the spheroidization structure of high-carbon steel can withstand, thereby effectively shortening the process cycle while ensuring the quality of spheroidization annealing.

[0062] Step S44: When the temperature reaches 580°C, the temperature is reduced to 500°C at a rate of 0.8°C / min. Understandably, this embodiment uses a cooling rate of 0.8℃ / min to reduce the temperature from 580℃ to 500℃, effectively balancing cooling efficiency and microstructure stability while ensuring no new phase precipitation. Although no phase transformation occurs during this cooling stage, excessively rapid cooling may still increase the temperature difference between the inside and outside of the workpiece, leading to residual stress accumulation. This embodiment, however, achieves sufficient temperature uniformity through slow cooling at 0.8℃ / min, thereby shortening the process time compared to traditional extremely slow furnace cooling while avoiding the risk of material deformation or cracking.

[0063] Step S45: When the temperature reaches 500°C, allow the high-carbon steel wire to cool naturally to room temperature.

[0064] It is understandable that in this embodiment, natural cooling to room temperature is switched at 500°C. However, 500°C is far below the Ac1 temperature and above the initiation point of diffusionless phase transformation. High-carbon steel wire no longer undergoes microstructural evolution below this temperature, so there is no need for continued temperature control. In this embodiment, natural cooling at this point completely avoids the ineffective energy input of the annealing furnace in the low-temperature range, thereby significantly reducing the overall process energy consumption and simplifying the operation process.

[0065] In summary, this embodiment stops the central heating element of the annealing furnace and starts a convection system with a wind speed of 0.8–1.2 m / s to uniformly lower the temperature to the holding temperature. When the temperature drops to 690°C, the edge heating element is activated to precisely maintain the temperature of the high-carbon steel wire at 685°C–695°C for 30–40 minutes. Subsequently, it is cooled to 580°C at a rate of 1.5°C / min, and then further cooled to 500°C at a rate of 0.8°C / min. When the temperature reaches 500°C, all active temperature control measures are stopped, allowing the high-carbon steel wire to cool naturally to room temperature.

[0066] Because the annealing furnace in this embodiment is equipped with independently adjustable central heating and edge heating components, and the central heat source is shut down in the initial cooling stage, with edge heating only activated near 690°C for local compensation, the temperature field inside the furnace remains highly uniform in the critical spheroidization range, avoiding central overheating. Subsequently, two levels of controlled slow cooling at 1.5°C / min and 0.8°C / min are used to match the needs of microstructure stability in the high-temperature zone and stress release in the low-temperature zone, respectively. Finally, at 500°C, it switches to energy-free natural cooling. Thus, while ensuring the full development and uniform distribution of spherical carbides, the overall cooling cycle is significantly shortened and energy consumption is greatly reduced.

[0067] It should be noted that the above examples are only for understanding this application and do not constitute a limitation on the energy-saving spheroidizing annealing process for high-carbon steel wire in this application. Any simple modifications based on this technical concept are within the scope of protection of this application.

[0068] The above description is only a part of the embodiments of this application and does not limit the scope of protection of this application. All equivalent structural transformations made under the technical concept of this application and using the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included in the patent protection scope of this application.

Claims

1. An energy-saving spheroidizing annealing process for high-carbon steel wire, characterized in that, The process includes: High-carbon steel wire is placed in an annealing furnace and heated to a preset critical temperature. A preset carbon-rich atmosphere is introduced, wherein the critical temperature is lower than the austenitizing temperature. Within a preset fluctuation range of the critical temperature, the temperature of the high-carbon steel wire is periodically fluctuated based on a preset fluctuation period, while maintaining a preset austenitizing time. The temperature is controlled to a preset heat preservation temperature and maintained for a preset heat preservation time; Based on a preset cooling stage, the high-carbon steel wire is cooled to room temperature in stages to complete the spheroidizing annealing of the high-carbon steel wire.

2. The process as described in claim 1, characterized in that, The step of placing high-carbon steel wire into an annealing furnace, heating it to a preset critical temperature, and simultaneously introducing a preset carbon-rich atmosphere includes: The high-carbon steel wire is heated to the critical temperature at a rate of 200~300℃ / h, wherein the critical temperature is 20℃ lower than the austenitizing temperature. After reaching the critical temperature, the carbon-rich atmosphere is introduced and maintained for 15-25 minutes.

3. The process as described in claim 2, characterized in that, The step of introducing the carbon-rich atmosphere after reaching the critical temperature and maintaining it for 15-25 minutes includes: After reaching the critical temperature, the carbon-rich atmosphere is introduced to make the carbon activity of the high-carbon steel material 0.02 wt%C higher than the average carbon activity of the high-carbon steel material at the critical temperature, and this is maintained for 15 to 25 minutes.

4. The process as described in claim 1, characterized in that, The carbon-rich atmosphere consists of 99.5% N2 and 0.05% CH4.

5. The process as described in claim 1, characterized in that, The step of periodically fluctuating the temperature of the high-carbon steel wire within a preset fluctuation range of the critical temperature, based on a preset fluctuation period, and maintaining a preset austenitizing time includes: The critical temperature is subjected to a sinusoidal or square wave periodic change with a temperature variation range of ±15℃, and maintained for 40~60 minutes.

6. The process as described in claim 1, characterized in that, The annealing furnace includes a central heating component and an edge heating component. The central heating component heats the space within a preset range of the geometric center point of the annealing furnace, and the edge heating component heats the space outside the preset range of the geometric center point.

7. The process as described in claim 6, characterized in that, Before the step of controlling the temperature to a preset heat preservation temperature and maintaining it for a preset heat preservation time, the method further includes: The central heating component is stopped, and convection is carried out inside the annealing furnace to reduce the temperature to the holding temperature, wherein the convection wind speed is 0.8~1.2m / s.

8. The process as described in claim 6, characterized in that, The steps of controlling the temperature to a preset heat preservation temperature and maintaining it for a preset heat preservation time include: When the temperature drops to 690°C, it is heated by the edge heating component to maintain the temperature between 685°C and 695°C for 30 to 40 minutes.

9. The process as described in claim 1, characterized in that, The step of cooling the high-carbon steel wire to room temperature in stages based on a preset cooling phase includes: The temperature is lowered to 580°C at a rate of 1.5°C / min; When the temperature reaches 580°C, the temperature is reduced to 500°C at a rate of 0.8°C / min. When the temperature reaches 500°C, the high-carbon steel wire is allowed to cool naturally to room temperature.

10. The process as described in claim 1, characterized in that, The high-carbon steel wire is a wire with a carbon content higher than 0.6%.

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