A process method and system for improving the hardness of a steel pipe by heat treatment

Abstract

This invention discloses a process and system for improving the hardness of steel pipes through heat treatment, relating to the field of heat treatment technology, and applicable to steel pipe bending components after medium-frequency bending. The process includes clamping the bending component on a transfer fixture for austenitizing heating; after the bending component is removed from the furnace, it is transferred to the top of a quenching tank according to a preset transfer path and lifting posture, and the transfer time is recorded; the bending component is immersed in a cooling medium for quenching according to a preset immersion rhythm, and cooling is completed under the condition of circulating flow of the cooling medium; subsequently, the quenched bending component is tempered; by coordinating the control of the high-temperature transfer path, lifting posture, and immersion rhythm, the cooling uniformity of the inner and outer arcs of the bend and areas with different wall thicknesses is improved, the consistency of microstructure and hardness distribution is improved, and heat treatment deformation is reduced; this solves the technical problems of insufficient cooling control, uneven cooling, and inconsistent microstructure and hardness distribution in existing steel pipe heat treatment.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology, and in particular to a process and system for improving the hardness of steel pipes through heat treatment. Background Technology

[0002] WB36 steel pipe is a commonly used low-alloy steel pipe material for high-temperature and high-pressure pipelines in power plants. It possesses certain high-temperature strength, creep resistance, and weldability. In engineering, it is often used in medium-frequency induction heating bending process to produce elbows, bends, and other formed parts. Due to the localized rapid heating, plastic deformation, and temperature gradients during the medium-frequency bending process, the microstructure and properties of the base material and the bending zone are prone to inhomogeneity after the pipe is formed. Therefore, heat treatment is usually required to eliminate stress, stabilize the microstructure, and restore / improve the overall mechanical properties.

[0003] In current engineering practice, WB36 medium-frequency induction bending workpieces often adopt a "normalizing + tempering" heat treatment route: first, the workpiece is heated to the austenitizing region and held at that temperature before air cooling (or slow cooling) to achieve normalizing, refining the grains and obtaining a more uniform microstructure; then, tempering is performed to reduce brittleness, improve toughness, and stabilize the microstructure. This route is quite sensitive to the temperature uniformity, sufficient heat preservation, and cooling conditions of thick-walled bending pipes, different wall thickness areas, and the inner and outer arc regions of the bend. If the cooling process is limited by the workpiece size, clamping method, site environment, or insufficient cooling medium / volume, the actual cooling rate may be lower than the critical cooling rate required for material phase transformation, resulting in the preferential formation of relatively low-hardness microstructures such as pearlite and bainite, making it difficult to obtain the microstructure corresponding to higher hardness. This leads to problems such as lower hardness after tempering or batch quality fluctuations. Especially in the bending region, due to the complex cross-sectional shape, the difference in heat transfer between the inner and outer arcs, and the coupling of residual stress, lower hardness is more likely to occur, affecting subsequent assembly, service safety margin, and quality consistency.

[0004] To improve the hardness and consistency of WB36 steel pipes after medium-frequency bending, the industry has adopted a core approach of "quenching + tempering." This involves increasing the driving force of microstructure transformation through higher-intensity and more controllable cooling after austenitization, followed by tempering to achieve the target hardness and toughness balance. However, implementing this approach on steel pipe bending components still requires addressing engineering challenges such as heating uniformity, quenching cooling intensity and uniformity, deformation and cracking risk control, and the repeatability and traceability of process parameters. Otherwise, it will be difficult to stably improve hardness while ensuring dimensional accuracy and service reliability.

[0005] In summary, the existing technology has at least the following technical problems: Existing heat treatment methods for steel pipes suffer from insufficient or unstable cooling rate control, uneven cooling in the inner and outer arcs of bending and in areas with different wall thicknesses, inconsistent microstructure and hardness distribution, and a lack of technical solutions for quality control systems for bent pipe components. Summary of the Invention

[0006] The purpose of this invention is to provide a process and system for improving the hardness of steel pipes through heat treatment, in order to solve the technical problems of insufficient or unstable cooling rate control, uneven cooling in the inner and outer arcs of bending and in areas with different wall thicknesses, inconsistent microstructure and hardness distribution, and lack of a quality control system for bent pipe components in existing heat treatment methods.

[0007] The preferred technical solutions among the many technical solutions provided by this invention can produce a variety of technical effects, which are described in detail below.

[0008] To address the aforementioned technical problems, the present invention provides the following technical solution: This invention provides a process and system for improving the hardness of steel pipes through heat treatment, applicable to steel pipe bending components after medium frequency bending, including: S1, clamping and fixing: clamping the bending component to be treated on a transfer fixture for uniform support and attitude control of the bending component during heating, furnace transfer and immersion in the tank. S2, Austenitizing heating: The bent pipe component is sent into a heating furnace and heated to a preset quenching temperature and held at that temperature; S3. High-temperature transfer: After the bent pipe component exits the heating furnace, it is transferred from the furnace opening to the top of the quenching tank according to a preset transfer path and in a preset lifting posture, and the transfer time from the bent pipe component exiting the heating furnace to entering the quenching tank is recorded. S4. Quenching and cooling: The bent pipe component is immersed in the cooling medium in the quenching tank according to the preset immersion rhythm for quenching, and the cooling is completed under the condition of circulating flow of the cooling medium. S5. Tempering treatment: Temper the quenched pipe component. The preset transfer path, the preset lifting posture, and the preset grooving rhythm constitute an integrated high-temperature transfer and quenching process for medium-frequency bent pipes.

[0009] In one embodiment, the bending component is a medium-frequency bending component of WB36 steel pipe, and the wall thickness of the steel pipe is ≥30mm.

[0010] In one embodiment, the preset quenching temperature is 880-950℃; the tempering treatment includes: tempering the bent pipe component at a tempering temperature of 620-700℃ for 4-8 hours, and air-cooling the bent pipe component to room temperature after the tempering is completed.

[0011] In one embodiment, the preset transfer path is a preset path that minimizes the transfer distance of the bent pipe component from the furnace opening to the quenching tank, while meeting the requirements of safe distance and obstacle avoidance, and the lifting swing amplitude and path deviation are limited by the guide / limiting structure.

[0012] In one embodiment, the preset lifting posture includes posture control of the bending plane of the bent pipe component, and symmetrical multi-point support of both ends and / or the bending area of ​​the bent pipe component through the transfer fixture.

[0013] In one embodiment, the transfer time is no more than 120 seconds, and the outer surface temperature of the bent pipe component at the moment of entering the quenching tank is no less than 50°C below the preset quenching temperature; when the transfer time of the bent pipe component exceeds the limit and / or the outer surface temperature of the bent pipe component at the moment of entering the quenching tank is less than 50°C below the preset quenching temperature, an alarm and / or interlock signal is output and the process of prohibiting the bent pipe component from entering the quenching tank or reheating is executed.

[0014] In one embodiment, the length, width, and height of the quenching tank are all greater than the combined external dimensions of the bent pipe component and the transfer fixture to ensure complete immersion; the cooling medium is water, and the water temperature is monitored and controlled in real time to ensure that the water temperature does not exceed 40°C during the cooling process of the bent pipe component, and the water is driven to circulate in the quenching tank through a circulation device.

[0015] In one embodiment, the preset immersion cycle includes controlling the entry of the bent pipe component into the quenching tank in segments or at a constant speed, and after the bent pipe component enters the quenching tank, controlling the bending pipe component to swing or rotate, or directionally rinsing the bent pipe component with the quenching liquid in the quenching tank / adjusting the flow direction of the quenching liquid in the quenching tank.

[0016] In one embodiment, a quality control step is also included: recording and tracing the quenching temperature, holding time, transfer time, circulation state of the immersed cooling medium, and hardness test results of the bent pipe component; wherein, the circulation state parameters include at least circulation temperature, circulation flow rate, and circulation interruption state; when the hardness of the bent pipe component is lower than the preset lower hardness limit, the reprocessing process of S1 to S5 is allowed to be executed again, and the number of reprocessing times is constrained by a preset upper limit.

[0017] A process system for improving the hardness of steel pipes through heat treatment is also provided. This system includes a heating unit for heating the clamped bent pipe component to the quenching temperature and holding it at that temperature; a transfer fixture and lifting unit for multi-point support clamping of the bent pipe component and transferring it from the furnace to the quenching tank according to a preset transfer path and lifting posture; a quenching tank unit for containing the cooling medium and providing circulation and temperature control; and a control and recording unit for monitoring and recording the transfer time of the bent pipe component, the outer surface temperature at the moment of entry into the quenching tank, and the temperature and circulation state of the cooling medium. The unit outputs alarm and / or interlock signals when the transfer time exceeds 120 seconds, the outer surface temperature at the moment of entry into the quenching tank is less than 50°C below the preset quenching temperature, and / or the temperature of the cooling medium is higher than 40°C, or the circulation is interrupted. The transfer fixture and lifting unit, along with the quenching tank unit, constitute an integrated high-temperature transfer and quenching execution link to improve the hardness of the bent pipe component and enhance the consistency of its microstructure and hardness distribution.

[0018] The beneficial effects of this invention are as follows: (1) To achieve controllable and stable cooling rate of bent pipe components and improve quenching effectiveness. This technical solution targets steel pipe bending components after medium-frequency bending. After austenitizing heating, it introduces a "high-temperature transfer-quenching integrated process". By coordinating the control of the transfer path, lifting posture and quenching cycle, the high-temperature transfer process from furnace exit to quenching is shortened and stabilized. This effectively reduces heat loss caused by natural cooling during the transfer process, ensuring that the bending component maintains a sufficient temperature when entering the quenching medium. This guarantees that the cooling rate meets the requirements for forming a high-hardness structure and avoids the problem of low hardness due to insufficient cooling rate.

[0019] (2) Improve the cooling uniformity of the inner and outer arcs of the bend and areas with different wall thicknesses, and improve the consistency of microstructure and hardness. This technical solution implements controlled lifting posture and multi-point load-bearing support during the transfer stage, and adopts a preset entry rhythm and cooling medium circulation during the quenching stage. This makes the heat exchange conditions of each part of the bent pipe component tend to be consistent during the quenching process, effectively reducing the cooling difference between the inner and outer arcs of the bend and areas with different wall thicknesses, suppressing uneven transformation of the microstructure, and thus improving the consistency of microstructure and hardness distribution along the length and cross-sectional direction of the entire bent pipe component.

[0020] (3) Reduce the risk of heat treatment deformation and local overcooling, and improve the finished product quality stability of bent pipe components. This technical solution ensures that the bent pipe component remains under uniform load and with controlled posture throughout the heating, transfer, and cooling stages by limiting the transfer path, lifting posture, and immersion rhythm during the high-temperature transfer and quenching process. This avoids additional bending, torsional deformation, or local overcooling caused by uneven local stress or sudden cooling, thereby improving the geometric stability and dimensional reliability of the bent pipe component after heat treatment.

[0021] (4) Construct a complete heat treatment process system for bent pipe components to improve process repeatability and quality traceability. This technical solution not only provides a specific process for improving the hardness of steel pipes through heat treatment, but also forms a heat treatment process system suitable for medium-frequency bent pipe components through the systematic organization of transfer time, cooling process and tempering treatment. This provides a technical foundation for the mass and stable production of bent pipe components, and is conducive to improving the consistency of process execution, the traceability of quality control and the overall production reliability.

[0022] In summary, this invention effectively solves the problems of insufficient cooling rate control, uneven cooling, and lack of a dedicated quality control system for bending pipes in existing steel pipe heat treatment by specifically optimizing the entire process of medium-frequency bending pipe components during the heating, transfer, and quenching stages. This significantly improves the hardness level and microstructure consistency of the bent pipe components after heat treatment. Attached Figure Description

[0023] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the process steps for improving the hardness of steel pipes through heat treatment according to the present invention. Figure 2 This is a schematic diagram of the process steps for improving the hardness of steel pipes through heat treatment according to the second embodiment of the present invention. Figure 3 This is a schematic diagram of the structural composition of the steel pipe heat treatment hardness improvement process system of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0026] The specific implementation provides a process and system for improving the hardness of steel pipe heat treatment, applicable to steel pipe bending components after medium-frequency bending. The process includes clamping the bending component on a transfer fixture for austenitizing heating; after the bending component is removed from the furnace, it is transferred to the top of the quenching tank according to a preset transfer path and lifting posture, and the transfer time is recorded; the bending component is immersed in the cooling medium for quenching according to a preset immersion rhythm, and cooling is completed under the condition of circulating flow of the cooling medium; subsequently, the quenched bending component is tempered; by coordinating the control of the high-temperature transfer path, lifting posture and immersion rhythm, the cooling uniformity of the inner and outer arcs of the bend and different wall thickness areas is improved, the consistency of microstructure and hardness distribution is improved, and heat treatment deformation is reduced; a process system for improving the hardness of steel pipe heat treatment is also provided for implementing the process method, applicable to the stabilization and high-quality heat treatment production of bending components; thus effectively solving the technical problems of insufficient or unstable cooling rate control, uneven cooling of the inner and outer arcs of the bend and different wall thickness areas, inconsistent microstructure and hardness distribution, and lack of a quality control system for bending components in existing steel pipe heat treatment.

[0027] The first implementation of a process for improving the hardness of steel pipes through heat treatment, for example Figure 1 As shown, the method is applicable to steel pipe bending components after medium frequency bending, including S1, clamping and fixing: clamping the bending component to be processed on the transfer fixture, which is used to uniformly support and control the attitude of the bending component during heating, furnace transfer and immersion in the tank. S2. Austenitizing heating: The bent pipe component is sent into a heating furnace and heated to the preset quenching temperature and held at that temperature; S3. High-temperature transfer: After the bent pipe component exits the heating furnace, it is transferred from the furnace opening to the top of the quenching tank according to the preset transfer path and in the preset lifting posture, and the transfer time from the moment the bent pipe component exits the heating furnace to the moment it enters the quenching tank is recorded. S4. Quenching and Cooling: The bent pipe component is immersed in the cooling medium in the quenching tank according to the preset immersion rhythm and is quenched, and the cooling is completed under the condition of circulating flow of the cooling medium. S5. Tempering treatment: Tempering treatment is performed on the quenched bent pipe components. Among them, the preset transfer path, preset lifting posture and preset groove entry rhythm constitute the high temperature transfer and quenching integrated process of medium frequency bending pipe, which is used to reduce the uneven cooling of the inner and outer arcs of the bending area and the area with different wall thicknesses of the bending pipe component, resulting in inconsistent microstructure and hardness distribution and deformation.

[0028] Specifically, by optimizing the entire process of medium-frequency bent pipe components during the transfer and quenching stages after heating, this approach effectively solves the problems of insufficient cooling rate control, uneven cooling, and lack of a dedicated quality control system for bending pipes in existing steel pipe heat treatment. It significantly improves the hardness and microstructure consistency of the pipe components after heat treatment and has at least the following technical advantages: It achieves controllable and stable cooling rate for bent pipe components, improving quenching effectiveness. This technical solution introduces a "high-temperature transfer-quenching integrated process" for medium-frequency bent steel pipe components after austenitizing heating. Through coordinated control of the transfer path, lifting posture, and quenching cycle, the high-temperature transfer process from furnace exit to quenching is shortened and stabilized, effectively reducing heat loss due to natural cooling during the transfer process. This ensures that the bent pipe components maintain sufficient temperature when entering the quenching medium, thereby guaranteeing that the cooling rate meets the requirements for forming a high-hardness microstructure and avoiding the problem of low hardness due to insufficient cooling rate.

[0029] This technical solution improves the cooling uniformity of the inner and outer arcs of the bend and areas with different wall thicknesses, thereby enhancing the consistency of microstructure and hardness. During the transfer phase, controlled lifting posture and multi-point load-bearing support are implemented. In the quenching phase, a preset quenching rhythm is adopted, coupled with circulating cooling medium. This ensures that the heat exchange conditions of each part of the bent pipe component are consistent during quenching, effectively reducing cooling differences between the inner and outer arcs of the bend and areas with different wall thicknesses, suppressing uneven microstructure transformation, and thus improving the consistency of microstructure and hardness distribution along the length and cross-sectional direction of the entire bent pipe component.

[0030] This technical solution reduces the risk of heat treatment deformation and localized overcooling, and improves the quality stability of the finished pipe bending components. During the high-temperature transfer and quenching process, by limiting the transfer path, lifting posture, and immersion rhythm, the pipe bending components are always in a state of uniform load-bearing and posture control during the heating, transfer, and cooling stages. This avoids additional bending, torsional deformation, or localized overcooling caused by uneven local stress or sudden cooling, thereby improving the geometric stability and dimensional reliability of the pipe bending components after heat treatment.

[0031] This technical solution constructs a complete heat treatment process system for pipe bending components, improving process repeatability and quality traceability. It not only provides a specific method for improving the hardness of steel pipes through heat treatment, but also forms a heat treatment process system suitable for medium-frequency pipe bending components through the systematic organization of transfer time, cooling process, and tempering treatment. This provides a technical foundation for the mass and stable production of pipe bending components, and is conducive to improving the consistency of process execution, the traceability of quality control, and the overall reliability of production.

[0032] As one alternative implementation method: Regarding the materials of the aforementioned bending components, the bending components are medium-frequency bending components made of WB36 steel pipes, and the wall thickness of the steel pipes is ≥30mm.

[0033] When applied, WB36 steel pipe, being a low-alloy heat-resistant steel, exhibits significant differences in microstructure and heat conduction conditions between the inner and outer arcs of the bending zone and between thick and thin-walled regions after medium-frequency bending. Conventional heat treatment processes can easily lead to insufficient or uneven cooling rates in the bending zone. By applying the high-temperature transfer-quenching integrated process of this technical solution to the aforementioned thick-walled medium-frequency bent pipe components, under conditions of large overall dimensions and high heat capacity, the synergistic effects of transfer control, immersion cycle time, and circulating cooling are verified and utilized. This effectively improves the cooling efficiency and stability of thick-walled bent pipe components during the quenching process, solving the problem of achieving uniform hardness distribution in existing technologies for thick-walled bent pipe components.

[0034] Regarding the specific parameters of the preset quenching temperature and tempering treatment of the above-mentioned bent pipe components, the preset quenching temperature is 880~950℃; the tempering treatment includes: tempering and holding the bent pipe components at a tempering temperature of 620~700℃ for 4~8h, and air cooling the bent pipe components to room temperature after the tempering and holding is completed.

[0035] During application, the bent pipe component is heated to a preset quenching temperature range of 880–950°C during the austenitizing heating stage and held at that temperature for an extended period to ensure that the overall cross-section of the bent pipe component reaches a uniform austenitizing state. After quenching and cooling, the bent pipe component undergoes tempering treatment, held at a tempering temperature range of 620–700°C for 4–8 hours, and then air-cooled to room temperature after tempering. Through the coordinated setting of the above quenching and tempering parameters, the bent pipe component achieves high quenching hardness while further releasing residual quenching stress, stabilizing the microstructure, and avoiding service risks caused by excessive hardness or stress concentration. By combining the quenching and tempering parameter combination with the aforementioned high-temperature transfer and uniform quenching control, the bent pipe component maintains good comprehensive mechanical properties while improving its hardness level.

[0036] Specifically, the selection of the preset quenching temperature is related to the wall thickness of the bent pipe component. For medium-frequency bent pipe components made of WB36 steel pipe with a wall thickness of 30-50mm, the preferred quenching temperature is 880-920℃ to ensure that the core reaches the austenitizing temperature and avoids grain coarsening. For medium-frequency bent pipe components made of WB36 steel pipe with a wall thickness greater than 50mm, the preferred quenching temperature is 920-950℃. The higher temperature increases the stability of austenite to compensate for the heat loss during the transfer and cooling process of the thick-walled section, thereby increasing the depth of the hardened layer.

[0037] Regarding the specific methods of the aforementioned bent pipe component in the preset transfer path and preset lifting posture, the preset transfer path is the preset path with the minimum transfer distance of the bent pipe component from the furnace mouth of the heating furnace to the quenching tank under the premise of meeting the safety distance and obstacle avoidance requirements. The lifting swing amplitude and path deviation are limited by the guide / limiting structure to suppress the additional bending and torsional deformation of the bent pipe component during the transfer process.

[0038] The preset lifting posture includes posture control of the bending plane of the bent pipe component, and symmetrical multi-point support of the two ends and / or bending area of ​​the bent pipe component through the transfer tooling, for uniform support of the bent pipe component during lifting, translation and entry into the quenching tank.

[0039] In application, after the bent tube component exits the self-heating furnace, it is transferred to the top of the quenching tank along the shortest transfer path while meeting safety distance and obstacle avoidance requirements. The swing amplitude and path deviation during the lifting process are limited by the guide structure and limiting structure. At the same time, by limiting the posture of the bending plane of the bent tube component and implementing symmetrical multi-point support at both ends and / or the bending area, the bent tube component is always in a uniform load-bearing and stable stress state during the lifting, translation and tank entry process. By coordinating and controlling the transfer path and lifting posture, not only is the high temperature exposure time shortened, but additional bending and torsional deformation caused by self-weight or inertia is also effectively suppressed, thereby creating stable initial conditions for subsequent uniform quenching.

[0040] The guiding and limiting structure can be implemented using a track-type, frame-type, or flexible limiting structure, and the number and position of the lifting support points can also be adjusted according to the curvature and length of the bend.

[0041] Specifically, the core of the preset lifting posture is to control the direction of the bending plane. Preferably, the bending plane of the bent pipe component is placed perpendicular to the surface of the quenching tank before entering the tank. This posture can minimize the difference in vapor film formation time caused by the difference in the geometry of the inner and outer arcs of the bent pipe, and ensure that the inner and outer arcs obtain relatively consistent heat transfer conditions in the early stage of quenching. This is the key to improving the consistency of hardness distribution.

[0042] To enable the development of process cards and the completion of trial production more conveniently and directly based on this technical solution, further details are provided regarding the selection and coordination of parameters for the preset transfer path, preset lifting posture, and preset tank entry cycle: (I) Selection principles of the preset transfer path Path composition: The preset transfer path includes at least the exit point, the transition alignment point, and the entry alignment point; wherein, the transition alignment point can be composed of a guide frame, a limiting frame, or a ground marking area, which is used to achieve the convergence of the lifting swing and the stability of the attitude before entering the tank.

[0043] Shortest path and obstacle avoidance: Under the premise of meeting the requirements of safe distance and obstacle avoidance, the path with the shortest transfer distance and the fewest turning times is preferred to reduce the high temperature exposure time and natural cooling heat loss, and reduce the swaying and torsional tendencies caused by inertia.

[0044] Sway suppression: The swing amplitude and path deviation during the lifting process are limited by the guide / limiting structure, so that the bent pipe component is in a stable state when it reaches the insertion point. The guide / limiting structure can be a track type, frame type or flexible limiting structure, and can also be implemented in conjunction with the slow start and slow stop control of the lifting device.

[0045] (II) Principles for Selecting the Pre-set Lifting Posture Bending plane attitude: It is preferable to implement directional attitude control on the bending plane so that the heat exchange conditions of the inner and outer arcs in the bending area tend to be consistent during the immersion and cooling stages; this attitude control can be achieved through special lifting tools, limiting components or guide frames.

[0046] Symmetrical multi-point support: It is preferable to set symmetrical multi-point support lifting points at both ends and / or the bending area of ​​the bent pipe component, so that the load is uniform throughout the lifting, translation and entry into the trench, and the additional bending and torsional deformation caused by its own weight is suppressed; the number and position of the lifting points can be adapted and adjusted according to the curvature radius, length and weight of the bent pipe.

[0047] Attitude-path coordination: The preset lifting attitude should match the preset transfer path so that when the bent pipe component reaches the entry point, it can be directly entered into the trench according to the entry rhythm without secondary major adjustments, thereby reducing unnecessary time occupation and temperature loss.

[0048] (III) Selection Principles for Preset Inlet Cycle Tank entry method: The preset tank entry cycle can be segmented entry or uniform entry; segmented entry can be used to reduce instantaneous heat transfer abrupt changes and reduce the cooling difference between inner and outer arcs and thick and thin wall regions, while uniform entry can be used to obtain a more repeatable entry process.

[0049] Dynamic heat exchange after entering the tank: After the bent pipe component is fully entered into the quenching tank, it is preferable to control the swinging and rotating motion of the bent pipe component, or to control the quenching liquid with directional rinsing / recirculation, so that each part of the bent pipe component is in a dynamic heat exchange environment, thereby reducing the heat exchange differences between the inner and outer arcs of the bending zone and areas with different wall thicknesses.

[0050] Cyclic rhythm-medium state coordination: The preset inlet cycle should be coordinated with the cooling medium temperature control and circulation flow state; when the water temperature rises or the circulation flow is insufficient, which may lead to a decrease in cooling intensity, the cooling intensity and uniformity can be restored to the process state that can achieve the target hardness and microstructure consistency by increasing the circulation flow, optimizing the flow direction, or adjusting the inlet cycle and dynamic action parameters.

[0051] (iv) Key interlocks and feasibility assurance To ensure the repeatability and feasibility of the process, it is preferable to set the transfer time, the outer surface temperature at the moment of entering the tank, the water temperature, and the circulation interruption status as interlock / alarm parameters: when the transfer time exceeds 120s and / or the outer surface temperature at the moment of entering the tank is 50°C below the preset quenching temperature, the process of prohibiting entry into the tank or reheating is executed; when the water temperature is higher than 40°C or the circulation is interrupted, an alarm is executed and the quenching process is paused / stopped, and quenching is carried out again after the medium condition is restored.

[0052] Based on the above selection principles and collaborative relationships, it is convenient to directly combine and adjust the path, posture, rhythm and medium state during application, thereby achieving the improvement of the hardness of the pipe component and the improvement of the consistency of the structure.

[0053] To improve the quality of quenching, the requirements for the transfer time of the above-mentioned bent pipe components, the outer surface temperature at the moment of quenching, and the state of the quenching tank are as follows: the transfer time shall not exceed 120s, and the outer surface temperature of the bent pipe component at the moment of entering the quenching tank shall not be lower than 50°C below the preset quenching temperature; when the transfer time of the bent pipe component exceeds the limit and / or the outer surface temperature at the moment of entering the quenching tank is lower than 50°C below the preset quenching temperature, an alarm and / or interlock signal shall be output and the process of prohibiting the bent pipe component from entering the quenching tank or reheating shall be executed.

[0054] The length, width, and height of the quenching tank are all larger than the combined external dimensions of the bent pipe component and the transfer fixture to ensure complete immersion. The cooling medium is water, and the water temperature is monitored and controlled in real time to ensure that the water temperature does not exceed 40°C during the cooling process of the bent pipe component. The water is driven to circulate in the quenching tank through a circulation device to maintain the cooling intensity and uniformity.

[0055] In application, the entire process from the bent pipe component exiting the furnace to entering the quenching tank is timed and controlled to ensure the transfer time does not exceed 120 seconds. The outer surface temperature of the bent pipe component upon entering the quenching tank is monitored to ensure it is not lower than 50°C below the preset quenching temperature. If the transfer time or tank temperature does not meet the requirements, the system outputs an alarm or interlock signal and prohibits the bent pipe component from directly entering the quenching tank or entering the reheating process. Simultaneously, the quenching tank is designed to completely immerse the bent pipe component and the transfer fixture assembly. Water is used as the cooling medium, and the water temperature is controlled to not exceed 40°C through real-time monitoring and circulation. This coordinated control of the bent pipe component's transfer time, temperature, and cooling conditions ensures that the bent pipe component receives sufficient and stable cooling intensity in the early stages of quenching, fundamentally solving the quenching failure problem caused by excessive transfer cooling or unstable cooling medium conditions.

[0056] In other embodiments, the temperature of the tank is detected by infrared thermometry or contact thermometry. Other water-based media or the circulation flow rate can also be introduced as needed to adapt to different component specifications.

[0057] Regarding the control of the aforementioned bent pipe components entering the quenching tank, the preset entry cycle includes controlling the bent pipe components to enter the tank in segments or at a constant speed. After the bent pipe components enter the quenching tank, the bent pipe components are given swing or rotation control, or the quenching liquid in the quenching tank is used to directionally spray / adjust the flow direction of the quenching liquid in the quenching tank, in order to reduce the heat transfer differences between the inner and outer arcs of the bending area and the areas with different wall thicknesses of the bent pipe components.

[0058] In application, when the bent pipe component enters the quenching tank, it is controlled to enter in stages or at a constant speed according to a preset entry rhythm. After fully entering the quenching tank, the bent pipe component is controlled to swing, rotate, or undergo directional rinsing / recirculation. Through the entry rhythm and the cooling action of the bent pipe component in the quenching tank, all parts of the bent pipe component are in a dynamic heat exchange environment during the quenching process. This reduces the heat exchange differences between the inner and outer arcs of the bending zone and between areas with different wall thicknesses, avoiding microstructural deviations caused by excessively strong or weak instantaneous cooling in local areas. The synergistic effect of the entry and quenching control methods with the aforementioned transfer posture control and cooling medium circulation control further improves the overall quenching uniformity.

[0059] In other implementations, the amplitude, frequency, and direction of the oscillation or rotation need to be optimized based on the curvature radius and wall thickness differences of the bend component.

[0060] Specifically, the preset immersion cycle time needs to be selected based on the bending radius and wall thickness differences of the bent pipe component. For bent pipe components with small bending radii and large wall thickness differences, to avoid cracking caused by a large cooling temperature difference between the inner and outer arcs due to instantaneous immersion, a "segmented immersion" method is preferred. For example, first immerse the bent section and hold it for 2-3 seconds, then immerse the remaining part at a uniform speed to reduce the instantaneous thermal stress in the bending area. For components with large bending radii and uniform wall thickness, a "uniform speed immersion" method can be used to improve production efficiency.

[0061] A second implementation of the process for improving the hardness of steel pipes through heat treatment, for example... Figure 2 As shown, the difference between this embodiment and the first embodiment is that it also includes a quality control step: recording and tracing the quenching temperature, holding time, transfer time, circulation state of the immersed cooling medium, and hardness test results of the bent pipe component; wherein, the circulation state parameters include at least the circulation temperature, circulation flow rate, and circulation interruption state; when the hardness of the bent pipe component is lower than the preset lower hardness limit, the reprocessing process of S1 to S5 is allowed to be executed again, and the number of reprocessing times is constrained by a preset upper limit.

[0062] In application, after the heat treatment of the bent pipe component is completed, parameters such as quenching temperature, holding time, transfer time, and the circulating temperature, flow rate, and interruption status of the cooling medium are recorded and stored in conjunction with the hardness test results to achieve full-process quality traceability. When the hardness of the bent pipe component is detected to be lower than the preset lower hardness limit, the S1 to S5 heat treatment process is allowed to be repeated under controlled conditions, with an upper limit set on the number of re-treatments to prevent microstructure deterioration caused by repeated heat treatments. By introducing the above quality control and re-treatment mechanisms, this technical solution can not only improve the success rate of single heat treatment but also significantly improve the stability and consistency of the finished product quality of bent pipe components in mass production.

[0063] Furthermore, in order to establish a mechanism for process improvement and quality replication, the quality control steps can be combined with a digital management system to create independent process files for different batches or specifications of bent pipe components, so as to further improve process optimization and quality management capabilities.

[0064] Through actual production verification of the bent pipe components made from WB36 medium-frequency bending pipes, the following embodiments and comparative data were obtained: Example 1: Workpiece information: A bending component is made from WB36 steel pipe using medium frequency bending, with specifications of Φ457 (diameter) × 55mm (wall thickness) and a bending radius of 1.5D.

[0065] Process execution: Clamping: A special transfer fixture is used to symmetrically support the two ends and the bending area of ​​the bent pipe component.

[0066] Austenitizing: Heat to 930℃ (select according to wall thickness) and hold for 125 minutes.

[0067] High-temperature transfer: Transfer along the preset shortest path, control the lifting posture to keep the bending plane vertical, transfer time is 95s, and the temperature upon entering the tank is detected as 885℃ (meeting the requirement of ≥50℃ below the preset quenching temperature).

[0068] Quenching: The process involves immersing the bent section first, followed by full immersion after 2 seconds. The water temperature is controlled at 25-30℃, and the circulation flow rate is 200 m³ / h.

[0069] Tempering: Hold at 680℃ for 6 hours, then air cool.

[0070] Performance testing: Hardness: Samples were taken from the outer arc, inner arc and neutral layer of the bent section of the pipe component. The Brinell hardness values ​​(HBW) were 255, 248 and 252 respectively, with a range of 7 HBW, which is much lower than the range of conventional processes (about 25 HBW).

[0071] Microstructure: The microstructure consists of tempered bainite with a small amount of ferrite, with a grain size of grade 8 and a uniform microstructure.

[0072] Deformation: After heat treatment, the change in ellipticity is ≤0.5%D, and the change in bending angle is ≤0.2°, which meets the dimensional accuracy requirements.

[0073] Comparative Example 1: Using conventional normalizing + tempering process Workpiece information: Same as in Example 1.

[0074] Process execution: Heat to 930℃, hold for a period of time, then air cool (normalizing), and then temper at 680℃.

[0075] Performance testing: Hardness: The hardness of the outer arc, inner arc and neutral layer of the bent section of the pipe component are 210, 190 and 200 HBW respectively. The hardness is too low and the hardness of the inner arc is obviously insufficient.

[0076] Analysis: Due to insufficient air cooling rate, a large amount of ferrite precipitated, and a high-hardness bainitic structure was not obtained.

[0077] Comparative Example 2: Quenching process without optimized transfer and immersion. Workpiece information: Same as in Example 1.

[0078] Process execution: Heating to 930℃ and holding, but the transfer process was arbitrary, the posture was not controlled, the transfer time was as long as 150s, and after the temperature in the tank was lower than 820℃, the whole thing was directly immersed in cold water.

[0079] Performance testing: Hardness: The hardness distribution is extremely uneven, with some areas reaching 300 HBW (martensite) and others only 180 HBW, resulting in a very large range.

[0080] Deformation: Microcracks appear in the bent section of the pipe component, and the ellipticity deformation reaches 1.8%D, rendering the product unusable.

[0081] Analysis: Excessive transfer time leads to uneven temperature, and poor entry posture exacerbates the difference in heat transfer between the inner and outer arcs, resulting in both localized overcooling (martensite formation) and localized undercooling, generating huge internal stress that causes cracking and deformation.

[0082] Based on the above embodiments of the steel pipe heat treatment hardness improvement process, a steel pipe heat treatment hardness improvement process system is provided for implementing the steel pipe heat treatment hardness improvement process, such as... Figure 3As shown, the system includes a heating unit for heating the clamped bent pipe component to the quenching temperature and maintaining that temperature; a transfer fixture and lifting unit for multi-point support and clamping of the bent pipe component, and for completing the transfer from the furnace and into the quenching tank according to a preset transfer path and preset lifting posture; a quenching tank unit for containing the cooling medium and providing circulation and temperature control; and a control and recording unit for monitoring and recording the transfer time of the bent pipe component, the outer surface temperature at the moment of entering the quenching tank, and the temperature and circulation status of the cooling medium, and outputting alarm and / or interlock signals when the transfer time exceeds 120s, the outer surface temperature at the moment of entering the quenching tank is lower than 50°C below the preset quenching temperature, and / or the temperature of the cooling medium is higher than 40°C, or the circulation is interrupted; wherein, the transfer fixture and lifting unit and the quenching tank unit constitute an integrated execution link for high-temperature transfer and quenching, so as to improve the hardness of the bent pipe component and improve the consistency of its microstructure and hardness distribution.

[0083] When applied, the steel pipe heat treatment hardness improvement process system of this technical solution forms an integrated execution link for high-temperature transfer and quenching of medium-frequency bent pipe components through the coordinated cooperation of the heating unit (including heating furnace), transfer tooling and lifting and transfer unit, quenching tank unit (including quenching tank), and control and recording unit.

[0084] Specifically, after the bent pipe component is austenitized and held at a temperature by the heating unit under multi-point support and clamping conditions, it is transferred out of the furnace along a preset transfer path and in a preset lifting posture with the help of transfer fixtures and lifting transfer unit, so that the bent pipe component maintains uniform load and posture control under high temperature conditions; then it enters the quenching tank unit according to the predetermined tank entry rhythm, and completes quenching and cooling under the conditions of circulating cooling medium and temperature control.

[0085] Meanwhile, the control and recording unit monitors and records the transfer time of the bent pipe component, the outer surface temperature at the moment of entering the quenching tank, and the temperature and circulation status of the cooling medium in real time. When it is detected that the transfer time exceeds 120s, the outer surface temperature at the moment of entering the tank is 50°C below the preset quenching temperature, the cooling medium temperature is higher than 40°C, and / or the circulation is interrupted, it outputs alarm and / or interlock signals in a timely manner to prevent the bent pipe component that does not meet the process conditions from entering the quenching stage or trigger the reprocessing process, and re-enter steps S1 to S4.

[0086] If the parameters during the heating and quenching process are not properly controlled, tempering is not required, which further reduces the production cost of defective products and thus lowers the production cost of finished bent pipe components.

[0087] By implementing a systematic approach, the bending components are kept under control throughout the critical stages from furnace exit to quenching. This effectively solves the problems of insufficient or unstable cooling rates caused by uncontrolled transfer processes and fluctuating cooling conditions in existing steel pipe heat treatment. At the same time, through the synergistic effect of uniform force transfer and cyclic cooling, the heat transfer consistency of the inner and outer arcs of the bend and regions with different wall thicknesses is significantly improved. This enhances the consistency of the microstructure and hardness distribution after quenching, reduces the risk of heat treatment deformation and local overcooling, and improves the stability and reliability of the heat treatment quality of the bending components.

[0088] Furthermore, the control and recording unit can be connected to the host computer system or production management system to establish process parameter files for bent pipe components of different specifications or batches; the structural form of the transfer tooling and lifting transfer unit is adapted and adjusted according to the length, radius of curvature or weight of the bent pipe component; in addition, the circulation mode, flow guiding structure and cooling medium status monitoring method of the quenching tank unit are also optimized in an engineering manner according to the length, radius of curvature or weight of the bent pipe component.

[0089] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described.

Claims

1. A process for improving the hardness of steel pipes through heat treatment, applicable to steel pipe bending components after medium-frequency bending, characterized in that, include, S1. Clamping and fixing: The bent pipe component to be processed is clamped on the transfer fixture for uniform support and attitude control of the bent pipe component during heating, furnace transfer and tank entry. S2, Austenitizing heating: The bent pipe component is sent into a heating furnace and heated to a preset quenching temperature and held at that temperature; S3. High-temperature transfer: After the bent pipe component exits the heating furnace, it is transferred from the furnace opening to the top of the quenching tank according to a preset transfer path and in a preset lifting posture, and the transfer time from the bent pipe component exiting the heating furnace to entering the quenching tank is recorded. S4. Quenching and cooling: The bent pipe component is immersed in the cooling medium in the quenching tank according to the preset immersion rhythm for quenching, and the cooling is completed under the condition of circulating flow of the cooling medium. S5. Tempering treatment: Temper the quenched pipe component. The preset transfer path, the preset lifting posture, and the preset grooving rhythm constitute an integrated high-temperature transfer and quenching process for medium-frequency bent pipes.

2. The process for improving the hardness of steel pipes through heat treatment according to claim 1, characterized in that, The bending component is a medium-frequency bending component of WB36 steel pipe, and the wall thickness of the steel pipe is ≥30mm.

3. The process for improving the hardness of steel pipes through heat treatment according to claim 1, characterized in that, The preset quenching temperature is 880–950℃; The tempering treatment includes: tempering the bent pipe component at a tempering temperature of 620-700°C for 4-8 hours, and then air-cooling the bent pipe component to room temperature after the tempering is completed.

4. The process for improving the hardness of steel pipes through heat treatment according to claim 1, characterized in that, The preset transfer path is the path with the shortest transfer distance from the furnace opening of the heating furnace to the quenching tank, provided that the safety distance and obstacle avoidance requirements are met, and the lifting swing amplitude and path deviation are limited by the guide / limiting structure.

5. The process for improving the hardness of steel pipes through heat treatment according to claim 1, characterized in that, The preset lifting posture includes posture control of the bending plane of the bent pipe component, and symmetrical multi-point support of the two ends and / or bending area of ​​the bent pipe component through the transfer fixture.

6. The process for improving the hardness of steel pipes through heat treatment according to claim 1, characterized in that, The transfer time is no more than 120 seconds, and the outer surface temperature of the bent pipe component at the instant it enters the quenching tank is no less than 50°C below the preset quenching temperature. When the transfer time of the bent pipe component exceeds the limit and / or the outer surface temperature of the bent pipe component is 50°C below the preset quenching temperature at the moment of entering the quenching tank, an alarm and / or interlock signal is output and the bent pipe component is prohibited from entering the quenching tank or from reheating.

7. The process for improving the hardness of steel pipes through heat treatment according to claim 1, characterized in that, The length, width, and height of the quenching tank are all greater than the combined external dimensions of the bent pipe component and the transfer fixture to ensure complete immersion. The cooling medium is water, and the water temperature is monitored and controlled in real time to ensure that the water temperature does not exceed 40°C during the cooling process of the bent pipe component. The water is also driven to circulate in the quenching tank by a circulation device.

8. The process for improving the hardness of steel pipes through heat treatment according to claim 7, characterized in that, The preset quenching cycle includes controlling the entry of the bent pipe component into the quenching tank in segments or at a constant speed, and after the bent pipe component enters the quenching tank, controlling the bending pipe component to swing or rotate, or using the quenching liquid in the quenching tank to directionally rinse the bent pipe component / adjust the flow direction of the quenching liquid in the quenching tank.

9. The process for improving the hardness of steel pipes through heat treatment according to claim 1, characterized in that, It also includes quality control steps: recording and tracing the quenching temperature, holding time, transfer time, circulation status of the cooling medium immersed in the bent pipe component, and hardness test results; The cycle state parameters include at least cycle temperature, cycle flow rate, and cycle interruption status; When the hardness of the bent pipe component is lower than the preset lower hardness limit, the reprocessing process of S1 to S5 is allowed to be executed again, and the number of reprocessing times is constrained by the preset upper limit.

10. A process system for improving the hardness of steel pipes through heat treatment, used to implement the process method for improving the hardness of steel pipes through heat treatment according to any one of claims 1 to 9, characterized in that, Includes a heating unit for heating the clamped bent pipe component to the quenching temperature and holding it at that temperature; The system also includes a transfer tooling and a lifting and transfer unit, which are used to achieve multi-point support and clamping of the bent pipe component, and to complete the transfer from the furnace and into the tank according to a preset transfer path and a preset lifting posture. And a quenching tank unit, used to contain the cooling medium and provide circulation and temperature control; And a control and recording unit, used to monitor and record the transfer time of the bent pipe component, the outer surface temperature at the moment of entering the quenching tank, and the temperature and circulation status of the cooling medium, and output alarm and / or interlock signals when the transfer time exceeds 120s, the outer surface temperature at the moment of entering the quenching tank is lower than 50°C below the preset quenching temperature, and / or the temperature of the cooling medium is higher than 40°C and the circulation is interrupted. The transfer tooling, the lifting and transfer unit, and the quenching tank unit constitute an integrated execution link for high-temperature transfer and quenching, so as to improve the hardness of the bent pipe component and improve the consistency of its microstructure and hardness distribution.

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