Local heat treatment method for D406A thin-walled cylinder welding seam

Abstract

The invention provides a local heat treatment method for a D406A thin-walled cylinder welding seam. The method comprises the steps that firstly, a first center line of a D406A thin-walled cylinder subjected to laser welding is precisely aligned with a second center line of an induction heating coil of a medium-frequency induction heating device; secondly, the position of a welding seam of the D406A thin-walled cylinder is adjusted, and the welding seam is located in the center area of the induction heating coil; then, alternating current is introduced into the induction heating coil so as to carry out local induction heating treatment on the welding seam; and finally, the heated D406A thin-walled cylinder is cooled, and a component obtained after heat treatment is obtained. According to the local heat treatment method provided by the invention, by combining the characteristic that induction heating directly emits heat depending on electromagnetic induction, targeted local heating of the welding seam is realized, the treatment period of annealing and tempering is greatly shortened, the energy loss of an unnecessary area is reduced, the occupied area and energy consumption of equipment are reduced, and cost reduction and efficiency improvement are achieved; and meanwhile, the residual tensile stress of the welding seam is completely eliminated, and the pressure stress, tensile strength and bendability meet production standards.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology for ultra-high strength steel, and in particular to a method for local heat treatment of weld seams in D406A thin-walled cylindrical bodies. Background Technology

[0002] D406A ultra-high strength steel, with its high strength, lightweight, excellent resistance to extreme environments, and high reliability, has become an ideal material for modern aerospace, shipbuilding, and other manufacturing fields, driving the development of alloy materials. D406A has a tensile strength exceeding 1600 MPa, significantly improving structural strength when used in load-bearing structures. Its oxidation resistance and high-temperature strength ensure structural stability, preventing thermal stress deformation when used in rocket engine nozzles and combustion chambers. The micro-grain refinement technology of D406A extends component lifespan and reduces the risk of failure under high-frequency vibration and large instantaneous overloads. D406A allows for integrated molding of complex components using advanced welding techniques, reducing weight redundancy from traditional riveting, and its low work hardening rate makes it suitable for precision cold stamping processes. Compared to titanium alloys or composite materials, D406A has lower raw material and processing costs, making it suitable for large-scale manufacturing of rocket engine nozzles, combustion chambers, and other components.

[0003] During laser welding of D406A thin-walled cylinders, excessively high welding temperatures and rapid cooling rates can easily generate significant residual stress at the weld seam, leading to cylinder cracking or deformation. Tensile stress is more harmful than compressive stress. To reduce residual stress at the weld seam of the D406A cylinder, it is necessary to promptly perform appropriate post-weld stress-relieving heating treatment.

[0004] Current technology typically employs resistance furnace heating for annealing and tempering of welded D406A thin-walled cylinders to eliminate residual welding stress. However, this post-weld treatment process suffers from drawbacks such as long heating time, large equipment footprint, high energy consumption, and low heating efficiency. These disadvantages hinder the continuity and cycle control of industrial-scale mass production, increase energy costs, and restrict the flexibility of production line layout due to the large equipment footprint.

[0005] Therefore, there is an urgent need for a local heat treatment method for the weld of D406A thin-walled cylindrical body to solve the above-mentioned technical problems. Summary of the Invention

[0006] The purpose of this invention is to provide a local heat treatment method for weld seams of D406A thin-walled cylindrical bodies. This process has the advantages of small equipment footprint, simple temperature control, high heating efficiency, and low cost, and can overcome the technical shortcomings of post-weld treatment processes using resistance furnace heating.

[0007] To solve the above-mentioned technical problems, the present invention provides a method for local heat treatment of weld seams in D406A thin-walled cylindrical bodies, the method comprising: S10, precisely align the first center line of the laser-welded D406A thin-walled cylinder with the second center line of the induction heating coil of the medium-frequency induction heating device; S20, adjust the position of the weld seam of the D406A thin-walled cylinder so that the weld seam is in the center area of ​​the induction heating coil; S30, an alternating current is passed through the induction heating coil to perform local induction heating treatment on the weld; S40 involves cooling the heated D406A thin-walled cylinder to obtain the heat-treated component.

[0008] Preferably, in step S10: the material of the D406A thin-walled cylinder is D406A ultra-high strength steel, which, by weight percentage, comprises: C content of 0.27~0.32%, Mn content of 0.70~1.00%, Si content of 1.40~1.70%, Cr content of 1.00~1.30%, Mo content of 0.40~0.55%, V content of 0.08~0.15%, S content ≤0.008%, P content ≤0.010%, Cu content ≤0.25%, and Ni content of 0.25%. Preferably, in step S10: the medium-frequency induction heating device further includes an infrared thermometer, which is used to monitor the temperature at the weld position of the D406A thin-walled cylinder in real time.

[0009] Preferably, in step S10: the induction heating coil is moved along the length direction perpendicular to the D406A thin-walled cylinder by the lifting mechanism of the medium-frequency induction heating device.

[0010] Preferably, in step S20: the D406A thin-walled cylinder is placed on the conveying and supporting mechanism of the medium-frequency induction heating device, and the D406A thin-walled cylinder is moved along the length direction parallel to the D406A thin-walled cylinder by the conveying and supporting mechanism.

[0011] Preferably, in step S30: when the D406A thin-walled cylinder is in the annealed state before post-weld heat treatment, the weld is subjected to medium-frequency induction annealing heating treatment by induction heating coil, the heating temperature is 680~720℃, and the heating and holding time is 5~15min.

[0012] Preferably, in step S40: the compressive stress of the component at the weld position after heat treatment is 20~120MPa, the tensile strength is 680~720MPa, and the component after heat treatment has no cracks after being bent 180°.

[0013] Preferably, in step S30: when the D406A thin-walled cylinder is in a quenched and tempered state before post-weld heat treatment, the weld is subjected to medium-frequency induction tempering heating treatment by an induction heating coil, the heating temperature is 305~345℃, and the heating and holding time is 25~35min.

[0014] Preferably, in step S40: the compressive stress of the component at the weld position after heat treatment is 24~140MPa, the tensile strength is greater than 1510MPa, and the component after heat treatment has no cracks after being bent at 40°.

[0015] Preferably, in step S40: the cooling treatment is air cooling, and the tensile stress of the component at the weld position after heat treatment is 0.

[0016] The beneficial effects of this invention are as follows: Unlike existing technologies, this invention provides a method for localized heat treatment of weld seams in D406A thin-walled cylindrical bodies. The method first precisely aligns the first centerline of the laser-welded D406A thin-walled cylindrical body with the second centerline of the induction heating coil of a medium-frequency induction heating device. Second, the position of the weld seam in the D406A thin-walled cylindrical body is adjusted so that the weld seam is located in the central region of the induction heating coil. Then, an alternating current is passed through the induction heating coil to perform localized induction heating treatment on the weld seam. Finally, the heated D406A thin-walled cylindrical body is cooled to obtain the heat-treated component. The local heat treatment method for the weld seam of D406A thin-walled cylinder provided in this application involves placing the laser-welded cylinder in a medium-frequency induction heating device and precisely aligning the coil with the center line of the cylinder. After adjusting the weld seam to the center area of ​​the coil, an alternating current is applied. Combining the characteristics of induction heating, which relies on electromagnetic induction to directly heat the weld seam, targeted local heating is achieved. Since local heating replaces the overall heating of traditional resistance furnaces, and induction heating has a faster heating rate, the annealing and tempering processing cycle is significantly shortened, energy loss in unnecessary areas is reduced, and equipment footprint and energy consumption are lowered, achieving cost reduction and efficiency improvement. At the same time, by precisely controlling the heating temperature, holding time, and air cooling method, the residual tensile stress in the weld seam is completely eliminated, and the compressive stress, tensile strength, and bending performance all meet production standards. This effectively solves the problem of cracking or deformation of the cylinder due to residual stress after laser welding, thereby improving production efficiency while ensuring product quality stability. Especially for the mass production of D406A thin-walled cylinders, it can significantly improve process yield and enterprise competitiveness. Attached Figure Description

[0017] Figure 1 A flowchart illustrating a method for local heat treatment of weld seams in a D406A thin-walled cylindrical body, as provided in an embodiment of the present invention. Figure 2 A simplified structural diagram of the medium-frequency induction heating device for the local heat treatment method of the weld seam of D406A thin-walled cylinder provided in an embodiment of the present invention; Figure 3 The induction heating annealing and tempering process curves of the local heat treatment method for the D406A thin-walled cylindrical weld provided in Embodiment 1 of the present invention are shown. Figure 4 Traditional annealing process curve for D406A thin-walled cylindrical body in annealed state; Figure 5 This is a traditional tempering process curve diagram for quenched and tempered D406A thin-walled cylinders; In the accompanying drawings, 100—medium-frequency induction heating device; 10—supporting mechanism; 11—first supporting table; 12—second supporting table; 20—transmission and support mechanism; 21—first transmission and support component; 22—second transmission and support component; 30—liftable mechanism; 40—induction heating coil. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] To address the shortcomings of existing technologies, this application introduces induction heating technology into the heat treatment process of D406A high-strength steel to improve production efficiency. Compared to current resistance furnace heating, induction heating offers advantages such as rapid heating, high heating efficiency, simple temperature control, non-contact operation, localized treatment only, and smaller size. For cylinders made of D406A high-strength steel, there is no need for overall furnace heating, and the heating time is significantly reduced compared to resistance furnace heating, effectively improving efficiency and reducing energy consumption while reducing equipment footprint.

[0020] The technical problem to be solved by the present invention is to provide an induction heating annealing and tempering process for D406A thin-walled cylinders. This process has the advantages of small equipment footprint, simple temperature control, high heating efficiency and low cost, and can overcome the technical shortcomings of resistance furnace heating annealing and tempering.

[0021] To achieve the above objectives, the present invention provides the following technical solution: Please see Figure 1 , Figure 1 A flowchart of a local heat treatment method for the weld seam of a D406A thin-walled cylindrical body provided by the present invention; wherein the local heat treatment method includes the following steps: S10, precisely align the first center line of the laser-welded D406A thin-walled cylinder with the second center line of the induction heating coil 40 of the medium-frequency induction heating device 100.

[0022] Specifically, step S10 also includes: First, a medium-frequency induction heating device 100 is provided, the specific structure of which is as follows: Figure 2 As shown; wherein, the medium frequency induction heating device 100 includes a bearing mechanism 10, a conveying and supporting mechanism 20, a lifting mechanism 30 and an induction heating coil 40.

[0023] Secondly, by adjusting the relative position of the lifting mechanism 30 and the bearing mechanism 10, the induction heating coil 40 is moved along the length direction perpendicular to the D406A thin-walled cylinder, thereby precisely aligning the first center line of the laser-welded D406A thin-walled cylinder with the second center line of the induction heating coil 40 of the medium-frequency induction heating device 100.

[0024] Specifically, through the coordinated operation of the lifting mechanism 30, the carrying mechanism 10, and the conveying support mechanism, it can flexibly adapt to and stably support different specifications of D406A thin-walled cylinders, and also achieve precise alignment of the cylinder with the center line of the induction heating coil 40, laying the foundation for the subsequent positioning of the weld seam in the center area of ​​the coil. This operation not only ensures that the induction heating energy is concentrated on the weld seam, avoiding overheating or underheating caused by heating deviation, but also reduces workpiece performance fluctuations through stable positioning accuracy, enhances the compatibility of the device with diverse workpieces, and ultimately provides reliable structural support and process stability guarantee for efficient and high-quality local heat treatment.

[0025] Specifically, the material of the D406A thin-walled cylinder is D406A ultra-high strength steel, which, by weight percentage, includes: Fe content of 94.11%~95.00%, C content of 0.27%~0.32%, Mn content of 0.70%~1.00%, Si content of 1.40%~1.70%, Cr content of 1.00%~1.30%, Mo content of 0.40%~0.55%, V content of 0.08%~0.15%, S content ≤0.008%, P content ≤0.010%, Cu content ≤0.25%, Ni content of 0.25%, with the balance being unavoidable impurities.

[0026] Please see Figure 2 The supporting mechanism 10 includes a first supporting table 11 and a second supporting table 12 arranged at intervals between each other. The conveying and supporting mechanism 20 includes a first transmission and supporting member 21 and a second transmission and supporting member 22 arranged at intervals between each other. The first transmission and supporting member 21 is mounted on the first supporting table 11 and is slidably connected to the first supporting table 11. The second transmission and supporting member 22 is mounted on the second supporting table 12 and is slidably connected to the second supporting table 12.

[0027] Specifically, the above design can flexibly adapt to D406A thin-walled cylinders of different lengths by sliding and adjusting the distance between the two transmission support components, ensuring stable support for the cylinder (especially for the easily deformable characteristics of thin walls, avoiding workpiece damage or positioning displacement caused by unstable support); it can also achieve fine adjustment of the relative position between the D406A thin-walled cylinder and the induction heating coil 40 through sliding adjustment, and further improve the accuracy of centerline alignment with the lifting mechanism 30, laying the foundation for the precise alignment of the weld seam and the center area of ​​the coil, and ultimately enhancing the compatibility of the device with diverse workpieces and the stability of the overall process.

[0028] Please see Figure 2 The lifting mechanism 30 is located between the first support table 11 and the second support table 12. The first end of the lifting mechanism 30 is slidably connected to the table leg of the first support table 11, and the second end of the lifting mechanism 30 is slidably connected to the table leg of the second support table 12 on the side closer to the first support table 11. The induction heating coil 40 is installed on the top of the lifting mechanism 30 and is integrally formed with the lifting mechanism 30.

[0029] Specifically, the lifting mechanism 30 is located between the first support table 11 and the second support table 12 and is slidably connected to the table legs. Together with the induction heating coil 40 integrally formed on the top, the height of the induction heating coil 40 can be adjusted by means of the lifting function to achieve precise alignment with the center line of D406A thin-walled cylinders of different specifications. The integral design ensures the connection stability between the induction heating coil 40 and the lifting mechanism 30, avoiding heating deviation caused by the shaking of the induction heating coil 40 during the heating process. At the same time, the dual adjustment function of sliding and lifting enhances the adaptability of the device to variables such as cylinder diameter and placement position, providing a reliable adjustment guarantee for the precise positioning of the weld seam in the center area of ​​the coil, and further improving the positioning accuracy and process stability of local heating.

[0030] Specifically, the medium-frequency induction heating device 100 also includes an infrared thermometer, which is used to monitor the temperature of the weld seam of the D406A thin-walled cylinder in real time. By monitoring the temperature of the weld seam of the D406A thin-walled cylinder in real time, the temperature changes during the heating process can be accurately captured, providing real-time data support for the adjustment of the alternating current of the induction heating coil 40. This real-time monitoring function can effectively avoid the problem of excessively high weld seam temperature (causing cylinder burn-out or performance degradation) or excessively low temperature (incomplete stress relief) caused by fluctuations in heating parameters, ensuring that the heating temperature is strictly controlled within the process setting range. At the same time, combined with the precise positioning of centerline alignment, it further improves the temperature stability and process controllability of local heating, ensuring the consistency of weld stress relief effect and mechanical properties after heat treatment, and providing reliable temperature monitoring guarantee for efficient and high-quality mass production.

[0031] S20, adjust the position of the weld seam of the D406A thin-walled cylinder so that the weld seam is in the center area of ​​the induction heating coil 40.

[0032] Specifically, step S20 also includes: The D406A thin-walled cylinder is placed on the conveying and supporting mechanism 20 of the medium-frequency induction heating device 100. The conveying and supporting mechanism 20 moves the D406A thin-walled cylinder along the length direction parallel to the D406A thin-walled cylinder, thereby adjusting the position of the weld of the D406A thin-walled cylinder so that the weld is located in the central area of ​​the induction heating coil 40.

[0033] Specifically, by utilizing the directional movement function of the conveying and supporting mechanism 20, the displacement distance of the D406A thin-walled cylinder can be precisely controlled, ensuring that the weld seam is stably located in the central area of ​​the induction heating coil 40. This avoids errors caused by manual positioning, ensures that the induction heating energy is concentrated on the weld seam, and improves the targeting and efficiency of local heating. At the same time, the coordinated operation of the conveying and supporting mechanism 20 can stably support the D406A thin-walled cylinder during movement (especially considering the easily deformable characteristics of thin-walled structures), reducing workpiece damage during positioning. It also adapts to the weld seam position adjustment requirements of cylinders of different lengths, enhancing the compatibility of the device with diverse workpieces. This lays the foundation for subsequent precise heating and stress relief effects, further ensuring the stability of the heat treatment process and the uniformity of product quality.

[0034] S30, an alternating current is passed through the induction heating coil 40 to perform local induction heating treatment on the weld.

[0035] Specifically, step S30 also includes: Maintaining the D406A thin-walled cylinder and induction heating coil 40 in a relatively stationary state, an alternating current is applied to locally heat the weld area: when the D406A thin-walled cylinder is in an annealed state before post-weld heat treatment, the weld is subjected to medium-frequency induction annealing heating treatment via induction heating coil 40, with a heating temperature of 680~720℃ and a heating and holding time of 5~15 minutes; in terms of temperature adaptability, this temperature range precisely matches the stress relief requirements of the weld of the annealed D406A thin-walled cylinder—within this range, the weld… The residual tensile stress in the metal material of the region can be fully released through atomic diffusion and dislocation movement, while avoiding excessively high temperatures that lead to coarse grains in the base material of the cylinder (affecting mechanical properties) or excessively low temperatures that lead to incomplete stress elimination (risk of residual cracking). In terms of time control, the heating and holding time of 5 to 15 minutes, combined with the characteristics of "rapid local heating and high thermal efficiency" of medium frequency induction heating, can ensure that the weld seam completes stress relaxation at the target temperature, and is significantly shorter than the time required for overall annealing in traditional resistance furnaces, reducing unnecessary energy consumption and production cycle.

[0036] Specifically, when the D406A thin-walled cylinder is in a quenched and tempered state before post-weld heat treatment, the weld is subjected to medium-frequency induction tempering heating treatment by induction heating coil 40. The heating temperature is 305~345℃, and the heating and holding time is 25~35min. This temperature range can promote the softening of the hardened structure of the weld (reducing brittleness) and release residual tensile stress, while avoiding the decrease in the strength of the base material due to high temperature. The 25~35min holding time, combined with the advantage of rapid local heating of induction heating, can ensure that the stress is fully eliminated and the processing cycle is significantly shortened. Local heating reduces the thermal impact on the overall cylinder and ensures that the base material maintains high strength.

[0037] S40 involves cooling the heated D406A thin-walled cylinder to obtain the heat-treated component.

[0038] Specifically, step S40 also includes: The heated D406A thin-walled cylinder is cooled to obtain a heat-treated component. The cooling process is air cooling. When the D406A thin-walled cylinder is in the annealed state before post-weld heat treatment, the compressive stress at the weld position of the heat-treated component is 20~120MPa, the tensile stress is 0, and the tensile strength is 680~720MPa. The heat-treated component shows no cracks after being bent 180°. When the D406A thin-walled cylinder is in the quenched and tempered state before post-weld heat treatment, the compressive stress at the weld position of the heat-treated component is 24~140MPa, the tensile stress is 0, and the tensile strength is greater than 1510MPa. The heat-treated component shows no cracks after being bent 40°.

[0039] Specifically, for annealed cylinders, air cooling completely eliminates the tensile stress in the weld (tensile stress is 0), stabilizes the compressive stress at 20~120MPa, achieves a tensile strength of 680~720MPa, and exhibits no cracks when bent at 180°, meeting the toughness and stress relief requirements of the annealed state. For quenched and tempered cylinders, air cooling avoids secondary hardening or stress rebound caused by rapid cooling, ensuring that the tensile stress in the weld is zero (tensile stress is 0), controlling the compressive stress at 24~140MPa, maintaining a tensile strength >1510MPa, and exhibiting no cracks when bent at 40°, balancing high strength and crack resistance. This cooling method simplifies the process and, through synergy with heating parameters, ultimately ensures that the performance of cylinders in different states meets the standards after heat treatment, providing efficient and stable process assurance for mass production.

[0040] The local heat treatment method for the weld of the D406A thin-walled cylindrical body described above will be detailed below through specific embodiments.

[0041] Example 1: Please see Figure 3Embodiment 1 of the present invention provides a method for local heat treatment of weld seams of D406A thin-walled cylindrical bodies. The material of the D406A thin-walled cylindrical body is D406A ultra-high strength steel. The D406A ultra-high strength steel comprises, by weight percentage: 94.2% Fe, 0.28% C, 0.8% Mn, 1.41% Si, 1.02% Cr, 0.41% Mo, 0.09% V, 0.008% S, 0.010% P, 0.25% Cu, 0.25% Ni, with the balance being unavoidable impurities.

[0042] The specific steps of the local heat treatment method provided in Embodiment 1 of the present invention include: Step (1): Place the laser-welded D406A thin-walled cylinder into a... Figure 2 The side of the medium-frequency induction heating device 100 shown is close to the induction heating coil 40.

[0043] Step (2): Adjust the liftable structure of the medium frequency induction heating device 100 so that the center line of the induction heating coil 40 is aligned with the center line of the D406A thin-walled cylinder.

[0044] Step (3): Place the D406A thin-walled cylinder on the conveying and supporting mechanism, and adjust the position of the D406A thin-walled cylinder so that its weld position is exactly in the middle of the induction heating coil 40 (the weld of the induction heating coil 40 and the D406A thin-walled cylinder is on a parallel plane, and the weld position is in the middle of the vertical direction of the induction heating coil 40).

[0045] Step (4): For the annealed / tempered D406A thin-walled cylinder, set different heating temperatures and turn on the induction heating coil 40. At this time, the induction heating coil 40 and the D406A thin-walled cylinder are relatively stationary. The temperature during the induction heating process is monitored in real time by an infrared thermometer.

[0046] Step (5): After the predetermined heat preservation time is reached, turn off the induction heating coil 40 (since the induction heating coil 40 heats up quickly, the heating time used is ignored and the heating and heat preservation time are regarded as a whole).

[0047] Step (6): The heated D406A thin-walled cylinder is air-cooled to obtain the heat-treated component.

[0048] Specifically, in steps (4) and (5): when the D406A thin-walled cylinder is in the annealed state before post-weld heat treatment, the weld is subjected to medium-frequency induction annealing heat treatment by induction heating coil 40, the heating temperature is 700℃, and the heating and holding time is controlled within 10 minutes; when the D406A thin-walled cylinder is in the tempered state before post-weld heat treatment, the weld is subjected to medium-frequency induction tempering heat treatment by induction heating coil 40, the heating temperature is 325℃, and the heating and holding time is 30 minutes. Specifically, in step (6): when the D406A thin-walled cylinder is in the annealed state before post-weld heat treatment, the compressive stress of the component at the weld position after heat treatment is 100MPa, the tensile stress is 0, the tensile strength is 700MPa, and the component after heat treatment is free from cracks after being bent 180°; when the D406A thin-walled cylinder is in the quenched and tempered state before post-weld heat treatment, the compressive stress of the component at the weld position after heat treatment is 100MPa, the tensile stress is 0, the tensile strength is 1600MPa, and the component after heat treatment is free from cracks after being bent 40°.

[0049] Comparative Example 1: Comparative Example 1 provides a local heat treatment method for the weld of a D406A thin-walled cylindrical body. The material of the D406A thin-walled cylindrical body is D406A ultra-high strength steel. The D406A ultra-high strength steel comprises, by weight percentage: 94.2% Fe, 0.28% C, 0.8% Mn, 1.41% Si, 1.02% Cr, 0.41% Mo, 0.09% V, 0.008% S, 0.010% P, 0.25% Cu, 0.25% Ni, with the balance being unavoidable impurities.

[0050] The specific steps of the local heat treatment method provided in Comparative Example 1 include: Step (1): Place the laser-welded D406A thin-walled cylinder into an electric resistance furnace.

[0051] Step (2): For the annealed / tempered D406A thin-walled cylinder, set different heating temperatures and turn on the heating components of the resistance furnace to heat the D406A thin-walled cylinder.

[0052] Step (3): Turn off the heating element after the predetermined heat preservation time has been reached.

[0053] Step (4): The heated D406A thin-walled cylinder is subjected to air cooling treatment to obtain the heat-treated component.

[0054] Please see Figure 4 , Figure 4The diagram shows the traditional annealing process curve for D406A thin-walled cylinders in the annealed state. When the material of the D406A thin-walled cylinder is D406A ultra-high strength steel and it is in the annealed state before post-weld heat treatment, the traditional annealing process for the D406A thin-walled cylinder is carried out by heating in a resistance furnace: the heating temperature is 680℃, the heating time is about 20 minutes, the holding time is 90 minutes, and the cooling method is air cooling.

[0055] Please see Figure 5 , Figure 5 The diagram shows the traditional tempering process curve for annealed D406A thin-walled cylinders. When the material of the D406A thin-walled cylinder is D406A ultra-high strength steel and it is in a quenched and tempered state before post-weld heat treatment, the traditional tempering process is carried out on the D406A thin-walled cylinder using a resistance furnace: the heating temperature is 300℃, the heating time is about 9 minutes, the holding time is 180 minutes, and the cooling method is air cooling.

[0056] Will Figures 3 to 5 A comparison shows that the local induction heating method provided in this embodiment 1 saves a lot of heating time compared with the traditional annealing and tempering processes of the traditional resistance furnace heating method (Comparative Example 1). At the same time, the medium frequency induction heating device 100 provided in this embodiment 1 is small in size and can effectively improve the heat treatment production efficiency.

[0057] This invention discloses a stress-relieving process for weld seams of D406A thin-walled cylinders based on local induction heating, belonging to the field of ultra-high strength steel heat treatment technology. Addressing the residual stress problem in laser-welded seams of annealed and tempered D406A thin-walled cylinders, two processes are proposed: (1) an induction heating annealing process is used for the weld seams of annealed D406A cylinders, with the heating temperature controlled at 700±20℃ and a holding time of approximately 10 minutes; (2) an induction heating tempering process is used for the weld seams of tempered D406A cylinders, with the heating temperature controlled at 325±20℃ and a holding time of approximately 30 minutes. This method overcomes the limitations of traditional overall heat treatment, featuring small footprint, rapid heating, high heating efficiency, precise heating positioning, and low energy consumption. It can effectively remove residual tensile stress in the weld seams, resulting in good mechanical properties, and is of great significance in the field of ultra-high strength steel heat treatment and manufacturing.

[0058] Compared with the prior art, the present invention has the following beneficial effects: First, the process adopted in this invention is medium-frequency induction heating, which has the advantages of fast heating speed, accurate heating positioning, small device footprint, and only local heat treatment required compared with traditional resistance furnace heating. More induction heating devices can be arranged in the same area, effectively improving heat treatment efficiency.

[0059] Secondly, in the process of this invention, when using medium-frequency induction heating annealing for annealed D406A thin-walled cylinders, the heating temperature is controlled at 700±20℃, the heating and holding time is controlled at 10min, the cooling method is air cooling, the tensile stress is completely eliminated after annealing, the compressive stress is about 20~120MPa, the tensile strength is about 700MPa, and there are no cracks when bent at 180°.

[0060] Third, when using medium-frequency induction heating tempering process for quenched and tempered D406A thin-walled cylinders, the heating temperature is controlled at 325±20℃, the heating and holding time is controlled at 30min, the cooling method is air cooling, the tensile stress is completely eliminated after tempering, the compressive stress is about 24~140MPa, the tensile strength is greater than 1510MPa, and there are no cracks when bending 40°.

[0061] Fourth, the heating and holding times of the process of this invention are shorter than those of traditional resistance furnace heating. By replacing overall heating with local heating, the energy consumption generated during heat treatment can be significantly reduced.

[0062] Fifth, the process of this invention is a practice of reducing costs and increasing efficiency in the heat treatment process of D406A thin-walled cylinder. The device has a smaller footprint, is simpler to operate, and has a shorter heating and holding time. It can perform precise heating by replacing whole heating with local heating, while reducing energy consumption. Furthermore, the tensile stress of D406A thin-walled cylinder after induction heating annealing and tempering is removed. On this basis, the mechanical properties can meet the production standards.

[0063] Sixth, this invention has low energy consumption, effectively reducing production costs and improving production efficiency. The innovation of the heat treatment process for D406A thin-walled cylinders can effectively implement the concept of cost reduction and efficiency improvement, which is of positive help to enterprises to maintain competitiveness.

[0064] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not exhaustive, please refer to the descriptions in other embodiments. The above embodiments only illustrate the implementation of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the inventive concept, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for local heat treatment of weld seams in D406A thin-walled cylindrical bodies, characterized in that, The method includes: S10, precisely align the first center line of the laser-welded D406A thin-walled cylinder with the second center line of the induction heating coil of the medium-frequency induction heating device; S20, adjust the position of the weld seam of the D406A thin-walled cylinder so that the weld seam is located in the central area of ​​the induction heating coil; S30, an alternating current is passed through the induction heating coil to perform local induction heating treatment on the weld. S40, the heated D406A thin-walled cylinder is cooled to obtain the heat-treated component.

2. The method for local heat treatment of the weld seam of D406A thin-walled cylindrical body according to claim 1, characterized in that, In step S10: the material of the D406A thin-walled cylinder is D406A ultra-high strength steel, which, by weight percentage, comprises: Fe content of 94.11%~95.00%, C content of 0.27%~0.32%, Mn content of 0.70%~1.00%, Si content of 1.40%~1.70%, Cr content of 1.00%~1.30%, Mo content of 0.40%~0.55%, V content of 0.08%~0.15%, S content ≤0.008%, P content ≤0.010%, Cu content ≤0.25%, Ni content of 0.25%, and the balance being unavoidable impurities.

3. The method for local heat treatment of the weld seam of D406A thin-walled cylindrical body according to claim 1, characterized in that, In step S10: the medium-frequency induction heating device further includes an infrared thermometer, which is used to monitor the temperature of the weld seam of the D406A thin-walled cylinder in real time.

4. The method for local heat treatment of the weld seam of D406A thin-walled cylindrical body according to claim 1, characterized in that, In step S10: the induction heating coil is moved along the length direction perpendicular to the D406A thin-walled cylinder by the lifting mechanism of the medium frequency induction heating device.

5. The method for local heat treatment of the weld seam of D406A thin-walled cylindrical body according to claim 1, characterized in that, In step S20: the D406A thin-walled cylinder is placed on the conveying and supporting mechanism of the medium-frequency induction heating device, and the D406A thin-walled cylinder is moved along the length direction parallel to the D406A thin-walled cylinder by the conveying and supporting mechanism.

6. The method for local heat treatment of the weld seam of D406A thin-walled cylindrical body according to claim 1, characterized in that, In step S30: when the D406A thin-walled cylinder is in an annealed state before post-weld heat treatment, the weld is subjected to medium-frequency induction annealing heating treatment by the induction heating coil. The heating temperature is 680~720℃, and the heating and holding time is 5~15min.

7. The method for local heat treatment of the weld seam of D406A thin-walled cylindrical body according to claim 6, characterized in that, In step S40: the compressive stress of the heat-treated component at the weld position is 20~120MPa, the tensile strength is 680~720MPa, and the heat-treated component has no cracks after being bent 180°.

8. The method for local heat treatment of the weld seam of D406A thin-walled cylindrical body according to claim 1, characterized in that, In step S30: when the D406A thin-walled cylinder is in a tempered state before post-weld heat treatment, the weld is subjected to medium-frequency induction tempering heating treatment by the induction heating coil. The heating temperature is 305~345℃, and the heating and holding time is 25~35min.

9. The method for local heat treatment of the weld seam of D406A thin-walled cylindrical body according to claim 8, characterized in that, In step S40: the compressive stress of the heat-treated component at the weld position is 24~140MPa, the tensile strength is greater than 1510MPa, and the heat-treated component has no cracks after being bent at 40°.

10. The method for local heat treatment of the weld seam of D406A thin-walled cylindrical body according to claim 7 or 8, characterized in that, In step S40: the cooling process is air cooling, and the tensile stress of the component at the weld position after heat treatment is 0.

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