A method for welding nickel-based alloys to ferrous-based alloys

Abstract

The application provides a welding method for nickel-based alloy and iron-based alloy dissimilar materials, and belongs to the technical field of dissimilar metal welding, and comprises the following steps: sequentially cleaning the surfaces to be welded of the nickel-based alloy and the iron-based alloy, performing two-stage preheating treatment on the nickel-based alloy side, the first stage being hydrogen removal preheating, and the second stage being thermal equilibrium preheating, according to the specific type of the iron-based alloy, simultaneously performing adaptive preheating on the side of the iron-based alloy, using double-layer flux-cored wire, performing welding operation by using double-pulse arc welding in a helium-argon mixed protective atmosphere environment, during the welding process, applying mechanical vibration linked with the welding speed to the rear of the weld, and after the welding is completed, sequentially performing slow cooling temperature control treatment, gradient hydrogen removal treatment and high-frequency vibration treatment on the welded part. The welding method for nickel-based alloy and iron-based alloy dissimilar materials can improve the welding quality of dissimilar materials and reduce the risk of welding cold cracks and hydrogen-induced cracks.

Description

Technical Field

[0001] This invention belongs to the field of dissimilar metal welding technology, and more specifically, relates to a welding method for dissimilar materials such as nickel-based alloys and iron-based alloys. Background Technology

[0002] Nickel-based alloys are widely used in high-end equipment manufacturing due to their excellent high-temperature resistance (above 1000℃), corrosion resistance (such as resistance to strong acids and high-temperature steam), and creep resistance, as well as their dissimilar welded structures with iron-based alloys (low cost and high strength). However, nickel-based alloys and iron-based alloys differ significantly in their thermophysical and chemical properties. For example, the thermal conductivity of nickel-based alloys is 70-90 W / (m·K), while that of iron-based alloys is 45-50 W / (m·K) for carbon steel and 15-18 W / (m·K) for stainless steel; the coefficient of thermal expansion of nickel-based alloys is 15-17 × 10⁻⁻⁻⁶. 6 / ℃, Carbon steel 11-13×10⁻ 6 The differences mentioned above (e.g., / ℃) can lead to the following problems during the welding process of nickel-based alloys and iron-based alloys: 1. The difference in thermal conductivity between nickel-based alloys and iron-based alloys causes heat to accumulate on the nickel-based alloy side (over-melting) and heat to dissipate rapidly on the iron-based alloy side (incomplete melting) during welding, resulting in problems such as asymmetrical weld pool and uneven weld depth. 2. The difference in thermal expansion coefficients between nickel-based alloys and iron-based alloys leads to high residual stress, which easily causes cold cracks. At the same time, during the cooling of the weld, hydrogen tends to accumulate in the stress zone, resulting in local hydrogen cracks. 3. At high temperatures, carbon in iron-based alloys diffuses towards nickel-based alloys, forming a brittle carburized layer and a weak decarburized layer. Summary of the Invention

[0003] The purpose of this invention is to provide a welding method for dissimilar materials such as nickel-based alloys and iron-based alloys, aiming to solve at least one problem mentioned in the background art regarding the welding of nickel-based alloys and iron-based alloys.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is: to provide a welding method for dissimilar materials such as nickel-based alloys and iron-based alloys, comprising the following steps: S1. Clean the surfaces of nickel-based alloys and iron-based alloys to be welded in sequence; S2. Perform a two-stage preheating treatment on the nickel-based alloy side. The first stage of preheating is hydrogen removal preheating at a temperature of 180-220℃ for 1.0-1.5 hours. The second stage of preheating is thermal equilibrium preheating at a temperature of 220-250℃ for 0.5 hours. Depending on the type of iron-based alloy, perform simultaneous and appropriate preheating on the iron-based alloy side for 0.5-1.0 hours. S3. Use double-layer flux-cored welding wire and perform welding using a double-pulse arc welding method under a helium-argon mixed protective atmosphere. S4. Apply mechanical vibration linked to the welding speed behind the weld; S5. After welding, the weld area is subjected to slow cooling and temperature control treatment, gradient hydrogen removal treatment and high frequency vibration treatment in sequence.

[0005] In one possible implementation, in step S2, when the iron-based alloy is carbon steel, its preheating temperature is 120-150℃; when the iron-based alloy is austenitic stainless steel, its preheating temperature is 80-120℃; the preheating range is 50mm on both sides of the weld center, the heating rate is 5-8℃ / min, and the temperature gradient between the nickel-based alloy and the iron-based alloy is ≤±5℃.

[0006] In one possible implementation, the structure and composition of the double-layer flux-cored welding wire in step S3 are as follows: the outer layer is an ERNiCrFe-7 alloy with a Ti content of 1.2-1.8wt%, and the inner layer is a pure nickel strip with a purity of ≥99.9%; the welding wire diameter is 1.2-1.4mm, and the mass percentage of the outer ERNiCrFe-7 layer is: Ni 50-55%, Cr 18-22%, and C≤0.08%.

[0007] In one possible implementation, in step S3, the welding parameters for the dual-pulse arc welding are: base current 45-65A, pulse current 65-85A, pulse frequency 40-70Hz, welding voltage 9-12V, welding speed 1.2-1.8mm / s, and shielding gas is 97-98% high-purity argon and 2-3% helium.

[0008] In one possible implementation, in step S3, ultrasonic emission devices are provided on both the front and rear sides of the welding torch along the welding forward direction. The front ultrasonic emission device performs ultrasonic pretreatment on the unwelded area to be welded to refine the surface grains of the base material; the rear ultrasonic emission device performs ultrasonic stirring on the just-solidified molten pool area to promote the elemental mixing of nickel-based alloys and iron-based alloys.

[0009] In one possible implementation, the front ultrasonic transmitter is 40-100mm from the center of the welding torch, with a frequency of 15-20kHz and a power of 80-120W; the rear ultrasonic transmitter is 30-80mm from the center of the welding torch, with a frequency of 15-20kHz and a power of 120-200W; and the distance between the front and rear ultrasonic transmitters and the upper surface of the workpiece is ≤0.5mm.

[0010] In one possible implementation, the parameters of the mechanical vibration in step S4 are: vibration frequency 50-100Hz, amplitude 20-50μm; the vibration device is located 10-15mm behind the weld, and the vibration direction is perpendicular to the weld axis.

[0011] In one possible implementation, the parameters for the high-frequency vibration treatment in step S5 are: vibration frequency 200-300Hz, time 2-4h, and vibration range covering the weld and the 50mm heat-affected zone on both sides.

[0012] In one possible implementation, the specific process of slow cooling and temperature control in step S5 is as follows: wrap the weld and heat-affected zone with asbestos cloth and control the cooling rate to 5-10℃ / min.

[0013] In one possible implementation, the gradient hydrogen removal process in step S5 includes: a first stage of hydrogen removal at a temperature of 250-280℃, followed by holding the weld and heat-affected zone at that temperature for 2 hours; a second stage of hydrogen removal at a temperature of 200-220℃, followed by holding the weld and heat-affected zone at that temperature for 1 hour; and finally, air cooling to room temperature.

[0014] The beneficial effects of this invention in providing a welding method for dissimilar materials of nickel-based alloys and iron-based alloys are as follows: Compared with the prior art, the welding method of this invention for dissimilar materials of nickel-based alloys and iron-based alloys, through step S2, the two-stage preheating of the nickel-based alloy side and the synchronous adaptation preheating of the iron-based alloy side can balance the uneven heat distribution caused by the difference in thermal conductivity between the two, avoid over-melting of the nickel-based alloy side and incomplete melting of the iron-based alloy side, solve the problems of molten pool asymmetry and uneven melting depth, and at the same time alleviate the initial residual stress caused by the difference in thermal expansion coefficients, reducing the basis for cold cracking; through step S3, the double-layer flux-cored welding wire and the helium-argon mixed protective atmosphere are used for welding. Pulsed arc welding optimizes the molten pool composition and protective effect, suppressing the diffusion of carbon from iron-based alloys to nickel-based alloys at high temperatures and preventing the formation of brittle carburized and weak decarburized layers. In step S4, mechanical vibration linked to the welding speed behind the weld can release residual stress in real time during the welding process. In step S5, slow cooling and temperature control and gradient hydrogen removal treatment after welding can further remove hydrogen residue and avoid stress concentration. High-frequency vibration treatment can improve the weld microstructure, ultimately comprehensively reducing the risk of hydrogen cracking and cold cracking, significantly improving the high temperature resistance, corrosion resistance and creep resistance of dissimilar welded joints, and meeting the reliability requirements of this type of welded structure in the field of high-end equipment manufacturing. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art 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.

[0016] Figure 1 This invention provides a flowchart of a welding method for dissimilar materials, nickel-based alloys and iron-based alloys, as an embodiment of the present invention. Detailed Implementation

[0017] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0018] Please see Figure 1 This invention provides a method for welding dissimilar materials of nickel-based alloys and iron-based alloys. The method includes the following steps: S1. Clean the surfaces of nickel-based alloys and iron-based alloys to be welded in sequence.

[0019] In this step, the cleaning process includes mechanical cleaning and ultrasonic cleaning performed sequentially. During mechanical cleaning, 120-180 grit sandpaper can be used to mechanically grind the surfaces of nickel-based alloys and iron-based alloys to be welded (20mm on each side of the weld center), with the grinding depth controlled to 0.1-0.2mm. The focus should be on grinding the Cr2O3 oxide layer on the surface of the nickel-based alloy until the metallic luster is exposed.

[0020] When performing ultrasonic cleaning, first immerse the workpiece in acetone solution for 10-15 minutes, then transfer it to ultrasonic cleaning equipment for 5-8 minutes to remove oil and residual impurities from the surface micropores, and then let it air dry naturally.

[0021] After cleaning the nickel-based alloy and the iron-based alloy, the nickel-based alloy and the iron-based alloy are butt-welded together. The butt gap is controlled between 0.5-1.0 mm. In application, if the butt gap is too small, slag is easily trapped, and if it is too large, incomplete fusion is likely. Then, the nickel-based alloy and the iron-based alloy are fixed by spot welding using the "three-point symmetrical spot welding method". The spot welding points are located at 0°, 120° and 240° positions of the butt joint. The spot welding material is the same as the formal welding material. The spot welding length is 10-15 mm and the height is 2-3 mm to avoid incomplete fusion at the spot welding point.

[0022] S2. Perform a two-stage preheating treatment on the nickel-based alloy side. The first stage of preheating is hydrogen removal preheating at a temperature of 180-220℃ for 1.0-1.5 hours. The second stage of preheating is thermal equilibrium preheating at a temperature of 220-250℃ for 0.5 hours. Depending on the type of iron-based alloy, perform simultaneous and appropriate preheating on the iron-based alloy side for 0.5-1.0 hours.

[0023] In this step, during the first stage of preheating treatment of the nickel-based alloy, a tracked electric heater can be used to heat the area of ​​the nickel-based alloy to be welded to 180-220℃ and hold it at that temperature for 1.0-1.5 hours. At this temperature, the diffusion coefficient of hydrogen in the nickel-based alloy can reach 1×10⁻¹.0 With a capacity of m² / s, more than 60% of the original hydrogen in the base material can be removed, thus enabling preliminary hydrogen removal from nickel-based alloys and preventing hydrogen-induced cracking after welding.

[0024] In this step, after the first stage of preheating treatment of the nickel-based alloy is completed, the nickel-based alloy to be welded area is heated to 220-250℃ by a track-type electric heater and held at that temperature for 0.5h to carry out the second stage of preheating treatment of the nickel-based alloy. During the second stage of preheating treatment, an infrared thermometer can be used for real-time monitoring to ensure that the temperature gradient of the nickel-based alloy side section is ≤±3℃.

[0025] In this step, if the iron-based alloy is carbon steel (such as T22), the preheating temperature is controlled at 120-150℃; if it is austenitic stainless steel (such as 304), the preheating temperature is controlled at 80-120℃. The heating range and heating rate are consistent with those of the nickel-based alloy side, and the holding time is 0.5-1.0h to ensure that the temperature gradient between the nickel-based alloy and the iron-based alloy is ≤±5℃.

[0026] In this step, preheating the nickel-based alloy side to a higher temperature than the iron-based alloy side is a crucial method for resolving the issues of "asymmetric molten pool and uneven melt depth." In application, if the preheating temperature of the nickel-based alloy side is low or the same as that of the iron-based alloy side, the iron-based alloy side conducts heat quickly and responds rapidly, reaching its melting point quickly. However, the nickel-based alloy side, due to its slower heat conduction and response, has a lower initial temperature and requires a longer time to reach its melting point. This results in an asymmetric molten pool where the iron-based alloy side melts first, followed by the nickel-based alloy side. Preheating the nickel-based alloy side to 220-250℃ in this step raises its base temperature, allowing it to melt synchronously with the iron-based alloy. Moreover, since the coefficient of thermal expansion of nickel-based alloys is higher than that of iron-based alloys, if the preheating temperature of nickel-based alloys is low, the temperature of the nickel-based alloy side will rise sharply during welding. The difference in thermal expansion between the nickel-based alloy side and the iron-based alloy side will exacerbate the stress. Therefore, a higher preheating temperature on the nickel-based alloy side can allow the nickel-based alloy to generate a certain amount of thermal expansion in advance, reduce the "temperature difference expansion difference" during welding, and indirectly reduce residual stress.

[0027] In this step, preheating both the nickel-based and iron-based alloys removes adsorbed moisture and oil from the iron-based alloy surface, reducing the source of hydrogen. Simultaneously, it lowers the carbon diffusion activation energy, preventing rapid carbon migration to the nickel-based alloy at high welding temperatures. The first preheating of the nickel-based alloy utilizes the hydrogen diffusion coefficient at this temperature to expel the original hydrogen from the base material, preventing its accumulation and superposition with hydrogen from the iron-based alloy. This synergistic preheating of the nickel-based and iron-based alloys significantly reduces the thickness of the carbon migration layer and the content of diffusible hydrogen, thereby lowering the risk of carbon migration embrittlement and hydrogen-induced cracking.

[0028] S3. Use double-cored welding wire and perform welding using a double-pulse arc welding method under a helium-argon mixed protective atmosphere.

[0029] In this step, a DC positive polarity dual-pulse TIG welding machine can be used for welding. The welding parameters are: base current 45-65A, pulse current 65-85A, pulse frequency 40-70Hz, welding voltage 9-12V, and welding speed 1.2-1.8mm / s. The welding material used is double-layer flux-cored wire. The outer layer of the double-layer flux-cored wire is ERNiCrFe-7 alloy, with the following mass percentages: Ni 50-55%, Cr 18-22%, Ti 1.2-1.8%, and C≤0.08%. The inner layer of the double-layer flux-cored wire is pure nickel strip with a purity ≥99.9%. The shielding gas is 97-98% high-purity argon and 2-3% helium.

[0030] In this step, a dual-pulse arc welding method is used, which alternates between base current and pulse current for heat input. The base current (45-65A) can maintain stable arc combustion and prevent nickel-based alloys from over-melting due to excessive heat accumulation caused by low thermal conductivity. The pulse current (65-85A) can provide instantaneous high energy to ensure full penetration of iron-based alloys. At the same time, the high-frequency pulse (40-70Hz) can periodically stir the molten pool and reduce local temperature gradients.

[0031] In this step, the outer layer of the double-cored welding wire contains 1.2-1.8 wt% Ti, which can form stable TiC with carbon in the iron-based alloy, locking in carbon elements and inhibiting carbon diffusion into the nickel-based alloy. At the same time, Ti acts as a grain refiner, further reducing the grain size of the weld. The inner layer of the double-cored welding wire is a pure nickel strip (purity ≥99.9%), which can compensate for the loss of nickel elements on the nickel-based alloy side during welding, avoid the mechanical property deterioration caused by the sharp drop in Ni content in the weld center, and ensure the metallurgical compatibility of the joint.

[0032] In this step, ultrasonic transmitting devices can also be installed at both the front and rear sides of the welding torch along the welding direction. The front ultrasonic transmitting device is 40-100mm from the center of the welding torch, with a frequency of 15-20kHz and a power of 80-120W. This ultrasonic pretreatment is performed on the unwelded area to be welded, aiming to refine the surface grains of the base material, reduce the temperature gradient in the area to be welded, and avoid the problem of poor molten pool fluidity caused by coarse grains in the area to be welded. The rear ultrasonic transmitting device is 30-80mm from the center of the welding torch, with a frequency of 15-20kHz and a power of 120-200W. This ultrasonic stirring is performed on the newly solidified molten pool area to promote the elemental mixing of nickel-based alloys and iron-based alloys and eliminate compositional segregation during molten pool solidification.

[0033] In this step, the distance between the front ultrasonic transmitter and the rear ultrasonic transmitter and the upper surface of the workpiece is ≤0.5mm.

[0034] S4. Apply mechanical vibration linked to the welding speed behind the weld.

[0035] When implementing this step, an electromagnetic mechanical vibrator is installed 10-15mm behind the weld along the welding direction, with the vibration direction perpendicular to the weld axis. The vibration parameters of the electromagnetic mechanical vibrator are linked to the welding speed through a controller. When the welding speed is 1.2-1.5mm / s, the vibration frequency of the electromagnetic mechanical vibrator can be set to 50-80Hz; when the welding speed is 1.5-1.8mm / s, the controller will automatically increase the vibration frequency of the electromagnetic mechanical vibrator to 80-100Hz. In this step, the amplitude of the electromagnetic mechanical vibrator is uniformly controlled to 1 / 3 of the weld height.

[0036] During welding, the differences in thermophysical properties (thermal conductivity and coefficient of thermal expansion) between nickel-based alloys and iron-based alloys lead to uneven solidification rates in the molten pool. Iron-based alloys conduct heat faster, resulting in a higher cooling and solidification rate on the iron-based alloy side compared to the nickel-based alloy side. This causes asynchronous solidification on both sides. Consequently, when the molten pool transitions from liquid to solid, the weak grain boundary bonding forces, if not addressed in real time, can cause the shrinkage difference between the nickel-based and iron-based alloy sides to directly generate "instantaneous stress" that is locked in the weld.

[0037] This step involves vibrating the weld during welding to induce minute plastic deformation in the freshly solidified weld metal, activating grain boundary slip and preventing stress concentration at grain boundaries. Furthermore, the vibration energy is transferred through the workpiece to stress concentration areas, giving lattice atoms kinetic energy and reducing stress-induced lattice distortion, thereby lowering the stress amplitude. This step also links the vibration frequency to the welding speed, matching the vibration energy with the stress generation rate. As the welding speed increases, solidification accelerates, and stress becomes more concentrated, the vibration frequency is simultaneously increased to counteract the generated stress, thus preventing untimely stress release.

[0038] In addition, the mechanical vibration in this step also disrupts some of the microstructures that are formed during the solidification of the molten pool to accommodate hydrogen atoms, such as micropores and grain boundary gaps. This promotes the diffusion and escape of hydrogen atoms to the surface, increases the hydrogen escape rate of the molten pool, and indirectly solves the hidden danger of hydrogen-induced cracking.

[0039] S5. After welding, the weld area is subjected to slow cooling and temperature control treatment, gradient hydrogen removal treatment and high frequency vibration treatment in sequence.

[0040] In this step, the specific process of slow cooling and temperature control is as follows: The weld and heat-affected zone are wrapped with asbestos cloth, and the cooling rate is controlled at 5-10℃ / min to avoid excessive temperature difference and secondary stress. During the slow cooling and temperature control process, real-time monitoring is performed using an infrared thermometer. When the weld temperature drops to 150-200℃, it is transferred to a constant temperature furnace for gradient heat preservation, entering the gradient hydrogen removal treatment stage. In this step, the gradient hydrogen removal treatment includes a first-stage hydrogen removal and a second-stage hydrogen removal. In the first-stage hydrogen removal, the hydrogen removal temperature is 250-280℃, and the weld and heat-affected zone are kept at this temperature for 2 hours. In the second-stage hydrogen removal, the hydrogen removal temperature is 200-220℃, and the weld and heat-affected zone are kept at this temperature for 1 hour. Afterwards, it is air-cooled to room temperature. Through this hydrogen removal treatment, hydrogen trapped in the molten pool can be further removed, reducing the hydrogen-induced cracking rate. After cooling to room temperature, the welded joints of nickel-based alloys and iron-based alloys are subjected to high-frequency vibration treatment. The parameters for high-frequency vibration treatment are: vibration frequency 200-300Hz, vibration time linked to the base metal thickness; when the base metal thickness is >10mm, the vibration time is no less than 4 hours; when the base metal thickness is ≤10mm, the vibration time is no less than 2 hours; the vibration range covers the weld and the 50mm heat-affected zone on both sides. The high-frequency vibration energy generated by the high-frequency vibration can give kinetic energy to the lattice atoms of the weld metal, breaking the "stress-induced lattice distortion" state, promoting the release of macroscopic residual stress to the outside, thereby reducing residual stress.

[0041] After completing step S5 above, lightly grind the weld surface with 200-300 grit sandpaper to remove the oxide scale.

[0042] This invention provides a welding method for dissimilar materials, nickel-based alloys and iron-based alloys. Compared with existing technologies, it effectively solves the core welding problems mentioned in the background art through multi-step collaborative design. Its beneficial effects are as follows: Step S2, with its two-stage preheating of the nickel-based alloy side and simultaneous adaptive preheating of the iron-based alloy side, balances the uneven heat distribution caused by the difference in thermal conductivity between the two, avoiding over-melting of the nickel-based alloy side and incomplete melting of the iron-based alloy side, thus solving the problems of molten pool asymmetry and uneven melting depth. Simultaneously, it alleviates the initial residual stress caused by the difference in thermal expansion coefficients, reducing the basis for cold cracking. Step S3 employs a double-layer flux-cored wire and a helium-argon mixed shielding gas. The dual-pulse electric arc welding of the atmosphere optimizes the composition and protection effect of the weld pool, inhibits the diffusion of carbon from the iron-based alloy to the nickel-based alloy side at high temperatures, and prevents the formation of brittle carburized layers and weak decarburized layers. Through step S4, the mechanical vibration linked to the welding speed behind the weld can release the residual stress in real time during the welding process. Through step S5, the slow cooling and temperature control and gradient hydrogen removal treatment after welding can further remove hydrogen residue and avoid stress concentration. The high-frequency vibration treatment can improve the weld microstructure, ultimately comprehensively reducing the risk of hydrogen cracking and cold cracking, significantly improving the high temperature resistance, corrosion resistance and creep resistance of dissimilar welded joints, and meeting the reliability requirements of this type of welded structure in the field of high-end equipment manufacturing.

[0043] The present invention provides a welding method for dissimilar materials of nickel-based alloys and iron-based alloys. The nickel-based alloys include, but are not limited to, Incoloy 800H, Hastelloy C-276, and Monel 400, and the iron-based alloys include, but are not limited to, carbon steel T22, Q345R, and austenitic stainless steel 304 and 316L.

[0044] Example 1: Welding a 12mm thick nickel-based alloy plate to a 10mm thick iron-based alloy plate.

[0045] 1. Base Material Parameters The nickel-based alloy plate is made of Incoloy 800H material, with the following chemical composition: Ni 30%, Cr 21%, Fe 48%, C≤0.08%, and Ti 0.3-0.7%. The carbon steel plate is made of T22 material, with the following chemical composition: C 0.15-0.25%, Cr 1.9-2.6%, Mo 0.87-1.13%, Mn 0.3-0.6%, and the remainder Fe.

[0046] 2. Implementation Steps 2.1 Pre-welding cleaning: First, use 120-grit sandpaper to polish the surface to be welded to a depth of 0.15mm. Then, soak it in acetone for 12 minutes, rinse it clean, and then perform ultrasonic cleaning at 40kHz for 6 minutes. After drying, perform a roughness test on the surface to be welded to ensure that the surface roughness Ra≤1.2μm.

[0047] Assembly and fixing: After cleaning, the nickel-based alloy plate and carbon steel plate are assembled and fixed by spot welding. The assembly gap is 0.8mm, and the plates are fixed at three points (0°, 120°, 240°). ERNiCrFe-7 double-layer welding wire is used for spot welding. The length of the spot is 12mm and the height is 2.5mm.

[0048] 2.2 Preheating before welding: Nickel-based alloy plate side: First stage preheating treatment, preheating temperature 180-220℃, holding temperature for 1.2h; Second stage preheating treatment, preheating temperature 220-250℃, holding temperature for 0.5h, heating rate 6℃ / min, temperature gradient ≤±3℃.

[0049] Carbon steel plate side: preheating temperature 120-150℃, holding temperature for 0.8h, heating rate 6℃ / min, temperature gradient ≤±3℃.

[0050] Preheating of the carbon steel plate side needs to be carried out simultaneously at the end of the second preheating treatment on the nickel-based alloy plate side, so that the preheating of the nickel-based alloy plate side and the carbon steel plate side can be completed at the same time.

[0051] 2.3 Welding: A double-cored welding wire with a diameter of 1.2 mm and an outer Ti content of 1.5 wt% was used. The shielding gas consisted of 97% argon and 3% helium, with a flow rate of 20 L / min. The DC positive polarity double pulse TIG welding was used, with the following welding parameters: base current 55A, pulse current 75A, pulse frequency 50Hz, welding voltage 10V, and welding speed 1.5mm / s. During welding, ultrasonic transmitting devices are installed on both the front and rear sides of the welding torch along the welding direction. The front ultrasonic transmitting device is 50mm from the center of the welding torch, with an ultrasonic frequency of 18kHz and a power of 100W. The rear ultrasonic transmitting device is 40mm from the center of the welding torch, with an ultrasonic frequency of 18kHz and a power of 150W.

[0052] 2.4 Dynamic vibration during welding: The electromagnetic mechanical vibrator is located 12mm behind the weld, with a vibration frequency of 80Hz and an amplitude of 30μm.

[0053] 2.5 Post-weld composite treatment: The joint area was wrapped with asbestos, and the slow cooling rate was controlled at 8℃ / min. The slow cooling temperature was monitored in real time using an infrared thermometer. When the weld temperature dropped to 200℃, the welded plate was transferred to a holding furnace for gradient holding. The first stage holding temperature was 280℃ for 2 hours, and the second stage holding temperature was 220℃ for 1 hour. Afterwards, it was air-cooled to room temperature. The welded plate was then subjected to high-frequency vibration treatment at 250Hz for 3 hours. Finally, the weld was polished with 300-grit sandpaper.

[0054] 3. Weld inspection and inspection results The symmetry of the molten pool is 96%, the molten depth is 4.8 mm, and the difference in molten depth is 0.12 mm. The weld is free of porosity and slag inclusions; Tensile strength 590MPa, elongation 27%, no cracks in bending test.

[0055] Example 2: Welding an 8mm thick nickel-based alloy plate to a 6mm thick iron-based alloy plate.

[0056] 1. Base Material Parameters The nickel-based alloy plate is made of Hastelloy C-276 material, with the following chemical composition: Ni 54%, Cr 16%, Mo 16%, Fe 5%, C ≤ 0.01%; The carbon steel plate is made of 316L stainless steel with the following chemical composition: Cr 16-18%, Ni 10-14%, Mo 2-3%, C≤0.03%, and the remainder is Fe.

[0057] 2. Implementation Steps 2.1 Pre-welding cleaning: First, use 180-grit sandpaper to polish the surface to be welded to a depth of 0.1 mm. Then, soak it in anhydrous ethanol for 10 minutes, rinse it clean, and then perform ultrasonic cleaning at 40 kHz for 5 minutes. After drying, perform a roughness test on the surface to be welded to ensure that the surface roughness Ra ≤ 1.0 μm.

[0058] Assembly and fixing: After cleaning, the nickel-based alloy plate and carbon steel plate are assembled and fixed by spot welding. The assembly gap is 0.6mm, and the plates are fixed at three points (0°, 120°, 240°). ERNiCrFe-7 double-layer welding wire is used for spot welding. The length of the spot is 10mm and the height is 2mm.

[0059] 2.2 Preheating before welding: Nickel-based alloy plate side: First stage preheating treatment, preheating temperature 180-220℃, holding for 1h; Second stage preheating treatment, preheating temperature 220-250℃, holding for 0.4h, heating rate 5℃ / min, temperature gradient ≤±3℃.

[0060] Carbon steel plate side: preheating temperature 80-100℃, holding temperature for 0.8h, heating rate 5℃ / min, temperature gradient ≤±3℃.

[0061] Preheating of the carbon steel plate side needs to be carried out simultaneously at the end of the second preheating treatment on the nickel-based alloy plate side, so that the preheating of the nickel-based alloy plate side and the carbon steel plate side can be completed at the same time.

[0062] 2.3 Welding: A double-cored welding wire with a diameter of 1.4 mm was used. The outer layer of the welding wire contained 1.2 wt% Ti. The shielding gas consisted of 97% argon and 3% helium, and the shielding gas flow rate was 19 L / min. The DC positive polarity double pulse TIG welding was used, with the following welding parameters: base current 48A, pulse current 68A, pulse frequency 60Hz, welding voltage 9.5V, and welding speed 1.3mm / s. During welding, ultrasonic transmitting devices are installed on both the front and rear sides of the welding torch along the welding direction. The front ultrasonic transmitting device is 40mm from the center of the welding torch, with an ultrasonic frequency of 15kHz and a power of 80W. The rear ultrasonic transmitting device is 30mm from the center of the welding torch, with an ultrasonic frequency of 15kHz and a power of 120W.

[0063] 2.4 Dynamic vibration during welding: The electromagnetic mechanical vibrator is located 10 mm behind the weld, with a vibration frequency of 60 Hz and an amplitude of 25 μm.

[0064] 2.5 Post-weld composite treatment: The joint area was wrapped with asbestos, and the slow cooling rate was controlled at 7℃ / min. The temperature was monitored in real time using an infrared thermometer. When the weld temperature dropped to 180℃, the welded plate was transferred to a holding furnace for gradient holding. The first stage holding temperature was 260℃ for 2 hours, and the second stage holding temperature was 200℃ for 1 hour. Afterwards, it was air-cooled to room temperature. The welded plate was then subjected to high-frequency vibration treatment at 220Hz for 2 hours. Finally, the weld was polished with 200-grit sandpaper.

[0065] 3. Weld inspection and inspection results The symmetry of the molten pool is 95%, the molten depth is 3.5 mm, and the difference in molten depth is 0.15 mm. The weld is free of defects; Tensile strength 580MPa, elongation 28%, no cracks in bending test.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for welding dissimilar materials, namely nickel-based alloys and iron-based alloys, characterized in that, include: S1. Clean the surfaces of nickel-based alloys and iron-based alloys to be welded in sequence; S2. Perform a two-stage preheating treatment on the nickel-based alloy side. The first stage of preheating is hydrogen removal preheating at a temperature of 180-220℃ for 1.0-1.5 hours. The second stage of preheating is thermal equilibrium preheating at a temperature of 220-250℃ for 0.5 hours. Depending on the type of iron-based alloy, perform simultaneous and appropriate preheating on the iron-based alloy side for 0.5-1.0 hours. S3. Use double-layer flux-cored welding wire and perform welding using a double-pulse arc welding method under a helium-argon mixed protective atmosphere. S4. Apply mechanical vibration linked to the welding speed behind the weld; S5. After welding, the weld area is subjected to slow cooling and temperature control treatment, gradient hydrogen removal treatment and high frequency vibration treatment in sequence.

2. The welding method for dissimilar materials of nickel-based alloys and iron-based alloys as described in claim 1, characterized in that, In step S2, when the iron-based alloy is carbon steel, its preheating temperature is 120-150℃; when the iron-based alloy is austenitic stainless steel, its preheating temperature is 80-120℃; the preheating range is 50mm on both sides of the weld center, the heating rate is 5-8℃ / min, and the temperature gradient between the nickel-based alloy and the iron-based alloy is ≤±5℃.

3. The welding method for dissimilar materials of nickel-based alloys and iron-based alloys as described in claim 1, characterized in that, In step S3, the structure and composition of the double-layer flux-cored welding wire are as follows: the outer layer is an ERNiCrFe-7 alloy with a Ti content of 1.2-1.8wt%, and the inner layer is a pure nickel strip with a purity of ≥99.9%; the welding wire diameter is 1.2-1.4mm, and the mass percentage of the outer ERNiCrFe-7 layer is: Ni 50-55%, Cr 18-22%, and C≤0.08%.

4. The welding method for dissimilar materials of nickel-based alloys and iron-based alloys as described in claim 1, characterized in that, In step S3, the welding parameters for double-pulse arc welding are: base current 45-65A, pulse current 65-85A, pulse frequency 40-70Hz, welding voltage 9-12V, welding speed 1.2-1.8mm / s, and shielding gas is 97-98% high-purity argon and 2-3% helium.

5. The welding method for dissimilar materials of nickel-based alloys and iron-based alloys as described in claim 1, characterized in that, In step S3, ultrasonic emission devices are set on both the front and rear sides of the welding torch along the welding forward direction. The front ultrasonic emission device performs ultrasonic pretreatment on the unwelded area to be welded to refine the surface grains of the base material; the rear ultrasonic emission device performs ultrasonic stirring on the just-solidified molten pool area to promote the mixing of elements between nickel-based alloys and iron-based alloys.

6. The welding method for dissimilar materials of nickel-based alloys and iron-based alloys as described in claim 5, characterized in that, The front ultrasonic transmitter is 40-100mm from the center of the welding torch, with a frequency of 15-20kHz and a power of 80-120W; the rear ultrasonic transmitter is 30-80mm from the center of the welding torch, with a frequency of 15-20kHz and a power of 120-200W; the distance between the front and rear ultrasonic transmitters and the upper surface of the workpiece is ≤0.5mm.

7. The welding method for dissimilar materials of nickel-based alloys and iron-based alloys as described in claim 1, characterized in that, In step S4, the mechanical vibration parameters are: vibration frequency 50-100Hz, amplitude 20-50μm; the vibration device is located 10-15mm behind the weld, and the vibration direction is perpendicular to the weld axis.

8. The welding method for dissimilar materials of nickel-based alloys and iron-based alloys as described in claim 1, characterized in that, The parameters for the high-frequency vibration treatment in step S5 are: vibration frequency 200-300Hz, time 2-4h, and vibration range covering the weld and the 50mm heat-affected zone on both sides.

9. The welding method for dissimilar materials of nickel-based alloys and iron-based alloys as described in claim 1, characterized in that, The specific process of slow cooling and temperature control in step S5 is as follows: wrap the weld and heat-affected zone with asbestos cloth and control the cooling rate to 5-10℃ / min.

10. The welding method for dissimilar materials of nickel-based alloys and iron-based alloys as described in claim 1, characterized in that, The gradient hydrogen removal process in step S5 includes: first stage hydrogen removal at a temperature of 250-280℃, and holding the weld and heat-affected zone at that temperature for 2 hours; second stage hydrogen removal at a temperature of 200-220℃, and holding the weld and heat-affected zone at that temperature for 1 hour; and air cooling to room temperature.

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