The weldability of high-temperature alloys is one of the scientific basis for selecting high-temperature alloy materials, and it is also an important basis for the design of welding parts and the formulation of welding processes. However, the chemical composition of superalloys becomes more and more complex as the service temperature increases, making welding increasingly difficult. Weldability refers to the ability of the same material or different materials to be welded to form a complete joint and meet the expected use requirements under manufacturing process conditions. The four major factors that affect weldability are material factors, design factors, process factors and service environment. In the welding of high-temperature alloys, crack susceptibility, joint structure inhomogeneity and iso-strength of the welded joint are important considerations.
There are usually two types of welding cracks in high-temperature alloys: hot cracks and reheat cracks. The former is divided into crystal cracks and liquefaction cracks, while the latter mainly refers to strain aging cracks. During the welding process of high-temperature alloys, the welding cracks produced when the metal in the weld and the heat-affected zone cool to the high-temperature zone near the solidus line are called hot cracks. Crystallization cracks only occur in the weld. They are mostly distributed longitudinally in the center of the weld, and some are distributed in an arc on both sides of the center line of the weld, and are perpendicular to the welding wave. The common characteristic of crystallization cracks is that they are distributed along the grain boundaries of primary crystallization, especially along the grain boundaries of columnar crystals.
The author et al. studied the weldability of Ni3Al alloy, which is the main strengthening phase of high-temperature alloys. The welding method uses electron beam welding, which is fusion welding. After vacuum induction melting, it is cast into cylindrical ingots, homogenized and annealed, and cold-rolled through multiple passes into thin plates with a thickness of approximately 1.5mm. The intermediate heat treatment temperature during rolling is 1050°C, and the holding time is 30 minutes. The welding test equipment is a domestic ZSH-150 high-voltage vacuum electron beam welding machine, with an acceleration voltage of 100kV and a vacuum degree of 0.132Pa. The rolled thin plates of three alloys were autogenously welded at different welding speeds. The thin plates were mechanically cleaned before welding. During the welding process, the thin plates were not clamped. The welding direction was perpendicular to the rolling direction. The beam current and welding speed were related to each other. Matching is based on exact penetration. After electron beam welding of rolled thin plates of three alloys, it was found that during high-speed welding, varying numbers of intergranular cracks appeared in the weld metal of the three alloys, but the macro and micro morphology of the cracks were similar. The morphology is typical hot cracks concentrated in the center of the weld, and the scanned image of the crack fracture surface shows typical potato-shaped intergranular cracking characteristics. During low-speed welding, the number of cracks is significantly reduced or even completely eliminated, and the mechanical properties of the welded joint are also improved. This shows that the welding speed has a significant impact on the welding cracks of high-temperature alloys.
In order to reduce the occurrence of high temperature alloy welding cracks, the following measures can be taken:
1. Optimize the welding process parameters, such as adjusting welding speed, beam power, welding sequence, etc., to reduce the temperature gradient and residual stress during the welding process, thereby reducing the occurrence of thermal cracks and strain aging cracks.
2. Optimize the chemical composition and organizational structure of the welding material to improve the crack toughness and crack resistance of the welding material, thereby reducing the occurrence of welding cracks.
3. Increase the stress reduction treatment of the weld, such as preheating, heat treatment, cooling, etc., to reduce the residual stress and changes in the organizational structure during the welding process, thereby reducing the occurrence of welding cracks.
In short, the welding performance of high-temperature alloys is affected by many factors, and welding cracks are one of the problems that require special attention during the welding process. By optimizing the welding process and material composition, and taking appropriate stress reduction treatments, the occurrence of high-temperature alloy welding cracks can be effectively reduced and the quality and reliability of welded joints can be improved.
Tianjin Anton Metal Manufacture Co., Ltd. is a company specializing in the production of various nickel-based alloys, Hastelloy alloys and high-temperature alloy materials. The company was established in 1989 with a registered capital of 10.0 million, specializing in the production and sales of alloy materials. Anton Metal’s products are widely used in aerospace, chemical industry, electric power, automobile, nuclear energy and other fields, and can also provide customized alloy material solutions according to customer needs. If you need to know the price consultation of alloy materials or provide customized alloy material solutions, please feel free to contact the sales staff.
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Post time: Oct-21-2023
