What are the precautions to be taken in high-temperature alloy welding?

High temperature alloys are widely used in high-end industrial fields such as aerospace, energy and power due to their excellent high-temperature strength, oxidation resistance and corrosion resistance. However, the welding process is full of challenges due to the complex material composition and special physical properties, requiring strict control of process details from multiple dimensions to ensure welding quality. ​

High temperature alloys can be divided into nickel based, cobalt based, iron-based and other types according to their substrates. Welding of different types of alloys requires the use of welding wires or electrodes with corresponding compositions. For example, when welding nickel based high-temperature alloys, the welding wire needs to ensure that the nickel content matches the base metal, while adding appropriate amounts of chromium, molybdenum and other elements to maintain high-temperature strength; Cobalt based alloys require control of carbon content to avoid grain boundary embrittlement. If the composition difference between the welding material and the base metal is too large, brittle phases are easily formed in the weld zone, leading to a significant decrease in the high-temperature performance of the joint. ​

The control of welding heat input directly affects the quality of the joint. High temperature alloys have poor thermal conductivity and high coefficient of thermal expansion. Excessive heat input can cause severe grain coarsening in welds and heat affected zones, reducing the toughness and creep resistance of the material; Insufficient heat input may result in defects such as incomplete fusion and incomplete penetration. In practical operation, welding current, voltage, and welding speed need to be adjusted according to the type of alloy. For example, for precipitation strengthened high-temperature alloys, smaller heat input is usually used to reduce the dissolution and loss of strengthening phases. ​

Protective measures during the welding process are crucial. Most high-temperature alloys are prone to react with elements such as oxygen, nitrogen, and hydrogen in the air at high temperatures, forming brittle compounds or causing the formation of pores. Therefore, inert gas must be used for full protection during welding, and the protection range should not only include the molten pool, but also cover the heat affected zone with a temperature higher than a certain value. For certain easily oxidizable alloys, it is necessary to strictly clean the welding groove, remove the surface oxide film and oil stains, and if necessary, take back protection measures. ​

The post weld treatment process is a crucial step in ensuring the performance of the joint. High temperature alloys usually generate significant residual stresses after welding, which need to be relieved through heat treatment while restoring the mechanical properties of the material. There are significant differences in heat treatment processes among different types of high-temperature alloys. Solid solution strengthening alloys require solid solution treatment to refine grain size, while precipitation strengthening alloys require precipitation of strengthening phases through aging treatment. In addition, for welded components with large thickness, it is necessary to control the cooling rate to avoid cracking caused by rapid cooling. ​

In short, high-temperature alloy welding is a systematic project that requires full process control from material matching, process parameters, protective measures to post weld treatment. Only by strictly following scientific welding standards can welding defects be reduced and the reliability and stability of joints in high-temperature service environments be ensured. With the continuous expansion of the application field of high-temperature alloys, the requirements for their welding technology will also continue to increase, promoting the development of welding processes towards more precise and efficient directions.