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Maraging steel can be welded using all fusion welding methods other than gas welding, such as shielded metal arc welding, submerged arc welding, tungsten inert gas welding, and gas tungsten arc welding. Due to the high susceptibility of this steel to cold cracking, it is necessary to thoroughly clean the workpieces and dry the electrodes before welding, in order to maintain low-hydrogen or even ultra-low-hydrogen conditions during welding. When the restraint on the welded joint is high, TIG welding or MIG welding is preferable. Appropriately increasing the welding heat input, without causing overheating and embrittlement in the near-weld area, can reduce the tendency to form cold cracks. 02 Welding Materials: The selection of welding materials should vary depending on the type of steel, the welding method, and the operating conditions of the joint. To meet the requirements for performance, the chemical composition of the weld should be as close as possible to that of the base material; therefore, welding materials with a composition similar to that of the base material are preferable. However, in this case, the weld and heat-affected zone tend to harden and become brittle. To prevent cold cracking, heat treatment is generally required after welding. When heat treatment is not permissible for the welded parts, it is advisable to use 25-20 and 25-13 type austenitic steel welding materials in order to form an austenitic weld seam, relieve welding stresses, and accommodate more hydrogen, thereby reducing the tendency to cold cracking. Austenitic welds possess high plasticity and toughness, but lower strength; as a result, they are only suitable for weldments that operate under static loads with low stress levels. Moreover, due to the significant differences in thermophysical properties between the weld and the base material, high additional stresses can arise at the joint interface when operating at high temperatures, leading to premature failure of the joint; hence, they are also not suitable for weldments that function at high temperatures. In shielded metal arc welding, low-hydrogen electrodes are typically used, and they are dried at 400–450°C for two hours before welding. For submerged arc welding, low-silicon, high-alkaline or weakly acidic fluxes should be used, such as HJ172, HJ173, HJ251, etc. TIG welding is mainly used for the root pass welding in multi-layer welding and for welding thin materials. 03 Preheating and interlayer temperature: Preheating and maintaining the interlayer temperature is an important process measure to prevent cold cracks. The selection of the preheating temperature takes into account first the carbon content in the steel, and secondly factors such as the degree of restraint on the joint, the composition of the filler metal, and the welding method. Table 1 shows the recommended preheating temperatures, heat input, etc., classified by carbon content. If the constraint on the joint is high, the preheating temperature and interlayer temperature should be increased accordingly. The interlayer temperature should not be lower than the preheating temperature. When welding with austenitic steel welding materials, preheating may not be necessary or only light preheating is required, depending on the thickness of the workpiece. Image 04: Post-weld heat treatment. Post-weld heat treatment is another important process measure to prevent cold cracks. When selecting welding materials with composition similar to that of the base material, post-weld heat treatment is generally required. When welding with austenitic steel welding materials, post-weld heat treatment is generally not required. To ensure that the austenite after welding is completely transformed into martensite, tempering immediately after welding is not allowed; instead, the joint must be cooled to a temperature below the Ms point and held there for a certain period of time before high-temperature tempering is carried out. Because if tempering is carried out immediately after welding, austenite will transform into pearlite and carbides will precipitate along the austenite grain boundaries, resulting in a very brittle microstructure. However, to prevent cold cracking, it is also not allowed to wait until the joint has cooled to room temperature before performing high-temperature tempering; usually, tempering is carried out when the temperature has dropped to 100–150°C.