Evolution of Microstructures and Mechanical Properties of Laser-Welded Maraging Steel for Aerospace Applications: The Past, Present, and Future Prospect

Maraging steels encounter tremendous aerospace applications, such as in landing gears, rocket motor casing, pressure vessels, satellite launch vehicles, etc. Laser welding is considered one of the most effective manufacturing processes due to its minimal instances of wider heat-affected zones (HAZs), precipitate accumulation, and other benefits. However, it should also be noted that their severe effect is still evident in terms of the tensile strength and fatigue strength of laser-welded maraging steel. This paper provides a critical review of the evolution of microstructural features and mechanical properties of laser-welded maraging steel, including corresponding factors in terms of microstructures and the formation of reverted austenite, as well as precipitation hardening from various studies on maraging steels. We examined the influence of precipitation, reverted austenite, welding, and post-weld heat treatment on mechanical properties like hardness, tensile strength, yield strength, elongation, and fatigue strength of laser-welded maraging steel. It is worth mentioning that the laser welding process is generally insufficient for welding sheets with a thickness over 10 mm or those requiring multi-pass welding. The reheating process becomes unfavorable for maraging steel in the multi-pass welding process since it may induce localized heat treatment. Although hybrid welding may resolve an arising thickness issue, the reversion of austenite and complexity are still difficult to overcome due to the dual nature of welding processes, resulting from the use of both arc and laser. Furthermore, maraging steel produced via additive manufacturing tends to avoid austenite reversion with effective heat treatment prior to any welding process. Post-weld heat treatment and cryogenic treatment have been found to be favorable for desired reverted austenite formation. Finally, the proposed constructive framework specifically applies to the welding process of maraging steel, particularly for aerospace applications.