Effect of tool material and process parameters on friction stir weld formation of maraging steel

18% Ni maraging steel is an ultra-high strength steel widely used in defence and aerospace applications. Fusion welding of maraging steel is encountered with a drop in properties due to the segregation of alloying element and hence, solid-state welding process such as friction stir welding (FSW) is a possible alternative. However, welding of high strength material using FSW is a challenge considering the tool material durability, tool material cost, and selection of tool geometry and process parameters. Therefore, the main focus of this paper is towards the selection of tool geometry, tool material, and process parameters that will result in least tool wear/failure in addition to obtaining defect-free welds of maraging steel using FSW. It was observed that polycrystalline cubic boron nitride (PCBN) and tungsten-molybdenum are durable tool material for welding maraging steel. It is recommended to use a minimum tool pin diameter (top 12 mm and bottom 8 mm) and shoulder diameter (20 mm) below which failure of pin and surface defects are encountered during FSW. It is also observed that there exists a narrow range of tool rotational speed (250-450 rpm) and tool travel speed (25 mm/min) at which defect-free maraging steel welds can be obtained.