Studies on multiple weld repairs of M250 maraging steel for solid motor casing used in satellite launch vehicle application

Maraging steel (M250) is extensively used in aerospace industries for the fabrication of solid propellant tanks in the welded and repair welded condition. The purpose of the investigation is to study the effect of multiple weld repairs on the microstructure and mechanical behavior of the alloy. The microstructure of the alloy in the as-welded condition contains two distinct heat-affected zones (HAZ) with different contents of reverted austenite. The results indicate that increased weld repair reduced the weld strength from 1722 to 1405 MPa whereas elongation increased from 5.8 to 6.1%. Fracture toughness was found to increase from 79 to 87.2 MPa√m. This is due to the increased content of reverted austenite of HAZ, which is a result of heat experienced by the zone during welding. The location of failure was predominantly along the HAZ 2 which is the mechanically weaker zone of the weld joint as revealed by microhardness measurements. Further, minor improvement in corrosion resistance is found due to increased content of austenite in HAZ in repair weld conditions.