Tensile properties and fracture toughness of 18Ni (250 grade) maraging steel weldments

Gas tungsten are welding was performed on 18Ni (250 grade) maraging steel s heet using two different filler wires: one of the same composition as the b ase material and the other containing more cobalt and aluminium and less mo lybdenum and titanium. Weld specimens were then aged under four different s ets of conditions. After metallographic characterisation, mechanical proper ties including hardness, tensile strength and ductility, and fracture tough ness were evaluated. Results showed that use of the matching filler materia l led to lower strength but higher ductility than in the other case; this w as attributed to the presence of reverted austenite in the former (caused b y segregation, especially of molybdenum) at the fusion zone substructure bo undaries. In both types of weld metal, a re-solution treatment followed by aging at 480 degreesC resulted in optimum tensile properties. Fracture toug hness of the aged weldments was in general close to that of the parent mate rial aged at 480 degreesC; some deterioration occurred only when welds with pronounced segregation were made at high temperature.