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Gas tungsten arc welding was performed on 18Ni (250 grade) maraging steel sheet using two different ®ller wires: one of the same composition as the base material and the other containing more cobalt and aluminium and less molybdenum and titanium. Weld specimens were then aged under four different sets of conditions. After metallographic characterisation, mechanical properties including hardness, tensile strength and ductility, and fracture toughness were evaluated. Results showed that use of the matching ®ller material led to lower strength but higher ductility than in the other case; this was attributed to the presence of reverted austenite in the former (caused by segregation, especially of molybdenum) at the fusion zone substructure boundaries. In both types of weld metal, a re-solution treatment followed by aging at 480³C resulted in optimum tensile properties. Fracture toughness of the aged weldments was in general close to that of the parent material aged at 480³C; some deterioration occurred only when welds with pronounced segregation were made at high temperature.

The stress corrosion characteristics of 18 wt-%Ni (MDN ± 250) maraging steel and its weldments made under different welding conditions have been investigated. The threshold stress intensity factor K ISCC in stress corrosion conditions has been determined in 3 . 5 wt-%NaCl environment for the base metal and weldments. The fractured surfaces were analysed to study the types of fracture during stress corrosion cracking in base and weld metals. Fracture toughness tests were carried out and the results obtained from these tests have been compared with K ISCC values.MST/5229