As welded metal toughness of gas tungsten arc welds has been found to be higher than that of their electron beam welded counterparts. In general, air cooling from 930°C for 1 h resulted in the best possible toughness for both base and weld metals. Prolonged exposure at 930°C or slow cooling from 930°C decreased the toughness values of weld metals. Heat treatment above the β transus resulted in poor toughness values. After heat treatment, the toughness values of gas tungsten arc weld metals were either equal to or better than their electron beam weld counterparts. The effect of prior heat input was found to be nullified after post-weld heat treatment above the β transus. Commercial grade weld metals showed relatively poor toughness values compared with their extra low interstitial grade counterparts. © 1997 The Institute of Materials.