Fig. 11 presents the austenite volume fraction in the weld region at the end of the weld (phase (ii)) before cooling and is indicative of the volume of material which will transform to martenstite upon cooling (phase (iii)). It can be seen that the higher pressure weld (Weld 2) results in a narrower region of austenite material,approximately 5 mm across compared to around 8 mm in Weld 1.This is also highlighted in Fig. 12 which shows the volume fraction variation with distance from the weld line near the OD of the components for both welds, this location is consistent with where the hole drilling data has been taken for the residual stress measurements. This data is compared with the microstructural cross-section for Weld 1 in Fig. 13 where it can be seen that the width of the region of material which transforms to austenite on heating can clearly be seen to match closely to the corresponding width of affected material from the weld cross-section.