Abstract:
The objective of the current study was to develop SMAW electrodes to American
Welding Society (AWS SFA 5.5 E9018-B9) with an Ac1 temperature above the post
weld heat treatment (PWHT) temperature (760⁰C). The weld metal microstructure
should be tempered martensite with hardness close to that of the P91 base metal after
PWHT. About 30 different electrodes were formulated, with 15 of the formulated
laboratory electrodes and three commercial electrodes along with the base metal
characterised by depositing bead-on-plate welds. The AC1 temperatures of the welds
were measured on the Bähr 805D dilatometer. Two previous published empirical
equations for the AC1 temperature were used to verify the results. The measured AC1
temperatures of the laboratory developed and commercial electrodes weld metals
were found to be above the PWHT temperature. A predictive equation for the A1
temperature equation was developed in this study. The microstructure was
predominant martensite in as-welded and after PWHT. However, delta () and alpha
() ferrite was observed in the microstructure of some weld metals in both these
conditions. Zhang et al. and Merchant ferrite factor prediction in some of the weld
metal microstructures were found to be contradictory to the findings in the present
study. The Vickers hardnesses of the weld metals after PWHT were below 265HV with
soft spot (hardnesses below 200 HV) shown in some of the weld metals.
