Development and Characterization of 9%Cr Shielded Metal Arc Welding Electrodes

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.