Effect of TIG arc surface melting process on weld metal toughness of modified 9Cr-1Mo (P91) steel

Modified 9Cr-1Mo steel is widely used in the construction of power plants. Flux-shielded processes result in inadequate weld metal toughness due to the presence of inclusions. An acidic-coated electrode with primary constituent of rutile in flux coating tends to produce inferior toughness due to the presence of coarse microinclusions in the resultant weld. In the present study, welds produced using acidic-coated electrodes were given a surface melting using TIG process to refine the inclusions. There was significant reduction in number of coarse microinclusions and increase in number of fine microinclusions. Charpy V-notch test was conducted at room temperature to evaluate the toughness of weld. Surface melted welds have superior toughness compared to unmelted welds. Fractographic features correlate well with the observed impact energy values of welds.