Detailed Examinations to Determine the Percentage of Ferrite in the Heat Affected Zone of a Welded Duplex Stainless Steel.

Duplex stainless steels contain a nearly equal phase balance of ferrite to austenite to have the most favorable properties. During welding the heat affected zone (HAZ) nearest the weld can transform completely to ferrite, which upon cooling, can disrupt the final phase balance and resulting properties. Therefore, weldments are often subjected to independent examination for qualification testing where the percentage of ferrite must fall within an acceptable range. While conventional metallographic testing has been one of the most popular techniques, it is often stated that, “Accurate metallographic determination of the phase balance in the HAZ is nearly impossible”(1), and as a result experts have attempted several other techniques to characterize the HAZ.
In this study, 2205 duplex stainless steel plates were joined via multi-pass fillet welds using gas-shielded flux-cored arc welding (FCAW-G) with 100% CO2 and ER2209 filler wire. Standard micro cross sections of the fillet welds were prepared and etched using conventional metallographic procedures. The percentage of ferrite was examined in the weld, HAZ and base metal. At 1000X magnification, a narrow heat affected zone (HAZ) was observed with a large amount of ferrite. Different methods were used to investigate the percentage of ferrite including an unconventional metallographic method for more accurate characterizations in the HAZ.