Sigma formation in austenitic clad metals

In a previous study type 347 submerged arc clad metals were found to be prone to sigma formation after exposing them to 600 deg C for 1 h, when the initial ferrite content was relatively high (12 FN). In the present study the same samples (low ferrite (4 FN) and high ferrite (12 FN)) were studied for their chemical composition in each phase using energy-dispersive x-ray analysis. The STEM /EDAX study presented shows that users of austenitics should choose flux/filler combinations with care when deposited by the submerged-arc welding process. It has demonstrated the deleterious effect of higher silicon contents on ferrite to sigma phase transformation at lower temperatures and shorter times than previously reported.