Publication

Abstract : In this study, dissimilar weld joints were investigated consisting of SA508 Gr.3 Cl.1 low alloy steel and SA312 Type 304LN stainless steel. Two weld joints were fabricated initially with buttering alloy ER309/E309L SS and Inconel 82 (IN82). Thereafter, buttered LAS pipe was welded to SA312 Type 304 LN stainless steel material with filler material as 308L SS and Inconel 182 (IN182) respectively. Main focus was given to explore the heterogeneity at fusion boundary of dissimilar weld along with qualitative / semi-quantitative assessment of the same. The same was accompanied by evaluating microhardness profile to identify the region prone to failure in service. Low alloy steel revealed two distinct regions; close to fusion boundary it was a carbon depleted thin coarse grain region and away from fusion boundary it was relatively wide fine grain region. Adjacent to the fusion boundary, butter side was characterised by Type-I and II grain boundaries and discrete islands of martensite cluster. Butter-filler and filler-304 LN SS fusion boundaries exhibited unmixed zone. Adjacent to the filler-304 LN SS fusion boundary, localised region consisting of polygonal grains were found due to thermal effect. Microhardness change across weld zone was governed by phase transformation. Microhardness profile exhibited a sharp peak in profile near martensitic region. Minima in the profile was observed in second layer of buttering alloy thus making it the weakest region in the weld joint. Depending on the nature of buttering alloy, the width and maximum / minimum of hardness at different zones were varied significantly.