Butter-weld Interface Microstructural Analysis Employing NCS and LAMS Sections

Abstract

The formation of brittle microstructures around the fusion line in dissimilar welds has required a deeper microstructural analysis in this region. The study becomes more relevant when these welds are used in environments that facilitate hydrogen embrittlement. The present work aims to characterize the microstructure and hardness at the diluted zone interface in joints welded with dissimilar materials. Aiming for a better efficacy in the microstructural characterization of this zone, samples of both normal cross-section (NCS) and section with slope were used, according to the low-angle microsectioning (LAMS) technique, which allows a greater amplification of partially mixed zones (PMZs). The results indicated the diffusion of carbon from the heat-affected zone (HAZ) towards the fusion line which, in combination with other alloying elements, form highly brittle carbides. In turn, the hardness of the base metal and the HAZ was reduced after post weld heat treatment, whereas in the weld metal an opposite behavior was observed. The dissimilar interface was promising for applications in environments facilitating hydrogen embrittlement, especially regarding the characteristics of zone Φ.

Effect of Hydrogen on the Mechanical Properties of ASTM A182 F22 and ASTM A36 Steels Welded Joint Using Inconel 625 as Filler and Buttering Metal

“…Figure 10a and b, shows images extracted by the LAMS technique 18 , showing macrosegregations of "island" and "swirl" type, with some of the microhardness values surveyed at the dissimilar interface, which is also shown in Table 9. Within the red rectangle of Figure 10b, there are dark regions, on the steel side, known as M zones.…”