Butter-weld Interface Microstructural Analysis Employing NCS and LAMS Sections

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.

异种焊缝（dissimilar welds）熔合线周边脆性显微组织的形成，需对该区域开展更为深入的显微组织分析。当此类焊缝应用于易诱发氢脆（hydrogen embrittlement）的工况时，本研究的意义更为凸显。本研究旨在对异种材料焊接接头的稀释区界面处的显微组织与硬度进行表征。为优化该区域的显微组织表征效果，本研究采用低角度显微制样（low-angle microsectioning, LAMS）技术，制备常规横截面（normal cross-section, NCS）与斜面横截面两类试样，该技术可实现对部分混合区（partially mixed zones, PMZs）的更大倍率观测与表征。结果表明，碳从热影响区（heat-affected zone, HAZ）向熔合线扩散，并与其他合金元素结合形成脆性极高的碳化物。此外，经焊后热处理（post weld heat treatment）后，母材（base metal）与热影响区的硬度均有所降低，而焊缝金属的硬度则呈现相反的变化趋势。该异种接头界面在易诱发氢脆的工况下具有较好的应用前景，尤其针对Φ区的性能特征而言。