PSI - Issue 54

Paulo Mendes et al. / Procedia Structural Integrity 54 (2024) 340–353 Mendes et al. / Structural Integrity Procedia 00 (2023) 000–000

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likely originated from a region far from the fusion zone, as the inclusions examined consist mainly of MnS, similar to those found in the base material, implying that this region experienced of less thermal input. Conversely, the fracture surface in Figure 12.f) may have been near the transition from the heat-a ff ected zone to the fusion zone, as it contains complex oxides with compositions similar to those found in weld material specimens. This zone may have experienced extremely high temperatures during the welding process, allowing complex reactions between oxygen and the existing elements due to its proximity to the fusion zone.

5. Concluding remarks

This investigation involved a comprehensive analysis of the hardness properties using Vickers hardness testing, coupled with microstructural observations using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Through these testing and analytical techniques, several noteworthy observations can be pointed out: • The HAZ displayed notable hardness changes due to diverse morphologies and constituents at di ff erent welding process stages. These variations reflect the intricate thermal history experienced by this region during welding; • Hardness values consistently proved to be higher in the weld material zone compared to the base material, proving the high reliability and quality of the weld; • The upper sections exhibited elevated hardness values throughout all welding process stages, potentially linked to the increased heat input during the final tempering steps. Later welding stages can significantly impact the mechanical properties of earlier weld passes. • In the thicker joint (J60), the slower cooling rate led to lower HAZ hardness values. • The weld material contained more inclusions than the heat-a ff ected zone, which, in turn, has more than the base material; • Inclusions were more prevalent in the weld material than in the HAZ, which, in turn, presented more inclusions than the base material. The composition, shape, and nature of these inclusions varied across the HAZ, depending on their proximity to the weld material. • Hardness was observed to increase with a finer grain size, underscoring the importance of grain refinement in enhancing mechanical properties, particularly in critical regions of the weldment. • The HAZ subjected to intercritical temperatures revealed the presence of ferrite in grain boundaries. This ferritic phase is softer than other constituents, potentially making these regions more susceptible to stress concentration and crack initiation. To optimize weld quality and ensure the long-term integrity of high-strength steel joints in demanding applications, it is important to implement controlled pre-heating and tailored post-weld heat treatment regimes. Future research should continue to explore the intricate interplay between welding parameters, microstructure, mechanical properties, and residual stresses to advance welding techniques and improve material performance.

Acknowledgements

This research was supported by the project grant AARM 4.0 - Ac¸os de Alta Resisteˆncia na Metalomecaˆnica 4.0 with the reference POCI-01-0247-FEDER-068492, co-financed by the European Regional Development Fund (ERDF), through the Operational Programme for Competitiveness and Internationalization (COMPETE2020), un der the PORTUGAL 2020 Partnership Agreement. Jose´ A.F.O. Correia would like to thank the individual project grant (2020.03856.CEECIND) awarded by national funds (PIDDAC) through the Portuguese Science Foundation (FCT / MCTES).

References

Ahiale, G.K., Oh, Y.J., 2014. Microstructure and fatigue performance of butt-welded joints in advanced high-strength steels. Materials Science and Engineering: A 597, 342–348. doi: https://doi.org/10.1016/j.msea.2014.01.007 .