PSI - Issue 71

Ganesan G et al. / Procedia Structural Integrity 71 (2025) 438–444

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3.2 Mechanical Properties The distribution of austenite and ferrite phases in heterogeneous stainless steels plays a crucial role in determining mechanical properties such as microhardness (Vickers) and ultimate tensile strength (UTS). Increasing the wire feed rate of SS-304 in the multi-wire GTAW-based WAAM process enhances austenite formation, impacting these properties. Ferrite is harder and has higher yield strength but is less ductile, while austenite improves toughness and UTS. A combination of both phases enhances strength and ductility. Micro Hardness The microhardness increases with rising SS-304 feed rates during multi-wire GTAW-based WAAM, as shown in Fig. 6. Heterogeneous steel alloy maintains its strength through the interaction of combined phases, and the relationship between austenite percentage and microhardness is evident. At 0% austenite, microhardness ranges from 204 to 213 HV. As austenite content increases to 2-3%, hardness rises to 212 – 225 HV, and 5.5 – 6% austenite further increases to 248 – 264 HV. At 9 – 10% austenite, hardness continues to rise to 262 – 275 HV, reaching 281 – 293 HV at 12.5 – 13.5% austenite. This gradual increase is attributed to solid solution strengthening from chromium (Cr) and nickel (Ni), which enhance lattice distortion and stabilize the austenite phase. Additionally, higher SS-304 feed rates refine the microstructure through increased cooling rates, reducing grain size and improving hardness via the Hall-Petch relationship. Cr, Ni, and Mn enrichment strengthen the alloy through multiple mechanisms. This combination of phases and compositional gradients enables the material to distribute stresses effectively, preserving structural integrity and heterogeneity while gradually increasing microhardness as the SS-304 feed rate rises. Conventional ER70S-R alloy has microhardness between 180 – 210 HV, and SS-304 ranges from 200 – 230 HV. The heterogeneous alloy shows a progressive increase in microhardness, reaching 287 HV, a total increment of 78.5 HV (~37.6%), due to the combined effect of ferrite and austenite phases, strengthening, and refined microstructure.

Fig.6. Effect of % of Austenite on Micro Hardness

Ultimate Tensile Strength (UTS) Increasing austenite content enhances energy absorption during deformation, leading to higher ultimate tensile strength (UTS) and improved toughness. Ferrite, though strong, can be brittle. Adding austenite improves UTS by