Microstructural and mechanical characterization of robotic-MAG welded armor-grade steel: effect of filler metal selection

Abstract This study examined the microstructural and mechanical behavior of 15-mm Armor 500 steel plates welded by robotic metal active gas (MAG) using four filler wires: ER70S-6, ER110S-G, ER309LSi, and ER2209. The plates were prepared with 22.5° bevelled edges and welded using ceramic backing with a five-pass technique. The characterization was carried out using X-ray fluorescence (XRF) for weld-metal composition, stereo/optical/scanning electron microscopy for macro- and microstructural observations, and mechanical tests comprising tensile, Charpy impact (− 40 °C) and Vickers hardness (HV 5 ). The ferritic wires (ER70S-6/ER110) yielded AF-dominated weld metals (with local martensite/austenite constituents in ER110 roots), while austenitic/duplex wires (ER309LSi/ER2209) formed austenitic matrices with delta-ferrite; dilution created unmixed regions and modified the ferrite–austenite balance near the fusion boundary. The compositional analysis showed that ER309LSi and ER2209 welds exhibited noticeable dilution, with significant Cr and Ni reduction compared to the base metarial (BM). ER110 welds provided the highest strength (tensile strength 1052 ± 6 MPa; yield strength 737 ± 77 MPa), while ER309LSi welds delivered the best toughness (97 ± 4 J at − 40 °C). Hardness values in weld regions followed the order ER110S-G > ER2209 > ER70S-6 > ER309LSi. These findings suggest ER110 as the preferred filler when high strength and hardness are required, and ER309LSi when low-temperature toughness is critical.