Mechanical and microstructural assessment of conventional carbon and stainless steel shear stud welded connections

Shear studs are crucial for composite action between a bridge’s superstructure and deck. While carbon steel shear studs weld well onto ASTM A709 Grade 50 steel, their use with weathering bridge steels, particularly ASTM A709 Grade 50CR, has been associated in the literature with potential service-life concerns such as galvanic corrosion arising from metallic dissimilarities. Austenitic stainless steel shear studs have therefore been proposed for use with martensitic ASTM A709 Grade 50CR; however, literature on their mechanical behavior is limited, and code guidance is lacking. This study aims to investigate the mechanical performance and failure mechanisms in conventional carbon and austenitic stainless steel shear studs welded to ASTM A709 Grade 50 and Grade 50CR base metals. Shear and tensile tests were performed on three stud–base metal configurations: (1) a carbon steel shear stud welded to an ASTM A709 Grade 50 plate, (2) a carbon steel shear stud welded to an ASTM A709 Grade 50CR plate, and (3) an austenitic stainless steel shear stud welded to an ASTM A709 Grade 50CR plate. Weld-zone microstructural analysis and microhardness traverses were conducted for each stud–plate assembly. Tensile and shear testing demonstrated an increase in tensile and shear capacities and an increase in ductility for austenitic studs compared with carbon steel studs. Microstructural analysis revealed martensite formation in the coarse-grained heat-affected zone (CGHAZ) of the carbon steel stud welds with Vickers hardness measurements reaching 390 HV0.5. The stainless steel shear stud welds consistently reached 430 HV0.5 in the CGHAZ and weld microstructure, which may be attributed to the formations of martensite, secondary phases, and carbides in these regions. These elevated hardness levels may affect local toughness and increase susceptibility to cold cracking. This significant hardness increase underscores the need to maintain pre‑qualified stud‑welding parameters including heat input, correct stud seating and hold, and surface cleanliness, to ensure consistent weld reliability. The results obtained from this study aim to provide bridge owners valuable insights into the performance and reliability of stainless steel shear studs for bridge applications.