Effects of flashing and upset sequences on microstructure, hardness, and tensile properties of welded structural steel joints

Highlights: → Flash butt welding ASTM A529 steel specimens with varied process settings. → Tensile, hardness, and nondestructive evaluation of welds and HAZs. → Acicular ferrite in weld zone provides necessary strength and ductility. → Maximum hardness achieved within the weld zone. → Quantity of interfacial inclusions depends on upset dimension and flashing time. -- Abstract: In this study, ASTM A529 carbon-manganese steel angle specimens were joined by flash butt welding and the effects of varying process parameter settings were investigated. The resulting weld metal and heat affected zones were examined and further processed using tensile testing, Rockwell hardness testing, ultrasonic scanning, optical microscopy, and scanning electron microscopy with energy dispersive spectroscopy. Test results showed that hardness was increased in the weld zone for all specimens, which can be attributed to the extensive deformation of the upset operation. Statistical analysis of experimental data highlighted the sensitivity of weld strength and the presence of weld zone inclusions and interfacial defects to the process factors of upset current, flashing time duration, and upset dimension. Microstructural analysis revealed various phases within the weld and heat affected zone, including acicular ferrite, Widmanstatten or side-plate ferrite, and grain boundary ferrite. Fractography of tensile specimens indicated brittle cleavage fracture within the weld zone for certain factor combinations. The significance of process factor levels on microstructure, fracture characteristics, and weld zone strength, inclusions, and embrittlement was analyzed.