Effect of welding heat input on the corrosion behaviour of high strength steel rebars

High-strength steel rebars are widely used in reinforced concrete columns and prone to failure due to corrosion in welded rebars causing loss of structural integrity. The present study aims to understand the effect of welding heat input and corrosion behaviour on 12 mm Fe550D grade high-strength steel rebars. Microstructural and mechanical characterizations of welded rebars were done to critically assess the weld joint performance. Different heat-affected zones (HAZ), i.e. coarse-grain heat-affected zone (CGHAZ), fine-grain heat-affected zone (FGHAZ), and inter-critical heat-affected zone (ICHAZ) regions, were produced through thermal simulations to mimic the actual heat-affected zones, followed by corrosion behaviour studies. Three heat inputs were chosen to study the microstructural transformations within the heat-effected zones, followed by their response to a corrosive chloride environment. Phases of ferric oxyhydroxides, lepidocrocite (γ-FeOOH) and geothite (α-FeOOH), were reported as main phases in inter-critical heat-affected zone (ICHAZ) and fine grain heat-affected zone (FGHAZ) samples, while traces of magnetite (Fe3O4) were observed in the coarse-grain heat-affected zone (CGHAZ). The susceptibility of corrosion towards ICHAZ was least, while the highest corrosion rate was observed for CGHAZ, owing to phase transformed microstructure in the heat-affected zones. High-heat input samples exhibited lower corrosion rates as compared to low-heat input samples for the same HAZ region.