Evaluation of mechanical properties across micro alloyed HSLA steel weld joints using Automated Ball Indentation

The object of the present investigations is to evaluate the mechanical properties across the SMAW, SAW, FCAW and A-GTAW weld joints of micro alloyed HSLA steel. The correlation between microstructure, micro-hardness and tensile properties obtained using automated ball indent (ABI) has been undertaken. The variation of yield strength (YS), ultimate tensile strength (UTS) and strain hardening component (n) values across base metal, heat affected zone and weld metal were obtained from the ABI results and validated with the standard conventional tensile test results. The cross-weld joints were found to have minor increase in yield strength with corresponding decrease ductility as compared to the base steel. The high strength of weld metals was attributed to the presence of high percentage of bainitic and acicular ferritic microphases. The transformation of base metal to bainitic structure was found to be the significant factor contributing to the strength of HAZ in the weld joints. The tensile strength was observed to vary significantly across the weld joints. The strength values (YS and UTS) decreased systematically across the weld joint from weld metal to base metal. The strain hardening exponent was found to be comparable across the weld joints with marginal higher values for HAZ. The comparable values of strain hardening exponent for weld metal and base metal showed the balanced strength and ductility of the welds. The FCAW and SAW were found to be better welding techniques that provide sufficient strength and least variation in mechanical properties across the weld joints.