A parametric optimization and the effect of dwell time on mechanical and microstructure of WAAM specimens of high strength low alloy steels

The present study aims to fabricate multi-walled structure of TM-B9 high strength low alloys (HSLA) steel at optimized conditions and investigate the effect of different dwell time (DT) on microstructure and mechanical characterizations. For parametric optimization, wire-feed speed (WFS), voltage (V), and travel speed (TS) were considered as input factors of gas-metal arc welding (GMAW) based wire-arc additive manufacturing (WAAM) process along with bead width (BW), & bead height (BH) as output characteristics. Box-Behnken was utilized to perform the experiments, and its statistical significance was assessed by ANOVA. The WAAM process variables were optimized using the teaching-learning based optimization (TLBO) approach. A 90-layer multi-walled structure of HSLA steels was fabricated on mild steel substrate at optimized condition with 30 layers each at 30s, 60s, and 90s DT from bottom to top. The fabricated wall structure has revealed absence of disbanding with seamless fusion across the layers. The macrostructure has shown successive fusion among the deposited layers without any substantial defects, confirming the effective metallurgical bonding without signs of oxidation. The increase in DT observed finer grains at 90s of DT in comparison with coarse grains at 30s of DT. The increase in DT from 30s to 90s has shown a substantial enhancement of UTS, YS and EL by 28.33 %, 35.36 %, and 18.88 % respectively. The fractography of tensile specimen has shown high toughness and ductility for all conditions of DT. The increase in DT has shown increased MH value by 15.78 % due to higher cooling rate.