Improving the Weld Performance of A-1011 Steel Joints Using TiO2 Nanoparticles-Based E7018-H4R Electrodes

Abstract The aim of this work is to examine the effect of TiO2 nanoparticles-coated E7018-H4R electrode on microstructure and mechanical characteristics of A-1011 steel welded joints. The shielded metal arc welding (SMAW) process is used to join the base metal, and output responses including ultimate tensile strength, hardness, percentage elongation, and residual stresses of joints have been evaluated. The effects of SMAW parameters such as welding current, welding speed and dipping time of electrodes in TiO2 solution on mechanical responses and microstructure have been analyzed through Response surface methodology (RSM) with central composite design. Mathematical models have also been developed to predict the output responses. Results revealed that tensile strength has been primarily influenced by welding current followed by dipping time and welding speed. The maximum tensile strength of 509 MPa, hardness of 230 HV and percentage elongation of 23% has been achieved by using 60 min dipping time of electrodes in TiO2 solution. The optimum combination of parameters, i.e., welding current of level 2 (130 A), welding speed of level 2 (35 cm/min), and dipping time of electrodes in TiO2 solution of level 2 (60 min) has been attained. The residual stress results showed that the specimen welded with coated electrodes have less residual stress value 142.32 MPa as compared to specimen with uncoated electrode (179 MPa). The optical and scanning electron microscopic (SEM) analysis confirmed the presence of TiO2 nanoparticles in the welded zone resulted in a smaller grains boundary of ferrite and presence of acicular ferrite, which ultimately led to increase in tensile strength and hardness of a specimen. The EDX analysis confirmed the presence of Ti peaks, along with Mn and Si, suggest inclusion formation favorable for acicular ferrite nucleation, leading to grain refinement and enhanced mechanical properties.