Improvement of impact toughness of AWS E6010 weld metal by adding TiO2 nanoparticles to the electrode coating

The effect of TiO2 nanoparticles in the electrode coating on the impact toughness of three weld metals prepared by the shielded metal arc welding process was investigated and the main factors affecting the impact toughness were discussed. The microstructure, mechanical properties and fracture surface morphology of the weld metals have been evaluated and the results are compared. When the content of TiO2 nanoparticles in the composition of electrode coating is increased, the morphology of ferrite in the microstructure of columnar zone will change from Widmanstätten ferrite to acicular ferrite. This finally changes to allotriomorphic ferrite when the amount of TiO2 nanoparticles in the electrode coating goes relatively high. Furthermore, the addition of TiO2 nanoparticles is effective in refining the ferrite grain size of the reheated microstructures of weld metals. This effect is attributed to the increased number of nucleation sites on the oxide nanoparticles. The impact toughness of the weld metal was improved by adding TiO2 nanoparticles, especially when a medium TiO2 nanoparticle content was used in the electrode coating. A significant increase in the impact toughness of weld metal was shown to be due to the increased percentage of acicular ferrite and refinement of microstructure.