Effect of Ti-containing inclusions on the nucleation of acicular ferrite and mechanical properties of multipass weld metals

In the present study, the influence of Ti-containing inclusions on the development of acicular ferrite microstructure and mechanical properties in the multipass weld metals has been studied. Shielded metal arc weld deposits were prepared by varying titanium content in the range of 0.003-0.021%. The variation in the titanium content was obtained by the addition of different amounts of titanium oxide nanoparticles to the electrode coating. The dispersion of titanium oxide nanoparticles, composition of inclusions, microstructural analysis, tensile properties and Charpy impact toughness were evaluated. As the amount of Ti-containing inclusions in the weld metal was increased, the microstructure of the weld metal was changed from the grain boundary allotriomorphic ferrite structure to acicular ferrite with the intragranular nucleation of ferrite on the Ti-containing inclusions, and the mechanical properties were improved. This improvement is attributable to the increased percentage of acicular ferrite due to the uniform dispersion of Ti-containing inclusions and the pinning force of oxide nanoparticles against the growth of allotriomorphic ferrite and Widmanstatten ferrite from the austenite grain boundaries. (C) 2012 Elsevier Ltd. All rights reserved.