Influences of titanium and manganese on high strength low alloy SAW weld metal properties

The objective of this work was to study the influence of titanium on API 5L-X70 steel weld metal properties at manganese levels of 1.4 and 2%. The best mechanical properties in the weld series were obtained in two compositions, i.e. 1.92%Mn–0.02%Ti and 1.40%Mn–0.08%Ti. In both groups of welds, acicular ferrite in the microstructure was increased with addition of titanium in the range of 0.02–0.08%. Manganese helped to refine and homogenize weld microstructures. Increased hardenability of the weld due to further addition of titanium or manganese encouraged grain boundary nucleation of bainite with greater frequency than intragranular nucleation of acicular ferrite. Also, the amount of manganese in inclusions was decreased with the addition of titanium to the weld. The impact toughness of the weld metal was improved by addition of titanium, but beyond the optimal titanium percentage, the quasi-cleavage fracture mode appeared in the specimens again.