The weld metal of titanium-bearing nano precipitated high-strength steel reveals that the allotriomorphic ferrite on the prior austenite grain boundary coarsens with increased welding heat input. Besides the welding penetration with depth-to-width ratio increases with heat input, the solidified weld metal microstructures, depending on various heat inputs, exhibit the microstructure constituents of allotriomorphic ferrite, very little Widmanstatten ferrite, acicular ferrite, and bainite. Dislocations formed and multiplied with higher welding heat-input, in accordance to residual stress induced by the temperature gradient field. The dislocation morphology is intertwined at the highest welding heat-input (3.0 kJ mm (1)). Twin martensite forms under different welding heat inputs, and very little TiC reprecipitates in ferrite grains during the welding. (c) 2012 Elsevier B.V. All rights reserved.