Microstructure evolution and mechanical properties of Q690D steel repaired by wire based laser directed energy deposition

A wire-based laser directed energy deposition process was developed to repair Q690D steel. The microstructure evolution, phase transformation and mechanical properties of the repaired specimens were investigated in detail. Excellent metallurgical bonding was achieved between the repaired zone and the substrate free of macroscopic defects. Typical columnar dendrites with grains grew perpendicularly from the fusion line to the deposition zone (DZ) centre. Microstructure in the DZ and heat-affected zone (HAZ) of the repaired specimen was predominated by lath martensite. The tensile properties of the repaired specimens were comparable to those of the substrate. The repaired specimens presented ∼200 MPa higher flexural strength than that of the substrates, while they have inferior ductility compared to the substrates under the three-point bend test. The average impact absorbed energy value for the repaired specimens achieved ∼85–90% of the substrates. This study introduces a novel restoration technique for offshore engineering platform maintenance.