Study on the influence of substrate preheating and deposition environment on the structural integrity of high carbon steel LMD parts of increased geometrical complexity

Laser Metal Deposition is finding growing industrial attractiveness thanks to its unique capability to locally restore worn metal components. In recent years, the industry is focusing on the application of metal Additive Manufacturing for the restoration of moulds and dies to improve process efficiency by reducing machine downtime and spare parts storage expenses. Although mould repair proved to be a cost-effective technological solution, the restoration of geometrically complex high carbon steel alloys through laser-based Additive Manufacturing still presents criticalities due to the low material weldability, high material oxygen reactivity, and high residual stresses generated by thermal cycling. This research work aims to analyse the influence of substrate preheating and the building environment on the structural integrity of steel specimens exhibiting 0.85% carbon content and implementing geometrical features which are generally critical to restore by laser-based processes since they behave as thermal stress concentration. The performed preliminary observations highlight no delamination and no oxide regardless of process conditions. High-density (99.99%) and crack-free high carbon steel depositions are achieved by reducing melt pool cooling rates during part manufacturing as a result of the increased environmental temperature surrounding the as-deposited material. Metallographic analysis demonstrates that carbide size decreases as cooling rates increase.