In Situ Heat Treatment of Additively Manufactured High Strength Low Alloyed Steel

Additive manufacturing techniques such as Powder Bed Fusion – Laser Beam (PBF-LB), holds significant promise for enhancing the efficiency and sustainability of the spare parts industry. By enabling on-site production, PBF-LB could reduce lead times and shipping distances, while also eliminating the need for storage. However, many printed parts still require extensive post-processing, such as heat treatments.
This study explores the PBF-LB processing of a low alloyed high-strength martensitic steel (C 0.2 wt.%, Si 1.0 wt.%; Mn – 0.8 wt.%; Cr -1.2 wt.%; Mo 0.2 wt.%; V - 0.1 wt.%) and the possibility to obtain a ready-to-use component directly out of the printer. Due to the high cooling rates, a quenched martensitic microstructure is obtained during the first melting of a layer. Upon adding layers, an in-situ heat treatment takes place in previous layers, resulting in tempered martensite. By controlling the process parameters, the tempering condition can be changed. Consequently, the need for post heat treatments is eliminated, while making it possible controlling local material properties.
The powder was processed on an SLM280, varying laser scanning parameters, layer thickness and interlayer time. A dense material (>99.9%) with a quenched and temper martensite was obtained for all investigated sets of parameters. Depending on interlayer time, the hardness varied between 300 and 400 HV5. An ultimate tensile strength >1200, yield strength >1100, and Charpy-V impact toughness ≥90 J were achieved for horizontal specimens for all parameter sets. The material also performed better in fatigue testing than a plate of heat-treated martensitic steel with similar chemical composition. The material was evaluated by printing a plastic injection mold, resulting in a higher production rate and a longer tool life.
In summary, the in-situ heat treatment during PBF-LB processing produces a ready-to-use material with improved material properties, as well as allowing for controlled hardness.