Despite the growing prominence of powder bed fusion – laser beam (PBF-LB) there remains a scarcity of approved material for the process. An important alloy group that has yet to be developed is structural steel. This is in part due to its low processability, as these alloys are susceptible to cold cracking due to their high carbon content. A common technique to alleviate this issue is preheating of the build plate. However, the application of build plate preheating to control other aspects such as the microstructure and mechanical properties has received little attention. The current study examined the influence of build plate preheating during PBF-LB of Fe-0.45C steel at temperatures of 25˚C, 300˚C and 500˚C. Specific focus was put on how these preheating temperatures influenced processing, microstructure, and mechanical properties. To carry out this investigation, pre-alloyed, gas atomized Fe-0.45C steel powder was processed using a customized Aconity3D PBF-LB machine that can achieve build plate preheating temperatures of up to 800˚C.

Results found that increasing the build plate preheating temperature improved processability, as cold cracking was completely avoided in specimens produced at 300˚C and 500˚C. Additionally, higher build plate preheating temperatures improved material densification, see Figure 1. In terms of the produced microstructure, each preheating temperature induced a specific microstructure; 25˚C (martensite), 300˚C (tempered martensite), and 500˚C (bainite), see Figure 1. Further tensile testing found that specimens produced at 300˚C and 500˚C outperformed those processed without build plate preheating. This was due to improved material densification, as well as improved martensite tempering and the presence of bainite for the 300˚C and 500˚C specimens, respectively. These results provide an improved understanding of how build plate preheating can tailor the microstructure and mechanical properties that can further the development of structural steels for PBF-LB.