Effect of Scanning Speeds on Microstructure and Property of Reduced Activation Ferritic–Martensitic Steel Additively Manufactured by Selective Laser Melting

In this study, selective laser melting (SLM) was employed to additively manufacture a newly developed reduced activation ferritic–martensitic (RAFM) steel at different scanning speeds (600, 800 and 1000 mm/s). Densities, hardnesses and wear properties of the SLMed specimens were examined with their microstructures characterized by x-ray diffraction, electron channeling contrast imaging, electron backscatter diffraction and energy-dispersive spectrometry. Results show that all these SLMed specimens consist of a mixture of ferritic and martensitic structures, along with many nanoscale precipitates. With increasing scanning speeds, the fraction and grain size of the ferrite increase gradually but the content of the precipitates is reduced. This makes the specimen hardness decrease from 392.3 to 352.2 HV as the scanning speed increases from 600 to 1000 mm/s. All the SLMed specimens have mainly experienced abrasive, adhesive and oxidative wear during the wear test, exhibiting considerably improved wear resistance compared to the conventionally prepared RAFM steel. Among the SLMed specimens, the 1000 mm/s specimen has the lowest hardness but the best wear resistance, which should be related to its specific heterostructure.