This study investigates the influence of tailored heat‐treatment strategies on phase constitution, hardness, and microstructure of a high‐nitrogen (N) martensitic chromium (Cr) steel processed by laser powder bed fusion (PBF‐LB/M). Previous alloy modifications to X50CrMoV15 enhanced N solubility during gas atomization and enabled crack‐free processing. However, the resulting predominantly austenitic as‐built microstructure requires post‐treatment to achieve application‐relevant properties. Three heat‐treatment routes were examined: (1) hardening and tempering, (2) hardening combined with cryogenic treatment, and (3) austenitizing followed by isothermal bainitizing. Thermodynamic calculations were used to assess austenitizing temperatures by evaluating carbide and nitride dissolution. Austenitizing between 900°C and 1150°C showed a strong dependence of hardness and retained austenite on interstitial C + N content. The highest hardness, 652 ± 8 HV10 with 6 ± 1 vol.% retained austenite, was achieved by following route 1 at 1000°C. Bainitizing at 250°C after austenitizing at 1000°C produced 681 ± 5 HV10 with 8 ± 1 vol.% retained austenite. Scanning electron microscope (SEM) analysis revealed ultrafine bainitic structures with 20–50 nm subunits and nanoscale precipitates. The combination of low‐temperature transformation and nanoscale refinement explains the high hardness, showing that isothermal bainitizing is a promising postprocessing route for N‐alloyed Cr steels produced by PBF‐LB/M.
König et al. (Thu,) studied this question.