Gaseous nitriding of additively manufactured maraging steel; nitriding kinetics and microstructure evolution

The nitriding response of additively manufactured M300 maraging tool steel was investigated through a series of nitriding treatments at different temperatures in the range 360–480 °C for a duration of 40 h. The interaction between nitrogen and alloying element nitrides (Ti and Mo) and intermetallics (Ni3Ti and Ni3Mo) was studied by comparing nitriding responses of as-solution treated and subsequently aged specimens. The nitriding behavior was found to depend strongly on the initial condition of the material and the nitriding temperature applied. Ultra-low temperature nitriding at 360 °C was found to be feasible as it resulted in a nitrided case, albeit with incomplete precipitation hardening of the bulk structure, thus resulting in a softer core. The application of a post-ageing treatment resulted in full bulk hardening and distinctly changed the appearance of the hardness profile. •Nitriding of solution treated and not aged maraging steel creates deeper case.•Nitride and intermetallic formation competes at increased nitriding temperatures.•Ultra-low temperature nitriding of maraging steel is feasible.•Post-ageing of ultra-low temperature nitriding creates promising hardness profile.