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.