Maraging steel containing 0, 6, 12, 15, and 24 vol.-% retained austenite was subjected to gas nitriding at 450°C in ammonia gas atmosphere where the cracking of ammonia was ∼ 35%. The predominant nitride phase formed was Fe4N. The concentration of the nitride phase was shown to depend on the austenite content and decreased from surface to the depth of the nitride layer. Growth of the nitride layer decreased with an increase in the austenite content. A depth of the diffusion zone obtained was between 30 and 90 μm.
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