Impact of the Process Atmosphere During Hot Isostatic Pressing on the Near‐Surface Composition of an Additively Manufactured Austenitic High‐Interstitial Steel

High interstitial steels (HIS) combine high corrosion resistance, strength, and ductility while being Ni‐free, making them cost‐efficient starting material for additive manufacturing (AM), particularly laser powder bed fusion (PBF‐LB/M), of components for demanding applications. The Fe–Mn–Cr–(C) system forms the basis of HIS and provides high N solubility, primary austenitic solidification, and a stable austenitic matrix. However, Mn and N evaporate at elevated melt pool temperatures, promoting pore formation during PBF‐LB/M. To obtain fully dense material hot isostatic pressing (HIP) is routinely applied. However, little is known about the temperature‐ and pressure‐dependent interactions between the HIP atmosphere and the AM part, especially concerning N and Mn. In this study, the effect of the Ar and N 2 HIP atmospheres on the near‐surface composition and microstructure of PBF‐LB/M‐processed HIS was investigated. By means of glow discharge optical emission spectrometry, electron microscopy, X‐ray diffraction, and CALPHAD, a distinct influence of the process gas on local chemical and phase composition was revealed. The N 2 atmosphere led to an approximately tenfold N enrichment at the surface and to Cr nitride precipitation. Ar atmosphere leads to near‐surface Mn and N depletion. Optimized HIP parameters for the postprocessing of HIS are proposed.