Oxidation Behavior of Heat-Resistant Type HK Steel (HK30Nb) at 800 & DEG;C

The cyclic oxidation behavior of HK30Nb heat-resistant steel processed by laser powder bed fusion (LPBF) was compared to its cast counterpart during exposures in air and air + 10% H2O at 800 & DEG;C. The specific finer microstructure and lower Mn of the LPBF alloy resulted in lower oxidation rates in dry air and faster establishment of a continuous Cr2O3 scale in air + 10% H2O compared to coarse-grained cast HK30Nb with higher Mn. Differences in alloy mechanical strength and therefore their ability to accommodate high temperature and oxidation-induced stresses as well as differences in thermal expansion coefficients between the alloy and the formed oxides (Cr2O3 only for the LPBF and Cr2O3 and MnCr2O4 for the cast specimens) during temperature cycling were found to result in a greater extent of spallation for the LPBF than for the cast alloy in dry air at 800 & DEG;C.