Microstructure and Mechanical Properties of Hot-Pressed 21-4N Oxide-Dispersion-Strengthened Austenitic Stainless Steels

Abstract

In this study, austenitic stainless steels of composition containing Fe–21Cr–4Ni–9Mn–0.5C–0.4Si with and without addition of Y2O3 were developed from iron and ferro-alloy powders (Fe–Ni, Fe–Mn and Fe–Cr) using mechanical alloying. Both the powders were hot-pressed under a vacuum of 10−3 mbar at 1200 °C and at a pressure of 50 MPa. Further, the hot-pressed billets were solution-annealed at 1150 °C for 90 min and subsequently quenched in water. Further the steels were aged at 750 °C for 90 min followed by air-cooled. The powder morphology and crystal structure were analyzed with respect to milling time using scanning electron microscopy and X-ray diffraction, respectively. The density of hot-pressed samples was found to be 96–98% of its theoretical value. The microstructure revealed austenite grains containing grain boundary carbides in the hot-pressed condition. However, the carbide precipitates disappeared after the solution treatment, which was confirmed by scanning electron microscopy with energy dispersive spectrum analysis. The hot-pressed and oxide-dispersion-strengthened austenitic stainless steel and austenitic stainless steel samples have exhibited a hardness value of 349 ± 10 and 327 ± 10 HV1.0, respectively. Aged steels have attained the intermediate hardness values in the range of 324–336 HV1.0.