Microstructure and Mechanical Properties of Hot Pressed Oxide Dispersion Strengthened NITRONIC-60 Austenitic Stainless Steels Developed Through Mechanical Alloying

In the present study, three different steels were developed from water atomized pre-alloyed powder such as N60 (17Cr-8Mn-4Si), MM-N60 (Mechanical Milled 17Cr-8Mn-4Si) and MM-N60-Y (Mechanical Milled 17Cr-8Mn-4Si-0.3Y(2)O(3)) with and without addition of Yttria. MM-N60 and MM-N60-Y were mechanically milled under high energy ball mill for the period of 2, 4, 6, 8 and 10 h to obtain nanocrystallite structure followed by hot pressing at the temperature of 1250 +/- 10 degrees C with a pressure level of 56 MPa. For comparison, the un-milled powder was also consolidated into a bulk sample under the same processing condition. The microstructure of all three hot-pressed samples was examined under optical, scanning electron, and transmission electron microscopes. Using a Hounsfield tensometer and Vicker's microhardness tester, the mechanical characteristics of these samples were assessed. The grain size of hot pressed samples from the milled powders is lesser than the compact of the un-milled powder. The Y2O3 added austenitic stainless steel (MM-N60-Y) shows the least austenite grains size around 2.8 mu m compared to MM-N60 (without Y2O3). Such a highly refined austenitic grain with Y2O3 dispersoid resulted in the highest hardness, yield, and tensile strength among the three samples. The tensile strength of as high as 758 MPa and a hardness of 484 VHN were obtained in the nano-Y2O3 dispersed ODS austenitic alloy.