Improvement in the Mechanical Properties of Different Cooling Medium-treated 56Fe25Ni16Cr Austenitic Stainless Steel for Advanced Nuclear Reactor Applications

This study investigates the mechanical characteristics of 56 Fe 16 Cr 25 Ni austenitic stainless steel (ASS) that were annealed/quenched with air, water, and oil cooling media. Hardness (Vickers test), tensile (ASTM E8M-04), and Charpy impact (ASTM E23-05) tests were conducted to assess the influence of cooling media. The steel is annealed at 850◦C for 30 minutes, followed by quenching in different cooling media through the normalized air, oil and water. Microstructural analysis shows γ-austenite dendritic matrix and eutectic structure containing carbide particles. Post-annealing, a clear dendritic structure was observed compared to the normalized specimens. When ASS was quenched in air, oil, or water, its hardness increased by approximately 4%, 18%, and 14%, respectively. As the change of the cooling medium from air to water and oil, the yield strength and impact energy decrease by 59% to 33%, and 7% to 12%, respectively. However, the primary appealing force remains consistent across all media. Optical and electron microscopy were used to provide additional microstructural information, such as grain structure, precipitates, and stacking defects. This study shows that the 56 Fe 16 Cr 25 Ni ASS outperforms conventional nuclear reactor structural steels at elevated temperatures.