Effect of high-temperature degradation on microstructure evolution and mechanical properties of austenitic heat-resistant steel

Abstract

21-4N austenitic heat-resistant steel is widely used as the material for automobile engine valves because of its high strength, excellent creep resistance, oxidation resistance and corrosion resistance under high-temperature circumstances. Engine valves, which are exposed to high temperatures for long periods, undergo material degradation in which the initial microstructure of the material is changed, resulting in deterioration of mechanical properties. This degradation can cause valve failure. Therefore, the microstructure and mechanical characteristics of degraded valves are important issues in designing the hot-section engine components. In this study, the changes in the microstructure evolution and mechanical properties of 21-4N austenitic steel were investigated after exposure at high temperature (1123K) for 10–200h, using accelerated degradation testing. To evaluate the degradation characteristics of 21-4N austenitic heat-resistant steel, we analyzed the microstructure evolution (e.g., grains, surface oxides, carbides, and phase) and the change in mechanical properties (e.g., tensile strength and, hardness) for virgin and degraded specimens. Finally, analyses and tests results demonstrate the correlation between microstructure evolution and changes in mechanical properties.