The Implications of Fabrication and Cast-to-Cast Variability on Thermal Aging in the Creep Range for AISI Type 316H Stainless Steel Components

Life prediction is critical for safe operation of plant within the creep regime. This study investigates the influence differences in specific composition and fabrication routes have on creep degradation for components with compositions within the design specification. Four ex-service AISI 316H austenitic stainless steel components exhibiting different manufacturing techniques and a range of compositions were used in the study. The boiler header component was found to contain localized chromium-rich regions arising from the original cast microstructure which result in a wide range of phases and show enhanced creep cavitation. Chi-phase precipitates contribute a significant role in creep damage accumulation via phosphorus segregation to the chi-austenite inter-phase boundaries. Tubular components with a homogenous microstructure and similar composition to the header showed limited secondary phase evolution. In one tubular specimen, creep cavitation was linked to phosphorus segregation at M₂₃C₆—austenite inter-phase boundaries. The remaining two tubular components, with a higher (but within specification) silicon content, showed homogeneous microstructures with limited creep cavitation and no phosphorus segregation was observed.