Effects of Thermal Aging on Precipitate Development of Alloy Ht-9

Abstract

Electron microscopy of carbon extraction replicas was performed to identify and evaluate precipitate evolution in the 12Cr-1Mo ferritic-martensitic alloy HT-9 during long-term aging of two different heats, 84425 and 91354. All samples were heat treated at 1078°C/0.5 h/AC + 760°C/2 h/AC. Thermal aging was conducted in the temperature range of 500 to 800°C and for 30 to 10 000 h. Precipitates were identified using electron microdiffraction patterns and energy dispersive X-ray spectroscopy (EDX) analysis. M23C6, MX. Laves. M3X phases, and aluminum oxide (Al2O3) inclusions were found in various specimens of both heats, while the M2X phase and manganese sulfide (MnS) inclusions were present only in some of the 91354 series specimens. M23C6 was the predominant precipitate in all samples. The MX phase was found in all samples from Heat 91354 but was not found below 700°C in the 84425 series. The Laves phase was present up to 700°C in both heats. M3X was found at 800°C in both series and also after long-term aging at 700 and 750°C in 91354.