Abstract
The microstructure of SANICRO 31HT (alloy 800HT) creep tested to a maximum of 85,388 hours in the temperature range of 600 °C to 1000 °C was investigated. Coarse Ti(C, N) precipitates were found to form in the melt and remained stable after solution annealing and aging at all temperatures investigated. M23C6 precipitating in the range of 600 °C to 700 °C was found in two different distributions: as intergranular precipitates and as small intragranular particles. The γ′ precipitation sequence was followed at 600 °C, 650 °C, and 700 °C, and the volume fraction and precipitate diameter was assessed using energy-filtered transmission electron microscopy (EFTEM). The γ′ precipitates grew and coarsened slowly at 600°C (10 to 30 nm) but somewhat faster at 650°C (25 to 50 nm). The volume fraction was largest at 600°C. The γ′ precipitates formed at 700°C were not homogeneously distributed in the matrix. Instead, γ′ was observed in the immediate vicinity of M23 C6 and Ti(C, N) precipitates. Atom probe field ion microscope analysis of γ′-precipitate showed that it contained slightly more Ti than Al and that its Fe content was a few atomic percent. Nitrogen uptake was very pronounced in creep-deformed material aged at 1000 °C, and AlN formed as grain boundary needles and in the interior of grains.
| Original language | English |
|---|---|
| Pages (from-to) | 539-550 |
| Number of pages | 12 |
| Journal | Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science |
| Volume | 40 |
| Issue number | 3 |
| DOIs | |
| State | Published - 2009 |
| Externally published | Yes |
Funding
The authors thank Sandvik Materials Technology for financial support and for permission to publish this article. The authors thank Ahmed Shariq for operating the atom probe. The authors thank Dr. Thomas Helander, Sandvik Materials Technology, for calculating the phase diagram. The authors thank Professor John Ågren, the Royal Institute of Technology (Stockholm), and Dr. Martin Schwind, Outokumpu Stainless Steel (Avesta), for many helpful discussions.