Session: MF-16-01 Creep and Creep-Fatigue Interaction

Paper Number: 61848

Start Time: Tuesday, July 13, 2021, 05:00 PM

61848 - The Relation Between Precipitation and Creep Cavitation at Grain Boundary During High Temperature Service 

Grain boundary creep cavitation is a significant degradation mechanism for determining creep life for components operated at a high temperature. The formation of creep cavities is strongly related with stress, temperature as well as the associated local microstructure that evolves. In this study, the interaction between microstructure evolution and grain boundary cavitation during a long-term creep exposure is investigated in an ex-service AISI type 316H stainless steel boiler header which operated at 490 to 530°C for 65,000 hours in an advanced gas-cooled reactor. The microstructure and creep cavities of the material were characterised by multiple 2D and 3D techniques including secondary electron microscopy, focused ion beam tomography, electron backscatter diffraction and scanning transmission electron microscopy. Creep cavities and M₂₃C₆ and ferrite precipitates are present at random grain boundaries, while Σ3 coincidence site lattice (CSL) boundaries exhibit less precipitation (absence of ferrite) and higher creep cavitation resistance. At random grain boundaries, the growth of M₂₃C₆ cause local depletion of austenite stabilisers promoting austenite-ferrite transformation with a near Kurdjumov-Sachs orientation relationship. The ferrite plays an important role in accelerating the creep cavitation in addition to M_23­C₆ precipitation. The implications of this study for more improved predication of creep life for high-temperature components are discussed.

Presenting Author: Siqi He university of bristol

Authors:

Siqi He university of bristol
Hao Shang University of bristol
Antonio Fernandez-Caballero University of Oxford
Alexander Warren University of bristol
David Knowles University of bristol
Peter Flewitt University of bristol
Tomas Martin University of bristol