Multiscale Modelling of Type 316H Stainless Steel to Inform Creep - Fatigue Assessment Procedures

Abstract

The problem of carburisation in austenitic stainless steels poses a risk to the on- going servicability of the UK’s Advanced Gas Cooled Reactors. Carburisation affects boiler components due to their exposure to a high temperature, carbon rich environ- ment which leads to a material modification resulting in a hardened, embrittled outer layer. A functionally graded material model is fitted to hardness and EPMA data and used in conjunction with finite element analysis to examine the impact of differing ma- terial property distributions consistent with those observed in carburised components on an internally pressurised pipe; this is compared with the existing R5 method of defining properties in a duplex structure. A positionally dependent form of Fick’s Law is solved in a phase field model to predict the evolution of carbon distribution into a grain structure exposed to a carburising environment. The effect of varying the ratio of grain to grain boundary diffusivity is examined with regard to its effect on carbon distribution in the grains and boundaries after the exposure period. Subsequently, ar- tificial hydrostatic stress is introduced to a phase field model of a representative grain structure to determine the extent to which carburisation is impacted by the presence of stress in a component. This is applied both homogenously across the entire examined volume and preferentially on grain boundaries in order to provide a basic analogy to the stresses observed in creep.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Michael Smith (Supervisor)