PSI - Issue 42

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Kai Donnerbauer / Structural Integrity Procedia 00 (2019) 000 – 000

Kai Donnerbauer et al. / Procedia Structural Integrity 42 (2022) 738–744 © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

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Peer-review under responsibility of 23 European Conference on Fracture - ECF23 Keywords: Fatigue life evaluation; Nuclear engineering; AISI 347, Short-time evaluation procedure

1. Introduction In order to secure a reliable electricity supply, many European member states will continue to use nuclear power plants (NPP) in the future. Therefore, the reliable assessment of components and materials used in such plants, will continue to play an important role. Especially when considering lifetime extensions, nondestructive testing (NDT) methods can be a valuable tool to increase reliability and thus also economic efficiency for the operation of NPPs. The objective of NDT methods is to describe changes in the material and detect damage timely and reliably. Methods to evaluate fatigue and remaining fatigue life of materials and components based on well accessible NDT signals could also improve operations of power plants. Metastable austenitic steels are for example used in NPPs for pipe components and various testing methods have already been studied. Especially magnetic methods are commonly chosen due to the change of magnetic properties during phase transformation from paramagnetic austenite to ferromagnetic martensite, Dobmann (2017) and Li et al. (2011). A self-developed magnetic test method and an electrochemical instrumentation are applied in instrumented fatigue tests of metastable austenite AISI 347 (X6CrNiNb18-10, 1.4550) in distilled water and fatigue life evaluations based on the short time evaluation procedure StrainLife are presented. In addition, scanning electron microscopic analyses were carried out to characterize the austenite stability and phase transformation behavior.

Nomenclature E OCP

Open circuit potential E OCP,a Open circuit potential amplitude HV Hall voltage l 0 Extensometer gauge length N Number of cycles N f Number of cycles to failure t Time ε̇ Strain rate ε a,t Total strain amplitude ε a,c Correlated strain amplitude σ a Stress amplitude

2. Experimental setups and material 2.1. Material and heat treatment

The chemical composition of the material used is in accordance with DIN EN 10088-1, Tab. 1. It is an austenitic stainless steel stabilized with Niobium to prevent intercrystalline corrosion. Austenite stabilizing elements Nickel, Manganese and Carbon are at the lower allowed limit of the permissible values, leading to a relatively low austenite stability. Solution annealing was done at 1060 °C with a holding time of 30 min followed by quenching in water.