Issue 42

A. Strafella et alii, Frattura ed Integrità Strutturale, 42 (2017) 352-365; DOI: 10.3221/IGF-ESIS.42.36 352 15-15Ti(Si) austenitic steel: creep behaviour in hostile environment Alessandra Strafella, Antonino Coglitore, Paride Fabbri, Elena Salernitano ENEA- Italian National Agency for New Technologies, Energy and Sustainable Economic Development-Laboratory of Materials Technologies Faenza, Via Ravegnana, 186 - 48018 - Faenza, Italy alessandra.strafella@enea.it, antonino.coglitore@enea.it , paride.fabbri@enea.it , elena.salernitano@enea.it A BSTRACT . This work aims at studying the creep behaviour of 15-15Ti(Si) austenitic steel, under uniaxial stress (range of 300-560 MPa), and its interaction with liquid lead. The steel was tested to verify its sensitivity to Liquid Metal Embrittlement (LME) and to simulate its behaviour in operating thermal and mechanical stress conditions of the IV generation Lead-cooled fast reactor. The experimental results permitted to plot the time-strain creep curve and the characteristic Norton-based curve, simulating the creep behaviour at all stress values. The comparison between the creep curves in air and in lead showed that the LME produces a decrease of creep-rupture time, a reduction of creep strain and then the loss of steel ductility. Moreover, the raw material and fracture surfaces were analyzed by Optical Microscope and Scanning Electron Microscope (SEM). SEM micrographs highlighted that lead changes both the mode and the type of specimen fracture. In addition, it was analyzed the lead action time, as the time after which the corrosion appears with macroscopic effects. Although some tests are still ongoing, it can be assumed that at high stresses, LME takes place after a long time of steel/lead contact while at low stresses, LME tends to prevail on creep effect. K EYWORDS . 15-15Ti(Si); Austenitic stainless steel creep; Creep curves; Steady Strain Creep Rate; Liquid Metal Embrittlement (LME); Creep tests in lead. Citation: Strafella, A., Coglitore, A., Fabbri, P., Salernitano, E., Frattura ed Integrità Strutturale, 42 (2017) 352-365. Received: 08.08.2017 Accepted: 12.09.2017 Published: 01.10.2017 Copyright: © 2017 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. and source are credited. I NTRODUCTION ince several years, austenitic stainless steels are object of a great interest for their properties and then their applications in nuclear field. Creep strength and resistance to irradiation-induced void swelling are the main requirements for high temperature components of fast reactors. For these reasons, type 15-15Ti(Si) material which is a Ti-stabilized austenitic stainless-steel alloy, is one of most suitable for nuclear industry [1-3]. 15-15Ti(Si) was designed around the standard AISI 316 stainless steel with a specifically tailored composition, especially regarding the carbon and titanium content, in order to limit irradiation induced void swelling [1]. The French work on irradiation of Rapsodie–Fortissimo demonstration reactor demonstrated that addition of titanium led to improved void swelling resistance of austenitic steel. Accordingly, the 15 Ni-15 Cr-Ti (named AIM1 or 15-15 Ti steel) S