Abstract
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.
Highlights
Since several years, austenitic stainless steels are object of a great interest for their properties and their applications in nuclear field
When steel comes in contact with liquid metal, the loss of ductility in normally ductile steel could occur; this phenomenon is named Liquid Metal Embrittlement (LME) and takes place when steel is stressed in temperature under contact with liquid metal
LME tends to prevail on creep effect: the shape of curve changes, the sscr is higher than the test in air and the tertiary stage occurs at lower time
Summary
Austenitic stainless steels are object of a great interest for their properties and 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 [1,2,3]. The addition of Ti improves the high temperature mechanical properties due to the precipitation of carbide particles, either M23C6, or TiC in relation to the contents of Ni and Cr and to the matrix structure, grain size and dislocation density It has been noticed for a long time that the high dislocation density found in cold-worked steels reduces the swelling. The creep behaviour was investigated at 550° C, under a wide range of applied stresses, in hostile condition or in air , following by a morphological analysis of fracture surfaces
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