Investigation of liquid metal embrittlement of AISI 316L steels

To support the feasibility and the deployment of LFRs one of the main issues to be solved is the reliability of structural materials to be exposed to liquid metal coolant. Particularly the Liquid Metal Embrittlement (LME) of steels is of interest for nuclear reactors and spallation sources projects because structural materials for these systems are selected according to their corrosion resistance, irradiation embrittlement and compatibility with the coolant. This study was performed in the framework of MYRRHA project, a new-generation sub-critical reactor (based on the Accelerator Driving System concept) that uses Lead-Bismuth Eutectic (LBE) as coolant. LME phenomenon has been investigated by performing theoretical and experimental activity profiting and basing on the results obtained for the T91 m/f steel in contact with LBE. This paper first reviews the model of Kamdar: weak points and contradictions are highlighted. From an experimental point of view to verify the occurrence of LME, Slow Strain Rate Tensile tests were performed on the AISI 316L in LBE environment at SCK-CEN laboratories. Besides, a fracture surface analysis was carried out together with a microstructural analysis by using that Scanning Electron Microscopy. This was done in order to confirm the results obtained by the mechanical tests and to look for impurities in the metallic matrix. These impurities are an interesting feature in case of high scatter in the results. Indeed one of the difficulties was the opacity and conductivity of the medium. The methodological approach and the procedure are also duly described along with preliminary results

Characterization of 14YWT As-Atomized, Milled, Milled and Annealed Powders and HIP Consolidated Alloys

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Effect of variation in oxygen concentration in static Pb–Bi eutectic on long-term corrosion performance of Al-alloyed austenitic steels at 500 °C

Aluminium-alloyed austenitic steels Fe-14Cr-2Mn-20Ni-0.5Cu-3Al and Fe-14Cr-5Mn-12Ni-3Cu-2.5Al were tested at 500 °C in static Pb-Bi eutectic for 10,000 h. The concentration of oxygen in the liquid metal was changed in a controlled way over the course of the test from ∼10−6 to ∼10−9 mass% which provided conditions for oxidation and dissolution, respectively. Both steels showed slight oxidation of surface. Steel with higher Ni content revealed also initiation of dissolution corrosion in the view of rare pit-type damages. The structural and compositional features of oxide films, sub-oxide zones and corrosion damages are discussed

Investigation of the Dynamic Strain Aging Effect in Austenitic Weld Metals by 3D-DIC

Austenitic stainless steels similar to type AISI 316L are widely used structural materials in current and future nuclear reactors. Careful development and characterization of these materials and their welds is needed to verify the structural integrity of large-scale multicomponent structures. Understanding the local deformation behavior in heterogeneous materials and the mechanisms involved is key to further improve the performance and reliability of the materials at the global scale and can help in developing more accurate models and design rules. The full-field 3D digital image correlation (3D-DIC) technique was used to characterize two 316L multi-pass welds, based on cylindrical uniaxial tensile tests at room temperature, 350 °C, and 450 °C. The results were compared to solution annealed 316L material. The inhomogeneous character and dynamic behavior of the 316L base and weld materials were successfully characterized using 3D-DIC data, yielding high-quality and accurate local strain calculations for geometrically challenging conditions. The difference in character of the dynamic strain aging (DSA) effect present in base and weld materials was identified, where local inhomogeneous straining in weld material resulted in discontinuous type A Portevin–Le Châtelier (PLC) bands. This technique characterized the difference between local and global material behavior, whereas standard mechanical tests could not.Team Maria Santofimia Navarr

Influence of plastic deformation on dissolution corrosion of type 316L austenitic stainless steel in static, oxygen-poor liquid lead-bismuth eutectic at 500°C

This study addresses the effect of plastic deformation on the dissolution corrosion behavior of a Type 316L austenitic stainless steel. Dissolution corrosion was promoted by low oxygen conditions in liquid lead-bismuth eutectic (LBE). Specimens with controlled degree of plastic deformation (20%, 40%, and 60%) and a non-deformed, solution-annealed specimen were simultaneously exposed for 1,000 h at 500°C to static LBE with low oxygen concentration ([O] < 10−11 mass%). The corroded specimens were analyzed by various material characterization techniques. All exposed specimens exhibited dissolution corrosion. The non-deformed steel showed the least dissolution attack (maximum depth: 36 μm), while the severity of attack increased with the degree of steel deformation (maximum depth in the 60% steel: 96 μm). It was, thus, concluded that increasing the amount of plastic deformation in a Type 316L stainless steel results in higher dissolution corrosion damages for steels exposed to low oxygen LBE conditions. Additionally, it was observed that the presence of chemical bands and δ-ferrite inclusions in a Type 316L steel affected its dissolution corrosion behavior.status: publishe

Multiscale investigation of quasi-brittle fracture characteristics in a 9Cr-1Mo ferritic-martensitic steel embrittled by liquid lead-bismuth under low cycle fatigue

Liquid metal embrittlement (LME) induced quasi-brittle fracture characteristics of a 9Cr–1Mo ferritic–martensitic steel (T91) after fatigue cracking in lead–bismuth eutectic (LBE) have been investigated at various length scales. The results show that the LME fracture morphology is primarily characterized by quasi-brittle translath flat regions partially covered by nanodimples, shallow secondary cracks propagating along the martensitic lath boundaries as well as tear ridges covered by micro dimples. These diverse LME fracture features likely indicate a LME mechanism involving multiple physical processes,such as weakening induced interatomic decohesion at the crack tip and plastic shearing induced nano/micro voiding in the plastic zone.status: publishe