1 Dynamic deformation of Metastable Austenitic Stainless 1 Steels at the nanometric length scale 2 3 J.J. Roa 1,2,* , I. Sapezanskaia 1,2,3 , G. Fargas 1,2 , R. Kouitat 2 , A. Redjaïmia 2 , 4 A. Mateo 1,2 5 6 1 CIEFMA-Dept. of Materials Science and Engineering, Universitat Politècnica de Catalunya, 7 EEBE-Campus Diagonal Besòs, 08019 Barcelona, Spain 8 2 Centre for Research in NanoEngineering, Universitat Politècnica de Catalunya, EEBE- 9 Campus Diagonal Besòs, 08019 Barcelona, Spain 10 3 Institut Jean Lamour, UMR 7198 CNRS, Université de Lorraine, 54840 Nancy Cedex, France 11 12 * Corresponding author, e-mail: joan.josep.roa@upc.edu 13 14 15 Abstract: Cyclic indentation was used to evaluate the dynamic deformation on 16 metastable steels, particularly in an austenitic stainless steel, AISI 301LN. In 17 this work, cyclic nanoindentation experiments were carried out and the obtained 18 loading-unloading (or P-h) curves were analyzed in order to get a deeper 19 knowledge on the time-dependent behavior, as well as the main deformation 20 mechanisms. It was found that the cyclic P-h curves present a softening effect 21 due to several repeatable features (pop-in events, ratcheting effect, etc.) mainly 22 related to dynamic deformation. Also, observation by transmission electron 23 microscopy highlighted that dislocation pile-up is the main responsible of the 24 secondary pop-ins produced after certain cycles. 25 26 Keywords: metastable stainless steels, cyclic nanoindentation tests, 27 transmission electron microscopy, time-dependent, plastic deformation, 28 ratcheting effect. 29 30 1. Introduction 31 During the last decade, TRansformation Induced Plasticity (TRIP) steels have 32 received special attention in the automotive industry due to their interesting 33 features as manufacturability, crashworthiness and feasibility for weight 34 reduction [1,2,3]. In the particular case of metastable austenitic stainless steels, 35