Austenitic stainless steel | EPFL Graph Search

Austenitic stainless steel is one of the five classes of stainless steel by crystalline structure (along with ferritic, martensitic, duplex and precipitation hardened). Its primary crystalline structure is austenite (face-centered cubic) and it prevents steels from being hardenable by heat treatment and makes them essentially non-magnetic. This structure is achieved by adding enough austenite-stabilizing elements such as nickel, manganese and nitrogen. The Incoloy family of alloys belong to the category of super austenitic stainless steels. AISI 200 and 300 series There are two subgroups of austenitic stainless steel. 300 series stainless steels achieve their austenitic structure primarily by a nickel addition while 200 series stainless steels substitute manganese and nitrogen for nickel, though there is still a small nickel content, making 200 series a cost-effective nickel-chromium austenitic type stainless steel. 300 series stainless steels are the larger subgroup. The

On the formation of stacking fault tetrahedra in irradiated austenitic stainless steels – A literature review

Robin Schäublin, Raluca Schibli

Irradiated austenitic stainless steels, because of their low stacking fault energy and high shear modulus, should exhibit a high ratio of stacking fault tetrahedra relative to the overall population of radiation induced nanometric defects. Experimental observations of stacking fault tetrahedra by transmission electron microscopy in commercial-purity stainless steels are however scarce, while they abundantly occur in high-purity or model austenitic alloys irradiated at both low and high temperatures, but not at around 673 K. In commercial alloys, the little evidence of stacking fault tetrahedra does not follow such a trend. These contradictions are reviewed and discussed. Reviewing the three possible formation mechanisms identified in the literature, namely the Silcox and Hirsch Frank loop dissociation, the void collapse and the stacking fault tetrahedra growth, it seems that the later dominates under irradiation. (C) 2013 Elsevier B. V. All rights reserved.

Elsevier Science Bv2013

Modélisation de la tribocorrosion d'aciers inoxydables dans l'eau à haute pression et haute température

Jonathan Perret

Several metallic components of pressurized water reactors (PWR) used in nuclear power plants are exposed to the combined degradation by friction and corrosion (tribocorrosion). In PWR, corrosion arises from the water pressurized at 150 bars and maintained at 300°C and results in the build up of a micrometer thick surface oxide film. Tribocorrosion is of complex nature as it involves multi-scale interactions between mechanical, chemical and material factors. Nevertheless, PWR component manufacturers are interested in understanding the deterioration mechanisms in order to select appropriate materials as well as predicting the component lifetime. This thesis is a contribution towards the elucidation of the tribocorrosion mechanisms of a specific PWR component (austenitic stainless steel control rods). The research is focused on two inter-related aspects related to the subsurface deformation induced by friction and to the high temperature and high-pressure oxidation kinetics of austenitic stainless steel under tribocorrosion conditions. The subsurface deformation is investigated by using a model tribocorrosion system consisting in an alumina ball sliding against a 304L austenitic stainless steel in sulphuric acid at ambient temperature under electrochemical control. This model system allows studying subsurface deformation in absence of a thick high temperature oxide films that can complicate the interpretation of the results. Subsurface deformation was characterized using SEM, EBDS and FIB cross-sections. Good correlation was found with the deformation found in pressurized water. Subsurface deformation was found to result in the formation of a recrystallised layer of nano-grains close to the surface and an underlying layer exhibiting a deformation gradient. The thickness of the recrystallized zone is highly affected by the presence or the absence of a few nm thick oxide in the contact. However, no obvious correlation between the thickness of the recrystallized zone, or any other measured deformation appearance, and wear could be found. The effect of oxidation was studied using a simulator (Aurore), reproducing the chemical and mechanical PWR conditions of control rods. It includes an electrochemical set-up allowing measuring in-situ and in real time the oxidation kinetic. The oxidation kinetic was found to follow a parabolic law (diffusion controlled oxide growth). Rubbing resulted in repeated scratching of the surface leading to a thinning of the oxide film and thus to an enhanced anodic oxidation. A quantitative model of the electrochemical response of stainless steel in PWR conditions was developed. Based on these results and on the third body theory of wear, a mechanistic model was proposed for describing the material behaviour in contacts operating in pressurized water. This model explains a certain number of practical observations obtained in nuclear plants or in simulators concerning chemical and materials effects on component degradation.

EPFL2010

Role of mean stress on fatigue behavior of a 316L austenitic stainless steel in LWR and air environments

Hans-Peter Seifert, Philippe Spätig

Mean stress effects on fatigue life of a stainless steel in air and boiling water reactor (BWR) environments were evaluated by load-controlled tests. In stress-life, non-zero mean stresses increase life in low cycle fatigue regime in both environments and in high cycle regime in air. In high cycle fatigue regime in BWR environment, higher fatigue life was observed with negative mean stress while a decrease of the fatigue limit was found for positive one. In strain-life, the mean stress effects are insignificant. All data are well correlated with a Smith-Watson-Topper parameter showing no interaction between mean stress and BWR environment.

ELSEVIER SCI LTD2021

Modélisation de la tribocorrosion d'aciers inoxydables dans l'eau à haute pression et haute température

Jonathan Perret

EPFL2010