Nanostructure evolution during low temperature aging of three binary Fe-Cr alloys has been investigated by atom probe tomography. A new method based on radial distribution function (RDF) analysis to quantify the composition wavelength and amplitude of spinodal decomposition is proposed. Wavelengths estimated from RDF have a power-law type evolution and are in reasonable agreement with wavelengths estimated using other more conventional methods. The main advantages of the proposed method are the following: (1) Selecting a box size to generate the frequency diagram, which is known to generate bias in the evaluation of amplitude, is avoided. (2) The determination of amplitude is systematic and utilizes the wavelength evaluated first to subsequently evaluate the amplitude. (3) The RDF is capable of representing very subtle decomposition, which is not possible using frequency diagrams, and thus a proposed theoretical treatment of the experimental RDF creates the possibility to determine amplitude at very early stages of spinodal decomposition.

There is high scientific and technological interest to develop photocatalytic coatings on stainless steels surface to remove fouling under light radiation. In this study, a novel method is described to prepare photocleanable stainless steel by anodization to form aligned nanopore arrays (NPAs) on the surface in ethylene glycol containing perchloric acid. Perchloric acid concentration, applied voltage and anodization time of anodization process were investigated. The NPAs are mainly composed of iron (III) oxide and chromium (III) oxide. This photocleanable stainless steel has remarkable visible-light photocatalytic activities, which show potential applications particularly for outdoor purpose. Moreover, the stainless steel surface remains highly polished and exhibits good corrosion resistance after anodization.

Since contradictory data can be found in the literature, it is often difficult to assess the susceptibility of crevice corrosion of stainless steels in service conditions for a given marine application. The initiation and propagation of crevice corrosion in natural seawater were evaluated for five different duplex stainless steel grades together with some austenitic grades. A CREVCORR-type assembly was used to simulate crevice configurations involving the use of plastic crevice formers. The standard pressure applied on the crevice assembly was 3 N/mm2. Pressure of about 20 N/mm2 was also applied on some selected specimens in order to assess the effect of crevice geometry on crevice corrosion. The effect of environmental parameters (i.e. temperature, flowing conditions, residual chlorine, and dissolved oxygen content) and of surface roughness on the crevice corrosion initiation and propagation were investigated, allowing the assessment of limits of applications for some tested stainless steel grades. The less alloyed duplex stainless steels were evaluated in stagnant seawater at 5 °C and 20 °C. The duplex stainless steel UNS S32205, with PREN = 37, was also evaluated under the same conditions of exposure. The high alloyed stainless steels with PREN above 40 were evaluated in the expected most severe conditions of exposure, namely in 0.5 ppm-chlorinated seawater at 20 °C, in seawater at 30 °C (not chlorinated and with 0.5 ppm of residual chlorine) and in seawater at 50 °C (not chlorinated and with 0.5 ppm of residual chlorine). As expected the less alloyed duplex stainless steels showed limited crevice corrosion resistance in the tested media while UNS S32205 showed better resistance in the less severe tested condition of exposure. In demanding media it was shown that the limits of application of highly alloyed stainless steels are highly dependent on the crevice geometry (i.e. specimen roughness and applied pressure at gasket location).

Cet article est dédié à la description de la problématique de la corrosion sous contrainte assistée par l’irradiation (IASCC – Irradiation Assisted Stress Corrosion Cracking). Ce mode d’endommagement est observé dans les structures d’internes de réacteurs nucléaires à eau légère (REL) qui sont soumises à un milieu caloporteur chimiquement agressif et à l’irradiation. Après une présentation de la problématique industrielle liée à l’IASCC, notamment pour les réacteurs à eau pressurisée (REP) où les structures d’internes sont essentiellement en aciers austénitiques inoxydables (AISI 304 et 316), les facteurs contribuant potentiellement à l’endommagement par IASCC et leur effet individuel sur l’altération des propriétés du matériau sont passés en revue. La nature multiphysique du phénomène d’IASCC est ensuite présentée. Les stratégies et les outils mis en œuvre pour développer un modèle prédictif unifié sont ensuite présentés et discutés.

Crevice corrosion chemistry is modeled in galvanostatic mode using finite element method calculations. The results lead to the formulation of critical conditions for crevice propagation in terms of applied current and depassivation pHd. For a given stainless steel grade, the model predicts a linear relation IC(pHd) between a “critical propagation current” IC and the depassivation pHd. Detailed computing is performed to compare the behavior of duplex 2304, ferritic AISI 430 and austenitic AISI 304 stainless steels. The model is shown to capture correctly the major asymptotic behaviors and to fairly predict the better corrosion resistance of the duplex grade, which is attributed to its slower dissolution kinetics in acidic environment. When comparing duplex stainless steels to ferritic or austenitic ones, it is now evident that the dissolution law and the depassivation pHd are the key factors that control the resistance to crevice corrosion propagation.

Mechanical properties, such as hardness and impact toughness, of ferrite-containing stainless steels are greatly affected by long-term aging at intermediate temperatures. It is known that the α-α′ spinodal decomposition occurring in the iron–chromium-based ferrite is responsible for this aging susceptibility. This decomposition can be characterized unambiguously by atom probe analysis, allowing comparison both with the existing theories of spinodal decomposition and the evolution of some mechanical properties. It is then possible to predict the evolution of hardness of industrial components during service, based on the detailed knowledge of the involved aging process.