Corrosion Fatigue of Austenitic Stainless Steels for Nuclear Power Engineering
Significant structural steels for nuclear power engineering are chromium-nickel austenitic stainless steels. The presented paper evaluates the kinetics of the fatigue crack growth of AISI 304L and AISI 316L stainless steels in air and in corrosive environments of 3.5% aqueous NaCl solution after the application of solution annealing, stabilizing annealing, and sensitization annealing. Comparisons were made between the fatigue crack growth rate after each heat treatment regime, and a comparison between the fatigue crack growth rate in both types of steels was made. For individual heat treatment regimes, the possibility of the development of intergranular corrosion was also considered. Evaluations resulted in very favourable corrosion fatigue characteristics of the 316L steel. After application of solution and stabilizing annealing at a comparable ∆K level, the fatigue crack growth rate was about one half compared to 304L steel. After sensitization annealing of 316L steel, compared to stabilizing annealing, the increase of crack growth rate during corrosion fatigue was slightly higher. The obtained results complement the existing standardized data on unconventional characteristics of 304L and 316L austenitic stainless steels.
Exploring factors controlling pre-corrosion fatigue of 316L austenitic stainless steel in hydrofluoric acid
Abstract While the low-cycle fatigue performance of metals is significantly influenced by corrosion, the corrosion damages and therefore the fatigue mechanisms induced by different solutions are different. In this paper, the pre-corrosion fatigue behavior of 316L austenitic stainless steel in hydrofluoric acid (HF) are studied. To characterize the corrosion type as well the extent of corrosion, the corrosion behavior of 316L austenitic stainless steel at different HF concentrations are investigated. Combined uniform corrosion and pitting corrosion are observed, with grooves formed by the superposition of several etched pits. Two methods are proposed to characterize corrosion damages, and the fatigue life is found to negatively correlate with the corrosion damage. To characterize fatigue crack initiation mechanisms, fracture surfaces of corroded fatigue specimens are examined with an emphasis on crack initiation sites. It is found that the crack initiates from multiple sources caused by multiple pits, and the surface average annular width of the pitting is found to be a more important factor controlling the fatigue life than the depth of pits. The results in this study are expected to provide insights into the understanding of failure mechanisms of equipment in fluorine chemical industry.
Quantitative prediction of surface segregation
Abstract An assessment has been made of the 32 available equilibrium measurements for surface segregation in substitutional pure binary alloy systems. These measurements have been analyzed in relation to the various terms proposed for the free energy of segregation. Three terms have been selected, the surface energies of the constituents, their enthalpy of mixing and a term related to the release of strain energy on segregation. A least squares fitting of the measurements to the three terms shows that some of the current theories are valid but that the importance of each term may not have been correctly emphasized. The assessment leads to a simple predictive relationship, valid for both dilute and concentrated alloy systems, which correlates with the experimental results over the range of free energies of segregation from −80 to 20 kJ/mol, with a standard deviation of less than 9 kJ/mol.