Abstract
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.
Highlights
Chromium-nickel austenitic stainless steels are used in nuclear power engineering to a significant extent.304L and 316L austenitic stainless steels represent important structural materials for the construction of primary circuit components and internal in-building of light water nuclear power plants, and 316L for building components for nuclear power systems with fast reactors [1].A certain disadvantage of these types of steel is their relatively low strength level achieved after annealing
The images suggest the possibility of depletion of chromium at grain boundaries, or annealing twins in the austenite matrix, and they provide basic information on potential susceptibility to the development of intergranular corrosion
Austenitic stainless steels in air and under corrosion fatigue in 3.5% aqueous NaCl solution was evaluated after three modes of heat treatment; namely, after solution annealing, stabilizing annealing, and sensitization annealing at different frequencies of loading
Summary
Chromium-nickel austenitic stainless steels are used in nuclear power engineering to a significant extent. From the perspective of a comprehensive evaluation of austenitic steels and nuclear power plants operating conditions, it is important to study fatigue stress—especially the kinetics of fatigue crack growth, including superposition of the effect of external environment [2,3]. Corrosion fatigue during cyclic stress is characterized by the existence of a threshold value KIscc in the area of the validity of Paris’s Law [6] da/dN = C·(∆K)m , where da/dN is the fatigue crack growth rate, ∆K is the stress intensity factor range at the crack tip, and C and m are material constants. Cracks generated during corrosion fatigue are usually transgranular with characteristic branching and are perpendicular to the applied tensile stress [4,8]. Other important factors that affect the rate of fatigue crack growth are, for example, dislocation substructure, deformation induced by phase transformation in the plastic zone adjacent to the top of the fatigue crack, residual stresses, temperature, etc
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