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Contributing Editor: Jürgen Eckert
I.
INTRODUCTION
316L stainless steel is a promising material for application in reactor vessels and piping systems in nuclear power plants owing to a good combination of its excellent creep strength, corrosion resistance, and high sensitization resistance.1Generally, the service temperature range for 316L stainless steel is from 450 to 600 °C, which is right in the regime of its dynamic strain aging (DSA) effect.2
DSA, which depends on strain rate and temperature, is the phenomenon of interactions between diffusing solute atoms and mobile dislocations during plastic deformation. DSA is manifested as serrations on a stress-strain curve, which is one of the most prominent examples of plastic instabilities known as serrated yielding (Portevin-Le Chatelier effect).3Scholars worldwide have paid more attention to the essence and occurrence condition of DSA and proposed different physical models, for example, Cottrell model,4McComick model,5and Van den Beukel model.6These models have held that the serrated flow results from the repeated pinning and unpinning of mobile dislocations with the presence of solute atoms. Schoeck et al.7further extended the original DSA theory by referring the collective behavior of dislocations. Considering the integral behavior of dislocations and the interaction between solute atoms and dislocations, Xiao et al.8proposed a physical model to determinate the critical strain corresponding to the appearance and disappearance of serration and discussed the strain rate-temperature ranges when serration occurred.
Recently, some studies have been conducted on DSA for stainless steel. The results showed that the dislocation structure of austenitic stainless steels involving 316L(N) stainless steel transited from a cell structure below 200 °C to a planar one between 200 and 550 °C and returned to a cell or subgrain structure beyond 550 °C.9-11Hong et al.12characterized the fatigue deformation of 316L stainless steel at elevated temperature and concluded that DSA caused a reduction in fatigue life. Jiang et al.13investigated the effect of DSA pretreatment on creep-fatigue behavior for 316L stainless steel. It was found that DSA was a macroscopic phenomenon due to a displacement or mean strain abrupt jumping during the cyclic deformation for stress controlled fatigue tests....