Dynamic Strain Ageing and EAC of Deformed Nitrogen-alloyed AISI 316 Stainless Steels
Intergranular stress corrosion cracking has occurred in BWR environments in non-sensitised, cold-worked austenitic stainless steel materials. The affecting parameters are so far not fully known, but deformation mechanisms may be decisive. The effect of cold deformation and nitrogen content on the deformation behaviour of austenitic stainless steels was investigated. The materials were austenitic stainless steels of AISI 316L type with different amounts of nitrogen (0.03...0.18%) and they were deformed in tension 0, 5 and 20% before further investigations. The investigations were focused on the dynamic strain ageing (DSA) behaviour as a function of nitrogen level and deformation. A few crack growth rate measurements are performed on nuclear grade AISI 316NG stainless steel with different degrees of deformation (0, 5 and 20%). The effects of DSA on mechanical properties of these materials were evaluated based on peaks in tensile strength and minimum in ductility in the DSA temperature range. Also the strain rate sensitivity in the DSA temperature range was investigated. Internal friction measurements were performed in the temperature range of -100...600 C for determining nitrogen interactions with other alloying elements and dislocations. The results show effects of nitrogen on the stainless steel deformation behaviour, i.e. clear indications of dynamic strain ageing: serrated yielding, negative strain rate sensitivity and changes in the internal friction behaviour as a function of nitrogen content and amount of deformation. The apparent activation energy calculated from the DSA serration occurrence map corresponds to that of nitrogen diffusion. Fully intergranular cracking was obtained in the 20% deformed, nonsensitised AISI 316NG stainless steel in simulated BWRenvironment. The crack growth data and the mechanism are discussed based on the unstable plastic flow of the material.
Dynamic Strain Aging Behaviour in AISI 316L Austenitic Stainless Steel under As-Received and As-Welded Conditions
In the current study, dynamic strain ageing (DSA) phenomena in 316L austenitic stainless steel was investigated under as-received and as-welded conditions. A tensile test was carried out on as-received and as-welded samples for the temperatures of 25–800 °C at a strain rate of 1 × 10−3 s−1. Microstructure and fracture surfaces were investigated by optic and scanning electron microscopes (SEM). 316L austenitic stainless steel showed different DSA behavior under as-received and as-welded conditions, which are discussed in terms of microstructure and mechanical properties.
SR topography of plastically deformed Fe-Si bicrystals - observation in situ and post mortem
SR reflection topography was applied to study the interaction of slip dislocations with the grain boundaries in Fe-4at%Si bicrystals deformed by compression. Three experimental settings with either a white or monochromatic beam were used and the corresponding orientation contrast analysed. Dislocation transmission through the grain boundary was observed in bicrystals with favourable geometry of the slip systems.