The influence of low‐strain thermo‐mechanical processing on grain boundary network characteristics in type 304 austenitic stainless steel

Abstract

Summary Grain boundary engineering of austenitic stainless steel, through the introduction of plastic strain and thermal annealing, can be used to develop microstructures with improved resistance to inter‐granular degradation. The influence of low‐strain thermo‐mechanical processing on grain boundary network development, with systematic variations of annealing treatments, has been investigated. Three stages of the microstructure development during grain boundary engineering in low‐strain processing conditions are identified, and correlated with changes in grain boundary character and deviation distributions. Low‐energy connected length segments at triple junctions, which have been proposed to be responsible for crack bridging during inter‐granular stress corrosion cracking, can be influenced by the choice of the annealing treatment parameters. The development of individual grain boundary length segments of different character showed consistent trends with increasing grain size. Crack length predictions are consistent with the beneficial effect of designing microstructures with high fractions of twin grain boundaries and smaller grain size.

Five‐parameter grain boundary analysis of a grain boundary–engineered austenitic stainless steel

“…Longer annealing times resulted in reduced levels of Σ3 n boundaries. These observations support previous reports about the development of grain boundary network characteristics after low‐strain processing (Engelberg et al , 2008). Similar trends were observed when length proportions of Σ3 n boundaries were considered.…”

In situ observation of intergranular crack nucleation in a grain boundary controlled austenitic stainless steel

“…This indicates the onset of multiple twinning during the TMP process. The higher‐order twin grain boundary fraction in the TMP microstructure is less abundant than typically observed in grain boundary engineering–processed type 304 microstructures (Engelberg et al , 2008). The term grain boundary controlled , rather than grain boundary engineered , is therefore used for the TMP material.…”

Effects of initial microstructure on the grain boundary network during grain boundary engineering in Hastelloy N alloy

“…4, including Σ1 (grey, low-angle boundaries, misorientation angle range: 2-15˚), Σ3 (red), Σ9 (blue), Σ27 (green) and random boundaries (black). The Σ3 n (n = 1, 2, 3…) grain boundaries connected with each other forming many triple junctions, such as Σ3-Σ3-Σ9, Σ3-Σ9-Σ27, inside the area encircled by random grain boundaries [23]. The highly twinned microstructures featured by clustering of Σ3 n (n=1, 2, 3…) type boundaries could be observed after full recrystallization.…”