Effects of various grain boundary engineering processing on microstructure and corrosion behaviors of 304 stainless steel analyzed with a fractal model

Abstract

Grain boundary engineering (GBE) is designed for metals to optimize the grain boundary characteristics and improve their resistance to intergranular corrosion (IGC). In this study, the effect of various GBE processing on the fraction of low ΣCSL grain boundaries and random large-angle grain boundary connectivity in 304 stainless steel was investigated quantitatively with a fractal model. The corrosion weight loss rate, corrosion current density and sensitization degree of samples with various grain boundary characteristics were measured, and these corrosion behaviors were studied in term of the fractal dimension. The results showing the specimen after alternating directions cold rolling plus annealed at 1100 °C obtained the highest ΣCSL score that was 67.4%. And the value of fractal dimension for specimen after solid solution annealing, cold rolled 5% or cold rolled 20% reduction plus annealed at 1100 °C for 5 min in GBE was 1.75, 1.53 and 1.46, respectively. An indicator defined by fractal dimension for grain boundary characteristic on corrosion behaviors of 304 stainless steel was verified and clarified, and the mechanisms of GBE to improve corrosion resistance were confirmed with the observation of low-energy grain boundary fragments introduced by annealing twins and triple junctions in grain boundaries.

Keywords

• Grain boundary engineering
• Intergranular corrosion
• Coincidence site lattice
• Grain boundary connectivity
• Fractal model