Twin-induced grain boundary engineering in 304 stainless steel

Grain boundary character distributions (GBCD) of type 304 stainless steel cold rolled and then annealed at 1173 K were analyzed by electron back scatter diffraction (EBSD). The results showed that low strain (6–10%) followed by long-time annealing (24–96 h) resulted in a GBCD containing a high fraction of ∑9 and ∑27 boundaries. The ratio of fraction summation of ∑9 and ∑27 boundaries (f∑9+∑27) to the fraction of ∑3 boundaries (f∑3), i.e. f∑9+∑27/f∑3, reached 0.14 for the specimen strained by 6% and annealed at 1173 K for 96 h. The connectivity of general high angle grain boundary (HAB) network was interrupted significantly by ∑3n (n = 1–3) boundaries (special boundaries). However, intermediate strain (20–50%) followed by long-time annealing introduced a GBCD of a much lower fraction of ∑9 and ∑27 boundaries, the value of f∑9+∑27/f∑3 was only around 0.03 and the connectivity of HAB network was not interrupted basically. Additionally, it was observed that a fair number of clusters consisting of ∑3–∑9–∑27 boundaries were developed in the process of low strain followed by long-time annealing (96 h), while the same phenomenon was hardly seen in the process of intermediate strain followed by long-time annealing.