Inverse PLC behavior of type A serration in Fe–18Mn-0.55C steel

In the present study, the behavior of type A serrations according to strain rate was investigated using the room-temperature tensile flow curves of Fe-18Mn-0.55C (wt%) steel specimens. In the strain rate range from 1 × 10⁻¹ /s to 5 × 10⁻⁵ /s, a critical strain (e_c^A) of type A serrations was reduced with decreasing strain rate, indicating a normal Portevin-Le Chatelier (PLC) behavior. However, at the slow strain rates ranging from 5 × 10⁻⁵ /s to 1 × 10⁻⁶ /s, e_c^A was increased again with decreasing strain rate, although dynamic strain aging occurred just after yielding. This inverse PLC behavior of type A serrations was explained by applying the concept of the drag force (F_d) by the Cottrell atmosphere on aged dislocations to the existing mechanism of negative strain rate sensitivity. F_d was reduced with decreasing strain rate from 5 × 10⁻⁵ /s to 1 × 10⁻⁶ /s, suppressing the formation of the PLC band for type A serration.