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 (ecA) 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, ecA 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 (Fd) by the Cottrell atmosphere on aged dislocations to the existing mechanism of negative strain rate sensitivity. Fd 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.