The effects of Al (0∼3wt.%) addition to Fe-25Mn-0.5C alloys on the tensile behavior and vibration damping charareristic have been investigated. In particular, two austenitic alloys with aluminum contents of 0.1 and 1.0 wt.% were strained between 77 K and 693 K in order to establish a relationship between strain hardening behavior and formation of deformation twinning.
In the alloy containing 1 wt.% Al, the inverse ductility behavior has been observed, that is, the increase of elongation and strain hardening exponent with decreasing test temperature ranged from 293K to 77K, while the tensile strength and elongation peak occurred in the vicinity of 493K. On the other hand, the alloy containing 0.1 wt% Al didn't show inverse ductility behavior, the elongation peak occurred at about 493 K. X-ray diffractions showed that both the two alloys were fully austenitic before and after tensile tests, numerous microtwins were observed after tensile deformations. When the two alloys were strained in tension at temperatures ranging from 293 K to 493 K, it exhibited serrated flow, characteristic of dynamic strain aging (DSA). The critical strain ($\varepsilon{c}$), at which serrations first appeared, increased with Al contents and decreasing test temperatures below 493 K. This is consistent with the known effects of aluminum on the diffusivity and activity of carbon in austenitic high-manganese steel. The strain hardening exponent showed the maximum at about 393 K which is in the DSA temperature range. However, the temperature showing the minimum $\varepsilon{c}$ was higher than that at which peak of the strain hardening exponent appeared. These results indicate that rapid work hardening is not necessarily related with the dynamic strain aging in the intermediate temperature region (293K-493K).
The logarithmic decrement, δ showed the minimum at about 0.3 wt.% carbon content in the Fe-22Mn-C alloys. The Al addition to Fe-25Mn-0.5C resulted in the decrease of the logarithmic decrement. On the other hand, annealing treatments (800℃, 30-60 mins) after cold-rolling increased the logarithmic decrement. The exact mechanisms for these are unclear at this time, and are need to be studied.