Serrated flow and dynamic precipitation in elevated temperature tensile deformation of Fe-Mn-Al-C alloys

To investigate the characteristics and effects of dynamic strain aging (DSA) and dynamic precipitation of austenitic Fe-Mn-AI-C alloys, a hot-rolled alloy (Fe-26Mn-9Al-0.9C, in mass%) and two cast alloys (Fe-35Mn-9Al-1C, Fe-32Mn-9Al-1C) were selected to perform tensile test al various temperatures from 298 to 1073 K. The strain rates were chosen in the range from 9.4 x 10(-5) to 9.4 x 10(-3) s(-1). As indicated from the appearance of serrated flow, DSA occurs in two temperature regimes. Judging from the apparent activation energy obtained at the onset temperatures of serration, carbon atmosphere drag plays a role in the serration and the temperature independent flow stress in the low temperature regime. In the high temperature regime, the serration cannot be solely accounted for by the diffusion of manganese or aluminum solute atoms, or both. During high temperature deformation, the precipitation of Fe3AlCx occurs on active slip planes and along grain boundaries, giving rise to a substantial strengthening effect as compared with that normally associated with DSA. Grain boundary precipitation also leads to grain boundary embrittlement at the temperatures higher than about 773 K. All the above features and effects are common in the three test alloys although the hot-rolled alloy contains about 4 vol% ferrite.