Compressive Flow Behaviour and Deformation Instabilities of Fe-Mn-Al-Ni-C Lightweight Duplex Steel

Abstract

In this work, uniaxial hot compression tests of Fe-Mn-Al-Ni-C steel are conducted in the domain of strain rates (0.001–10 s−1) and temperatures (1223–1423 K). The apparent activation energy of the present steel is estimated as ~400 kJ mol−1. A constitutive equation is formulated by using the experimental flow stress data to depict the flow characteristics of the steel. An excellent correspondence (R = 0.99 and AARE = 5.2%) between the experimental and predicted flow stress data has been obtained. Further, we have predicted the deformation instabilities in the present steel based on the various existing criteria (viz. Prasad, Gegel, Alexander, Jonas, and Semiatin). The predicted unstable domains are further validated by the microstructural characterization. The instability features like boundary decohesion, micro-cracks, and flow localization are observed in the regions 1223 K/0.1–10 s−1 and 1273–1373 K/1–10 s−1 while the wedge-cracks at the triple junctions of the boundaries are observed in the region 1350–1423 K/0.001 s−1. The Prasad’s instability criterion could precisely identify the flow instabilities in the present steel. However, the Gegel’s and Alexandar’s criteria over-estimated the unstable regions (<1300 K/0.003–0.1 s−1), (1300–1373 K/0.003–1 s−1) and (1373–1423 K/0.002–5.62 s−1) in the material. The Jonas’ and Semiatin’s criteria, on the other hand, underrated the extent of flow instabilities in the lightweight duplex steel.