On the negative strain rate sensitivity of Hadfield steel

The digital image correlation (DIC) technique was utilized in conjunction with mechanical experiments carried out at different strain rates to study the negative strain rate sensitivity (NSRS) in face-centered cubic (fcc) Hadfield steels. The results shed light onto the variation of local strain fields and serrations in the stress– strain curves of Hadfield steels as a function of strain rate within the NSRS range. Contradictory explanations regarding the main cause of rapid work hardening of Hadfield steel, such as twin boundaries, stacking faults and dynamic strain aging (DSA), warrant a detailed investigation of the proposed causes [1–14]. This particular study focuses on DSA and its role on the strain hardening behavior of Hadfield steel, and presents a new systematic set of results on the influence of DSA on the rapid work hardening in Hadfield steel. Previously, DSA was investigated by means of classical thermo-mechanical experimentation techniques [1] and numerical models utilizing a statistical approach [3]. Specifically, DSA is brought about by the reorientation of carbon members of manganese–carbon (Mn–C) couples in the cores of dislocations. At elevated temperatures this reorientation of Mn–C couples is enhanced due to increased energy of the system, promoting the diffusivity of C atoms, eventually leading to rapid strain hardening in the absence of twin formation [1,3].