Mechanical behavior and crack tip plasticity of a strain aging sensitive steel

Abstract : C–Mn steels are prone to static and dynamic strain aging (SSA and DSA) that induce Lüders or Portevin–Le Chatelier strain localization phenomena. Tensile tests and fracture tests were carried out between 20 °C and 350 °C. Negative strain rate sensitivity (SRS) and discontinuous yielding were evidenced, in relation with a drop in fracture toughness. The Kubin–Estrin–McCormick (KEMC) constitutive law, well suited for this kind of material response, was identified so as to model the mechanical behavior of the ferritic steel from 20 °C up to 350 °C. It is shown that both static and dynamic strain aging can be modeled by introducing a monotonic temperature dependence of all the parameters except the strain hardening parameter. Extra-hardening due to dynamic strain aging is clearly evidenced. The influence of SSA and DSA on the plastic zone development at the crack tip of CT specimens is analyzed on the basis of a finite element study.