Serrated flow and failure behaviors of a Hadfield steel at various strain rates under extensometer-measured strain control tensile load

A Hadfield steel has been investigated to clarify the serrated flow and to explore the failure behavior at room temperature. The tensile experiments were performed under extensometer-measured strain control, rather than under conventional cross-head displacement control, at strain rates ranging from 6 × 10−3 s−1 to 6 × 10−6 s−1. Three types of serrations, including type A, B and C ones, are observed. The occurrence of different types of serrations depends on both strain rate and strain level. The type C serration is identified in Hadfield steels at room temperature for the first time. At high strain rates, there is substantially higher serration density and reduction in stress compared with that observed at low strain rates. Furthermore, two different initiation modes of deformation bands are revealed. The fracture crack nucleates at a position with dense twins, and propagates primarily in the direction perpendicular to the tensile axis and deflects frequently due to the interaction with the boundary of grains and twins.