The influence of Widmanstätten ferrite on yielding behavior of Nb-containing reinforcing steel bars

The engineering stress–strain curves for a series of civil-structured steel bars have been investigated. The yield plateau existed in the corresponding curves for niobium-free steel bars, but continuous plastic flow occurred for niobium-containing steel bars. The results from optical metallography and transmission electron microscopy provide evidence to suggest that the absence of a yield plateau in niobium-containing steel bars is associated with a substantial amount of Widmanstätten ferrite, which forms with a displacive mechanism.