Investigation on cyclic deformation behaviour of reinforced steel bars

In this study, cyclic deformation behaviours of 8-mm diameter reinforced steel bars produced by the hot rolling and the tempcore processes, whose carbon equivalent values were 0.52% and 0.41% respectively, were compared. The microstructure of the hot rolled bar was composed of ferrite and pearlite with a homogenous hardness distribution throughout the cross-section. On the other hand, the tempcored bar exhibited a microstructure consisting of tempered martensite in the outer sections and ferrite/pearlite in the center. This microstructure was accompanied with a hardness profile where the hardness decreased as the distance from the surface increased. In spite of its low carbon equivalent value, the tempcored bar exhibited higher yield strength than the hot rolled bar. However, low cycle fatigue tests conducted under the frequency of 1 Hz. in sinusoidal wave form revealed that, above the critical strain amplitude of 0.33%, the tempcored bars exhibited shorter fatigue life than the hot rolled bars. At the strain amplitude values lower than 0.33%, fatigue life of the tempcored bars was superior when compared to the hot rolled bars.