Effect of ferrite grain size on tensile deformation behavior of a ferrite-cementite low carbon steel

Stress–strain curves for ferrite-cementite (FC) steels with ferrite grain sizes between 0.47 and 13.6 μm were studied by tensile tests with strain rates of 103, 100, and 3.3 × 10−4 s−1 at 296 K. The stress–strain curves for the FC steels are categorized into two different types. In one type, the Lüders deformation is interrupted due to the onset of necking, and in the other type, the Lüders band propagates throughout the gage section of a tensile specimen followed by work-hardening. The lower yield and flow stresses increase while uniform and total elongations decrease with a decrease in ferrite grain size. The effect of ferrite grain size on flow stress is hardly dependent on strain rate. These experimental results reveal that the grain refinement strengthening contributes mainly to an increase in the athermal stress component.