True Stress–True Strain Relationship up to the Plastic Deformation Limit in Ferrite–Pearlite Steel at Various Temperatures

This study investigated the true stress (σ)–true strain (ε) relationship up to the plastic deformation limit in ferrite–pearlite (FP) steel at various temperatures. We found that a decrease in the deformation temperature resulted in an increase in the lower yield strength (LYS) and the tensile strength (TS), and a decrease in both the uniform and the total elongations. When the temperature was increased from 673 to 773 K, the TS increased and the uniform and total elongations decreased due to the blue brittleness. In the σ–ε relationship up to the plastic deformation limit of the FP steel at various temperatures, ε at the plastic deformation limit increased with an increase in the temperature and was correlated with the reduction of cross-sectional area of tensile specimen. Microcracks were observed in the cementite plates as well as tearing in the pearlite lamellae. The temperature dependence of fracture stress (σZ) was small. In particular, the values of σZ in the temperature range of ductile fracture was almost the same, and is applicable to the condition of the plastic deformation limit. When the ratio of LYS to σZ was 0.5, the area fraction of brittle fracture was 50%.