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Evaluation of tensile properties of ferrite single-phase low-carbon steel with different initial microstructures

The tensile properties of ferrite single-phase low-carbon steel with different initial microstructures were evaluated. Three types of hot-rolled sheet specimens with different microstructures—specimen P (consisting of ferrite and pearlite), specimen B (consisting of bainitic structures), and specimen M (consisting of fully martensitic structures) were used. After hot rolling, these specimens were cold-rolled, subsequently heated to the finishing temperature of ferrite recrystallization, and then water-quenched to room temperature. The recrystallized ferrite grain size decreased in the specimen order of B > P > M. The distribution of cementite was comparatively homogeneous in specimens B and M, whereas that in specimen P was heterogeneous. The yield and tensile strengths decreased in the specimen order of M > P > B. Calculations using the Hall–Petch equation revealed that the yield strength of each specimen depended mainly on the recrystallized ferrite grain size. The total elongation decreased in the specimen order of B > P > M, whereas the local elongation was approximately the same in all of the specimens. In addition, the number of dimples decreased in the specimen order of M > B > P, whereas the size of dimples decreased in the specimen order of P > B > M. These results suggest that the homogeneous distribution of cementite and the fine recrystallized ferrite grains in specimen M suppress void coalescence, thereby resulting in a good balance between the tensile strength and the local elongation.