Abstract
Bulk ultrafine-grained (UFG) low carbon steel bars were produced by warm caliber rolling, and the impact and tensile properties were investigated. The microstructures in the rolled bars consisted of an elongated UFG structure with a strong α-fiber texture. The rolled bar consisting of spheroidal cementite particles that distributed uniformly in the elongated ferrite matrix of transverse grain size of 0.8-1.0μm exhibited superior strength-ductility balance and impact properties. In the rolled bars, cracks during an impact test branched parallel to the longitudinal direction of the test samples as temperatures decreased. Delamination caused by such crack branching remarkably appeared near the ductile-to-brittle transition temperature. In conclusion, the strength-toughness balance is improved by refining crystal grains and controlling their shape and orientation; in addition, delamination effectively enhances the low-temperature toughness.
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