Ratchetting in Cold-Drawn Pearlitic Steel Wires

The microscopic mechanisms that accommodate uniaxial ratchetting in cold-drawn pearlitic steel wires were explored. A two-stage evolution of ratchetting strain as a function of cycle numbers was observed. The initial sudden increase of plastic strain leads to a rapid decomposition of cementite, followed by a constant ratchetting strain rate with critical role of decomposed carbon atoms played in blocking dislocation motion. The dislocation configuration transforms from low-density lines and tangles to high-density cells and sub-grains with increasing strain. A possible mechanism of cementite decomposition is discussed in terms of carbon-dislocation interactions and an unfavorable cementite surface-to-volume ratio.