Making high strength pearlite steel ductile by engineering boundary carbon concentration gradient at low temperature

Highly deformed cold-drawn pearlitic steel wires are well-known for the high strength, but with very limited tensile elongation (typically below 3 %). In this study, we developed an efficient way of recovering tensile elongation up to triple through low-temperature annealing at 275 °C for 30 min, i.e., the tensile strength of the pearlite steel wires remains almost unchanged (∼2088 MPa) while the tensile elongation increases from 2.1 % to 8.8 %. In comparison to the cold-drawn state pearlite consisting of highly orientated nanoscale laminates with sharp interfaces between ferrite and cementite, we found that low-temperature annealing promotes a carbon partitioning from cementite to adjacent ferrite grains, resulting in the formation of carbon concentration gradient across cementite/ferrite boundaries. The diffused boundaries may relieve the stress concentration during plastic deformation, facilitating the transmission of mobile dislocations across boundaries, making the high-strength pearlite steel ductile. The findings in this study may provide a general routine of ductile high-strength materials through boundary composition and structural configuring.