One-step annealing optimizes strength-ductility tradeoff in pearlitic steel wires

In this paper, the mechanical properties of a cold-drawn wire (epsilon = 2.43) are modulated by simple annealing and the variation of its microstructure is characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and molecular dynamics (MD) simulation. The tensile ductility of the wire can be improved for about three times without compromising its strength when being annealed at 325 degrees C for 10-30 min. It is convinced that solid solution of carbon atoms from decomposed cementite lamellae improve the wire strength at low temperature annealing (up to 250 degrees C) and make the wire strength basically equal the as-drawn state even though cementite lamellae are weakened by cementite recrystallization at 325 degrees C. And reversely the weakening cementite layers lead to the great improvement of wire ductility at this time since it relaxes the restriction to the moving of dislocations. At higher annealing temperature, the wire strength decreases with the growth of cementite and ferrite grains. The appearance of nano-recrystallized cementite grains at a medium annealing temperature may be a critical factor governing the enhanced wire mechanical properties.