Change in carbon state by low-temperature aging in heavily drawn pearlitic steel wires

Atom probe tomography analysis of heavily drawn pearlitic steel wires was performed with and without low-temperature aging. In the as-drawn wire, the lamellar cementite hardly decomposed and remained in a sufficient amount. By contrast, almost homogeneous carbon atomic distribution of the concentration near the average carbon content was observed in the wire with maximum tensile strength aged at 150 °C for 30 min. In the 200 °C × 30 min aging, carbon atoms were enriched at the boundary (prior lamellar cementite) and the carbon concentration in the lamellar ferrite was lower. The change in carbon state was explained by the presence of the high number density of vacancies that was introduced by heavy drawing. These results indicate that cementite decomposition occurred during the thermal aging after, and not during, drawing. The mechanism of the change in strength by low-temperature aging was discussed.