Influence of Tempering on Macro- and Micro-Residual Stresses and Yield Stress of Ferritic-Pearlitic Drawn, Coiled, and Straightened Wires

Abstract

Residual stresses caused by different deformation steps during the processing of wires significantly affect the mechanical properties of the final product. However, in the literature, there is a lack of detailed information about their correlation with mechanical properties. Therefore, the proposed work focuses on the influence of tempering on the macro- and micro-residual stresses, and related mechanical properties of a ferritic-pearlitic 27MnSiVS6 steel wire in the deformed state after hot rolling, drawing, coiling, and straightening. Characterization of the wire in the deformed state indicates macro-residual stresses that remain high after tempering at a temperature of 400 °C for 10 minutes and decrease significantly after tempering at 475 °C for 10 minutes. In situ high-energy X-ray diffraction measurements during heating of wires in the deformed state reveal that micro-residual stresses remain unchanged up to temperatures of 200 °C, while they decrease at 300 °C. Investigations of the mechanical properties show that a reduction of micro-residual stresses correlates with a reduction of the curvature of the stress–strain curve below the yield point, which increases the yield stress. Conversely, the reduction of macro-residual stresses begins in the temperature regime of recovery and relaxation, where a reduction of yield stress and tensile strength occurs.