An experimental study on stress relaxation behaviour of high strength steel wire: Microstructural evolution and degradation of mechanical properties

•Microstructure includes the fragmented cementite/ferrite lamellae.•Dislocation slip distance tends to broaden with increasing initial stress.•Relaxation rates are highly sensitive to initial stress relaxation.•H and σy show a decrease, while there is no variation of E under stress relaxation.•Degradation of H and σy is attributed to the broadening interlamellar spacing. In this study, a series of experiments including stress relaxation, nanoindentation, tension loading experiments, and transmission electron microscope (TEM) examination were performed to investigate microstructural evolution, the stress relaxation behavior, and the influences of stress relaxation on mechanical properties of high strength steel wire. The stress relaxation experiments were performed on a single steel wire for 1000 h at three initial stress levels to characterize the stress relaxation behavior of the tested material. Microstructural evolution of the specimens deformed by stress relaxation was observed and analyzed using TEM examination. Long-term relaxation behavior was then calculated and investigated. Finally, the influences of stress relaxation on material properties were studied by performing nanoindentation and tension loading experiments on the deformed relaxation specimens. The degradation of mechanical properties under stress relaxation was interpreted through a micro-mechanism regarding the microstructural evolution and the grain boundary strengthening. The results from the present study can be used for practical designs as well as for assessing the stress relaxation behavior of high strength steel wire.