Cold compression deformation method for reducing residual stress and uniformizing micro-property in ferrite steel

Abstract

To reduce internal residual stress and homogenize micro-property of hot-rolled ferrite steel, the cold compression deformation method with small reduction rate has been performed in the hot-rolled samples, and X-ray diffraction and nanoindentation test have been used to detect the residual stress and micro-property. The samples with deformation rate of 0–5.59% or annealing at 550 °C are analyzed. The results show that, due to the coupling effect of thermal expansion and cold contraction and the volume expansion of microstructural transformation from austenite to ferrite, compressive residual stress was found inside the hot-rolled samples. With the increase in cold compression deformation, the dislocation density increased and the microhardness increased gradually, and there is no obvious rule for the change of mean nano-hardness in micro-zone for the center of samples. However, the uniformity of nano-hardness in the micro-zone increased first and then decreased, and the value of residual stress has obvious corresponding relationship with the uniformity of micro-zone property. The cold compression deformation with appropriate reduction rate can reduce residual stress and improve nano-hardness uniformity of the hot-rolled samples, but more deformation (such as reduction rate ε = 5.59%) makes residual stress increase and makes uniformity of nano-hardness deteriorate.