Surface nanocrystallization of SAE 1008 steel by single and multipass thread rolling process

In this study, the layers are investigated which are obtained on the surfaces of the single and multi-pass thread rolled screws. It is observed that deformation is more homogenous depending on the pass number and thread laps failure do not form on the 3-passed threads. A nanocrystallized layer that thicknesses and size depends on deformation amount is determined on the surfaces of the thread rolled SAE 1008 steel. While top of this layer has finer grain sizes, depending on the deformation amount grains coursed and oriented by the deformation direction. The finer grains are observed in the single pass thread rolled sample as size of 136 nm at the 15 mm inside from the surface of the root of the thread. Compared with bulk material, significant hardness increase is observed on the surfaces of the all thread rolled samples. The effect of pass number on the hardness is very low, increases of the pass number, hardness increases slightly. But thicknesses of layer are enhanced to increase the pass number.