Formation of White Etching Layers by Deep Rolling of AISI 4140 Steel

Deep rolling is an effective mechanical surface treatment method; however, the induced deformation may eventually lead to changes that result in a structure known as a white etching layer (WEL). The WEL possesses a distinct constitution and properties compared with the surrounding bulk material. The presence of the WEL drastically affects the surface integrity of the part and impairs the performance of the metallic components. However, the influence of deep rolling on WEL formation has not been fully clarified. Therefore, the goal of this study was to investigate WEL formation after deep rolling AISI 4140 steel with various microstructures (obtained through four heat treatment routes) and employing distinct rolling pressure and feed values. The results show that larger lattice distortion (resulting from refined martensitic structures) and higher deep rolling feed (increased work hardening) lead to the formation of a thicker WEL. Moreover, the increase in rolling pressure does not affect the WEL within the tested range. Finally, the mechanisms involved in WEL formation are discussed. It is suggested that the shear energy associated with deep rolling and applied along the surface grains leads to WEL formation by grain refinement.