Estudo experimental e numérico sobre o roleteamento do aço ABNT 4140 endurecido

Abstract

Deep rolling is a mechanical surface treatment capable of reducing roughness, increasing hardness and inducing compressive residual stresses on the workpiece surface, thus increasing the mechanical fatigue life of the component. This behavior is only achieved with use of a suitable combination of parameters, that is usually obtained by experimental analysis, procedure that can be expensive and time consuming, given that they depend on performing new tests for each value of the input parameters. In this case the use of finite element analysis is interesting because the cost to select suitable parameters can be reduced. The present study investigates the influence of the roughness promoted by turning and of the parameters employed in the subsequent deep rolling operation on roughness, surface topography, surface microstructure and microhardness, fatigue life, and fatigue fracture of hardened AISI 4140 steel (41 HRC). The samples were initially turned obtaining different surface roughness values. Afterwards, the samples were deep rolled using distinct feed and pressure values. Numerical simulation by finite elements considered a condition close to the actual deep rolling of small diameter cylindrical workpieces, using a deep rolling tool with multiple rolling elements, situation that has not been previously found in the literature. Deep rolling was able to reduce the roughness for all tested conditions, being observed an interaction between deep rolling feed and pressure, as the behavior changed depending on the selected values. Areal power spectral density analysis (APSD) was capable of indicating the incapacity of the lower pressure value to mitigate the effects of the turning parameter on the surface, in addition to the capacity of the higher deep rolling parameter values to generate a new surface pattern, that was also identified by morphology. Deep rolling was capable of increasing microhardness and of promoting a surface deformation. Fatigue life increased after deep rolling, and the samples with highest surface roughness after turning were able to achieve longer mechanical fatigue lives after deep rolling. Fatigue fracture was also affected, reducing the number of nucleation regions on the deep rolled samples. Numerical simulation evaluated the influence of deep rolling parameters, indicating larger plastic strains and compressive residual stresses for higher deep rolling pressures and more uniform residual stresses for lower deep rolling feeds.