Efeito dos parâmetros de shot peening no perfil de tensões residuais de um ferro fundido nodular temperado

Abstract

The Group for Research on Materials, Tribology and Surfaces (GrMaTS) from Federal University of Technology -Paraná (UTFPR) have been studying over the past years the contact fatigue resistance of ductile cast iron. According to the literature, residual compressive stresses increase contact fatigue life. However, previous studies, in which compressive stresses were induced by means of mechanical compression, plasma nitriding and shot peening, revealed no increase on endurance of hardened ductile cast iron specimens submitted to pure rolling contact fatigue. In the study concerning shot peening, it was found that the compressive stress, measured by the X - ray diffraction method, wasn’t as deep as the maximum shear stress, about 100 m deep, generated by the non-conformal loading contact. As a result of this situation, this paper aims to evaluate shot peening process parameters, as blast particles diameter and blast pressure, in order to extend the depth of the residual stress profile. For this purpose, six specimens were submitted to 3 different shot-peening conditions. Each condition had a different diameter and blast pressure, but a constant Almen height. Xray diffraction and chemical removal were employed on stress profile measurements. Samples were characterized by metallography analysis, microhardness - measurement and topographic analysis. Results showed that changes in shot-peening process, with respect to previous works, were successful on creating compressive residual stresses in the zone of depth of maximum shear stress (obtained, previously, by the fatigue process). The maximum compressive residual stress of 815 MPa was a result of an intermediate particle size and blast pressure. Such condition has also lead to the higher compressive stress at a depth of 100m, which was 300 MPa.