Resumo:
Residual stresses were induced in quanched and tempered ABNT 4340 steel specimens by means
of orthogonal turning operation, varying the machining parameters based on a statistical surface response design. The experiment analyzed the variation of the cutting speed (Vc), the feed rate ( f ),
the depth of cut (ap) and the hardness (H) of the material. To characterize the specimens, residual
stresses in the directions of feed (sf ) and cutting speed (sVc) were measured using the incremental
hole drilling technique, in addition to the measurement of the average roughness profile (Ra) and the
maximum height of the roughness profile (Rt). Metallographies of the cross sections of each sample
were also obtained, showing the region close to the machined face to characterize the microstructure
of the material. For the medium roughness, only the feed, its quadratic interaction ( f 2) and the interaction Vcxap were considered statistically significant, with contributions of 92.80%, 5.14% and 0.26%
in answer. As for the maximum height (Rt), only feed rate and its second-order interaction had any
significance, with contributions of 92.77% and 5.72%. The results showed that it is possible to obtain
class N5 and N6 roughnesses, which show the potential of hard turning in the replacement of grinding operations. In addition, the regression models had excellent adjustment coefficients, which can be
used to predict and control the final roughness. Residual stresses in both directions, in general, were
close to zero, with a slight tendency to compression. The lowest values found were sf = −115:2MPa
and sVc = −152:1MPa. However, the proposed regressive model does not have a good correction
with the experimental data, making it impossible to analyze the behavior of residual stresses. The
formation of a white layer was not registered in any of the evaluated specimens, and no changes in
the microstructure of the samples were seen. No significant wear was found in the coated carbide
inserts used.
