Análise de tensões residuais de juntas soldadas em engrenagens de moenda de cana em aço baixa liga

Abstract

Residual stresses are those which remain in the part when all the external mechanical stress applied previously are removed. These residual stresses often appear in parts subjected to different thermal or mechanical processing along its thickness, among then may be cited the welding process. The objective of this work is the analysis of residual stresses generated by the recovery process for shielded metal arc welding” (SMAW) of sugarcane milling gear in Low Alloy Mild Steel ASTM C-148 for the identification of conditions with lower levels of residual stresses, aiming materials less susceptible to failure and longer service life. A comparative assessment of the levels of residual stresses in the aforementioned samples was performed by opting for performance or nonperformance of pre-heating and heat treatment of stress relieving after the completion of the welds in the field. It will be characterized by metallography and hardness profile. In order to determine the way the macro and microscopic residual stresses non-destructive, it was decided in this work by the diffraction of X-ray method. The characterization was carried out by optical microscopy, scanning electron microscopy and Vickers microhardness. The microstructure present in the base metal was characterized as microconstituent bainite, when there is a stress relieving treatment. When there isn`t such treatment, the microstructure is ferrite / pearlite. Although in the weld metal, due to the electrode composition, the microstructure is acicular ferrite. The Vickers microhardness analysis for the sample without pre-heating gave higher microhardness values along line profile (range of 250 – 325 HV) than the other conditions (range of 150 – 275 HV). Regarding the residual stresses, it can be concluded that the pre-heating and the combination of it with a subsequent heat treatment reduces the levels of both longitudinal and transverse residual stress along the weld bead.