Análise de tensões residuais em ferro fundido vermicular após tratamento de têmpera superficial a laser e nitretação a plasma

Abstract

Nowadays, one of the world’s biggest diesel engine block producer, Tupy uses the vermicular cast iron as the diesel engine block producing material. This iron, is also known as CGI and its use has been increasing in the automotive industry in recent times due to its mechanical properties, that enable the manufacture engines with higher pressures in the combustion chamber and thinner walls, which can imply in lighter, smaller and more lasting products. Aiming for a greater realiability to the engine block, the study of residual stresses is more than necessary, since theresidual stresses are present in all the mechanical components submitted to conformation processes. In this work presented, after been submitted to surface treatments as plasma nitriding and laser surface hardening with the aim of improving its surface properties, especially wear resistance, the CGI was submitted to residual stresses analysis that emerged due the high thermal gradient (heating followed by cooling), changes in chemical composition and surface volume generated by the treatments. By being a low cost method, easily portable and a high degree of reliability in the results, the chosen method for this analysis was the Hole-Drilling method. Aiming to analyse and evaluate the behavior of residual stresses after the above metioned treatments, this work may collaborate with a higher wear resistance to the CGI, consequently a longer life for the diesel engine block. The results showthat the residual stresses generated during the laser surface hardening are higher than those generated by plasma nitriding and that the grinding process stresses can be clearly seen in the base material.