Verificação da conformidade de grampos de fixação em aço SAE 4140 reprocessados no tratamento térmico

Abstract

Quenching and tempering heat treatments have fundamental importance in industries, playing an essential role in improving the mechanical properties of materials for their specific applications. However when variables such as temperature, time and cooling speed are not controlled there can be undesirable consequences. The purpose of this study is to evaluate the mechanical properties of U-bolts which had their hardening or tempering process interrupted in the first cycle and had to be reprocessed in the hardening and tempering heat treatments. The U-bolts are safety items responsible for fixing the spring beam to the vehicle's axle. They must be rigorously heat treated in order to achieve the specified mechanical properties. Ten U-bolts were reprocessed which their heat treatment was interrupted, under the same conditions as the first cycle, austenitizing temperature of 860°C, cooling in oil with a maximum temperature of 100°C and tempering temperature of 560°C. The U-bolts showed values within those specified by the ISO 898-1/2013 standard and obtained the expected tempered martensite microstructure.