Estudo da abrasão e do comportamento mecânico de ferro nodular com carbonetos de cromo austemperado

Abstract

Austempered ductile iron alloys have achieved important prominence in engineering projects due to recent advances in their processing technology, resulting in materials with high mechanical strength, excellent toughness and good wear resistance, increasing interest in several industrial segments. The abrasive wear resistance of these alloys can be increased with the use of carbides in the metallic matrix, however this can to reduce the toughness properties. The present study analyzed the influence of chromium eutectic carbides contained in an austempered ductile iron, on the abrasion and mechanical properties through variations in temperatures and austempering times. Therefore, four alloys were developed with variations in the levels of chromium in type Y specimens with 13 mm thickness. The microstructural characterizations of the gross alloy, showed eutectic carbides when using chromium. These alloys were austenitized at 900ºC for 1.5 hours and austempered at two temperatures, 300ºC and 360ºC. Different times were used for the treatment of austempering: 30 minutes, 90 minutes and 180 minutes. The austempering treatments in the alloys with carbides generated ausferritic matrices. For the highest austempering temperatures, greater amounts of austenite were found, with lower averages of hardness and microhardness. For lower austempering temperatures, the amount of austenite was reduced, resulting in the highest averages for hardness and microhardness. However, for each allow in this study, greater hardness and microhardness did not lead to greater resistance to abrasive wear in alloys with carbides in the tests carried out on a rubber wheel, indicating that the abrasion resistance was more dependent on the volume of carbides than surface hardness, given the protection that these carbides provide the metal matrix. Nevertheless, the gradual increase in abrasion resistance through the increase in the volume of chromium carbides in this study, significantly reduced the toughness of the alloy in the impact tests performed.