Efeito da adição de elementos de liga nas propriedades mecânicas a quente de ferros fundidos cinzentos aplicados a discos de freio

Abstract

The present work evaluated the impact of metallurgical modifications on a grey cast iron FC200 intended for brake disc applications through the controlled addition of alloying elements: chromium (0.15 wt. %), vanadium (0.10 wt. %), molybdenum (0.30 wt. %), copper (0.15 wt. %), and niobium (0.07 wt. %). Compared to the base alloy, the modified alloy exhibited superior mechanical properties, with a 70 % increase in tensile strength at room temperature and an average gain of 79 % under elevated temperatures over the entire temperature range evaluated. In addition, the modified alloy demonstrated enhanced high-temperature mechanical stability, with only a 1 % reduction in tensile strength up to 250 °C, compared to a 12 % loss observed in the base alloy. Brinell and Vickers hardness values increased by an average of 34 % and 46 %, respectively. Microstructural analysis revealed a 54.5 % reduction in the ferrite fraction (from 1.1 % to 0.5 %) and an increase in the pearlite volume fraction (from 86.6% to 89.3%), confirming the formation of a predominantly pearlitic matrix. This microstructural modification was accompanied by refinement effects, evidenced by a reduction in the graphite fraction from 12.4 % to 10.2 % and an increase in the number of fine graphite flakes. Regarding in-service performance, thermal fatigue resistance increased by 56 % at crack initiation and by 16 % at catastrophic failure. The results demonstrate that the proposed metallurgical modifications led to a material with superior mechanical performance, characterized by improved mechanical stability and enhanced thermal fatigue resistance for high-demand brake disc applications. [resumo fornecido pelo autor]