Avaliação do efeito da microestrutura de diferentes ligas metálicas na resistência ao desgaste abrasivo por tamboreamento

Abstract

In mineral processing, comminution is the stage that requires the most investment, with 45% of costs associated with the consumption of grinding media during milling. Since the wear rate of these grinding media is a key factor in these costs, this study aims to correlate the microstructure and mechanical behavior of materials with their resistance to abrasive wear through tumbling tests. The research characterized eight commercial metal alloys used as grinding media. It analyzed their chemical composition, microstructure, and Rockwell C hardness. After characterization, the samples underwent abrasion testing with quartz sand and iron ore, generating a performance ranking based on wear resistance. The surfaces of the samples were also evaluated via SEM after wear. The chemical composition analysis classified two samples as white cast irons, one of which was high chromium cast iron with approximately 12.9% Cr. The other six samples were categorized as low-alloy steels, with a maximum alloying element content of 2.5%. Optical micrography revealed a predominantly martensitic matrix with primary and secondary chromium carbides in the cast iron samples. In the steel samples, a predominantly martensitic matrix was identified, with islands of pearlite and small fractions of retained austenite in four of the samples. Hardness results ranged from 53 HRC to 69 HRC, with low-alloy steels exhibiting higher surface hardness compared to their center. Linear hardness profiles indicated more effective heat treatments, while profiles with slope changes suggested lower uniformity in the heat treatment. Abrasion test results showed higher wear when sand was used as the abrasive, with greater variability in results compared to iron ore. A comparison of wear resistance results across abrasive type showed an inversion in the performance ranking of the cast irons, indicating that material performance is strongly influenced by the type of abrasive. However, regardless of the abrasive type, the high-Cr cast irons exhibited the lowest mass and volumetric losses (samples A and B), while cast carbon steel showed the highest mass loss and the worst performance (sample C). For the forged carbon steel samples, similar abrasion resistance results were observed. SEM analyses after wear revealed selective wear of the martensitic matrix around primary carbides in the cast iron samples, which can be explained by the corrosion protection provided by Cr and the high carbide density, resulting in a microstructure more resistant to wear than pure martensite. In the steel samples, numerous corrosion pits were identified, suggesting that corrosion had a significant impact on the tests, possibly greater than friction, due to the low-stress testing conditions.