Avaliação do desgaste microabrasivo de aços ferramenta para fabricação de roscas de extrusoras

Abstract

This work aimed to study the abrasive wear resistance, microstructure, and hardness of two sintered tool steels (Böhler S790 Microclean and Uddeholm Vanadis 8). This behavior was compared with that of two tool steels currently used in the manufacture of extruder screws (AISI D2 and Uddeholm Sleipner). The four steels were studied in the quenched and tempered state. The microstructure of the four materials was analyzed by optical microscopy (OM), field emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray spectroscopy (EDS). The hardness of the materials was determined using Vickers microhardness tests, which allowed the quantitative evaluation of their mechanical behavior. Micro-abrasive wear tests were conducted using a free-ball micro-abrasion test whose tribological system consisted of tool steel blocks, an AISI 52100 bearing steel ball, and a slurry suspension with abrasive particles of silicon carbide (SiC). After the tests, the wear craters were analyzed by FE-SEM to identify the micro-abrasive wear mechanisms. The diameter and wear volume of all craters were determined by three-dimensional optical profilometry. The dimensional wear coefficient or the specific wear rate (k, wear volume per unit force per unit distance) of the tool steels was determined through the graphical interpretation of the Archard equation ('linear adjustment method') and from the variation of the wear coefficient as a function of time ('steady-state wear regime'). The AISI D2 steel exhibited large and irregular primary carbides besides finely dispersed secondary carbides, which provided the lowest hardness of the four materials. The Uddeholm Sleipner steel presented secondary carbides with similar shapes, small, spherical and dispersed in the tempered martensite matrix, which resulted in intermediate hardness values when compared to other materials. In contrast, the sintered steel Böhler S790 Microclean showed the highest hardness due to the formation of two types of secondary carbides finely dispersed in its microstructure. The Uddeholm Vanadis 8 steel presented carbides with small, spherical shapes, dispersed in the tempered martensitic matrix and rich in vanadium, which is consistent given its chemical composition and resulted in hardness values close to those of the Uddeholm Sleipner steel. From the micro-abrasive wear conditions used in this work, no significant difference in wear resistance was obtained between the materials, probably because the steady-state micro-abrasive wear regime (RPD) was not reached. [resumo fornecido pelo autor]