Resumo:
Duplex stainless steels (DSS) are so named because they exhibit a biphasic microstructure, with roughly equal volumetric proportions of ferrite and austenite. They find extensive use in industries such as oil, pulp and paper, chemical, nuclear, and others, typically when a material with high mechanical strength and corrosion resistance is required. Powder metallurgy can provide a means of recycling scraps and leftovers from production processes like machining. This study focused on investigating the influence of different particle sizes and pressing methods (uniaxial and isostatic) on the densification of a DSS composite, specifically the UNS S31803 grade, produced through powder metallurgy. The powders were subjected to milling for 20, 40, and 80 hours, with the addition of 3% vanadium carbide and 1% methanol as a process control agent. Heat treatment at 1050 ºC for 30 minutes was applied to relieve the stresses resulting from the milling process. The powders obtained at different milling times were classified and characterized in terms of morphology and particle size distribution using scanning electron microscopy and laser granulometry techniques. Subsequently, the powders with different particle sizes were pressed using uniaxial and isostatic pressing methods. Pellets were produced using powders milled for 20, 40, and 80 hours, as well as mixtures of equal weight fractions of powders milled for 20 and 40 hours, 40 and 80 hours, and 20, 40, and 80 hours. Green density measurements were conducted on the obtained pellets, which were then sintered at 1250 ºC for 1 hour. The sintered pellets were characterized in terms of porosity, pore size, and densification using optical microscopy, X-ray diffraction, and density measurements using the Archimedes method. The results showed that particle dimensions decreased with longer milling times. The average particle size decreased from 60.57 μm at 20 hours of milling to 52.35 μm at 40 hours and 39.02 μm at 80 hours. The porosity values were similar for uniaxial and isostatic pressing. The highest densification value (determined using the Archimedes method) was achieved with the mixture of powders milled for 20, 40, and 80 hours using isostatic pressing, resulting in a density of 6.9528 g/cm³. The density value for UNS S31803 DSS produced via casting is 7.80 g/cm³.
