Desgaste abrasivo de revestimentos depositados por soldagem a arco transferido por plasma (PTA) para uso em implementos agrícolas

Abstract

The present study investigated the wear resistance of two alternative coatings deposited by powder-fed plasma on tools specifically used in soil preparation. Initially, the wear mechanisms present in the tribological system tool/soil of two specific agricultural implements, the stump cutter and the subsoiler, were evaluated using scanning electron microscopy. Subsequently, the methodology for making hard coatings on common carbon steel was presented, the analysis of the microstructures obtained and the abrasive wear performance of these surfaces in comparison with commercial wear-resistant steel. Hardfacings with potential to increase the wear life of agricultural implements were then selected. The first family is composed of nickelbased alloys reinforced with WC (NiCrBSi-WC) and the second family is composed of FeCrC alloys with addition of Vanadium (FeCrC-V). The coating of the surface of a common carbon steel, with two different thicknesses, was carried out by the Plasma Transferred Arc (PTA) welding process with measurement of the heating and cooling temperatures. After welding the hardfacings, the resulting microstructures, morphology and dilution of the coatings formed were evaluated. The abrasive wear resistance of hardfacings and of a commercial anti-wear steel, commonly used in soil preparation machinery, was evaluated by a rubber-wheel abrasometer. The hardfacings produced with the NiCrBSi-WC and FeCrC-V alloys showed an average hardness in the fusion zone of 763 HV10 and 716 HV10, respectively, with distinct microstructures. Loads of 48 N and 160 N and two abrasive particles size distributions (150-300 µm and 300- 600 µm) were used in the wear test. The NiCrBSi-WC coating was at least twice as wear-resistant while the FeCrC-V coating was at least three times as wear-resistant as the commercial anti-wear steel. Although the welding parameters and cooling rates were the same, the coatings deposited on thicker substrates showed less dilution compared to thinner ones. The dilution effect influenced the microstructural change of the coatings, which promoted greater wear resistance for lower applied load and smaller abrasive particles. Its effect was only significant when rolling abrasion was predominant. For higher loads and higher abrasives there was abrasion with sliding and the wear rate was higher.