Avaliação do desgaste de camadas de carbonetos e boretos produzidas no aço AISI 4340 por meio de tratamento termo-reativo

Abstract

In the present work, coatings of elevated hardness and wear resistance, made of FeB, Fe2B and NbC were realized in an AISI 4340 steel, by the means of thermo- reactive deposition treatment using a molten salt (Borax) bath. For the NbC coating, niobium was introduced to the salt bath in the Fe-Nb format. Optical microscopy, Vickers micro hardness and resistance to wear with the use of a tribometer using a sphere against disc system characterized the samples. For the bath using B4C, layers of FeB and Fe2B were obtained, with a thickness in the order of 150 μm and an average hardness in a range from 1800 to 1900 HV. When Fe-Nb/B4C were added, a NbC layer was obtained, which presented a thickness of 10μm and the hardness in a range about 2200 HV. In the disc against sphere experiments, it could be observed a decrease in wear, by analyzing the width of the wear tracks in the samples. The sample in the supplied conditions resulted in a 0,75mm track width and a maximum 22,97μm depth, when applied an axial force of 50N, while the samples that went through the boriding treatment resulted in smaller tracks. The track obtained by the axial force of 50N had a width of 0,10mm and depth of 9,129μm, while the track obtained by the axial force of 70N showed a width of 0,64mm and a depth of 16,36μm. These results indicates the wear decrease after the treatment. All coatings showed a wear resistance much larger than the substrate.