Resistências à cavitação de um aço inoxidável austenítico AISI 304L nitretado em alta temperatura sob atmosfera gasosa.

• Autor(a) principal: Santos, José Francisco dos
• Data de Publicação: 2003
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/3/3133/tde-02082024-083255/
• topic: Aço inoxidável austenítico; Austenitic stainless steel; Cavitação; Cavitation

The cavitation erosion resistance of AISI 304L austenitic stainless steel was improved by means of high temperature gas nitriding treatments (HTGN). The effect of the nitrogen content in solid solution) between 0.0 and 0.48 wt%) was studied in a set of five samples with equal microstructures. Nitrided and solubilized treated samples were tested in distilled water using vibratory indirect cavitation erosion equipment. The test was carried through in a 293 K cooled bath. Indirect cavitation erosion experiments were carried out according to ASTM G32-92 standard using a vibratory device Telsonic SG 1000, operating at a vibratory frequency of 20 kHz and an amplitude of 40 µm. the gap between the samples and the vibrating horn was 1mm. Characterization of the test specimens was made by optical microscopy, electron back scattering diffraction coupled to a scanning electron microscope, x-ray diffraction, wave-length dispersive spectroscopy microanalysis and depth sensing indentation tests. The results had shown that increasing the nitriding pressure during HTGN led to an increase in the nitrogen content, and to an increase in cavitation resistance. Nitrided samples exhibited much better cavitation erosion resistance than the non-nitrided one, being the wear rate reduced up to 8.6 times. Depth-sensing indentation tests showed that the increase in the nitrogen content led to an increase in the resistance to plastic deformation (hardness) and to a decrease in the plastic fraction of the total deformation energy (irreversible work indentation), without significant variations of the strain hardening coefficient. It was observe that the damage due to cavitation erosion could be assigned to a combination of impact and fatigue. The increase in the nitrogen content increased the fatigue resistance of the steel reducing the influences of this mechanism on the damage. ) In the samples with minor nitrogen contents (up to 0.18 wt%) the cavitation erosion damage started at grain boundaries and at slip lines; the higher nitrogen content samples damage started preferentially at grain boundaries.