Study of micromechanics of cavitation damage in UNS S 31803 high nitrogen stainless steel with and without work hardening.

Author(s)

Luis Bernardo Varela Jiménez

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
• Defense date: 2013-10-04

Examining board members

André Paulo Tschiptschin; Fernando José Gomes Landgraf; Cherlio Scandian

• Advisor: André Paulo Tschiptschin

Abstract

This work aims to establish relationships between micro and nanostructure and cavitation-erosion resistance in high nitrogen stainless steels. These relations will be determined through the study of plastic deformation mechanisms and surface damage, as well as micro and nanostructure during vibratory cavitation testing. An UNS S 31803 samples with 0.9 N (%wt) were obtained by high temperature gas nitriding. Two sample groups were obtained: solubilized in solid solution and solubilized and work hardened. Vibratory cavitation tests were performed in distilled water. The damage mechanisms operating in different stages of wear were analyzed for different times in the same location using scanning electron microscopy (SEM). Mass losses were periodically measured during the cavitation-erosion tests. From the results, it was observed that the (318HTGN+Sol) samples, with nitrogen in solid solution showed wear rates 16.1 times smaller compared to those of the solubilized UNS S30403 steel. The work-hardened (318HTGN+Enc) samples showed wear rates 172.4 times smaller than UNS S30403specimens. The comparison of the 318HTGN+Sol samples with the work-hardened 304L+Enc specimens showed wear rates 2 times smaller, while the 318HTGN+Enc samples showed a wear rate 17 times smaller. Finally, a considerable increase of incubation time was readily observed, which allowed the detailed observation of the deformation mechanisms and the identification of the slip bands formation during the early stages of cavitation erosion. Additionally it was possible to observe the way the grain boundaries and twin boundaries are damaged, acting as preferential sites where the damage initially occurs. (AU)

• FAPESP's process: 11/16211-5 - Evolution of the micro/nanostructureof high nitrogen stainless steels, related to the deformation mechanisms on the cavitation erosion resistance of stainless steels
• Grantee: Luis Bernardo Varela Jiménez
• Support Opportunities: Scholarships in Brazil - Master