Untitled in english

Author(s)

Marcio Gustavo di Vernieri Cuppari

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
• Defense date: 2002-09-24

Examining board members

Amilton Sinatora; Sinésio Domingues Franco; Mário Boccalini Júnior; Claudio Geraldo Schön; Roberto Martins de Souza

• Advisor: Amilton Sinatora

Abstract

Since the early 1970\'s, it has been realized that the microstructure of a material plays a key role on its cavitation resistance. Since then, research has been conducted to determine which microstructural feature controls the cavitation resistance. Some of these features are martensitic transformation, stacking fault energy and the presence of a second phase. Among them, the effect of a second phase in the microstructure has received little attention. This work is concerned with the effect of a hard second phase on the cavitation erosion resistance of cast Fe-Cr-Ni-C alloys. Two main groups were tested: one with chromium content of 25% and a second one with 35%. Several compositions were tested in each group, varying the contents of carbon and nickel. By changing the chemical composition, it was possible to change the carbide fraction and morphology. The cast microstructure obtained for all alloys is an austenitic matrix with carbides (´M IND.7´´C IND.3´ and ´M IND.23´´C IND.6´) formed during the solidification. The cavitation tests were performed in an ultrasonic equipment using distilled water. The results showed that alloys with 35% of chromium content had a better cavitation resistance, due to a finer carbide morphology. To better understand the role of carbide morphology, the stress distribution between the matrix and the carbide was calculated by finite element modeling (FEM) analysis. The meshes used in the simulations were generated based onthe microstructure of the material itself using the software OOF. The FEM analysis showed a different stress distribution between the matrix and the carbides and the latter withstand higher stress levels than the former. Using instrumented hardness tests it was possible to measure the matrix mechanical properties and correlate these properties with the mass loss once the wear mechanism is established. (AU)