Efeito do jateamento abrasivo na integridade superficial e na vida em fadiga do aço Maraging 18Ni300 nas condições: solubilizada, envelhecida e super-envelhecida
Arquivos
Data
2022-09-21
Autores
Palau, José Carlos Fortes
Orientadores
Travessa, Dilermando Nagle
Tipo
Tese de doutorado
Título da Revista
ISSN da Revista
Título de Volume
Resumo
O jateamento abrasivo a seco, também conhecido como "grit blasting", é um processo erosivo de
tratamento superficial mecânico a frio amplamente utilizado no meio industrial para remoção de
contaminantes superficiais e preparação de superfície para aplicação de revestimentos diversos.
Os aços maraging são uma classe especial de aços de ultra-alta-resistência que apresentam uma
combinação única de altos níveis de resistência mecânica aliada a uma excelente tenacidade "e,
por essas razões" são empregados principalmente em setores estratégicos como o aeroespacial
e o nuclear. Alterações na textura superficial (rugosidade), no estado de tensões residuais e na
microestrutura da superfície deformada estão entre os principais efeitos produzidos pelo processo
de jateamento abrasivo na integridade da superfície jateada. Dessa forma, o objetivo desse
presente trabalho foi avaliar se os efeitos produzidos pelo processo de tratamento superficial
mecânico de jateamento abrasivo a seco com partículas metálica abrasiva angular na superfície
do aço maraging 18Ni300 poderiam influenciar em sua vida em fadiga, uma vez que, a fadiga é o
mecanismo de falha dominante de vários componentes de engenharia e, por sua vez, sofre forte
influência de sua qualidade superficial. O estudo foi conduzida em duas etapas: i) na primeira etapa
amostras de aço maraging 18Ni300 foram tratadas por diferentes rotas de tratamentos térmicos,
para obtenção de diferentes microestruturas e níveis de resistência mecânica e, posteriormente
submetidas ao processo de jateamento abrasivo, utilizando-se dois ângulos de impacto das
partículas (45◦e 75◦). Os efeitos produzidos pelo jateamento na superfície deformada foram
avaliados através de caracterização microestrutural, caracterização mecânica, perfilometria de
contato e difração de raios-X. ii) na segunda etapa as condições mais desfavoráveis para a vida
em fadiga, encontrados após análise dos resultados obtidos nos corpos de prova da primeira
etapa, foram replicados em corpos de prova de fadiga divididos em dois grupos com diferentes
condições superficiais: um com a superfície polida, adotado como a condição superficial padrão e
o outro com a superfície jateada. Os corpos de provas nas condições superficiais polido e jateado
foram testados em condições de fadiga axial com carregamento de amplitude reversa (R=-1) em
vários níveis de tensões e seu desempenho avaliado pelas curvas S-N e as superfícies fraturadas
analisadas por microscopia eletrônica de varredura. Os resultados obtidos nos ensaios de fadiga
e nas análises fractográficas revelaram que o jateamento abrasivo apesar de ter aumentado
significativamente a rugosidade superficial (em mais de 10 vezes), resultou na melhora da vida
em fadiga ao induzir na superfície jateada uma combinação de efeitos benéficos como o trabalho
à frio (encruamento) que aumentou a dureza superficial (aproximadamente em 6,74%) e tensões
residuais compressivas na profundidade (até 180-200 µm) da superfície jateada, que contribuíram
para retardar o início e a propagação das trincas e, assim, aumentar a vida em fadiga no aço
maraging 18Ni300.
Dry abrasive blasting, also known as "grit blasting", is an erosive process of cold mechanical surface treatment widely used in the industrial environment to remove surface contaminants and to prepare surfaces for the application of various coatings. Maraging steel is a special class of ultra-high-strength steel that has a unique combination of high levels of mechanical strength combined with excellent toughness and for these reasons are used mainly in strategic sectors such as aerospace and nuclear. Changes in surface texture (roughness), in the state of residual stresses and in microstructure of the deformed surface are among the main effects caused by the grit blasting process on the integrity surface treated by grit blasting. Thus, the objective of this work is to assess whether the effects produced by the grit blasting process with angular abrasive particle on the surface of 18Ni(300) maraging steel, can directly affect its fatigue life, since fatigue is the mechanism of dominant failure of various engineering components and, in turn, it is strongly influenced by surface quality. The project was conducted in two stages: i) in the first stage, samples of 18Ni(300) maraging steel were treated by different heat treatment routes to obtain different microstructures and levels of mechanical strength and later, submitted to the grit blasting process, using two blasting angles (45◦and 75◦). The effects produced by blasting on the deformed surface were evaluated through microstructural characterization, mechanical characterization, contact profiling, and X-Ray diffraction. ii) in the second stage, the most unfavorable conditions for fatigue life, found after analyzing the results obtained in the samples of the first stage, were replicated in fatigue samples divided into two groups with different surface conditions: one with the surface polished, adopted as the baseline and the other with blasted surface.The samples in the polished and blasted surface conditions were tested under axial fatigue conditions with reverse amplitude loading (R=-1) at various stress levels and their performance was evaluated by the S-N curves and the fractured surfaces were analyzed by scanning electron microscopy.The results obtained in the fatigue test and the fractographic analysis revealed that grit blasting, despite having significantly increased the surface roughness (by more than 10 times), resulted in improved fatigue life by inducing the blasted surface a combination of beneficial effects such as cold working ( work hardening) which increased surface hardness (approximately 6.74%) and compressive residual stresses at the depth (up to 180-200 µm) of the blasted surface, which contributed to delaying the initiation and propagation of cracks and, thus, increasing fatigue life in 18Ni(300) maraging steel.
Dry abrasive blasting, also known as "grit blasting", is an erosive process of cold mechanical surface treatment widely used in the industrial environment to remove surface contaminants and to prepare surfaces for the application of various coatings. Maraging steel is a special class of ultra-high-strength steel that has a unique combination of high levels of mechanical strength combined with excellent toughness and for these reasons are used mainly in strategic sectors such as aerospace and nuclear. Changes in surface texture (roughness), in the state of residual stresses and in microstructure of the deformed surface are among the main effects caused by the grit blasting process on the integrity surface treated by grit blasting. Thus, the objective of this work is to assess whether the effects produced by the grit blasting process with angular abrasive particle on the surface of 18Ni(300) maraging steel, can directly affect its fatigue life, since fatigue is the mechanism of dominant failure of various engineering components and, in turn, it is strongly influenced by surface quality. The project was conducted in two stages: i) in the first stage, samples of 18Ni(300) maraging steel were treated by different heat treatment routes to obtain different microstructures and levels of mechanical strength and later, submitted to the grit blasting process, using two blasting angles (45◦and 75◦). The effects produced by blasting on the deformed surface were evaluated through microstructural characterization, mechanical characterization, contact profiling, and X-Ray diffraction. ii) in the second stage, the most unfavorable conditions for fatigue life, found after analyzing the results obtained in the samples of the first stage, were replicated in fatigue samples divided into two groups with different surface conditions: one with the surface polished, adopted as the baseline and the other with blasted surface.The samples in the polished and blasted surface conditions were tested under axial fatigue conditions with reverse amplitude loading (R=-1) at various stress levels and their performance was evaluated by the S-N curves and the fractured surfaces were analyzed by scanning electron microscopy.The results obtained in the fatigue test and the fractographic analysis revealed that grit blasting, despite having significantly increased the surface roughness (by more than 10 times), resulted in improved fatigue life by inducing the blasted surface a combination of beneficial effects such as cold working ( work hardening) which increased surface hardness (approximately 6.74%) and compressive residual stresses at the depth (up to 180-200 µm) of the blasted surface, which contributed to delaying the initiation and propagation of cracks and, thus, increasing fatigue life in 18Ni(300) maraging steel.