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Master's Dissertation
DOI
10.11606/D.88.1997.tde-25072012-113812
Document
Author
Full name
Valdinei Ferreira da Silva
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1997
Supervisor
Committee
Crnkovic, Ovídio Richard (President)
Canale, Lauralice de Campos Franceschini
Spinelli, Isa Maria Müller
Title in Portuguese
Influência da austenita retida no crescimento de trincas curtas superficiais por fadiga em camada cementada de aço SAE 8620
Keywords in Portuguese
Austenita retida
Camada cementada
Crescimento de trincas curtas por fadiga
Abstract in Portuguese
A austenita retida está sempre presente na microestrutura de camada cementada de aços, em maior ou menor quantidade. Como é uma fase dúctil comparada à martensita, sua presença tem sido alvo de muita controvérsia. Este trabalho apresenta um estudo sobre a influência da austenita retida na propagação de trincas curtas por fadiga em camada cementada de aço SAE 8620. Foram feitos ensaios de fadiga por flexão em quatro pontos, a temperatura ambiente, em corpos de prova sem entalhe com três níveis de amplitude de tensão e razão de tensões de 0,1. Através de diferentes ciclos de cementação e tratamentos térmicos, foram obtidas camadas cementadas com quatro níveis de austenita retida na microestrutura. O teor de austenita retida foi medido através da técnica de difração de Raios-X. Trincas superficiais foram monitoradas por meio da técnica de réplicas de acetato. Como resultados foram obtidos tamanho de trinca em função do número de ciclos e taxa de crescimento de trincas curtas. Corpos de prova com maiores níveis de austenita retida apresentaram maior vida em fadiga.
Title in English
The influence of retained austenite on short fatigue crack growth in case carburized SAE 8620 steel
Keywords in English
Case carburized
Retained austenite
Short fatigue crack growth
Abstract in English
The retained austenite is always present in case carburized steel microstructure in small or high percentages. Since it is a ductile phase, its presence has long been a controversial subject. The influence of retained austenite on short fatigue crack propagation in case carburized SAE 8620 steel was studied in this work. Four-point-bend fatigue tests were carried out at room temperature in specimens without notch using three levels of stress range and a stress ratio of 0.1. Four different amount of retained austenite in the case carburized microstructure were obtained through different cycles of carburizing and heat treating. The retained austenite content was measured by X-ray technique, and the surface short crack growth was monitored by means of acetate replication technique. Crack length versus number of cycles and crack growth rate versus mean crack length were obtained as results. Specimens with higher levels of retained austenite in the carburized case showed longer fatigue life.
 
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Publishing Date
2012-07-25
 
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