Failure analysis of an automotive component (cardan yoke) by scanning electron microscopy

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Defect and Diffusion Forum
Citações (Scopus)
Couto A.A.
Andrade A.H.P.
Reis D.A.P.
Vatavuk J.
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Two SAE 1541 (0.39%C; 1.44%Mn; 0.23%Si; 0.16%Ni; 0.16%Cr) carbon steel cardan yokes that were forged, machined, quenched and tempered, as part of the manufacturing process to ensure long term operation under specific loading conditions, failed during its manufacture. The cardan yokes ruptured in the bearing seat region while these were being straightened by bending. This study deals with fracture analysis that was carried out by visual inspection and scanning electron microscopic examination. The focus of this study was to investigate the fracture mechanism associated with the failures. Fractographs of the broken components indicated that the rupture initiated at the edges of the component, from preexisting cracks, due to the bending stresses during the straightening process. The initial stage of rupture was predominantly intergranular in the tempered martensite surface layer, revealing the brittle nature of the component. Cracks were observed at regions prone to stress concentration. Eventual rupture of the component probably initiated at these cracks. This behavior is probably related to metallurgical processing steps like quenching, that causes the formation of a banded structure and promotes circumferential and radial cracking before the tempering. The fracture surface revealed regions with micro dimples and a large smooth area with some elongated inclusions. The morphology of these inclusions was cellular and originated at the grain boundaries of the primary austenite. These inclusions are probably MnS with a dendrite structure, capable of causing brittle intergranular rupture. © (2012) Trans Tech Publications.
Assuntos Scopus
Automotive component , Dendrite structures , Intergranular rupture , Manufacturing process , Metallurgical processing , Scanning electron microscopic , Straightening process , Tempered martensite