Effects of graphite nodules on crack growth behaviour of austempered ductile iron
Effects of graphite nodules on crack growth behaviour of austempered ductile iron
Austempered ductile iron (ADI) is a candidate material for camshafts, where however, the early stages of fatigue damage are of major concern during service. A fundamental microstructurally based assessment of the mechanisms of fatigue failure is important. An ADI microstructure austenitised at 900°C and austempered at 390°C has been investigated in detail. Crack initiation and growth behaviour was assessed under three-point bend testing conditions. Primary initiation events occurred exclusively at pores with further micro-crack initiation occurring at decohered graphite nodules in the monotonic plastic zone ahead of the advancing dominant macro-crack tip. Lifetime was however determined by propagation behaviour rather than coalescence events. The changes in the as-cast microstructure generated by this heat treatment have resulted in improved fatigue crack propagation performance due to the reduction in eutectic carbides and the relatively high quantity of retained austenite compared with previous studies, giving rise to greater crack path tortuousity and shielding.
austempered ductile iron, crack growth behaviour, graphite nodules, heat treatment
374-385
Stokes, B.
ba91e45c-12a2-48c3-ab9f-4f10a464334d
Gao, N.
9c1370f7-f4a9-4109-8a3a-4089b3baec21
Reed, P.A.S.
8b79d87f-3288-4167-bcfc-c1de4b93ce17
15 February 2007
Stokes, B.
ba91e45c-12a2-48c3-ab9f-4f10a464334d
Gao, N.
9c1370f7-f4a9-4109-8a3a-4089b3baec21
Reed, P.A.S.
8b79d87f-3288-4167-bcfc-c1de4b93ce17
Stokes, B., Gao, N. and Reed, P.A.S.
(2007)
Effects of graphite nodules on crack growth behaviour of austempered ductile iron.
Materials Science and Engineering: A, 445-446, .
(doi:10.1016/j.msea.2006.09.058).
Abstract
Austempered ductile iron (ADI) is a candidate material for camshafts, where however, the early stages of fatigue damage are of major concern during service. A fundamental microstructurally based assessment of the mechanisms of fatigue failure is important. An ADI microstructure austenitised at 900°C and austempered at 390°C has been investigated in detail. Crack initiation and growth behaviour was assessed under three-point bend testing conditions. Primary initiation events occurred exclusively at pores with further micro-crack initiation occurring at decohered graphite nodules in the monotonic plastic zone ahead of the advancing dominant macro-crack tip. Lifetime was however determined by propagation behaviour rather than coalescence events. The changes in the as-cast microstructure generated by this heat treatment have resulted in improved fatigue crack propagation performance due to the reduction in eutectic carbides and the relatively high quantity of retained austenite compared with previous studies, giving rise to greater crack path tortuousity and shielding.
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Published date: 15 February 2007
Keywords:
austempered ductile iron, crack growth behaviour, graphite nodules, heat treatment
Organisations:
Engineering Mats & Surface Engineerg Gp
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Local EPrints ID: 65052
URI: http://eprints.soton.ac.uk/id/eprint/65052
ISSN: 0921-5093
PURE UUID: 92bdbb47-bc51-4403-9c75-13a9398e6ef7
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Date deposited: 29 Jan 2009
Last modified: 16 Mar 2024 03:21
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Author:
B. Stokes
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