Modelling of microstructural effects in the fatigue of austempered ductile iron

Effects of graphite nodules on crack growth behaviour of austempered ductile iron

“…The toughness ranking was 950/400>850/400>950/250>850/250 indicating that the lower temperature austemper produced a higher hardness, but lower toughness material and the higher temperature austemper generally improved toughness and damage tolerance, but with lower strength/hardness. It was concluded that the coarser lath size and large amounts of retained austenite promoted by the 400°C austemper promote a more tortuous crack path, and intrinsic crack shielding [18]. We have also shown that a carbide initiated failure mechanism is dominant for another ADI alloy austenitised at 800°C and austempered at 260°C due to significant numbers of brittle carbides remaining from insufficient austenitising [19].…”

“…We have also shown that a carbide initiated failure mechanism is dominant for another ADI alloy austenitised at 800°C and austempered at 260°C due to significant numbers of brittle carbides remaining from insufficient austenitising [19]. Obviously the combination of alloying composition together with the austenitisation and austempering heat treatments, determines the microstructure produced and subsequently the dominant fatigue failure mechanisms [18,20,21]. Linking microstructural models (based on alloy composition and heat treatment parameters) to micromechanistically based models of relevant mechanical properties will provide a much better informed route to alloy optimisation.…”

“…Previously we have conducted work on an ADI alloy with four different heat treatment conditions, which consisted of austenitising at 950 or 850°C for 1 h followed by austempering at 250 or 400°C for 2 h, denoted: (950/400, 850/400, 950/250, 850/250) [18]. These results have demonstrated that ADI alloys austempered at 400°C gave better fatigue crack initiation and growth resistance than those austempered at 250°C at similar stress ranges.…”

Fracture toughness characterization of austempered ductile iron produced using both conventional and two-step austempering processes

“…This structure results in an exceptional combination of strength, ductility, wear resistance [2,3] and impact resistance [4,5]. The austempering heat treatment converts ductile iron into ADI, bringing about excellent strength, toughness and fatigue characteristics [6][7][8][9][10][11][12][13][14][15]. This heat treatment cycle involves two steps.…”

Effects of carbides on fatigue characteristics of austempered ductile iron

“…Building upon previous work, [5,6,7] this research further investigates the microstructure and related failure mechanisms of a specific ADI by conducting short and long fatigue crack testing, hardness testing, and extensive image analysis. The objective of this research is to explicitly quantify the effects of local microstructural features on fatigue failure in this ADI material.…”