Influence of heat treatments on microstructure and toughness of austempered ductile iron
- 1 March 1992
- journal article
- research article
- Published by Maney Publishing in Materials Science and Technology
- Vol. 8 (3), 263-274
- https://doi.org/10.1179/026708392790170568
Abstract
High silicon content in nodular cast iron leads to a large amount of retained austenite (γ) during isothermal transformation in the bainitic zone by inhibiting the precipitation of carbides. The presence of γ phase results in high toughness, with an optimum fracture toughness KIc of about 85 MN m−3/2 for a 0·2% proof stress of 1000 MN m−2 being observed at 30% retained austenite. The presence of martensite after transformation for short times and of coarse carbides after transformation for long times greatly reduces the toughness. For lower bainite having austenite volume fractions less than 30%, optimum fracture toughness is obtained when the fracture is predominantly transgranular ductile. For austenite volume fractions greater than 30% in the upper bainite region, γ⇛α′ (martensite) transformation induced plasticity occurs, leading to superior toughness compared with conventional cast irons. In this case the fracture, although predominantly ductile, also contains some intergranular zones due to the transformation of austenite to martensite in the plastic zone ahead of the crack, and the strain hardening exponent for the tensile tests increases with strain, also indicating strain induced transformation of austenite to martensite. MST/1537Keywords
This publication has 14 references indexed in Scilit:
- FRACTURE TOUGHNESS OF BAINITIC NODULAR CAST IRONFatigue & Fracture of Engineering Materials & Structures, 1989
- Development of austempered ductile iron (ADI) for automobile crankshaftsJournal of Heat Treating, 1987
- Embrittlement of austempered nodular irons: Grain boundary phosphorus enrichment resulting from precipitate decompositionMetallurgical Transactions A, 1985
- The effects of metallurgical process variables on the properties of austempered ductile ironsJournal of Heat Treating, 1984
- Optimization of Fe/Cr/C base structural Steels for improved strength and toughnessMetallurgical Transactions A, 1982
- The Bainite Reaction in Fe-Si-C Alloys: The Secondary StageMetallurgical Transactions A, 1982
- The Bainite reaction in Fe-Si-C Alloys: The primary stageMetallurgical Transactions A, 1982
- The lower bainite transformation and the significance of carbide precipitationActa Metallurgica, 1980
- Structure-property relations and the design of Fe-4Cr-C base structural steels for high strength and toughnessMetallurgical Transactions A, 1980
- Theory for determining K Ic from small, non-LEFM specimens, supported by experiments on aluminumInternational Journal of Fracture, 1979