Influence of austenitizing temperature on fracture toughness of a low manganese austempered ductile iron (ADI) with ferritic as cast structure

An investigation was carried out to examine the influence of austenitizing temperature on the resultant microstructure and mechanical properties of an unalloyed and low manganese ADI and with an as cast (solidified) ferritic structure. The investigation also examined the influence of austenitizing t...

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Bibliographic Details
Published in:Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 1999-08, Vol.268 (1), p.15-31
Main Authors: Putatunda, Susil K, Gadicherla, Pavan K
Format: Article
Language:English
Subjects:
Applied sciences
Austenitizing temperature
Carbon content
Cross-disciplinary physics: materials science
rheology
Exact sciences and technology
Fracture toughness
Low manganese
Materials science
Metals. Metallurgy
Microstructure
Other heat and thermomechanical treatments
Physics
Tensile properties
Treatment of materials and its effects on microstructure and properties
Unalloyed
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Summary:An investigation was carried out to examine the influence of austenitizing temperature on the resultant microstructure and mechanical properties of an unalloyed and low manganese ADI and with an as cast (solidified) ferritic structure. The investigation also examined the influence of austenitizing temperature on the fracture toughness of this material. Compact tension and round cylindrical tensile specimens were prepared from a nodular cast iron without any alloying elements (e.g. nickel, molybdenum or copper) and with very low manganese content and with an as cast (solidified) ferritic structure. These were then austenitized at several temperatures ranging from 871°C (1600°F) to 982°C (1800°F) and then austempered at a constant austempering temperature of 302°C (575°F) for a fixed time period of 2 h. Microstructure was characterized through optical microscopy and X-ray diffraction. Tensile properties and plane strain fracture toughness of all these materials were determined and correlated with the microstructure. Fracture surfaces were examined under scanning electron microscope to determine the fracture mode. The results of this investigation indicate that the austenitizing temperature above 982°C (1800°F) has a detrimental effect on the fracture toughness of this material. Both volume fraction of austenite and its carbon content increased with austenitizing temperature. The strain hardening exponent of this material was found to increase with increase in the austenitic carbon content i.e. ( X γ C γ ) 1/2 where X γ is the volume fraction of austenite and C γ is the carbon content of austenite. A Hall–Petch type relationship was found to exist between yield strength and mean free path of dislocation motion, d in ferrite. A model for fracture toughness of ADI has been developed. Present test results indicate good agreement with the model.
ISSN:0921-5093
1873-4936
DOI:10.1016/S0921-5093(99)00120-3