Dependence of fracture toughness of austempered ductile iron on austempering temperature

Abstract

Ductile cast iron samples were austenitized at 927 ЊC and subsequently austempered for 30 minutes, 1 hour, and 2 hours at 260 ЊC, 288 ЊC, 316 ЊC, 343 ЊC, 371 ЊC, and 399 ЊC. These were subjected to a plane strain fracture toughness test. Fracture toughness was found to initially increase with austempering temperature, reach a maximum, and then decrease with further rise in temperature. The results of the fracture toughness study and fractographic examination were correlated with microstructural features such as bainite morphology, the volume fraction of retained austenite, and its carbon content. It was found that fracture toughness was maximized when the microstructure consisted of lower bainite with about 30 vol pct retained austenite containing more than 1.8 wt pct carbon. A theoretical model was developed, which could explain the observed variation in fracture toughness with austempering temperature in terms of microstructural features such as the width of the ferrite blades and retained austenite content. A plot of against y (X ␥ C ␥ ) 1/2 resulted in a 2 K IC straight line, as predicted by the model.

The effect of copper additions to the mechanical properties of austempered ductile iron (ADI)

“…4) consist of graphite nodules in an ausferrite structure, comparable with other workers material [19,20]. When compared with the plain ADI, the copper addition does not cause any observable change to the austempered microstructure.…”

Investigation on grinding wear behaviour of austempered ductile iron as media material during comminution of iron ore in ball mills

“…The best fracture toughness is obtained when retained austenite content is about 30 volume percent and its carbon content is more than 1.8 weight percent [17]. In the present study the values of retained austenite and carbon content of retained austenite is almost similar to the above mentioned values and hence the toughness and wear resistance of ADI.…”

Microstructures and Mechanical Properties of a Wear-Resistant Alloyed Ductile Iron Austempered at Various Temperatures

“…Carbon finds its way into the surrounding austenite from regions transforming to ferrite due to diffusion rates as well as kinetics of ferrite formation. [32,33] At lower austempering temperature, little carbon diffuses into the austenite because of lower diffusion rate and fast kinetics of ferrite formation. The lowered rate of carbon diffusion leads to the reduction of carbon-rich and stable austenite.…”