Abstract
Solid-state transformation during heat treatment is of great practical importance because it significantly affects the final structure, properties, and thermal stability of cast components. The present study highlights the issue of structure formation and its effect on the thermal stability of high-quality cast iron, namely, austempered ductile iron (ADI). In this study, experiments were carried out for castings with a 25-mm-walled thickness and under variable heat treatment conditions, i.e., austenitization and austempering within ranges of 850 °C to 925 °C and 250 °C to 380 °C, respectively. The X-ray diffraction (XRD) investigations were carried out within a range of − 260 °C to + 450 °C to study the structure parameters related to the XRD tests, which provided information related to the phase participation, lattice parameters, and stresses in the microstructure as well as with an expansion of the crystal lattice. The results also provide insight into the role of the structure and its homogeneity on the thermal stability of ADI cast iron. The present work also aims to develop strategies to suppress the formation of blocky-shaped austenite in the ADI structure to maintain a homogeneous microstructure and high thermal stability.
Highlights
AUSTEMPERED ductile iron (ADI) is a modern casting alloy with very good mechanical and functional properties
The aforementioned literature data related to structure homogeneity and thermal stability mainly refer to ADI cast iron that is heat treated at different austempering conditions and tested within a range of up to 500 °C, while there are limited data related to the ADI cast iron behavior both attained at different austenitization temperatures and when subjected to subzero working temperatures
The analyzed ADIs contain copper and nickel, which are usually used in ADI cast iron to attain a pearlitic matrix of the base iron and increase the hardenability during the austempering process
Summary
AUSTEMPERED ductile iron (ADI) is a modern casting alloy with very good mechanical and functional properties. The microstructure of ADIs is usually carbide free; this is the result of the high silicon level, which retards the precipitation of the cementite from the austenite This results in the low solid solubility in the cementite crystal structure. The aforementioned literature data related to structure homogeneity and thermal stability mainly refer to ADI cast iron that is heat treated at different austempering conditions and tested within a range of up to 500 °C, while there are limited data related to the ADI cast iron behavior both attained at different austenitization temperatures and when subjected to subzero working temperatures. The test results consider the variable conditions of heat treatment that indicate its key role in shaping the homogeneity and thermal stability of ADI cast iron
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