The standard processing window of alloyed ADI materials

Abstract

In present paper the effect of austempering conditions and alloying elements on the microstructure, mechanical properties and processing window of Cu and Cu + Ni alloyed austempered ductile irons has been studied. A new concept of "standard" processing window was suggested as an alternative to the well-known "microstructure" processing window. This concept is based on the ability to achieve mechanical properties required by different standards, namely ASTM, ISO and EN. The results obtained show that alloying with Cu + Ni produced ductile grades of ADI, while alloying with Cu grades of higher strength. The standard processing window depends on the austempering parameters and alloying elements, as well as standard used. The ISO and EN standards give a larger standard processing window compared to the ASTM. It was also shown, that from the engineering point of view, determination of a standard processing window gives great advantage compared to the microstructure processing window where special methods and procedures have to be used. K e y w o r d s : austempered ductile iron, microstructure, mechanical properties, standard processing window

The Effects of Molybdenum and Manganese on the Mechanical Properties of Austempered Ductile Iron

“…Hence, the optimum mechanical properties of ADI material can be achieved upon completion of the first reaction, but before the second reaction starts, i.e. inside the processing window, [7,8].…”

“…A "microstructure" processing window is defined by microstructural features and it is best determined with the criterion proposed by Elliott and Bayati, [3,15]. The beginning of the processing window represents a point when the unreacted austenite volume decreases to 3 % (value obtained using quantitative metallography), while the end of the window is correlated to a decrease of reacted (carbon enriched) retained austenite volume (Vγ) to 90 % of its maximum (where Vγ was determined by Xray diffraction), [8]. On the other hand, "standard" processing window is defined regarding mechanical properties of ADI material produced in microstructure processing window, which have to satisfy ASTM A897M:1990 standard.…”

“…However, there are three ADI standards used currently worldwide: ASTM A897M-06 (first edition from 1990), EN 1564:1997 and ISO 17804:2005, [16]. As those standards vary in some details regarding the number of grades and minimal requirements of ultimate tensile strength and elongation for different grades, the processing window will differ and depend on the standard used, [8].…”

“…Presence of nickel reduces the transformation speed and lowers the temperature of the isothermal reaction. The synergetic effect of Cu and Ni on suppressing the nucleation and early growth of ferrite plates and thus expanding the time for isothermal reaction is especially important, [8,9,10].…”

Influence of the Salt Bath Agitation and Austempering Temperature on the Microstructure of Austempered Ductile Iron

“…Therefore, the optimal mechanical properties of ADI are achieved upon the completion of the first stage of the transformation but before the beginning of the second stage of the transformation, i.e. within the so-called "time window", [7,8].…”