Effect of Austempering Time and Temperature on Structure and Properties of Unalloyed Ductile Iron

Abstract

Austempered ductile irons are characterized by a combination of high tensile and fatigue strength, ductility and wear resistance combined with impact toughness. However, the use of these irons has been limited due to lack of metallurgical knowledge available to show how the excellent properties of austempered irons can be obtained consistently in production; and identifying and controlling the heat treatment parameters to obtain optimum properties. There is also insufficient data available to the design engineers identifying the full engineering properties of bainitic irons. Using indigenously available raw materials, a detailed investigation was carried out with unalloyed ductile iron to produce austempered ductile iron. It was found possible to produce austempered unalloyed iron with consistent properties by suitable austenitising and austempering treatments. The structure and properties of these irons were studied and correlated with the process parameters such as austempering temperature and time and compared with the as-cast structure and properties.