Comparison of the Mechanical Properties of Austempered Ductile Cast Iron (ADI) Processed by Conventional and Step-Down Austempering Process

Abstract

An investigation was carried out to examine the influence of step-down austempering process on the mechanical properties of austempered ductile cast iron (ADI). Compact tension and cylindrical tensile specimens were prepared from nodular cast iron as per ASTM standards and were subjected to two different austempering heat treatments; that is, conventional and step-down austempering in the upper bainitic temperature range. The specimens were austempered at four different temperatures; that is, 343, 357, 371, and 385°C. The influence of these austempering processes on the microstructure and the mechanical properties of the material was examined at room temperature and ambient atmosphere. The influence of these austempering processes on the plane strain fracture toughness of the material was also investigated. The present test results indicate no significant difference in the mechanical properties and fracture toughness in ADI processed by conventional as well as step-down austempering process at the same austempering temperature. However, the step-down austempering process has the advantage of lower processing cost compared to the conventional austempering process, without compromising any of the mechanical properties.