Heat treating the ductile cast iron produced austempered ductile iron (ADI), which has outstanding mechanical properties that can be varied over a wide range by varying the heat treatment parameters. In the present work a series of test were conducted and the effects of austempering temperature and times onto the material properties was investigated. The machinability of ADI was evaluated by comparing tool life, tool wear rate, cutting forces, and surface finish produced on a job as general criteria. Machinability tests were carried out following ISO 3685: 1993 (E) standard "Tool Life Testing with Single Point Turning Tools". The cutting force data used in the analyses were gathered by a tool breakage detection system that detects the variations of the cutting forces measured by a three-dimensional force dynamometer. Six pairs of ductile iron specimens, austempered at 300, 350 and 400 degrees C for 1 and 2 h were tested. The cutting tools used in the tests were coated carbide inserts, ISO SNMG 120408 (K10), clamped on tool holders CSBNR 2525 M12. No cutting fluid was used during the turning operations. During the experiments cutting forces, flank wear and surface roughness values were measured throughout the tool life and the machining performance of ADI having different structures were compared. (c) 2005 Elsevier B.V. All rights reserved.