Wear 263 (2007) 663–668 Short communication Effect of specimen preparation on contact fatigue wear resistance of austempered ductile cast iron C. Brunetti, M.V. Leite, G. Pintaude ∗ Postgraduate Program in Mechanical and Materials Engineering, Contact and Surface Laboratory, Federal University of Technology – Paran´ a, Av. Sete de Setembro, 3165 Curitiba/PR, Zip code: 80230-901, Brazil Received 1 September 2006; received in revised form 10 January 2007; accepted 16 January 2007 Available online 23 May 2007 Abstract Austempered ductile iron (ADI) has been tested as a wear resistance material for applications where the applied loads are very high and cyclic, such as gears. This paper analyzed the endurance lifetime of this material in wear testing equipment that applies contact fatigue stresses in a lubricated ball-on-flat system. The tests were performed at 3.0 or 3.7 GPa of maximum Hertz pressure, using ISO 46 lubricant at 85 ◦ C, until spalling occurrence. The effect of specimen preparation was studied for ground or polished specimens. The worn surfaces were characterized by means of an optical and electron microscope and by the difference between unworn and worn surface profiles. It was found that the graphite nodules were exposed at the surface in two ways: cracked and partially exposed. These morphologies were not found in polished specimens, but the wear process in all test conditions produces them. The low endurance lifetime observed in ground specimen was explained based on these defects, which were present before the tests. The slope of Weibull curves was related to the width of the worn track. For polished specimens the slope was smaller than that observed for ground conditions. Thus, any manual process for preparation can be considered as forbidden in order to obtain better results. © 2007 Elsevier B.V. All rights reserved. Keywords: Contact fatigue; Austempered ductile iron; Surface roughness; Endurance lifetime 1. Introduction A mechanical system is usually composed of elements that are in contact and under loading. Wear can take place as a result of this contact after a certain period of time. A particular mode of wear is that caused by contact fatigue, which occurs in com- ponents subjected to cyclic pressures such as gears. This mode of wear is the main cause of failure in these kind of components [1]. During the design of these components the reduction in sever- ity of operational conditions is desired. A way to reduce the contact fatigue wear is the appropriate materials selection. Usu- ally, ultra cleaned and hardened steels are used in components subjected to high contact pressures. Nevertheless, nowadays components such as gears have been made using steel with high level of alloying elements, following heat treatment. Another ∗ Corresponding author. Tel.: +55 41 3310 4660; fax: +55 41 3310 4660. E-mail address: pintaude@utfpr.edu.br (G. Pintaude). possibility is the use of cast irons, especially the austempered ductile iron—ADI. Although the graphite nodules could be act as stress raisers, ADI has shown a satisfactory performance when subjected to contact fatigue wear [2]. The surface roughness has a huge impact on endurance lifetime of components subject to contact fatigue [3]. The austempered ductile iron has been used in some researches [4–6]. This paper analyzes the effect of specimen preparation on endurance lifetime of austempered ductile iron, tested in a lubri- cated ball-on-flat system. 2. Experimental procedure Austempered ductile iron (ADI) was subjected to contact fatigue wear and its chemical composition is presented in Table 1. The bars with 95 mm of diameter and 45 mm of thick- ness were produced through continuous casting process. These bars were austenitized at 910 ◦ C for 1.5 h followed by austem- pering in a salt bath at 290 ◦ C for 2 h. The metallographic characterization was performed by following the ASTM A247 0043-1648/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2007.01.078