Wear 273 (2011) 2–8 Contents lists available at ScienceDirect Wear j o ur nal ho me p age: www.elsevier.com/locate/wear Tribological behaviour of carbide-free bainitic steel under dry rolling/sliding conditions Alejandro Leiro ∗ , Anusha Kankanala, Esa Vuorinen, Braham Prakash Department of Applied Physics and Mechanical Engineering, Luleå University of Technology, 97187 Luleå, Sweden a r t i c l e i n f o Article history: Received 30 September 2010 Received in revised form 18 March 2011 Accepted 29 March 2011 Available online 5 April 2011 Keywords: Rolling–sliding Carbide-free bainite Friction Wear Surface topography a b s t r a c t The dry rolling/sliding wear behaviour of Si alloyed carbide free bainitic steel austempered at different temperatures and sliding distances has been evaluated. 60SiCr7 spring steel samples were austempered in a salt bath maintained at 250, 300 and 350 ◦ C respectively for 1 h. Rolling with 5% sliding wear tests were performed using self mated discs for three different test cycles, namely 6000, 18,000 and 30,000 cycles. The aim was to study the wear performance of the 60SiCr7 steel with a carbide-free microstruc- ture containing different amounts of retained austenite. An in-depth microstructural characterization has been carried out before and after the wear tests in order to link the wear behaviour to the microstruc- ture of each sample. The wear resistance has been expressed by means of the specific wear calculated from the mass loss after the tests. The worn surfaces were analysed by scanning electron microscopy and X-ray diffraction. Microhardness profiles were also obtained in order to analyse strain-hardening effects beneath the contact surfaces. The results indicate that the material with highest hardness—the one austempered at 250 ◦ C—exhibited the lowest wear rate in every case. It was also observed that the hardness increment and thickness of the hardened layer increases with increasing the austempering temperature and number of test cycles. Finally, the results appear to indicate that the initial rough- ness of the samples has no major effect in the wear rate of the samples above 2500 cycles. The higher wear performance of the sample austempered at 250 ◦ C has been attributed to its superior mechanical properties provided by its finer microstructure. It has been evidenced that all samples undergo the TRIP phenomenon since, after wear; no retained austenite could be detected by XRD. © 2011 Elsevier B.V. All rights reserved. 1. Introduction For years the industrial needs for high-strength steels have been met mainly with the use of high alloy steels, especially in tribology applications where the common goal is to obtain surfaces that can withstand large loads without suffering severe damage. The steels used vary widely according to the application. For instance, bearings are commonly manufactured in quenched and tempered 100Cr6 (DIN) steel which has a tempered marten- sitic microstructure and a considerable content of carbides. On the other hand, rail steels, which are subjected to slightly lower con- tact stresses than bearings, are manufactured mainly in pearlitic steel, basically because the cost of making a homogeneous rail in quenched and tempered 100Cr6 steel would be unaccept- able. There have been many attempts in the past to support bainitic steels for their use in the rail industry [1–5]. However, the literature in this field is somewhat contradictory. While a study by Clayton ∗ Corresponding author. Tel.: +46 920493109; fax: +46 920491399. E-mail address: alejandro.leiro@ltu.se (A. Leiro). et al. [1] shows pearlitic steels to be superior to bainitic, another study by Shipway et al. shows the opposite [6]. A possible reason for this could be that conventional bainitic microstructures tend not to be homogeneous. In this study, the tribological behaviour of a relatively new microstructure initially developed in steels by Bhadheshia and Edmonds [7], has been investigated. The main goal has been to provide an increased understanding of the tribological perfor- mance of austempered high-silicon steel in order to contribute to the on-going work of discovering its possible applications. Hence, this research involves the microstructural study of carbide free bainitic steel (also referred to as ausferritic steel) subjected to rolling/sliding wear. These steels, in particular with a car- bide free bainitic microstructure—a combination of lath-like ferrite and high carbon austenite—have several advantages including high-strength, high toughness and ductility depending upon the transformation temperature and time used in their heat treatment [8,9]. Therefore, since these steels present an unusual combination of good mechanical properties and low manufacturing cost, in com- parison with conventional high-strength steels; they may find their use in a wide variety of applications such as automotive, rails and in heavy engineering industries [10]. 0043-1648/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2011.03.025