Reciprocating Sliding Wear Behavior of Newly Developed Bainitic Steels

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INTRODUCTION

THERE have been considerable efforts to find better substitutes for the rail materials for improving the load carrying ability and durability.[1–3] At present, the material used for the rail application is eutectoid pearlitic steel. With progressive increase in axle load and speed, degradation of materials by fatigue, brittle failure, plastic deformation, excessive wear, etc., is rapidly increasing. There has also been a continuous need for the attainment of higher strength in rail materials. Some of the usual techniques, which would increase the strength, are by increasing carbon content of the steel, and alloying addition to achieve solid solution strengthening, or by appropriate heat treatment to achieve finer pearlitic microstructures.[4] Unfortunately, the increase in strength by most of the routes is accompanied with decrease in toughness. Bainitic steel, which has already been established as better performer in terms of mechanical properties, is considered to be a good option except for its wear performance. Bainite, as an alternative for the conventional pearlitic rail steels, has been suggested 35 years ago by Morton et al.,[5] and many follow-up studies have been performed. Few studies show that bainitic steels are better or comparable wear resistant[6–8] than the pearlitic one, while others have shown the pearlitic steels to give better response against wear.[9–13] Hence, earlier investigations are scattered, and there is greater scope to explore the research on bainitic microstructure and its applicability in rail material. In majority of the cases,[6,7,14,15] where S. SHARMA, Research Fellow, S. SANGAL, Professor, and K. MONDAL, Associate Professor, are with the Department of Materials Science and Engineering, Indian Institute of Technology, Kanpur, Uttar Pradesh, India 208016. Contact e-mails: [email protected], [email protected] Manuscript submitted January 1, 2014. Article published online August 20, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A

bainitic steels have shown better wear performance, it can be observed that the researchers have designed the steels to give carbide-free morphology. The carbide-free bainitic steels have invariably shown better mechanical and wear properties than the pearlitic steel possessing same composition.[6,7,16,17] However, the bainitic steels with higher carbon percentage as compared to carbide-free bainitic steels are known to possess better mechanical properties, which can be achieved by suitable tailoring of heat treatment conditions. But on the other hand, these steels have shown poor wear resistance under ambient conditions.[18,19] This indicates that depending on the composition of the steel and the type of bainite formed, wear resistance of bainitic steel is better in some cases[20,21] and poor in others[7,22,23] in comparison to that of pearlitic steel. Bainitic steel has been made operational as rail steel at many places.[5,24] But under the severe operating conditions, these steels fail to give good wear resistance.[5,24] The viability