SLIDINGANDABRASIVEWEARBEHAVIOUROF CONTINUOUSLY COOLED CARBIDE FREE BAINITIC STEEL

Abstract

Wear and tear at ambient temperature and at high temperature are one of the principal modes of failure during service for several engineering components including railway wheels, earth moving equipments used in mining sector, brake pads etc. In this work entitled ‘Sliding and abrasive wear behaviour of continuously cooled carbide free bainitic steel’, dry sliding wear behaviour of a continuously cooled carbide-free bainitic (CFB) steel at different tempering conditions as well as at elevated temperature and abrasive wear behaviour of as received CFB steel was studied in detail. The prime objective of this thesis was to study the wear response of material in different conditions, wear mechanisms and the subsequent evolutions of microstructure at surface as well as subsurface region in the through thickness direction by different characterisation techniques. Additionally, a machine learning approach was used to quantify and predict the volume loss in case of sliding wear involving several parameters such as composition, microstructure, hardness, load, sliding distance, temperature etc. Carbide-free bainitic (CFB) steel with outstanding strength and ductility has been extensively used in many applications, such as automobiles, bearings, gears, wheels, and railway frogs. The high-silicon steel comprises of bainitic ferrite laths or plates surrounded by untransformed retained austenite (RA) enriched with carbon. High silicon is added to avoid the formation of carbides. The displacive mechanism takes place during carbide-free bainite transformation from austenite. Retained austenite is a metastable phase, hence its fraction decreases due to its transformation or decomposition with increasing tempering temperature. However, the existence of an optimum fraction of RA shows work hardening ability through transformation induced plasticity effect. This process involves the conversion ofmetastable RA to strain induced martensite under mechanical straining. Layer-by-layer X-ray diffraction method was used to compute phase fraction of retained austenite at different depths of the pin sample in the through thickness direction. It was seen that the wear mechanisms had been changed with the change in tempering conditions during dry sliding wear. A good amount of hardness increment was seen below the worn surface indicating high work hardening nature of the material.