MICROSTRUCTURAL DEVELOPMENT DURING DRY SLIDING WEAR OF CARBIDE FREE BAINITIC STEEL

Abstract

In this work entitled ‘Microstructural Development During Dry Sliding Wear of Carbide Free Bainitic Steel’, the dry sliding wear behaviour of a novel continuously cooled carbide free bainitic steel was studied in detail. This work comprises of detail surface and subsurface characterization, in the through thickness direction of samples subjected to varying conditions of load and sliding distance, to study their wear response, wear mechanisms and the subsequent evolutions of microstructure. It was seen that the wear mechanism was changing with the change in applied load. A good amount of hardness increment was seen beneath the worn surface indicating very high work hardening nature of the material. A sharp plastic deformation was also seen in the deformed tribologically transformed region. In carbide free bainitic steel, the presence of an optimum fraction of retained austenite show work hardening ability by showing transformation induced plasticity effect. This process involves the transformation of metastable retained austenite to strain induced martensite under mechanical straining. However, retained austenite regions can have different level of stability against any strain induced transformation based on its chemical composition, morphology and size. Predicting the extent of transformations of those RA regions thus depend on many aspects. However proper quantification of strain after wear is very difficult because no direct measurement of by extensometer is not possible. Thus, an effort has been put into the current work to develop a theoretical model to understand the stability aspect of retained austenite under shear type of deformation during dry sliding wear in a pin-on-disc tribometer. Effective post processing technique has been designed to quantify strain at different depths from the worn surfaces of samples after subjected to varying conditions of wear. For validation of model specially designed layer by layer X-ray diffraction scheme was used to quantify phase fraction of retained austenite at different layers of the pin sample in the through thickness direction. Theoretical model showed very promising agreement with the experimentally obtained results.