Evaluation of potential of high Si high C steel nanostructured bainite for wear and fatigue applications

The present study is concerned with the potential of high carbon, high silicon steel grades isothermally transformed to bainite at low temperature (<300°C). The first part gives an overview of the design principles, allowing very high strength and ductility to be achieved while minimising transformation duration. Wear and fatigue properties are then investigated for over 10 variants of such materials, manufactured in the laboratory or industrially. The results are discussed against published data. Tensile strengths above 2 GPa are routinely achieved, with, in one case, an exceptional and unprecedented total elongation of over 20. Bainite plate thickness and retained austenite content are shown to be important factors in controlling the yield strength, though additional, non-negligible parameters remain to be quantified. Rolling–sliding wear performances are found to be exceptional, with as little as 1 of the specific wear rate of conventional 100Cr6 isothermally transformed to bainite. It is suggested that this results from the decomposition of retained austenite in the worn layer, which considerably increases hardness and presumably introduces compressive residual stresses. Fatigue performance was slightly improved over 100Cr6 for one of the two industrially produced materials but significantly lower otherwise. Factors controlling fatigue resistance require further investigations.