Standing contact fatigue analysis of steels with different microstructures

High performance steels has been studied in this master thesis. The main objective was to understand the contact fatigue resistance of one silicon containing steel which can be treated in order to give it a carbide free bainitic microstructure. Different microstructures of the steels were produced by austenitizing followed by different cooling cycles as austempering processes with which microstructures with high strength, good ductility, high toughness and excellent wear resistance can be achieved. The work is divided into three-main parts. The first part treats the production of different micro structure as austenitic-ferritic structure, fully pearlitic, fully martensitic, quenched & tempered and lower bainitic structure respectively, including metallographic observations. The second part treats the special Standing Contact Fatigue (SCF) analysis used in the work, which consists of cyclic loading of a hard ball in contact with the flat surface of the specimen, which is meant to simulate asperity contact in surface contact fatigue analysis. The third part deals with the characterization and analysis of the results obtained for the ausferritic and the other microstructure in the work. The experimental results have shown that the ausferritic structure has a very good combination of material properties like good contact fatigue resistance, high strength, ductility and toughness properties. The microstructure before and after the tests were analyzed with the help of Optical microscopy, SEM microscopy, XRD analysis and additional analysis was performed by micro hardness measurements.Validerat; 20101217 (root