Abstract
The aim of this paper is to compare the microstructure, mechanical and fatigue properties of three types of the nodular cast irons - unalloyed nodular cast iron, nodular cast iron alloyed by Si and Mo and nodular cast iron alloyed by Si and Cu. For all the types, microstructure, mechanical properties and fatigue properties were investigated. Microstructure of the specimens was evaluated according to STN EN ISO 945 and by automatic image analysis. The image analysis system NIS Elements, interfaced with the light microscope, was used for the evaluation of the shape factor, equivalent diameter of graphite, count of graphitic nodules and content of ferrite. The mechanical properties were evaluated by the tensile test, impact bending test and Brinell hardness test. Fatigue tests were realised at sinusoidal cyclic push-pull loading (stress ratio R = -1) at ambient temperature (T = 20 ± 5 °C). They were carried out in the high cycle fatigue region (from 105 to 107 cycles) at frequency f ≈ 75 Hz using the fatigue experimental machine Zwick/Roell Amsler 150HFP 5100. The relationship between the amplitude of stress σa and the number of cycles to failure N, as well as the fatigue strengths, were determined.
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