-77- Chapter 7 Alan Vaško 1 , Mária Chalupová 2 , Robert Ulewicz 3 DEPENDANCE BETWEEN CHARGE COMPOSITION AND FATIGUE PROPERTIES OF NODULAR CAST IRONS Abstract: The contribution deals with comparison of microstructure and fatigue properties of synthetic nodular cast irons. The basic charge of experimental meltages was formed by the different ratio of pig iron and steel scrap. The chemical composition of individual meltages was regulated alternatively by carburizer and ferrosilicon (FeSi) or metallurgical silicon carbide (SiC). The fatigue tests were run at high-frequency sinusoidal cyclic push-pull loading (frequency f  20 kHz, load ratio R = –1, temperature T = 20  5 °C) using the ultrasonic testing equipment KAUP-ZU. The paper shows the influence of charge composition on microstructure, fatigue properties and micromechanisms of failure. Key words: nodular cast iron, charge composition, microstructure, fatigue test, microfractography 7.1. Introduction Nodular cast iron is a group of cast construction materials with a wide application in engineering practice. It combines high tensile strength and plasticity with high fatigue strength. Nodular cast iron can be produced according to the classical or synthetic casting procedure, which is more economical because cheaper steel scrap is added to the charge instead of more expensive pig iron (KONEČNÁ R. 2008). The tran- 1 Ing. PhD., University of Žilina, Faculty of Mechanical Engineering, Department of Materials Engineering, e-mail: alan.vasko@fstroj.uniza.sk 2 Ing., University of Žilina, Faculty of Mechanical Engineering, Department of Materials Engineering 3 prof. P.Cz. dr hab. inż, Czestochowa University of Technology, Faculty of Management, Institute of Production Engineering