V předložené práci jsou uvedeny výsledky výzkumu zaméřeného na vysokocyklové únavové vlastnosti litin s kuličkovým grafitem sbainitickou strukturou matrice. Únavové vlastnosti jsou hodnoceny na základě stanovení Wöhlerových křivek a meze úavy. Zvláštní pzornost je věnována vlivu asymetrie zátěžného cyklu na hodnoty meze únavy. Pro studovaný materiál byl stanoven Smithůdv a Haighův diagram.
Austempered ductile iron (ADI) is usually obtained by isothermal heat treatment. Owing to its excellent mechanical as well as technological properties, ADI belongs among prospective structural materials. Recently it is applied also to castings for dynamically loaded machine details, e.g. gear and traversing wheels, crankshafts of motor-cars, vans and trucks, swivel pins, rail brakes and pressure pipes in oil industry [1]. Generally said, ADI castings are applied (i) as a substitution of details made of steel (forged pieces, workpieces or weldments), (ii) instead of the castings made of nodular cast iron with lower level of strength properties to increase its loading capacity and/or its service life, (iii) for the details designed specially for ADI application. Microstructure and mechanical properties of ADI can be substantially influenced by the condition of heat treatment. While the austenitization conditions play only marginal role, the conditions of isothermal transformation, i.e. transformation temperature and the dwell at it, influence the resulting structure of ADI and consequently its mechanical properties very substantially [2-6]. Present paper is devoted to the study how the dwell of isothermal transformation in the range of 2 minutes to 9 hours influences the structure as well as the static and fatigue properties of unalloyed ADI transformed at temperature of 380 °C.