<div class="htmlview paragraph">Recent research on carburized steels has demonstrated a correlation between the toughness properties of a carburized steel and the fatigue performance in combined load testing (high-cycle fatigue plus overload). The data presented suggest that, for applications where loads above the fatigue limit are encountered, both processing and alloying must be considered. Results from a number of investigations are reviewed to illustrate that high-cycle fatigue properties are controlled primarily by the processing, whereas toughness characteristics, such as resistance to random cyclic loading, are a result of the alloying.</div>