Answer
Elgiloy (UNS R30003) is a 'super-alloy' used in the most demanding environments, particularly in oil and gas downhole tools where $H_2 S$, $CO_2$, and high temperatures are present. It offers an exceptional combination of high strength, ductility, and excellent fatigue life. Its resistance to sulfide stress cracking (SSC) is superior to most stainless steels. Processing involves a high degree of cold work followed by an aging heat treatment at approximately $900^{\circ}F$. This results in a material that can operate at temperatures up to $850^{\circ}F$ without significant relaxation. For wave springs, Elgiloy provides the necessary 'springiness' while remaining almost entirely immune to the embrittling effects of the hydrogen-rich fluids found in deep-well drilling.
