Answer
SAE 1070 carbon steel is the standard for general-purpose retaining rings due to its high carbon content and cost-effectiveness, providing a yield strength around $160$-$200$ ksi after oil quenching and tempering. However, SAE 1070 becomes brittle at cryogenic temperatures and loses strength rapidly above $250^{\circ}F$. In contrast, Inconel X-750 (AMS 5699) is a nickel-chromium alloy that remains ductile at temperatures as low as $-300^{\circ}F$ and maintains mechanical integrity up to $1300^{\circ}F$. Inconel X-750's precipitation hardening involves the formation of $\gamma'$ phase ($Ni_3(Al, Ti)$), which provides excellent creep-rupture strength. For subsea or aerospace applications where corrosion and temperature extremes coincide, Inconel X-750 is the mandatory selection despite the significant cost premium over carbon steel.
