Official Answer
Answer
After coiling, SAE 1070 carbon steel spiral rings are 'oil-quenched and tempered' or 'austempered' to achieve a hardness typically between 45-52 HRC. The tempering process (heating to $700-900^{\circ}F$) is critical to transform the brittle martensite into tempered martensite, which provides the necessary toughness and ductility. Without proper tempering, the rings would snap during installation when expanded over a shaft. The final hardness must be tightly controlled: too high leads to brittleness, while too low leads to 'set' and loss of retention force.
