Discuss the role of cryogenic tempering in the production of carbon steel wave springs for industrial pumps.

While not standard for all carbon steels, cryogenic tempering (sub-zero treatment at $-300^{\circ}F$) is used for high-carbon alloys like SAE 1070 to ensure complete transformation of retained austenite to martensite. For wave springs used in industrial pumps that may experience thermal cycling, retained austenite is problematic because it is unstable and can transform into martensite over time or under stress, causing dimensional growth and changes in the spring rate. By implementing a cryogenic cycle following the primary quench, the microstructure is stabilized. This results in improved wear resistance and greater dimensional stability, ensuring that the preload on pump seals remains constant over the life of the component.