Answer
For high-carbon steel rings (SAE 1070-1090), 'Austempering' involves quenching the ring from the austenitic temperature into a salt bath held at $550-750^{\circ}F$ to produce a Bainitic structure. This results in superior toughness, higher ductility, and minimal distortion, which is critical for maintaining the tight 'flatness' tolerances of spiral rings. 'Martempering' (or Marquenching) involves quenching to just above the martensite start ($M_s$) temperature, then air cooling to form Martensite, followed by tempering. While Martempering provides higher hardness, Austempering is generally preferred for spiral rings because it significantly reduces the risk of 'quench cracking' and yields a ring that can withstand greater 'winding' stresses during installation without permanent deformation.
