SAE AMS 6488H:2008

This specification covers a low-alloy steel in the form of bars,
forgings, and forging stock.

These products have been used typically for parts requiring a
steel capable of through-hardening to a minimum hardness of 50 HRC
in section thicknesses up to 12 inches (305 mm) with relatively
high levels of strength, fatigue resistance, ductility, and thermal
stability in service from -100 degrees to +1000 degrees F (-73
degrees to +538 degrees C), but usage is not limited to such
applications.

Certain design and processing procedures may cause these
products to become susceptible to stress-corrosion cracking after
heat treatment; SAE ARP 1110 recommends practices to minimize such
conditions.