About 9310|Nickel-chromium-molybdenum case-hardening steel. The premium gear steel for aerospace and high-performance applications. Carburizes to a deeper, more uniform case than
8620 with better core toughness after heat treatment. Used in aircraft transmission gears, helicopter main rotor gears, and any gear set where failure means lives at risk. More expensive than 8620 and requires more precise heat treatment. Machines well in the annealed condition. Compare to 8620 (cheaper, adequate for most industrial gears) and 4320 (intermediate performance between 8620 and 9310).
