AMS 6525 is a sub-specification of Steel HP 9-4-20, which is low-alloy high-strength steel with a high concentration of cobalt and nickel. Available as bar, forging, ring and tubing, AMS 6525 can be used for structural components in aircraft
s such as rocket motor casings, armor plate, pressure vessels, and it can also be used for gears.
AMS 6525 is known to have excellent weldability and hardenability. This specification can be tempered to 400-1100° F (205-595° C) depending on the usage scenario and the desired properties.
The heat treatment is the following:
Annealing – 4 hours at a temperature 1300°F (705°C), followed by air cooling to room temperature. Then, reheat to 1150°F (620°C) for 4-8 hours and air cool again to room temperature. For sub-critical anneal, the second step can be prolonged to 12-24 hours, followed by air cooling.
Normalizing – this process should always be carried out before hardening and tempering. Heat the part to 1650-1750°F (900-955°C) for one hour and then air cool to room temperature.
Hardening – heat the part to 1600°F (845-870°C) for one hour and use the oil quenching method for cooling.
Tempering – carried out at 400-1100°F (205-595°C).
Refrigeration – if austenite is present after hardening, cool to -100°F (-73°C) for 2 hours and then air-warm it to achieve room temperature.