HP9 – 4 – 30 Alloy Steel

General characteristics of HP9 – 4 – 30 Alloy Steel

This is a low-alloy, high-strength steel with high nickel and cobalt additions to promote toughness. The alloy has good hardenability and weldability and excellent fracture toughness. It is typically used in the 220/240 ksi (1520/1655Mpa) tensile strength range. For optimum cleanliness, the alloy is produced by the consumable electrode vacuum arc re-melting process.

Applications

Aircraft structural components, rocket motor cases, armor plate, pressure vessels, gears.

Forging HP9 – 4 – 30 Alloy Steel

For ingot breakdown heat to 2200ºF (1205ºC) and to 1900ºF (1040ºC) for finish forging. Do not forge below 1700ºF (925ºC). Parts may be transferred to an annealing furnace after forging – see heat treatment.

Heat Treatment

Annealing

1250ºF (675ºC) for 4 hours, air cool to room temp, plus 1150ºF (620ºC) for 4-8 hours and air cool. Alternative is a sub-critical anneal at 1150ºF (620ºC) for 12-24 hours and air cool.

Normalizing

Would normally be carried out prior to hardening and tempering, at 1600-1700ºF (870-925ºC) for 1 hour followed by air cooling.

Hardening

Austenitize at 1525-1575ºF (830-850ºC) for 1 hour and oil quench.

Tempering

At 400-1100ºF (205-595ºC) depending upon desired properties. Double tempering is recommended.

Refrigeration

This treatment would be carried out to remove any retained austenite, and might be performed at –100ºF (-73ºC) for 2 hours followed by air warm back to room temperature.

Machinability

Those practices used for machining 4340 steel at similar hardness levels are recommended for HP 9-4-30 grade.

Weldability

Helium-shielded TIG welding is the preferred method, using HP 9-4-30 filler wire.