MONEL K-500 ALLOY

GENERAL CHARACTERISTICS OF MONEL K-500 ALLOY

This alloy has the corrosion resistance of Monel 400 Alloy together with greater strength and hardness. Aluminum and titanium additions, plus controlled heat treat cycles, are responsible for the added strength of this alloy.

APPLICATIONS

Some typical applications for K-500 alloy are chains and cables, fasteners and springs for marine service; pump and valve parts for chemical processing; doctor blades and scrapers for pulp processing in paper production; oil well drill collars and instruments, pump shafts and impellers, and safety lifts and valves for oil and gas production.

FORGING

Forging of K-500 alloy is carried out between 2100ºF (1150ºC) and 1600ºF (870ºC), with heavier reductions being performed between 2100ºF and 1900ºF (1150 and 1040ºC.) Parts should be quenched after forging from a temperature of 1450ºF (790ºC) minimum, otherwise self-age-hardening will be set up in the forged part, leading to stress and possible cracking.

HEAT TREATMENT

Heat treatment of this alloy may involve solution and process annealing, followed by age hardening. The aluminum and titanium additions are responsible for age hardening in this alloy.

Solution annealing will effect solution of any phases that will later effect the age hardening process. For hot-finished products, solution annealing is carried out at 1800ºF (980ºC) and for cold-finished products at 1900ºF (1040ºC). Time at temperature should be around 30 minutes maximum and cooling would normally be in water.

Process annealing is normally performed at 1400/1600ºF (769/870ºC), preferably for no longer than one hour.

Age hardening is carried out for 16 hours at 1100/1125ºF(595/610ºC), followed by furnace cooling at 15/25ºF per hour to 900ºF (480ºC) for soft material, and for 8 hours for moderately cold-worked material. For fully cold-worked material, the temperature is 980/1000ºF (525/540ºC) for six hours, with furnace cooling as previously.

MACHINABILITY

Heavy machining is best carried out in the annealed or hot-worked and quenched conditions, although better surface finishes may be obtained on age-hardened materials. It is recommended to machine slightly oversize, then age harden, then finish machine.

WELDABILITY

Welding of K-500 alloy is normally carried out using the gas-tungsten-arc method, using a Monel filler metal. Such weldments cannot, however, be age hardened and as such if the weldment strength is critical then filler metal of similar composition to the base metal should be used.