Alloy K-500
QQ-N-286 Rev E¹ and QQ-N-286 Rev G²
Description:
Alloy K-500, commonly referred to as “K-MONEL®”, is a precipitation hardenable, nickel-copper alloy. It has similar corrosion resistance to that of alloy 400, with the additional advantage of greater strength and hardness. The additions of aluminum and titanium to the nickel-copper base allow for subsequent heat treat that increases the mechanical properties. Alloy K-500 also has low magnetic permeability and strong non-magnetic characteristics over a wide range of temperatures, including subzero.
Industries & Applications
Alloy K-500 is frequently used in the marine, chemical processing, oil and gas, pulp and paper, pharmaceutical, food processing and electronic industries. End use applications for alloy K-500 include fasteners, springs, chains, pump and valve components, drill collars, doctor blades, scrapers, mixing shafts, impellers, sensors, electrical components and other highly corrosive applications where strength and hardness are important.
Resistance to Corrosion:
The corrosion resistance of alloy K-500 is similar to alloy 400. However, when in the age-hardened condition, alloy K-500 can experience stress corrosion cracking in certain environments. Resistance to hydrogen sulfide makes alloy K-500 useful in sour gas environments, making it an ideal choice for applications in the oil patch. Low corrosion rates in seawater make alloy K-500 optimal for use in the marine industry. Pitting may occur in stagnant or low velocity seawaters, but the rate of pitting eventually slows following the initial incursion.
Fabrication and Heat Treat:
Alloy K-500 can be fabricated by using standard commercial procedures. Hot working of alloy K-500 should be performed at temperatures between 1600°F and 2100°F, but care should be taken to avoid prolonged soaking time at the higher temperatures. Material should be water quenched from a temperature no lower than 1450°F after hot working. Cold forming in the annealed condition can also be performed using standard methods, although may require considerable force to form. Machining of alloy K-500 is easiest in the annealed condition. Therefore, the best practice is to machine oversize, age harden, then machine finish to size. Contraction can occur during aging and 0.0002 in/in should be accounted for in size prior to aging.
Welding alloy K-500 is best achieved by gas tungsten arc welding (GTAW). Filler metal AWS A5.14 ERNiCu-7 is typically used for joining. Weldments using this filler metal will not have the strength of the base metal because it cannot be age-hardened. For welds that require strength, AWS 5.14 ERNiFeCR-2 filler metal can be used.
Solution annealing of the alloy should be performed prior to aging to dissolve phases in the microstructure that may have formed during previous processing. If the material is hot finished, then the anneal temperature should be 1800°F. If the material is cold worked, then the temperature should be 1900°F. Time at temperature should be kept at a minimum to avoid excessive grain growth. Quenching in water immediately after solution annealing will avoid any partial precipitation of age hardening constituents. Age hardening of annealed (soft) material to obtain maximum properties should be performed as follows: heat material between 1100°F & 1125°F and hold temperature for 16 hours followed by furnace cooling at a rate of 15°F to 25°F per hour until the material reached a temperature of 900°F. Once the material reached 900°F, cooling can continue via furnace cooling, air cooling or quenching.
Common Trade Names:
MONEL® alloy K-500
MONEL® is a registered trademark of the Special Metals Corporation group of companies.
