What is K500?
Description:
Alloy K-500, commonly referred to as "K-MONEL", is a precipitation-hardened nickel-copper alloy. It has corrosion resistance similar to Alloy 400 with increased strength and hardness. The addition of aluminum and titanium to the nickel-copper base allows for subsequent heat treatment to improve mechanical properties. Alloy K-500 also has low magnetic permeability and strong non-magnetic properties over a wide temperature range, including below zero.
Industries and Applications
Alloy K-500 is frequently used in the marine, chemical processing, oil and gas, pulp and paper, pharmaceutical, food processing, and electronics industries. End uses for Alloy K-500 include fasteners, springs, chains, pump and valve components, drill collars, scrapers, scrapers, agitator shafts, impellers, sensors, electrical components, and other highly corrosive applications where strength and hardness are important.
Corrosion Resistance:
The corrosion resistance of K-500 alloy is similar to that of Alloy 400. However, in the age-hardened condition, K-500 alloy may be subject to stress corrosion cracking in certain environments. The hydrogen sulfide resistance makes K-500 alloy very useful in sour gas environments, making it ideal for oilfield applications. The low corrosion rate in seawater makes K-500 alloy an excellent choice for the marine industry. Pitting may occur in stagnant or low velocity seawater, but the pitting rate will eventually slow after the initial intrusion.
Fabrication and Heat Treatment:
K-500 alloy can be fabricated using standard commercial procedures. Hot working of K-500 alloy should be performed at temperatures between 1600°F and 2100°F, but care should be taken to avoid prolonged immersion at higher temperatures. After hot working, the material should be water quenched from a temperature not less than 1450°F. Cold forming in the annealed condition can also be performed using standard methods, although considerable force may be required to form. K-500 alloy is easiest to machine in the annealed condition. Therefore, best practice is to machine oversize, age harden, and then machine to size. Shrinkage may occur during aging, and 0.0002 inch/inch of size should be considered before aging.
Welding K-500 alloy is best accomplished by gas tungsten arc welding (GTAW). The filler metal AWS A5.14 ERNiCu-7 is typically used for the joint. Welds made with this filler metal will not have the strength of the parent metal because it cannot be age hardened. For welds where strength is desired, AWS 5.14 ERNiFeCR-2 filler metal may be used.
The alloy should be solution annealed prior to aging to dissolve microstructural phases that may have formed during previous processing. If the material was hot worked, the annealing temperature should be 1800°F. If the material was cold worked, the temperature should be 1900°F. The time at temperature should be minimized to avoid excessive grain growth. Quenching in water immediately after solution annealing avoids any precipitation of the age-hardening constituents. Maximum properties are obtained by age hardening annealed (soft) material by heating the material to between 1100°F and 1125°F and holding that temperature for 16 hours, then cooling in a furnace at a rate of 15°F to 25°F per hour until the material reaches a temperature of 900°F. Once the material reaches 900°F, cooling may be continued by furnace cooling, air cooling, or quenching.
