Monel K500 UNS N05500 2.4375 Nickel Alloy

Introduce

Monel nickel-copper alloy K-500 combines the excellent corrosion resistance characteristic of Monel alloy 400 with the added advantages of greater strength and hardness. The increased properties are obtained by adding aluminum and titanimum to the nickel-copper base, and by heating under controlled conditions so that submicroscopic particles of Ni3 (Ti, Al) are precipitated thoughout the matrix. The thermal processing used to effect precipitation is commonly called age hardening or aging.

Application

Typical applications for Monel Alloy K-500 products are chains and cables, fasteners and springs for marine service; pump and valve components for chemical processing; doctor blades and scrapers for pulp processing in paper production; oil well drill collars and instruments, pump shafts and impellers, non-magnetic housings, safety lifts and valves for oil and gas production; and sensors and other electronic components.

Chemical Composition

Mechanical Properties Nominal Mechanical Property Ranges(a)

Corrosion Resistance

The corrosion resistance of Monel alloy K-500 is subtantially equivalent to that of alloy 400 except that, when in the age-hardened condition, alloy K-500 has a greater tendency toward stress-corrosion cracking in some environments. Monel alloy K-500 has been found to be resistant to a sour-gas environment. After 6 days of continuous immersion in saturated (3500ppm) hydrogen sulfide solutions at acidic and basic pH's (ranging from 1.0 to 11.0), U-bend specimens of age-hardened sheet show no cracking. There was some tightly adherent black scale. Hardness of the specimens ranged from 28 to 40 Rc.

The combination of very low corrosion rates in high-velocity sea water and high strength make alloy K-500 particularly suitable for shafts of centrifugal pumps in marine service. In stagnant or slow-moving sea water, fouling may occur followed by pitting, but this pitting slows down after a fairly rapid initial attack.

Heat Treatment

Annealing is performed both for softening of the matrix after working and for solutioning of the age-hardening phase. Adequate softening may be achieved with temperatures as low as 1400-1600°F, but heating at 1800°F for hot-finished products and 1900°F for cold-drawn products is recommended for optimum response to subsequent age hardening. Grain growth becomes fairly rapid above 1800°F, and if a fine-grained structure is desired heating time should be kept to a minimum at these higher temperatures. For optimum aging response and maximum softness, it is important to obtain an effective water quench from the heating temperature without delay. A dely in quenching or a slow quench can result in partial precipitation of the age-hardening phase and subsequent impairment of the aging response. Addition of about 2% by volume of alcohol to the water will minimize oxidation and facilitate pickling. The following age-hardening procedures are recommended for achievement of maximum properties.

Machining

Heavy machining of alloy K-500 is best accomplished when the material is in the annealed condition or hot-worked and quenched condition. Age-hardened material, however, can be finish-machined to close tolerances and fine finished. The recommended practice, therefore, is to machine slightly oversize, age-harden, then finish to size. During aging, a slight permanent contraction (about 0.0002 in/in) takes place, but little warpage occurs because of the low temperatures and slow cooling rates involved.