Type Analysis | Description | Application | Corrosion Resistance
Physical Properties | Mechanical Properties | Workability

Type Analysis

Description

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 alloy K-500 are pump shafts and impellers; doctor blades and scrapers; oil-well drill collars and instruments; electronic components; springs; and valve trim.

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.

Physical Properties

Density, lb/cu in.......................................................................... 0.3054
              gram/cc............................................................................ 8.434
Melting Range, °F............................................................... 2400-2460
Modulus of Elasticity, 10(6) psi, Tension..................................... 26.0
                                                     Torsion....................................... 9.5
Poisson's Ration............................................................................ 0.32

Thermal Properties

(a) Material was in the annealed condition prior to test.
(b) Electrical resistivity is markedly influence by thermal history because of the age-hardening characteristics of the alloy. The data represent values measured on decreasing temperature on material in an equivalent to annealed condition with a small amount of age hardening.
(c) Resistivity of sample from this test at room temperature: 355.5 ohm/circ mil/ft.
* Extrapolated.

Magnetic Characteristics

A useful characteristic of the alloy is that it is virtually nonmagnetic, even at quite low temperatures (see table). It is possible, however, to develop a magnetic layer on the surface of the material during processing. Aluminum and copper may be selectively oxidized during heating, leaving a magnetic nickel-rich film on the outside of the piece. The effect is particularly noticeable on thin wire or strip where there is a high ratio of surface to weight. The magnetic film can be removed by pickling or bright dipping in acid, and the nonmagnetic properties of the material will be restored.
The combination of low magnetic permeability, high strength, and good corrosion resistance has been used to advantage in a number of applications, notably oil-well surveying equipment and electronic components.

Mechanical Properties

Nominal Mechanical Property Ranges(a)

(a) The ranges shown are composites for various product sizes and therefore ar not suitable for specification purposes.
(b) Nominal properties for material age-hardened to produce maximum properties.

Workability

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.

• 1.Soft material (140-180 Brinell, 75-90 RB). Hold for 16 hrs at 1100 to 1125°F followed by furnace cooling at the rate of 15 to 25°F per hr to 900°F. Cooling from 900°F to room tempertature may be carried out by furnace or air cooling, or by quenching, without regard for cooling rate. This procedure is suitable for as-forged and quenced or annealing forgings, for annealed or hot-rolled rods and large cold-drawn rods (over 1-1/2" diameter) and for soft -temper wire and strip.

• 2. Moderately cold-worked material (175-250 Brinell, 8-25 RB). Hold for 8 hrs or longer at 1100 to 1125°F, followed by cooling to 900°F at a rate not to exceed 15 to 25°F per hr. Higher hardnesses can be obtained by holding for as long as 16 hrs at temperature, particularly if the material has been cold-worked only slightly. As a general rule, material with an initial hardness of 175-200 Brinell should be held the full 16 hrs. Material close to the top figure of 250 Brinell (25Rc) should attain full hardness in 8 hrs. These procedures are applicable to cold-drawn rods, haft-hard strip, cold-upset pieces and intermediate-temper wire.

• 3. Fully cold-worked material (260-325 Brinell, 25-35 Rc). Hold for 6 hrs or longer at 980 to 1000°F followed by cooling to 900°F at a rate not exceeding 15 to 25°F per hour. In some instances slightly higher hardnesses may be obtained (particularly with material near the lower end of the hardness range) by holding 8 to 10 hrs at temperature. This procedure is suitable for spring-temper strip, spring wire or heavily cold-worked pieces such as small, cold-formed balls.
  NOTE: Cooling may be done in steps of 100°F, holding the furnace 4 to 6 hrs at each step. For example, procedure 1 could be 16 hrs at 1100°F + 4 to 6hrs at 1000°F + 4 to 6 hrs at 900°F. Procedures described under 1,2, and 3, however, will usually give higher properties.
  In some instances it may be desired to decrease heat-treating time, either for cost saving or for obtaining intermediate properties. It is difficult to make specific recommendations which would cover the full range of possibilities. The best procedure is to make pilot tests on specimens which duplicate the cross section of the material to be hardened.

Material which has been heated for any appreciable length of time in the temperature range 1100°F to time and temperature of exposure. Overaged material will have lower mechanical properties than properly aged metal, and the properties cannot be raised by subsequent aging treatments. In order to strengthen overaged material, it must be solution-annealed (1800-1900°F) to redissolve the age-hardening constituents, and then re-aged. All benefits of cold work are lost in annealing. The highest strength obtainable is that corresponding to the annealed and aged condition.
Material that has been age-hardened to produce maximum hardness will not show an appreciable change in properties if again heated to or held at any temperature up to that at which the original heat treatment was carried out. There may be a small increase in properties if the rate of cooling in the original heat treatment was too rapid between 1050 and 800°F. If the hardened material is subsequently heated above 1100°F and then cooled, there will be a decrease in properties. Hardened Monel alloy K-500 has been subjected to long continued heating at 800°F. A further slow aging occured during the first month of exposure, but continued heating caused no further significant change in 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.

Monel K-500 - Current Inventory Stock