Monel is a trademark of Special Metals Corporation for a series of nickel alloys, primarily composed of nickel (up to 67%) and copper, with some iron and other trace elements. Monel was created by David H. Browne, chief metallurgist for International Nickel Co. Monel alloy 400 is binary alloy of the same proportions of nickel and copper as is found naturally in the nickel ore from the Sudbury (Ontario) mines. Monel was named for company president Ambrose Monell, and patented in 1906 ( U.S. patent 811,239).

MONEL® ALLOY 400

UNS N04400

Other common names: Alloy 400

Monel 400 is a nickel-copper alloy (about 67% Ni – 23% Cu) that is resistant to sea water and steam at high temperatures as well as to salt and caustic solutions. Alloy 400 is a solid solution alloy that can only be hardened by cold working. This nickel alloy exhibits characteristics like good corrosion resistance, good weldability and high strength. A low corrosion rate in rapidly flowing brackish or seawater combined with excellent resistance to stress-corrosion cracking in most freshwaters, and its resistance to a variety of corrosive conditions led to its wide use in marine applications and other non-oxidizing chloride solutions. This nickel alloy is particularly resistant to hydrochloric and hydrofluoric acids when they are de-aerated. As would be expected from its high copper content, alloy 400 is rapidly attacked by nitric acid and ammonia systems.

Monel 400 has great mechanical properties at subzero temperatures, can be used in temperatures up to 1000° F, and its melting point is 2370-2460° F. However, alloy 400 is low in strength in the annealed condition so, a variety of tempers may be used to increase the strength.

Available forms of  Monel 400

  • Sheet
  • Plate
  • Bar
  • Pipe & Tube (welded & seamless)
  • Fittings (i.e. flanges, slip-ons, blinds, weld-necks, lapjoints, long welding necks, socket welds, elbows, tees, stub-ends, returns, caps, crosses, reducers, and pipe nipples)
  • Wire

Characteristics of Monel 400

  • Resistant to seawater and steam at high temperatures
  • Excellent resistance to rapidly flowing brackish water or seawater
  • Excellent resistance to stress corrosion cracking in most freshwaters
  • Particularly resistant to hydrochloric and hydrofluoric acids when they are de-aerated
  • Offers some resistance to hydrochloric and sulfuric acids at modest temperatures and concentrations, but is seldom the material of choice for these acids
  • Excellent resistance to neutral and alkaline salt
  • Resistance to chloride induced stress corrosion cracking
  • Good mechanical properties from sub-zero temperatures up to 1020° F
  • High resistance to alkalis

Chemical Composition, %

C Mn S Si Ni Cu Fe
.30 max 2.00 max .024 max .50 max 63.0 min 28.0-34.0 2.50 max

Corrosion Resistant Monel 400

Alloy 400 is virtually immune to chloride ion stress corrosion cracking in typical environments. Generally, its corrosion resistance is very good in reducing environments, but poor in oxidizing conditions. It is not useful in oxidizing acids, such as nitric acid and nitrous. Nevertheless, it is resistant to most alkalis, salts, waters, food products, organic substances and atmospheric conditions at normal and elevated temperatures.

This nickel alloy is attacked in sulfur-bearing gases above approximately 700° F and molten sulfur attacks the alloy at temperatures over approximately 500° F.

Monel 400 offers about the same corrosion resistance as nickel but with higher maximum working pressures and temperatures and at a lower cost due to its superior ability to be machined.

Applications of Monel 400

  • Marine engineering
  • Chemical and hydrocarbon processing equipment
  • Gasoline and freshwater tanks
  • Crude petroleum stills
  • De-aerating heaters
  • Boiler feed water heaters and other heat exchangers
  • Valves, pumps, shafts, fittings, and fasteners
  • Industrial heat exchangers
  • Chlorinated solvents
  • Crude oil distillation towers

Fabrication with Monel 400

Alloy 400 can easily be welded by gas-tungsten arc, gas metal arc or shielded metal arc processes using appropriate filler metals. There is no need for post weld heat treatment, however, thorough cleaning after welding is critical for optimum corrosion resistance, otherwise there is the risk of contamination and embrittlement.

Finished fabrications can be produced to a wide range of mechanical properties when proper control of the amount of hot or cold working and the selection of appropriate thermal treatments is done.

Like most other nickel alloys, Monel 400 is typically tough to machine and will work harden. However, excellent results can e obtained if you make the correct choices for tooling and machining.

 

ASTM Specifications

Pipe Smls Pipe Welded Tube Smls Tube Welded Sheet/Plate Bar Forging Fitting Wire
B165 B725 B163 B127 B164 B564 B366

Mechanical Properties
Typical room temperature Tensile Properties of Annealed Material

Product Form Condition Tensile (ksi) .2% Yield (ksi) Elongation (%) Hardness (HRB)
Rod & Bar Annealed 75-90 25-50 60-35 60-80
Rod & Bar Cold-Drawn Stress Relieved 84-120 55-100 40-22 85-20 HRC
Plate Annealed 70-85 28-50 50-35 60-76
Sheet Annealed 70-85 30-45 45-35 65-80
Tube & Pipe Seamless Annealed 70-85 25-45 50-35 75 max *

*The ranges shown are composites for various product sizes and therefore are not suitable for specification purposes. Hardness values are suitable for specification purposes provided tensile properties are not also specified.

 

MONEL® K-500

UNS N05500

Other common names: Alloy K500

Monel K500 is a precipitation-hardenable nickel-copper alloy that combines the excellent corrosion resistance characteristic of Monel 400 with the added advantage of greater strength and hardness. These amplified properties, strength and hardness, are obtained by adding aluminum and titanium to the nickel-copper base and by a thermal processing used to effect precipitation, typically called age hardening or aging. When in the age-hardened condition, Monel K-500 has a greater tendency toward stress-corrosion cracking in some environments than Monel 400. Alloy K-500 has approximately three times the yield strength and double the tensile strength when compared with alloy 400. Plus, it can be further strengthened by cold working prior to precipitation hardening. The strength of this nickel steel alloy is maintained to 1200° F but stays ductile and tough down to temperatures of 400° F. Its melting range is 2400-2460° F.

This nickel alloy is spark resistant and non-magnetic to -200° F. However, it is possible 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. Pickling or bright dipping in acid can remove this magnetic film and restore the non-magnetic properties.

Available form of Monel K500

  • Bar
  • Rod

Corrosion Resistant Monel K-500

The corrosion resistance of alloy K-500 is substantially equivalent to that of alloy 400 except that when in the age-hardened condition, nickel alloy K-500 has a greater tendency toward stress-corrosion cracking in some environments. Monel K-500 has been found to be resistant to a sour-gas environment. The combination of very low corrosion rates in high-velocity sear 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.

What are the characteristics of Monel K500?

  • Corrosion resistance in an extensive range of marine and chemical environments. From pure water to non-oxidizing mineral acids, salts and alkalis.
  • Excellent resistance to high velocity sea water
  • Resistant to a sour-gas environment
  • Excellent mechanical properties from sub-zero temperatures up to about 480C
  • Non-magnetic alloy

Chemical Composition, %

Ni
Cu
Al
Ti
C
Mn
Fe
S
Si
63.0-70.0
Remainder
2.30-3.15
.35-.85
.25 max
1.5 max
2.0 max
.01 max
.50 max

In what applications is Monel K-500 used?

  • Sour-gas service applications
  • Oil and gas production safety lifts and valves
  • Oil-well tools and instruments like drill collars
  • Oil well industry
  • Doctor blades and scrapers
  • Chains, cables, springs, valve trim, fasteners for marine service
  • Pump shafts and impellers in marine service

Fabrication with Monel K-500

Monel K-500 is readily fabricated by standard commercial procedures.

Welding alloy K-500 is best accomplished by the gas-tungsten-arc welding process. It is recommended that Monel K-500 be annealed when it is welded and that any weldments be stress relieved prior to aging.

Heavy machining of this alloy 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 finishes. Therefore, the recommended practice is to machine slightly oversize, age-harden, then finish to size. During aging, a slight permanent contraction takes place, but little warpage occurs because of the low temperatures and slow cooling rates involved.

 

Specifications

Bar
Rod
AMS 4676
AMS 4676

Mechanical Properties
Typical Room Temperature Tensile Properties of Annealed Material

Product Form
Condition
Tensile (ksi)
.2% Yield (ksi)
Elongation %
Hardness
Rod & Bar
Hot-Finished/Aged
140-190
100-150
30-20
27-38 HRC
Rod & Bar
Hot Finished/Annealed
90-110
40-60
45-25
75-90 HRB
Rod & Bar
Hot Finished/Annealed/Aged
130-165
85-120
35-20
24-35 HRC
Rod & Bar
Cold-Drawn/Aged
135-185
95-160
30-15
25-41 HRC
Rod & Bar
Cold-Drawn/Annealed/Aged
130-190
85-120
30-20
24-35 HRC
Plate
Hot-Finished/Aged
140-180
100-135
30-20
27-37 HRC
Sheet
Cold-Rolled/Annealed
90-105
40-65
45-25
85 HRB Max

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