Monel K-500: High Strength & Marine Shafting Applications

← Back to Knowledge Center

Overview

Monel K-500 (UNS N05500 / W.Nr. 2.4375) is a precipitation-hardenable nickel-copper alloy that builds on the proven corrosion resistance of Monel 400 by adding controlled amounts of aluminum and titanium. Through a carefully managed age-hardening heat treatment, these elements form microscopic intermetallic precipitates (primarily Ni₃(Al,Ti)) that dramatically increase strength and hardness while preserving the excellent ductility and toughness inherent to the nickel-copper matrix. The result is an alloy that delivers approximately two to three times the yield strength of Monel 400, making it a preferred material for highly stressed components in marine, chemical, and oil & gas environments.

Like Monel 400, Monel K-500 retains outstanding resistance to seawater, chlorides, and a wide range of acids and alkalis. It remains essentially non-magnetic at room temperature, with only minor magnetic permeability developing after age hardening. This combination of high strength, excellent corrosion resistance, and low magnetic signature has made it indispensable for critical marine hardware, pump and valve components, fasteners, springs, and instrumentation parts where reliability is paramount.

Chemical Composition (ASTM B865 / AMS 4676)

The balanced chemistry of Monel K-500 is designed to provide a stable austenitic nickel-copper matrix with controlled precipitation-hardening capability. Aluminum and titanium are the key strengthening elements, while carbon, sulfur, and other impurities are kept low to avoid embrittlement and ensure consistent mechanical response during aging.

Element	Min %	Max %
Nickel (Ni)	63.0	Balance
Copper (Cu)	27.0	33.0
Aluminum (Al)	2.30	3.15
Titanium (Ti)	0.35	0.85
Iron (Fe)	—	2.0
Manganese (Mn)	—	1.5
Silicon (Si)	—	0.5
Carbon (C)	—	0.25
Sulfur (S)	—	0.01

Physical Properties

Monel K-500 shares many physical characteristics with Monel 400, including high density and a relatively low coefficient of thermal expansion compared to carbon steels. Its thermal conductivity is lower than that of pure copper but comparable to other nickel-base alloys, which is advantageous in reducing thermal gradients during service.

Property	Value	Unit
Density	8.44	g/cm3
Melting Point	1315 - 1350	°C
Specific Heat (21°C)	419	J/kg·K
Thermal Conductivity (21°C)	17.5	W/m·K
Electrical Resistivity (21°C)	0.615	μΩ·m
Modulus of Elasticity (21°C)	179	GPa
Mean Coefficient of Thermal Expansion (21-93°C)	13.1	μm/m·°C
Magnetic Permeability (annealed)	< 1.001	—

Mechanical Properties at Room Temperature

The mechanical properties of Monel K-500 depend strongly on the thermal processing history. The values below represent typical minimum properties for hot-finished and age-hardened bar and rod per ASTM B865, condition H (annealed and aged). Cold-worked plus aged conditions can achieve even higher strengths.

Property	Value
Tensile Strength	1100 MPa (160 ksi) min
Yield Strength (0.2% offset)	790 MPa (115 ksi) min
Elongation in 2 inches	20% min
Reduction of Area	35% typical
Hardness (Rockwell C)	27 - 35 HRC
Hardness (Brinell)	265 - 325 HB
Charpy V-notch Impact	55 J typical

Effect of Heat Treatment

Monel K-500 is typically supplied in one of three conditions. The annealed condition (A) offers the lowest strength and highest ductility for forming. The hot-finished and aged condition (H) provides a balance of strength and toughness for general engineering. Cold-drawn and aged material (CDA) achieves the highest tensile properties, often exceeding 1275 MPa (185 ksi), and is selected for springs and high-strength fasteners.

High-Temperature Mechanical Properties

Monel K-500 retains useful strength at moderately elevated temperatures, but its maximum long-term service temperature is generally limited to about 538°C (1000°F). Above this range, the strengthening precipitates begin to over-age and coarsen, leading to a progressive reduction in strength. Short-term exposure at higher temperatures is possible, but designers should account for the associated softening.

Temperature (°C)	Tensile Strength (MPa)	Yield Strength (MPa)	Elongation (%)
21 (Room)	1150	860	24
93	1120	820	25
204	1070	780	26
316	1010	720	27
427	930	650	28
538	760	520	30
649	520	340	35

Corrosion Resistance

Monel K-500 exhibits corrosion resistance that is broadly similar to Monel 400, which is expected because the two alloys share the same nickel-copper base matrix. The age-hardening precipitates do not significantly impair general corrosion resistance, although under certain conditions the slightly higher aluminum content can influence localized behavior.

Resistance to Specific Media:

• Seawater and Marine Environments: Exceptional resistance to corrosion, pitting, and crevice attack in flowing and stagnant seawater. It is widely used for propeller shafts, rudders, pump impellers, and valves exposed to marine atmospheres and immersion.
• Acid Environments: Excellent resistance to hydrofluoric acid over a wide range of concentrations and temperatures. Good performance in sulfuric, hydrochloric, and phosphoric acids under moderate conditions. Avoid strong oxidizing acids such as nitric acid.
• Alkaline Media: Highly resistant to caustic alkalis including sodium hydroxide and potassium hydroxide, maintaining integrity in evaporators and chemical handling equipment.
• Stress Corrosion Cracking: Generally resistant to chloride-induced stress corrosion cracking, a key advantage over many stainless steels in marine and chloride-bearing process streams.
• Oxidation: Moderate oxidation resistance in air up to approximately 540°C. For prolonged high-temperature service in oxidizing atmospheres, nickel-chromium alloys such as Inconel 600 or Incoloy 800H are usually preferred.

Applications

The unique combination of high strength, excellent seawater corrosion resistance, and low magnetic permeability makes Monel K-500 suitable for a wide range of critical applications across multiple industries:

• Marine Engineering: Propeller and tail shafts, rudders, tiller arms, anchor cables, pump shafts, impellers, and valves. Its resistance to biofouling and seawater corrosion reduces maintenance and extends component life in hull and deck machinery.
• Oil and Gas: Drill collars, instrumentation housings, valve trim, pump shafts, and fasteners for subsea and surface production equipment. The alloy resists sour service environments containing hydrogen sulfide when correctly heat treated.
• Chemical Processing: Agitator shafts, pump and valve components, and fasteners exposed to hydrofluoric acid, alkalis, and neutral chloride solutions. The alloy's non-sparking characteristics are beneficial in certain hazardous environments.
• Aerospace: High-strength fasteners, springs, and sensor components where corrosion resistance and non-magnetic behavior are required alongside elevated strength-to-weight performance.
• Power Generation: Components for marine and land-based turbines, pump shafts, and valve stems handling cooling water, brine, and demineralized water.
• Instrumentation: Bourdon tubes, diaphragms, springs, and precision parts in gauges and control devices, particularly where exposure to corrosive atmospheres is anticipated.

Available Product Forms

Hangbo Alloy Group manufactures and supplies Monel K-500 in a full range of product forms, conforming to ASTM, AMS, and proprietary specifications. Material can be supplied in the annealed, hot-finished and aged, or cold-worked and aged condition to suit the intended application.

• Round Bars and Rods: ASTM B865, AMS 4676, QQ-N-286, diameters from 6 mm to 300 mm, hot-rolled, forged, or cold-drawn.
• Wire: Cold-drawn spring wire, flat wire, and shaped wire for fasteners, springs, and precision components.
• Forgings: Custom-forged rings, discs, flanges, and step-shafts produced to customer drawings and heat treated to specification.
• Plates and Sheets: Limited availability; solution-annealed and aged material for structural and corrosion-resistant parts.
• Seamless Tubes: For instrumentation, hydraulic lines, and heat exchanger applications where high strength is required.
• Fasteners: Custom bolts, nuts, studs, and washers machined from bar stock and aged to required mechanical properties.

Related Standards

Standard	Description
ASTM B865	Bar, Rod, Wire, and Forgings (Monel K-500)
AMS 4676	Nickel Alloy Bars, Forgings, and Rings
QQ-N-286	Federal Specification for K-500 Alloy
ASTM B164	Referenced for Monel 400 base forms; often cross-referenced
ASTM B127	Plate, Sheet, and Strip (companion Monel 400 standard)
ISO 6208	Nickel and Nickel Alloy Plate, Sheet, and Strip
DIN 17743	Werkstoff 2.4375 specification
BS 3076	Monel K-500 bars and sections
ASME SB-865	Boiler and Pressure Vessel Code equivalent

Contact Us for Monel K-500

Hangbo Alloy Group maintains a comprehensive inventory of Monel K-500 in round bars, wire, forgings, and custom-machined components. We provide full material certification including mill test reports, third-party inspection by SGS or TUV, and heat treatment documentation to ASTM and AMS requirements.

For quotations, technical data sheets, or material selection assistance, contact our sales team or call +86-136-1165-6360. We typically respond within 10 minutes and can arrange global shipment.