Specifications

Chemical composition and mechanical properties

Nickel includes cobalt. Limits as given in ASTM B127, B164 and B165 (alloy 400) and B865 (alloy K-500).

Annealed condition. Hot-rolled, cold-worked and stress-relieved conditions have higher strength, with size limits as given in each standard.

Monel K-500 bars are age hardened to a much higher strength than alloy 400; the values depend on condition and size and are given in ASTM B865. Bars in alloy 400 are also listed on the Monel 400 round bars page, and background on the Monel page.

Monel 400 or K-500 bar?

Monel 400 bar is used where corrosion resistance and good ductility are the priority: fittings and valve bodies machined from bar, pump and valve components, fasteners, and parts for HF acid and caustic service. Its strength can be raised by cold drawing, but not by heat treatment.

Monel K-500 contains aluminium and titanium, which form fine particles during age hardening at around 600 °C. This raises yield strength to roughly three times that of annealed alloy 400 and increases hardness, while corrosion resistance stays close to that of 400. K-500 bar is used for pump shafts, propeller shafts, impellers, valve stems, drill collars and oil-well tools, doctor blades and high-strength fasteners. It also remains non-magnetic down to low temperatures, which suits instrumentation and some downhole tools.

How we manufacture Monel bars

We manufacture Monel round bars from certified billets by hot rolling or forging to size, followed by annealing where required. Bright bars are peeled, turned or centreless ground to a close tolerance and smooth finish. Cold-drawn bars are drawn through dies for higher strength and closer tolerance. K-500 bars are supplied in the annealed or hot-finished condition for machining and ageing by the customer, or aged to the specified hardness. Every bar is marked with alloy and heat number, and ultrasonic testing is carried out on request.

Machining Monel bars

Monel work-hardens during machining, so it should be cut with rigid set-ups, sharp carbide or high-speed steel tools with a positive rake, and steady feeds deep enough to cut below the hardened layer from the previous pass. Cold-drawn and stress-relieved bar generally machines better than soft annealed bar, because the chips break more cleanly. For K-500, rough machining is done before ageing, and finish machining after, with an allowance for the slight dimensional change that ageing causes.

Corrosion resistance

Monel bars resist seawater, brackish water and many acids and alkalis. In flowing seawater they perform well; in stagnant seawater, pitting can occur. Monel 400 resists hydrofluoric acid and caustic soda across a wide range of conditions and is not prone to chloride stress corrosion cracking. It is not suitable for oxidising acids such as nitric acid. For sour service, Monel 400 and K-500 can be supplied to NACE MR0175 / ISO 15156 on request, with hardness limits for each condition.

Ordering Monel round bars

Please give the alloy and specification, shape and size, tolerance, condition (annealed, cold drawn or aged), surface, length, quantity and any ultrasonic testing or inspection requirement. Bars are bundled or boxed, with bright bars wrapped, and each piece is traceable to its mill test certificate.

Applications and related products

Monel round bars are used for marine pump and propeller shafts, valve stems and trim, fasteners, chemical-plant fittings and valve bodies, oil-field tools and drill collars, and instrumentation parts. Matching products include Monel pipes and tubes, Monel sheets and plates, Monel flanges, Monel pipe fittings and Monel fasteners. Other bar materials are on the round bars, rods and wires page.