Monel K500 Tensile Strength and Composition to ASTM B865

Two different sets of numbers describe Monel K500, and they do different jobs. The producer publishes nominal ranges that show what the alloy is capable of across the full spread of sizes and tempers. The specification publishes minimums that a delivered lot has to meet. A specification written from the first set is not enforceable; a purchase order written from the second one is. This page is about the second set.

Monel K500 is UNS N05500 and W.Nr. 2.4375, classified as a precipitation hardening nickel-copper-aluminium alloy. In the United States the governing product standard for bar, rod, wire and forgings is ASTM B865, with ASME SB865 as the identical ASME designation. It is restricted to the forms named in its scope. Bar and rod are covered, and so is cold worked wire, plus forgings and forging stock. Sheet material is outside it, and so are strip and tube, which are ordered to different standards.

The composition of this alloy is nickel dominant. Nickel is 63.0 % minimum and copper is 27.0 to 33.0 %, with aluminium and titanium present in controlled ranges because they are what make the alloy age hardenable. A description that puts copper first is a description of the wrong alloy, and it is worth stating plainly because published supplier pages do exist that give copper as 63 to 70 % and nickel as 27 to 33 %.

The check analysis column is the part buyers most often overlook. If a purchaser re-tests a heat and the nickel comes back at 62.6 %, the material has not failed: the specification permits a check analysis to fall 0.45 % under the specified minimum. That allowance exists because the material is bought on a heat analysis and re-tested on a product analysis, and the two are not the same measurement.

One figure in that table is worth checking against whatever datasheet is in front of you. ASTM B865 specifies carbon at 0.18 % maximum. The producer technical bulletin for the same alloy gives carbon at 0.25 % maximum. The specification is the tighter of the two, and it is the one that governs if the order names B865. Where an order quotes a datasheet instead of a standard, the looser figure is what applies, and the difference is worth knowing before a heat is rejected on a technicality or accepted when it should not be.

These are the minima a delivered lot has to achieve in the age-hardened condition, and they are set by form and by section thickness, not by alloy alone. The structure of the table is the point: cold worked material carries a higher requirement than hot worked material of the same section, and the requirement falls as the section gets thicker.

The ageing treatment itself is specified, which is unusual and useful, because it means the condition can be reproduced, not merely described. The requirement is to hold at an aim temperature of 1,100 °F, which is 595 °C for 8 to 16 hours, then furnace cool to 900 °F, which is 480 °C, at a rate of 15 to 25 °F, or 10 to 15 °C, per hour, and then air cool. An alternative is permitted: hold at 1,100 °F for up to 16 hours, furnace cool to 1,000 °F and hold for about 6 hours, furnace cool to 900 °F and hold for about 8 hours, then air cool.

Two notes attached to that table answer questions that come up on almost every order. Rounds over 4 1/4 in, which is 108 mm, in diameter have an elongation requirement of 17 % minimum even when made from hot worked stock. And hardness values are given for information only, so they are not the basis for acceptance or rejection of a tensile-tested lot.

Cold drawn wire is the one product where the requirement changes with diameter instead of staying flat, and the direction of the change catches people out: the thinner the wire, the higher the minimum tensile strength. The table below is the published requirement.

One deduction attached to that table is easy to miss and can fail a lot on its own. The spring temper figures apply to material supplied in coil. For the same wire supplied straightened and cut to length, 15 ksi, or 105 MPa, is deducted from the requirement, because the straightening operation removes some of the cold work. A buyer who orders cut lengths to a coil figure will not get it.

This is the single most useful thing on the page for anyone buying the alloy in the unaged condition. The specification sets hardness maxima for unaged bar, rod and forgings, and states that no tensile tests are required unless a specific provision applies. Where the material is ordered unaged, the requirement is to take one specimen per lot, age it or anneal and age it as required, and test that. So a certificate for unaged material carries a tensile result obtained from a specimen that has been through the ageing treatment, not from the material as shipped.

Two smaller provisions belong with the table. Rounds over 4 1/4 in, or 108 mm, in diameter carry a hardness maximum of 260 HB even though the rows above stop at 4 in. And when forged rings or discs are specified, hardness measurements may be used in place of a tensile test, which is a concession worth taking on a shape where a tensile specimen is awkward to cut.

The specification opens with a list of the information an order should carry, and it is a better checklist than any quotation template. Material ordered as simply "Monel K500" is under-specified in at least four of these fields.

The testing regime is fixed, which means the size of the certificate can be worked out in advance. One chemical analysis, one tension test and one hardness test are required per lot, and a lot for mechanical testing is defined as all material from the same heat, the same nominal cross-sectional or forging size, and the same condition.

Nickel is 63.0 % minimum, copper is 27.0 % to 33.0 %, aluminium is 2.30 % to 3.15 % and titanium is 0.35 % to 0.85 %, with iron at 2.0 % maximum, manganese at 1.5 % maximum, silicon at 0.50 % maximum, carbon at 0.18 % maximum and sulfur at 0.010 % maximum. The alloy is nickel dominant. Some published pages give copper as 63 to 70 % and nickel as 27 to 33 %, which is the two elements reversed.

It depends on the form, the condition and the section. The lowest requirement in the bar, rod and forging table is 130 ksi, or 895 MPa, applying to material that was annealed and then age hardened. Hot worked and age hardened material has to reach 140 ksi, or 965 MPa, at all sizes. Cold worked and age hardened round bar from 1/4 in to 1 in has the highest requirement at 145 ksi, or 1,000 MPa, with an elongation minimum of 15 %.

Because they are different kinds of number. The producer bulletin publishes nominal ranges that cover the full spread of sizes and tempers, and it states that they are composites which are not suitable for specification purposes. The standard publishes the minimum a delivered lot has to meet. Something in the middle of a nominal range is what the alloy can do; the minimum in the standard is what has to be proved.

Not as a requirement. For unaged bar, rod and forgings the specification sets hardness maxima and states that no tensile tests are required unless a specific provision applies. Where material is ordered unaged, one specimen per lot is taken and then aged and tested, so the tensile result on the certificate comes from a specimen that has been through the ageing treatment and not from the material as shipped.

Yes, within the permitted variations. The specification publishes a separate allowance for product check analysis against each specified limit, and it is not zero. Nickel may fall 0.45 % under the 63.0 % minimum; copper may go 0.15 % under or 0.20 % over its range; titanium may go 0.03 % under or 0.04 % over. These allowances exist because the material is bought on a heat analysis and may be re-tested on a product analysis, and the two are not the same measurement.

No, and this is the one figure worth checking against the document in front of you. ASTM B865 specifies carbon at 0.18 % maximum. The producer technical bulletin for the same alloy gives 0.25 % maximum. The specification is the tighter requirement, and it governs when the order names the standard. Where the order quotes a datasheet instead of a standard, the looser figure applies.

Monel K500 is nickel dominant at 63.0 % minimum with copper at 27.0 % to 33.0 %, and its aluminium and titanium additions make it precipitation hardening. The specification that governs bar, rod, wire and forgings is ASTM B865, and what it contains is minimums and not the nominal ranges a datasheet quotes. For age-hardened bar and rod those minimums run from 130 ksi, or 895 MPa, applying to material that was annealed before ageing, to 145 ksi, or 1,000 MPa, for cold worked round bar up to 1 in. Wire carries a size-dependent ladder that rises as the wire gets thinner, with a 15 ksi deduction for straightened and cut lengths. Unaged material is qualified by hardness and not by a tensile test, and a check analysis is allowed to fall outside a specified limit within published variations.

Monel K500 bar, rod, wire and forgings are supplied to UNS N05500 and W.Nr. 2.4375 from Changzhou, Jiangsu, in hot worked, cold worked, annealed and age hardened conditions, against ASTM B865 and ASME SB865, from a plant that holds ISO 9001 certification and is audited by SGS. Send the form, the dimension, the condition and the standard you are ordering to, and the requirements follow from those four answers.

1. ASTM B865-04, standard specification for precipitation hardening nickel-copper-aluminium alloy (UNS N05500) bar, rod and wire, plus forgings and forging stock. Source for the composition limits and the product check analysis variations, the scope of the standard and the forms it covers, the age-hardened tensile, yield, elongation and hardness minimums by form and section thickness, the specified ageing treatment and its permitted alternative, the description of rod, bar and wire, the ordering information list, the lot definition and the number of tests per lot, the rounding rule, the certification requirement and the marking list.
2. The same specification, Table 4 and clause 9.2.3. Source for the hardness maxima in the unaged condition, the statement that no tensile tests are required for unaged material, and the provision that a specimen be aged or annealed and aged for the test.
3. The same specification, Table 6. Source for the size dependent tensile requirements for cold drawn wire in coils and for the 15 ksi deduction applicable to straightened and cut lengths.
4. Special Metals technical bulletin SMC-062, MONEL alloy K-500. Source for the nominal property ranges against which the specified minimums are set, the carbon figure of 0.25 % maximum that differs from the standard, the physical constants, and the corrosion and magnetic behaviour.
5. ASME SB865 as the ASME designation of the same specification. Source for the alternative designation quoted in the summary.
6. UNS N05500 and W.Nr. 2.4375 as published for this alloy. Source for the identifiers used.
7. Delivery records held for DLX Alloy covering Monel K500 bar, rod, wire and forgings. Source for the forms and conditions supplied.

The values quoted are the requirements of the standard named and of the bulletin named, and they apply to material ordered to those documents. Requirements differ between standards and between forms, and an order that does not name the standard leaves the applicable minimum open. Acceptance of a delivered lot rests on the certificate and test report issued for that lot.