Cobalt-nickel multiphase alloy · Open-die forgings

MP35N Forgings (UNS R30035, ASTM F562, AMS 5758 / 5844 / 5845)

UNS R30035 · W.Nr. 2.4999 · ASTM F562 · ASTM F688 · AMS 5758 · AMS 5844 · AMS 5845 · ISO 5832-6 · BS 7252-6 · NACE MR0175 / ISO 15156-3 · NACE MR0103 · API 20F · 35Co-35Ni-20Cr-10Mo · MP-35N · Alloy MP35N

Published 18 May 2016 · Last updated 21 August 2026 · Reviewed by the Jiangyin Jiangnan Metal metallurgical engineering team

UNS

R30035W.Nr. 2.4999

Nominal

35-35-20-10Co-Ni-Cr-Mo, wt %

Density

8.43g/cm³ · 0.304 lb/in³

Annealed UTS

793-1000MPa · 115-145 ksi

CW + aged UTS

1793MPa min · 260 ksi (bar)

Solution anneal

1038-1052°C · 4-8 h · air cool

Ageing

538-649°C · 4-4.5 h · air cool

PREN

≈53Cr + 3.3 Mo, nominal

Melt route

VIM+VARrequired by AMS

Magnetic

Noμ ≈ 1.0009 annealed

What MP35N forged products can you buy?

Jiangyin Jiangnan Metal produces UNS R30035 by three routes, chosen by geometry and order size. Open-die forging covers shafts, blocks, discs and heavy blanks. Seamless ring rolling produces rings for pump, valve and wellhead housings. Upset forging is used for short, large-section hubs, flanges and stem blanks. Because VIM-VAR raw material costs an order of magnitude more per kilogram than alloy steel, near-net-shape dies pay for themselves quickly on this grade: removing 30-50% of the rough machining stock usually saves more than the tooling costs.

Wire, strip, foil, small-diameter cold-drawn bar and seamless tubing are mill products made by drawing, rolling or pilgering. We do not produce them; if that is what your drawing needs, buy from a wire or strip mill rather than a forge.

What is MP35N / UNS R30035?

MP35N is a multiphase cobalt-nickel base alloy. The four alloying elements are the same four that underpin corrosion resistance in most stainless steels, nickel alloys and cobalt alloys: cobalt, nickel, chromium and molybdenum. Here they sit in proportions that produce a metastable face-centred-cubic (FCC) matrix rather than a stable one, and that metastability is deliberate. Everything else about the alloy follows from it.

Three things matter in service:

• Strength that is created by deformation, not by quenching. Cold work partially transforms the FCC matrix into thin hexagonal-close-packed (HCP) platelets, 20 to 3,000 ångström thick, lying on FCC planes. The closer the platelet spacing, the higher the strength. Ageing between 538 °C and 649 °C then precipitates a cobalt-molybdenum (Co₃Mo) phase at the platelet-matrix interfaces, adding up to roughly a further 275 MPa (40 ksi). Ageing without prior cold work does almost nothing, because there are no interfaces for the precipitate to nucleate on.
• Corrosion resistance that does not fall away as strength rises. With 20% chromium and 10% molybdenum the pitting resistance equivalent number is about 53 on nominal chemistry, well beyond Type 316 and comparable to nickel alloy 625. MP35N is regarded as virtually immune to general, crevice and stress-corrosion attack in seawater regardless of strength level, which is unusual: in most high-strength alloys, cracking resistance collapses as hardness climbs.
• An FCC lattice that resists hydrogen. The tight atomic spacing of the FCC structure gives far better hydrogen-embrittlement resistance than the body-centred-cubic tempered martensites used for high-strength steels. This is why MP35N, uniquely, is accepted by NACE MR0175 for any combination of temperature, H₂S partial pressure, chloride concentration and pH found in downhole production.

The alloy is non-magnetic in every commercial condition (relative permeability about 1.0009 annealed), biocompatible, being specified for surgical implants under ASTM F562 and ISO 5832-6, and usable from cryogenic temperatures upward without a ductile-to-brittle transition.

Why a forged MP35N part is not a 260 ksi part

This is the most common and the most expensive misunderstanding on this grade, which is why it appears here rather than further down the page.

Nearly every MP35N datasheet on the internet quotes 1,793 MPa (260 ksi) tensile and 1,586 MPa (230 ksi) yield. Those are the AMS 5844 and AMS 5845 acceptance values, and they apply to round bar up to 44.4 mm (1.75 in) diameter, cold drawn to roughly 50% reduction of area and then aged. That strength was put in by the draw bench, and it cannot be put in by a hammer, a press or a furnace.

What follows from that:

1. If your design needs 1,793 MPa, it needs cold-drawn bar, and the part must be machined from it. Ask a bar mill, not a forge. Practical diameter limits are about 75 mm for drawn bar and about 82 mm (3.25 in) for rotary-forged bar with agreed reduced properties.
2. If your part is a large ring, disc, body or shaft, you are buying MP35N for its corrosion and sour-service performance, not for 260 ksi. That is a legitimate and common reason to specify it, and at annealed strength it is still a fully NACE-compliant material.
3. Cold work is additive and need not all happen at the mill. Drawing, rolling, extruding, cold forging, swaging, pilgering and flow forming all count toward the same total reduction. Where a component's geometry allows a cold-forming step after hot forging, we can build strength back in and then age. This has to be designed in from the start, and it is agreed case by case.
4. Never solution anneal a finished cold-worked MP35N part. It erases the strength irreversibly. Stress relief must be done inside the ageing window, not above it.

We say this in writing on every MP35N enquiry, because a purchase order that specifies "MP35N forged ring, AMS 5844, 260 ksi minimum" cannot be filled by anyone, and it is better to find that out at the quotation stage than at the test-certificate stage.

What are the equivalents of MP35N? (UNS R30035, 2.4999, ASTM F562, AMS 5844)

Buyers meet this alloy under a dozen names. They describe the same 35Co-35Ni-20Cr-10Mo chemistry and we accept purchase orders under any of them, but they are not interchangeable in scope: some cover bar only, some cover a delivery condition, and some cover an application sector rather than a product form.

Standards are cited by number. Always reference the revision in force at the contract date.

What is the chemical composition of MP35N?

The band below is the chemistry required by AMS 5758, AMS 5844 and AMS 5845, and it is identical to the limits carried in NACE MR0175. ASTM F562 uses the same ranges for the four principal elements. It is what we buy raw material against unless a drawing calls for something tighter.

Note how narrow the tramp-element ceilings are: manganese and silicon at 0.15%, carbon at 0.025%, sulphur at 0.010%. Those limits are not achievable in air melting, which brings us to the next point.

Why MP35N must be VIM + VAR (and why EAF + ESR will not do)

The reason is cleanliness rather than chemistry alone. VIM removes gases and volatile tramp elements and lets carbon, manganese and silicon be held at the levels in Table 2. VAR then directionally re-solidifies the electrode, which breaks up macrosegregation and removes the oxide and nitride inclusions that would otherwise become fatigue initiation sites in a highly cold-worked structure. Because the strengthening mechanism concentrates strain at platelet interfaces, an inclusion that would be tolerable in a 250 MPa steel is a crack nucleus here.

What that means for us as a forge: we do not melt MP35N. We buy VIM-VAR billet against your specification from a qualified mill, forge it, heat treat it, test it and certify it, and the mill certificate travels with the part alongside our own EN 10204 3.1 or 3.2 document. Heat number traceability is unbroken from electrode to finished forging. This also sets the honest limit on our size envelope: what we can forge in MP35N is governed by what VIM-VAR billet we can source for your order, so size and quantity should be settled early in the enquiry.

What are the mechanical properties of MP35N in each condition?

There is no single set of properties for MP35N. Where a part sits depends on how much cold work it has received and at what temperature it was aged afterwards. The three tables below cover the three rungs that matter commercially.

Rung 1: solution treated (as-forged and annealed), per AMS 5758

This is the condition in which hot-forged rings, discs, shafts and bodies are supplied, and it is the condition in which the alloy is machined and welded.

Rung 2: cold worked and aged, aerospace practice (AMS 5844 / AMS 5845)

Applies to round bar up to 44.4 mm (1.75 in) diameter, cold drawn to roughly 50% reduction of area, aged 538-649 °C for 4-4.5 hours and air cooled. Above 44.4 mm the specifications require properties to be agreed between purchaser and producer, and they fall off with diameter as the table shows.

Values above 44.4 mm are published mill minimums for capability-tested bar and are subject to agreement between purchaser and producer under the AMS specifications. AMS 5844 supplies material cold worked but not aged: the aged numbers are a demonstrated capability, and the ageing is done later by the part manufacturer.

Rung 3: cold worked and aged for sour service (NACE MR0175)

Sour-service ageing is deliberately hotter than aerospace ageing: 704 °C to 816 °C instead of 538-649 °C. That over-ages the alloy and gives away strength, and it is done on purpose: high ageing temperature dramatically improves resistance to hydrogen embrittlement under galvanic coupling. This is the trade the oil and gas industry has chosen, and it is why NACE-compliant MP35N is weaker than aerospace MP35N.

Published mill minimums for cold-worked-and-aged bar. The 774 °C / 6 h condition is the common choice for subsea bolting up to about 51 mm; above 51 mm the 704 °C / 4 h condition gives the highest strength still inside MR0175. Confirm the exact values on the mill certificate for your heat and size.

Is MP35N approved for sour service? NACE MR0175, ISO 15156-3 and API 20F

Yes, and it holds a position no other alloy holds. NACE MR0175 / ISO 15156-3 permits MP35N, processed to the specification, for any in-situ combination of temperature, H₂S partial pressure, chloride concentration and pH occurring in downhole production environments. Nickel alloys such as 718 and 725 carry environmental limits; MP35N does not. It is the highest-strength alloy in the document with that standing.

Compliance rests on two things: the ageing cycle and the hardness ceiling.

API 20F adds process control on top of MR0175 for corrosion-resistant bolting. It requires the bolting manufacturer to hold a written specification complying with AMS 5844 chemistry, melt practice, solution annealing, furnace tolerances and grain size; requires the ageing and hardness limits of MR0175; and, in the clause that catches people out, requires that heat treatment of MP35N be performed only by the raw material supplier or mill, with no further forging permitted. If your scope is API 20F bolting, the fastener has to be machined from mill-heat-treated stock, not forged from billet.

Hardness alone is a poor predictor of environmental cracking resistance in this alloy. Two samples at identical hardness, one cold worked without ageing and one cold worked and aged at 816 °C, behave very differently in a hydrogen-charging environment. The microstructure, not the indenter, decides.

What are the physical properties of MP35N?

How corrosion resistant is MP35N, and how hot can it run?

MP35N is the rare alloy where corrosion performance does not degrade as strength rises. It is regarded as virtually immune to general corrosion, crevice corrosion and stress-corrosion cracking in seawater at every strength level and in every processing condition. Chloride pitting and crevice resistance exceeds Type 316 and is comparable to nickel alloy 625. It resists hydrogen sulphide, salt water, chloride brines and the mineral acids (nitric, hydrochloric and sulphuric) within their usual concentration and temperature limits.

Service temperature

Two different numbers circulate and both are right, for different conditions:

• Fully cold worked, un-aged: about 400 °C (750 °F) maximum. Above that the stored strength starts to relax.
• Cold worked and aged: commonly quoted as usable to about 427-454 °C (800-850 °F).
• Absolute ceiling: about 649 °C (1,200 °F). The HCP platelets that carry the strength begin to dissolve, and the loss is not recoverable by any subsequent treatment short of re-cold-working the part.
• Solution-annealed forgings have no cold-work strength to lose, so they are limited instead by oxidation and by their own low yield strength. Treat them like an annealed austenitic alloy.

At the cold end there is no limit worth stating. MP35N keeps its toughness at cryogenic temperatures and is used as reinforcement in high-field superconducting magnets for exactly that reason.

MP35N vs Inconel 718, Inconel 725, Monel K-500 and A286

Comparing these five on peak strength alone gives the wrong answer. What MP35N buys is unrestricted sour-service approval and seawater immunity, and it charges for that in price, in size limits, and in the requirement that strength be earned by cold work rather than by a furnace cycle.

Published minimums for common product conditions and standards; each alloy has several. Confirm against the specification named on your drawing. Related pages: Inconel 718, Inconel 725, Monel K-500, MP159.

How is MP35N forged, machined and welded?

Forging

MP35N is hot forged in the 1,100-1,200 °C range. It is stiff under the hammer, with flow stress well above nickel-base 718 at the same temperature, so passes are kept incremental and the piece is returned to the furnace often. Finishing too cold is the main risk: the alloy work-hardens steeply, and a finish below roughly 950 °C invites surface tearing and internal bursts. Aim for a total reduction of at least 4:1 to break down the cast structure, forge to develop grain flow along the principal stress axis, then solution anneal after forging at 1,038-1,052 °C for 4-8 hours and air cool.

Machining

MP35N is difficult to machine in every condition, though comparative studies rate it slightly better than Waspaloy, the usual benchmark for this alloy class. It work-hardens instantly under a rubbing edge, so the governing rule is low surface speed, positive feed, never let the tool dwell. Rigid setups, sharp tooling, minimum overhang and flood coolant.

Starting values from published data for a rigid setup with flood coolant. Solution-annealed forgings machine considerably more easily than these figures suggest, being a 241 HB maximum material, but they are gummy, and the same "no dwell" rule applies.

Welding

Welding practice follows Type 304 stainless: the same joint preparation, the same cleanliness, the same processes. Two differences matter. Keep heat input per pass to roughly 50-65% of what you would use on 304, and understand what the weld does to strength.

Published GTAW starting parameters: argon at 9.4-11.8 L/min, travel speed about 140 mm/min, arc voltage around 10 V, MP35N filler fed at 355-560 mm/min; 50-60 A on 1.5 mm sheet, 100-160 A on 6.4 mm plate.

How does MP35N fail, and how do you prevent it?

What can Jiangyin Jiangnan Metal forge in MP35N?

MP35N is a made-to-order grade for us. We do not hold it in stock, and we buy the VIM-VAR billet against your specification once the order is placed, which is why the drawing, the condition and the quantity all matter at enquiry stage rather than after.

Rolled ring OD

200-2500mm, plant limit

Disc diameter

≤ 1800mm, plant limit

Shaft length

≤ 8000mm, plant limit

Bar diameter

25-500mm, plant limit

Single piece

≤ 8000kg, plant limit

Lead time

12-18weeks typical, MP35N

Which standards and certificates apply?

Third-party witness certificates are issued through the inspection body you nominate: Lloyd's Register, DNV, Bureau Veritas, ABS, TÜV or SGS. Customers keep an unrestricted right to witness any production stage, including chemistry, heat treatment and mechanical testing.

How do you specify an MP35N forging order?

1. Name the material generically. Write UNS R30035 / ASTM F562. A purchase order that only says "MP35N" names an SPS Technologies trademark and can strictly only be filled by material carrying that brand.
2. State the delivery condition, and be realistic about it. "Solution treated per AMS 5758, 1038-1052 °C, 4-8 h, air cool" for a hot-forged part. Only write a cold-worked-and-aged condition if the geometry can actually receive cold work.
3. If it is sour service, name the ageing cycle from Table 6, not just "NACE". For example "aged 774 °C / 6 h minimum per NACE MR0175, 51 HRC maximum". And decide whether AMS 5844 or MR0175 governs the hardness, because the two conflict.
4. Require the melt route explicitly. "VIM + VAR, mill certificate to accompany delivery." This is the clause that keeps non-compliant material out.
5. Give test direction and location. Above 50 mm section, state whether tensile tests are longitudinal or transverse and where the coupon is taken from. In a cold-worked alloy the difference is large.
6. Define NDE and the acceptance class. "UT per EN 10228-3, quality class 3" or "UT per ASTM A388 with acceptance stated on the order". An unqualified "ultrasonic test" is not a specification.
7. Choose the certificate. EN 10204 3.1 as standard; 3.2 with a named witness where the project demands it.
8. Give quantity, date, Incoterm and destination. Quantity drives the billet purchase, which on this grade drives both price and lead time more than the forging does.

Drawing callout you can copy

MATERIAL:      UNS R30035 / ASTM F562
               Melt route: VIM + VAR mandatory; mill certificate to accompany
CONDITION:     Hot forged, then solution treated 1038-1052 °C, 4-8 h, air cool
               (AMS 5758 practice). Grain size ASTM E112 No. 4 or finer.
PROPERTIES:    UTS 793-1000 MPa, YS 0.2% 241-448 MPa, El. 4D 50% min,
               RA 65% min, hardness 241 HB max. Longitudinal coupons.
SOUR SERVICE:  If applicable - age per NACE MR0175 / ISO 15156-3,
               774 °C / 6 h minimum, 51 HRC maximum. MR0175 governs
               hardness in place of AMS 5844.
GRAIN FLOW:    Parallel to the principal stress axis; verify per ASTM E381
NDE:           UT per EN 10228-3 quality class 3
               PT per ASTM E165, Type I Method C
CERTIFICATE:   EN 10204 3.1 (3.2 with third-party witness if stated on the PO)
SURFACE:       Ra <= 1.6 um on sealing and bearing surfaces
MARKING:       Heat number, condition and drawing number, low-stress stamped
NOTE:          No thermal operation above 649 °C after any cold work.

Eight mistakes buyers make with MP35N

1. Putting 260 ksi on a forging drawing. That is cold-drawn bar ≤ 44.4 mm. A forged ring cannot meet it. See the ladder.
2. Ordering "AMS 5844 + NACE MR0175" with no further detail. One requires ≥ 38 HRC, the other caps un-aged material at 35 HRC. Nothing satisfies both.
3. Accepting material without a VIM-VAR melt record. The chemistry can pass and the material still be non-compliant.
4. Specifying a post-weld or stress-relief cycle above 649 °C on cold-worked material. It permanently removes the strength you paid for.
5. Assuming a hardness number proves sour-service fitness. Two identical hardnesses can behave completely differently; the ageing cycle is what MR0175 controls.
6. Designing a welded joint on aged properties. The heat-affected zone reverts toward annealed strength and cannot be heat treated back.
7. Coupling MP35N to carbon steel or 316 in seawater without isolation. The MP35N is fine. The other metal is not.
8. Leaving the quantity vague on enquiry. Billet is bought per order on this grade; a small quantity may have to ride on someone else's heat, which changes both schedule and price.

Ask for an MP35N / UNS R30035 quotation

Send the drawing and the condition you need. We answer within 24 hours with price, lead time, the billet route we would use and the standards we will certify to. If the specification cannot be met as written, which happens often on this grade, we say so in the quotation rather than at the certificate stage.

Where is MP35N used?

A worked example: choosing the condition for a subsea valve stem

Given. Ø70 mm valve stem, UNS R30035, subsea service, 60 °C, sour gas at a partial pressure inside the MR0175 envelope, cathodic protection present on the assembly, design stress 620 MPa.

First question: can it be forged at all? At Ø70 mm the part sits above the 44.4 mm AMS bar limit but inside the 82.6 mm rotary-forged band, so cold-worked-and-aged material is obtainable, with reduced properties.

Second question: which ageing cycle? Two candidates from Table 5 at this diameter: 704 °C / 4 h giving 1,207 MPa minimum yield, or 774 °C / 6 h giving 1,103 MPa. Both clear 620 MPa with a wide margin, so strength is not the deciding factor.

Third question: what actually governs? Cathodic protection is present, and CP is the one condition under which MP35N is known to be susceptible to hydrogen embrittlement. Higher ageing temperature markedly improves resistance. Since the design does not need the extra 104 MPa, there is no reason to take the risk.

Decision. Specify 774 °C / 6 h, 51 HRC maximum, per NACE MR0175, with test coupons taken transverse to the working direction, which is where embrittlement has been reported, and hardness mapped rather than spot-checked. Had the design stress been 1,150 MPa instead of 620 MPa, the answer would have been to change the geometry rather than to drop to the lower ageing temperature.

Glossary

MP35N frequently asked questions

References

1. SAE AMS 5758, Alloy, Corrosion-Resistant, Bars 20Cr-35Ni-35Co-10Mo, Vacuum Induction Plus Consumable Electrode Vacuum Remelted, Solution Heat Treated for Work Strengthening, SAE International.
2. SAE AMS 5844, Alloy, Corrosion-Resistant, Round Bars 20Cr-35Ni-35Co-10Mo, … Solution Heat Treated and Work Strengthened, SAE International.
3. SAE AMS 5845, Alloy, Corrosion-Resistant, Round Bars 20Cr-35Ni-35Co-10Mo, … Solution Heat Treated, Work Strengthened and Aged, SAE International.
4. ASTM F562, Standard Specification for Wrought 35Cobalt-35Nickel-20Chromium-10Molybdenum Alloy for Surgical Implant Applications (UNS R30035), ASTM International.
5. ASTM F688, Standard Specification for Wrought Cobalt-35Nickel-20Chromium-10Molybdenum Alloy Plate, Sheet, and Foil for Surgical Implants, ASTM International.
6. ISO 5832-6, Implants for surgery — Metallic materials — Part 6: Wrought cobalt-nickel-chromium-molybdenum alloy, ISO.
7. ANSI/NACE MR0175 / ISO 15156-3, Petroleum and natural gas industries — Materials for use in H₂S-containing environments in oil and gas production — Part 3: Cracking-resistant CRAs and other alloys.
8. API Specification 20F, Corrosion-resistant Bolting for Use in Petroleum and Natural Gas Industries, American Petroleum Institute.
9. T. C. Williams, MP35N: A Superalloy for Critical Oil and Gas Applications, Carpenter Technology Corporation white paper. Microstructure, specification synopsis and mill minimum properties.
10. ASM International, Nickel, Cobalt, and Their Alloys, ASM Specialty Handbook, Materials Park, OH.
11. R. Kane, M. Watkins, D. Jacobs and G. Hancock, "Factors Influencing the Embrittlement of Cold Worked High Alloy Materials in H₂S Environments", Corrosion, 33(9), 1977.
12. R. Kane and B. Berkowitz, "Effect of Heat Treatment and Impurities on the Hydrogen Embrittlement of a Nickel Cobalt Base Alloy", Corrosion, 36(1), 1980.
13. ASTM A388/A388M, Standard Practice for Ultrasonic Examination of Steel Forgings; EN 10228-3, Non-destructive testing of steel forgings — Ultrasonic testing.
14. EN 10204, Metallic products — Types of inspection documents, CEN.

Standards are cited by number; always work to the revision in force at your contract date. Test results on our certificates are independent and traceable to calibrated equipment.

About the manufacturer

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, operating since 2008 with 460 employees including 9 senior and 32 intermediate engineers. The plant runs 1 t to 9 t open-die hammers, 4,500 t and 5,000 t hydraulic presses and radial-axial ring mills to 2,500 mm outside diameter, with in-house heat treatment, machining, mechanical testing and non-destructive examination. Alongside MP35N / UNS R30035 we forge carbon, alloy and tool steels, the precipitation-hardening and duplex stainless families, and the nickel and cobalt superalloys. Quality management is certified to ISO 9001:2015 and material is supplied with EN 10204 3.1 certification as standard, 3.2 with third-party witness on request.

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