Multiphase nickel-cobalt superalloy · Open-die forgings

MP159 Forgings (UNS R30159, AMS 5841 / AMS 5842 / AMS 5843)

• MP159
• UNS R30159
• MP-159
• AMS 5841
• AMS 5842
• AMS 5843
• GH6159
• Alloy MP159
• GE S-400 / S-1000
• RR SABRe

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

UNS

R30159

Cobalt

35.7wt % · largest element

UTS, solution treated

848MPa typical · 123 ksi

UTS, worked + aged

1793MPa min, AMS 5843 · 260 ksi

Service limit

649°C · 1200 °F

Density

8.30g/cm³ · 0.300 lb/in³

Max ring OD

2,500mm forged here

Max piece

8,000kg forged here

What MP159 forged products can you buy?

MP159 is rarely held in stock in large sections; it is melted and forged to order. The alloy work-hardens quickly, so the shaping route matters more than it would in steel. We use three routes, chosen by geometry and order weight.

Open-die forging covers shafts, blocks, heavy discs and any one-off geometry. Seamless ring rolling produces rings from 200 mm to 2,500 mm outside diameter and is the usual route for housings, casings and bearing races. Upset forging handles short heavy hubs, flange blanks and valve bodies. Near-net dies are worth more in this alloy than in most: at MP159 raw-material prices, removing 30–50% of the rough machining stock changes the part cost materially, and every kilogram of chip is a kilogram of superalloy paid for and scrapped.

• Seamless rolled rings
• Forged shafts & spindles
• Forged discs & hubs
• Forged flanges
• Valve bodies, stems & seat rings
• Forged sleeves & bushings
• Tube sheets
• Round, flat & square bar
• Forged blocks & blanks
• Trepanned hollow bar
• Fastener & bolting stock
• Custom near-net forgings to drawing

What is MP159 / UNS R30159?

MP159 belongs to the small family of multiphase (MP) alloys developed to break a trade-off that defeats most metals: strength normally arrives at the cost of ductility and corrosion resistance. The MP family gets around it by stacking three separate strengthening mechanisms in one material.

• Solid-solution strengthening from 7% molybdenum and 19% chromium in a cobalt-nickel matrix.
• Cold work, which in this face-centred-cubic matrix generates a very high density of stacking faults and a fine platelet structure rather than tangled dislocations alone. This is where most of the strength comes from.
• Gamma-prime precipitation during ageing, from the 3% titanium, 0.6% niobium and 0.2% aluminium. This is what separates MP159 from MP35N, and it is why MP159 keeps its strength several hundred degrees higher.

The practical consequence is a material that is soft, formable and machinable when you receive it and extremely strong after processing. In the solution treated condition it runs about 848 MPa (123 ksi) tensile with 60% elongation, softer than many stainless steels. Cold worked and aged, the same material exceeds 1,830 MPa (265 ksi). No heat treatment applied to the finished part alone can reproduce that: the cold work has to happen in between.

Three characteristics matter in service:

• Ultra-high strength with retained toughness. At 1,790 MPa minimum tensile per AMS 5843 the alloy still carries 6% minimum elongation and 20% reduction of area, which is why it is used for critical fasteners rather than a hardened low-alloy steel at similar strength.
• Temperature capability. Useful strength and ductility to around 593–649 °C (1100–1200 °F), well beyond the point where cold-worked-only alloys begin to recover.
• Corrosion and hydrogen resistance. The chromium-molybdenum content gives resistance to general corrosion, crevice attack and hydrogen embrittlement that high-strength steels of similar tensile strength cannot approach.

What are the equivalent designations of MP159?

Buyers meet this alloy under several names. All of them describe the same 36Co-25Ni-19Cr-7Mo-3Ti multiphase chemistry, and we accept purchase orders under any of them. The AMS numbers are conditions rather than synonyms, and that distinction causes more rejected certificates on this grade than anything else.

Always reference the specification revision in force at your contract date. AMS documents are revised, and the revision letter is part of the requirement.

What is the chemical composition of MP159?

The nominal composition below is the one published for MP159 / UNS R30159 and is what we buy raw material against unless a drawing calls for a tighter band. Read it as a nominal aim chemistry: the AMS specification sets the actual limits and the residual-element ceilings, and those govern the certificate.

Nominal values. Carbon, silicon, manganese, phosphorus, sulphur and other residuals are held to the ceilings given in the applicable AMS specification. Where a drawing calls out both an AMS number and a customer chemistry band, we buy to the intersection of the two.

What are the mechanical properties of MP159?

There is no single answer, and quoting one number for MP159 is the most common error on this grade. The alloy's tensile strength more than doubles between the condition it is delivered in and the condition it is used in. The table separates typical published values from specification minima, because a certificate has to beat the minimum, not the typical.

Rows marked typical are representative published values for correctly processed material; rows carrying an AMS number are specification requirements. Values apply to bar and fastener product forms, on which the specifications are written. Confirm against the revision in force at your contract date.

AMS 5841, AMS 5842 and AMS 5843: which one applies to your part?

These three specifications are not alternatives to choose between on price. They are sequential states of the same material, and which one you can legitimately demand depends on the product form.

How is MP159 heat treated?

Two thermal operations, with a mechanical one between them. There is no quench-and-temper cycle and no refrigeration step.

1. Solution heat treatment: 1038–1052 °C (1900–1925 °F), 4 to 8 hours, water quench. Dissolves the strengthening phases and resets the structure to a soft, uniform, single-phase matrix. The water quench is not optional. Slow cooling allows premature precipitation, which costs ductility for the subsequent cold work and caps the final aged strength. Hold roughly 30 minutes per 25 mm of section beyond the four-hour minimum on heavy pieces.
2. Work strengthening. Cold reduction, typically by drawing or rolling. Around 48% reduction takes tensile strength to roughly 1,586 MPa (230 ksi) before any ageing. AMS 5842 covers this condition with a 38 HRC minimum. This step is where most of the final strength is created.
3. Ageing: 649–677 °C (1200–1250 °F), 4 to 4.5 hours, air cool. Precipitates gamma prime on the deformation structure created in step 2. Strength rises by roughly a further 300 MPa and, more importantly, the structure becomes thermally stable to service temperature. Air cool; there is no benefit to quenching from the ageing temperature.

What are the physical properties of MP159?

Physical constants for MP159 vary slightly between published datasheets. Where a design calculation is sensitive to one of these values, such as thermal expansion in a shrink fit or modulus in a deflection limit, ask us for the values on the specific heat rather than designing to a nominal figure.

How corrosion resistant is MP159, and how hot can it run?

With 19% chromium and 7% molybdenum in a cobalt-nickel matrix, MP159 resists general corrosion, pitting and crevice attack at a level comparable to the corrosion-resistant nickel alloys, and it is markedly more resistant to hydrogen embrittlement and stress-corrosion cracking than any steel of comparable strength. That combination is what the alloy is bought for: a low-alloy steel at 1,790 MPa is acutely vulnerable to hydrogen, while MP159 tolerates it.

MP159 vs MP35N, Waspaloy, Inconel 718 and A286

The question we are asked most on this grade is whether MP35N will do instead. The answer usually turns on temperature. Below about 400 °C the two alloys are close enough that availability and price decide it. Above that, MP159's gamma-prime strengthening is the whole point and MP35N starts to give strength back.

The three questions that decide it

1. What is the metal temperature under load? Above roughly 430 °C, MP35N is the wrong alloy and MP159 is the answer. Above roughly 650 °C, MP159 is the wrong alloy and Waspaloy or Inconel 718 is.
2. Is the part a fastener, a spring or a wire form? Then the cold-work route is available and MP159 delivers its headline properties. If it is a large ring or disc, the achievable strength is much lower and Inconel 718 or Waspaloy will usually be the better engineering answer as well as the cheaper one.
3. Is hydrogen or chloride cracking the governing risk? That is where MP159 and MP35N earn their price over any steel, and where MP35N's longer seawater track record may matter more than MP159's temperature capability.

How is MP159 forged, welded and machined?

Forging

MP159 is a hard alloy to forge and the press has to be sized for it. Flow stress at temperature is several times that of carbon steel, and the workable temperature window is narrow. Soak and work in the range 1040–1150 °C (1900–2100 °F) and finish above roughly 980 °C: below that the alloy work-hardens fast enough that surface cracking becomes likely within a single blow. Reheat rather than pushing the last pass.

• Reduction: aim for at least 4:1 total to break down the cast ingot structure and develop grain flow along the principal axis.
• Incremental passes: light, frequent reductions with reheats beat heavy single blows. Heavy reductions concentrate strain and open centre bursts.
• Die temperature: preheated dies, because a cold die chills the surface below the finish temperature while the core is still hot, and the differential cracks the skin.
• Post-forge: solution treat after forging. Hot work leaves a mixed, partially recovered structure that has to be reset before any cold work or ageing.
• Ring rolling: practical to 2,500 mm outside diameter on this alloy with a minimum wall around 30 mm; thinner walls lose heat faster than the mill can work them.

Welding

Fusion welding is not generally recommended. Melting destroys the deformation structure that carries most of the strength, and the resolidified weld metal is a coarse cast structure with none of it. Resistance and friction welding are used successfully, because they combine little or no melting with forging pressure that reworks the joint. If a joint is unavoidable: qualify the procedure on the actual section, test across the joint rather than quoting parent-metal properties, and expect the joint to govern the design.

Machining

Plan for a machinability rating around 20% of free-machining B1112 steel, and allow for the fact that the alloy hardens under the tool. The usual sequence is that a tool which rubs instead of cutting glazes the surface, the next pass then cuts on hardened material, and tool life collapses. The practice below follows from it.

• Machine in the solution treated condition wherever the sequence allows.
• Rigid setup, minimum overhang, sharp tools, and no dwelling. Never let the tool stop in the cut.
• Positive feeds around 0.1–0.2 mm/rev; take the depth of cut below the previously work-hardened layer.
• Cutting speeds around 10–15 m/min for roughing with carbide; flood coolant on every heavy operation.
• Replace tools on a schedule, not on failure. A worn edge work-hardens the surface it is supposed to be cutting.

How does MP159 fail, and how do you prevent it?

What can Jiangyin Jiangnan Metal forge in MP159?

MP159 / UNS R30159 is a made-to-order grade for us. We buy the heat against your specification rather than pulling from stock, which is why the drawing, the melt route and the required condition all matter at enquiry stage rather than at inspection. The envelopes below are tested limits for this alloy on our equipment, not carbon-steel limits.

Rolled ring OD

200–2,500mm

Ring wall, min

30mm

Disc diameter

≤ 1,800mm

Shaft length

≤ 8,000mm

Bar diameter

25–500mm

Single piece

≤ 8,000kg

Condition

AMS 5841direct age on qualification

Lead time

12–16weeks typical

Equipment used on this grade

Which standards and certificates apply?

Quality management is certified to ISO 9001:2015. Third-party witness certificates are issued through the inspection body you nominate: Lloyd's Register, DNV, Bureau Veritas, ABS, TÜV or SGS.

How do you specify an MP159 forging order?

1. Name the material generically. Write UNS R30159 plus the applicable AMS number. A purchase order that only says "MP159" names a trademark and can strictly only be filled by the brand owner.
2. State the condition, and check it is achievable on the form. AMS 5841 for forgings; AMS 5842 or 5843 for bar, wire and fasteners. If you need aged properties on a forging, say so at enquiry so a direct-age cycle can be qualified.
3. State the melt route if your specification requires one. VIM + VAR for aerospace work. This is a price and lead-time driver, not a detail.
4. Send the drawing with test direction and grain flow. Above 50 mm section, say whether tensile tests are longitudinal or transverse; transverse minima are lower.
5. Define NDE and the acceptance class. "UT per EN 10228-3, quality class 3" is a specification; "ultrasonic test" is not.
6. Choose the certificate. EN 10204 3.1 as standard, 3.2 with a named witness where the project demands it.
7. Give quantity, date, Incoterm and destination. Quantity drives the melt: below roughly 300 kg in this alloy we consolidate onto a larger heat, which changes both price and schedule.

Drawing callout you can copy

MATERIAL:      MP159 / UNS R30159
SPECIFICATION: AMS 5841 (solution heat treated)
MELT ROUTE:    VIM + VAR, double melted
CONDITION:     Solution treat 1038-1052 C (1900-1925 F), 4-8 h, water quench
HARDNESS:      20 HRC max, verified at locations A, B, C
TENSILE:       1103 MPa (160 ksi) max UTS, 483 MPa (70 ksi) max YS,
               50% elongation min, 65% RA min - longitudinal
GRAIN FLOW:    Longitudinal, parallel to the principal 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:       Descaled, free of rolled-in scale and seams
MARKING:       Heat number, condition and drawing number, low-stress stamped
NOTE:          Aged properties are not achievable on this forged section without
               a qualified direct-age cycle; acceptance values per agreed coupon test.

Seven mistakes buyers make with MP159

1. Writing 260 ksi on a forging drawing. That is the AMS 5843 cold-worked-and-aged minimum for bar. A rolled ring cannot be cold reduced uniformly, so the requirement cannot be met by any forging route. Agree a direct-age acceptance value instead.
2. Treating AMS 5841, 5842 and 5843 as interchangeable. They are three conditions of one alloy, and the certificate has to match the one on the order.
3. Quoting the annealed 123 ksi row as though it were the material's strength. That is the softest state the alloy exists in, and it is the delivery condition, chosen so the material can be machined.
4. Assuming MP35N and MP159 are interchangeable. They diverge sharply above about 430 °C, which is often the reason MP159 was specified in the first place.
5. Leaving the melt route unstated. If your specification expects VIM + VAR and the quotation was priced on an ESR route, the price gap will surface at the worst possible moment.
6. Planning to weld it. Design the joint out, or qualify resistance or friction welding. Do not assume a fusion weld will carry parent-metal properties.
7. Machining after ageing to save a step. At 44 HRC in a work-hardening cobalt alloy, the machining cost can exceed the material cost. Machine soft.

Where is MP159 used?

In forged form specifically, we most often supply MP159 as seamless rolled rings, discs, shafts, flanges, valve components, sleeves, tube sheets and bar, used in chemical and plunger pumps, pressure vessels, heat exchangers, compressors, power transmission, and processing and wellhead equipment.

Two worked examples

Example 1: is MP159 worth it for a 500 °C flange bolt?

Given. A flange with 16 bolts, total required clamp load 2,400 kN, metal temperature 500 °C, design allowable set at 65% of yield strength at temperature.

Method. Load per bolt is 2,400 / 16 = 150 kN. Compare two candidate materials by the thread stress area each one needs.

• A286 (S66286), M30. Stress area 561 mm² gives 267 MPa. A286 holds roughly 520 MPa yield at 500 °C, so the allowable is 0.65 × 520 = 338 MPa. It passes, with about 27% margin.
• MP159 (R30159) cold worked and aged, M20. Stress area 245 mm² gives 612 MPa. Even taking a conservative 1,450 MPa yield at 500 °C against the 1,724 MPa room-temperature minimum, the allowable is 943 MPa. It passes with over 50% margin at two thread sizes smaller.

Result. Both work. MP159 lets the joint go from M30 to M20, which shrinks the bolt circle, the flange thickness and the assembly mass. That is the usual reason it appears on flight hardware. On a ground-based flange with no mass constraint, A286 does the same job at a small fraction of the material cost, and specifying MP159 there is money spent on margin nobody needs. The question to settle before ordering is what a kilogram of assembly mass is worth on this application.

Example 2: a drawing calls for a 1,200 mm MP159 ring at 260 ksi

Given. Seamless rolled ring, Ø1,200 mm OD × Ø1,000 mm ID × 250 mm high. Drawing states UNS R30159 per AMS 5843, 260 ksi (1,793 MPa) tensile minimum.

Assessment. Net weight is about 717 kg at 8.30 g/cm³, so the rough forging runs near 900 kg before machining. The material is available and the ring is well inside our 2,500 mm envelope. The strength requirement, however, is not achievable: AMS 5843 properties come from cold reduction of a uniform section, and a rolled ring of this size cannot be cold reduced. No forging route can meet that clause.

Options, in the order we would raise them.

1. Qualify a direct-age cycle and write the resulting coupon values onto the order as the acceptance criteria. This is the right answer when the alloy is specified for its corrosion or hydrogen behaviour rather than for peak strength.
2. Change the alloy. If the ring needs high strength through a heavy section, Inconel 718 reaches 1,275 MPa minimum in a fully heat treated forging with no cold work involved, and costs materially less than MP159.
3. Split the design. Keep MP159 for the fasteners or the bar-form components that need it, and forge the ring in an alloy that can be heat treated to strength.

We raise this before quoting rather than after inspection.

Glossary

MP159 frequently asked questions

References

1. AMS 5841, SAE International. Alloy bars, forgings and rings, 25.5Ni-35.7Co-19Cr-7Mo-3Ti, solution heat treated.
2. AMS 5842, SAE International. Same alloy, solution heat treated and work strengthened.
3. AMS 5843, SAE International. Same alloy, solution heat treated, work strengthened and aged.
4. SAE HS-1086 / Metals & Alloys in the Unified Numbering System, SAE International and ASTM International. UNS R30159 designation and chemistry.
5. ASM Handbook, Volume 1: Properties and Selection: Irons, Steels and High-Performance Alloys, ASM International. Cobalt-base and multiphase alloys.
6. ASM Specialty Handbook: Heat-Resistant Materials, ASM International. Strengthening mechanisms in cobalt-nickel multiphase alloys.
7. ASTM A388/A388M, Standard Practice for Ultrasonic Examination of Steel Forgings; EN 10228-3, ultrasonic testing of forgings; SEP 1921.
8. ASTM E8/E8M, tension testing of metallic materials; ASTM E18, Rockwell hardness; ASTM E112, grain size; ASTM E381, macroetch.
9. EN 10204, Metallic products: types of inspection documents, CEN.
10. ISO 15156-3 / NACE MR0175, materials for use in H₂S-containing environments in oil and gas production, part 3, cracking-resistant CRAs.
11. Published mill and distributor datasheets for MP159 / UNS R30159 (composition, condition properties and heat-treatment cycles), cross-checked against one another.

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, and how to cite this page

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 MP159 / UNS R30159 we forge carbon, alloy and tool steels, the precipitation-hardening and duplex stainless families, and the nickel, cobalt and superalloy grades listed in our nickel alloy section. Quality management is certified to ISO 9001:2015; material is supplied with EN 10204 3.1 certification as standard and 3.2 with third-party witness on request.

Contact for technical questions or a quotation: Jiangyin Jiangnan Metal Co., Ltd., No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China · 0086-189-2135-9659 · sales@steelforgepieces.com · WhatsApp

Related grades and forms we produce

• MP35N / R30035
• Waspaloy
• Inconel 718
• Inconel 625
• Rene 41
• Multimet N155
• Haynes 25
• Haynes 188
• Haynes 230
• All nickel & cobalt alloys
• Forged rings
• Forged discs
• MP159 forged shafts
• Forged tube sheets
• Forged pieces