MP159 / UNS R30159 / AMS 5843 Forging Parts

Published: 18 June 2022  |  Last updated: 15 August 2026  |  Technically reviewed by the Jiangyin Jiangnan Metal Co., Ltd. Metallurgical Engineering Team

UNS

R30159

Spec

AMS5841 / 5842 / 5843

UTS aged

1,830MPa · 265 ksi

UTS annealed

850MPa · 123 ksi

Density

8.37g/cm³ · 0.302 lb/in³

Max service

593°C · 1,100 °F

Magnetic

Noµᵣ ≈ 1.0

Melt route

VIM+ VAR

Jiangyin Jiangnan Metal Co., Ltd. produces MP159 / UNS R30159 (the generic chemistry behind the MP159® trademark) as open-die forged bar, forged shafts, discs, seamless rolled rings, sleeves, bushings and near-net-shape forgings. Our speciality in this grade is fastener and shaft stock for jet-engine, launch-vehicle and subsea service, supplied solution heat treated for the customer's own cold-work and ageing route, or fully processed to AMS 5843. All material is double vacuum melted (VIM + VAR), ultrasonically tested to ASTM A388 or EN 10228-3, and released with an EN 10204 3.1 certificate, or 3.2 with third-party witness by Lloyd's, DNV, BV, ABS or TÜV on request.

What is MP159 alloy (UNS R30159)?

MP159, designated UNS R30159, is a multiphase nickel-cobalt-chromium superalloy developed from MP35N by adding titanium, aluminium, niobium and iron. Those four additions are what separate the two alloys: they make MP159 age-hardenable through γ′ Ni₃(Al,Ti) precipitation, which MP35N is not. The practical consequence is that MP159 carries MP35N-class ultra-high strength and corrosion resistance upward in temperature, from roughly 400 °C for MP35N to about 593 °C (1,100 °F) for MP159.

The alloy is supplied as bar, wire and forgings, and reaches its published strength only after a fixed three-stage route: solution heat treatment, then controlled cold work, then ageing. Jiangyin Jiangnan Metal Co., Ltd. supplies MP159 at any of those three stages, because which stage you buy determines whether the material is soft enough to machine or already at full strength.

What MP159 is good at

• Ultimate tensile strength above 1,830 MPa (265 ksi) in the work strengthened and aged condition, roughly 30–40 % above Inconel 718 and about double a typical PH stainless.
• Strength retention to ~593 °C (1,100 °F), with useful properties reported to 649 °C (1,200 °F) for short exposures.
• Excellent ductility and toughness at high strength (unusual, because most routes to 1,800 MPa are brittle).
• Outstanding resistance to chloride SCC, crevice corrosion, H₂S and hydrogen embrittlement, comparable to MP35N.
• Essentially non-magnetic (µᵣ ≈ 1.0), usable in instrumentation and MWD assemblies.
• High fatigue strength and good creep resistance at intermediate temperature.

Where MP159 is the wrong choice

• Large, thick forgings. The strength depends on uniform cold work. A 600 mm disc cannot be cold worked to the same degree as a 30 mm bar, so bar-level properties are not achievable in heavy sections; see the honest capability note in production capability.
• Welded assemblies. Welding re-solutions the joint and drops local strength towards 850 MPa. MP159 is a mechanically fastened alloy.
• Continuous service above ~650 °C. Use Waspaloy, René 41 or Inconel 718 instead.
• Cost-driven structural parts. The high cobalt and molybdenum content makes MP159 several times the price of Inconel 718 per kilogram.

Why is MP159 called a "multiphase" alloy?

Because it is strengthened by two independent mechanisms operating in the same microstructure at the same time. Understanding this is not academic. It explains why the processing order on your purchase order cannot be changed, and why the alloy behaves the way it does on your machine tools.

What are the equivalent designations for MP159?

MP159 appears on drawings under several names. All of the designations below refer to the same chemistry, and Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders against any of them.

What is the chemical composition of MP159?

The nominal composition of MP159 / UNS R30159 is 35.7 % Co, 25.5 % Ni, 19.0 % Cr, 9.0 % Fe, 7.0 % Mo, 3.0 % Ti, 0.6 % Nb and 0.2 % Al by weight. Every element is doing a specific job, and the table below states which.

How the composition is verified

Jiangyin Jiangnan Metal Co., Ltd. verifies every MP159 heat by optical emission spectrometry against NIST-traceable standards, and reports the full elemental analysis on the EN 10204 3.1 certificate together with the heat number, melt route and ingot identity. Where the customer specifies EN 10204 3.2, an independent inspection body witnesses the analysis and countersigns.

AMS 5841 vs AMS 5842 vs AMS 5843: which condition do you need?

This is the single most important decision on an MP159 purchase order. The three AMS specifications describe the same alloy at three points along the same processing route, and tensile strength varies by more than a factor of two between them. An order that says only "MP159" is ambiguous and will be queried.

What are the mechanical properties of MP159?

The table below gives typical room-temperature properties. Values in the solution heat treated row are well established and reproducible; values in the work strengthened rows depend on the degree of cold reduction actually achieved, which in turn depends on section size and geometry.

Elevated-temperature behaviour

MP159 loses strength gradually rather than abruptly as temperature rises, and the γ′ precipitation is what makes this possible. Typical retention of room-temperature ultimate tensile strength in the AMS 5843 condition is approximately 95 % at 315 °C, 88 % at 480 °C, 82 % at 593 °C and roughly 72 % at 649 °C. Above the ageing temperature the structure begins to over-age and the loss becomes permanent rather than recoverable on cooling; see the service temperature check.

What are the physical properties of MP159?

How corrosion-resistant is MP159?

MP159 has corrosion resistance comparable to MP35N, which is among the best of any high-strength structural alloy. The 19 % chromium builds a stable passive film, and the 7 % molybdenum defends that film against chloride pitting and crevice attack. Reported service includes mineral acids, hydrogen sulphide environments, seawater and salt spray.

MP159 vs MP35N vs Inconel 718 vs Waspaloy vs A286

MP159 is frequently cross-shopped against four other alloys. The table below is the honest comparison, including the cases where MP159 is the wrong answer.

MP159 failure modes and how to prevent them

The following are the failure patterns most often traced back to MP159 material or processing rather than to design load. Every one of them is preventable at the specification stage.

Worked design examples using MP159 data

Three simplified examples showing how the data on this page feeds real decisions. Production designs require finite-element verification and the safety factors mandated by the governing code.

How do you machine, forge and join MP159?

Machining

MP159 is a difficult but predictable material. It work-hardens aggressively, conducts heat poorly, and is abrasive. The governing rules are simple and non-negotiable: machine in the solution heat treated condition wherever the design allows, keep the tool cutting at all times, and flood the cut.

• Speed. Turning typically 25–40 m/min in the AMS 5841 condition; 12–25 m/min in the aged condition. Roughly one third of what you would run on 4140.
• Feed. Heavy and positive: 0.15–0.30 mm/rev. A light feed rides on the work-hardened layer and destroys the tool.
• Depth of cut. Always deeper than the previously work-hardened layer, typically 1.5–3.0 mm on roughing. Never take a 0.1 mm skim pass.
• Tooling. Sharp positive-rake coated carbide (TiAlN or AlCrN). Rigid holders, minimum overhang, no chatter.
• Coolant. Flood, high concentration, aimed at the cutting edge. Through-tool coolant for drilling.
• Never dwell. A stationary rotating tool glazes the surface in under a second and the next pass will fail.

Hot forging

Jiangyin Jiangnan Metal Co., Ltd. forges MP159 in a narrow window with frequent reheating. The alloy's high hot strength means forces are high and the workable temperature band is short.

• Forging window approximately 1,065–1,175 °C (1,950–2,150 °F), finishing above ~1,010 °C.
• Reheat frequently; take modest reductions per pass. The alloy hardens rapidly during hot work and will crack if pushed cold.
• Forging ratio ≥ 4:1 to break down the as-cast VAR structure and develop uniform grain.
• Solution treat and water quench immediately after forging, before any cold work.
• Ultrasonic inspection after solution treatment, per ASTM A388 or EN 10228-3 as specified.

Cold work

Cold work is not a finishing operation on MP159. It is the primary strengthening step, and it has to be planned into the part geometry from the start. Bar is drawn or rolled; rings can be cold-expanded to a limited degree; discs and blocks essentially cannot be worked at the core. If your part cannot be cold worked, it cannot reach AMS 5843 properties, and the specification should say so.

Welding

MP159 can be GTAW welded, but the joint gives up the alloy's whole advantage: the fusion zone and heat-affected zone are effectively re-solutioned and drop toward 850 MPa. There is no post-weld treatment that restores full strength short of re-processing the entire assembly through solution, cold work and ageing. Design MP159 parts as mechanically fastened assemblies. Where a seal weld carries no load, it is acceptable, but it must be shown to carry no load.

MP159 production capability at Jiangyin Jiangnan Metal

MP159 is a specialist grade in our portfolio rather than a volume one, and we would rather say plainly what it can and cannot do in our shop than take an order we cannot fulfil.

Complete MP159 process flow: 9 controlled stages

Every MP159 forging passes through these stages. Each is logged and traceable on the final certificate.

Production and inspection equipment qualified for MP159

MP159 order delivery performance

Indicative dispatch performance for MP159 / UNS R30159 orders, measured from order confirmation to ex-works dispatch. Refreshed quarterly.

Which standards and quality systems apply to MP159 forgings?

For MP159 / UNS R30159 the governing documents are the AMS 5841 / 5842 / 5843 family, supplemented by engine-maker source specifications such as GE S-400 / S-1000 and the Rolls-Royce SABRe supply-chain requirements where the end use is a gas turbine.

* NACE MR0175 / ISO 15156 acceptance is granted per UNS number, condition and hardness limit, in the edition in force at the contract date. We will issue a compliance statement where the standard permits; see the screening tool.

Quality assurance and non-conformance policy

How to specify an MP159 forging order

MP159 carries one decision that does not exist on most grades: which of the three AMS conditions. Working through these seven steps removes almost all ambiguity from the order.

1. State the generic designation. Write UNS R30159 plus the AMS number rather than "MP159" alone. MP159® is a trademark; the generic designation lets any qualified producer supply it legally.
2. Choose the supply condition. AMS 5841 (solution treated), AMS 5842 (+ work strengthened) or AMS 5843 (+ aged). This changes tensile strength by more than 2×.
3. Provide the drawing and state the maximum section thickness. Section size governs achievable cold work and therefore achievable strength. This is the field most often left blank and most often disputed later.
4. Specify the melt route. VIM + VAR is standard for aerospace. State whether an alternative remelt route is acceptable for non-aerospace service.
5. Define testing and NDE. Tensile test direction and coupon location, hardness, ultrasonic acceptance per ASTM A388 or EN 10228-3, penetrant per ASTM E1417 where surfaces are critical.
6. Specify certification. EN 10204 3.1 mill certificate, or 3.2 with third-party witness, and name the inspection body if 3.2 is required.
7. Give quantity, delivery target, Incoterm and destination so that lead time and freight can be fixed in the quotation.

Ten mistakes engineers make when ordering MP159

1. Writing "MP159 per AMS 5843" on a thick section. The properties are not achievable in heavy sections. Fix: state the section thickness and agree a realistic property level, or change to Inconel 718.
2. Leaving the condition off the purchase order. "MP159" alone spans 850 to 1,830 MPa. Fix: always name AMS 5841, 5842 or 5843.
3. Letting a heat-treat vendor age before cold work. Reverses the strengthening mechanism and loses most of the strength. Fix: state the sequence on the router and require charts.
4. Specifying MP159 for a welded assembly. Welding re-solutions the joint. Fix: redesign as mechanically fastened, or change to Inconel 718.
5. Using MP159 above 650 °C. Over-ageing is permanent. Fix: use the service temperature check; move to Waspaloy or René 41.
6. Assembling threads dry. MP159 galls against itself. Fix: anti-seize or solid-film lubricant on every thread, every time.
7. Specifying MP159 where MP35N would do. If the part never gets hot, MP35N delivers the same strength and corrosion resistance without the ageing step. Fix: check the actual service temperature first.
8. Machining in the fully aged condition unnecessarily. Triples cycle time and destroys tooling. Fix: buy AMS 5841, machine, then cold work and age.
9. Not specifying where the test coupon is taken from. Surface coupons pass while the core fails. Fix: specify coupon location; mid-radius is the honest choice on anything substantial.
10. Screening incoming material for zirconium. A widespread datasheet error. The 0.6 % element in MP159 is niobium, not zirconium. Fix: correct your incoming-inspection checklist.

MP159 drawing callout template

Copying this format into your CAD material block removes most ordering ambiguity. Adjust condition, properties and NDE for your application.

Where is MP159 used?

MP159 goes where a part must be very strong, corrosion-resistant, non-magnetic and hot, and where the section is small enough to cold work. In practice that means fasteners first, and rotating hardware second.

Representative MP159 project scenarios

Illustrative of the work we do in this grade. Named references are available under NDA.

Glossary of MP159 terms

Multiphase alloy

An alloy strengthened by more than one microstructural mechanism at once. In MP159 these are deformation-induced HCP platelets from cold work and γ′ Ni₃(Al,Ti) precipitates from ageing. The "MP" in the name is short for multiphase.

UNS R30159

The Unified Numbering System designation for the MP159 chemistry, the correct generic name to write on a purchase order.

AMS 5841

SAE Aerospace Material Specification for MP159 bar in the solution heat treated condition: 1,038–1,052 °C for 4–8 hours followed by water quench. The soft, machinable condition, ≈ 850 MPa UTS.

AMS 5842

MP159 bar, solution heat treated and work strengthened. Cold work has generated the HCP platelet structure but no ageing has been performed.

AMS 5843

MP159 bar, solution heat treated, work strengthened and aged at 649–677 °C for 4–4.5 hours with air cool. The full-strength condition, ≥ 1,830 MPa UTS.

Work strengthening

Controlled cold deformation applied after solution heat treatment. Also called strain hardening. In MP159 it is the primary strengthening step, not a finishing operation.

HCP platelet

A hexagonal close-packed lamella formed from the FCC matrix during cold work. Acts as a barrier to dislocation motion and carries most of MP159's strength.

Gamma prime (γ′)

The ordered Ni₃(Al,Ti) precipitate formed during ageing. Adds strength and, critically, pins the cold-worked structure so it resists recovery at temperature.

Stacking-fault energy

A property of the crystal lattice that governs how readily the FCC → HCP transformation occurs. The high cobalt content of MP159 lowers it, which is why the multiphase mechanism works.

VIM + VAR

Vacuum induction melting followed by vacuum arc remelting, the double vacuum melt route used to produce aerospace-quality MP159 with tight chemistry control and low inclusion content.

MP35N

UNS R30035, the Co-Ni-Cr-Mo multiphase alloy from which MP159 was developed. Strengthened by cold work only, with no ageing response, and limited to about 400 °C.

Galling

Adhesive wear in which mating surfaces seize and tear. MP159 galls readily against itself, which is why anti-seize on threads is mandatory rather than advisory.

EN 10204 3.1 / 3.2

Inspection document types. 3.1 is a mill certificate issued by the manufacturer's own independent inspection function; 3.2 adds a third-party or customer witness.

Frequently asked questions about MP159

Technical references

Chemistry, property, heat-treatment and corrosion data on this page are drawn from the published standards and engineering literature listed below. Test results reported on our material certificates are independent and traceable to calibrated equipment.

1. AMS 5841, "Alloy Bars, Multiphase, 25.5Ni – 35.7Co – 19Cr – 9.0Fe – 7.0Mo – 3.0Ti – 0.6Cb – 0.2Al, Solution Heat Treated", SAE International.
2. AMS 5842, "Alloy Bars, Multiphase, Solution Heat Treated and Work Strengthened", SAE International.
3. AMS 5843, "Alloy Bars, Multiphase, Solution Heat Treated, Work Strengthened and Aged", SAE International.
4. SAE / ASTM Metals & Alloys in the Unified Numbering System, entry UNS R30159, SAE International and ASTM International.
5. Gu, J., Guo, L., Gan, B., Bi, Z., Song, M., et al., "Microstructure and mechanical properties of an MP159 alloy processed by torsional deformation and subsequent annealing", Materials Science and Engineering A, 2020.
6. Smith, G.D. and Patel, S.J., "The Role of Niobium in Wrought Precipitation-Hardened Nickel-Base Alloys", Superalloys 718, 625, 706 and Derivatives, TMS.
7. ASM Handbook, Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys, ASM International, Materials Park, OH: sections on cobalt-base and multiphase alloys.
8. ASM Specialty Handbook: Heat-Resistant Materials, J.R. Davis (ed.), ASM International.
9. ASM Handbook, Volume 14A: Metalworking: Bulk Forming, ASM International: forging of superalloys.
10. 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", ISO.
11. ASTM A388/A388M, "Standard Practice for Ultrasonic Examination of Steel Forgings", ASTM International.
12. EN 10228-3, "Non-destructive testing of steel forgings — Part 3: Ultrasonic testing of ferritic or martensitic steel forgings", CEN.
13. ASTM E1417/E1417M, "Standard Practice for Liquid Penetrant Testing", ASTM International.
14. ASTM E8/E8M, "Standard Test Methods for Tension Testing of Metallic Materials", ASTM International.
15. ASTM E112, "Standard Test Methods for Determining Average Grain Size", ASTM International.
16. ASTM E381, "Standard Method of Macroetch Testing Steel Bars, Billets, Blooms, and Forgings", ASTM International.
17. EN 10204, "Metallic products — Types of inspection documents", CEN.
18. Shigley, J.E. and Mischke, C.R., Mechanical Engineering Design, modified Goodman fatigue criterion and bolted-joint preload analysis, used for the worked examples on this page.
19. Bickford, J.H., An Introduction to the Design and Behavior of Bolted Joints, CRC Press, nut-factor torque-preload relationship.

Standards cited are the revisions known at the time of the last page review. For procurement, always reference the revision in force at the contract date. All trademarks are the property of their respective owners.