ALLOY 751 / UNS N07751 Forging Parts

Published: 12 May 2022 · Last updated: 13 August 2026 · Technically reviewed by the Jiangyin Jiangnan Metal Co., Ltd. Metallurgical Engineering Team · Reading time ≈ 18 min

What forged products are available in ALLOY 751 / UNS N07751?

Jiangyin Jiangnan Metal Co., Ltd. produces ALLOY 751 / UNS N07751 by three routes, chosen by part geometry and quantity. Open-die forging handles shafts, blocks, valve blanks and large discs, the dominant route for this grade, because N07751 billet is expensive and open-die work lets us place material only where the drawing needs it. Seamless ring rolling produces rings from 200 mm to 2,500 mm outside diameter with continuous circumferential grain flow, which is what hot-section flanges and casing rings are specified for. Upset forging is used for short, large-cross-section hubs and valve heads where the fibre must turn into the head radius.

Near-net-shape forging matters more in this alloy than in stainless: removing 30–50 % of the machining stock at the die saves both the raw nickel and a great deal of carbide tooling, since N07751 in the aged condition is hard to cut. For hollow shafts with a bore above roughly 100 mm, we recommend a trepanned billet rather than a solid bar, on a nickel superalloy the material saving alone usually pays for the trepanning.

• Seamless rolled rings
• Forged rings
• Forged discs & disks
• Forged shafts
• Forged flanges
• Round bar Ø25–400 mm
• Forged sleeves
• Forged bushings
• Tube sheets
• Valve blanks
• Valve seat rings
• Forged tubes & pipes
• Spindles
• Near-net-shape forgings

What is ALLOY 751 (UNS N07751)?

ALLOY 751 is a precipitation-hardenable nickel-chromium superalloy, designated UNS N07751, containing a minimum of 70 % nickel plus cobalt, 14–17 % chromium, 5–9 % iron, 2.0–2.6 % titanium and 0.9–1.5 % aluminium. It belongs to the γ′-strengthened family: during ageing, the supersaturated nickel matrix rejects an ordered face-centred-cubic Ni₃(Al,Ti) phase, γ′, as coherent particles a few tens of nanometres across. Those particles obstruct dislocation motion, and because γ′ is anomalously stronger as temperature rises up to about 700 °C, the alloy keeps its strength where conventional steels have long since softened.

The chromium content does the second job: it forms a continuous Cr₂O₃ scale that resists oxidation and, critically for the alloy's design application, resists chemical attack from the corrosive species in engine exhaust. The 5–9 % iron is a deliberate cost measure inherited from the X-750 chemistry. It dilutes nickel without materially harming the γ′ reaction.

ALLOY 751 was developed for a single application: the exhaust valve of an internal-combustion engine. The duty is severe. The valve head runs at 700–870 °C, it seats tens of times per second, and it sits in a gas stream carrying lead oxide, sulfur, bromine and chlorine compounds. The valve needs high strength at temperature, high hot hardness so the seat face does not deform or wear, and corrosion resistance in that gas. ALLOY 751 was formulated by taking the proven X-750 chemistry and pushing aluminium up to get more γ′, buying hot hardness at the cost of a slightly narrower processing window.

A consequence engineers frequently exploit: because hot hardness is high hardfacing of the valve seat face is unnecessary in most applications. On a Stellite-faced valve the seat is a separate deposited layer with its own bond line and its own failure mode. An ALLOY 751 valve can run bare, which removes a manufacturing step and a defect population. This is the commercial case for the grade, and the reason it remained in use after leaded fuel was withdrawn in most markets.

ALLOY 751 vs alloy X-750: what actually differs?

This is the most common technical question we receive on this grade, and the answer is narrower than most datasheets imply. The two alloys share the same nickel-chromium-iron base, the same titanium range and the same niobium addition. Their physical properties, thermal properties and corrosion resistance are, for engineering purposes, the same. The difference is aluminium, and everything that follows from it.

What are the equivalent designations for ALLOY 751?

ALLOY 751 has fewer cross-references than most grades, and this catches buyers out. There is no widely used dedicated EN/DIN Werkstoff number or GB grade for N07751. European and Chinese purchase orders for this alloy are normally placed against the UNS number and ASTM B637 directly. Be careful of datasheets that assign X-750's numbers to 751, see the warning below.

What is the chemical composition of ALLOY 751?

The limiting chemical composition below is the ASTM B637 / mill-datasheet chemistry for UNS N07751. Read it alongside the role column: in a γ′ alloy the individual elements are not interchangeable, and the aluminium and titanium figures are the ones that determine whether you actually received 751 or X-750.

How do ASTM B637 and SAE J775 HEV-3 differ?

Two specifications govern this alloy in practice, and they are not identical. ASTM B637 is the general product specification for precipitation-hardening nickel alloy bars, forgings and forging stock. SAE J775 is the engine poppet valve material standard, where this chemistry is listed as HEV-3. Valve manufacturers order to J775; forging and pressure-equipment buyers order to B637. The chemistry limits differ slightly, and if your drawing cites one while your customer audits against the other, the mismatch surfaces at the worst possible moment.

What are the mechanical properties of ALLOY 751?

Mechanical properties depend heavily on which heat-treatment route was used, see the next section. The values below are typical for material in the direct-aged condition (2 h at 732 °C), which is the basis on which the alloy's published valve-application data was generated.

Why hot hardness is the governing property

For most alloys, room-temperature tensile strength is the headline. For ALLOY 751 it is nearly beside the point. A valve seat fails by deforming or wearing at temperature not by fracturing at room temperature, so the property that determines service life is hardness retained at 700–870 °C. This is what the extra aluminium buys, and it is why an ALLOY 751 valve can run without a hardfaced seat while a lower-γ′ alloy cannot. When you compare quotations, compare the aluminium content and the ageing cycle, not the room-temperature UTS.

What heat treatment does ALLOY 751 need?

Two routes are in general use, and choosing the wrong one is the most expensive mistake made with this alloy. They are not interchangeable.

What are the physical properties of ALLOY 751?

The physical and thermal properties of ALLOY 751 correspond closely to those published for alloy X-750, the small aluminium difference does not meaningfully change density, expansion or conductivity. Two figures drive most design decisions: the low thermal conductivity which is why the alloy is hard to machine and why valve heads run hot, and the density of 8.28 g/cm³ which is what your quotation is priced on.

How does ALLOY 751 resist corrosion in exhaust gas?

ALLOY 751 was selected for valve duty on corrosion grounds as much as mechanical ones. In the standard lead-oxide screening test at 913 °C (1675 °F) used to rank exhaust-valve materials, the alloy returned corrosion rates averaging 4.31 g/dm²/h a consistently good result among nickel-chromium alloys. Like other Ni-Cr alloys it also resists attack by the other aggressive species carried in an exhaust stream: sulfur, bromine and chlorine compounds.

The protection mechanism is the chromium-rich Cr₂O₃ scale. Two practical consequences follow. First, anything that disrupts scale formation, surface contamination, sulfur-bearing lubricants left on before heat treatment, or a heat that ran to the bottom of the chromium band, degrades corrosion life disproportionately. Second thermal cycling is harder on the alloy than steady heat because differential expansion spalls the scale and each regrowth consumes chromium from the substrate.

ALLOY 751 vs X-750 vs Nimonic 80A vs alloy 718 vs 21-4N

These five materials cover almost every enquiry that arrives asking for "a valve or hot-section alloy". They sit at different points on the cost and capability scale, and the gaps are wide.

ALLOY 751 failure modes and how to prevent them

The failure patterns below are the ones that recur on γ′-strengthened nickel alloys in valve and hot-section service. Most are decided at the specification and processing stage rather than in service, so they are best reviewed before the purchase order is issued.

Worked design examples

Three simplified calculations showing how the data above feeds real decisions. They are teaching examples: production designs need finite-element verification and the safety factors required by the governing code.

How do you forge, machine and weld ALLOY 751?

Forging

The hot-working range for ALLOY 751 is 980–1205 °C (1800–2200 °F) and the alloy should be reheated to 1205 °C whenever its temperature falls below 980 °C. This is a narrower and less forgiving window than any stainless steel. Below the floor the alloy work-hardens so rapidly that ductility collapses and the piece cracks; above the ceiling, approaching a 1,390 °C solidus, grain-boundary films form and the piece tears. Cooling after forging can be in still air or under a fan; there is no quench requirement at this stage.

Practical shop rules we apply to every N07751 job:

• Reduce incrementally. Multiple moderate blows, not few heavy ones, heavy single reductions generate adiabatic heating and localised shear bands.
• Reheat on schedule, not on judgement. The window is too narrow to eyeball. Pyrometer readings are logged against the furnace chart.
• Forging ratio ≥ 4:1 to break down the as-cast structure and give a uniform recrystallised grain size.
• Watch the sulfur. Above 0.010 % this alloy is hot-short. We verify it on the certificate before the billet is released to the hammer.
• Finish above the floor. Plan the pass schedule so the final blow still lands above 980 °C, rather than discovering the piece has cooled mid-sequence.

Machining

ALLOY 751 machines best in the as-hot-finished condition. The standard sequence is: machine slightly oversize → precipitation heat treat → finish to size. Precipitation-treated material is significantly harder and slower to cut, so leave only genuine finishing stock. Remember the ≈0.03 % contraction during ageing when setting the pre-age dimensions.

Welding

ALLOY 751 is weldable but is regarded as a difficult alloy to weld and the reason is its own strengthening mechanism. High aluminium plus titanium makes the heat-affected zone susceptible to strain-age cracking: during post-weld heat-up, γ′ precipitates while residual stress is still relaxing, the HAZ hardens faster than it can creep, and it cracks. Higher aluminium makes 751 more susceptible than X-750.

• Weld in the solution-treated condition never in the fully aged condition.
• GTAW with close arc control and low heat input is the preferred process.
• Matching filler for full properties, or a non-hardenable filler (alloy 625 / ERNiCr-3 / alloy 82) where joint strength allows. This removes the γ′ reaction from the weld metal and is the pragmatic choice for restrained joints and repairs.
• Minimise restraint and heat rapidly through the γ′ precipitation range during PWHT.
• Full solution treat and re-age after welding to recover properties across the joint.
• Penetrant test after PWHT not merely after welding, strain-age cracks appear during the thermal cycle, not during deposition.

ALLOY 751 production capability at Jiangyin Jiangnan Metal

ALLOY 751 is a made-to-order grade in our nickel-alloy portfolio. Billet is procured against the confirmed order rather than held in stock, which is what sets the lead time, not shop capacity. The envelopes below are tested limits for this alloy and they are tighter than our carbon-steel limits because a γ′ superalloy takes more passes and more reheats to move the same volume of metal.

Process flow: every ALLOY 751 forging

Equipment used on this grade

Which standards and quality systems apply?

For ALLOY 751 / UNS N07751 the governing product specification is ASTM B637 with SAE J775 HEV-3 applying to engine valve material. Inspection documents are issued to EN 10204. Our quality management system is certified to ISO 9001:2015.

• ASTM B637
• SAE J775 HEV-3
• ASME SB-637 (where adopted)
• EN 10204 3.1
• EN 10204 3.2
• ASTM A388 (UT)
• EN 10228-3 (UT)
• SEP 1921 (UT)
• ASTM E165 (PT)
• ASTM E112 (grain size)
• ASTM E381 (macroetch)
• ASTM E8 (tensile)
• ISO 9001:2015

Quality assurance and non-conformance policy

How to specify an ALLOY 751 forging order

Superalloy orders go wrong at the specification stage far more often than in the shop. These seven steps close the ambiguities that cause the disputes we actually see.

1. State the generic designationWrite UNS N07751 per ASTM B637 or SAE J775 HEV-3 for engine valves. Ordering against a trademarked brand name alone legally restricts supply to that trademark holder and will slow your enquiry down.
2. Pin the aluminium rangeIf hot hardness governs the part, do not accept the full 0.9–1.5 % band. Specify Al 1.1–1.5 % on the purchase order. This single line is the difference between 751 behaviour and X-750 behaviour.
3. Specify the melt routeState EAF + AOD + ESR for general forgings, or VIM + VAR where inclusion cleanliness and fatigue life are critical. The melt route drives both cost and lead time, so decide it early.
4. Choose the heat-treatment routeSay explicitly whether you want Route A direct age (732 °C / 2 h) for hot hardness, or Route B solution + equalise + precipitate for creep strength. "Solution treated and aged" alone is ambiguous on this alloy.
5. Define grain size and grain flowGive the required ASTM E112 grain size. For rings and discs, require continuous circumferential grain flow verified by macroetch to ASTM E381 it is the whole reason to buy a rolled ring rather than a cut plate.
6. Define testingState the ultrasonic standard and acceptance class (ASTM A388 EN 10228-3 or SEP 1921), penetrant testing to ASTM E165 on machined surfaces, and whether elevated-temperature tensile or stress-rupture testing is required, with test-piece location and orientation.
7. Specify certification and markingState EN 10204 3.1 or 3.2 name the inspection body if 3.2 applies, and define heat-number marking and its location on the finished part.

Top 10 mistakes when ordering ALLOY 751

Drawing callout template for ALLOY 751

Copy this block into the material callout box on your drawing. It closes every ambiguity listed above.

MATERIAL:   UNS N07751 per ASTM B637
            (engine valve parts: also SAE J775 HEV-3)
            Aluminium 1.1-1.5 wt % REQUIRED
            (do NOT substitute UNS N07750 / X-750 / W.Nr 2.4669)

MELT:       EAF + AOD + ESR   // or VIM + VAR where specified

CONDITION:  ROUTE A - direct age 732 C / 2 h / air cool
            // or ROUTE B - solution ~1150 C + 845 C/24 h + 705 C/20 h
            State one. "Solution treated and aged" alone is not sufficient.

GRAIN:      Grain size per ASTM E112, size __ or finer
            Rings/discs: continuous circumferential grain flow,
            verified by macroetch per ASTM E381

NDE:        UT per ASTM A388 Class __  // or EN 10228-3 / SEP 1921
            PT per ASTM E165 on all machined surfaces

TEST:       Tensile per ASTM E8 at room temperature
            Elevated-temperature tensile at ___ C  [ ] required [ ] not required
            Stress rupture per ASTM B637           [ ] required [ ] not required

CERT:       EN 10204 3.1   // or 3.2 with third-party witness: __________

MARKING:    Heat number + specification, low-stress stamped or vibro-etched
            on non-functional surface

SURFACE:    Ra <= 0.8 um at fillets and stress transitions
            Generous radii - alloy is notch sensitive when fully aged

Where is ALLOY 751 used?

Glossary

ALLOY 751

Precipitation-hardenable nickel-chromium superalloy, UNS N07751, with aluminium raised above X-750 for greater precipitation hardening. Designed for internal-combustion engine exhaust valves.

UNS N07751

The generic Unified Numbering System designation for this chemistry. The correct callout on drawings and purchase orders.

ASTM B637

Standard specification for precipitation-hardening and cold-worked nickel alloy bars, forgings and forging stock for moderate or high temperature service. The governing product specification for N07751.

SAE J775 HEV-3

Engine poppet valve material designation for this chemistry, used across the automotive and diesel valve supply chain. Slightly different chemistry limits from ASTM B637.

γ′ (gamma prime)

The ordered FCC Ni₃(Al,Ti) precipitate that strengthens this alloy family. Coherent with the matrix, a few tens of nanometres across, and unusually stronger as temperature rises to about 700 °C.

Hot hardness

Hardness retained at elevated temperature. The property that determines exhaust-valve seat life, and the reason ALLOY 751 exists as a separate grade from X-750.

Direct age (Route A)

Ageing hot-finished material at 732 °C for 2 hours without a prior solution treatment. Standard practice for valve applications and the basis of the alloy's published property data.

Solution treatment

Heating to about 1,150 °C to dissolve precipitates into the matrix, then cooling fast enough to hold them in supersaturated solution ready for a controlled ageing step.

Strain-age cracking

Cracking in the weld heat-affected zone when γ′ precipitates during post-weld heat-up while residual stress is still relaxing. The principal weldability limitation of high Al + Ti superalloys.

Hot shortness

Loss of ductility at forging temperature caused by low-melting films, usually sulfur-bearing, on grain boundaries. The reason sulfur is capped at 0.010 % in this alloy.

Seamless rolled ring

A ring produced by piercing a billet and rolling it out on a ring mill, giving continuous circumferential grain flow. Stronger than a ring machined from plate or bar, and usually cheaper in nickel alloys.

EN 10204 3.1 / 3.2

Inspection document types. 3.1 is issued by the manufacturer's own independent inspection function; 3.2 is countersigned by a third party such as Lloyd's, DNV, BV, ABS or TÜV.

Trepanned billet

A billet with the bore removed by trepanning rather than drilling, so the core is recovered as usable material. On nickel alloys the saving usually exceeds the trepanning cost.

Forging ratio

The ratio of starting to finished cross-sectional area. A ratio of at least 4:1 is required to break down as-cast structure and give uniform recrystallised grain.

Frequently asked questions about ALLOY 751

Technical references

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

1. ASTM B637, Standard Specification for Precipitation-Hardening and Cold Worked Nickel Alloy Bars, Forgings, and Forging Stock for Moderate or High Temperature Service, ASTM International, West Conshohocken, PA.
2. SAE J775, Engine Poppet Valve Information Report, SAE International, designation HEV-3.
3. Special Metals Corporation, INCONEL® alloy X-750 and INCONEL® alloy 751 technical bulletins (publication numbers SMC-067 and related), Huntington, WV.
4. ASM Handbook, Volume 1: Properties and Selection: Irons, Steels, and High-Performance Alloys, ASM International, Materials Park, OH, sections on nickel-base precipitation-hardening alloys.
5. ASM Handbook, Volume 4E: Heat Treating of Nonferrous Alloys, ASM International, heat treatment of γ′-strengthened nickel alloys.
6. ASM Handbook, Volume 14A: Metalworking: Bulk Forming, ASM International, forging of heat-resistant alloys.
7. Donachie, M.J. and Donachie, S.J., Superalloys: A Technical Guide, 2nd Edition, ASM International, 2002.
8. Reed, R.C., The Superalloys: Fundamentals and Applications, Cambridge University Press, 2006, γ′ precipitation and coarsening kinetics.
9. Sims, C.T., Stoloff, N.S. and Hagel, W.C. (eds.), Superalloys II, John Wiley & Sons, 1987.
10. ASTM A388/A388M, Standard Practice for Ultrasonic Examination of Steel Forgings, ASTM International.
11. EN 10228-3, Non-destructive testing of steel forgings. Part 3: Ultrasonic testing of ferritic or martensitic steel forgings, CEN, Brussels.
12. SEP 1921, Ultrasonic testing of steel forgings, Stahl-Eisen-Prüfblatt, Verein Deutscher Eisenhüttenleute.
13. ASTM E165/E165M, Standard Practice for Liquid Penetrant Testing for General Industry, ASTM International.
14. ASTM E112, Standard Test Methods for Determining Average Grain Size, ASTM International.
15. ASTM E381, Standard Method of Macroetch Testing Steel Bars, Billets, Blooms, and Forgings, ASTM International.
16. ASTM E8/E8M, Standard Test Methods for Tension Testing of Metallic Materials, ASTM International.
17. EN 10204, Metallic products. Types of inspection documents, CEN, Brussels.
18. ISO 9001:2015, Quality management systems. Requirements, International Organization for Standardization.

Standards cited are the revisions known at the time of the last page review. For procurement, always reference the revision in force at your contract date. Typical property values on this page are for guidance and are not guaranteed minima; design to the governing specification. Trademarks referenced belong to their respective owners.

Request a quotation: ALLOY 751 / UNS N07751 forgings

Send the drawing or the basic dimensions, the quantity, the heat-treatment route and the certification level, and we will respond within 24 hours with price, lead time and confirmation of the applicable standards. If you are not sure which heat-treatment route or aluminium range suits the duty, describe the application instead and our engineering team will advise before quoting.