Alloy 75 / Nimonic 75 / UNS N06075 forging parts

Section 01What is Alloy 75, and why is it specified?

Alloy 75 is a wrought nickel-chromium alloy of the classic 80/20 type, with controlled additions of titanium (0.2-0.6 %) and carbon (0.08-0.15 %). The chromium forms a tenacious, self-healing Cr₂O₃ scale that gives the alloy its oxidation and scaling resistance; the titanium and carbon combine to form fine titanium carbides that pin grain boundaries and add a modest amount of strength. Nickel makes up the balance, typically 72-80 %, and gives a stable face-centred-cubic austenitic matrix with no phase transformation on cooling.

Alloy 75 was developed in the United Kingdom in the early 1940s as one of the first members of the Nimonic series, originally for turbine blades in early jet engines. Blade duty moved to the age-hardening grades within a few years, but the alloy stayed in production for applications where oxidation resistance and ease of fabrication matter more than strength. It is still specified today for furnace muffles and retorts, heat-treatment baskets and fixtures, gas-turbine ancillary hardware, boiler tube supports, exhaust components and nuclear engineering parts.

Alloy 75 is not age hardenable

The titanium content of Alloy 75 is too low and the alloy contains essentially no aluminium, so no useful volume fraction of the γ′ Ni₃(Al,Ti) precipitate can form. Every mechanical property quoted on this page applies to the solution-annealed condition, and no ageing cycle will raise it. Where a heat-treatable grade is required, Nimonic 80A (UNS N07080) uses the same 80/20 base with aluminium and titanium added, and gives roughly double the proof strength after ageing.

The absence of a precipitation reaction has practical benefits. Alloy 75 does not suffer strain-age cracking in the weld heat-affected zone, needs no controlled ageing cycle after fabrication, work-hardens slowly, and forms and machines more easily than the γ′-strengthened grades. These properties suit fabricated assemblies that run hot but carry little load.

Section 02What are the equivalent designations for Alloy 75?

Alloy 75 travels under a large number of names because it predates the modern unified numbering systems and was standardised independently in Britain, Germany and the United States. Every designation in the table below refers to the same base chemistry. Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders written against any of them and names every specification satisfied on the material certificate.

Designations compiled from BS 3072/3076, DIN 17742, ISO 9723 and published mill datasheets. AMS 5871 and ASTM B637 are sometimes miscited for this alloy on trading sites - AMS 5871 covers Alloy 800 flat product and ASTM B637 covers precipitation-hardening nickel alloys such as N07080 and N07718, neither of which is UNS N06075. If a drawing calls for Alloy 75 to ASTM B637, query it with the design authority before ordering.

Section 03What is the chemical composition of Alloy 75 / UNS N06075?

The commonly published composition window for Alloy 75 is nickel balance, chromium 18.0-21.0 %, titanium 0.2-0.6 % and carbon 0.08-0.15 %, with iron, manganese, silicon, copper, cobalt and aluminium held to maxima and tramp elements tightly restricted. The individual product standards - BS HR5, DIN 17742, the MSRR aerospace series and the wire specifications - differ slightly in the limits they impose, most noticeably on silicon, cobalt and aluminium, so the table below shows the widest generally accepted window together with the elements that only some standards call out.

* Only specified by some product standards. Where a drawing invokes a specific standard, that standard's limits govern. Jiangyin Jiangnan Metal Co., Ltd. reports both the ladle analysis and the product analysis for every heat on the EN 10204 certificate, so the actual delivered chemistry is always documented rather than assumed.

Function of the main alloying elements

Section 04What are the mechanical properties of Alloy 75?

All values below apply to solution-annealed forged product, tested at room temperature unless a test temperature is stated. Because Alloy 75 is not age hardenable, these are both the as-delivered and the in-service properties. No subsequent heat treatment will raise them.

Room-temperature values are the figures Jiangyin Jiangnan Metal Co., Ltd. has published for this grade and are consistent with the annealed band given in published mill datasheets. Actual tested values for your heat appear on the EN 10204 certificate.

How the strength falls with temperature

Tensile strength of Alloy 75 declines gradually to about 600 °C and then more steeply as creep begins to dominate. The pattern below is typical of solution-annealed 80/20 nickel-chromium alloys and is given for orientation. Design allowables must be taken from the applicable code rather than from a supplier datasheet.

Section 05What is the maximum service temperature of Alloy 75?

Two separate limits apply. Oxidation sets one ceiling and creep sets a second, much lower one. Which of the two governs depends on how hard the part is loaded, and confusing them is the most common specification error with this alloy.

The two ceilings explained

Oxidation ceiling, about 1,000 °C. The Cr₂O₃ scale stays adherent and protective in clean air to roughly this temperature. Above it the scale begins to volatilise and spall, and metal loss accelerates. Furnace muffles, retorts, baskets and radiant-tube supports that carry only their own weight operate in this band.

Creep ceiling, about 815 °C, and lower for long life. A stressed part fails by time-dependent deformation long before it fails by oxidation. Useful tensile and creep-rupture strength extends to about 815 °C (1,500 °F) for short-life or lightly stressed duty. For components expected to run for tens of thousands of hours under load, most designers stay at or below 650 °C. This is the number that matters for pressure parts, rotating parts and anything bolted.

Low-temperature end. Alloy 75 has a face-centred-cubic structure with no ductile-to-brittle transition, so it stays tough down to cryogenic temperatures, with published operating ranges extending to −200 °C (−330 °F).

Section 06What are the physical properties of Alloy 75?

Density, melting point, moduli and expansion coefficient are the published mill values for this alloy. Thermal conductivity, specific heat and resistivity are typical values for the 80/20 Ni-Cr family and are given for estimation, not for design calculation.

Section 07How does Alloy 75 behave in oxidising, carburising and sulphidising atmospheres?

Alloy 75 performs well in clean oxidising atmospheres and poorly in sulphur-bearing ones. This distinction decides whether the alloy suits an application more often than any strength figure does.

Section 08Alloy 75 vs Nimonic 80A vs Nimonic 90 vs Inconel 600 - which one do you need?

Alloy 75 is the lowest-strength member of the Nimonic series. The table below covers the grades it is most often compared with during selection.

Comparative values are nominal figures for orientation. Cost indices are relative and move with the nickel and cobalt markets. Jiangyin Jiangnan Metal Co., Ltd. forges every grade in this table.

Section 09What heat treatment is applied to Alloy 75?

Alloy 75 forgings are solution annealed for 30-60 minutes at 1,050 °C (1,920 °F) and air cooled. Thin sheet requires only 5-10 minutes at the same temperature. No ageing step follows, because the alloy has no precipitation-hardening response. Cold-worked material can be stress relieved at 450-470 °C (840-880 °F) for 30-60 minutes where dimensional stability after machining matters, but this is a stress-relief treatment, not a strengthening one.

Soak time scales with section thickness - roughly 30 minutes per 25 mm of ruling section once the part has reached temperature. Jiangyin Jiangnan Metal Co., Ltd. records the furnace chart for every batch and issues it with the EN 10204 certificate, so the actual cycle applied to your parts is documented rather than asserted.

Section 10How is Alloy 75 melted, and why does the route matter?

Jiangyin Jiangnan Metal Co., Ltd. melts Alloy 75 by electric arc furnace, vacuum oxygen decarburisation and electroslag remelting (EAF + VOD + ESR). Where a cleaner, lower-gas product is required, for example for aerospace or rotating components, vacuum induction melting followed by electroslag or vacuum arc remelting (VIM + ESR or VIM + VAR) is available. The melting route is stated on the material certificate.

The melting route determines inclusion cleanliness and therefore ultrasonic response. A part that must pass volumetric ultrasonic examination to a tight acceptance class needs a remelted ingot. Specifying EN 10228-3 quality class 3 or 4 against an air-melted ingot is a common cause of rejected forgings. State the UT class at enquiry stage and the melting route will be matched to it.

Section 11How is Alloy 75 forged?

Alloy 75 is forged from about 1,150-1,180 °C with a finishing temperature not below roughly 950 °C. The hot-working window is wide for a superalloy but still narrow compared with carbon steel, so reheating between passes is normal practice rather than an exception.

Process routes used for this grade

• Open-die forgingShafts, blocks, hollow forgings and large discs. The default route for one-off and low-quantity parts to drawing.
• Seamless ring rollingRings are pierced and expanded on a radial-axial mill, giving continuous circumferential grain flow and no weld.
• Upset forgingShort, large-cross-section discs and hubs where the billet is compressed axially.
• Near-net shapeProfiled dies remove 30-50 % of the rough machining on repeated geometries - worth it above roughly 20 pieces.

Complete production sequence

1. Raw materialEAF + VOD + ESR ingot or billet, heat number recorded, chemistry verified on receipt
2. Cut & heatBillet cut to weight, soaked at 1,150-1,180 °C, temperature logged
3. ForgeHammer or press, ≥ 4:1 ratio, multi-pass, reheat as needed, finish above 950 °C
4. Ring rollRadial-axial mill where the part is a ring; profile rolled to drawing
5. Solution anneal1,050 °C for 30-60 min, air cool, furnace chart recorded
6. Rough machineTo UT-ready surface, leaving agreed finishing stock
7. NDT & testUT to EN 10228-3 / SEP 1921 / ASTM A388, PT on machined surfaces, tensile and hardness
8. Certify & shipEN 10204 3.1 or 3.2, marked with heat number, packed for sea freight

Section 12How do you weld and machine Alloy 75?

Welding

Alloy 75 is one of the more weldable superalloys because it is not age hardenable. There is no γ′ precipitation reaction to drive strain-age cracking in the heat-affected zone, which is the failure mode that makes Nimonic 80A and 90 difficult to weld. GTAW (TIG), GMAW (MIG), plasma arc and resistance welding are all used. Matching filler or a nickel-chromium filler of the Inconel 82 / 625 type is selected according to the joint and the service atmosphere.

• Cleanliness first. Degrease and remove all marking paint, cutting fluid and sulphur-bearing residues before welding. Contamination causes hot cracking in the fusion zone.
• Low heat input, no weave. Stringer beads and controlled interpass temperature limit grain growth in the heat-affected zone.
• Preheat is normally unnecessary. The alloy is not hardenable and has no cold-cracking mechanism.
• Post-weld solution anneal at 1,050 °C is recommended for heavily restrained joints and for any assembly that will be creep loaded.
• Argon backing on full-penetration joints protects the root from oxidation.

Machining

Alloy 75 machines like other austenitic nickel alloys. It work-hardens, produces a stringy chip, and reacts badly to the tool dwelling in the cut. It is still easier to cut than the age-hardened Nimonic grades because it is delivered soft and stays soft.

• Rigid setup, sharp tools, positive rake. Tool deflection causes rubbing, which work-hardens the surface and makes the following pass harder to cut.
• Moderate speed, heavy positive feed. As a starting point for turning with coated carbide, roughly 20-35 m/min with 0.20-0.35 mm/rev; take the cut under the previously hardened layer rather than skimming it.
• Never let the tool dwell in the cut. Programme continuous engagement; peck-drill deep holes.
• Flood coolant. Sulphurised cutting oils must be fully removed before any subsequent heating operation.

Section 13How does Alloy 75 fail in service, and how do you prevent it?

The failure modes below are the ones seen most often on Alloy 75 parts. Most originate in the specification rather than in manufacture, so they are inexpensive to avoid at drawing stage and costly to find in service.

Section 14Which Alloy 75 forged product forms are available?

Jiangyin Jiangnan Metal Co., Ltd. produces Alloy 75 in open-die and ring-rolled forms, made to customer drawing. The list below covers the shapes ordered most often. Other geometries can be quoted from a drawing.

• Seamless rolled rings
• Contoured rolled rings
• Gear ring blanks
• Forged discs
• Forged hubs
• Forged blocks
• Forged shafts
• Spindles
• Eccentric shafts
• Forged flanges
• Forged round bars
• Forged flat bars
• Sleeves
• Bushings
• Tube sheets
• Hollow forgings
• Forged tubes and pipes
• Nozzles
• Valve bodies
• Valve stems
• Valve seat rings
• Near-net-shape open-die forgings

Section 15Where is Alloy 75 used?

Alloy 75 is selected where a part must survive a hot oxidising atmosphere for a long period without carrying much load. The sectors below account for most orders.

Section 16What is the Alloy 75 forging capability at Jiangyin Jiangnan Metal?

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. The plant covers raw material, forging, ring rolling, heat treatment, machining, testing and inspection on one site. The limits below apply specifically to Alloy 75 and other nickel-base superalloys, which have a narrower hot-working window than carbon and alloy steel and therefore a smaller maximum section than the plant's steel capability.

The works employs around 460 people including 9 senior engineers and 32 intermediate engineers. Capability figures are for nickel-base superalloys; carbon and alloy steel capacity is larger - see the forging products page.

Section 17What testing and certification comes with Alloy 75 forgings?

Every Alloy 75 forging is supplied with an EN 10204 3.1 mill certificate as standard. EN 10204 3.2 certificates witnessed by a third party - TÜV, BV, DNV, Lloyd's Register, ABS or a body you nominate - are available when specified at order stage. A 3.2 certificate cannot be added after the parts have been made, because the witness must be present at the tests, so it must appear on the purchase order.

What the certificate contains

• Heat number and full traceability from ingot to finished piece
• Ladle analysis and product analysis, element by element
• Melting route (EAF + VOD + ESR, or VIM + ESR / VIM + VAR)
• Heat-treatment record with the actual furnace chart
• Room-temperature tensile results; elevated-temperature and stress-rupture results where ordered
• Hardness and, where specified, grain size to ASTM E112
• Ultrasonic examination report with the standard and acceptance class applied
• Liquid penetrant examination report for machined surfaces where specified
• Dimensional inspection report against the drawing

Section 18How do you specify an Alloy 75 forging order?

Seven items are needed to quote an Alloy 75 forging without further correspondence.

1. DesignationWrite UNS N06075 / BS HR5 / W.Nr. 2.4951 rather than "Nimonic 75" alone. The generic designations are what an independent forge can legally certify against.
2. Product form & sizeRing, disc, shaft, flange, bar, sleeve, bushing or tube sheet - with OD, ID, height or length, and the machining stock you expect.
3. Delivery conditionNormally solution annealed at 1,050 °C, air cooled. State as-forged, rough machined or finish machined.
4. TestingRoom-temperature tensile is standard. Add elevated-temperature tensile, stress rupture, grain size or corrosion testing if needed.
5. NDEGive the ultrasonic standard and acceptance class: EN 10228-3, SEP 1921 or ASTM A388. Add penetrant examination for machined surfaces.
6. CertificateEN 10204 3.1 or 3.2. If 3.2, name the inspection body - it must be arranged before manufacture.
7. CommercialQuantity, required date and Incoterm (EXW Jiangyin, FOB Shanghai, CIF or DDP).

Drawing callout you can copy

MATERIAL:      UNS N06075 / BS HR5 / W.Nr. 2.4951 (NiCr20Ti)
               Nickel-chromium alloy, solid solution - NOT age hardenable

CONDITION:     Solution annealed 1050 °C (1920 °F), 30-60 min, air cooled
               Furnace chart to be supplied with certificate

MELTING:       EAF + VOD + ESR minimum
               (VIM + VAR where UT class 3 or tighter is specified)

FORGING:       Total forging ratio ≥ 4:1
               Finishing temperature ≥ 950 °C

TESTING:       Tensile at room temperature per EN ISO 6892 / ASTM E8
               Hardness; grain size per ASTM E112 [if required]
               Stress rupture per ASTM E139 [if creep loaded]

NDE:           UT per EN 10228-3 [class ___] or ASTM A388
               PT per EN ISO 3452 on all machined surfaces
               (No MT - material is non-magnetic)

CERTIFICATE:   EN 10204 3.1   [or 3.2 witnessed by ___________]

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

Section 19Eight mistakes engineers make when ordering Alloy 75

1. Treating 1,000 °C as a load-bearing limit. That is the oxidation limit. Stressed parts are governed by creep, with a practical ceiling near 815 °C and much lower for long design lives. Fix: state temperature and stress and design life on the enquiry.
2. Specifying an ageing treatment. Alloy 75 has no precipitation-hardening response. A drawing calling for "solution treat and age, N06075" contains an error. Fix: query it - the intended grade is usually Nimonic 80A.
3. Writing "Nimonic 75" alone on the purchase order. Nimonic® is a registered trademark; a PO written that way can strictly only be filled by the trademark holder. Fix: specify UNS N06075 / BS HR5 / W.Nr. 2.4951.
4. Invoking ASTM B637 or AMS 5871. Neither covers UNS N06075 - B637 is for precipitation-hardening nickel alloys and AMS 5871 is an Alloy 800 flat-product specification. Fix: use BS HR5, DIN 17742, ISO 9723 or the MSRR series.
5. Adding EN 10204 3.2 after the parts are made. A third-party witness must attend the tests. Fix: state 3.2 and name the inspection body on the order.
6. Specifying magnetic particle examination. Alloy 75 is non-magnetic and MT will not work on it. Fix: specify liquid penetrant examination for surface NDE.
7. Ordering a tight UT class against an air-melted ingot. Inclusion content drives ultrasonic noise. Fix: match the melting route to the UT acceptance class at enquiry stage.
8. Substituting GH3030 without checking. The Chinese grade is close but its titanium, aluminium and carbon limits differ. Fix: compare against the drawing chemistry, and have the certificate state which specification is actually met.

Section 20Glossary

Solid-solution strengthening

Strengthening produced by dissolving alloying elements such as chromium in the nickel matrix, distorting the lattice and impeding dislocation motion. This is the principal strengthening mechanism in Alloy 75.

Gamma prime (γ′)

The ordered Ni₃(Al,Ti) precipitate that strengthens age-hardening superalloys such as Nimonic 80A, Nimonic 90 and Waspaloy. Alloy 75 contains too little aluminium and titanium to form a useful volume fraction of it.

Solution anneal

A heat treatment that dissolves carbides and recrystallises the worked structure. For Alloy 75 the cycle is 1,050 °C (1,920 °F) for 30-60 minutes, air cooled.

Seamless rolled ring

A ring made by piercing a forged billet and expanding it on a radial-axial ring mill, giving continuous circumferential grain flow and no weld seam.

Forging ratio

Starting cross-sectional area divided by finished cross-sectional area. A ratio of 4:1 or more is normally needed to break down the as-cast ingot structure.

ESR - electroslag remelting

Secondary refining in which a consumable electrode is remelted through a molten slag layer, reducing inclusions and improving the solidification structure.

VOD - vacuum oxygen decarburisation

A refining step that removes carbon under vacuum while limiting chromium loss - important for a 20 % chromium alloy with a narrow carbon band.

EN 10204 3.1

An inspection certificate issued by the manufacturer's own independent inspection department, reporting results on the material actually supplied.

EN 10204 3.2

An inspection certificate validated jointly by the manufacturer's inspection representative and either the purchaser's representative or an independent inspection body named in the order.

Stress rupture

A test in which a specimen is held at constant load and temperature until fracture, reported as time to rupture at a given stress and temperature.

Green rot

Internal attack in nickel-chromium alloys cycled between carburising and oxidising atmospheres: chromium is consumed as carbide, the carbide oxidises, and a green-tinged depleted zone is left behind.

Sulphidation

Attack by sulphur-bearing gases forming low-melting nickel-sulphur eutectics at grain boundaries, causing rapid intergranular penetration. The main environmental limitation of this alloy family.

Section 21Frequently asked questions about Alloy 75

Section 22Standards and references

Property data on this page is compiled from the published standards and reference works listed below, together with production and test records held by Jiangyin Jiangnan Metal Co., Ltd. Standards are cited by number; always reference the revision in force at your contract date.

1. BS 3072:1989 and BS 3076:1989 - Nickel and nickel alloys: sheet, plate, bar and rod (designations HR5, HR203, HR403, HR504). British Standards Institution.
2. DIN 17742 - Wrought nickel alloys with chromium; and DIN 17750-17752 - Nickel and nickel alloy sheet, strip, bar and rod. Deutsches Institut für Normung.
3. ISO 9723, ISO 9724, ISO 9725 - Nickel and nickel alloy bars, wire, forgings and forging stock. International Organization for Standardization.
4. SAE / Rolls-Royce MSRR 7004 (bar) and MSRR 7104 (sheet) material specifications.
5. GB/T 14992 - Classification and designation of high-temperature alloys, including GH3030. Standardization Administration of China.
6. EN 10204:2004 - Metallic products: types of inspection documents. CEN, Brussels.
7. EN 10228-3 - Non-destructive testing of steel forgings: ultrasonic testing. CEN.
8. SEP 1921 - Ultrasonic testing of steel forgings. Stahl-Eisen-Prüfblatt, Verein Deutscher Eisenhüttenleute.
9. ASTM A388/A388M - Standard Practice for Ultrasonic Examination of Steel Forgings. ASTM International.
10. ASTM E8/E8M - Standard Test Methods for Tension Testing of Metallic Materials; ASTM E112 - Standard Test Methods for Determining Average Grain Size; ASTM E139 - Standard Test Methods for Conducting Creep, Creep-Rupture, and Stress-Rupture Tests. ASTM International.
11. EN ISO 3452 - Non-destructive testing: penetrant testing. CEN / ISO.
12. ASM Handbook, Volume 1: Properties and Selection - Irons, Steels and High-Performance Alloys. ASM International, Materials Park, OH.
13. ASM Specialty Handbook: Heat-Resistant Materials, J.R. Davis (ed.). ASM International.
14. Donachie, M.J. and Donachie, S.J., Superalloys: A Technical Guide, 2nd edition. ASM International.
15. Reed, R.C., The Superalloys: Fundamentals and Applications. Cambridge University Press.
16. Published mill datasheets for Nimonic® 75 / UNS N06075, consulted for density, melting point, elastic moduli and expansion coefficient.

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Related grades and product pages

Grades most often compared with Alloy 75, and the product pages for the shapes it is ordered in.

• Nimonic 80A
• Inconel 600
• Inconel 601
• Inconel 617
• Inconel 625
• Inconel 706
• Inconel X-750
• Incoloy 800
• Incoloy 800H
• Incoloy 800HT
• Haynes 230
• Haynes 188
• Haynes 25
• Hastelloy X
• Waspaloy
• Rene 41
• Multimet N155
• UNS N07252
• Forged & rolled rings
• Forged disks
• Forged tube sheets
• Forged valve seat rings
• Waspaloy forged pipes
• All forging products