Nimonic 75 (UNS N06075) is an 80/20 nickel-chromium superalloy with oxidation resistance to 1100°C, tensile strength 750 MPa, elongation 42%, and excellent weldability. It is the correct alloy when a component must survive a hot oxidizing environment at low-to-moderate stress and weldability matters. It is not the correct alloy for sustained high stress above 700°C, sulphidation environments, or aqueous corrosion service.
What Nimonic 75 Actually Is
If you are searching for a nickel alloy that resists oxidation at temperatures up to 1100°C, welds without the strain-age cracking headaches of age-hardened grades, and can be sourced in large forged sections — Nimonic 75 is almost always on the shortlist. But what exactly is it, and why does it keep appearing in turbine spec sheets, nuclear BOM documents, and furnace engineering standards decades after its invention?
Nimonic 75 (UNS N06075, W.Nr. 2.4951, BS HR5) is a first-generation wrought nickel-chromium superalloy. Its nominal composition is approximately 75% nickel and 20% chromium, with controlled additions of titanium (0.2–0.6%) and carbon (0.08–0.15%). There are no aluminum, cobalt, or niobium additions — a deliberately simple 80/20 alloy optimized for oxidation resistance and fabricability rather than maximum creep strength.
That tradeoff has made it the alloy of choice for furnace internals, gas turbine auxiliaries, nuclear structural components, and aerospace heat shields. This guide covers its chemistry, microstructure, full mechanical and thermal property dataset, key applications, and exactly when you should — and should not — specify it. If you need Nimonic 75 forged parts, Jiangsu Liangyi supplies open-die forgings and seamless rolled rings in this alloy from stock.
Where Nimonic 75 Came From
The Nimonic alloy family was born out of World War II urgency. In the early 1940s, British engineers at the Mond Nickel Company (later Special Metals) needed a material that could survive inside Frank Whittle's jet engine. Turbine blades were failing at temperatures and stresses that exceeded every available steel.
Nimonic 75 answered a specific sub-problem: the non-rotating structural components, casings, and supports that required oxidation resistance above all else. Introduced around 1941–1946, it was among the earliest commercially produced wrought nickel superalloys. What made it remarkable was the combination of a high-chromium matrix (enabling the protective Cr₂O₃ scale) with enough ductility to be sheet-formed and welded — something cast iron-based high-temperature materials of the era could not offer.
More than eighty years later, the specification is essentially unchanged. The 80/20 Ni-Cr ratio proved so well-optimized for its design targets that no significant revision has been needed — a testament to how precisely the alloy was originally engineered.
Chemical Composition of Nimonic 75 (UNS N06075)
The full Nimonic 75 composition per specification is shown below. Note that the alloy contains no aluminum, cobalt, or niobium — a design choice that keeps it solid-solution strengthened, weldable, and readily forgeable.
What Each Element Does
Nickel (Ni — ~75%): Base metal. Provides the face-centered cubic (FCC) austenitic matrix — stable from cryogenic temperatures to the solidus, inherently ductile, non-magnetic, and resistant to many corrosive environments. High nickel content also prevents sigma-phase embrittlement, a significant advantage over high-chromium ferritic steels.
Chromium (Cr — 18–21%): The oxidation-resistance engine. Above ~15% Cr, a continuous adherent Cr₂O₃ (chromia) scale forms on the surface in oxidizing atmospheres — thermodynamically stable, slow-growing, with very low oxygen permeability. At 18–21%, the scale remains robust well into the 1000°C range. Chromium also solid-solution strengthens the nickel matrix.
Titanium (Ti — 0.2–0.6%): Small but critical. Forms grain-boundary-pinning TiC carbides, resisting grain coarsening at high temperature. Also contributes TiO₂ to the outer oxide layer, improving scale adhesion and spall resistance under thermal cycling. Deliberately kept below ~0.6% to prevent γ' (Ni₃Ti) precipitate formation — preserving weldability and formability.
Carbon (C — 0.08–0.15%): Promotes M₂₃C₆ and MC grain-boundary carbides. In moderate amounts these strengthen grain boundaries and improve stress-rupture life. Too low: weak grain boundaries. Too high: continuous carbide networks that embrittle.
Mechanical Properties of Nimonic 75 (UNS N06075)
Room-Temperature Properties — Solution-Annealed Condition
Typical values per ASTM B637 / AMS 5683 specification for solution-annealed condition. Bars normalized for visual comparison against typical nickel superalloy ranges.
Tensile Properties at Elevated Temperature
| Temperature | Tensile Strength | 0.2% Yield Strength | Elongation |
|---|---|---|---|
| 20°C (RT) | 750 MPa / 109 ksi | 275 MPa / 40 ksi | 42% |
| 400°C | 680 MPa / 99 ksi | 220 MPa / 32 ksi | 45% |
| 600°C | 620 MPa / 90 ksi | 200 MPa / 29 ksi | 48% |
| 700°C | 540 MPa / 78 ksi | 185 MPa / 27 ksi | 46% |
| 800°C | 380 MPa / 55 ksi | 165 MPa / 24 ksi | 50% |
| 900°C | 180 MPa / 26 ksi | 110 MPa / 16 ksi | 60% |
| 1000°C | 95 MPa / 14 ksi | 60 MPa / 8.7 ksi | 70% |
Creep and Stress-Rupture Data
For components operating above ~550°C under sustained stress, creep governs design life. Nimonic 75 has moderate creep resistance, suitable for low-to-medium stress applications but not for heavily loaded rotating parts above 700°C:
| Temperature | 100-hr Rupture Stress | 1,000-hr Rupture Stress | 10,000-hr Rupture Stress |
|---|---|---|---|
| 600°C | 345 MPa | 270 MPa | 205 MPa |
| 700°C | 170 MPa | 125 MPa | 85 MPa |
| 800°C | 80 MPa | 55 MPa | 35 MPa |
| 900°C | 35 MPa | 22 MPa | 14 MPa |
If sustained stress above 700°C exceeds ~80 MPa, consider Nimonic 80A (UNS N07080), Waspaloy, or Inconel 718.
Physical and Thermal Properties
| Property | Value | Condition |
|---|---|---|
| Density | 8.37 g/cm³ (0.302 lb/in³) | Room temperature |
| Melting Range | 1340–1380°C (2444–2516°F) | Solidus–Liquidus |
| Specific Heat (Cp) | 461 J/(kg·K) | 20–100°C |
| Specific Heat (Cp) | 565 J/(kg·K) | At 800°C |
| Thermal Conductivity | 12.0 W/(m·K) | At 20°C |
| Thermal Conductivity | 22.8 W/(m·K) | At 800°C |
| Elastic Modulus (E) | 206 GPa | At 20°C |
| Elastic Modulus (E) | 175 GPa | At 600°C |
| Poisson's Ratio | 0.30 | At 20°C |
| Magnetic Behavior | Non-magnetic (FCC) | All service temperatures |
| Electrical Resistivity | 1.20 μΩ·m | At 20°C |
Coefficient of Thermal Expansion (CTE)
| Temperature Range | Mean CTE — Metric | Mean CTE — Imperial |
|---|---|---|
| 20–100°C | 11.6 × 10⁻⁶ /K | 6.4 × 10⁻⁶ /°F |
| 20–300°C | 13.2 × 10⁻⁶ /K | 7.3 × 10⁻⁶ /°F |
| 20–500°C | 14.2 × 10⁻⁶ /K | 7.9 × 10⁻⁶ /°F |
| 20–700°C | 15.2 × 10⁻⁶ /K | 8.4 × 10⁻⁶ /°F |
| 20–900°C | 16.5 × 10⁻⁶ /K | 9.2 × 10⁻⁶ /°F |
| 20–1000°C | 17.1 × 10⁻⁶ /K | 9.5 × 10⁻⁶ /°F |
Oxidation and Corrosion Resistance
Oxidation resistance is Nimonic 75's defining property. Above ~700°C, chromium in the alloy preferentially reacts with oxygen to form a dense, adherent Cr₂O₃ (chromia) scale — thermodynamically stable, slow-growing, and with very low oxygen permeability. This scale acts as a diffusion barrier protecting the underlying metal.
Titanium (0.2–0.6%) modifies the outer oxide layer with TiO₂, reducing cation diffusion and significantly improving spall resistance under thermal cycling — the condition where repeated rapid heating and cooling cracks and detaches the scale, exposing fresh metal to re-oxidize.
| Environment | Resistance | Temperature Limit |
|---|---|---|
| Oxidizing atmosphere (air, steam) | Excellent | To 1100°C |
| Nitriding atmosphere | Good | To ~950°C |
| Carburizing atmosphere | Good | To ~1050°C |
| Sulphidation (SO₂, H₂S) | Acceptable | To ~700°C only |
| Molten chloride salts | Not Recommended | — |
| Molten lead or zinc | Not Recommended | — |
| Aqueous acids (dilute) | Moderate only | Room temperature |
Microstructure and Metallurgy
Nimonic 75 is solid-solution strengthened — the single most important metallurgical fact about it. This distinguishes it from the precipitation-hardened Nimonic grades (80A, 90, 105, 115) that derive strength from γ' (gamma-prime) Ni₃(Al,Ti) precipitates.
Phase Constitution
γ matrix (FCC austenite): The continuous phase — a face-centered cubic nickel solid solution stable from cryogenic temperatures to the solidus, providing excellent ductility across the entire service range.
MC carbides (TiC — titanium-rich): Form during solidification and hot working. Remain stable near the solidus and pin grain boundaries, resisting grain coarsening during high-temperature service.
M₂₃C₆ carbides (chromium-rich): Secondary carbides precipitate on grain boundaries between ~550–900°C during service. In moderate amounts they strengthen grain boundaries and improve stress-rupture life. Continuous networks after very prolonged exposure (>10,000 hours above 800°C) may reduce room-temperature ductility — rarely a design constraint for most applications.
No γ' or γ'' precipitates: Ti content (0.2–0.6%) is below the γ' threshold. No aluminum is present. Therefore there is no γ' phase — which is exactly why Nimonic 75 is immune to post-weld strain-age cracking.
Nimonic 75 Global Designations — 12 Standard Systems
All designations below refer to the same 80/20 Ni-Cr superalloy (minor composition tolerance variations exist between standards):
| Region / Standard System | Designation |
|---|---|
| UNS (USA) | N06075 |
| AMS (USA Aerospace) | AMS 5683, AMS 5651, AMS 5542 |
| ASTM / ASME (USA) | ASTM B637; SB-637 (forgings) |
| W.Nr. / DIN (Germany) | 2.4951 (s-a) / 2.4630; NiCr20Ti (DIN 17742) |
| BS (United Kingdom) | BS HR5, HR203, HR403, HR504, HR600 |
| AFNOR (France) | NC20T; NC20TA |
| GOST (Russia) | ХН78Т (KhN78T) |
| GB / YB (China) | GH3030; NS311 |
| JIS (Japan) | NCF 75 |
| ISO | ISO 9723 NiCr20Ti |
| EN (Europe) | EN 10095 NiCr20Ti |
| Trade names | Nimonic® 75, Pyromet® 75, Alloy 75 |
Always verify against the supplier's Mill Test Certificate (MTC). Jiangsu Liangyi can supply Nimonic 75 forgings and will provide a Mill Test Certificate (MTC) with each order. Contact us to confirm which documentation is available: ✉️ sales@jnmtforgedparts.com · 📞 +86-135-8506-7993 (WhatsApp).
Nimonic 75 Applications by Industry
The combination of oxidation resistance to 1100°C, excellent weldability, and moderate cost has established Nimonic 75 in six main industry segments:
Steam & Gas Turbines
Valve bonnets, nozzle boxes, packing seal rings, diaphragms, exhaust casings, labyrinth seals, and high-temperature bolting for utility power plants.
Nuclear Power
Steam generator internals, flow limiters, reactor support rings, and containment penetration sleeves — non-pressure-boundary structural components.
Aerospace
Combustor casing blanks, exhaust nozzle rings, heat-shield structures, and afterburner components in aero gas turbines.
Industrial Furnaces
Radiant tube supports, muffle retort ends, hearth plates, basket grids, and beam components for walking-beam reheat furnaces above 1050°C.
Petrochemical
Reformer tube hangers, reactor internals, heat-exchanger tube sheets for ammonia, methanol, and hydrogen plants above 800°C.
Process Equipment
High-temperature fixtures, thermocouple protection tubes, and heat-treating equipment where repeated oxidizing exposure is the primary challenge.
Nimonic 75 vs Alternative Alloys — Comparison Table
| Property | Nimonic 75 | Nimonic 80A | Inconel 600 | 310S SS |
|---|---|---|---|---|
| UNS | N06075 | N07080 | N06600 | S31008 |
| Strengthening | Solid solution | γ' precipitation | Solid solution | Solid solution |
| RT Tensile | 750 MPa | 1240 MPa | 655 MPa | 620 MPa |
| Max oxidation temp. | 1100°C | ~815°C | 1150°C | ~1050°C |
| Weldability | Excellent | Difficult | Excellent | Good |
| Creep above 700°C | Moderate | High | Low | Low |
| Aqueous corrosion | Moderate | Moderate | Good | Moderate |
| Relative cost index | 1.0× | ~1.8× | ~0.9× | ~0.4× |
Five-Step Selection Framework
When NOT to Specify Nimonic 75
Six firm contraindications where Nimonic 75 is the wrong alloy for the application:
Sustained stress >80 MPa above 700°C — creep rupture will limit life. Use Nimonic 80A, 90, or Waspaloy.
Sulphur atmosphere (SO₂ / H₂S) above 700°C — catastrophic sulphidation. Use Haynes 188 or a Co-base grade.
Aqueous corrosion environments — acids, chlorides, seawater. Use Inconel 625 or Hastelloy C-276.
Molten chloride salts, lead, or zinc — liquid metal embrittlement regardless of temperature.
Nuclear primary pressure boundary — regulated tubing requires Inconel 690; Nimonic 75 is acceptable for non-pressure-boundary structural roles only.
High yield strength below 650°C — Inconel 718 or Waspaloy offer far higher strength at moderate temperatures.
Forging Nimonic 75: Process and Jiangsu Liangyi Capabilities
Nimonic 75 is among the more workable Nimonic alloys due to its lack of γ' strengtheners. However, controlled thermomechanical practice is essential to achieve the required grain size and freedom from internal defects.
| Parameter | Value | Reason for Limit |
|---|---|---|
| Preheat temperature | 1080–1170°C | Ensures uniform plastic flow |
| Maximum billet temperature | 1200°C | Above this: grain-boundary liquation risk |
| Minimum finish-forge temp. | 950°C | Below this: strain-induced cracking |
| Minimum forging ratio | 3:1 | Required for uniform wrought properties |
| Max soak time per reheat | 30 min at temperature | Prevents excessive grain coarsening |
| Solution anneal | 1050°C ± 15°C | 30 min min.; air cool (WQ for >500mm section) |
| Target grain size | ASTM 4–7 | Balance of creep and fatigue resistance |
Manufacturing Capabilities — Jiangsu Liangyi Co., Limited
| Product Form | Size / Weight Range |
|---|---|
| Round bars (open-die) | Ø 50 – 2,000 mm |
| Seamless rolled rings | OD 400 – 6,000 mm, wall thickness 25–400 mm |
| Discs, blocks, flanged blanks | To 3,000 mm OD / face |
| Shafts / step shafts | Length to 15 m |
| Unit weight per forging | 30 kg – 30,000 kg |
| Quality certification | ISO 9001:2015 |
| Quality certification | ISO 9001:2015 (Mill Test Certificate provided with each order) |
| Material traceability | Full chemical and mechanical MTC provided; specify required standard at enquiry stage |
| Standard lead time | 4–6 weeks (rough); 6–8 weeks (machined) |
To request a quotation or review full size and weight options, visit our Nimonic 75 open-die forgings and seamless rings product page. Quotations are returned within 2 business days.
Frequently Asked Questions about Nimonic 75
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