Nimonic 75 vs Nimonic 80A: Which Grade to Specify

By Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier | ISO 9001:2015 | Est. 2012

Contact: sales@hangboalloy.com | hangbo@nickel-alloy.com | WhatsApp (Lisa): +86 13611656360

Quick Answer: Nimonic 75 vs Nimonic 80A

Specify Nimonic 75 (UNS N06075) for high-temperature sheet fabrications, combustion chambers and non-load-critical components that need oxidation resistance and good forming rather than creep strength. Specify Nimonic 80A (UNS N07080) where the part must carry load at 700 to 750 C, as in turbine blades, bolts, valves and springs, because its gamma-prime ageing gives far higher strength.

Key Takeaways

• Only one of the two is age-hardenable. Nimonic 75 is an 80/20 nickel-chromium solid-solution alloy that does not respond to precipitation treatment; Nimonic 80A adds titanium and aluminium and is strengthened by gamma-prime precipitation during a controlled ageing cycle.
• The strength gap is large, not marginal. In the aged condition Nimonic 80A typically delivers a yield strength roughly twice that of Nimonic 75 at room temperature, and it retains a useful fraction of that strength at 700 to 750 C where Nimonic 75 has already lost most of its load-carrying capacity.
• Nimonic 75 wins on formability and weldability. Its solid-solution structure and lower strength make it easy to cold form and to weld into large sheet assemblies such as combustion chambers, where 80A would crack or need pre-heating and post-weld heat treatment.
• Nimonic 80A wins on creep and stress rupture. It is a creep-resisting alloy, and it is specified where a part must hold a shape and a load for thousands of hours at temperature, which is why it appears in turbine blades, bolts and valve stems.
• Both resist oxidation well. At 700 to 900 C both alloys form a protective chromium oxide scale; the difference between them is not oxidation resistance but whether the part must also carry load.
• The price difference follows the alloys, not the name. Nimonic 80A contains titanium and aluminium additions and needs an ageing cycle, so it typically costs more than Nimonic 75 in the same form and condition.

Nimonic 75 and 80A at a Glance

Nimonic 75 and Nimonic 80A are both members of the Nimonic family of nickel-chromium alloys, and they are frequently quoted interchangeably by buyers who assume that a higher number means a better grade. They are not interchangeable, and the reason is metallurgical rather than commercial. Nimonic 75 is essentially an 80 per cent nickel, 20 per cent chromium alloy with a small amount of titanium, and it is a solid-solution alloy: its strength comes from the nickel-chromium matrix and from the effects of cold work, and it does not gain strength from a precipitation heat treatment. Nimonic 80A is the same nickel-chromium base with deliberate additions of titanium and aluminium, and those additions form a fine gamma-prime precipitate during an ageing treatment that raises the strength substantially and, more importantly, keeps the strength high when the part is hot.

The distinction is best understood through what each alloy was invented to do. Nimonic 75 was developed for sheet-metal fabrications that must survive high-temperature oxidising environments without carrying heavy loads: combustion chambers, flame tubes, exhaust ducting and furnace internals, where the requirement is oxidation resistance, thermal fatigue tolerance and the ability to be formed and welded. Nimonic 80A was developed for components that must carry a load at temperature for long periods: turbine blades, bolts, studs, valve stems and exhaust valves, where the requirement is creep resistance and stress-rupture life, and where the alloy must resist the tendency to stretch slowly and then fail. That is why the two alloys, despite sharing a nickel-chromium base, are specified for entirely different classes of component.

The grade systems are also different, and a buyer should be aware of the trap. Nimonic 75 is designated UNS N06075 and corresponds to the German material number 2.4951; Nimonic 80A is UNS N07080 and corresponds to 2.4952. In the British system that the Nimonic family originates from, product specifications are issued in the BS HR series, with the sheet and the bar forms covered by different parts of that series. In the Chinese system the corresponding grades are quoted as GH3030 for the 80/20 nickel-chromium type and GH4080A for the titanium-and-aluminium-bearing type, classified through GB/T 14992, though the correspondence must be confirmed against the specific product standard rather than assumed from the grade number. Our Nimonic alloy range covers both grades in the forms described in this article, and because the two alloys are used together in many hot-section assemblies, the correct procurement question is usually which part requires which grade rather than which grade is better.

Chemical Composition Compared

The compositions show exactly where the two alloys diverge, and the divergence is concentrated in two elements. Nimonic 75 carries a small titanium addition but no aluminium and no substantial precipitation-hardening addition; Nimonic 80A carries both titanium and aluminium, and those two elements are the raw material of the gamma-prime precipitate. Everything else in the two chemistries is close enough that a purchased item could, at a glance, look like the other grade, which is why positive material identification matters when either grade is received.

Element (wt %)	Nimonic 75 (UNS N06075)	Nimonic 80A (UNS N07080)	Standard basis	Notes
Ni	balance	balance	BS HR series / DIN 17742	both nickel-base
Cr	approx. 18.0-21.0	approx. 18.0-21.0	BS HR series / DIN 17742	oxidation resistance
Ti	approx. 0.20-0.60	approx. 1.8-2.7	BS HR series / DIN 17742	gamma-prime former in 80A
Al	not specified	approx. 1.0-1.8	BS HR series / DIN 17742	gamma-prime former in 80A
Fe	max 5.0	max 3.0	BS HR series / DIN 17742	80A is the cleaner melt
C	max 0.12	max 0.10	BS HR series / DIN 17742	both kept low
Mn	max 1.0	max 1.0	BS HR series / DIN 17742	residual
Si	max 1.0	max 1.0	BS HR series / DIN 17742	residual
Cu	max 0.5	max 0.2	BS HR series / DIN 17742	residual
S	max 0.015	max 0.015	BS HR series / DIN 17742	residual
Co	not specified	max 2.0	BS HR series / DIN 17742	80A limit only

Table note: Composition ranges are the published wrought-product limits for the two grades and are shown as planning guidance; the controlling values are those of the edition named on the purchase order, which for the Nimonic family is normally a part of the BS HR series, with the equivalent European composition limits given in DIN 17742 and the product forms in DIN 17750 (sheet), DIN 17752 (bar) and DIN 17753 (wire). The Chinese equivalent grades GH3030 and GH4080A are classified through GB/T 14992, and equivalence should be confirmed against the specific product standard rather than inferred from the grade number. The decisive entries are titanium and aluminium: without them an alloy cannot form the gamma-prime precipitate that makes Nimonic 80A a creep-resisting material.

The chemistry has a direct procurement consequence. Because the two alloys can be difficult to distinguish by appearance and by a casual hardness check, and because a mix-up between them would put a non-creep-resistant alloy into a turbine blade or a bolt that must hold a load at 750 C, both grades should be verified by positive material identification to ASTM E1476 on receipt. The titanium-and-aluminium content of 80A is what a PMI check is looking for, and an alloy analyser set up for the nickel-chromium family will separate the two grades reliably. Where a supplier cannot provide heat-number traceability and a mill certificate, the risk is not merely commercial; it is a metallurgical substitution that could pass a visual inspection and fail in service.

Mechanical Properties: Annealed Versus Aged

The mechanical comparison is the heart of the choice, and it needs to be read in two columns rather than one, because Nimonic 75 has essentially a single service condition while Nimonic 80A has the supplied-and-aged distinction that dominates its properties. The table below sets out typical room-temperature values for both grades and indicates which figures are the result of a deliberate ageing treatment.

Property (typical)	Nimonic 75 (N06075)	Nimonic 80A (N07080)	Condition	Source type
Tensile strength, 20 C	approx. 700-780 MPa	approx. 1000-1250 MPa	75 annealed; 80A aged	typical, not a standard minimum
0.2 % yield strength, 20 C	approx. 280-380 MPa	approx. 680-800 MPa	75 annealed; 80A aged	typical, not a standard minimum
Elongation, 20 C	approx. 30-45 %	approx. 20-30 %	75 annealed; 80A aged	typical, not a standard minimum
Hardness	approx. 150-200 HV	approx. 250-350 HV	75 annealed; 80A aged	typical, not a standard minimum
Tensile strength, 750 C	approx. 250-350 MPa	approx. 600-750 MPa	both at temperature	typical, not a standard minimum
Creep resistance	limited; not a creep alloy	good to 750 C	80A aged	design guidance
Age hardenable	no	yes	—	metallurgical basis
Governing standard family	BS HR series (sheet)	BS HR series (sheet, bar)	—	see Standard Index

Table note: All values are typical values from mill data and published handbook ranges and are explicitly not the minimum values of any standard; a design that depends on a guaranteed minimum must take that minimum from the current edition of the governing standard named on the purchase order, which for the Nimonic family is normally a part of the BS HR series with European equivalents in the DIN 1775x series. Tensile testing is performed to ASTM E8/E8M at room temperature and to ASTM E21 at elevated temperature, hardness to ASTM E18, grain size to ASTM E112 and creep or stress rupture to ASTM E139, and where an aerospace specification applies, heat treatment must satisfy AMS 2750 pyrometry. The purpose of the table is to make the size of the strength gap visible: in the aged condition Nimonic 80A is roughly twice as strong in yield as Nimonic 75 at room temperature, and several times as strong in the range where creep governs.

Two practical readings follow. The first is that Nimonic 75 should never be selected on a strength basis. It is selected for oxidation resistance, thermal fatigue tolerance, formability and weldability, and a designer who needs strength at temperature has already left the Nimonic 75 envelope. The second is that Nimonic 80A should not be over-specified for a part that does not need it. Because 80A is the stronger and more expensive alloy, and because it is harder to form and weld, using it for a combustion chamber liner or a large sheet fabrication adds cost and fabrication difficulty without delivering a benefit. The correct split in a typical hot-section assembly is to use 75 for the sheet fabrications and 80A for the loaded fasteners, blades and springs, and to specify each grade against the requirement it actually serves rather than applying one grade across the whole assembly.

Heat Treatment and the Ageing Cycle

Heat treatment divides the two grades completely, and it is the single most useful question to ask a supplier when a specification is ambiguous. Nimonic 75 is normally supplied in the annealed condition and is not age hardened, so there is no precipitation cycle to specify, verify or repeat, and a fabricator who stress-relieves a welded Nimonic 75 assembly has not changed its metallurgical class. Nimonic 80A is supplied either annealed or annealed-and-aged, and where the aged condition is required the ageing cycle becomes a controlled manufacturing step that must be recorded, because the strength of the delivered part depends on it. A purchase order that names Nimonic 80A without naming the condition leaves the supplier free to deliver the weaker annealed material.

Thermal process	Nimonic 75 (N06075)	Nimonic 80A (N07080)	Standard basis	Notes
Solution anneal	approx. 1050-1100 C, air or water quench	approx. 1050-1100 C, air or water quench	BS HR series / DIN 1775x	dissolves precipitates
Ageing treatment	not applicable	two-stage cycle in the region of 700-800 C	BS HR series / AMS 2750	forms gamma-prime
Condition as supplied	annealed	annealed or annealed + aged	order requirement	name the condition
Stress relief after welding	permitted, low temperature	permitted, then re-age if required	mill practice	in-house, not a standard requirement
Pyrometry control	AMS 2750 where aerospace applies	AMS 2750 where aerospace applies	AMS 2750	furnace class and survey
Cold work	strengthens; anneal before severe forming	strengthens; annealing required before ageing	mill practice	affects final properties

Table note: The temperature bands are the normal mill practices for the wrought product and are given as planning guidance, not as standardised values; the controlling requirement is the condition named on the purchase order and the published limits of the governing standard. Where an aerospace or a critical rotating-part specification applies, the furnace must satisfy AMS 2750 pyrometry, which imposes instrument accuracy, uniformity survey and record-keeping requirements that the supplier must be able to demonstrate. The key commercial point is that Nimonic 80A has a condition that Nimonic 75 does not, so the phrase "Nimonic 80A, aged" is a complete and necessary part of the specification, while the same phrase applied to Nimonic 75 is meaningless.

The ageing cycle also interacts with fabrication in a way that catches out first-time users of 80A. Welding an aged 80A component disturbs the microstructure in the weld and heat-affected zone, and while the alloy can be welded, the procedure usually needs to account for the loss of properties in that zone and, where the design requires it, a post-weld ageing treatment to restore them. Nimonic 75, because it has no precipitate to disturb, is far more tolerant of welding and is the reason it remains the sheet-metal alloy of the family. Where a fabricated assembly must be both strong at temperature and easy to weld, the usual solution is a hybrid: Nimonic 75 for the formed and welded pressure envelope, with Nimonic 80A forgings or bolts carrying the concentrated loads. Our knowledge base covers the heat-treatment and pyrometry requirements that apply when either grade is ordered against a critical specification.

Standards and Specifications

The Nimonic family is unusual among the alloys in this catalogue because it originates in the British standard system and is therefore specified primarily through the BS HR series rather than through an ASTM product standard. Buyers who are used to ordering to ASTM B446 or ASTM B443 will not find an equivalent ASTM document for the Nimonic grades, and a quotation must be prepared against the correct system. The table below lays out the standard families that apply.

Area	Nimonic 75 (N06075)	Nimonic 80A (N07080)	Covers	Form
British wrought product	BS HR series (sheet, strip, plate, bar)	BS HR series (sheet, strip, plate, bar)	composition + mechanical	sheet, plate, bar
European composition	DIN 17742	DIN 17742	composition	all forms
European product forms	DIN 17750 (sheet) / DIN 17752 (bar) / DIN 17753 (wire)	DIN 17750 / DIN 17752 / DIN 17753	dimensions + properties	sheet, bar, wire
International	ISO 9722 (wrought Ni alloys)	ISO 9722 (wrought Ni alloys)	composition + properties	wrought forms
Chinese classification	GH3030 (quoted equivalent)	GH4080A (quoted equivalent)	grade classification	all forms
Heat treatment control	AMS 2750 where applicable	AMS 2750 where applicable	furnace control	all forms
Testing	ASTM E8 / E21 / E139 / E18 / E112	ASTM E8 / E21 / E139 / E18 / E112	test methods	all forms
Inspection documents	EN 10204	EN 10204	documents	all forms

Table note: The table names standard families by designation and scope, and where a part number or edition year is not quoted the controlling document is the one named on the purchase order; the BS HR series is issued in numbered parts covering different product forms and different grades, so the specific part must be named rather than the series. The Chinese designations GH3030 and GH4080A are commonly quoted as the equivalent of Nimonic 75 and Nimonic 80A respectively and are classified through GB/T 14992, but the correspondence is indicative and must be confirmed against the specific product standard, because the Chinese grades carry their own composition limits and mechanical requirements. Because no single ASTM product standard covers the Nimonic grades, a project that mixes ASTM-governed materials with Nimonic parts needs to state the governing document for each part rather than assuming a house standard applies.

That last point is the practical cause of most Nimonic procurement disputes. A drawing prepared in Europe will name a BS HR part; a project specification written around ASTM will not recognise it; and a supplier in a third country may quote a "Nimonic 80A equivalent" that is actually a different nickel-chromium alloy with a similar name. The remedy is to put four things on the enquiry: the grade name and the UNS number, the product standard and its part or edition, the supplied condition, and the inspection document type. Where the part is safety-related, add the hardness or the stress-rupture requirement that the end user intends to verify, because those are the values that will decide acceptance.

High-Temperature Performance and Creep Behaviour

At temperature the two alloys separate along the same axis as at room temperature, but the consequences are more serious, because the failure mode changes from a simple overload to slow deformation and rupture. Nimonic 75 at 700 to 900 C holds its shape well enough for a sheet fabrication but will creep under a sustained load; Nimonic 80A is designed to resist that creep and to keep a useful stress-rupture life at 700 to 750 C. The table below summarises the service envelopes and is written as engineering guidance rather than as a guaranteed performance table.

Service condition	Recommendation	Reason	Test / basis
Combustion chamber liner, flame tube	Nimonic 75	oxidation resistance with formability	ASTM E8 / E21
Furnace internals, low load, 800-900 C	Nimonic 75	oxidation resistance, no creep load	ASTM E21
Thermal fatigue sheet assembly	Nimonic 75	ductility and weldability	design-specific
Turbine blade or vane, 700-750 C	Nimonic 80A	gamma-prime creep resistance	ASTM E139
Bolts, studs and fasteners at temperature	Nimonic 80A	retains tensile strength when hot	ASTM E21
Exhaust valve, valve stem	Nimonic 80A	hot strength plus wear resistance	ASTM E139
High-temperature spring, non-critical	Nimonic 75 acceptable	adequate spring properties	ASTM E8
High-temperature spring, load-critical	Nimonic 80A	higher yield and stress relaxation resistance	ASTM E139
Nuclear reactor internals	grade-specific	qualification by reactor specification	project specification
Heat-treatment furnace fixtures with load	Nimonic 80A	resists sagging under load	ASTM E139

Table note: The recommendation column is engineering guidance based on the strengthening mechanism of each alloy and on the test standards named in the final column, and it is not a substitute for a design calculation. ASTM E8/E8M covers room-temperature tension testing, ASTM E21 covers elevated-temperature tension testing, ASTM E139 covers creep, creep-rupture and stress-rupture testing, and where a design depends on a specific creep-rupture life at a stated stress and temperature that life must be demonstrated by test rather than inferred from a room-temperature figure. Both alloys resist oxidation at high temperature through the formation of a protective chromium oxide scale, so the difference between them in service is almost always the mechanical one described here.

Two design consequences are worth stating explicitly, because they are where projects go wrong. The first is that a part may be limited by stress relaxation rather than by static strength, and relaxation is the loss of load in a bolted or sprung component as it creeps slowly under a constant strain. Nimonic 80A resists relaxation far better than Nimonic 75, which is the reason 80A is the standard material for high-temperature bolts and for springs that must hold load for years. The second is that creep is time-dependent, so a rating is meaningless without a time: a stated creep-rupture life is always a statement of stress, temperature and hours together, and a supplier asked for "creep resistance" without those three numbers cannot answer the question. Where a project needs a specific life, the enquiry should state the stress, the temperature and the hours, and should require the test results to ASTM E139 to be supplied with the certification.

Selection Guide: Springs, Blades, Bolts and Sheet Assemblies

The selection decision follows the load path rather than the alloy name. Where a component is essentially a shape that must survive a hot oxidising environment, it is Nimonic 75 territory; where a component must transmit or hold a load at temperature, it is Nimonic 80A territory. The table below turns that principle into a component-level guide.

Component	Recommended grade	Why	Alternative considered
Combustion chamber and flame tube	Nimonic 75	formability, weldability, oxidation resistance	Inconel 600 sheet for lower temperature
Transition duct and exhaust liner	Nimonic 75	thermal fatigue tolerance	Inconel 625 for higher strength
Turbine blade, small gas turbine	Nimonic 80A	creep strength at 700-750 C	Inconel 718 for lower temperature, higher strength
Hot bolts and studs	Nimonic 80A	resists stress relaxation	A286 for lower temperature
Valve stem and exhaust valve	Nimonic 80A	hot strength plus wear	Inconel 751 for some designs
High-temperature spring	75 for static, 80A for load-critical	relaxation resistance	Nimonic 90 for a higher envelope
Furnace fixture under load	Nimonic 80A	resists sag	RA330 or 253MA for lower duty
Sheet-metal ducting, low load	Nimonic 75	cheapest adequate grade	Inconel 601 for higher temperature

Table note: A component-level guide, not a code or a design basis; the recommended grade must be confirmed against the governing specification of the equipment and against the actual temperature and load, and the alternatives listed are intended to show the boundary of the two Nimonic grades rather than to be an exhaustive list. Where a component sits near the boundary, the deciding question is usually whether the failure mode is oxidation, which favours 75, or creep and stress relaxation, which favours 80A. For higher-temperature versions of the same applications the family continues through Nimonic 90, Nimonic 105, Nimonic 115 and Nimonic 263, while at the lower end of the same duties an Inconel sheet grade such as 600 or 601 may replace the Nimonic entirely, as set out in our Inconel alloy range.

The most common substitution error is to order Nimonic 80A where Nimonic 75 was specified, on the assumption that a stronger alloy is always a safe upgrade. It is not. Nimonic 80A is harder to cold form, less forgiving to weld, requires an ageing cycle and costs more, so substituting it into a large sheet fabrication such as a flame tube can turn a straightforward job into a difficult one without improving the part, because the flame tube was never load-limited. The reverse error is more serious: ordering Nimonic 75 where the part carries a sustained load at temperature, on the assumption that the two grades are equivalent because both are Nimonics. That substitution puts a non-creep-resisting alloy into a creep-limited application, and the failure appears as a slow deformation that is only noticed when clearances close or a blade touches a shroud.

Price, Stock and Procurement Notes for 2026

Nimonic 75 and Nimonic 80A are both specialist alloys with thinner stock positions than the high-volume grades, so availability and lead time influence a project as much as price does. The figures below are reference ranges only and they are not a quotation; the contract that governs is the one signed with the supplier.

Item	Grade	Reference range, 2026, EXW Shanghai	Basis
Sheet, 1-3 mm	Nimonic 75	USD 42-72/kg	2026, EXW Shanghai, reference range only
Sheet, 1-3 mm	Nimonic 80A	USD 50-85/kg	2026, EXW Shanghai, reference range only
Round bar, 20-100 mm	Nimonic 80A	USD 48-85/kg	2026, EXW Shanghai, reference range only
Round bar, 20-100 mm	Nimonic 75	USD 40-70/kg	2026, EXW Shanghai, reference range only
Wire, spring and welding	Nimonic 80A	USD 55-95/kg	2026, EXW Shanghai, reference range only
Forging stock	Nimonic 80A	quotation on drawing	2026, EXW Shanghai, reference range only
Ageing treatment adder	Nimonic 80A only	quoted with the heat treatment	2026, EXW Shanghai, reference range only
Titanium and aluminium surcharge exposure	Nimonic 80A	approx. 2-4 % of base metal cost	reference range only

Table note: Reference ranges only, 2026, EXW Shanghai, in USD per kilogram, and subject to movement in the LME nickel price and in the titanium and aluminium markets; these figures are indicative and are not a quotation. Delivered prices depend on quantity, specification, form, tolerance, test scope, documentation, delivery terms and on whether the material is stock or a mill order, and the percentage figures are planning conventions rather than published rates. The additional cost of Nimonic 80A over Nimonic 75 reflects its titanium and aluminium content and its ageing treatment rather than any difference in difficulty of melting.

Three procurement points complete the picture. First, name the condition, because an aged part and an annealed part are different products with different prices and different properties, and a quotation that omits the condition cannot be compared with one that names it. Second, expect the stock position to be thin, particularly for Nimonic 75 sheet in non-standard thicknesses and for Nimonic 80A forging stock, and place the enquiry early enough to allow a mill order. Third, require the usual documentary package: a mill certificate to EN 10204 3.1, heat-number traceability, positive material identification to ASTM E1476 to confirm the grade family and to distinguish the two Nimonics, and where the part is load-carrying, the stress-rupture results to ASTM E139 that support the design life. Our news and buying guides track which grades and forms are tight in a given quarter, and our contact page is the place to send a component list for a stock-versus-mill-order split.

Standard Index

Standard	Title / scope	Covers	Form
BS HR series	Wrought nickel-chromium heat-resisting alloys (Nimonic grades)	composition + mechanical	sheet, strip, plate, bar
DIN 17742	Wrought nickel alloys, chemical composition	composition	all forms
DIN 17750	Wrought nickel alloys, sheet and strip	dimensions + properties	sheet, strip
DIN 17752	Wrought nickel alloys, bar and rod	dimensions + properties	bar, rod
DIN 17753	Wrought nickel alloys, wire	dimensions + properties	wire
ISO 9722	Nickel and nickel alloys, wrought products	composition + properties	wrought forms
ASTM E8/E8M	Tension testing of metallic materials	test method	all forms
ASTM E21	Elevated-temperature tension testing	test method	all forms
ASTM E139	Creep, creep-rupture and stress-rupture testing	test method	all forms
ASTM E18	Rockwell hardness testing	test method	all forms
ASTM E112	Determining average grain size	test method	all forms
ASTM E1476	Metals identification and PMI	test method	all forms
AMS 2750	Pyrometry for heat-treatment equipment	furnace control	all forms
EN 10204	Inspection document types (2.2, 3.1, 3.2)	inspection documents	all forms
EN 10021	General technical delivery requirements	delivery conditions	all forms
ISO 9001	Quality management systems	system certification	all forms
GB/T 14992	Chinese superalloy and high-temperature alloy classifications	grade classification	all forms
GB/T 15007	Chinese corrosion-resistant alloy classifications	grade classification	all forms

Table note: Standards are listed by number and scope; where a part number or edition year is not quoted the controlling document is the one named on the purchase order, and for the Nimonic family that is normally a numbered part of the BS HR series which must be named specifically. The Chinese designations GH3030 and GH4080A are quoted as indicative equivalents and are not a substitute for the product standard named on the order. Where a project mixes ASTM-governed materials with Nimonic parts, each part should carry its own governing document, because the property and test requirements of the two systems are not identical.

FAQ

Q1: What is the main difference between Nimonic 75 and Nimonic 80A?

The main difference is that Nimonic 80A is a precipitation-hardening alloy and Nimonic 75 is not. Both share a nickel-chromium base of roughly 80 per cent nickel and 20 per cent chromium, but Nimonic 80A adds titanium and aluminium, which form a fine gamma-prime precipitate during a controlled ageing treatment and raise the strength substantially while keeping it high at temperature. Nimonic 75 has only a small titanium content and no aluminium addition, so it cannot form that precipitate and remains a solid-solution alloy whose strength comes from its matrix and from cold work. Everything else in the comparison follows from that single fact: 80A is stronger but harder to form and weld, requires an ageing cycle, and costs more, while 75 is easier to form and weld but has limited load-carrying capacity at temperature. That is why the two grades are specified for different classes of component rather than being alternatives for the same part.

Q2: Is Nimonic 80A stronger than Nimonic 75 at high temperature?

Yes, and the gap widens as temperature rises. In the aged condition Nimonic 80A typically shows a room-temperature yield strength roughly twice that of annealed Nimonic 75, and at 700 to 750 C the difference in load-carrying capacity is far greater because Nimonic 75 has lost most of its useful strength while Nimonic 80A retains a substantial fraction of its own. The reason is that the gamma-prime precipitate that strengthens Nimonic 80A resists the movement of dislocations in a way that persists to high temperature, whereas a solid-solution alloy depends on the intrinsic strength of its matrix, which falls away quickly when the metal is hot. For a component that carries a sustained load, this is the difference between a part that holds its shape for its design life and one that creeps and closes clearances. The correct way to compare the two at temperature is therefore not by a single room-temperature tensile figure but by a stress-rupture life at the actual stress and temperature, which is why load-carrying parts should be specified with a demonstrated test result.

Q3: Can I use Nimonic 80A instead of Nimonic 75?

You can, but it is usually wasteful and sometimes counterproductive. Nimonic 80A is stronger and more expensive, and it is harder to cold form and to weld than Nimonic 75, so substituting it into a large sheet fabrication such as a combustion chamber liner can make the fabrication more difficult without improving the part, because that part was never load-limited. The substitution is justified only where the higher strength and creep resistance are actually required, and where the fabricator can accommodate the harder working behaviour and the ageing treatment. The reverse substitution, using Nimonic 75 where Nimonic 80A was specified, is dangerous rather than merely uneconomic, because it puts a non-creep-resisting alloy into a creep-limited application. Any substitution in either direction should be treated as an engineering change and approved against the load case, not made as a procurement decision.

Q4: Is Nimonic 75 age hardenable?

No. Despite belonging to the same family as the age-hardenable Nimonics, Nimonic 75 is a solid-solution alloy and does not respond usefully to a precipitation heat treatment, because it lacks the aluminium and the higher titanium content that form the gamma-prime phase. It is normally supplied in the annealed condition, and its properties come from that anneal plus any cold work introduced during forming. This has a practical consequence for fabrication: a welded Nimonic 75 assembly can be stress-relieved without changing its metallurgical class, and there is no ageing cycle to specify, verify or repeat. The lack of an ageing response is not a defect; it is the design intent, because it is what makes Nimonic 75 formable and weldable enough for large sheet fabrications. Where an application genuinely needs an age-hardenable alloy at a similar temperature, Nimonic 80A is the grade to select, and if a higher envelope is required the family continues through Nimonic 90 and beyond.

Q5: What are the typical applications of Nimonic 75?

Nimonic 75 is used wherever a component must survive a hot oxidising environment but does not have to carry a significant sustained load. The classic applications are combustion chambers and flame tubes, transition ducts, exhaust liners and other gas-turbine sheet-metal parts, where its combination of oxidation resistance, thermal fatigue tolerance, formability and weldability is exactly what the fabrication needs. It is also used for furnace internals, heat-treatment fixtures that see little load, thermocouple sheathing and some instrument parts. Because it does not creep-resist, it is not the right choice for turbine blades, hot bolts or loaded springs, which belong to Nimonic 80A and the higher Nimonics. A useful rule is that Nimonic 75 is a shape that must survive heat, whereas Nimonic 80A is a part that must survive heat and load, and the two roles rarely overlap in the same component.

Q6: What are the typical applications of Nimonic 80A?

Nimonic 80A is used for components that must carry a load at high temperature for long periods, which is why it appears in turbine blades and vanes, hot bolts, studs and fasteners, exhaust valves and valve stems, high-temperature springs and loaded furnace fixtures. Its gamma-prime strengthening gives it the creep and stress-relaxation resistance those applications need at around 700 to 750 C, and it retains enough strength at temperature to keep clearances and bolt loads where they were designed. It is also used in nuclear reactor components where the reactor specification allows it. The common thread is not the temperature alone but the combination of temperature and sustained load, because a part that is merely hot can often be made from Nimonic 75 or an Inconel sheet grade at lower cost. Where the temperature or the load exceeds the 80A envelope, the family continues through Nimonic 90, 105, 115 and 263, and where a lower temperature with higher strength is required, Inconel 718 or A286 may be a better answer.

Q7: What condition should I specify when ordering Nimonic 80A?

Specify both the condition and the ageing requirement explicitly. Nimonic 80A is supplied either annealed or annealed-and-aged, and the two are different products with different properties and prices, so an order that names only the grade leaves the supplier free to deliver the weaker annealed condition. The order should state the grade and its UNS number, the product standard and its part or edition, the supplied condition, the required mechanical properties or the stress-rupture requirement, the inspection document type to EN 10204, and the heat-treatment control where an aerospace or critical-part specification applies, normally AMS 2750 pyrometry. Where the part will be welded after delivery, the order should also state whether a post-weld ageing treatment is required to restore properties in the weld and heat-affected zone. A specification that includes those items can be quoted, verified and accepted without argument, and it removes the most common cause of a Nimonic delivery being rejected.

Q8: Do Nimonic 75 and Nimonic 80A have ASTM equivalents?

Not in the way that Inconel 625 has an ASTM B443 or Inconel 718 an ASTM B637. The Nimonic family originated in the British standard system and its wrought product specifications are issued primarily as numbered parts of the BS HR series, with European composition limits in DIN 17742 and product forms in the DIN 1775x series, and international guidance in ISO 9722. A buyer who is used to ASTM product standards should therefore expect to name a BS HR part for Nimonic material rather than an ASTM document, and should not assume that an "ASTM equivalent" claimed by a supplier is a real standard. The testing, however, is commonly performed to ASTM methods such as E8/E8M for tension, E21 for elevated-temperature tension, E139 for creep and stress rupture, E18 for hardness and E112 for grain size, so the test methods and the product standard should be named separately on the enquiry.

Q9: How do I verify that the material delivered is the grade I ordered?

Use positive material identification to ASTM E1476 as the primary check, because the titanium and aluminium content that distinguishes Nimonic 80A from Nimonic 75 is exactly what an alloy analyser identifies, and a mixed delivery is the most likely failure mode for two alloys that look alike. Ask for the mill certificate to EN 10204 3.1 and check that the heat number on the certificate matches the heat number marked on the material and on the packing, so that the physical item can be tied back to the tested heat. Where the part is load-carrying, require the mechanical or stress-rupture test results that support the design life, and check that the supplied condition matches the condition ordered, because an annealed part delivered against an aged requirement will pass a PMI check and still fail the design case. Where a third party is used, require the inspection to be witnessed and the certificate to be endorsed, which converts a 3.1 document into a 3.2 document.

Q10: How does Shanghai Hangbo Alloy Group supply the Nimonic grades?

Shanghai Hangbo Alloy Group Co., Ltd. supplies Nimonic 75 and Nimonic 80A in sheet, strip, plate, bar, wire and forging stock, together with the higher Nimonics in the family, and we issue an inspection document to EN 10204 3.1 with third-party inspection by SGS, BV or TUV and positive material identification to ASTM E1476 on delivery. We operate an ISO 9001:2015 quality system, and where a part must carry load at temperature we will discuss the stress, the temperature and the required hours and will return the appropriate test evidence rather than a generic strength figure. Because the two grades are frequently used in the same hot-section assembly, we are used to splitting a bill of materials between 75 and 80A on a component-by-component basis and to explaining the reasoning, so that the sheet fabrications are not over-specified and the loaded parts are not under-specified. Send the component list, the forms, the quantities and the service conditions through our contact page and we will return a grade recommendation with the standards, the condition and the lead time stated.

Conclusion: Specify the Load, Then the Grade

Nimonic 75 and Nimonic 80A are often treated as two versions of the same material, and they are not. Nimonic 75 is a nickel-chromium solid-solution alloy built for sheet fabrications, combustion chambers and furnace internals, where the requirement is oxidation resistance, thermal fatigue tolerance, formability and weldability rather than strength. Nimonic 80A is a gamma-prime hardened alloy built for turbine blades, hot bolts, valves and load-carrying springs, where the requirement is creep and stress-relaxation resistance at 700 to 750 C. The decision is therefore not a matter of choosing the better alloy but of identifying whether the component carries a sustained load at temperature: if it does not, Nimonic 75 is adequate and easier to fabricate; if it does, Nimonic 80A is required and Nimonic 75 is not a substitute.

Three disciplines make the specification safe. First, state the condition, because Nimonic 80A supplied annealed is a different product from Nimonic 80A supplied aged, and the difference is the whole point of the grade. Second, name the governing document, because the Nimonic family is specified through the BS HR series and the European DIN 1775x series rather than through an ASTM product standard, and an "equivalent grade" claim should be tested rather than accepted. Third, verify by positive material identification, because the two grades look alike and a mixed delivery is the most likely failure. Shanghai Hangbo Alloy Group Co., Ltd. supplies both grades with ISO 9001:2015 process control, mill test certification to EN 10204 3.1, third-party inspection by SGS, BV or TUV, and PMI verification to ASTM E1476 on delivery, and will advise on the split between 75 and 80A for a mixed assembly. Send your component list and service conditions through our contact page and we will return a recommendation with the standards, the condition and the lead time stated.

Contact & Complete Product Range

Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier

Email: sales@hangboalloy.com | WhatsApp (Lisa): +86 13611656360 | www.nickel-alloy.com

All Grades

Ni: NI200-N6 | Monel: 400-502, K-500, R-405 | Inconel: 600-740H, X-750, 725 | Incoloy: 800-27-7MO | Hastelloy: C-276-HYBRID-BC1, N | Super Austenitic: 904L-AL-6XN | Chromium-Rich: Alloy 33 | High-Strength Stainless: Nitronic 50/60, PH13-8Mo | Chlorination: Alloy 45 | Nimonic: 75-263 | Haynes: 25-HR-160 | RA: 330/333 | Precision: 1J22-4J45 | High-Strength: 18Ni250-AerMet100 | Heating: Cr20Ni80/60 | Specialty: Alloy 20-602CA

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