In high-temperature engineering, bar stock for bolts, studs and turbine components must be selected for the exact duty. Nimonic 75 and Nimonic 80A are both nickel-chromium heat-resistant alloys, but their roles are distinct: 75 is ductile and weldable for structural and sheet-metal parts up to 800 °C, while 80A is age-hardened for high-load fasteners and turbine blades up to 815 °C. This guide covers both.
Key Takeaways
Nimonic 75 (UNS N06075, 2.4951) and 80A (UNS N07080, 2.4952) are the standard equivalents.
75: solid-solution strengthened, 42% elongation, easy to machine and weld.
80A: precipitation hardened, 994 MPa tensile, 300 HV minimum, excellent creep resistance.
Supply: round bars 3-800 mm, hex, flat, square and hollow bars to BS HR 5/504, DIN 17752, ISO 9723-9725.
What Is Nimonic 75?
Nimonic 75 is an 80/20 nickel-chromium alloy with added titanium and carbon, originally introduced in the 1940s for turbine blade manufacture. It is easy to machine and weld, with good corrosion resistance, mechanical properties and heat resistance, making it ideal for structural components, sheet-metal parts and static high-temperature components up to about 800 °C.
What Is Nimonic 80A?
Nimonic 80A is strengthened by precipitation aging through aluminum and titanium additions, giving significantly higher mechanical strength and creep resistance than Nimonic 75 at temperatures up to 815 °C. It is designed for components under heavy mechanical load that must not deform over time: fastener-level applications, bolts, exhaust valves and turbine blades.
Chemical Composition
Nimonic 75: carbon 0.08-0.15%, manganese 1.0% max, silicon 1.0% max, copper 0.5% max, iron 5.0% max, nickel balance, chromium 18.0-21.0%, titanium 0.2-0.6%. Nimonic 80A: aluminum 1.0-1.8%, boron 0.008% max, carbon 0.10% max, chromium 18.0-21.0%, cobalt 2.0% max, copper 0.20% max, iron 3.0% max, manganese 1.0% max, nickel balance, phosphorus 0.045% max, silicon 1.0% max, sulfur 0.015% max.
Mechanical Properties
Nimonic 75 rod: density 8.37 g/cm³, melting point 1340-1380 °C, tensile strength 104,000 psi, yield strength 40,000 psi, elongation 42%. Nimonic 80A in the solution-annealed and precipitation-treated condition: ultimate tensile strength 994 MPa, yield strength 616 MPa, minimum elongation 20% on 4D and minimum hardness 300 HV.
Bar Specifications and Stock
Round bars from 3 mm to 800 mm diameter, hex bars 2-100 mm A/F, flat bars 2-100 mm thick and 10-500 mm wide, square bars 4-100 mm, rectangular and hollow bars to the listed ranges, with tolerances H8-H13 or K9-K12 and finishes of black, bright polished, rough turned, No.4, matt or BA. Standards include BS HR 5, BS HR 504, DIN 17752, ISO 9723, ISO 9724 and ISO 9725. Bars are supplied precision ground, peeled or bright drawn, with MTC 3.1 included.
Selection Guidance
Choose Nimonic 75 when ease of machining and welding matters, when oxidation resistance and ductility are the priorities, and for furnace parts and exhaust ducting. Choose Nimonic 80A for high-load fasteners and bolts, exhaust valves and turbine blades, where precipitation hardening provides the creep resistance that prevents loosening and failure under thermal and mechanical stress.
Frequently Asked Questions
Q: Which alloy is better for high-temperature fasteners?
Nimonic 80A, whose precipitation hardening provides high creep resistance that prevents bolt loosening; Nimonic 75 is generally too soft for high-load bolting.
Q: Can Nimonic 75 and 80A be welded together?
Yes, with specialized consumables and post-weld heat treatment, especially on the 80A side, to maintain joint strength.
Q: What diameters are stocked?
Round bars from 5 mm to 250 mm in stock, with precision-ground bright bars in smaller diameters and larger sizes as peeled or forged.
Q: Is Nimonic 80A used for exhaust valves?
Yes, its hot hardness and corrosion resistance make it a standard choice for high-performance engine exhaust valves.
Q: What are the UNS numbers?
Nimonic 75 is UNS N06075 (2.4951) and Nimonic 80A is UNS N07080 (2.4952).
Q: What is the maximum service temperature?
Nimonic 75 serves to about 800 °C and Nimonic 80A to about 815 °C.
