What Is Nimonic 75?
Nimonic 75 is an 80/20 nickel-chromium alloy with controlled additions of titanium and carbon. It was first introduced in the 1940s for turbine blades in the Whittle jet engine prototype and became the foundation of the Nimonic family of high-temperature alloys. Today it is used in gas turbine technology, industrial heat treatment, furnace components, heat treatment equipment, nuclear technology, and environmental technology. The alloy is identified by UNS N06075, the EN designation NiCr20Ti, and the European material number 2.4951. It offers a useful combination of medium-strength sheet and rod properties, excellent oxidation and scaling resistance at high temperatures, good corrosion resistance, and easy manufacture and welding.
Composition and Properties
The composition of Nimonic 75 is a nickel base with chromium as the principal alloying element and controlled titanium and carbon additions for high-temperature strength and stability.
| Element | Limit or nominal (weight %) |
| Nickel | Balance (72.0 min) |
| Chromium | 21.0 (range 18.0-21.0) |
| Iron | 5.0 max |
| Cobalt | 5.0 max |
| Silicon | 1.0 max |
| Titanium | 0.6 (range 0.2-0.6) |
| Carbon | 0.08-0.15 |
The high chromium content provides the protective oxide scale that gives Nimonic 75 its outstanding resistance to oxidation and scaling in hot oxidizing environments, while titanium and carbon control grain structure and strength at service temperature.
Typical standard values at 20°C for rod are a 0.2% proof strength of 235 N/mm2, tensile strength of 640 MPa, elongation at break of 26%, and modulus of elasticity of 221 kN/mm2. The alloy retains useful mechanical properties at high temperature, which is the basis of its turbine and furnace applications.
| Property (20°C) | Typical value |
| 0.2% yield strength | 235 N/mm2 |
| Tensile strength | 640 MPa |
| Elongation at break | 26% |
| Modulus of elasticity | 221 kN/mm2 |
| Density | 8.2 g/cm3 |
| Specific heat | 420 J/(kg K) |
| Thermal conductivity | 13 W/(m K) |
| Electrical resistance | 1.03 ohm mm2/m |
In oxidizing service the alloy is resistant to scaling up to about 1000°C, which covers most gas turbine and furnace applications. Actual allowable stresses at temperature should be taken from the applicable design code and the mill's certified data.
Standards and Specifications
Nimonic 75 is designated in Europe as NiCr20Ti with material number 2.4951 and in the American system as UNS N06075. Plate and sheet are commonly supplied to EN 10095 and DIN 17752, and bar, rod, and forgings are supplied against the applicable EN/DIN specifications confirmed at inquiry. Because several ASTM nickel alloy standards have specific scope lists, the exact ASTM specification that covers N06075 for the required product form, for example rod or forging, should be verified with the mill before ordering rather than assumed from generic nickel alloy tables.
Applications of Nimonic 75
Main applications include steam and gas turbine components; furnace construction and heat treatment plant parts such as retorts, trays, and muffles exposed to hot oxidizing atmospheres; nuclear technology components requiring clean, stable alloys; and environmental technology equipment operating at elevated temperature. The alloy is also produced as tubing for heat exchangers and piping in high-temperature service, and as sheet for aerospace fabrication where medium strength and scaling resistance are the governing requirements. Its easy formability and weldability make it economical to fabricate into complex shapes compared with higher-strength precipitation-hardened superalloys.
Welding and Fabrication
Nimonic 75 is easy to manufacture and weld. The material should be annealed before welding, although a small amount of cold forming is tolerable and simple bending and rolling does not necessarily require pre-annealing prior to welding. The heat-affected zone does not suffer weld seam decay, and post-weld heat treatment is not normally required. If the equipment will operate in contact with caustic soda, fluorosilicates, or certain mercury salts, a stress-relieving treatment may be desirable. Matching nickel-chromium filler metals are used, and standard TIG, MIG, and resistance welding practices for nickel alloys apply, with clean joint surfaces and proper shielding to avoid contamination.
Frequently Asked Questions
What is Nimonic 75? Nimonic 75 is an 80/20 nickel-chromium alloy with controlled titanium and carbon additions, UNS N06075, EN NiCr20Ti, W.Nr. 2.4951, developed in the 1940s for jet engine turbine blades and now used for high-temperature sheet and rod applications in turbines, furnaces, and heat treatment equipment.
Is Nimonic 75 the same as nickel alloy UNS N06600? No. Although both are nickel-chromium alloys, Nimonic 75 (N06075) has higher chromium (18-21% versus 14-17%), controlled titanium, and is optimized for high-temperature scaling resistance, while nickel alloy UNS N06600 (N06600) has higher iron and different corrosion characteristics.
What is the maximum service temperature of Nimonic 75? In oxidizing environments the alloy resists scaling up to about 1000°C. The permissible design stress at temperature depends on the application and governing code, so certified data should be used for design.
Can Nimonic 75 be welded? Yes, it welds easily with standard nickel alloy practices. Anneal before welding where practical, keep surfaces clean, use matching filler metal, and note that post-weld heat treatment is normally not required.
Does Nimonic 75 need post-weld heat treatment? Normally no, because the heat-affected zone does not suffer weld decay. A stress-relieving treatment may be desirable when the equipment contacts caustic soda, fluorosilicates, or certain mercury salts.
What is Nimonic 75 used for? Gas turbine components, furnace construction and heat treatment plant parts, nuclear technology components, heat exchanger tubing, and aerospace sheet fabrications requiring medium strength with high-temperature oxidation resistance.
Is Nimonic 75 corrosion resistant? It has good corrosion resistance and excellent resistance to oxidation and scaling at high temperature, but it is not intended for strongly reducing acids or severe chloride service; for those duties, molybdenum-bearing nickel alloys are more appropriate.
