What Is Nimonic 75 (Nicrofer 7520)?
Nimonic 75, also sold under the trade name Nicrofer 7520 and the German material designation NiCr20Ti, is a nickel-chromium high-temperature alloy registered as UNS N06075. It was developed in the 1940s for the turbine blades of early jet engines and has since become one of the most widely used wrought nickel alloys for industrial heat service. The alloy consists mainly of nickel, at least 75 percent, with 18 to 21 percent chromium, plus controlled additions of titanium, aluminum, carbon, and other trace elements. In the German material numbering system the grade is referenced under both W.Nr. 2.4951 and W.Nr. 2.4630, and both numbers are encountered in trade documentation, so the material certificate should be checked against the number requested on the purchase order.
Chemical Composition and Mechanical Properties
The useful behavior of Nimonic 75 comes from the balance of its main constituents. Nickel provides the stable austenitic matrix, chromium 18 to 21 percent builds the protective oxide scale, titanium 0.2 to 0.6 percent and a small aluminum addition improve oxidation resistance, and carbon is held at a low maximum, around 0.12 percent, to control carbide precipitation and mechanical response. Careful composition control is the reason the alloy shows dependable properties from batch to batch.
At room temperature the tensile strength of Nimonic 75 typically reaches 750 to 950 N/mm2, the yield strength is at least 275 N/mm2, and elongation at break is 30 to 40 percent, which supports good formability. The modulus of elasticity is approximately 210,000 N/mm2, comparable with quality alloy steel. These values are typical results from published material data; certified values depend on the product form, temper, and section size and must be taken from the mill test certificate for the specific delivery.
High-Temperature and Corrosion Properties
The outstanding feature of Nimonic 75 is its behavior in sustained heat. The material retains structural integrity up to about 950 °C and shows a low tendency to creep under continuous load. Its coefficient of thermal expansion is 13.0 x 10-6 per kelvin, which permits accurate dimensional calculation in design, and its thermal conductivity is 11.2 W/(m·K), which supports controlled heat transfer in furnace and heat-exchanger service. The high chromium content forms a self-healing passive oxide layer that protects the alloy against aggressive media. Nimonic 75 resists hot gases and steam up to 950 °C, and in chloride-bearing environments it shows good resistance to pitting and stress corrosion cracking; salt spray tests confirm satisfactory behavior under marine conditions.
Applications and Industries
Nimonic 75 serves demanding industrial sectors. Its main applications include gas turbine components, exhaust systems, and heat treatment plant parts such as combustion chambers, heating coils, and furnace linings, where low creep and resistance to thermal cycling extend maintenance intervals. In measurement technology the alloy is used for sheathed thermocouples and sheathed resistance thermometers, which benefit from its stable high-temperature behavior and oxidation resistance. The chemical industry uses it for reactors and heat exchangers that must withstand corrosive process media, and nuclear technology applies the material where high demands are placed on long-term material stability. The alloy is supplied as sheet, plate, bar, rod, pipe, tube, and wire to match these applications.
Processing, Machining, and Welding
Despite its high-temperature strength, Nimonic 75 can be processed by conventional routes. Machining requires carbide tooling and adjusted cutting parameters because the alloy is harder than standard steels and work-hardens under the tool edge. For welding, the TIG process with shielding gas is recommended to produce sound, oxide-free joints. Cold forming is possible to a limited extent, and the high strength of the material should be taken into account when planning bending or deep drawing. Heat treatment is used to adjust final properties: solution annealing at approximately 1080 °C followed by controlled cooling restores the optimum combination of ductility and high-temperature performance, particularly for components that will be heavily worked before service.
Frequently Asked Questions
What is the difference between the designations 2.4951 and 2.4630? Both W.Nr. 2.4951 and W.Nr. 2.4630 appear in trade documentation for the nickel-chromium alloy NiCr20Ti (Nimonic 75 / Nicrofer 7520 / UNS N06075). Because usage varies by source, the material number on the certificate should be reconciled with the number in the purchase specification.
What is the maximum service temperature of Nimonic 75? The alloy is commonly rated for continuous service up to about 950 °C, where it retains oxidation resistance and structural stability. The practical limit depends on the stress level and the required component life.
Is Nimonic 75 weldable? Yes. TIG welding with shielding gas is the recommended process, and matching nickel-chromium filler metal produces joints suitable for high-temperature service. The alloy is frequently used in welded furnace and exhaust assemblies.
How does Nimonic 75 compare with austenitic stainless steel? Nimonic 75 offers significantly higher high-temperature strength and oxidation resistance than conventional austenitic stainless steels, which is why it is chosen for gas turbine and furnace components that operate above the practical limits of stainless grades.
What product forms are available for Nimonic 75? Nimonic 75 is available as sheet, plate, strip, round and flat bar, rod, seamless and welded pipe and tube, and wire, so fabricators can select the form best suited to the component geometry.
Does Nimonic 75 resist chloride stress corrosion cracking? The high chromium content gives the alloy good resistance to pitting and stress corrosion cracking in chloride-containing environments, and it performs well in marine exposure tests, making it suitable for coastal and offshore applications.
