What Material Is UNS N06600?
UNS N06600 is a nickel-chromium-iron alloy in which nickel is the dominant element, at about 72 percent minimum, balanced by 14 to 17 percent chromium and 6 to 10 percent iron. It is a solid-solution grade rather than a precipitation-hardening grade, so it does not depend on an ageing treatment for its strength. Strength comes from the nickel-rich matrix, from cold work and from grain size control.
The high nickel level gives the alloy outstanding resistance to caustic alkalies and to high-purity water, including resistance to chloride stress corrosion cracking, while chromium provides resistance to oxidising media and to high-temperature oxidation. It remains ductile at cryogenic temperatures and keeps useful strength in oxidising atmospheres up to roughly 1100 degrees Celsius.
Composition limits are fixed by the product specifications. Typical values are listed below.
| Element | Requirement |
|---|---|
| Nickel, Ni | 72.0 percent minimum |
| Chromium, Cr | 14.0-17.0 percent |
| Iron, Fe | 6.0-10.0 percent |
| Carbon, C | 0.15 percent maximum |
| Manganese, Mn | 1.0 percent maximum |
| Silicon, Si | 0.5 percent maximum |
| Copper, Cu | 0.5 percent maximum |
| Sulphur, S | 0.015 percent maximum |
Implementation Standards by Product Form
The grade is covered by a family of ASTM specifications, one for each product form, supported by AMS aerospace specifications and by the general requirement documents. State the product form and the specification on the purchase order, because mechanical property requirements differ between forms.
| Product form | Specification |
|---|---|
| Forgings and forging stock | ASTM B564 |
| Rod, bar and wire | ASTM B166, AMS 5665, AMS 5667 |
| Plate, sheet and strip | ASTM B168, ASTM B906, AMS 5540 |
| Seamless pipe and tube | ASTM B167 |
| Condenser and heat exchanger tube | ASTM B163 |
| Welded tube | ASTM B516, ASTM B517 |
| Fittings | ASTM B366 |
| General requirements | ASTM B751, ASTM B775, ASTM B829 |
Corrosion Resistance and High-Temperature Behaviour
UNS N06600 resists attack by most acidic media, including sulphuric, nitric, hydrochloric and phosphoric acid, and by alkaline solutions. It also resists chlorides and many oxidising agents, which is why chemical, petrochemical and marine engineering rely on it for corrosion-resistant equipment and piping systems.
At temperature the alloy performs well because its oxide scale remains protective and adherent. It has good creep and rupture strength, retains stiffness in hot service and tolerates thermal shock and thermal cycling. That behaviour suits it to furnace tubes, heaters, steam generators, burners and other high-temperature equipment in refining, chemical and power generation duty.
In the annealed condition the alloy is non-magnetic and has a face-centred cubic structure. Where cold work is applied, the material work-hardens readily, so heavy forming operations normally require intermediate annealing; the annealing temperature is normally in the range 980 to 1050 degrees Celsius followed by rapid cooling for the best corrosion performance.
Typical Applications
Heat treating equipment, retorts, muffles and furnace components
Furnace tubes, heaters, steam generators and burners in refining and chemical plants
Caustic evaporator and handling equipment in the pulp and paper and alumina industries
Nuclear and power plant components, including instrumentation and control rods
Corrosion-resistant process equipment and piping in chemical and petrochemical service
Aerospace and marine high-temperature engine and equipment parts
Frequently Asked Questions
Q: What material is UNS N06600?
It is a nickel-chromium-iron solid-solution alloy containing about 72 percent nickel, 14 to 17 percent chromium and 6 to 10 percent iron, used for corrosion and high-temperature service.
Q: What is the implementation standard for UNS N06600 plate?
Plate, sheet and strip are supplied to ASTM B168, with ASTM B906 as the general requirements document and AMS 5540 covering aerospace plate and sheet.
Q: Which specification covers UNS N06600 bar and forgings?
Rod and bar are covered by ASTM B166 together with AMS 5665 and AMS 5667, and forgings by ASTM B564.
Q: Is UNS N06600 precipitation hardened?
No. It is a solid-solution alloy, so it gains strength from the nickel matrix, from cold work and from grain size control rather than from an ageing treatment.
Q: Where is UNS N06600 commonly used?
In heat treating equipment, furnace tubes and heaters, steam generators and burners, caustic handling equipment, nuclear and power plant parts, and corrosion-resistant chemical process piping.
Q: Does UNS N06600 resist chloride stress corrosion cracking?
Yes. Its very high nickel content makes it far more resistant to chloride stress corrosion cracking than the austenitic stainless steels, and it also resists caustic alkalies and high-purity water.
