Alloy 600 at a Glance
Alloy 600 is a nickel-chromium-iron alloy, designated UNS N06600, in which nickel remains the matrix element at a minimum of 72%. It is one of the most widely used engineering nickel grades because it combines oxidation resistance, resistance to chloride stress-corrosion cracking and useful strength at temperature with good formability and weldability. The composition is fully austenitic, so the material is non-magnetic in the annealed condition and stays essentially non-magnetic after cold working.
The grade belongs to the solid-solution family rather than the precipitation-hardening family. It stays single phase through normal processing, which means it cannot be hardened by heat treatment and is supplied in the annealed condition with strength developed by cold work where higher values are needed.
Composition of UNS N06600
| Element | Requirement (weight %) |
|---|---|
| Nickel (Ni) | 72.0 minimum |
| Chromium (Cr) | 14.0–17.0 |
| Iron (Fe) | 6.0–10.0 |
| Carbon (C) | 0.15 maximum |
| Manganese (Mn) | 1.0 maximum |
| Silicon (Si) | 0.5 maximum |
| Copper (Cu) | 0.5 maximum |
| Sulphur (S) | 0.015 maximum |
These limits come from ASTM B166 for rod and bar, and the same chemistry is carried through ASTM B167 for wire, ASTM B168 for plate, sheet and strip and ASTM B163 for seamless condenser and heat-exchanger tubes, with ASME SB166, SB167 and SB168 as the equivalent ASME documents.
Two points are worth stating clearly, because commercial pages often blur them. First, the 0.15% carbon limit belongs to the standard grade; low-carbon and controlled-carbon versions of the same alloy are ordered separately when resistance to intergranular attack after welding is critical. Second, aluminium and titanium are not specified as deliberate additions in the base UNS N06600 composition, where they are treated as residuals. The ranges commonly published as Al 0.40–1.00% and Ti 0.40–1.00% actually describe Alloy 601, UNS N06601, in which aluminium is deliberately held between 1.0% and 1.7% to improve oxidation resistance. Applying the Alloy 601 range to a UNS N06600 enquiry will not match the mill certificate.
How the Chemistry Drives Performance
Chromium at 14–17% lets the surface form a tenacious chromium oxide film, which is the reason Alloy 600 resists scaling in air, in steam and in many combustion gases at high temperature. Nickel provides the austenitic matrix and gives the alloy its resistance to chloride stress-corrosion cracking and to caustic environments, where ferritic and duplex steels fail quickly.
The 6–10% iron addition lowers cost and improves hot workability while preserving the austenitic structure. Because the grade contains no deliberate molybdenum, it is not intended for strongly oxidising chloride solutions, where pitting and crevice attack would demand a molybdenum-bearing grade such as Alloy 625 or Alloy C-276. Selection should follow the actual medium rather than the generic reputation of the family.
Physical and Mechanical Properties
Density: approximately 8.47 g/cm³
Melting range: approximately 1354–1413 °C
Structure: austenitic, non-magnetic in the annealed condition
Annealed yield strength: typically 170–345 MPa
Annealed tensile strength: typically 550–690 MPa
Annealed elongation: typically 35–55%
The minimum values written into ASTM B166 for annealed bar are 550 MPa tensile strength and 240 MPa yield strength, so the ranges above describe what commercial material normally delivers rather than a specification floor. Cold working raises strength sharply: heavily cold-drawn small sections can exceed 1000 MPa tensile strength, with reports of values up to about 1500 MPa, and this is how fasteners and cold-formed parts obtain their properties. Ductility falls as strength rises, so forming and machining operations should be planned around the temper actually supplied.
Typical Applications by Industry
Chemical processing - high-temperature reactors, process piping, valves and heat exchangers handling chlorides, caustic solutions and other corrosive media.
Aerospace and defence - engine parts, combustion chamber components and turbine hardware that must combine high temperature strength with oxidation resistance and relatively low weight.
Power generation - furnace tubes, heat-exchanger tubing and boiler components operating under high temperature and high pressure, including nuclear steam-generator tubing.
Heat treatment - muffle retorts, radiant tubes, thermocouple sheaths and fixtures that cycle repeatedly through elevated temperatures.
Alloy 600 is supplied as bar, wire, plate, sheet, strip, seamless tube, pipe, forgings and welding consumables, which lets a single specification cover both the pressure boundary and its internal components.
Frequently Asked Questions
Q: What is the composition of Alloy 600?
A: UNS N06600 contains a minimum of 72% nickel, 14.0–17.0% chromium and 6.0–10.0% iron, with carbon at 0.15% maximum, manganese 1.0% maximum, silicon 0.5% maximum, copper 0.5% maximum and sulphur 0.015% maximum.
Q: Does Alloy 600 contain aluminium and titanium?
A: Not as deliberate additions. Aluminium and titanium are reported as residuals in the base UNS N06600 composition. The Al 0.40–1.00% and Ti 0.40–1.00% ranges seen on some commercial pages belong to Alloy 601, which is a different grade with 1.0–1.7% aluminium.
Q: What are the mechanical properties of Alloy 600?
A: Annealed material typically shows 550–690 MPa tensile strength, 170–345 MPa yield strength and 35–55% elongation. The specification minimums for annealed bar to ASTM B166 are 550 MPa tensile and 240 MPa yield, while cold-worked sections can exceed 1000 MPa tensile strength.
Q: Is Alloy 600 magnetic?
A: No. The alloy is fully austenitic and non-magnetic in the annealed condition, and it remains essentially non-magnetic after forming and cold working, since no ferromagnetic phase forms in normal processing.
Q: What is Alloy 600 used for?
A: It is used for heat exchangers, furnace tubes and fixtures, nuclear steam-generator tubing, chemical process equipment, aerospace combustion components and other parts that need oxidation resistance and resistance to chloride stress-corrosion cracking at elevated temperature.
Q: What is the maximum service temperature of Alloy 600?
A: The melting range is about 1354–1413 °C. In oxidising service the alloy is used at high temperature for long periods because of its protective oxide film, but the allowable temperature depends on stress, atmosphere and the presence of sulphur, which must be controlled.
