nickel alloy UNS N06600 vs 601: The Key Difference
Both nickel alloy UNS N06600 and nickel alloy UNS N06601 are nickel-chromium alloys, but the aluminum addition in 601 changes its behavior fundamentally. nickel alloy UNS N06601 contains 1.0–1.7% aluminum, which forms a dense, tightly adherent aluminum oxide scale during high-temperature exposure. That scale is what gives 601 its superior oxidation resistance, allowing service in oxidizing atmospheres up to about 2200 °F (1204 °C), compared with roughly 2000 °F (1093 °C) for nickel alloy UNS N06600. The trade-off is in aqueous corrosion: nickel alloy UNS N06600 offers excellent resistance to chloride stress corrosion cracking and remains the more economical, more widely available choice for general chemical processing. In short, choose 601 for furnace and high-temperature oxidizing service and 600 for high-stress chloride environments where its performance is sufficient.
Composition and Mechanical Properties
| Element | nickel alloy UNS N06600 (N06600) | nickel alloy UNS N06601 (N06601) |
| Nickel | 72.0% min | 58.0–63.0% |
| Chromium | 14.0–17.0% | 21.0–25.0% |
| Iron | 6.0–10.0% | Balance |
| Aluminum | - | 1.0–1.7% |
| Carbon (max) | 0.15% | 0.10% |
| Manganese (max) | 1.0% | 1.0% |
| Silicon (max) | 0.50% | 0.50% |
| Copper (max) | 0.50% | 1.0% |
| Sulfur (max) | 0.015% | 0.015% |
| Property (min, per ASTM B564) | nickel alloy UNS N06600 | nickel alloy UNS N06601 |
| Tensile strength | 655 MPa (95 ksi) | 550 MPa (80 ksi) |
| Yield strength (0.2%) | 310 MPa (45 ksi) | 205 MPa (30 ksi) |
| Elongation | 40% | 30% |
| Density | 8.47 g/cm³ | 8.11 g/cm³ |
| Melting range | 1354–1413 °C | 1301–1411 °C |
Neither grade contains molybdenum: alloying with 8–10% molybdenum is the signature of nickel alloy UNS N06625, which is a separate, stronger grade used where pitting resistance and high strength are required.
Standards and Product Forms
Forged pipe fittings in nickel alloy UNS N06600 and 601 are manufactured to ASTM B564 and ASME SB564, which cover nickel alloy forgings and define chemistry and mechanical requirements. Dimensional and pressure requirements follow ASME B16.11 for socket-welding and threaded fittings, with MSS SP-79, SP-83, SP-95, and SP-97 covering related forged fitting types and BS 3799 for British practice. Fittings are available in socket-weld and screwed-threaded ends from 1/8 inch to 4 inches nominal bore, in pressure classes of 2000, 3000, 6000, and 9000 pounds, and in additional grades including nickel alloy UNS N06625, 718, 690, and X-750. Always verify the grade, standard edition, and class on the order and the mill test certificate.
Selecting the Right Alloy
Select nickel alloy UNS N06601 when the application involves furnace components, industrial heating, radiant tubes, thermocouple sheaths, or continuous exposure above 2000 °F (1093 °C), where oxidation resistance and thermal shock resistance are critical and cost is secondary. Select nickel alloy UNS N06600 for general corrosive environments, high-stress chloride service such as chloride stress corrosion cracking conditions, heat exchangers, and caustic handling, where its combination of corrosion resistance, good strength, and lower cost is adequate. For highest room-temperature strength and pitting resistance, especially in seawater or mixed-acid service, nickel alloy UNS N06625 should be considered instead of either grade.
Application Guidance
nickel alloy UNS N06600 forged fittings are used in chemical processing, nuclear systems, heat-treatment equipment, and food processing, and they resist a wide range of oxidizing and reducing media at moderate temperatures. nickel alloy UNS N06601 fittings are used in furnace and heater piping, incinerators, petrochemical reformers, and power-generation equipment, where the aluminum-rich oxide scale prevents spalling under thermal cycling. In both cases, the fittings are typically joined to matching alloy pipe by socket welding, and welding procedures should use nickel-based filler metals such as ENiCrFe-2 or ENiCrFe-3 for 600 and matching or higher-alloy fillers for 601, with clean joint preparation to preserve corrosion and oxidation resistance.
Frequently Asked Questions
What is the difference between nickel alloy UNS N06600 and nickel alloy UNS N06601? nickel alloy UNS N06601 contains 1.0–1.7% aluminum, which creates a protective oxide scale and raises oxidation resistance to about 2200 °F (1204 °C) versus 2000 °F (1093 °C) for 600. nickel alloy UNS N06600 has better chloride stress corrosion cracking resistance in aqueous service and costs less.
Does nickel alloy UNS N06601 contain molybdenum? No. nickel alloy UNS N06601 is a nickel-chromium-iron-aluminum alloy with no intentional molybdenum. Molybdenum at 8–10% is characteristic of nickel alloy UNS N06625, a different grade with higher strength and pitting resistance.
What standard covers nickel alloy UNS N06600/601 forged fittings? Material requirements follow ASTM B564 / ASME SB564, with dimensions and ratings per ASME B16.11 (socket-weld and threaded), MSS SP-79/83/95/97, and BS 3799.
Which is stronger, nickel alloy UNS N06601 or 625? nickel alloy UNS N06625 is significantly stronger: its minimum annealed tensile strength is about 827 MPa versus 550 MPa for 601. The two are not substitutes; 625 is chosen for strength and pitting resistance, 601 for oxidation resistance at very high temperature.
When should I choose nickel alloy UNS N06601? Choose 601 for furnace components, radiant tubes, industrial heating, and thermal-cycling service above about 2000 °F (1093 °C), where oxidation resistance is the dominant requirement.
What is the maximum temperature for nickel alloy UNS N06600? nickel alloy UNS N06600 resists oxidation to about 2000 °F (1093 °C) in dry atmospheres, but in pressurized or corrosive service the design temperature is normally far lower and should be taken from ASME Section II, Part D allowable stress tables.
