Guides / Materials

Inconel 600 and 601: When Furnace and Heat-Treat Fixtures Need Them

August 1, 2026

Most Inconel RFQs are for a finished part going into service. Furnace and heat-treat fixture requests are different: the fixture is not the product, it is the tooling that holds and moves other parts through repeated high-temperature cycles, and it needs to survive far more thermal exposure over its life than almost anything else made from nickel alloy.

Why furnace fixtures need a different alloy

A basket, tray or rack that carries parts through a heat-treat oven sees the same temperature as the load, cycle after cycle, for years. Unlike a turbine part that runs hot in service but gets replaced on a maintenance schedule, a furnace fixture is expected to survive thousands of thermal cycles without the fixture itself failing, warping or shedding scale into the load. That calls for an alloy chosen almost entirely for high-temperature oxidation resistance and dimensional stability at temperature, with strength at room temperature being close to irrelevant.

What makes 600 and 601 resist oxidation

Inconel 600 is a nickel-chromium alloy with enough chromium to form a stable, adherent passivation layer of chromium oxide at high temperature, which is what actually protects the metal underneath from further oxidation. That protective layer is what lets 600 hold up to repeated cycling in air and combustion atmospheres well above where most stainless steels start to scale.

Inconel 601 builds on that with an aluminum addition. The aluminum forms its own oxide layer alongside the chromium oxide, and the combination holds up to higher continuous temperatures and more thermal cycling than 600 before the oxide layer breaks down and the alloy starts losing material. For fixtures that see the most cycles or the highest peak temperatures, 601 is usually the more durable choice, at a modest cost premium over 600.

Typical fixtures and why lead time runs longer

Furnace baskets, trays, hangers, muffles, radiant tubes and load-bearing fixtures inside heat treat, sintering and annealing furnaces are the most common parts we see quoted in 600 and 601. Compared with 625 and 718, demand for these grades is lower and fewer shops keep stock or run them regularly, since the applications sit outside the aerospace and oil and gas work that drives most nickel alloy volume.

That lower demand shows up directly in the quote cycle. Material lead time on 600 and 601 bar, plate or sheet stock tends to run longer than on 625 or 718, since mills produce less of it and distributors carry thinner stock. Buyers should expect the material lead time itself, not the machining time, to be the longer part of the schedule, and it is worth confirming stock availability early rather than assuming a shop can source it as fast as 718.

What to put on the RFQ

Since 600 and 601 fixtures are usually custom tooling rather than a part built to a released drawing, the RFQ benefits from more context than a standard part quote: the peak operating temperature, the atmosphere inside the furnace, whether it is air, inert gas or a combustion atmosphere, how many thermal cycles the fixture is expected to survive, and whether dimensional stability at temperature matters as much as oxidation resistance. If a specific grade has not been chosen yet, describing the operating conditions lets a shop that regularly builds furnace fixtures recommend 600 or 601 rather than guessing from the geometry alone.

Stock form matters too. Fixtures are often built from plate, sheet or tube rather than bar, and confirming what form is realistically available shortens the quote cycle considerably, since sourcing an unusual size in these grades can otherwise become the longest step in the whole order.

Designing the fixture, not just the material

Alloy choice is only part of a furnace fixture RFQ. Wall thickness and joint design matter almost as much, since a fixture that is too thin for its span will warp under repeated thermal cycling regardless of which grade it is cut from, and a welded fixture needs joint geometry that accounts for thermal expansion at operating temperature rather than just at room temperature. If a shop asks for the furnace’s thermal profile, ramp rate and hold time, that is a reasonable question, not a stall. Fixtures designed against the actual cycle the furnace runs tend to last considerably longer than a fixture copied from a similar-looking design used in a different oven. The guide to high temperature nickel alloys sets the oxidation limits of 600 and 601 beside the load-bearing grades.

Frequently asked questions

Keep reading

• Waspaloy and Rene 41 Machining: The Harder Superalloys Compared With Inconel
• Inconel X-750 vs 718: Which Alloy for Springs and High-Temperature Fasteners