What are the differences between Inconel Nickel Alloys 625, 330 and 600?
You may be familiar with the Inconel family of high-nickel alloys. This family of alloys is renowned for its performance under extreme thermal conditions, making each Inconel nickel alloy variant very popular for use in furnace applications such as heat treating or annealing steels. However, what are the differences between the Inconel range of nickel alloy products? This is a question often asked by Muyan Alloy salesmen. In fact, a customer recently did a test where they put their product in a furnace at 1975 degrees Fahrenheit for one hour and wanted to know which of three different Inconel alloys would be best for their application: 330, 600 Or 625?
To help answer this question, here's a quick comparison of these three high-heat specialty metals:
Incoloy330
Although it is part of the Inconel family of heat-resistant metal alloys, 330 is more commonly known as Incoloy or RA330. With a nickel content between 34% and 37% and a chromium content between 17% and 20%, Incoloy is incredibly resistant to oxidation at high temperatures up to 1148°C and has the ability to carburize and nitride.
Rapid changes in temperature (common in heat treatment applications) are not a big problem for 330 alloy because it resists thermal shock. Like many Inconel alloys, 330 retains a large degree of tensile strength under extreme temperatures compared to common steel alloys.
In fact, in the Alloy Performance Guide, Rolled Alloys lists RA330 as having "better" (above average) properties in strength, oxidation resistance, carburization resistance, and sulfur oxidation resistance, while also being Rated "Best" in thermal shock resistance among the high temperature alloys offered.
inconel600
Inconel600 is a very popular high temperature resistant oxidation material. With a minimum nickel content of 72%, this metal alloy has more than twice the nickel content of Incoloy 330.
While this helps improve the metal's resistance to high-temperature oxidation and carburization, it does make the metal susceptible to sulfur attack. As described in the Rolling Alloys Guide, Inconel 600 is used to oxidize sulfur, reduce sulfur or molten metals such as copper, zinc or magnesium. But it does have good tensile strength, above-average resistance to oxidation and thermal shock, and best-in-class resistance to carburization. It is also incredibly resistant to chloride stress corrosion cracking if the stress is relieved.
Inconel625
In terms of nickel content, Inconel625 is between alloy 330 and 600, with a minimum nickel content of 58%. The chromium content is between 20-23%, which is the most abundant element in the alloy. The addition of niobium and molybdenum improves the performance of the alloy at different temperatures, which is why Inconel600 has excellent strength and toughness in the temperature range of 0°C to 1093°C.
The alloy also has exceptionally high creep rupture strength, fatigue resistance and chloride pitting/crevice corrosion resistance. Also, this metal is very easy to weld compared to other Inconel nickel alloys. Recommended uses for this metal include jet engine exhaust pipes, flare stacks, seawater equipment and chemical plant equipment because of its high chemical and temperature resistance.
In corrosion tests of rolled alloys, 625's resistance to oxalic acid was particularly high compared to other materials, with the material experiencing only 6.0 mils/year of corrosion in a 10% boiling solution of oxalic acid. In comparison, 316L stainless steel experienced 44.9 mils/year of corrosion in the same solution. However, its resistance to sulfuric acid is less impressive, at 37mils/year in a 10% bath.
So which material is best for your needs?
GNEE Steel recommends that you: Depending on what your application process looks like, what chemicals, if any, will be involved? Inconel 600 has good temperature resistance, but not exceeding 330, making it completely unsuitable for any application involving the use of sulfuric acid compounds. At the same time, 330 has good resistance to sulfur oxidation but does not reduce the sulfur content. Inconel 625 is generally resistant to most acids but may cost more than the lower nickel-containing 330 alloy.
