Incoloy alloy is a widely used superalloy, commonly found in aerospace, chemical, and petroleum industries. When selecting materials, you might have the following questions:
What distinguishes Incoloy from Inconel, both being nickel-chromium alloys?
Why are there so many different grades of Incoloy?
What are the naming conventions for Incoloy grades?
In this article, we will explore Incoloy in terms of its chemical composition, mechanical properties, and physical properties, addressing most of your questions about Incoloy alloys.
Incoloy is a term for a series of superalloys with high iron content. Based on the proportions of nickel, chromium, and iron, Incoloy alloys can be categorized as nickel-iron-chromium alloys, iron-nickel-chromium alloys, or iron-chromium-nickel alloys.
Incoloy alloys are distinguished by their high iron content. To understand this better, it’s important to discuss the relationship between Incoloy and Inconel alloys.
Contrary to popular belief, Incoloy was developed after Inconel, despite having inferior performance. Inconel is a nickel-chromium alloy known for its excellent high-temperature corrosion resistance. Incoloy was created by adding a significant amount of iron to Inconel.
When Incoloy was developed, nickel was a scarce strategic metal. The goal was to create an alloy with lower nickel content that could still resist high-temperature corrosion effectively. Incoloy achieves this by using more iron to replace nickel. Although it doesn’t match the corrosion resistance of Inconel, Incoloy is adequate for many applications and is more cost-effective.
In summary, Incoloy is a nickel-saving alternative to Inconel, offering a lower cost while still providing sufficient high-temperature corrosion resistance.
Here are some common Incoloy grades:
-Incoloy 800
-Incoloy 800H
-Incoloy 800HT
-Incoloy 825
-Incoloy A-286
-Incoloy 330
-Incoloy 925
-Incoloy 926
-Incoloy 945
-Incoloy 25-6HN
Popular Grades of Incoloy Alloys
Incoloy 800 Alloy
INCOLOY alloy 800 (UNS N08800 / W.Nr. 1.4876) is a widely used material for construction of equipment requiring corrosion resistance, heat resistance, strength, and stability for service up to 1500°F (816°C). Alloy 800 offers general corrosion resistance to many aqueous media and, by virtue of its content of nickel, resists stress corrosion cracking. At elevated temperatures it offers resistance to oxidation, carburization, and sulfidation along with rupture and creep strength. For applications requiring greater resistance to stress rupture and creep, especially at temperatures above 1500°F (816°C), INCOLOY alloys 800H and 800HT are used.
The chromium in the alloy imparts both aqueous and heat resistance. Iron provides resistance to internal oxidation. The nickel content maintains a ductile, austenitic structure. Thus, alloy 800 is readily formed, welded, and machined.
Incoloy 800H Alloy
INCOLOY® alloy 800H (UNS N08810) had been known for some time that higher carbon alloy 800 had higher creep and rupture properties than low-carbon material.
For that reason, Special Metals had melted to a carbon range of 0.05 to 0.10% except for special orders where customers specified a lower carbon content.
The carbon range of 0.05 to 0.10% is within the ASTM and ASME specification limits for alloy 800 and is in the upper portion of that range.
Typical applications for the 800H alloy include ethylene pyrolysis, hydrocarbon cracking, cracking furnaces for vinyl chloride, diphenol and acetic acid.
Incoloy 800HT Alloy
Incoloy 800HT also referred to as the UNS N08811/W.Nr. 1.4959 alloy.
Incoloy 800HT is an iron-nickel-chromium alloy having the same basic composition as Incoloy alloy 800, with significantly higher creep rupture strength.
Special Metals knew the importance of maintaining the aluminum and titanium contents in the upper portion of the specified material range. This resulted in higher creep and stress rupture properties than competitive alloy 800H. Therefore, to maintain higher allowable design stresses, the company introduced a variation of INCOLOY alloy 800H which is called INCOLOY alloy 800HT (UNS N08811). INCOLOY alloy 800HT has a restricted chemistry, within the limits of alloy 800H, and requires a heat treatment of 2100°F (1149°C) minimum. The carbon is 0.06 to 0.10% (alloy 800H is 0.05 to 0.10%), the Al + Ti is 0.85 to 1.20% (alloy 800H is 0.30 to 1.20% Al + Ti).
Incoloy 825 Alloy
INCOLOY® alloy 825 (UNS N08825 / W.Nr. 2.4858) is a nickel-iron-chromium alloy with additions of molybdenum, copper, and titanium. The alloy’s chemical composition is designed to provide exceptional resistance to many corrosive environments.
The nickel content is sufficient for resistance to chloride-ion stress-corrosion cracking. The nickel, in conjunction with the molybdenum and copper, also gives outstanding resistance to reducing environments such as those containing sulfuric and phosphoric acids.
The molybdenum also aids resistance to pitting and crevice corrosion. The alloy’s chromium content confers resistance to a variety of oxidizing substances such as nitric acid, nitrates and oxidizing salt. The titanium addition serves, with an appropriate heat treatment, to stabilize the alloy against sensitization to intergranular corrosion.
Incoloy 925 Alloy
Incoloy alloy 925 (UNS N09925) is an agehardenable nickel-iron-chromium alloy with additions of molybdenum, copper, titanium and aluminum. The titanium and aluminium are specifically added to give a strengthening of the alloy during ageing, as Ni3(Al, Ti) gamma (‘ϒ’) prime precipitates form throughout the alloy matrix and greatly increases the hardness and strength in a similar way to alloy 718 and 725.
The alloy is designed to provide a combination of high strength and
excellent corrosion resistance. The nickel content is sufficient for protection against chloride-ion stresscorrosion cracking.
Incoloy 926 Alloy
Incoloy alloy 926 (UNS N08926 / W. Nr. 1.4529 / alloy 25-6MO) is a super-austenitic stainless steel containing 6% molybdenum and enhanced by an addition of nitrogen.
The nickel and chromium contents of this alloy make it resistant to a wide range of corrosive environments.
The alloy is especially resistant to non-oxidizing acids such as sulfuric and phosphoric. The high molybdenum content and nitrogen provide resistance to pitting and crevice corrosion, while copper enhances resistance to sulfuric acid.
Incoloy A-286 Alloy
Incoloy A-286 (UNS S66286/W.Nr. 1.4980) is an iron-nickel-chromium alloy with additions of molybdenum and titanium. It is agehardenable for high mechanical properties. The alloy maintains good strength and oxidation resistance at temperatures up to about 1300°F (700°C). The alloy is austenitic in all metallurgical conditions.
The high strength and excellent fabrication characteristics of INCOLOY alloy A-286 make the alloy useful for various components of aircraft and industrial gas turbines. It is also used for fastener applications in automotive engine and manifold components subject to high levels of heat and stress and in the offshore oil and gas industry.
Chemical Composition of Incoloy Alloys
| Composition | Content Range | Effect | Typical Alloy |
|---|---|---|---|
| Nickel | 9% ~ 55% | Stabilize the Austenitic Structure Corrosion Resistance | Incoloy 825 |
| Iron | 22% ~ 59% | Save Cost | Incoloy 832 |
| Chromium | 0% ~ 28.5% | Oxidation Resistance | Incoloy 890 |
| Molybdenum | 0% ~ 8% | Reduction Resistance | Incoloy 926 |
| Aluminum | 0% ~ 1.25% | Strength Corrosion Resistance | Incoloy 800 Incoloy 925 |
| Titanium | 0% ~ 2.5% | Strength Corrosion Resistance | Incoloy A-286 |
| Niobium | 0% ~ 4.5% | Strength | Incoloy 020 Incoloy 945 |
| Copper | 0% ~ 4% | Corrosion Resistance | Incoloy 825 Incoloy 020 |
| Vanadium | 0% ~ 0.5% | Strength | Incoloy A-286 |
| Silicon | 0% ~ 1.5% | Oxidation Resistance | Incoloy 330 |
| Cobalt | 0% ~ 17% | Low Expansion | Incoloy 909 |
Incoloy Alloys Chemical Compositions Comparison Table:
Nickel
Nickel is the foundation of all superalloys, stabilizing the austenite phase and providing some corrosion resistance. In Incoloy alloys, nickel is the primary source of high-temperature resistance. However, since Incoloy alloys typically have lower nickel content than other superalloys, their high-temperature and corrosion resistance are somewhat reduced.
Chromium
Chromium is the main element responsible for the corrosion resistance of Incoloy alloys. Like in stainless steel and other superalloys, chromium primarily acts as an anti-oxidation agent. To counterbalance the lower corrosion resistance due to reduced nickel content, Incoloy alloys usually have higher chromium content. Chromium also contributes to solid solution strengthening, enhancing the alloy’s strength. Incoloy 890 is an example of a grade with high chromium content.
Molybdenum
Molybdenum serves two main purposes in Incoloy alloys: enhancing corrosion resistance and providing solid solution strengthening. Molybdenum is effective in reducing environments where chromium is less effective. Additionally, due to its significant atomic radius difference from iron and nickel, molybdenum offers a pronounced solid solution strengthening effect. Incoloy alloys typically have limited molybdenum content due to its high cost, which contrasts with Incoloy’s cost-saving intent. Incoloy 926 is a typical molybdenum-containing alloy.
Aluminum
Aluminum has two roles in Incoloy alloys. In some alloys (such as Incoloy 800), aluminum is added to enhance corrosion resistance, compensating for the reduced nickel. In other precipitation-strengthened Incoloy alloys (such as Incoloy 925), aluminum acts as a precipitation strengthening element, significantly increasing the alloy’s strength.
Titanium
Titanium in Incoloy alloys primarily serves as a precipitation strengthening element. In alloys like Incoloy A-286, even a small amount of titanium combined with aluminum can significantly boost tensile strength.
Niobium
Niobium contributes to both solid solution strengthening and precipitation strengthening in Incoloy alloys. Except for Incoloy 020, niobium is mainly used for precipitation strengthening in high-end Incoloy alloys, such as Incoloy 945, due to its high cost.
Copper
Copper primarily enhances corrosion resistance in Incoloy alloys, compensating for reduced nickel content and increasing resistance to sulfuric acid. Incoloy 825 is a typical copper-containing alloy.
Vanadium
Vanadium is mainly found in Incoloy A-286, where it enhances both solid solution and precipitation strengthening.
Silicon
Silicon is unique to Incoloy 330, where it replaces some chromium to improve oxidation resistance. However, excessive silicon can be detrimental, so its content must be controlled to prevent reduced alloy performance.
Cobalt
Cobalt is primarily found in low expansion alloys (Incoloy 903, 907, and 909), providing better high-temperature resistance and strength and extending the low expansion temperature range. This significantly reduces the alloy’s linear expansion coefficient at high temperatures.
Mechanical Properties of Incoloy Alloys
Based on their microstructure, Incoloy alloys are categorized into two main types: solid solution strengthened alloys and precipitation strengthened alloys.
Precipitation strengthened alloys, through aging treatment, can achieve significantly higher strength compared to solid solution strengthened alloys.
| Alloy | Category | Tensile Strength | Yield Strength | Elongation |
|---|---|---|---|---|
| MPa | MPa | % | ||
| Incoloy 800 | Solid Solution Strengthened Alloy | 515 | 205 | 30 |
| Incoloy 825 | Solid Solution Strengthened Alloy | 586 | 241 | 30 |
| Incoloy 925 | Precipitation Strengthened Alloy | 965 | 758 | 18 |
| Incoloy A-286 | Precipitation Strengthened Alloy | 896 | 586 | 15 |
Physical Properties of Incoloy Alloys
Due to the lower nickel content and increased iron content of Incoloy alloy, it is also lower density than Inconel alloy. This also reduces the cost of Incoloy alloy to a certain extent.
| Inconel Grades | Density | Incoloy Grades | Density |
|---|---|---|---|
| Inconel 600 | 8.47 | Incoloy 800 | 7.94 |
| Inconel 625 | 8.44 | Incoloy 825 | 8.14 |
| Inconel 690 | 8.19 | Incoloy 890 | 7.94 |
| Inconel 725 | 8.31 | Incoloy 925 | 8.08 |
Applications of Incoloy Alloys
- Process piping, heat exchangers, carburizing equipment, heating-element sheathing, nuclear steam-generator tubing
- Chemical and petrochemical processing, power plants, industrial furnaces, heat-treating equipment
- Pollution-control equipment, oil and gas well piping, nuclear fuel reprocessing, acid production, pickling equipment
FAQs
1.What are the most commonly used Incoloy alloys?
The most commonly used Incoloy alloys are Incoloy 800 / 800H / 800HT, Incoloy 825, Incoloy 926, Incoloy A-286.
2.What is the difference between Incoloy alloy and stainless steel?
Compared to stainless steel, Incoloy alloy has a higher nickel content. Although it contains a significant amount of iron, it is still less than that found in stainless steel.
As a result, Incoloy offers superior high-temperature resistance and corrosion resistance compared to stainless steel. Naturally, this also makes it more expensive. In terms of the nickel-to-iron ratio, Incoloy alloys fall between Inconel alloys and stainless steel, with performance and cost reflecting this intermediate position.
However, some Incoloy alloys, such as Incoloy 926, have very high iron content, blurring the line between them and stainless steels. These can be considered both stainless steels and superalloys.
In practical applications, Incoloy alloys are more suited for high-temperature environments, while stainless steel is typically used in normal temperature conditions.
Conclusion
Incoloy is a superalloy characterized by its high iron content and reduced nickel content compared to Inconel. This makes Incoloy more cost-effective than Inconel alloys.
As a result, Incoloy can be used as a lower-cost alternative in some applications traditionally served by Inconel.
We offer a variety of Incoloy alloys to meaet your needs. Please feel free to contact us by email for any inquiries.
