Technical Resources

Generic C276/22 VS Hastelloy® C276/C22

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Hastelloy® is a trademark of Haynes International for a family of alloys which includes C276 and C22. Other mills cannot use the word “Hastelloy®” and have their own naming system. C22 is also a registered trade name, therefore other producers supply the material as alloy 22.

Universal governing systems

The universal governing system for the alloys is the Unified Numbering System (UNS) number, where UNS N10276 governs alloy C276 and UNS N06022 governs alloy 22.

Alloy C276 (UNS N10276) and alloy 22 (UNS N06022) meet all the composition requirements and characteristics as defined and specified by ASTM and ASME specifications. For UNS N10276 (C276), and UNS N06022 (22), ASTM and ASME specifications are required on all alloy stock and thus reported on all mill certificates.

The test certificates should also report relevant intergranular corrosion test results. ASTM G28A and ASTM G28B corrosion tests are qualitative tests, developed to demonstrate that the material  has not been sensitised and  is therefore not subject to intergranular corrosion.

General Chemistry and Key Characteristics

Here is some more detailed information about the general chemical make-up of alloys, and their most important characteristics.

Hastelloy C276/Alloy C276 – UNS N10276

Alloy

%

Ni

Cr

Mo

Fe

W

Co

C

Mn

Si

V

P

S

C276

Min.

balance

14.5

15

4

3

Max.

16.5

17

7

4.5

2.5

0.01

1

0.08

0.35

0.04

0.03

• Key alloying elements are chromium, molybdenum and tungsten.
• Carbon content must be maintained below 0.010% to minimise the formation of intermetallic carbides.
• Material must be fully solution annealed and have been subjected to quenching or air cooling processes to minimise the formation of intermetallic phases (mu phase), metallic carbides precipation at the grain boundaries, and the risk of sensitisation (intergranular corrosion attack).

Hastelloy C22/Alloy 22 – UNS N06022

Alloy

%

Ni

Cr

Mo

Fe

W

Co

C

Mn

Si

V

P

S

A22

Min.

balance

20.0

12.5

2.5

Max.

22.5

14.5

6.0

3.5

0.015

0.5

0.08

0.35

0.02

0.02

• Key alloying elements are chromium, molybdenum and tungsten.
• Higher chromium and lower molybdenum content make the alloy more corrosion resistant in highly oxidising media than C276.
• Carbon content must be maintained below 0.015% to minimise the formation of intermetallic phases, as well as metallic carbides precipitation at the grain boundaries and the risk of sensitisation (intergranular corrosion attack).

History of the development of the “C” family of alloys

Alloys have undergone big changes over the years, and it wasn’t easy to get them to where they are today.

1930’s to 1965: Alloy C

• The first nickel–chromium–molybdenum-tungsten alloy was developed. Based on the melting technology available, alloy C still had relatively high carbon and silicon contents i.e. carbon: 0.05% maximum and silicon: 0.70% maximum.
• The alloy demonstrated good corrosion resistance characteristics for both uniform corrosion and localised corrosion.
• However, when used in the as-welded condition, alloy C was susceptible to serious intergranular corrosion attack at the HAZ (heat affected zone). This meant that, for many applications, the vessels and process equipment fabricated from alloy C had to be solution annealed to remove the detrimental HAZ.
• Moreover, in severe oxidising media, the alloy did not have enough chromium to maintain useful passive behaviour and thus, exhibited high uniform corrosion rates.

1965 to present date: Alloy C276

• With the advent of a new melting technology, AOD (argon oxygen decarburisation) / VOD (vacuum – oxygen decarburisation), allowed the alloy to be manufactured with much lower carbon and silicon levels. Carbon and silicon levels were reduced ten-fold i.e. carbon: 0.005% maximum and silicon: 0.040% maximum.
• ASTM specifies that the carbon content has to be 0.010% maximum and silicon 0.08% maximum.
• This, coupled with the development of ESR (electro slag refining) and VIM (vacuum induction melting), meant the alloy could be produced with a highly controlled chemistry and low levels of impurities and inclusions.

1970’s to present date: Alloy C4

• The omission of tungsten and a reduction in the iron content to increase thermal stability: virtually eliminating the intermetallic phases and grain boundary precipitation of the intermetallics and metallic carbides (mu phase).

1982 to present date: Alloy C22

• Alloy C22 was developed following the expiration of the patent on C276. Increased chromium with an optimised balance of chromium, molybdenum and tungsten yielded an alloy with superior corrosion resistance and thermal stability, in highly oxidizing environments.

Intergranular corrosion and thermal stability

Want to know more about inter granular corrosion and thermal processing tests? They aren’t as complicated as they might seem.

ASTM G28A and G28B Corrosion Tests

Development over the past 70 years of the “C” family of alloys has been focused on improvements in alloy metallurgy, in melting technology and in thermo-mechanical processing. ASTM G28A and G28B tests where developed later as qualitative corrosion tests, to verify that the metallurgy, melting process and thermo-mechanical processing had been completed correctly. This ensures that the material is in the fully solution-annealed condition and is not subject to intergranular corrosion resulting from the presence of intermetallic / carbide precipitates at the grain boundaries. There is no pass or fail criteria for the tests. The results are agreed between buyers and suppliers.

ASTM G28A

• Ferric sulphate and sulphuric acid boiling test.
• 50% H2SO4 + 42g/litre Fe2 (SO4)3

ASTM G28B

• Mixed acid (sulphuric acid, hydrochloric acid, ferric chloride and cupric chloride) – oxidising salt boiling test.
• 23% H2SO4 + 1% HCl + 1% FeCl3 = 1% CuCl2

Published industry accepted corrosion rates for C276 and C22/Alloy 22.

Producers

Alloy C276 G28A

(mm per annum)

Alloy C276 G28B

(mm per annum)

Alloy 22/ C22 G28A

(mm per annum)

Alloy 22/ C22 G28B

(mm per annum)

Haynes International

6.10

1.40

0.61

0.178

Special Metals

7.00

1.50

1.50

0.50

ThyssenKrupp VDM

9.00

1.50

0.90

0.17

Results based on taking the average of a minimum of 10 mill test certs/heats.

Producers

Alloy C276 G28A

(mm per annum)

Alloy C276 G28B

(mm per annum)

Alloy 22/ C22 G28A

(mm per annum)

Alloy 22/ C22 G28B

(mm per annum)

Haynes International

6.172

Not reported

0.807

0.145

ATI ( Allegheny)

5.985

1.330

0.822

0.151

Special Metals Huntington , U.S.A

4.315

0.736

–

–

Special Metals Wiggin, UK

6.835

0.858

1.135

0.143

BGH – Germany

4.050

0.780

ThyssenKrupp VDM

–

–

0.809

0.172

Bohler

–

–

0.590

0.094

Special Metals

Huntington. U.S.A.

–

–

0.821

0.119

Overview

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Hastelloy C-22 and Hastelloy C-276 are both high performance alloys. They are widely used in corrosive applications in extreme environments. They play a key role in the chemical industry, marine engineering, oil and gas and other fields.

If you have some knowledge about nickel alloys, you must know that both these two Hastelloy alloys are nickel-chromium-molybdenum alloys. But, you might be wondering what exactly is the difference between them? Why is Hastelloy C-276 more commonly used than Hastelloy C-22?

This article will make an in-depth comparison of Hastelloy C-22 and Hastelloy C-276, and discuss their similarities and differences in chemical composition, mechanical properties, corrosion resistance, and applicable fields. By comparing the properties of these two alloys, I believe you will be able to better understand how to choose between these two alloys and how to take full advantage of their characteristics to ensure the reliability and performance of your equipment.

Basic Information

Name

Hastelloy C-22

UNS N06022

W.Nr. 2.4602

Brand

 HASTELLOY®

Matrix

Nickel

Chromium

Molybdenum

Type

Solid Solution
Strengthened Alloy

Density

8.69 g/cm³

Use Temperature

High Temperature

Name

Hastelloy C-276

UNS N10276

W.Nr. 2.4819

Brand

 HASTELLOY®

Matrix

Nickel

Chromium

Molybdenum

Type

Solid Solution
Strengthened Alloy

Density

8.89 g/cm³

Use Temperature

High Temperature

Introduction

Hastelloy C-22

HASTELLOY® C-22® alloy (UNS N06022) is one of the well-known and well-proven nickel-chromium-molybdenum materials, the chief attributes of which are resistance to both oxidizing and non-oxidizing chemicals, and protection from pitting, crevice attack, and stress corrosion cracking.

Hastelloy C-276

HASTELLOY® C-276 alloy (UNS N10276) was the first wrought, nickel-chromium-molybdenum material to alleviate concerns over welding (by virtue of extremely low carbon and silicon contents). As such, it was widely accepted in the chemical process and associated industries, and now has a 50-year-old track record of proven performance in a vast number of corrosive chemicals.

Chemical Composition

C-22

C-276

C-22

C-276

C-22

C-276

C-22

C-276

C-22

C-276

C-22

C-276

C-22

C-276

C-22

C-276

C-22

C-276

C-22

C-276

C-22

C-276

C-22

C-276

Purity

Hastelloy C-22

WIN

Hastelloy C-276

lose

C-22

C-276

C-22

C-276

C-22

C-276

Overall, Hastelloy C-22 has better purity than Hastelloy C-276. Hastelloy C-22 has stricter controls on harmful elements such as sulfur, manganese, and phosphorus than Hastelloy C-276.

The higher purity allows Hastelloy C-22 to obtain higher high-temperature corrosion resistance, high-temperature mechanical properties, transient performance and durable performance than Hastelloy C-276.

Corrosion Resistance

Hastelloy C-22

Oxidation Resistance

Hastelloy C-276

Reduction Resistance

C-22

C-276

C-22

C-276

The biggest difference between Hastelloy C-22 and Hastelloy C-276 is the corrosion resistance. Although they are both nickel-chromium-molybdenum alloys, their elemental ratios are not the same. Compared to Hastelloy C-276, Hastelloy C-22 has a higher chromium content and a lower molybdenum content. Therefore, relatively speaking, Hastelloy C-22 has better antioxidant properties, while Hastelloy C-276 has better anti-reduction properties.

In addition, because Hastelloy C-22 has better control of trace elements, it has better resistance to crevice corrosion at high temperatures than Hastelloy C-276.

Mechanical Behavior

Hastelloy C-22

Tie

Hastelloy C-276

Tie

C-22

C-276

C-22

C-276

Both Hastelloy C-22 and Hastelloy C-276 are solid solution alloys. Moreover, their mechanical properties are very balanced. Both alloys achieve decent strength through solid solution strengthening with molybdenum and tungsten.

However, strictly speaking, the mechanical properties of Hastelloy C-22 are slightly better than Hastelloy C-276. This is still due to its stricter control of harmful elements. This purity advantage is particularly evident in the yield strength. Hastelloy C-22 also has better plasticity than Hastelloy C-276.

Physical Properties

Physical properties of alloy C-22 and alloy C-276 Hastelloy C-22 Hastelloy C-276 Density, g/cm³ 8.69 8.89 Density, lb/in.³ 0.314 0.321 Melting Range, °F 2475-2550 2415-2500 Melting Range, °C 1357-1399 1323-1371

Application

Hastelloy C-22 Hastelloy C-276 has a very similar range of applications. In practical applications, we should consider more details, such as the specific working environment of the material. We need to select corresponding materials according to different corrosive substances.

Supported Products

Main Standards

Hastelloy C-22

Seamless Pipe and Tube: ASTM B622

Welded Pipe: ASTM B619

Welded Tube: ASTM B626

Fittings: ASTM B366, ASTM B462

Billet, Rod and Bar: ASTM B574

Forgings: ASTM B564, ASTM B462

Plate, Sheet, and Strip: ASTM B575

Hastelloy C-276

Seamless Pipe and Tube: ASTM B622, ASTM B983

Welded Pipe: ASTM B619

Welded Tube: ASTM B626

Fittings: ASTM B366, ASTM B462

Billet, Rod and Bar: ASTM B574

Forgings: ASTM B564, ASTM B462

Plate, Sheet, and Strip: ASTM B575

Price

Hastelloy C-22

high

Hastelloy C-276

LOW

Compared to Hastelloy C-276, the price of Hastelloy C-22 will be higher.

On the one hand, Hastelloy C-22 has higher requirements for the control of trace elements, which forces it to use higher purity metal raw materials during smelting. This in itself adds significant cost.

On the other hand, Hastelloy C-276 is used in larger quantities, and the larger quantity creates a scale advantage. The Hastelloy C-22 is relatively rare, and the cost of customization is relatively higher.

Therefore, even though Hastelloy C-276 has more high-priced elements (molybdenum and tungsten), it still costs less than Hastelloy C-22.

Conclusion

Hastelloy C-22 and Hastelloy C-276 are both nickel-chromium-molybdenum alloys. The biggest difference between them is the content of chromium and molybdenum. For this reason, Hastelloy C-22 is more suitable for working in oxidative corrosive environments, while Hastelloy C-276 is more suitable for reducing environments. But in general, they all have excellent overall corrosion resistance. In addition, Hastelloy C-22 has tighter controls on harmful elements. This gives it better overall performance at high temperatures. Hastelloy C-276 is relatively cheaper and therefore more commonly used than Hastelloy C-22.

We manufacture various products of Hastelloy C-22 and Hastelloy C-276 in strict compliance with standards. If you have corresponding purchasing needs, please contact us by email.

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