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Nickel-Based Alloys: Properties, Classifications, and Applications
Introduction:
Nickel-based alloys, as the name suggests, are primarily composed of nickel (typically with a nickel content exceeding 50%), along with other alloying elements such as iron, chromium, cobalt, molybdenum, and copper. These alloys are renowned for their exceptional high-temperature strength and outstanding corrosion resistance.
Characterized by high melting points, nickel-based alloys maintain stable performance in environments exceeding 700°C, with some grades capable of withstanding temperatures up to 1000°C or more. Their excellent oxidation resistance makes them particularly suitable for applications involving prolonged exposure to extreme thermal conditions, such as gas turbine blades, rocket engine nozzles, and other critical high-temperature components.
In turbine engines, blades must withstand both extreme temperatures and significant mechanical stresses. Materials with inadequate high-temperature strength and toughness would experience rapid degradation and shortened service life. Premium nickel-based alloys provide the necessary combination of high-temperature strength and oxidation resistance that enables these advanced systems to operate reliably under extreme conditions.
Furthermore, nickel-based alloys exhibit remarkable microstructural stability. Even after extended exposure to high temperatures and pressures, their microstructure remains virtually unchanged. This exceptional stability positions them as essential materials for critical applications in the aerospace and power generation industries.
Classification Standards in China:
China established and promulgated its first trial standard for nickel-based corrosion-resistant alloys, YB-687-75, in 1975. This initial standard included eight corrosion-resistant alloy grades. With advancements in metallurgical technology and equipment, nickel-based alloy varieties have developed rapidly.
The common designation method in China uses element symbols and content numbers to represent alloy grades. A prefix of "0" indicates carbon content ≤ 0.08%, while "00" indicates carbon content ≤ 0.03%. For example, 00Cr16Ni65Mo16 represents an alloy with C ≤ 0.03%, Cr approximately 16%, Ni approximately 65%, and Mo approximately 16%. Due to lagging domestic standards, this designation method has not been fully adopted in practice.
Fig 2. Nickel Alloy Round Bar and Heat Resistance Wires
Three Major Internationally Renowned Nickel-Based Alloy Trademarks:
1. Inconel® Alloys
Inconel is a registered trademark of Special Metals Corporation (USA) and has become synonymous with a class of high-performance nickel-chromium-based high-temperature and corrosion-resistant alloys.
Performance Characteristics
- Excellent High-Temperature Strength: Through solid solution strengthening and/or precipitation strengthening, these alloys maintain exceptional mechanical properties at high temperatures (up to 1000°C and above).
- Superior Oxidation and Hot Corrosion Resistance: High chromium content forms a stable Cr₂O₃ protective film.
- Good Corrosion Resistance: Particularly suitable for oxidizing media and high-temperature environments.
Fig 3. Application of Nickel Alloys in Aerospace and Seawater
Common Grades and Characteristics:
Grade | Characteristics |
Inconel 600 | Early classic grade, solid solution strengthened, resistant to high-temperature oxidation, alkali corrosion resistant |
Inconel 625 | Universal corrosion-resistant alloy, strengthened by molybdenum and niobium, excellent pitting and crevice corrosion resistance, good fatigue strength, weldable |
Inconel 718 | Most widely used precipitation-strengthened alloy, strengthened by γ" phase, extremely high strength at intermediate and high temperatures, relatively good workability |
Inconel X-750 | Precipitation-strengthened, high-temperature spring alloy, good strength and oxidation resistance below 980°C |
Inconel 738 | Cast alloy, high aluminum and titanium content, γ" phase strengthened, excellent hot corrosion resistance |
Table 1. List of common grades and their characteristics
2. Monel® Alloys
Monel is a registered trademark of Special Metals Corporation (same parent company as Inconel). These alloys are primarily nickel-copper based corrosion-resistant alloys, characterized by exceptional resistance to seawater, salt spray, and reducing media corrosion. Typically, nickel content ranges from 60-70%, copper from 20-30%, with small additions of iron, manganese, and other elements. Monel represents one of the earliest high-performance alloys developed and applied by humanity.
Performance Characteristics
- Excellent Seawater Corrosion Resistance: This is its most renowned property. It resists erosion corrosion from high-velocity flowing seawater, cavitation corrosion, and exhibits excellent resistance to chloride-induced stress corrosion cracking. It is considered one of the premier materials for marine engineering.
- Resistance to Reducing Media: Performs better than ordinary stainless steels and nickel-chromium alloys in non-oxidizing acids and salt solutions (such as hydrofluoric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and their salts).
- Good Mechanical Properties: Maintains high strength and toughness over a wide temperature range, and is non-magnetic.
- Work Hardening Tendency: Machining and cold working present certain challenges.
Fig 4. Monel Alloy application in Offshore Oil & Gas field.
Common Grades and Applications:
Grade | Characteristics |
Monel 400 | Most versatile grade Composition: Ni ~67%, Cu ~30%, Fe ~1.5%. Solid solution strengthened single-phase alloy, non-heat treatable, comprehensive corrosion resistance |
Monel K-500 | Based on 400 with addition of ~3% Al and 0.5% Ti, age-hardenable through precipitation of Ni₃(Al,Ti) strengthening phase, significantly improved strength (approximately 2-3 times that of Monel 400), while maintaining similar corrosion resistance |
Table 2. Monel 400 common grades and their applications.
Application Areas
- Marine and Shipbuilding: Propellers, shafting, pumps and valves, seawater heat exchangers, seawater piping systems
- Petrochemical Industry: Offshore platform equipment, refinery components, containers for handling halogens and acid solutions
- Specialty Chemical Industry: Hydrofluoric acid and alkali production and storage equipment, power plant feedwater heaters
3. Hastelloy® Alloys
Hastelloy alloys are primarily nickel-molybdenum-chromium or nickel-molybdenum alloys. Through high contents of molybdenum and chromium, they achieve superior resistance to general corrosion, pitting, and crevice corrosion.
Hastelloy is a registered trademark of Haynes International (USA). The core concept is design for the most demanding industrial corrosive environments, serving as the "last line of defense" material in chemical, petroleum, and environmental protection industries. While Inconel alloys excel in "heat resistance + corrosion resistance," Hastelloy alloys reign as "specialists in extreme corrosion resistance," particularly advantageous in non-oxidizing or alternating oxidizing-reducing complex media.
Performance Characteristics
- General Corrosion Resistance: In non-oxidizing acids such as hydrochloric acid, sulfuric acid, and phosphoric acid across wide concentration and temperature ranges, performance far exceeds stainless steels and other nickel-based alloys.
- Excellent Localized Corrosion Resistance: High molybdenum and chromium contents provide outstanding resistance to pitting and crevice corrosion, making them ideal for media containing chloride ions.
- Superior Resistance to Stress Corrosion Cracking: Good thermal stability and intermediate-temperature strength.
- Fabrication and Weldability: Certain grades (such as C-276) exhibit good weldability, though overall work hardening tendency is relatively strong.
Grade | Characteristics |
Hastelloy B-2 | Ni-Mo alloy, Mo ~28%, chromium-free, designed specifically for reducing media, champion in hydrochloric acid resistance. Optimal performance in reducing acids (hydrochloric acid, sulfuric acid). Sensitive to oxidizing media |
Hastelloy C-276 | Ni-Mo-Cr alloy (16% Mo, 16% Cr). Most famous and widely used "universal" corrosion-resistant alloy. Optimal balance: excellent reducing media resistance and adequate oxidizing media resistance, weldable without post-weld heat treatment, excellent processability |
Hastelloy C-22 | Advanced version of C-276 (13% Mo, 22% Cr, 3% W). Higher chromium content, slightly reduced molybdenum. Superior oxidizing media and localized corrosion resistance, overall corrosion resistance considered better than C-276. Better weld zone corrosion resistance |
Hastelloy C-2000 | Next-generation product (16% Mo, 23% Cr, 1.6% Cu). Copper addition provides more comprehensive performance, top-level corrosion resistance in both oxidizing and reducing media, truly universal alloy |
Hastelloy X | Ni-Cr-Fe-Mo alloy. High chromium, moderate molybdenum, iron addition. Excellent high-temperature strength and oxidation resistance, bridging corrosion-resistant and high-temperature alloys within the Hastelloy family |
Hastelloy G-30 | High chromium, copper-containing alloy (30% Cr, 5% Mo, 2% Cu). Particularly resistant to phosphoric acid and complex acids, good hot corrosion resistance |
Table 3. Performance characteristics of different hastelloy grades.
Application Areas
- Chemical Processing Industry: Reactors, heat exchangers, piping, valves, pumps for acid production, pesticides, pharmaceutical intermediates
- Flue Gas Desulfurization Systems: Absorption towers, flues, baffles, resisting wet flue gas corrosion containing chlorides and sulfuric acid
- Oil and Gas Industry: Highly corrosive oil and gas wells, subsea pipelines, sour gas processing equipment
- Waste Incineration and Treatment: High-temperature chlorine-containing waste gas heat exchangers
- Additional applications in nuclear waste treatment facilities and aerospace (Hastelloy X for high-temperature engine components)
Fig. 5 Hastelloy Alloys Application in H2SO4, HCL Acidic & Corrosive environment.
Comparative Summary of the Three Alloy Types:
Characteristic | Hastelloy | Inconel | Monel |
Core | Ni-Mo-Cr | Ni-Cr | Ni-Cu |
Primary | Extreme, comprehensive chemical corrosion resistance, especially pitting/crevice corrosion | High-temperature strength and oxidation resistance, comprehensive performance | Seawater and reducing media resistance |
Typical | Mixed acids, chloride-containing solutions, strongly reducing media | High-temperature oxidizing environments, hot corrosion, oxidizing acids | Seawater, hydrofluoric acid, alkali solutions |
Representative Grades | C-276, C-22, B-2 | 718, 625, 600 | 400, K-500 |
Relative | Typically highest (high content of precious elements Mo, Cr) | Very high | High |
Table 4. Comparative summary of three alloy types (Hastelloy, Inconel and Monel)
Roles of Alloying Elements:
Molybdenum | Chromium | Boron, Silicon | Copper |
Large atomic radius, causes significant lattice distortion upon solid solution, markedly strengthens alloy matrix, improves high-temperature strength and red hardness; can interrupt/reduce network structures in coatings; enhances resistance to cavitation and erosion | Solid solution strengthening; passivation effect; improves corrosion resistance and high-temperature oxidation resistance; excess chromium readily forms chromium carbides/borides, increasing alloy hardness and wear resistance | Significantly lowers alloy melting point, expands solid-liquid phase temperature range, forms low-melting eutectics; deoxidation and slag-forming functions; hardening/strengthening effects on coatings; improves processing characteristics | Improves corrosion resistance in non-oxidizing acids |
Table 5. The roles of alloying elements in a metal.
Nickel-Based Alloy Composition/Properties Table:
Common | UNS No. | DIN/ EN | Typical Composition (wt%) | Characteristics |
Nickel 200 | N02200 | 2.4066 | 99Ni*-0.15Fe-0.2Mn-0.1Si-0.1Cu-0.10C | Commercially pure nickel, good corrosion resistance in alkaline environments |
Nickel 201 | N02201 | 2.4068 | 99Ni*-0.15Fe-0.2Mn-0.1Si-0.1Cu-0.01C | Low-carbon version of Nickel 200, better corrosion resistance at high temperatures |
Nickel 270 | N02270 | 2.405 | 99.9Ni*-0.02Fe-0.001Mn-0.002Si-0.005Cu-0.01C | High-purity nickel, low hardness, high ductility |
A-286 | S66286 | 1.498 | 25Ni-15Cr-1.5Mo-2Ti-1Mg-0.03C | Fe-Ni-Cr alloy with Mo and Ti, good mechanical properties below 700°C |
25-6Mo | N08926 | 1.4529 | 25Ni-20Cr-6.5Mo-1Cu-0.2N-1.0Mg-0.01P-0.005S-0.01C | Used in wet FGD systems, effective chloride stress corrosion cracking resistance |
25-6HN (AL-6XN) | N08367 | — | 25Ni-20Cr-6.3Mo-0.25Cu-0.2N-0.01P-0.005S-0.01C | Used in wet FGD systems, equivalent to AL-6XN |
27-7Mo | S31277 | — | 27Ni-22Cr-7.0Mo-1Cu-0.3N-0.01P-0.005S-0.01C | 7% Mo super stainless steel, excellent performance in both oxidizing and reducing media |
Alloy 020 | N08020 | 2.466 | 36Ni-21Cr-3.5Cu-2.5Mo-1Mn-0.01C | Excellent sulfuric and phosphoric acid corrosion resistance, good mechanical properties below 500°C |
Alloy 028 | N08028 | 1.4563 | 32Ni-27Cr-3.5Mo-1Cu-0.01C | Primarily for petrochemical industry, excellent performance in oxidizing and reducing media |
Alloy 330 | N08330 | 1.4886 | 35Ni-18Cr-2Mg-1Si-0.03C | Si addition improves oxidation resistance, widely used in industrial furnaces |
Alloy 800 | N08800 | 1.4876 | 32Ni-21Cr-0.30-1.20(Al+Ti)-0.02C | Good corrosion and high-temperature resistance, excellent mechanical properties from cryogenic to 600°C |
Alloy 800H | N08810 | 1.4876 | 32Ni-21Cr-0.30-1.20(Al+Ti)-0.08C | High-carbon version of Alloy 800, better creep properties |
Alloy 800HT | N08811 | 1.4876 | 32Ni-21Cr-0.85-1.20(Al+Ti)-0.08C | Increased Al and Ti content, higher allowable stress |
Alloy 825 | N08825 | 2.4858 | 42Ni-21Cr-3Mo-2Cu-0.8Ti-0.1Al-0.02C | Ti-stabilized Ni-Fe-Cr alloy, excellent stress corrosion cracking resistance |
Inconel | N06600 | 2.4816 | 72Ni*-15Cr-8Fe-0.2Cu-0.02C | Good resistance to reducing, oxidizing, and nitriding media corrosion |
Inconel | N06601 | 2.4851 | 60Ni-22Cr-1.2Al-0.5Cu-0.02C | Al and Ti addition, excellent high-temperature oxidation resistance |
Inconel | N06625 | 2.4856 | 58Ni*-21Cr-9Mo-3.5Nb-1Co-0.02C | Low-carbon Ni-Cr-Mo-Nb alloy, excellent corrosion resistance in various media |
Inconel 625LCF | N06626 | 2.4856 | 58Ni*-21Cr-9Mo-3.5Nb-1Co-0.02C | Enhanced low-cycle fatigue resistance, primarily for bellows manufacturing |
Inconel | N06686 | 2.4606 | 57Ni*-21Cr-16Mo-4W-0.01C | Excellent corrosion resistance, universal weld filler metal |
Inconel | N06690 | 2.4642 | 58Ni*-30Cr-9Fe-0.2Cu-0.02C | High-chromium Ni-Fe-Cr alloy, excellent high-temperature oxidation resistance |
Inconel | N07718 | 2.4668 | 52Ni-19Cr-5Nb-3Mo-1Ti-0.6Al-0.02C | Precipitation-hardened Ni-Fe-Cr alloy, high-temperature strength, excellent creep properties |
Inconel | N07750 | 2.4669 | 70Ni*-15Cr-6Fe-2.5Ti-0.6Al-1Nb-0.02C | Precipitation-hardened Ni-Fe-Cr alloy with Ti, Nb, Al, good performance below 600°C |
Monel | N04400 | 2.436 | 63Ni*-32Cu-1Fe-0.1C | Solid solution strengthened Ni-Cu alloy, good corrosion resistance in seawater environments |
Monel | N05500 | 2.4375 | 63Ni*-30Cu-1Fe-3Al-0.6Ti-0.1C | Age-hardenable Ni-Cu alloy with Al and Ti, excellent chloride stress corrosion cracking resistance |
Hastelloy C-276 | N10276 | 2.4819 | 57Ni-16Mo-16Cr-5Fe-4W-2.5Co-1Mn-0.35V-0.08Si-0.01C | Excellent resistance to oxidizing and moderate reducing corrosion, outstanding resistance to localized corrosion |
Hastelloy C-4 | N06455 | 2.461 | 65Ni-16Cr-16Mo-0.7Ti-3Fe-2Co-1Mn-0.08Si-0.01C | Good thermal stability, excellent toughness and corrosion resistance at 650-1040°C |
Hastelloy C-22 | N06022 | 2.4602 | 56Ni-22Cr-13Mo-3Fe-3W-2.5Co-0.5Mn-0.35V-0.08Si-0.01C | Better uniform corrosion resistance in oxidizing media compared to C-4 and C-276 |
Hastelloy C-2000 | N06200 | 2.4675 | 59Ni-23Cr-16Mo-1.6Cu-0.08Si-0.01C | Most comprehensive corrosion-resistant alloy, excellent performance in both oxidizing and reducing environments |
Hastelloy X | N06002 | 2.4665 | 47Ni-22Cr-18Fe-9Mo-1.5Co-0.6W-0.10C-1Mn-1Si-0.008B | Combines high strength, oxidation resistance, and good fabricability, widely used in aerospace industry |
Hastelloy B-2 | N10665 | 2.4617 | 69Ni-28Mo-0.5Cr-1.8Fe-3W-1.0Co-1.0Mn-0.01C | Ni-Mo alloy, excellent corrosion resistance in reducing environments |
Hastelloy B-3 | N10675 | 2.46 | 65Ni*-28.5Mo-1.5Cr-1.5Fe-3W-3Co-3Mn-0.01C | Enhanced version of B-2, excellent resistance to hydrochloric acid at any temperature and concentration |
Hastelloy G-30 | N06030 | — | 43Ni-30Cr-15Fe-5.5Mo-2.5W-5Co-2Cu-1.5Mn-0.03C | High-chromium nickel-based alloy, excellent corrosion resistance in phosphoric acid and other strongly oxidizing mixed acid media |
Table 6. Nickel-based alloy compositions (inconel, monel, hastelloy, pure nickel etc). Note: ® indicates registered trademarks. Inconel, Monel, and Hastelloy are registered trademarks of their respective owners. | ||||