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Overview of Nickel Alloy
2024-07-22
Nickel alloys generally consist of nickel, chromium, molybdenum, aluminum, iron, and some other elements in small quantities.
Nickel-based Superalloys: Alloying
Nickel and Nickel Alloys: An Overview; Nickel: Alloying; Nickel Alloys: Nomenclature; Nickel Alloys: Thermal Treatment and Thermomechanical Processing; Nickel-based Superalloys: An Overview; Nickel-based Superalloys: Alloying Methods and Thermomechanical Processing; Nickel Alloys: Corrosion.
SELECTION OF MATERIALS FOR CORROSIVE ENVIRONMENT
CLASSIFICATION OF NICKEL ALLOYS
The nickel alloys can be classified in the following groups on the basis of their chemical compositions:
(1)Nickel Pure nickel (99.56%)
▪ Commercially pure nickel (wrought) 99.6–99.7%.
(2)Nickel and copper
▪ Low nickel alloys (2–13% Ni)
▪ Cupronickel (10–30% Ni)
▪ Non-magnetic alloys (~60% Ni)
▪ High nickel alloys (over 50% Ni)
(3)Nickel and iron
▪ Wrought alloys steels (0.5–9% Ni)
▪ Cast alloy steels (0.5–0.9% Ni)
▪ Alloy cast iron (1–6, 14–36% Ni)
(4)Iron-nickel and chromium alloys
▪ Stainless steels (2–25% Ni)
▪ Maraging steels (18% Ni)
(5)Nickel-chromium-molybdenum and iron-nickel base precipitation hardened alloys.
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Electrochemistry of elements | NickelNickel alloysNickel is the main component of many well-known alloys, for example, corrosion-resistant alloys such as Monel (Ni, Cu), Inconel 600 (Ni, Cr, Fe), Hastelloy (Ni, Mo, Fe), and the already-mentioned stainless steels. Nickel is also present in strong magnetic alloys such as Alnico (Al, Ni, Co), Permalloy (Ni, Fe), and mu-metal (Ni, Fe, Cu, Mo). A very well-known nickel alloy is constantan (Cu 60%, Ni 40%) characterized by a constant resistance over a wide temperature range.
The annual nickel price increase in 2021 was attributed to the expected stronger use of nickel for EV batteries and the high demand for stainless steel. To be noted, the nickel production growth of the last years has been driven by expansion of capacity for nickel pig iron, i.e., the class 2 product that is unsuitable for EV batteries. The high-grade class 1 nickel required for batteries requires more intense processing.
SELECTION OF MATERIALS FOR CORROSIVE ENVIRONMENT
NICKEL AND ITS ALLOYS
Nickel is well-known as an essential alloying element in stainless steels, Ni-Cu alloys, Ni-Fe alloys, Ni-Cr-Fe alloys, super alloys, as nickel-chromium alloys and special corrosion-resistant and high temperature alloys. Nickel ferromagnetic with a density of 8.9 g/cm3. It is ductile and malleable like steel. Nickel alloys are well-known for their high temperature strength and good resistance to corrosion.
Nominal chemical composition (wt%)
Material |
Ni |
Cu |
Fe |
Cr |
Mo |
Al |
Ti |
Nb |
Mn |
Si |
C |
Nickel |
|
|
|
|
|
|
|
|
|
|
|
Nickel 200 |
99.6 |
- |
- |
- |
- |
- |
- |
- |
0.23 |
0.03 |
0.07 |
Nickel 201 |
99.7 |
- |
- |
- |
- |
- |
- |
- |
0.23 |
0.03 |
0.01 |
Nickel-Copper |
|
|
|
|
|
|
|
|
|
|
|
Monel alloy 400 |
65.4 |
32 |
1.00 |
- |
- |
- |
- |
- |
1.0 |
0.10 |
0.12 |
Monel alloy 404 |
54.6 |
45.3 |
0.03 |
- |
- |
- |
- |
- |
0.01 |
0.04 |
0.07 |
Monel alloy R-405 |
65.3 |
31.6 |
1.25 |
- |
- |
0.1 |
- |
- |
1.0 |
0.17 |
0.15 |
Monel alloy K-500 |
65.0 |
30 |
0.64 |
- |
- |
2.94 |
0.48 |
- |
0.70 |
0.12 |
0.17 |
Nickel-Chromium-Iron |
|
|
|
|
|
|
|
|
|
|
|
Inconel alloy 600 |
76 |
0.25 |
8.0 |
15.5 |
- |
- |
- |
- |
0.5 |
0.25 |
0.08 |
Inconel alloy 601 |
60.5 |
0.50 |
14.1 |
23.0 |
- |
1.35 |
- |
- |
0.5 |
0.25 |
0.05 |
Inconel alloy 690 |
60 |
- |
9.0 |
30 |
- |
- |
- |
- |
- |
- |
0.01 |
Nickel-Iron-Chromium |
|
|
|
|
|
|
|
|
|
|
|
Incoloy alloy 800 |
31 |
0.38 |
46 |
20 |
- |
0.38 |
0.38 |
- |
0.75 |
0.50 |
0.05 |
Incoloy alloy 800H |
31 |
0.38 |
46 |
20 |
- |
0.38 |
0.38 |
- |
0.75 |
0.50 |
0.07 |
Incoloy alloy 825 |
42 |
1.75 |
30 |
22.5 |
3 |
0.10 |
0.90 |
- |
0.50 |
0.25 |
0.01 |
Incoloy alloy 925 |
43.2 |
1.8 |
28 |
21 |
3 |
0.35 |
2.10 |
- |
0.60 |
0.22 |
0.03 |
Pyromet 860 |
44 |
- |
Bal |
13 |
6 |
1.0 |
3.0 |
- |
0.25 |
0.10 |
0.05 |
Nickel-Chromium-Molybdenum |
|
|
|
|
|
|
|
|
|
|
|
Hastelloy alloy X |
Bal |
- |
19 |
22 |
9 |
- |
- |
- |
- |
- |
0.10 |
Hastelloy alloy G |
Bal |
2 |
19.5 |
22 |
6.5 |
- |
- |
2.1 |
<1 |
1.5 |
<0.05 |
Hastelloy alloy C-276 |
Bal |
- |
5.5 |
15.5 |
16 |
- |
- |
- |
<0.08 |
<1 |
<0.01 |
Hastelloy alloy C |
Bal |
- |
<3 |
16 |
15.5 |
- |
< 0.7 |
- |
<0.08 |
<1 |
<0.01 |
Inconel alloy 617 |
54 |
- |
- |
22 |
9 |
1 |
- |
- |
- |
- |
0.07 |
Udimet 600 |
Bal |
- |
<4 |
17 |
4 |
4.2 |
2.9 |
- |
- |
- |
0.04 |
(1) Nickel-Copper Alloys
These alloys are well-known for their excellent corrosion resistance to seawater. They have been used as propellers, pump shafts, impellers and condenser tube materials. The best known is Monel (Alloy 400). It is resistant to brine and immune to stress corrosion cracking and pitting in chloride and caustic alkaline solutions. It is also resistant to HF and fluorine containing media.
Monel alloy R-405 has specified amounts of sulfur for improved machining characteristics. Monel K 500 has the dual advantage of improved mechanical strength and excellent corrosion resistance. It can retain strength up to 650°C and ductility up to 134°C.
(2) Nickel-Chrome-Iron Alloys
These alloys contain a high percentage of nickel and excellent capability to withstand high temperature oxidizing environment. Alloys, such as Inconel 600, 690, 718 and X750, belong to this category. Alloy Inconel 600 (Ni 76, Cr 15.5, Fe 8) is the basic alloy in this class with excellent corrosion resistance at elevated temperatures (~1092°C). It can, however, be subjected to pitting or crevice corrosion. Other alloys in this family include alloy 690 (29% Cr) which shows excellent resistance to SCC in chloride media and low corrosion rates at high temperatures. It is used in furnaces for petrochemical processing and in coal gasification units.
Alloy Inconel X750 contains additions of aluminum, niobium and titanium which form an intermetallic compound, Ni3(Al, Ti) to make it age hardenable and provide high strength. It is extremely resistant to SCC in chloride environment. It is used in gas turbines, vacuum envelopes, extrusion dies and springs.
(3) Nickel-Iron-Chromium Alloys
These alloys represent another version of Ni-Cr-Fe alloys and contain 30–44 % of nickel. Alloy 800 of this series has been extensively used in heat exchangers in the petrochemical industry, because of its excellent resistance to stress corrosion cracking in chloride environments and cracking in polythionic acid. It offers an excellent resistance to creep and rupture. They are used for high environments where resistance to oxidation and corrosion is required. Incoloy 825 has proved highly successful in applications in H2SO4, HCl, phosphoric acid and clean and polluted seawater.
(4) Nickel-Chromium-Molybdenum Alloys
This family of alloys are mainly used in the chemical processing industry and contain 45–60% Ni. Hastelloy has been successfully used in high temperature applications (up to 1204°C). The Hastelloy C series have served the chemical industry for a long time. The modified version of Hastelloy C is Hastelloy C-276 in which silicon and C content are substantially reduced (0.005% C, 0.04% Si). It is used successfully in the petrochemical industry. Alloys 625 and 617are high temperature strength alloys and exhibit a high resistance to corrosion. Alloy 625 is used extensively in seawater applications. It is highly resistant to pitting and stress corrosion cracking. Other alloys, like Udimet 500, 520, 600 and 700 retain high temperature strength up to 982°C.
Effect of alloying elements on the corrosion resistance of nickel
Alloy element |
Contribution to corrosion resistance |
Copper |
Improves resistance to non-oxidizing acids, sulfuric acid (non aerated) and HF. Addition of 2–3% Ni offers improved resistance to HCl, H2SO4, and H3PO4. |
Chromium |
Improves resistance to oxidizing acids (HCl, H2SO4 and H3PO4) and high temperature oxidation. |
Mo |
Improves resistance to pitting and crevice corrosion. High Mo content (28%) show improved resistance to HCl, H3PO4, H2SO4 and HF. |
Iron |
Improves resistance to de-carburization. It has no role in the improvement of corrosion resistance. |
Tungsten |
Alloys with 3–4% W in combination with 13–16% Mo, offer excellent resistance to corrosion. Tungsten provides a high resistance to non-oxidizing acids. |
Silicon |
Improves resistance to hot concentration H2SO4 when added in larger amounts (9–11%). It is generally added in smaller quantities. |
Cobalt |
Increases the resistance to carburization, like iron. |
Niobium and tantalum |
Reduce hot cracking during welding. |
Aluminum and titanium |
The combination produces aluminum scale which resists oxidation and carburization. |
Carbon and carbides |
The formation of carbides weakens resistance to corrosion. Ni3C may decompose to graphite and thus weaken the grain boundaries. |
LOCALIZED CORROSION SUSCEPTIBILITY OF NICKEL ALLOYS
1) Stress Corrosion Cracking
Although nickel alloys on the whole offer a better resistance to stress corrosion cracking over the steels, their application in high temperature chloride or alkaline environment and hydrogen sulfide environment may put them to the risk of stress corrosion cracking. Cases of SCC have been observed in high temperature pressurized water in steam generating turbines. Incoloy 800 is a good choice to be used in such environments. A major class of nickel-base alloys are susceptible to SCC in alkaline environment (for example, NaOH at 350°C). Alloys 400, 600 and 800 may be subject to SCC in an alkaline environment. Alloys 800, 718 and 600 have shown failures in pressurized water reactors. Increasing chromium concentration to 30% (for example alloy 690) increases the resistance to SCC. The following factors promote SCC:
(a)Temperatures above 205°C.
(b)Low pH < 4.
(c)Presence of H2S and high level of stress. Despite the risk, nickel alloys offer minimum risks against SCC.
2) Intergranular Corrosion
Nickel-iron-chromium (for example, alloy 800) and nickel-chromium-iron (alloy 600) may become sensitized by precipitation of chromium carbides and subject to intergranular corrosion in a highly oxidizing environment. The carbide range in chemistry is from Cr23C6 in simple nickel alloys to Cr21(Mo, N)C2C6 in alloys containing Mo and W. Alloys 600 and 800 may become susceptible to intergranular attack. Control of elements, such as phosphorus, carbon, nitrogen and niobium, and minimizing their segregation, reduces susceptibility to intergranular attack and minimizes the risk of SCC.
3) Hydrogen Embrittlement
Like stainless steels, some nickel alloys may fail by hydrogen embrittlement. Inconel alloy X750 is reported to be susceptible to hydrogen embrittlement.
RESISTANCE TO AQUEOUS ENVIRONMENT
Nickel and its alloys are known to offer an outstanding resistance to corrosion in distilled water, fresh water, high purity water and in steam hot water systems. For example, Monel alloy 400 is extensively used in valves, pumps, propeller shafts, boiler feed water heaters and heat exchangers. Alloys 600 and 690 are used in nuclear steam generators to prevent SCC. Pitting of nickel-copper alloys may be caused by soft water.
The corrosion resistance of nickel alloys has been extensively explored in seawater and saltwater (brackish water). Although stainless steel 316 is known to resist pitting in seawater, stainless steels are, in general, susceptible to pitting in the tidal zones of seawater. The nickel alloys, more expensive than steels, have been extensively used in seawater service. Inconel alloy 625 offers an excellent resistance to corrosion in seawater. It also offers an excellent resistance to SCC. Nickel alloys are best used for pump shafts, bodies and impellers while other materials, like 90–10 Cu-Ni and austenitic steels are used for other parts, such as heat exchangers and valves. Table 9.47 shows the classification of selected nickel alloys in seawater service.
Heat treatment
Solid-solution nickel-based alloys are generally used in the annealed or annealed and cold-worked condition. These alloys are not designed for strengthening by heat treatment.
Mechanical properties
The maximum yield strength is governed by alloy composition, the cold-working characteristics of the alloy, the maximum yield strength permitted by the application, and the ductility specified. Room-temperature yield strengths can range from about 210 to 1380 MPa (30 to 200 ksi), depending on composition and the degree of cold-working. The minimum yield strength for tubing is generally in the range of 760–970 MPa (110–140 ksi). Casing and liners often have higher yield strength.
Fabrication
Annealed alloys can be welded using GTAW, SMAW, GMAW, SAW, and FCAW.
Cold-worked alloys are usually not welded because the mechanical strength of the weldments would be lower than that of the cold-worked region. The mechanical properties of cold-worked tubing, especially in thicker sections, can vary through the section.
The high-nickel alloys are more prone to casting defects such as hot tears, cracking, porosity, and gassing. These defects can appear at any stage of the manufacturing process such as shakeout, heat treating, machining, or final pressure testing. Although the wrought high-nickel alloys are routinely welded and some even hardfaced, welding the cast alloys is considerably more difficult. Stringent specifications developed in close cooperation with the foundry have typically been used to optimize weldability and casting integrity. For production of good quality casting, the foundry processes, raw material quality, filler material composition, weld repair procedures, and heat treatment are closely controlled and monitored.
Precipitation hardenable nickel-based alloys
Precipitation hardenable nickel chromium alloys often contain a fair amount of iron (Fe); these alloys are used for corrosion resistance, higher strength, and excellent weldability.
Heat treatment of PH nickel alloys
These alloys are usually used in solution-annealed, solution-annealed and aged, hot-worked and aged, or cold-worked and aged conditions.
In sour gas applications, the heat treatment of UNS N07718 is typically selected to give good toughness, yield strength, and corrosion resistance. A solution anneal followed by a single-step aging is often used. For sour gas applications, UNS N07716 and N07725 are solution-annealed and aged.