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Valve material and valve standards-(7)- Monel alloy

Monel alloy for corrosion resistant valve
1. Introduction/overview of Monel alloy:
Monel alloy, cast nickel alloy, Hastelloy alloy, etc. are all materials for making special purpose valves. Monel alloy is a Ni-Cu alloy in nickel-based corrosion-resistant alloys. It was first developed by the US Nickel Company. Its typical composition is 70% Ni and 30% Cu. It is the most widely used nickel-based corrosion-resistant alloy.

Monel alloy not only has high strength and toughness, but also has excellent resistance to corrosion by reducing acid and strong alkali media and sea water, so it is usually used to manufacture and transport hydrofluoric acid (HF), salt water, neutral media, and alkali salts. And reducing acid medium equipment. Monel alloy is also suitable for dry chlorine, hydrogen chloride, high temperature chlorine (425°C) and high temperature hydrogen chloride and other media, but it is not resistant to corrosion by sulfur-containing media and oxidizing media (such as nitric acid, media with high oxygen content), and it is nickel It reacts violently with sulfur and oxygen and easily forms Ni3S2 and NiO.

2. Performance of Monel alloy:
Monel alloy is a Ni-Cu solid solution, where Cu is used as a non-oxidizing resist added to Ni, which improves the corrosion resistance of nickel alloys and acts as a strengthening alloy. The addition of C can improve the casting performance of the alloy, but only 0.15% of C can be dissolved in the alloy at room temperature, and the excess C will be precipitated as a graphite phase. Adding 1.5%-3.5% Fe can also improve the casting performance of the alloy. Adding Mn and Si can improve the mechanical properties of the alloy, especially the content of Si has an important influence on the mechanical and physical properties of the Monel alloy.

3. Classification of Monel alloy:
Monel alloys are classified into casting alloys and deformed alloys.
3.1 Deformation alloy: There are more than 10 types of deformed Monel alloys in the United States, such as Monel400, MonelC, Monel403, Monel404, Monel R2405, Monel406, Monel411, MonelK500, MonelK501 and Monel502. Because Monel has its own representation methods in different American standard systems, SAE and ASTM jointly developed ASTM2SAE unified digital system (unified numbt system2 UNS) in order to facilitate the use and unified management of calculations. In the United States’ UNS, nickel alloys have 5 grades of deformed Monel alloys, including solid solution hardened No5500 (Monel400), No4404 (Monel404) and No4405 (MonelR2405), and precipitation hardened NO5500 (MonelK500) and NO5502 (Monel502). ) Etc. (refer to Table 1). Among them, the deformed Monel alloy commonly used in the manufacture of corrosion-resistant valves is Monel400 and MonelK500.
Table 1. Chemical composition of deformed Monel alloy in United States UNS

Grade name chemical composition/ %
C Si Mn S Ni Fe others
NO4400(Monel400) ≤0.3 ≤0.5 2 ≤0.024 63-70 ≤2.5 Cu base
No4404(Monel404) ≤0.15 ≤0.1 ≤0.1 ≤0.024 52-57 ≤0.5 Cu base, Al≤0.05
No4405(MonelR2405) ≤0.3 ≤0.5 ≤2.0 0.025-0.06 63-70 ≤2.5 Cu base
No5500(MonelK500) ≤0.25 ≤0.5 ≤1.5 ≤0.01 63-70 ≤2 Cu base, Al213-3115,Ti0135-0185
NO5502(Monel502) ≤0.10 ≤0.5 ≤1.5 ≤0.01 63-70 ≤2 Cu base, Al215-315

3.2 Casting alloy: The American cast Monel alloy has five grades of M35-1, M35-2, M-30H, M-25S and M-30C in ASTM A494 (Table 2), which is in the US Federal Standard QQ-N2-88 There are also 5 cast Monel alloys (Table 3).
Table 2. Cast Monel alloy in ASTM A494:

grade name chemical composition /% mechanical properties
C Mn Si P.S Cu Fe Ni Nb Compressive strength/Mpa Tensile strength/Mpa Elongation rate/% HB
M35-1(a) ≤0.35 ≤1.5 ≤1.25 ≤0.03 26-33 ≤3.5 Ba ≥450 ≥170 ≥25
M35-2 ≤0.35 ≤1.5 ≤2.00 ≤0.03 26-33 ≤3.5 Ba ≥450 ≥205 ≥25
M-30H ≤0.30 ≤1.5 2.7-3.7 ≤0.03 27-33 ≤3.5 Ba ≥690 ≥415 ≥10
M-25S ≤0.25 ≤1.5 3.5-4.5 ≤0.03 27-33 ≤3.5 Ba 243-294(b)
M-30C(a) ≤0.30 ≤1.5 1.0-2.0 ≤0.03 26-33 ≤3.5 Ba 1-3 ≥450 ≥225 ≥25 125-130(b)

1.Ba=balance, means the balance is all Ni content.
2. To remove the weldability, it should be M3521 or M230C
3. This table is a data parameter
4. HB minimum is 300
Table 3 QQ2N2288 cast Monel alloy:

QQ-N-288 chemical composition /% mechanical properties
C Si Mn Cu Fe Ni Nb Compressive strength/Mpa Tensile strength/Mpa Elongation rate/% HB
A ≤0.35 ≤2.0 ≤1.5 26-33 ≤2.5 62-68 ≥448 ≥224 ≥25 125-150
B ≤0.30 2.7-3.7 ≤1.5 27-33 ≤2.5 61-68 ≥689 ≥455 ≥10 240-290
C ≤0.20 3.3-4.5 ≤1.5 27-31 ≤2.5 ≥60 ≥825 ≥550 ≥10 250-300
D ≤0.25 3.5-4.5 ≤1.5 27-31 ≤2.5 ≥60 ≥300
E ≤0.30 1.0-2.0 ≤1.5 26-33 ≤2.5 ≥60 1-3 ≥448 ≥221 ≥25 125-150

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