Precision Alloy parts

Introduction to corrosion resistance of nickel and nickel alloys
(HY-industry technical centre)

1.The types and chemical composition ratios of the main nickel and nickel-based alloys are shown in the table below: (Weight%)

Number

Type

Alloy

UNS NO.

Ni

Cr

Mo

W

Fe

Cu

C

Else

1

pure
nickel

Nickel
200

N02200

≥99.0

≤0.15

2

Nickel
carbide

Nickel
201

N02201

≥99.0

≤0.02

3

Ni-Cu
Alloy

Monel
400

N04400

≥63.0

1

31.5

≤0.3

4

Monel

K500

N05500

≥63.0

1

30

≤0.25

Al:2.5,Ti:0.5

5

Ni-Cr-Fe
Alloy

Inconel 600

N06600

Rest

15

8

≤0.15

6

Ni-Mo
Alloy

Hastelloy  B

N10001

Rest

≤1

28

5

≤0.05

 

2. Development status of various nickel-based alloys and examples of their corrosion resistance

1)Ni

NC-Ni (medium carbon nickel-based alloy) has resistance to alkalis, halogen gases and reducing acids. However, the corrosion resistance is weak in acidic environments such as ammonium salt, ammonia, sulfide, and nitric acid, and pitting can also occur in neutral saline and under static conditions. In addition, after being left at high temperature for a long time, carbides will be precipitated at the grain boundaries. Therefore, LC-Ni (low-carbon nickel-based alloy) is used at s315nc level or higher.

2)Ni-Cu

Monel 400 is corrosion resistant to fluoric acid, fluoride, and flowing seawater. The addition of Cu makes the alloy more resistant to corrosion than pure Ni in a reducing environment and more resistant to corrosion than pure Cu in an acid environment.

Monel K500 is a precipitation hardened Ni alloy used in bolts or valve shafts.

3)Ni-Cr-Fe

Inconel 600 has low sensitivity to chloride stress corrosion, and has good processability and mechanical properties. It is widely used in atomic energy pipelines. It has a certain resistance to acidic and alkaline environments and has good heat resistance.

The Cr of Inconel alloy is solid-dissolved on the grain boundary. It has good performance and strong heat resistance in a strong acidification environment.

4)Ni-Mo

Hastelloy B-2 has the ability to resist hydrochloric acid corrosion at the full concentration and the full temperature range up to the boiling point, and is one of the most suitable materials in the reducing environment. However, since there is no resistance to oxidizing factors, it is necessary to pay attention to mixing in.

Hastelloy B-3 is an alloy developed based on HB-2 with improved thermal stability.

5)Ni-Cr-Mo

These alloys have corrosion resistance in both acidic and reducing environments, and have become the main force of Ni-based corrosion resistant alloys. The reasonable content of Cr and Mo in hastelloy C-2 is that it has good resistance to local corrosion and stress corrosion. MAT21 is the most resistant to local corrosion among Ni-Cr-Mo alloys.

6)Ni-Cr-Fe-Mo-Cu

The high content of Fe is added in order to reduce the cost, and the effect of increasing the corrosion resistance is added when Cu is added. hastelloy G-30 has good corrosion resistance to phosphoric acid and is used in industries related to fertilizer manufacturing. Incoloy 825 is an alloy at the junction of high-grade stainless steel and Ni-based corrosion-resistant alloys. It has better resistance to local corrosion and stress corrosion than stainless steel.

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