HY Incoloy 825 corrosion resistant alloy

(HY-industry technical centre)

HY INCOLOY825 Material grades and equivalents:

NS1402 (NS142)
German standard: 2.4858
Japanese standard: NCF825
American Standard: UNS N08825
National standard: 0Cr21Ni42Mo3Cu2Ti

Incoloy825 is a nickel-iron-chromium austenitic alloy with added molybdenum, copper and titanium. It has special corrosion resistance in oxidizing and reducing environment. Incoloy alloy has good general corrosion resistance and local corrosion resistance and good process performance. Therefore, it has been widely used in the chemical, energy, petrochemical, and hydrometallurgical industries.

Chemical composition and organizational characteristics

The balance between the nickel equivalent and the chromium equivalent in the alloy composition determines the pure austenite structure of the alloy under solid solution conditions. However, during medium temperature aging, carbides and intermetallic compounds will be precipitated on the austenite matrix and intergranular. These precipitation phases will harm the mechanical properties and corrosion resistance of the alloy.

Table 1: Incoloy 825 grade and chemical composition comparison table:

Grade NS1402 N08825 2.4858 NCF825
C ≤0.05 ≤0.05 ≤0.025 ≤0.05
Si ≤0.50 ≤0.50 ≤0.50 ≤0.50
Mn ≤1.00 ≤1.00 ≤1.00 ≤1.00
P ≤0.030 ≤0.020 ≤0.030
S ≤0.030 ≤0.030 ≤0.015 ≤0.015
Ni 38.0~46.0 38.0~46.0 38.0~46.0 38.0~46.0
Cr 19.0~23.5 19.5~23.5 19.5~23.5 19.5~23.5
Mo 2.5~3.5 2.5~3.5 2.5~3.5 2.5~3.5
Cu 1.5~3.0 1.5~3.0 1.5~3.0 1.5~3.0
Ti 0.60~1.20 0.6~1.2 0.60~1.20 0.6~1.2
Al ≤0.20 ≤0.20 ≤0.20 ≤0.20
Co ≤1.00
Fe Rest ≥22.0 Other 残部

Corrosion resistance

Incoloy825 has good corrosion resistance to various processing environments, including sulfuric acid, sulfurous acid, phosphoric acid, nitric acid, hydrofluoric acid, organic acids and alkalis such as sodium, potassium hydroxide, and acid chlorides.
Compared with general austenitic stainless steel, the nickel in Incoloy825 makes it resistant to chloride stress corrosion, while molybdenum and copper make it highly resistant to corrosion in a reducing environment. Chromium and molybdenum components can resist chloride pitting corrosion and corrosion in various oxidizing environments. The addition of titanium makes the material more stable during welding and is not easy to sensitize. This non-sensitization property allows the material to resist intergranular corrosion even when exposed to the sensitization temperature range.
It is not sensitive to intergranular corrosion under the condition of solution treatment at 1150~1204℃. When the medium temperature sensitization treatment for 1 hour, such as 760℃, chromium-rich M23C6 will precipitate on the grain boundaries, which will lead to the boiling of 65% HNO3 The intergranular corrosion. However, a stabilization treatment at 940°C for 1 hour before sensitization can prevent intergranular corrosion caused by sensitization.

 

Mechanical properties

Table 2: Room temperature mechanical properties of Incoloy825

Material heat treatment state Mechanical properties
σb/MPa σ0.2/MPa δ5/% ψ/%
Solution Annealed Pipe 608~647 264~323 44~53

 

Processing and forming performance

The hot forming temperature of Incoloy825 is 927~1065℃. It is not suitable for forming operation at the temperature sensitive to intergranular corrosion (650℃). If it is formed at a temperature higher than 1065℃, the final molding should be carried out in the range of 870~980℃ to obtain a good Resistance to intergranular corrosion. Incoloy825 is also suitable for cold forming, similar to Cr-Ni austenitic stainless steel.

Heat treatment process

The suitable final heat treatment of Incoloy825 is 940℃ stabilization treatment. The intermediate annealing temperature is preferably higher than 1050°C for solution softening annealing temperature.

application

As a typical austenitic corrosion resistant alloy, Incoloy825 can be easily formed and welded through technical processing. Applications are petroleum exploration, chemical equipment, etc., such as heat exchangers and condensers; heat exchangers, pipes, valves, pumps, etc., which are mainly used for processing hot sulfuric acid, chloride-containing solutions, sulfurous acid and other environments. Oil and gas pipelines, oil and gas coolers; nuclear waste disposal devices. It has also been widely used in the field of wood pulp extractor and deep source gas well in the paper industry.

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