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hastelloy C-4 —general corrosion,intergranular corrosion,point corrosion

hastelloy C-4 —general corrosion,intergranular corrosion,point corrosion

The uniform corrosion resistance of hastelloy C-4 alloy is basically the same as that of hastelloy C alloy in various media. The most important feature of this alloy is that the C, Si and Fe contents are controlled at a low level, so the carbide and intermetallic phase precipitates are small, making it resistant to uniform corrosion. Hastelloy C and Hastelloy C-276 alloys, especially after welding. The corrosion resistance of the or aged alloy remains substantially at the solid solution level (Tables 8-40). Figures 8-31 and 8-32 show the iso-corrosion patterns for this alloy H2SCV and HN03. In strong reducing media (such as hydrochloric acid), its corrosion resistance is not as good as hastelloy C-276 alloy, but it is worse than hastelloy C-276 alloy in strong oxidative corrosion medium.

Table 8-40 Corrosion resistance of hastelloy C-4 alloy in some acid media

medium

acid concentration/%

temperature/T

corrosion rate/mm •â」

Solid solution water cooling

TIG welded status

aging status(900℃,100h)

20

boiling

0.0725

0. 0875

0. 0875

Formic acid

10

75

0.900

0. 850

0.875

Nitric acid

10

boiling

0. 1475

0. 1775

0. 2300

phosphoric acid

85

boiling

1.525

1.300

0. 2125

sulfuric acid

10

boiling

0.550

0. 750

0. 500

sulfuric acid

85

75

0.575

0.425

0.525

 

B intergranular corrosion
Hastelloy C-4 alloy has better thermal stability than hastelloy C and hastelloy C-276 alloy, so the precipitation sensitivity of hastelloy C-4 alloy precipitate phase is lower than that of the earlier two Ni-Cr-Mo-W alloys. 8-33). This property determines the best sensitizing intergranular corrosion resistance of this alloy.
The accelerated corrosion test results of boiling 10% hydrochloric acid and boiling 50% H2SO4 +42g/L Fe2(S04)3 for 24h also showed that hastelloy C-4 alloy has the best sensitization state intergranular corrosion ability (Table 8- 41).
C point corrosion
Since hastelloy C-4 alloy does not contain W, it reduces the pitting and crevice corrosion resistance of the alloy, and its pitting and crevice corrosion resistance is slightly lower than hastelloy C alloy and hastelloy C-276 alloy.

Table 8-41 Accelerated corrosion test results of hastelloy C-4 alloy

Accelerated test method

腐蚀速度/mm – a’1

solution anneal®

welded status®

aging status®

Hydrochloric acid bending test®

6.250

7. 125

6. 900

No intergranular cracking after bending

Ferric sulfate test®

2.500

2. 775

2.850

1 1066 ° C, water cooled.
2 After TIG welding.
3 900 ° C aging lOOli.
4 Tested in 10% boiling I.IC1 acid for 24 h, then the sample was bent 180 ゚ and magnified 10 times to observe. If the intergranular crack is formed, it is determined that there is intergranular corrosion.
5 Tested in 50% H2SO4 + 42g / L iron sulfate boiling solution for 24h, if there is grain boundary precipitation, the corrosion accelerates.

 

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Post time: Jun-04-2019