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