Inconel 625 , NS 3306

Inconel 625 alloy is a Ni-Cr-Mo corrosion-resistant alloy with good corrosion resistance and high strength. This alloy is especially suitable for service conditions requiring high corrosion resistance and high strength.
Chemical composition and organizational structure
The chemical composition of Inconel 625 alloy is shown in Table 8-7. The alloy has a single austenitic structure in the solid solution state, and there will be precipitation of MC, carbide and intermetallic phase in the aging state, and the precipitation of these phases is related to the heat history. This alloy is insensitive to the precipitation of phase a, and no phase precipitation is observed even after long-term residence at 540~980 °C.
Mechanical properties
The room temperature tensile properties of 0Cr22Ni60Mo9NM alloy are shown in Table 8-79, and the fatigue properties of the alloy are shown in Figure 8-70.

Table 8-79 Hastelloy 625 Alloy Room Temperature Tensile Properties®

Table 8-81 shows the impact properties of hastelloy 625 alloy. It can be seen that the alloy still has similar toughness at room temperature.

Table 8-81 Impact absorption work of hot rolled frozen hastelloy 625 alloy 12.5mm sheet

Corrosion resistance

A general corrosion
The alloy does not substantially corrode in the atmosphere, natural water, sea water, neutral salt and other media. In the strong corrosive medium, the corrosion resistance of the alloy varies with the acid concentration, temperature and impurity content.
a nitric acid
In boiling 65% HN03, the maximum corrosion rate in the solid solution state is ≤0. 75mm/a.
b sulfuric acid
The relationship between corrosion resistance and concentration of hastelloy 625 alloy in sulfuric acid at 80 °C is shown in Table 8-82. In the pickling solution (28% H2SO4 + 5.9% HF acid, 50 to 79 ° C), the alloy has a corrosion rate of 1.225 mm/a. The alloy Hastelloy C-2000 is not resistant to boiling temperature sulfuric acid corrosion.

Table 8 Corrosion resistance of 2 Inconel 625 alloy in 80 ° C H2SO4

1 The solution is filled with air.
2 The solution is filled with nitrogen.

c hydrochloric acid
Due to the high Mo content of Hastelloy C-2000 alloy, it has certain corrosion resistance in room temperature hydrochloric acid, and the corrosion resistance decreases with the increase of solution temperature. Table 8-83 Corrosion data of this alloy in different concentrations of hydrochloric acid at 66 °C In 10% HC1 acid, the alloy has the highest corrosion rate.

Table 843 Corrosion test results of Inconel 625 alloy in 66 ° C hydrochloric acid

d phosphoric acid
Inconel 625 alloy has excellent corrosion resistance in boiling reagent grade phosphoric acid with concentration ≤50%. When the concentration of phosphoric acid is higher than this value, the corrosion rate of this alloy increases sharply with the increase of concentration. This alloy is only suitable for concentration. ≤ 50% boiling temperature phosphoric acid (Figure 8-75) in the environment.
Among the wet-process phosphoric acid, Inconel 625 alloy has good corrosion resistance, and the test results are summarized in Table 8-84.

e Alkali
In the laboratory 50% NaOH, the annual corrosion rate of hastelloy C-2000 alloy was 0.0125 mm.After 500 h test, no stress corrosion was observed.
f hydrofluoric acid
The fluorite is reacted with sulphuric acid to produce a hydrofluoric acid. The lining of the HF stripper is shown in the form of the HF stripping tower. The uniform corrosion rate of the alloy is only 0. 075. Mm/a.

B  intergranular corrosion
Inconel 625 alloy has good resistance to intergranular corrosion. The TTS pattern determined by boiling 50% H2S04 +42g/L Fe2(S04)3 ( ASTM G-28A) shows that its anti-sensitization ability is superior to that of all other Ni- Cr-Mo corrosion resistant alloy (Fig. 8-56), Fig. 8-76 shows the effect of sensitization of this alloy in 65% boiling nitric acid on the corrosion resistance of the alloy.

The sensitization sensitivity of the alloy was evaluated in boiling 50% H2SO4 + 42 g/L Fe2(SO4)3. The results showed that lh sensitization did not significantly affect the corrosion rate of the alloy, as shown in Table 8-85. The above results indicate that the Hastelloy C-2000 alloy does not have to be solution treated after welding.

C pitting and crevice corrosion
Inconel 625 alloy has good pitting resistance. In the medium which is prone to pitting and crevice corrosion, the corrosion resistance of this alloy is only slightly lower than that of hastelloy C-276 alloy and alloy 59.
Table 8-73.

D stress corrosion
Some of the test results in an environment susceptible to stress corrosion are shown in Table 8-86 to Table 8-88. The results show that the alloy has excellent stress corrosion resistance and is significantly superior to the comparative alloy.

Table 8 5 sensitization treatment of Inconel 625 alloy sheet at 50% H2SO4 + 42g / L Fe2 (SOJ3
Effect of corrosion resistance in boiling solution (the plate is sensitized by different temperatures after 1204 °C x 20 mm water cooling)

Table 8 Test results of 204 in the simulated autoclave of deep source gas wells

Note: Medium: 25% NaCl + 0.5g / L S +9.7MPa H2S, test 672h. 1 After heat treatment or cold processing, the materials are aged at 260 ° C x 720 h.

Table 8-87 Test results in 5% NaCl + 0.5% acetic acid + H2S (according to NACE TM-007)

Thermal processing, cold working, heat treatment and welding performance
A hot processing
The alloy has high temperature deformation resistance, and the general hot working temperature is 1170 ° C. The deformation of large deformation is preferably carried out at 1010 to 170 ° C, and the micro deformation can be carried out at 930 ° C or higher.
B cold working
Inconel 625 alloy has good cold deformation properties and is suitable for cold working and cold forming operations. Cold working can harden the alloy. Due to the high tendency of the alloy to work hard (Fig. 8-77), intermediate softening annealing is required in the cold working and cold forming.
C heat treatment
The solution treatment temperature of Inconel 625 alloy is 1093~1204 °C, and the annealing temperature after cold and hot processing and molding is 927 ~ 1038 °C. Generally, the softening temperature after cold working and cold forming is 1000 ~ 1038 °C. In order to eliminate residual stress, it is effective to heat above 871 °C, and in order to reduce the residual stress after cold drawing of the alloy, heating at 600~760 °C has obvious effect.
D welding
Hastelloy C alloy has good welding performance and can be welded by the usual welding method (TIG, MIG, manual arc welding).

Physical properties The physical properties of this alloy are shown in Table 8-90.

Application
Because Inconel 625 alloy has both high corrosion resistance and high heat strength. Therefore, it can be used as both a corrosion-resistant alloy and a heat-resistant alloy, and can also be used as a corrosion-resistant alloy at a high temperature. In the chemical industry, 0Cr22Ni60Mo9Nb4 alloy can be used for pitting corrosion resistance to seawater, stress corrosion resistance to chloride, and resistance to corrosion with F-phosphate. For example, the manufacture of thinner walls and tubes, corrosion resistant pipes, reactors, distillation columns, heat exchangers and valve parts.