hastelloy C-276 Corrosion resistance ——Intergranular corrosion

The intergranular corrosion sensitivity of Hastelloy C-276, NS 3304, 00Cr16Ni60Mol6W4 alloy is much lower than that of 0Crl6Ni60Mol6W4 alloy. When it is sensitized or cooled after welding, the alloy still has secondary carbide and some intermetallic phases. W, the existence of these harmful phases is still a potential danger of intergranular corrosion. In the general welding thermal cycle, the intergranular corrosion resistance of this alloy is much better than Hastelloy C-276 alloy (Table 8-32), but there is still a tendency of intergranular corrosion after sensitization or large R face welding.
Table 8-32 shows the evaluation results of the corrosion resistance of Hastelloy C-276 alloy by boiling 10% HC1 acid and 50% H2SO4 + 42g/L Fe2(SO4) 3 solution for 24h. The two test methods are to evaluate the nickel base. Standard method for the sensitivity of intergranular corrosion of corrosion resistant alloys. The hydrochloric acid bending test is carried out in 10% boiling HCl acid for 24h, then the sample is bent 180°, and the welded sample is required to turn perpendicular to the weld direction. The middle of the bend is located in the heat affected zone, and the bend is observed under a magnifying glass of 10 times. Whether or not cracks appear, and no cracks pass the test. The test for ferric sulphate [50% H2SO4 + 42g/LFe2(S04)3, boiling], after 24h test, if intergranular corrosion is present, the corrosion rate of the sample is increased. The maximum permissible corrosion rate for Hastelloy C-276 alloy is 1. 022 mm / month (12. 24 mm / a). The test results show that the intergranular corrosion resistance of this alloy after welding is good.

Table 8_32 Typical results of accelerated corrosion testing of Hastelloy C-276 alloy