Abstract
In order to investigate the influence of chemical compositions on the intergranular corrosion (IGC) resistance of the Super304H steel, the chemical compositions and IGC levels of as received Super304H tubes were analysed and evaluated respectively by spectral analysis, scanning electron microscopy and immersion test in H2SO4–CuSO4–Cu chip solution. The results show that there exist four IGC levels in all the tubes. In condition of similar C content or similar Nb content, the IGC susceptibility is revealed to change randomly with the increasing Nb content or C content, respectively. Further more, when C content is more than 0·10%, Super304H steel will be easily sensitised to IGC, while almost all the tubes without IGC susceptibility have Nb content close to 0·60% of upper Nb limit. As to the influence of Nb/C mass ratio on IGC resistance, the sample with Nb/C ratio less than 5·00 will be easily sensitised and the sample with Nb/C ratio more than 8·15 will have no IGC susceptibility, but the IGC levels of tubes with Nb/C ratio between 5·00 and 8·15 incline to fluctuate randomly. The high susceptibility of some samples in this Nb/C region is attributed to the improper heat treatment process.
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