Abstract
In order to investigate the influence of the nature of corrosion products on apparent difference in the susceptibility to sulfide corrosion cracking between nickel-free and nickel-containing high strength steels, the corrosion products formed on surfaces of these steels in hydrogen sulfide aqueous solution have been compared and discussed by means of optical microscopy, X-ray diffraction and electron diffraction. The corrosion weight losses of the steels in the similar medium were also determined.
The results are summarized as follows:
1) The corrosion product formed on the steel surface in saturated aqueous hydrogen sulfide appears to be composed primarily of tetragonal iron sulfide and it is not kansite as so far considered.
2) Nickel in these steels acceralates the crystallization of tetragonal iron sulfide formed on the steel surface.
3) Nickel also increases the corrosion rate of the steels in hydrogen sulfide solution.
4) The structure of corrosion products in the initial stage of corrosion reaction differs from that of nickel-containing steel to that of nickel-free steel and the difference in the structure of sulfide becomes more distinctive after aging. The particular sulfide formed on nickel-containing steel is believed to be relevant to the sulfide stress-corrosion cracking.
