Abstract
The mechanism of stress corrosion cracking (SCC) of low alloy steel in liquid ammonia has been investigated by measuring potentiostatic polarization curve, potential- or current-time curve under a constant tensile load and electro-chemical hydrogen permeation.
The results obtained are as follows;
1) In liquid ammonia containing strong electrolyte, such as NH4NO3, anodic polarization curve of steel shows active, passive and trans-passive states as in aqueous solutions. The passive state is eliminated by the addition of CO2.
2) By the existence of CO2 in liquid ammonia the corrosion rate of steel increases, and a corrosion product film is formed on the surface of steel. The film formation is considerably accelerated by the addition of O2.
3) A potential rise or current decay in the constant load test under anodic polarization is observed before the failure of specimen, this indicating the growth of the corrosion product film on the surface of steel.
4) The addition of water or the decrease of temperature inhibits the formation of corrosion product film and the cracking of specimen.
5) Under anodic polarization, no hydrogen permeation is observed but cracking is stimulated.
These results indicate that SCC of steel in liquid ammonia is due to an active path corrosion mechanism.
