Role of Bayer solution concentration and temperature in stress corrosion cracking susceptibility of steel

To improve the efficiency of the Bayer process for the extraction of alumina from Bauxite ore, there is a push for increasing processing temperature and caustic concentrations, which has also led to an increased concern for caustic embrittlement. In this study, the caustic cracking behaviour of steel in Bayer solutions of 2.5, 5, 7.5 and 10 mol dm^-3 ‘‘free caustic’’ concentrations have been studied at different temperatures using pre-cracked circumferential notch tensile specimens. It has been observed that at 100 ^oC, steel is susceptible to caustic cracking in each of the four Bayer solutions. Caustic cracking has also been observed at temperatures as low as 55 ^oC. Tests were also conducted using only the notched specimens (i.e., without pre-cracking) in a 7.5 mol dm^-3 ‘‘free caustic’’ Bayer solution at 120 ^oC to study the stress corrosion crack formation and propagation behaviour in blunt notches.