The stress corrosion cracking(SCC) behavior of low alloy steels in high temperature(200 ～ 300 ℃), high pressure concentrated caustic solutions was studied with slow strain rate tests(SSRT), potentiodynamic polarization and cyclic voltammetry techniques. To analyze the chemical composition and construction of films formed in 4.78MNaOH and 7.42MNaOH + 1.32MAl_2O_3·3H_2O solutions at 260 ℃, EPM, XRD, XPS were used. The results showed that the SCC susceptibility of 16MnR steel increased with increasing concentration of sodium hydroxide or temperature of imitative Bayer solutions. Stringered sulfide inclusion severely affected the caustic embrittlement of steel in different direction. The inclusions in the rare-earth-treated steel(16MnRE) were predominantly globular rare-earth sulfides or oxysulfides, so the rare-earth added in steel improved the transversal property. The effect of inclusion on SCC behavior correlated with the projected area of inclusions per unit volume in plastic zone at crack tip, Av, on the plane perpendicular to the tensile direction. The SCC susceptibility increased with increasing of Av. Aluminate species(AlO_2~-)showed a inhibition effect on caustic embrittlement at 260 ℃. The mechanism of the effect of AlO_2~- species and SCC for a low alloy steel in high temperature caustic solution was discussed.
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