engleski

Investigation of the Passivity: Hydrogen Embrittlement and Threshold Stress of Duplex Stainless Steel

The electrochemical behavior of duplex stainless steel has been studied in various environments. Its passivity state was investigated in borate/buffer cyclic voltammetry and impedance spectroscopy techniques. The susceptibility toward sulfide stress cracking and hydrogen embrittlement were tested at a constant load under cathodic polarization in the NACE solution saturated with H_2S and 0.5 M sulfuric acid solution containing As_2O_3 as a promoter. SEM analysis accompanied theses investigations. It is proposed that the highly protective quality of the passive film formed on the investigated duplex stainless steel may be associated with the presence of multiple oxidation states (Cr^3+ and Cr^6+) formed in the solid state along with (CrO_4^2- and MoO_4^2-) anions and the great variety of possible bridging ligand states (OH^-, H_2O, O^2-). This leads to a significant degree of bonding flexibility and supports amorphous i.e. glassy structure of the passive film. Therefore, the stresses that would be associated with epitaxy, are easily alleviated without the creation of long-range defect structures. The investigated duplex stainless steel shows high resistance to hydrogen embrittlement and sulfide stress cracking. The embrittlement index was determined to be 26%, while the threshold stress amounts to 84% of the yield strength.

duplex stainless steel; stress corrosion; hydrogen embrittlement; impedance spectroscopy; cyclic voltammetry; SEM

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