The effect of silicon on electron structure and corrosion-electrochemical behavior of a X20H20 type phosphorus-containing steel

The effect of silicon (0.13-5.40%) on the corrosion-electrochemical behavior of phosphorus-containing (similar to0.1% P) austenitic stainless steels of a X20H20 type is studied in a 1.0 mol/l HClO4 + 0.25 mol/l NaCl solution at 22degreesC, as well as boiling 27 and 65% HNO3 solutions. The steel is tested either in quenched or sensitized states (i.e., with a single-phase or heterogeneous structure with precipitated second phases, respectively). The variation in the electron density on Fe-57 nuclei under the action of silicon is studied with the use of Mossbauer spectroscopy by determining the isomeric (chemical) shift delta (mm/s) of singlet and doublet, the quadrupole electric splitting Deltaeq (mm/s) of doublet, and a fraction of area S (%) of each spectrum component in the total spectrum. The mechanism of the effect of silicon on the passivability of test steels and their susceptibility to intergranular corrosion at potentials of the active-passive transition and the end of the passive range is proposed based on the corrosion-electrochernical data and the calculated parameters of Mossbauer spectra.