Abstract
This study is to evaluate the anticorrosion behaviors of alloyed Fe-20Cr ferritic stainless steels with microaddition of Cu-Sn and Ge, by means of LSV, EIS, CV, OCP, microstructure and composition analysis of etchant after immersion, as well as by use of ESCA and AES analyses of the passive film of the alloys. Although LSV results in H2SO4 for alloys of Cu-Sn addition show improved corrosion resistance at the alloy active corrosion region, which promotes the passive film formation, the passivation corrosion current density increases. For Ge-alloyed, LSV results in H2SO4 show improved stability of passive film. EIS data in H2SO4 for the Cu-Sn-alloyed have a decreased passive film thickness and lower impedance, while for the Ge-alloyed, data not only show a decreased film thickness, but also show increased impedance, indicating that the Ge-alloyed changes the type and property of the passive film. Data for OCP in H2SO4 manifest the Cu-Sn- alloyed has no obvious trend for added amount of Cu-Sn, while the Ge- alloyed has improved stability for increasing the content of Ge addition. Microstructure and composition analyses on corrosion surface show general corrosion behavior for both the Cu-Sn- and the Ge-microalloyed cases. However, the Cu-Sn-alloyed has deteriorated corrosion resistance vs the non-alloyed, while the Ge-alloyed has superior behavior. Data for ESCA and AES analyses of passive film in H2SO4 show the passive film for both kinds of alloys is principally composed of Fe3O4, FeO/Fe2O3, Cr2O3, CuO, SnO2, and GeO2. As mentioned above, no matter what the Cu-Sn- or Ge-microalloyed, the passive film thickness decreases, and the composition of the film changes. Data from the LSV in NaCl have no obvious effect on the corrosion behavior for the Cu-Sn-added, while for the Ge-added, the cross-over voltage for passivation corrosion enlarges, pitting corrosion voltage increases, and passivation corrosion current density drops, mentioning its improved corrosion behavior. Data from the EIS in NaCl also show no obvious trend in results for the Cu-Sn-added, while for the Ge-added there is a rise in impedance for passive film, and as the amount of Ge addition increases to a specific amount, ionic diffusion occurs. CV data in NaCl show an inferior effect of Cu-Sn, while there is a superior effect of Ge. The NaCl solution after alloy immersion of Cu-Sn-alloyed shows an obvious Cu dissolution but without Sn content. It shows general corrosion behavior for the Ge-added in NaCl. Results of the Cu-Sn-added for LSV in NaCl observe only a lower corrosion current density in its active region, while for the Ge-added, both active and passive corrosion current densities are lowered. EIS results in NaCl demonstrate a rise in impedance for the Cu-Sn-added, and even a more rise for the Ge-added. Therefore it is concluded that the Fe-20Cr microalloyed with Ge is an innovative corrosion resistance alloy.