Electronic Theoretical Study of the Influence of Cr on Corrosion Resistance of Fe-Cr Alloy

Based on the empirical electron theory (EET) of solids and molecules, the valence electron structure caculation results of Fe-Cr alloy containing (0 similar to 30%) Cr were analyzed semi-quantitatively. The electron density differences of interface (triangle p) between Fe-Cr alloy and Cr2O3, Fe2O3 passivation films were calculated. According to the results, adding Cr to alpha-Fe matrix can strengthen the matrix by improving the number of hybid atomic orbitals sigma(n), the number of the strongest bond covalent electron pairs n(A) and the strongest covalent bond energy E-A of Fe-Cr alloy. Once the content of Cr rises up to 12.52% and 24.3%, the corrosion resistance of Fe-Cr alloy is improved because of Cr being changed to a higher hybrid level, where Cr becomes more unstable and easily reacts with environment to form a complete passivation layer of Cr2O3. Moreover, among the electronic density differences of 24 low-index faces between Fe-Cr and Cr2O3, Fe2O3, only the triangle p of Fe-Cr(112)/Cr(2)O3(0001), Fe-Cr(112)/Cr2O3 (1010)(Cr), Fe-Cr (112)/Fe2O3(1120) are lower than 10%. For the matrix with same content of Cr, the triangle p between Fe-Cr (112) and Cr2O3(1010)(Cr) is the lowest, but the number of hybid atomic orbitals sigma satisfied triangle p<10% is the largest. triangle p (s) of Fe-Cr(112)/Cr2O3(0001) and Fe-Cr(112)/Fe2O3(1120) is decreased (increased) with the increase of Cr, therefore the interface bonding strength between Cr2O3, Fe2O3 and matrix will be enhanced, it has been found that the corrosion resistance of Fe-24.3% Cr is better. The calculation results of variation of Fe-Cr corrosion resistance with Cr content are in better agreement with Tammann's law.