|LASEK Stanislav||VSB-Technical University of Ostrava|
|Spoluautoři MAZANCOVÁ Eva|
High-manganese steels (20-30% Mn, suitable for cars) have higher toughness and ductility compared to unalloyed structural steels at comparable strength properties. The corrosion resistance of these steels can be reduced by a high content of manganese, which is electrochemically relatively plain, non-forming the protective layer and it is part of the sulphides and carbides, which favor certain types of corrosion. In this paper are compared the results of corrosion tests of TWIP (X70Mn22) and TRIPLEX (X100MnAl28-12) steels in rolled and annealed state with structural carbon steel C20 (CSN 411375). Exposition standard salt spray test was conducted and a gravimetric method, as well as microscopic observations of corrosion and structure (stereo-microscope, metallographic, scanning electron microscope), were used. Furthermore, the cyclic potentiodynamic polarization method, in particular for comparing the susceptibility to pitting in neutral NaCl solution, and potentiokinetic method for assessing the resistance to uniform corrosion in acidic conditions (sulfuric acid water solution) were also applied. Based on the exposure tests and measurements the average corrosion rates (non-uniform and pitting) were taken and the ranking of steel resistance was established: X70Mn22, X100MnAl28-12 and C20 steel. On the basis of the polarization tests in solutions with chlorides there were found much higher values of corrosion rate of X70Mn22 (TWIP) steel compared with X100MnAl28-12 (TRIPLEX) one, while a positive effect of aluminum for corrosion resistance was confirmed. In the sulfuric acid solution slightly lower resistance TWIP steels compared with TRIPLEX was measured, but both Mn steels have unacceptably high corrosion rate.