Effects of Austempering Temperature on the Corrosion Behavior of Fe – Ni Bainitic Steel with Al Addition for Railroad Tracks

The effect of austempering temperatures varied from 300 to 400°C to form bainite in the structure on the corrosion resistance and mechanical properties of two newly developed FeNi steels containing 1 and 2 wt.% Al is investigated. Corrosion tests of the steels are carried out in a 3.5 wt.% NaCl solution. It is found that an increase in the Al content and in the austempering temperature promotes formation of a bainite lath structure in the steels; however, this has an insignificant effect on the hardness. The results of an electrochemical test show that the corrosion resistance of the steel in marine-like atmosphere increases upon increasing the Al content from 1 to 2 wt.%. The increase of the austempering temperature tends to improve the corrosion resistance of both steels, except for the steel with 1 wt.% Al processed at the highest temperature. It is shown that the corrosion resistance of the steels is more affected by the hardness than by the volume fraction of bainite laths in the structure.