Abstract
Phosphoric irons (i.e. Fe-P alloys containing low phosphorous in the range 0.1 to 0.7 wt. %) with/without addition of chromium were prepared by powder forging route. The corrosion behaviour of these alloys was studied in different environments. The various environments chosen were acidic (0.25 M H2SO4 solution of pH 0.6), neutral/marine (3.5 % NaCl solution of pH 6.8) and alkaline (0.5 M Na2CO3 + 1.0 M NaHCO3 solution of pH 9.4). The corrosion studies were conducted using Tafel Extrapolation and Linear Polarization techniques. The results were compared with the corrosion resistance of electrolytic Armco iron. It was observed that, chromium improved the resistance to corrosion in marine conditions only. Corrosion rates were higher in acid medium due to the enhanced hydrogen evolution and hence, the cathodic reaction. The corrosion rates were minimal in alkaline medium and low in neutral solution.
Highlights
Corrosion of iron or steel is affected by exposed environment [1]
Important electrolyte variables affecting corrosion of iron are pH, concentration, fluid flow, temperature and oxidizing power of the solution [2].The diffusion controlled oxygen reduction predominates in weak acid and neutral solutions
The corrosion rate is dependent on hydrogen ion concentration in case of acidic solutions [2]
Summary
Corrosion of iron or steel is affected by exposed environment [1]. Segregation of phosphorus to grain boundaries can strongly affect intergranular stress corrosion cracking (SCC) of irons [4] and steels [5] in carbonate/bicarbonate solutions. Phosphorus additions are deleterious in its effect on alloy corrosion resistance and chromium did not affect the behaviour in de-aerated 0.1 N. In contrast to carbon steel, ancient phosphoric irons that were used for constructing large beams and located at Konark and Puri in India, have revealed excellent atmospheric corrosion resistance in saline seashore environments for several hundred years. The corrosion behavior of two P/M phosphoric irons with 0.00 wt % C alloyed with/without chromium has been investigated in three different solutions
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