Corrosion tests of stainless steel X6 Cr Mo 17 and of microcracked chromium surface layers by electrochemical techniques

Abstract Electrode potential- and current density-time curves in dilute sulphuric acid and in 3% NaCl solution were measured in order to compare the corrosion resistance of microcracked chromium layers and of X6 Cr Mo 17 steel. The surface potentials of the two materials were registered in another series of trials in weak acid alcoholic solution. The results allowed the following conclusions to be drawn: 1. 1. The X6 Cr Mo 17 steel has the better corrosion resistance in weak sulphuric acid; this means that it is the better suited for an industrial atmosphere. 2. 2. In solutions with chlorine ions a more or less superficial attack on the microcracked chromium layer can be observed, but the pitting of the X6 Cr Mo 17 steel is to be expected. 3. 3. In electrolytes the production of local cells on the microcracked chromium layer is to be expected and for that reason some local corrosion, too; there is no pitting, however. The corresponding differences of potential were not observed with the X6 Cr Mo 17 steel. Therefore the steel must react more advantageously. Accelerated corrosion tests completed the trials and brought results which agree with these conclusions.