Micro abrasion-corrosion of ferritic stainless steels

Abstract

The synergistic effect between abrasion and corrosion has been widely investigated and debated, where according to some works this synergy accentuates wear, and for others attenuates it. Despite the considerable effort to understand the synergy between abrasion and corrosion, little progress has been made to understand this phenomenon for ferritic stainless steels. This paper analyses the micro abrasion-corrosion performance of ferritic stainless steel with different chemical compositions (11%wt Cr with and without Ti stabilization; 16%wt Cr with and without Nb stabilization) and, for comparative purposes, austenitic stainless steel (18%wt Cr − 8%wt Ni) and carbon steel (0.2%wt C). The specimens were tested for corrosion (turbulent and aerated environment), micro abrasion and micro abrasion-corrosion. For the corrosion tests, a 1N H2SO4 solution was used, a 10%wt mixture of SiO2 in distilled water for the micro abrasion tests, and an abrasive-corrosive environment of 10%wt SiO2 in 1N H2SO4 for the micro abrasion-corrosion tests. In the micro abrasive wear tests there was not a clear trend between the different materials tested, despite differences in their chemical composition, mechanical properties and microstructure. On the other hand, their performance was ruled by their chemical composition, in particular the Chromium content, under abrasion-corrosion conditions. This indicated the predominant role played by corrosion in abrasive-corrosive environments in this particular tribo-system. For all materials tested, micro abrasion wear coefficients were higher (4×) than those measured under abrasion-corrosion conditions. Friction coefficients could also be measured by a 3D load cell strategically positioned in the specially developed micro abrasion-corrosion device, showing a strong reduction (2×) in friction coefficient under abrasion-corrosion conditions when compared with solely abrasion conditions. This was attributed to the formation of a corrosion product, mainly constituted of iron sulphate (identified via FTIR), which has lubricant properties.