Surface modification of martensitic stainless steels by laser marking and its consequences regarding corrosion resistance
Résumé
Marking is of prime importance in the field of biomaterials to allow the identification of surgical tools or implants. Markings are obtained under industrial conditions with a pulsed Nd:YAG laser on a X30C13 martensitic stainless steel. Depending on laser parameters, two modes of marking are considered: a surface oxidisation mode and a matter photoablation mode. Electrochemical behaviour, i.e. passive state, corrosion rate, resistance to pitting, is evaluated in Ringer's saline solution. Results are then explained on the basis of metallurgical modifications regarding the phases composition and the distribution of alloying elements. In oxidative regime, laser treatment drastically affects both microstructure and chemical composition. Specially, chromium depletion is measured in subsurface, leading to a loss of passive ability. In ablative mode the surface is transformed into a thin favourable layer of austenite. Moreover, the overall chromium distribution is little modified. Therefore, the passive character is maintained, but with nevertheless a shorter passive domain than base material one.