Permanent marking on stainless steels for corrosion resistance through control of oxide growth

A requirement exists to permanently mark medical instruments and implants. These materials are selected for the specific applications by mechanical properties and resistance to corrosion and aggressive cleaning methods. The major challenge presented for laser marking is to create a visible mark without compromising the corrosion resistance of the material. This requires that the surface of the material does not become molten, and that the mark is produced by building up an oxide layer that becomes visible and enriched with chromium to maintain corrosion resistant properties. The paper examines the marking conditions required for corrosion resistant marking, in line with ASTM F1089-02, of stainless steels including 304, 17-4 and 17-7 using a 1070nm fiber laser marker. The effect of parameters such as peak power density, pulse frequency, pulse shape, fill overlap and marking speed on the level of corrosion resistance are presented. In addition to the experimental data, a moving point source thermal model is presented to provide a more in depth understanding of the heat input during the laser marking process, and gain further insight into the thermal control necessary during the oxide growth process to enable corrosion resistant marks.