This study was undertaken as an effort to understand the effect of laser marking on corrosion behavior of metallic materials. Two laser-marking companies and two metallic materials low alloy steel AISI 4140 (UNS G41400) and stainless steel AISI 420M (UNS S42000) were selected for this study. The obtained results indicate that the laser marking process created a thin black oxide layer on the metal surfaces without significantly affecting the base materials. In term of corrosion performance, the obtained results suggest that the laser marking does not have a significant effect on pitting corrosion resistance after 72 testing hours per ASTM G481 or general corrosion resistance after 42 days of salt spray test per ASTM(1) B1172 or Sulfide Stress Cracking (SSC) resistance after 720 hours per NACE(2) TM03163 of the low alloy steel. However, in the case of stainless steel, the laser marking process was found to slightly to significantly affect the general corrosion resistance and SSC resistance of the stainless steel. One set of the laser marked stainless steel failed the SSC test while the unmarked specimen, tested in the same testing batch, passed. This illustrates the need to understand the potential effect of laser marking on corrosion resistance for a given material grade.
Laser marking of materials, especially metallic materials, has been widely used in many industrial fields from automotive to aerospace to decorative applications among others thanks to its fast marking time and its ability to work on a lot of materials. However, laser marking is a thermal process that could modify the metallic surface property without significantly changing the basic material properties4. It forms one or more layers of oxides and/or nitrides (depending on the operating conditions) on the metal surface5. Therefore, the corrosion behavior of the marked area could be different from that of the unmarked area. There were several studies on the effect of laser marking parameters on the corrosion resistance of metallic materials6,7, although most research until now has been focusing on studying the readability and repeatability of the marking8-10. In this study, we aim to systematically compare the corrosion performance of different metallic materials in a variety of corrosive environments from atmospheric corrosion to pitting corrosion and CO2/H2S corrosion. Low alloy steel and stainless steel are selected for Phase I of this study. Other materials such as duplex stainless steel and Nickel based alloys will be studied at a later stage.