Microstructural characterization of austenitic stainless steel nuclear grade tubes submitted to laser marking process

Laser marking is a non-contact printing method used to create high-precision markings. The laser beam interacts with the material surface, causing physical, chemical and metallurgical changes that result in a visible mark, which can be in the form of text, logos, bar codes, or other formats. This method has been widely used for product identification and traceability in a variety of industrial sectors, including the nuclear. In nuclear reactors type PWR (Pressurized Water Reactor) fuel rods can be laser-marked with bar codes to facilitate identification and traceability during the manufacturing, operation, and maintenance processes. The process is based on optical properties alteration of the material surface during interaction with a laser beam. This interaction can lead to different processes: heating, oxidation, melting, vaporization, ionization, sublimation, and direct dissociation. These processes can occur depending on the laser parameters, the material properties and the machine's optical configuration. The laser marking configuration affects mark visual properties and also affects the material local. Consequently, although laser marking is an effective and precise method, the use of inadequate parameters can lead to local changes that can be harmful to the marked material, such as a Heat-Affected Zone (HAZ) formation, grain growth, surface roughness alteration, change in corrosion resistance and accumulation of residual stresses. Therefore, the laser marking parameters must be properly established so that the marking does not alter the chemical, metallurgical, and mechanical properties and does not compromise the fuel rod performance during its useful life in the nuclear reactor. Several parameters influence the laser marking process and need to be carefully controlled to achieve the desired results. The most important laser marking parameters are: the laser spot size and focus, laser beam power, scanning speed, line spacing, pulse frequency and pulse duration. The objective of this study was to characterize the microstructure of the surface of austenitic stainless steel tubes, used for the manufacture of PWR fuel rods, after being subjected to the laser marking process. (author)