Use of Laser Markers for Supplementary Marking of Steel Billets

This paper discusses whether laser technology holds promise for use in marking steel billets in a continuous-production environment. A laser-marking experiment was performed on “dull metal” and “bright metal,” which have different oxidation layers. The experiment was performed on rolled-shape samples produced using a wide variety of carbon steels and differing scale produced by using different cooling rates during heat treatment (in water, or in a furnace). A QR code or bar code was applied to the heat-treated samples using laser markers where the laser exposure and laser power used for application of the code were varied. The experimental results revealed significant technical difficulties preventing use of this technology with “dull metal” (application of the code to areas coated with scale causes the corresponding areas to change color — gray instead of bronze resulting in the code being impossible to read using standard equipment). Delamination of the oxide coating on the billet will lead to loss of code, and make the code impossible to subsequently read. Successful laser marking of “dull metal” requires initial preparation of the surface for marking in order to remove scale inclusions, so that the code will have uniform color and contrast. A clean surface requires less time to laser mark and lower laser-marker power because of the high contrast between the code and the surface. The code remained intact and readable after long storage (on the order of 9 months) under standard conditions.