Effect of Laser Cleaning on the Structural Steel Surface Caused by Removal of Oxide and Carbon-Containing Films

Abstract—The paper presents comparative assessment of the effect of laser cleaning of the surface of metallic structural materials from oxide layers and carbon-containing organic polymers on the base metal condition. Using lamellar samples of structural steels as an example, it has been demonstrated that, in the case of organic film removal (approximately 100 μm thick) employing an experimental system with continuous wave laser, it is relatively easy to achieve simultaneous removal of the original organic coating and the formation of a significantly hardened surface layer on steel with a thickness of at least 80 μm. This effect is observed for medium-carbon steel (such as grade 65Г steel), but not for low-carbon steels. According to the obtained data, the surface hardening factor, defined as the increase in microhardness of the metal surface layer (relative to the bulk steel) after laser cleaning, falls within the range ks = 1.9–2.9. The highest level of the base surface hardening ks ≈ 2.9) is achieved at a laser heating power of at least 300 W in the scanned spot (with a side effect of partial surface melting after removal of organic film). In this mode, the specific energy consumption is about 920 J/(cm2 of film) for an estimated dimensionless heating process parameter KP varying within the range of 350–500. As it has been revealed, a lower surface hardening factor can be obtained at heating powers not exceeding 200 W, but with increased energy consumption and without the side effect of melting the steel base. The results obtained regarding the ability to vary the physical and mechanical properties of the cleaned steel surface create prerequisites for further industrial application of this combined method for cleaning and surface hardening of various parts.