Laser micro-welding of high carbon steels [Microsaldatura laser di acciai ad elevato tenore di carbonio]

High carbon steels are commonly used in modern mechanical industry due to their good mechanical properties and to their relatively low cost. Unfortunately, when dealing with welding processes, these materials must be set aside because of their very high crack susceptibility and more refined and expensive steels must be taken into consideration, such as HSLA, DP and TRIP ones, thanks to their lower carbon equivalent and similar, or even better, mechanical properties. In micro-scale components industry the use of high carbon steels is also very common, in particular in precision mechanics, watch and MEMS industry. Considering the very low thicknesses typical of these components and the intrinsic welding difficulty related to the material, several studies stressed on the possibility to exploit nanosecond pulsed lasers in welding this kind of steels. These sources, taking advantage from the short duration of the pulse and from a repetition rate as high as I MHz, allow a very accurate control of the heat input delivered to the material and pave new ways in micro-welding of medium and high carbon steels. The present paper deals with the exploitation of a 20 W nanosecond pulsed laser source in welding low thickness C70 (AISI1070) plain carbon steel. The process is studied by evaluating the influence of the main parameters on its feasibility. The activity pointed out that, by properly selecting the main parameters, it is possible to achieve sound and crack-free weld beads with a maximum penetration as high as 200 μm and a very small heat affected zone. The main interesting point concerning this specific welding process is related to the fact that, by simply selecting the proper process parameters, it is possible to achieve high productivity working cycles involving laser cutting, welding and marking on the same machine and exploiting the same workpiece positioning.