Laser absorption in CO₂ laser welding of medium, high and ultra high strength steels

Laser welding of carbon steels are quite common. The absorption of steel for a wavelength of CO2 laser is 12% at normal room temperature. The previous studies have shown absorption increases rapidly once keyhole is formed. In this paper three different grades of carbon steels of medium, high and ultra high strengths have been CO2 laser welded. Different approaches can be adopted to measure their absorption. Usually calorimeter is used in which the estimation of absorption of laser energy is made by water temperature rise. In yet another method the absorption is calculated from weld cross section using thermal transformation during heating and cooling of the weld. The distance between the two specific microstructural changes are measured from real weld macrographs and then a modified analytical equation for heat flow is used for calculating absorption values. The paper evaluates the measured absorption in terms of process parameters.