1994 Volume 12 Issue 3 Pages 351-357
Transformation hardening of cabon steel (S45C) by CO2 laser beam was analyzed by using a novel beam shaping optics, which provides linear-polarized beam spot with uniform intensity distribution and variable aspect ratios. At normal incidence, the absorptivity of CO2 laser beam was 20% in the bare specimen (in Ar), and 45% in graphite coated specimen (in air). The absorptivity in p-polarization, AP, increased significantly with increasing incident angle, θ, reaching 50% at θ=80 degrees with bare specimen in Ar, which exceeds the value of graphite coated specimen at θ=0. In the graphite coated specimen, AP also increased with increasing incident angle, reaching 80% at θ=80 degrees. In the bare metal, the case depth was approximately 0.4 mm at normal incidence, and increased with increasing incident angle, reaching 2.5 mm at θ=80 degrees. The depth of laser hardening was estimated by a simple approximation equation, showing satisfactory agreement with the experimental values. It was also shown that the hardened depth can be changed independently of the surface temperature by using the shaping optics, which can provide laser beam spot with variable aspect ratios.
