Laser transformation hardening of steel: Effects of beam mode, beam size, and composition

Laser transformation hardening experiments have been carried out on three model steel alloys of nominal composition Fe-0.4C, Fe-0.4C-1.0Mn, and Fe-0.4C-1.0Si (wt-%). A 1 kW continuous wave laser with a near Gaussian beam and a 5 kW continuous wave laser fitted with a beam integration device have been employed. Thus, it has proved possible to isolate the effects of alloy chemistry and beam mode on the kinetics of the hardening process. The dimensions of the hardened zones have been characterised and the results compared with calculations made using process models. It is shown that the results from experiment and theory are in broad agreement. Hardened zones resulting from the uniform source had a larger width/depth ratio than those resulting from the Gaussian source, although the effect was not as enhanced as suggested by theory. A comparison of the Fe-C, Fe-C-Mn. and Fe-C-Si specimens revealed that manganese and silicon increased the width of the transformed zone, and that this effect was more significant at higher processing speeds.