Effect of laser beam irradiation on AISI 1045 steel

Abstract

The effect of the parameters of laser irradiation (beam power and travel velocity) as well as of various surface coatings and protecting atmospheres on the size, structure, and hardness of the laser-affected region was studied in the case of commercial 1045 steel and a continuous CO2 laser. The action of the laser beam depends more strongly on its traverse velocity than on its power. When the power density exceeds a certain threshold level, a drastic decrease in the size of the laser-affected region takes place. The action can be enhanced by surface treatment in orthophosphoric acid as well as by some painted surface coatings. Unlike the latter, electroplated Cr and Ni layers were found to cause substantial alloying of the laser-treated layer. The laser-affected region formed by a single pass consists of two distinct zones: a melt zone, surrounded by an austenitization zone with a duplex structure representing former pearlite and ferrite regions. The hardness of the melt zone (about HV 750) exceeds that of conventionally hardened 1045 steel; even higher values (up to HV 900) are observed in the former pearlite regions of the austeniti zation zone, that of the former ferrite regions being about HV 250. In the case of an extended surface processed by a series of equidistant passes, a relatively wide region of tempered martensite is formed (with minimum hardness values down to HV 400) due to the heating generated by each pass in the previously hardened layer. As a result, a periodic hardness distribution is observed, whose fcatures depend on the degree of overlapping. High tensile residual stresses were found by x-ray diffraction in surface layers both in the cases of overlapping and separated passes.