Laser transformation hardening is applicable for a number of different steel types ranging from structural steels to high alloy tool steels and martensitic stainless steels. The physical properties of these steels vary considerably and therefore it is important to recognize how the variation of steel properties affects the hardening process.
In this study, two very different steel types, AISI 420 L martensitic stainless steel and 42CrMo4 heat treatable steel, were examined. Samples were hardened with a 3 kW direct diode laser with a 10x5 mm spot size. Surface temperatures during hardening were measured with a dual-wavelength off-axis pyrometer and the absorptivities with a liquid calorimeter. The reflectivity of the laser beam was found to have the greatest effect on the optimization of processing parameters. In these experiments the absorptivity of the laser beam varied from 35 to 70 percent depending on surface oxidation, material and surface temperature. Case depths measured from cross sections of the samples varied from thin surface layers up to ca. 1 mm.