SURFACE INVESTIGATION OF EXCIMER-LASER IRRADIATED PHOSPHATIZED STEEL PLATES

Steel plates (St 14-05) of 1.5 mm thickness and coated with 1.5 mu m o f ironzinc-phosphatehydrate (ASTM 29-1429) were irradiated with an XeC l-excimer laser (Siemens XP 2020) at energy densities of 20-80 mJ/mm(2 ) and with 2-32 pulses per spot. Depth-sensitive Mossbauer spectroscop y was carried out by means of conversion electron (CEMS) and conversio n X-ray (CXMS) Mossbauer spectroscopy in order to determine the phases produced by the excimer laser treatment. Although the phosphate layer is mainly ablated during the laser treatment, there is a significant formation of Fe2P. The phosphorous phase and the wustite, with changin g stoichiometries, were found in the very surface (CEMS). In deeper la yers and in correlation with the energy density and the number of puls es, austenite was found in surprisingly high amounts (CEMS and CXMS). The austenite was found to be nitrogen austenite. The high Fe-N austen ite content as well as the presence of some ferromagnetic Fe-N phase ( epsilon-Fe2+xN) must be ascribed to an unexpectedly high nitriding eff ect during the laser treatment.