Effect of overlaps on phase composition and crystalline orientation of laser-melted surfaces of 321 austenitic stainless steel

Understanding the effect of overlaps on microstructure and performance of laser treated surface layer is of fundamental importance for the development and application of laser surface treatment of engineering materials. In the present work, laser surface melting of 321 austenitic stainless steel with overlaps and single laser track was carried out using a 2 kW CO2 laser and a 3 kW CW Nd:YAG laser respectively. The crystallization of the melted surface layers and their preferred orientation were characterized by X-ray diffraction. It was found that the heat treatment effect at overlap regions caused not only the transformation of some delta-ferrite formed in previous laser tracks reversed into gamma-austenite, but also the increase in the extent of the preferred orientation of gamma-austenite along [200] direction. Relationships between phase composition and laser process parameters such as laser power lever, beam size, scanning velocity and overlap ratio have been also studied. (C) 2003 Elsevier B.V. All rights reserved.