Surface Laser Treatment on Ferritic Ductile Iron: Effect of Linear Energy on Microstructure, Chemical Composition, and Hardness

Abstract

Surface transformation treatments like laser surface melting and laser surface hardening have been mostly developed in austempered ductile iron and gray cast iron. In this work, we explore the effects of the linear laser energy of the treatment on the microstructure, chemical composition, and hardness of ferritic nodular cast iron, using a fiber delivery diode laser. We found changes in the microstructure above 120 J/mm, characterized by the presence of graphite nodules surrounded by martensitic/dendritic shells. Above 316 J/mm, Fe3C and γ-Fe2O3 phases arise, together with a saturation of the microhardness around 1000 HV0.3 within the first 200 μm of depth, and of the surface hardness around 90 HR15N. Changes in microstructure and composition due to the laser treatment directly affect the thermal diffusion between the surface-modified zones and the nodular cast iron bulk. Our work highlights the importance of the linear energy in the design and planning of laser treatments.