Laser surface alloying of low carbon steel electroplated with thin (10 mu m) Ni using an 850 W CW CO2 laser is reported for the first time. Fe-Ni binary alloys of different concentrations are formed by varying laser traverse speed from 0.5 to 5 m/min. The phase transformation from alpha to alpha + gamma is discussed as a function of Ni contents. Development of microstructure in the modified zone is analysed in terms of solidification rate and Ni concentration. A three-fold increase in the microhardness of the binary alloy is observed. Formation of homogenous, adherent and crack free surface alloys is reported. (c) 2006 Elsevier B.V. All rights reserved.