Laser surface melt-hardening of gray and nodular irons

The procedure of laser heat treatment by surface remelting has recently been increasingly used on products from gray and nodular irons for modifying the surface layer. Since in laser treatment the surface or surface layer is heated above the melting temperature, greater depth of the austenite transformation in the material is achieved, which contributes to the formation of a modified layer deeper than that obtained by conventional hardening procedures. For the case of laser surface-melt hardening, a mathematical model was used to determine the temperature cycles in gray and nodular irons and the depth of the modified layer. The mathematically obtained results are critically assessed and compared with the results in the experiments. The microstructural changes which can be predicted from the temperature cycles on heating and cooling are confirmed by microhardness measurements.