Modification of nitride layer on cold-work tool steel by laser melting and friction stir processing

The microstructural control of the nitrided case on a cold-work tool steel (SKD11) plate by laser melting and friction stir processing (FSP) was studied. The laser melting and the FSP were used as a pretreatment for the nitriding to refine the microstructure of the SKD11. The diffusion zone of the nitrided case on the SKD11 plate contained thick brittle boundary lines consisting of local formed nitride particles. On the other hand, the microstructure of the diffusion zone was very uniform and the thick brittle boundary lines disappeared as a result of the combined treatment of the laser melting and the FSP before the nitriding process.