Laser alloying of hot working steel followed by nitriding

Hot working tools like forging and die casting tools are subjected to a complex set of mechanical and thermal stresses. Wear, thermal fatigue and breakage causes an early break down of such tools. Proportional tool costs account for a high percentage of the production costs of that parts. The previously applied surface treatment operations (e. g. nitriding, CVD and PVD coating processes) cannot bring about a sustainable reduction in damage. One disadvantage shared by these operations is, that the produced coatings are not only very thin, but are also very brittle. Laser surface treatment, in the forms of alloying and dispersing, open up avenues for the production of wear-resistant outer layers. The different types of damage can be specifically targeted and treated locally by making thermochemical modifications to the outer layer. The good metallurgical bond to the base material guarantees excellent coating adhesion. The layer characteristics can be adapted by careful selection of the additional materials and of the process control to suit whatever the principle strain may be. If additional nitriding is applied after laser alloying with special nitride forming elements, the thin and extreme hard nitride layer is supported by the laser alloyed layer. Therefore the nitride layer does not chip off prematurely during production use. The combination of alloying and nitriding of real production tools has shown higher tool life time compared to the single surface treatment processes. In this paper results of metallography and wear tests of laser alloyed and nitrided hot working steel will be presented.