Extending the die service time is for engineers in practice an important task for improvement the economy of hot extrusion of Al profiles since the dies have an important proportion in the price of the extruded profile. The formation of cracks, wear, crushing of nitride layers, plastic deformation, fractures, etc., are the most common causes of failure of dies, i.e. the time when used dies can not ensure the customer's requirements regarding the quality of extruded profiles, i.e. dimension tolerances, surface finish and mechanical properties. Which of the damages will be decisive at service time of dies depends on the construction of the dies (Al flow), the quality of die steels, loads and technological deformation parameters, selected parameters of nitriding, maintenance, etc., i.e. it is a complex problem. Improving the wear resistance of the sliding surfaces is important for extending the die service time whereas gas nitriding process is mostly used for improving of wear resistance of bearing surface. The process of nitriding can be repeated several times during the service lime of dies. An analysis of the causes leading to damages and a reconstruction of their development on selected dies for hot extrusion of Al were performed as well as improvements for extension of service time of the analysed dies are given. Excessive occurrence of nitrides on grain boundaries is the result of improper nitriding parameters, i.e. time, temperature and nitriding potential. This leads to the cracking of nitrides on grain boundaries and thus to accelerated adhesive removal of small parts from die bearing surface. Different contact pressures prevail around the perimeter of the bearing surface of dies and mandrels; higher contact pressures leads to increase of wear, i.e. increased density of adhesive removed parts (craters) from bearing surface. The wear progress continues with the formation of small furrows between the adhesively removed craters from the surface and their lengthening in the direction of aluminium sliding, as well as the lateral expansion of the furrows or formation of the groove in the lateral direction. Upon lateral contact of two parallel furrows in the direction of sliding of the material, a groove begins to form in the lateral direction as well, which with further development of wear leads to the formation of a longer groove around the perimeter of the bearing surface.
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