Tools for aluminium extrusion have limited life due to wear of the extrusion die. The extrusion process takes place at elevated temperature 550-600°C. This process is defined as the process of transforming a metal billet into long sections for example profiles, beams or rods. One heated round aluminium bar is pressed through a die and out comes an extruded profile. For higher wear resistance and longer life the bearing surface is often surface treated by nitriding. Four different tool steel grades were investigated i.e. new tool steel developed for aluminium extrusion dies. These tool steel grades were surface treated by the gas nitrocarburizing processes and one untreated tool steel for reference. The wear test used is a block-on-cylinder set up at temperature 550°C. The aluminum alloy AA 6063 is used as a counter material. The tool steel block is pressed against a rotating aluminium cylinder. The worn volume was measured by OP (Optical Profilometry). The properties of the new tool steel were investigated by LOM, their microstructure before and after surface treatment, and compared with the reference material H13.Four different types of tool steels were studied by SEM to characterize the wear pattern and to identify the wear mechanisms. It is concluded that for the nitrocarburizing treatment, chemical wear is a common wear mechanism due to the formation of intermetallic compounds. Delamination wear also observed on the worn surface. The alloy Unimax 1593A and ExW 2090A have good properties for aluminium extrusion dies due to higher hardness of the diffusion zone and lower wear rate than the other experimental tool steel.