DIE FOR EXTRUDING ALUMINUM AND METHOD FOR NITRIDING THE SAME

摘要

PROBLEM TO BE SOLVED: To produce a die for extruding free from breaking at the time of extruding by forming a white layer and a nitrogen diffused layer of which thicknesses are specified. SOLUTION: This die is the one in which a white layer having 4 to 8μm thickness is formed via a nitrogen diffused layer having 100 to 150μm thickness on the surface of a die steel for extruding to be contacted with an aluminum alloy as the material to be extruded. The ratio of (the area of the white layer+ nitrogen diffused layer)/(the total area of the cross sections) is preferably regulated to <=70% as for the cross section of the die parts vertical to the extruded direction. In nitriding treatment, the die steel is held to 300 to 520 deg.C in a gaseous fluorine atmosphere and is next held to 450 to 520 deg.C in an NH3 -RX gaseous mixture atmosphere. Furthermore, in the case the white layer is extinguished by wear, renitriding treatment is executed under the similar conditions. Thus, the breaking of the part small in the cross section such as the mandrel part small in the cross secton is prevented to prolong the service life of the die.