Method for surface treatment of a die-casting die

Abstract

The present invention is to provide a method for surface treatment that substantially provides no nitride compound layer that causes heat checks and abrasion to a die, while nitride is introduced in large quantities into the die internally, and as a result a die-casting die with excellent heat check resistance and excellent abrasion resistance can be produced. The method comprises a step of a nitriding process for forming on an aesthetic surface of the die-casting die a nitrided layer that includes at least a compound layer composed of a nitrogen compound by introducing gas containing at least ammonia gas to a heating furnace, a step of decomposing the compound by exhausting the ammonia gas from the heating furnace and for introducing ambient gas to the heating furnace, to carry out a thermal process to decompose the nitrogen compound, and a step of processing a shot peening process on the aesthetic surface of the die. The thickness of the compound layer contained in the nitrogen layer that is formed in the step of nitriding process is within the range of from 2∫ m to 7∫ m.

1 . A method for surface treatment of a die-casting die, which is provided by applying the compression residual stress to an aesthetic surface of the die-casting die using a shot-peening process, the method comprising the steps of:
 nitride processing for forming on an aesthetic surface of the die-casting die a nitrided layer that includes at least a compound layer composed of a nitrogen compound by introducing gas containing at least ammonia gas to a heating furnace;   decomposing the compound by exhausting the ammonia gas from the heating furnace and introducing ambient gas to the heating furnace to carry out a thermal process to decompose the nitrogen compound; and   shot-peening processing OR the aesthetic surface of the die;   wherein the thickness of the compound layer contained in the nitrogen layer that is formed in the step of the nitriding process is within the range of from 2 μm to 7 μm.   
     
     
         2 . The method for surface treatment of a die-casting die of  claim 1 , wherein the step of decomposing the compound carries out the thermal process at a temperature that is lower than that of the step of the nitriding process. 
     
     
         3 . A die casting die to which the method for surface treatment of  claim 1  or  2  is applied.