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.

Description

TECHNICAL FIELD [0001]This invention relates to a method for the surface treatment of a die-casting die is provided by applying the compression residual stress in an aesthetic surface of the die-casting die using a shot-peening process.BACKGROUND OF THE INVENTION [0002]In a die-casting molding in which a casting cycle that includes pouring a molten metal, solidification, and stripping a cast product is repeated, small heat checks on an aesthetic surface of a die-casting the can be readily produced by a thermal history to be given by the casting cycles. Thus abrasions caused by mechanical contacts can be readily produced. The heat checks may develop into a crack or cracks to damage the die, and the abrasion may degrade the dimensional accuracy of the cast product. Therefore, to enhance heat check resistance and abrasion resistance to extend a product's life, processes such as a surface nitriding process-to enhance the hardness of the aesthetic surface of the die and a shot-peening pr...

AI Technical Summary

Benefits of technology

[0017]Therefore, based on the high hardness and the high compression residual stress, a die-casting die having excellent abrasion resistance and excellent heat check resistance can be produced.

[0018]In the above method, the step of decomposing the compound preferably carries out the thermal process at a temperature that is lower than that of the step of the nitriding process. In this case, higher hardness and higher compression residual stress can be imparted on the die-casting die such that the the having more excellent abrasion resistance and more excellent heat check resistance can be produced.

Problems solved by technology

The heat checks may develop into a crack or cracks to damage the die, and the abrasion may degrade the dimensional accuracy of the cast product.

However, the depth of the nitrogen diffusion layer also becomes shallow.

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