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Summary of three major categories of surface treatment of die casting mold

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  Die-casting molds are a method of casting liquid die forging and are a large class of molds.Die casting molds are required to have high heat fatigue resistance,thermal conductivity wear resistance,corrosion resistance,impact toughness,red hardness,good release properties,and the like.The surface treatment technology of die-casting molds is relatively high.In recent years,various new techniques for surface treatment of die-casting molds have emerged,but in general they can be divided into the following three categories:

  (1)Improved techniques for conventional heat treatment processes;

  (2)Surface modification technology,including surface thermal diffusion treatment,surface phase transformation strengthening,and electric spark strengthening technology;

  (3)Coating technology,including electroless plating.

  The traditional heat treatment process for die-casting molds is quenching-tempering,and surface treatment techniques have been developed in the future.Because of the variety of materials that can be used as die-casting molds,the same surface treatment techniques and process applications can have different effects on different materials.Schkov recently proposed a substrate pretreatment technology for mold substrate and surface treatment technology.Based on the traditional process,a suitable processing technology is proposed for different mold materials to improve mold performance and improve mold life.Another development direction of heat treatment technology improvement is to combine the traditional heat treatment process with advanced surface treatment technology to improve the service life of the die casting mold.For example,carbonitriding by chemical heat treatment,combined with conventional quenching and tempering processes,NQN(ie carbonitriding-quenching-carbonitriding)composite strengthening,not only obtains high surface hardness,but also effectively hardens.The layer depth is increased,the hardness gradient distribution of the layer is reasonable,the tempering stability and the corrosion resistance are improved,so that the surface quality and performance of the die-casting mold are greatly improved while obtaining good core performance.

  This type includes carburizing,nitriding,boronizing,carbonitriding,and sulfur-carbonitriding.

  The carburizing process is applied to cold,hot work and plastic mold surface strengthening to improve mold life.For example,3Cr2W8V steel die-casting mold,first carburized,then quenched at 1140~1150°C,tempered twice at 550°C,the surface hardness can reach HRC56~61,which improves the die life of die-casting non-ferrous metals and their alloys by 1.8~3.0 times..When carburizing is carried out,the main processes are solid powder carburizing,gas carburizing,vacuum carburizing,ion carburizing,and carbonitriding formed by adding nitrogen in a carburizing atmosphere.Among them,vacuum carburizing and ion carburizing are technologies developed in the past 20 years.The technology has the characteristics of fast percolation speed,uniform permeability,gentle carbon concentration gradient and small deformation of the workpiece,which will be on the mold surface,especially the precision mold.Surface treatment plays an increasingly important role.

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