Research On Injection Process For Vermicular Graphite Cast Iron

Vermicular graphite cast iron has a unique excellent performance,which was greatly used in supercharged diesel engine cylinder block, cylinder head and railway locomotive brake, and it is one of the direction of the cast iron material development. In recent years,vermicular cast iron obtained fast development, the production process has been improved.This study combined with the experience of the injection method and the advantages of the pour-over process, one vermicularing method in the injection process was summarized.Passivation of Magnesium and Rare-earth magnesium ferrosilicon alloy was choosed as vermicularizing alloys, the two different kinds of proportion of vermicularizing alloys influence on graphite morphology was analyzed; The content of Mg element, inoculation effect and the casting wall thickness influence on vermicular graphite rate, the temperature of liquid iron influence on magnesium absorption rate was explored, reasonable parameters was put forward for injection vermicularizing process;The difference of the two-dimensional shape was observed by Inverted metallurgical microscope between flake graphite, vermicular graphite and spheroidal graphite,Vermicular cast iron was deep-etched, using FESEM to observe the three-dimensional morphology of vermicular graphite; The microstructure and properties of vermicular cast iron treated by injection and pour-over process were studied, including vermicular stability, graphite morphology, vermicular graphite rate, pearlite content and mechanical properties, etc.It was found that good vermicularizing effect can be achieved by injecting passivation of granular magnesium and small amount of rare earth alloys, the addition of rare earth alloys can be greatly reduced and the cost can be reduced. The vermicular graphite rate is related to the casting thickness, with the increase of casting wall thickness,the vermicularizing rate showed a trend of increase, the faster the cooling rate of castings,the easier it is to promote the formation of spheroidal graphite. It has been proved that the vermicular cast iron treated by injection process is relatively stable with better vermicular graphite morphology and uniform distribution of graphite, and the vermicular graphite rate was higher, the castings presented good mechanical properties, RuT350 brand requirements can be achieved; Injection method is in a relatively closed package to deal with liquid iron, in terms of the pour-over process, the air pollution was reduced; It is one of the effective methods to obtain high vermicular graphite rate.