A Study On Electric Furnace Smelting Process And Casting Defect Control For Heavy Section Ductile Iron Castings

Lower nodulizing grade,unstable mechanical properties,surface slag inclusion and shrinkage cavity defects are often seen in heavy section ductile iron castings production,which is serious disadvantages for product quality.In this paper,boring machine ram ductile iron was considered as the research object,production test and microstructure analysis were done in order to improve the quality of casting products,the system research of graphite iron casting were conducted,such as chemical composition design,raw materials,melting,pretreatment,spheroidization and inoculation,pouring,common defects,the control strategy and actual effect,etc.The research results have very important realistic meaning to improve the quality of casting products.Some key technology were studied,such as chemical composition of heavy section ductile iron castings in the production of electric furnace smelting process,raw materials for pig iron,scrap steel and carburant,some measures on prolong the service life of furnace lining,smelting,pretreatment,spheroidization and inoculation,pouring,etc.Chemical composition,parameters and technical essentials were recommended for large section boring machine ram ball casting production;The casting surface slag inclusion,shrinkage cavity defects were studied by SEM and energy spectrum analysis according to iron product quality requirements,defect control countermeasures are discussed based on the analysis on the formation mechanism of casting defects,two sets of production plan were provided for large section boring machine ram ball casting production,such as YFY-1A and SiRE stream instantaneous inoculation,production effect of castings was further tracked,some analysis were done for actual control,correspondence relationship between chemical composition of molten iron,graphite crystal core and mechanical properties in the different stage of the production process,and the spot defects characteristics.SEM and energy spectrum analysis were done,and the results showed that the shrinkage defect,such as surface of the casting,slag inclusion and shrinkage,were formed because graphitization expansion was not enough to compensate the liquid and solidification shrinkage;The production test confirm that under YFY-1A stream instantaneous inoculation,small shrinkage hole and shrinkage are seen in production castings;while SiRE stream instantaneous inoculation,shrinkage hole is eliminated,and shrinkage is reduced;reject rate of casting is decreased for two sets of plans,product quality is greatly enhanced for heavy section ductile iron ram casting of the company.Under YFY-1A stream instantaneous inoculation,waste casting defects are serious shrinkage and more shrinkage hole,while SiRE stream instantaneous inoculation,waste casting defects are the inclusions of spheroidization and inoculation.Shrinkage of SiRE stream inoculation production is eliminated,some factors plays a leading role,such as reasonable improvement of casting structure,the gating system,riser and cold iron,casting waste of YFY-1A stream inoculation are caused by the unreasonable material control in addition to the actual control of casting structure and process design.SiRE stream inoculation solution casting is better than YFY-1A,it is important for graphitizing expansion,reasonable improvement of the casting structure combined with scientific design of the riser and cold iron,etc.