A New Practical The Development Of Low Carbon Equivalent Ductile Iron

The recarburing agent for induction furnace melting was introduced. It was explained that the suspending fine particles of graphite was favorable for the formation of the nuclei of graphite that would reduce supercooling and chilling tendency of the cast iron. The practice of using recarburation process to produce nodular iron with steel scrap could not only economize lots of high grade pig iron, but also the charge cost could be reduced effectively. However, there were not enough reports on the recarburing process, the recaruration effect was bad and not stabile. As a result, the research on the recarburation and its stability was very important on theory and application.Under the conditions of laboratory and production, the effect of recarburation process and the K/Na-RE compound modification on the structures and properties of ductile cast iron was investigated, and the optimum operating scheme of recarburation and modification was selected. By combining the recarburation process with K/Na-Re modification, a new type of practical low carbon ductile cast iron was successfully developed.The result showed that the recarburation process produced lots of dispersedly distributed nucleus that would the supercooling of the melt. The heredity effect of the pig iron was greatly reduced. Factors influence the recarburation were granularity of recarburing agents, recarburing temperature, stirring time and chemical composition. Recarburation treatment reduced size, distribution and morphology of graphite, fined the graphite, made it to distribute more uniformly. It could increase the pearlite amount obviously, short the interval of flakes, increase tensile strength and macro hardness, increased the elongation to quite high level, reduce chilling tendency, and improve section sensitivity obviously.The K/Na-RE compound modification purified the iron liquid and grain boundary, produced heterogeneity core for the graphite nucleation and made grown of the un-activated nucleus. It could increase the melt quality and nucleation state remarkably. K/Na-RE has an excellent effect of calcium on deoxidization, desulphurization and purification of the liquid steel as well as change of the inclusion shape. With the increase of K/Na-RE addition, the grain size is reduced, And the ductile cast iron has the best morphology and mechanical property with 1.0wt.% modifier. Further analysis shows that, the K/Na-RE compound modification increases the amount of ferrite, reduces the grain size. It weakened the harmful effect of P by preventing precipitation of iron phosphide eutectic. Consequently, the impact ductility and elongation of the ductile cast iron was greatly increased under a low content of C(3.0 w_b.%-3.2 w_b.%) and Si (2.4 w_b.%～2.6 w_b.%).The effect of the K/Na-RE modificator added into nodular cast iron that was produced by the recarburation process was investigated. The results indicate that K/Na-RE has an excellent effect on the recarburation process. As a result, the nodule amount has an obvious increase and the nodules became fine and homogeneous. The cooperation of two treatments improved the comprehensive mechanical properties of the ductile cast iron (such as the strength, hardness and toughness), and has already reached the QT800-6 level in as-cast condition.