Production Process And Application Of New Type Of High-quality Nodularizer

Ductile cast iron is one of the most widely used metal materials in modern industry. It is becoming more and more widespread because of its high tensile strength and elongation and good resistance to fatigue and casting properties and lower cost of production. Ductile cast iron devotes itself to a broader prospect. As the main means of obtaining ductile cast iron, spheroidizing treatment is achieved by nodularizer. Spheroidizing treatment makes graphite into the ball shape and effectively improves the comprehensive mechanical properties of ductile cast iron.At present the most widely used nodularizer is rare earth magnesium alloy in domestic which has the problems including:oxidation of Mg in nodularizer pouring process, the effective content of Mg in nodularizer need to improve,the density of nodularizer is unstable; the burning loss of Mg is serious in spheroidizing; the burning of Mg produces a lot of white smoke and pollutes the environment, the addition of nodularizer is large. Facing with the above problems, to make nodularizer has stable and high quality, reduce production cost and achieve energy conservation and emissions reduction, achieve the reduction of environmental pollution is the target of nodularizer currently.In this study, we develop pressurized and iron coated high-quality nodularizer respectively by the process improvement such as design of gating system and melt temperature. The spheroidizing effect will be summarized and analyzed by the change of nodularizer types. At the same time, we will study the effect of high-quality nodularizer on chemical composition and microstructure and mechanical properties of ductile cast iron, so as the effect of nodularizer addition.Research results show that because of the design of the mould cover the pressurized nodularizer has the compact structure, defect reduction and quality improvement as the nodularizer is pressed by high temperature in the mould system when cooling. And it will decrease melt temperature to about1250℃on the premise of high quality which will decrease the burning loss of Mg and benefit to the environment. The process of iron coated nodularizer includes the design of gating system and pouring temperature at1250℃, galvanized pipe length25cm to2x3arrangement, which could obtain iron coated nodularizer with high density.The high-quality nodularizer (pressured and iron coated) compared with the ordinary nodularizer increases the content of Mg while reduce MgO content and MgO/Mg. Its compactness is also increased to some degree. The composition of nodularizer is the rich Si phase (Si-Fe phase) which constitutes matrix structure and rich Mg phase (Mg-Si-Ca phase) which is located in the rich Si phase clearance. The shape of rich Mg phase affects the performance of nodularizer as rich Mg phase with discontinuous form can produce a large number of tiny Mg bubbles during spheroidizing treatment, which is helpful for absorption of magnesium and spheroidizing effect.The spheroidizing time of same size and addition of ordinary nodularizer and pressured nodularizer is within the normal range of70-80s. The40×20×1.5iron coated nodularizer is significantly prolonged the spheroidizing time, as a result of the coated iron has the effect of passivation magnesium and decrease the nodularizer rising speed, make the spheroidizing stably to fully absorbed nodularizer and raise the residual amount of Mg.As with the microstructure and mechanical properties analysis, the graphite distribution of ordinary nodularizer and pressurized nodularizer and40×20×1.5iron coated nodularizer is uniform and spheroidization rate is over85%with level3of nodulizing grade. Their tensile strength and elongation are meet quality standards while apparent necking fracture a number of toughening nest could be observed easily that belongs to the ductile fracture. When under tensile force, the graphite and matrix which belongs to the weak link form the cavity and tiny cracks with expanding lead to fracture.Compared with different addition of different nodularizer we find that ordinary nodularizer and pressurized nodularizer and40x20x1.5iron coated nodularizer the addition of best distribution of graphite morphology and mechanical properties is 1.2%(ordinary),1.1%(pressured) and1.0%and1.1%(iron coated), which is consistent with spheroidization rate and nodulizing grade.The results shows that under the premise of good quality, the addition of pressured nodularizer could be reduce to1.1%, which could effectively reduce the production cost. The cost of iron coated nodularizer can also be reduced by15%while ferrosilicon powder and plant ash is not necessary. So high-quality nodularizer can improve the utilization rate of effective elements and save natural resources and in achieving higher economic and social benefits.