Dissertation > Industrial Technology > Metallurgy and Metal Craft > Casting > Casting of raw materials and preparation

Contrast and Development of Compound Inoculants for Gray Cast Iron That Respectively Fit for Cupola and Induction Furnace

Author WangShouHui
Tutor YuHuaShun
School Shandong University
Course Materials Engineering
Keywords gray cast iron inoculants cupola induction furnace trace elements
Type Master's thesis
Year 2012
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Gray cast iron is one kind of the most widely used metallic materials in the world and it is also an important basis for machinery manufacturing industry. As a kind of structural material, gray cast iron has many good characteristics. For example, it is very resistant to heat, abrasion, impact, oxidation and it has a good performance of damping. What’s more, comparing with other alloys, gray cast iron has a low melting temperature and it is easy to process. And the production facility of gray cast iron is very simple, moreover, its price is very low. Inoculation is an essential part in the production process of gray cast iron, which aims to promote the nucleation of graphite, to reduce the chilling tendency, to promote the growth of graphite, to improve the graphite morphology and distribution and it also can thin the eutectic and matrix organization, moreover, it has the function of reducing the sensitivity of the cross section.The inoculants used in the production of gray cast iron are usually75SiFe, but the inoculation effect is very bad and in order to eliminate the free cementite, we have to increase the amount of inoculants. However, in order to control the final silicon content, we must reduce the silicon content of the original molten iron, which brings much difficulty to use the charge. If we use good inoculants, small quantities can achieve the same effect. What’s more, the silicon is increasing little, thereby reducing production costs.Sulfur and Oxygen are very important in the process of the nucleation of graphite. The two elements are combined with other elements in the molten iron and form sulfide and oxide which become the core of the graphite nucleation. The content of sulfur and oxygen in molten iron of cupola and induction furnace is different. The content of sulfur in cupola is higher than in induction furnace, while oxygen higher in induction furnace and lower in cupola. If we use75SiFe to perform inoculation in both cupola and induction furnace, the capability can’t be the best.In summary, by trial we developed two new inoculants that are separately suitable for cupola and induction furnace. The two new inoculants are both consisted of FeS, Fe2O3, CaSi and75SiFe. In order to ensure the percentage of every matter, we apply inoculants to molten iron in cupola and induction furnace and do orthogonal experiment with three factors and three levels. And through the range analysis of the results of orthogonal test and the follow-up experiments, finally we determined the best ratio of each component in the two inoculants. And then we continue to explore the impact of the two new inoculants on the micro structure an mechanical properties of gray cast iron.The result has showed that the inoculants that fits for the cupola are consisted of S5-6%、O1-3%、Ca10-14%、Si60-65%and the inoculants that fits for the induction furnace are consisted of S7%-8%、O0-1%, Ca5-8%、Si60-65%and the other components are75SiFe. The weight of the inoculants that add to the iron is0.2percent of the molten iron’s weight. When we add the corresponding inoculants to the gray cast iron of HT200in cupola, the morphology of the graphite is changing obviously and the distribution is more equably. When we add the corresponding inoculants to the gray cast of HT250in induction furnace, the graphite is mostly A-type graphite and the distribution is well-proportioned and eutectics have been refined. The mechanical properties of the castings have also been upgrading. When we add the corresponding inoculants to the cupola and the induction furnace, the tensile strength of the gray cast iron we get has been improved by%and%.In addition, two new inoculants are both helpful to the reducing of the sensitivity of the cross-section of the gray cast iron. What’s more, the organization is more equably which helps to improve the homogeneity of the mechanical properties of castings that have different thickness. With the addition of the new inoculants, as to the cupola, from the thick parts to the thin parts of the step sample, the hardness value has increased from168.7N/mm2to176.0N/mm2and compared with the castings without the new inoculants whose changes is from158.7.7N/mm2to182.0N/mm2, the range is small. This has showed that the section-sensitivity of gray cast iron is smaller when we add the new inoculants to the molten iron in cupola and it is helpful to manufacture the Heavy Variable Cross Section Gray Cast Iron. As to the induction furnace, from the thick parts to the thin parts of the step sample, the hardness value has increased from161.0N/mm2to178.3N/mm2and compared with the castings without the new inoculants whose changes is from150.0N/mm2to171.3N/mm2, we can see the range is small. This has showed that the two new inoculants that separately suits to cupola and induction furnace are both helpful to reduce the section-sensitivity.The two new inoculants can significantly reduce the usage amount of the traditional75SiFe, so the operating factor of the returns is improved. And this brings great economic and social benefits. The market prospect is very broad.

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