The Research Of Pre-treatment And Inoculation Processes In Strengthening Spheroidal Graphite Iron

Due to the slow solidification process of heavy section ductile iron, the graphitedegeneration, especially the chunky graphite often appeared in the center part of the casting,which lowers the mechanical properties of the casting greatly. In the past40years, scientistsand producers around the world has given this problem much attention, and made a greatprogress in realizing and resolving the problem. But until now, the reason and mechanism forthe formation of chunky graphite are still unavailable. The related researches on this issue arestill in process.This paper firstly designed and made a1500-300solidification simulating testingmachine to simulate the cooling process of heavy section ductile iron. With the reference of aheavy section ductile iron casting (size: Φ590×800mm) made in a foundry factory, this testingmachine was used in some research about the solidification, microstructure and mechanicalproperties of ductile iron castings, as well as the reason for the formation of chunky graphite.The effects of minor elements Sb and rare earth La addition was studied, and the influence ofthe selected inoculants compounds, which was added in the casting through an in-streaminoculation way, was studied. The results were as follows:(1) It was easy and safe to use the1500-300solidification simulating testing machine.The testing machine was multi-functional and smart enough to be used in several kinds ofoccasions. The cooling curve of simulating casting controled by the furnace was similar to thereal cooling curve of the casting Φ590×800mm. The maximal comparative error between thetwo curves was2.1%. The results showed that it was effective in simulating the solidificationprocess of heavy section casting by this furnace.(2) The minor elements Sb and rare earth La were effective in improving themorphology of the graphite in the simulation castings, and the specimen with0.1wt%La and0.03%Sb addtion was better than the others, and the tensile strength and elongation were448.8MPa and8.6%respectively, which were11.5%and19.4%higher than that of simulationcasting without additional elements. When0.1wt%La and0.05%Sb were added, the morphology of graphite and mechnical properties of the simulation casting decreased, and thetensile strength and elongation were420.4MPa and7.5%respectively, which were still betterthan the one without additional elements.(3) The morphology of graphite and mechanical properties of the in-stream inoculatedspecimen were all better than the original one.8#specimen, with0.2%CeO2treated, was thebest among all the others, and the tensile strength, elongation and hardness were543.5MPa,4%and229HW, respectively, which were6.5%14.3%and9.5%higher than the original one.(4) Compouds inoculation with CeO2or BaO addition can improve the graphitemorphology made the simulated casting better in mechanical properties. But the effects werenot so obvious as it was awys hard for this kind of substances to get dissolved in the matrixcasting.