Research On Inoculation Effects Of Heavy Section Ductile Iron Castings

More and more attentions have been paid to ductile iron by countries and regions, since it comes out. Compared with steel castings, ductile iron has a lot of advantages, such as simple production process, low cost and excellent wear-resistant. Therefore, it is widely used in every trade of national economy and gradually becomes the most important part in heavy industry. In recent years, the production of heavy section ductile iron casting gains a continuous increase to make overpressure resistant, wear resistant, heat resistant parts. Compared to general ductile iron, there are many defects in heavy section ductile iron such as inoculating recession, graphite deformation, graphite floatation, segregation, shrinkage. This has been a headache for the manufacturers.This research is about inoculation treatment effects of different inoculants to analyse the influence on inoculating attenuation time of the various elements in different inoculants and find the inoculating recession law of different inoculants. Based on the work above, this research will provide theoretical foundation to reveal the long and effective inoculating mechanism and improve the production stability of large and thick iron castings.This study selects widely-used75FeSi, Si-Ba-Ca and rare earths inoculants to set comparison groups and then prepare samples. The study is supplemented by procast casting simulation software application, and finally comes to a conclusion. The results show that under experimental conditions, the inoculating effect of Si-Ba-Ca inoculant is the best, then75FeSi inoculant and rare earths inoculant the worst. In the meantime, the study on various elements shows that Ba, Ca and Cr involved in Si-Ba-Ca inoculant increase ability of resistance to recession directly or indirectly to some extend. The elements Mn and RE could lower inoculants’melting point and delay inoculating recession effectively.This study also sets different ratio of CeO2-75FeSi new inoculants as comparison groups and prepare samples, mechanical test bars. The study is supplemented by SEM detection, and finally comes to a conclusion. The results show that under the experimental conditions, the inoculating effects of the same thickness castings change similarly. With the increase of CeO2content in the inoculants, the graphite sphere rates all increase and then decrease. The graphite sphere rate becomes largest in the20%castings. The test bars made by the thickest castings are ductile fractures. With the increase of CeO2content in the inoculants, the tensile strength increases and then decreases. The tensile strength becomes largest in the20%castings by9%increase to the75FeSi group. When the counts are at0-30%, the elongations don’t have big changes, but significantly improve at40%. Under experimental conditions, CeO2lowers eutectic temperature. The supercooling degree decreases and then increases, but a positive correlation relationship between eutectic solidification time and the CeO2content. When the CeO2content is20%, the eutectic temperature is the highest and eutectic time is the largest, which delays inoculating recession effectively.