Research And Preparation Of Cementite Magnetic Powder

As one common phase in the Fe-C alloy, cementite has distinctive mechanical properties and intriguing, optical, electrical, acoustic, thermal, magnetic features, etc. Owing to their meritorious properties, cementite has a wide range of application, such as wave-absorbing material, magnetic recording materials, catalysts and medical carriers and receives much attention around the world. Therefore, how to prepared cementite with a simple and economical method tends to be an increasingly important problem which is worth being intensively investigated.Currently, the preparation of Fe3C mainly involves gas reduction, CO2laser pyrolysis, carburizing, arc pyrolysis, high-temperature powder metallurgy, etc. Some of these methods have relatively high requirements on equipment and operator. Or the conditions of the reaction are relatively harsh. Or by-products will be produced. In this paper, a novel method of preparing Fe3C has been explored by observing the formation of cementite in carbon steel and cast iron. In the research it has been found that carbide (usually as Fe3C) in carbon steel and cast iron could be extracted by corrosion. The detailed contents are as follows:(1) The ductile iron firstly has been rapidly cooled with a single roller melt spinning apparatus (rotate speed of the roller is800r/min or1000r/min), and then be corroded with HCl. The results show that rotation speed of the roller has no obvious effect on the results and both samples with high purity have several morphologies (porous, flake, dendritic, etc.). And it is also found that the remanent magnetization and coercive force of the samples equal to zero which is similar to the paramagnetic-like behavior called superparamagnetic.(2) The T12A carbon tool steel has undergone heat treatment with different spheroidization processing and then the mechanism of spheroidization has been explored. The results show that the best processing is that the sample successively undergoes normalizing at950℃for60min, heat preservation at760℃for30min, furnace cooling to690℃and heat preservation for90min. The key to the formation of a ball is that when the materials heating to austenitization. there are sufficient cementite core and in heat preservation at690℃, the cementite cores have enough time to grow up. (3) Corrode the samples which were spheroidization processing in step (2) with HCl. The research has shown that there are several types of carbide in the powder but mainly in the form of cementite. And it is obviously found that other cementite particles have the trend to form a ball except some globular cementite particles. The size of the particles is small and the average size is about200nm.The output and purity of cementite are not very ideal because of the limit of carbon content of raw materials and formation of carbon. In the future, use the white cast iron (high carbon content and the formation of carbon is cementite) as raw materials in order to enhance the output and purity of cementite.