Preparation of lead-free free-cutting graphite brasses bygraphitization of cementite
(School of Materials Science and Engineering, Nanchang University, Nanchang 330031, China)
Abstract: Graphite brasses were prepared by graphitizing annealing of cast brasses containing cementite particles, which were in-situ formed during the fasting process. The eutectic cast iron as carbon source was added into common brasses by casting. SEM and EDS were used to analyze the microstructure of graphite brasses, and the relationship between the microstructure and machinability was investigated. The results show that graphite particles are formed by the decomposition of cementite particles in cast brasses. The graphite particles are uniformly dispersed in the brass matrix with the average size of 5.0 μm and the volume fraction of ~1.1%. The machinability in the graphite brass is dramatically increased relative to the common brass, because of the lubricating properties of graphite particles and its role in chip breaking. The workpiece surface of the graphite brasses chips is smooth and burr-free, and the chips of graphite brasses are short (C-shape) and discontinuous, which is much better than that of the long spiral chips of common brasses.
Key words: lead-free graphite brass; graphitization annealing; microstructure; machinability