Research On The Preparation And Properties Of Lead-free Free-cutting Graphite-brass

Lead brasses are widely used because of excellent cutting performance and low price. However, the lead overflow during lead brass application lead to the environment pollution and health problems. Hence, developing the nonlead free-cutting brass has became a difficult problem to overcome urgently. The purpose of this paper is to prepare a lead-free free-cutting graphite-brass uniform dispersed with graphite particles by the graphitization of cementite.This paper use graphite as a substitute of Pb by adding iron powder instead of direct addition of graphite powder and using graphitizing annealing process to prepare lead-free free-cutting brass. In order to study the influence of graphite brass with different eutectic cast iron on microstructures and properties, the composition, microstructure, mechanical properties, cutting performance and corrosion resistance were tested and analysed. The conclusions are as followings:(1) Cast iron will be added into brasses as carbon source by melting and graphite-brass will be made by the liquid phase in-situ formation of cementie particles during casting and the graphitization of cementite particles during annealing in the applying project. During melting, cementite will be priority nucleate under high cooling speed, brass melt depend core to nucleation and growth. Cementite particles distributed and distributed in the α phase(Cu0.64Zn0.36), β phase(CuZn) and grain boundaries. During annealing, cementite occur the graphitized phenomenon in brass matrix. Cementite particles convert into graphite particles completely due to the plastic deformation process. On the other hand, the position and the size of graphite particles are decided by cementite particles under annealing. Hence, dispersion of graphite partilces and α phase(Cu0.64Zn0.36) and β phase(Cu Zn) can be obtained.(2) The tensile strength and microhardness are increased and the cutting performance are improved, but the plasticity are decreased gradually with the cast iron content increased from 1% to 7%. While adding 7% cast iron, the cutting performance are degraded. The improvement of cutting performance due to the uniform dispersion of graphite particles. Graphite particles are equivalent to small region in brass matrix that cause the notch effect by cutting off the continuity of the matrix. The existence of these regions make cutting process to be easier. In addition, graphite is easier to achieve a smooth surface as a good lubricant due to forming a layer of graphene in tool and metal surface.(3) The corrosion resistance property of graphite brasses are increased with the cast iron content increased from 1% to 5%, but decreased with the content of 7% cast iron. The corrosion resistance property of graphite-brass is a result of joint action by microstructure, the component and the distribution of graphite particles.(4) The tensile strength, elongation, Vickershardness and dezincification depth of graphite-brass added with 5% eutectic cast iron are 502 MPa, 22.6%, 148.9 HV and 144.2 μm, respectively. The chips are desired. The sample’s surface smoothness is relatively high after machining. The mechanical properties, cutting performance and corrosion performance of the graphite-brass are the best, that are far superior to bare brass. So it is feasible that the graphite-brass replaces leaded brass.