Abstract
The influence of the zinc sulfide ratio in the sulfide particle in the lead free bronze castings on the machinability is studied. Also, the influence of alloying elements of the zinc sulfide ratio of the sulfide particle is studied for understanding the mechanism of the zinc sulfide formation during the solidification. The zinc sulfide ratio is evaluated with the analysis of the microstructure in the lead free bronze prepared by the sand mold casting. The condition in which the zinc sulfide stably exists during the solidification is estimated with thermodynamic calculation. The machinability is improved with the decrement of the zinc sulfide ratio. The sulfide is formed as the copper sulfide and the zinc sulfide through eutectic reaction, and also appears as the liquid phase through monotectic reaction. The zinc sulfide is formed with the copper sulfide at the temperature, at which the zinc sulfide was predicted to be unstable by the thermodynamic calculation. The ratio of the zinc sulfide increases with increasing zinc content. Tin does not affect the zinc sulfide ratio when the tin content is less than about 4 mass%. There is no effect of nickel on the zinc sulfide ratio.
