There are two kinds of lead free free-cutting brass developed. One is bismuth substituted free-cutting brass, and the other is hard phase dispersed one. In the former case, machinability of bismuth substituted one is inferior to leaded free-cutting brass because of the difference of wettability between bismuth and lead. So these developed alloys are improved by the addition of a few components such as tin and/or rare earth metals, and by the control of dispersing bismuth particle by productive conditions. However total machinery index of these alloys are inferior to leaded free-cutting brass because of the difference of lubricant between bismuth and lead. Furthermore there exists the significant problem that bismuth is rare on mine. In the latter case, intermetallic compounds which are formed by addition of silicon, tin and aluminum play roll as tip breaker. These additive materials are comparatively easy to gain. However these alloys make cutting force higher than leaded free-cutting brass, so it is suggested to select the suitable cutting tool.
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