|Lead brasses are used for their high machinability and atmospheric corrosion resistance. The machinability of brass is increased by the addition of lead because it acts as a microscopic chip breaker and tool lubricant. The leaded brasses are used for copper base screw machine material. The alloys have excellent machinability, good strength and corrosion resistance. Lead can be added to any brass to increase machinability and provide pressure tightness by sealing the shrinkage pores. There are low, medium and high leaded brasses, with lead contents up to 3.5%.|
|The lead brasses are used for architectural hardware, general purpose screw machine parts, screws, valves, fittings, bearings and specialty fasteners. The wrought lead brasses are designated by UNS C31200 through C38500. The cast lead brasses are grouped with their unleaded counter parts, and fall in the range of alloys between C83600 through C97300.
The microstructure of the leaded brasses is similar to that of the unleaded brasses. The microstructure of the leaded brasses contain discrete lead particles primarily in the grain boundaries or inter-dendritic regions. Lead is practically insoluble in solid copper and is present in the cast and wrought materials as discrete particles that appear dark in the structure. The microstructure of the as cast lead brasses is a function of the zinc content. The lower zinc containing alloys are single phase solid solution alpha dendrites, with lead particles dispersed throughout the interdendritic regions. Those with a higher zinc content have a two phase structure, consisting of alpha and beta. The higher zinc containing alloys have a microstructure of all beta. The lead appears as discrete particles, appearing dark in the microstructure. The microstructure of the wrought low zinc leaded brasses consists of twinned grains of alpha with lead particles throughout the matrix. The higher zinc containing alloys contain a mixture of alpha and beta phases and lead particles.