鉛入黄銅中の鉛粒子の析出と粗大化

抄録

The machinability of leaded brass is well known to be affected by the microstructural properties of its matrix and microconstituents, particularly by the size and distribution of lead particles, and of course, by variation in machining conditions. The behavior of precipitation and coarsening of Pb particles during solidification and subsequent annealing of α- and β-single phase pure leaded brass was initially assessed by conventional metallographic methods. The size distribution was treated by a new statistical method. The results were later extended to α+β phase commercial leaded α+β brasses.
The size and distribution of Pb particles were quite different in the two types of brasses. In as-cast conditions, Pb particles in α-brass were much coarser and precipitated mainly on grain boundaries, while the distribution of Pb particles in β phase brass was relatively homogeneous and its size was much smaller.
The diffusion path and preferred nucleation sites of Pb atoms such as dislocations, sub-boundaries and grain boundaries were needed to the coarsening of Pb particles.
The solid solubility of Pb was likely to be larger in β-phase than in α-phase, and therefore, the distribution of Pb particles in β-phase was more homogeneous than in α-phase.
It was concluded that the size and distribution of Pb particles in commercial leaded brass are determined through the change in the grain structure of α and β phases.