Casting Structure, Mechanical Properties and Machinability with Changes in Amount of Alloyed Elements of Sulfide Dispersed Lead Free Bronze Castings

Sulfide dispersed lead-free bronze does not contain rare metals such as bismuth (Bi) or selenium (Se). There alloys produce smaller amount of porosities and have excellent castability characteristics. The sulfide has solid lubrication properties and functions as a chip breaker. This report summarizes how the alloy structure affects the cast structure, mechanical properties and machinability, and discusses the pressure resistance properties of the alloys. Furthermore, the alloy composition for JIS application was also determined based on the present results. It was concluded that (1) when the amount of Zn exceeds 4mass%, the sulfide profile collapses, the amount of ZnS increases and elongation lowers, (2) when the amount of S becomes 0.7mass% or higher, a hyper-monotectic structure is produced and, the liquid phase L2 is separated from the liquid phase L1, causing large sulfides to appear, after which the mechanical properties deteriorate, (3) the composition ranges for JIS applications of sulfide dispersed lead free bronze are determined to be 3.0mass% to 5.0mass% for Sn, 1.0mass% to 3.0mass% for Zn, 0.1mass% to 1.0mass% for Ni, and 0.2mass% to 0.6mass% for S, and (4) the investigation verified that the cutting coefficient, fluidity and pressure resistance capacity, the JIS application alloys are equivalent to those of the JIS CAC406 alloy.