1989 年 38 巻 430 号 p. 765-770
The superplastic behavior was investigated for 60/40 brass and free cutting brass containing 3% lead. The former alloy was cut off from a large ingot and was grain refined by the low temperature extrusion process after β quenching. The latter alloy was extruded at a low temperature from a 50mm diameter rod on market. Tensile specimens of 8mm diameter and 30mm gauge-length were machined, and tensile tests were carried out between 500-750°C at the initial strain rates from 2.78×10-4 to 2.78×10-2S-1.
The following results were obtained:
(1) A maximum neck-free total elongation of 640% for 60/40 brass was obtained at 675°C and the strain rate of 2.78×10-4S-1.
(2) The volume of cavities increased as the true strain increased, while at the same true strain, the volume of cavities at a small strain rate was smaller than that at a large strain rate for 60/40 brass.
(3) The strain enchanced grain growth of α and β phases showed a small increase with increment of true strain at 675°C and 2.22×10-3S-1, but that of soft β phase was considerably larger than that of α phase at 675°C and 5.56×10-4S-1 for 60/40 brass.
(4) By refining grain size, superplasticity was recognized even in free cutting brass which has low Pb content and thus essentially shows low ductility at high temperatures.