錫青銅の恒温過冷変態

抄録

The isothermal transformation for 22,23.5,25,26 and 28%Sn-Cu alloys were tested microscopically and the isothermal transformation diagrams were obtained as shown in Fig. 2. The processes of eutectoid transformation in alloy of hypo-eutectoid composition were upper-bainitic at the temperatures above 350° and lower-bainitic at the temperatures below 350°. The martenstic structures appeared below 150° and 100° in 22 and 23.5%Sn alloys, respectively. In 25 and 26%Sn alloys the martenstic structures were obtained by immersing them in liquid oxygen. The processes of eutectoid transformation in alloys of hyper-eutectoid composition, which are pearlitic, being accompanied by pro-eutectoid precipitation of δ at the temperatures not far below the eutectoid temperature,could not be examined sufficiently because the transformation was very rapid and the sample was not etched uniformly.
The changes in structure on tempering of quenched alloys were also tested microscopically. When the tempering temperatures were below 300° distinct precipitations were not recognized and only retained β and became sensitive to etching, but when the tempering temperatures were above 350° δ precipitated from α_m(=β′) and retained β.
Above results could be explained favorably on the basis of meta-stable diagram shown in Fig. 1.