关于Cu—Zn—Al贝氏体相变的阶段性──Ⅰ．TTT图

On Mechanism Underlying Pure Bainitic Transformation

从理论上证明了相变过程中形成混合产物的可能性．通过测定Ｃｕ－Ｚｎ－Ａｌ合金ＴＴＴ图，讨论了贝氏体相变阶段性并定义了贝氏体相变阶段．

In 1967, Flewitt proposed the concept of mised-product zone of the bainitic transformation of CU-Zn alloyf[1]. But up to now, to the authors' best knowledge. neither Flewitt nor anyone else succeeded in explaining the mechanism underlying the mixed-product zone and then defining the stage in which the single-phase bainitic transformation occurs.The authors now present their two findings:(1) Mechanism underlying the mixed-product zone. The authors, theoretical analysis indicates that the transformation of any phase product follows its own peculiar C-curve and that when tWo C-curves intersect, mixed product zone appears. In experimentally determined TTT diagram of Cu-Zn (26.84wt.%)-Al(4.22wt.%) alloy, the C-curves of the bainite α1 (plate-like, 9R structure) and the equilibrim phase α (rod-like, fee structure) intersect at the bay temperature (Fig3). Fig.3 of this paper is clearly different from the corresponding TTT diagram in Ref[1] in that the lower C curve corresponding to al does not show a cutoff at the temperature (bay) of intersecting point of the tWo C-curves, i.e., the transition temperature, Bs. varies with transformation time even at a temperature higher than buy temperature.Therefore, the existence of the mixed product zone is inevitable in the process ofbainitic transformation.(2) Definition of stage of pure bainitic transformation. From the explanation jUst explained in (1), it naturally follows that the needed definition is: pure bainitic transformation for Cu-Zn (26.84wt%)-Al(4.22wt%) alloy occurs only when the point representing temperature and tim e falls within area P of Fig.3.