Improvement of Ductility in an Intermetallic Compound

Fe-6.5mass%Si合金具有优良的Transformer性能。然而，由于它的低延展性，我们不能用通常的冷轧来制造薄板。本研究旨在改善合金的塑性。主要研究结果如下：1.订单结构：在Fe-Si合金中，通过常规热处理程序获得的有序相与热等轴相图中报道的有序相不同，B2有序相的范围向高Si含量方向扩展。在6.5%Si合金中，B2结构在800 K左右是稳定的，然后转变为无序相.屈服应力的温度依赖性：6.5%Si合金的屈服应力-温度曲线在600 K处有一峰值。此峰归属于DO_3B_2转化。然而，相变实际上并不发生在峰值温度下;需要进一步的研究来阐明峰值的起源。韧脆转变：6.5%Si合金在低于约600 K时以脆性方式断裂（区域B），而在高于该温度时变形而不开裂（区域D）。在韧性区，当试样在低应变率下拉伸时，断裂面包含解理刻面（D和B的混合区）。随着应变速率的增加，B区和D区之间的边界向低温方向移动。这表明我们可以在较低的温度下以足够高的变形速率成功地轧制6.5%Si合金。轧制：合金在较低的轧制速度下开裂，但在较高的轧制速度下可以轧制而不开裂。这一事实证明了上述的期望。如果轧制速度足够高，合金的加工温度可低至473 K。

Fe-6.5mass%Si has excellent properties as a transformer sheet. Because of its low ductility, however, we cannot make thin sheet by usual cold rolling. This study aimed at improving ductility of the alloy. Results are summarized as follows:1. Order structure : In the Fe-Si alloys, ordered phases obtained by usual heat treatment procedures are different from those reported in the thermally equiribrium phase diagrams; The range of B2 ordered phase extends toward higher Si Content. In the 6.5%Si alloy, the B2 structure is stable up to about 800K and then transforms to the disorder phase above the temperature.2. Temperature dependence of yield stress : The yield stress vs. temperature curve of the 6.5%Si alloy has a peak at 600K. This peak has been attributed to DO_3 B2 transformation. However, the transformation does not actually take place at the peak temperature; A further investigation is needed to elucidate the origin of the peak.3. Ductile-brittle transition : The 6.5%Si alloy fractures in a brittle manner below about 600K (region B), whereas it deforms without cracking above the temperature (region D). In the ductile region, when specimens are stretched at low strain rates, fracture surfaces contain cleavage facets (mixed region of D and B). The boundary between regions B and D moves toward lower temperature as strain rate increases. This suggests that we may successfully roll down the 6.5%Si alloy at a sufficiently high deformation rate at a lower temperature.4. Rolling : The alloy cracked at lower rolling speeds, but it could be rolled down without cracking at higher rolling speeds. This fact proves the expectation mentioned above. The alloy was workable down to 473K if rolling speed is sufficiently high.