铝元素抑制超高碳钢中网状碳化物析出机理

借助相图计算、能谱分析及组织观察研究了铝元素对超高碳钢中网状碳化物析出过程的影响,含碳1．5wt％的超高碳钢添加不同含量的铝后显著影响网状碳化物的析出：随铝含量增加,奥氏体晶粒尺寸愈小、晶界愈多,导致网状碳化物减薄;未溶碳化物愈多、奥氏体固溶碳含量愈少,导致网状碳化物析出量减少;晶界聚集铝量增加,聚集的铝抑制碳化物的形核及长大。当铝含量接近2．0wt％时,网状碳化物出现断续,甚至有的晶界没有碳化物析出,在球化过程中,该网状碳化物很容易球化。     

Role of defects on microstructure development of beta titanium alloys

Microstructures of α precipitation from a deformed β matrix by thermomechanical processing were studied in a representative β titanium alloy, i.e. Ti-15V-3Cr-3Sn-3Al alloy. In the aged specimens, after solution treatment, the grain boundary is the most preferential nucleation site in the a precipitation. Localized slip occurs in the β matrix by cold rolling after solution treatment whereas (332)<113> deformation twins are formed by subzero rolling at 77 K. After subsequent aging of the rolled specimens, the α phase preferentially forms on those defects in the β matrix with a low energy orientation relationship (Burgers relationship). There is strong variant restriction in heterogeneous nucleation on such defects. Controlled short time annealing above the β transus (β recovery treatment) after cold rolling produces the fine β subgrain. By subsequent aging, α precipitates form preferentially on β subgrain boundaries and also within β subgrains. A great number of α variants are observed locally in the recovered and aged specimens than those in the cold rolled and aged specimens. β recovery treatment prior to aging improves the strength-ductility balance mostly because of the increase of local elongation.