难变形材料环件双向辗轧过程轧制曲线设计方法

Design Method of Rolling Curve During Radial-axial Ring Rolling Process for Difficult-to-deform Materials

轧制曲线描述了环件双向辗轧过程中径向与轴向变形量的瞬时分配关系,决定了变形过程的历史和轧辊路径,因而对轧制环件的几何精度、特别是微观组织具有重要影响作用,对钛合金和铸坯等难变形材料的环件辗轧成形更是如此。提出一种环件双向辗轧过程轧制曲线的设计方法,该方法只要给定环件及环坯尺寸,便可设计'上凸形'、'直线形'和'下凹形'三类轧制曲线。以某TC4钛合金环件双向辗轧为研究对象,采用有限元建模仿真方法,揭示上述三类轧制曲线对环件圆度及组织(?相晶粒尺寸及体积分数)均匀性的影响规律。结果表明,相对于'直线形'轧制曲线,'下凹形'轧制曲线有利于提高环件圆度,而'上凸形'轧制曲线有利于提高环件的组织均匀性。为了同时发挥'下凹形'和'上凸形'轧制曲线的优势,提出并设计一种'S形'轧制曲线,可获得同时具有较高形状尺寸精度与良好组织均匀性的TC4钛合金环件。

The rolling curve, which is defined as the instantaneous relationship between the radial and axial deformation degrees during the radial-axial ring rolling（RARR） process thus determines the deformation history and roll paths, plays an important role in the geometry precision and microstructure of the rolled ring, especially for rolling of difficult-to-deform materials such as titanium alloy and as-cast billet. A design method of rolling curves for radial-axial ring rolling process is proposed. The method can be used to design three kinds of rolling curves, namely the convex, linear and concave ones, for known sizes of ring product and ring blank. And then the effects of different rolling curves on the circularity and microstructure （mainly including α phase volume fraction and grain size） uniformity of the rolled TC4 titanium alloy ring by finite element（FE） simulations are numerically revealed. The results show that：Compared with the linear rolling curve, the concave rolling curve contributes to increasing the circularity of the rolled ring;and the convex rolling curve contributes to improving the microstructure uniformity. So in order to combine the advantages of the concave and convex rolling curves, An “S” form rolling curve is designed which is helpful to obtain TC4 titanium alloy ring simultaneously having precise dimensions and favorable microstructure uniformity.