Void Closure Behavior in Large Diameter Steel Rod during H-V Rolling Process

In order to reveal the mechanism and condition of void closure in large diameter steel rod during horizontal- vertical （H-V） groove rolling process, a three-dimensional thermomechanicaily coupled finite element model was es- tablished for 9-stand H-V groove rolling process aiming at a 4150 mm steel rod production line. A spherical hole with diameter from 2 to 10 mm was preset into the center of continuous casting billet with a rectangle cross section of 300 mmX 360 mm in this model to simulate the void defect, and then finite element analyses were carried out to observe and quantify the void shape evolution in each pass on the three orthogonal coordinate plane sections. The re- suits showed that the void was formed roughly in the reduction and extension directions, and crushed gradually from spherical shape to an approximate ellipsoid, micro-crack and finally to be closed. A quantitative analysis was carried out by using elliptic radii and closure ratio to describe this evolution process; it indicated that the longest axis of the ellipsoid coincided with the rolling line, and the second and third axes were alternatively ihorizontal and vertical on the exit cross section according to change of the reduction direction in H-V groove. The void closure behavior during H- V rolling was more complicated than that of common horizontal rolling, and the influence of groove type and the ex- tension coefficient on the void closure ratio was presented. Finally, a pilot rolling experiment was performed on a 5- stand H-V experimental mill to verify the numerical simulation results, and the experimental results are in good agree- ment with the numerical simulation results.

花键轴增量式滚轧成形坯料直径计算及有限元分析

根据塑性成形体积不变原则,提出一种新型的花键轴增量式滚轧成形坯料直径的计算公式,该公式计算简单且相对误差小于0.1%。其主要思想为:初步计算单齿圆周角范围内的齿形面积,进一步根据分度圆半径与中线圆半径的比较结果进行补偿,从而获得精确的单齿面积、花键轴及其坯料的截面积。此外,对该计算公式进行了不同坯料直径下的花键轴增量式滚轧成形有限元分析验证,结果表明,由该计算公式获得的坯料直径符合工艺要求,成形的花键轴齿廓清晰、齿形填充饱满。