In order to reveal the mechanism and condition of void closure in large diameter steel rod during horizontalvertical(H-V)groove rolling process,a three-dimensional thermomechanically coupled finite element model was established for 9-stand H-V groove rolling process aiming at a150mm steel rod production line.A spherical hole with diameter from 2to 10mm was preset into the center of continuous casting billet with a rectangle cross section of300mm×360mm 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 results 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 horizontal and vertical on the exit cross section according to change of the reduction direction in H-V groove.The void closure behavior during HV rolling was more complicated than that of common horizontal rolling,and the influence of groove type and the extension coefficient on the void closure ratio was presented.Finally,apilot 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 agreement with the numerical simulation results. In order to reveal the mechanism and condition of void closure in large diameter steel rod during horizontal (hg) groove rolling process, a three-dimensional thermomechanically coupled finite element model was established for 9-stand HV groove rolling process aiming at a150 mm steel rod production line. A spherical hole with diameter from 2to 10mm was preset into the center of continuous casting billet with a rectangle cross section of 300mm × 360mm in this model to simulate the void defect, and then finite element analyzes were carried out to observe and quantify the void shape evolution in each pass on the three orthogonal coordinate plane sections. The results 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 horizontal and vertical on the exit cross section according to change of the reduction direction in HV groove. void closure behavior during HV rolling was more complicated than that of common horizontal rolling, and the influence of groove type and the extension coefficient on the void closure ratio was presented. Finally, apilot rolling experiment was performed on a 5-stand HV experimental mill to verify the numerical simulation results, and the experimental results are in good agreement with the numerical simulation results.