Crushing and diffusion welding are two critical healing stages of interior void defects in heavy forgings.The healing result depends on many factors during the forging process,such as stress,temperature,deformation and type of material,while the void diffusion welding condition is still not well known at the present.This paper is concerned with the deformation welding condition of the closed void interface in heavy ingot during the hot forging process.A void crushing experiment is carried out to recognize the microstructure of the closed void interface.According to the healing mechanism at high temperature,a new physical simulation model is setup to study the deformation welding process of the closed void interface based on the theory of atom diffusion and the interface contact mechanics prototype.Compared with the experimental results,the influence of deformation degree,forming temperature and holding time on the welding quality is discussed,and then the deformation welding condition of closed void interface is presented.The proposed condition helps to improve forging technology and product quality.
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.
