Numerical Simulation Research On Void Evolution In Large Continuous Casting Billet During Stretching Process

Heavy forgings are widely used as key parts of heavy machines and equipments. The specialties in load and poor working conditions make it require high safety and reliability technique requirement. However, heavy continuous casting billets have many severe internal metallurgy defects, such as void. In practical production, stretching process must be used on heavy forgings to minimize or eliminate the voids to get qualified products. In order to provide a guideline for optimizing stretching process, numerical simulation about void evolution during the stretching of heavy continuous casting billet is carried out in this paper.The void topography distribution is obtained based on the experiment of42CrMo steel heavy continuous casting billet with a600mm initial diameter. On the platform of DEFORM-3D, a thermo-mechanical coupled finite element model has been built to simulate the single-pass stroking process and multi-pass stretching process. Based on the established simulation model, the stress-strain field has been simulated, and explained by rigid-plastic mechanical model. Then, numerical simulations for the closing evolution of voids in the scope of200mm core diameter are performed. The result shows that, the closure of void differs depending on its location since the deformation is inhomogeneous in the forging. The void size effect can be negligible when the void initial size is smaller than5mm. In the single-pass stroking process, for ellipsoid voids the closing difficulty increases as the ratio of vertical radius to horizontal radius goes higher, and spherical void is the most difficulties to close during the multi-pass stretching process. The width anvil is beneficial for void closure.At last, numerical simulations for stretching processes of Wide Die Heavy Blow Forging and Narrow Die Light Blow Forging are carried out and the effects of the two schemes on void closure evolution are compared. It shows that, the former method is more beneficial for the void closure, but it cannot ensure the homogeneous distribution of internal deformation. The later method can guarantee the deformation homogeneity but the poor effect to the quality of forging. The indication to evaluate the stretching processes should not only be the forging rate, but also the matching of the anvil width ratio and blank width ratio.