MODELLING THE EVOLUTION OF CASTING DEFECT CLOSURE BY RADIAL SHEAR ROLLING

Abstract

This paper studies the behavior of a transverse through defect in an ingot during complex vortex flow of metal deformed by the radial shift rolling (RSR) method. The aim of the work was to investigate the applicability of the RSR method for the deformation treatment of oxide-dispersed strengthened steel (ODS-steel) ingots into a final semi-finished product. Vortex flow of metal promotes dispersion of alloying solid oxides and refinement of steel structure. However, the question of development or closure of possible casting defects of ODS-steel ingot remains open. For this purpose, an ODS-steel ingot with a through-hole modelling the defect was rolled according to the assumed process scheme. Also, to visualize the evolution of the defect in more detail during the rolling process, a simulation of thesame defect development in an aluminum bar has been performed in 2 mm steps. The results of both rolls showed good correlation. Based on many cross-sections of the experimental bars, detailed 3D models of the defect evolution were built. An average reduction of 50 % in defect volume was found. Welding of the outer areas occurs immediately, but the central areas remain unclosed, stretching proportionally with the drawing of the rod during rolling. For this reason, RSR cannot be used with large cavity defects in the axial zone, but this method is guaranteed to weld surface defects even at low reductions.