Internal Damage Mechanism and Deformation Process Window of a Free-Cutting Stainless Steel Bar Rolled by Three-Roll Planetary Mill

In order to determine the deformation process window and inquire the cause of internal cracks and voids, three-roll planetary rolling process was modeled by three-dimensional finite element method, and internal cracks and voids were investigated by real rolling of a bismuth-containing austenitic stainless steel bar. It shows that improper process parameters will lead to cracks and voids in the rolled bar. The Brozzo ductile fracture criteria revised can be used to determine the damage factor. The deformation process window to avoid internal cracks and voids can be described by rolling elongation and temperature. The three positive principal stresses in the center of the rolled bar, the alternating stress caused by periodically discontinuous contact between the rolls and the rolled piece, and the uneven radial strain distribution can be counted to be the main reasons for internal cracks and voids in the rolled bar. This study shows that the elongation has an upper limitation for avoiding internal cracks and voids in the bismuth-containing austenitic stainless steel bar rolled by three-roll planetary mill.