Process Optimization of Planetary Rolling of Bismuth-Containing Austenitic Stainless Steel

The three-roll planetary rolling is one of the most efficient methods of stainless steel bars production. However, the core of rolled products often cracks in the course of rolling bismuth-containing austenitic stainless steel as a result of the properties or stress state of rolled bars, causing remarkable reduction of finished product rate. Thermal compression tests and three-roll planetary rolling experiments were first carried out to solve this contradiction. The stress–strain curves obtained from the thermal compression experiments were modified due to the effect of the plastic deformation heat. The Ayada ductile fracture criterion was selected as the cracking criterion. Based on the rolling experiments, the damage limit of the bismuth austenitic stainless steel during the formation of the bars on the three-roll planetary rolling mill was determined by numerical simulations. Then, several key process parameters which impose a significant influence on the forming were selected to design the orthogonal test. The possibility of rolled parts crack under different process conditions was evaluated by the finite element simulation. The significance of the several process parameters to rolling crack was analyzed based on the standard deviation of the maximum damage values. A set of optimal rolling process parameters were obtained: the heating temperature 1200 °C, the friction coefficient between roll and rolled piece 0.9, the deflection angle 5°, the inclination angle 54°, and the roll speed 100 r/min. The reliability of the above process parameters was verified by the field rolling experiments. The significance of the five process parameters to rolling crack was discussed based on the standard deviation of the maximum damage values.