Evolution Behaviors of Inclusions in Warm‐Rolled L605 Thin‐Walled Tubes and Their Effects on Machinability

Abstract

This paper investigates the evolution behaviors of inclusions in the warm rolling process of L605 thin‐walled tubes and analyzes their influencing mechanism. Homogeneous spherical and irregular SiO2–Al2O3–Cr2O3(MnO + CaO) inclusions are observed in the cast tubes. After warm rolling, the homogeneous inclusions are changed into heterogeneous spherical ones with gray‐colored (Al2O3)‐rich phase and dark‐colored (SiO2)‐rich phase and Cr2O3(MnO + CaO)‐rich phase due to different deformability of various inclusions under the combined effects of diameter reduction and wall pressure. As the rolling times of tubes increases, large‐sized inclusions are crushed continuously, and the average size of the inclusions gradually decreases. At the same time, the number density of inclusions presents a first increasing and then decreasing trend. It is estimated that the critical size of the inclusions that are hard to further crack in warm rolling is about 0.5 μm. Meanwhile, the inclusions would lead to stress concentration at the positions near large‐sized irregular inclusions, causing cracks and penetrating defects. The simulation results show that the stress near the outer diameter of the inclusions is twice that in the middle and the changes of stress in the 30 μm inclusions and nearby areas exhibit a significant increase compared to the small‐sized 2 μm inclusions.