Microstructure and mechanical properties evolution of aviation M50 steel fabricated by the multiple electro-assisted rolling

The poor plastic forming ability of aviation M50 steel has seriously affected the high-performance manufacturing of aero-engine bearings. In this work, the multiple electro-assisted rolling (ESR) was applied by introducing the multiple electroshocking treatments into the rolling of M50 steel. The evolution of microstructure, mechanical properties, and damage of M50 steel fabricated by ESR has been investigated. The microstructure observation indicates that the dislocation density and residual stress of the ESR specimens decrease by 14.0% and 31.3%, respectively. Besides, fewer microcracks around the carbides are generated during the ESR. The mechanical property tests of ESR specimens show that the Vickers hardness is decreased by 8.7%, while the tensile elongation is increased by 33.4% without significant change in ultimate tensile strength as comparing with the CR specimens. Moreover, the TEM observation shows that subgrains are formed and higher lattice distortions are generated at grain boundaries after the ESR process. This could significantly promote the nucleation of recrystallization. After quenching and tempering, the prior austenite grain of ESR specimens is refined from 13.23 μm to 11.52 μm, while the ultimate tensile strength and Vickers hardness are increased by 12.1% and 6.1%, accompanied by an increase in elongation by 16.0%. This work develops a novel method to improve the forming limit and comprehensive properties of M50 steel by tailoring the microstructure and dislocation state, which is of great engineering significance for the manufacturing of aviation M50 bearing.