Abstract
The voids caused by the cold rolling (CR) quite deteriorates the final performance of M50 bearing steel. In this work, the effect of electropulsing treatment (EPT) on the voids has been investigated, finding that the nano-size voids around carbides have been extensively healed. Moreover, it is interesting to find that the Cr-rich carbides are partially dissolved and consequently refined by EPT, which could be attributed to the decreased thermodynamic dissolution barriers and accelerated kinetic diffusion of carbon atoms towards dislocation. These results inspire people to develop a novel strategy (CR + EPT) to fully take advantage of CR and tailor the carbides size in bearing steels.
Highlights
M50 bearing steel has been widely used in the aerospace industry as main shaft bearing in gas-turbine engines due to its excellent elevated temperature performance[1]
It is worth noting that the voids resulted from cold rolling (CR) process mainly locate around high resistance second-phase, making the application of electropulsing treatment (EPT) to affect the nano-size voids more complicated
This inhomogeneous temperature rise can lead to inhomogeneous thermal expansion, so that the voids will be subjected to a strong thermal compressive stress and healed[19]
Summary
M50 bearing steel has been widely used in the aerospace industry as main shaft bearing in gas-turbine engines due to its excellent elevated temperature performance[1]. As a key shape-forming procedure prior to heat treatment, the cold rolling (CR) technology has been proven to have great potential in improving the strength and toughness of low-alloyed bearing steel owing to grain refinement[2,3], martensite refinement[4], bainite refinement[5,6] and solution strengthening[7] This raises the speculation that whether the application of CR process will be positive to the comprehensive performance of high-alloyed M50 bearing steel as well. Many researches[11,12,13,14] have experimentally proven that the macro cracks can be effectively repaired by electropulsing treatment (EPT) due to the temperature rise and compressive stress This crack-healing effect gives us a vision that the combination of CR and EPT may further improve the mechanical properties of M50 bearing steel if the nano-size voids around carbides can be healed as well. It is interesting to find that the nano-size voids around carbides have been healed extensively, and the carbides have been refined by the EPT technology
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