Degradation of Cr5 backup roll material under rolling contact fatigue

摘要

Progressive degradation and microstructural changes of Cr5 backup roll material with rolling contact fatigue cycles was investigated. Changes in the hardness and micro-structure of the tested samples were characterized using micro-indentation, scanning electron microscopy, transmission electron microscopy and X-ray diffraction. Tests performed on the samples at different intervals followed by mechanical and microscopically method lead to the conclusion that hardening mechanism is accumulation and extension of dislocations with accumulation of fatigue damage, followed by progress fracture of large bainite and martensite laths that even lead to the formation of nanocrystallites. Huge densities of interfaces were introduced by formation of nanocrystallites. Interfaces decohesion of nanocrystallites and diffusion of dislocation motions under cyclic stress allows formation and joint of micro-cracks along the nanocrystallites' interfaces, and ultimately cracks. The formation of nanocrystallites that cannot act as barriers to crack propagation and the diffusion effect of dislocation motions in the process of fatigue accumulation were responsible for the progressive degradation of Cr5 backup roll materials.