Cementite decomposition in 100Cr6 bearing steel during high pressure torsion

Severe plastic deformation leads to cementite decomposition in pearlitic and martensitic alloys, resulting in high-strength nanocrystalline ferrite. This effect can be employed to strengthen pearlitic wires but it can also be associated with material failure by white etching cracks (WECs) that are primarily known to concern bearings or rails. We investigate the decomposition of cementite in the martensitic bearing steel 100Cr6 during high pressure torsion [1]. Matrix and cementite behave plastically very differently. In the hardened state of the alloy, the enforced macroscopic plastic deformation is almost entirely carried by the matrix. Plastic material flow of the matrix around the spheroidal cementite leads to wear of the cementite as indicated by continuously increasing levels of chromium in the matrix. Plastic deformation of cementite via dislocation gliding supposedly accelerates this process as slip steps generated thereby are preferential sites of wear at the matrix/cementite interface. Larger cementite precipitates are more prone to plastic deformation and to decomposition than smaller ones.

Figure: Plastic flow of martensite around cementite during high pressure torsion

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