A new interpretation of temper embrittlement dynamics by non-equilibrium segregation of phosphor in steels

A new interpretation of temper embrittlement dynamics is proposed, which is based on the diffusion of phosphor atoms to grain boundaries by the complex of phosphor atom-vacancy. The dynamics of temper embrittlement in a medium-carbon Cr steel during 538°C tempering was carefully examined. The results show that the dependence of 50% fracture appearance transition temperature (FATT) on tempering time has a maximum, which can be satisfactorily elucidated by diffusion of the complex of phosphor atom-vacancy. However, the dependence of hardness on tempering duration decreases all the time. The fracture morphology was observed by scanning electron microscopy (SEM), the variation of intergranular fracture ratio also has a maximum during tempering treatment at 538°C, which is at the near same time as the one in the dynamic of temper embrittlement. The concentration of phosphor on grain boundary was measured by Auger electron microscopy (AES).