Thermodynamic and kinetic modeling of grain boundary equilibrium segregation of P in α-Fe

Phosphorus is a primary contributor to interface fracture and embrittlement in steels because of its strong segregation tendency at grain boundaries (GBs). The lack of consistency in literature data imposes great difficulties in performing segregation modeling that is compatible with both the Langmuir-Mclean segregation theory and the thermodynamic description of the Bcc(Fe,P) phase. This work carefully evaluated experimental data for phosphorus segregation at GBs in α-Fe and provided a new formula for converting the auger electron spectroscopy (AES) peak height ratio to GBs. Based on newly assessed literature data, this work proposes that the major driving force for phosphorus segregation is the formation of Fe3P-type clusters at GBs, which is supported not only by the almost equivalent Gibbs energy of α_Fe using the Bcc(Fe,P) substitutional model and the Bcc(Fe,Fe3P, P) associate model, but also by the good agreement between thermodynamic/kinetic modeling results and experimental data.