The Effects of Prior-γ Grain Boundary Segregation of Phosphorus, Manganese and Molybdenum on Intergranular Fracture Stress in Low Carbon Martensite Steels

Influence of prior-γ grain boundary segregation of alloy elements on intergranular fracture stress is important for the mechanism of temper embrittlement. There are a few efforts based on pure-iron [1], but no report on low carbon martensitic steels. In this study, the effect of segregation of phosphorus (P), manganese (Mn) and molybdenum (Mo) was investigated. The samples were melted by changing the amount of P, Mn and Mo based on the base Fe-0.1%C-3%Mn-90 ppmP. The martensitic steels with coarse prior-gamma (γ) were made by quenching and tempering. The segregation was measured by Auger electron spectroscopy, and the intergranular fracture stress was regarded as the yield strength at ductile brittle transition temperature of Charpy V-notch test. This study revealed that the segregation of P weakened the fracture stress mostly in the order of P and Mn, and that of Mo strengthened the fracture stress quantitatively. Mn-P co-segregation was not observed. The segregation of P was decreased by the addition of Mo.