Fractographic changes caused by phosphorus grain boundary segregation for a low alloy structural steel

A P-doped 2.25Cr1Mo steel was embrittled through ageing at 480 °C after quenching from 980 °C and tempering at 650 °C. When subsequently Charpy tested at different temperatures, the steel samples would experience, on going from 250 °C down to −150 °C, ductile fracture, intergranular fracture, and mixed intergranular and cleavage fracture. A descriptive diagram showing variation of fracture stress with temperature for the cases of small and large phosphorus grain boundary segregations was proposed to rationalize the experimental phenomena.