Effects of phosphorus grain boundary segregation and hardness on the ductile-to-brittle transition for a 2.25CrlMo steel

The combined effect of phosphorus grain boundary segregation and hardness on the ductile-to-brittle transition was examined for a P-doped 2.25Cr1Mo steel by using Auger electron spectroscopy in conj. unction with hardness measurements, Charpy impact tests and scanning electron microscopy. With prolonging time at 540 degrees C after water quenching from 980 degrees C, the segregation of phosphorus increases and the hardness decreases. The DBTT (FATT) increases with increasing phosphorus segregation and decreases with decreasing hardness. The effect of phosphorus segregation is dominant until 100 h aging and after that the hardness effect becomes dominant. This effect makes the DBTT (FATT) decrease with further prolonging ageing time although the segregation of phosphorus still increases strongly.