Relation of ductile-to-brittle transition temperature to phosphorus grain boundary segregation for a Ti-stabilized interstitial free steel

Equilibrium grain boundary segregation of phosphorus in a Ti-stabilized interstitial free (IF) steel is measured using Auger electron spectroscopy (AES) after the specimens are aged for adequate time at different temperatures between 600 and 850 °C. Based on the experimental data of equilibrium grain boundary segregation along with the McLean equilibrium segregation theory, the free energy of segregation of phosphorus is evaluated to be ∼44.8 kJ/mol, being independent of temperature. With the AES results being combined with the ductile-to-brittle transition temperatures (DBTTs) determined by impact tests, a relationship between DBTT and phosphorus boundary concentration is established. Predictions with the relationship indicate that cold work embrittlement may be severe if the steel is annealed at relatively low temperatures after cold rolling.

► The free energy of phosphorus grain boundary segregation in IF steel is ∼44.8 kJ/mol.
► A relationship between DBTT and phosphorus segregation is established.
► The DBTT increases linearly with increasing phosphorus boundary concentration.
► Cold work embrittlement may be severe if the steel is annealed at relatively low temperatures.