Abstract
The effect of boron on the grain boundary segregation of phosphorus in a high-purity Fe-0.2 pct P alloy has been investigated by Auger electron spectroscopy (AES). The segregation of phosphorus decreases markedly with the segregation of boron; phosphorus atoms are replaced by boron atoms at grain boundaries. The free energy of segregation of boron at 1073 K is determined to be 100 kJ/mol. The effect of boron on the phosphorus-induced intergranular fracture (IGF) has been examined with impact testing, and the fractography has been studied with scanning electron microscopy (SEM). Addition of 12.5 wt · ppm boron completely prevents the IGF induced by the segregation of phosphorus and decreases the ductile-brittle transition temperature (DBTT) by about 170 K when quenched from 1073 K. The suppression of the IGF due to the addition of boron is caused by two mechanisms. One is the increased grain boundary cohesion of iron caused by the segregated boron as its inherent effect. The other is the decrease in the segregation of phosphorus caused by the segregation of boron. The former has been shown to be more effective than the latter in suppressing the IGF.
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