Measurement of the Distribution of Boron on Prior Austenite Grain Boundaries by Means of Time-of-Flight Secondary Ion Mass Spectrometry Method

To understand the effect of Fe-23(C,B)(6) precipitation on hardenability of boron (B) added low carbon steels, we investigated the distribution of B at prior austenite grain boundaries by the advanced analysis using time-of-flight secondary ion mass spectrometry (ToF-SIMS). The Mo-B combined steel which has no precipitation of Fe-23(C,B)(6) showed flat intensity profiles of BO2- ions at prior y grain boundaries, while the B added steel showed the decrease in signal intensities of BO2- ions at the prior y grain boundary between two Fe-23(C,B)(6) precipitates. The results suggested that "solute B depleted zone" is formed near the precipitates and the Fe-23(C,B)(6) precipitation promotes ferrite transformation not only by assisting itself but also by forming the solute B depleted zone.