2020 年 106 巻 6 号 p. 321-330
To understand the effect of Fe23(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 Fe23(C,B)6 showed flat intensity profiles of BO2– ions at prior γ grain boundaries, while the B added steel showed the decrease in signal intensities of BO2– ions at the prior γ grain boundary between two Fe23(C,B)6 precipitates. The results suggested that “solute B depleted zone” is formed near the precipitates and the Fe23(C,B)6 precipitation promotes ferrite transformation not only by assisting itself but also by forming the solute B depleted zone.
