Distribution of Boron at Austenite Grain Boundaries and Bainitic Transformation in Low Carbon Steels

The segregatioll alld /JI"eci/l itatioli behavior oj boroll ill austenite /lhase has been studied by means oj au torad-iogra/lllY, with /)articula r r~reret1ce to bainitic transformation oj low carbon medium alloy steels .The main results obtained are as Jollows :(1) Boron atoms migrate to austenite grain boundaries during cooling from the aUJten-itiz ing temperature .(2) The e.ffect oj boron on bain-it£c transJormat-ion de/Jends predominantl.)'on the distribution oj boron at austenite grain boundaries; Ihe rate oj bail/itic transjormation is most retarded when boron atoms are segregated homogeneously along the boundaries, but the retarding e.ffect decreases as the degree oj the preci/J itation increases when boron atoms begin to precipitate.(3) Th e loss -in hardenability e.ffect oj boron due to the addition oj nitrogen is caused by the decrease in effective boron during quenching.(4) These changes in the distribution if boron cannot be detected at all by the ordinary elching leclmique used jar detecting the boron-constituent.