1980 Volume 66 Issue 5 Pages 506-513
This paper deals with the identification of boron constituent and its transition to other ferrous boroncarbides during heat treatment. In order to observe boron constituent clearly, the present authors adopted a new technique by which boron constituent on intergranular fractured surface is observed without performing etching.
Boron constituent forms at austenite grain boundaries by step quenching, but this boron constituent begins to transform to fine M23(CB)6 particles from the periphery during holding below AC1. Boron constituent never forms in carbon free steels, and thus it must contain carbon atoms.
It is considered that the boron constituent is not identical with M23(CB)6 bacause of 1) the above mentioned transition during heat treatment and 2) the difference in response to etching between them.
Globular M23(CB)6 directly forms from ferrite by reheating at temperature below AC1 after the specimen is quenched with so high cooling rate that martensite is produced from austenite without forming boron constituent.