Effect of Boron on Transformation of Low-Carbon Low-Alloy Steels

Abstract

The effect of boron on the transformation of low-arbon-1/2 Mo steels has been investigated by means of dilatometry and microstructural observations.
The steels containing below 30 ppm of boron exhibit the largest hardenability in case of austenitization at 930°C, but the hardenability is reduced by austenitization at higher temperatures. The hardenability of the steel containing boron of 60 ppm does not vary with the austenitizing temperature.
The steel with higher boron content of about 95 ppm increases its hardenability with increasing the austenitizing temperature up to 1 130°C.
Such behaviour can be explained in terms of grain boundary segregation of boron and the precipitation of Fe₂₃ (B, C) ₆. In addition to this, the effects of the precipitation of BN on hardenability and the crystallography of Fe₂₃ (B, C) ₆ are discussed.