A serial sectioning technique for evaluating grain and twin boundary precipitate growth kinetics in bulk specimens

A new measurement technique for the growth kinetics of both grain boundary and twin boundary bainite precipitates in bulk specimens is demonstrated. The key advance is the use of coarse-scale serial sectioning to determine the angle made by the grain or twin boundary to the plane of polish, so an explicit stereological correction to the precipitate thickness can be made. This technique is applied to the thickening of bainite at the bay temperature of Fe–0.24C–4Mo, where grain boundary bainite growth kinetics had been measured previously in much thinner specimens using the “bamboo-specimen” method developed by Bradley et al. Several key assumptions implicit in the “bamboo-specimen” method are critically examined using the data obtained from this new technique. Twin boundary bainite growth thickening kinetics, which cannot be obtained using the bamboo method, are also obtained for the first time, and are measured in the same steel.