Superplastic behavior during warm deformation of martensite in medium carbon steel

A (ferrite + carbide) microduplex structure formed by dynamic recrystallization of ferrite during warm deformation of martensite was found to exhibit superplastic characteristics. The value of m = 0.4 was obtained at 973 K and a strain rate of 10−4 s−1. Microstructural analysis shows that submicron carbides are located at the ferrite grain boundary, while nanometer ones are dispersed inside ferrite grains. This kind of carbide distribution may suppress the growth of ferrite grains and form a dynamic equilibrium of average grain size during superplastic deformation.