Comparison of the deformation characteristics of a Ni-30wt% Fe alloy and plain carbon steel

A major barrier confronting researchers studying the hot deformation of plain and low carbon steels is the inability to directly observe the deformation microstructures of hot worked austenite due to the unavoidable transformation to martensite on quenching to room temperature. Various model materials, such as austenitic stainless steels have been used to overcome this difficulty. However, these materials have markedly different stacking fault energies from plain and low carbon steels and this will affect the evolving deformation structure. In this work, a model austenitic Ni-30wt%Fe alloy, calculated to have a stacking fault energy similar to that of low carbon steel, has been tested using hot compression. Stress-strain curves obtained during hot deformation show characteristics similar to those generated during identical tests on a 0.15wt%C steel. This suggests that the two materials behave similarly during deformation under similar experimental conditions. An application of the Ni-Fe alloy in the study of microstructural changes in austenite during hot deformation is demonstrated. A series of hot torsion experiments on a 0.11wt%C steel have been found to produce deformation-induced, intragranular nucleation of ferrite from austenite when a single deformation pulse is applied at 675 degrees C. A similar set of experiments have also been performed on the Ni-Fe alloy at 750 degrees C. Transmission electron microscopy carried out on the Ni-Fe alloy torsion specimens has revealed that likely preferred sites for intragranular ferrite nucleation appear to be microbands produced in the austenite during deformation.