Effect of electrolytic hydrogen saturation on deformation mechanisms of Fe-17Cr-13Ni-3Mo-0.01C austenitic stainless steel during cold rolling

Abstract

In this work, we investigated the effect of the current density during electrolytic hydrogen-charging before deformation on the mechanisms of plastic deformation of stable austenitic stainless steel Fe-17Cr-13Ni-3Mo-0.01C during rolling. Using transmission electron microscopy and backscattered electron diffraction, it has been shown that plastic deformation by rolling at room temperature with 25 % reduction causes the formation of a high density of crystal lattice defects in the initially coarse-grained steel samples. The main deformation mechanism during rolling is dislocation slip, which is accompanied by mechanical twinning as an additional mechanism contributing the structure fragmentation. Regardless of the mode of preliminary hydrogen-charging, it promotes more active development of twinning. The higher the current density during hydrogen pre-charging, the higher the density of twin boundaries and dislocation density in the steel structure during rolling. After hydrogen-charging at a current density of 200 mA / cm 2 , the γ → ε transformation is also realized upon deformation. At the same time, an increase in the current density upon hydrogen pre-charging from 10 to 200 mA / cm 2 does not contribute to a significant increase in the concentration of hydrogen adsorbed by the material (0.0017 -0.0018 mass.%), which, together with microstructural studies, indicates a different distribution of hydrogen in the samples immediately before deformation and the important role of the hydrogen concentration gradient on the deformation mechanisms of the steel during subsequent rolling. With a decrease in the deformation temperature (due to the cooling of the samples before rolling to the temperature of liquid nitrogen), hydrogen-charging also causes an increase in the linear density of twin boundaries and the formation of ε-martensite, but these effects are more significant compared to room-temperature deformation. The data obtained indicate that at similar values of the concentration of adsorbed hydrogen in the structure of steels, the saturation mode affects the deformation mechanism and phase transformations in austenitic steel.