PLASTIC STRAIN LOCALIZATION IN ALLOYED γ-Fe SINGLE CRYSTALS ELECTROLYTICALLY SATURATED WITH HYDROGEN

Abstract

The effect of interstitial hydrogen atoms on mechanical properties and plastic strain localization patterns in tensile tested alloyed γ-Fe single crystals of austenite steel with low stacking-fault energy has been studied using a double-exposure speckle photography technique. The hydrogenation of [ 11] oriented single crystals of Fe–18Cr–12Ni–2Mo steel led to decrease in the yield stress, 1,3 times increase in plasticity (strain at break), and suppression of the neck formation in single crystals oriented for the multiple slippage. On the stress-strain curve of plastic flow measured in tension in the initial (hydrogen free) state, the transition from elasticity to developed plastic flow is followed by the stages of linear deformation hardening, and parabolic hardening. The stress-strain curve of single crystals saturated with hydrogen exhibit a small tooth and a flow trough and is followed by the stages of linear deformation hardening; parabolic hardening and prefracture. The main parameters of plastic-flow localization at various stages of the deformation hardening of crystals have been determined in single crystals of steel electrolytically saturated with hydrogen in a three-electrode electrochemical cell at controlled constant cathode potential. It is established that hydrogenation of alloyed γ-Fe specimens enhances the localization of straining, leads to significant changes in the characteristics distances between plastic shear bands and local straining zones in all scale levels.