Hydrogen Effect on Macrolocalization of Plastic Deformation of Low Carbon Steel

Infrared thermography and two-exposure speckle interferometry have been used to study the plastic deformation of low-carbon steel under the action of pulsed electric current. It was established that external electric effect leads to an increase in velocity of plastic waves by 65 %. Analysis of the velocity distribution patterns showed that they have the profile of “shock transition”. At the origin, velocity of the material is zero (motionless gripping), and at the right end of the curve material velocity is equal to stretching speed specified by testing machine. The effect of electric current leads to splitting of the displacements velocities, both at moving and stationary ends of the samples. It is assumed that the observed splitting is related to the Stark splitting of energy levels of the deformed system. This splitting leads to a decrease in the potential barrier for the motion of defects in crystal lattice. Thermographic studies have shown presence of a temperature gradient directed from clamps to center of the sample, which does not coincide with pattern of displacement distribution. It was determined that during the primary treatment with high power current pulses in the central area of the sample, sample temperature reaches 351 K, and 330 K in the area adjacent to clamps. Subsequent treatments result in a slight increase in temperature. This behavior of temperature can be explained by the fact that heat does not dissipate at a repetition rate of 10 Hz. On an average, sample temperature increases by 30 K. Theoretical calculation has shown that the Joule effect leads to an increase in temperature of the sample by 21 K per pulse, which is practically in agreement with experimental results. Estimates of thermal energy and energy of elastic deformation have shown that the fastest channel for converting the energy of electric pulse is structural changes in deformable system, which lead to the observed decrease in deforming force.

Section: материал и методика экспериментаunclassified

Influence of Pulsed Electric Current on the Waves Motion Character of Plastic Deformation at Tension of a Steel Plate

Гагарин¹,

Sarychev²,

Невский³

et al. 2019

Localized deformation at initial stages of plastic flow in high-manganese steel

Баранникова

2022

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The work is devoted to the study of macroscopic localization of plastic deformation during uniaxial tension of single crystals of the Hadfield steel (Fe – 13 % Mn – 1.03 % C). In the course of studies at the stage of easy sliding, significant differences were found in the nature of macrolocalization of plastic deformation in the single-crystal samples under study. All patterns of deformation localization observed in these cases can be divided into two types. The first type of strain localization corresponds to the initiation at the upper yield point and further propagation of the strain front, which gradually transfers the sample material from undeformed state to deformed one. This manifested itself most clearly in single crystals oriented along the tension axis [377] and [355], where the strain localization pattern appears as a single zone of localized deformation on the yield plateau. Such a deformation front passes through the sample volume only once as a Chernov-Luders band. In this case, the flow of the material is carried out without hardening until all its elements are transferred to the deformed state. Single zones of strain localization were also observed at the stages of easy sliding and yield plateau in the Hadfield steel single crystals oriented along the tension axis [123] and [012]. In the second type of localization, at the stage of easy sliding, synchronous movement along the pattern of several deformation centers occurs. Their movement can be unidirectional and counter, and the speeds are both the same and different from each other. Further deformation of the Hadfield steel single crystals oriented along the tension axis [355] or [012], led to the movement of two deformation localization centers at the stages of easy sliding. In single crystals oriented along [111], the strain localization pattern is respectively represented as four localized strain sites. Consequently, the synchronous movement of deformation fronts occurs along an already deformed, albeit to a small extent, material. As a reason for the difference between the two types of macrostrain localization at stage I (the easy sliding stage and the yield plateau), the number of active sliding systems or tensile twinning in the studied single crystals can be discussed based on crystallographic analysis and metallographic studies.

Patterns of localized deformation at pre-fracture stage in carbon steel – stainless steel bimetal

Баранникова

2023

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The work is devoted to the study of strain localization at macroscale level during parabolic mechanical hardening and pre-fracture under quasi-static loading of a carbon steel – stainless steel bimetal. The problem of estimating the scale of the phenomena that determine plasticity is decisive in the development of any theories of plastic deformation, in particular, dislocation theories. The main difficulty in constructing such theories is the reconciling the dislocation scales, characteristic for most deformation and mechanical hardening mechanisms, with macroscopic parameters of deformation processes. In the framework of the autowave model of localized plastic deformation, this problem can be reduced to the possibility of obtaining parameters from the results of macroscale observations of localized plastic flow development. During the experiments, it was confirmed that in a bimetal at any forming stage, a specific pattern of localization centers distribution is spontaneously generated - a pattern of localized plastic flow. The shape of such patterns is determined by the law of mechanical hardening acting in the material. It is shown that the observed localization patterns can be used as an informative feature in predicting the plasticity margin. In the process of uniaxial tension at the stage of parabolic mechanical hardening of the bimetal, the deformation mode is realized with the formation of several potential fracture centers. It was established that at the pre-fracture stage, during the time evolution of the wave pattern of deformation localization, the zone of active plastic deformation narrows, but the number of centers in it either remains the same with a decrease in the distance between them, or even increases. The result of this process is the formation of a macroscopic neck, and then fracture. At the pre-fracture stage, the collapse point indicates the place of future fracture and signals the need to stop the deformation process in order to avoid the fracture of the bimetallic material. Thus, the well-known manifestation of deformation macroscopic localization – formation of a neck – is preceded by complex phenomena of mutually coordinated motion of localized plasticity centers at the pre-fracture stage.