Hydrogen Permeability of the Surface Nanocrystalline Structures of Carbon Steel

Abstract

We studied the hydrogen permeability of the surface nanocrystalline structures formed by the mechanical-pulse treatment on 45 steel with the use of various technological media. It is shown that these structures are characterized by a much lower hydrogen permeability as compared with the untreated steel, thus revealing the formation of a large number of hydrogen traps in the course of treatment. The hardened surface layer is more susceptible to the development of dissipated damage in the course of hydrogenation but may also serve as a barrier for the penetration of hydrogen into the matrix material.The nanocrystalline structures (NCS) formed on structural steels are characterized by an improved complex of physicomechanical properties. Thus, they combine high strength with elevated plasticity [1][2][3][4]. Moreover, severe plastic deformation is the most common method used for their production [5]. However, the same is also true for the surface NCS obtained by the mechanical-pulse treatment (MPT), i.e., by the severe thermoplastic deformation of the layers on cylindrical and plane surfaces caused by the high-speed friction of a special metal tool against the treated workpiece [6]. To harden these surfaces, it is customary to perform MPT on the lathes or surface-grinding machines after their insignificant modernization. Special technological media (TM) are delivered to the zone of treatment. They not only rapidly cool the metal surface, which leads to its thermal treatment, but can also saturate the surface layers with alloying elements (carbon, nitrogen, hydrogen, oxygen, etc.) because their thermal destruction is realized in the zone of friction contact [7,8]. The high-speed heating above the point of phase transformations in the course of MPT and cooling as a result of heat removal into the TM, tool, and workpiece cause structural-phase transformations accompanied by the formation mainly of the martensite-austenitic structure. Thus, the MPT combines severe shear deformation (guaranteeing the formation of NCS), alloying with the components of cooling media, and the thermal treatment of the alloyed and highly deformed surface layer.As an important characteristic of the surface NCS, we can mention their resistance to hydrogen embrittlement [9] revealed by mobility of hydrogen in the metals and their ability to be hydrogenated [10]. On the other hand, we can also consider the surface layer as a barrier for the realization of negative processes in the matrix material. Therefore, it is reasonable to study the influence of surface NCS on the hydrogen brittleness of the base metal. Thus, in the present work, we investigate the hydrogen permeability of the surface NCS obtained on carbon steel in different TM.

Wear Resistance of Steels with Surface Nanocrystalline Structure Generated by Mechanical-Pulse Treatment

“…A rise of the wear resistance of the steel surface NCS could be expected in the case of the hydrogen saturation of the metal, which frequently happens in real service conditions. As it was showed before [ 6 , 17 ], the NCS on steels obtained by MPT can weaken the hydrogen penetration in the metal and can increase the resistance of the hydrogen embrittlement. It leads to reduction of wear intensity, at least, by the chipping mechanism.…”

Evaluation of the Degree of Degradation of Brake Pad Friction Surfaces Using Image Processing

“…In studies [54,116], the temperature and force conditions for the formation of white layers on steel and cast iron were determined. It should be noted that the results of research [117,118] indicate that such nanostructures can serve as a barrier for the penetration of hydrogen into steel. Mechanisms of initiation and propagation of cracks in metals under high-temperature loads were developed by researchers [119,120], and the influence of hydrogen on the properties of metals in various environments was discussed in detail in papers [121][122][123].…”

The Mode Deformation Effect on Surface Nanocrystalline Structure Formation and Wear Resistance of Steel 41Cr4

“…It was demonstrated [31] that it enables the formation of a nanostructure with a lower energy expenditure and higher dislocation density and, therefore, with a lower grain size in the top surface layer and a greater thickness compared with that which is generated using unidirectional deformation. The application of a multidirectional SPD resulted in increasing wear resistance, contact, and corrosion fatigue, and the decreasing hydrogen permeability of the nanostructured materials [11,[32][33][34][35][36].…”