The destruction surface and defect substructure of the Fe-0.1C-1.71Mn-0.92Ti-18.2Cr-10.4Ni-0.71Si steel subjected to high-cycle fatigue tests is investigated by the methods of scanning and transmission electron microscopy. It is demonstrated that the fatigue tests, irrespective of the loading scheme (continuous or under conditions of intermediate stimulation by pulse current), result in the formation of a structural gradient in the material manifested through regular changes of the relief parameters of the destruction surface and defect substructure with increasing distance from the loading surface (face or back specimen side). It is revealed that scalar and excess dislocation density, volume fraction of grains that comprise deformation microtwins, and degree of dislocation substructure organization maximize near the free specimen surface.

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The process of gradual damage accumulation under alternating stresses resulting in changes of the properties, phase structure, and defect substructure of the material and in the initiation of cracks, their further growth, and finally failure of the material is called the metal fatigue. The application of modern structural methods of research has allowed to make the certain steps in uinderstanding of the nature of fatigue failure of metals and alloys, however the diversity of the given phenomenon does not allow to construct the general theory [I-4].The transmission electron microscopy was used to analyze formation of the structural phase states in the fatigue crack growth area in 08X18HlOT austenite (O,1%C; 17,5%Cr; 10%N; 1%Ti) and annealed (ferrite-perlite structure) and quenched (martensite) 60FC2 (0,6% C, 1% Mn, 2% Si) stainless steels subjected to high-cycle fatigue.In the initial state of 08X18HlOT steel up to 75% of the total volume was occupied by a chaotic dislocation substructure, the rest was shared in equal proportion by reticular and cellular-reticular substructures. Average scalar density of dislocations amounted to l.5*10'0cm-2. Carbide phase was represented by chromium carbides M23C6 sized 0.1-1 1tm comprised of (FeCr)23C6 and TiC with average size of 62±5 nm. High-cycle fatigue testing resulted in higher (up to 5.2* 1010cmO2) scalar density of dislocations in the ruptured zone which increased share of material in the total volume with ordered dislocation substructures against the chaotic ones.In steel fractured after 170 thousands stress cycles the fatigue growth area has the following proportion of dislocation substructures: chaotic 5%, reticular -70%, cells and balls comprise the rest in equal proportion. In strained steel stacking faults and microtwins are formed, channels for slip and twinning steel deformation are triggered. In fractured material grain body contains differently oriented microtwin stacks substantially increasing density of bend extinction contours which are the sources of longrange stress fields. Deformation twinning leads to martensite y-*c transformation. Steel fatigue loading entails partial dissolution of carbides M23C6 near grain boundaries and isolation of Cr3C2 on carbide interlayer boundaries, as well as coagulation of TiC particles up to 120±7 nm in ruptured state. At the same time their size variety is substantially expanded. Microcracks form near carbide-mnatrix phase boundaries and within the volume of carbide phase particles that are some nanometers in size. Such locations are stress concentrators which lead to failure of the whole sample [5][6][7][8].The annealed 6017C2 steel in the initial state was a polycrystalline aggregate and consisted of perlite and ferrite grains. In most cases, perlite had plate-like morphology or less often globular one. Cemnentite particles were localized on the boundaries (in the form of thin interlayers) and in joints of the boundaries of free ferrite grains (in the form of globules). Chaotic or network dislocation substructure was o...

Electron-microscopic examinations of the evolution of the defect substructure and phase composition have been carried out for quenched 60GS2 carbon steel subjected to multiple cycles of fatigue loading. The mechanisms by which the fatigue durability of the steel processed at an intermediate stage of loading by alternating electric current is increased have been investigated.