STRUCTURE-PHASE TRANSFORMATIONS DURING DIAMOND POLISHING

Abstract

The obtained results show that the plastic deformation of the tempered 15XГ2СМФР and 12ГН2МФАЮ steels with polishing is observed with an increase in the density of dislocations and a fragmentation of the structure. Due to the fact that the density of dislocations in the local zones of the surface reaches a critical level during polishing under the conditions of forces greater than the optimal force, in some cases, the appearance of submicroscopic cracks and a decrease in strength may occur in the deformed metal layer. Due to the increased pressure on the surface of the part, the metal layer strengthened by diamond polishing is characterized by microdistortions. After polishing, the crystal lattice of steel is distorted and the density of dislocations increases. As a result of surface-plastic deformation, intensive splitting of residual austenite and its transformation into martensite occur. After polishing and tempering, a significant amount of residual austenite is observed in the upper layers of the studied steel. The initial 16-20% amount of residual austenite decreases to 4-7% after polishing with a force of 270 N. As a result of diamond polishing, the microstructure of the steel is crushed, the density of dislocations increases, and the transformation of residual austenite into martensite leads to additional strengthening of 15XГ2СМФР and 12ГН2МФАЮ steels.