RAIL STEEL OPERATION: DEGRADATION OF STRUCTURE AND PROPERTIES OF SURFACE LAYER

Abstract

Using the methods of optical, scanning and transmission electron diffraction microscopy as well as microhardness and tribology parameters measurement the authors have established the changes regularities of structure-phase states, defect substructure of rails surface after the long term operation (passed tonnage of gross weight of 500 and 1000 mln. tons). It has been shown that the wear rate increases in 3 and 3.4 times after passed tonnage of gross weight of 500 and 1000 mln. tons, accordingly, and the friction coefficient decreases in 1.4 and 1.1 times. The cementite plates are destroyed absolutely and cementite particles of around form with the sizes of 10–50 nm are formed after passed tonnage of 500 mln. tons. The appearance of dynamical recrystallization initial stages is marked after the passed tonnage of 1000 mln. tons. The possible mechanisms of established regularities have been discussed in the work. It has been noted that two competitive processes can take place during rails long term operation: 1. process of cutting of cementite particles followed by their carrying out into the volume of ferrite grains or plates (in the structure of pearlite); 2. process of cutting, the subsequent dissolution of cementite particles, transition of carbon atoms to dislocations (into Cottrell atmospheres), transition of carbon atoms by dislocations into volume of ferrite grains or plates followed by repeat formation of nanosize cementite particles.