INFLUENCE OF SHOCK VOLTAGE FROM THE ELECTRIC DISCHARGE ON THE FATIGUE ENDURANCE OF CARBON STEEL IN WATER

Abstract

Purpose. The research supposes the explanation of influence of stress impulses from an electrical discharge in water on the level of the limited endurance at a cyclic loading of the thermally work-hardened carbon steel. Methodology. Material for research was steel 45 (0,45 % carbon) with сoncentration of chemical elements within the limits of steel composition. Specimens for tests are made as plates in 1 thick, width 15 and length 120-180 mm. The structural state of steel corresponded to quenching on a martensite from the normal temperatures of annealing and tempering at 300C, duration of 1 h. Microstructure was investigated with the use of electronic microscopy, the density of dislocations was estimated on the methods of X-ray analysis. Hardness was measured on the method of Rockwell (scale of «C»). A cyclic loading was carried out in the conditions of symmetric bend on a tester «Saturn-10» at a temperature +20C. The treatment by shock voltage from the electrical discharge was carried out in water on setting of bath type «Iskra-23», used for cleaning of castings manufactures. Electric impulses were formed at 15-18 kV with energy of 10-12 kJ and amplitude of 1-2 GPа. Findings. As a result of processing pulses of a pressure wave of heat-strengthened steel 45 found the increase of endurance under the cyclic loading corresponds to an increased amount of accumulated dislocations on the fracture surface. The use of Coffin–Manson Equation allowed finding the decrease of deformation per cycle of loading as a result of arising stress from an electrical discharge in water. On the fracture surface (after pulse exposure) was found the increased number of dislocations, located in different crystallographic systems, that is a testament to the rather complicated development of dislocation transformations in the structure of steel, which provide an increase of endurance at a fatigue. The increase of the limited endurance became as a result of impulsive treatment largely related with the number change of mobile dislocations. For the area of low-cyclic fatigue the growth of amplitude of loading is accompanied with the decrease of distinction in the values of the limited endurance (before and after the treatment of shock voltage). Originality. For the field of high-cycle fatigue, the result of shock voltage of carbon steel with the structure of the improvements, the increase of limited endurance is accompanied with a decrease in deformation per cycle. As far as growth of amplitude of stress cycle the effect of increase of endurance from treatment of metal by the shock voltage declines. Practical value. Treatment of metal by the impulses of pressure waves from an electrical discharge in water can be used for the time extending of exploitation details of the rolling stock, which are subjects of the cyclic loading.