Abstract
Cyclic testing of 40X structural steel with the implementation of the intermediate surface plastic deformation of the samples by the proposed special technique using the striker-ball tool is described. Changing the level of degradation of the material was determined by the coercive force method. The tests were carried out with the purpose to ascertain the possibility of increasing the durability of the material as the result of the surface treatment by reducing the concentration of accumulated fatigue defects.The test results showed an increase of durability of steel from 3-5 up to 10 times or more (with larger amplitudes), accompanied by a decrease in the values of the coercive force, and the increase in the samples endurance limit by 20-40 MPa. The authors attributed this effect to healing of the material defects occurred as a result of surface treatment, and refinement of the surface layer structure and improving the level of compressive macrostrains on it which was established with the help of the X-ray method. The obtained results indicate the possibility of using this kind of surface treatment to heal defects in products which were in operation and the need to reduce the level of degradation of the metal in order to prolong their life.
Highlights
Issues of increasing reliability and durability of engineering products become of key importance due to the increasing requirements for the mechanical properties of materials because of intensification of different technological processes and use under conditions of high temperature and power loads.Technological support of operational properties of machine parts is inextricably connected with parameters of their surface layer state
The endurance limit of parts mainly depends on the magnitude of the residual stress of the surface layer; the irregularities formed on the surface of the part during processing are one of the reasons for the decline of the endurance limit, as are stress concentrators
Cyclic tests of two batches of samples of 40X normalized steel were conducted, which for the second batch were conducted in two stages
Summary
Issues of increasing reliability and durability of engineering products become of key importance due to the increasing requirements for the mechanical properties of materials because of intensification of different technological processes and use under conditions of high temperature and power loads.Technological support of operational properties of machine parts is inextricably connected with parameters of their surface layer state. The endurance limit of parts mainly depends on the magnitude of the residual stress of the surface layer; the irregularities formed on the surface of the part during processing are one of the reasons for the decline of the endurance limit, as are stress concentrators. As it is known, the mechanism of fatigue failure is related to the development and accumulation of microplastic deformations in the surface layer and is based on the motion of dislocations. To increase resistance to fatigue failure of mechanical engineering products, different types of surface treatment (thermo-mechanical, chemical and thermal processing, surface plastic deformation, applying various kinds of coverings and so on) allowing to modify the surface layers while maintaining the necessary ductility and toughness throughout the material are widely used [1, 2]
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