International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The subject of our study is the effect of the tempering duration /for up to 7 hours, at 180°C/ on the mechanical properties of 20CrMo5 quenched steel samples. Possibilities were studied, including through eddy currents, to control the final tempering of parts which have gone through carburizing, double-quenching and interim high-temperature tempering. The parts were 20CrMo5 steel shafts, which had their carburized layer removed in certain zones before the thread was made.

It has been established that a strong correlation exists between the HV50 quality indices and the eddy currents characteristic Z.

The process of low-temperature tempering has been studied by eddy current testing and measuring the hardness HRC at a constant temperature as well as at increasing temperature and duration. Technological factors of tempering were considered in their interdependence, according to the Hollomon-Jaffe equation. It has been argued that the factor levels, temperature and duration, are determined by the carburization and quenching results. Eddy current testing has been introduced as an indicator of quality with high sensitivity to changing technological factors; it has integral importance in terms of structural changes and electromagnetic properties of the parts. Hardness and electromagnetic characteristics, as indicators of quality after low-temperature tempering, were presented as a function of the tempering parameter Pa.

The usage of the high-energetic source of the electron beam enables a repeated surface quenching of the chosen areas of an engineering part surface. Different techniques of the electron beam deflections allow the creation of hardened layers of different shapes and above all the thicknesses. The deflection was tested at one point, six points, a line and a field on the material 42CrMo4 (1.7225). The effect of the process speed and defocusing of the electron beam was studied. The electron beam surface quenching resulted in a very fine martensitic microstructure with the hardness over 700 HV0.5. The thickness of the hardened layers depends on the type of deflection and depends directly on the process speed. The maximum observed depth was 1.49 mm. The electron beam defocusing affects the width of the hardened track and can cause an extension of the trace up to 40%. The hardness values continuously decrease from the surface to the material volume.

The article deals with the investigation of plastic deformations of carburized medium carbon stainless steel after quenching and tempering. After carburization the specimens were heated at 1020 °C temperature and then air quenched. At the process of air quenching the specimens were bent within the temperature dropping interval approximately from 550 °C to room temperature. The bending caused tension or compression in different parts of the specimen, so interstitial distortion was formed. As the bending stress was much lower than the yield stress, the specimen didn’t bend during the first minutes of experiment, and then started bending during the martensitic transformation (transformation plasticity effect). The curved quenched specimens then were tempered at temperatures 200, 300, 400, 500, 600 and 700 °C for 1 hour and the deflection of specimen after each tempering was measured.

The results showed different influence of tension and compression on transformations occurring in steel during quenching and tempering. The tempering temperature effect on self-deformation of curved specimen was revealed.