Abstract
The results of complex studies on the structure, microhardness and depth of the hardened surface layer of 40Kh grade steel formed using electromechanical treatment with the dynamic application of a deforming force (EMT under impact) are shown. Investigations have been carried out using the methods of optical microscopy, XRD structural analysis, and microhardness measurement. The method of the electromechanical treatment with a dynamic force impact consists in a simultaneous transmission of electric current pulses and deforming force through the contact zone between a tool and a part. As a result of thermal impact with different current densities (j = 100, 300, 600 A/mm2), hardened layer segments with different sizes and different structural compositions are formed on the steel surface within cross-section. The analysis of structural and phase transformations in the surface layer of 40Kh grade steel subjected to electromechanical treatment indicates the formation of a specific white layer structure. The structure and properties of this layer are close to the metal amorphous state with maximum hardness HV = 8.0–8.5 GPa. As the distance from the surface increases, a transient zone is formed behind the segment of the white layer that does not have a needle structure inherent in martensite. With increasing current density under the impact the electromechanical treatment, the hardening depth exhibits a four-to-five-fold increase together with a simultaneous increase in the heterogeneity of strength properties, with the microstress level increasing by 25%. The experimental data obtained for the structural state, microhardness and depth of the surface layer of 40Kh grade steel show that the electromechanical treatment under the dynamic (impact) application of deforming forces causes much more profound transformations in the steel structure as compared with the traditional static EMT. According to electromechanical treatment under impact, results show that the intensity of the thermal-and-force action on the steel surface layer increases, which makes it possible to control the formation of the structural and phase states of 40Kh grade steel.
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Translated by O. Polyakov
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Dudkina, N.G., Arisova, V.N. Surface Layer of 40Kh Grade Steel after Electromechanical Treatment under Dynamic Force Impact. Steel Transl. 51, 235–240 (2021). https://doi.org/10.3103/S0967091221040021
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DOI: https://doi.org/10.3103/S0967091221040021