PHYSICAL FOUNDATIONS OF THE FORMATION OF A STRENGTHENED STRUCTURE OF STRUCTURAL STEELS DURING ELECTROLYTIC-PLASMA HARDENING

This article presents the results of a comprehensive study on the effect of electrolytic-plasma hardening (EPH) on the microstructure and mechanical properties of structural steel grade St4. This steel is widely used in heavy engineering and railway transport, where components operate under conditions of severe wear and variable loads, which highlights the relevance of developing effective strengthening methods. The experiments were carried out on specimens cut from a railway wheel rim, which makes the obtained results practically significant. The treatment was performed in an electrolyte consisting of 10% urea + 20% sodium carbonate + 70% water. The EPH regime included a voltage of 280 V, a current of 40 A, and a treatment duration of 9 seconds. This regime provided rapid heating of the surface layer to the austenitic state followed by instantaneous quenching in the electrolyte. Investigations carried out using scanning electron microscopy and metallographic analysis revealed that after EPH, the surface layer with a thickness of 1.0–1.5 mm consisted of a characteristic needle-shaped martensitic structure. Microhardness measurements confirmed a significant strengthening effect: the hardness increased fourfold from 200 HV to 800 HV. The substantial increase in hardness was accompanied by improved wear resistance and crack resistance, while maintaining the plastic properties of the material core. The obtained results demonstrate the high efficiency of EPH as an environmentally friendly and energy-saving local heat treatment method, which can be recommended to enhance the operational reliability and service life of critical components made of St4 structural steel.

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