Spectroscopic Study of Electrolytic-Plasma Discharge During Hardening of 20GL Steel and Its Effect on Microstructure and Mechanical Properties
Rakhadilov B. Kurmangaliyev R. Kadyrbolat N. Kussainov R. Satbayeva Z. Maulit A. Shayakhmetov Y.
November 2025Multidisciplinary Digital Publishing Institute (MDPI)
Crystals
2025#15Issue 11
This study investigated the electrolytic-plasma hardening (EPH) of cast 20GL steel, used for railway spring beams. The main objective was to analyze the spectral characteristics of the cathodic discharge and establish correlations between the plasma parameters, processing regimes, and resulting surface properties. Optical emission spectroscopy revealed that the plasma at 260 V exhibited a high-energy state with an electron density of ~5.3 × 1016 cm−3 and an electron temperature of 10,031 K. Using these parameters, the heat flux from the plasma to the steel surface was estimated at ~1.5 × 107 W/m2, confirming that the discharge provides sufficient energy for surface austenitization. Microstructural analysis demonstrated that the electrolyte flow rate, which determines the cooling rate, is the key parameter controlling phase transformations. At low flow rates, ferrite–pearlite and bainitic structures formed, while a fully martensitic structure and maximum hardness (1046 HV) were achieved at 10 L/min. Tribological tests confirmed the superior wear resistance of the martensitic layers, showing a friction coefficient of 0.454 and a wear volume 3.4 times lower than in the as-cast state. These findings verify that EPH offers an energy-efficient, low-cost method for improving the surface performance and service life of 20GL steel components in heavy-duty railway applications.
electrolyte-plasma hardening , electron density , electron temperature , flow rate , martensite , microhardness , plasma , tribological test
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Plasma Science LLP, Ust-Kamenogorsk, 070000, Kazakhstan
Engineering Center “Strengthening Technologies and Coatings”, Shakarim University, Semey, 071412, Kazakhstan
Research School of Physical and Chemical Sciences, Shakarim University, Semey, 071412, Kazakhstan
Graduate School of Digital Technologies and Construction, Shakarim University, Semey, 071412, Kazakhstan
Plasma Science LLP
Engineering Center “Strengthening Technologies and Coatings”
Research School of Physical and Chemical Sciences
Graduate School of Digital Technologies and Construction
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