Title: Formation of the structure and properties of chromium-Nickel steel during plasma electrolytic hardening

Abstract

This work is devoted to research the effect of plasma electric hardening (PEH) on changing in the phase structural and tribological properties of 0.34C-1Cr-1Ni-1Mo-Fe steel, which used for the manufacture of heavily loaded gears. PEH of steel samples was performed on an installation that consists of a power source, an electrolyte-plasma material processing chamber, and a personal computer. The process of electrolytic-plasma hardening of steel samples 0.34C-1Cr-1Ni-1Mo-Fe was performed in electrolyte containing an aqueous solution of 20 % calcined soda (Na2CO3) and 10 % carbamide ((NH2)2CO). Morphological and elemental analysis of the samples was performed using a JSM-6390LV scanning electron microscope. The phase composition of the samples was researched by X-ray diffraction analysis using X’PertPRO diffractometers. Research of the morphology of the thin structure was performed on an EM-125 electron microscope at an accelerating voltage of 125 kV. The micro-hardness of steel samples was measured using the Vickers method on the PMT-3 device. For the samples, the nano hardness of the coatings was determined using the Oliver and Farr nano-indentation system, using the Berkovich indenter at a load of 100 mN and exposure time of 5s. Tribological sliding-friction tests were performed on the THT-S-BE-0000 tribometer using the standard «ball-disk» method according to the international standard ASTM G 133-95. It was determined that after PEH, the wear resistance of 0.34C-1Cr-1Ni-1Mo-Festeel increased by 3.4 times, and the microhardness increased by 2.6 times. Based on the study of the structure and phase composition, it was found that after РЕН, a modified layer consisting of the α’- phase (martensite), γ’-phase, cementite М3C and carbide М23С6 is formed. It is established that the bending-torsion of the crystal lattice is pure plastic (χ = χel), which does not lead to the formation of microcracks in the material. According to TEM studies, PEH steel 0.34 C-1Cr-1Ni-1Mo-Fe bring to the change of structural-phase state and the structure of the packet-plate martensite and the provision of small particles of cementite and carbide of M23C6 type uniformly located throughout the volume of the material. It is determined that the increase in microhardness and wear resistance of 0.34C-1Cr-1Ni-1Mo-Festeel after PEH. It is particularly related to the formation of martensite, as well as the formation of a defective substructure.