Effect of Electrolytic-Plasma Nitrocarburizing on the Structural and Phase State of Ferrite-Pearlitic Steels

• Published in: Steel in translation Vol. 49; no. 10; pp. 671 - 677
• Main Authors: Popova, N. A., Nikonenko, E. L., Nikonenko, A. V., Gromov, V. E., Peregudov, O. A.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.10.2019; Springer Nature B.V
• Subjects: Aqueous solutions; Carbon nitride; Carbonitriding; Cemented carbides; Cementite; Chemistry and Materials Science; Ferrite; Ferritic stainless steels; Foils; Lamellar structure; Martensite; Materials Science; Pearlite; Phase composition; Steel; Steel structures; lath and lamellar martensite; steel; nitride; carbonitride; phase composition; ferrite; pearlite; nitrocarburizing; modified layer; carbide
• ISSN: 0967-0912; 1935-0988
• DOI: 10.3103/S0967091219100127

Using transmission electron microscopy (TEM), phase composition and fine texture changes in the ferrite-pearlitic steels 0.18C–1Cr–3Ni–1Mo–Fe, 0.3C–1Cr–1Mn–1Si–Fe and 0.34C–1Cr–1Ni–1Mo–Fe due to electrolytic plasma nitrocarburizing has been studied in thin foils. The procedure of electrolytic-plasma enhanced nitrocarburizing has been performed by steel surface saturation with nitrogen and carbon in an aqueous solution at a temperature of 800–860°C for 5 min. All the steels under investigation have been studied before and after the nitrocarburizing procedure. In the initial state, the steels were discovered to be composed of a pearlitic and ferritic grain mixture. The nitrocarburizing procedure leads to the formation of modified layers. Thus, the greater is the amount of pearlite before nitrocarburizing, the thicker is the modified layer. Nitrocarburizing results in significant qualitative changes in the phase state and the steel structure. In the modified layer surface area alongside the matrix, the particles of other phases such as carbides, nitrides and carbonitrides occur. As the distance from the surface of a nitrocarburized sample increases, the phases of set and volume decrease, whereas the only carbide phase—cementite—occurs at the end of modified layer in the case of all the steels. After nitrocarburizing, the matrix of all the steels represents tempered lath and lamellar martensite. In the nitrocarburized layer surface zone, the volume fractions of lath and lamellar martensite depend on the initial steel state: the greater is the amount of pearlite in steel, the less is the amount of lath martensite; then a greater amount of lamellar martensite is formed. Such a dependence is not observed in the nitrocarburized layer central zone, whereas the volume fractions of lath and lamellar martensite at the end of the layer are close to each other.