Response of a DIN 18MnCrSiMo6-4 Continuous Cooling Bainitic Steel to Different Plasma Nitriding Gas Mixtures

• Published in: Materials research (São Carlos, São Paulo, Brazil) São Paulo, Brazil), 2020-01, Vol.23 (5), p.1
• Main Authors: Dalcin, Rafael Luciano, Oliveira, Leonardo Fonseca, Diehl, Carla Adriana Theis Soares, da Silva Rocha, Alexandre
• Format: Article
• Language: English
• Subjects: Bainitic steel; Compressive properties; Cooling; Decarburization; Decarburizing; Diffusion layers; DIN 18MnCrSiMo6-4 Steel; ENGINEERING, CHEMICAL; Fracture Toughness; Gas composition; Gas mixtures; Ion nitriding; Layer Growth Constant; MATERIALS SCIENCE, MULTIDISCIPLINARY; Mechanical components; Mechanical properties; METALLURGY & METALLURGICAL ENGINEERING; Microhardness; Nitrogen; Phase composition; Phase Composition and Residual Stress Analysis; Plasma Nitriding; Residual stress; Surface properties
• ISSN: 1516-1439; 1980-5373; 1980-5373
• DOI: 10.1590/1980-5373-mr-2020-0269

Continuous cooling bainitic steels has been widely used in industrial processes owing to its excellent mechanical properties and toughness. Although the surface properties of them are acceptable for many purposes, for their use in mechanical components like gears, it is necessary to improve their surface properties. Plasma nitriding treatments was carried out of a DIN 18MnCrSiMo6-4 steel at 500 °C, with three different nitrogen gas composition: 76, 24 and 5 vol.% nitrogen in hydrogen, for 3, 6 and 9 hours. The surfaces were characterized concerning the microstructure, microhardness, fracture toughness, nitrogen concentration and carbon composition, phase composition and residual stress states. Based on the results presented, layer growth constants (k) for different nitrogen gas composition was determined. The carbon profiles of samples indicate that there was decarburization during the plasma nitriding. The nitrided samples with thicker compound layers presented a fracture behavior dominated by the formation of Palmqvist cracks. X-ray phase analysis indicated the formation of biphasic compound layer on the surface of all nitrided samples with 76 and 24 vol.% nitrogen, while the nitrided samples with 5 vol.% nitrogen indicated the formation of monophasic compound layer. The diffusion zone presented compressive residual stresses with highest values near the surface.