Influence of gas nitriding pressure on the surface properties of ASTM F138 stainless steel

✍ Scribed by S.D. de Souza; M. Kapp; M. Olzon-Dionysio; M. Campos

• Publisher: Elsevier Science
• Year: 2010
• Tongue: English
• Weight: 772 KB
• Volume: 204
• Category: Article
• ISSN: 0257-8972
• DOI: 10.1016/j.surfcoat.2010.03.005

✦ Synopsis

The present work investigates the influence of gas nitriding pressure on the modification of surface properties of ASTM F138 stainless steel. Nitrided surfaces were characterized by X-ray diffraction, Conversion Electron Mössbauer Spectroscopy, Scanning Electron Microscopy and Vickers microhardness. Plasma nitriding was carried out in a medium of 80% H 2 and 20% N 2 , at 400 °C, for 4 h, pressures between 3 and 7 torr. A modified layer, whose depth ranging from 5.4 to 6.6 μm, was observed for all the nitrided samples, regardless of the nitriding pressure. The sample treated at 7 torr showed the best result of hardness. Besides γ N phase, the hexagonal ε phase (Fe 2 + x N) was also observed on the Mössbauer spectra up to 0.4 μm depth of the nitrided samples. X-ray diffraction spectra were analyzed by full profile fitting, using the triclinic structure for the γ N phase. The results indicated that nitrogen concentration reaches a maximum for a pressure of 4 torr.