Influence of chromium content on corrosion of plasma-nitrided steels
- Univ. of South Australia, Adelaide, South Australia (Australia). Ian Wark Research Inst.
Commercial steels with varying chromium contents were plasma nitrided for 25 h in a 70% nitrogen + 30% hydrogen gas atmosphere at 520 C under a pressure of 670 Pa. Steels tested included AISI types 4140, with 1% Cr (UNS G41400); H-13, with 5% Cr (UNS T20813); D-2, with 12% Cr (UNS T30402); and 431, with 16% Cr (UNS S43100). Surface layers obtained were characterized using optical microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and scanning electron microscopy with energy dispersive x-ray spectroscopy. Potentiodynamic polarization curves were obtained at room temperature (RT) on samples immersed in an aerated 0.05 M sodium sulfate solution of pH 3.0. Polarization tests were repeated at various depths beneath the surface after grinding successively with abrasives and finishing with 3-{micro}m diamond paste. Potential-vs-time graphs were recorded. Nitrided steels with up to and including 12% Cr showed an increase in corrosion resistance, whereas a decrease was observed for the 16% Cr steel compared to untreated samples. The nitrogen diffusion zones in all the steels studied exhibited reduced corrosion resistance compared to both the nitrided surface and to untreated specimens. Observations were discussed in light of the passivation theory. The role of chromium in nitriding was found to be mainly in hardness enhancement rather than improvement of corrosion resistance.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 514780
- Journal Information:
- Corrosion, Vol. 53, Issue 7; Other Information: PBD: Jul 1997
- Country of Publication:
- United States
- Language:
- English
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