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Thermodynamic control of H2-N2 bright annealing atmospheres to inhibit nitrogen uptake by stainless steel

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Journal of Heat Treating

Abstract

Passive SiO2 films that inhibit undesirable nitrogen uptake form on the surface of stainless steel during bright annealing in H2-N2 atmospheres. The SiO2 films can form at H2O/H2 ratios that are reducing to Cr in the alloy. Algebraic expressions were thermodynamically derived to predict the minimum H2O/H2 ratios required for forming SiO2 (to inhibit nitriding) and the maximum H2O/H2 ratios allowed for preventing formation of Cr2O3 (to prevent surface dulling), as functions of annealing temperature and concentrations of the elements in stainless steels. Predicted results agreed well with observed laboratory and field test data obtained over a range of annealing temperatures and H2O/H2 ratios for stainless steels with varying Si levels. This understanding of the surface chemistry can be used to improve control of H2-N2 annealing atmospheres to inhibit nitriding and prevent surface dulling. In addition, the literature suggests that SiO2 films that inhibit nitrogen uptake during annealing will also improve subsequent corrosion resistance of annealed parts.

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Authors and Affiliations

  1. Air Products and Chemicals, Inc., 18195, Allentown, PA, USA

    John F. Kirner & Alejandro L. Cabrera

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  1. John F. Kirner
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  2. Alejandro L. Cabrera
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Kirner, J.F., Cabrera, A.L. Thermodynamic control of H2-N2 bright annealing atmospheres to inhibit nitrogen uptake by stainless steel. J. Heat Treating 7, 27–33 (1989). https://doi.org/10.1007/BF02833185

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  • DOI: https://doi.org/10.1007/BF02833185

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